WO2010046654A1

WO2010046654A1 - Transmission system

Info

Publication number: WO2010046654A1
Application number: PCT/GB2009/002527
Authority: WO
Inventors: William Wesley Martin; Richard Neil Quinn
Original assignee: Zeroshift Ltd
Current assignee: Zeroshift Ltd
Priority date: 2008-10-22
Filing date: 2009-10-22
Publication date: 2010-04-29
Anticipated expiration: 2011-04-22
Also published as: WO2010046652A4; GB2464572A; GB2464571A; GB2464702B; GB0819365D0; WO2010046654A4; GB0905946D0; GB0906230D0; GB2464702A; WO2010046655A1; WO2010046652A1

Abstract

A transmission system including a first shaft (3), a first gear element (13) rotatably mounted on the shaft, a selector assembly (29) including first and second sets of engagement members (35,36) that are arranged to selectively lock the first gear element (13) for rotation with the first shaft (3), said selection including selecting from at least the following operational modes: lock the first gear element (13) for rotation with the first shaft (3) in the clockwise and anti- clockwise directions; lock the first gear element (13) for rotation with the first shaft (3) in a clockwise direction and unlocked in an anti-clockwise direction; lock the first gear element (13) for rotation with the first shaft (3) in the anti-clockwise direction and unlocked in the clockwise direction, wherein said gear element includes first and second parts (202,204) that are arranged to rotate relative to each other and a damping system (238,240), wherein the first part (202) includes a first set of drive formations (212), the second part (204) includes a second set of drive formations (220), wherein when selecting the first gear element (13) with one of the first and second sets of engagement members (25,36), that set of engagement members (35,36) is arranged to drivingly engage the second set of drive formations (220) to cause relative rotational movement between the first and second parts (202,204) of the gear element, the damping system (238,240) is arranged to damp the relative rotational movement between the first and second parts (202,204) of the gear element, and after some damping has occurred the engagement members are arranged to drivingly engage the first set of drive formations (212). A gear element (13) and a gear selector assembly (29) having a damping system (238,240) is also disclosed.

Description

Transmission system

The present invention relates to transmission systems, in particular to dog-typε transmission systems, gear elements and gear selector assemblies for transmission systems.

In conventional single clutch synchromesh transmission systems for vehicles it is necessary to disengage the transmission from the power source, such as an engine or motor, by operating the clutch before the current gear is deselected and the new gear is engaged. If the power is not disengaged when attempting to engage a new gear the synchromesh is unable to engage the new gear wheel or has to be forced into engagement with the risk of damaging the transmission and creating torque spikes in the transmission. This is because in most cases the speed of the engine is not matched to the speed of the new gear. For motor vehicles such as cars having conventional gearboxes and powered by an engine, the selection of a new gear ratio typically takes between 0.5 and 1 second to complete. So, for example, when a higher gear is selected the time delay allows the engine to reduce its speed [due to its own inertia] to more closely match the speed of the new gear before the clutch re-connects the engine and the transmission, thereby reducing the possibility of torque spikes occurring when the power is reapplied.

An instantaneous transmission system is arranged such that a new gear can be selected before the current gear is disengaged under power. These transmission systems include at least one instantaneous gear selector mechanism, which typically has four modes of operation with respect to each of the rotatably mounted gear wheels associated with it:

Fully engaged in both torque directions (fully in gear);

Disengaged in both torque directions (neutral);

Engaged in the forward torque direction while disengaged in the reverse torque direction;

Disengaged in the forward toque direction while engaged in the reverse torque direction.

It is the last two modes that enable a discrete ratio gearbox to have the ability to shift up or down ratios instantly under load without torque interruption, hi some embodiments it is not necessary to have a neutral mode.

In transmission systems where the selection of a new gear ratio takes place almost instantaneously without substantial power interruption, such as the transmissions described in WO 2004/099654, WO 2005/005868, WO 2005/005869, WO 2005/024261 and WO 2005/026570 the contents of which are incorporated by reference, large torque spikes can be generated when the new gear is engaged under certain shift conditions because the load impacting the gear wheel can be as high as 6OkN.

The torque spikes cause shock waves to propagate through the transmission that can be heard and felt by the occupants of the vehicle. The Shockwaves can produce a jerky ride for the car occupants and can lead to wear of transmission components and the possibility of components failing. Nevertheless it is highly desirable to use this type of transmission in vehicles since for many shift types there is no loss of drive during a gear change. This makes the vehicle more efficient thereby requiring less fuel and producing lower emissions while at the same time increasing the performance of the vehicle since the vehicle does not noticeably decelerate during an instantaneous shift.

WO 2005/005868 has addressed the torque spike problem by using a control system that reduces the vehicle clutch pressure prior to making a shift to at least partially absorb the large torque spikes generated when a new gear is engaged by relative rotational movement of the input and output sides of the clutch. However even with this system in place, known instantaneous transmission systems are noisy due to the inertia of the selector assembly colliding with the gear wheel at engagement. Thus such systems can fall below acceptable limits of Noise, Vibration and Harshness tests.

WO 2008/062192 discloses the use of gear elements each having a damping system built-into its structure to absorb the load when a new gear is selected. This effectively solves the torque spike problem since it reduces the magnitude of the spikes to a level that is not noticeable by the occupants of a vehicle. However, the designs disclosed in WO 2008/062192 are limited in their robustness and life expectancy. In some instances, the repeated loading that occurs when selecting a new gear causes the gear elements to fail in a period of time that is too short to be acceptable for use in road vehicles. In practice, it would be necessary for the transmission system to be repaired or replaced too frequently, which would be costly for the owner of the vehicle. Thus there is a need for instantaneous type transmission systems having means that mitigates the torque spike problem while at the same time having an arrangement that is sufficiently robust to meet the required life expectancy for road vehicles.

Accordingly the present invention seeks to provide an improved transmission system that mitigates at least one of the aforementioned problems, or at least provides an alternative to existing systems.

According to one aspect of the invention there is provided a transmission system including a first shaft, a first gear element rotatably mounted on the shaft, a selector assembly including first and second sets of engagement members that are arranged to selectively lock the first gear element for rotation with the first shaft, said selection including selecting from at least the following operational modes: lock the first gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the first gear element for rotation with the first shaft in a clockwise direction and unlocked in an anti-clockwise direction; lock the first gear element for rotation with the first shaft in the anti-clockwise direction and unlocked in the clockwise direction, wherein said gear element includes first and second parts that are arranged to rotate relative to each other and a damping system, wherein the first part includes a first set of drive formations, the second part includes a second set of drive formations, wherein when selecting the first gear element with one of the first and second sets of engagement members, that set of engagement members is arranged to drivingly engage the second set of drive formations to cause relative rotational movement between the first and second parts of the gear element, the damping system is arranged to damp the relative rotational movement between the first and second parts of the gear element, and after some damping has occurred the engagement members are arranged to drivingly engage the first set of drive formations. Having first and second sets of drive formations on the gear element enables damping to take place when the gear element is initially engaged and subsequently provides a rigid drive connection between the first part of the gear element and the selector assembly such that the damping system is not continuously loaded when the gear element is selected. This significantly increases the time to failure of the gear element, and hence the transmission system, which makes the transmission system suitable for road vehicles. This provides a significant improvement on the systems disclosed in WO 2008/062192.

The damping system allows lost motion between the first shaft and at least one of the first gear element and the selector assembly after the selector assembly engages the first gear element. The inventors have discovered that lost motion between the selector assembly and the first gear element reduces noise to an acceptable level, that is, such that it cannot be heard in an automobile during normal use. This is because the lost motion increases the time that it takes the selector assembly to lock the first gear element for rotation with the first shaft after the initial engagement thereby softening the impact.

Advantageously at least one of the first and second parts is substantially annular, or includes a substantially annular part. The first and second parts are arranged co-axially. When the first and second parts of the gear element are fitted together, the first and second sets of drive formations are located on the same side face.

The damping system is a fluid damping system, and preferably a hydraulic damping system, that is arranged to damp relative rotational movement between the first and second parts in the clockwise and anti-clockwise directions. Advantageously the damping system can include first and second piston chambers located in the second part of the gear element and a first piston that is arranged to move with the first part of the gear element and to move into and out of the first and second piston chambers according to the relative rotational movement of the first and second parts of the gear element. The first piston chamber damps clockwise movement and the second piston chamber damps anticlockwise movement.

The transmission system can include third and fourth piston chambers located in the second part of the gear element and a second piston that is arranged to move with the first part of the gear element and to move into and out of the third and fourth piston chambers according to the relative rotational movement of the first and second parts of the gear element. The third piston chamber damps clockwise movement and the fourth piston chamber damps anticlockwise movement. This is a more robust and reliable arrangement than the hydraulic system disclosed in WO 2008/062192.

The first and second pistons and each of their respective piston chambers are arranged to allow hydraulic fluid to leak from the chambers during a damping action. Typically the leakage rate is less than 10%.

Advantageously the damping fluid can be supplied to the interior of the gear element via a feed line in the first shaft.

One of the first and second parts of the gear element includes meshing means for meshing with another gear element, and the other of the first and second parts of the gear element includes means for mounting the gear element on a shaft. Advantageously the meshing means can comprise gear teeth. Preferably the gear teeth are included in the first part of the gear element. Advantageously the means for mounting the gear element on a shaft includes a bearing or bush.

The first set of drive formations includes x drive formations, wherein x is in the range 2 to 24, preferably 3 to 16 and more preferably 3 to 6. The second set of drive formations includes y drive formations, wherein j> is in the range 2 to 10, preferably 3 to 6. hi some embodiments the first and second sets of drive formations have the same number of drive formations. The drive formations in the first set of drive formations are distributed on the first part of the gear element such that they are substantially equally angularly spaced. The drive formations in the second set of drive formations are distributed on the second part of the gear element such that they are substantially equally angularly spaced.

Advantageously the first gear element can include means for limiting the axial movement of the first and second sets of engagement members. The means for limiting the axial movement of the first and second sets of engagement members can include at least one of: a set of raised abutments, wherein the raised abutments are located on the second part of the gear element and are arrange alternately with the drive formations in the second set second set of drive formations; and the first set of drive formations, the depth dimension being selected to determine the extent of axial limitation of the first and second sets of engagement members.

Advantageously the first gear element can include means for self-centring the relative rotational orientations of the first and second parts of the gear element. Preferably the means for self-centring includes resilient means, such as a spring element. In some embodiments, the first gear element is arranged such that when in an unloaded condition, the drive formations of the first set of drive formations are rotationally offset from the drive formations in the second set of drive formations. In other embodiments, when in an unloaded condition, the drive formations of the first set of drive formations are rotationally aligned with the drive formations in the second set of drive formations.

Advantageously the gear selector assembly can be arranged to select the following operational mode with respect to the first gear element: the first gear element is not locked for rotation with the first shaft in the clockwise or anticlockwise directions.

Advantageously the transmission system can include a second gear element rotatably mounted on the first shaft. The second gear element can be arranged similarly to the first gear element.

Advantageously the selector assembly is arranged to selectively lock the second gear element for rotation with the first shaft from the following operational modes: lock the second gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the second gear element for rotation with the first shaft in a clockwise direction and unlocked in an anti-clockwise direction; lock the second gear element for rotation with the first shaft in the anti-clockwise direction and unlocked in the clockwise direction.

The selector assembly can be arranged to select the following operational mode with respect to the second gear element: the second gear element is not locked for rotation with the first shaft in the clockwise or anticlockwise directions.

Advantageously the selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition. Preferably the selector assembly is arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is then in an unloaded condition.

Advantageously the transmission system may include a first actuator device for actuating the first set of engagement members and a second actuator device for actuating the second set of engagement members to select between the modes. Advantageously the selector assembly can include first and second actuator members and a first resiliently deformable means between the first actuator and the first actuator member and a second resiliently deformable means between the second actuator and the second actuator member. The resilient means are arranged to bias movement of the engagement members towards the unengaged gear element.

Advantageously the transmission system may include a third gear element rotatably mounted on the first shaft and a second selector assembly for selectively locking the third gear element for rotation with the first shaft. Advantageously the second selector assembly can be similar to any configuration of the first selector assembly described herein. Advantageously the third gear element may include a damping system similar to any configuration described herein.

Advantageously the transmission system can include a control system for controlling operation of the first and second actuators for the or each selector assembly. Preferably the control system is an electronic control system. For example, the control system may include a processing device that is programmed to control operation of the selector assemblies. This can prevent transmission lock up occurring by appropriate sequence control.

The or each selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition, and the unloaded set is moveable to engage the new gear element. For transmissions having at least first and second selector assemblies and for shifts requiring operation of at least two selector assemblies, the control system can be arranged to move the unloaded set of engagement members out of engagement with the currently engaged gear element before actuating the other selector assembly to engage its new gear element. This is an important factor in preventing transmission lock up when torque reversals occur during a shift requiring the operation of more than one selector assembly since it removes the set of engagement elements out of engagement with the current gear element that would otherwise lock the transmission if a torque reversal occurred. For example, if the second gear element is locked for rotation in the acceleration and deceleration directions (fully engaged) with the second set of engagement members drivingly engaging the second gear element, then the first set is in an unloaded condition. Before the second selector assembly engages the third gear element, the control system actuates the first actuator to move the first set of engagement members out of engagement with the second gear element. Thus the second gear element is no longer fully engaged but is locked for rotation in one of the acceleration and deceleration directions only and is unlocked in the other direction. The control system then actuates the second selector assembly to select the third gear element with the complementary set of engagement members (acceleration or deceleration direction to match the direction of torque) whilst the second gear element is still engaged by the first gear selector assembly, and thus performs an instantaneous gear shift. If a torque reversal occurs during the shift, the transmission does not lock up since both gear elements are locked for rotation in the same direction and are unlocked in the other direction.

Advantageously the first gear selector assembly is arranged to move the unloaded set of engagement members of the first gear selector assembly into driving engagement with the unengaged gear element whilst the current gear wheel is still engaged by the other set of engagement members to effect a gear change between the first and second gear elements for at least one shift type. Thus the first gear selector assembly is arranged to selectively lock the first and second gear elements for rotation with the first shaft simultaneously, at least momentarily. Typically, this is only happens for a very short period of time during the shift, since when the new gear has been selected the loaded element set becomes unloaded and the control system is arranged to disengage it from it gear element and move it into engagement with the new gear element. This is an instantaneous gearshift. Preferably the transmission includes at least three gear selector assemblies. Preferably each gear selector assembly is similar to the first gear selector assembly. Any practicable number of gear selector assemblies can be included in the transmission. Typically, each gear selector assembly will be arranged to selectively lock two gear elements for rotation with a shaft. Typically, each rotatably mounted gear element will form part of a gear train that transfers drive between the first shaft and a second shaft. Preferably transmissions include between three and twenty gear trains (cars tend to have four to six gear trains, plus reverse and lorries around twelve to twenty gear trains plus reverse), and more preferably between four and eight gear trains. For example, the first gear element can be part of a first gear train that includes a fourth gear wheel fixed to the second shaft. The second gear element can be part of a second gear train that includes a fifth gear wheel fixed to the second shaft and the third gear element can be part of a third gear train that includes a sixth gear wheel fixed to the second shaft.

Advantageously, each of the gear elements that are engageable by a selector assembly can include a damping system similar to those described herein.

According to another aspect of the invention there is provided a transmission system including first and second rotatable shafts, and means for transferring drive from one of the shafts to the other shaft including first and second gear elements each rotatably mounted on the first shaft and having drive formations formed thereon, a gear selector assembly for selectively transmitting torque between the first shaft and the first gear element and between the first shaft and the second gear element, said selector assembly including first and second sets of engagement members that are moveable into and out of engagement with the first and second gear elements and an actuator system, wherein the gear selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition, and the actuator system includes a first actuator device for controlling operation of the first set of engagement members and a second actuator device for controlling operation of the second set of engagement members and the actuator system is arranged to move the unloaded set of engagement members into driving engagement with the unengaged gear element to effect a gear change, wherein at least one of the first and second gear elements includes first and second parts that are arranged to rotate relative to each other and a damping system, wherein the first part includes a first set of drive formations, the second part includes a second set of drive formations, and when selecting one of the gear elements so arranged with one of the first and second sets of engagement members, that set of engagement members is arranged to drivingly engage the second set of drive formations to cause relative rotational movement between the first and second parts of the gear element, the damping system is arranged to damp the relative rotational movement between the first and second parts of the gear element, and after some damping has occurred the engagement members are arranged to drivingly engage the first set of drive formations.

Advantageously the damping system can be arranged to damp the locking of the first and second gear elements with the first shaft. Advantageously the damping system can be arranged according to any configuration described herein.

Advantageously the selector assembly is arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is then in an unloaded condition. The actuator assembly is arranged to bias the loaded set of engagement members towards the unengaged gear element without disengaging the loaded set of engagement members from the engaged gear element.

Advantageously the first and second sets of engagement members are arranged to rotate, in use, with the first shaft. Preferably the first shaft is an input shaft and the second shaft is an output shaft and drive is transferred from the input shaft to the output shaft.

Preferably the selector assembly is arranged such that when the first and second sets of engagement members engage one of the first and second gear elements the backlash when moving between acceleration and deceleration is less than or equal to four degrees.

Preferably the drive formations on the first and second gear elements comprise first and second groups of dogs respectively. For example, the first and second groups of dogs each comprise between two and eight dogs, evenly distributed on the first and second gears respectively. Preferably the first and second groups of dogs each comprise between two and four dogs, and more preferably three dogs.

The first and second sets of engagement members preferably comprise between two and eight members, more preferably between two and four members, and more preferably still three members.

Advantageously the first shaft may include keyways arranged such that the first and second sets of engagement members can slide axially along the keyways and to radially restrain the positions of the sets of engagement members. Preferably the cross-section of the keyways is one of T-shaped, slotted, and dovetailed.

Preferably the actuator assembly includes at least one resiliently deformable means arranged to move at least one of the first and second sets of engagement members into engagement with the first and second gear elements when the engagement members are in unloaded conditions. Preferably the or each resiliently deformable means is arranged to bias at least one of the first and second sets of engagement members towards the first or second gear element when the engagement members are drivingly engaged with a gear element.

The transmission system may further include third and fourth gears mounted on the first shaft and a second selector assembly to provide additional gear ratios between the first and second shafts.

According to another aspect of the invention, there is provided a gear element for a transmission system, said gear element including first and second parts that are arranged to rotate relative to each other and a damping system, wherein the first part includes a first set of drive formations arranged for engagement by a gear selector assembly, the second part includes a second set of drive formations for engagement by the gear selector assembly, the damping system is arranged to damp the relative rotational movement between the first and second parts.

Advantageously the gear element can be arranged according to any configuration described herein.

According to another aspect, there is provided a gear selector assembly for a transmission system that is arranged to selectively lock a gear element for rotation with a shaft from the following operational modes: lock the gear element for rotation with the shaft in the clockwise and anti-clockwise directions; lock the gear element for rotation with the shaft in a clockwise direction and unlocked in an anti-clockwise direction; lock the gear element for rotation with the shaft in the anti-clockwise direction and unlocked in the clockwise direction, wherein the selector assembly includes first and second parts that are arranged for relative rotational movement and first and second sets of engagement members that are arranged to move independently of each other to selectively engage the gear element, wherein the first part is arranged for mounting on the shaft and the second part supports the first and second sets of engagement members, and a damping system that is arranged to damp locking of the gear element for rotation with the shaft.

The first and second sets of engagement members can move axially along the second part.

Advantageously the damping system includes a fluid damping system, and preferably a hydraulic damping system.

Advantageously the fluid damping system is arranged to damp relative rotational movement between the first and second parts in the clockwise and anti-clockwise directions.

Advantageously they transmission system can include first and second piston chambers located in the second part of the gear element and a first piston that is arranged to move with the first part of the gear element and to move into and out of the first and second piston chambers according to the relative rotational movement of the first and second parts of the gear element. The first piston chamber damps clockwise movement and the second piston chamber damps anticlockwise movement.

Advantageously they transmission system can include third and fourth piston chambers located in the second part of the gear element and a second piston that is arranged to move with the first part of the gear element and to move into and out of the third and fourth piston chambers according to the relative rotational movement of the first and second parts of the gear element. The third piston chamber damps clockwise movement and the fourth piston chamber damps anticlockwise movement.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which like references indicate equivalent features, wherein:

Figure 1 is a sectional view of a general arrangement of a transmission system in accordance with the present invention;

Figures 2a to 2j show a gear wheel having a damping mechanism;

Figure 3 is a schematic that illustrates the interaction of a selector mechanism and the dogs on the side of a gear wheel;

Figure 4 is a perspective view of an engagement element from the selector mechanism;

Figure 5a-e & 6 illustrate diagrammatically operation of the selector mechanism by showing movement of one engagement member from each set;

Figures 7-22 illustrate diagrammatically operation of the damping mechanism when selected by the selector mechanism by showing movement of one engagement member from each set.

Figure 1 shows a transmission including an output shaft 1, an input shaft 3 and first, second, third, fourth, fifth and sixth gear trains (or gear ratios) 5,7,9,11,12,14 (1^st, 2^nd, 3^rd, 4^th, 5^th and 6^th) arranged to transmit drive between the input and output shafts 3,1. The first gear train 5 comprises a first gear wheel 13 rotatably mounted on the input shaft 3 via a bearing and a second gear wheel 15 fixed to the output shaft 1 in mesh with the first gear wheel 13. The second gear train 7 comprises a third gear wheel 17 rotatably mounted on the output shaft 3 and a fourth gear wheel 19 fixed to the input shaft 1 in mesh with the third gear wheel 17. The third gear train 9 comprises a fifth gear wheel 21 rotatably mounted on the input shaft 3 and a sixth gear wheel 23 fixed to the output shaft 1 in mesh with the fifth gear wheel 21. The fourth gear train 11 comprises a seventh gear wheel 25 rotatably mounted on the input shaft 3 and an eighth gear wheel 27 fixed to the output shaft 1 in mesh with the seventh gear wheel 25. The fifth gear train 12 comprises a ninth gear wheel 16 rotatably mounted on the input shaft 3 and a tenth gear wheel 18 fixed to the output shaft 1 in mesh with the ninth gear wheel 16. The sixth gear train 14 comprises an eleventh gear wheel 22 rotatably mounted on the input shaft 3 and a twelfth gear wheel 24 fixed to the output shaft 1 in mesh with the seventh gear wheel 25.

First, second and third selector mechanisms 29,31,33 are also mounted on the input shaft 3. Each selector mechanism 29,31,33 is arranged to selectively transmit drive between the input shaft 3 and output shaft 1 via the gear trains by selectively locking the gear wheels rotatably mounted on the input shaft 3 for rotation with the input shaft 3. The first selector mechanism 29 is arranged to selectively lock the first gear wheel 13 from the 1^st gear ratio and third gear wheel 17 from the 2^nd gear ratio for rotation with the input shaft 3. The second selector mechanism 31 is arranged to selectively lock the fifth gear wheel 21 from the 3rd gear ratio and the seventh gear wheel 25 from the 4th gear ratio for rotation with the input shaft 3. The third selector mechanism 31 is arranged to selectively lock the ninth gear wheel 16 from the 5th gear ratio and the eleventh gear wheel 22 from the 6^th gear ratio for rotation with the input shaft 3.

When a gear wheel is engaged by a gear selector mechanism it is locked for rotation with the input shaft 3. So, for the third gear train 9, when the second gear selector mechanism 31 engages the fifth gear wheel 21 and the first and third gear selector mechanisms 29,33 are in neutral (no gear wheels engaged) drive is transmitted between the input and output shafts 3,1 via the third gear train 9.

Each selector mechanism 29,31,33 is similar and is mounted on the input shaft 3 in a similar manner. Each rotatably mounted gear wheel 13,17,21,25,16,22 is similar and is mounted on the input shaft 3 in a similar manner. The structure of the first gear selector mechanism 29, the first gear wheel 13 and the way in which it selectively engages the first and third gear wheels 13,17 will now be described. However the general structure and principles of operation are applicable to the second and third gear selector mechanisms 31,33 and their respective gear wheels.

Figures 2a-j shows the first gear wheel 13 including a hydraulic damping mechanism 200 that is arranged to allow limited relative rotational movement between the first gear wheel 13 and the input shaft 3 and / or the selector mechanism 29. The arrangement is such that the limited relative rotational movement softens the engagement of the new gear wheel 13 by the selector mechanism 29 thereby reducing the noise generated to acceptable levels. The relative rotational movement effectively increases the time that it takes for the gear wheel 13 to be locked for rotation with the input shaft 3 and thereby provides a longer period of time over which the energy generated by the collision is dissipated.

The first gear wheel 13 comprises an outer annular part 202 and an inner annular part 204. The inner part 204 is arranged co-axially with the outer part 204 and is arranged for limited relative rotational movement therewith. The outer part 202 includes gear teeth 210 formed in a peripheral portion that are arranged to mate with teeth on a corresponding gear wheel fixed to the output shaft 3, and a set of drive formations in the form of a first set of dogs 212. The first set of dogs 212 includes six dogs 214 that are arranged to be engaged by the selector mechanism 29. The dogs 214 are preferably formed integrally with the outer part 202 of the gear wheel, but this is not essential, and are evenly circumferentially distributed about the side face, i.e. the angle subtended between the centres of a pair of dogs 214 is approximately 60° (see Figure 2a). Each dog 214 is arcuate, extends through an angle of approximately 30°, and includes two drive faces 216, one at each end, and a substantially planar upper surface 218.

The inner part 204 is rotatably mounted on the input shaft 3 via a bearing 203 and includes a second set of dogs 220 on a side face that are arranged to be engaged by the selector mechanism 29. The second set of dogs 220 is located on one side of the inner part of the gear wheel. The first set of dogs 220 comprises three dogs 222 evenly circumferentially distributed about the gear face, i.e. the angle subtended between the centres of a pair of dogs is approximately 120° (see Figures 2a and 3), and are preferably formed integrally with the first gear wheel, but this is not essential. Each dog 222 extends through angle of approximately 30°, and includes two drive faces 224, one at each end, and a substantially planar upper surface 226. Three dogs are used because this arrangement provides large engagement windows, that is spaces between the dogs, to receive the engagement elements. Large engagement windows provide greater opportunities for the first gear selector mechanism 29 to fully engage the gear wheel 13 before transmitting drive thereto.

A set of raised abutments 228 is located on the same side face of the inner part of the gear wheel 204 as the second set of dogs 220 to prevent the selector mechanism 29 from engaging the first set of dogs 212 before the second set of dogs 220 is engaged. The set of raised abutments 228, includes three raised abutments 230 that are arranged alternately with the dogs 222. Each raised abutment 230 includes inclined end faces 232 and a substantially planar upper surface 234. Each raised abutment 230 extends through an arc of approximately 60°, is spaced by 15° from each adjacent dog 222, and has a depth that is substantially equal to the depth of the dogs 214 in the first set of dogs 212.

The inner gear part 204 includes two arcuate tracks 236 that are arranged about the longitudinal axis of the inner gear part in the manner shown in Figure 2h. Each track includes two piston chambers 238: one located towards each end of the track 238. Each track 236 is arranged to house a piston 240. Each piston 240 is arcuate and includes a connector 242 that protrudes through a slot 244 in the curved surface 246 of the inner gear part that sits in a recess formed in the outer gear part 202, the arrangement being such that each piston 240 rotates with the outer gear part 202. Thus each piston 240 is arranged to move along its track 236 into and out of each of the piston chambers 238 according to the relative rotational orientations of the inner and outer parts 204,202 of the gear.

Preferably the inner gear 204 part is manufactured from first and second inner gear parts 205,207 that are welded together, for example by electron beam welding.

The piston chambers 238 are filled with a hydraulic fluid, which is fed through the input shaft 3 along an axial feed line 248 formed in the input shaft 3 along its central axis, and to the chambers 238 via radial feed lines 250 and a feed ring 252. The feed ring 252 includes an annular groove formed in its outer surface to enable it to continuously supply oil to the interior of the gear wheel. The oil supply system can be a closed system or an open system. For example, an open system can use the gearbox lubricating oil and include a system for pumping it from the sump of the gearbox to the interior of each gear wheel including the damping mechanism.

The movement of the pistons 240 along the tracks 236 is limited by hydraulic fluid being compressed within the piston chambers 238 and ultimately by the selector mechanism 29 drivingly engaging the first set of dogs 212 (see below).

The arrangement of the piston chambers 238, the pistons 240, and hydraulic fluid is such that there is a predetermined leakage rate under a given load as each piston 240 moves into one of the piston chambers 238. This is achieved by dimensioning the piston 240 such that there are gaps between it and the inside of the piston chamber 238 to enable a small amount of hydraulic fluid to escape. The leakage rate provides a means of designing into the gear wheel 13 the stiffness of the damping mechanism when the gear wheel 13 is selected by the gear selector mechanism 29. For example, a typical leakage rate is typically less than 10% and preferably around 5%.

The gear wheel 13 includes a circlip 254, which acts as a self centring spring. The circlip 254 sits in a groove 256 formed in the curved surface 246 of the inner part of the gear. A lug 258 attached to the outer part of the gear 202 loads the circlip 254 when there is relative rotation between the inner and outer parts 204,202 of the gear. Thus when the load causing relative rotation between the inner and outer parts 204,202 reduces, the circlip 254 biases the inner and outer parts 204,202 to the neutral position. A further advantage of using a circlip 254 is that it can be arranged such that it is rotationally balanced.

When the selector mechanism 29 engages the first gear wheel 13, abutments 238 and first set of dogs 212 initially prevent full engagement from taking place. Thus the selector mechanism 29 is only able to drivingly engage the second set of dogs 220. When engagement takes place, the selector mechanism 29 drives the second set of dogs 220, which causes relative rotational movement between the inner and outer parts 204,202 of the gear wheel. The relative rotational movement causes each of the pistons 240 to move into one of its respective piston chambers 238 according to the direction of movement thereby loading the hydraulic fluid located therein and causing a quantity to be forced out of the chamber 238. The effect of this is to damp the engagement of the gear wheel 13.

The first set of dogs 212 also acts as drive formations. When a predetermined amount of relative rotational movement occurs between the inner and outer parts 204,202 of the gear wheel, the selector mechanism 29 drivingly engages the first set of dogs 212. This prevents further relative rotational movement since the selector mechanism 29 then drives the outer part 202 of the gear wheel directly.

A similar effect occurs if the selector mechanism 29 engages the gear wheel 13 in the opposite torque direction. Thus damping takes place in both the clockwise and anti-clockwise directions.

This reduces the noise of the impact such that it is not audible by the driver of the vehicle or so that it is reduced to an agreeable level. The resilient means 208 compresses until it reaches its compression limit and is unable to compress any further. This can be influenced by controlling the volume of the recess 206 to achieve the desired resiliency response. During operation of the transmission the resilient means 208 will try to restore its position to the neutral position.

The third, fifth, seventh, ninth and eleventh gear wheels 17,21,25,16,22 are arranged similarly to the first and third gear wheel 13.

The first gear selector mechanism 29 includes a sleeve 34, first and second sets of engagement elements 35,36 and an actuator assembly 38.

The first gear selector mechanism 29 is mounted on the input shaft 3 between the first and third gear wheels 13,17. The gear selector mechanism 29 is arranged to engage the first and second sets of dogs 212,220 located on the first and third gear wheels 13,17. The first and third gear wheels 13,17 are mounted spaced apart on the input shaft 3 and are arranged such that the sides including the first and second dog groups 212,220 face each other. Similar drive formations are located on the fifth, seventh, ninth and eleventh gear wheels 21,23,28,32. The first and second sets of engagement elements 35,36 are mounted on the sleeve 34. The first set of engagement elements 35 comprises three elements 28 that are evenly distributed about the input shaft 3 such that their bases face inwards, and the axes of the elements 28 are substantially parallel with each other and the input shaft 3. The second set of engagement elements 36 comprises three elements 30, which are similarly arranged about the input shaft 3. The sets of engagement elements 35,36 are arranged to rotate with the input shaft 3 but are able to slide axially along the sleeve 34, and hence the input shaft 3, in response to a switching action of the actuator assembly 38. To facilitate this, the sleeve 34 includes six keyways 41 formed in its curved surface with each engagement element 28,30 having a complementary formation in its base. The keyways 41 may have substantially T-shaped profiles such that the elements are radially and tangentially (but not axially) restrained within the keyways 41 (see Figure 3). Alternatively, the keyways 41 can have slotted or dovetailed profiles to radially restrain the elements.

Preferably the elements are configured to be close to the input shaft 3 to prevent significant cantilever effects due to large radial distances of loaded areas thus reducing the potential for structural failure.

The arrangement of the engagement element sets 35,36 is such that elements of a particular set are located in alternate keyways 41 and the sets 35,36 can slide along the sleeve 34. The engagement elements in each set are rigidly connected to each other by an annular member 100 and move as a unit. Each set 35,36 can move independently of the other. The annular member 100 has a groove 102 formed in its outer curved surface that extends fully around the annular member. The engagement elements 28 in the first set of engagement elements 35 are preferably integrally formed with its annular member 100, though this is not critical. The engagement elements 28 are evenly distributed about the annular member 100. The second set of engagement elements 36 comprises three elements 30, which are held in a similar fixed arrangement by a second annular member 100. When there is relative movement between the first and second sets of engagement elements 35,36, the annular member 100 of the first engagement element set 35 moves over the second set of engagement elements 36 and the annular member 100 of the second engagement element set 36 slides over the first set of engagement elements 35. Each engagement element 28 in the first engagement element set 35 has a first end 28a arranged to engage the first and second group of dogs 212,220 attached to the first gear wheel 13 and a second end 28b arranged to engage the first and second groups of dogs 212,220 on the third gear wheel 17. The first and second ends 28a,28b typically have the same configuration but are opposite handed, for example the first end 28a is arranged to engage the first and second groups of dogs 212,220 during deceleration (reverse torque direction) of the first gear wheel 13 and the second end 28b is arranged to engage the first and second group of dogs 212,220 during acceleration (forward torque direction) of the third gear wheel 17. Each engagement element 30 in the second engagement element set 36 is similarly arranged, except that the first end 30a is arranged to engage the first and second group of dogs 212,220 during acceleration of the second gear wheel 15 and the second end 30b is arranged to engage the first and second group of dogs 212,220 during deceleration of the third gear wheel 17.

When both the first and second sets of engagement elements 35,36 engage a gear wheel drive is transmitted between the input and output shafts 3,1 whether the gear is accelerating or decelerating.

The first and second ends 28a,30a,28b,30b of each engagement element include an engagement face 43 for engaging the first and second sets of dogs 212,220, a ramp 45, an end face 42 and may include a shoulder 44 (shown diagrammatically in Figure 4). The end faces 42 limit the axial movement of the engagement elements 28,30 by abutting the sides of the gear wheels and also the upper surfaces 218,234 of the first set of dogs and abutments respectively. The engagement faces 43 may be angled to complement the drive faces of the dogs 216,224 so that as the engagement elements 28,30 rotate into engagement, there is face- to-face contact to reduce wear. Each ramp 45 is preferably helically formed and slopes away from the end face 42. The angle of inclination of the ramp 45 is such that the longitudinal distance between the edge of the ramp furthest from the end face 42 and the plane of the end face 42 is larger than the height of the dogs 212,220. This ensures that the transmission does not lock up when there is relative rotational movement between the engagement elements 28,30 and the dogs 212,220 that causes the ramp 45 to move towards engagement with the dogs 212,220. The dogs 212,220 do not crash into the sides of the engagement elements 28,30 but rather engage the ramps 45. As further relative rotational movement between the dogs 212,220 and the engagement elements 28,30 occurs, the dogs 212,220 slide across the ramps 45 and the helical surfaces of the ramps cause the engagement elements 28,30 to move axially along the input shaft 3 away from the dogs 212,220 so that the transmission does not lock up. The ramps 45 are also arranged to interact with the inclined end faces 232 of the abutments in order to move axially away from the gear wheel 13.

The arrangement of the gear selector mechanism is such that it inherently prevents lockup of the transmission occurring when selecting a new gear.

When the engagement elements of the first and second sets 35,36 are interleaved, as in Figure 3, the engagement faces 43 of the first ends 28a of the first set of engagement elements 35 are adjacent the engagement faces 43 of the first end 30a of the second set of engagement elements 36. When the first and second sets of engagement elements 35,36 are fully engaged with a gear, a dog 214 from the first set of dogs and a dog 222 from the second set of dogs is located between each pair of adjacent engagement faces 43. The dimensions of the dogs 214,222 and the ends of the elements are preferably such that there is little movement of each dog between the engagement face 43 of the acceleration element and the engagement face 43 of the deceleration element when the gear moves from acceleration to deceleration, or vice versa, to ensure that there is little or no backlash in the gear.

The actuator assembly 38 controls the movement of the first and second sets of engagement elements 35,36. The assembly 38 includes first and second actuators 46,64 and first and second actuator members 48,58. The first and second actuators 46,64 are force generator actuators and preferably part of an electrical system for example, an electro-mechanical system or an electro-hydraulic system. The first and second actuator members 48,58 are preferably in the form of independently controllable forks. Movement of the first set of engagement elements 35 is controlled by movement of the first actuator member 48, which is controlled by the first actuator 46. Movement of the second set of engagement elements 36 is controlled by movement of the second actuator member 58, which is controlled by the second actuator 64. Thus the first and second sets of engagement elements move totally independently of each other unlike known systems, such as the system of WO 2004/099654, which only has a single actuator for controlling actuation of both sets of engagement elements. With the known systems the sets of engagement elements can move relative to each other however the actuation of each set of engagement elements is interdependent since there is only a single actuator for initiating movement.

Each actuator member 48,58 is arranged to extend approximately 180 degrees around the groove 102 of its respective set of engagement elements and includes a semi-annular part that is located within the groove 102 . Each set of engagement elements 35,36 can rotate relative to its respective actuator member 48,5.8 and is caused to move axially along the input shaft 3 by the actuator member 48,58 applying a force to the annular member 100.

Optionally the actuator assembly 38 may include resilient means, such as helical springs (not shown). The springs are arranged to bias the first and second sets of engagement elements to move in an axial direction when they are in driving engagement with a gear wheel and are unable to move. For example, the springs may be positioned between the first actuator 46 and the first actuator member 48 or between the first actuator member 48 and the first set of engagement elements 35,36.

Operation of the first and second actuators 46,64, and hence movement of the first and second sets of engagement elements is controlled by a transmission control unit. The transmission control unit may include sensors for determining the operational conditions of selector mechanisms 29,31,33 in the transmission. Typically these monitor the positions of the actuator members 48,58 and hence the positions of the sets of engagement elements, for example whether they are engaged with a gear wheel or not. The sensors can be included in the actuators 46,64, and may be, for example, Hall effect type sensors.

The transmission control unit is preferably in the form of an electronic logic control system driven by a processor, which runs software that is arranged to control operation of the first and second actuators 48,64 and hence the first and second sets of engagement elements 35,36. The sequence programming is typically arranged to control movement of the gear selector mechanisms 29,31,33 together with controlling the direction of torque in the transmission such that it prevents conflict shifts occurring. Being able to control the actuation of the first and second sets of engagement elements 35,36 totally independently by use of first and second actuators 46,64 has the advantage that the magnitude and the timing of application of the biasing force applied by each actuator can be independently controlled. This means that even at low rotational gear speeds the engagement elements sets 35,36 do not accidentally disengage from the engaged gear wheel and thus no loss of drive is experienced.

The operation of the first gear selector mechanism 29 will now be described with reference to Figures 5a-5e and 6 which for clarity illustrate diagrammatically the movement of the first and second element sets 35,36 by the relative positions of only one element from each set.

Figure 5a shows the first and second engagement element sets 35,36 in a neutral position, that is, neither engagement element set is engaged with a gear wheel. Figure 5b shows the first and second engagement element sets moving into engagement with the first gear wheel 13 under the action of the first and second actuators 46,64 in response to a gearshift request from the input device 94. Preferably, the clutch is opened for the first gear shift.

Figure 5c shows a condition when the first gear wheel 13 is fully engaged, that is, the engagement elements 28,30 are interleaved with the first and second sets of dogs 212,220. The first and second actuators 46,64 are arranged such that the actuator members 48,58 maintain the first and second engagement element sets 35,36 in engagement with the first gear wheel 13. Accordingly, drive is transferred through the first gear wheel 13 to the input shaft 3 via the first engagement element set 35 when decelerating and via the second engagement element set 36 when accelerating.

Whilst accelerating (first gear wheel 13 rotating in the direction of arrow B in Figure 5c) using the first gear train 5, the engagement faces 43 of the engagement elements of the first engagement element set 35 are not loaded, whilst the engagement faces 43 of the engagement elements of the second element set 36 are loaded. When a user, or an engine control unit wishes to engage the second gear train 7 an input signal is sent from an input device or the engine control unit to the processor. The processor instructs the transmission control unit to actuate the first actuator 46 to drive the first actuator member 48, which causes the engagement elements 28 of the first engagement element set 35 to slide axially along the keyways 41 in the sleeve 34 thereby disengaging the first engagement element set 35 from the first gear wheel 13 (see Figure 5d). The second actuator 64 is activated to move the second actuator member 58 and hence the second engagement element set 36 towards the third gear wheel 17. However, because the second engagement element set 36 is loaded, i.e. is driving the first gear wheel 13, it cannot be disengaged from the first gear wheel 13, and the second engagement element set 36 remains stationary, with the second actuator 64 biasing it towards the third gear wheel 17.

When the first engagement element set 35 slides axially along the input shaft 3, the third gear wheel 17 is in the neutral position is shown in Figures 7 to 10. In the neutral position the first set of dogs 212 is rotationally offset from the second set of dogs 222. The raised abutments 228 and the first set of dogs 212 are arranged to block full engagement of the second set of dogs 220. Each piston 240 is located outside of its respective piston chambers 238, substantially centrally along its track 236, and each chamber 238 is substantially filled with hydraulic fluid. When the gear wheel 17 is selected by the first engagement set the initial contact is with the end faces 42 on the upper surfaces 218,234 of the first set of dogs and the raised abutments (see Figures 8 and 9). As the first set of engagement elements rotate relative to the third gear wheel 17 their engagement faces 43 subsequently engage the drive faces 224 of the second set of dogs 220 (see Figures 11 to 14), which causes relative rotational movement between the outer and inner parts of the gear 202,204. The relative rotational movement causes the pistons 240 to move along their tracks 236 into the piston chambers 238 in the direction of torque applied by the selector mechanism 29. As each piston 240 moves into its respective piston chamber 238 the hydraulic fluid located in therein is pressurised, which causes some of the hydraulic fluid to leak from the chamber 238. This action absorbs a significant proportion of the engagement energy thereby reducing the noise and Shockwave of the impact and hence damps the engagement. The relative rotational movement between the inner and outer parts 204,202 of the gear wheel also loads the circlip 254.

When sufficient relative rotational movement has taken place to enable the first set of engagement elements 35 to move past the dogs 214 on the outer part 202 of the gear that initially blocked axial movement, the first set of engagement elements 35 is able to move axially into the gaps between adjacent dogs 214 such that the drive faces 43 of the engagement elements 35 engage the drive faces 216 of the first set of dogs 212 (see Figures 15 to 18). Engaging the drive faces 216 of the first set of dogs prevents further relative rotation between the first and second parts of the gear 204,202 (see Figure 5e). Thus the first set of dogs 212 now takes the driving load, which prevents the continued loading of the piston chambers 238. This significantly increases the useful life of the gear element, while preserving its ability to reduce torque spikes.

When relative rotation is arrested, the engagement elements 28 drive the outer part 202 of the third gear wheel 17 in the direction of Arrow C in Figure 5e and wherein drive is transmitted between the input and output shafts 3,1 via the second gear train 7. As this occurs, the second engagement element set 36 ceases to be loaded, and is free to disengage from the first group of dogs 212 on the first gear wheel 13 Since the second engagement element set 36 is biased by the second actuator 64 it slides axially along the keyways 41 in the sleeve 34 thereby completing the disengagement of the first gear wheel 13 from the input shaft 3. The second engagement element set 36 slides along the keyways 41 until it engages the third gear wheel 17, thereby completing engagement of the third gear wheel 17 with the input shaft 3 (see Figure 6 and Figures 19 to 22).

This method of selecting gear trains substantially eliminates torque interruption since the second gear train 7 is engaged before the first gear train 5 is disengaged, thus momentarily, the first and second gear trains 5,7 are simultaneously engaged and locked for rotation with the input shaft 3, until the newly engaged gear wheel overdrives the original gear wheel. This type of gearshift is said to be instantaneous since a new gear is selected before the existing gear is released.

When a gear wheel is engaged by both the first and second engagement element sets 35,36 it is possible to accelerate or decelerate using a gear wheel pair with very little backlash occurring when switching between the two conditions. Backlash is the lost motion experienced when the dog moves from the engagement face 43 of the acceleration engagement element to the engagement face 43 of the deceleration engagement element when moving from acceleration to deceleration, or vice versa. A conventional dog-type transmission system has approximately 30 degrees of backlash. A typical transmission system for a car in accordance with the current invention has backlash of less than five degrees. Backlash is reduced by minimising the clearance required between an engagement member and a dog during a gearshift: that is, the clearance between the dog and the following engagement member (see measurement 'A' in Figure 5b). The clearance between the dog and the following engagement member is in the range 0.5mm - 0.03mm and is typically less than 0.2mm. Backlash is also a function of the retention angle, that is, the angle of the engagement face 43, which is the same as the angle of the undercut on the engagement face of the dog 20a. The retention angle influences whether there is relative movement between the dog and the -engagement face 43. The smaller the retention angle, the less backlash that is experienced. The retention angle is typicaily between 2.5 and 15 degrees.

Transition from the second gear train 7 to the first gear train 5 whilst decelerating is achieved by a similar process.

Whilst decelerating in the second gear train 7 the engagement surfaces 43 of the elements of the first element set 35 are not loaded, whilst the engagement surfaces 43 of the elements of the second element set 36 are loaded. When a user, or an engine control unit wants to engage the first gear train 5 a signal is sent from the input device or the engine control unit to the processor. The processor instructs the transmission control unit to actuate the first actuator 46 to move the first actuator member 48 axially, causing the first engagement element set 35 to slide axially in the keyways 41 along the input shaft 3 in the direction of the first gear wheel 13, thereby disengaging the first engagement element set 35 from the third gear wheel 17.

The transmission control system activates the second actuator 64 however 60 since the second engagement element set 36 is loaded, i.e. it is drivingly engaged with the dogs 212,220 on the third gear wheel 17, it remains stationary but is urged towards the first gear wheel 13.

As the first engagement element set 35 slides axially in the keyways 41 the first gear wheel 13 is in the neutral position. In the neutral position the first set of dogs 212 is rotationally offset from the second set of dogs 222. The raised abutments 228 and the first set of dogs 212 are arranged to block full engagement of the second set of dogs 220. Each piston 240 is located outside of its respective piston chambers 238, substantially centrally along its track 236, and each chamber 238 is substantially filled with hydraulic fluid. When the gear wheel 17 is selected by the first engagement set the initial contact is with the end faces 42 on the upper surfaces 218,234 of the first set of dogs and the raised abutments. As the first set of engagement elements 35 rotates relative to the first gear wheel 13 its engagement faces 43 subsequently engage the drive faces 224 of the second set of dogs 220, which causes relative rotational movement between the outer and inner parts of the gear 202,204. The relative rotational movement causes the pistons 240 to move along their tracks 236 into the piston chambers 238 in the direction of torque applied by the selector mechanism 29. As each piston 240 moves into its respective piston chamber 238 the hydraulic fluid located therein is pressurised, which causes some of the hydraulic fluid to leak from the chamber 238. This action absorbs a significant proportion of the engagement energy thereby reducing the noise and shockwave of the impact and hence damps the engagement. The relative rotational movement between the inner and outer parts 204,202 of the gear wheel also loads the circlip 254.

When sufficient relative rotational movement has taken place to enable the first set of engagement elements 35 to move past the dogs 214 on the outer part 202 of the gear that initially blocked axial movement, the first set of engagement elements 35 is able to move axially into the gaps between adjacent dogs 214 such that the drive faces 43 of the engagement elements 35 engage the drive faces 216 of the first set of dogs 212. Engaging the drive faces 216 of the first set of dogs prevents further relative rotation between the first and second parts of the gear 204,202 (see Figure 5e). Thus the first set of dogs 212 now takes the driving load, which prevents the continued loading of the piston chambers 238. Thus energy is transmitted between the input and output shafts 3,1 by way of the first gear train 5.

As this occurs, the second engagement element set 36 ceases to be loaded and biasing of the second actuator 64 causes it to slide axially within the keyways 41 along the input shaft 3 towards the first gear wheel 13, thereby completing disengagement of the third gear wheel 17. The second engagement element set 36 continues to slide within the keyways 41 along the input shaft 3 until it engages the first gear wheel 13, thereby completing engagement of the first gear wheel 13 with the input shaft 3.

Kick-down shifts, that is a gear shift from a higher gear train to a lower gear train but where acceleration takes place, for example when a vehicle is travelling up a hill and the driver selects a lower gear to accelerate up the hill, require a brief torque interruption to allow disengagement of the driving element set prior to the shift.

The transmission system can be used in any vehicle for example, road cars, racing cars, lorries, motorcycles, bicycles, trains, trams, coaches, earth removal vehicles such as bulldozers and diggers, cranes, water craft such as hovercraft and ships, aircraft including aeroplanes and helicopters, and military vehicles. The system can also be used in any machine that has first and second rotatable bodies wherein drive is to be transmitted from one of the rotatable bodies to the other with variable speed and torque characteristics, such as transportation systems and manufacturing equipment including lathes, milling machines and dedicated production systems.

Use of instantaneous type gear selector mechanism leads to improved performance, lower fuel consumption and lower emissions since drive interruption during gear changes is substantially eliminated. Also the system is a more compact design than conventional gearboxes leading to a reduction in gearbox weight.

It will be appreciated by the skilled person that the damping mechanism 200 can be adapted in ways that still fall within the scope of the invention, for example the first set of dogs 212 can be arranged to have the same number of dogs as there are dogs in the second set of dogs 220. In this instance the dogs 214 in the first set extend through a smaller arc than the dogs 222 in the second set, and the centres of the dogs 214,222 are substantially aligned when in the neutral position. Because of the difference in size and because of the centring the sets of engagement elements 35,36 will always engage the second set of dogs 220 initially from either direction. Thus this arrangement obviates the need for the raised abutments 230 since it is not necessary to limit the axial movement of the engagement elements 35,36 initially.

Another alternative is to include eight to sixteen dogs 214 in the first set of dogs 212. In this arrangement, the engagement elements 35,36 select the next available dog 214 after driving the second set of dogs 220.

The above arrangement can be repeated for any number of selector mechanisms mounted on the input shaft 3. Also, the selector assemblies and rotatably mounted gear wheels can be mounted on the output shaft, and the fixed gear wheels on the input shaft.

The damping mechanism 200 included in one of the gear selector mechanisms 29,31,33. This arrangement can be used in addition or as an alternative to the damping mechanism 200 located in each of the gear wheels. When used as an alternative, the gear rotatable gear elements are then of the conventional type such as used in WO2004/099654. The damping mechanism operates similarly to the damping mechanism 200 in the gear wheels.

In some transmissions, it may not be necessary to include the damping mechanism 200 in all selectable gear wheels, since for some gear ratios / shift conditions the torque spikes generated may already be within acceptable Noise, Vibration and Harshness limits, for example in some higher gears. In such circumstances, the non-damped gear wheels can be of a conventional type.

Claims

1. A transmission system including a first shaft, a first gear element rotatably mounted on the shaft, a selector assembly including first and second sets of engagement members that are arranged to selectively lock the first gear element for rotation with the first shaft, said selection including selecting from at least the following operational modes: lock the first gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the first gear element for rotation with the first shaft in a clockwise direction and unlocked in an anti-clockwise direction; lock the first gear element for rotation with the first shaft in the anti-clockwise direction and unlocked in the clockwise direction, wherein said gear element includes first and second parts that are arranged to rotate relative to each other and a damping system, wherein the first part includes a first set of drive formations, the second part includes a second set of drive formations, wherein when selecting the first gear element with one of the first and second sets of engagement members, that set of engagement members is arranged to drivingly engage the second set of drive formations to cause relative rotational movement between the first and second parts of the gear element, the damping system is arranged to damp the relative rotational movement between the first and second parts of the gear element, and after some damping has occurred the engagement members are arranged to drivingly engage the first set of drive formations.

2. A transmission system according to any one of the preceding claims, wherein the damping system is arranged to allow lost motion between the first shaft and at least one of the first gear element and the selector assembly after the selector assembly engages the first gear element.

3. A transmission system according to any one of the preceding claims, wherein the damping system is a fluid damping system, and preferably a hydraulic damping system.

4. A transmission system according to any one of the preceding claims, wherein at least one of the first and second parts is substantially annular, or includes a substantially annular part.

5. A transmission system according to any one of the preceding claims, wherein the first and second parts are arranged co-axially.

6. A transmission system according to any one of the preceding claims, wherein the damping system includes a fluid damping system, and preferably a hydraulic damping system.

7. A transmission system according to claim 6, wherein the fluid damping system is arranged to damp relative rotational movement between the first and second parts in the clockwise and anti-clockwise directions.

8. A transmission system according to any one of the preceding claims, including first and second piston chambers located in the second part of the gear element and a first piston that is arranged to move with the first part of the gear element and to move into and out of the first and second piston chambers according to the relative rotational movement of the first and second parts of the gear element.

9. A transmission system according to any one of the preceding claims, including third and fourth piston chambers located in the second part of the gear element and a second piston that is arranged to move with the first part of the gear element and to move into and out of the third and fourth piston chambers according to the relative rotational movement of the first and second parts of the gear element.

10. A transmission system according to claim 8 or 9, wherein the first and second pistons and each of their respective piston chambers are arranged to allow hydraulic fluid to leak from the chambers during a damping action.

11. A transmission system according to any one of the preceding claims, wherein one of the first and second parts of the gear element includes meshing means for meshing with another gear element, and the other of the first and second parts of the gear element includes means for mounting the gear element on a shaft.

12. A transmission system according to any one of the preceding claims, wherein when the first and second parts of the gear element are fitted together, the first and second sets of drive formations are located on the same side face.

13. A transmission system according to any one of the preceding claims, wherein the first set of drive formations includes n drive formations, wherein n is in the range 2 to 24, preferably 3 to 16 and more preferably 3 to 6.

14. A transmission system according to any one of the preceding claims, wherein the second set of drive formations includes n drive formations, wherein n is in the range 2 to 10, preferably 3 to 6.

15. A transmission system according to any one of the preceding claims, including means for limiting the axial movement of the first and second sets of engagement members.

16. A transmission system according to claim 15, wherein the means for limiting the axial movement of the first and second sets of engagement members includes at least one of: a set of raised abutments, wherein the raised abutments are located on the second part of the gear element and are arrange alternately with the drive formations in the second set second set of drive formations; and the first set of drive formations, the depth dimension being selected to determine the extent of axial limitation of the first and second sets of engagement members.

17. A transmission system according to any one of the preceding claims, wherein the drive formations in the first set of drive formations are distributed on the first part of the gear element such that they are substantially equally angularly spaced.

18. A transmission system according to any one of the preceding claims, wherein the drive formations in the second set of drive formations are distributed on the second part of the gear element such that they are substantially equally angularly spaced.

19. A transmission system according to any one of the preceding claims, including means for self centring the relative rotational orientations of the first and second parts of the gear element.

20. A transmission system according to claim 19, wherein the means for self-centring includes resilient means, such as a spring element.

21. A transmission system according to claim 19 or 20, wherein, when in an unloaded condition, the drive formations of the first set of drive formations are rotationally offset from the drive formations in the second set of drive formations.

22. A transmission system according to claim 19 or 20, wherein, when in an unloaded condition, the drive formations of the first set of drive formations are rotationally aligned with the drive formations in the second set of drive formations.

23. A transmission system according to any one of claims 6 to 22, wherein the damping fluid is supplied to the interior of the gear element via the first shaft.

24. A transmission system according to any one of the preceding claims, wherein the gear selector assembly is arranged to select the following operational mode with respect to the first gear element: the first gear element is not locked for rotation with the first shaft in the clockwise or anticlockwise directions.

25. A transmission system according to any one of the preceding claims, including a second gear element rotatably mounted on the first shaft, wherein the selector assembly is arranged to selectively lock the second gear element for rotation with the first shaft from the following operational modes: lock the second gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the second gear element for rotation with the first shaft in a clockwise direction and unlocked in an anti-clockwise direction; lock the second gear element for rotation with the first shaft in the anti-clockwise direction and unlocked in the clockwise direction.

26. A transmission system according to claim 25, wherein the selector assembly is arranged to select the following operational mode with respect to the second gear element: the second gear element is not locked for rotation with the first shaft in the clockwise or anticlockwise directions.

27. A transmission system according to claim 25 or 26, wherein the second gear element is similarly arranged to the first gear element.

28. A transmission system according to any one of claims 25 to 27, wherein the selector assembly is arranged to select one of the first and second gear elements while the other of the first and second gear elements is still engaged by the selector assembly.

29. A transmission system according to any one of the preceding claims, wherein the selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition.

30. A transmission system according to claim 29, wherein the selector assembly is arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is then in an unloaded condition.

31. A gear element for a transmission system, said gear element including first and second parts that are arranged to rotate relative to each other and a damping system, wherein the first part includes a first set of drive formations arranged for engagement by a gear selector assembly, the second part includes a second set of drive formations for engagement by the gear selector assembly, the damping system is arranged to damp the relative rotational movement between the first and second parts.

32. A gear element according to claim 31, wherein at least one of the first and second parts is substantially annular, or includes a substantially annular part.

33. A gear element according to any claim 31 or 32, wherein the first and second parts are arranged co-axially.

34. A gear element according to any one of claims 31 to 33, wherein the damping system includes a hydraulic damping system.

35. A gear element according to claim 35, wherein the hydraulic damping system is arranged to damp relative rotational movement between the first and second parts in the clockwise and anti-clockwise directions.

36. A gear element according to any one of claims 31 to 35, including first and second piston chambers located in the second part of the gear element and a first piston that is arranged to move with the first part of the gear element and to move into and out of the first and second piston chambers according to the relative rotational movement of the first and second parts of the gear element.

37. A gear element according to any one of claims 31 to 36, including third and fourth piston chambers located in the second part of the gear element and a second piston that is arranged to move with the first part of the gear element and to move into and out of the third and fourth piston chambers according to the relative rotational movement of the first and second parts of the gear element.

38. A gear element according to claim 36 or 37, wherein the first and second pistons and their respective piston chambers are arranged to allow hydraulic fluid to leak from the chambers during a damping action.

39. A gear element according to any one of claims 31 to 38, wherein one of the first and second parts of the gear element includes meshing means for meshing with another gear element, and the other of the first and second parts of the gear element includes means for mounting the gear element on a shaft.

40. A gear element according to claim 39, wherein the means for mounting the gear element on the shaft includes means for rotatably mounting the gear element on a shaft.

41. A gear element according to any one of claims 31 to 40, wherein when the first and second parts of the gear element are fitted together, the first and second sets of drive formations are located on the same side face.

42. A gear element according to any one of claims 31 to 41, wherein the first set of drive formations includes n drive formations, wherein n is in the range 2 to 24, preferably 3 to 16 and more preferably 3 to 6.

43. A gear element according to any one of claims 31 to 42, wherein the second set of drive formations includes n drive formations, wherein n is in the range 2 to 10, preferably 3 to 6.

44. A gear element according to any one of claims 31 to 43, including means for limiting the axial movement of the selector assembly.

45. A gear element according to claim 44, wherein the means for limiting the axial movement of the selector assembly includes at least one of: a set of raised abutments, wherein the raised abutments are located on the second part of the gear element and are arrange alternately with the drive formations in the second set second set of drive formations; and the first set of drive formations, the depth dimension being selected to determine the extent of axial limitation.

46. A gear element according to any one of claims 31 to 45, wherein the drive formations in the first set of drive formations are distributed on the first part of the gear element such that they are substantially equally angularly spaced.

47. A gear element according to any one of claims 31 to 46, wherein the drive formations in the second set of drive formations are distributed on the second part of the gear element such that they are substantially equally angularly spaced.

48. A gear element according to any one of claims 31 to 47, including means for self centring the relative rotational orientations of the first and second parts of the gear elements.

49. A gear element according to claim 48, wherein the means for self-centring includes resilient means, such as a spring element, and preferably a circlip.

50. A gear element according to claim 48 or 49, wherein, when in an unloaded condition, the drive formations of the first set of drive formations are rotationally offset from the drive formations in the second set of drive formations.

51. A gear element according to claim 48 or 49, wherein, when in an unloaded condition, the drive formations of the first set of drive formations are rotationally aligned with the drive formations in the second set of drive formations.

52. A gear selector assembly for a transmission system that is arranged to selectively lock a gear element for rotation with a shaft from the following operational modes: lock the gear element for rotation with the shaft in the clockwise and anti-clockwise directions; lock the gear element for rotation with the shaft in a clockwise direction and unlocked in an anti-clockwise direction; lock the gear element for rotation with the shaft in the anti-clockwise direction and unlocked in the clockwise direction, wherein the selector assembly includes first and second parts that are arranged for relative rotational movement and first and second sets of engagement members that are arranged to move independently of each other to selectively engage the gear element, wherein the first part is arranged for mounting on the shaft and the second part supports the first and second sets of engagement members, and a damping system that is arranged to damp locking of the gear element for rotation with the shaft.

53. A gear selector assembly according to claim 53, wherein the first and second sets of engagement members can move axially along the second part.

54. A gear selector assembly according to claim 52 or 53, wherein the damping system includes a fluid damping system, and preferably a hydraulic damping system.

55. A gear selector assembly according to claim 54, wherein the fluid damping system is arranged to damp relative rotational movement between the first and second parts in the clockwise and anti-clockwise directions.

56. A gear selector assembly according to any one of claims 52 to 55, including first and second piston chambers located in the second part of the gear element and a first piston that is arranged to move with the first part of the gear element and to move into and out of the first and second piston chambers according to the relative rotational movement of the first and second parts of the gear element.

57. A gear selector assembly according to any one of claims 52 to 56, including third and fourth piston chambers located in the second part of the gear element and a second piston that is arranged to move with the first part of the gear element and to move into and out of the third and fourth piston chambers according to the relative rotational movement of the first and second parts of the gear element.

58. A gear selector assembly according to claim 56 or 57, wherein the first and second pistons and their respective piston chambers are arranged to allow hydraulic fluid to leak from the chambers during a damping action.