192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
1999-08-06
2001-05-22
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S090000
Reexamination Certificate
active
06234290
ABSTRACT:
SUMMARY OF THE INVENTION
1. Field of the Invention
The present invention relates to an actuating installation for a friction clutch arranged in the drive line of a motor vehicle, in particular a commercial vehicle, between a drive unit, in particular an internal combustion engine, and a transmission. Such an installation has an actuating arrangement for the actuation of the friction clutch, a clutch-pedal arrangement connected to the actuating arrangement and having a clutch pedal for the actuation of the friction clutch by means of the actuating arrangement. The clutch pedal, in at least one first operating state of the actuating installation and/or of the friction clutch and/or of the motor vehicle, is actuable according to a force/travel characteristic of a first type.
2. Discussion of the Prior Art
Such an actuating installation has been disclosed by German reference DE 197 16 600 A1, the disclosure contents of which are included in the present application. In this actuating installation, the actuating arrangement comprises a positioning arrangement, which has a control valve, and a release-bearing arrangement, which serves to actuate the friction clutch. The positioning arrangement comprises a pneumatic-power cylinder arrangement, which acts on the release-bearing arrangement and which, via the control valve connected to a pneumatic source, can be actuated as a function of a hydraulic or mechanical reference variable and an actual variable representing the position of the release-bearing arrangement. The reference variable can be produced by means of the clutch-pedal arrangement and can be transmitted to the positioning arrangement by means of a mechanical or hydraulic transmission section.
The positioning arrangement comprises a hydraulic measuring-cylinder arrangement, which detects the actual variable representing the position of the release-bearing arrangement and feeds it back hydraulically to the control valve. The control valve, working according to the pressure-balance principle, controls the feed of pneumatic medium into the pneumatic-power cylinder arrangement or the discharge of pneumatic medium from the pneumatic-power cylinder arrangement in such a way that, during a clutch-pedal actuation, an essentially constant hydraulic pressure is maintained at a hydraulic-system-side inlet of the control valve. To this end, the positioning arrangement works with the control valve as a hydraulic/mechanical control loop.
In such an actuating installation, there is the problem that, if the pneumatic source cannot provide sufficient pneumatic pressure, for example after a prolonged stoppage of the motor vehicle having the actuating installation, the positioning arrangement is inoperative. The positioning arrangement could also be inoperative for another reason, for example because the control valve is defective. If the clutch pedal is actuated when the positioning arrangement is inoperative, the hydraulic pressure in the hydraulic system rises above the pressure level which normally occurs. Such a rise in the hydraulic pressure may be controlled, for example, by the hydraulic system being designed to be sufficiently burst-proof and by the hydraulic measuring-cylinder arrangement being designed as a hydraulic emergency-actuating-force cylinder arrangement. This will often generally be the case when the positioning arrangement is designed as a so-called “positioning servo arrangement”, in which the positioning arrangement thus produces an auxiliary release force, which assists the hydraulic or mechanical release force produced by pedal force.
When in this case a positioning arrangement is referred to below, unless expressly indicated otherwise this generally means an arrangement in which the positioning arrangement not only produces an “auxiliary force”, assisting the release, in addition to a release force exerted hydraulically or mechanically on the release-bearing arrangement and originating directly from the clutch-pedal actuation, but rather the only or solely essential release force. According to this usage, the term “positioning arrangement”—thus implies “external energy” - actuation of the clutch in contrast to a “servo actuation”—with two components producing release force, that is in contrast to a clutch actuation—assisted by “external energy”—by means of the pedal force exerted on the clutch pedal and transmitted to the release-bearing arrangement.
If it is not desired to design the hydraulic measuring-cylinder arrangement as a hydraulic emergency-actuating-force cylinder arrangement, for example because the hydraulic measuring-cylinder arrangement is contained in a control-valve construction unit removable independently of the pneumatic-power cylinder arrangement and only has a hydraulic cylinder which acts eccentrically or non-coaxially on the release-bearing arrangement, the following problems or disadvantages occur when a positioning arrangement is inoperative:
If the hydraulic system is designed in such a way that hydraulic pressures which may occur during a clutch-pedal actuation without an operative positioning arrangement can be withstood without bursting, this increases the costs and the weight of the hydraulic system without being of further advantage. Since extremely high hydraulic pressures may briefly occur during a rapid clutch-pedal actuation, for example in dangerous situations, the hydraulic system ought to be designed to be even extremely burst-proof at a corresponding cost.
Due to the high hydraulic pressures, damage to the positioning arrangement or to the release-bearing arrangement may occur, in particular at the hydraulic measuring cylinder and at the control valve as well as at a carrier arrangement connecting the release-bearing arrangement to the hydraulic measuring cylinder. In order to avoid such damage, said components ought to be designed for absorbing extremely high forces, which again means a high cost and a corresponding increase in the weight of the system.
If all the components can withstand the high pressures or forces, there is still the grave risk that, in the case of a hydraulic measuring-cylinder arrangement acting eccentrically or non-coaxially on the release-bearing arrangement or the pneumatic-power cylinder arrangement, the pneumatic-power cylinder arrangement will jam in a self-locking manner due to the tilting moments which occur, as a result of which the operability of the actuating installation is put at risk.
In the search for a remedy, said German reference DE 197 16 600 A1 proposes to provide an overload-protection arrangement in the form of a hydraulic cylinder with spring-preloaded piston in the hydraulic system. The overload-protection arrangement works as a pressure accumulator, since the spring preloading is proportioned in such a way that, when the positioning arrangement is operative, the hydraulic pressures which occur are not sufficient to noticeably move the piston against the spring preloading in the direction of an increase in volume of the hydraulic cylinder space, which is constantly in flow connection with the hydraulic system.
On the other hand, if the positioning arrangement is inoperative, for example on account of a lack of compressed air, the overload-protection device, after a preset pressure threshold has been reached, by appropriate increase in volume of the hydraulic cylinder space against the spring preloading, can absorb the hydraulic volume displaced from a hydraulic master cylinder of the clutch-pedal arrangement, so that the hydraulic pressure is limited and kept essentially constant in the process, and damage to components of the actuating installation is avoided.
German reference DE 197 16 600 A1 proposes as a further possible remedy to connect an overload valve to the hydraulic line connecting the hydraulic master cylinder to the control valve, which overload valve permits a flow of hydraulic medium from the hydraulic line to a supply side of the master cylinder only when the hydraulic pressure exceeds a preset pressure threshold. The pressure threshold is selected in such a way tha
Drexl Hans-Jurgen
Ester Barbara
Hirschmann Frank
Liebler Jurgen
Lindner Joachim
Cohen & Pontani, Lieberman & Pavane
Lorence Richard M.
Mannesmann Sachs AG
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