Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1998-07-30
2001-04-10
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C180S407000, C701S043000
Reexamination Certificate
active
06213249
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in an electric power steering apparatus which provides power of an electric motor to the steering system of a vehicle to thereby reduce the manual steering effort or force needed to turn the steering wheel.
2. Description of the Related Art
Automotive electric power steering apparatuses having an engine running-state sensor, such as an engine speed (rpm: revolutions per minute) sensor or an alternator, for detecting running of an automotive engine are known. The term “running” is used herein to refer to a condition or state in which the engine is in active or operation. When the engine runningstate sensor detects running of the engine, a power supply voltage from a battery is supplied to a bridge circuit (motor drive circuit) consisting of a plurality of switching elements such as power field-effect transistors (FETs), to thereby activate the motor drive circuit for driving the electric motor to provide the output power (steering assist) of the electric motor to the steering system of a motor vehicle.
In the conventional electric power steering apparatuses, the electric motor is kept inoperative until after running of the engine is detected. Accordingly, when a failure arises in the engine running-state sensor, the electric motor cannot be started even though the engine is running to drive the vehicle. Since there is no power assist available from the electric motor, a great muscular effort or force should be exerted by the driver to turn the steering wheel. Such steering operation is contrary to the driver's anticipative power-assisted steering operation and hence disconcerts the driver. As a result, the steering operation is performed unnaturally and a good steering feel cannot not be obtained.
One solution for the foregoing problems may include an arrangement in which start of operation of the electric motor is independent from the detection of running of the electric motor. This arrangement, however, has another problem that if the steering wheel is turned repeatedly during stop of the engine with the ignition switch kept in the ON state, the battery will become discharged in a relatively short period of use because the battery power is consumed by the electric motor without being recharged by the alternator which is connected in driven relation to the engine.
SUMMARY OF THE INVENTION
With the foregoing drawbacks in view, it is an object of the present invention to provide an electric power steering apparatus for a vehicle, which when the vehicle is running, can start operation of an electric motor to apply a steering assist force to a steering system of the vehicle even if detection of running of an engine becomes impossible due to a failure in an engine running-state sensor, such as an engine speed sensor or an alternator.
According to the present invention, there is provided an electric power steering apparatus for a vehicle, comprising: a vehicle velocity sensor for detecting a velocity of the vehicle and generating a vehicle velocity signal corresponding to the detected vehicle velocity; an electric motor for applying a steering assist force to a steering system of the vehicle; a control unit for generating a motor control signal on the basis of at least a steering torque applied to the steering system; a motor drive unit for driving the electric motor on the basis of the motor control signal; an engine running-state sensor for detecting a running state of an engine of the vehicle and generating an engine running-state signal corresponding to the detected running state of the engine; and a fail-safe circuit for, on the basis of the engine running-state signal from the engine running-state sensor, enabling the electric motor to be driven by said motor drive unit. The fail-safe circuit, when the vehicle velocity detected by the vehicle velocity sensor is above a predetermined value, also enables the electric motor to be driven by the motor drive unit even if the engine running-state sensor fails to detect the running state of the engine.
With the fail-safe circuit thus arranged, the electric power steering apparatus can apply the steering assist force to the steering system even when detection of the running state of the engine becomes impossible due to a failure in the engine running-state sensor.
The fail-safe circuit preferably includes an engine running-state comparator for comparing the engine running-state signal and a first predetermined value, a vehicle velocity comparator for comparing the vehicle velocity signal and a second predetermined value, an OR logic operator for performing a logic sum of the result of comparison made by the engine running-state comparator and the result of comparison made by the vehicle velocity comparator, and a switching unit for, on the basis a logic signal output from the OR logic operator, enabling the electric motor to be driven by the motor drive unit.
Even if the engine running-state signal is below the first predetermined value, the vehicle is regarded as being in the running state when the vehicle velocity signal is above the second predetermined value with the result that operation of the motor is continued to thereby enable the motor to apply the steering assist force to the steering system.
The switching unit preferably includes a relay circuit having a normally-open contact relay. When at least one of the engine running-state signal and the vehicle velocity signal is above the corresponding predetermined value, the normally-open contact relay is activated or switched on to thereby enable the electric motor to be driven by the motor drive unit.
The above and other objects, features and advantages of the present invention will become apparent to those versed in the art upon making reference to the following description and accompanying sheets of drawings in which certain preferred structural embodiments of the present invention are described by way of illustrative examples.
REFERENCES:
patent: 4702334 (1987-10-01), Takeshima et al.
patent: 4869334 (1989-09-01), Marumoto et al.
patent: 5097420 (1992-03-01), Morishita
patent: 5259473 (1993-11-01), Nishimoto
patent: 5339243 (1994-08-01), Matsuoka et al.
patent: 5809438 (1998-09-01), Noro et al.
Mukai Yoshinobu
Noro Yoshiki
Honda Giken Kogyo Kabushiki Kaisha
Johnson Brian L.
Lerner Avraham H.
Merchant & Gould P.C.
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