JPH0526738U - Four-wheel steering vehicle - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the maneuverability of a four-wheel steering vehicle. A front wheel steering mechanism 4 and a rear wheel steering mechanism 5 are mechanically independent of each other, and the rear wheel steering mechanism is controlled by a metering pump 32 driven by an electric motor 30 to synchronize in-phase or reverse phase in synchronization with a steering angle. The mode switching means 55 for switching the steering mode of the rear wheels 3 to the phase direction mode, and the electric motor is controlled by receiving a signal from the mode switching means, and when the steering mode is switched with the steering turned off, the switching is performed. The control unit 7 for steering the rear wheels in the selected steering mode is provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a four-wheel steering vehicle.

[0002]

[Prior Art]

 As a crane vehicle, a truck-crane vehicle is known, which has evolved from mounting a crane on a truck base. Many of these truck cranes are equipped with a cab (carrying house) for general traveling and a crane house for crane work independently, have the same traveling performance as ordinary trucks, and can travel long distances. .. In addition, since there are few restrictions on the crane bodywork, a large suspension capacity can be provided for the tonnage. On the other hand, truck cranes are difficult to enter narrow alleys due to the large size of the vehicle, restrictions on the steering system, etc., poor mobility on rough terrain, approach angles or There is a problem that it is inferior in maneuverability in the field, such as not being able to take a large departure angle.

On the other hand, there is known a rough terrain crane vehicle that places importance on maneuverability on site. In this rough terrain mobile crane, the vehicle driving operation during traveling and the crane operation during crane work are performed in the same crane house, and further, all-wheel drive function (4WD) and all-wheel steering function (4WS) are provided. In particular, the all-wheel steering function is to provide a steering angle in-phase or anti-phase with the front wheels to the rear wheels in synchronization with the front wheels and in synchronization with the front wheels to reduce the minimum turning radius. It is extremely effective for work that frequently involves entering narrow alleys or turning in narrow spaces.

[0004]

[Problems to be solved by the device]

 By the way, the conventional all-wheel steering vehicle has a structure in which the front wheels and the rear wheels are mechanically connected, so when the rear wheels are switched from the in-phase steering angle synchronization mode to the anti-phase steering angle synchronization mode. However, if it is not done in the neutral position, the rudder angle ratio will change, so it is necessary to return to the neutral position once. For example, as shown in FIGS. 9 and 10, 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 without interfering with the wall surface A to the right. When moving around to move close to the wall B without buffering the wall B, the front wheels are steered to the right at a steering angle (for example, 20 °) at the initial position a and the rear wheels are moved to the front wheels. In the same phase and at the same rudder angle, the vehicle moves diagonally forward from position b → c to the front right and away from the wall surface A, then returns to the neutral position once and advances to position c ′, and then the front wheels. Steer to the right at the maximum steering angle (eg, 54 °) and steer the rear wheels to the maximum steering angle (eg, 20 °) in anti-phase to make a right turn from position c ′ to position d → e. I try to get along the wall B.

Therefore, the vehicle M moves forward from the position c to the position c ′, returns the rear wheels from the in-phase steering angle synchronization mode to the neutral position, and switches to the anti-phase steering angle synchronization mode at the position c ′. There is a problem that the time (distance) from the position c to c'belongs, and a small turn cannot be made by this amount, resulting in poor turnability. The present invention has been made in view of the above points, and provides a four-wheel steering vehicle in which the rear wheels can be easily switched to the in-phase or the anti-phase even when the steering is turned to improve the small turning ability. With the goal.

[0006]

[Means for Solving the Problems]

 In order to achieve the above object, 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 a metering pump driven by an electric motor, and the steering angle is controlled. The mode switching means for switching the rear wheel steering mode in the in-phase or anti-phase direction in synchronism with the above, and for controlling the electric motor by receiving a signal from the mode switching means, and with the steering turned off, When the steering mode is switched, the control unit that steers the rear wheels to the switched steering mode is provided.

[0007]

[Action]

 The control unit controls the electric motor by a signal input from the mode switching means, synchronizes with the steering angle of the front wheels in accordance with the selected steering mode, steers the rear wheels in the same phase or in the opposite phase direction, and When the mode switching means is switched while the steering is off, the rear wheels are steered to the switched mode. That is, when the mode switching means is switched to the in-phase mode and synchronized with the steering angle, for example, when the control unit is switched to the anti-phase mode while controlling the rear wheels in the in-phase direction, the steering operation is performed. The rear wheels are steered in the opposite direction even when the gear is turned off.

[0008]

【Example】

 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 relation of the control unit of FIG. 1 and 2, the steering system 1 includes a steering mechanism 4 for front wheels 2 and 2, a steering mechanism 5 for rear wheels 3 and 3, a hydraulic control device 6 for controlling the steering mechanism 5, and a control unit (C / U). ) 7, a switch box 8, a display box 9 and various sensors described later.

The steering mechanism 4 that steers the front wheels 2 and 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. A hydraulic control section (not shown) is connected to the arm 15 and is connected to the steering hydraulic pump 16 via oil passages 40 and 41.

The steering mechanism 5 that steers the rear wheels 3 and 3 includes rear-wheel steering hydraulic cylinders 22 and 23, a rear lock mechanism 24 (FIG. 2), and the like. The tip of each rod is connected to the bracket 20a of the rear differential 20 to one end of each arm 21, 21 that supports the rear wheels 3, 3. 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. The neutral control solenoid valve 26 is provided between the oil passages 44 and 45. Is connected. The rear lock mechanism 24 is locked or unlocked by the rear lock solenoid valve 25 (FIG. 1).

The hydraulic control device 6 is composed of an electric motor, that is, a DC 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 DC motor 30 is a speed reducer. It is connected to the input shaft of the metering pump 32 via the machine 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 performed between these oil passages 42 and 43. Is connected to the relief valve 39. Further, 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.

A steering angle detection sensor 50 that detects a steering angle is provided on the steering shuff 12 of the front wheel steering mechanism 4, and a steering angle of a rear wheel is detected between the rear differential 20 and the arm 21 of one rear wheel 3. A steering angle detection sensor 51 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 includes a vehicle speed sensor 53 on the input side and transmission (T / M) gear stages (first speed, second speed, reverse, neutral). Gear position detection switch 54, front wheel steering (2WS), all-wheel steering (rear wheel in-phase synchronization 4WS-1), all-wheel steering (rear wheel anti-phase synchronization 4WS-2), all-wheel steering (rear) Push-button mode changeover switch 55 for switching modes such as wheel manual independent 4WS-3), seesaw type manual independent steering switch 56 for independently steering control of the rear wheels 3, forcibly moving the rear wheels to the neutral position. A forced neutral control switch 57 for controlling, a rear shaft fixing switch 58 for fixing the rear axle to the neutral position, a rear shaft fixing detecting switch 59 for detecting that the rear shaft is fixed at the neutral position, etc. are connected. There is. 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 lock solenoid valve 25 for fixing the rear shaft, a neutral control solenoid valve 26, and a metering pump 32 provided on a rear lock mechanism 24 (FIG. 2) are driven. DC motor 30, rear lock lamp 70, front wheel steering angle display indicator 71, rear wheel steering angle display indicator 72, buzzer 73, failure display lamp 74, 4WS-1 mode display lamp 75, 4WS-2 mode display lamp 76, The 4WS-3 mode display lamp 77 and the like are connected. The rear lock lamp 70, the front wheel rudder angle display indicator 71, the rear wheel rudder angle display indicator 72, the buzzer 73, the failure display lamp 74, and the mode display lamps 75 to 7777 are arranged on the display box 9 (FIG. 1). Has been done. The control unit 7 drives the DC motor 30 of the hydraulic control device 6 based on each input signal 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 is connected to a power source in parallel with the control unit 7 via a changeover switch 47 and an emergency switch 48 (FIG. 2). The changeover switch 47 is for switching the rotation direction of the DC motor 30, that is, for forward or reverse rotation, and the common contacts c and f are the DC motor 30 (note that only one line is drawn in the figure). , The contacts b and d are grounded, the contacts a and e are 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 enables all-wheel steering (4WS-1 to 4WS-3) control at a low speed (for example, 20 km / h or less). It is assumed that the rear wheels 3 are steered so as to make a small turn at the work site. 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 detection 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, and then , Go to the sensor check routine (step 3) and check whether or not all the sensors have a failure (step 4), and the determination result is negative (NO), that is, if all the sensors are normal. It is determined whether or not the mode changeover switch 55 is switched to the 4WS-1 (in-phase synchronization) mode (step 5). When the answer is YES (YES), the 4WS-1 control, that is, the front wheel is set. On the other hand, the routine shifts to the routine for synchronously controlling the rear wheels (step 6) and returns to step 3.

When the answer in step 5 is negative (NO), that is, when the mode switch 55 is switched to a mode other than the 4WS-1 described above, the control unit 7 causes the mode switch 55 to switch. Is switched to the 4WS-2 (reverse phase synchronization) mode (step 7), and if the answer is affirmative (YES), the 4WS-2 control is performed, that is, the rear wheels are compared with the front wheels. Shifts to a routine for synchronously controlling the reverse phase (step 10) and returns to step 3.

When the determination result of step 7 is negative (NO), the control unit 7 determines whether or not the mode is switched to the 4WS-3 (manual independent steering) mode (step 9), and the determination result. Is affirmative (YES), 4WS-3 control, that is, the routine shifts to a routine in which the rear wheels 3 can be manually and independently steered with respect to the front wheels 2 (step 10) and returns to step 3, and when negative (NO). 2WS, that is, the routine proceeds to a steering control routine for only the front wheels (step 11) and returns to step 3.

The control unit 7 displays a sensor failure (step 12) when the answer to the determination in step 4 is affirmative (YES), that is, when any sensor has a failure, and the display box 9 displays The failure display lamp 74 (FIG. 3) is turned on, and 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, each control of 2WS (front wheel steering), 4WS-1 (rear wheel in-phase synchronization), 4WS-2 (rear wheel reverse 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 in response to this, hydraulic pressure is supplied from the hydraulic pump 16 to the hydraulic control unit of the power cylinder 11. As a result, the power cylinder 11 is actuated 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 rudder angle display indicator 71 of the display box 9 by the signal from the steering angle detection sensor 50 to display the rudder angle of the front wheels 2.

The control unit 7 does not drive the DC motor 30 and neutralizes the spool 33 (FIG. 2) of the metering pump 32 when the mode selector switch 55 is switched to the 2WS (front wheel steering) mode. Hold in position and lock the rear lock mechanism 24. As a result, the rear wheels 3 and 3 are fixed in 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 switch 55 is switched to the 4WS-1 (rear wheel in-phase synchronization) mode, the control unit 7 turns on the 4WS-1 mode display lamp 75 of the display box 9 (FIG. 1). At the same time, 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 rotates the DC motor 30 in the positive direction according to the signal input from the steering angle detection sensor 50 to drive the metering pump 32, and the spool 32 is rotated. It is moved to the right in FIG. As a result, hydraulic pressure is supplied through the oil passage 45, the cylinders 22, 23, and the oil passage 44 of the rear wheel steering mechanism 5, the cylinder 22 extends, the cylinder 23 shortens, and the arms 21, 21 move rightward in the drawing. The rear wheels 3 and 3 are steered to the right.

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. The 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 drives the front wheel steering angle display indicator 71 and the rear wheel steering angle display indicator 72 of the display box 9 by the signals input from the steering angle detection sensor 50 and the steering angle detection sensor 51 to drive the front wheels. The steering angle of 2 and the steering angle of the rear wheel 3 are displayed.

When the mode selector switch 55 is switched to the 4WS-2 (reverse phase synchronization) mode, the control unit 7 turns on the 4WS-2 mode display lamp 76 of the display box 9 (FIG. 1) and neutralizes it. The 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 unlock the rear lock mechanism 24. When the steering wheel 13 is operated to the right, the control unit 7 reversely rotates the DC motor 30 in response to the signal input from the steering angle detection sensor 50 to drive the metering pump 32 and the spool 32. Is moved to the left in FIG. As a result, hydraulic pressure is supplied from the oil passage 44 of the rear wheel steering mechanism 5 through the passages of the cylinders 22, 23 and the oil passage 45, the cylinder 22 is shortened, the cylinder 23 is extended, and the arms 21, 21 are moved leftward in the drawing. The rear wheels 3, 3 are turned 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. The 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 reverse-phase controlled in synchronization with the front wheels 2. Further, the control unit 7 drives the front wheel steering angle display indicator 71 and the rear wheel steering angle display indicator 72 of the display box 9 by the signals input from the steering angle detection sensor 50 and the steering angle detection sensor 51 to drive the front wheels. The steering angle of 2 and the steering angle of the rear wheel 3 are displayed.

When the switching mode switch 55 is switched to the 4WS-3 (manual independent) mode, the control unit 7 turns on the 4WS-3 mode display lamp 77 of the display box 9 (FIG. 1). At the same time, 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 30 to rotate in the forward direction to move the spool 34 of the metering pump 32 to the right in FIG. As a result, the cylinder 22 of the rear wheel steering mechanism 5 extends, the cylinder 23 shortens, the arms 21, 21 rotate to the right, and the rear wheels 3, 3 are steered to the right. Then, when the manual independent steering switch 56 is returned to the neutral position, the DC motor 30 is stopped and the rear wheels 3 are held at the turning angle.

On the contrary, when the manual independent steering switch 56 is operated in the “left” direction, the control unit 7 reversely rotates the DC motor 30 to move the spool 34 of the metering pump 32 leftward in FIG. Let As a result, the cylinder 22 of the rear wheel steering mechanism 5 is shortened, the cylinder 23 is extended, the arms 21, 21 are rotated leftward, 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 (step 20). In the case of YES), that is, when the vehicle speed exceeds 20 km / h, the front wheel steering (forced 2WS) control is forcibly transferred (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 makes a negative (NO) answer to the determination in step 20, that is, when the vehicle speed is 20 km / h or less, further determines whether or not the transmission gear stage is at the third or higher speed position (step 22). However, if the answer is YES (YES), it is determined that the vehicle speed exceeds 20 km / h, and the routine proceeds to step 21, and if NO (NO), that is, the gear is 1st, 2nd, or neutral. Alternatively, when the vehicle is in the reverse position, it is determined that the vehicle speed is 20 km / h or less or the vehicle is stopped, and the steering angle of the rear wheel 3 is determined by the signal from the steering angle detection sensor 51 of the rear wheel 3 (FIG. 1). For example, it is determined whether the angle is smaller than 20 ° (step 23).

The control unit 7 determines whether the forced neutral control switch 57 (FIG. 3) is on or off when the answer in step 23 is affirmative (YES) (step 24), and when the switch is off, the rear wheels are turned off. It is determined that the steering wheel 3 is steerable manually, and it is determined whether 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 26) to steer the rear wheels 3 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. 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 (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 determination result of 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 the determination result is affirmative (YES). ), The DC motor 30 (FIG. 2) is normally rotated (step 31) to steer the rear wheels 3 to the right, and the process proceeds 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 stopped (step 32) and the process proceeds to step 27.

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

When the mode changeover switch 55 is switched to and controlled by 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 forcibly returned to the neutral position quickly. If necessary, the operator operates the forced neutral control switch 57 to turn it on. The control unit 7 responds immediately when the determination result in step 24 is affirmative (YES), and when the forced neutral control switch 57 is on, based on the input signal from the steering angle detection sensor 51, the current steering direction of the rear wheel 3 is detected. Is detected, the rotation direction of the DC motor 30 is calculated to return the rear wheel 3 to the neutral position (step 33), and the duty ratio of the voltage applied to the DC motor 30 is calculated (step 34). Based on the above, the DC motor 30 is normally or reversely rotated (step 35) to return the rear wheel 3 to the neutral position. The control unit 7 determines whether or not the rear wheel 3 has returned to the neutral position based on the signal from the steering angle detection sensor 51 (step 36). When the determination result is affirmative (YES), the DC motor 30 is stopped (step 36). 32), and if negative (NO), the above control is continued. This forces the rear wheels to return to the neutral position.

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. Has been done. 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 even when the steering wheel is turned off.

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. 6, 7 and 8. It is assumed that the vehicle is located at a position a close to the wall surface A as shown in FIG. 6 and turns from the position a at a right angle to approach the wall surface B. The control unit 7 detects the steering angle of the front wheels 2 from the signal from the steering angle detection sensor 50 (step 40), and detects the steering angle of the rear wheels 3 from the signal from the steering angle detection sensor 51 (step 40). 41), and it is determined whether the mode switch 55 is switched to the in-phase synchronization (4WS-1) mode or the anti-phase synchronization (4WS-2) mode (step 42).

At the position a, the mode changeover switch 55 of the vehicle is switched to the basic in-phase synchronization (4 WS-1) mode, and the driver moves the front wheel 2 to the right at the position a, for example, When steered at 20 ° (Fig. 7), the control unit 7 rotates the DC motor 30 (Fig. 2) forward to drive the metering pump 32, so that the rear wheel 3 is in phase (right) in synchronization with the steering angle of the front wheel 2. ), The DC motor 30 is stopped (step 44). At this time, the rear wheel 3 is steered rightward to the maximum steering angle (for example, 20 °) as shown by the dotted line in FIG. 7.

When the driver moves the vehicle forward in this state, the vehicle moves from the position a to the position b 1 and the position c in parallel with respect to the side wall A and separates without interfering with the side wall A. . Then, at the position c, when the driver switches the mode changeover switch 55 to the anti-phase synchronization (4WS-2) mode and steers the front wheels 2 to the maximum steering angle (for example, 54 °), the control unit 7 makes a step. At 42, it is determined that the mode changeover switch 55 is switched to the anti-phase synchronization (4WS-2) mode, the DC motor 30 is rotated in the reverse direction to drive the metering pump 32, and the rear wheel 3 is shown by a dotted line in FIG. As indicated by, the steering wheel is steered to the maximum steering angle (for example, 20 °) in the opposite phase direction synchronized with the steering angle of the front wheels 2 (step 45), and when synchronized, the DC motor 30 is stopped (step 46). 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 switching switch 55, and the vehicle reaches the position e from the position c through the position d. It approaches the wall surface B without interfering with the wall surface B. As a result, the vehicle moves directly from the position c to the position d, shortens by the time (distance) corresponding to the position c'to the position c'shown in FIG. 9, and can make a smaller turn.

[0041]

[Effect of the device]

 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 a metering pump driven by an electric motor to synchronize with the steering angle. Then, the mode switching means for switching the steering mode of the rear wheels in the same phase or the opposite phase direction, and the electric motor is controlled by receiving a signal from the mode switching means, and the steering mode is switched while the steering is turned off. At this time, the control unit for steering the rear wheels is provided in the switched steering mode, so that the mode switching means can be switched to the in-phase mode or the anti-phase mode even when the steering is turned off. This makes it possible to improve the maneuverability.

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

7 is a graph showing the relationship between the vehicle position of FIG. 6 and the steering angles of the front and rear wheels.

FIG. 8 is a flowchart showing the control procedure of FIG.

FIG. 9 is a diagram showing in-phase / negative-phase switching control of a conventional all-wheel steering vehicle.

FIG. 10 is a graph showing the relationship between the vehicle position and the steering angles of the front and rear wheels in 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)

[Scope of utility model registration request] 1. A front wheel steering mechanism and a rear wheel steering mechanism are mechanically independent of each other, and the rear wheel steering mechanism is controlled by a metering pump driven by an electric motor, and in-phase or anti-phase directions are synchronized with a steering angle. And a mode switching means for switching the steering mode of the rear wheels, a signal from the mode switching means for controlling the electric motor, and when the steering mode is switched with the steering turned off, the switched steering A four-wheel steering vehicle, comprising: a control unit that steers the rear wheels in a mode.