JPH06127396A - Rear wheel steering system for vehicle - Google Patents

Abstract

PURPOSE:To provide a rear wheel steering system for a vehicle constituted in such a way as to control switching elements, forming a bridge, by PWM signals to drive an electric motor for rear wheel steering. CONSTITUTION:An H-bridge is formed of FET1-FET4 and a battery power source 35 is connected to the input of this bridge. A rear wheel steering direct current motor 16 is connected between the output ends, and parasitic diodes D1-D4 exist in the respective FET1-FET4. Direction signals are supplied to the gates of the FET1, FET3, and PWM signals are supplied to the gates of the FET2, FET4. In the case of rotating in a first direction, the FET1 is turned on by the direction signal, and the FET 4 is turned on/off by the PWM signal. A by-pass condenser C is connected between the output ends of the bridge, and current detecting resistances R1, R2 are respectively series-connected to the FET1, FET3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a vehicle, which carries out four-wheel steering, in which a DC motor steers the rear wheels.

[0002]

2. Description of the Related Art In a four-wheel steering vehicle, the steering angle of the rear wheels is determined in accordance with the steering angle of the steering wheel, the vehicle speed, etc., and the rear wheel steering is performed. An actuator for performing such rear wheel steering uses hydraulic pressure or the like as a drive source, and it has been considered to use a DC motor having good controllability.

Japanese Unexamined Patent Publication No. 2-274666 shows an example of a rear wheel steering device using such a DC motor as a drive source. In this device, a circuit for driving the DC motor is shown in FIG. 10, for example. 4 FETs 1 to F
An H-bridge circuit composed of switching elements composed of ET4 is used. The battery power source E is connected between the input terminals of the H bridge circuit, and the DC motor M is connected between the output terminals of the H bridge circuit. By controlling, the DC motor M is rotated in a designated direction to steer the rear wheels.

Here, for the pair of power elements selected from the FET drive circuit DR, a pulse width modulation signal (PW
M) to supply a gate signal to the switching element corresponding to the ON period of the PWM signal so that the DC drive power is supplied from the predetermined direction to the DC motor M via the ON-controlled switching element. I have to. The switching element is set to be off during the off period of the PWM signal.

In the drive circuit of the DC motor configured as described above, a predetermined drive power is supplied to the DC motor M as shown by the solid line arrow during the ON period of the PWM signal. In the off period of the PWM signal, all the FETs 1 to FE that form the bridge circuit
T4 is set to the off state.

Therefore, the motor current that has been flowing up to that point comes to flow back in the direction of the power source E from the motor M side via the parasitic diode of each FET as indicated by the broken line arrow, and a spike voltage is generated by this current. This spike voltage causes radio noise to be generated. Further, since the resistor R for detecting the motor current comes to be installed outside the bridge circuit, there is a problem that the motor current cannot be detected with high accuracy.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in particular, the current from the electric motor is circulated in the bridge circuit during the off period of the pulse width modulation signal. This is to suppress the generation of unnecessary spike voltage and prevent the generation of radio noise. Furthermore, even in the off period of the pulse width modulation signal, the motor current can be accurately detected and measured. It is intended to provide a rear wheel steering device.

[0008]

A rear-wheel steering system for a vehicle according to the present invention drives a rear-wheel steering mechanism by an electric motor, and the electric motor is connected between output terminals so as to be connected in series. A bidirectional rotation / rotation driving unit configured by a bridge circuit in which connected switch element groups are connected in parallel is provided, and a diode is set in parallel to each of the switching elements forming the bridge circuit. The rear wheel steering angle calculation means calculates the rear wheel steering direction and the steering angle of the vehicle based on the rear wheel steering signal obtained corresponding to the steering angle and the vehicle speed of the vehicle, and the steering direction output means calculates the rear wheel steering direction and the steering angle. A direction signal is output corresponding to the steering direction of the rear wheels, and a pulse width modulation signal corresponding to the steering angle is output by the PWM output means.
The direction signal is supplied as a gate signal to one of the switching elements connected in series as the gate signal, and the pulse width modulation signal is supplied to the other switching element, and the switching element is supplied with the gate signal. And a current flows between the switching element to which the gate signal is supplied and the switching element in the parallel position to which the pulse width modulation signal is supplied.

Further, resistors for current detection are respectively connected in series to the switching elements forming the bridge circuit.

[0010]

In the vehicle rear wheel steering system configured as described above, the direction of the drive power supplied to the electric motor is set by the switching element which is on-controlled by the direction signal, and the drive power is pulse width modulated. ON by signal
It comes to be controlled off. Then, the driving direction and the rotation amount of the electric motor are controlled, and the rear wheels are steered. Here, at the ON timing of the pulse width modulation signal, drive power is supplied to the electric motor via the switching element that is turned on by the switching element and the direction signal that are turned on by the pulse width modulation signal. Further, during the off period of the pulse width modulation signal, the switching element controlled by the pulse width modulation signal is off, but the switching element to which the direction signal is supplied is in the on state, and therefore is connected to the switching element. The motor current loops half of the bridge circuit via the diode, and the motor current is reliably detected by the current detection resistor. Further, the generation of spike voltage is effectively suppressed, and the generation of radio noise is prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A rear wheel steering system according to an embodiment of the present invention using a DC motor as a drive source will be described below with reference to the drawings. FIG. 1 shows a system configuration of a four-wheel steering vehicle, in which a front wheel 12 is steered by a steering wheel 11, and the steering angle is detected by a steering sensor 13. Rear wheel 14
A rear wheel steering mechanism 15 is provided in the vehicle, and the rear wheel steering mechanism 15 is driven by a DC motor 16. A rear wheel steering angle sensor 17 is provided corresponding to the rear wheel steering mechanism 15, and a motor rotation angle sensor 18 is provided at the DC motor 16. Further, this vehicle is provided with a vehicle speed sensor 19 for detecting the traveling speed.

Steering sensor 13, rear wheel steering angle sensor 1
The detection signals from the motor rotation angle sensor 18, the vehicle speed sensor 19, and the vehicle speed sensor 19 are supplied to the electronic control unit (ECU) 20. In the ECU 20, the detection signals from the steering sensor 13 and the vehicle speed sensor 19 are used. Based on this, the rear wheel steering direction and steering angle are calculated, and the DC motor 16 is drive-controlled in accordance with the rear wheel steering target value obtained from the calculation result. In this case, the motor rotation angle sensor
The rotation angle of the motor 16 is monitored based on the detection signal from 18, and the rear wheel 14 is steered corresponding to the rear wheel steering angle target value based on the detection signal from the rear wheel steering angle sensor 17. To do so.

FIG. 2 shows the configuration of a control system for performing such rear wheel steering. The detection signal from the steering sensor 13 and the detection signal from the vehicle speed sensor 19 are E
It is supplied to the rear wheel steering arithmetic unit 31 configured in the CU 20,
The steering direction and steering angle of the rear wheels 14 are calculated. And
The rear wheel steering direction and the steering angle obtained from the calculation result from the calculation device 31 are supplied to the steering direction output device 321 and the steering angle output device 322 that form the switching element drive device 32.

From these output devices 321 and 322,
A pulse width modulation (PWM) signal that represents the direction signal and the steering angle, respectively, is output, and these direction signal and P
The WM signal is supplied to the motor bidirectional rotation drive device 33.
This motor bidirectional rotation drive device 33 is composed of an H bridge circuit by a switching element composed of, for example, an FET or a bipolar transistor.
The rotation of the DC motor 16 is controlled by the output from the bridge circuit. The DC motor 16 drives the rear wheel steering mechanism 15 to carry out rear wheel steering.

FIG. 3 shows the motor bidirectional rotation drive unit 33 in detail. It is composed of a series circuit of FET1 and FET2, which are first and second switching elements, and third and fourth switching elements. The H bridge circuit is composed of the series circuit of FET3 and FET4, and the DC motor 16 is connected between the output terminals of this bridge circuit, specifically between the connection point of FET1 and FET2 and the connection point of FET3 and FET4. To be done. Here, the parasitic diodes D1 to D4 respectively exist in parallel in the FET1 to FET4.

A battery power supply 35 is connected between the input ends of this bridge circuit, and between the FET1 and the power supply 35, and FE.
Resistors R1 and R2 for current detection are respectively connected in series between T3 and the power supply 35, and a bypass capacitor C is connected between the output terminals of this bridge circuit. Then, FE which is a switching element driving device is provided for each of the gates of FET1 to FET4 which constitute this bridge circuit.
The drive signals a to d from the T drive circuit 36 are respectively supplied as gate signals.

FIG. 4 shows a specific structure of the FET drive circuit 36. A steering direction signal corresponding to the steering direction of the rear wheels and a PWM signal corresponding to the steering angle are input. The FET drive circuit 36 includes gate drive circuits 361 to 364 corresponding to the FET1 to FET4, respectively. The input direction signal is supplied to the FET1 gate drive circuit 361, and the gate signal corresponding to the level of the input direction signal is supplied. Output a. The direction signal is inverted by the inverter 365 and supplied to the FET3 gate drive circuit 363. From this gate drive circuit 363, the gate signal c having the opposite polarity to the gate signal a is supplied.
Are output, and these signals a and c are FET
It is supplied to the gates of 1 and FET3 so that one of FET1 or FET3 is turned on and the other is turned off according to the steering direction.

The PWM signal is output to AND circuits 366 and 367.
To the AND circuit 366, the output of the inverter 365 to which the input direction signal is supplied is supplied as a gate signal, and the AND circuit 367 is supplied with the direction signal as it is as a gate signal. The outputs from the AND circuits 366 and 367 are supplied to the FET2 gate drive circuit 362 and the FET4 gate drive circuit 364, respectively, and the supplied PWM signal is output b.
And d, which will be fed to the gates of FET2 and FET4 respectively.

That is, when the direction signal is at the high level, the output a becomes the high level, and the direction signal causes F
ET1 is turned on and the PWM from the AND circuit 367
A signal is output and the gate of FET4 is PW by the output d.
It is on / off controlled by the M signal. Further, when the direction signal is at the low level, the output of the inverter 365 becomes the high level, the output c from the FET3 driving circuit 363 becomes the high level, and the FET3 is turned on. And circuit 36 at the same time
The gate of 6 is opened, the PWM signal b is output from the FET2 gate drive circuit 362, and the gate of FET2 is on / off controlled by the PWM signal.

In the apparatus configured as described above, a case where a current flows from the left brush to the right brush in the figure of the DC motor 16 by, for example, PWM control will be described.
In the case of the rotation direction value in which the motor current in this direction flows, that is, the steering direction, the direction signal is set to a high level.
Therefore, in the high level state of this direction signal, F
The output a from the FET1 gate drive circuit 361 of the ET drive circuit 36 becomes high level, the gate of the AND circuit 367 is opened, and the PWM signal is output from the FET4 gate drive circuit 364. That is, the FET1 is turned on, and the FET4 in the diagonal position is on / off controlled by the PWM signal. Then, FET2 and FET3 are set to the off state.

When both FET1 and FET4 are turned on in such a state, the current from the battery power source 35 flows in the order of resistance R1 → FET1 → DC motor 16 → FET4 as shown by the solid arrow. However, when the PWM signal is turned off while the FET1 is turned on by the direction signal, the FET4 is turned off. In such a state, the current flowing through this circuit portion is the DC motor as indicated by the broken line arrow. 16 → diode D3 → resistor R2 → resistor R
1 → Flows through the FET1 circuit. That is, the current flows in the upper half (in the figure) of the bridge circuit and is not returned to the battery power source 35.

Further, by providing a bypass capacitor C such as a film capacitor having excellent high frequency characteristics, the current from the power supply 35 is absorbed when the input PWM signal is switched from ON to OFF, and the motor cable is gradually added. To reduce the current flowing through. Also, P
When the WM signal is switched from OFF to ON, a current is discharged to the DC motor 16 and a current from the battery power source 35 is gradually flown to the DC motor 16 to smooth the change of the current flowing in the motor cable. .

That is, the return current from the DC motor 16 to the battery power source 35 when the PWM signal is off is prevented,
Furthermore, since the change in the current flowing from the battery power source 35 to the DC motor 16 is made gradual, the spike voltage generated in the motor cable can be reduced, and the generation of radio noise is effectively suppressed. Become so.

Further, in this bridge circuit, the resistors R1 and R2 for current detection are arranged in the bridge, so that the current flowing through the DC motor 16 can be accurately observed.

FIG. 5 shows the waveform of the current flowing in the DC motor 16 observed at the resistor R in the conventional circuit as shown in FIG. 10, and the motor current corresponding to the PWM signal in (A). Changes like (B). In the case of this circuit, the current detection resistor R is installed outside the bridge circuit, and the direction of current flow is reversed, so that an absolute value circuit is required for current detection. Further, since the current becomes zero at the time of reversal, when it is used for current feedback control of the motor or abnormality detection, filter processing or the like is required. However, such a waveform after filtering is not accurate.

FIG. 6 shows a circuit diagram of the embodiment circuit shown in FIG.
Current detection resistor R when current flows as shown by the solid arrow
1 shows the motor current detected by R2, and the motor current detected by the resistors R1 and R2 for the PWM signal shown in (A) is as shown in (B) and (C), respectively. Become. That is, the motor current observed by the electric resistance R1 is PWM
It can be accurately observed because it continuously flows in the same direction regardless of whether the signal is on or off, and it can be used as feedback control of motor current or as an abnormality detection means. . Further, the absolute value circuit and the like are not required, and there is no need for filter processing or the like, so that the circuit configuration is inevitably simplified.

In the above-described embodiments, the direction signals are supplied to the FET1 and FET3 which form the bridge circuit, and F
The PWM signal was supplied to ET2 and FET4, but the same applies when the PWM signal is supplied to the gates of FET1 and FET3 and the direction signal is supplied to the gates of FET2 and FET4 as shown in FIG. The effect of is obtained.

In the above embodiments, a DC motor is used as a drive source for steering the rear wheels, but a three-phase brushless motor 161 can be used as shown in FIG. In this case, the rotation driving circuit of the motor 161 is composed of a three-phase bridge circuit composed of FET1 to FET6, and the direction signals from the FET driving circuit 36 are supplied to the gates of FET1, FET3, and FET5, respectively. The PWM signal is FET2, FET4,
Supply to the gate of FET6.

Also in the embodiment using the three-phase brushless motor 161, the FET1 and FE are connected as shown in FIG.
Supply PWM signal to the gate of T3 and FET5
Even if a direction signal is supplied to the gates of FET 2, FET 4 and FET 6, the rear wheel steering can be controlled similarly.

[0030]

As described above, according to the vehicle rear wheel steering system of the present invention, the switching element which is constructed so that the rear wheels are steered by the electric motor and which is on / off controlled by the PWM signal is used. When the rotation of the electric motor is controlled by the bridge circuit,
During the OFF period of the WM signal, the current from the electric motor is circulated in the bridge circuit, the generation of unnecessary spike voltage is effectively suppressed, and the generation of radio noise, for example, is effectively prevented.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a system configuration of a vehicle four-wheel steering system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a rear wheel steering system in this embodiment.

FIG. 3 is a diagram showing a circuit example of a rotation drive circuit device section of a DC motor in the rear wheel steering system.

FIG. 4 is a diagram showing a configuration of an FET drive circuit constituting the rotation drive circuit device.

FIG. 5 is a diagram illustrating a detected current in a conventional device.

FIG. 6 is a diagram showing a detected current in a current detection resistor in the above embodiment in relation to a PWM signal.

FIG. 7 is a circuit configuration diagram illustrating a second embodiment of the present invention.

FIG. 8 is a circuit configuration diagram illustrating a third embodiment of the present invention.

FIG. 9 is a circuit configuration diagram illustrating a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a drive circuit of a conventional DC motor.

[Explanation of symbols]

11 ... Steering, 12 ... Front wheel, 13 ... Steering sensor, 14 ... Rear wheel, 15 ... Rear wheel steering mechanism, 16 ... Electric motor, 17
... rear wheel steering angle sensor, 18 ... motor rotation angle sensor, 19 ... vehicle speed sensor, 20 ... electronic control unit, 31 ... rear wheel steering calculation device, 32 ... switching element drive device, 33 ... motor bidirectional rotation drive device (bridge) Circuit), FET1-FET4 ...
Switching element.

Claims (2)

[Claims] 1. An electric motor for driving a rear wheel steering mechanism of a vehicle, and a bridge circuit in which switching element groups connected in series are connected in parallel, and a DC power supply is connected to an input terminal of the bridge circuit, and an output terminal. A bidirectional rotation drive means in which the electric motor is connected in between, a diode connected in parallel with each of the switching elements forming the bridge circuit, and a steering angle and a vehicle speed of the vehicle. A rear-wheel steering angle calculating means for calculating the rear-wheel steering direction and steering angle of the vehicle based on the obtained rear-wheel steering signal, and a direction signal corresponding to the rear-wheel steering direction obtained by the calculating means. Steering direction output means, and PWM output means for outputting a pulse width modulation signal corresponding to the steering angle of the computing means, the steering direction output means The direction signal from is supplied as a gate signal to one switching element of the switching elements connected in series, and the pulse width modulation signal from the PWM output means is supplied to the other switching element, It is characterized in that a current flows between a switching element supplied with a gate signal and a switching element supplied with a pulse width modulation signal in a parallel position with the switching element supplied with the gate signal. Rear wheel steering system for vehicles. 2. A rear wheel steering system for a vehicle according to claim 1, wherein a resistance for current detection is connected in series to each of the switching elements forming the bridge circuit.