192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
2001-04-12
2003-03-25
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S090000
Reexamination Certificate
active
06536573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to an actuation system for a friction clutch installed in the drive train of a motor vehicle, especially a commercial motor vehicle, between a drive unit, especially an internal combustion engine, and a transmission. This actuation system includes a pressure medium-powered cylinder assembly which is used to actuate the friction clutch; a pilot/automatic control valve assembly connected to the source of the pressure medium, by means of which the pressure medium-powered cylinder assembly can be actuated as a function of a control input representing a desired actuation state, possibly the desired position of a disengaging device, and an actual value representing an actual actuation state, possibly the actual position of the disengaging device. An auxiliary actuating assembly is provided for clutch actuation independently of the ability of the valve assembly to function and/or independently of the ability of a pilot/automatic control unit driving the valve assembly to function and/or independently of the instantaneous pressure of the pressure being made available by the pressure medium source.
2. Description of the Related Art
An actuation system of this type is known from, for example, DE 197 16 600 A1, the disclosure of which is incorporated herein by reference.
In the known actuation system, the actual position of a disengaging bearing assembly is detected by a hydraulic measuring cylinder assembly, which cooperates with a pilot/automatic control valve assembly operating according to the principle of the pressure scale. The pressure medium-powered cylinder assembly, which can be designed, for example, as a pneumatic cylinder, is actuated via the pilot/automatic control valve assembly as a function of the actual value detected by hydraulic means and a hydraulic signal, which represents the control input and which is transmitted by a hydraulic master cylinder associated with a clutch pedal assembly. According to a variant, the hydraulic measuring cylinder assembly is designed as a slave cylinder assembly, which acts on the disengaging bearing assembly. The slave cylinder assembly is used for the emergency or auxiliary actuation of the clutch. According to another variant, a hydraulic slave cylinder assembly is provided in addition to the pneumatically powered cylinder assembly to make possible an emergency or auxiliary actuation of the clutch.
An emergency or auxiliary actuation of the friction clutch is desirable for a number of different reasons. For example, after the vehicle in question has been parked for a certain period of time, the compressed air tank of the pressure medium source can become completely empty as a result of leaks in the individual receivers. If the vehicle was parked with a gear engaged, the tension of the drive train would make it impossible to disengage the gear without emergency or auxiliary actuation of the clutch, and the vehicle's engine could therefore not be started to fill the compressed air tank back up again. Auxiliary actuation of the clutch is therefore extremely important in practical terms, both for passenger and commercial vehicles.
An extremely high degree of operational reliability is also required for commercial vehicles for another reason. It is generally known, for example, that various components, such as electronic components, can fail and that in such a situation the vehicle must be taken to the nearest garage still under its own power if possible and possibly in a manner deprived of a certain convenience. We speak in this situation of a so-called “limp-home” function.
In themselves, these requirements are fulfilled by the known solutions according to DE 197 16 600 A1. An auxiliary actuation system designed in this way, however, suffers from several disadvantages. For example, the auxiliary actuation of a clutch of this type requires the driver to exert a great deal of force on the clutch pedal, which the driver can do only with great effort. In addition, the auxiliary actuation system represents a high degree of mechanical and hydraulic complexity. For example, a master cylinder assembly designed for high pressures, an appropriately massive clutch pedal, and a hydraulic slave cylinder assembly designed for high pressures (and possibly a measuring cylinder assembly) are all required. Because the components must be very strong, they must also be correspondingly heavy and bulky. The auxiliary actuation system therefore also occupies a considerable amount of space. In addition, it is disadvantageous on principle to provide a hydraulic slave cylinder assembly inside a clutch cover, because these cylinders can leak, and the escape of the hydraulic oil can cause damage. In contrast to a pneumatically powered cylinder assembly, in which a certain amount of leakage can be readily tolerated, a hydraulic slave cylinder assembly must be leak-tight, or else the leaky hydraulic slave cylinder assembly must be repaired or replaced. Depending on the design of the hydraulic slave cylinder assembly (a ring-type hydraulic slave cylinder, for example), the corresponding repair and maintenance work may require that the drive train be separated, possibly including the removal of the clutch cover from the internal combustion engine. A disengaging system of this type appears to be too complicated for modern, electronically controlled drive trains, nor is it very satisfactory with respect to positioning accuracy.
SUMMARY OF THE INVENTION
Against this background, it is the object of the present invention to provide an actuation system of the general type described above in which the auxiliary actuating assembly is improved with respect to at least some of the aspects discussed above.
To achieve this object, in accordance with a first aspect of the invention, the auxiliary actuating assembly includes an auxiliary actuating valve assembly, which can be switched to a pressure medium feed position and/or to a pressure medium discharge position. By means of this valve assembly, the pressure medium-powered cylinder assembly can be brought into pressure medium flow connection with the pressure medium source or with a separate, auxiliary pressure medium source for the emergency actuation of the clutch (pressure medium feed position of the valve assembly) or into pressure medium flow connection with a pressure compensation port or a pressure compensation tank (pressure medium discharge position of the valve assembly).
According to the invention, the auxiliary actuation by the pressure medium-powered cylinder assembly, preferably a pneumatically powered cylinder assembly, is accomplished by means of an auxiliary actuating valve assembly, which can be switched into a pressure medium feed position, in which the pressure medium-powered cylinder assembly is in pressure medium flow connection with the pressure medium source or with a separate auxiliary pressure medium source for the emergency actuation of the clutch. Alternatively or additionally, the auxiliary actuating valve assembly can be switched to a pressure medium discharge position, in which the pressure medium-powered cylinder assembly is in pressure medium flow connection with a pressure compensation port or a pressure compensation tank for the emergency actuation of the clutch. A central auxiliary actuation function is present as soon as it becomes possible for the clutch to be disengaged by the intermediate action of the auxiliary actuating valve assembly, so that, even though a gear is engaged and the drive train is under tension, the gear can still be disengaged and the drive unit (the engine) can be started for the purpose of, for example, refilling the pneumatic or compressed air tank of the pressure medium source, which in this case is designed as a pneumatic source. Preferably, however, the clutch can be both disengaged and engaged by the intermediate action of the auxiliary actuating valve assembly. Thus it becomes possible not only for an engaged gear to be disengaged and for the drive unit to be started, but also for a
Fliege Hans
Nagler Franz
Cohen & Pontani, Lieberman & Pavane
Lorence Richard M.
Mannesmann Sachs AG
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