Motor vehicles – Steering gear – No mechanical connection between steering shaft and steering...
Reexamination Certificate
1999-09-02
2001-06-12
Olszewski, Robert P. (Department: 2167)
Motor vehicles
Steering gear
No mechanical connection between steering shaft and steering...
C180S406000
Reexamination Certificate
active
06244371
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of 198 39 951.0-21, filed Sep. 2, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a steering system for non-track-bound motor vehicles, with a steering handle, e.g. steering wheel, actuated by the driver, a steering actuating drive for steering displacement of steerable vehicle wheels, a desired steering-angle transmitter which can be actuated by the steering handle, and an actual steering-angle transmitter which can be actuated by the steerable vehicle wheels. A regulating arrangement controls the steering actuating drive as a function of a comparison between the desired values and actual values of the steering angle and continuously checks itself and sensors interacting with it for malfunctions. A mechanical or hydraulic positive coupling is arranged between the steering handle and the steerable vehicle wheels and, when the regulating arrangement is operating correctly, is opened or remains open (inactive normal state) and, if the regulating arrangement is defective, is automatically closed (active special state).
Known steering systems which operate on the “steer-by-wire” concept are fundamentally familiar and are being developed for future motor vehicles. These systems offer the fundamental advantage that, at least as regards the regulating arrangement and the associated sensors, they are suitable for a very wide variety of vehicles without design modifications. On one hand, virtually any transmission ratio between the actuating displacement of the steering handle and the change in the steering angle of the steered vehicle wheels can be achieved by appropriate programming. There is moreover the possibility of connecting the regulating arrangement to additional sensors in order to automatically allow for or eliminate parameters to be specified, e.g. the effects of side winds.
In order to be able to guarantee the required degree of safety in the event of system faults, provision is made to automatically activate an operating mode for abnormal operation or emergency operation if a fault occurs in the regulating arrangement or signals that are to be evaluated by the regulating arrangement fail. In this operating mode, a positive coupling is provided between the steering handle and the steered vehicle wheels. The steering system thus operates in principle in the manner of a conventional steering system, although the mechanical steering column customary in conventional steering systems can be replaced, if required, by other mechanical systems or by hydraulic systems, in particular hydrostatic systems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide advantageous measures as regards the operating reliability of a steering system of the above-mentioned type.
According to the invention, this object has been achieved by providing that the regulating arrangement activates the special state, i.e. active positive coupling between the steering handle and the steered vehicle wheels, if
(i) a deviation which exceeds a first threshold value occurs between the desired value and the actual value of the steering angle and/or
(ii) a deviation which exceeds a second threshold value is maintained between the desired value and the actual value of the steering angle for a time to be specified and/or
(iii) the time average of the desired/actual value deviation, of the steering angle exceeds a third threshold value during a second time period to be specified.
The invention is based on the recognition of the advantages of monitoring not only the correct operation of the regulating arrangement and the associated sensors but also characteristic variables correlated with the desired/actual value deviation of the steering angle. In this way, a switch is made to the special mode a sufficiently long time before a critical state in the case of creeping functional impairments of the steering system. It is advantageous here that whatever the functional impairments of the actuating drive, e.g. increasing stiffness due to wear or dirt, they cannot impair the safety of the steering system.
According to a preferred embodiment of the invention, the monitored characteristic variables of the desired/actual value deviation of the steering angle are varied as a function of parameters to be specified.
For example, the permissible maximum value of the desired/actual value deviation, i.e. the abovementioned first threshold value, can be reduced as the speed of travel of the vehicle increases and/or as the actuating forces of the actuating unit decrease. This ensures that the steering movements of the steered vehicle wheels are monitored more strictly at a high speed of travel.
Similarly, the second and/or third threshold value can be varied, and the growth with time or speed of a reduction in at desired/actual value deviation can thus be monitored in a corresponding parameter-dependent manner.
REFERENCES:
patent: 5275250 (1994-01-01), Müller et al.
patent: 5862878 (1999-01-01), Bohner et al.
patent: 5893427 (1999-04-01), Bohner et al.
patent: 6047788 (2000-04-01), Bohner et al.
patent: 198 01 393 C1 (1999-07-01), None
patent: 0 818 382 A2 (1998-01-01), None
patent: 0 983 926 (2000-03-01), None
patent: WO 90/12723 (1990-11-01), None
patent: 2 308 107 (1997-06-01), None
patent: 2 309 675 (1997-08-01), None
patent: 2 339 178 (2000-01-01), None
Bohner Hubert
Moser Martin
Schneckenburger Reinhold
Daimler-Chrysler AG
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Fischer Andrew J.
Olszewski Robert P.
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