GB2413615A

GB2413615A - A clutch friction plate assembly

Info

Publication number: GB2413615A
Application number: GB0409825A
Authority: GB
Inventors: Daryl Keith Amos; Laurence Albon
Original assignee: SAFE DEVELOPMENTS Ltd
Current assignee: SAFE DEVELOPMENTS Ltd
Priority date: 2004-05-01
Filing date: 2004-05-01
Publication date: 2005-11-02
Also published as: GB0409825D0

Abstract

A clutch friction plate assembly (1) comprises a hub (7a, 7b) with a friction plate (2) coaxially mounted on the hub (7a, 7b) such tat rotation of friction plate (2) relative to the hub (7a, 7b) is possible. Acting between the friction plate (2) and hub (7a, 7b) is a relatively high stiffness spring to absorb high torque pulses applied between the friction plate (2) and hub (7a, 7b). Low stiffness springs are arranged to act between the friction plate (2) and the hub (7a, 7b). This in combination with the inertia associated with the input shaft of the gear box provides a mass spring system which can have a sufficiently small resonant frequency so that compression torque pulse associated with the engine at idle can be absorbed, reducing gearbox rattle.

Description

A CLUTCH FRICTION PLATE ASSEMBLY

The present invention relates to clutch friction plate assembly and in particular to clutches for internal combustion engines, where cyclic torque fluctuations are experienced.

Internal combustion engines produce power in pulses which occur only on the expansion stroke of the engine, for example a single cylinder, four stroke engine will produce one pulse every two revolutions of the crank. Multi-cylinder engines produce more frequent torque pulses and thus have a smoother torque output. The most commonly used engine for passenger cars is the in line four cylinder engine which produces two pulses per revolution. The diesel engine produces significantly higher levels of torque fluctuation due to the higher compression ratios used and, at idle, the engine is unthrottled which further exacerbates the problem. The torque fluctuations can have undesirable affects on the vehicle drivability but more significantly can result in gearbox noise and rattle which is difficult to suppress.

A flywheel is attached to the engine primarily to ensure that there is sufficient energy stored to keep the engine running and secondarily to smooth torque delivery. The flywheel effectiveness is a function of speed, the energy stored being related to the square of the angular velocity. Thus, at low engine speed, particularly at idle, it is difficult to obtain smooth engine operation with a flywheel designed for mild-range performance.

Using a heavy flywheel specifically for a low speed torque control, would result in a flywheel of high inertia that would adversely affect the vehicle performance.

The problem has been addressed in the past by use of a twin mass flywheel to isolate torque pulses from the transmission. A twin mass flywheel is of similar size and overall inertia to a conventional flywheel but consists of two inertia flywheel components joined together via energy storage devices, for example torsional springs. The first component is attached to the engine crankshaft and provides sufficient inertia to keep the engine turning at idle, whilst the second component is attached to the vehicle clutch plate.

The torsional spring rate is chosen so that the natural frequency of the second component, and clutch plate is lower (typically about half) than the idle torque pulse frequency of the engine, but higher than that associated with the engine cranking speed. This ensures that the spring mass system will attenuate the engine torque pulses at all normal engine speeds.

One disadvantage of the twin mass flywheel is that engine vibration is poorly controlled by the light part of the flywheel which is directly attached to the crankshaft, so that the amplitude of vibrations on the engine side can be significantly worse than those with a conventional flywheel. This can result in expensive component upgrading to withstand these vibrations, so that an engine with a twin mass flywheel may require a chain rather than belt for the cam drive. Furthermore, the drive line behaviour can be adversely affected resulting in poor response due to the soft spring in the twin mass flywheel.

The problems associated with torque pulses of internal combustion engines at idle are further compounded by the continual drive to reduce the overall weight of a vehicle, and inertial associated with the vehicle, in order to make the vehicle more responsive. This has resulted in low inertia gearboxes which, together with high efficiency engines having - 3 higher compression ratios, thus larger amplitude torque pulses, tends to increase idle gear rattle in the gear box.

Most clutch friction plate assemblies comprise a spline for locating the assembly on the input shaft to the gearbox. The spline supports the clutch friction plate and possibly high stiffness compression springs (for smoothing large torque spikes that may be experienced when the clutch is rapidly engaged). The spline comprises a mechanism to permit relative movement between the spline and the remainder of the friction plate assembly which it supports, the mechanism employing a number of relatively low stiffness springs. When the gearbox is engaged and is driven by the engine these low stiffness springs remain in a compressed state. However, at idle with the gearbox in neutral these springs absorb the low energy torque pulses generated by the engine. The resonant frequency of this spring mass system must be significantly below the frequencies associated with the engine at idle. Since the resonant frequency is determined by the square root of the torsional stiffness divided by the moment of inertia, any reduction in the moment of inertia associated with the input shaft of the gearbox (which includes those components which are engaged with the input shaft when the gearbox is in neutral) require a corresponding reduction in the stiffness of the low stiffness springs if the same resonant frequency is to be maintained. However, the stiffness of the springs in some applications cannot be further reduced without those springs being overcome by the drag associated with the input shaft of the gearbox and related components, even when the gearbox is in neutral.

According to a first aspect of the present invention there is provided a clutch friction l

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plate assembly comprising: a central hub arranged to be mounted in a rotationally fixed position on the input shaft of a gearbox; a friction plate coaxially mounted on the hub; and a relatively high stiffness resilient means arranged to act between the friction plate and the hub to permit limited rotation of the friction plate relative to the hub when a relatively large torque is applied between the friction plate and the hub; a relatively low stiffness resilient means arranged to act between the friction plate and the hub to permit limited rotation of the friction plate relative to the hub when a relatively small torque is applied between the friction plate and the hub; wherein the low stiffness resilient means and high stiffness resilient means are arranged in series, with the low stiffness resilient means acting between the friction plate and the high stiffness resilient means.

As used in context of the present specification, "high stiffness" is defined as a stiffness sufficient to suppress high energy torque pulses, that would be experienced by the clutch friction plate assembly, when the gearbox to which the clutch friction plate assembly is to be attached is "in gear". Similarly, the term "a relatively low stiffness" is defined as a stiffness value sufficiently small that the resilient means would be distorted by torque pulses experienced by the clutch friction plate assembly when attached to a gearbox in neutral, driven by an engine at idle, namely those due to the compression cycles of the engme.

Employing the present invention, where the mass of the hub of the clutch friction plate assembly is mounted in a rotationally fixed position on the input shaft of a gearbox, results in the inertia associated with the hub becoming part of the inertia of the gearbox - 5 input shaft, significantly increasing the inertia of the gearbox input shaft as a result of the hub having a relatively large moment of inertia due to its comparatively large diameter.

The clutch friction plate assembly, comprising a relatively low stiffness resilient means arranged to act between the friction plate and the hub to permit limited rotation of the friction plate relative to the hub when a relatively small torque is applied between the friction plate and the hub, permits torque pulses associated with an engine at idle (and a gearbox in neutral) to be absorbed by the low stiffness resilient means. However, because of the increased inertia associated with the gearbox input shaft, the stiffness of the low stiffness resilient means can be greater for a given resonant frequency, thus the stiffness can be sufficient to overcome the drag associated with the input shaft of the gearbox.

The low stiffness resilient means and high stiffness resilient means are arranged in series, with the low stiffness resilient means acting between the friction plate and the high stiffness resilient means. The high stiffness resilient means may comprise a plurality of relatively high stiffness compression springs. The mass associated with these springs will remain in a fixed position on the hub and therefore also add to the inertia of the input shaft of the gearbox. The hub will typically have a plurality of apertures with each aperture retaining one of the respective high stiffness compression springs.

Preferably, the assembly further comprises a camplate on which the friction plate is coaxially mounted, the camplate being coaxially mounted on the hub such as to permit relative rotation of the camplate and friction plate relative to the hub, the camplate - 6 comprising a plurality of cam surfaces arranged to engage with the high stiffness compression springs.

More preferably, the hub comprises two discs between which the camplate is S sandwiched, the two discs having corresponding pairs of apertures, each pair of apertures retaining respective sides of an associated high stiffness compression spring, wherein a cam surface of the camplate extends between the two discs of the carnplate and acts upon the high stiffness compression spring.

In one embodiment of the invention the low stiffness resilient means may comprise a plurality of low stiffness compression springs, each low stiffness compression spring being arranged in series with a respective high stiffness compression spring, each pair of springs being arranged such that a torque applied between the friction plate and the hub acts to first compress the low stillness compression spring before compressing the high stiffness compression spring. The low and high stiffness compression springs may be arranged coaxially, with the cam surface of the camplate initially acting to compress the low stiffness spring prior to compressing the high stiffness spring.

The hub may comprise additional high stillness compression springs alone, wherein the camplate is arranged to first compress the low stiffness springs. The advantage of this arrangement is that only a small number of springs may be necessary to transmit idle torque pulses, whereas a large number of high stiffness springs may be necessary to cope with high energy torque pulses or spikes.

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Preferably, the assembly comprises at least one mechanical stop to limit rotation of the friction plate relative to the hub, thus preventing the springs from becoming coil bound.

It is preferable that the mass of the hub and stiffness of the low stiffness resilient S means are selected such that the hub has a resonant frequency of less than 1.4 of the second order frequency of an engine with which the clutch assembly is intended to be used, when that engine is at idle. This will result in efficient isolation of torque pulses at idle speeds and thus significantly reduce gearbox rattle. Preferably, the mass of the hub and the stiffness of the low stiffness resilient means are such that the hub has a resonant frequency of less than 20 Hz.

According to a second aspect of the present invention there is provided a clutch friction plate assembly having an idle spring mass (spring/moment of inertia) system with a resonant frequency of less than 20 Hz.

One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying figures, of which: Figure 1 is an exploded perspective view of a clutch friction plate assembly in accordance with the present invention; Figure 2a is a front elevation of the camplate illustrated in Figure 1; Figure 2b is a side elevation of the camplate of Figure 2a; Figure 2c is a rear elevation of the camplate of Figure 2a; Figure 2d is a cross-section along the line II- II of Figure 2c;

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Figure 3a is a front elevation of a front disc of the hub of Figure 1; Figure 3b is a side elevation of the disc of Figure 3a; Figure 3c is a rear elevation of the disc of Figure 3a; Figure ad is a cross-section along the line IIIa-IIIa of Figure 3c; Figure Be is a cross-section along the line IIlb-IIIb of Figure 3c; Figure 4a is a front elevation of the rear disc of the hub of Figure 1; Figure 4b is a side elevation of the disc of Figure 4a; Figure 4c is a cross-section along the line IV-IV of Figure 4a; Figure Sa is a front elevation of the clutch friction plate assembly of Figure 1; Figure Sb is a cross-section along the line V-V of Figure Sa; Figure 6a corresponds to Figure Sb; Figure 6b shows the components of the friction plate of Figure 6a; Figure 6c shows the components of the hub assembly of Figure 6a; and Figure 7 is a crosssection along the line VI-VI of Figure Sb.

Referring to Figure 1, the clutch friction plate assembly 1, comprises a friction plate 2 arranged to be sandwiched between a flywheel (not shown) and the pressure plate of the clutch (not shown) such that when the clutch is engaged the flywheel drives the friction plate in a conventional manner.

The friction plate 2 is mounted by means of segments 4 and segment rivets S to a camplate 6. The camplate 6 is shown in more detail in Figures 2a to 2d, which are a front elevation, a side elevation, a rear elevation and a cross-section along the line II-II of Figure - 9 - 2c respectively.

The clutch friction plate assembly additionally comprises a hub 7 comprising the front disc 7a and a rear disc 7b, which are bolted together by bolts 8 sandwiching the camplate 6 therebetween. As will become clearer from the description below of Figures 6a to 6c, the camplate 6 can rotate relative to the hub 7. The front disc 7a of the hub 7 is shown in more detail in Figures 3a to Be, a front elevation, a side elevation, a rear elevation, a cross-section along the line IIIa-IIIa and the cross-section along the line IIIb-IIIb of Figure 3c respectively.

The rear disc 7b of the hub 7 is shown in more detail in Figures 4a to 4c, a front elevation, a side elevation and a cross-section a long the line IV-IV of Figure 4a respectively.

IS The camplate 6 comprises four slots 9 for receiving stop pins 10. These stop pins are retained in a fixed positional relationship relative to the hub 7 by screws 11, extending through holes 12 in the front disc, through respective stop pins 10 to engage with threaded holes 13 in the rear disc 7b of the hub 7. These stop pins engaging with the slots 9 limit the maximum relative rotation that can occur between the hub 7 and the camplate 6 and thus between the hub 7 and the friction plate 2.

The front disc 7a of the hub 7 has a plurality of apertures 14 corresponding to similar apertures 15 in the rear disc 7b. The width of each aperture is tapered away from the - 10 central plane, defined between the front and rear discs 7a and 7b, of the hub 7. Between each associated pair of apertures of the front disc and rear disc is sandwiched a respective spring assembly 16. The spring assemblies 16, in addition to being sandwiched transversely between the front and rear discs 7a, 7b of the hub 7 are also sandwiched axially between cam faces 17a and 17b of the camplate 6, as will be described below in more detail with reference to Figure 7.

The hub 7 additionally comprises a splined member 18 which is splined internally and extemally, the internal splines are arranged to engage with splines on an input shaft of the gearbox (not shown) and the external splines engage with the hub front disc 7a and rear disc 7b. However, it will be appreciated that the front disc 7a and the rear disc 7b could have an internal spline of appropriate dimensions such that they can be directly fitted to the input shaft of a gearbox, without employing splined member 18.

Referring to Figure 5a, the assembled clutch friction plate assembly 1 is shown in plan view with Figure 5b a cross-section along the line V-V of Figure 5a. The camplate 6 can rotate about the hub 7 via bearing surfaces 31. For clarity, Figures 6a to 6c have been included, Figure 6a is identical to Figure 5b, Figure 6b shows those components rotating with the friction plate 2 and camplate 6 and Figure 6b shows those components that remain fixed with the hub 7.

Figure 7 a cross-section along the line VI-VI of Figure 5b. The spring assemblies 16 comprise two types, multi-stage spring assembly 16a and single stage spring assembly - 11 16b. Regardless of the spring assembly type, each is held in associated apertures 15 in the rear disc 7b of hub 7. On application of a torque applied by friction plate 2 to the camplate 6, in the direction of arrow 19, appropriate cam faces 17b act on spring assemblies 16a. As the spring assemblies 16a are compressed, the camplate 6 rotates in the direction of arrow 19 relative to the hub 7. As the torque increases, appropriate cam faces 17b engage and start to compress spring assembly 16b. As the torque is increased, the camplate 6 will further rotate in the direction of arrow 19, relative to the hub 7, until stop pins 10 engage the ends 20 of respective slots 9, preventing the springs within the spring assemblies 16 becoming coil bound.

The spring assemblies 16b each comprise two high stiffness coaxial compression springs 21, 22 sandwiched between end caps 23a and 23b. Spring assemblies 16a comprise similar pairs of high stiffness compression springs 24 and 25 retained at one end by an end cap 27. The spring assemblies 16a, at the other end to the end cap 27, include an inner top hat end cap 28 and an outer top hat end cap 29. The inner top hat end cap 28 has an aperture through which the outer top hat end cap 29 can slide. Between the inner 28 and outer 29 top hat end caps are located low stiffness compression springs 30.

On application of a small torque between camplate 6 and hub 7 the low stiffness compression springs 30 are compressed by the action of cam surfaces 17b acting on the spring assemblies 16a.

The stiffness of the low stiffness compression springs 30 is selected such that the - 12 two springs are sufficient to overcome the drag of the input shaft of the gearbox to which the hub 7 is mounted, when the gearbox is in neutral. However, the stiffness of the springs is sufficiently weak that the resonant frequency of the spring mass system, comprising the springs 30 and the inertia of the input shaft of the gearbox, with the hub 7 mounted thereon, is less than 1.4 of the second order frequency of an engine with which the assembly is intended to be used, where the resonant frequency CDr = : K = spring stiffness I = inertia of gearbox input shaft.

When the engine is at idle and the gearbox is in neutral torque pulses, associated with the compression cycles of the engine, will be absorbed by the springs 30 and thus the high stiffness compression springs 21, 22, 24 and 25 will all remain in an fixed positional relationship relative to the hub. Thus the mass of those springs add to the inertia of the hub.

When a gear is engaged in the gearbox, a high torque can be applied between the camplate 6 and hub 7. This causes the top hat end caps 28 and 29 to engage each other and to prevent further compression of springs 30. Further increases in the torque thus then acts directly to compress high stiffness springs 21, 22, 24 and 25.

The above describes a preferred embodiment of the present invention. However, a - 13 skilled person will realise that many alternative embodiments of the invention are possible within the scope of the appended claims. l - 14

Claims

1. A clutch friction plate assembly comprising: a central hub arranged to be mounted in a rotationally fixed position on the input shaft of a gearbox; a friction plate coaxially mounted on the hub; and a relatively high stiffness resilient means arranged to act between the friction plate and the hub to permit limited rotation of the friction plate relative to the hub when a relatively large torque is applied between the friction plate and the hub; a relatively low stiffness resilient means arranged to act between the friction plate and the hub to permit limited rotation of the friction plate relative to the hub when a relatively small torque is applied between the friction plate and the hub, wherein the low stiffness resilient means and high stiffness resilient means are arranged in series, with the low stiffness resilient means acting between the friction plate and the high stiffness resilient means.

2. An assembly as claimed in Claim 1, wherein the high stiffness resilient means comprises a plurality of relatively high stiffness compression springs and the hub has a plurality of apertures each holding a respective high stiffness compression spring in position on the hub.

3. An assembly as claimed in Claim 2, further comprising a camplate on which the friction plate is coaxially mounted, the camplate being coaxially mounted on the hub such - 15 as to permit relative rotation of the camplate and friction plate relative to the hub, the camplate comprising a plurality of cam surfaces arranged to engage with the high stiffness compression springs.

4. An assembly as claimed in Claim 3, wherein the hub comprises two discs between which the camplate is sandwiched, the two discs having corresponding pairs of apertures, each pair of apertures retaining respective sides of an associated high stiffness compression spring, wherein the cam surfaces of the camplate extend between the two discs of the camplate and act upon the compression springs.

5. An assembly as claimed in Claim 4, wherein the low stiffness resilient means comprises a plurality of low stiffness compression springs, each low stiffness compression spring being arranged in series with a respective high stiffness compression spring, each pair of springs being arranged such that a torque applied between the friction plate and the hub acts to first compress the low stiffness compression spring prior to compressing the high stiffness compression spring.

6. An assembly as claimed in Claim 5, wherein the hub comprises at least one pair of high and low stiffness compression springs arranged coaxially, wherein the cam of the camplate initially acts to compress the low stiffness compression spring prior to compressing the high stiffness compression spring.

7. An assembly as claimed in Claim 6, wherein the hub comprises a plurality of low - 16 stiffness and high stiffness compression spring pairs and a plurality of high stiffness compression springs alone, wherein the camplate is arranged to first compress the low stiffness springs.

8. An assembly as claimed in any preceding claim, further comprising at least one mechanical stop to limit rotation of the friction plate relative to the hub.

9. An assembly as claimed in any preceding claim, wherein the moment of inertia of the hub and stiffness of the low stiffness resilient means are such that the hub has a resonant frequency of less than 1.4 of the second order idle frequency of an engine with which the assembly is intended to be used.

10. An assembly as claimed in any preceding claim, wherein the moment of inertia of the hub and the stiffness of the low stiffness resilient means are such that the hub has a resonant frequency of less than 20 Hz.

11. A clutch friction plate assembly having an idle spring mass system having a resonant frequency of less than 20 Hz.

12. A clutch friction plate assembly, substantially as hereinbefore described, with reference to, and/or as illustrated in, one or more of the accompany figures.