Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-08-20
2002-10-01
Beaulieu, Yonel (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S043000, C701S080000, C180S006200, C180S443000, C180S446000
Reexamination Certificate
active
06459971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a control system of an electric power steering apparatus for vehicles in which an electric motor generates a torque for assisting a steering torque generated through manipulation of a steering wheel by a driver and to a method for controlling the system.
2. Background Art
FIG. 9
is a block diagram showing a construction of a conventional electric power steering control system similar to, for example, a system described in the Japanese Patent Publication (unexamined) No. 186994/1995.
In the drawing, reference numeral
1
is a steering torque detector for detecting a steering torque generated in a steering wheel when a driver manipulates the steering wheel. Numeral
2
is a steering torque controller for computing an assisting (auxiliary) torque and outputting an assisting torque signal on the basis of an output of the steering torque detector
1
. Numeral
3
is a motor speed detector for detecting a motor speed. Numeral
4
is a damping compensator for computing a damping compensation signal on the basis of the motor speed detected by the motor speed detector
3
. Numeral
5
is a motor acceleration detector for detecting a motor acceleration using an output of the motor speed detector
3
. Numeral
6
is an inertia compensator for computing an inertia compensation signal on the basis of the motor acceleration detected by the motor acceleration detector
5
.
Numeral
7
is a judgment (determination) unit for judging whether or not the direction of the output of the steering torque detector
1
and that of the output of the motor speed detector
3
are the same. The result of judgment is outputted to each of the steering torque controller
2
, the damping compensator
4
, and the inertia compensator
6
.
Numeral
8
is a first adder for computing a sum (i.e., this sum is a target torque) of the assisting torque signal, the damping compensation signal, and the inertia compensation signal. Numeral
9
is a motor current determiner for computing a target current signal from the target torque computed by the first adder
8
. Numeral
10
is a motor in which a motor current value corresponding to an applied voltage is generated. By this motor
10
, an assisting torque that is approximately in proportion to the motor current value is generated, and a steering mechanism not shown is driven. Numeral
11
is a motor current detector for detecting a current value of the motor
10
. Numeral
12
is a second adder for obtaining a difference between the target current signal outputted by the motor current determiner
9
and the motor current value detected by the motor current detector
11
. Numeral
13
is a motor drive for determining a voltage to be applied to the motor
10
on the basis of the difference between the target current signal computed by the motor current determiner
9
and the motor current value detected by the motor current detector
11
. The motor drive
13
applies the determined voltage to the motor
10
. Numeral
14
is a speed detector for detecting a speed of the vehicle and outputting the detected speed signal to the steering torque controller
2
, the damping compensator
4
, and the inertia compensator
6
, respectively.
Described below is operation of the conventional electric power steering control system of above construction.
When a driver of a vehicle manipulates a steering wheel not shown, the steering torque detector
1
and outputted to the steering torque controller
2
measures a steering torque applied to the steering wheel. The steering torque controller
2
computes the assisting torque signal that is approximately in proportion to the output signal of the steering torque detector
1
. Accordingly, the motor
10
is driven and an assisting torque is generated on the basis of the assisting torque signal, and a steering torque of the driver is assisted to reduce the steering torque that the driver feels.
At this time, the judgment unit
7
judges whether or not the direction of the output of the steering torque detector
1
and the direction of the output of the motor speed detector
3
are the same. If they are judged the same, the damping compensator
4
and the inertia compensator
6
do not work, but only the steering torque controller
2
works. The steering torque controller
2
determines an assisting torque signal according to the output of the steering torque detector
1
and the speed signal from the speed detector
14
. A target torque is determined on the basis of the determined assisting torque signal, and the motor current determiner
9
determines a motor drive current.
In the case that the direction of the output of the steering torque detector
1
and the direction of the output of the motor speed detector
3
are not the same, the steering torque controller
2
does not work, but the damping compensator
4
and the inertia compensator
6
work. In this case, the target torque is determined on the basis of the outputs of the damping compensator
4
and the inertia compensator
6
, and the motor current determiner
9
determines the motor drive current.
The direction of the target torque is arranged to be the same as that of rotation of the motor when the vehicle is driven at a low speed. The direction is arranged to be opposite to that of rotation of the motor when the vehicle is driven at a high speed. Therefore, when the driver is turning (steering) the steering wheel, the steering torque of the driver is assisted so as to reduce the torque necessary for the steering manipulation. When the driver is returning the steering wheel, the motor
10
is controlled so as to assist the steering wheel to return to the starting point if the vehicle is driven at a low speed and prevents the steering wheel from returning at an excessive speed of rotation if the vehicle is driven at a high speed.
The foregoing flow is shown in FIG.
10
. The flow shown in this drawing is hereinafter referred to as main routine. For better understanding,
FIG. 11
shows the relation between the directions of the steering torque caused by increase and decrease in speed of the vehicle and of the motor speed.
In general, the driver turns the steering wheel when the vehicle goes round a curve or an intersection. Then the driver returns the steering wheel utilizing a spontaneous returning force of the steering wheel due to road surface reaction torque of tires when the vehicle goes back to a straight running after going round the curve or the intersection. However, when the vehicle is driven at a low speed or when the vehicle is driven at a high speed but the steering wheel is steered a little, the road surface reaction torque of the tires is weak. Consequently, the road surface reaction torque is smaller than friction torque in the steering mechanism, and in many cases the steering wheel does not return when the vehicle goes back to the straight running. To cope with this problem, in the prior art shown in
FIGS. 9
to
11
, whether or not the output of the steering torque detector
1
and that of the motor speed detector
3
are the same is judged when the vehicle is driven at a low speed. If the outputs are not the same, the motor drive current is established so as to rotate the motor
10
in the same direction as the motor rotation, thereby the returning property of the steering wheel in driving at a low speed is improved. However, in most cases, it is necessary for the driver to add a torque to the steering wheel in order to return the steering wheel, which results in a phenomenon that steering sense or feeling is deteriorated.
In the prior art, when the steering wheel is manipulated within a range where the road surface reaction torque of the tires is small such as going round a curve at a low speed or going round a gentle curve at a high speed, the steering wheel stops and the motor
10
will not rotate unless the driver applies a certain torque in the direction of returning the steering wheel. That is, in this case, it is not possible for the judgment unit
7
to judge whether or n
Inoue Noriyuki
Kifuku Takayuki
Kurishige Masahiko
Nishiyama Ryoji
Tsutsumi Kazumichi
Beaulieu Yonel
Mitsubishi Denki & Kabushiki Kaisha
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