WO2010086669A1

WO2010086669A1 - A pulley assembly

Info

Publication number: WO2010086669A1
Application number: PCT/GB2010/050148
Authority: WO
Inventors: Martin Hall
Original assignee: BELLE ENGINEERING (SHEEN) Ltd
Current assignee: BELLE ENGINEERING (SHEEN) Ltd
Priority date: 2009-01-30
Filing date: 2010-01-29
Publication date: 2010-08-05
Anticipated expiration: 2011-07-30
Also published as: EP2391774A1

Abstract

A pulley assembly (7) has an axis of rotation and includes first and second pulley sections (20 and 23) defining first and second contact surfaces (42 and 43) respectively which are separated from each other, which together form a frusto-conical surface and which, when considered in cross-section, converge towards the axis, the first and second pulley sections (20 and 23) being movably coupled to each other so that relative movement of the first and second pulley sections in an axial direction changes the separation of the first and second contact surfaces (42 and 43), and resilient means acting between the first and second pulley sections to bias the first and second contact surfaces towards each other and in the form of an undulating ring (33) that is elastically deformable in the axial direction.

Description

A PULLEY ASSEMBLY

The invention relates to a pulley assembly, and especially a pulley assembly for a drive belt.

Large plate compactors are used for ground compaction, such as compaction of soil, asphalt, interlocking blocks and aggregates. The compaction is usually carried out during road and highway maintenance, footpath construction and maintenance prior to application of the top layer or general construction and repair work to compact replaced soil or aggregates, such as may be required during underground pipe and cable works.

Compactors generally include a power unit (such as a petrol or diesel engine) that rotates an offset mass within a gearbox. Rotation of the offset mass creates a vibratory moment in the gearbox that causes vibrating movement of a compaction plate attached to the base of the gearbox. The power is transferred from the power unit to the gearbox via a drive belt that is entrained around a pulley mounted on the drive shaft of the power unit and a pulley mounted on the rotating shaft of the offset mass in the gearbox.

The power unit is usually isolated from the vibrated mass by anti-vibration mounts. This is to help prevent vibrational/ damage to the power unit.

However, this means that there is relative movement between the power unit and the gearbox and therefore, relative movement between the power unit pulley and the gearbox pulley. This relative movement between the pulleys has the problem that it results in a continuous stressing and de-stressing of the drive belt that shortens the service life of the drive belt and can lead to premature failure of the drive belt.

A number of attempts have been made to solve this problem with compensating pulleys and jockey tensioners but with little success. For example, the compensating pulley operates by automatically altering its circumference to compensate for changes in the belt tension caused by the relative movement between the pulleys. Compensating pulleys have used a disc spring or helical spring to adjust the circumference to compensate for changes in belt tension.

However, it has been found that, in practice, both disc springs and helical springs tend to fail prematurely.

In addition, using helical springs has the additional disadvantages of requiring pins to be formed on one of the pulley sections to facilitate mounting of the helical springs and the axial length of the helical springs results in an undesirable increase in the size of the pulley assembly as the spring length has to be accommodated within the pulley assembly.

The main object of the present invention is to provide a pulley assembly and a plate compactor incorporating a pulley system in which the aforesaid disadvantages are overcome or at least substantially reduced.

To this end and in accordance with one aspect of the present invention, there is provided a pulley assembly comprising a first pulley section defining a first contact surface; a second pulley section defining a second contact surface coupled to the first pulley section so that the first and second contact surfaces are facing each other at a transverse angle to each other and spaced from each other, the first and second sections being movably coupled to each other so that relative movement of the first and second pulley sections changes the separation of the first and second contact surfaces; and a spring mechanism mechanically coupled between the first and second pulley sections to bias the first and second contact surfaces towards each other, and wherein the spring mechanism comprises an undulating ring that is elastically deformable in its axial direction to create a restoring force. In this specification the word "ring" as used in the term "undulating ring" has a continuous outer rim surrounding an inner space and includes within its ambit a rim of circular, oval, polygonal or any other suitable configuration.

Expressed in another way, the present invention resides in a pulley assembly having an axis of rotation and including first and second pulley sections defining first and second contact surfaces respectively which are separated from each other, which together form a frusto-conical surface and which, when considered in cross-section converge towards the axis, the first and second pulley sections being movably coupled to each other so that relative movement of the first and second pulley sections in an axial direction changes the separation of the first and second contact surfaces, and resilient means acting between the first and second pulley sections to bias the first and second contact surfaces towards each other and in the form of an undulating ring that is elastically deformable in the axial direction.

From another aspect, the present invention resides in a plate compactor incorporating a frame, a power unit having a drive shaft and being mounted on the frame, a compactor plate assembly fixed to the frame through anti- vibration mounts, a gear box mounted to the compactor plate assembly and including a mass which is mounted on a rotatable shaft with its centre of gravity offset from the rotational axis of the shaft and a drive pulley mounted on the gear box shaft, a pulley assembly having an axis of rotation and being coupled to the power unit drive shaft, and a drive belt entrained around the pulley assembly and the gear box pulley, the pulley assembly including first and second pulley sections defining first and second contact surfaces respectively which are separated from each other, which together form a frusto-conical surface and which when considered in cross-section converge towards the axis, the first and second pulley sections being movably coupled to each other so that relative movement of the first and second pulley sections in an axial direction changes the separation of the first and second contact surfaces, and resilient means acting between the first and second pulley sections to bias the first and second contact surfaces towards each other and in the form of an undulating ring that is elastically deformable in the axial direction.

An advantage of the invention is that by having a spring mechanism/resilient means that comprises an undulating ring that is elastically deformable in its axial direction, premature spring failure is reduced. In addition, when the separation of the first and second contact surface changes, the position of a drive belt located between the surfaces will move radially inwardly or radially outwardly, due to the transverse angle between (frusto-conical surface formed by) the first and second contact surfaces, thereby changing the effective circumference of the contact surfaces which the belt contacts.

Furthermore, by using an undulating ring, in particular an undulating ring in the form of a wave washer, to compensate dynamically for changes in belt tension it is possible to extend the service life of the belt. It has been found that by using an undulating ring, the effective service life of the drive belt can be increased by enabling the circumference of the pulley assembly to change to compensate for changes in the tension of the belt caused by relative movement between the gear box drive pulley and the pulley assembly. The invention also has the advantage that the service life of an undulating ring such as a wave washer is greater than the typical service life for disc springs and helical springs in this application.

Furthermore, the use of an undulating ring and in particular a wave washer enables a relatively compact pulley assembly compared with a pulley assembly using helical springs.

In a preferred embodiment of the invention, the wave washer has three undulations but any suitable number such as two, four or more may be used.

It is important that the pulley assembly be as compact as possible, particularly when used in a plate compactor which needs to have a width enabling ease of entry of the compactor into trenches. To this end, and preferably, the second pulley section is slidably mounted for axial movement on the first pulley section, with the first and second pulley sections being rotationally fixed and the undulating ring is accommodated in a recess in the second pulley section and held and compressed within the recess by a cover member fixed to the first pulley section to act between the recess bottom and the cover member and bias the first and second contact surfaces towards each other.

Compactness is further enhanced by arranging for the second pulley section to be slidably mounted for axial movement on the first pulley section by means of an axially extending hub which engages in a complementary bore in a hub of the second pulley section with the recess accommodating the undulating ring extending around the hubs of the first and second pulley sections respectively.

Moreover, by arranging for the recess accommodating the undulating ring to have an inner wall defined by the hub of the second pulley section and an outer wall projecting axially from the second pulley section in parallel with the inner wall with the cover member having a periphery that fits against an inner surface of the outer wall, it is possible to guard against ingress of dust into the recess and thus protect the undulating ring from wear.

Typically the first and second contact surfaces are at an oblique angle relative to each other, and preferably, define a generally V=shape.

The pulley may be adapted to be used with a drive (or transmission) belt, that is located between the first and second contact surfaces and opposite edges of the belt, which is ideally a V-belt, contact the first and second contact surfaces, respectively, in use.

In preferred embodiments of the invention, the first and second pulley sections are movable, typically slidably movable, relative to each other in a direction substantially parallel to the axis of rotation of the pulley assembly, and the movement is typically slidable. In another preferred embodiment of the invention, typically, the pulley assembly further comprises an undulating ring housing mounted on one of the first and second pulley sections and the undulating ring acts between the housing and the other of the first and second pulley sections to bias the first and second contact surfaces towards each other.

Preferably, the pulley assembly is coupled to a drive shaft of a power unit, such as an engine or motor, so that a belt entrained around the pulley assembly is used to drive another unit, such as a gearbox. However, the drive belt entrained around the pulley assembly could be used to drive any appropriate device, such as a pump.

Alternatively, the pulley assembly could be coupled to the other unit, such as a gearbox, instead of a power unit.

Typically, the pulley assembly may be used with a drive belt that drives or rotates a device that generates a vibrating force. For example, the device that generates the vibrating force may be mechanically isolated from the power unit which drives the drive belt. In this example, changes in drive belt tension generated by movement of the device generating the vibrating force are compensated for by relative movement between the first and second sections under the biasing action of the spring mechanism which causes the first and second contact surfaces to move relative to each other to change the effective circumference of the pulley assembly which the belt contacts. This helps to compensate for changes in the belt tension generated by relative movement between the device creating the vibrating force and the power unit.

In another example of the invention, the pulley assembly may be used as an automatic belt tensioning device to compensate for changes in belt tension, for example as a result of stretching of a belt during use and/or to reduce the accuracy in the positioning between multiple pulleys around which the belt is entrained. In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:

Figure 1 is a side view of a plate compactor; Figure 2 is an exploded view of a pulley assembly used in the compactor shown in Figure 1 ;

Figure 3 is a cross-sectional view of the pulley assembly in a first position;

Figure 4 is a cross-sectional view of the pulley assembly in a second position;

Figure 5 is a plan view of an undulating ring in the form of a wave washer used in the pulley assembly shown in Figures 2 to 4;

Figure 6 is a side view of the wave washer of Figure 5; and

Figure 7 is a perspective view of the wave washer of Figures 5 and 6;

Figure 1 shows a plate compactor 1 that has a main frame assembly 2 on which is mounted a power unit 3 in the form of a petrol or diesel engine. The frame assembly 2 comprises two upper tubes 12 (only one shown) that are each in the form of an inverted U-shape and are interconnected by cross- tubes 13, which also forms a lifting eye to permit lifting off the compactor 1 , such as for lifting of the compactor 1 on or off a truck . Fixed across the ends of each upper tube 12 is a cross-plate 15 (only one shown), Attached to the cross-plates 15 by bolts 16 and rubber anti-vibration mounts (not shown) is a compactor plate assembly 17 that includes a compactor plate 5. Mounted on the compactor plate assembly 17 is a gearbox 4 that is bolted to the compactor plate assembly 17. A handle support 10 is coupled at one end to the frame assembly 2 and a handle 11 is attached to its opposite end to facilitate operation and manoeuvring of the compactor 1 by an operator. Within the gearbox 4 is a mass (not shown) mounted on a rotatable shaft (not shown). The mass is mounted on the rotatable shaft so that the centre of gravity of the mass is offset from the axis of rotation of the rotatable shaft. The power unit 3 includes a drive shaft 6 on which is mounted a pulley assembly 7. Entrained around the pulley assembly 7 is a drive belt 8, which is also entrained around a pulley 9 mounted on an end of the rotatable shaft in the gearbox 4 and which is preferably a V-belt.

Rotation of the pulley 9 rotates the rotatable shaft in the gearbox, thereby rotating the mass. Because the centre of gravity of the mass is offset from the axis of rotation of the rotatable shaft, when the mass is rotated by the shaft this causes a vibrationary movement of the gearbox 4 and hence, vibrational/ movement of the compactor plate 5 attached to the base of the gearbox.

The anti-vibration mounts help to mechanically isolate the compactor plate assembly 17 and the gearbox 4 from the frame assembly 2, the power unit 3 and the handle 11. The mechanical isolation of the power unit 3 from the compactor plate assembly 17 and the gearbox 4 reduces the amount of vibration that the power unit 3 is exposed to. This means that the reliability of the power unit 3 is increased as it is subjected to less vibration than if it was not isolated from the gearbox 4. The anti-vibration mounts also help to mechanically isolate the handle 11 from the compactor plate assembly 17 and the gearbox 4 so that vibration experienced by an operator holding the handle 11 is reduced.

However, mechanically isolating the power unit 3 from the gearbox 4 has the disadvantage that the gearbox 4 moves relative to the frame assembly 2 and the power unit 3, which means that the pulleys 7, 9 move relative to each other during operation of the compactor 1. This relative movement of the pulleys 7, 9 generates a continuous stressing and de-stressing of the drive belt 8 if there is no mechanism to compensate for the changes in tension in the drive belt 8 caused by the relative movement of the pulleys 7, 9.

The pulley assembly 7 is shown in more detail in Figures 2, 3 and 4 and comprises a first pulley section 20, a second pulley section 23, a hub 21 , a cover plate 31 and an undulating ring in the form of a wave washer 33 having a continuous outer rim surrounding an inner space and being of circular configuration. The first pulley section 20 is mounted on the hub 21 so that the first pulley section 20 is rotationally fixed with respect to the hub 21. The hub 21 includes an axial hole 22 which is adapted to be engaged with the drive shaft 6. The second pulley section 23 is slidably mounted on the first pulley section 20 so that the second pulley section 23 slidably moves in an axial direction with respect to the first pulley section 20 but is rotationally fixed to the first pulley section 20 and the hub 21.

This rotational fixing is achieved by means of pins 24 mounted on the second pulley section 23 that are slidably located in holes 25 in the first pulley section 20. The sliding movement is facilitated by the internal surface 26 of hub 27 formed on the second pulley section 23 being slidably mounted on external surface 28 of hub 29 formed on the first pulley section 20.

The wave washer 33 is accommodated in an annular recess 32 in the second pulley section 23 and held and compressed within the annular recess 32 by a cover member constituted by a cover plate 31 fixed to end 30 of the hub 29 to act between the recess bottom 35 and the cover plate 31 and bias the first and second contact surfaces 42, 43 of the pulley sections 20, 23 towards each other.

The annular recess 32 extends around the hubs 27 and 29 and has an inner wall 27a defined by the hub 27 of the second pulley section 23 and an outer wall 27b projecting axially from the second pulley section 23 in parallel with the inner wall 27a. The periphery of the cover plate 31 fits against an inner surface of the outer wall 27b, as can be seen more readily from Figures 3 and 4 to guard against the ingress of dust into the recess 33 and thus to the wave washer 33. The wave washer 33 is compressed, by a pre-set amount, within the annular 32 between surface 34 of the cover plate 31 and the recess bottom 35 of the second pulley section 23. The compression of the wave washer 33 biases the pulley sections 20, 23 towards each other to the position shown in Figure 3 so that the pins 24 are pushed into the holes 25.

The cover plate 31 is fixed to the end 30 of the hub 29 of the first pulley section 20 by six bolts 36 which pass through holes 37 in the cover plate 31 to engage in threaded bores 38 in the end 30 of the hub 29. The first pulley section 20 also has a circumferentially extending flange 40 with a first belt contact surface 42 and the second pulley section 23 also has a circumferentially extending flange 41 with a second belt contact surface 43. When the first and second pulley sections are mounted together, the flanges 40, 41 are adjacent each other but spaced from each other, as shown in Figures 3 and 4, so that the first and second contact surfaces 42, 43 face each other but are spaced from each other. As shown in Figure 3, the contact surfaces 42, 43 form a generally "V" shape when the first and second pulley sections 20, 23 are pushed together.

The wave washer 33 is shown in more detail in Figures 5, 6 and 7 where it can be seen that the wave washer 33 is in the form of a circular annular disc that has undulations 34 formed in the disc 33. In the example of the wave washer 33 shown in Figures 5 to 7 and used in the pulley assembly 7, there are three undulations 34 formed in the washer 33. However, any suitable number of undulations could be used, such as wo, four or more.

In use, the pulley assembly 7 is mounted on the drive shaft 6 so that the drive shaft 6 engages with the hole 22 in the hub 21. The drive belt 8 is entrained around pulley 9 and positioned between the flanges 40, 41 so that opposite edges of the drive belt 8 engage with the respective first and second contact surfaces 42, 43, as shown in Figures 3 and 4. When the power unit 3 is operating, the drive shaft 6 rotates the pulley assembly 7, which in turn causes the drive belt 8 to rotate and drive the pulley 9. Rotation of the pulley 9 rotates the mass within the gearbox 4, which causes a vibratory moment in the gearbox 4 that, in turn, causes vibrating movement of the compaction plate 5 to generate a compacting force on the ground underneath the compactor 1.

As explained above, when the mass is rotated and the gearbox 4 is generating vibrationary movement of the compact plate 5, there is a corresponding vibrationary movement of the pulley 9, which results in relative movement between the pulley 9 and the pulley assembly 7. When the pulley 9 moves towards the pulley assembly 7, the tension in the belt 8 will decrease. This reduction in tension means that the contact force between the belt 8 and the belt contacting surfaces 42, 43 is reduced and this permits the wave washer 33 to expand from its compressed position to move the pulley section 23 closer to the pulley section 20, as shown in Figure 3. In this position, the external surface 38 of the drive belt 8 is in line with line 50 shown in phantom in Figure 3.

However, as the pulley 9 moves away from the pulley assembly 7, this results in an increase in the tension of the drive belt 8, causing the force that the drive belt 8 exerts on the contact surfaces 42, 43 to increase. This increase in force on the contact surfaces 42, 43 acts to push the contact surfaces 42, 43 apart, causing the first and second sections, 20, 23 to move apart relative to each other and compress the wave washer 33, as sections 20, 23 move to the positions shown in Figure 4. As the contact surfaces 42, 43 move apart, the drive belt 8 also moves to the position shown in Figure 4 in which the external surface 38 of the drive belt 8 is a distance "y" radially inwardly from the line 50 shown in phantom in Figure 4. This corresponds to an increase in separation of the flanges 40, 41 of δx = X2 - Xi. When the belt 8 moves to the position shown in Figure 4 such that the external surface 38 of the belt 8 is a distance "y" from the line 50, this means that the effective radius of the pulley assembly 7 has been reduced by y and the effective circumference of the pulley assembly 7 has been reduced by 2πy. This enables the tension in the belt 8 to be maintained within acceptable limits as the pulley 9 moves relative to the pulley assembly 7.

The invention as described has the advantage that by using a wave washer 33 to dynamically compensate for changes in belt tension it is possible to extend the service life of the belt 8. In particular, it has been found that by using a wave washer 33, the effective service life of the belt 8 can be increased by enabling the circumference of the pulley assembly 7 to change to compensate for changes in the tension of the belt 8 caused by relative movement between the pulley 9 and the pulley assembly 7. The invention also has the advantage that the service life of the wave washer 33 is greater than the typical service life for disc springs and helical springs in this application.

Furthermore, using the wave washer 33 enables a relatively compact pulley assembly compared with a pulley assembly using helical springs.

Various modifications may be to the invention described with reference to the drawings without departing from the scope of the invention as defined in the appended claims. For example, the rotational fixing pins 24 on the first pulley section 20 with their complementary location holes 25 in the second pulley section 20 which allow relative sliding movement between the pulley sections may be replaced by any other suitable rotational fixing means such as providing the outer surface of the first pulley section hub 29 with flats, splines or other suitable formations with which the second pulley section hub 27 bore complementarily engages.

Claims

1. A pulley assembly having an axis of rotation and including first and second pulley sections defining first and second contact surfaces respectively which are separated from each other, which together form a frusto-conical surface and which, when considered in cross-section converge towards the axis, the first and second pulley sections being movably coupled to each other so that relative movement of the first and second pulley sections in an axial direction changes the separation of the first and second contact surfaces, and resilient means acting between the first and second pulley sections to bias the first and second contact surfaces towards each other and in the form of an undulating ring that is elastically deformable in the axial direction.

2. A pulley assembly as claimed in claim 1 , wherein the undulating ring is a wave washer.

3. A pulley assembly as claimed in claim 2, wherein the wave washer has at least two undulations.

4. A pulley assembly as claimed in any of claims 1 to 3, wherein the second pulley section is slidably mounted for axial movement on the first pulley section, with the first and second pulley sections being rotationally fixed and wherein the undulating ring is accommodated in af^-amytaf recess in the fifst second pulley section and held and compressed within the afmytef recess by a cover member fixed to the first pulley section to act between the recess bottom and the cover member and bias the first and second contact surfaces towards each other.

5. A pulley assembly as claimed in claim 4, wherein the second pulley section is slidably mounted for axial movement on the first pulley section by means of an axially extending hub which engages in a complementary bore in a hub of the second pulley section with the recess accommodating the undulating ring extending around the hubs of the first and second pulley sections respectively.

6. A pulley assembly as claimed in claim 5, wherein the recess accommodating the undulating ring has an inner wall defined by the hub of the second pulley section and an outer wall projecting axially from the second pulley section in parallel with the inner wall and wherein the cover member has a periphery that fits against an inner surface of the outer wall.

7. A pulley assembly as claimed in any of claims 4 to 6, wherein first pulley section hub has an axial bore which is adapted to be engaged with a drive shaft of a power unit.

8. A pulley assembly as claimed in any of claims 1 to 7 is adapted to be used with a V-belt to be located between the first and second contact surfaces of the first and second pulley sections.

9. A pulley assembly as claimed in claim 8, as appendant to claim 7, and coupled to the drive shaft of the power unit with the V-belt entrained around the pulley assembly and being used to drive another unit, such as a gear box or pump.

10. A plate compactor incorporating a frame, a power unit having a drive shaft and being mounted on the frame, a compactor plate assembly fixed to the frame through anti-vibration mounts, a gear box mounted to the compactor plate assembly and including a mass which is mounted on a rotatable shaft with its centre of gravity offset from the rotational axis of the shaft and a drive pulley mounted on the gear box shaft, a pulley assembly having an axis of rotation and being coupled to the power unit drive shaft, and a drive belt entrained around the pulley assembly and the gear box pulley, the pulley assembly including first and second pulley sections defining first and second contact surfaces respectively which are separated from each other, which together form a frusto-conical surface and which when considered in cross- section converge towards the axis, the first and second pulley sections being movably coupled to each other so that relative movement of the first and second pulley sections in an axial direction changes the separation of the first and second contact surfaces, and resilient means acting between the first and second pulley sections to bias the first and second contact surfaces towards each other and in the form of an undulating ring that is elastically deformable in the axial direction.

11. A plate compactor as claimed in claim 10, wherein the undulating ring is a wave washer.

12. A plate compactor as claimed in claim 11 , wherein the wave washer has at least two undulations.

13. A plate compactor as claimed in any of claims 10 to 12, wherein the second pulley section is slidably mounted for axial movement on the first pulley section with the first and second pulley sections being rotationally fixed and wherein the undulating ring is accommodated in an annular recess in the first pulley section and held and compressed within the annular recess by a cover member fixed to the first pulley section to act between the recess bottom and the cover member and bias the first and second contact surfaces towards each other.

14. A plate compactor as claimed in claim 13, wherein the second pulley section is slidably mounted for axial movement on the first pulley section by means of an axially extending hub which engages in a complementary bore in a hub of the second pulley section.

15. A plate compactor as claimed in claim 14, wherein the recess accommodating the undulating ring has an inner wall defined by the hub of the second pulley section and an outer wall projecting axially from the second pulley section in parallel with the inner wall and wherein the cover member has a periphery that fits against an inner surface of the outer wall.

16. A plate compactor as claimed in any of claims 13 to 15, wherein the first pulley section hub has an axial bore which engages with the power unit drive shaft.

17. A plate compactor pulley as claimed in any of claims 10 to 16, wherein the drive belt is a V-belt which is located between the first and second contact surfaces of the first and second pulley sections.