Motor vehicles – Compensating devices
Patent
1988-12-28
1990-04-03
Mitchell, David M.
Motor vehicles
Compensating devices
180141, 180142, 36442405, B62D 504
Patent
active
049132490
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is concerned with an auxiliary power steering mechanism, especially for motor vehicles.
An auxiliary power steering mechanism of a pertinent type is known from EP 0101579 A2. In the embodiment according to FIG. 8 of that document, an electro-magnetic coupling is located between the electric motor and the steering gear. The coupling curves to separate the motor from the stearing gear when the motor is not being provided with current. A mechanism is thus obtained by means of which steering can be activated purely mechanically, if there is a current failure, without having a couple in the electric motor. However, the known device provides no assurance of proper functioning if a malfunction occurs in the torque-measuring device or in the electronic control circuit. Such a malfunction could consist of an apparent torque being sensed in the torque-measuring device and the electric motor being started although the steering wheel has not been turned. As a result, the vehicle would suddenly swerve from straight line travel.
Such a malfunctioning could consist of the steering wheel being turned in one direction while the electronic control device drives the electric motor in the opposite direction. In this case, too, the coupling would close, so that the electric motor would act fully on the steering mechanism.
OBJECT AND SUMMARY OF THE INVENTION
The object of the invention is to create an auxiliary power steering mechanism in which the electric motor cannot exert an undesired torque on the steering mechanism in case of malfunctioning.
By means of the installation of an additional, redundant safety circuit along with the control circuit and the installation of a second torque-measuring device that measures the motor torque, the correlation of the two moments can be checked and a disconnecting element can be actuated in case of a malfunction. Thus, a faulty controlling of the electric motor is prevented.
The safety circuit arrangement can be obtained in an especially easy manner by letting the safety device of the safety circuit have two signal outlets, one of which is always used, through the two switches of the switching device, to activate the coupling or the disconnecting switch when operation of the steering mechanism is troublefree. The two switches are actuatable, by turns, by the second torquemeasuring device. It is advantageous for the switches to be mechanically actuatable.
Having the disconnecting element closed before the engine starts or receives the signal to start is achieved by the different levels of the actuation thresholds of the safety device and the control device.
In order to be able to recognize an incident of malfunctioning in the safety device in time, a monitoring device in the form of an AND gate is located between the two signal outlets. An indicator is activated by it when both signal outlets deliver a torque signal.
To raise the safety redundancy even higher, an electronic monitoring device is located between the control circuit and the safety circuit by means of which the signals of the two circuits are compared with each other and the control circuit and/or the coupling are disconnected when the torque signal values are different.
The invention will be explained in greater detail with the help of several embodiments represented in the following drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a diagrammatic representation of the auxiliary power steering mechanism of the invention in a first embodiment with a coupling.
FIG. 2 shows a second embodiment of the auxiliary power steering mechanism with a disconnecting switch instead of the coupling.
FIG.3 shows a block wiring diagram of the control circuit with the connection of steering gear and electric motor in accordance with a third embodiment.
FIG. 4 shows a block wiring diagram of the safety circuit.
FIG. 1 is the preferred embodiment.
DETAILED DESCRIPTION
The mechanical part of the auxiliary power steering mechanism contains a steering gear 1, for example, a rack-and-pinion st
REFERENCES:
patent: 4476529 (1984-10-01), Nakamura et al.
patent: 4573545 (1986-03-01), Kalns
patent: 4703821 (1987-11-01), Shimizu
Boehler Anne Marie
Mitchell David M.
Zahnradfabrik Friedrichshafen AG.
Zalkind Albert M.
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