Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1999-10-25
2001-05-15
Boehler, Anne Marie (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
C180S441000
Reexamination Certificate
active
06230839
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a servo-assisted steering system with hydraulic servo-assistance for motor vehicles. Here, a steering shaft, which is provided with a steering wheel, is connected via a torsion spring with an input member of a steering gear. An output member of the steering gear is connected with the wheels of the vehicle which are to be steered. In case of a relative rotation of the steering shaft in respect to the input member, two work chambers of a servo motor of a force amplification device can be pressurized by a servo pump via a steering valve with a pressure medium. At least one sensor for detecting a rotation angle and/or a torque is arranged on the steering shaft. A sensor for detecting a steering angle is arranged on the output member of the steering gear. This sensor can also be integrated into the rotation angle sensing mechanism of the steering shaft. A returning device is used for the hydraulic assistance of the returning of the steering gear and the wheels to be steered after the steering wheel is released following a steering process.
Such a servo-assisted steering system is known from EP 0 440 63 8 B1. In this case an electric motor used to affect the reaction force, which can be noted on the steering wheel, as a function of various parameters, is arranged in addition to a complete servo-assisted steering system with hydraulic servo-assistance. Moreover, the electric motor is used to center the steering valve exactly in its center. Finally, it is possible to achieve a hydraulic steering axle return in that, following the release of the steering wheel, the steering valve is displaced past its neutral position into a steering position, which corresponds to a reversal of the steering direction. A steering system is known from U.S. Pat. No. 4,745,985, which contains several features of the invention. With this steering system the amount and the direction of the hydraulic servo-assistance, as well as the return of the wheels to be steered, are controlled by means of a common electronically-controlled electromagnetic valve. Steering errors could appear in case of the possible appearance of a malfunction in the electronic control device, which could lead to endangerment.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is based on realizing the positive properties present in the known servo-assisted steering system, such as the exact centering of the valve and the hydraulic steering axle return, by simpler means without the use of an electric motor. Moreover, the steering ability of the vehicle is to be assured if a malfunction in the electronic system occurs.
This object is attained with the servo-assisted steering system featured in that the amount and the direction of the hydraulic servo-assistance, as well as the return of the wheels to be steered are controlled by means of a common electronically-controlled electromagnetic valve which thus acts as a return device. The electromagnetic valve can be integrated into the actual servo-assisted steering system, or it can be arranged outside of it at any arbitrary place. The auxiliary power for the hydraulic servo-assistance is exclusively provided by the servo pump. No electric motor is required.
In order to prevent danger in case of a possibly occurring error, a bypass valve is arranged between the steering shaft and the input member of the steering gear. With other known servo-assisted steering systems the steering valve is located at this location. The bypass valve is designed as a rotary slide valve with a closed center, so that in its neutral position there is no possible connection between the two work chambers of the servo motor. Only when an error occurs is the bypass valve switched into its open position, so that the two work chambers of the servo motor are connected with each other. The two work chambers are then bypassed, so that no pressure buildup can take place in the servo motor. In this case the steering energy is exclusively provided by the mechanical actuation of the steering wheel.
Advantageous and useful embodiments of the invention are recited subsequently.
The electromagnetic valve can be controlled in a simple manner as a function of at least one parameter, for example the road speed of the vehicle, the steering speed, the yaw speed, the load of the vehicle, the acceleration of the vehicle and others.
By means of an appropriate programming of the electronic unit and appropriate sensor devices it is possible to control the electromagnetic valve by means of signals, which provide information regarding the present position of the vehicle and regarding desired future positions. With this, the option for automatic steering is contained in the servo-assisted steering system.
REFERENCES:
patent: 4457390 (1984-07-01), Abe et al.
patent: 4825751 (1989-05-01), Kervagoret
patent: 4940105 (1990-07-01), Matsunaga et al.
patent: 5086687 (1992-02-01), Elser et al.
patent: 5513720 (1996-05-01), Yamamoto et al.
Braun Andreas
Elser Dieter
Zeitz Wolfgang
Boehler Anne Marie
Larson & Taylor PLC
Winner Tony
ZF Friedrichshafen AG
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