Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-02-01
2002-12-03
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S443000, C318S432000
Reexamination Certificate
active
06490514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an improvement in an electric power steering control system in which an electric motor generates torque for assisting steering torque generated by driver's steering wheel manipulation.
2. Background Art
A power steering control system is used as a system in which driving force of another power source (such as a hydraulic pump or an electric motor) assists driver's steering wheel manipulation to reduce driver's force necessary for manipulation of the steering wheel and facilitate manipulation of the steering wheel. In the following description, a system in which an electric motor is used as the foregoing another power source is referred to as an electric power steering control system in order to distinguish the system from other systems.
An example of an electric power steering control system,
FIG. 10
shows a construction of a system described in Japanese Patent Application No. 016026/2000 previously filed by the applicant. In the drawing, reference numeral
10
is an electric motor (hereinafter simply referred to as motor) for driving the steering system (not shown). Numeral
1
is a steering torque detector (which is referred to as steering torque detecting means) for detecting a steering torque generated by driver's steering wheel manipulation (not shown) and outputs a steering torque signal. Numeral
2
is a steering torque controller (which is referred to as steering assist controlling means) for computing a steering assist torque signal on the basis of the steering torque signal. Numeral
17
is a return torque compensator which outputs a steering wheel return assist torque signal for generating a torque of the motor
10
in the direction of returning the steering wheel to a starting point on the basis of a road surface reaction torque signal which is an output of a road surface reaction torque detector
15
. Numeral
5
is a motor speed detector, numeral
3
is a damping compensator which receives a motor speed signal and compensates its damping, numeral
4
is an inertia compensator, numeral
6
is a motor acceleration detector, numeral
7
is a motor current determiner, numeral
9
is a motor drive, numeral
11
is a motor current detector, numeral
12
is a first adder, numeral
13
is a second adder, and numeral
14
is a speed detector.
Numeral
15
S is a road surface reaction torque detector provided with a low-pass filter. The road surface reaction torque detector
15
S computes a road surface reaction torque signal on a S/W of a microcomputer on the basis of a steering torque signal which is an output of the steering torque detector
1
, a motor acceleration signal which is an output of the motor acceleration detector
6
, and a motor current value outputted by the motor current detector
11
. Then, the road surface reaction torque detector
15
S outputs the road surface reaction torque signal.
FIG. 12
shows a diagram for explaining the processing operation of the road surface reaction torque detector
15
S in the computation, and the computation is described later in detail.
Operation of the electric power steering control system of
FIG. 12
is described below with reference to a flowchart of FIG.
11
.
First, in Step S
301
, a steering torque signal detected by the steering torque detector
1
is read and stored in a memory. Next, in Step S
302
, a motor speed signal detected by the motor speed detector
5
is read and stored in the memory. In Step S
303
, the motor acceleration detector
6
differentiates the motor speed signal, and a motor acceleration signal is obtained and stored in the memory. In Step S
304
, a motor current signal is read and stored in the memory.
Then, in Steps S
305
to S
306
, the following computation is conducted in the road surface reaction torque detector
15
S, and a road surface reaction torque signal is obtained.
First, in Step S
305
, a stationary reaction force signal T′rea-est is obtained from the fogoing Equation (1) using a steering torque signal Tsens, a motor acceleration signal d&ohgr; equivalent to a rotational acceleration of the steering shaft, and a motor current signal Imtr.
T′rea
-
est=Tsens+Kt·Imtr−J·d&ohgr;
(1)
where:
Kt: torque constant of the motor (computed in terms of steering shaft)
J: moment of inertia of the steering mechanism
Next, in Step
306
, the low-pass filter arranged in the road surface reaction torque detector
15
S conducts a primary filter computation as shown in the following Equation (2) to obtain a road surface reaction torque signal Trea-est, and this road surface reaction torque signal Trea-est is stored in the memory.
dTrea
-
est/dt=−Trea
-
est/T
1+
T′rea
-
est/T
1 (2)
where: T1 is a time constant of a primary filter in Equation (2), and is established so that a cutoff frequency fc=1/(2&pgr;·T1) may be in the range of 0.05 Hz to 1.0 Hz.
Next, in Steps S
307
to S
308
, in the steering torque controller
2
, the steering torque signal is passed through a phase compensator and phase-compensated, mapping operation is conducted with respect to the phase-compensated steering torque signal, and a steering assist torque signal is obtained and stored in the memory.
In Step S
309
, in the return torque compensator
17
, mapping operation is conducted for the foregoing road surface reaction torque signal Trea-est, and a steering wheel return assist torque signal is obtained and stored in the memory.
In Step S
310
, in the damping compensator
3
, a damping compensation signal is obtained by multiplying the motor speed signal and the proportional gain and the product is stored in the memory.
In Step S
311
, in the inertia compensator
4
, an inertia compensation signal is obtained by multiplying the motor acceleration signal and the proportional gain and is stored in the memory.
Next, advancing to Step S
312
, the first adder
12
adds the steering assist torque signal, steering wheel return assist torque signal, damping compensation signal, and inertia compensation signal obtained in the foregoing Steps S
308
to S
311
, thus a target torque is obtained and stored in the memory.
In Step S
313
, in the motor current determiner
7
, a target current is obtained by multiplying the target torque obtained in the foregoing step S
312
by a gain, and the target current is stored in the memory. The gain obtained at this time is an inverse (reciprocal) of the torque constant of the motor
10
computed in terms of steering shaft.
The foregoing Steps S
301
to S
313
are repeated.
Described below is the reason why it is possible to detect the road surface reaction torque from the foregoing Equation (1) and Equation (2).
The equation of motion of the steering mechanism is expressed by the following Equation (3).
J·d&ohgr;s/dt=Thdl+Tmtr−Tfric−Treact
(3)
where:
d&ohgr;s/dt: rotational acceleration of the steering shaft
Thdl: steering torque
Tmtr: motor output torque (computed in terms of steering shaft)
Tfric: friction torque in the steering mechanism
Treact: road surface reaction torque (computed in terms of steering shaft)
When solving the foregoing Equation (3) for the road surface reaction torque Treact, the following Equation (4) is obtained.
Treact=Thdl+Tmtr−J·d&ohgr;s/dt−Tfric
(4)
Accordingly, the road surface reaction torque Treact is obtained by using the respective values of the steering torque, motor output torque, rotational acceleration of the steering shaft, and friction torque in the steering mechanism. In this respect, it is possible to use the steering torque signal Tsens as the steering torque Thdl, and it is possible to use a value obtained by multiplying the motor current signal Imtr by the torque constant Kt as the motor output torque Tmtr. It is also possible to use the motor acceleration signal d&ohgr; as the rotational acceleration of the steering shaft (d &ohgr;s/dt). After all, it becomes possible to detect the road surface reac
Inoue Noriyuki
Kifuku Takayuki
Kurishige Masahiko
Satake Toshihide
Wada Shunichi
Cuchlinski Jr. William A.
Hernandez Olga
Leydig , Voit & Mayer, Ltd.
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