GB2095772A - A friction clutch pressure plate - Google Patents

Abstract

The friction clutch annular pressure plate has a friction surface 12 for engagement with a friction disc 3 and a back face 13 for engagement with a clutch spring 14. The back face 13 carries an array of knobs 17 which project therefrom and which allow air passing over the knobs to cool the pressure plate, effectively increasing the surface area of the back face. <IMAGE>

Description

SPECIFICATION A friction clutch pressure plate This invention relates to a friction clutch pressure plate particularly, but not exclusively, for use in a motor vehicle friction clutch.

Friction clutches on motor vehicles generally include a friction disc which drives the transmission and which is clamped between the flywheel of an internal combustion engine and a clutch pressure plate. A problem associated with friction clutches is that during clutch take-up when the vehicle is moving off from a standing start, particularly at periods of high engine torque demand e.g. a hill start, or when the vehicle is towing a caravan, the friction clutch is allowed to slip during clutch engagement. This relative rubbing movement between the friction disc and friction surfaces on the vehicle flywheel and pressure plate cause a large amount of heat to be generated.

It is undesirable to allow the friction material of the friction disc to become too hot. This is because the friction material generally comprises asbestos fibre bound by a phenolic resin and temperatures in excess of 3000C can cause a rapid breakdown of the organic binder.

The present invention provides a pressure plate for the rapid dissipation of heat.

Accordingly there is provided a friction clutch annular pressure plate having a friction surface for engagement with a friction disc, and a back face for engagement with a clutch spring characterised in that there is an array of knobs projecting from the back face.

The provision of an array of knobs on the back face of the pressure plate effectively increases the surface area of the back face so that air drawn into a bell housing of the clutch can pass over the knobs and cool the pressure plate.

The knobs may be arranged in groups which effectively form vanes. In such a case each group may comprise a number of radially aligned knobs.

An example of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a plan view of an automobile friction clutch pressure plate, Fig. 2 is a cross section through the pressure plate of Fig. 1 on the line Il-Il of Fig. 1, and Fig. 3 is a cross section through one of the knobs on the pressure plate.

An annular cast iron pressure plate 11, has a friction surface 1 2 for engagement with a friction disc in the form of a clutch driven plate 3 (see broken lines in Fig. 2) and a back face 13 including an annular boss 14 for engagement with a diaphragm spring 4. The spring 4 biases the pressure plate 11 so as to clamp the driven plate 3 between the friction face 1 2 and a clutch driving plate 5. The back face 13 of the pressure plate could be modified for use with a coil spring clutch.

The annular boss 14 is interrupted by circumferentially space apertures or cut-outs 1 5 defining passages through which air can flow from the interior (1 6 in Figs. 1 and 2) to the exterior of the clutch. Each of the passages is inclined to the radial direction by an angle a.

A radially inner margin 13' of the back face 13 within the boss 14 has an array of knobs 1 7 projecting therefrom. The knobs 1 7 are evenly distributed around the annular plate to maintain balance. The knobs 1 7 are arranged in circumferentially spaced radially aligned groups which could be said to form radial vanes. It is possible for the groups of knobs to be aligned in other ways, for example tangentially to the axis of rotation of the pressure plate or randomley.

As seen from Fig. 3, the knobs are substantially of semi-elliptical cross section and effectively increase the surface area of the back face 13 of the drivenplate. The major axis M of each knob 1 7 is perpendicular to the surface 13'. As the driven plate rotates in the direction of arrow A (Fig. 1), air within the open centre region 1 6 flows outwardly over the knobs to cool the pressure plate.

1. A friction clutch annular pressure plate having a friction surface for engagement with a friction disc, a back face for engagement with a clutch spring and an array of knobs projecting from the back face.

2. A friction clutch annular pressure plate according to claim 1, in which the knobs are arranged in aligned groups spaced circumferentially around the plate.

3. A friction clutch annular pressure plate according to claim 2 in which the groups of knobs are radially aligned.

4. A friction clutch annular pressure plate according to any preceding claim in which the back face of the pressure plate includes an annular boss which defines a radially inner margin of the back face from which the knobs project.

5. A friction clutch annular preesure plate according to claim 4 in which the annular boss is formed with a plurality of cut-outs defining passages through which air passing over the knobs can flow.

6. A friction clutch annular pressure plate according to claim 5 in which the passages defined by the cut-outs are inclined to the radial direction.

7. A friction clutch annular pressure plate according to any preceding claim in which each knob is substantially semi-elliptial in cross section with its major axis perpendicular to the inner margin of the back face.

8. A friction clutch pressure plate substantially as described herein and with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A friction clutch pressure plate This invention relates to a friction clutch pressure plate particularly, but not exclusively, for use in a motor vehicle friction clutch. Friction clutches on motor vehicles generally include a friction disc which drives the transmission and which is clamped between the flywheel of an internal combustion engine and a clutch pressure plate. A problem associated with friction clutches is that during clutch take-up when the vehicle is moving off from a standing start, particularly at periods of high engine torque demand e.g. a hill start, or when the vehicle is towing a caravan, the friction clutch is allowed to slip during clutch engagement. This relative rubbing movement between the friction disc and friction surfaces on the vehicle flywheel and pressure plate cause a large amount of heat to be generated. It is undesirable to allow the friction material of the friction disc to become too hot. This is because the friction material generally comprises asbestos fibre bound by a phenolic resin and temperatures in excess of 3000C can cause a rapid breakdown of the organic binder. The present invention provides a pressure plate for the rapid dissipation of heat. Accordingly there is provided a friction clutch annular pressure plate having a friction surface for engagement with a friction disc, and a back face for engagement with a clutch spring characterised in that there is an array of knobs projecting from the back face. The provision of an array of knobs on the back face of the pressure plate effectively increases the surface area of the back face so that air drawn into a bell housing of the clutch can pass over the knobs and cool the pressure plate. The knobs may be arranged in groups which effectively form vanes. In such a case each group may comprise a number of radially aligned knobs. An example of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a plan view of an automobile friction clutch pressure plate, Fig. 2 is a cross section through the pressure plate of Fig. 1 on the line Il-Il of Fig. 1, and Fig. 3 is a cross section through one of the knobs on the pressure plate. An annular cast iron pressure plate 11, has a friction surface 1 2 for engagement with a friction disc in the form of a clutch driven plate 3 (see broken lines in Fig. 2) and a back face 13 including an annular boss 14 for engagement with a diaphragm spring 4. The spring 4 biases the pressure plate 11 so as to clamp the driven plate 3 between the friction face 1 2 and a clutch driving plate 5. The back face 13 of the pressure plate could be modified for use with a coil spring clutch. The annular boss 14 is interrupted by circumferentially space apertures or cut-outs 1 5 defining passages through which air can flow from the interior (1 6 in Figs. 1 and 2) to the exterior of the clutch. Each of the passages is inclined to the radial direction by an angle a. A radially inner margin 13' of the back face 13 within the boss 14 has an array of knobs 1 7 projecting therefrom. The knobs 1 7 are evenly distributed around the annular plate to maintain balance. The knobs 1 7 are arranged in circumferentially spaced radially aligned groups which could be said to form radial vanes. It is possible for the groups of knobs to be aligned in other ways, for example tangentially to the axis of rotation of the pressure plate or randomley. As seen from Fig. 3, the knobs are substantially of semi-elliptical cross section and effectively increase the surface area of the back face 13 of the drivenplate. The major axis M of each knob 1 7 is perpendicular to the surface 13'. As the driven plate rotates in the direction of arrow A (Fig. 1), air within the open centre region 1 6 flows outwardly over the knobs to cool the pressure plate. CLAIMS

1. A friction clutch annular pressure plate having a friction surface for engagement with a friction disc, a back face for engagement with a clutch spring and an array of knobs projecting from the back face.

2. A friction clutch annular pressure plate according to claim 1, in which the knobs are arranged in aligned groups spaced circumferentially around the plate.

3. A friction clutch annular pressure plate according to claim 2 in which the groups of knobs are radially aligned.

4. A friction clutch annular pressure plate according to any preceding claim in which the back face of the pressure plate includes an annular boss which defines a radially inner margin of the back face from which the knobs project.

5. A friction clutch annular preesure plate according to claim 4 in which the annular boss is formed with a plurality of cut-outs defining passages through which air passing over the knobs can flow.

6. A friction clutch annular pressure plate according to claim 5 in which the passages defined by the cut-outs are inclined to the radial direction.

7. A friction clutch annular pressure plate according to any preceding claim in which each knob is substantially semi-elliptial in cross section with its major axis perpendicular to the inner margin of the back face.

8. A friction clutch pressure plate substantially as described herein and with reference to the accompanying drawings.