JP3013641B2 - Electric motor driven four-wheel steering system - 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 motor driven four-wheel steering system for controlling a rear wheel steering angle by an electric motor.

[0002]

2. Description of the Related Art Conventionally, a power cylinder-driven four-wheel steering device in which a rear cylinder steering angle is controlled by a power cylinder has been known.
For example, Japanese Patent Application Laid-Open No. 2-29976 and Japanese Utility Model Publication 2-2
The one described in Japanese Patent No. 4700 is known.

[0003] The former conventional source discloses a technique for starting rear wheel steering angle control as soon as the neutral position of the steering angle is detected in order to achieve earlier control start timing while maintaining high control accuracy. Have been.

In the latter conventional source, when the vehicle is started after parking the vehicle while steering the front wheels, the neutral state of the steering wheel is detected in order to prevent the rear wheels from being suddenly steered. A technique for prohibiting the steering operation of the rear wheels until the operation is performed is disclosed.

[0005]

However, when the above-mentioned prior art is applied to an electric motor-driven four-wheel steering device that controls the rear wheel steering angle by an electric motor, the former device detects the neutral position of the steering steering angle. Since only the control start condition is used as the control start condition, if the rear wheel steering angle detection value or the rear wheel steering angle target value is out of the rear wheel steering angle neutral position, the rear wheel steering angle changes suddenly at the same time as the control starts, and the Unnecessary current is generated at the time.

In the latter device, the control is prohibited from being started until the steering wheel detects a neutral state, that is, until the rear wheel steering angle target value reaches the rear wheel steering angle neutral position. When the steering angle position of the rear wheel is not at the neutral position at the time when the rear wheel steering angle is detected, a large deviation is calculated between the rear wheel steering angle detection value and the rear wheel steering angle target value. It changes suddenly and generates unnecessary current in the electric motor.

[0007] The reason that the above problem occurs is that, in a system in which the rear wheels are steered using an electric motor, the neutral position of the rear wheels is not returned to the neutral position during control stop by a centering spring like a power cylinder, and The rear wheel steering angle target value is calculated by using the steering angle position obtained at the end of the control and the steering angle obtained by the width between the steering angle neutral position obtained by the calculation and the steering angle actual measurement value. In order to obtain the rear wheel steering angle target value, the power cylinder is determined based on the fact that the current value to the motor is determined by feedback control according to the deviation between the rear wheel steering angle target value and the detected rear wheel steering angle value. It is different from the driving type.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a four-wheel steering apparatus driven by an electric motor in which a rear wheel steering angle is controlled by an electric motor. An object of the present invention is to prevent generation of unnecessary current to the motor and a sudden change in the rear wheel steering angle at the start.

[0009]

In order to solve the above-mentioned problems, in an electric motor-driven four-wheel steering system according to the present invention, a neutral position of a steering angle is calculated, and a rear wheel angle position is a neutral position . the rear wheel steering angle target value is a neutral zone, that 3
When the vehicle is running straight, the start condition of the rear wheel steering angle control is
And, providing the motor drive control means for starting the output of the motor control current corresponding to the deviation of the rear wheel steering angle target value and rear wheel steering angle detected value to the electric motor.

That is, as shown in the claim correspondence diagram of FIG. 1, an electric motor a for controlling a rear wheel steering angle by driving by applying a motor control current, and a steering steering angle for detecting a measured steering angle and a neutral range. Detecting means b, rear wheel steering angle detecting means c for detecting a rear wheel steering angle, and rear wheel steering angle target value calculating means for calculating a rear wheel steering angle target value based on predetermined input information including the steering steering angle d, a steering rudder angle neutral position calculation judging means e for judging whether a steering rudder angle neutral position for keeping the straight running is calculated, and a rear wheel rudder judging whether the rear wheel rudder angle position is in the neutral position. Angle neutral position determining means f, rear wheel steering angle target value neutral area determining means g for determining whether the rear wheel steering angle target value is in a neutral area, neutral position of the steering wheel angle is calculated, and wheel steering angle position is in the neutral position, Wheel steering angle target value is a neutral zone, and
The start condition of the rear wheel steering angle control is determined when the vehicle is running straight ahead with the three conditions
And matter, and a motor drive control means h to start output of the motor control current corresponding to the deviation of the rear wheel steering angle target value and rear wheel steering angle detected value to the electric motor a.

[0011]

When the ignition is turned on, the steering angle neutral position calculating / judging means e determines the steering angle neutral position based on the actual measured steering angle and the detection value from the steering angle detecting means b for detecting the neutral region. It is determined whether or not the position has been calculated, and the rear wheel steering angle neutral position determining means f determines whether or not the rear wheel steering angle position is at the neutral position, and the rear wheel steering angle target value neutral area determining means g. It is determined whether the rear wheel steering angle target value from the rear wheel steering angle target value calculation means d is in the neutral range.

Then, in the motor drive control means h,
The neutral position of the steering angle is calculated, and the rear wheel angle position is the neutral position, and the rear wheel angle target value is the neutral range .
When the vehicle is running straight, the rear wheel steering angle control starts.
As a condition, the output of the motor control current corresponding to the deviation between the rear wheel steering angle target value and the rear wheel steering angle detection value from the rear wheel steering angle detection means c is started for the electric motor a.

Therefore, the rear wheel steering angle control is started at the time of straight running in which the three conditions of the neutral position calculation condition of the steering angle, the neutral position condition of the rear wheel angle position, and the neutral condition of the target rear wheel angle are satisfied. As a result, unnecessary current generation to the electric motor a at the start of the rear wheel steering angle control and a sudden change in the rear wheel steering angle are prevented.

[0014]

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

First, the configuration will be described.

FIG. 2 is an overall system diagram showing a vehicle to which the electric motor-driven four-wheel steering device according to the embodiment of the present invention is applied, and FIG. 3 is an electric rear wheel steering of the electric motor-driven four-wheel steering device according to the embodiment. FIG. 4 shows the mechanism, and FIG.
FIG. 2 is an electronic control system diagram centered on an S control unit.

In FIG. 2, 1 and 2 are front wheels, 3 and 4 are rear wheels, 5 is a mechanical front wheel steering mechanism, and 6 is an electric rear wheel steering mechanism.

The mechanical front wheel steering mechanism 5 increases a steering force input from a steering wheel 7 steered by a driver via a steering shaft 8 by a power steering (not shown), and increases the increased steering force to a rack shaft 9. Through the side rods 10 and 11 and the knuckle arms 12 and 13 to provide a steering angle to the front wheels 1 and 2.

The electric rear wheel steering mechanism 6 includes four
The rotational force of the high cas motor 15 (corresponding to the electric motor a) controlled by the motor output from the WS control unit 14 is transmitted to the worm 16 and the worm wheel 17.
And the rotational motion of the worm wheel 17 is converted into linear motion of the rack shaft 19 by meshing the gear portion of the pinion shaft 18 with the gear portion of the rack shaft 19, and the side rods 20, 21 and the knuckle arm are transferred from the rack shaft 19. Via the rear wheels 3,
4 to provide a steering angle.

The 4WS control unit 14 includes:
As shown in FIG. 4, the power supply circuit 14a and the sensor power supply circuit 1
4b, input interface 14c, CPU1, CPU
2, monitoring circuit 14d, D / A conversions 14e, 14f, 14
g, 14h, 14i, a CPU output monitoring circuit 14j, a relay output driver 14k, a motor output driver 14m, and a power steering solenoid output driver 14n.

The power supply circuit 14a includes a battery power supply directly from the battery 24 and an ignition switch 25.
The ignition power from is input.

The input interface 14c includes sensor signals from a rear steering angle main sensor 26 (corresponding to rear wheel steering angle detecting means c) and a rear steering angle sub-sensor 27 using a potentiometer, and a steering sensor 28 (steering steering angle detecting means). b), a sensor signal from the vehicle speed sensor 29, and switch signals from the stop lamp switch 30, the brake switch 31, and the inhibit switch 32. Here, the rear steering angle main sensor 26 is a sensor that detects the rotation amount of the pinion shaft 18, and the rear steering angle sub-sensor 27 is a sensor that detects the stroke amount of the rack shaft 19.

As shown in FIG. 6, the steering sensor 28 includes a sensor disk 28a fixed to the steering shaft 8, a slit 28b for detecting a steering angle formed in the sensor disk 28a, and a neutral position detecting sensor. A first optical sensor 28d and a second optical sensor 28e arranged at the position of the slit 28c and the steering angle detecting slit 28b.
And a third optical sensor 28f arranged at the position of the neutral position detecting slit 28c.

The relay output driver 14k receives the monitoring output from the monitoring circuit 14d and the warning valve output from the warning valve 33, and
Sends a high cas relay output to

The motor output driver 14m is driven by a motor power supply via a high cas relay 34,
A rear wheel steering angle command is input from PU1 via D / A converters 14g and 14h, and a motor output is sent to the high cas motor 15.

The power steering solenoid output driver 14
n inputs a power steering command from the CPU 1 via the D / A converter 14i, and sends a power steering solenoid output to the power steering solenoid 35.

Next, the operation will be described.

[Rear Wheel Steering Angle Control Operation] FIG. 5 is a flowchart showing the flow of the rear wheel steering angle control operation performed by the 4WS control unit 14, and each step will be described below.

Ignition switch 2 in step 50
The switching operation of the switch 5 from OFF to ON starts the processing described later.

In step 51, an initial check of the 4WS control unit 14 (for example, a CPU initial check) is performed.

In step 52, the relay output driver 1
The high cast relay 34 is driven by the output from 4k to secure the motor power.

In step 53, it is determined whether or not to execute the rear steering angle neutral position return processing based on the sensor value from the rear steering angle main sensor 26 (rear steering angle neutral position return position). (Corresponds to the determination means f)).

In step 54, when it is determined in step 53 that the rear steering angle neutral position is deviated and the rear steering angle neutral position return processing is to be performed, the motor 15 is driven until the rear steering angle neutral position return end determination is made. To return the rear steering angle to the neutral position.

The specific rear rudder angle neutral position return process is as follows.
Calculate the target value at the time of returning the rear steering angle neutral position every 0 msec,
This is performed by a slope process for applying a motor servo.
The determination of the end of the return of the rear steering angle neutral position is determined to be ended when the state where the sensor value from the rear steering angle main sensor 26 is in the neutral range continues for a predetermined time (360 msec) or more.

In step 55, it is determined whether or not the latest steering angle neutral value θcn as a reference of the steering angle θ has been calculated (corresponding to the steering angle neutral position calculating / determining means e).

The neutral steering angle neutral value θcn is
As shown in FIG. 7, the actual measured steering angle based on the pulse count of the sensor signals output from the first optical sensor 28d and the second optical sensor 28e, and output from the third optical sensor 28f as shown in FIG. It is calculated by another routine using the neutral range sensor signal according to the method described in Japanese Patent Application Laid-Open No. 2-299977.

In step 56, the rear steering angle target value δr is calculated based on the vehicle speed V and the steering angle θ, subject to the calculation of the steering angle neutral latest value θcn in step 55 (the rear wheel steering angle target value). (Equivalent to the calculating means d).

The rear steering angle target value δr is calculated, for example, according to a phase inversion control law that turns the rear wheels to the opposite phase at the beginning of turning and momentarily turns the rear wheels to the same phase.

In step 57, when it is determined in step 55 that the latest steering angle neutral value θcn has not been calculated, the rear steering angle target value δr is initialized.

In step 58, the following rear steering angle control start conditions are determined (corresponding to the rear wheel steering angle control start condition determination means c).

The conditions for starting the rear steering angle control are as follows:
km / h or more, and the rear steering angle target value δr is 0 ± 0.01.
After the degree is satisfied, the deviation between the target motor rotation angle and the neutral motor rotation angle becomes equal to or larger than a set value (corresponding to the rear wheel steering angle target value neutral range determining means g).

In step 59, if the condition of step 58 is satisfied or has already been satisfied, the vehicle speed becomes 2
The rear steering angle control end condition of whether the speed is equal to or less than km / h is determined.

In step 60, if the condition in step 59 is not satisfied, the motor control current is calculated by the following equation using the rear wheel steering angle deviation δε due to the difference between the rear steering angle target value δr and the rear steering angle sensor value δrSEN. The value IM is calculated.

IM = L.delta..epsilon.-m.d (.theta.M) + Kp L; proportional constant m; damping constant d (.theta.M); motor rotational angular velocity Kp; friction correction constant In step 61, the motor control by the motor control current value IM is performed. A current is output.

Steps 60 and 61 are as follows:
It corresponds to the motor drive control means h.

In step 62, if the rear steering angle target value δr has been initialized in step 57, step 58
If the rear steering angle control start condition is not satisfied in step 59, step 59
When the condition for terminating the rear steering angle control is satisfied, the motor control current is initialized.

In step 63, the output of the motor control current is prohibited.

At step 64, it is determined whether or not the ignition switch 25 is OFF or fail-safe is established. If No, the processing from step 55 is repeated.
Then, the rear steering angle control is prohibited.

[Rear wheel steering angle control start operation] When turning, the rear wheel steering angle is controlled in accordance with the rear wheel steering angle control operation shown in FIG. 5, but the rear wheel steering angle is focused on conditions other than the vehicle speed condition. The starting operation of the angle control will be described.

Determination step 53 in the flowchart of FIG.
, The condition that the rear steering angle is in the neutral position, and the steering steering angle neutral latest value θcn in the decision step 55
Are not calculated, and the output of the motor control current is not started unless both the condition that the rear steering angle target value δr in the determination step 58 is 0 ± 0.01 degrees is not satisfied. When the condition that the rear steering angle is in the neutral position is not satisfied, the rear steering angle neutral position is forcibly returned by the rear steering angle neutral position return process in step 54, and the rear steering angle neutral position is always returned before the determination in step 55 is started. It tries to create a situation that satisfies the neutral position condition of the rear rudder angle.

That is, in the system in which the rear wheels are steered using the electric motor, the rear wheel steering angle position is not automatically returned to the neutral position, and the motor control current I
As is apparent from the equation for calculating M, the motor control current value IM is calculated by feeding back the rear wheel steering angle position.

Therefore, when the control is started, the rear steering angle sensor value δrSEN is not at the neutral position, or the rear steering angle target value δr
If is not in the neutral range, unnecessary current is generated, and the rear wheel steering angle suddenly changes. If the neutral position of the steering angle θ is not calculated, the calculation accuracy of the rear steering angle target value δr calculated using the steering angle θ as input information is impaired, and the control accuracy is reduced.

On the other hand, if the output of the motor control current is not started unless all three conditions are satisfied as described above, unnecessary current to the motor 15 at the start of the rear wheel steering angle control is prevented. Can be prevented, and a sudden change in the rear wheel steering angle can be prevented.

When the rear wheel steering angle control is resumed during traveling, the rear wheel steering angle is restarted without judging the condition that the rear steering angle is in the neutral position. The steering angle target value always changes in the direction of the neutral position depending on the neutral range condition, and in addition, there is little discomfort during traveling.

[Rear Wheel Steering Angle Control Operation Based on Vehicle Speed Condition] During turning, the rear wheel steering angle is controlled according to the rear wheel steering angle control operation shown in FIG. The rear wheel steering angle control operation will be described focusing on the vehicle speed condition included in the control end condition.

First, the vehicle speed at the start condition of the rear steering angle control is 20.
km / h, and the vehicle speed under the rear steering angle control termination condition is 2 km / h. Hysteresis is provided in both vehicle speed conditions, and the output of the motor control current and the output stop are performed according to these conditions.

The meaning of this condition is that the rear steering angle control aiming at turning stability and turning response is effective only when the vehicle speed is increased to a certain extent at the start of running or the like. The vehicle speed at the start condition of the rear steering angle control is set to 20 km / h because sufficient stability can be achieved only by steering.

The vehicle speed at the end condition of the rear steering angle control is 2 km.
The reason for setting / h is that the rear steering angle control is continued until the vehicle speed is almost the same as the stopped state, so that the rear steering angle neutral position return process is not performed in step 54 as much as possible, and the rear steering angle neutral position is set when the next control is started. This is to ensure that the position is out.

Since hysteresis is provided for both vehicle speed conditions as described above, hunting in which the start and end of the control are repeated as in the case of the same vehicle speed at the start and end of the rear steering angle control is prevented. Control stability is ensured.

Further, when the vehicle starts running or after the rear wheel steering angle control is completed, other control start conditions such as a rear wheel steering angle neutral position condition and a rear wheel steering angle target value setting condition may be satisfied. Vehicle speed is 2
As long as the speed does not exceed 0 km / h, the motor control current to the motor 15 is not output, and the rear steering angle control start condition and the rear steering angle control end condition do not include the vehicle speed or are compared with the case where a certain low vehicle speed is used. Thus, the output time of the motor control current is greatly reduced, and the energy consumption is reduced.

Next, the effects will be described.

(1) In an electric motor-driven four-wheel steering system in which the rear wheel steering angle is controlled by the high-cass motor 15,
The start conditions of the motor drive control include a condition that the rear steering angle is at the neutral position and a steering latest steering angle neutral value θcn.
And the condition that the rear steering angle target value δr is 0 ± 0.01 degrees is set, and the motor drive control is not started if all three conditions are not satisfied. It is possible to prevent generation of unnecessary current to the high cas motor 15 at the start of the rear wheel steering angle control,
A sudden change in the rear wheel steering angle can be prevented.

(2) If the condition that the rear steering angle is at the neutral position is not satisfied when the ignition is turned on, the neutral position of the rear steering angle is forcibly executed immediately by the rear steering angle neutral position return processing without judging other conditions. Since the return is performed, the rear wheel steering angle control can be started as early as possible as long as other conditions are satisfied.

(3) In an electric motor-driven four-wheel steering system in which the rear wheel steering angle is controlled by the high-cass motor 15,
As a vehicle speed condition for starting and ending the motor drive control, a hysteresis for setting the start side to a high vehicle speed of 20 km / h and the end side to a low vehicle speed of 2 km / h is set, and performing motor drive control according to the vehicle speed condition. As a result, control stability against changes in vehicle speed can be ensured, and energy consumption can be reduced.

Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to the embodiment, and any changes or additions without departing from the spirit of the invention are included in the invention. It is.

[0066]

As described above, according to the present invention, the neutral position of the steering angle is calculated in the electric motor-driven four-wheel steering apparatus that controls the rear wheel steering angle by the electric motor. Straight ahead with the three conditions that the rear wheel steering angle position is the neutral position and the rear wheel steering angle target value is the neutral range
Motor driving control means for starting output of a motor control current according to a deviation between a rear wheel steering angle target value and a rear wheel steering angle detection value for an electric motor is provided as a start condition of rear wheel steering angle control when traveling. Therefore, an effect is obtained that unnecessary current generation to the motor and a sudden change in the rear wheel steering angle can be prevented at the start of the rear wheel steering angle control.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim showing an electric motor-driven four-wheel steering device of the present invention.

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

FIG. 3 is a diagram showing an electric rear wheel steering mechanism of the electric motor driven four-wheel steering device of the embodiment.

FIG. 4 is an electronic control system diagram centering on a 4WS control unit of the embodiment apparatus.

FIG. 5 is a flowchart illustrating a flow of a rear wheel steering angle control operation performed by a 4WS control unit of the embodiment device.

FIG. 6 is a diagram showing a steering sensor used in the embodiment device.

FIG. 7 is a waveform diagram of a sensor signal for detecting a steering angle.

FIG. 8 is a waveform diagram of a sensor signal for detecting a neutral position.

[Explanation of symbols]

 a electric motor b steering steering angle detecting means c rear wheel steering angle detecting means d rear wheel steering angle target value calculating means e steering steering angle neutral position calculating and judging means f rear wheel steering angle neutral position judging means g rear wheel steering angle target value Neutral area judgment means h Motor drive control means

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI B62D 113: 00 (58) Field surveyed (Int.Cl. ⁷ , DB name) B62D 6/00 B62D 5/04 B62D 7/14

Claims (1)

(57) [Claims] 1. An electric motor for controlling a rear wheel steering angle by driving by applying a motor control current, a steering angle detection means for detecting a measured steering angle and a neutral range, and a method for detecting a rear wheel angle. A wheel steering angle detecting means, a rear wheel steering angle target value calculating means for calculating a rear wheel steering angle target value based on predetermined input information including a steering steering angle, and a steering steering angle neutral position for maintaining straight traveling are calculated. Steering wheel neutral position calculation determining means for determining whether or not the rear wheel steering angle position is at the neutral position; rear wheel steering angle neutral position determining means for determining whether the rear wheel steering angle position is at the neutral position; A rear wheel steering angle target value neutral range determining means for determining whether or not the steering wheel steering angle neutral position is calculated, and the rear wheel steering angle position is a neutral position, and the rear wheel steering angle target value is a neutral range. Is ,
Start the rear wheel steering angle control when driving straight ahead with the three conditions
The condition, and characterized in that it comprises a motor drive control means for starting the output of the motor control current corresponding to the deviation of the rear wheel steering angle target value and rear wheel steering angle detected value to the electric motor Electric motor-driven four-wheel steering system.