JP2925356B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus.

[0002]

2. Description of the Related Art Conventionally, as a power steering device for a vehicle, an electric power steering device using a motor as a power source is known.

A current is supplied to the motor while detecting the steering direction and the steering force of the steering wheel, and the motor is operated in response to the steering of the steering wheel to power-assist turning operation of the wheels.

[0004]

In such an electric power steering apparatus, when a key switch is turned off, for example, when the vehicle is stopped, the supply of current to the motor is interrupted, and the power assist is also stopped. When the wheels (front wheels) are stopped while being held, steering wheel shock may occur due to the restoring force of the tires.

If the direction of the tire is slightly cut to the left or right from the straight traveling position, a restoring force in the straight traveling direction acts,
The tire tries to return to the neutral position. When the torque is applied to the steering wheel but the rotation is not performed, the current to the motor is cut off and the steering wheel is loosened. When the steering wheel is loosened, the rotor of the motor is forcibly rotated (reversed) by the restoring force of the tire. The vehicle suddenly stops after passing through, but a steering wheel shock occurs in response to the impact at this time.

[0006] Of course, in a manual steering without power assist, a force for returning the steering wheel to the neutral position is generated due to the restoring force of the tire. However, unlike the electric power steering device, there is no rotational inertia of the motor. Only, the handle shock is small.

[0007] The motor can also function as a generator, and when the rotor is forcibly rotated by external energy, an induced electromotive force is generated. The driving torque (load) required to rotate this generator is proportional to the generated power. Therefore, if the motor functions as a generator and the rotor is driven by the restoring force of the tire, this driving load acts as a braking force on the rotation of the handle shaft, and the handle shock can be reduced.

However, conventionally, since the motor drive circuit is cut off at the same time as the engine key switch is turned off, no regenerative current flows even if the motor is driven by the restoring force of the tires, so that it may function as a generator. Can not. For this reason, the rotor freely rotates based on the tire restoring force, and this inertial turning force has promoted the steering wheel shock.

Therefore, the present invention provides a regenerative current that flows to the motor when the engine key switch is turned off to function as a generator, and absorbs the restoring force of the tire based on the driving load, thereby improving the steering wheel shock. The aim is to reduce

[0010]

Therefore, according to the present invention, as shown in FIG. 1, a motor 50 for power assisting the steering operation and a detecting means 51 for detecting the operating state of the steering wheel are provided.
And a motor drive circuit 52 comprising a bridge circuit for controlling the control current and the direction of conduction of the motor 50, and a controller 53 for controlling the motor drive circuit 52 in accordance with the handle operation state. An off-timer circuit 54 that operates for a predetermined time after the engine key switch is turned off; and a direction switching circuit that short-circuits the motor drive circuit 52 while the off-timer circuit 54 is operating so that regenerative current can flow to the motor. 55 and the engine key switch turned off
That the steering is being maintained from the output of the steering wheel operation detector
Means 56 for determining whether
The direction switching circuit is switched.

[0011]

Further, there is provided means 57 for judging the stopping state of the vehicle based on the vehicle speed, so that the direction switching circuit 55 is switched only when the vehicle is kept stationary in the stopped state.

[0013]

When the engine key switch is turned off, a circuit is connected so that a regenerative current flows to the motor, and an electromotive force is generated when the rotor is rotated by the restoring force of the tire. As for the driving force for rotating the motor, a portion corresponding to the generated electromotive force is consumed,
This works as a braking force of the rotor.

Therefore, when the vehicle is stopped with the steering wheel being maintained, the steering wheel tends to return toward the neutral point due to the restoring force of the tire. However, the braking force by the motor absorbs the restoring force, and the steering wheel shock is released. To reduce.

The braking operation by applying a regenerative current to the motor
By performing the control only at the time of the steering holding in which the restoring force of the tire is exerted, appropriate control without waste can be performed. Furthermore, even when the engine key switch is turned off except when the vehicle is stopped, the braking operation by the motor is stopped, thereby preventing a feeling of strangeness with respect to the operation of the steering wheel.

[0016]

FIG. 2 shows a first embodiment of the present invention.
3 is a motor control circuit of the electric power steering device.

A controller (CPU) 1 reversibly drives a motor 2 in response to a steering wheel operation.
In addition to the signal from the engine key switch (IG) 3,
Signals from the steering wheel torque detector 4 and the vehicle speed detector 5 are input. The steering wheel torque detector 4 outputs a signal according to the rotation (operation) direction of the steering wheel (for example, the sign differs depending on the rotation direction) and a signal according to the rotation torque.

The controller 1 has a drive circuit 10 for the motor 2.
A pulse width modulation (PWM) circuit 12 for controlling the energization of the relay coil 11A of the power supply relay switch 11 and controlling the magnitude of the motor drive current in accordance with the rotation (operation) torque of the handle; The output from the direction switching circuit 13 which controls the direction of the drive current flowing through the motor 2 in accordance with the control signal is controlled.

The motor drive circuit 10 reversibly controls the drive current for the motor 2, so that a current control switch (current control FET switch) A1 that turns on and off in accordance with a pulse signal from the PWM circuit 12 to adjust the current value. And B
1 and a bridge circuit comprising direction control switches (FET switches) B2 and A2 which are turned on and off in accordance with the output from the direction switching circuit 13.

In addition to the PWM signal for increasing / decreasing the current in accordance with the steering wheel operating torque, the PWM circuit 12 outputs A1 or B1 in accordance with the steering wheel operating direction.
In order to select the switch, the steering direction signals (A and B signals) are input from the controller 1 together with the direction switching circuit 13.

Therefore, when the switches A1 and A2 are turned on, the motor 2 rotates in one direction (A), and when the switches B1 and B2 are turned on, the motor 2 rotates in the opposite direction (B).

The supply voltage of the PWM circuit 12 is boosted by a booster circuit 15 which amplifies a voltage from a power supply (battery) 6 via a key switch 3. Direction switching circuit 1
As the power supply voltage 3, a voltage from the off timer circuit 16 is supplied via the key switch 3. The off timer circuit 16 holds the power supply voltage of the direction switching circuit 13 for a predetermined short time (T seconds) after the key switch 3 is turned off, and is composed of a resistor and a capacitor. A relay signal from the controller 1 is input to the direction switching circuit 13. When the relay signal is off, the two-way signal is turned on, and both the switches B2 and A2 are turned on.

Thus, the direction switching circuit 13 switches the switches B2 and A for a predetermined time after the key switch 3 is turned off.
2 and the bridge circuit is short-circuited so that a regenerative current can flow through the motor 2.

When the vehicle is driven with the engine key switch 3 turned on, a relay signal from the controller 1 activates the relay switch 11 to turn on the power of the drive circuit (bridge circuit) 10 of the motor 2. When the steering wheel torque detector 4 detects the steering wheel operation in this state, a signal is output from the controller 1 to the PWM circuit 12 and the direction switching circuit 13 in accordance with the rotation operation direction and the operation torque, and for example, the steering wheel is operated in the A direction. Switch A1 and A2 are turned on and switch A
1 is increased or decreased according to the operating torque, and the drive current value to the motor 2 and the direction of the current are controlled.
Rotates to perform power assist in the steering operation direction (A direction) of the steering wheel.

When the steering operation direction of the steering wheel is reversed (direction B), the switches B1 and B2 are turned on correspondingly, and the motor 2 rotates in the opposite direction with the driving torque corresponding to the steering wheel operating torque.

The driving torque generated by the motor 2 is proportional to the control current value. However, when the vehicle runs at high speed, the steering resistance is small, and the vehicle speed detector is used to prevent the steering wheel from becoming too light due to power assist. The current value is controlled to be relatively small according to the detected vehicle speed of No. 5.

On the other hand, when the engine key switch 3 is turned off, the controller 1 immediately turns off both the relay signal, the PWM signal, and the direction signal as shown in the flowchart of FIG. 3 (steps 1 to 3). Relay switch 11
Is turned off, the switches A1 and B1 and the switches A2 and B2 are turned off, and the power supply to the motor 2 is cut off.

However, the power supply of the direction switching circuit 13 is energized for a predetermined time after the key switch 3 is turned off by the off timer circuit 16, and at the same time, the direction switching circuit 13 turns on both direction outputs by turning off the relay signal to switch on. B2
And A2 are conducted (step 9), and the bridge circuit of the motor 2 is short-circuited so that a regenerative current can flow for a predetermined time.

For this reason, when a tire restoring force acts, such as when the key switch 3 is turned off while the steering wheel is being held, the steering wheel is returned to the neutral position while rotating the motor 2 in the reverse direction. An induced electromotive force is generated as the rotor of the motor 2 rotates, and the switches B2 and A2
, A regenerative current flows and a braking force acts on the rotation of the rotor. In other words, since the motor 2 functions as a generator, a driving torque corresponding to the regenerative current is required to rotate the rotor, and this acts as a brake against the restoring force of the tire. As a result, the return of the steering wheel is suppressed, and Handle shock due to inertial rotation is greatly reduced.

When a predetermined time (T seconds) elapses and the power of the direction switching circuit 13 is turned off by the off timer circuit 16, the switches B2 and A2
Is turned off and cut off (steps 10 and 11).

The restoring force of the tire works when the engine key switch 3 is turned off during steering, and when the tire is at the neutral position, no restoring force is generated and there is no steering wheel shock. For this reason, it is determined from the output of the steering wheel torque detector 4 whether the steering is being held when the key switch 3 is turned off (step 6), and the braking operation by the motor 2 is executed only during the steering is being held. I tried to make it.

When the key switch 3 is turned off, the torque detector 4
When it is determined that there is no output and the steering is not being maintained, the process proceeds to step 11, where all the direction outputs of the direction switching circuit 13 are turned off, and the controller 1 switches to the sleep mode.

The direction switching circuit 13 is designed so that both the direction outputs are turned on when the key switch 3 is turned off by a signal from the controller 1, and the controller 1 is in the sleep mode while the output from the off timer circuit 16 is present. So that it does not shift to

Therefore, when no tire restoring force is generated and the braking operation by the motor 2 is unnecessary, useless operation can be omitted. Since the output of the off-timer circuit 16 is input to the controller 1, the controller 1 can monitor the abnormality of the off-timer circuit 16.

In this case, the switches B2 and A2 are periodically turned on and off, and the pulse width is changed with time, so that the braking force of the motor 2 can be gradually reduced.

In the embodiment shown in FIG . 4 , when the key switch 3 is turned off while the vehicle is running other than when the vehicle is stopped, the braking operation by the motor 2 is stopped even during steering, and the steering wheel operation is performed. This does not cause a sense of discomfort.

In step 6, when the vehicle is stopped, it is determined from the output of the vehicle speed detector 5, and when the vehicle speed is extremely low below a predetermined value, it is determined that the vehicle is stopped. In this case, the regenerative current is supplied to the motor 2 as described above. The braking operation is started by flowing
2. Turn off A2.

In the normal driving operation, the key switch 3 is not turned off during running. However, if such a situation occurs, the braking by the motor 2 is not applied and the steering wheel operating force becomes extremely heavy. Can be prevented.

[0039]

As described above, according to the present invention, when the engine key switch is turned off, a regenerative current flows to the motor to function as a generator, and the driving load absorbs the restoring force of the tire. Therefore, it is possible to effectively reduce the steering wheel shock at the time of stopping. And Mo
Braking by applying a regenerative current to the tire
By performing only during steering, proper control without waste can be performed.
I can.

[0040]

Furthermore, except when the vehicle is stopped, the braking by the motor is stopped even if the engine key switch is turned off.
It is possible to prevent a sense of incompatibility with the operation of the steering wheel.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention.

FIG. 3 is a flowchart showing the control operation.

FIG. 4 is a flowchart illustrating a control operation according to a second embodiment.
It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Controller 2 Motor 3 Key switch 4 Handle torque detector 5 Vehicle speed detector 10 Drive circuit 12 PWM circuit 13 Direction switching circuit 16 Off timer circuit A1 switch B1 switch A2 switch B2 switch

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-147468 (JP, A) JP-A-2-290779 (JP, A) JP-A-62-247661 (JP, A) JP-A-63-1987 41277 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B62D ^6/ 00-6/02 B62D 5/04

Claims (2)

(57) [Claims] 1. A motor for power assisting a steering wheel operation, a detecting means for detecting an operating state of the steering wheel, a motor driving circuit including a bridge circuit for controlling a control current and an energizing direction of the motor, and a motor driving circuit comprising: An electric power steering apparatus comprising: a controller that controls the motor in accordance with an operation state; an off-timer circuit that operates only for a predetermined time after an engine key switch is turned off; and the motor drive circuit while the off-timer circuit is operating. A direction switching circuit that switches so that a regenerative current can flow to the motor due to a short circuit, and an engine key switch
Steering from the output of the steering wheel operation detector when
Means for determining that
An electric power steering device, wherein the direction switching circuit is switched . 2. A stopped state of a vehicle is determined based on a vehicle speed.
Means for maintaining the vehicle in a stationary state when the vehicle is stationary.
The electric power steering device according to claim 1, wherein the switching circuit is switched .