Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2002-08-30
2004-10-05
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S443000
Reexamination Certificate
active
06799656
ABSTRACT:
This application is based on Application No. 2002-58606, filed in Japan on Mar. 5, 2002, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a control apparatus for a motor-driven power steering system of a motor vehicle (hereinafter also referred to simply as the motor-driven power steering control apparatus) which is adapted to generate a motor current required for generation of a steering assist torque on the basis of steering angular information and a steering torque in the power steering. More particularly, the present invention is concerned with a motor-driven power steering control apparatus which is capable of detecting abnormality of a steering angular information detecting means with high accuracy to thereby ensure enhanced reliability for the control of an electric motor employed in the power steering system.
2. Description of Prior Art
For better understanding of the concept underlying the present invention, description will first be made of a hitherto known or conventional motor-driven power steering control apparatus.
FIG. 12
is a block diagram showing schematically, by way of example, a general arrangement of a conventional motor-driven power steering control apparatus which is disclosed in Japanese Patent Application Laid-Open Publication No. 2173/1992 (JP-A-4-2173).
Referring to
FIG. 12
, a controller
10
designed for controlling an electric motor
7
is supplied with an electric power from an vehicle-on-board battery
1
directly or by way of an ignition switch
2
.
A steering mechanism
3
which is interlocked with a handle of a motor vehicle (not shown) includes a steering wheel implemented integrally with the handle for steering the motor vehicle with a steering torque Ts applied to the steering wheel.
The steering mechanism
3
is provided with a torque sensor
4
for outputting a detection signal indicating the steering torque Ts applied upon steering by a driver or operator as well as a steering angle sensor
5
for outputting a detection signal indicative of a steering angle &thgr;s.
On the other hand, the motor vehicle is equipped with a vehicle speed sensor
6
for generating a detection signal indicative of a vehicle speed Vo.
The detection signals derived from the outputs of the various sensors
4
to
6
mentioned above (i.e., the signals indicative of the vehicle speed Vo, the steering angle &thgr;s of the steering mechanism
3
and the steering torque Ts, respectively) are inputted to the controller
10
which responds thereto by supplying to the electric motor
7
a motor current im generated on the basis of the steering angle &thgr;s as well as magnitude and direction of the steering torque Ts to thereby drive the electric motor
7
.
The electric motor
7
is operatively or mechanically coupled to the steering mechanism
3
and generates a steering assist torque Ta applied to the steering wheel in accordance with the motor current im supplied from the controller
10
.
To this end, the controller
10
includes a power supply circuit
11
, an interface
12
, a control unit generally denoted by
13
, a motor drive circuit
18
, a motor current detecting means
19
, a relay driving circuit
20
and a fail relay
21
.
The power supply circuit
11
is connected to the vehicle-onboard battery
1
by way of the ignition switch
2
and designed to supply an electric power to the control unit
13
when the ignition switch
2
is closed (i.e., turned on).
For performing control of the electric motor
7
, the control unit
13
includes a steering assist torque control means
14
, a steering angle detecting means
15
, a steering velocity detecting means
16
and an abnormality decision means
17
.
The motor drive circuit
18
supplies the motor current im to the electric motor
7
under the control of the control unit
13
.
On the other hand, the motor current detecting means
19
is designed to detect the motor current im being supplied to the electric motor
7
.
The relay driving circuit
20
is designed to drive or actuate the fail relay
21
when occurrence of abnormality is detected or decided by the control unit
13
.
The fail relay
21
is supplied with electric power from the battery
1
to thereby stop operation of the motor drive circuit
18
in response to the relay driving circuit
20
.
The steering angle detecting means
15
incorporated in the control unit
13
is designed to detect the steering angle &thgr;s of the steering mechanism
3
on the basis of the detection signal derived from the output of the steering angle sensor
5
. The steering angle &thgr;s is then inputted to the steering assist torque control means
14
, the steering velocity detecting means
16
and the abnormality decision means
17
as the steering angular information.
Further, the steering velocity detecting means
16
is designed to detect a steering angular velocity Vs on the basis of the rate of change of the steering angle &thgr;s as a function of time to thereby input a steering angular velocity Vs as the steering angular information to the steering assist torque control means
14
and the abnormality decision means
17
.
When the steering angle signal &thgr;s or the steering velocity signal Vs indicates an abnormal value (when the steering angle &thgr;s or the steering angular velocity Vs exceeds a maximum permissible value &thgr;max or Vmax), the abnormality decision means
17
supplies to the steering assist torque control means
14
an abnormality decision signal indicating that the steering angle detecting means
15
including the steering angle sensor
5
or the steering velocity detecting means
16
suffers failure or abnormality.
At this juncture, it is to be added that in the system arrangement shown in
FIG. 12
, the steering angle &thgr;s and the steering angular velocity Vs are detected as the steering angular information of the steering mechanism
3
while the motor current im is detected as rotational information of the electric motor
7
.
The abnormality decision means
17
incorporated in the control unit
13
compares the steering angle &thgr;s and the steering angular velocity Vs with the maximum permissible values &thgr;max and Vmax, respectively, which conform with the vehicle speed Vo. When the steering angle &thgr;s exceeds the maximum permissible value &thgr;max or alternatively when the steering angular velocity Vs exceeds the maximum permissible value Vmax, the abnormality decision means
17
decides that the steering angle detecting means
15
or the steering velocity detecting means
16
is in a failure state (i.e., the state suffering abnormality).
Further, the abnormality decision means
17
is so designed as to decide as an abnormal state such situation where the steering angle &thgr;s remains unchanged notwithstanding the change of the steering torque Ts brought about by the steering operation.
As is apparent from the foregoing, in the conventional motor-driven power steering system described above, parameters such as the vehicle speed Vo and the steering torque Ts which do not directly reflect the actual rotational operation of the steering mechanism
3
are adopted in the conditions for making decision as to occurrence of abnormality in the steering angle detecting means
15
and the steering velocity detecting means
16
. Consequently, great difficulty is encountered in setting the conditions for the abnormality decision, giving rise to a problem that abnormality decision can not be made with high accuracy and reliability.
SUMMARY OF THE INVENTION
In the light of the state of the art described above, it is an object of the present invention to provide a motor-driven power steering control apparatus which is capable of making decision as to abnormality with ease and high accuracy upon occurrence of abnormality in the steering angle detecting means or the steering velocity detecting means by resorting to the use of only the parameters which directly reflect the actual rotational operation of the steering mechanism without m
Kimura Kazushi
Miura Kazunori
Ohtagaki Shigeki
DePumpo Daniel G.
Mitsubishi Denki & Kabushiki Kaisha
LandOfFree
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