Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1999-09-17
2001-09-04
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S422000, C180S443000, C701S043000
Reexamination Certificate
active
06285936
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of 198 42 627.5-21,filed Sep. 17, 1998.
The present invention relates to a steering system for vehicles, which can be operated in a normal mode, in which a steering handle and steered vehicle wheels are connected to one another via an electric or electronic control system (steer-by-wire level), and in an emergency mode, in which the steering handle and the steered vehicle wheels are positively coupled mechanically and/or hydraulically (fall-back level).
A two level steering system of this kind generally has a control unit which continuously monitors the functionality of the steer-by-wire components of the steering system and, in particular, checks redundantly available information for plausibility. As soon as the control unit detects a fault, it switches from normal mode to emergency mode to enable higher operational reliability to be ensured for the vehicle.
The so-called “fall-back level” of the steering system, i.e. the mechanical and/or hydraulic positive coupling which is activated in the emergency mode between the steering handle and the steered vehicle wheels, can be formed, for example, by a conventional steering line containing a clutch by way of which the mechanical steering line can be activated for emergency operation.
As an alternative to a mechanical steering line, hydraulic positive coupling via a so-called “hydraulic rod” can also be provided. A hydraulic rod of this kind has a manual-side, first piston-cylinder unit, the piston of which is displaced axially in the associated cylinder by actuations of the steering handle. Hydraulic fluid is displaced out of a chamber formed by the piston in the cylinder and fed to a wheel-side, second piston-cylinder unit. The hydraulic fluid displaced out of the first piston-cylinder unit displaces the associated piston in the second piston-cylinder unit, this piston being coupled mechanically to the steered vehicle wheels, which turn as a result.
DE 196 22 731 A1 discloses a hydrostatic steering device which has two control systems. Each of these control systems has a hydraulic pump, a servo valve and a servomotor. The servo valves are actuated by a common steering wheel. The known steering device furthermore has a change-over valve which, in its operating position, hydraulically connects the motor lines of the second control system and, in an emergency position, hydraulically connects the motor lines of the first control system. Also provided is an actuating device which responds when a fault occurs in the first control system and switches the change-over valve from the operating position into the emergency position. With the known steering device. Therefore, servo-assisted steering is possible even if the first control system fails. A steering device of this kind, which has two complete, separately operating control systems, is relatively expensive.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a configuration for a two-level steering system which increases the operational reliability of the steering system by simple measures.
According to the invention, this object has been achieved by a steering system in which the steering handle and the steered vehicle wheels are positively coupled mechanically and/or hydraulically (fall-back level), having a steering-angle control unit for a steering-angle actuator, e.g. an electric hydraulic servomotor, which actuates the steered vehicle wheels, the said control unit containing a first steering-angle control system which compares the actual steering-angle values from an actual steering-angle transmitter actuated with the steered vehicle wheels and desired steering-angle values from a desired steering-angle transmitter actuated with the steering handle and, as a function thereof, actuates the steering-angle actuator, and having a manual-torque control unit for a manual-torque actuator which actuates the steering handle for the purpose of simulating manual torques, the said control unit containing a first manual-torque control system, which generates desired manual-torque values correlated with the forces acting at the steered vehicle wheels and compares them with actual manual-torque values from an actual. manual-torque transmitter actuated with the steering handle and, as a function thereof, actuates the manual-torque actuator, the-control units monito ring themselves and the steering system for functional reliability and plausibility and switching between the normal mode and the emergency mode of the steering system as a function of this monitoring, the steering-angle control unit comprising a second manual-torque control system, which is connected redundantly with the first manual-torque control system of the manual-torque control unit, and the manual-torque control unit comprising a second steering-angle control system, which is connected redundantly with the first steering-angle control system of the steering-angle control unit.
The invention is based on the recognition of the advantages providing a first control unit (steering-angle control unit) for the steer-by-wire level, the first control device being intended for the actuation of a wheel-angle actuator, and a second control unit (manual-torque control unit) for simulating manual torques at the steering handle. The control units in each case are configured such that each control unit can additionally perform sub- functions or even all functions of the other control unit, there thus being a redundant control unit available for each control unit. The control units preferably operate in a computer-assisted manner and are thus programmable. Thus, additional functions can be integrated into the control units with little effort by altering the programming. The fail-safe nature of the steering system is thereby significantly improved.
According to an advantageous embodiment of the steering system according to the invention, the control units and the sensors assigned to them are connected to one another via a databus. This allows complete information exchange between the control units and the respectively assigned sensors with little outlay.
In a particularly advantageous embodiment of the steering system according to the invention, the steering system can be operated in a maintained-comfort emergency mode. That is, servo assistance is provided for the mechanical and/or hydraulic positive coupling of the fall-back level. This servo assistance reduces the manual torques required to actuate the steering handle and thereby facilitates steering actuation of the steering handle. The servo assistance is preferably implemented by still-functional elements of the steer-by-wire level of the steering system. For example, servo assistance can be provided by the manual-torque actuator which, given appropriate control, reduces the manual torques required for steering actuation by virtue of its coupling to the steering handle.
In a steer-by-wire level operating with, for example, a hydraulic servo motor and a hydraulically positively coupled fall-back level, appropriate coupling of the hydraulic systems can be employed to enable the hydraulic circuit provided for the actuation of the servo motor to be used for servo assistance for the hydraulic positive coupling of-the fall-back level.
The steering characteristics of the vehicle in normal mode differ very markedly from those in emergency mode as regards the required manual torques to be applied by the driver at the steering handle. As a result, a change between the operating states during a journey, particularly while cornering, is dangerous. Due to the maintained-comfort emergency mode according to the invention, the steering system advantageously provides an operating mode for a (partial) failure of the steer-by-wire level that corresponds essentially to conventional servo-assisted steering. The transition between the normal mode and the maintained-comfort emergency mode can be such that it is not noticed by the driver. The driver, can, however, expediently be given a corresponding warning encouraging a
Bohner Hubert
Hartl Mathias
Kurz Gerhard
Moser Martin
Schneckenburger Reinhold
Crowell & Moring , L.L.P.
Cuchlinski Jr. William A.
Daimler-Chrysler AG
Pipala Edward
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