192 clutches and power-stop control – Clutches – Progressive engagement
Reexamination Certificate
1999-07-15
2001-02-20
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Progressive engagement
C192S054500, C192S070180, C192S070230, C192S070300, C192S089230
Reexamination Certificate
active
06189667
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a friction clutch for motor vehicles having a clutch casing which is connectable in a rotationally fixed manner to a driven flywheel, a pressure plate arranged inside the clutch casing, and a pressure spring which is supported on the clutch casing for exerting a varying pressure force on the pressure plate during engagement of the clutch to press a clutch disk with friction linings onto the flywheel.
2. Description of the Related Art
A prior art friction clutch is known, for example, from German reference DE 39 40 917 A1. This reference discloses a friction clutch having a clutch casing in which a pressure plate is rotatably fixed and axially movable. A pressure spring is actuatable for pressing the pressure plate relative to the clutch casing onto a clutch disk. An actuation device which acts on the pressure spring and is mechanically or hydraulically actuated is provided to engage and disengage the clutch. The actuation device is arranged partly inside the clutch casing and the actuating member is guided out of the clutch casing. The friction clutch transmits the torque via the clutch disk which is connected to a transmission input shaft. Both sides of the clutch disk have friction linings arranged on a radially outer area. The clutch disk is pressed onto the flywheel of an internal combustion engine by the pressure plate. The pressure spring is designed as a diaphragm spring, and the actuating force which it applies determines the amount of torque which can be transmitted. If the pressure spring is lifted off the pressure plate, the pressure plate is released from the clutch disk and the torque which can be transmitted is reduced, possibly to zero. If the internal combustion engine fails to run smoothly—a characteristic of the internal combustion engines which in design terms is impossible to rule out—the resulting torque fluctuations and torque peaks, which would otherwise lead to increased wear, have to be transmitted without the clutch slipping. A similar problem arises during acceleration of a high-torque internal combustion engine or when a vehicle is moved off in a high gear. As a consequence of these factors, the pressure force which the diaphragm spring has to apply to the pressure plate must be correspondingly high, a fact which in principle requires the clutch to have excessive dimensions.
Since the space available in a motor vehicle—and therefore the available clutch friction radius—are limited, it is necessary to achieve a higher clutch moment by a higher pressure force, resulting in higher actuating forces. To avoid a reduction in comfort for the driver of the vehicle as a result of the high disengagement force required, servo devices are fitted, which boost the actuating force of the clutch pedal.
Inorganic friction linings which have a high coefficient of friction &mgr; (for example greater than or equal to 0.3) may also be used to increase the torque which can be transmitted and therefore to reduce the pressure force required. However, the use of such friction linings has the undesirable side effect that the coefficient of friction &mgr; of these friction linings, within a certain range, falls as the relative speed increases. Such friction linings may cause clutch grabbing when the clutch is engaged, which represents a considerable reduction in comfort for the passengers of the vehicle.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved friction clutch such that a torque which can be transmitted is influenced so that comfort is improved and/or so that a disengagement force is variable.
The object of the present invention is achieved by a friction clutch according to a first embodiment of the present invention including a device which acts on the pressure plate of the friction clutch and varies the pressure force on the pressure plate essentially proportionally to the force of the pressure spring when the clutch is in the engaged position. At least during operation, the device of this embodiment acts as a booster device and applies, for example, an additional force to the pressure plate which boosts the actuating force. The result is that the clutch has a self-reinforcing action. At the same time, this design of the booster device advantageously allows automatic readjustment of a position of the pressure plate in the event of a reduction in the thickness of the friction linings. Moreover, the preloading force of the pressure spring may be reduced over the prior art for an equal torque to be transmitted, resulting in reduced disengagement forces.
Another embodiment of the device is arranged for reducing the force of the pressure spring during operation instead of boosting the force of the pressure spring. This embodiment is useful in clutches having friction linings which are made from an inorganic material and which have a coefficient of friction that falls, within a certain range, as the relative sliding speed increases. This embodiment of the device acts on the pressure plate and, during engagement of the clutch, applies a pressure force to the pressure plate for proportionally reducing the force provided by the spring. This design increases the torque which can be transmitted by friction linings with a higher coefficient of friction. The clutch grabbing which is normally associated with these inorganic friction linings is avoided by the generation of a force which counteracts the spring force. As a result, a clutch fitted in this way produces a self-attenuating action. Therefore, in this embodiment of the clutch it is possible to reduce the preloading force of the pressure spring while achieving the same transmissible torque as that of conventional clutches, resulting in reduced disengagement forces, since suitable friction linings are used.
Furthermore, according to the invention it is advantageous if the pressure plate is permitted to rotate relative to the clutch casing within a predetermined range and the device is formed by at least one lever which is arranged pivotably between clutch casing or flywheel and pressure plate. Given suitable attachment of the device during a pulling mode—when internal combustion engine applies a driving force to the clutch disk such as when the vehicle is moving off and during accelerated travel—this pivotable lever enables the application of an additional pressure force to the pressure plate. Then, in a corresponding manner, the same arrangement in a pushing mode—when the vehicle pushes the engine—will result in attenuation of the additional pressure force. This arrangement can be utilized as an overload protector, e.g. when changing down to too low a gear, so that the engine is not forced to rotate too fast.
In the above-described embodiment, the device of the invention has at least one closed link. As a result, the corresponding lever is guided captively by the closed link and the other link may be open or may also be closed. For example, if the device is connected between the clutch casing and the pressure plate, one end of the device may be held onto the clutch casing (closed link) while the other end of the device merely abuts a portion of the pressure plate (open link). If two closed links are used, it is possible to transmit both compressive forces and tensile forces via the device.
It is also possible for the device to have two open links. In this case, it is only possible to transmit force in one direction, and an independent guide for the corresponding lever must be provided.
According to the invention, the lever may exert a compressive force on the pressure plate in the event of a relative movement between the pressure plate and the clutch casing or the flywheel. In such a case, it is possible, for example, to use a design including two open links, which is particularly simple to manufacture and assemble.
However, it is also entirely possible for the lever to exert a tensile force on the pressure plate in the event of a relative movement between the pressure plate and the clutch casing. This em
Dörfler Mathias
Heiartz Markus
Bonck Rodney H.
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
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