US 4,981,052 AGranted

Transmission control fail safe system

AssigneeZahnradfabrik Friedrichshafen AG

InventorGeorg Gierer

Life of this patent

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Abstract

Electrohydraulic control for an automatically shiftable automotive transmission with a selection slide valve (2), at least for the neutral position (N), as well as for the drive mode (D) and reverse mode (R), an electronic control device (3) having solenoid valves (4) held in neutral position by spring action, a pressure-medium source (1), pressure control and gear control valves (5, 6, 7) for the actuation of gear engagement couplings and brakes (A-F), as well as with a R-gear safety valve (8), for preventing the shifting into the R-gear when the forward drive speed is still too high, and a system which, in the case of electronic failure, holds or shifts the automatic transmission to one gear insuring that the maximum permissible rotational speed of the engine is not exceeded when the vehicle travels at maximum speed, whereby, in the event of failure of the electronic control device (3) during driving, a control system holds or shifts the gear, and in the event of failure of the electronic control device (3) before the start or the restart of the engine, this control system (5, 6, 7, 8, 9) engages a lower gear. This way, in the case of electronic failure during travel, travel can be continued unhampered, for instance also in the highest gear, and no shifting down takes place. When the electronic device fails at start or at restart after a failure during travel, a lower gear is engaged, wherein it is also possible to start the vehicle.

Claims14

Dependent claims

An automatically shiftable transmission for a vehicle including a gear mechanism and having a plurality of clutches and of brakes effective to switch the gear mechanism into a respective forward and rear speeds, and an electrohydraulic control system, said electrohydraulic control system comprising:

a pressure medium source supplying a system pressure to said electrohydraulic system;
a selection slide valve receiving said system pressure from said pressure medium source for selecting between at least a forward drive mode including a first, second, third and forth forward speeds, a neutral mode and a reverse drive mode;
a first solenoid valve and a second solenoid valve operatively connected with said pressure medium source and supplying a control pressure to control shifting between said speeds, said solenoid valves having a switched off position and a switched on position corresponding to said modes selected by said selection valve;
an electronic control device for controlling said first and second solenoid valves:
a first, second and third pressure-control and gear-shift control valves for actuating the gear engagement clutches and brakes receiving said control and pressure system upon reaching the respective first, second, third and forth speeds of the transmission;
a reverse gear-shift safety valve for preventing shifting of the transmission into said reverse mode upon an output speed of the transmission exceeding a given forward output speed, said reverse-gear safety valve being hydraulically interconnected with said pressure-control and with said solenoid valves and receiving said system and control pressures;
and
a safety valve hydraulically interconnected with said pressure-control and reverse-gear valves and receiving said control and pressure systems, said reverse-gear, pressure-control and safety valves constituting a controlling system for holding the transmission in a respective gear upon not exceeding of the maximum permissible rotational speed or for shifting said transmission into said gear upon failure of said electronic device, said controlling system shifting said transmission into a lower gear upon starting of the engine.

5 more elements

An automatically shiftable transmission for a vehicle including a gear mechanism and having a plurality of clutches effective to switch the gear mechanism into a respective forward and rear speeds, and an electrohydraulic control system, said electrohydraulic system comprising:

a pressure medium source supplying a system pressure to said system;
a manual valve receiving said system pressure from said source and selecting a forward drive mode including at least a first speed, a second speed, a third speed and a fourth speed, a neutral mode and a reverse mode;
electronic means connected with said manual valve for determining the respective output speed of the transmission and including a first and second solenoid valves, said solenoid valves supplying a control pressure to control shifting between said speeds, said first solenoid valve being switched on in said first speed of said manual valve;
a plurality of hydraulic switch valves receiving said system and control pressures for controlling actuation the respective clutches upon reaching the respective forward speed of the transmission;
a reverse-gear valve receiving said system and control pressures and hydraulically connected with one of said switch valves actuating the respective clutch upon said first forward speed, said reverse-gear valve preventing the shifting of the gear mechanism into said reverse mode upon the output speed of the transmission exceeding a given speed;
and
a safety valve hydraulically interconnected with said switch and reverse-gear valves., said safety valve maintaining the fourth speed upon discontinuing of the control pressure supply, said safety valve, said reverse and switch valves hydraulically controlling the subsequent actuation of said clutches in response to the change of said system pressure upon failure of said electronic means and upon a start of an engine.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/328,080Filed 7 Feb 1989
Priority: LU 004698 Aug 1986
Granted: 1 Jan 1991
Term ends: Not estimatedThe source records don’t support an estimate.

Classification14 codes

F16H 61/12
Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid…
F16H 61/16
Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid…
F16H 59/40
Of gearing elements: output shaft speed
F16H 61/0206
For gearshift control, e.g. control functions for performing shifting or generation of shift signal: layout of electro-hydraulic control circuits,…