Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2000-03-31
2002-09-03
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S430000, C318S432000, C318S466000, C318S265000, C318S266000, C318S465000, C180S165000, C701S041000, C701S042000, C701S047000, 36, 36
Reexamination Certificate
active
06445151
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a controller for a motor-driven power steering mechanism which assists steering operation of a steering wheel by means of the drive force of an electric motor.
2. Description of the Related Art
FIGS. 6
to
8
show a typical motor-driven power steering mechanism and a conventional controller for the motor-driven power steering mechanism.
FIG. 6
is an explanatory view schematically showing the overall structure of the motor-driven power steering mechanism;
FIG. 7
is a an explanatory view showing a torque-sensing mechanism provided in the motor-driven power steering mechanism shown in
FIG. 6
; and
FIG. 8
is a block diagram of the conventional controller for the motor-driven power steering mechanism.
First, the overall structure of the motor-driven power steering mechanism will be described with reference to FIG.
6
.
A steering wheel
70
is fixed to a shaft
61
, which is connected to a torque-sensing mechanism
60
. To the torque-sensing mechanism
60
is connected a shaft
75
having a reduction gear
71
a
provided thereon. The reduction gear
71
a
is in meshing engagement with a reduction gear
71
b
fixed to an output shaft of an electric motor
50
. The shaft
75
is also connected to a steering gear
72
. Wheels
73
to be steered are attached to the opposite ends of a rod
74
, which is connected to the steering gear
72
.
Next, the structure of the torque-sensing mechanism
60
will be described with reference to FIG.
7
.
The torque-sensing mechanism
60
comprises the shaft
61
, which is hollow and whose lower portion penetrates an upper portion
62
a
of a housing
62
. The shaft
75
penetrates a lower portion
62
b
of the housing
62
, and the above-described reduction gear
71
a
(see
FIG. 6
) arranged in meshing engagement with the reduction gear
71
b
is attached to the shaft
75
.
A torsion bar
65
is accommodated within the interior of the shaft
61
. The upper end of the torsion bar
65
is coupled with the shaft
61
by use of a pin
66
, and the lower end of the torsion bar
65
is in spline-engagement with an inner portion of the shaft
75
.
That is, the torque-sensing mechanism
60
is configured such that when a steering torque is transmitted to the shaft
61
upon operation of the steering wheel
70
, the torsion bar
65
is twisted, resulting in generation of a relative displacement between the shaft
61
and the shaft
75
.
Two paired sensor rings
67
formed of a magnetic material are disposed within the housing
62
to surround the shaft
61
One of the sensor rings
67
is secured to the shaft
61
, and the other sensor ring
67
is secured to the shaft
75
. A sensor coil
68
is provided within the housing
62
at such a position that the inner circumferential surface of the sensor coil
68
faces the outer circumferential surfaces of the sensor rings
67
When a relative displacement is produced between the shafts
61
and
75
, the amount of overlap between the end surfaces of the sensor rings
67
changes, with the result that the inductance of the sensor coil
68
changes. Thus; a signal representing steering torque (hereinafter referred to as a “torque sensor signal”) is obtained.
The sensor coil
68
is electrically connected to a controller
100
for the motor-driven power steering mechanism (see FIGS.
6
and
8
).
Next, the electrical configuration of the controller
100
will be described with reference to FIG.
8
.
The controller
100
includes an interface circuit (hereinafter referred to as an “I/F circuit”)
69
, which receives the torque sensor signal and converts it to a torque signal representing the steering torque. Two microcomputers; i.e., a microcomputer
80
and a microcomputer
90
, are connected to the I/F circuit
69
. The microcomputer
80
includes a torque calculation section
81
and a motor control section
82
. The torque calculation section
81
receives the torque signal from the I/F circuit
69
and calculates the steering torque. The motor control section
82
outputs to a drive circuit
83
a control signal corresponding to the steering torque calculated by the torque calculation section
81
. The drive circuit
83
supplies drive current to the electric motor
50
in accordance with the control signal output from the motor control section
82
.
The microcomputer
90
includes a torque calculation section
91
, which calculates the steering torque in a manner similar to that employed in the torque calculation section
81
of the microcomputer
80
. The microcomputer
90
further includes a torque monitor section
93
, which compares the steering torque calculated by the torque calculation section
81
of the microcomputer
80
with the steering torque calculated by the torque calculation section
91
, in order to detect a difference there between. When the difference is determined to have exceeded a predetermined level one time, the torque monitor section
93
determines that the controller
100
has come into an anomalous-state. The microcomputer
90
further includes a current monitor section
92
, which detects an anomalous-state of the electric motor
50
by monitoring motor current flowing through the electric motor
50
.
The operation of the controller
100
will now be described.
When a steering torque is applied to the steering wheel
70
(FIG.
6
), the torsion bar
65
FIGS. 7
) twists, resulting in generation of a relative displacement between the shaft
61
and the shaft
75
. As a result, the overlap between the end surfaces of the sensor rings
67
changes, and thus, the inductance of the sensor coil
68
changes. This change in inductance is detected, as a torque sensor signal, by the I/F circuit
69
of the controller
100
(
FIG. 8
) and is converted to a torque signal corresponding to the steering torque. Subsequently, the torque signal is sent to the torque calculation section
81
of the microcomputer
80
, in which the steering toque is calculated on the basis of the torque signal.
Subsequently, a torque command value corresponding to the calculated steering torque is output to the motor control section
82
, which in turn outputs to the drive circuit
83
a control signal corresponding to the torque command value. The drive circuit
83
supplies drive current to the electric motor
50
in accordance with the control signal, so that the electric motor
50
rotates.
Rotation of the electric motor
50
is transmitted to the shaft
75
via the reduction gears
71
a
and
71
b
in order to rotate the shaft
75
. Thus, rotational torque of the shaft
75
, i.e., steering toque, is increased in order to assist the steering operation.
When the torque monitor section
93
or the current monitor section
92
detects an anomalous-state, an anomaly signal is sent to the motor control section
82
, in response to which the motor control section
82
stops the issuance of the control signal in order to stop control of the electric motor
50
.
However, the controller
100
is configured to determine occurrence of an anomalous-state through only one-time detection of a state in which the difference obtained through the comparison operation of the torque monitor section
93
exceeds a predetermined level, and to stop the control of the electric motor
50
instantaneously after the detection of the anomalous-state.
Therefore, there is a possibility of the control of the electric motor
50
being stopped even when the steering torque value changes due to external noise which enters the electrical system extending from the torque sensing mechanism
60
to the controller
100
or external noise which enters the controller
100
itself.
That is, the conventional controller has a drawback of insufficient reliability in terms of anomalous-state judgment, or a difficulty in properly judging whether the control of the electric motor
50
is truly stopped due to an anomalous-state of the controller
100
.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a controller for
Nagashima Ichiro
Nakano Jiro
Nappi Robert E.
Smith Tyrone
Toyoda Koki Kabushiki Kaisha
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