Motor vehicles – Steering gear – With alternate emergency power means
Reexamination Certificate
1999-09-15
2001-08-07
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With alternate emergency power means
C180S403000, C180S405000, C180S402000
Reexamination Certificate
active
06269903
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of 198 42 066.8-21, filed Sep. 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a vehicle steering system that can be switched between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, and to methods for function-checking such a steering system.
In a known type of steering system, a steering handle, e.g. a steering wheel, is actuated by a driver. During normal operation of this steering system, i.e. on its steer-by-wire level, the steering handle is connected to steered vehicle wheels by an electric or electronic control system. Steering commands input into the steering system via the steering handle are converted into steering-angle adjustments of the steered vehicle wheels on the steer-by-wire level by the control system. In the emergency mode of the steering system, i.e. on its fall-back level, the steering handle is positively coupled, mechanically and/or hydraulically, to the steered vehicle wheels. On the fall-back level, a steering actuation of the steering handle is converted directly into a steering actuation of the steered vehicle wheels by the positive coupling.
SUMMARY OF THE INVENTION
An object of the present invention is to configure a steering system such that high functional reliability can be guaranteed.
According to the invention, this object has been achieved by a steering system for a vehicle, which can be switched between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level having a hydraulic system which contains a manual-side double-acting piston-cylinder unit which is actuated with a steering handle, e.g. steering wheel, and is positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit which actuates steered vehicle wheels, a hydraulic charging system being provided that has a hydraulic pump, the inlet side of which is connected to a hydraulic-fluid reservoir, switchable hydraulic coupling means being provided by means of which the hydraulic system of the fall-back level and the hydraulic charging system can be coupled to one another and decoupled from one another hydraulically.
The invention is based on the general recognition of the advantages of providing the fall-back level for implementing the mechanical or hydraulic positive coupling with a hydraulic system and furthermore to equip the steering system with a hydraulic charging system. The two hydraulic systems communicate with one another or are decoupled from one another hydraulically in dependence on switchable hydraulic coupling means. This measure allows the hydraulic system of the fall-back level to be influenced in many different ways by the hydraulic charging system. For example, it can be used to vary the pressure of the hydraulic fluid in the hydraulic system of the fall-back level.
The quantity of hydraulic fluid in the hydraulic system of the fall-back level can be varied, making it possible, for example, to replace slight losses due to leaks in the hydraulic system of the fall-back level from the hydraulic charging system, which is equipped with a corresponding hydraulic-fluid reservoir. Moreover, the coupling proposed according to the invention allows various function tests to be carried out on the steering system.
An important aspect is that the function tests on the fall-back level are also carried out on its, steer-by-wire level during the normal operation of the steering system. This means that the ability of the steering system to function in an emergency can be ensured. If the steering system detects a defect on the fall-back level during normal operation, then measures appropriate to the extent of the fault can then be indicated. For example, the maximum achievable speed of the vehicle can be reduced and a warning given to the effect that the vehicle should be taken to a workshop without delay.
According to a particularly advantageous embodiment of the steering system according to the invention, the steer-by-wire level has a hydraulic system for actuating the steered vehicle wheels which additionally acts as a hydraulic charging system. A high-grade and high-performance hydraulic charging system is thus available.
The object underlying the invention is also achieved by novel function checking methods.
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Bohner Hubert
Hartl Mathias
Moser Martin
Schrock Wolfgang
Crowell & Moring , L.L.P.
Daimler-Chrysler AG
Johnson Brian L.
Yeagley Daniel
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