Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2000-05-31
2002-11-19
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S422000
Reexamination Certificate
active
06484081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering system.
2. Description of the Related Art
A power steering system has been widely used in an automobile or an industrial vehicle as a device for assisting the steering operation of a steering wheel. Especially, for an industrial vehicle such as a forklift, etc., the steering operation of a steering wheel is heavy if the vehicle does not comprise a power steering system. Therefore, such an industrial vehicle is equipped with a power steering system in most cases.
FIG. 1
schematically shows an existing power steering system. In this system, when an operator or a driver steers a steering wheel
101
, a sensor (such as a rotational angular sensor or a torque sensor)
103
, which is attached to a steering shaft
102
, detects this steering operation. A controller
104
controls a motor
106
for driving an oil pump
105
based on the output of the sensor
103
. In this way, an oil pressure (output) corresponding to the steering operation of the steering wheel
101
is generated. Then, the generated oil pressure is transmitted from a PS valve
107
to a PS cylinder
108
. This oil pressure generates a thrust for changing the angle of wheels
110
, so that the angle of the wheels
110
is controlled.
In the system having the above described configuration, when the steering wheel
101
is turned fast, a large output is required to quickly change the angle of the wheels
110
. Therefore, the controller
104
rotates the motor
106
at a high speed. In the meantime, when the steering wheel
101
is turned slowly, a small output is sufficient. Accordingly, the controller
104
rotates the motor
106
at a low speed.
The controller
104
controls a revolution speed of the motor
106
with a PWM (Pulse-Width Modulation) method. That is to say, when rotating the motor
106
at a low speed, the controller
104
provides the motor
106
with a pulse signal having a small duty (duty cycle or duty ratio) as a control signal. In the meantime, when rotating the motor
106
at a high speed, the controller
104
provides the motor
106
with a pulse signal having a large duty. Note that “duty” is a time ratio of an operation period in a cycle to a entire period of the cycle.
FIG. 2A
explains a motor controlling method for use in the existing system shown in FIG.
1
. Here, the revolution speed of the motor
106
is determined by the duty of the control signal generated by the controller
104
.
With this system, the revolution speed of the motor
106
is controlled to be low so as to consume less power while the steering wheel
101
is not being turned. In the example shown in
FIG. 2A
, the controller
104
controls the motor
106
at a duty of 30 percent, during the steering wheel
101
is not being turned. When the steering wheel
101
is being turned, the duty of the control signal provided to the motor
106
changes depends on the rotational speed of the steering wheel
101
. Namely, the duty of the control signal increases as the rotational speed of the steering wheel
101
becomes faster.
As described above, in the power steering system having the above described configuration, the motor
106
is controlled by using the control signal generated by the controller
104
, so that the angle of the wheels
110
is controlled according to the steering operation of the steering wheel
101
.
Furthermore, in the system having the above described configuration, the angle of the wheels
110
is controlled by using an oil pressure. However, the thrust required to change the angle of the wheels
110
may differ depending on the off-center angle of the wheels
110
at that timing, as shown in FIG.
2
B. Namely, when the wheels
110
are in a neutral state, and when the off-center angle of the wheels
110
against the car body is small, the thrust required to change the angle of the wheels
110
is relatively small. In the meantime, when the off-center angle of the wheels
110
against the car body becomes large, the thrust required to change the angle of the wheels
110
increases. This results from a configurations of the PS cylinder
108
and a rod
109
and so on.
As described above, when the steering wheel
101
is not being turned, the revolution speed of the motor
106
is set to be low so as to consume less power. Thus, when the steering wheel
101
starts to be turned, the motor
106
is being driven at a duty of 30 percent at this timing, as shown in FIG.
2
A. Therefore, at this timing, the revolution speed of the motor
106
is low, and the output generated by the oil pump
105
is small.
Accordingly, if the steering wheel
101
starts to be turned when the wheels
110
are in the neutral state or in a state close thereto, the steering operation is smooth. However, if the steering wheel
101
starts to be turned when the off-center angle of the wheels
110
against the car body is large, the steering operation feels heavy.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a power steering system which consumes less power, and implements a smooth steering operation in all cases.
With the power steering system according to the present invention, the thrust (such as an oil pump output) for changing the angle of a wheel is determined based on the rotational speed of a steering wheel and the off-center angle of the wheel.
With this configuration, since the output for generating a thrust is determined based on the rotational speed of a steering wheel and the off-center angle of a wheel, even if the thrust required to change the angle of the wheel differs depending on the off-center angle of the wheel at a timing when the steering wheel is steered, a necessary and sufficient thrust can always be obtained, thereby a smooth steering operation can be implemented in all cases.
A power steering system according to another preferred embodiment of the present invention assumes a hydraulic system. This power steering system comprises a rotational speed detector detecting the rotational speed of a steering wheel; an angle detector detecting the off-center angle of a wheel; an oil pump generating the output for changing the angle of the wheel; and a controller driving the oil pump based on the rotational speed of the steering wheel, which is detected by the rotational speed detector, and the off-center angle of the wheel, which is detected by the angle detector.
Also with the system having this configuration, a smooth steering operation can be implemented in all cases by a function similar to that of the system according to the above described preferred embodiment. Specifically, for example, the controller controls the output of the oil pump so that the thrust generated in the case where the off-center angle of the wheel is large becomes larger than that generated in the case where the off-center angle of the wheel is small, when the steering wheel stops.
REFERENCES:
patent: 5323866 (1994-06-01), Simard et al.
patent: 5469928 (1995-11-01), Adler et al.
patent: 6069460 (2000-05-01), Grabowski et al.
patent: 6173223 (2001-01-01), Liubakka et al.
patent: 0 926 042 (1999-06-01), None
patent: 9-301209 (1997-11-01), None
patent: 253876 (1995-08-01), None
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
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