Motor vehicles – Steering gear – With alternate emergency power means
Reexamination Certificate
1999-09-17
2001-09-04
Swann, J. J. (Department: 3611)
Motor vehicles
Steering gear
With alternate emergency power means
C180S421000, C180S419000, C180S402000
Reexamination Certificate
active
06283243
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of 198 42 624.0-21, filed Sep.17, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for operating a vehicle steering system which can be operated in a normal mode and in an emergency mode. The system can be switched between a steer-by-wire level assigned to the normal mode, and a fall-back level assigned to the emergency mode. In this arrangement, a steering handle, e.g. steering wheel, which can be actuated by the driver is connected via an electric or electronic control system to steered vehicle wheels. On the fall-back level, the steering handle is positively coupled mechanically and/or hydraulically to the steered vehicle wheels.
In a steering system which can be operated in a steer-by-wire mode or level, the steering handle generally actuates a desired steering-angle transmitter, while the steered vehicle wheels actuate an actual steering-angle transmitter. Such a steering system also has a control unit which carries out a comparison between the desired values and the actual values. As a function thereof, a steering-angle actuator, e.g. a servomotor, is actuated and, in turn, actuates the steered vehicle wheels.
On the steer-by-wire level of the steering system, the steering handle operates without being positively coupled to the steered vehicle wheels. Therefore, it is not possible for the driver to notice side forces acting on the steered vehicle wheels. In particular, the driver cannot tell when the steered vehicle wheels have reached a steering stop with a maximum steering lock.
U.S. Pat. No. 5,347,458 discloses a steer-by-wire steering system for a vehicle, which has a manual-torque actuator which actuates a steering handle in order to simulate at the wheel side forces acting on the steered vehicle wheels. The driver is thereby given steering feedback which corresponds essentially to the steering feedback obtained with a steering system that has positive coupling between the steering handle and the steered vehicle wheels. This improves the “feel” that the driver obtains during driving and the steering stability of the vehicle because the driver receives information on the current driving situation via the side forces that can be felt at the steering handle.
In this context, it is problematic when the steered vehicle wheels are displaced as far as the steering stop since extreme forces or moments at the steering handle must be simulated in order to impart the sense of the steering stop. For example, an electric motor used as a manual-force actuator must be very large to provide the moments required to simulate the steering stop.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a way in a vehicle steering system of imparting the impression of steered vehicle wheels displaced as far as the steering stop by simple measures on the steer-by-wire level or mode.
According to the present invention, this object has been solved by a method in which a steering handle, e.g. steering wheel, is connected to steered vehicle wheels via an electric or electronic control system, and a fall-back level assigned to the emergency mode, on which level the steering handle is positively coupled mechanically and/or hydraulically to the steered vehicle wheels, characterized in that the fall-back level is activated in normal mode if the steered vehicle wheels are displaced into the region of a steering stop.
The invention is based on the recognition of exploiting the positive coupling between the steering handle and the steered vehicle wheels on the fall-back level for the purpose of transmitting the steering stop to the steering handle. According to the invention, this purpose is served by activating the fall-back level when the steered vehicle wheels reach the steering stop or reach steering angles in the vicinity of the steering stop, because the side forces acting on the steered vehicle wheels at the steering stop can be felt directly at the steering handle by way of the positive coupling that is then present, i.e. the steering handle cannot be actuated further without a considerably greater expenditure of force. Although large forces or moments can then be felt at the steering handle, the manual-torque actuator is subject to no load whatsoever and can therefore be made considerably smaller and cheaper.
The features according to the invention are implemented without a high outlay on design. It is, for example, sufficient to specify a new switching criterion for the steering-system control system that initiates switching to the fall-back level when the steer-by-wire level malfunctions. This criterion is namely the reaching of the steering stop by the steered vehicle wheels.
According to a currently preferred embodiment, the fall-back level should be activated in such a way that it is added to the active steer-by-wire level. This means that the control and regulation efforts required, for example, when the steered vehicle wheels reach the steering stop for only a relatively short time are particularly small.
In another embodiment of the method according to the present invention, the fall-back level is deactivated again as soon as a steering command input into the steering system via the steering handle no longer actuates the steered vehicle wheels against the steering stop reached but in a direction away from the steering stop. It is likewise possible for the deactivation of the fall-back level to take place when there is no longer any steering actuation of the steering handle. These measures are worthwhile particularly if, for the purpose of forming a transition zone, the fall-back level is activated before the steered vehicle wheels have even reached the steering stop and are only at a steering angle in the vicinity of the steering stop.
The method proposed by the present invention is of particular significance when the steer-by-wire level has a variable steering-angle transmission system, in which the actuation of the steered vehicle wheels brought about by the actuation of the steering handle depends on at least one vehicle operating parameter. For example, a quarter turn of a steering handle can be assigned a relatively small change in the steering angle at the steered vehicle wheels at high vehicle speeds, while the same quarter turn of the steering handle brings about a relatively large change in the steering angle at the steered vehicle wheels at low speeds, e.g. when manoeuvring. It is readily apparent from the foregoing that, with a variable steering-angle transmission ratio, the steered vehicle wheels reach their steering stop after steering actuations of different magnitude of the steering handle, depending on the current transmission ratio. The method proposed by the present invention ensures that the steering stop can be felt directly at the steering handle, whatever the transmission ratio.
To preserve the electric-motor manual-torque actuator when the steering stop is reached, the actuator can expediently be deactivated when the fall-back level is activated.
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Bohner Hubert
Hartl Mathias
Schneckenburger Reinhold
Crowell & Moring , L.L.P.
DaimChrysler AG
Shriver J. Allen
Swann J. J.
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