JPH06127418A - Control device at abnormality for rear wheel steering device of vehicle - Google Patents

Abstract

PURPOSE:To provide a control device at abnormality of a rear wheel steering device of a vehicle in which stopping system of a motor is improved at generating abnormality in the motor circuit part in particular, in a system of steering rear wheels with an electric motor. CONSTITUTION:An ECU 19 searches for rear wheel steering angle based on the detected signals from a steering sensor 16, a vehicle speed sensor 21, and a motor rotation angle and rear wheel steering angle sensor 22, selectively controls FET1-FET4 connected together in state of a bridge through a driver circuit 25, and rotationally controls an electric motor 14 for steering rear wheels. When the ECU 19 detects abnormality by current detecting resistance R, the FET1 and the FET3 are made off, the FET2 and the FET4 are made on, both ends of the motor 14 are short-circuited so as to perform regenerative braking, a relay circuit 26 is changed over in the condition of decreased motor current so as to short-circuit both ends of the motor 14, the motor 14 is stopped, and the rear wheels are set on the neutral position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system for steering rear wheels by means of an electric motor, and especially for a rear vehicle for fail-safe operation when a rear-wheel steering mechanism for driving the rear wheels is abnormal. The present invention relates to an abnormal time control device for a wheel steering device.

[0002]

2. Description of the Related Art In a four-wheel steering system for a vehicle, a steering angle and a steering direction of rear wheels are required in accordance with a steering operation angle and a traveling speed. I try to control the mechanism.

In such a rear wheel steering mechanism, it is considered to use an electric motor as disclosed in, for example, Japanese Patent Application Laid-Open No. 2-74470, and based on detection signals from a vehicle speed sensor and a steering sensor. The target steering angle of the rear wheels is calculated, and the electric motor is driven according to the calculated target steering angle. When such four-wheel steering is performed, particularly the rear wheels have a very important effect on the steering stability of the vehicle, so that the steering angle may be set abnormally. It becomes a problem.

In this respect, the use of the electric motor enables highly accurate control of the rear wheel steering angle. However, if a failure such as a short circuit occurs in the motor circuit or the like, the steering angle of the rear wheel becomes abnormal. It is set so that stable steering cannot be performed.In the event of an abnormality, both ends of the motor are quickly electrically short-circuited, and the counter electromotive force is generated to stop the motor. The position is set automatically.

For example, a normally closed first relay circuit is provided in a circuit that supplies drive power to an electric motor from an electronic control unit, and a normally open second relay circuit is provided in a circuit that short-circuits both ends of the electric motor. When the abnormality is detected, the first relay circuit is opened to shut off the driving power, and the second relay circuit is closed to short-circuit both ends of the motor so that the regenerative braking acts and the electric motor is quickly stopped. ing.

However, if both ends of the electric motor are short-circuited only by the relay circuit as described above, this is the case in which a large current is generated due to the short-circuit of the motor circuit, which is a typical example of an abnormal situation. Due to the large current, the normally-closed contact portion of the first relay circuit is seized and cannot be opened, so that the motor stop control cannot be performed. In addition, by turning off the first relay circuit through which the drive current is flowing during operation of the motor and turning on the second relay circuit so that a short circuit is formed, the second relay circuit is controlled to a large extent. There is a practical problem in that the contact circuit burns when current is passed and the second relay circuit cannot be turned off to operate the motor again.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and reliably stops the electric motor when an abnormality occurs in the electric motor or the like for driving the rear wheel steering mechanism. To allow you to
In this case, an attempt is made to provide an abnormal-time control device for a rear wheel steering system of a vehicle, which reliably prevents a failure such as a seizure in the relay circuit, and executes highly reliable rear wheel steering. To do.

[0008]

According to the present invention, there is provided a control device for a rear wheel steering system of a vehicle in an abnormal state, in which four switching elements are bridge-connected and a rear wheel steering mechanism is driven between output ends of the bridge circuit. A diagonal line of a bridge circuit which constitutes the motor drive circuit by a driver circuit to which a steering command is supplied from an electronic control unit for obtaining a rear wheel steering angle and a steering direction. Each pair of switching elements located above is turned on or off in accordance with the steering direction. Further, a relay device is normally provided which has an electric motor connected between the output ends of the bridge circuit and has a switching terminal for short-circuiting both ends of the electric motor when an abnormality occurs, and this relay device is provided when the electronic control unit detects an abnormality. The electronic control unit first turns on the two switching elements of the bridge circuit to short-circuit both ends of the electric motor, and then switches the relay device.

[0009]

According to the abnormality control device for the rear wheel steering system constructed as described above, when an abnormality is detected, the switching element of the bridge circuit is first controlled so that both ends of the electric motor are short-circuited and the counter electromotive force is reduced. Is generated and the regenerative braking is activated. Then, the relay circuit is switched in a state where the short circuit current is reduced to form a circuit that short-circuits both ends of the electric motor, and the relay is switched while the amount of the short circuit current flowing in the relay circuit is surely reduced. The regenerative braking is realized without the contacts of this relay circuit sticking to the normally closed side. In addition, regenerative braking can be realized by the relay circuit even in the case of an abnormality in which the switching element is destroyed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a system configuration of a rear wheel steering system in which a front wheel 12 is steered by a steering wheel 11, and a rear wheel 13 is steered by a rear wheel steering mechanism 15 driven by an electric motor 14. The steering wheel 11 is provided with a steering sensor 16 for detecting the operation amount thereof, and the electric motor 14 is provided with a motor rotation angle sensor 17. Further, a rear wheel steering angle sensor 18 is provided on the rear wheel 13 to detect the steering angle of the rear wheels. The detection signals from these sensors 16-18 are electronic control units (ECU). Entered in 19.

A detection signal from the vehicle speed sensor 21 is further input to the ECU 19 so that the rear wheel steering angle is calculated by the ECU 19, and the ECU 19 drives and controls the electric motor 14. To do. That is, the target steering angle of the rear wheels 13 is obtained based on the operating angle of the steering wheel 11 and information such as the vehicle speed, the electric motor 14 is driven corresponding to the target steering angle, and the rear wheel steering mechanism 15 drives the rear wheels. The rudder angle of 13 will be controlled. ECU19
In this case, the occurrence of such an abnormality of the rear wheel steering device is also monitored. When the abnormality is detected, for example, the alarm lamp 22 is turned on.

FIG. 2 shows a drive control circuit for the electric motor 14. The ECU 19 detects detection signals from the sensor mechanism 22 for the motor rotation angle and the rear wheel steering angle, and further detects signals from the steering sensor 16 and the vehicle speed sensor 21. Is input, a steering angle target value for the rear wheels is calculated based on these input signals, and a rear wheel steering command corresponding to this target value is output and supplied to the driver circuit 25.

The driver circuit 25 supplies signals to the gates of the four FETs 1 to 4 that are semiconductor switching elements, and these FETs 1 to FE are used.
Control T4 on / off. These four FET1
~ FET4 is a bridge connection, one input end of this bridge circuit is connected to the power supply through the detection resistor R, the other is connected to the ground point, between the output terminals of the electric motor 14 To be connected. In this case, parasitic diodes D1 to D4 exist between the source and drain of each FET1 to FET4.

Between the one end of the electric motor 14 of the motor drive circuit thus constructed and one output of the bridge circuit,
The switching relay circuit 26 is connected via a normally open contact b that is closed when the relay circuit 26 is excited. The normally closed terminal a that is closed when the relay circuit 26 is not excited is connected to both ends of the electric motor 14. Connected to short circuit. The relay circuit 26 is switched according to a command from the ECU 19. The ECU 19 detects the terminal voltage of the resistor R and detects it when a large current of a predetermined value or more flows in the circuit of the electric motor 14. It is determined that there is an abnormality, and an operation command is output to the relay circuit 26 when this abnormality is determined.

FIG. 3 shows the flow of the control operation of the rear wheel steering system constructed as described above. First, in step 101, the relay circuit 26 is turned on as an initial state, and its normally open side contact b is shown in the figure. It is turned on as shown so that the electric motor 14 is connected and set between the output ends of the bridge circuit. In this state, detection signals from various sensors are input in step 102, the rear wheel target steering angle is obtained, and the electric motor 14 is controlled in step 103.

For example, turning on FET1 and FET2,
By controlling the FET3 and FET4 to be off, the drive current is supplied to the motor 14 through the FET1, and the FE
The electric motor 14 is rotated in the normal direction by flowing through T2 to the ground. On the contrary, FET3 and FET4
When the FET1 and the FET2 are turned off together with turning on the electric motor 14, the electric motor 14 is rotated in the reverse direction, and the forward rotation or the reverse rotation of the electric motor 14 causes the rear wheels to be steered in the forward and reverse directions. The outputs of the motor rotation angle sensor 17 and the rear wheel steering angle sensor 18 are monitored along with the rear wheel steering, and the electric motor 14 is rotationally driven until the rear wheels are steered to the rear wheel target steering angle. .

In step 104, the voltage generated in the current detection resistor R is monitored to determine whether an abnormality has occurred. If no abnormality is determined in step 104, the process returns to step 102 and the rear wheel steering is continued. Step
When an abnormality is detected in 104, step 105
Then, the FET1 and FET3 are turned off and the FET2 and FET4 are turned on. Therefore, in this state, the relay circuit set to the steady state
Both ends of the electric motor 14 are short-circuited via 26, and regenerative braking is realized.

In step 106, the elapsed time of such a state of regenerative braking is compared with the set predetermined time, and it is determined that the predetermined time has elapsed since the regenerative braking circuit formed by FET2 and FET4 was formed. If it is confirmed, the process proceeds to step 107 to control the relay circuit 26 in the non-excited state. That is, both ends of the electric motor 14 are connected through the normally closed contact a of the relay circuit 26.
To form a regenerative braking circuit.

That is, if an abnormality is detected, first F
A regenerative braking circuit is formed by ET3 and FET4, and a short circuit is formed by the relay circuit 26 in a state where the current flowing due to the short-circuiting of both ends of the electric motor 14 is reduced. That is, since the short circuit is formed by the relay circuit 26 after the motor current is reduced by the regenerative braking by the FET3 and FET4, a large current does not flow to the closed contact of the relay circuit 26, and therefore the contact is closed. Regenerative braking is realized without causing seizure on the part.

Further, even if a large current flows due to a short circuit of the electric motor 14 or the like, and the normally open contact b of the relay circuit 26 is burned and cannot be connected to the normally closed contact a, FET3 and FE at 105
Since the regenerative braking circuit of the electric motor 14 is formed by T4, the stop control of the electric motor 14 is executed even if the relay circuit 26 does not operate, and the steering angle of the rear wheels is set to the safe side. Furthermore, even if the FET circuit is destroyed, the relay circuit 26 will cause the electric motor 14
Regenerative braking is performed.

When regenerative braking is performed in step 105, for example, when a short-circuit current flows through FET2, even if FET4 is turned on, no current flows through this FET4, but the diode attached to this FET4. Bypassing at D4, the current flows and the short circuit of the motor 14 is realized.

As the diode D4 at this time, the diode parasitic on the FET4 can be used as it is, but a diode may be newly connected to the diode D4.

When the short-circuit current is in the opposite direction, the current flowing through the FET4 starts flowing through the diode D2, and a short-circuit circuit is similarly formed. This diode D2
Also, it can be configured by a parasitic diode of FET2, but a diode may be newly connected by external attachment. It is also possible to form a regenerative braking circuit of the electric motor 14 by turning on the FET1 and FET3 and turning off the FET2 and FET4.

Here, FET2 which constitutes the regenerative braking circuit
Alternatively, when it is determined that the FET4 has an open failure, specifically, when the motor current is found to be zero, F
Immediately stop the regenerative braking by the ET circuit and use the relay circuit.
The regenerative braking circuit by 26 is formed.

[0025]

As described above, according to the abnormal time control system for a rear wheel steering system according to the present invention, when an abnormality occurs in the electric motor circuit for steering the rear wheels, the motor current is first controlled. The regenerative braking circuit of the electric motor is formed by the switching element, and the regenerative braking circuit is formed by the relay circuit while the motor current is reduced in this regenerative braking. Especially, the occurrence of accidents due to burn-in of the relay circuit is effective. This prevents the rear wheel steering from being set to the neutral state on the safe side. Further, even when the switching element is destroyed, the relay circuit effectively backs it up, so that the fail-safe steering of the rear wheels is surely ensured.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of a vehicle including a rear wheel steering device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a control circuit of the rear wheel steering system.

FIG. 3 is a flowchart illustrating a control flow in this control circuit.

[Explanation of symbols]

11 ... Steering, 12 ... Front wheel, 13 ... Rear wheel, 14 ... Electric motor, 15 ... Rear wheel steering mechanism, 16 ... Steering sensor, 17
... Motor rotation angle sensor, 18 ... Rear wheel steering angle sensor, 19 ... Electronic control unit (ECU), 21 ... Vehicle speed sensor, 25 ... Driver circuit, 26 ... Relay circuit, FET1 to FET4 ... Switching element.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuhiro Shimizu, 1-1, Showa-cho, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Takashi Inaba, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nidec Within the corporation

Claims (1)

[Claims] 1. An electric motor for driving a rear wheel steering mechanism, a motor drive circuit in which four switching elements are bridge-connected, and the electric motor is set between output ends of the bridge circuit, and a vehicle. The electronic control unit for obtaining the rear wheel steering angle and the steering direction based on the output signals from the various sensors set in the above, and the diagonal line of the bridge circuit constituting the motor drive circuit based on the steering command from the electronic control unit. Is connected between a driver circuit for controlling ON / OFF of each pair of switching elements located at the position corresponding to the steering direction, and an output end of the bridge circuit and the electric motor, and normally outputs the bridge circuit. And a relay device having a switching terminal that connects an electric motor between the ends and short-circuits both ends of the electric motor when an abnormality occurs. The electron when the control unit detects an abnormality, short the two switching elements turned on of the electric motor at both ends of the electronic control unit first the bridge circuit,
After that, the relay device is switched over, and the control device at the time of abnormality of the rear wheel steering device of the vehicle.