Emergency hydraulic control with control valves for continuously

Details Emergency hydraulic control with control valves for continuously Emergency hydraulic control with control valves for continuously

1997-10-06

1999-08-31

Jeffery, John A.

Endless belt power transmission systems or components

Pulley with belt-receiving groove formed by drive faces on...

Fluid pressure actuator for adjustment of member

474 18, 477 48, 477906, F16H 5900, H02P 304

Patent

active

059446269

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a hydraulic emergency control for a continuously variable transmission.
2. Prior Art
In German Patent Application DE 195 19 162.5, which had not been published by the filing date of the present application, a hydraulic emergency control for an electronically controlled continuously variable transmission (CVT) is described. The CVT that is preferably used in passenger cars has a control unit for emergency operation that assures tension of the transfer means by simple hydraulic means if the electrohydraulic triggering for normal driving operation should fail. These simple hydraulic means are described in conjunction with FIG. 1.
They assure on the one hand startup at full load, for instance, without slippage of the transfer means, and on the other after startup assure gear shifting from a high startup gear ratio to a low overdrive ratio.
The hydraulic valves, which switch over from the normal driving mode to the emergency operation mode, are held in the normal driving mode in the switching and/or control positions necessary for this driving mode with the aid of electromagnetic actuators.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved hydraulic emergency control with preswitching valves of the above-described kind for a continuously variable transmission.
These objects and others which will be made more apparent hereinafter are attained in a hydraulic emergency control for a gear-ratio-dependent change in hydraulic fluid pressure in a first and second hydraulic bevel-gear axial adjuster of a continuously variable transmission, in which a pump supplies a piston chamber of the second hydraulic bevel-gear axial adjuster, at least one downstream pressure limiting valve limits the hydraulic fluid pressure at the at least one downstream pressure limiting valve and the pump supplies a piston chamber of the first hydraulic bevel-gear axial adjuster via a continuous path valve controlled with the aid of a pressure differential acting on a throttle valve integrated in a switching valve downstream of the pump.
According to the invention the hydraulic emergency control comprises a plurality of pilot control valves connected to the switching valve, the continuous path valve and the at least one pressure limiting valve, so that the switching valve, the continuous path valve and the at least one pressure limiting valve are each hydraulically triggered via at least one of the pilot control valves counter to the action of a mechanical or hydraulic actuator associated therewith.
The hydraulic emergency control is needed in order to enable emergency operation of a continuously variable transmission without the support of an electrohydraulic triggering means that is active in the normal driving mode. In the hydraulic emergency control of the invention, among other things, the switching valve, which if the triggering electronics fail switches over from the normal driving mode to emergency operation, is controlled hydraulically such that it changes its switching position on the basis of control pressure changes in the system. For instance, it switches over from the normal driving mode to the emergency operation mode. The pressures used to control the switching valve occur only if the triggering electronics fail or have already failed. As soon as the control pressure changes in the system again correspond to a normal driving situation of the kind existing when the triggering electronics are intact, the switching valve switches back over to the switching position for the normal driving mode. In general, the switching valve is responsible for the activation of an arbitrary function.
With the hydraulic emergency control according to the invention, among other things, the entire electric triggering means for the switching valve described is dispensed with.
Various preferred embodiments of the invention are described in more detail in the following detailed description.


BRIEF DESCRIPTION OF THE DRAWINGS

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REFERENCES:
patent: 4543077 (1985-09-01), Yamamuro et al.
patent: 4545265 (1985-10-01), Abo et al.
patent: 4663991 (1987-05-01), Nakamura et al.
patent: 4669336 (1987-06-01), Okada et al.
patent: 4685357 (1987-08-01), Sawada et al.
patent: 5169365 (1992-12-01), Friedmann

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