Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-02-13
2002-09-03
Arthur, Gertrude (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S022000, C701S084000, C180S410000, C180S443000
Reexamination Certificate
active
06445987
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an electric power steering controller and a control method, and more particularly to an electric power steering controller and a control method for an automotive vehicle to aid a steering force of a driver by generating an assistant torque in a steering system.
2. Background Art
In an example, Japanese laid open Patent No. 7-186994, in
FIG. 13
shows a configuration of an electric power steering controller. In this figure a steering torque detector
1
detects a steering torque of a driver. A steering torque control unit
2
computes an auxiliary torque based on an output of the steering torque detector
1
. A motor speed detector
3
detects a speed of a motor. A damping compensator
4
computes a damping compensating signal based on the speed of the motor detected by the motor speed detector
3
. A motor acceleration detector
5
detects a acceleration of a motor using an output of the motor speed detector
3
. An inertia compensator
6
computes an inertia compensating signal based on the acceleration of the motor detected by the motor acceleration detector
5
. A judging unit
7
judges whether a direction of an output of the steering torque detector
1
and an output of the motor speed detector
3
are identical, and outputs the judgment result to the steering torque control unit
2
, the damping compensator
4
, and the inertia compensator
6
. A first adder
8
adds the auxiliary torque signal, the damping compensating signal, and the inertia compensating signal. A motor current determiner
9
computes an aimed, i.e., target, current signal from an aimed torque, which is equal to an output of the first adder
8
. A motor
10
drives a steering mechanism by generating an auxiliary torque approximately proportional to a motor current, which is generated according to an applied voltage. A motor current detector
11
detects a current of the motor
10
. A second adder
12
computes a difference between the aimed current signal, which is the output of the motor current determiner
9
, and the current of the motor detected by the motor current detector
11
. A motor driver
13
determines and applies a voltage to the motor
10
based on an error signal between the aimed current signal computed by the motor current determiner
9
and the current of the motor detected by the motor current detector
11
. A vehicle speed detector
14
detects a speed of the vehicle, and outputs the speed of the vehicle detected to the steering torque controller
2
, the damping compensator
4
, and the inertia compensator
6
.
When a driver handles a steering wheel, the steering torque is measured by the steering torque detector
1
, and is output to the steering torque controller
2
. The steering torque controller
2
computes an auxiliary torque signal approximately proportional to the output signal of the steering torque detector
1
, and assists the steering torque of the driver by controlling the motor
10
based on the auxiliary torque signal.
At this time, the judging unit
7
judges whether the direction of an output of the steering torque detector
1
and that of the motor speed detector
3
are same or not, and if the directions are same, both the damping compensator
4
and the inertia compensator
6
are stopped and only the torque controller
2
is operated. The steering torque controller
2
determines the auxiliary torque signal according to the output of the steering torque detector
1
and the speed signal from the vehicle of the vehicle speed detector
14
. The aimed torque is determined based on the auxiliary torque signal, and a motor driving current is determined by the motor current determiner
9
.
When the directions mentioned above are different, the steering torque controller
2
is stopped, and both the damping compensator
4
and the inertia compensator
6
are operated. The aimed torque is determined based on the outputs of the damping compensator
4
and the inertia compensator
6
, and the motor driving current is determined by the motor current determiner
9
. In this case, the direction of the aimed torque is made to coincide with a direction of a motor rotation when the vehicle speed is low, and, similarly, the direction of the aimed torque is made to oppose the direction of the motor rotation when the vehicle speed is high. Therefore, when a driver is handling the steering wheel in the direction for the steering angle to increase, the steering torque required by the driver is assisted to mitigate the steering torque required. Moreover, the motor
10
is also controlled in the following fashion. When a driver is turning the steering wheel in the direction for the steering angle to decrease, he is assisted in returning the steering wheel to its original position when the vehicle speed is low, and is also assisted to prevent the steering wheel from returning excessively when the vehicle speed is high.
In general, a driver turns the steering wheel at a curve or a crossing of a road, and then returns the steering wheel, for returning to straight running making use of a voluntary return force from the road surface reaction torque of a tire. However, there are frequently cases, wherein the road surface reaction torque of the tires is small enough to cause the road surface reaction torque to become smaller than a friction torque in the steering mechanism, and the steering wheel does not return to a straight path when the vehicle speed is low or steering operation is minute. Therefore, in this case, a driver himself has to return the steering wheel by adding steering torque, hence there is a problem that the steering feeling is reduced.
Regarding this point in the prior art, the output of the steering torque detector
1
and the output of the motor speed detector
3
are checked for their coincidence, and if the result is different, the return ability of the steering wheel is raised by determining the motor driving current so that the motor
10
is rotated in the same direction as the rotating motor.
As heretofore explained, in the prior art the steering wheel is in a halted condition and the motor
10
does not rotate unless a driver applies a steering torque to the steering wheel into a returning direction when the steering wheel is handled in a range of the small road surface reaction torque of the tier in case the vehicle is curving a crossing at a low speed or running along a loose curve at a high speed. In this case the judging unit
7
is unable to judge whether or not the direction of the output of the steering torque detector
1
and that of the motor speed detector
3
is identical. Accordingly, there is a problem, wherein the motor driving current can not be determined so as to drive the motor
10
into the same direction with the rotating motor, hence the returnable ability of the steering wheel can not be raised. There is also another problem, wherein a running becomes difficult in a bad condition like a slippery snowy road as no control according to the road surface condition is executed.
SUMMARY OF THE INVENTION
In view of the above, it is the object of the present invention to provide an electric power steering controller and a control method for an automotive vehicle capable of promoting a returnable ability of a steering wheel under the various driving conditions, wherein the steering wheel is returnable without a torque being applied by a driver into a returning direction , and instead a returning control of the steering wheel is executed depending on a steering angle at will of the driver even in a running condition such that a vehicle is turning a crossing at a low speed or curving along a road at a high speed.
Furthermore, it is another object of the present invention to provide a control method of the electric power steering controller to attain the above object.
According to this invention ,an electric power steering controller for an automotive vehicle to assist a steering torque of a driver to a steering wheel comprising:
a motor for generating an assistant torque
Inoue Noriyuki
Kifuku Takayuki
Kurishige Masahiko
Nishiyama Ryoji
Wada Shunichi
Arthur Gertrude
Leydig Voit & Mayer LTD
Mitsubushi Denki Kabushiki Kaisha
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