Electricity: motive power systems – Automatic and/or with time-delay means – Movement – position – or limit-of-travel
Reexamination Certificate
2001-05-23
2003-06-24
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
Movement, position, or limit-of-travel
C318S432000, C318S434000
Reexamination Certificate
active
06583594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an electric power steering apparatus for assisting steering force by power of a motor.
2. Background Art
FIG. 18
is a control block diagram of a conventional electric power steering apparatus disclosed in, for example, Japanese Patent Publication (unexamined) No. 17424/1995.
In
FIG. 18
, reference numeral
1
is a torque sensor for outputting. a steering torque of a driver as a steering torque signal Vt, and numeral
2
is a speed sensor for outputting a speed of a vehicle as a speed signal Vs. Numeral
3
is a CPU for outputting a motor drive signal Sm corresponding to an inputted signal such as the steering torque signal Vt and detecting failure in the electric power steering apparatus, and numeral
4
is drive inhibiting means for judging a direction of inhibiting drive of the motor corresponding to the steering torque signal Vt and outputting a rightward drive inhibition signal InhR and a leftward drive inhibition signal InhL. Numeral
5
is motor driving means outputting a motor current Im corresponding to the value of the motor drive signal Sm, the right drive inhibition signal InhR, and the left drive inhibition signal InhL, and numeral
6
is a motor for generating a steering assist force corresponding to the motor current Im.
FIG. 19
is a diagram showing the mentioned conventional electric power steering apparatus in the form of whole constitution.
In
FIG. 19
, numerals
1
,
2
, and
6
are the same as those in FIG.
18
. Numeral
7
is a steering wheel, numeral
8
is a steering shaft, numeral
9
is a reduction gear for transmitting the outputted torque of the motor
6
to the steering shaft
8
, numeral
10
is a controller for driving the motor
6
on the basis of signals inputted from the torque sensor
1
and the speed sensor
2
, and numeral
11
is a battery for serving as a power source of the controller
10
.
FIG. 20
is a diagram showing a characteristic of the drive inhibiting means in the conventional electric power steering apparatus.
In
FIG. 20
, in a case that the steering torque signal Vt is larger than a threshold value Tth1, i.e., in the case that steering to the right is conducted, the rightward drive inhibition signal InhR is authorized, while the leftward drive inhibition signal InhL is inhibited. In the case that the steering torque signal Vt is smaller than a threshold value −Tth1, i.e., in the case that steering to the left is conducted, the rightwad drive inhibition signal InhR is inhibited and the leftward drive inhibition signal InhL is authorized. It is established that the drive inhibition signals InhR and InhL are both inhibited in the case that the steering torque signal Vt is not more than the threshold value Tth1 and not less than the threshold value −Tth1, i.e., in the case that steering is not operated or steering is operated with a very small steering force.
FIG. 21
is a table showing the conditions of outputting a motor current in the conventional electric power steering apparatus.
FIG. 22
is a flow diagram showing a process of judging whether or not there is any failure in the drive inhibiting means of the conventional electric power steering apparatus.
FIG. 23
is a graph showing operation of the controller when it is judged that there is any failure in the drive inhibiting means of the conventional electric power steering apparatus.
Described below is operation of the foregoing conventional electric power steering apparatus.
The torque sensor
1
determines the steering torque of the driver and outputs the steering torque signal Vt. The speed sensor
2
determines the speed of the vehicle and outputs the speed signal Vs. The CPU
3
outputs the motor drive signal Sm of a predetermined characteristic corresponding to the steering torque signal Vt and the speed signal Vs. The drive inhibiting means
4
outputs the drive inhibition signals InhR and InhL of predetermined characteristics corresponding to the steering torque signal Vt. The motor driving means
5
outputs the motor current Im driving the motor
6
corresponding to the motor drive signal Sm and the drive inhibition signals InhR and InhL.
As shown in
FIG. 21
, the motor driving means
5
outputs the motor current Im corresponding to the motor drive signal Sm in the case that the driving direction of the motor drive signal Sm is not inhibited by the drive inhibition signal InhR or InhL. On the dother hand, in the case that the driving direction is inhibited by the drive inhibition signal InhR or InhL, the motor current Im is set to 0. The motor
6
outputs the steering assist force corresponding to the motor current Im, thereby reducing the steering force of the driver.
In the case that the CPU
3
fails and is in a failure mode wherein the motor drive signal Sm is outputted regardless of the steering torque signal Vt, the output of the motor
6
in the direction opposite to the steering torque signal Vt is inhibited when the driver is steering the vehicle. Therefore it is possible to prevent increase in steering force of the driver caused by the motor
6
. Moreover, when the driver is not steering the vehicle, the output of the motor
6
in both directions is inhibited, and therefore it is possible to prevent undesirable self-turning of the steering.
As shown in
FIG. 22
, whether or not there is any failure in the drive inhibiting means
4
is judged by comparing the state of the steering torque signal Vt with that of the drive inhibition signals InhR and InhL.
In
FIG. 22
, in step S
1
, the absolute value of the steering torque signal Vt and the threshold value Tth1 are compared with each other, and when it is judged that the absolute value of the steering torque signal Vt is not larger than the threshold value Tth1, the drive inhibition signals InhR and InhL are monitored in step S
2
and step S
3
. If at least one of the drive inhibition signals InhR and InhL is authorized, the process proceeds to step S
7
, where it is judged that there is any failure in the drive inhibiting means
4
.
In the case that it is judged in the step S
1
that the absolute value of the steering torque signal Vt is larger than the threshold value Tth1, the process proceeds to step S
4
to judge the direction of the steering torque signal Vt. If the direction is judged rightward, the process proceeds to step S
5
to monitor the leftward drive inhibition signal InhL. If the signal is authorized, the process proceeds to step S
7
to judge that there is any failure in the drive inhibiting means
4
. In the case that the direction of the steering torque signal Vt is judged leftward, the process proceeds to step S
6
to monitor the rightward drive inhibition signal InhR. If the signal is authorized, the process proceeds to the step S
7
to judge that there is any failure in the drive inhibiting means
4
.
As a result of the foregoing processing, if it is judged that there is any failure, occurrence of the failure is definitely concluded, and the motor current Im is set to 0 in order to interrupt the drive of the motor
6
as shown in FIG.
23
.
As described above, the electric power steering apparatus for reducing the steering torque of the driver is achieved in the conventional apparatus by driving the motor
6
corresponding to the steering force of the driver and generating the steering assist force.
In the case that the CPU
3
fails and outputs the motor drive signal Sm regardless of the steering torque signal Vt, the drive inhibiting means
4
restricts the output of the motor
6
, whereby it is possible to prevent undesirable self-turning of the steering.
In the case that the CPU
3
judges that the drive inhibiting means
4
fails and can not restrict the output of the motor
6
, the drive of the motor
6
is interrupted, whereby safety is assured against a failure mode in which the CPU
3
fails after the failure of the drive inhibiting means
4
.
FIG. 24
is a control block diagram showing a further conventional electric power steering apparatus disclosed in, for example, Japanese Pat
Nishimura Hiroshi
Ohtagaki Shigeki
Dang Khanh
Mitsubishi Denki & Kabushiki Kaisha
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