192 clutches and power-stop control – Clutches – Axially engaging
Reexamination Certificate
2000-02-11
2001-12-04
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Axially engaging
C192S111400
Reexamination Certificate
active
06325192
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to improvements in friction clutches, especially for use in motor vehicles. More particularly, the invention relates to improvements in friction clutches wherein a pressure plate is non-rotatably connected to a rotary housing so that it can perform limited axial movements relative to the housing, and wherein a clutch disc or clutch plate can be clamped between the pressure plate and a counterpressure plate (such as a flywheel) under the action of a diaphragm spring which bears against the pressure plate in the engaged condition of the friction clutch. The diaphragm spring is axially stressed between the pressure plate and the housing and is tiltable relative to a seat which is carried by the housing. The friction clutch further employs an adjusting unit which compensates for wear upon the friction linings of the clutch disc.
Automatic compensating devices which ensure that the pressure plate is acted upon by the diaphragm spring with a substantially constant force are disclosed, for example, in published German patent applications Serial Nos. 29 16 755 and 35 18 781. These compensating devices are adjustable in response to signals from a sensor and are disposed or operate between the pressure plate and the diaphragm spring. The pressure plate is coupled to the housing by tangentially extending leaf springs which must be designed to exert a relatively small force because such force opposes the bias of the diaphragm spring. Therefore, when the friction clutch is disengaged, the pressure plate (whose mass is rather substantial) is likely to perform axial reciprocatory movements which involve repeated stray movements into and out of contact with the diaphragm spring. This not only adversely influences the operation of the friction clutch, but can actually cause the friction clutch to become a safety risk because the compensating device is being adjusted in the disengaged condition of the friction clutch until the pressure plate comes into contact with the clutch disc, i.e., when it is no longer possible to disengage the friction clutch. Therefore, compensating devices which are disclosed in the aforediscussed published German patent applications failed to gain acceptance by the makers of friction clutches.
Presently known proposals to compensate for wear upon the friction linings of a friction clutch are further disclosed, for example, in German Pat. No. 29 20 932. According to that patent an axially movable adjusting device is installed between the diaphragm spring and the pressure plate. The actual axial adjustment is or can be effected by wedges which bear against the pressure plate and can move the adjusting device toward the diaphragm spring in response to angular displacement of the adjusting device relative to the pressure plate. It is also proposed in that patent to change the positions of the wedges for the purpose of moving the adjusting device relative to the pressure plate.
The means for ascertaining the extent of wear upon the friction linings in conventional friction clutches of the above-outlined character comprises a plurality of sensors which operate between the pressure plate and the counterpressure plate (normally a flywheel) or between the pressure plate and the cover. When the clutch is engaged, the sensors are displaced by a distance depending on the extent of wear upon the friction linings, and the extent of movement of the pressure plate away from the counterpressure plate in response to disengagement of the clutch is altered depending on the extent of adjustment of the sensors. The operation of conventional automatic wear compensating systems is based on the assumption that, when the friction clutch is new, the disengagement involves a movement of the pressure plate (away from the counterpressure plate) which exactly matches the extent of movement of the diaphragm spring. When the friction linings undergo a certain amount of wear, the pressure plate moves toward the counterpressure plate (flywheel) through a distance which is dependent on the extent of wear. Therefore, in the absence of any undertakings to the contrary, the diaphragm spring is then required to cover a greater distance from the cover toward the counterpressure plate in order to bias the pressure plate against the adjacent friction linings, i.e., to clamp the friction linings of the clutch disc between the pressure plate and the counterpressure plate. In other words, the distance which is covered by the diaphragm spring then exceeds the distance covered by the pressure plate. This results in appropriate axial displacement of the adjusting device in a direction toward the diaphragm spring.
A drawback of the conventional proposals is that the adjustment does not always correspond to the extent of wear upon the friction linings. The reason is that the extent of movement of the diaphragm spring in response to engagement or disengagement of the friction clutch fluctuates within a certain range, even if the extent of movement to disengage or engage the friction clutch is constant. The bearing or bearings which form part of the disengaging means and serve to displace the customary prongs of the diaphragm spring during disengagement of the friction clutch are particularly likely to perform movements which depart from the expected or prescribed movements within a rather wide range. Furthermore, when the clutch disengaging mechanism (e.g., a mechanical disengaging system) is adjusted, its actual adjustment is likely to depart from an optimal adjustment, for example, because the clearance between the disengaging system and the diaphragm spring is too small and/or because the initially selected stress between the disengaging system and the diaphragm spring is too pronounced. This results in the establishment of operating points which depart from the optimal operating point of the friction clutch.
If a friction clutch is equipped with an automatically adjustable disengaging system e.g., with a hydraulic system which employs a master cylinder and a slave cylinder, the aforediscussed means which is to compensate for wear upon the friction linings cannot be operated at all because the extent of movement to disengage the friction clutch is the same during the entire useful life of the clutch. Thus, no adjustment will take place as long as the movement of the diaphragm spring in the region of the adjusting device during disengagement of the friction clutch is less than or at most matches the extent of movement of the pressure plate. On the other hand, if the extent of movement of the diaphragm spring exceeds the extent of movement of the pressure plate, the adjusting device is actuated and carries out an adjustment during each disengagement of the friction clutch irrespective of the extent of wear (or any wear) upon the friction linings so that the friction clutch is totally misadjusted after a relatively small number of disengagements.
An additional problem which arises in conventional self-adjusting friction clutches (i.e., in clutches wherein the relative positions of the pressure plate and the diaphragm spring are to be automatically changed as the wear upon the friction linings progresses) is that the pressure plate is likely to become disengaged from the diaphragm spring in the axial direction of the clutch in response to characteristic resonant vibrations. This results in the activation of the adjusting device which induces a total misadjustment of the friction clutch and renders it useless for its intended purpose.
Friction clutches of the above-outlined character are further disclosed in published German patent application Serial No. 24 60 963, in German Pat. No. 24 41 141, in German Pat. No. 898 531 and in German Auslegeschrift No. 1 267 916.
A clutch assembly has a friction clutch comprising a pressure plate which is non-rotatably connectable with a counterpressure plate for limited axial movement with respect thereto, and at least one biasing spring provided to urge the pressure plate toward a clutch disc which can be clamped between the pressure
Kimmig Karl-Ludwig
Maucher Ed
Maucher Paul
Meinhard Rolf
Reik Wolfgang
Darby & Darby
Lorence Richard M.
Luk Lamellen und Kupplungsbau
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