Clutch Release Mechanisms

This invention relates to a clutch release mechanism, and more particularly to means for indicating when the clearance between a clutch release bearing and a co-operating clutch release plate is taken up. The invention is particularly, but not exclusively, applicable to vehicle clutches.

Said clearance is intended to be temporarily taken up, and the release plate then displaced axially, each time the clutch is released. There are, however, three ways in which said clearance can be deleteriously taken up, namely by incorrect adjustment of the clutch, by wear of the clutch drive plate beyond the designed limit, and by the vehicle driver simply resting his foot on the clutch pedal when not operating the clutch.

The object of the present invention is to avoid these occurrences by providing a warning when said clearance is taken up.

According to the invention, means for indicating when the clearance between a clutch release bearing and a co-operating clutch release plate is taken up comprise an electrically-insulating mounting for the bearing, a power line connecting an electric supply to the bearing, and a warning device interposed in said line, the clutch release plate being connected electrically to the vehicle chassis.

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which shows an axial section through a clutch release bearing and its carrier sleeve, and an electric circuit associated therewith.

Referring now to the drawing, a vehicle clutch release mechanism includes a drive plate (not shown), a pressure plate (not shown), a release plate 10, a release bearing indicated generally at 11, and an axially-slideable non-rotating carrier sleeve 12 for said bearing, all of which are well known per se and operate in conventional manner. Instead of the release bearing 11 being pressed directly on to its carrier sleeve 12 in the usual way, an electrically-insulating layer is disposed between said bearing and said sleeve. Said layer consists of a plastics sleeve 13 disposed between the bore of an inner race 14 of the bearing 11 and its seating on the carrier sleeve 12, and a plastics washer 15 disposed between a shoulder on the carrier sleeve 12 and the adjacent end face of the inner race 14. An insulated wire, herein referred to as the power line 16, is secured by adhesive in an axial slot 17 formed in the periphery of the carrier sleeve 12, and its bared end is connected to the inner race 14 between said end face thereof and the plastics washer 15. The other end of the power line 16 is connected at 18 to an electric supply of, say, 12 volts, and a warning light 19 mounted on the vehicle instrument panel (not shown) is interposed in said line. The release plate 10, due to its conventional mounting arrangement, is inherently connected electrically to the vehicle chassis (not shown) which constitutes in known manner the return shown symbolically at 20 to the electric supply. Thus the release bearing 11 and the release plate 10 together act as a switch to complete the circuit and illuminate the warning light 19 when the clearance between said bearing and said plate is taken up. The invention can be used perfectly well in the form thus far described, but the warning light 19 will be illuminated unnecessarily each time that normal operation of the clutch occurs. We therefore interpose an automatic delay circuit, including a switch consisting of a transistor 21, in the power line 16. A delay of, say, 7 seconds is sufficient to prevent illumination of the warning light 19 during normal operation of the clutch. The delay circuit comprises a first line 22 connected in parallel with the warning light 19, two resistors 23 and 24 being disposed in series in the first line 22, a second line 25 connected in parallel with the warning light 19, a resistor 26 and a capacitor 27 being disposed in series in the second line 25 with the resistor 26 upstream of the capacitor 27; and a third line 28 connected in parallel with the warning light 19, an operational amplifier connected as hereinafter described so as to operate as a voltage comparator 29 being interposed in the third line 28. The transistor 21 is interposed in that part of the power line 16 in parallel with the first, second and third lines 22, 25 and 28 respectively and containing the warning light 19, and is connected to an output point 30 of the voltage comparator 29 by way of a resistor 31. One input point 32 of the voltage comparator 29 is connected to the first line 22 at a point between the two resistors 23 and 24 in said line, and another input point 33 thereof is connected to the second line 25 at a point between the resistor 26 and the capacitor 27 in said line.

In operation, immediately the clearance between the release bearing 11 and the release plate 10 is taken up, current can pass through the first, second and third lines 22, 25, and 28 respectively. Thus a fixed voltage of an amplitude determined by the relative values of the two resistors 23 and 24 in the first line 22 is applied to the input point 32 of the voltage comparator 29, and a voltage which increases progressively from zero at a rate determined by the respective values of the resistor 26 and the capacitor 27 in the second line 25 is applied to the input point 33 of said comparator. The values of the three resistors 23, 24 and 26 and the value of the capacitor 27 are chosen so that the increasing voltage equals the fixed voltage when the desired delay has elapsed. When this occurs the voltage at the output point 30 of the voltage comparator 29 changes instantaneously from zero to the full supply voltage, and actuates the transistor 21 so as to complete the circuit through the power line 16 and thus illuminate the warning light 19. The resistor 31 disposed between the output point 30 of the voltage comparator 29 and the transistor 21 acts to limit the current passing from said point to the transistor 21 so as to prevent said comparator overheating.

In a modification, the warning light 19 is replaced by an audible warning device. In another modification, the clutch release bearing carrier sleeve is formed entirely of electrically-insulating material having suitable mechanical properties.