Motor vehicles – Compensating devices
Patent
1988-09-20
1990-07-10
Marmor, Charles A.
Motor vehicles
Compensating devices
B62D 504
Patent
active
049401025
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a motor-driven power steering system for use, in applying auxiliary steering force to an automobile vehicle steering device through the rotation force of the motor.
DESCRIPTION OF THE PRIOR ART
In conventional systems of this type, a normally open contact of a fail-safe relay is disposed on a (+) power supply line common to both a direct current motor (hereinafter referred to as DC motor) to be driven so as to apply an auxiliary steering force to a steering device, and an electromagnetic clutch for making the rotation force of the DC motor effective and ineffective. In case of abnormality, the fail-safe relay is de-energized so that its normally open contact which has been closed is opened, whereby both the DC motor and the electro-magnetic clutch are simultaneously disconnected from the common power supply thereof. The conventional motor driven power steering system, being of such arrangement as above described, involves a problem that in the case where a short-circuit trouble occurs with power transistors, power MOS.FET, and the like which drive the DC motor by determining the direction of current flow in the motor or otherwise, a lock current for the DC motor must be cut off at the normally open contact. For this reason, the normally open contact of the fail-safe relay is necessarily of a large volume. This naturally means that the fail-safe relay is of a large size, of a large volume, and of high cost. Another difficulty is the possibility of power loss being caused due to a voltage drop resulting from the normally open contact. A further difficulty is that if the normally open contact is of a large capacity, the opening and closing results in fusion of the contact, which poses a problem in respect of safety.
This invention is intended to overcome the foregoing difficulties. The first object thereof is to provide a motor-driven power steering system which can use a fail-safe relay of a small capacity and which provides a high degree of safety.
SUMMARY OF THE INVENTION
A motor-driven power steering system according to the present invention is provided with a fail-safe relay having a normally open contact which is disposed on a line for supplying power to an electromagnetic clutch adapted to make the rotational force of a DC motor effective or ineffective as an auxiliary steering force, whereby a drive coil of the fail-safe relay is controlled to be energized and de-energized through fail-safe drive means on the basis of steering torque and vehicle speed signals. According to this arrangement the fail-safe relay can be of a smaller size and a smaller capacity, since the normally open contact of the fail-safe relay simply operates only to turn on and off the electromagnetic clutch.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing the arrangement of one embodiment of the invention, and
FIG. 2 is a schematic diagram showing the example of the arrangement of the control unit shown in FIG. 1.
MOST PREFERRED EMBODIMENTS FOR ENFORCING INVENTION
One embodiment of the invention will now be described with reference to the accompanying drawings.
In FIG. 1, reference numeral 1 designates a steering wheel 1 which receives the steering rotational force of the driver; 2 is a steering torque sensor which outputs an electric signal corresponding to the rotational force applied to the steering wheel; 3a is a first universal joint; 3b is a second universal joint; 4a is a first steering shaft interconnecting the steering wheel 1 and the steering torque sensor 2; 4b is a second steering shaft interconnecting the steering torque sensor 2 and the first universal joint 3a; and 4c is a third steering shaft interconnecting the first and second universal joints 3a, 3b. Numeral 5 is a first pinion shaft connected to the second universal joint 3b; 6 is a rack shaft having a first rack tooth portion 6a and a second tooth portion 6b, these portions having been machined simulataneously with or separately from each other and being engageable with the fi
REFERENCES:
patent: 3739738 (1973-06-01), Cavil
patent: 4573545 (1986-03-01), Kalns
patent: 4621327 (1986-11-01), Dolph et al.
European Search Report, Jun. 7, 1989, EP 87 90 7827.
Camby Richard
Marmor Charles A.
Mitsubishi Denki & Kabushiki Kaisha
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