Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-06-21
2002-06-11
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S434000
Reexamination Certificate
active
06404156
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering equipment of a vehicle, etc. and, more particularly, an improvement of a steering feeling at the time of fault of a torque sensor input circuit.
FIG. 1
shows a configuration of an electric power steering equipment in the prior art. In
FIG. 1
,
1
denotes a steering wheel;
2
, a steering shaft;
3
, a torque sensor for detecting a steering force of the driver;
4
, a motor for assisting the steering force of the driver;
5
, reduction gears for transmitting an output torque of the motor
4
to the steering shaft
2
;
6
, a speed sensor for detecting a travel speed of a vehicle;
7
, a battery installed in the vehicle; and
8
, a controller for driving the motor
4
based on output signals of the torque sensor
3
and the speed sensor
6
.
FIG. 2
is a view showing details of the controller
8
of the electric power steering equipment. A reference
9
denotes a microcontroller which includes a microprocessor MPU, memory devices (ROM and RAM), an input/output port I/O, an analog/digital converter A/D, and a pulse-width modulation signal output circuit PWM, etc. A reference
10
denotes a motor driver circuit which is composed of a bridge circuit consisting of four power MOSFETs;
11
, a gate driver circuit for driving the motor driver circuit
10
; and
13
, an amplifier and phase compensation circuit for processing an output signal of the torque sensor
3
.
Such electric power steering equipment in the prior art detects a steering force, i.e., an input torque, by the torque sensor
3
when the driver turns the steering wheel
1
, and then processes a torque sensor signal by the amplifier and phase compensation circuit
13
.
The amplifier and phase compensation circuit
13
amplifies and phase-compensates the torque sensor signal. The microcontroller
9
executes an arithmetic operation in compliance with a predetermined control program based on the processed torque sensor signal, and then causes the motor
4
to generate a necessary assisting torque. In this manner, in the electric power steering equipment in the prior art, the amplifier and phase compensation circuit
13
assures the resolution required for the control to thus secure the responsibility in the motor current feedback control.
In the electric power steering equipment above-mentioned in the prior art, the amplifying and phase-compensating process is executed by the amplifier and phase compensation circuit
13
in response to the torque sensor signal detected by the torque sensor
3
, and then the control of the motor
4
is carried out based on the processed torque sensor signal. Therefore, if the amplifier and phase compensation circuit
13
gets out of order, such a situation is brought about that the signal having no correlation with the torque sensor signal detected by the torque sensor
3
, i.e., the driver's steering force is output. Thus, there is a problem that the control cannot be achieved in accordance with the driver's will.
In order to overcome such problem, as shown in
FIG. 3
, another controller
8
of the electric power steering equipment has been proposed in the prior art. That is, signals before and after the amplifier and phase compensation circuit
13
, i.e., signals detected before and after the amplifying and phase-compensating process are input into the microcontroller
9
respectively, and then the fault of the amplifier and phase compensation circuit
13
is decided by monitoring the correlation between them.
In such controller, in order to decide the fault, the event that the correlation between the signals detected before and after the amplifying and phase-compensating process is abnormal over a predetermined time period is monitored. In this case, there are following problems. That is, if such predetermined time period is set long, a long time is needed to decide such fault after the fault has occurred, and thus the motor is controlled in response to the false torque sensor signal during such predetermined time period to generate the assisting torque, so that the behavior of the vehicle becomes unstable. On the contrary, if such predetermined time period is set short, since the signals detected before and after the amplifying and phase-compensating process have different phases by the amplifier and phase compensation circuit
13
respectively, the amplifier and phase compensation circuit
13
is decided as the fault in its transient state although the electric power steering equipment is normal.
SUMMARY OF THE INVENTION
The present invention has been made to overcome such problems, and it is an object of the present invention to provide an electric power steering equipment which is capable of suppressing the control which is made based on a false torque sensor signal at the time of the fault of an amplifier and phase compensation circuit even until such fault can be detected.
An electric power steering equipment according to the present invention comprises a motor for providing a steering assisting force to a steering shaft; a torque detecting means for detecting a steering torque; an amplifying and phase-compensating means for amplifying and phase-compensating a detected value of the torque detecting means; and a controlling means for controlling a drive of the motor based on an output of the amplifying and phase-compensating means; wherein the controlling means restricts a control signal for driving the motor by an upper limit value and a lower limit value which are set in response to the detected value of the torque detecting means.
An electric power steering equipment according to the present invention comprises a motor for providing a steering assisting force to a steering shaft; a first torque detecting means and a second torque detecting means for detecting a steering torque respectively; an amplifying and phase-compensating means for amplifying and phase-compensating a detected value of the first torque detecting means; and a controlling means for controlling a drive of the motor based on an output of the amplifying and phase-compensating means; wherein the controlling means restricts a control signal for driving the motor by using an upper limit value and a lower limit value which are set in response to the detected value of the second torque detecting means.
An electric power steering equipment according to the present invention comprises a motor for providing a steering assisting force to a steering shaft; a first torque detecting means and a second torque detecting means for detecting a steering torque respectively; an amplifying and phase-compensating means for amplifying and phase-compensating a detected value of the first torque detecting means; and a controlling means for controlling a drive of the motor based on an output of the amplifying and phase-compensating means; wherein the controlling means selects a smaller upper limit value and a smaller lower limit value out of a first upper limit value and a first lower limit value, which are set in response to the detected value of the first torque detecting means, and a second upper limit value and a second lower limit value, which are set in response to a detected value of the second torque detecting means, as an upper limit value and a lower limit value, and then restricts a control signal for driving the motor by using the upper limit value and the lower limit value.
Also, the controlling means has an amplification and phase-compensation calculating means for calculating amplification and phase compensation of the detected value of the torque detecting means, and the upper limit value and the lower limit value are set in response to a calculated result of the amplification and phase-compensation calculating means.
Also, the controlling means restricts an output of the amplifying and phase-compensating means by using the upper limit value and the lower limit value.
Also, the controlling means restricts a motor current calculated in response to an output of the amplifying and phase-compensating means by using the upper
Ikemoto Katsuya
Kifuku Takayuki
Okanoue Takahiro
Dang Khanh
Mitsubishi Denki & Kabushiki Kaisha
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