JPH0569850A - Steering system for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To mechanically independently control front/rear wheel steering mechanisms of a four-wheel steering vehicle. CONSTITUTION:Front/rear wheel steering mechanisms 4, 5 are mechanically independently formed to control the rear wheel steering mechanism by a metering pump 32 driven by an electric motor 30 and constituted by providing a mode switching means 55 for switching a steering mode to front wheel steering and four-wheel steering, command means 8 for commanding steering of a rear wheel 3, steering angle detecting sensors 50, 51 for respectively detecting each steering angle of front/rear wheels and a control unit 7 for controlling the electric motor by inputs of these mode switching means, command means, steering angle detecting sensors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering system for a four-wheel steering vehicle.

[0002]

2. Description of the Related Art As a crane vehicle, a truck crane vehicle is known which has been developed from a crane mounting on a truck base. Many of these truck crane vehicles have a cab (carrier house) for general traveling and a crane house for crane work independently, have the same traveling performance as a general truck, and can be moved over a long distance. . In addition, since there are few restrictions on the crane body, it is possible to provide a large suspension capacity for the tonnage. On the other hand, a truck crane truck is difficult to enter a narrow alley due to the large size of the vehicle and the restriction of the steering system.It has poor mobility on rough terrain. There is a problem that it is inferior in maneuverability in the field such as not being able to take a large aperture angle.

On the other hand, there is known a rough terrain mobile crane which emphasizes mobility on site. In this rough terrain crane vehicle, the vehicle operation during traveling and the crane operation during crane work are performed in the same crane house, and further equipped with all-wheel drive function (4WD) and all-wheel steering function (4WS), In particular, the all-wheel steering function depends on the steering angle of the front wheels.
Moreover, since the minimum turning radius is made smaller by synchronizing the front wheels with the steering angle in-phase or anti-phase with the front wheels, the approach to a narrow alley or turning in a narrow place is frequent. It is extremely effective for the work to be performed on.

[0004]

However, the conventional steering system for an all-wheel steering vehicle has a complicated structure because the steering mechanism for the front wheels and the rear wheels is mechanically connected by a link mechanism or the like. As a result, the hydraulic circuit becomes complicated, a large number of hydraulic circuit parts and piping are required, assembly work is difficult, maintenance is also troublesome, and the steering system becomes expensive.

The present invention has been made in view of the above points, and an object of the present invention is to provide a steering system for a four-wheel steering vehicle in which the configuration of the steering control system for the rear wheels is simplified.

[0006]

In order to achieve the above object, according to the present invention, a front wheel steering mechanism and a rear wheel steering mechanism are mechanically independent, and the rear wheel steering mechanism is driven by an electric motor. A mode switching means that controls the steering mode by a ring pump to switch the steering mode between front wheel steering and four-wheel steering, command means that commands the steering of the rear wheels, and a steering angle detection sensor that detects each steering angle of the front wheels and the rear wheels. A control unit for controlling the electric motor by inputting these mode switching means, command means and each steering angle detection sensor.

[0007]

The control unit controls the electric motor to rotate normally or reversely or stop in response to the steering angle signals from the steering angle sensors for the front and rear wheels, and the signals from the mode switching means and the command means to make the rear wheels have the same phase as the front wheels. Period, reverse phase synchronization, or the rear wheels are controlled to be manually steerable independently of the front wheels. The steering mechanism for the rear wheels is controlled by a metering pump driven by an electric motor, and is mechanically completely independent of the steering mechanism for the front wheels.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows the overall configuration of a steering system for a four-wheel steering vehicle according to the present invention, FIG. 2 is an enlarged view of the entire steering mechanism of FIG. 1, and FIG. 3 shows the input / output relationship of the control unit of FIG. 1 and 2, the steering system 1
Is a steering mechanism 4 for the front wheels 2 and 2, a steering mechanism 5 for the rear wheels 3 and 3, a hydraulic control device 6 for controlling the steering mechanism 5, a control unit (C / U) 7, a switch box 8, a display box 9 and It is composed of various sensors described later.

The steering mechanism 4 for steering the front wheels 2, 2 is a power steering system. The input shaft of the power steering gear boss 11 is a steering shaft 12 and the output shaft of the power steering gear boss 11 is via a link 14 of one of the front wheels 2. The hydraulic control unit (not shown) connected to the arm 15 is connected to the oil passage 4
It is connected to the steering hydraulic pump 16 via 0 and 41.

The steering mechanism 5 for steering the rear wheels 3 and 3 includes a rear wheel steering hydraulic cylinders 22 and 23 and a rear lock mechanism 24.
(FIG. 2) and the like, and the cylinders 22 and 23 of these cylinder bottoms are mounted on the bracket 20a of the rear differential 20,
The tip of each rod has an arm 21, which supports the rear wheels 3, 3.
21 is connected to each end. Each of these hydraulic cylinders 22 and 23 has one port connected to the oil passage 44 and the other port connected to the oil passage 45.
A neutral control solenoid valve 26 is connected between the control valve 5 and the control valve 5.
Further, the rear lock mechanism 24 includes a rear lock solenoid valve 25.
It is locked or unlocked by (FIG. 1).

The hydraulic control device 6 includes an electric motor, that is, a DC
It includes a motor 30, a speed reducer 31, a metering pump 32, a rear wheel steering hydraulic pump 37, and the like.
The output shaft of the C motor 30 is connected to the input shaft of the metering pump 32 via the speed reducer 31. The input ports 32a and 32b of the metering pump 32 are connected to the rear wheel steering hydraulic pump 37 and the tank 38 via oil passages 42 and 43, respectively, and pressure adjustment is provided between these oil passages 42 and 43. The relief valve 39 of is connected. In addition, the discharge ports 32c and 32d of the metering pump 32.
Are connected to the oil passages 44 and 45 of the rear wheel steering mechanism 5.

The steering shuff 12 of the front wheel steering mechanism 4
There is a steering angle detection sensor 50 for detecting the steering angle, and a steering angle detection sensor 5 for detecting the steering angle of the rear wheel between the rear differential 20 and the arm 21 of the one rear wheel 3.
1 is provided, and a pressure switch 52 for detecting the hydraulic pressure supplied to the metering pump 32 is connected to the oil passage 42 of the hydraulic control device 6 downstream of the relief valve 31. The steering angle detection sensor 50, the steering angle detection sensor 51, and the pressure switch 52 are connected to the control unit 7.

As shown in FIGS. 1 and 3, the control unit (C / U) 7 has a vehicle speed sensor 53 on the input side and a transmission (T / M) gear stage (first speed, second speed, reverse, neutral, etc.). Gear position detection switch 54, front wheel steering (2WS), all-wheel steering (rear wheel in-phase synchronization 4WS-
1), all-wheel steering (rear wheel reverse-phase synchronization 4WS-2), all-wheel steering (rear wheel manual independent 4WS-3), and other push-button mode changeover switches 55, and rear wheels 3 independently. A seesaw type manual independent steering switch 56 for steering control, a forced neutral control switch 57 for forcibly controlling the rear wheels to a neutral position, a rear axle fixing switch 58 for fixing the rear wheel axle to the neutral position, and a rear axle A rear shaft fixed detection switch 59 and the like for detecting that the fixed shaft is fixed at the neutral position is connected. The mode changeover switch 55, the manual independent steering switch 56, and the forced neutral control switch 57 are arranged in the switch box 8 (FIG. 1) arranged in the cab.

On the output side of the control unit 7, a display box 9, a rear shaft fixing rear lock solenoid valve 25 provided in a rear lock mechanism 24 (FIG. 2), a neutral control solenoid valve 26, and a metering pump 32 are driven. DC motor 30, rear lock lamp 70, front wheel steering angle display indicator 71, rear wheel steering angle display indicator 72, buzzer 7
3, failure display lamp 74, 4WS-1 mode display lamp 75, 4WS-2 mode display lamp 76, 4WS-3 mode display lamp 77, etc. are connected. The rear lock lamp 70, the front wheel steering angle display indicator 71, the rear wheel steering angle display indicator 72, the buzzer 73, the failure display lamp 74, the mode display lamps 75 to 7777, etc.
It is located on the display boss 9 (FIG. 1). The control unit 7 controls the hydraulic control device 6 based on each input signal.
The DC motor 30 is driven to control the steering angle of the rear wheel 3.
As a result, the front wheel side and the rear wheel side are mechanically separated and completely independent.

The DC motor 30 has a changeover switch 47 and an emergency switch 48 in parallel with the control unit 7.
It is connected to the power supply via (FIG. 2). The changeover switch 47 switches the rotation direction of the DC motor 30, that is,
Common contact points c and f for forward or reverse rotation
Are respectively connected to the DC motor 30 (only one line is drawn in the figure), the contacts b and d are grounded, and the contacts a and e are grounded.
Is connected to one contact of the emergency switch 48, and the other contact of the emergency switch 48 is connected to the power supply.
The changeover switch 47 and the emergency switch 48 are arranged in the switch box 8. When an abnormality occurs in the control unit 7, the operator can manually drive the DC motor 30 to steer the rear wheels.

The vehicle is, for example, a rough terrain crane vehicle, and the control unit 7 has a low speed (for example,
All wheels steering (4WS-1 to 4WS-) at 20km / h or less)
3) The rear wheels 3 should be steered so that control is possible and a small turn at the work site is effective. Next, the operation will be described with reference to the flowcharts shown in FIG.

First, the control unit 7 clears the count value of the steering angle detecting sensor 50 to zero (step 2) when the key switch of the vehicle is operated and the power is turned on (step 1) in the main routine,
Next, shift to the sensor check routine (step 3)
Then, it is checked whether or not all the sensors have a failure (step 4), and if the determination result is negative (NO), that is, if all the sensors are normal, the mode changeover switch 55 is set to 4
It is determined whether or not the mode is switched to the WS-1 (in-phase synchronization) mode (step 5), and when the determination result is affirmative (YES), 4WS-1 control, that is, the rear wheels are synchronized in phase with the front wheels. The routine proceeds to the control routine (step 6) and returns to step 3.

When the answer in step 5 is negative (NO), that is, when the mode changeover switch 55 is changed over to a mode other than 4WS-1, the control unit 7 causes the mode changeover switch 55 to change to 4WS. -2
It is determined whether or not the mode is switched to the (reverse phase synchronization) mode (step 7), and when the determination result is affirmative (YES), 4WS-2 control, that is, the rear wheels are synchronously controlled in reverse phase with respect to the front wheels. Go to routine (step 10) and step 3
Return to.

Further, the determination result of step 7 is negative (NO).
When it is, the control unit 7 determines whether or not the mode is switched to the 4WS-3 (manual independent steering) mode (step 9), and when the determination result is affirmative (YES), the 4WS-3 control, that is, the front wheels 2 is performed. In contrast, the rear wheel 3 is manually and independently steerable (step 10) and returns to step 3, and when negative (NO), 2WS, that is, a steering control routine of only the front wheel is performed (step 1).
1) Then, return to step 3.

Further, the control unit 7 displays the sensor failure (step 1 if the determination result in step 4 is affirmative (YES), that is, if any of the sensors has a failure.
2) is performed, and the failure display lamp 74 of the display box 9
(FIG. 3) is turned on, the steering angle control of the rear wheels is forcibly prohibited, and the routine proceeds to the steering control routine of only the front wheels (forced 2WS) (step 13).

Next, 2WS (front wheel steering), 4WS-1
Each control of (rear wheel in-phase synchronization) and 4WS-2 (rear wheel anti-phase synchronization) will be described. When the steering wheel 13 shown in FIG. 1 is operated to the right, for example, the steering shaft 12 rotates to the right, and hydraulic pressure is supplied from the hydraulic pump 16 to the hydraulic control unit of the power cylinder 11 accordingly. The power cylinder 11 operates to rotate the left and right arms 15 and 15 to the right and steer the front wheels 2 and 2 to the right. The steering angle detection sensor 50 detects the rotation direction and the rotation amount of the steering shaft 12 and outputs a corresponding steering angle signal. The control unit 7 drives the front wheel steering angle display indicator 71 of the display box 9 by the signal from the steering angle detection sensor 50 to display the steering angle of the front wheels 2.

The control unit 7 does not drive the DC motor 30 and holds the spool 33 (FIG. 2) of the metering pump 32 at the neutral position when the mode selector switch 55 is switched to the 2WS (front wheel steering) mode. Then, the rear lock mechanism 24 is locked. As a result, the rear wheels 3 and 3 are fixed to the neutral position, and only the front wheel 2 is steered. Further, the rear wheel steering angle display indicator 72 displays the steering angle 0 of the rear wheels 3.

When the mode selector switch 55 is switched to the 4WS-1 (rear wheel in-phase synchronization) mode, the control unit 7 displays the 4WS- of the display box 9 (FIG. 1).
The 1st mode display lamp 75 is turned on and the neutral control solenoid valve 26 is closed to disconnect the communication between the oil passages 44 and 45, and the rear lock solenoid valve 25 is driven to drive the rear lock mechanism 2
Unlock 4 When the steering wheel 13 is operated to the right, the control unit 7
Responds to a signal input from the steering angle detection sensor 50 to rotate the DC motor 30 in the forward direction to drive the metering pump 32 and move the spool 32 to the right in FIG. As a result, hydraulic pressure is supplied through the oil passage 45, the cylinders 22 and 23, and the oil passage 44 of the rear wheel steering mechanism 5, the cylinder 22 extends, and the cylinder 23 shortens to cause the arm 2 to move.
1, 21 are rotated to the right in the figure, and the rear wheels 3, 3 are steered to the right.

The rudder angle detection sensor 51 detects the rudder angle of the rear wheels 3 and 3 and applies a corresponding signal to the control unit 7 as a feedback signal. Control unit 7
Accurately controls the steering angle of the rear wheel 3 by the feedback signal from the steering angle detection sensor 51 and the signal from the steering angle detection sensor 50. As a result, the rear wheels 3 are in-phase controlled in synchronization with the front wheels 2. Further, the control unit 7 uses the signals input from the steering angle detection sensor 50 and the steering angle detection sensor 51 to display the display box 9
The front wheel rudder angle display indicator 71 and the rear wheel rudder angle display indicator 72 are driven to steer the front wheel 2 and the rear wheel 3.
The rudder angle of is displayed.

Further, the mode selector switch 55 is set to 4WS-
When switched to the 2 (reverse phase synchronization) mode, the control unit 7 displays the 4WS of the display box 9 (FIG. 1).
The -2 mode display lamp 76 is turned on and the neutral control solenoid valve 26 is closed to cut off the communication between the oil passages 44 and 45, and the rear lock solenoid valve 25 is driven to unlock the rear lock mechanism 24. When the steering wheel 13 is operated to the right, the control unit 7
2 rotates the DC motor 30 in reverse according to the signal input from the steering angle detection sensor 50 to drive the metering pump 32 and move the spool 32 leftward in FIG. As a result, hydraulic pressure is supplied from the oil passage 44 of the rear wheel steering mechanism 5 to the cylinders 22, 23 and the oil passage 45,
The cylinder 22 is shortened, the cylinder 23 is extended, the arms 21, 21 are rotated leftward in the figure, and the rear wheels 3, 3 are steered to the left.

The steering angle detection sensor 51 detects the steering angles of the rear wheels 3 and 3 and applies a corresponding signal to the control unit 7 as a feedback signal. Control unit 7
Accurately controls the steering angle of the rear wheel 3 by the feedback signal from the steering angle detection sensor 51 and the signal from the steering angle detection sensor 50. As a result, the rear wheel 3 is reverse-phase controlled in synchronization with the front wheel 2. Further, the control unit 7 uses the signals input from the steering angle detection sensor 50 and the steering angle detection sensor 51 to display the display box 9
The front wheel rudder angle display indicator 71 and the rear wheel rudder angle display indicator 72 are driven to steer the front wheel 2 and the rear wheel 3.
The rudder angle of is displayed.

Further, the changeover mode switch 55 is 4WS-
When the mode is switched to the 3 (manual independent) mode, the control unit 7 displays 4W of the display box 9 (FIG. 1).
The S-3 mode display lamp 77 is turned on and the rear wheels are steered according to the switching position of the manual independent steering switch 56. For example, when the manual independent steering switch 56 is operated in the “right” direction, the control unit 7 causes the DC motor 3 to operate.
Spool 3 of metering pump 32 by rotating 0 forward
4 is moved to the right in FIG. As a result, the cylinder 22 of the rear wheel steering mechanism 5 is extended, the cylinder 23 is shortened, the arms 21, 21 are rotated rightward, and the rear wheels 3, 3 are steered to the right. When the manual independent steering switch 56 is returned to the neutral position, the DC motor 30 is stopped and the rear wheel 3
Is held at the steering angle.

On the contrary, when the manual independent steering switch 56 is operated in the "left" direction, the control unit 7 causes the DC motor 30 to rotate in the reverse direction and the metering pump 32.
2 is moved to the left in FIG. As a result, the cylinder 22 of the rear wheel steering mechanism 5 is shortened, and the cylinder 2
3 is extended to rotate the arms 21, 21 to the left, and the rear wheels 3, 3 are steered to the left.

Next, the control in the 4WS-3 (rear wheel manual independent) mode will be described in detail with reference to the flowchart shown in FIG. First, in the 4WS-3 (rear wheel manual independent) mode, the control unit 7 determines whether the vehicle speed exceeds a predetermined vehicle speed, for example, 20 km / h (step 20), and the determination result is affirmative (YES). ), That is, when the vehicle speed exceeds 20 km / h, the front wheel steering (forced 2WS) control is forcibly made (step 21) and only the front wheel steering is performed, and the rear wheel steering is not performed. This is because the behavior of the vehicle becomes unstable if the rear wheels are steered when the vehicle speed is 20 km / h or more.

The control unit 7 executes step 20.
Is negative (NO), that is, when the vehicle speed is 20 km / h or lower, it is further determined whether or not the transmission gear position is in the third speed or higher (step 22), and the positive answer (YES) is obtained. Sometimes it is judged that the vehicle speed exceeds 20 km / h and the process proceeds to step 21. When the result is negative (NO), that is, when the gear is in the 1st, 2nd, neutral or reverse position, the vehicle speed is 20km / h or less. Alternatively, it is determined that the vehicle is stopped, and the steering angle detection sensor 51 of the rear wheel 3 (FIG. 1)
The steering angle of the rear wheel 3 is determined by a signal from
It is determined whether the angle is smaller than 20 ° (step 23).

The control unit 7 proceeds to step 23.
If the answer is YES, then it is determined whether the forced neutral control switch 57 (FIG. 3) is on or off (step 2).
4) When the switch is off, it is determined that the rear wheels 3 are in a state where they can be steered manually, and it is determined whether or not the manual independent steering switch 56 (FIG. 3) is operated in the “left” direction ( Step 25). Then, when the answer in step 25 is affirmative (YES), the control unit 7 rotates the DC motor 30 (FIG. 2) in the reverse direction (step 2).
6) Then, the rear wheel 3 is steered to the left.

At the same time, the control unit 7 calculates the steering angle of the front wheels 2 based on the signal input from the steering angle detection sensor 51 (step 27), and calculates the steering angle of the rear wheels 3 based on the signal from the steering angle detection sensor 51. (Step 28) Then, the steering angle of the front wheel 2 and the steering angle of the rear wheel 3 are displayed on the front wheel steering angle display indicator 71 and the rear wheel steering angle display indicator 72 of the display box 9, respectively (step 29).

The driver detects the turning angle of the rear wheels while looking at the rear wheel steering angle display indicator 72, and returns the manual independent steering switch 56 to the neutral position when the desired turning angle is reached. When the manual independent steering switch 56 is returned to the neutral position, the control unit 7 stops the DC motor 30 and holds the rear wheels 3 at the turning angle. When the answer in step 25 is negative (NO), the control unit 7
Determines whether or not the manual independent steering switch 56 is operated in the “right” direction (step 30), and when the determination result is affirmative (YES), rotates the DC motor 30 (FIG. 2) forward (step 31). ) To steer the rear wheels 3 to the right and proceed to step 27. When the determination result in step 30 is negative (NO), that is, when the manual independent steering switch 56 is in the neutral position, the DC motor 30 is turned on. It is stopped (step 32) and the process proceeds to step 27.

The control unit 7 stops the DC motor 30 (step 32) when the answer in step 23 is negative (NO), that is, when the steering angle of the rear wheels is larger than 20 °. The process proceeds to step 27 while keeping the rear wheel 3 at the current steering angle. At this time, the driver can know that the steering angle of the rear wheel 3 is larger than 20 ° by the rear wheel steering angle display indicator 72 of the display box 9.

By the way, when the mode changeover switch 55 is controlled by being switched to the 4WS-3 (rear wheel independent steering) mode, for example, the vehicle body is likely to contact the wall surface and the rear wheel 3 is forced to the neutral position. It may be necessary to return it quickly. In such a case, the operator operates the forced neutral control switch 57 to turn it on. The control unit 7 gives a positive answer to the determination in step 24 (YE
In S), that is, when the forced neutral control switch 57 is on, the current turning direction of the rear wheels 3 is detected based on the input signal from the steering angle detection sensor 51, and DC is applied to return the rear wheels 3 to the neutral position. Calculate the rotation direction of the motor 30 (step 3
3) At the same time, the duty ratio of the voltage applied to the DC motor 30 is calculated (step 34), and the DC motor 30 is normally or reversely rotated (step 35) based on the calculation result to move the rear wheel 3. Return to neutral position. The control unit 7 determines whether the rear wheel 3 has returned to the neutral position based on the signal from the steering angle detection sensor 51 (step 3).
6) If the answer is YES (YES), the DC motor 30 is stopped (step 32), and if the answer is NO (NO), the control is continued. This forces the rear wheels to return to the neutral position.

Further, when the steering angle of the rear wheels 3 is manually controlled independently, the cutting angular velocity of the rear wheels is set according to the vehicle speed, that is, it is faster at low speed and slower as vehicle speed increases. It is preferable that the behavior of (1) does not violate the driver's will and the turning performance is improved. Therefore, such control will be described with reference to the flowchart of FIG.

The control unit 7 determines whether or not the vehicle speed exceeds a predetermined vehicle speed, for example, 20 km / h (step 40), and when the answer is YES (YES), that is,
When the vehicle speed exceeds 20 km / h, the front wheel steering (forced 2WS) control is forcibly transferred (step 41) and only the front wheel steering is performed, and the rear wheel steering is not performed. The control unit 7 determines that the answer to step 40 is negative (NO), that is,
When the vehicle speed is 20 km / h or less, it is determined whether or not the transmission gear is in the third or higher speed position (step 4).
2) If the answer is YES, then go to step 41. If the answer is NO, NO, that is, the gear is 1.
When the vehicle is in the second speed, the second gear, the neutral position, or the reverse position, it is determined whether or not the steering angle of the rear wheel 3 is smaller than a predetermined steering angle, for example, 20 ° by a signal from the steering angle detection sensor 51 (FIG. 1) (step 43). ) Do.

The control unit 7 proceeds to step 43.
When the answer to the question (4) is affirmative (YES), the duty ratio of the voltage applied to the DC motor 30 is calculated (step 44). This duty ratio is large at low speed and becomes smaller as the vehicle speed increases. For example, as shown in FIG. 7, the maximum value 100% decreases from a maximum value of 100% as shown in FIG. When the value exceeds, a constant value A% is set.

Next, the control unit 7 determines whether or not the manual independent steering switch 56 (FIG. 3) is operated to the left (ON) (step 45), and the determination result is affirmative (YES). Sometimes DC motor 30 (Fig. 2)
Is reversely rotated with the voltage having the duty ratio calculated in step 44 (step 46), and the rear wheel 3 is steered to the left so as to be fast at low speed and slow as vehicle speed increases. At the same time, the control unit 7 calculates the steering angle of the front wheels 2 from the signal from the steering angle detection sensor 50 (step 47), and calculates the steering angle of the rear wheels 3 from the signal from the steering angle detection sensor 51 (step 4).
8) Then, the front wheel steering angle display indicator 71 indicates the steering angle of the front wheel 2, and the rear wheel steering angle display indicator 72 indicates the rear wheel 3.
The steering angle of is displayed (step 49).

Further, the determination result of step 45 is negative (N
When it is O), the control unit 7 determines whether or not the manual independent steering switch 56 is operated to the right (ON) (step 50), and the determination result is affirmative (YE).
In S), the DC motor 30 is positively rotated (step 51) with the voltage having the duty ratio calculated in step 44,
The rear wheel 3 is steered to the right in such a manner that the rear wheel 3 is steered at a low speed and is slowed as the vehicle speed increases, and the routine proceeds to step 47.
When the answer to the step 50 is negative (NO), that is, when the manual independent steering switch 56 is returned to the neutral position, the control unit 7 stops the DC motor 30 (step 52) and proceeds to step 47.

When the answer to the step 43 is negative (NO), that is, when the steering angle of the rear wheels is larger than 20 °, the DC motor 30 is stopped (step 52) to move the rear wheels 3 to the present steering angle. With the corner held, proceed to step 47. The control unit 7 is composed of a complicated electronic circuit, and there is a possibility that an abnormality may occur for some reason and the steering of the rear wheels becomes impossible. Therefore, particularly when an abnormality occurs in the control unit 7 during steering of the rear wheels, it is necessary for the operator to manually return the rear wheels to the neutral position.

When an abnormality occurs in the control unit 7 itself, the control unit 7 drives the buzzer 73 (FIG. 3) of the display box 9 (FIG. 1) to generate an alarm and turn on the failure lamp 74 to operate. Inform the person. In this emergency, the driver detects whether the rear wheel 3 is being steered by the rear wheel steering angle display indicator 72 of the display box 9 to detect the DC of the hydraulic control device 6.
It is determined whether the rotation direction of the motor 30 should be rotated forward or reverse to return to the neutral position, the changeover switch 47 is switched to the normal rotation position or the reverse rotation position, and then the emergency switch 48 (Fig. 2) is turned on. For example, when the changeover switch 47 is changed over as shown by a solid line in FIG. 2, a current flows through a path of power source → contact a → contact c → DC motor 30 → contact f → contact d → ground, and DC.
The motor 30 rotates forward. On the contrary, when the switching switch 47 is switched as shown by the dotted line, the current is changed from the power source to the contact point e to
The flow of the contact f → DC motor 30 → contact c → contact b → ground flows, and the DC motor 30 rotates in the reverse direction.

The operator judges that the rear wheel 3 has returned to the neutral position by the rear wheel steering angle display indicator 72 of the display box 9, or the rear wheel 3 has returned to the neutral position according to the information from the guide outside the vehicle. When this is known, the emergency switch 48 is turned off. As a result, even if the control unit 7 becomes abnormal, the operator can manually return the rear wheel 3 to the neutral position.

The driver turns on the rear axle fixing switch 58 (FIG. 3) after returning the rear wheels 3 to the neutral position. When the rear shaft fixing switch 58 is turned on, the control unit 7 urges the rear lock solenoid valve 25 to fix the rear lock mechanism 24 and fix the rear shaft to the neutral position. When the rear shaft is fixed at the neutral position, the rear shaft fixed detection switch 59 (FIG. 3) detects this and outputs a signal. The control unit 7
When the signal from the rear shaft fixing detection switch 59 is input, the rear lock solenoid valve 25 is deenergized. As a result, the rear wheels 3 are fixed in the neutral position, and thereafter the vehicle is steered by the front wheels (2 W
S).

When the rear wheel 3 is steered manually, the steered speed needs to be slowed down to some extent in order to make a fine angle adjustment. Therefore, DC is used when the rear wheels 3 are steered in synchronization with the steering angle of the front wheels 2 and when the rear wheels are steered by the manual independent steering switch 56.
The duty ratio of the motor 30 is changed to change the steering speed. When the rear wheels 3 are manually steered, the voltage applied to the DC motor 30 is duty-controlled, and the duty ratio is set to, for example, the maximum steered speed.
Make it 50%.

In the control unit 7, the mode selector switch 55 is switched to the 4WS-3 (manual independent steering) mode, and as shown in the flowchart of FIG. When turned on (step 55), the voltage applied to the DC motor 30 is set to a duty ratio of 50% (step 56), and the rotation speed of the DC motor 30 is reduced to 1/2 of the maximum rotation speed. Along with this, the metering pump 3 of the hydraulic control device 6
The rotation speed of No. 2 becomes low (1/2 of the maximum), and the amount of oil supplied to each hydraulic cylinder 22, 23 of the steering mechanism 5 of the rear wheel 3 becomes small. The hydraulic cylinders 22 and 23 operate according to the hydraulic pressure supplied from the metering pump 32, and the rear wheel 3
Steering (step 57). The steered speed at this time becomes 1/2 of the maximum steered speed, and the rear wheels 3 are slowly steered.

The rear wheels 3 are steered to a desired steering angle, and the operator turns off the manual independent steering switch 56 (step 5).
8) Then, the control unit 7 turns on the DC motor 3
0 is stopped (step 59). As a result, the metering pump 32 is stopped, and the hydraulic cylinders 22 and 23 of the steering mechanism 5 of the rear wheel 3 are stopped at that position and the steering angle is maintained. Thereby, the operator can easily adjust the steering angle of the rear wheel 3 to a delicate angle according to the situation at the site.

Further, in the vehicle, the centrifugal force at the time of turning becomes very large as the vehicle speed increases, and the lateral G (force acting in the lateral direction) also increases accordingly. Particularly, in a low-speed all-wheel steering vehicle, when both the front wheels and the rear wheels are steered largely, there is a risk that the stability may be lost when the vehicle speed becomes 20 km / h or more. Therefore, it is necessary to set a limit that gradually reduces the maximum turning angle of the rear wheels when the vehicle speed exceeds a certain speed.

The control unit 7 detects the steering angle of the rear wheel 3 by the input signal from the steering angle detection sensor 51 of the rear wheel as shown in the flowchart of FIG. 9 (step 60).
At the same time, the vehicle speed is detected by the input signal from the vehicle speed sensor 53 (step 61), and it is determined whether or not the steering angle of the rear wheel at this time is equal to or larger than the maximum steering angle at the detected vehicle speed (step 62). To do.

The relationship between this vehicle speed and the maximum turning angle of the rear wheels is
For example, it is set as shown in FIG. That is, the steering angle of the rear wheels, the maximum turning angle from the vehicle speed 0 to V ₁ (ma
It is possible to steer at x), and the vehicle speed gradually decreases in a substantially linear manner from V ₁ to V ₂ (> V ₁ ). V ₂ For example, 20 km
It is set to 0 when / m is exceeded. This relationship is set in the map, and the maximum turning angle is selected according to the vehicle speed and the maximum turning angle is limited.

The control unit 7 proceeds to step 62.
Is negative (NO), that is, the steering angle of the rear wheels is
When it is smaller than the maximum steering angle at the vehicle speed, the steering control of the rear wheels is enabled as it is, and when the determination is affirmative (YES), the steering angle of the rear wheels is returned to the maximum steering angle or less (step 63). Such steering restriction is performed in both the in-phase mode and the anti-phase mode of the rear wheels. In this way, when the vehicle speed becomes higher than a certain speed, the maximum turning angle of the rear wheels is restricted so as to be gradually reduced, so that the stability during turning of the vehicle is secured.

When the vehicle speed exceeds a certain speed, for example, 20 km / h, the control unit 7 restricts the vehicle speed to prohibit the rear wheels from being steered, and once the vehicle speed is restricted, the vehicle is stopped. Rear wheel steering is prohibited. This is because in a low-speed all-wheel steering vehicle, when the vehicle travels at a high speed in the all-wheel steering mode and the vehicle speed is limited and then decelerates and turns, the vehicle speed becomes less than the speed limit and the rear wheels are steered suddenly. This is to prevent such instability because the behavior becomes unstable.

The control unit 7 detects the vehicle speed of the vehicle as shown in the flowchart of FIG. 11 (step 65) and determines whether the vehicle speed is lower than the speed limit (20 km / h) (step 66). However, when the answer is NO (NO), steering of the rear wheels is prohibited (step 67).
At the same time, the flag is set (step 68) and the control is repeated. That is, when the vehicle speed exceeds the limit vehicle speed of 20 km / h, steering of the rear wheels is prohibited.

Further, the determination result of step 66 is affirmative (YE
In S), the control unit 7 has a vehicle speed of 0.
That is, it is determined whether or not it is stopped (step 69),
When the answer is YES (YES), the flag is reset (step 70), and then it is determined whether the flag is 0 or 1 (step 71), that is, the steering of the rear wheels is prohibited or released. When the flag is 0, that is, when the vehicle is stopped, the rear wheels can be steered (step 72). When the flag is 1 (NO), that is, when the flag is 1, the rear wheels are turned on. Steering is prohibited (step 74). That is, when the rear wheels are once prohibited from being steered beyond the vehicle speed limit, the prohibition of rear wheels from being steered is not released until the vehicle is temporarily stopped.

However, if the vehicle speed is once restricted, that is, if the rear wheel steering angle is prohibited by exceeding the vehicle speed limit, it may be inconvenient if all wheels cannot be steered until the vehicle stops. Therefore, the rear wheels can be steered only under a specific condition, for example, when the driver operates the mode changeover switch 55 or the manual independent steering switch 56 to recognize all-wheel steering.

The control unit 7 goes to step 69.
Is negative (NO), that is, when the vehicle is running at the vehicle speed limit (20 km / h) or less after the vehicle speed limit is once applied, the mode switching switch 55 or the manual independent steering switch 5
It is determined whether or not 6 is operated and the switch is turned on (step 73), and when the determination result is affirmative (YES), that is, the driver operates the mode changeover switch 55 or the manual independent steering switch 56. Then, under the specific condition that the steering of all the wheels is recognized, the rear wheels can be steered and the flag is reset (step 70), and if negative (NO), the routine proceeds to step 71. When the flag is determined to be 0 in step 71, that is, when the specific condition is satisfied, the rear wheels can be steered (step 72), and when it is determined to be 1, that is, the condition other than the specific condition is satisfied. At times, steering of the rear wheels is prohibited (step 74).

In addition, the rear wheels 3 (FIG. 1) may be steered while running in a state where all the wheels are steered, for some reason, for example, hitting a curb or falling into a groove to overload the rear wheels 3. If the hydraulic pressure is supplied to the hydraulic cylinder to steer the vehicle when it disappears, the hydraulic pressure rises, and an excessive load acts on the linkage and the like of the rear wheel steering mechanism 5 (FIG. 2). Therefore, in such a case, the supply of hydraulic pressure to the hydraulic cylinder is stopped to stop the steering of the rear wheels, and thereafter the steering of the rear wheels is prohibited until the vehicle travels for a certain distance.

The control unit 7 controls the steering angle detection sensor 51 for the rear wheels 3 as shown in the flow chart of FIG.
The steering speed of the rear wheels is detected by the signal input from (FIG. 2) (step 80), and it is determined whether the steering speed is slower than normal (step 81). When the answer is negative (NO), the DC motor 30 (FIG. 2) is operated (step 82) to drive the metering pump 32, and hydraulic pressure is supplied to the hydraulic cylinders 22 and 23 of the rear wheel steering mechanism 5 (step 83). ) To enable the steering of the rear wheels 3 (step 84).

The control unit 7 proceeds to step 81.
If the answer is YES (YES), that is, if it is determined that the turning speed of the rear wheels 3 is slower than in the normal case, the DC motor 30 is stopped (step 85), and the steering mechanism 5 for the rear wheels is turned off. The supply of hydraulic pressure to the hydraulic cylinders 22 and 23 is stopped, and the hydraulic pressure is temporarily fixed to the turning angle to prevent an excessive load from being applied to the linkage and the like. Then, the driver moves forward or backward while keeping the rear wheels fixed at the turning angle.

Next, the control unit 7 determines whether or not the vehicle has traveled a certain distance (step 86).
When the answer is YES (YES), that is, when the vehicle moves, it is determined that the overload on the rear wheels has been eliminated, and the steering control of the rear wheels is restarted (step 87), and the negative ( If NO, it is determined that the overloaded state of the rear wheels has not been released, and steering control of the rear wheels is prohibited (step 88). In order to escape from such an overloaded state, it may be effective to steer the rear wheels in the opposite direction. Therefore, the control unit 7 enables steering control by manual steering in a direction opposite to the current steering angle in which the rear wheels are in an overloaded state.

By the way, in order to drive the hydraulic cylinders 22 and 23 (FIG. 2) of the rear wheel steering mechanism 5, it is necessary to supply a predetermined hydraulic pressure. For this purpose, a hydraulic pressure source driven by the engine of the vehicle concerned. That is, the rear wheel steering hydraulic pump 37
(Fig. 2) needs to be driven normally. Therefore, in order to determine whether the engine of the vehicle is rotating, it is necessary to detect the number of rotations of the engine and input the signal to the control unit 7.

However, in the steering system, in order to use the engine rotation sensor to input the engine rotation signal to the control unit 7 due to its configuration, it is not necessary to newly provide the engine rotation sensor, and the electric circuit is also provided. Is also complicated. Therefore, a pressure switch is provided on the hydraulic pressure source so that a failure of the hydraulic pressure source can be diagnosed relatively easily without using an engine rotation sensor.

As shown in the flow chart of FIG. 13, the control unit 7 takes in a signal from the pressure switch 52 (FIG. 2) when giving a steering command to the rear wheels (step 90), and the output signal of the pressure switch 52 is It is determined whether it is on or off (step 91). This pressure switch 52
Turns on when the hydraulic pressure supplied to the oil passage 42 is a predetermined pressure, and turns off when the hydraulic pressure is lower than the predetermined pressure. When the pressure switch 52 is turned on in step 91, the control unit 7 determines that the hydraulic pump 37 is normally driven, that is, the engine is rotating normally, and there is no abnormality in the hydraulic power source. When the pressure switch 52 is off, that is, when the hydraulic pressure discharged from the hydraulic pump 37 is low and the hydraulic pressure in the oil passage 42 is low, the vehicle speed signal input from the vehicle speed sensor 53 determines whether the vehicle speed of the vehicle is present. Is determined (step 92).

When it is determined in step 92 that the vehicle speed is not present, that is, the vehicle is stopped, the control unit 7 determines that the engine is also stopped and repeats the determination. That is, when the steering command is issued from the control unit 7 and the oil pressure does not rise, there is a possibility of erroneous diagnosis if the engine is not rotating, and when the vehicle speed signal is not input, the failure diagnosis of the oil pressure source is temporarily suspended. Control unit 7 is step 2
When it is determined that the vehicle speed is present in No. 2, it is determined that there is an abnormality in the hydraulic pressure source (step 93), and the display box 9
The failure display lamp 74 (FIG. 1) is turned on to notify the driver that an abnormality has occurred in the hydraulic pressure source. This means that the hydraulic pressure of the oil passage 42 supplied to the metering pump 32 is low, and the vehicle speed is still present even when the hydraulic switch 52 is off, and the hydraulic pump 37, the relief valve 39, or the like is abnormal. If there is.

By the way, when the steering system fails, the failure indicator lamp is turned on to inform the driver, where the failure has occurred, and whether the driver can drive or not. Can effectively deal with failures. So, in this steering system,
The control unit 7 has a failure diagnosis function, and if the DC motor 30 that drives the metering pump 32, the rear lock mechanism 24 (FIG. 2), etc. that directly affects the rear wheel steering control fails, the vehicle cannot run. That is,
When the sensors are out of order, the driver is warned and the driver is informed that traveling is possible or impossible. The display at the time of the failure will be described with reference to the flowchart of FIG.

In the sensor check routine, the control unit 7 diagnoses whether or not the sensor of the steering system has failed (step 100). When the determination result is negative (NO), the diagnosis is repeated and affirmative (Y).
ES), that is, when any sensor failure occurs, it is determined whether or not the steering angle detection sensor 51 that detects the steering angle of the rear wheels is normal (step 101), and the determination result is affirmative (step 101). YES) That is, when there is no failure, it is determined whether or not the DC motor 30 that drives the metering pump 32 is normal (step 102).

The control unit 7 performs step 10
The determination answer of 2 is affirmative (YES), and the steering angle detection sensor 5
When the signal is input from 1 and the rear wheels 3 are steered, the DC motor 30 is driven to return the rear wheels 3 to the neutral position (step 103). When the rear wheel 3 returns to the neutral position, the rear lock mechanism 24 locks the rear wheel 3 at the neutral position. Next, the control unit 7 determines whether or not it is locked at the neutral position by the signal from the rear axle fixed detection switch 59 (FIG. 3) (step 104). If the determination result is affirmative (YES), it is displayed. The rear lock lamp 70 of the box 9 (FIG. 1) is turned on (step 105) and the failure display lamp 74 is turned on (step 106). In this way, when the rear wheel 3 is returned to the neutral position and fixed, normal traveling is not affected and traveling is possible. Therefore, the driver can determine that the vehicle can be driven by front wheel steering (2WS) when the rear lock-on lamp 70 of the display boss 9 is lit and the failure display lamp 74 is lit.

Further, the determination result of step 102 is negative (N
O), that is, when the DC motor 30 is out of order, the metering pump 32 cannot be driven, and therefore, when the rear wheels 3 are steered, it is impossible to return to the neutral position. Is. At this time, the control unit 7 determines that the vehicle cannot run and turns on the failure display lamp 74. Similarly, if the answer to step 104 is negative (NO), that is, if the rear shaft cannot be locked at the neutral position, the control unit 7 determines that the vehicle cannot run and turns on the failure indicator lamp 74 (step 107). Therefore, when the failure display lamp 74 is turned on, the driver can directly drive the steering mechanism 5 for the rear wheels,
Alternatively, it is determined that the rear lock mechanism 24 that locks the rear shaft to the neutral position is out of order, and the vehicle is immediately stopped when the vehicle is running.

The control unit 7 performs step 10
When the determination result of 1 is negative (NO), that is, when the steering angle detection sensor 51 of the rear wheel is out of order (for example, the wire is broken),
The failure display lamp 74 of the display box 9 is blinked (step 108). The driver determines that the steering angle detection sensor 51 has a failure when the failure display lamp 74 is blinking, and sets the mode changeover switch 55 to 4WS-3.
(Rear wheel manual independent steering) mode is switched, the current turning direction of the rear wheels 3 is confirmed, and the manual independent steering switch 56 (FIGS. 1 and 3) is operated to the right or left, or the changeover switch 4 is operated.
7 and the emergency switch 48 (FIG. 2) are operated (step 10).
9) Then, the rear wheels are returned to the neutral position (step 110).

The control unit 7 determines whether or not the rear lock mechanism 24 has locked the rear shaft at the neutral position after the rear wheel 3 is returned to the neutral position, based on the signal from the rear shaft fixed detection switch 59 (step 111). If the determination is negative (NO), that is, if the rear wheels are not locked at the neutral position, the failure display lamp 74 is turned on (step 107). The driver determines that the rear lock mechanism 24 has a failure when the failure display lamp 74 is lit, and immediately stops the vehicle when the vehicle is running.

Further, the determination result of step 111 is affirmative (Y
In the case of ES), that is, when the rear lock mechanism 24 locks the rear shaft to the neutral position, the rear lock lamp 70 of the display box 9 is turned on (step 112), and the failure display lamp 74 is turned on (step 113). The driver can determine that the vehicle can travel by front wheel steering (2WS) when the rear lock-on lamp 70 is lit and the failure display lamp 74 is lit.

In this way, the control unit 7
Locks the rear wheels to the neutral position due to a failure of the steering system that drives the steering mechanism 5 for the rear wheels, and steers the front wheels (2 W
It is possible to travel by S), and it is impossible to travel when the rear wheels cannot be returned to the neutral position or the rear wheels can be returned to the neutral position but cannot be locked at the neutral position. Inform the person.

By the way, in the conventional all-wheel steering vehicle, since the front wheels and the rear wheels are mechanically connected, the rear wheels are switched from the in-phase steering angle synchronization mode to the anti-phase steering angle synchronization mode. If the steering angle ratio is not adjusted in the neutral position, it is necessary to return to the neutral position once.
For example, as shown in FIGS. 15 and 16, the wall surfaces A and B intersect each other at a substantially right angle, and the vehicle M is separated from the wall surface A close to the wall surface A without interfering with the wall surface A. When moving around to move closer to the wall B without buffering the wall B, the front wheels are steered to the right at a certain steering angle (for example, 20 °) at the initial position a and the rear wheels are set to the front wheels. In the same phase and at the same steering angle, the vehicle moves diagonally forward from position b → c to the front right and away from the wall surface A, and then returns to the neutral position at that position c and advances to position c ′,
Then move the front wheels to the right to the maximum steering angle (eg
The rear wheels are steered at a maximum steering angle (for example, 20 °) in reverse phase while being steered at 54 °) so as to bend along the wall surface B at a right angle from the position c ′ to the position d → e.

Therefore, the vehicle M returns the rear wheels from the in-phase steer angle synchronization mode to the neutral position while moving forward from the position c to the position c ', and at the position c', switches to the anti-phase steer angle synchronization mode. The time (distance) from to c'becomes longer, and it becomes impossible to make a tight turn. However, the steering system of the present invention does not have such a problem because the steering mechanism 5 for the rear wheels is mechanically completely separated and independent from the steering mechanism for the front wheels 2. That is, in the present invention, the rear wheels can be steered by the DC motor 30 independently of the front wheels, and the in-phase steering angle synchronization mode can be switched to the anti-phase steering angle synchronization mode by the mode changeover switch 55. It is said that. Therefore, the driver can directly switch from the in-phase synchronization mode (4WS-1) to the anti-phase synchronization mode (4WS-2) by operating the mode switching switch 55.

The steering control when switching from the in-phase synchronization (4WS-1) mode to the anti-phase synchronization (4WS-2) mode will be described below with reference to the flowcharts of FIGS. 17, 18 and 19. It is assumed that the vehicle is located at a position a close to the wall surface A as shown in FIG. 17, turns at a right angle from the position a, and approaches the wall surface B. The control unit 7 detects the steering angle of the front wheels 2 based on the signal from the steering angle detection sensor 50 (step 120), and detects the steering angle of the rear wheels 3 based on the signal from the steering angle detection sensor 51 (step 121). It is determined whether the mode changeover switch 55 has been switched to the in-phase synchronization (4WS-1) mode or the anti-phase synchronization (4WS-2) mode (step 122).

At the position a, the mode changeover switch 55 of the vehicle is switched to the basic in-phase synchronization (4WS-1) mode, and the driver steers the front wheel 2 to the right, for example, 20 ° at the position a. (FIG. 18) Then, the control unit 7 rotates the DC motor 30 (FIG. 2) forward to drive the metering pump 32 to rotate the rear wheel 3 in the in-phase (right) direction in synchronization with the steering angle of the front wheel 2. When the rudder (step 123) is operated and synchronized, the DC motor 30
Is stopped (step 124). At this time, the rear wheel 3
As shown by the dotted line in FIG. 18, the maximum steering angle (for example,
Steered up to 20 °.

When the driver advances the vehicle in this state, the vehicle moves from the position a to the position b and the position c on the side wall A.
While moving in parallel with respect to the side wall A, the side wall A is separated from the side wall A without interference. Then, at the position c, when the driver switches the mode changeover switch 55 to the reverse phase synchronization (4WS-2) mode and steers the front wheels 2 to the maximum steering angle (for example, 54 °), the control unit 7
18 determines that the mode changeover switch 55 has been switched to the reverse phase synchronization (4WS-2) mode in step 122, rotates the DC motor 30 in the reverse direction, drives the metering pump 32, and causes the rear wheel 3 to move as shown in FIG. As indicated by the dotted line, the steering wheel is steered to the maximum steering angle (for example, 20 °) in the antiphase direction synchronized with the steering angle of the front wheels 2 (step 125), and when synchronized, the DC motor 30 is stopped (step 12).
6) Let it do. At this time, the rear wheels 3 are steered to the left as opposed to the front wheels 2 as shown by the dotted line in FIG.

The switching of the rear wheels from the in-phase synchronization mode to the anti-phase synchronization mode is performed by the switching operation of the mode changeover switch 55, and the vehicle reaches the position e from the position c through the position d and the wall surface B. It comes close to the wall surface B without interfering with. As a result, the vehicle moves directly from the position c to the position d, shortens the time (distance) corresponding to the position c ′ shown in FIG. 15 corresponding to the position c ′, and can make a smaller turn.

Further, when the steering control of the rear wheels 3, particularly when the steering control is manually performed, if the steering speed is set to a constant speed as shown in FIG. 20, fine adjustment is performed when the steering speed is too fast. On the contrary, when the steering speed is too slow, there is a problem that the steering takes too long, and in any case, the condition is not good. Therefore, in the present invention, when the rear wheels are steered by a manual switch, the steered speed is slower when the switch-on time, that is, the steered time is shorter, and the steered speed is faster as the steered time is longer. The fine adjustment can be easily performed, and the steering is swiftly performed when the steering angle is large. Next, such control will be described with reference to the flowchart of FIG.

In the case where the steering control of the rear wheels is performed manually, the driver switches the mode changeover switch 55 (FIG. 3) to the manual independent (4WS-3) mode to steer the rear wheels 3. First, the manual independent steering switch 56 is operated rightward or leftward from the neutral position. The control unit 7
Whether the manual independent steering switch 56 is turned on when the mode switch 55 is switched to the 4WS-3 (manual independent) mode, that is, whether the manual independent steering switch 56 is operated (turned on) in the “right” or “left” direction from the neutral position. It is determined whether or not (step 130), and if the determination result is negative (NO), D
The C motor 30 is stopped (step 131) and the determination is repeated. When the determination result in step 130 is affirmative (YES), the control unit 7 determines the duty ratio of the on time of the drive signal for driving the DC motor 30 according to the switch on time of the manual independent steering switch 56 (step 132). This duty ratio is, for example, as shown in FIG.
As shown in 2, when the manual independent steering switch 56 is turned on, it is set to 50%, and if it continues to be turned on, it increases linearly with the passage of time.
The duty ratio is 0%, and the duty ratio (100%) is set thereafter.

The control unit 7 executes step 13
A drive signal is output to the DC motor 30 based on the duty ratio set in step 2 (step 133). That is, the control unit 7 calculates the time when the manual independent steering switch 56 is turned on by a built-in counter, and determines the duty ratio from the map of the drive duty ratio of the DC motor 30 based on the calculated time. Calculation is performed based on the determined duty ratio to turn on the DC motor 30,
Send the drive signal of OFF. This DC motor drive signal is, for example, t = duty ratio × (10 m
sec) × (1/100), resulting in a signal as shown in FIG.

As a result, the turning angle of the rear wheels 3 is small, that is,
When the on-time of the manual independent steering switch 56 is short (1 second or less), the duty ratio of the drive signal of the DC motor 30 is reduced to slow the steering speed of the rear wheels 3 and facilitate fine adjustment of the steering angle. Becomes Also, the steering angle of the rear wheels 3 is large,
That is, the ON time of the manual independent steering switch 56 is long (1
(Exceeding a second), the steered speed can be increased by increasing the duty ratio of the drive signal of the DC motor 30.

[0083]

As described above, according to the present invention, the front wheel steering mechanism and the rear wheel steering mechanism are mechanically independent, and the rear wheel steering mechanism is controlled by the metering pump driven by the electric motor, Mode switching means for switching the steering mode to front wheel steering and four-wheel steering, command means for instructing steering of the rear wheels, steering angle detection sensors for detecting the respective steering angles of the front and rear wheels, and mode switching means for these. And a control unit for controlling the electric motor by inputting the command means and each steering angle detection sensor, it is possible to simplify the configuration of the rear wheel steering control system,
Along with this, the hydraulic circuit is simplified, the number of parts is reduced, the assemblability is improved, and the cost of the steering system is reduced.

[Brief description of drawings]

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

FIG. 2 is a partially enlarged view of the steering mechanism shown in FIG.

FIG. 3 is a block diagram showing an input / output relationship of the control unit of FIG.

FIG. 4 is a flowchart showing control of the entire steering system of FIG.

FIG. 5 is a flowchart showing a procedure for manually steering the rear wheels independently.

FIG. 6 is a flowchart showing a procedure for manually and independently steering-controlling rear wheels.

7 is a graph showing the relationship between the vehicle speed and the duty ratio of the motor for controlling the steering angle of the rear wheels in the control of FIG.

FIG. 8 is a flowchart showing a procedure for changing the steering speed by changing the duty ratio of the steering angle control motor for the rear wheels.

FIG. 9 is a flowchart showing a procedure for controlling a maximum steering angle of rear wheels according to a vehicle speed.

FIG. 10 is a graph showing the relationship between the vehicle speed and the turning speed of the rear wheels.

FIG. 11 is a flowchart showing a procedure for enabling or prohibiting steering of rear wheels.

FIG. 12 is a flowchart showing a procedure for prohibiting steering when the rear wheels are overloaded.

FIG. 13 is a flowchart showing a procedure for determining an abnormality of a hydraulic power source.

FIG. 14 is a flowchart showing a procedure when the steering system fails.

FIG. 15 is a diagram showing in-phase / opposite-phase switching control of a conventional all-wheel steering vehicle.

16 is a graph showing the relationship between the vehicle position of FIG. 15 and the steering angles of the front and rear wheels.

FIG. 17 is a diagram showing in-phase / negative-phase switching control of the four-wheel steering vehicle according to the present invention.

FIG. 18 is a graph showing the relationship between the vehicle position and the steering angles of the front and rear wheels in FIG.

19 is a flowchart showing the control procedure of FIG.

FIG. 20 is a graph showing a conventional steered speed of rear wheels.

FIG. 21 is a flowchart showing a procedure for changing the turning speed of the rear wheels in the steering system of the present invention.

22 is a graph showing the duty ratio of the drive signal of the DC motor in the steering control of FIG.

23 is a diagram showing a drive signal waveform of a drive motor in the steering control of FIG.

[Explanation of symbols]

 1 Steering system 2 Front wheel 3 Rear wheel 4 Front wheel steering mechanism 5 Rear wheel steering mechanism 6 Hydraulic control device 7 Control unit 8 Switch boss 9 Display box 30 DC motor 31 Reducer 32 Metering pump 47 Changeover switch 48 Emergency switch 50 Steering angle Detection sensor 51 Steering angle detection sensor 55 Mode selector switch 56 Manual independent steering switch 57 Forced neutral control switch

Claims (1)

[Claims] 1. A front wheel steering mechanism and a rear wheel steering mechanism are mechanically independent, the rear wheel steering mechanism is controlled by a metering pump driven by an electric motor, and the steering mode is switched between front wheel steering and four-wheel steering. Mode switching means, command means for instructing steering of the rear wheels, steering angle detection sensors for detecting the respective steering angles of the front wheels and rear wheels, and inputs of these mode switching means, command means, and steering angle detection sensors And a control unit for controlling the electric motor according to the above.