Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Patent
1995-12-18
1998-08-04
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
60494, 192 12C, F16D 3102
Patent
active
057877106
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an hydraulic emergency circuit.
An hydraulic emergency circuit for an electronically-controlled continuously variable transmission (continuously variable transmission CVT) is known from EP 0 324 928, which is preferably employed in passenger cars. A portion of the emergency hydraulic circuit relates to the control of a clutch device connecting a vehicle engine with a continuously operating transmission without the interposition of a hydrodynamic torque converter. For this purpose the circuit contains a pressure limiting valve which opens a non-return valve, with which it is mechanically coupled, when the pump pressure falls below a preselected value. The non-return valve places a downstream located clutch valve into its reverse position so that the clutch is opened. When the preselected pump pressure is exceeded, the non-return valve takes up a flow-through position. As a result the clutch valve is placed into the forward position. The clutch is closed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a hydraulic emergency control which avoids the disadvantages of the prior art.
In accordance with the present invention, a throttle valve is disposed in the working line, and at least one control line branches off upstream and downstream of the throttle valve, wherein the control lines are connected with a switch valves which controls and operates the supply of pressure for the friction clutch.
The hydraulic emergency circuit in accordance with the invention is used to control a friction clutch, which can be a wet clutch, without the assistance of an electro-hydraulic clutch management which is active during normal driving operations. Since during the starting operation and up to a defined lower engine rpm, at which sufficient torque can be made available for the vehicle operation, the friction coupling must compensate for the difference between internal combustion rpm and the drive train rpm by slipping, great demands are made on the hydraulic emergency circuit. A suitable circuit, such as the hydraulic emergency circuit in accordance with the invention represents, prevents the unintended shut-down or stalling of the internal combustion engine and keeps the clutch wear small by gentle engagement in spite of the use of simple circuit components. Rapid and assured declutching also acts in a wear-reducing way.
The engine rpm which are relevant for opening and closing of the friction clutch are measured as a function of the pressure drop at a throttle point in a working line of the hydraulic emergency circuit. The throttle valve required for this can be integrated without problems into known hydraulic circuits.
The emergency valve furthermore prevents a control interference between the electro-hydraulic clutch management and the hydraulic emergency circuit during normal driving operations.
Furthermore, with the aid of a throttle check valve disposed upstream of the friction clutch, in combination with a hydraulic pressure reservoir, it is accomplished that the hydraulic oil pressure in the clutch rises slowly and in a defined manner during a closing operation of the friction clutch, by means of which a jerk-free start with little stress on the clutch is made possible.
A check valve element in the throttle check valve causes the sufficiently rapid opening of the friction clutch.
BRIEF DESCRIPTION OF THE DRAWINGS
Two exemplary embodiments of the invention are schematically represented in the drawings in the form of hydraulic circuit diagrams and are explained in more detail in the following description of the drawing figures. Shown are in:
FIG. 1, a clutch control with one emergency valve and two reversing valves;
FIG. 2, a clutch control with one emergency valve and one reversing valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Normally an optimal clutch pressure is set with the aid of an electro-hydraulic control device in accordance with the rpm and the torque of the internal combustion engine. In case of a fa
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patent: 4531624 (1985-07-01), Ideta
patent: 4748809 (1988-06-01), Sumiya et al.
patent: 5040653 (1991-08-01), Vukovich et al.
patent: 5105929 (1992-04-01), Schmid et al.
Nguyen Hoang
Robert & Bosch GmbH
Striker Michael J.
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