Electricity: motive power systems – Constant motor current – load and/or torque control – Control of motor load or device driven
Reexamination Certificate
2001-03-27
2002-09-10
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
Control of motor load or device driven
C318S432000, C318S476000, C318S488000, C180S443000
Reexamination Certificate
active
06448728
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electric motor power steering apparatus, which allows an electric motor power to act upon a steering system to reduce the steering force of a driver. More particularly, it relates to an electric power steering apparatus, which not only provides stability of the steering system at a high vehicle speed range but also operates to require reduced steering assistance at a low vehicle speed range even at the time of failure of a vehicle speed sensor.
BACKGROUND OF THE INVENTION
An electric power steering apparatus reduces (assists) steering force of a driver by the direct action of driving force of an electric motor steering. A vehicle having an electric power steering apparatus mounted thereon has a function of reducing the movement of the steering wheel whereby the driver needs not to operate the steering with strong force.
As one runs a vehicle at a higher speed, because of the reaction force from a road surface the steering wheel can move in a light manner as a rule. Therefore, at a time of running the vehicle at a high speed range, as large an assist steering torque is not required as is needed at the time of a low speed range. For this reason, the electric power steering apparatus controls in such a manner that the higher the vehicle speed based on the vehicle speed sensor, the lower the assist steering torque needed. Likewise, the steering force through a large assist steering torque at a low speed range makes it possible to enjoy steering operation in an easy manner, while decreasing the assist steering torque at a high speed thereby stabilizes the steering system.
FIG. 9
is the block configuration diagram of the electric system of a conventional electric power steering apparatus.
In this figure, a controller
112
is composed of a target current setting unit
121
, a deviation calculator
122
, a PDI controller
123
, and a control signal output unit
124
. The operation of the conventional electric power steering apparatus in
FIG. 9
will now be described.
(1) The target current setting unit
121
inputs a steering torque signal from a steering torque sensor TS, which detects the steering torque of the driver and a vehicle speed signal from a vehicle speed sensor VS. According to a “steering torque signal/vehicle speed signal-target current” map (not shown), which is increased when the steering. torque is increased and/or vehicle speed signal is decreased, the target current setting unit
121
decides the target current and outputs the detected target current to the deviation calculator
122
. The target current setting unit
121
decides the target value of the current running though the electric motor.
(2) The deviation calculator
122
receives as input the target current and an electric motor current from an electric motor current sensor IS to calculate the deviation of them and outputs a deviation signal to the PID control unit
123
.
(3) The PID controller
123
performs the procedure of P [proportion], I[integration], and D[differentiation] of the deviation signal and generates a PID signal, which is outputted to the control signal output unit
124
.
(4) The control signal output unit
124
inputs the PID signal to generate an electric motor control signal composed of a direction signal and a PWM signal and outputs it to an electric motor driver
113
.
(5) The electric motor driver
113
is composed of a gate driving circuit (not shown) and a bridge circuit having electric field effect transistors (not shown), and outputs an electric motor driving signal for driving an electric motor
108
.
(6) The electric motor
108
is driven based on the electric motor driving signal, i.e., the steering torque signal and the vehicle speed signal; and the electric motor
108
applies an assist steering torque to a steering system (not shown).
By such a configuration, the steering operation is assisted by a large assist steering torque at a low vehicle speed range, making it possible to perform steering operation in a light manner. Conversely, at a high vehicle speed range, the assist steering torque becomes small to stabilize the steering system.
When the vehicle speed sensor fails, the assist steering torque cannot be controlled based on the vehicle speed. In this case, the electric power steering apparatus stops the control based on the vehicle speed and controls the assist steering torque at a constant level by setting a given dummy speed as a fail-safe action. For example, Japanese Patent Laid open publication No.60-80976 discloses a power steering apparatus which controls the steering force responding to the vehicle speed at the time of normal mode, and at the time of failure of the vehicle speed sensor, which generates control output so as to set the steering force (assist steering torque) at the middle value in a control range by a vehicle speed response. This is the same as the vehicle speed of the middle value being set as the dummy vehicle speed.
On the other hand, a vehicle having a “hydraulic power steering apparatus” provided thereon, which varies an assist steering torque according to the revolution number of the engine until a vehicle speed signal is obtained and which varies the assist steering torque to respond to the vehicle speed at the time of obtaining the vehicle speed signal, has been known. According to our Japanese Patent Laid open publication No.9-86421, as a fail-safe measure dealing with the situation where no vehicle speed signal can be obtained in “electric power steering apparatus” due to any cause, a technique has been taught which varies the assist steering torque according to the revolution number of the engine until a vehicle speed signal is obtained, and switches the control of the assist steering torque to respond to the vehicle speed at the time of obtaining the vehicle speed signal. For example, the situation where the vehicle speed signal V in
FIG. 9
is switched to the signal of the revolution number of the engine.
However, if a small value is taken as the dummy vehicle speed, although a light steering operation can be performed at a low vehicle speed range with a large assist steering torque, the movement of the steering wheel becomes too light, thereby lacking the stability of the steering system at a high vehicle speed range. In contrast, if a large value is taken as the dummy vehicle speed, the steering system is stabilized at a high vehicle speed range due to the small assist steering torque, but a strong force for steering operation must be applied at a low vehicle speed range. The steering force (assist steering torque) fixed at the middle value in the control range (dummy vehicle speed being set at a middle value) in order to respond to the vehicle speed as mentioned in Japanese Laid open publication No. 60-80976 leads to a lackadaisical result in terms of the facts that the assist steering torque becomes insufficient and steering operation becomes heavy at a low vehicle speed range, while the assist steering torque becomes in excess and stability of the steering system becomes insufficient at a high vehicle speed.
Furthermore, in the situation where the assist steering torque is varied according to the revolution number of the engine when no vehicle speed signal is obtained, the relation between the revolution number and the vehicle speed depends upon the gear ratio of a transmission (gear position). The change in the revolution number of the, engine totally has a relation with the vehicle speed, but sometimes occurs in a sharp manner in comparison with the change in the vehicle speed. Specifically, although the change in the revolution number of the engine is associated with the vehicle speed as a whole, the revolution number of the engine is sometimes changed irrelevant to the change in the vehicle speed. Consequently, such a configuration is not preferable because the change in the revolution number of the engine sensitively irrelevant to the vehicle speed has an affect upon the magnitude of the assist steering torque, changing steering
Mukai Yoshinobu
Noro Yoshiki
Honda Giken Kabushiki Kaisha
Merchant & Gould P.C.
Ro Bentsu
LandOfFree
Electric power steering apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric power steering apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric power steering apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2883909