Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1998-07-31
2001-05-01
Swann, J. J. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S443000, C701S043000
Reexamination Certificate
active
06223852
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
There are known electric power steering apparatus in which as shown in Japanese Patent Publication No. HEI 7-94227, when an ignition switch is deactivated or switched off during operation of the apparatus, a steering assist force or torque generated by an electric motor is caused to gradually decrease with time.
The conventional electric power steering apparatus is constructed to stop operation of the electric motor to terminate supply of the steering assist force to the steering system when the ignition switch is switched off. Accordingly, if a sensor signal indicative of the off state of the ignition switch is output during movement of the vehicle due to a failure in a sensor provided to detect the on state of the ignition switch, supply of electric power to the electric motor will be stopped to thereby terminate supply of the steering assist force to the steering system even though the vehicle is actually in the running state with the engine operating continuously. 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. Additionally, 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 the electric motor can be driven independently from detection of operating condition of the ignition switch. 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 which can continue operation of an electric motor to apply a steering assist force to the steering system of a vehicle while the vehicle is running even if a detecting device, such as an ignition sensor, for detecting an operating condition of an ignition switch causes an operation failure generally called “off failure” (where a signal indicative of an off state of the ignition switch is continuously output from the detecting device).
According to a first aspect of the present invention, there is provided an electric power steering apparatus for a vehicle, comprising: 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 ignition sensor for detecting an operating condition of an ignition switch of the vehicle; 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 protection circuit for stopping operation of the electric motor when a signal indicative of an off state of the ignition switch (ignition off signal) is supplied from the ignition sensor and the engine running-state signal supplied from the engine running-state sensor falls below a predetermined value.
Even if a signal indicative of an ignition on state of the ignition switch (ignition on signal) is not supplied from the ignition sensor, when the engine running-state signal is above the predetermined value, the vehicle is regarded as being in the running state and operation of the electric motor is continued to apply the steering assist force to the steering system.
According to a second aspect of the present invention, there is provided an electric power steering apparatus which differs from the apparatus of the first aspect in that in place of the engine running-state sensor, a vehicle velocity sensor is provided for detecting a running-state of the vehicle and generating a vehicle velocity signal corresponding to the detected running-state of the vehicle. The protection circuit is arranged to stop operation of the electric motor when the ignition off signal is supplied from the ignition sensor and the vehicle running-state signal supplied from the vehicle velocity sensor falls below a predetermined value.
Even if an ignition on signal is not supplied from the ignition sensor, when the vehicle running-state signal is above the predetermined value, the vehicle is regarded as being in the running state and operation of the electric motor is continued to apply the steering assist force to the steering system.
An electric power steering apparatus provided in accordance with a third aspect of the present invention differs from the apparatuses of the first and second aspects in that it includes both of the engine running-state sensor and the vehicle velocity sensor, and in that the protection circuit is operable to stop operation of the motor when the ignition off signal is supplied from the ignition sensor, the engine running-state signal supplied from the engine running-state sensor falls below a first predetermined value, and the vehicle running-state signal supplied from the vehicle velocity sensor falls below a second predetermined value.
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: 4753310 (1988-06-01), Hashimoto
patent: 4984647 (1991-01-01), Morishita et al.
patent: 5339243 (1994-08-01), Matsuoka et al.
patent: 5659472 (1997-08-01), Nishino et al.
patent: 5758741 (1998-06-01), Tomioka
patent: 5788010 (1998-08-01), Mukai et al.
patent: 5881836 (1999-03-01), Nishimoto et al.
patent: 5913913 (1999-06-01), Okanoue et al.
patent: 5992556 (1999-11-01), Miller
patent: 7-94227 (1995-10-01), None
Kurosawa Takao
Mukai Yoshinobu
Noro Yoshiki
Shimizu Yasuo
Sugitani Nobuo
Bottorff Christopher
Honda Giken Kogyo Kabushiki Kaisha
Merchant & Gould P.C.
Swann J. J.
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