GB2165320A - Clutch - Google Patents

Abstract

A clutch has exchange of the friction member (24, 26) simplified by a free space (12) between the flywheel (10) and the friction member (24, 26), enabling the latter to be removed or inserted laterally through a cover (39) of the housing (27) of the assembly. The friction member (24, 26) is located within a rim (21) around the face of a piston (16) presented toward the flywheel (10). Teeth (15) on the inner periphery of the piston (16) engage splines (14) on the driven shaft (11) so that the piston (16) is non- rotatable relative to the shaft (11) but can be urged by a spring (19) into contact with the flywheel (10). Retraction of the piston (16) away from the flywheel to disengage the clutch and to permit removal and replacement of the friction member assembly (24, 26) is effected by a lever (33) which is subjected to hydraulic pressure when the clutch pedal (not shown) of the vehicle is depressed. <IMAGE>

Description

SPECIFICATION Clutch This invention relates to improvements in clutches, and more particularly to an improved clutch for use in road vehicles of the kind wherein the output of an internal combustion engine is transmitted via a gear box to the driven wheel or wheels, the clutch having to be disengaged whenever a gear change is effected.

The friction material used in such clutches is necessarily subject to wear and even with the most careful driving the friction element will have to be replaced several times in the working life of a vehicle. The replacement of this friction element, or clutch disc, is a complex operation beyond the skill of most car owners and requiring workshop facilities and tools, so that clutch failure while driving is a serious inconvenience. The time taken by skilled labour to change a clutch disc in a properly equipped garage varies somewhat with the make of vehicle, but in all cases it involves considerable disturbance, and subsequent reassembly of adjacent parts so that an annular clutch disc can be positioned on the output shaft to the gear box, the end of said output shaft remote from the gear box being jour nalled in the engine flywheel.

Another problem associated with conventional automobile clutches is that because the clutch disc is annular and fits round the gear box shaft its central area, occupied by a hub and usually a sprung, anti-rattle assembly, is unusable as a friction surface. The engine flywheel engaged by the clutch disc is usually bell-shaped, having a skirt which contains the clutch disc and the pressure-applying member positioned behind it, and in order to provide adequate friction surfaces radial of the common axis of rotation of the drive and driven shafts this bell-shaped flywheel is of substantial diameter and gives rise to design problems in accommodating it-for example it is common to provide, in the passenger-carrying compartment, a transmission tunnel which enlarges into a "hump" between the two forward seats, which is both space-wasting and unsightly.

Another drawback of conventional clutches is that any adjustment facility provided is, in general, limited to altering the travel of the clutch members. No means is provided for effecting in a simple manner an adjustment of the pressure load which will be applied to the clutch when it is engaged. The ability to effect such an adjustment will be of particular utility in connection with goods vehicles which may be either lightly or heavily loaded, or vehicles such as military vehicles which may have to travel over rough terrain as well as on roads.

Among the objects of the present invention are to provide a clutch of relatively small and compact dimensions, wherein the changing of the clutch element will be a simple operation which can be carried out, if necessary, by the roadside by an unskilled person without requiring special tools. Another object of the present invention is to provide a device which will give an indication of the state of wear of the friction element of a clutch at a remote location, say on the dashboard of the vehicle, so that periodic inspection is not necessary in order to avoid clutch failure while the vehicle is in use.

In accordance with the present invention there is provided a clutch comprising an interchangeable friction element which can be interposed between drive and driven members to transmit torque therebetween when the clutch is engaged, wherein when the clutch is disengaged there is a free and unobstructed space between said members permitting insertion or removal of said element transversely of said members in a whole condition.

The drive member may be a flywheel mounted at one end of a drive shaft and the driven member may be a driven shaft one end of which is in spaced relation to the flywheel, there being non-rotatably but axially displaceably mounted on the driven shaft a piston which is biased toward the flywheel but retractable therefrom to disengage the clutch, and said friction element may be a friction disc secured to a metal backing plate which is exchangeably mounted on the face of the piston presented toward the flywheel.

Means is preferably provided to render the friction element non-rotatable relative to the piston when mounted thereon.

The piston may be biased by one or more compression springs acting between the piston and a pre-tensioning member on the driven shaft, means being provided to adjust the position of the pre-tensioning member axially of the driven shaft thereby to adjust the loading of the spring or springs. In this arrangement the pretensioning member may be an annular plate which surrounds the driven shaft and said adjustment means may comprise a nut in screw-threaded engagement with the driven shaft, which nut limits the displacement of the pre-tensioning plate away from the piston by the spring or springs.

The piston may have a skirt extending away from the flywheel in which one or more chambers are provided to accommodate the spring or the respective springs.

The piston is preferably retractable by a piston-and-cylinder assembly to which fluid under pressure is supplied to disengage the clutch, and the supply line to the cylinder preferably includes a tap by-passed by a by-pass line which includes a non-return valve, the arrangement being such that the piston can be maintained in the clutch-disengaged position, against the action of the spring or springs, by closing the tap and then supplying fluid under pressure to the cylinder via the by-pass line.

The friction element may comprise an imperforate disc of friction material, and means may be provided magnetically to hold the backing plate of the friction element on the piston. Said magnetic means may be electromagnetic.

A common electrical circuit may be provided both to magnetise the piston and backing plate and to measure resistance across the friction element.

The clutch is preferably located in a constant-diameter, cylindrical housing which has a laterally-disposed access cover removable for the removal and insertion of the friction element.

Preferred embodiments of the invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side sectional elevation, some parts shown schematically, of a clutch assembly in accordance with the present invention, Figures 2 and 3 are respectively views taken on the line ll-ll and on the line Ill-Ill of Fig. 1, and Figure 4 is a side sectional elevation of a modified piston assembly.

Referring first to Figs. 1-3, the clutch assembly illustrated transmits torque between a drive shaft (not shown) whereby the prime mover of a vehicle rotates a flywheel 10 and a driven shaft 11 which extends to the gear box (not shown). There is a free space 12 between the flywheel 10 and the nearer end portion 13 of the shaft 11 which is formed longitudinally with feathers or splines 14.

These are engaged by teeth 15 on the inner periphery of a piston member 16 so that the latter is non-rotatable relative to the shaft 11 but is relatively axially displaceable. At a position spaced along the length of the shaft 11 from the splines 14 it is formed with a screwthread 50 which is engaged by a nut 17. This limits the rearward displacement of a reaction plate 18 under the influence of a compression spring 19 so that the latter biases the piston 16 toward the flywheel 10. The spring 19 is housed within a tubular portion or skirt 20 of the piston which extends away from the flywheel, and the face of the piston 16 presented toward the flywheel is in the form of a flat, shallow dish having a rim 21 the inner periphery of which is scalloped, or formed with alternate projections 22 and recesses 23 as shown in Fig. 2.

The outer periphery 25 of an imperforate metal backing member 24 has a shape corresponding to that of the inner periphery of the rim 21 so that when housed therein, as shown in Fig. 1, the backing member 24 is non-rotatable relative to the piston 16. It is, however, easily removable therefrom when the piston 16 is retracted away from the flywheel 10, as shown in Fig. 1, e.g. by prising it out with a suitable tool such as a screwdriver.

The backing member 24 is one part of a composite friction element, the other part being an imperforate disc 26 of a suitable friction material of the kind commonly used for the discs or pads of conventional clutches or brakes. The diameter of the friction disc 26 is greater than the overall diameter of the backing member 24 and, as shown, is preferably equal to that of the flywheel 10 with which it is coaxially aligned. The entire clutch assembly is located within a cylindrical housing 27 of uniform diameter throughout its length. The inner periphery of this housing serves as a bearing for the piston 16 through the provision of piston rings 51 to prevent any deflection out of coaxial alignment between the piston 16 and the flywheel 10.

In use the clutch is engaged by the compression spring 19 which presses the friction disc 26 against the flywheel 10. To disengage the clutch the driver of the vehicle depresses a pedal (not shown), thereby supplying fluid under pressure to a servo or slave cylinder 28 via a line 29. This causes displacement from right to left, as viewed, of a piston (not shown) in the cylinder 28 whereby a piston rod 30 is moved in the direction of the arrow A in Fig. 1.

Between its leading end housing the friction element 24,26 and the skirt 20 the piston 16 has a circumferential groove 31. In this are located, on opposite sides of the piston 16 a pair of rollers, one of which is shown at 32 in Fig. 1, and these provide a journalled connection between the piston 16 and a fork or yoke 33. The yoke 33 has a stem 34 from which arms 34A extend on opposite sides of the piston 16. The stem 34 is articulated at its lower end 35 to the piston rod 30 and intermediate its ends to the housing 27. Consequently when the piston rod 30 moves in the direction of arrow A in Fig. 1 the piston 16 is moved in the direction of arrow B, retracting the friction element 24,26 away from the flywheel 10 and disengaging the clutch.

In normal use as soon as the driver ceases to depress the clutch pedal fluid can flow back from the cylinder 28 through the line 29, enabling the spring 19 to return the friction element 24,26 into engagement with the flywheel. When it is desired to exchange the friction element 24,26 of the clutch, however, the clutch can be held in the disengaged position position shown in Fig. 1 in the following way: In the fluid line 29 is a tap 36 by-passed by a branch line 37 in which there is a non-return valve 38. If the tap 36 is closed fluid can still be "pumped" into the cylinder 28 through the branch line 37 but the non-return valve prevents escape of fluid from the cylinder 28 so that the clutch is held in the disengaged position.

To replace the friction element 24,26, a cover 39 is removed from the housing 27 to give access to the space 12. The backing member 24 is now dislodged from the rim 21 allowing the composite friction element to be taken out and replaced by a similar, unworn one. The cover 39 is replaced and the tap 36 reopened, allowing trapped fluid to flow out of the cylinder 28 so that the clutch is re-engaged by the spring 19.

The simplicity of this procedure is to be compared with the operations necessary to replace the friction element of a conventional clutch. Moreover inspection of the friction member 26 simply involves removal of the cover 39, whereas in a conventional clutch the friction element is inside a relatively massive bell-shaped housing. Because the shaft 11 ends short of the flywheel 10, to provide the free space 12, the friction element 24,26 need not be annular and therefore the whole of its radial extent is usable as a friction surface. Consequently adequate friction is obtainable using a friction element and flywheel of relatively small diameter. This in turn means that the housing 27 may be of relatively small and of uniform diameter, avoiding the problems presented to car designers of accommodating a larger one.

The backing member 24 will fit tightly within the rim 21, but to avoid any possibility that the friction element 24,26 may fall out of place it may be held by magnetic attraction between the piston 16 and the metal backing member 24. This may be effected by electromagnetic means (not shown) under the control of the driver.

Electrical means (not shown) may also be provided to give an indication to the driver at a remote location, such as the dashboard, of the state of wear (remaining thickness) of the friction member 26 by passing an electric current across the latter and measuring its resistance. The two electrical systems could be combined to have a common circuit.

The modified piston assembly illustrated in Fig. 4 is generally similar to that of Figs. 1-3 and like parts have like references. It differs by the provision of additional or auxiliary springs 1 9A mounted in respective, tubular recesses 40 distributed in a circumferential array around the central part 41 of the skirt 20 of the piston 16 to reinforce the main spring 19 which surrounds the shaft 11. This assembly provides a more firmly engaged clutch for heavier or more heavily laden vehicles.

In addition to providing a smaller and more compact clutch in which changing the friction element is greatly simplified the present invention also provides a clutch the pressure of which, when engaged, is adjustable simply by rotating the nut 17. By this means the pressure exerted by the spring 19, or springs 19 and 19A, can be altered to suit different driving or load conditions.

Although described as primarily of benefit in relation to road vehicles the clutch of the invention is, of course, usable in all other applications of clutches such as for marine engines or stationary plant.

Claims (14)

1. A clutch comprising an interchangeable friction element which can be interposed between drive and driven members to transmit torque therebetween when the clutch is engaged, wherein when the clutch is disengaged there is a free and unobstructed space between said members permitting insertion or removal of said element transversely of said members in a whole condition.

2. A clutch as claimed in claim 1, wherein the drive member is a flywheel mounted at one end of a drive shaft and the driven member is a driven shaft one end of which is in spaced relation to the flywheel, there being non-rotatably but axially displaceably mounted on the driven shaft a piston which is biased toward the flywheel but retractable therefrom to disengage the clutch and said friction element being a friction disc secured to a metal backing plate which is exchangeably mounted on the face of the piston presented toward the flywheel.

3. A clutch as claimed in claim 2, wherein means is provided to render the friction element non-rotatable relative to the piston when mounted thereon.

4. A clutch as claimed in claim 2 or claim 3, wherein the piston is biased by one or more compression springs acting between the piston and a pre-tensioning member on the driven shaft, means being provided to adjust the position of the pre-tensioning member axially of the driven shaft thereby to adjust the loading of the spring or springs.

5. A clutch as claimed in claim 4, wherein the pre-tensioning member is an annular plate which surrounds the driven shaft and wherein said adjustment means comprises a nut in screw-threaded engagement with the driven shaft, which nut limits the displacement of the pre-tensioning plate away from the piston by the spring or springs.

6. A clutch as claimed in claim 4 or claim 5, wherein the piston has a skirt extending away from the flywheel in which one or more chambers are provided to accommodate the spring or the respective springs.

7. A clutch as claimed in any one of claims 2 to 6, wherein th piston is retractable by a piston-and-cylinder assembly to which fluid under pressure is supplied to disengage the clutch, and wherein the supply line to the cylinder includes a tap by-passed by a bypass line which includes a non-return valve, the arrangement being such that the piston can be maintained in the clutch-disengaged position, against the action of the spring or springs, by closing the tap and then supplying fluid under pressure to the cylinder via the bypass line.

8. A clutch as claimed in any one of the preceding claims, wherein the friction element comprises an imperforate disc of friction material.

9. A clutch as claimed in any one of claims 2 to 8, wherein means is provided magnetically to hold the backing plate of the friction element on the piston.

10. A clutch as claimed in claim 9, wherein said magnetic means is electro-magnetic.

11. A clutch as claimed in any one of the preceding claims, wherein means is provided to pass an electrical current across the friction element and to measure the resistance thereof, said measuring means giving a remote indication of the state of wear of the friction element.

12. A clutch as claimed in claim 11 as appendant to claim 10, wherein a common electrical circuit is provided both to magnetise the piston and backing plate and to measure resistance across the friction element.

13. A clutch as claimed in any one of the preceding claims and located in a constantdiameter, cylindrical housing which has a laterally-disposed access cover removable for the removal and insertion of the friction element.

14. A clutch substantially as hereinbefore described with reference to and as shown in Figs. 1 to 3 or Fig. 4 of the accompanying drawings.