GB2461545A

GB2461545A - A centrifugal clutch

Info

Publication number: GB2461545A
Application number: GB0812116A
Authority: GB
Inventors: John Westwood Moore
Original assignee: Antonov Automotive Technologies BV; Antonov Automotive Europe BV
Current assignee: Antonov Automotive Technologies BV; Antonov Automotive Europe BV
Priority date: 2008-07-02
Filing date: 2008-07-02
Publication date: 2010-01-06
Anticipated expiration: 2028-07-02
Also published as: GB0812116D0; GB2461545B

Abstract

A centrifugal clutch 10, for a transmission unit that drives ancillary devices, comprises one or more flyweights or balls 46 that engage facing reaction surfaces 40, 42 of input and output parts 14, 18 and rotate about an axis of rotation of an input shaft 12. When the input shaft 12 rotates the balls apply a separation force acting to separate a first clutch surface 16 on the input part and a second clutch surface 20 on the output part. In a first range of rotational speeds of the input shaft the first and second clutch surfaces are engaged and the output part is locked to the input part and rotates with the rotating input shaft and in a second range of rotational speeds of the input shaft the output part is allowed to rotate independently from the input part.

Description

A CLUTCH DEVICE AND A TRANSMISSION UNIT

The present invention relates to a clutch device, in particular to a clutch device incorporating flyweights which effect disengagement of the clutch. The present invention also relates to a transmission unit, which is suitable for driving ancillary devices of an internal combustion engine, such as an alternator, a supercharger, a power steering pump, a water pump and an oil pump.

It is typical for internal combustion engines to be provided with a pulley mounted to the crankshaft which rotates at a crankshaft speed. This pulley is then connected by a belt or by belts to various devices driven by the internal combustion engine which are ancillary to the internal combustion engine itself (or, in certain applications, ancillary to the vehicle in which the internal combustion engine is provided) . To date, the ratio of the speed of rotation of the crankshaft to the speed of rotation of the ancillary devices is typically fixed for all engine speeds. However, this is disadvantageous. For instance, it is advantageous for a supercharger at low engine speeds to run at a speed which is a first higher multiple of crankshaft speed whilst at higher engine speeds the supercharger runs at second lower multiple of crankshaft speed. Traditional drive arrangements for superchargers do not permit this. The same logic also applies to the operation of alternators, power-assisted steering pumps, air-conditioning pumps, etc. The present invention provides a clutch device comprising an input shaft having an axis of rotation and an input part having a first clutch surface. The input part is mounted on the input shaft. An output part has a second clutch surface engageable with and disengageable from the first clutch surface. The output part is mounted around the input shaft and is rotatable relative thereto. Biasing means applies a biasing force acting to force the first and second clutch surfaces into engagement with each other. The input part and output part have facing reaction which a spacing therebetween which reduces outwardly from the input shaft. The input part and the input shaft abut along surfaces inclined to the axis of the rotation of the input shaft and torque is transmitted from the input shaft to the input part via the inclined abutting surfaces, the transmitted torque rotating the input part with rotation of the input part and also giving rise to an axial force which acts to force the first and second clutch surfaces into engagement with each other, the input part being moveable axially along the input shaft. One or more flyweights engage the reaction surfaces of the input and output parts and facing each flywieght rotates about the axis of rotation of the input shaft when the first input shaft rotates. The flyweights when rotating about the input shaft axis each apply a separation force acting to separate the first and second clutch surfaces. In a first range of rotational speeds of the input shaft the sum of the biasing force applied by the biasing means and the axial force resulting from torque transmission exceeds the separation force applied by the flyweight(s) and thereby the first and second clutch surfaces are engaged and the output part is locked to the input part and rotates with the rotating input shaft.

In a second range of rotational speeds of the input shaft, higher than the rotational speeds of the first range, the separation force applied by the flyweight(s) exceeds the sum of the biasing force and the axial force arising from torque transmission and thus the separation force disengages the first and second clutch surfaces and thereby the output part is allowed to rotate independently from the input part.

The clutch device provides for automatic shifting of gear ratios, without a need for electronics. The transmission unit provides two transmission ratios, using two pulleys, which are suitable for driving an ancillary device of an internal combustion engine. The shifting between two transmission ratios is provided by the clutch device.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a cross-section through the clutch device; Figure 2 is a front elevation view of a ball cage of the clutch device of Figure 1; and Figure 3 is a schematic representation of the transmission unit and auxiliary devices driven by the transmission unit.

In Figure 1 a clutch device 10 can be seen. The clutch device 10 is connected to an input shaft 12 which is driven by an internal combustion engine. The shaft 12 could be a crankshaft of the engine or could be a separate shaft mounted on or connected to the crankshaft to rotate therewith. An input part 14 of the device 10 engages the input shaft 12 via one or more helical spline(s) 28 which extend(s) around the input shaft 12. Drive is transmitted from the input shaft 12 to the input part 14 via the helical spline(s) 28, which mesh with matching helical groove(s) on a radially inwardly facing surface of an inner annular flange 40. Since the engaged surfaces of the input part 14 and input shaft are inclined relative to the rotational axis shaft 12, transmission of torque from the input shaft 12 to the input part 14 via the splined engagement gives rise to an axial force on the input part 14, acting along the axis of the input shaft 12. This urges the input part 14 to the right as seen in Figure 1. The input part 14 is movable axially relative to the input shaft 12, with rotation of the input part relative to the input shaft 12.

A spring 34 acts between the input part 14 and a fixed end stop 70 formed by a circlip encircling the spring shaft 12. The spring 34 biases the input part 14 to the right as shown, in the same direction as the input part 14 is urged by the axial force arising from the meshing of the helical splines 28 with their matching grooves during torque transmission.

The input part 14 is provided with an frusto-conical input clutch surface 16 spaced radially outwardly from the drive shaft 12. The input clutch surface 16 is angled to the axis of input shaft 12 preferably by an angle of around 8°.

The clutch device 10 comprises an output part 18. The output part 18 has a frusto-conical output clutch surface 20 facing the input clutch surface 16. The input clutch surface 16 and output clutch surface 20 together form a cone S clutch. The output part 18 has an annular outer surface 22 radially spaced from the drive shaft 12. The outer surface 22 is shown grooved to receive a belt, but may be toothed to engage with a gear. The output part 18 has an inner annular flange 26 spaced radially outwardly from and extending over a radially outwardly facing surface of the inner annular flange 40 of input part 14, a bearing 30 acting between facing surface of the flanges 26, 40. An additional bearing 32 is provided to act between an end face of the output part 18 and a facing surface of an annular shoulder 24 provided on input shaft 12.

The input part 14 and output part 18 have facing reaction surfaces, a reaction surface 40 on the input part and a reaction surface 42 on the output part 18. These surfaces 40, 42 face each other and are inclined relative to a radial place perpendicular to the axis of shaft 12. They are profiled to define a tapering spacing therebetween, the width of the space 44 reducing as the radial distance from the input shaft 12 increases. The reaction surfaces 40,42 are preferably each inclined at a 10° angle to the radial plane, with a separation distance between them reducing with increasing radial distance from the axis of input shaft 12.

The reaction surfaces 40,42 are spaced apart along the axis of the input shaft 12.

Flyweights in the form of a spherical ball bearings 46 are located in a ballcage 44, seen best in Figure 2. Each ball bearing 46 may have a radius of 1cm. The clutch device illustrated comprises four flyweights in the form of four ball bearing 46 equally spaced in a ring around the annular clutch device 10. Each ball bearing 46 is located between a pair of walls of the ball cage, a separate pair of walls being provided for each ball bearing; four pairs of walls are shown in Figure 2: a first pair 70,71; a second pair 72,73; a third pair 74,75; and a fourth pair 76,77. The walls provide four identically-shaped pockets spaced circumferentially around the input shaft 12. Each ball bearing 46 can move radially inwardly and outwardly along the pocket defined by the walls associated therewith, but is constrained from moving in other directions. Each ball bearing 46 is free to rotate within its pocket and the ball cage 44 is free to rotate about the axis of the input shaft 12; this allows for relative motion between the reaction surfaces 40,42 engaged by the ball bearings 46, with the ball bearings 46 rotatably within their pockets. The ball cage 44 has an inner annular ring 80 which surrounds the inner annular flange 26 of the output part 18 and an inter annular flange 26 of the output part 18 and an outer annular ring 81 which lies alongside an inwardly facing surface of the clutch surface section of the input part 14. The ball cage 44 will typically be made of a plastic and serves to maintain spacing between the ball bearings 46.

The reaction surfaces 40,42 are profiled such that when the ball bearings 46 are at the innermost ends of their pockets, closest to the input shaft 12, the clutch plates 16,20 fully engage each other, such that the cone clutch is engaged. The clutch plates 16, 20 engage each other under the axial force applied by the spring 34 and the axial force arising from the interaction of the helical splines with their matching grooves.

Each ball bearing 46 has a diameter greater than the s separation distance by which the outer the parts of reaction surfaces 40,42, furthest from the drive shaft 12 are separated when the clutch plates 16, 20 are fully engaged as illustrated in Figure 1. Rotation of the input shaft 12 can cause ball bearings 46 to move radially outwardly from the shaft 12, along the reaction surfaces 40, 42, forcing the reaction surfaces 40,42 and hence the input part 14 and the output part 18 to separate. When the ball bearings 46 move to their radially outermost locations then a the clutch plates 16,20 are completely separated. When the clutch plates 16,20 are separated, then the output part 18 is not driven and can rotate relative to the input part 14. The bearing 30 acting between the output part 18 and input part 14 allows the output part 18 and input part 14 to rotate at different speeds. The bearing 32 acting between the output part 18 and the input shaft 12 also allows the output part 18 to rotate at a different speed to the input shaft 12.

The output part 18 is prevented from moving axially along the axis of the drive shaft 12 by the shoulder 24, which is shown integrally formed with the drive shaft 12, but could be a separate component attached to the input shaft 12.

At low rotational speeds of the drive shaft 12, the axial forces arising from torque transmitted via the helical spline 28 to the output part 14 and the spring force applied by spring 34 urge the clutch surfaces 16,20 to engage each other and thus the input part 14 and output part 18 rotate together at the same speed. Each ball bearing 46 sits in a radially inner portion of its pocket, relatively close to the input shaft 12, and does not exert sufficient force on the reaction surfaces 40,42 to force the input and output parts 14,18 apart.

As the speed of rotation increases above a pre-determined speed, e.g. 1600 r.p.m., a shift point is reached. At this point, the separation force applied to reaction surfaces 40,42 by the rotating ball bearings 46 overcomes the sum of the axial force arising from the helical splines 28 and the axial force applied by the spring 34. Each ball bearing 46 moves radially outwardly along the inclined reaction surfaces 40,42, causing axial movement of the input part 14 along shaft 12 (to the left as seen in Figure 1) . The clutch surfaces 16,20 then disengage. The output part 18 is then no longer driven by the input part 14 and input shaft 12, and so reduces in speed. The belt or gear (not shown) connected to outer surface 22 is then not driven by the drive shaft 12. Once the clutch surfaces 16,20 separate and drive is no longer transmitted from the input part 14 to output part 19, torque is no longer applied by the input shaft 12 to the input part 14 and therefore the axial force on the input part 14 arising from the applied torque substantially reduces. This ensures good reliable disengagement of the clutch, since at the threshold point increased rotational speed of the ball bearings results not only in increased separation force applied by the ball bearings, but also a reduced axial force resisting separation. The same applies in reverse since when the clutch surfaces engage following disengagement, the engagement increases the torque transmitted and therefore increases the axial force applied acting to engage the clutch surfaces.

Figure 3 shows a transmission unit 50, which includes the clutch device 10. The transmission unit 50 receives drive from a driveshaft. The transmission unit 50 comprises a primary pulley 56 engaging a primary belt 52. The primary pulley 56 is provided by the surface 22 of the clutch device 10. The primary belt 52 engages with one or more engine ancillaries 62 and or more belt tensioners.

The transmission 50 unit also comprises a secondary pulley 58, of smaller diameter than the primary pulley 56. A one-way clutch (not shown) connects the secondary pulley 58 to the drive shaft 12. The one-way clutch can overrun the input shaft whilst the primary pulley 56 is driving the belt 52. The one-way clutch allows the secondary pulley 58 to run faster than the drive shaft, but not slower (i.e. the one-way clutch allows the secondary pulley 58 to rotate relative to the drive shaft in one rotational sense only) A secondary belt 54 connects secondary pulley 58 with a tertiary pulley 60. The primary belt 52 also engages with tertiary pulley 60 and the ancillaries 62. The tertiary pulley 60 has the same diameter for both the primary belt 52 and the secondary belt 54.

At low engine rotational speeds, the clutch device 10 connects the primary pulley 56 to the drive shaft to rotate the primary pulley 56. At low engine speeds the clutch 10 is engaged. The output part 18 drives belt 52 to drive the -10 -ancillaries at a first transmission ratio. The tertiary pulley 60 is also rotated by the belt 52, which causes the belt 54 to be driven and the secondary pulley 58 to rotate faster than the primary pulley 56. The one-way clutch allows S the secondary pulley 58 to over-run the drive shaft.

At high engine rotational speeds, the clutch device disengages the pulley 56, such that the pulley 56 is not driven by the driveshaft. In the clutch device 10, the ball bearing flyweights 46 are urged radially outwardly by the speed of rotation of the drive shaft 12, urging apart the input part 14 and output part 18 and thus the clutch surfaces 16,20 are disengaged.

Since the clutch 10 is disengaged at high engine speeds the primary belt 52 is no longer driven via the device and the belt speed slows until the one-way clutch locks the pulley 58 to the drive shaft, the pulley 58 driving the belt 54, which drives pulley 60. The pulley 60 also drives the primary belt 52, and hence the ancillaries 62. Since the pulley 58 has a smaller diameter than pulley 56, the pulley is driven with a second, lower, transmission ratio than at lower rotational speeds. Thus, a lower transmission ratio is achieved when the input rotational speed is above the shifting point.

The switching between transmission ratios allows operation of the ancillaries to be improved. For example, an alternator would generate more electrical power at lower engine speeds than it would otherwise. Smaller-sized ancillaries, e.g. alternators, can be used than in comparable engines with fixed transmission ratios at present -11 -the size is dictated by the need to produce enough output at low rotational speeds.

Although the two-speed transmission unit has been described above in its use in connection with an internal combustion engine and in use driving engine ancillaries, it is not limited to such use and could be used in any application where a two-speed drive is needed with the speed change occurring mechanically without the need for supply of hydraulic pressure to the transmission unit or electrical/electronic control. Nevertheless, the unit is of particular advantage in its use with an internal combustion engine since a plurality of different ancillaries of the engine can be driven from a single transmission unit which requires no connection to the hydraulic circuits of the engine, nor any electronic or electrical control by the engine management system. The transmission unit can easily be fitted with existing engine designs without requiring substantial modifications of the existing engine designs.

Whilst above conical clutch surfaces 16,20 are disclosed, other clutch surfaces could be used, e.g. clutch plates or multiple conical surface at different radii. Any frictional engagement between two surfaces would suffice.

Whilst above ball bearings are used as flyweights, other types of flyweights could be used, e.g. roller bearings mounted in radially slidable carriages.

The spring 34 mentioned above could be replaced by a resilient biasing member, e.g. a compliant block.

-12 -The arrangement of helical splines and helical grooves mentioned above could be replaced by an arrangement of threads on both the input shaft 12 and input part 40, or by engaging ramped surfaces. Only a very short travel of the S input part 14 is needed. Any arrangement of engaging surfaces in which an applied torque gives to an axial force Above, the engagement surfaces 40,42 are frusto-conical in profile. However, other profiles may be preferred with more complicated profiles giving the possibility of greater variation rotational speed for clutch disengagement with variation in applied torque, e.g. the mechanical advantage can be altered by the selection of profiled surfaces. 13 -

Claims

CLAIMS1. A clutch device comprising: an input shaft having an axis or rotation; an input part having a first clutch surface, the input part being mounted on the input shaft; an output part having a second clutch surface engageable with and disengageable from the first clutch surface, the output part being mounted around the input shaft and being rotatable relative thereto; and biasing means which applies a biasing force acting to force the first and second clutch surfaces into engagement with each other; wherein: the input part and output part have facing reaction surfaces with a spacing therebetween which reduces radially outwardly from the input shaft; the input part and the input shaft abut along surfaces inclined to the axis of rotation of the input shaft and torque is transmitted from the input shaft to the input part via the inclined abutting surfaces the transmitted torque rotating the input part with rotation of the input part with rotation of the input shaft and also giving rise an axial force acting to force the first and second surfaces into engagement with each other the input part being movable axially along the input shaft; one or more flyweight(s) engage the facing reaction surfaces of the input and output parts and each flyweight rotates about the axis of rotation of the input shaft when the input shaft rotates and each flyweight when rotating about the input shaft axis applies a separation force acting to separate the first and second clutch surfaces; -14 -in a first range of rotational speeds of the input shaft the sum of the biasing force applied by the biasing means and the axial force resulting from torque transmission exceeds the separation force applied by the flyweight(s) and thereby the first and second clutch surfaces are engaged and the output part is locked to the input part and rotates with the rotating input shaft; and in a second range of rotational speeds of the input shaft, higher than the rotational speeds of the first range, the separation force applied by the flyweight(s) exceeds the sum of the biasing force and the axial force arising from torque transmission and thus the separation force disengages the first and second clutch surfaces and thereby the output part is allowed to rotate independently from the input part.
2. A clutch device as claimed in claim 1 wherein the input part and the input shaft abut along inclined surfaces provided by helical splines on one of the input shaft or input part meshing in helical grooves on the other of the input shaft or input part.
3. A clutch device as claimed in claim 1 or claim 2 wherein each of the first and second clutch surfaces is frusto-conical in configuration.
4. A clutch device as claimed in any one of the preceding claims wherein each flyweight is a ball bearing.
5. A clutch device as claimed in claim 4 wherein each ball bearing is mounted in a ball cage provided between the facing reaction surfaces, the ball cage having for each ball -15 -bearing a pocket which locates the ball bearing while allowing the ball bearing to move radially relative to the input shaft and to rotate by engagement with the reaction surfaces.
6. The clutch device as claimed in any one of the preceding claims wherein the output part has an annular outer surface radially spaced apart from the input shaft, the annular outer surface being engageable by a belt.
7. A clutch device as claimed in any one of the preceding claims wherein the ouput part has a radially inner flange which overlies a radially inner flange of the input part and is separated therefrom by a bearing.
8. A clutch device as claimed in any one of the preceding claims wherein a shoulder is coupled to or integral with the input shaft and provides an end stop limiting axial motion of the output part relative to the input shaft.
9. A clutch device as claimed in claim 8 comprising a second shoulder coupled to or integral with the input shaft which provides an end stop limiting axial motion of the input part relative to the input shaft.
10. A clutch device as claimed in claim 9 wherein the biasing means acts between the second flange and the first part.
11. A transmission unit comprising: -16 -a clutch device as claimed in any one the claims 1 to 10; a primary pulley provided by or attached for rotation with the output part of the clutch device; a secondary pulley coupled to the input shaft by a one-way clutch and driven by the input shaft in the second range of high rotational speeds of the input shaft; a first belt driven by the primary pulley which relays drive to engine ancillaries; a second belt driven by the secondary pulley; a tertiary pulley engaged by both the first belt and the second belt; wherein: in the first range of low rotational speeds the clutch device connects the input shaft to the primary pulley such that the primary pulley drives the first belt with a first transmission ratio; and in the second range of high rotational speeds the clutch device disengages the primary pulley from the input shaft and the one-way clutch locks the secondary pulley to the input shaft to rotate therewith, such that the secondary pulley drives the tertiary pulley via the second belt, the tertiary pulley driving the first belt in a second transmission ratio different from the first transmission ratio.
12. A transmission unit as claimed in claim 11 wherein the primary pulley has a diameter greater than the secondary pulley, and the tertiary pulley has the same diameter for both the first and second belts, such that the first transmission ratio is higher than the second transmission ratio.

-17 -
13. An internal combustion engine comprising: a crankshaft; a transmission unit as claimed in claim 11 or claim l2in which the input shaft is provided by or driven by the crankshaft; an engine-driven ancillary having an ancillary pulley via which drive is relayed to the ancillary; and an output belt connecting the transmission unit to the ancillary pulley.
14. An internal combustion engine as claimed in claim 13 which comprises a plurality of engine-driven ancillaries, each of which has an ancillary pulley, wherein: the output belt connects the output pulley of the transmission unit to all of the ancillary pulleys of the engine-driven ancillaries.
15. An internal combustion engine as claimed in claim 13 or claim 14 wherein the engine-driven ancillaries comprise one or more of: a supercharger; an alternator; an oil pump; a water pump; power-assisted steering pump and/or an air conditioning pump.
16. A clutch device as hereinbefore described with reference to and as shown in the accompanying figures 1 and 2.
17. A transmission unit as hereiribefore described with reference to and as shown in the accompanying figure 3.