Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2001-03-29
2003-03-04
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C701S043000
Reexamination Certificate
active
06527079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a control unit for an electrical-motor-driven power steering apparatus used for an automotive vehicle and so on.
2. Description of the Related Art
FIG. 16
is a block diagram schematically showing a conventional control unit according to an electrical-motor-driven power steering apparatus used for an automotive vehicle and so on.
With a steering shaft
42
connected to a steering wheel
41
, there is provided a torsion bar
43
to which a torque sensor
44
is secured. In a force acts on the torsion bar
43
upon rotation of the steering shaft
42
, the torsion bar
43
is twisted in correspondence with the added force, and its torsion of the torsion bar
43
is detected by the torque sensor
44
.
To the steering shaft
42
, there is fixedly attached a reducer
45
with which a gear
47
joined with a rotational axis of a motor is engaged. Further, a pinion shaft
48
is secured to the reducer
45
. At a top portion of the pinion shaft
48
, there is fixed a pinion
49
with which a rack
51
is engaged.
At both ends of the rack
51
, there is secured each of tie-rods
52
. Each of knuckles
53
is rotatably connected to each both ends of the tie-rods
52
. A front wheel
54
is fixed to the knuckle
53
. Further, the knuckle
53
is rotatably connected to a cross-member
55
.
Accordingly, when the motor
46
is rotated, the number of its rotation is reduced by the reducer
45
and the reduced rotation is transferred to the pinion shaft
48
. Thereafter, the rotation is transferred to the rack
51
through a rack-and-pinion mechanism
50
. The knuckle
53
connected to the tie-rod
52
fixed to the rack
51
moves rightward or leftward in correspondence with a rotational direction of the motor
46
. Besides, a vehicle speed sensor
56
is provided on the front wheel
54
.
The rotational number and direction of the motor
46
is determined by positive or negative assist current supplied from a motor drive unit
57
. The assist current that the motor drive unit
57
supplies to the motor
46
is calculated by an assist current determination means
58
for controlling the motor drive unit
57
. The assist current determination means
58
calculates a steering torque Th of the steering wheel
41
based upon a detection signal VT from the torque sensor
44
, and a vehicle speed V based upon a detection signal from the vehicle speed sensor
56
.
The assist current determination means
58
calculates the assist current based upon the calculated steering torque Th and vehicle speed V. This calculation is led from an assist map previously stored in a memory of the assist current determination means
58
.
In the conventional control unit for the electrical-motor-driven power steering apparatus as constructed above, in a case that the vehicle travels on a snowed road or on a crust (eisbahn), its road-surface reaction force is small, so that the assist torque by the motor
46
becomes to excess. This phenomenon is caused by that the aforementioned assist map is set based upon a dry road. Namely, the dry road is a high-&mgr; road having a high coefficient of friction in which the road-surface reaction force is large, so that the assist force is set corresponding to the reaction force of the high-&mgr; road by the assist map.
In the conventional control unit of the electrical-motor-driven power steering apparatus, supplemental controls such a handle-return control and a damper control exclusive of the aforementioned assist control are executed. In these control operations, the control command value is however calculated by the standard value obtained with dry road. Due to this control operation, in a case that the vehicle travels on a snowed road or on a crust (eisbahn), the road-surface reaction is small in the supplemental control, so that there is a problem such that a stability of the steering feeling is lacked.
SUMMARY OF THE INVENTION
In a control unit for an electrical-motor-driven power steering apparatus, there are provided an assist current command value calculated based upon a steering torque of a steering wheel, an assist current control value calculated based upon a motor current value of a motor and the assist current command value. A motor outputs an assist force based upon the assist current control value. Further, the control unit provides an estimation means for estimating a road surface &mgr; based upon at least one of the motor current value and the steering torque.
To the aforementioned control unit, there are further inputted a vehicle speed obtained based upon rotation of a wheel, and a steering angle obtained based upon rotation of the steering wheel. Therefore, the estimation means estimates the road surface &mgr; by comparing with a previously memorized standard value corresponding to the vehicle speed and the steering angle.
Further, the estimation means is executed when the vehicle speed and the steering angle exist within a predetermined vehicle speed range and within a predetermined steering angle range, respectively. A motor control means is also provided to control the motor based upon the estimated road surface &mgr;. The road surface &mgr; is estimated with the estimation means by executing a leveling processing taking account into the previously estimated road surface &mgr;.
In the control unit, there is further provided an abnormal detection means for judging whether the estimated road surface &mgr; is abnormal or not.
For the abnormal detection, the control unit includes a memory storing a formal road surface &mgr; before the abnormal detection means detects the abnormal value, so that the estimation means can alternate a present road surface &mgr; to the road surface &mgr; when the abnormal detection means judges that the present road surface &mgr; is the abnormal value.
Further, the estimation means respectively estimates the road surface &mgr; corresponding to a right-steering operation and a left-steering operation.
REFERENCES:
patent: 5904223 (1999-05-01), Shimizu et al.
patent: 5996724 (1999-12-01), Shimizu et al.
patent: 6059068 (2000-05-01), Kato et al.
patent: 6097286 (2000-08-01), Discenzo
patent: 6148950 (2000-11-01), Mukai et al.
patent: 6161068 (2000-12-01), Kurishige et al.
patent: 6240350 (2001-05-01), Endo
patent: 9-58506 (1997-03-01), None
patent: 10-76968 (1998-03-01), None
patent: 11-48999 (1999-02-01), None
patent: 11-99956 (1999-04-01), None
Kato Hiroaki
Suzuki Hiroshi
Suzuki Hirotsune
Takahashi Toshihiro
Takeuchi Shinji
Morris Lesley D.
Toyoda Koki Kabushiki Kaisha
Winner Tony
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