Motor vehicles – Steering gear – With fluid power assist
Patent
1998-08-03
2000-06-20
Hurley, Kevin
Motor vehicles
Steering gear
With fluid power assist
180403, B62D 506
Patent
active
060766271
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to power steering for automobiles with a mechanical drive connection between a steering device, particularly a steering wheel, and a steering gear arrangement for steering of vehicle wheels, a servo motor coupled with the steering gear arrangement and a connection for separating the drive connection. The servo motor is controllable over a control valve which, in turn, can be controlled by a control system as a function of a difference between a first value, correlated with the steering angle of the vehicle wheels, and at least one second value, correlated with the adjusting travel of the steering device. A servo valve additionally is connected with the drive connection and analogous thereto, can be controlled by the forces or moments transferred by the drive connection, over which servo valve the servo motor can be connected in a controllable manner with delivery and low-pressure connections. Thereby, the servo motor produces a servo power reducing the actuation force necessary at the steering device and the servo motor being connected through a reversing valve arrangement either to the motor connections of the control valve or to the motor connections of the servo valve.
Such power steering arrangements are known from JP-A-40 19271. Steering arrangements of this type have two operating states. In one operating state, a mechanical forced connection is provided between the steering device and the steered vehicle wheels whereby, as a function of the forces transferred between the steered vehicle wheels and the steering device, a servo valve is controlled which, in turn, actuates a hydraulic servo motor. In this operating state, the steering therefore works like conventional hydraulic power steering. In the other operating state, the steering device is disconnected from the steered vehicle wheels, and the servo motor is controlled by a control system as a function of a difference between a first value correlated with the steering angle of the steered wheels of the vehicle and a second value correlated at least with the adjusting travel of the steering device. In this state, the steering therefore works according to the "steer by wire" concept.
To switch between the two operating states at need, a reversing valve arrangement connects the servo motor either with the motor connections of the servo valve or with the motor connections of the servo valve actuated by the control system. Therefore, in the event that the control system malfunctions, it is possible to switch over to the operating method of the conventional power steering system.
In JP-A-40 19271, the valve arrangement, which is provided for the above-cited switching, normally is in the position provided for the "steer by wire" operating state. The reversing valve arrangement is switched hydraulically from this normal position when the servo valve is actuated with the mechanical forced connection switched on between the steering device and the steered wheels of the vehicle. The servo motor is built in a special manner for this purpose. There are objections to this concept for safety reasons.
A vehicle steering system is described in WO 90/12723 in which the mechanical forced connection, provided for emergency purposes between a steering wheel and the wheels steering the vehicle, is normally separated. In this normal state, a first hydraulic adjusting unit, serving to adjust the steering of the wheels steering the vehicle and a second hydraulic adjusting unit, serving to produce a manual force perceptible at the steering wheel, are actuated. Both adjusting units are controlled by electronics. These control electronics, on one hand, actuate the first hydraulic adjusting unit assigned to the steering wheels of the vehicle in accordance with signals from a nominal value transmitter actuated by the steering wheel for the desired angle of steering. On the other hand, the second hydraulic adjusting unit, assigned to the steering wheel and serving for production of manual power, is actuated
REFERENCES:
patent: 4473128 (1984-09-01), Nakayama et al.
patent: 4476529 (1984-10-01), Nakamura et al.
patent: 4626994 (1986-12-01), Yabe et al.
patent: 4702335 (1987-10-01), Cage et al.
patent: 5320191 (1994-06-01), Sudo et al.
Bohner Hubert
Moser Martin
Daimler-Chrysler AG
Hurley Kevin
McKinley Kevin
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