Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Pump and motor in series with planetary gearing
Patent
1993-02-22
1994-04-26
Wright, Dirk
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Pump and motor in series with planetary gearing
475141, F16H 6112
Patent
active
053062159
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a drive device with a power-shiftable transmission driven by a prime mover, specially for mobile excavators, wheeled loaders and similar work machines. The separate speed levels of the transmission are here alternatively engaged and disengaged by a gear-shift valve via a respective friction clutch. At least two of the friction clutches are designed as spring-accumulator clutches and controllable by oil pressure generated by an oil pump. At least one of the friction clutches is designed as brake and has a static, leakage-oil-free oil supply.
Such a drive device is an object of older German patent application P 38 08 067.2. Under different travel conditions, falling below a specific value of the oil pressure generated by the oil pump can lead to deficiencies of the drive of the vehicle. In the 2-gear transmission shown, for instance, the leakage that occurs could make impossible a further forward movement of the vehicle when the pressurized oil that flows is insufficient due, for instance, to an unforeseeable, sudden braking until parking.
Therefore, the problem to be solved by the invention is to improve the drive device so that even when the oil pressure falls the vehicle can still be safely removed from the traffic by its own power and, for instance, driven to the edge of the road. In addition, in case of partial failure of an electric control current, a safe further travel should remain possible.
The drive device of the present invention solves said problem by the fact that when the oil pressure generated by the oil pump falls below a first specific value, the gear-shift valve is adjusted to a position in which only the brake can be actuated with pressurized oil. The oil pressure thus disengages the one of the two friction clutches which has an oil supply fixed to the housing. A brake is provided when a 2-gear transmission is used. In transmissions having more than two gears, more than only one of the friction clutches can be designed as brakes all of which can then be supplied with pressurized oil. Unlike in a friction clutch having one oil supply via a self-turning shaft, none or only a minimal leakage occurs here. The remaining amount of oil such as still conveyed by an oil pump with slipping drive V-belt or existing in a hydraulic accumulator will therefore be capable of keeping the brake disengaged over a specific period of time so that the vehicle can be driven to a safe place.
When using a 2-gear transmission it is convenient if the 2nd gear is engaged upon actuation of the brake with pressurized oil. Thereby a sudden delay which would occur when downshifting from the 2nd gear to the 1st gear is avoided. The engagement of the 2nd gear or of the gear engaged by actuating the brake(s) with pressurized oil when the oil pressure falls is advantageously obtained by attaching to the pressure line, which leads from the oil pump to the gear-shift valve, a pressure switch by which the gear-shift valve is adjusted to the adequate shift position when the oil pressure falls.
In case of complete failure of the oil pump, the required pressure can be maintained over a certain period of time by a hydraulic accumulator attached to the pressure line leading from the oil pump to the friction clutches.
In case of failure of an electric control current, a sudden deceleration can be prevented by adjusting the gear-shift valve to said shift position even in such a case.
If the oil pressure in the pressure line sinks further below to a pressure no longer sufficient to keep the brake disengaged, it is advantageous to brake the prime mover by a second pressure switch. If as prime mover is used a hydraulic motor supplied with pressurized oil by a hydraulic pump via a steering valve, then the steering valve is adjusted by the second pressure switch to its neutral shift position which shuts off a communication from the hydraulic pump to the hydraulic motor.
The invention is not limited to the combination of features of the claims. Depending on the existing problem, other logical possible combinations re
REFERENCES:
patent: 3969957 (1976-07-01), DeLalio
patent: 4185520 (1980-01-01), Henneman et al.
patent: 4407399 (1983-10-01), Wolff
patent: 4453430 (1984-06-01), Sell
patent: 4516444 (1985-05-01), Herr, Jr.
Eymuller Helmut
Mann Egon
Wright Dirk
Zahnradfabrik Friedrichshafen AG
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