GB2096249A - Grooved metallic friction face for a clutch - Google Patents

Abstract

The invention is concerned with a friction clutch or brake of any kind in which a metallic friction face (22) engages with a non-metallic friction face (18) in the presence of a fluid to establish frictional engagement between the friction faces. The metallic friction face is provided with grooves (32) between flat sections (31) to allow fluid to be squeezed into the groove (32) during clutch engagement and to allow fluid within the grooves (32) to act as a reservoir fluid during the early stages of clutch engagement. The grooves (32) traverse the direction of relative movement of the friction faces, preferably at a small angle and may be formed as a single continuous spiral groove of wide V-section. <IMAGE>

Description

SPECIFICATION Friction clutches or brakes The invention relates to friction clutches or brakes of the kind in which a member having a metallic friction face and a member having a nonmetallic friction face are urged into mutual contact in the presence of a fluid to establish frictional engagement therebetween.

The invention will be described primarily in relation to clutches, which are intended for selective engagement and disengagement of two rotatable members, but could be applied equally to brakes in which one member is stationary and engages selectively with the other member to bring that other member to rest.

It is known for wet clutches, that is clutches that operate in the presence of a fluid, to have a flat metallic friction face and a grooved nonmetallic friction face. The grooves provide a reservoir for fluid for the inter-engaging friction faces while there is sliding movement between them and also provide a local sink into which fluid can be squeezed by the contacting friction faces as full frictional contact builds up. However, the structural limitations of a typical non-metallic friction material are such that the grooves have to be widely spaced. Also, as there is some tendency for the non-metallic friction facing to wear, the depth of the grooves reduces significantly during the life of the clutch so that the grooves become less effective.

In accordance with the present invention there is provided a friction clutch or brake of the kind in which a member having a metallic friction face and a member having a non-metallic friction face are urged into mutual contact in the presence of a fluid to establish frictional engagement therebetween, characterised in that the metallic friction face is grooved in a direction which traverses the direction of relative movement of the friction faces to provide sections which engage the non-metallic friction face alternating with sections which are set back from the non-metallic friction face.

Preferably the grooving is provided by a spiral groove on an annular friction face. A spiral groove is particularly advantageous because it can be cut by a turning operation, resulting in a well controlled uniform groove.

Preferably the non-metallic friction face covers the whole of the metallic friction face.

Preferably the non-metallic friction face is flat so that the whole of its surface is swept by the metallic friction face. Preferably the grooves in the metallic friction face have diverging walls. An advantage of diverging walls in the operation of the clutch or brake is that any debris which might otherwise collect in the grooves, such as material worn from the non-metallic friction face, tends to escape from the groove. A wide V-groove, in which the width of the groove is at least twice its depth is particularly desirable for this reason. A groove of this form is also very simple to manufacture.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of the main parts of a friction clutch according to the invention but on a scale which does not show the nature of the friction faces; and Figure 2 is a cross section through a part of a friction face on a larger scale.

The friction clutch shown in the drawings incorporates a flywheel 11 adapted to be mounted to the crankshaft of an internal combustion engine (not shown) by means of a central boss 12. The flywheel is of the type having an external peripheral flange 13 extending away from the engine and thus is of the type known as a pot-type flywheel. An annular pressure plate 14 is arranged within the pot-type flywheel. The clutch also incorporates other conventional components which are not shown as they form no part of the present invention.These include a cover secured to the flywheel 13, a spring acting between the cover and the pressure plate to urge the pressure plate further into the flywheel, a rotational coupling which may include lugs 1 5 on the pressure plate provide a driving connection between the flywheel and pressure plate through the cover and a release mechanism for retracting the pressure plate away from the flywheel against the spring load. Both the flywheel 11 and the pressure plate 14 are manufactured from a metal and are typically cast iron.

The clutch also incprporates a driven plate 1 6 which is shown diagrammatically as a carrier disc 17 supporting two annular friction facings 1 8 and 1 9. These friction facings are of a non-metallic material such as a resin or resin and asbestos based friction material. Friction facing 1 8 has a flat annular friction face 21 which is shown in contact with a corresponding friction face 22 in the flywheel 13, friction face 22 appearing flat as shown in Figure 1. Similarly, a friction facing 19 incorporates a flat annular friction face 23 which in use co-operates with a corresponding friction face 24 on the pressure plate 14. A clearance is shown between faces 22 and 23 to illustrate diagrammatically that the clutch is in a released condition.In use, to engage the clutch, the release mechanism described above is released so that the spring urges the pressure plate towards the flywheel and clamps the driven plate between flywheel 11 and pressure plate 14. This results in a driving connection between the driving part of the clutch represented by the flywheel 11 and pressure plate 14 and the driven part of the clutch represented by the driven plate 1 6. In practice, the release mechanism is actuated in a controlled manner to increase the clamp load gradually and thus engage the clutch in a controlled manner.

The clutch under consideration is of the kind known as a wet clutch in that a supply of cooling and lubricating fluid such as oil is supplied to the mating friction faces.

As thus far described, the clutch could be virtually any wet friction clutch, the invention residing in details of the surface of the friction faces 22 and 24 on the flywheel and pressure plates respectively.

Figure 2 shows part of the friction facing 22 on the flywheel 11 on a much larger scale. The friction face has flat sections 31 which have the smooth surface finish normally required by a wet clutch. Interposed between these sections 31 are grooves 32 which provide sections of the friction facing which are set back from the portions 31 and thus in use are set back from the non-metallic friction face 21 which engages the face 22. The flat sections 31 are typically 0.5 mm wide and the width of the grooves 32 may also be approximately 0.5 mm. In this example, the depth of each groove is approximately 0.1 mm. The above dimensions are given for purposes of illustration only to illustrate a typical order of magnitude but these dimensions may be varied within wide limits. Each groove has diverging walls 33 and 34 so that it is in the form of a wide V-groove.Other shapes of groove may be used but widely diverging walls are particularly desirable for several reasons. Firstly, they facilitate automatic clearance of debris which may collect in the grooves, for example from wear of the friction facings. Secondly, they are simple to machine.

Thirdly, the corners such as 35 also automatically are very wide angled so that they allow a good flow of heat from the edges of the flat sections 31 adjacent to the corners 35, thereby reducing the danger of local excessive temperatures. Fourthly, the temperature gradients resulting from generating heat by friction at only some sections of the friction face and the associated stresses, are less likely to damage the surface of the friction material when the angles of the grooves are wide.

The grooves 32 do not run directly circumferentially, i.e. in a direction parallel to relative movement between the friction faces, because in such a situation it would be possible for the metallic and non-metallic friction faces to bed together in such a way that the non-metallic friction material would fill the grooves. However, it is desirable for the grooves to extend broadly along the direction of travel but only at a slight angle thereto. This ensures that during clutch engagement, when fluid is being squeezed away from the flat sections 31 into the grooves 32, the fluid does not tend to be drawn back onto the next flat section 31 by the movement of the friction face 21 over the friction face 22.A particularly convenient way of arranging for the direction of the grooves 32 to traverse the direction of relative movement of the friction faces at a small angle is to machine a single spiral groove in the friction face 22 with a pitch equal to the spacing between adjacent grooves, in this example approximately 1 mm.

In engagement of the clutch, the grooves 32 act as a reservoir during the early stages of engagement and ensure a continuous supply of lubricant to the whole of the clutch surface to ensure a smooth take up. As the clutch clamp load increases, the grooves 32 act as a sink into which fluid can be squeezed by the force of the nonmetallic friction face acting on the flat section 31.

The above discussion has been in relation to the friction face 22 on the flywheel 11. Friction face 1 9 of the pressure plate 14 is identical with the face 22.

Although the invention has been described in detail with reference to a single plate wet clutch, the invention could alternatively be used in a multi-plate clutch, either with non-metallic friction facings of the kind described above or with the very thin paper type of friction facing normally used in clutches in automatic transmissions. The invention could also be applied to brakes, particularly but not necessarily the kind of multiplate brake with paper type linings frequently used in automatic transmissions.

The invention may also be applied to brakes or clutches which have friction faces which are not flat, for example cone clutches or drum brakes.

Claims (6)

1. A friction clutch or brake of the kind in which a member (11) having a metallic friction face (22) and a member (18) having a non-metallic friction face (21) are urged into mutual contact in the presence of a fluid to establish frictional engagement therebetween, characterised in that the metallic friction face is grooved (32) in a direction which.traverses the direction of relative movement of the friction faces to provide sections (31) which engage the non-metallic friction face alternating with sections which are set back from the non-metallic friction face.

2. A clutch or brake as claimed in claim 1 wherein the grooving (32) is provided by a spiral groove on an annular friction face.

3. A clutch or brake as claimed in claim 1 or claim 2 wherein the non-metallic friction face covers the whole of the metallic friction face.

4. A clutch or brake as claimed in any preceding claim wherein a non-metallic friction face is flat so that the whole of its surface is swept by the metallic friction face.

5. A clutch or brake as claimed in any preceding claim wherein the grooving incorporates diverging walls (33) and (34).

6. A clutch or brake as claimed in claim 5 wherein the grooving is in the form of a wide angled V-groove.