Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Patent
1999-04-22
2000-07-18
Cuchlinski, Jr., William A.
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
701 72, 7447331, 74484R, 180 644, 180 65, 180422, 180429, 180416, B62D 1200, G06F 700
Patent
active
060920122
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power steering apparatus which applies a steering assist force to a steering mechanism by a hydraulic pressure generated by a pump driven by an electric motor.
BACKGROUND ART
Power steering apparatuses are conventionally utilized which assist operation of a steering wheel by supplying a working oil from an oil pump to a power cylinder coupled to a steering mechanism. The oil pump is driven by an electric motor, and a steering assist force is generated by the power cylinder in accordance with the speed of the electric motor. Since the steering assist force is not required when the steering is not turned, a so-called "stop-and-go control" is conducted, wherein the electric motor is off when the steering assumes a straight travel steering state virtually at a steering angle midpoint and, in response to detection of a steering angle change greater than a predetermined level, the electric motor is actuated.
During a several-millisecond period immediately after the actuation of the electric motor, the target speed of the electric motor is set at an assist starting speed that is greater than an assist speed which is a target speed corresponding to a required steering assist force. This suppresses a delay between the actuation of the electric motor and the generation of the required steering assist force.
As a more urgent steering operation is required, for example, for avoiding a forward obstacle, the delay in application of the steering assist force should be reduced. To this end, Japanese Patent Application No. 8-129060 (1996) (U.S. patent application Ser. No. 08/733,644) previously filed by the applicant proposes that the assist starting speed be determined in accordance with the steering speed.
Since it is impossible to accurately detect a steering urgency level and driver's intention on the basis of the steering speed alone, the arrangement according to the previous patent application cannot always properly determine the assist starting speed. When the steering wheel is suddenly turned at a lower steering urgency level immediately after the start of the steering operation, or when the steering wheel is operated relatively slowly at a higher steering urgency level immediately after the start of the steering operation, for example, the detection of the steering urgency level on the basis of the steering speed is liable to be erroneous.
Although the assist starting speed may be determined in accordance with the time-related change rate of a steering torque, the same problem as encountered by the steering-speed based control is unavoidable.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to solve the aforesaid problem and to provide a power steering apparatus which is capable of determining an assist starting speed upon accurate reflection of a steering urgency level thereby to properly effecting steering assist.
The power steering apparatus of the present invention, which is adapted to generate a steering assist force by a hydraulic pressure generated by a pump driven by an electric motor, comprises: steering torque detecting means (corresponding to torque sensor 13 in FIG. 1) for detecting a steering torque; steering urgency level calculating means (corresponding to CPU 31 in FIG. 1 and Step S5 in FIG. 5) for calculating a steering urgency level by using a time-based second-order differential value of the steering torque detected by the steering torque detecting means; target speed determining means (corresponding to CPU 31 in FIG. 1 and Steps S6 and S7 in FIG. 5) including means for determining, on the basis of the steering urgency level calculated by the steering urgency level calculating means, an assist starting speed as an initial target speed at which the electric motor is actuated; and control means (corresponding to CPU 31 in FIG. 1) for controlling driving of the electric motor to equate the speed of the electric motor to the target speed determined by the target speed determining means.
With this arrangement, the time-base
REFERENCES:
patent: 5279380 (1994-01-01), Frank et al.
patent: 5508929 (1996-04-01), Harada
patent: 5904222 (1999-05-01), Liubakka et al.
patent: 5921335 (1999-07-01), Straetker
patent: 5927430 (1999-07-01), Mukai et al.
patent: 5941338 (1999-08-01), Miller et al.
patent: 5948029 (1999-09-01), Straetker
Cuchlinski Jr. William A.
Hernandez Olga
Koyo Seiko Co. Ltd.
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