WO1995002135A1

WO1995002135A1 - Electro-hydraulic transmission control

Info

Publication number: WO1995002135A1
Application number: PCT/US1994/006707
Authority: WO
Inventors: Jerry A. Wear
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 1993-07-06
Filing date: 1994-06-15
Publication date: 1995-01-19
Anticipated expiration: 1996-01-06
Also published as: AU7207594A

Abstract

In many transmission control systems, electro-hydraulic valves have been used to condition the various clutches in the transmission. In various applications, it is desirable to have a system where clutches can be engaged and remain engaged in the event of an electrical malfunction. In the subject invention, an electro-hydraulic transmission control (10) is provided having a plurality of electro-hydraulic valve mechanisms (50) to control a plurality of hydraulically controlled clutches (20). Each of the electro-hydraulic valve mechanisms (50) being movable between first and second operative positions and respectively latched in each operative position by a latching mechanism (54). An electrical signal is needed to overcome the bias of the latching mechanism (54) in order to move each of the electro-hydraulic valve mechanisms (50) between its operative positions. Once the respective ones of the plurality of electro-hydraulic valve mechanisms (50) are moved from one operative position to the other, the electrical signal is discontinued and the respective ones of the plurality of electro-hydraulic valve mechanisms (50) remain in their established positions. This arrangement provides a transmission control that effectively controls the operation of the transmission (14) while also providing the ability for the transmission (14) to remain in a selected gear in the event of an electrical malfunction.

Description

Electro-Hydraulic Transmission Control

Technical Field

This invention relates generally to a transmission control system and more specifically to an electro-hydraulic transmission control.

Background Art

It is well known to have control arrangements that automatically place a transmission in neutral if the electrical or hydraulic systems malfunction. Likewise, there are electro-hydraulic valve arrangements that automatically condition the transmission to a pre-established speed ratio whenever an electrical malfunction occurs with the transmission being operated in a selected range of ratios. Electro-hydraulic servo systems are known in which the output from the servo system is either hydraulically or mechanically locked in the event that the electrical input signal to the servo system varies from a predetermined range of values. It is desirable to provide, in a reliable and simple arrangement, a transmission control system that maintains the transmission in the selected speed ratio in the event there is a malfunction in the system's electrical energy. Furthermore, it is desirable to provide a transmission control system that is efficient in the use of electrical energy.

The present invention is directed to overcoming one or more of the problems as set forth above. Disclosure of the Invention

In one aspect of the present invention, an electro-hydraulic transmission control is provided for a machine which includes an engine, a source of electrical energy, a source of pressurized fluid, a transmission having a plurality of hydraulically controlled clutches for controlling movement of the machine and an electronic controller for sensing system parameters and controlling operation of the plurality of clutches in response thereto. A plurality of electro-hydraulic valve mechanisms are provided and are operative to selectively control pressurized fluid from the source of pressurized fluid to and from the selected ones of the plurality of hydraulically controlled clutches. Each of the electro-hydraulic valve mechanisms is movable between first and second operative positions in response to an electrical signal. Likewise, each electro-hydraulic valve mechanism has a latch mechanism operative to latch each in its respective operative positions and remains there in the absence of the electrical signal.

The present invention provides an electro- hydraulic transmission control that effectively ensures that in the event of an electrical malfunction, the transmission is maintained in the gear that it is operating in at the time the malfunction occurred. The subject invention is simple in arrangement, reliable in operation and utilizes electrical energy efficiently.

Brief Description of the Drawings

Fig. 1 is a partial diagrammatic and partial schematic representation of a control system incorporating an embodiment of the present invention; Fig. 2 is a schematic representation of another embodiment of the present invention;

Fig. 3 is a schematic representation of yet another embodiment of the present invention; and Fig. 4 is a schematic representation of still another embodiment of the present invention.

Best Mode for Carrying Out the Invention

Referring to the drawings, and more specifically to Fig. 1, an electro-hydraulic transmission control 10 is illustrated for a machine (not shown) having an engine 12, a transmission 14, a source of electrical energy 15, an electronic controller 16, and a source of pressurized fluid 18. The engine 12 has an output shaft 19 drivingly connected to the transmission 14. The transmission 14 includes a plurality of hydraulically controlled clutches 20, such as a forward clutch 22, a reverse clutch 24, and respective first, second and third speed clutches 26,28,30. A drive shaft 31 directs the torque from the transmission 14 to power the drive wheels (not shown) .

The electronic controller 16 is operatively connected to the engine 12, the transmission 14, a direction selector 32, and a speed selector 34 to sense the various system parameters. A speed sensor 38 senses the rotational speed of the output shaft 19 and directs the sensed rotational speed through an electrical line 40 to the electronic controller 16. A speed sensor 42 senses the output rotational speed from the drive shaft 31 of the transmission 14 and directs the sensed rotational speed through an electrical line 44 to the electronic controller 16. An electrical line 46 directs a signal from the direction selector 32 representative of the position thereof to the electronic controller 16. An electrical line 48 likewise directs a signal from the speed selector 34 that is representative of the selected speed to the electronic controller 16. The electronic controller 16 receives electrical energy from the source of electrical energy 15 by an electrical supply line 49. The electro-hydraulic transmission control

10 includes a plurality of electro-hydraulic valve mechanisms 50. It is recognized that each of the electro-hydraulic valve mechanisms 50 may be electrically actuated by a solenoid actuator, a voice coil actuator, a piezoelectric actuator or any other similar actuators without departing from the essence of the invention. The plurality of electro-hydraulic valve mechanisms 50 herein includes a plurality of electrically actuated, two-position, three-way valves 52. Each of the electrically actuated, two-position, three-way valves 52 are movable between first and second operative positions and are mechanically latched in their respective operative positions by a latching mechanism 54. Each of the electrically actuated, two-position, three-way valves 52 are movable between their respective operative positions by a bi-directional^•actuator 56. Each of the bi¬ directional actuators 56 of the respective electrically actuated, two-position, three-way valves 52 is operatively connected to the electronic controller 16 by respective electrical connections 58,60,62,64,66.

The source of pressurized fluid 18 receives fluid from a reservoir 68 and delivers the fluid to the respective electrically actuated, two-position, three-way valves 52 by a supply conduit 70. A plurality of conduits 72 respectively interconnects respective ones of the plurality of electrically actuated, two-position, three-way valves 52 to respective ones of the plurality of hydraulically controlled clutches 20. Likewise, a plurality of conduits 74 respectively interconnect respective ones of the plurality of electrically actuated, two- position, three-way valves 52 to the reservoir 68. In the first operative position of each of the electrically actuated, two-position, three-way valves 52, the supply conduit 70 is blocked from the conduit 72 leading to the hydraulically controlled clutches 20 and the conduit 72 is in open communication with reservoir 68 through the conduit 74. In the second operative position thereof, the supply conduit 70 is in communication with the conduit 72 and the conduit 74 is blocked from the conduit 72. Referring to Fig. 2, an alternate embodiment of the respective ones of the plurality of electro- hydraulic valve mechanisms 50 is illustrated. This embodiment can be readily substituted for the electrically actuated, two-position, three-way valves 52 illustrated in Fig. 1. In this embodiment, a pair of electrically actuated two-position, two-way valves 78 is utilized in place of each of the electrically actuated, two-position, three-way valves 52 illustrated in Fig. 1. Each of the electrically actuated, two-position, two-way valves 78 is mechanically latched in each of its operative positions by the mechanical latching mechanism 54. Likewise, each of the electrically actuated, two- position, two-way valves 78 are movable between their respective operative positions by the bi-directional actuator 56. The pair of electrically actuated, two- position, two-way valves 78 are readily substituted for the respective ones of the plurality of electrically actuated two-position, three-way valves 52 illustrated in Fig. 1. One valve of the pair of electrically actuated, two-position, two-way valves 78 is connected to the supply conduit 70 and to the conduit 72 leading to the respective ones of the plurality of hydraulically controlled clutches 20.

The other electrically actuated, two-position, two-way valve is connected to the conduit 72 by a conduit 80 and is connected to the reservoir 68 by the conduit 74. The electrical connection 58 connects the bi- directional actuator 56 of the one electrically actuated, two-position, two-way valve 78 to the electronic controller 16. An additional electrical connection 82 connects the bi-directional actuator 56 of the other electrically actuated, two-position, two- way valve 78 with the electronic controller 16. Each valve of the pair of electrically actuated, two- position, two-way valves 78 is movable between a closed, flow blocking position and an open flow communicating position. When the one electrically actuated, two-position, two-way valve 78 is in the flow blocking position, the other electrically actuated, two-position, two-way valve 78 is in the flow communicating position.

Referring to Fig. 3, another embodiment of the respective ones of the plurality of electro- hydraulic valve mechanisms 50 is illustrated. This embodiment can also be readily substituted for the electrically actuated, two-position, three-way valves 52 illustrated in Fig. l. This embodiment includes an electrically actuated, two-position, three-way pilot valve 86 and a hydraulically actuated, two-position, three-way valve 88. The electrically actuated, two- position, three-way pilot valve 86 is mechanically latched in each of its operative positions by the mechani.cal latchi.ng mechani.sm 54 and is movable between its operative positions by the bi¬ directional actuator 56. The hydraulically actuated, two-position, three-way valve 88 is spring biased to its first operative position and movable to its second operative position in response to a hydraulic signal received through a conduit 90 from the electrically actuated, two-position, three-way pilot valve 86. The electrically actuated, two-position, three-way pilot valve 86 is operatively connected to the supply conduit 70 and to the reservoir 68 by the conduit 74. The hydraulically actuated, two-position, three-way valve 88 is likewise operatively connected to the supply conduit 70, to the respective one of the plurality of hydraulically controlled clutches 20 by the conduit 72 and to the reservoir 68 by the conduit 74. In the first operative position of the electrically actuated, two-position, three-way pilot valve 86, the conduit 70 is blocked from the conduit 90 and the conduit 90 is in communication with the reservoir 68 through the conduit 74. In the second operative position, the conduit 70 is in communication with the hydraulically actuated, two-position, three- way valve 88 through the conduit 90 and the communication with the reservoir 68 is blocked. In the first operative position of the hydraulically actuated, two-position, three-way valve 88, the supply conduit 70 is blocked from communication with the conduit 72 and the conduit 72 is in communication with the reservoir 68 through the conduit 74. In the second operative position, the supply conduit 70 is in communication with the respective one of the plurality of hydraulically controlled clutches 20 through the conduit 72 and the communication of the conduit 72 with the reservoir 68 is blocked. The electrical connection 58 connects the bi-directional actuator 56 of the electrically actuated, two-position, three-way pilot valve 86 with the electronic controller 16. Referring now to Fig. 4, yet another embodiment of the respective ones of the plurality of electro-hydraulic valve mechanisms 50 is illustrated. As noted with respect to Figs. 2 and 3, this embodiment can likewise be readily substituted for the electrically actuated, two-position, three-way valves 52 illustrated in Fig. 1. The electro-hydraulic valve mechanism 50 of this embodiment includes a pair of electrically actuated, two-position, two-way pilot valves 94 and the hydraulically actuated, two- positioned, three-way valve 88 described above. Each of the electrically actuated, two-position, two-way pilot valves 94 is mechanically latched in their respective operative positions by the mechanical latching mechanism 54 and movable between their respective operative positions by the bi-directional actuator 56. As previously noted with respect to Fig. 3, the hydraulically actuated, two-position, three-way valve 88 is spring biased to its first operative position and movable to its second operative position by a hydraulic signal received through the conduit 90 from the one of the pair of electrically actuated, two-position, two-way valves 94. Likewise, the one electrically actuated, two-position, two-way pilot valve 94 and the hydraulically actuated, two-position, three-way valve 88 are operatively connected to the supply conduit 70. The other electrically actuated. two-position, two-way pilot valve 94 is connected to the conduit 90 by a conduit 96 and connected to the reservoir 68 by the conduit 74. The hydraulically actuated, two-position, three-way valve 88 is connected to the respective ones of the plurality of hydraulically controlled clutches 50 by the conduit 72 and to the reservoir 68 by the conduit 74. In the first operative position of the one electrically actuated, two-position, two-way pilot valve 94, the supply conduit 70 is blocked from communication with the conduit 90. In the first operative position of the other electrically actuated, two-position, two-way pilot valve 94, the conduit 90 is in fluid communication with the reservoir 68 through the conduit 96 and the conduit 74. In the second operative position of the one electrically actuated, two-position, two-way pilot valve 94, the supply conduit 70 is in communication with the conduit 90. In the second operative position of the other electrically actuated, two-position, two-way pilot valve 94, the communication of the conduit 90 with the reservoir 68 is blocked. The electrical connection 58 connects the one electrically actuated, two-position, two-way pilot valve 94 with the electronic controller 16 and the additional electrical connection 82 connects the other electrically actuated, two- position, two-way pilot valve 94 to the electronic controller 16.

It is recognized that various forms of the electro-hydraulic transmission control 10 could be utilized without departing from the essence of the invention. For example, the electrical signals being utilized could be in the form of electrical pulses. Also, in each of the embodiments illustrated in Figs. 1, 2, 3 and 4, the mechanical latching mechanism 54 could be replaced with a magnetic latching mechanism. This could be in a form of a permanent magnet material or in the form of a soft magnet material which can retain magnetism after being subjected to an electrical field. It is also recognized that various forms of hydraulic latching are available as well as electrical devices to latch the valving element of the respective electro-hydraulic valve mechanisms 50. It is likewise recognized that the bi-directional actuators 56 could be constructed with a combination of electrical, mechanical and magnetic elements and controlled by.a uni-directional electrical signal. Furthermore, the bi-directional actuators 56 could be replaced by a pair of uni-directional actuators, the respective uni-directional actuator of the pair being located on opposite ends of the respective electro- hydraulic valve mechanisms 50. Likewise, additional control sensors could be operatively connected to the electronic controller 16 to indicate other system parameters.

Industrial Applicability

In the operation of the electro-hydraulic transmission control illustrated in Fig. 1, the speed sensor 38 directs a signal representative of the revolution per minute of the output shaft 19 to the electronic controller 16 and the speed sensor 42 directs a signal thereto representative of the revolutions per minute of the transmission output shaft 31. A signal representative of the position of the direction selector 32 and a signal representative of the position of the speed selector 34 are directed to the electronic controller 16 through the electrical lines 46,48. With the direction selector 32 in the neutral position as illustrated in Fig. 1, the rpm of -li¬

the transmission output shaft 31 is zero since each of the plurality of hydraulically controlled clutches 20 is being vented to the reservoir 68 through the respective conduits 72, the respective electro- hydraulic valve mechanisms 50, and the conduits 74. Even though the speed selector 34 is illustrated as being in the first speed ratio position, the electronic controller 16 does not transmit any signal to the first speed clutch 26 since the direction selector 32 is in its initial, neutral position.

Upon movement of the direction selector 32 to the forward travel position and leaving the speed selector 34 in the first speed ratio position, the electronic controller 16 directs electrical signals through the electrical connections 58,62 to the respective bi-directional actuators 56. The respective electrically actuated, two-position, three- way valves 52 move to their second operative position transmitting pressurized fluid from the source of pressurized fluid 18 to the forward clutch 22 and the first speed clutch 26. The electronic controller 16 provides electrical signals to the respective electrically actuated, two-position, three-way valves 52 to progressively pressurize the first speed clutch 26 to its fully engaged condition, then sequentially to progressively pressurize the forward clutch 22. It is well known to fully engage the speed clutch first then to sequentially engage the directional clutch so that the directional clutch absorbs the increasing torque loads. Pressure modulation is obtained by rapidly changing the respective electrically actuated, two-position, three-way valves 52 from their first operative position to their second operative position in a controlled manner. That is, the pressure is varied by varying the amount of time the respective electrically actuated, two-position, three-way valves 52 are open to the source of pressurized fluid 18 versus the time they are open to the reservoir 68. This pressure modulation method is well known as pulse width modulation (PWM) .

The force being generated by the bi¬ directional actuator 56 is sufficient to move the respective electrically actuated, two-position, three- way valves 52 from their first operative position to their second operative position against the bias of the mechanical latching mechanism 54. Once the forward clutch 22 and the first speed clutch 26 are fully engaged, the respective electrically actuated, two-position, three-way valves 52 remain in their second operative position and latched therein by the mechanical latching mechanism 54. At this time, the electrical signals to the respective bi-directional actuators 56 are discontinued without concern of the respective electrically actuated, two-position, three- way valves 52 moving from their second operative position. An electrical signal from the electronic controller 16 to the other leg of the bi-directional actuators 56 is needed to move the electrically actuated, two-position, three-way valves 52 from their second operative position back to their first operative position. Consequently, in the event of an electrical malfunction, the transmission 14 remains in the gear that it was in prior to the electrical malfunction. In order to change from the first speed ratio forward to the second speed ratio forward, the operator moves the speed selector 34 to the second speed ratio position. This directs an electrical signal from the electronic controller 16 through the electrical connection 62 to the electrically actuated, two-position, three-way valve 52 moving it back to its first operative position, thus, venting the pressurized fluid from the first speed clutch 26 to the reservoir 68. Simultaneously, an electrical signal is delivered from the electronic controller 16 through the electrical connection 64 to another one of the electrically actuated, two-position, three-way valves 52 moving it to its second operative position. This directs pressurized fluid from the source of pressurized fluid 18 to the second speed clutch 28 through the conduit 72. The electrical signal being controllably delivered to the electrically actuated, two-position, three-way valve 52 progressively increases the fluid pressure in the second speed clutch 28 until the second speed clutch 28 is fully engaged. At this point, the electrical signal is discontinued and the electrically actuated, two- position, three-way valve 52 is retained in its second operative position by the mechanical latching mechanism 54. Changing to the third speed ratio is accomplished in a similar manner.

In the arrangement illustrated, the machine can be conditioned to move in a reverse direction in three different speed ratios. This is accomplished by moving the direction selector valve 32 to the "R" position which effectively releases the forward clutch 22 and engages the reverse clutch 24. As previously noted with respect to the forward direction operation, the speed selector 34 is moved between the first, second and third speed ratios which respectively engages and disengages the respective first, second and third speed clutches 26,28,30.

In the operation of the embodiment illustrated in Fig. 2, the operation of the system is identical to the operation as set forth above with• respect to Fig. 1. In this embodiment, moving the direction selector 32 to the forward position directs an electrical signal from the electronic controller 16 through the electrical connection 58 to the bi- directional actuator 56 of the one electrically actuated two-position, two-way valves 78 moving it to its second operative position directing pressurized fluid thereacross to engage the forward clutch 22. Simultaneously, the other electrically actuated two- position, two-way valve 78 moves from its first operative position to its second operative position in response to an electrical signal received through the additional electrical connection 82 wherein fluid flow from the conduit 72 to the reservoir 68 is blocked. Likewise, just prior to engagement of the forward directional clutch 22, simultaneous signals are delivered from the electronic controller 16 to the corresponding pair of electrically actuated, two- position, two-way valves 78 controlling the engagement of the first speed clutch 26.

In order to shift from the first speed ratio to the second speed ratio, the speed selector 34 is moved from its first speed ratio position to its second speed ratio position. An electrical signal is delivered through the electrical connection 62 to the one of the two electrically actuated, two-position, two-way valves 78 moving it from its second operative position to the first operative position. The other electrically actuated, two-position, two-way valves 78 moves from its second operative position to its first operative position in response to an electrical signal received through the additional electrical connection 82. This effectively disengages the first speed clutch 26. Simultaneously, electrical signals are delivered to the pair of bi-directional actuators 56 of the two electrically actuated, two-position, two- way valves 78 controlling engagement of the second speed clutch 28. The electrical signals delivered thereto through the electrical connections 64 and 82 results in the one electrically actuated, two- position, two-way valve 78 moving from its first flow blocking position to its second operative flow passing position and the other electrically actuated, two- position, two-way valve 78 moving from its first operative flow passing position to its second operative flow blocking position. As a result, the first speed clutch is disengaged and the second speed clutch 28 is progressively engaged. As is well known, the torque to the directional clutch 22 is interrupted during a speed shift. This is accomplished by the electronic controller 16 directing the needed signals to the pair of electrically actuated, two-position, two-way valves 78 to momentarily disconnect the forward drive clutch 22. In each situation, the electrical signals from the electronic controller 16 is utilized to move the electrically actuated, two-position, two-way valves 78 from the first operative latched position to the second operative latched position. Once the respective hydraulically controlled clutch 20 is engaged or disengaged, the electrical signal is shut off and the mechanical latching mechanism 54 maintains the respective electrically actuated two-position, two-way valves 78 in their established positions. The same operation of the pair of electrically actuated, two-position, two-way valves 78 occurs during any shifting of either the direction selector 32 or the speed selector 34.

Referring to Fig. 3, the embodiment illustrated herein can be readily substituted for the electrically actuated, two-position, three-way valves 52 illustrated in Fig. 1. The supply conduit 70 of Fig. 1 connects to the supply conduit 70 noted in Fig. 3. Likewise, the conduit 72 of Fig. 1 connects to the conduit 72 of Fig. 3. The major difference between the embodiment of Fig. 3 and that set forth with respect to Fig. 1 is that the arrangement of Fig. 3 utilizes a electrically actuated, two-position, three- way pilot valve 86 to control a hydraulically actuated, two-position, three-way valve 88.

Upon movement of the direction selector 32 to its forward position with the speed selector remaining in its first speed ratio position, the electronic controller 16 directs an electrical signal to the first speed electrically actuated two-position, three-way pilot valve 86 moving it from its first operative position to its second operative position in which pressurized fluid from the conduit 70 is directed thereacross to the conduit 90. Pressurized fluid in the conduit 90 moves the hydraulically actuated, two-position, three-way valve 88 from its first operative position to its second operative position wherein pressurized fluid from the source 70 is directed thereacross to the conduit 72 engaging the first speed clutch 26. As noted above with respect to the previous embodiments, the mechanical latching mechanism 54 maintains the electrically actuated, two- position, three-way pilot valve 86 in its second operative position until an electrical signal is provided to move it back to its first operative position. Subsequently thereto, an electrical signal is directed through the electrical connection 58 to the respective electrically actuated, two-position, three-way pilot valve 86 moving it to its second operative position directing pressurized fluid to act against the hydraulically actuated, two-position, three-way valve 88. The hydraulically actuated, two- position, three-way valve 88 moves to its second operative position directing pressurized fluid thereacross to the conduit 72 actuating the forward clutch 22.

When moving the speed selector 34 from its first speed ratio position to its second speed ratio position, as noted with respect to Fig. 2, the electronic controller 16 directs an electrical signal to the electrically actuated, two-position, three-way pilot valve 86 to momentarily disconnect the forward direction clutch 22. The electronic controller 16 then directs an electrical signal to the electrically actuated, two-position, three-way pilot valve 86 moving it from its second operative position back to its first operative position wherein the conduit 90 is connected to the reservoir 68, thus, venting the conduit 72 to the reservoir 68 to release the first speed clutch 26. Simultaneously, an electrical signal is directed through the electrical connection 64 to the respective electrically actuated, two-position, three-way pilot valve 86 directing pressurized fluid to the hydraulically actuated, two-position, three-way valve 88 moving it to its second operative position directing pressurized fluid to the second speed clutch 28. Since the electrically actuated, two-position, three-way pilot valve 86 is mechanically latched in each operative position, it remains in its established position in the event the system's electrical system malfunctions. Consequently, the selected hydraulically controlled clutches 20 are maintained in their established positions.

Referring to Fig. 4, operation of the yet another embodiment of the respective plurality of electro-hydraulic valve mechanisms 50 is described. The subject embodiment of Fig. 4 can readily be substituted for the respective electrically actuated, two-position, three-way valves 52 of Fig. 1. The supply conduit 70 of Fig. 1 connects with the supply conduit 70 of Fig. 4 and, likewise, the conduit 72 of Fig. 1 connects with the conduit 72 of Fig. 4. Upon movement of the direction selector 32 to its forward direction position with the speed selector 34 remaining in the first speed position, the electronic controller 16 delivers an electrical signal to the one electrically actuated, two-position, two-way pilot valve 94 moving it from its first operative flow blocking position to its second operative flow passing position. This delivers pressurized fluid flow from the conduit 70 through the conduit 90 moving the associated hydraulically actuated, two-position, three-way valve 88 from its first operative position to its second operative position. Simultaneously, an electrical signal is delivered through the additional electrical connection 82 to the other electrically actuated, two-position, two-way pilot valve 94 moving it from its first operative flow passing position to its second operative flow blocking position blocking flow from the conduit 90 to the reservoir 68. As a result of the hydraulically actuated, two-position, three-way valve 88 being moved from its first operative position to its second operative position, pressurized fluid from the supply conduit 70 is directed thereacross to the conduit 72 and, subsequently, to the first speed clutch 22. Additionally, the forward clutch 26 is subsequently engaged as a result of an electrical signal being delivered from the electronic controller 16 to the respective bi-directional actuators 56 of the corresponding pair of electrically actuated, two- position, two-way pilot valves 94. This, likewise, results in the hydraulically actuated, two- position, three-way valve 88 being moved to a position to direct pressurized fluid thereacross to actuate the forward clutch 26.

When moving the speed selector 34 from the first speed ratio position to the second speed ratio position, as noted with respect to Figs. 2 and 3, the electronic controller 16 directs an electrical signal to the pair of electrically actuated, two-position, two-way pilot valve 94 to momentarily disconnect the forward direction clutch 22. The first speed clutch 26 is then released by an electrical signal being delivered to the associated pair of electrically actuated, two-position, two-way pilot valves 94. This blocks pressurized fluid flow across the one electrically actuated, two-position, two-way pilot valve 94 and allows pressurized fluid in the conduit 90 to pass across the other electrically actuated, two-position, two-way pilot valves 94 to the reservoir 68. By venting the conduit 90, the hydraulically actuated, two-position, three-way valve 88 is spring biased back to its first operative position wherein the first speed clutch 26 is released by venting the pressurized fluid therein to the reservoir 68. Simultaneously, the second speed clutch 28 is engaged by an electrical signal being delivered to the respective pair of electrically actuated, two- position, two-way pilot valves 94 moving them to their respective second operative positions. This results in the hydraulically actuated, two-position, three-way valve 88 moving to its second operative position, thus, directing pressurized fluid thereacross to engage the second speed clutch 28. Each clutch of the plurality of hydraulically controlled clutches 20 is engaged or disengaged by directing electrical signals to the respective pair of electrically actuated two- position, two-way pilot valves 94. In view of the foregoing, it is readily apparent that the electro-hydraulic transmission control 10 of the present invention provides a simple arrangement that allows the various ones of the plurality of hydraulically controlled clutches 20 of the system to be engaged and disengaged efficiently and effectively. Likewise, the electro-hydraulic transmission control 10 maintains the respective ones of the plurality of hydraulically controlled clutches 20 in their respective positions in the event of an electrical malfunction. It is further noted that this system requires electrical energy to the plurality of electro-hydraulic valve mechanisms 52 only when necessary to move them from one operative position to the other operative position. Consequently, since each of the electro-hydraulic valve mechanisms 52 is actuated for only short intervals, i.e. approximately one second or less, there is a large savings in the amount of electrical energy needed. This is especially true when comparing this system to systems having electro-hydraulic valves that require continuous electrical energy to hold them in their actuated condition. This further reduces the level of heat being generated in the area where the controls are located and allows the possibility of using bi- directional actuators 56 that are less costly.

Other aspects, objects and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

Clai s

1. .An electro-hydraulic transmission control (10) for a machine including an engine (12) , a source of electrical energy (15) , a source of pressurized fluid (18), a transmission (14) having a plurality of hydraulically controlled clutches (20) for controlling movement of the machine, and an electronic controller (16) for sensing system parameters and controlling operation of the plurality of hydraulically controlled clutches (20) in response thereto, the electro-hydraulic transmission control (10) comprising; a plurality of electro-hydraulic valve mechanisms (50) having first and second operative positions and operative to selectively control pressurized fluid from the source of pressurized fluid (18) to and from the selected ones of the plurality of hydraulically controlled clutches (20) , each electro- hydraulic valve mechanism (50) being movable between first and second operative positions in response to an electrical signal, and each electro-hydraulic valve mechanism (50) having a latch mechanism (54) operative to hold it in its respective operative positions in the absence of the electrical signal.

2. The electro-hydraulic transmission control (10) of claim 1, wherein each electro- hydraulic valve mechanism (50) includes a single electrically actuated, two-position, three-way valve (52).

3. The electro-hydraulic transmission control (10) of claim 1, wherein each electro- hydraulic valve mechanism (50) includes two electrically actuated, two-position, two-way valves (78).

4. The electro-hydraulic transmission control of claim 1, wherein each electro-hydraulic valve mechanism (50) includes a single electrically actuated, two-position, three-way pilot valve (86) having the latch mechanism (54) thereon to latch it in each of its operative positions and a single hydraulically actuated, two-position, three-way valve (88) spring biased to a first operative position and movable to a second operative position in response to a hydraulic signal directed thereto from the single electrically actuated, two-position, three-way pilot valve (86) .

5. The electro-hydraulic transmission control (10) of claim 1, wherein each electro- hydraulic valve mechanism (50) includes two electrically actuated, two-position, two-way pilot valves (94) each having the latch mechanism (54) thereon to latch it in each of its operative positions and a single hydraulically actuated, two-position, three-way valve (88) spring biased to a first operative position and movable to a second operative position in response to a hydraulic signal directed thereto from one of the two electrically actuated, two-position, two-way pilot valves (94) .

6. The electro-hydraulic transmission control (10) of claim 1, wherein the latch mechanism

(54) on each of the electro-hydraulic valve mechanism

(50) is a mechanical latch.