JPH0597045A - Four-wheel steering device - Google Patents

Abstract

(57) [Abstract] [Purpose] In a four-wheel steering system in which the rear-wheel steering angle is controlled by an electric motor when the steering wheel is operated, when the rear-wheel steering angle has a deviation amount, the rear-wheel steering angle neutral position can be accurately measured in a short time. Initialize the points. [Configuration] At the time of initial setting of the rear wheel steering angle neutral point, first, the electric motor a is rotated at a high speed to a rough neutral permissible region based on the detection signal from the sub sensor d, and then the detection signal from the main sensor c is changed. Based on this, a means for rotating the electric motor a at a low speed up to the severe neutral permissible region is used.

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 controlling a rear wheel steering angle by an electric motor when a steering wheel is operated.
This relates to the neutral point initial setting technology for the rear wheel steering angle.

[0002]

2. Description of the Related Art Conventionally, as a four-wheel steering system having a steering mechanism using an electric motor as an actuator for rear wheels, for example, one disclosed in JP-A-61-46766 is known.

In such a motor steering mechanism using an electric motor as an actuator, when the ignition switch is turned on to start the rear wheel steering angle control,
For the initial setting of the neutral point that serves as the control reference, the main sensor that detects the rear wheel steering angle based on the motor shaft rotation angle of the electric motor is used, and the electric motor is commanded to move from the misaligned position based on the sensor signal It is done by outputting.

[0004]

However, in such a four-wheel steering system, only the main sensor is used to make the speed of the electric motor constant and the neutral point is initialized. There is a problem like enumeration.

(1) When the motor speed is increased with the intention of setting the neutral point in a short time, as shown in FIG. 6, due to overshoot, a small front-back width is provided from the true neutral point. Hunting occurs in the vicinity of the neutral permissible region (θNM to −θNM) and the convergence does not occur. As a result, it takes a long time to set the neutral point.

(2) In order to improve the convergence to the neutral allowable range, the motor speed must be reduced, and in this case as well, as shown in FIG. 6, the neutral point is initialized. The required time T0 becomes longer.

Therefore, in addition to the main sensor for detecting the motor shaft rotation angle before deceleration, which has a large shaft rotation angle with respect to the predetermined rear wheel steering angle, there is a relationship of approximately 1: 1 with respect to the predetermined rear wheel steering angle. By using a sub-sensor that detects the rear wheel rudder angle by the rack stroke of the motor steering mechanism that has a stroke amount, the neutral point initial position is output by outputting a command to the electric motor to move from the misaligned position to the rough neutral allowable range based on the sensor signal. It is possible to make settings.

Here, it is necessary to roughly set the neutral permissible region with a large front-back width from the true neutral point, because the steering angle detection resolution of the sub sensor for detecting the rack stroke is larger than that of the main sensor. Very low (about 1 /
30) It depends.

In this case, although the neutral point setting time can be shortened by increasing the motor speed, the initially set neutral point is separated from the true neutral point. As a result, in the rear wheel steering angle control that is performed after the initial setting of the neutral point, the control accuracy is reduced, and for example, there is an effect that the desired turning stability etc. cannot be obtained by four-wheel steering. Will end up.

The present invention has been made in view of the above problems, and in a four-wheel steering system in which the rear wheel steering angle is controlled by an electric motor when the steering wheel is operated, when the rear wheel steering angle has a deviation amount. The problem is to initialize the neutral point of the rear wheel steering angle in a short time and with high accuracy.

[0011]

In order to solve the above-mentioned problems, in the four-wheel steering system of the present invention, at the time of initial setting of the rear wheel steering angle neutral point, first, a rough neutral allowable area is set based on the detection signal from the sub sensor. The electric motor is rotated at a high speed, and then the electric motor is rotated at a low speed to a sensitive neutral allowable range based on the detection signal from the main sensor.

That is, as shown in the claim correspondence diagram of FIG. 1, the electric motor a is used as an actuator, and the motor steering mechanism b is provided for controlling the rear wheel steering angle when the steering wheel is operated, and the motor shaft of the electric motor a. Main sensor c provided on the side for detecting the rear wheel steering angle based on the shaft rotation angle
And a sub sensor d provided on the rack shaft side of the motor steering mechanism b for detecting a rear wheel steering angle by a rack stroke, and a sub sensor d when the neutral point is initially set when the rear wheel steering angle has a deviation amount. By the first neutral point setting means e for outputting to the electric motor a a high speed rotation command for moving from the true neutral point to the neutral allowable area having a large front-back width based on the detection signal of the first neutral point setting means e. After the neutral point is set, second neutral point setting means f for outputting to the electric motor a a low speed rotation command for moving from the true neutral point to the neutral permissible region having a small front-back width based on the detection signal from the main sensor c. It is characterized by having.

[0013]

When the neutral point is initially set when the rear wheel steering angle has a deviation amount, first, the first neutral point setting means e has a large front-back width from the true neutral point based on the detection signal from the sub sensor d. A high-speed rotation command for moving to the neutral permissible region is output to the electric motor a. Then, the first neutral point setting means e
After the neutral point is set by, the second neutral point setting means f
Based on the detection signal from the main sensor c, a low speed rotation command for moving from the true neutral point to the neutral allowable area having a small front-rear width is output to the electric motor a.

As a result, with respect to the deviation amount of the rear wheel steering angle neutral point, the deviation amount is corrected to the rough neutral tolerance region in a short time by the high rotation rough adjustment in the first step, and the low rotation fine adjustment in the second step. As a result, the deviation amount is corrected up to the severe neutral allowable area without causing overshoot.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

The configuration will be described.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system according to the embodiment of the present invention is applied.

Steering of front wheels 1 and 2 of a vehicle to which the four-wheel steering system of the embodiment is applied is performed by a steering handle 3 and a mechanical link type steering mechanism 4, as shown in FIG. This is composed of, for example, a steering gear, a pitman arm, a relay rod, side rods 5, 6 and knuckle arms 7, 8.

The rear wheels 9 and 10 are steered by an electric steering device 11 (corresponding to a motor steering mechanism).
Done by. The rear wheels 9 and 10 are connected by a rack shaft 12, side rods 13 and 14, and knuckle arms 15 and 16, and a rack tube 17 in which the rack 12 is inserted has a reduction mechanism 18 and a motor 19 (electric motor). And a fail-safe solenoid 20. The motor 19 and the fail-safe solenoid 2 are provided.
0 is a vehicle speed sensor 21, a front wheel steering angle sensor 22, a stroke sensor 23 (corresponding to a sub sensor), an encoder 24.
The drive is controlled by the controller 26 which inputs a signal from (corresponding to the main sensor).

FIG. 3 is a cross-sectional view showing a specific structure of the electric steering device 11, in which a rack tube 17 in which the rack 12 is inserted is fixed to the vehicle body via a bracket. The side rods 13 and 14 are connected to both ends of the rack 12 via ball joints 30 and 31, respectively. The reduction mechanism 18 includes a motor pinion 32 connected to a motor shaft of a motor 19 and the motor pinion 32.
And a rack pinion 35 fixed to the ring gear 33 and meshing with the rack gear 12a. Therefore, the motor 19
Is rotated, the motor pinion 32 → ring gear 33 →
The rotation is transmitted to the rack and pinion 35, and the rack shaft 12 is axially moved by the meshing of the rotating rack and pinion 35 and the rack gear 12a to steer the rear wheels 9 and 10. The turning amount of the rear wheels 9 and 10 is proportional to the moving amount of the rack shaft 12, that is, the rotating amount of the motor 19.

A sensor shaft 24a of an encoder 24 for detecting the rotation angle of the rack and pinion 35 is connected via a coupler 36.

The fail-safe solenoid 20 includes:
The lock pin 20a is provided so as to be able to move forward and backward, and when the electronic control system or the like fails, the rack pin 12 is fitted into the lock groove 12b formed in the rack shaft 12 so that the rear shafts 9 and 10 can be moved. It is fixed at a position that maintains the neutral rudder angle position.

The operation will be described.

FIG. 4 is a flow chart showing the flow of the processing operation of the neutral point initialization performed by the controller 26 when the ignition is turned from ON to ON.
Each step will be described.

In step 40, it is judged whether or not the initial setting of the neutral point of the rear wheel steering angle has been completed. Then, when the initial setting of the neutral point of the rear wheel steering angle has been completed, the routine proceeds to step 41, where the normal control of the rear wheel steering angle is started. Further, if the initial setting of the neutral point of the rear wheel steering angle has not been completed, the neutral point initial setting process of step 42 and subsequent steps is executed.

In step 42, the stroke sensor 23
The sub-sensor output value SSout from is in the neutral allowable range | θNS |
It is judged whether it is in or not.

Incidentally, the neutral permissible region | θNS | is set as a region having a large front-back width from the true neutral point corresponding to the low resolution of the sub-sensor output value SSout, as shown in FIG.

When NO is determined in step 42, the process proceeds to step 43, and in step 43, it is determined whether the vehicle speed V is equal to or lower than the set vehicle speed Vo.

The set vehicle speed Vo is set as a vehicle speed at which the neutral point of the rear wheel steering angle can be initially set.

When NO is determined in step 43, this vehicle speed determination is repeated every predetermined time, and the process waits until YES is determined. Then, if YES is determined in the step 43, the process proceeds to a step 44, and a command for rotating the electric motor 19 at a high speed in a direction approaching the true neutral point is output.

The above steps 40, 42, 43 and 44 correspond to the first neutral point setting means.

In step 42, the sub sensor output value SSou
If it is determined that t is within the neutral permissible range | θNS |, the process proceeds to step 45. At step 45, it is determined whether the main sensor output value MSout from the encoder 24 is within the neutral permissible range | θNM |. To be judged.

As shown in FIG. 5, the neutral allowable area | θNM | is set as an area having a small front-back width from the true neutral point corresponding to the high resolution of the main sensor output value MSout. ..

In step 46, similarly to step 43, it is determined whether the vehicle speed V is equal to or lower than the set vehicle speed Vo at which the neutral point can be initialized, and if YES in step 46, the process proceeds to step 47. , A command to rotate the electric motor 19 at a low speed in the direction approaching the true neutral point is output.

The above steps 45, 46, and 47 correspond to the second neutral point setting means.

In step 45, the main sensor output value
If it is determined that MSout is within the neutral permissible region | θNM |, the process proceeds to step 48, at which the neutral point initial setting completion flag is set, and then the process proceeds to step 40 → step 41, The normal control of the rear wheel steering angle will be started.

As the normal control of the rear wheel steering angle, for example, motor control is performed by the motor control formula shown below.

IM = Lθε-md (θM) + Kp IM: Motor current L: Proportional constant θε: Deviation between target value and follow-up value m: Damping constant d (θM): Motor rotation angular velocity Kp: Friction correction Constant Next, a description will be given of the neutral point correction operation in the case where the neutral point deviation amounts when the ignition is turned off and then on are different.

(A) When the neutral point deviation amount is │θNM│ or less When the neutral point deviation amount is │θNM│ or less, step 40 →
The flow proceeds from step 42 → step 45 → step 48 → step 40 → step 41.

That is, since the neutral point deviation amount is equal to or less than the neutral permissible range | θNM | from the time of ignition OFF to ON, the rear wheel is immediately corrected without rotating the electric motor 19 to correct the neutral point. The rudder angle normal control is started.

(B) If the deviation of the neutral point is │θNM│ or more, │θ
When NS ｜ or less When the neutral point shift amount is ｜ θNM ｜ or more and ｜ θNS ｜ or less,
Step 40-> step 42-> step 45-> step 46-> step 47, and main sensor output value MSou
The shift amount of the neutral point is corrected by using t, and then the flow proceeds to step 45 → step 48 → step 40 → step 41.

That is, since the neutral point deviation amount is equal to or less than the neutral allowable range | θNS | from the beginning of the ignition OFF → ON, only the neutral point is corrected by rotating the electric motor 19 at a low speed, and the rear wheels are corrected. The rudder angle normal control is started.

(C) When the neutral point shift amount is │θNS│ or more When the neutral point shift amount is │θNS│ or more, step 40-
Proceed to step 44, and as the first step, the sub sensor output value
The deviation amount of the neutral point is corrected using SSout, and then the process proceeds to step 45 to step 47. As the second step, the deviation amount of the neutral point is corrected using the main sensor output value MSout, and then step 45 → step 48 → Step 4
The flow proceeds from 0 to step 41.

That is, when the amount of deviation of the neutral point is in the neutral permissible range | θNM | or more during the ignition OFF → ON state, as shown in FIG. The deviation amount is corrected up to the neutral allowable range | θNS | (there is some overshoot due to the high speed), and the tight neutral allowable range without causing overshoot due to the second stage low rotation fine adjustment | θNM
The amount of deviation will be corrected up to |. Then, the time required for the neutral point initial setting becomes T1, and the initial setting of the neutral point is completed in a shorter time than the time T0 in the conventional technique.

The effect will be described.

(1) In the four-wheel steering system in which the rear wheel steering angle is controlled by the electric motor 19 when the steering wheel is operated, when the rear wheel steering angle neutral point is initially set, first, based on the sub sensor output value SSout from the stroke sensor 23. The electric motor 19 is rotated at a high speed up to a rough neutral allowable range | θNS |, and then the main sensor output value MS from the encoder 24
Since the electric motor 19 is rotated at a low speed up to the severe neutral permissible range | θNM | based on out, when the rear wheel steering angle has a deviation amount, the initial position of the neutral point of the rear wheel steering angle can be accurately measured in a short time. You can make settings.

(2) When the electric motor 19 is rotated to initialize the rear-wheel steering angle neutral point, the electric motor 19 is set only when the vehicle speed V is equal to or lower than the set vehicle speed Vo at which the neutral point can be initialized.
Since it is a device for rotating the vehicle, it is possible to prevent an unexpected sudden change in vehicle behavior due to the neutral point initial setting during traveling.

Although the embodiments have been described above with reference to the drawings, the specific structure is not limited to the embodiments, and modifications and additions within the scope of the present invention are included in the present invention. Be done.

[0049]

As described above, according to the present invention, in the four-wheel steering system in which the rear wheel steering angle is controlled by the electric motor when the steering wheel is operated, the sub sensor is first set when the rear wheel steering angle neutral point is initially set. Based on the detection signal from, the electric motor is rotated at a high speed to a rough neutral allowable range, and then the electric motor is rotated at a low speed to a delicate neutral allowable range based on the detection signal from the main sensor. When the rear-wheel steering angle has a deviation amount, the effect that the initial setting of the rear-wheel steering angle neutral point can be made accurately in a short time is obtained.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a four-wheel steering system according to the present invention.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system of the embodiment is applied.

FIG. 3 is a cross-sectional view showing a specific configuration of the electric steering device of the embodiment apparatus.

FIG. 4 is a flowchart showing a flow of processing operation of neutral point initialization performed by the controller when the ignition is turned from ON to ON.

FIG. 5 is a time chart showing the neutral point correction operation when the deviation amount of the rear wheel steering angle is large in the embodiment apparatus.

FIG. 6 is a time chart showing the neutral point correction operation when the amount of deviation of the rear wheel steering angle is large in the conventional device.

[Explanation of symbols]

 a electric motor b motor steering mechanism c main sensor d sub sensor e first neutral point setting means f second neutral point setting means

Claims (1)

[Claims] 1. A motor steering mechanism provided with an electric motor as an actuator for controlling a rear wheel steering angle when a steering wheel is operated, and a motor steering mechanism provided on the motor shaft side of the electric motor, wherein the rear wheel steering angle is controlled by the shaft rotation angle. A main sensor for detecting, and provided on the rack shaft side of the motor steering mechanism,
A sub sensor that detects the rear wheel steering angle by the rack stroke, and a neutral point that has a large front-back width from the true neutral point based on the detection signal from the sub sensor when the neutral point is initially set when the rear wheel steering angle has a deviation amount. First neutral point setting means for outputting to the electric motor a high speed rotation command for moving to an allowable range, and after setting the neutral point by the first neutral point setting means, from the true neutral point based on the detection signal from the main sensor. A four-wheel steering system comprising: a second neutral point setting means for outputting to the electric motor a low speed rotation command for moving to a neutral permissible region having a small front-rear width.