JPH04349067A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To reduce handle shock by allowing a regenerative current to flow through a motor when an engine key switch is put off, permitting the motor to function as a generator, and absorbing the tire restrative force with the drive load at this time. CONSTITUTION:A power steering device as per invention comprises a motor 2 to assist turning a steering wheel, a sensor 5 to sense the turned condition of the steering wheel, and a motor driving circuit 10 consisting of a bridge circuit to control the control current of motor 2 and the current feeding direction. The device is further equipped with a controller 1 to control the circuit 10 in accordance with the turned condition of the steering wheel, an off-timer 16 which operates for a specified period of time since an engine key switch 3 is put off, and a direction changeover circuit 13 which shortcircuits the motor driving circuit 10 while the off-timer circuit 16 is in operation and makes therewith changing-over so that a regenerative current flows through the motor 2.

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 device.

0002

2. Description of the Related Art Conventionally, electric power steering devices using a motor as a power source are known as power steering devices for vehicles.

[0003] Current is applied to the motor while detecting the steering direction and steering force of the steering wheel, and the motor is operated in response to the steering wheel steering to power-assist the turning operation of the wheels.

0004

[Problem to be Solved by the Invention] In such an electric power steering device, when the key switch is turned off when the vehicle is stopped, the supply of current to the motor is also cut off and the power assist is also stopped. ring(
When the vehicle was stopped with the front wheels (front wheels) held in place, steering shock could occur due to the restoring force of the tires.

[0005] If the orientation of the tire is even slightly to the left or right from the straight-ahead position, a restoring force acts in the straight-ahead direction,
The tires try to return to the neutral position. When the electric current to the motor is cut off and the steering wheel is loosened while the steering wheel is in a holding state where torque is applied to the steering wheel but the steering wheel is not rotated, the restoring force of the tires forces the motor rotor to rotate (reverse), and the play in the steering wheel is reduced. After passing this point, the vehicle suddenly stops, and the shock at this point causes a steering shock.

Of course, even in manual steering without power assist, the restoring force of the tires generates a force that attempts to return the steering wheel to the neutral position, but unlike electric power steering systems, there is no rotor rotational inertia of the motor. However, the steering wheel shock is small.

By the way, 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 is made to function as a generator and the rotor is driven by the restoring force of the tires, this drive load acts as a braking force on the rotation of the handle shaft, reducing steering shock.

However, conventionally, the motor drive circuit is cut off at the same time as the engine key switch is turned off, so even if the motor is driven by the restoring force of the tires, no regenerative current flows and the motor cannot function as a generator. Can not. As a result, the rotor rotates freely based on the restoring force of the tire, and this inertial rotational force aggravates steering wheel shock.

[0009] Therefore, the present invention causes a regenerative current to flow through the motor when the engine key switch is turned off, so that it functions as a generator, and absorbs the restoring force of the tires based on this driving load, thereby reducing the steering wheel shock. The purpose is to reduce the

0010

[Means for solving the problem] Therefore, this invention
As shown in FIG. 2, a motor 50 power assists the steering wheel operation, and a detection means 51 detects the operating state of the steering wheel.
In an electric power steering device, the motor drive circuit 52 includes a bridge circuit that controls the control current and current direction of the motor 50, and the controller 53 that controls the motor drive circuit 52 according to the steering wheel operation state. An off-timer circuit 54 that operates for a predetermined period of time after the engine key switch is turned off, and a direction switch that short-circuits the motor drive circuit 52 to allow regenerative current to flow through the motor while the off-timer circuit 54 is operating. A circuit 55 is provided.

Furthermore, means 56 is provided for determining whether the steering wheel is being held from the output of the steering wheel operation detector when the engine key switch is turned off, and the direction switching circuit 55 is switched only when the steering wheel is being held. do.

Furthermore, means 57 is provided for determining whether the vehicle is in a stopped state based on the vehicle speed, and the direction switching circuit 55 is switched only when the vehicle is in a stopped state and the steering wheel is being held.

[0013]

[Operation] When the engine key switch is turned off, the circuit is connected so that regenerative current flows to the motor, and when the rotor is rotated by the restoring force of the tires, an electromotive force is generated. The driving force to rotate the motor is consumed in an amount equivalent to the generated electromotive force,
This acts as a braking force for the rotor.

Therefore, when the vehicle is stopped while the steering wheel is held, the restoring force of the tires tends to return the steering wheel toward the neutral point, but the braking force of the motor absorbs the restoring force and prevents steering shock. Reduce.

Braking operation with regenerative current flowing through the motor is as follows:
By performing this only when the steering is held, where the restoring force of the tires is activated, efficient and appropriate control can be achieved. Furthermore, by stopping the braking operation by the motor even if the engine key switch is turned off except when the vehicle is stopped, it is possible to prevent the occurrence of discomfort when operating the steering wheel.

[0016]

[Embodiment] FIG. 2 shows a first embodiment of the present invention.
This is a motor control circuit for an electric power steering device.

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

The controller 1 is a drive circuit 10 for the motor 2.
Pulse width modulation (pulse width modulation) that controls the energization of the relay coil 11A of the power relay switch 11 and controls the magnitude of the motor drive current according to the rotation (operation) torque of the handle.
(PWM) circuit 12 and a direction switching circuit 13 that controls the direction of the drive current flowing through the motor 2 according to the rotation direction of the handle.

In order to reversibly control the drive current for the motor 2, the motor drive circuit 10 includes a current control switch (current control FET switch) A1 that adjusts the current value by turning on and off in accordance with the pulse signal from the PWM circuit 12. and B
1, and direction control switches (FET switches) B2 and A2 that are turned on and off according to the output from the direction switching circuit 13.

The PWM circuit 12 has a PWM signal for increasing/decreasing the current in accordance with the steering wheel operating torque, as well as a PWM signal A1 or B1 depending on the direction of the steering wheel rotation operation.
In order to select the switch, steering wheel direction signals (A, 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 voltage supplied to the PWM circuit 12 is boosted by a booster circuit 15 that amplifies the voltage from the power source (battery) 6 via the key switch 3. Direction switching circuit 1
The voltage from the off-timer circuit 16 is supplied as the power supply voltage No. 3 through the key switch 3. The off-timer circuit 16 holds the power supply voltage of the direction switching circuit 13 for a predetermined short period of time (T seconds) after the key switch 3 is turned off, and is composed of a resistor and a capacitor. Further, a relay signal from the controller 1 is input to the direction switching circuit 13, and when the relay signal is off, the bidirectional signal is turned on, turning on both switches B2 and A2.

As a result, the direction switching circuit 13 switches the switches B2 and A for a predetermined period of time after turning off the key switch 3.
2 and short-circuit the bridge circuit to allow regenerative current to flow to the motor 2.

When the engine key switch 3 is turned on to drive the vehicle, the relay switch 11 is actuated by a relay signal from the controller 1, and the power to the drive circuit (bridge circuit) 10 of the motor 2 is turned on. When the steering wheel torque detector 4 detects a 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 according to the rotational operation direction and operating torque, and the steering wheel is operated in the A direction, for example. When it is done,
Switches A1 and A2 are turned on, and the resistance value of switch A1 increases or decreases according to the operating torque, and the drive current value and energization direction for motor 2 are controlled. ) rotates to provide power assist.

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

Note that the drive torque generated by the motor 2 is proportional to the control current value, but when the vehicle is running at high speed, the steering resistance is small, and in order to prevent the steering wheel from becoming too light due to power assist, the vehicle speed detector The current value is controlled to be relatively small according to the detected vehicle speed in step 5.

On the other hand, when the engine key switch 3 is turned off, the controller 1 immediately turns off the relay signal, PWM signal, and direction signal (steps 1 to 3), as shown in the flowchart of FIG. Note that the controller 1 shifts to sleep mode by turning off the key switch 3 (step 4). Relay switch 11 is turned off, and switches A1 and B1 and switches A2 and B are also turned off.
2 is turned off, and power to the motor 2 is cut off.

However, the power supply to the direction switching circuit 13 is turned on by the off timer circuit 16 for a predetermined time after the key switch 3 is turned off, and at the same time, the relay signal is turned off, causing the direction switching circuit 13 to turn on both direction outputs and switch. B2
and A2 (step 9), the bridge circuit of the motor 2 is short-circuited, and the regenerative current is allowed to flow for a predetermined period of time.

Therefore, when the restoring force of the tires is activated, 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 the motor 2 is reversed. An induced electromotive force is generated as the rotor of motor 2 rotates, and switches B2 and A2 are generated from the motor 2.
A regenerative current flows through the rotor, and a braking force acts on the rotation of the rotor. In other words, since the motor 2 functions as a generator, a drive 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 the rotor The steering wheel shock caused by inertial rotation is greatly reduced.

When the power to the direction switching circuit 13 is turned off by the off timer circuit 16 after a predetermined time (T seconds) has elapsed, the regenerative current to the motor 2 is supplied to the switches B2 and A2.
is turned off and shut off (steps 10, 11).

By the way, the restoring force of the tires comes into play when the engine key switch 3 is turned off while the vehicle is holding the steering wheel, and when the tires are in the neutral position, no restoring force is generated and there is no steering wheel shock. For this reason, as shown in the embodiments of FIGS. 4 and 5, it is determined from the output of the steering wheel torque detector 4 whether or not the steering wheel is being held when the key switch 3 is turned off (step 6). The above-mentioned braking operation by the motor 2 is performed only when this happens.

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

The direction switching circuit 13 is configured so that when the key switch 3 is turned off by a signal from the controller 1, both direction outputs are turned on, and while the off timer circuit 16 is outputting, the controller 1 is in sleep mode. It is set so that it does not move to .

[0034] Therefore, when the restoring force of the tire is not generated and the braking operation by the motor 2 is unnecessary, unnecessary operations can be omitted. Note that since the output of the off-timer circuit 16 is input to the controller 1, the off-timer circuit 1
6 can be monitored by the controller 1.

Furthermore, in this case, the braking force of the motor 2 can be gradually weakened by periodically turning on and off the switches B2 and A2 and changing the pulse width with time.

In the embodiment shown in FIG. 6, 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 if the steering wheel is being held, and the steering wheel operation is stopped. This is to avoid causing any discomfort.

In step 6, it is determined whether the vehicle is stopped based on the output of the vehicle speed detector 5, and when the vehicle speed is extremely low below a predetermined value, it is recognized as stopped. The braking operation begins with the flow of
2. Turn off A2.

In normal driving operations, the key switch 3 is not turned off while the vehicle is running, but in the unlikely event that such a situation occurs, the motor 2 will not apply the brakes and the steering force will become extremely heavy. can be prevented.

[0039]

As described above, according to the present invention, the motor includes a motor that power assists the steering wheel operation, a detection means that detects the operating state of the steering wheel, and a bridge circuit that controls the motor control current and current direction. a drive circuit;
In an electric power steering device comprising a controller that controls a motor drive circuit according to the steering wheel operation state, an off timer circuit that operates for a predetermined time after an engine key switch is turned off; The motor is equipped with a direction switching circuit that shorts the motor drive circuit and switches the motor drive circuit to allow regenerative current to flow through the motor when the engine key switch is turned off. Since the restoring force of the tire is absorbed by this driving load, it is possible to effectively reduce steering shock when the vehicle is stopped.

[0040] Furthermore, by applying regenerative current to the motor to perform braking only when the restoring force of the tires is active,
Appropriate control can be performed without waste.

Furthermore, by stopping braking by the motor even if the engine key switch is turned off except when the vehicle is stopped,
It is possible to prevent the occurrence of discomfort when operating the steering wheel.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the 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 same control operation.

FIG. 4 is a circuit diagram showing a second embodiment.

FIG. 5 is a flowchart showing the same control operation.

FIG. 6 is a flowchart showing the control operation of the third embodiment.

[Explanation 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

Claims (3)

[Claims] 1. A motor drive circuit consisting of a motor for power assisting the handle operation, a detection means for detecting the operating state of the handle, and a bridge circuit for controlling the control current and current direction of the motor; An electric power steering device comprising a controller that controls according to an operating state, an off timer circuit that operates for a predetermined time after an engine key switch is turned off, and the motor drive circuit while the off timer circuit is operating. An electric power steering device characterized by comprising: a direction switching circuit that short-circuits and switches the circuit so that regenerative current can flow through the motor. 2. The vehicle is characterized by comprising means for determining that the steering wheel is being held from the output of the steering wheel operation detector when the engine key switch is turned off, and the direction switching circuit is switched only when the steering wheel is being held. The electric power steering device according to claim 1. 3. The electric power steering device according to claim 2, further comprising means for determining whether the vehicle is stopped based on the vehicle speed, and the direction switching circuit is switched only when the vehicle is being steered while the vehicle is stopped. .