GB2294300A

GB2294300A - Transmission assembly having clutches

Info

Publication number: GB2294300A
Application number: GB9521470A
Authority: GB
Inventors: Ian Antony Nash
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1994-10-21
Filing date: 1995-10-19
Publication date: 1996-04-24
Anticipated expiration: 2015-10-19
Also published as: GB9521470D0; GB2294300B

Abstract

A transmission assembly for a motor vehicle including a primary clutch (30) having a first predetermined maximum torque capacity and a secondary clutch 40 having a second predetermined torque capacity which is lower than the first predetermined maximum torque capacity and which enables the second clutch to slip on the imposition of torque impulses above said second predetermined torque capacity. The primary and secondary clutches may (as shown) be disposed concentrically relative to each other and form part of a single transmission clutch assembly. Alternatively the primary clutch may form part of a transmission clutch assembly and the secondary clutch may form part of a transmission flywheel. <IMAGE>

Description

A FRICTION CLUTCH The present invention relates to transmission assemblies for motor vehicles, and in particular but not exclusively to transmission assemblies including multi-plate friction clutches.

A known multi-plate friction clutch comprises a plurality of drive plates rotationally fast with a cover and a plurality of driven plates which are rotationally fast with a hub and which are interleaved between the drive plates.

The cover is rotationally fast with a flywheel and the flywheel is rotationally fast with the crankshaft of an engine. The hub is rotationally fast with an input shaft of a gear box. The gear box is functionally connected to driven road wheels to transmit torque. The series of components which transmit torque from the crankshaft to the road wheels is known as a drive line.

A bias means forces the drive and driven plates axially together enabling the clutch to transmit torque. The maximum torque capacity of the clutch is considerably above the maximum torque produced by the engine since the clutch torque capacity will vary, e.g. with wear and temperature, and it is desirable that any reduced torque capacity of the clutch should not fall below the maximum torque developed by the engine.

Since the engine rotates faster than the driven road wheels, the effective rotational inertia of the engine as seen from the driven road wheels is increased by a factor equal to the overall gear ratio. This effective rotational inertia of the engine is a significant proportion of the total rotational inertia of the whole drive line (especially when the vehicle is in the lower gear ratios). This inertia is always coupled to the transmission when the clutch is engaged and not slipping.

Occasionally, sudden large torque impulses are briefly transmitted along the drive line from the wheels, especially in racing cars for example when inter car wheel to wheel contact occurs or when leaping cars land. These large torque impulses are higher than the maximum engine torque and come about because the drive wheels attempt to rotationally accelerate or decelerate the drive line and engine. The large torque impulses can be sufficiently high to damage drive line components.

Large torque impulses higher than maximum engine torque can also briefly be generated by the engine, for example when the vehicle is required to move off from rest quickly, the engine speed is increased and the clutch is engaged suddenly. These large torque impulses can also damage drive line components.

It is an object of the present invention to provide a transmission assembly which can absorb the said large torque impulses and eliminate drive line component damage.

Thus according to the present invention there is provided a transmission assembly including a primary clutch means having a first predetermined maximum torque capacity and a secondary clutch means having a second predetermined torque capacity which is lower than the first predetermined maximum torque capacity and which enables the second clutch means to slip on the imposition of torque impulses above said second predetermined torque capacity.

Typically the torque capacity of the primary clutch means will vary during use from 1.4 times to 3.5 times the maximum torque capability of the engine. Typically the torque capacity of the secondary clutch means will be 1.3 times the maximum capability of the engine and will substantially remain at this value during use.

Such a transmission assembly has the capability to absorb torque impulses by slippage of secondary clutch means by putting an upper limit on the maximum torque within the drive line.

Because the large brief torque impulses occur only occasionally the secondary clutch only slips occasionally and therefore no significant wear takes place. Also because the large torque impulses are brief the occasionally slipping secondary clutch does not generate significant amounts of heat. These two factors allow a secondary clutch to be designed which has a torque capacity which will substantially remain the same during use.

There is also provided a tranmission assembly for a motor vehicle including a primary clutch means, a hub assembly comprising an intermediate hub which is rotationally fast with a clutch plate of the primary clutch means and an inner hub which is rotationally fast with an input shaft of an associated gear box in which said intermediate hub can be assembled in more than one axial position relative to the inner hub.

Two embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an elevation of a clutch assembly according to the invention; Figure 2 is a section on line x-x of Figure 1, Figure 3 is a larger scale view of the hub assembly of the clutch assembly shown in Figure 2, Figure 4 is a view of a modified hub assembly similar to Figure 3, Figure 5 is a sectional view of a flywheel assembly according to the invention, and Figure 6 is a larger scale view of the hub of the flywheel assembly as shown in figure 4.

With reference to figures 1 to 3, there is illustrated a primary multi-plate clutch assembly 30 comprises a cover 1 which in use is mounted on a flywheel 2 and a hub assembly 25. Four annular drive plates 4 are axially slidable on but rotationally fast with the cover 1. Three driven plates 5 interleaved between plates 4 and are axially slideable but rotationally fast with the hub assembly 25. The drive plates 4 and driven plates 5 are made from carbon fibre in a carbon matrix, known in the trade as a carbon-carbon friction material, though other friction materials could be used. A pressure plate 6 engages the drive plate 4a furthest from the flywheel, and a diaphragm spring 7 is mounted on the cover such that it reacts between the cover 1 and the pressure plate 6 to urge the drive plates 4 and driven plate 5 towards the flywheel to engage the clutch.

The clutch is disengageable by a push release bearing (not shown) acting on spring fingers 8 of diaphragm spring 7 in a manner known in the art.

The hub assembly 25 comprises an intermediate hub 3, an inner hub 9 and a secondary multi-plate clutch assembly 40.

The secondary multi-plate clutch assembly 40 is mounted in the centre of intermediate hub 3, and comprises three annular drive plates 10 which are axially slidable on but rotationally fast with the intermediate hub 3, and two annular driven plates 11 and a pressure plate 14 which are axially slidable on but rotationally fast with the inner hub 9. The drive plates 10 are interleaved with the driven plates 11 and pressure plate 14 such that they can frictionally engage to transmit torque between the intermediate hub 3 and the inner hub 9. The frictionally engaging surface of each drive and driven plate and pressure plate is known as a working surface and has inner ana outer diameters WI and WO respectively.

At one axial end of the of the stack of drive plates 10 and driven plates 11 there is an L-shaped cross section abutment ring 12 which is axially slidable on but rotationally fast with the inner hub 9. This abutment ring is prevented from sliding off the end of the inner hub 9 by a circlip 13 which is axially fast with the inner hub 9. At the other axial end of the stack of drive plates 10 and driven plates 11 there is the pressure plate 14. A belleville spring 15 applies a load to the pressure plate 14 forcing drive plates 10 and driven plates 11 together and enabling torque to be transmitted between the intermediate hub 3 and the inner hub 9. The belleville spring 15 is reacted by a spacer 16 which in turn abuts a circlip 17 which is axially fast with the inner hub 9.

The outer periphery 18 of the abutment ring 12 is rotatable relative to intermediate hub 3 but is held axially captive between an abutment face 19 on the hub 3 and a circlip 20.

The concentricity of the intermediate hub 3 with the drive hub 9 is controlled by the abutment ring 12.

The belleville spring 15 has a high spring rate, made higher by the geometry of installation where the pressure plate fulcrum 21 is at the belleville spring's 15 mean diameter.

Also the outer diameter BO of the belleville spring is larger than the outer diameter of the working surface WO of the drive and driven plates and the inner diameter BI of the belleville is smaller than the inner diameter WI of the working surface of the drive and driven plate i.e. the belleville spring spans the radial extent of the working sufaces of the secondary clutch.

It is apparent that the belleville spring could have an outer diameter equivalent to the diameter of the pressure plate fulcrum 21, in which case the belleville spring would not span the radial extent of the working surface. However in this circumstance the spring rate of such a spring would be lower and may not be able to achieve the desired clamp load. Such a reduced diameter spring could be thickened to restore the spring rate but this would be at the expense of increasing the axial length of the inner hub 9. A belleville spring which spans the working surface provides an axially compact design of clutch assembly.

Figure 4 shows a modified form of hub assembly 225 comprising an intermediate hub 203, a secondary clutch 240 and a drive hub 209 similar to respective components 3, 40, and 9 on hub assembly 25 however:a) screw threaded rings 217a, 217b fixed to the intermediate hub retain all the drive and driven plates 210, 211, the pressure plate 214 and the belleville spring 215.

b) there are 4 drive plates 210a,210b,210c,210d and four driven plates 211a,211b,211c,211d c) pressure plate 214 is rotationally fast with the intermediate hub 203 d) a circlip 250 fixed axially fast on the inner hub 209 and sandwiched between two adjacent driven plates 211b,211c determines the axial position of the inner hub 209 relative to the intermediate hub 203 To assemble the hub assembly 225 the screw threaded ring 217a is screwed into the intermediate hub 203 followed by alternating drive and driven plates. After the second driven plate 211b has been inserted, the hub 209 with pre-assembled circlip 205 is assembled followed by the remaining components. Finally the threaded ring 217b is tightened until the desired predetermined torque capacity is achieved.

The torque capacity can be determined directly by measuring the torque required to rotate the intermediate hub 203 relative to the inner hub 209. The screw threaded ring 217b allows fine adjustment of the torque setting without the need to disassemble any components which is particularly advantageous when the secondary clutch 240 needs to be readjusted following use. Contrast this with the embodiment shown in figure 3 in which adjustment of secondary clutch 40 following wear can only be achieved by disassemDiy and substitution of different components, in particular spacer 16.

It is possible to assemble the hub assembly 225 with the circlip 250 between driven plates 211a and 211b. This would result in the inner hub 209 being offset to the left relative to the intermediate hub 203 when viewing figure 4.

Similarly by assembling the circlip between driven plates 211c and 211d the inner hub could be offset to the right.

Similarly the threaded ring 217a could be screwed into the intermediate hub less far (say 1/2 mm less far) and the threaded ring 217b could be screwed into the intermediate hub by a corresponding greater amount (1/2 mm) this would have the effect of moving the inner hub 209 axially to the left relative to the intermediate hub 203.

This ability to move the inner hub 209 axially relative to the intermediate hub 203 can be advantageous when the hub assembly 225 is to be fitted in more than one installation which have different shaped space envelopes for the hub assembly 225. In particular it is possible to design a hub assembly without a secondary clutch in which the intermediate hub can be positioned in different axial positions relative to the inner hub.

The threaded rings 217a and 217b can be secured in position by means well known in the art such as wire locking, glueing with thread locking compounds, or interference fit mating thread profiles.

With reference to figures 5 and 6 there is as illustrated a flyheel assembly 101 containing a secondary clutch 140. The flywheel assembly 101 has a flywheel mass 102 which is rotationally fast with the clutch cover of a primary clutch (not shown). The flywheel mass 102 has an annular flywheel facing 102b against which a driven plate acts. The flywheel assembly 101 has a hub 150 which is fixed to the end of an engine crankshaft 161 via bolts 160. Two drive plates 110 are mounted rotationally fast but axially slideable on hub 150. Two circlips 162 are mounted axially fast on hub 150.

Drive plate ll0a is mounted between the two circlips 162 in an axially and rotationally fast manner on hub 150. Three driven plates 111, 114 are mounted axially slidedable but rotationally fast on flywheel mass 102. The drive plates 110 and the driven plates 111, 114 are interleaved such that they can frictionally engage to transmit torque between the hub 150 and the flywheel mass 102.

At one axial end of the stack of drive plates 110 and driven plates 111, 114 there is a belleville spring 115 which biases the drive plates 110 and the driven plates 111, 114 into frictional engagement. The belleville spring 115 is installed in an initially stressed condition and is reacted by circlip 117 which is axially fast on flywheel mass 102.

The driven plate 110 which is axially most remote from the belleville spring 115 reacts against a flange iuLa or flywheel mass 102.

The axial position of flywheel mass 102 relative to the crankshaft 161 is determined by driven plate 110a.

The torque capacity of the secondary clutch 40, 140 can be easily varied at the assembly stage for use with different engines, for example, by altering the installed height of the belleville spring 15, 115 or by machining the thickness of the spacer 16 or driven plate 114. Appropriate selection of the spacer thickness 16 or driven plate thickness 114 enables the desired belleville spring loading to be achieved taking into account the build-up of axial tolerances on all the components of the secondary clutch.

Also the material of the secondary clutch's drive plates 10, 110 or driven plates 11, 111, 114, can be varied to give different friction co-efficient characteristics, i.e. bronze based sintered friction material could be used or a carbon-carbon friction material could be used.

Typical values for the maximum and minimum torque capacities of the primary clutch and the torque capacity of the secondary clutch are as follows: Vehicle 1 Vehicle 2 Maximum engine torque capability 450 Nm 600 Nm Secondary clutch torque capacity 585 Nm 780 Nm Primary clutch minimum in use torque capacity 630 Nm 840 Nm Primary clutch maximum in use torque capacity 1575 Nm 2100 Nm

Claims

CLAIMS 1. A transmission assembly for a motor vehicle including a primary clutch means having a first predetermined maximum torque capacity and a secondary clutch means having a second predetermined torque capacity which is lower than the first predetermined maximum torque capacity and which enables the second clutch means to slip on the imposition of torque impulses above said second predetermined torque capacity.
2. A transmission assembly as defined in Claim 1 in which the primary and secondary clutch means both form part of a single transmission clutch assembly.
3. A transmission assembly as defined in Claim 2 in which the primary and secondary clutch means are disposed concentrically relative to each other.
4. A transmission assembly as defined in Claim 3 in which the secondary clutch means is radially within the primary clutch means.
5. A transmission assembly as defined in any one of claims 2 to 4 in which torque transmission from the primary clutch to the secondary clutch is via an intermediate hub.
6. A transmission assembly as defined in Claim 5 in which the intermediate hub is connected with an inner hub via the secondary clutch and the intermediate hub can be assembled in more than one axial position relative to the inner hub.
7. A transmission assembly as defined in Claim 1 in which the primary clutch means forms part of a transmission clutch assembly and the secondary clutch means forms part of a transmission flywheel.
8. A transmission assembly as defined in Claim 7 in which the secondary clutch means is radially within the flywheel facing contacted by the transmission clutch assembly.
9. A transmission assembly as defined in any previous claim in which the secondary clutch means is a multi-plate clutch.
10. A transmission assembly as defined in any previous claim in which the secondary clutch is engaged by a bias means in the form of one or more belleville springs.
11. A transmission assembly as defined in Claim 10 in which the outside diameter of at least one of the bellevilles is larger than the outside diameter of the working surface of the secondary clutch plates and the inside diameter of said belleville is smaller than the inside diameter of the working surface of the secondary clutch plate.
12. A tranmission assembly for a motor vehicle including a primary clutch means, a hub assembly comprising an intermediate hub which is rotationally fast with a clutch plate of the primary clutch means and an inner hub which is rotationally fast with an input shaft of an associated gear box in which said intermediate hub can be assembled in more than one axial position relative to the inner hub.
13. A transmission assembly as defined in claim 6 or 12 in which the intermediate hub can be moved axially relative to the inner hub via screw threaded means.
14. A transmission assembly clutch as defined in any previous claim in which the primary clutch means is a multiplate clutch.
15. A transmission assembly being constructed and arranged substantially as hereinbefore described with reference to and as shown in figures 1 to 3 or 4 or 5 to 6 of the accompanying drawings.