Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2002-04-02
2003-07-29
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S446000, C701S041000, C701S043000
Reexamination Certificate
active
06598698
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electric power steering apparatus, which applies power of an electric motor directly to a steering system so as to ease steering effort of the driver.
BACKGROUND OF THE INVENTION
Electric power steering apparatus assists steering effort of the driver by way of applying an assist torque that is generated by directly utilizing a driving force of an electric motor to a steering system. To this end, the electric power steering apparatus is furnished with a motor control section for setting a target current supplied to the electric motor as well as for applying the target current to the electric motor with feed back control. In the motor control section, the target current is set at least on the basis of vehicle speed detected by the vehicle speed sensor. The target current is set to a higher value in the case of a lower vehicle speed having a greater road reaction force, and is set to a lower value in the case of a higher vehicle speed to secure the stability during driving. For this reason, when the vehicle speed sensor malfunctions, the vehicle speed sensor always detects the vehicle speed of 0 km/h and the motor control section sets the target current to a greater value, so that a large assist torque continues to act on the steering system. Various methods for determining failure of the vehicle speed sensor have been proposed in order to avoid applying a greater assist torque at the time of failure of the vehicle speed sensor.
The methods for determining failure of the vehicle speed sensor are given below. In a first failure determination method, two vehicle speed sensors are employed and each sensor detects the vehicle speed, so that failure of the vehicle speed sensor is detected based on the comparison between the two vehicle speeds detected. In a second failure determination method, the vehicle speed detected by the vehicle speed sensor and the engine rotational speed detected by the engine rotational speed sensor are compared to each other so as to determine failure of the vehicle speed sensor. Japanese Laid-open Patent Publication Hei.3-114974 discloses a method for determining failure of the vehicle speed sensor in a four-wheel steering apparatus. According to a third failure determination method in this four-wheel steering apparatus, the vehicle speed sensor is determined as failure in the case that the vehicle speed detected by the vehicle speed sensor is 0 km/h, that the output of the engine is capable of moving the vehicle (in the preferred embodiment, it is determined by the engine rotational speed to be detected by the engine rotational speed detecting means), and that the shift range detected by the driving range detecting means is in a driving range.
However, the first failure determination method requires two vehicle sensors, which leads to increased cost. In the second failure determination method, if the driver races (viz. idly blows) the engine while the vehicle is parked, the vehicle speed is 0 km/h notwithstanding that the engine rotational speed is equal to or greater than a predetermined rotational speed (rpm) and therefore the vehicle speed sensor is determined as failure. Especially in the case of a hybrid vehicle provided with an engine and an electric motor, because racing frequency becomes higher to charge the onboard battery, a determination error occurs frequently. In the third failure determination method, failure is determined only when the shift range is set in a driving range, and therefore, the vehicle speed sensor cannot be determined as failure when the driver races the engine while the vehicle is parked (with the shift range set in a non-driving range). However, in this third failure determination method, a determination error may arise to determine failure of the vehicle sensor at the time of abrupt starting because the shift range is set in a driving range and the engine rotational speed may be equal to or greater than a predetermined rotational speed notwithstanding that the actual vehicle speed is 0 km/h or substantially 0 km/h (the vehicle speed sensor detects the vehicle speed as 0 km/h). Moreover, in the third failure determination method, if the driving range detecting means malfunctions, it is impossible to determine failure of the vehicle speed sensor because the driving range detecting means is always off and indicates that the shift range is set in a non-driving range.
Accordingly, it is an object of the present invention to provide an electric power steering apparatus which is capable of highly accurately determining failure of the vehicle speed sensor without errors.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided an electric power steering apparatus comprising:
an electric motor applying an assist torque to a steering system;
a vehicle speed detecting section detecting a vehicle speed of the vehicle;
a shifting state detecting section detecting a shifting state of the vehicle;
an engine rotational speed detecting section detecting an engine rotational speed; and
a motor control section for controlling drive of the electric motor based on an output from the vehicle speed detecting section, wherein the motor control section includes a failure determination section for determining failure of the vehicle speed detecting section on the basis of the vehicle speed detected by the vehicle speed detecting section, the shifting state detected by the shifting state detecting section, and the engine rotational speed detected by the engine rotational speed detecting section, and wherein the failure determination section determines that the vehicle speed detecting section malfunctions if the engine rotational speed is equal to or greater than a predetermined rotational speed for a determinative continuous-time and/or a first determinative integrated time while the vehicle speed is zero and the shifting state is a vehicle driving state.
With such a constitution of the electric power steering apparatus, the failure determination section determines that the vehicle speed detecting section malfunctions, if the vehicle speed detecting section detects the vehicle speed of zero on condition that while the shifting state is a vehicle driving state, the engine rotational speed is equal to or greater than the predetermined rotational speed wherein the expected vehicle speed is greater than zero (viz. the actual vehicle speed of the vehicle would no be zero), and if such a condition continues for the determinative continuous-time and/or the first determinative integrated time. By this determination, it is possible to eliminate a determination error such that the vehicle speed detecting section is determined falsely as failure, even in the case of abrupt starting. This is because the determination conditions consider the determinative continuous-time and/or the first determinative integrated time as sufficiently long time for which the vehicle speed detected by the vehicle speed detecting section after abrupt starting would be greater than zero.
In this electric power steering apparatus, since the determination of failure of the vehicle speed detecting section concerns the vehicle speed, the engine rotational speed and the shifting state as determination factors, and further concerns the determinative continuous-time and/or the first determinative integrated time as determination conditions, it is possible to eliminate a determination error even in the case of abrupt starting. Therefore, the electric power steering apparatus ensures highly accurate determination of failure of the vehicle speed detecting section.
According to a second aspect of the present invention, there is provided an electric power steering apparatus comprising:
an electric motor applying an assist torque to a steering system;
a vehicle speed detecting section detecting a vehicle speed of the vehicle;
a shifting state detecting section detecting a shifting state of the vehicle;
an engine rotational speed detecting section detecting an engine rotational speed; and
a motor con
Kurauchi Atsushi
Murata Makoto
Sugano Tomoaki
Tsurumiya Osamu
Honda Giken Kogyo Kabushiki Kaisha
Merchant & Gould P.C.
Morris Lesley D.
Winner Tony
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