Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1989-02-07
1991-01-01
Wright, Dirk
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
B60K 4118
Patent
active
049810529
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national phase application corresponding to PCT/EP87/00423 filed Aug. 1, 1987 and based in turn upon an application filed in Luxembourg as PCT/EP86/00469 filed Aug. 8, 1986 under the International convention.
FIELD OF THE INVENTION
My present invention relates to an electrohydraulic control for an automatically shiftable automotive transmission. More particularly, the invention relates to an electrohydraulic control for an automatically shiftable automotive transmission with a selection slide valve at least for the neutral position as well a for the drive mode and the reverse mode, an electronic control device, solenoid valves held in the neutral position by spring action, a pressure-medium source, pressure control valves and gear shift control valves for actuating the gear engagement clutches and brakes, a reverse-gear safety valve which prevents the shifting into the reverse gear when the forward drive speed is too high and a system which, in the event of failure in the electronic circuitry, holds or shifts the automatic transmission into a gear insuring that the maximum permissible rotational speed of the engine is not exceeded when the vehicle travels at maximum speed.
BACKGROUND OF THE INVENTION
A 4-speed automatic transmission with electronic-hydraulic control is known from two publications in ATZ 85 (1983), 6 pages 393 to 405. From paragraph 4, Transmission Control (page 402) and paragraph 5, Safety Functions, as well as from FIGS. 6 and 7 of these prior art publications, it is known that in a currentless state, the vehicle can be driven purely hydraulically, corresponding to the selection slide valve shift, either forward in the 3rd speed or in reverse, whereby a neutral position (idling setting) is also possible.
In the publication 4 HP 22 E of the ZF GETRIEBE GMBH SAARBRUCKEN, Oil Circuit Diagrams, this electronic-hydraulic transmission is illustrated in detail and completes FIG. 6. This system is possible because it controls an overdrive transmission, wherein the 4th speed is a high-speed gear--overdrive- and the engine does not reach the highest rotational speed. However, such a control is not appropriate for a 4-speed transmission with a direct 4th speed or an overdrive transmission wherein the highest rotational speed is reached in the highest gear, because a shifting down from the 4th to the 3rd speed in case of electric-current supply failure leads to excessively high rotational speeds in the engine and could result in damage to the engine.
OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved electronic-hydraulic control of the type described, so that in case of electric-current supply failure no unacceptable downshifting occurs.
It is also an object to achieve this result without an increase in the cost of construction.
SUMMARY OF THE INVENTION
This object is attained providing the electronic device so that the gear in which the maximum permissible rotational speed is not exceeded is held only during travel by a control system or the transmission is shifted into this gear, and during failure of the electronic control device, this system engages a lower gear before starting or restarting of the engine.
During operation at high speed, the driver does not become aware of a failure in the electronic control from the behavior of the vehicle, until the provided signal appears on the dashboard, and under such conditions he can continue to drive unimpaired. Also, the engine is not overloaded, since no inadmissible shifting down, which could lead to engine damage, takes place. Only when certain requirements can no longer be met in this speed, e.g. driving uphill, will the driver have the possibility to shift the transmission into a lower gear. However, for this purpose the system pressure has to be interrupted for a short while for the hydraulic part of the electronic-hydraulic control to respond. For safety reasons, the driver has to stop the engine for this purpose and then r
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patent: 4628772 (1986-12-01), Nishikawa et al.
patent: 4635508 (1987-01-01), Tatsumi
patent: 4827806 (1989-05-01), Long et al.
patent: 4841816 (1989-06-01), Bullock
patent: 4858501 (1989-08-01), King
Dubno Herbert
Wright Dirk
Zahnradfabrik Friedrichshafen AG
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