JP4518316B2 - Industrial vehicle steering device - Google Patents

Description

  The present invention relates to a steering device for an industrial vehicle that turns a wheel supported by the support member together with the support member.

Conventionally, as a steering device used for an industrial vehicle, there is a so-called power steering device in which a wheel is turned by a driving device in accordance with a steering operation, and an electric power steering device or a hydraulic power steering device is employed.
For example, in the technique disclosed in Patent Document 1, a main pump that supplies hydraulic oil to a front wheel steering power steering device and a sub pump that supplies hydraulic oil to a rear wheel steering power steering device are driven by a single internal combustion engine. In the technique described in Patent Document 2, the hydraulic power steering device is controlled based on the rotation angle (operation angle) of the steering wheel and the steering angle of the wheel. Furthermore, in the technique described in Patent Document 3, a pump driven by a vehicle engine and a pump driven by an electric motor are provided so that hydraulic oil can be supplied from any pump to the cylinder device.

JP-A 61-150871 JP-A-61-200060 Japanese National Patent Publication No. 11-507894

  An object of the present invention is to provide a steering apparatus that has good operability and functions efficiently in place of the conventional techniques as described above.

  In order to achieve the above object, according to the present invention, a support member for supporting a wheel is provided on a vehicle body so as to be able to turn about a vertical axis, and a double-acting steering cylinder connected to the support member is rotated by a steering handle. A steering apparatus for an industrial vehicle that operates according to an operation and turns the wheel together with the support member, and includes an electric motor as a drive source, a tank that stores hydraulic oil supplied to the steering cylinder, and the electric motor And a first hydraulic pump that draws hydraulic oil from the tank and discharges it toward one oil chamber of the steering cylinder when the electric motor is driven forward, and is connected to the electric motor. When the electric motor is driven in reverse, hydraulic oil is drawn from the tank and discharged toward the other oil chamber of the steering cylinder. And a motor control device that drives and controls the electric motor in a forward rotation direction or a reverse rotation direction corresponding to a direction in which the wheel is turned, and the one oil chamber and the first hydraulic pump. The first hydraulic pipe branched from the hydraulic pipe connecting the first hydraulic pipe connected to the tank, and the hydraulic pipe connecting the second hydraulic chamber and the second hydraulic pump branched from the hydraulic pipe connected to the tank. Second hydraulic piping, a first control valve interposed in the first hydraulic piping, and a second control valve interposed in the second hydraulic piping, and An operation angle detector that detects an operation angle that is an angle at which the steering handle is rotated, a turning angle detector that detects a turning angle that is an angle at which the support member turns, and the operation angle and the turning angle. Based on It has a configuration which is characterized by comprising a valve control device which controls the opening and closing of the first and second control valves.

According to this, when the electric motor is driven forward, hydraulic oil is supplied from the first hydraulic pump to one oil chamber of the steering cylinder, and the other oil chamber of the steering cylinder operates to the tank. Since the oil is recovered, the rod of the steering cylinder moves to the other oil chamber side, and accordingly, the wheel can be turned together with the support member.
When the electric motor is driven in reverse, the hydraulic oil is collected from one oil chamber of the steering cylinder to the tank, and the hydraulic oil is supplied from the second hydraulic pump to the other oil chamber of the steering cylinder. Therefore, the rod of the steering cylinder moves to the one oil chamber side, and accordingly, the wheel can be turned together with the support member. Furthermore, when the wheels are not turned, it is only necessary to stop the electric motor, so that power is not wasted.

  In the present invention, the valve control device calculates a target turning angle based on an operation angle by the operation angle detector, and determines the first turning angle according to an angle difference between the target turning angle and the turning angle by the turning angle detector. The first and second control valves are controlled to open and close, and the first control valve is closed when the angle difference is not more than a predetermined value as an absolute value when the electric motor is driven forward. The second control valve is opened, and the first control valve is opened and the second control valve is opened when the angle difference is not more than a predetermined value as an absolute value when the electric motor is driven in reverse. The control valve can be closed.

According to this, when the angle difference is equal to or less than a predetermined value as the absolute value when the electric motor is driven in the forward rotation, the first control valve is closed and the first hydraulic pump is connected to one of the steering cylinders. The hydraulic oil is supplied to the oil chamber, the second control valve is opened, and the hydraulic oil is recovered from the other oil chamber of the steering cylinder to the tank through the second control valve. Thus, the rod of the steering cylinder can be moved to the other oil chamber side, and the wheel can be turned together with the support member.
When the electric motor is driven in reverse and the angle difference is not more than a predetermined value as an absolute value, the first control valve is opened, and the first control valve is passed from one oil chamber of the steering cylinder. The hydraulic oil is collected in the tank, the second control valve is closed, and the hydraulic oil is supplied from the second hydraulic pump to the other oil chamber of the steering cylinder. Thus, the rod of the steering cylinder can be moved to the one oil chamber side, and the wheel can be turned together with the support member.

  In the present invention, the valve control device is configured to increase the target turning angle when the turning angle is larger than the target turning angle and the angle difference exceeds the predetermined value. When the steering handle is rotated, the first and second control valves can be opened.

  According to this, when the turning angle is larger than the target turning angle and the angle difference exceeds the predetermined value, when the electric motor is driven to rotate forward, the first hydraulic pump to the steering cylinder When at least a part of the hydraulic oil supplied to the tank is collected in the tank through the first control valve and the electric motor is driven in reverse, at least one of the hydraulic oil supplied from the second hydraulic pump to the steering cylinder. Part is withdrawn into the tank through the second control valve. In this way, since the hydraulic oil from the first or second hydraulic pump is recovered, the movement of the rod of the steering cylinder, and hence the turning of the wheel, is suppressed. Even if becomes larger, the turning angle does not become as large as the target turning angle, and as a result, the angle difference between the target turning angle and the turning angle can be reduced.

  Furthermore, in the present invention, the valve control device is configured to reduce the target turning angle when the turning angle is smaller than the target turning angle and the angle difference exceeds the predetermined value. When the steering handle is rotated, the first and second control valves can be opened.

  According to this, when the turning angle is smaller than the target turning angle and the angle difference exceeds the predetermined value, when the electric motor is driven to rotate forward, the first hydraulic pump to the steering cylinder When at least a part of the hydraulic oil supplied to the tank is collected in the tank through the first control valve and the electric motor is driven in reverse, at least one of the hydraulic oil supplied from the second hydraulic pump to the steering cylinder. Part is withdrawn into the tank through the second control valve. In this way, since the hydraulic oil from the first or second hydraulic pump is recovered, the movement of the rod of the steering cylinder, and hence the turning of the wheel, is suppressed. However, the turning angle does not become as small as the target turning angle, and as a result, the angle difference between the target turning angle and the turning angle can be reduced.

  In the present invention, there is provided a torque detector for detecting an operation torque when the steering handle is rotated, and the motor control device outputs the output of the electric motor from the detection result by the torque detector. The electric motor can be calculated and controlled to drive in the forward direction or the reverse direction based on the output.

  According to this, the electric motor can be appropriately driven according to the rotation operation of the steering handle, and the driver can turn the wheel as intended.

  In the present invention, there is provided a torque transmission device that is interposed between the steering handle and the electric motor and transmits an operation torque when the steering handle is rotated to the electric motor. It can be set as the structure to do.

  According to this, since the electric motor can be driven by the torque transmitted from the steering handle via the torque transmission device, and the hydraulic pump can be driven, the motor control device that controls the electric motor temporarily fails. In addition, by rotating the steering handle, the steering cylinder can be operated to turn the wheel.

  According to the present invention, hydraulic oil can be supplied to the steering cylinder by the first or second hydraulic pump in accordance with the rotation operation of the steering handle, and the wheels can be turned together with the support member. Further, when the wheels are not turned, it is only necessary to stop the electric motor, so that power is not wasted. Furthermore, the hydraulic oil supplied to the steering cylinder and the hydraulic oil recovered from the steering cylinder can be appropriately controlled by opening and closing the first and second control valves based on the operation angle and the turning angle. The wheel can be turned as intended by the driver.

  Hereinafter, an embodiment in which the present invention is applied to a counterbalance forklift will be described with reference to the drawings.

  As shown in FIG. 1, this forklift is provided with a mast 2 at the front portion of a vehicle body 1, and a fork 3 is supported on the mast 2 so as to be able to move up and down. A pair of left and right front wheels 4 as drive wheels are provided at the front lower part of the vehicle body 1, and a pair of right and left rear wheels 5 are provided at the rear lower part of the vehicle body 1. A weight 6 is fixed to the rear portion of the vehicle body 1. A driver's seat 7 on which a driver sits is provided at the center in the front-rear direction of the vehicle body 1, and a steering handle 8 is rotatably provided at the front of the vehicle body 1 so as to face the driver's seat 7. Further, as shown in FIG. 1, a head guard 9 is provided so as to cover from the front part to the rear part of the vehicle body 1.

  As shown in FIG. 2, the rear wheel 5 is provided on the vehicle body 1 via a rear wheel suspension device 10. This rear wheel suspension device 10 supports an axle frame 11 supported by the vehicle body 1 and a rear wheel 5 so as to be rotatable about a horizontal axis, and is provided at both left and right ends of the axle frame 11 so as to be rotatable about a vertical axis. Main axles, left and right arms 13 having one end connected to each axle 12, and a steering cylinder 14 connected to the other end of the arm 13 and provided to operate in the left-right direction of the vehicle body 1. Yes. Here, since each axle 12 and the rear wheel 5 supported by each axle turn integrally, the turning angle of the axle 12 is detected as the turning angle of the rear wheel 5 on the turning shaft of the axle 12. A turning angle sensor 15 is provided. The steering angle sensor 15 sets the angle when the rear wheel 5 is in the straight traveling state to 0, and is a positive value when turning from this state clockwise in plan view, and when turning from the same state counterclockwise in plan view. The angle is detected as a negative value. Each arm 13 is connected to the rear part of the axle 12 and to the end of the rod of the steering cylinder 14, and the steering cylinder 14 is disposed somewhat rearward of the pivot shaft of the axle 12. .

  The rotating shaft of the steering handle 8 is provided with a torque sensor 16 for detecting torque associated with the operation of the steering handle 8 and an operation angle sensor 17 for detecting the rotation angle of the steering handle 8 as an operation angle. A signal from each sensor is input to a control device 30 described later. The torque sensor 16 sets the torque when the steering handle 8 is not operated to 0, the torque when operated clockwise in plan view, and the torque when operated counterclockwise in plan view. Detect as a negative value. The operation angle sensor 17 is operated by setting the angle when the rear wheel 5 is in the straight traveling state to 0 and setting the angle when operated clockwise from the above state to a positive value, and operating from the same state counterclockwise when viewed from the top. Is detected as a negative value. Further, the rotating shaft of the steering handle 8 and the rotating shaft of the electric motor 23 described later are mechanically connected via a reduction gear (not shown), and when the steering handle 8 is operated clockwise in a plan view, the electric motor 23 is properly connected. When the steering handle 8 is rotated counterclockwise when viewed in plan, the electric motor 23 rotates in the reverse direction.

  Now, the vehicle body 1 drives a tank 20 that stores hydraulic oil supplied to and discharged from the steering cylinder 14, hydraulic pumps 21 and 22 for supplying hydraulic oil to the steering cylinder 14, and both hydraulic pumps 21 and 22. An electric motor 23 is mounted. As shown in FIG. 2, the suction ports of both the hydraulic pumps 21 and 22 are connected to the tank 20 by hydraulic piping, and the discharge port of the hydraulic pump 21 is connected to the right side (in FIG. 2) of the steering cylinder 14 by the hydraulic piping L1. Is connected to the oil chamber on the upper side, and the discharge port of the hydraulic pump 22 is connected to the oil chamber on the left side of the steering cylinder 14 in plan view (lower side in FIG. 2) via the hydraulic pipe L2. The hydraulic pumps 21 and 22 are both connected to the rotating shaft of the electric motor 23. When the electric motor 23 is driven in the reverse rotation direction, the hydraulic pump 21 draws hydraulic oil from the tank 20 to the steering cylinder 14. When the electric motor 23 is driven in the forward direction, the hydraulic pump 22 draws hydraulic oil from the tank 20 and discharges it toward the steering cylinder 14. That is, hydraulic oil is supplied from one of the hydraulic pump 21 or the hydraulic pump 22 to the steering cylinder 14 depending on the rotation direction of the electric motor 23. As shown in FIG. 2, a hydraulic pipe L3 is connected in the middle of the hydraulic pipe L1, a hydraulic pipe L4 is connected in the middle of the hydraulic pipe L2, and the hydraulic pipes L3 and L4 are both connected to the tank 20. It is connected.

Here, when hydraulic oil is supplied from the hydraulic pump 21 to the oil chamber on the right side of the steering cylinder 14 and the hydraulic oil is collected from the left oil chamber to the tank 20, the rod of the steering cylinder 14 moves to the left in plan view. To do. Accordingly, the left and right axles 12 turn clockwise in plan view, and the rear wheel 5 also turns clockwise in plan view about the turning axis of the axle 12. As a result, the forklift turns and turns counterclockwise in plan view.
On the other hand, when the hydraulic oil is recovered from the oil chamber on the right side of the steering cylinder 14 to the tank 20 and the hydraulic oil is supplied to the left oil chamber from the hydraulic pump 22, the rod of the steering cylinder 14 moves to the right in plan view. . As a result, the left and right axles 12 turn counterclockwise in plan view, and the rear wheel 5 also turns counterclockwise in plan view about the turning axis of the axle 12. As a result, the forklift turns in the clockwise direction in plan view.

  As shown in FIG. 2, a control valve 24 is provided in the middle of the hydraulic pipe L3, and a control valve 25 is provided in the middle of the hydraulic pipe L4. Each of the control valves 24 and 25 is a normally closed electromagnetic valve, and is closed by a built-in spring in a non-operating state. When the operation state, that is, a state where a predetermined voltage is applied to the solenoid, the control valve 24 is opened, the flow of hydraulic oil from the hydraulic pipe L1 side to the tank 20 side is allowed, and the control valve 25 Is opened, and the flow of hydraulic oil from the hydraulic pipe L2 side to the tank 20 side is allowed. Note that a battery (not shown) is mounted on the vehicle body 1, and electric power is supplied from the battery to the electric motor 23 and the control valves 24 and 25 via a control device 30 described later.

  As shown in FIG. 3, the control device 30 includes a motor control unit 31 that controls the electric motor 23 and a valve control unit 32 that controls the control valves 24 and 25. The motor control unit 31 controls driving of the electric motor 23 in the forward rotation direction or the reverse rotation direction based on the input from the torque sensor 16, and the valve control unit 32 includes the turning angle sensor 15, the torque sensor 16, and the operation angle sensor. The control valves 24 and 25 are controlled to open and close based on the input from 17.

  As shown in FIG. 4, the motor control unit 31 calculates a voltage V corresponding to the torque T detected by the torque sensor 16 and applies it to the electric motor 23. When the torque T is a positive value, Drives the electric motor 23 in the forward direction, and when the torque T is a negative value, drives the electric motor 23 in the reverse direction. The motor control unit 31 controls the electric motor 23 with a predetermined torque range centered on a state where the torque T is zero as a dead zone. When the torque T exceeds the dead zone, the motor control unit 31 applies a voltage V proportional to the torque T to the electric motor 23, and when the torque T becomes equal to or greater than a predetermined value T2, the motor T is set to the voltage V2, and the torque T is a predetermined value − When T2 or less, the voltage is -V2.

  As shown in FIG. 5, the valve control unit 32 derives a target turning angle B that is proportional to the operation angle A detected by the operation angle sensor 17, and further, the target turning angle B and the turning angle sensor 15. An angle difference D (= target turning angle B−steering angle C) with respect to the turning angle C detected by the above is derived. In addition, the valve control unit 32 controls opening and closing of the control valves 24 and 25 according to the torque T and the angle difference D.

That is, as shown in FIG. 6, the valve control unit 32 opens the control valve 24 when the torque T is a positive value (T ≧ T1) and the angle difference D is equal to or less than a predetermined value d (range X). At the same time, the control valve 25 remains closed, and when the torque T is a negative value (T ≦ −T1) and the angle difference D is equal to or greater than the predetermined value −d (range Y), the control valve 24 is closed The valve is kept open and the control valve 25 is opened.
Further, the valve control unit 32 has a negative value (T ≦ −T1) when the torque T is a positive value (T ≧ T1) and the angle difference D is larger than the predetermined value d (range Z). When the angle difference D is smaller than the predetermined value −d (range Z), both the control valves 24 and 25 are opened.
When the torque T is in the range of -T1 <T <T1, the valve control unit 32 keeps both the control valves 24 and 25 closed regardless of the value of the angle difference D.

Therefore, when the driver rotates the steering handle 8 clockwise in plan view, that is, in a direction in which the operation angle A increases, the electric motor 23 is driven in the forward direction, the control valve 24 is opened, and the control valve 25 is It remains closed. Accordingly, the hydraulic oil is supplied from the hydraulic pump 22 to the left oil chamber of the steering cylinder 14 through the hydraulic pipe L2, and the hydraulic oil is recovered from the right oil chamber to the tank 20 through the hydraulic pipes L1 and L3. Thus, the rod of the steering cylinder 14 moves to the right in the plan view, and the rear wheel 5 turns counterclockwise in the plan view, that is, turns in the direction in which the turning angle C decreases.
Here, when the angle difference D between the target turning angle B and the turning angle C is larger than a predetermined value d, that is, when the turning of the rear wheel 5 is advanced with respect to the rotation operation of the steering handle 8, the hydraulic pump 22 A part of the hydraulic oil is recovered to the tank 20 through the hydraulic pipe L4, and the rest is supplied to the oil chamber on the left side of the steering cylinder 14 through the hydraulic pipe L2. Further, the hydraulic oil is recovered from the right oil chamber to the tank 20 through the hydraulic pipes L1 and L3. As a result, the target turning angle B decreases as the operation angle A increases, but the turning of the rear wheel 5 is suppressed, and the turning angle C does not become as small as the target turning angle B. The angle difference D between the angle B and the turning angle C is reduced.

On the other hand, when the steering handle 8 is rotated counterclockwise in a plan view, that is, in a direction in which the operation angle A is reduced, the electric motor 23 is driven in the reverse direction, and the control valve 25 is opened while the control valve 24 is closed. Is done. Thus, the hydraulic oil is supplied from the hydraulic pump 21 to the right oil chamber of the steering cylinder 14 through the hydraulic pipe L1, and the hydraulic oil is recovered from the left oil chamber to the tank 20 through the hydraulic pipes L2 and L4. Thus, the rod of the steering cylinder 14 moves leftward in plan view, and the rear wheel 5 turns clockwise in plan view, that is, turns in the direction in which the turning angle C increases.
Here, when the angle difference D between the target turning angle B and the turning angle C is smaller than the predetermined value −d, that is, when the rear wheel 5 is turning with respect to the rotation operation of the steering handle 8, the hydraulic pump 21 is driven. A part of the hydraulic oil from is recovered to the tank 20 through the hydraulic pipe L3, and the rest is supplied to the oil chamber on the right side of the steering cylinder 14 through the hydraulic pipe L1. Further, the hydraulic oil is recovered from the left oil chamber to the tank 20 through the hydraulic pipes L2 and L4. As a result, the target turning angle B increases as the operation angle A decreases, but the turning of the rear wheel 5 is suppressed, and the turning angle C does not increase as much as the target turning angle B. The angle difference D between the angle B and the turning angle C is reduced.

  According to such an embodiment, when the steering handle 8 is rotated clockwise in plan view or counterclockwise in plan view, the electric motor 23 is driven in the forward direction or the reverse direction in response to this, and the control valves 24, Since 25 is opened and closed, the driver can turn the rear wheel 5 together with the left and right axles 12 as intended. In addition, the control valves 24 and 25 are opened and closed based on the operation angle A and the steering angle C to appropriately control the hydraulic oil supplied to the steering cylinder 14 and the hydraulic oil recovered from the steering cylinder 14. Since the rear wheel 5 can be turned while reducing the angle difference D between the target turning angle B and the turning angle C, the driver has excellent operability.

  In addition, when the steering handle 8 is not rotated (the steering handle 8 is held in an arbitrary state), the electric motor 23 is stopped, so that power is not wasted. Further, by rotating the steering handle 8, the electric motor 23 can be driven by the torque transmitted through the torque transmission device, and the hydraulic pumps 21 and 22 can be driven. Thus, the electric motor 23 is temporarily controlled. Even if the motor control unit 31 breaks down, the rear cylinder 5 can be turned by operating the steering cylinder 14.

1 is a side view of a forklift according to an embodiment of the present invention. It is a hydraulic circuit diagram of an embodiment of the present invention. It is a functional block diagram of an embodiment of the present invention. It is a control characteristic figure of an embodiment of the present invention. It is a control characteristic figure of an embodiment of the present invention. It is a control characteristic figure of an embodiment of the present invention.

Explanation of symbols

1 Body 5 Rear wheel (steering wheel)
8 Steering handle 10 Rear wheel suspension device 12 Axle 14 Steering cylinder 15 Steering angle sensor 16 Torque sensor 17 Operation angle sensor 20 Tank 21 Hydraulic pump 22 Hydraulic pump 23 Electric motor 24 Control valve 25 Control valve 30 Control device 31 Motor control unit 32 Valve controller L1-L4 Hydraulic piping

Claims (4)

A support member for supporting a wheel is provided on the vehicle body so as to be rotatable about a vertical axis, and a double-acting steering cylinder connected to the support member is operated in accordance with a rotation operation of a steering handle. A steering device for an industrial vehicle that turns a wheel, and is connected to the electric motor as a driving source, a tank that stores hydraulic oil supplied to the steering cylinder, and the electric motor, and the electric motor is driven to rotate forward. The hydraulic oil is sucked from the tank and discharged to one oil chamber of the steering cylinder, and the electric motor is connected to the electric motor. A second hydraulic pump that sucks hydraulic oil from the tank and discharges the hydraulic oil toward the other oil chamber of the steering cylinder; and the electric motor, A motor control device that controls driving in the forward direction or the reverse direction corresponding to the direction in which the wheel turns, and branches off from a hydraulic pipe that connects the one oil chamber and the first hydraulic pump. A first hydraulic pipe connected to the tank; a second hydraulic pipe branched from the hydraulic pipe connecting the other oil chamber and the second hydraulic pump; and connected to the tank; A first control valve interposed in one hydraulic pipe and a second control valve interposed in the second hydraulic pipe, and further at an angle at which the steering handle is rotated. An operation angle detector that detects a certain operation angle, a turning angle detector that detects a turning angle that is an angle at which the support member turns, and the first and second rotations based on the operation angle and the turning angle. Open / close control of control valve A that valve control device, the valve control device calculates the target turning angle based on the operating angle by the operation angle detector, depending on the angular difference between the turning angle according to the target turning angle and the turning angle detector The first and second control valves are controlled to open and close, and when the electric motor is driven to rotate forward, when the angular difference is not more than a predetermined value as an absolute value, the first control valve Is closed and the second control valve is opened. When the electric motor is driven in reverse, the first control valve is opened when the angle difference is not more than a predetermined value as an absolute value. At the same time, the second control valve is closed, and when the turning angle is smaller than the target turning angle and the angle difference exceeds the predetermined value, the target turning angle becomes small. A steering apparatus for an industrial vehicle, wherein when the steering handle is rotated in a direction, the first and second control valves are opened . A support member for supporting a wheel is provided on the vehicle body so as to be rotatable about a vertical axis, and a double-acting steering cylinder connected to the support member is operated in accordance with a rotation operation of a steering handle. A steering device for an industrial vehicle that turns a wheel, and is connected to the electric motor as a driving source, a tank that stores hydraulic oil supplied to the steering cylinder, and the electric motor, and the electric motor is driven to rotate forward. The hydraulic oil is sucked from the tank and discharged to one oil chamber of the steering cylinder, and the electric motor is connected to the electric motor. A second hydraulic pump that sucks hydraulic oil from the tank and discharges the hydraulic oil toward the other oil chamber of the steering cylinder; and the electric motor, A motor control device that controls driving in the forward direction or the reverse direction corresponding to the direction in which the wheel turns, and branches off from a hydraulic pipe that connects the one oil chamber and the first hydraulic pump. A first hydraulic pipe connected to the tank; a second hydraulic pipe branched from the hydraulic pipe connecting the other oil chamber and the second hydraulic pump; and connected to the tank; A first control valve interposed in one hydraulic pipe and a second control valve interposed in the second hydraulic pipe, and further at an angle at which the steering handle is rotated. An operation angle detector that detects a certain operation angle, a turning angle detector that detects a turning angle that is an angle at which the support member turns, and the first and second rotations based on the operation angle and the turning angle. Open / close control of control valve A that valve control device, the valve control device calculates the target turning angle based on the operating angle by the operation angle detector, depending on the angular difference between the turning angle according to the target turning angle and the turning angle detector The first and second control valves are controlled to open and close, and when the electric motor is driven to rotate forward, when the angular difference is not more than a predetermined value as an absolute value, the first control valve Is closed and the second control valve is opened. When the electric motor is driven in reverse, the first control valve is opened when the angle difference is not more than a predetermined value as an absolute value. And the second control valve is closed, and the target turning angle is increased when the turning angle is larger than the target turning angle and the angle difference exceeds the predetermined value. When the steering handle is rotated in the direction, the first and second control valves are opened, the turning angle is smaller than the target turning angle, and the angle difference exceeds the predetermined value. When the steering handle is rotated in such a direction that the target turning angle is reduced, the first and second control valves are opened . A torque detector for detecting an operation torque when the steering handle is rotated; and the motor control device calculates an output of the electric motor from a detection result of the torque detector, and uses the output to calculate the output of the electric motor. 3. The industrial vehicle steering apparatus according to claim 1, wherein the electric motor is driven and controlled in the forward direction or the reverse direction. It is interposed between the steering wheel and the electric motor, according to claim 1 to claim the steering wheel is characterized in that the operating torque at the time of the rotation operation comprises a torque transmission device for transmitting to said electric motor 4. The steering device for an industrial vehicle according to any one of 3 above.

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