JP3864296B2 - Forklift steering control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steering control device for a forklift, and more particularly to a steering control device in which a handle and a steering wheel are not mechanically connected.
[0002]
[Prior art]
5A and 5B are a plan view and a side view of a reach forklift (hereinafter referred to as reach fork 1) as an example of a forklift. A fork device 4 on which a lift mechanism and a tilt mechanism of the fork 3 are mounted is attached to a pair of left and right reach legs 2, 2 provided at the front portion of the reach fork 1 so as to be movable forward and backward. The fork 3 is moved up and down and tilted by operation of a lift lever and a tilt lever (not shown) provided on a panel portion (not shown) of the driver's seat 5. Further, the operation of the reach lever (not shown) allows the fork device 4 to move forward and backward on the reach legs 2 and 2.
The reach fork 1 is rotatably arranged at the front part of the reach legs 2 and 2 and is provided below the left rear part of the vehicle body and a pair of left and right front wheels 6 and 6 that support the vehicle body, and functions of driving and steering. And a single steered wheel (hereinafter referred to as a tire 7) and a caster wheel 8 provided below the right rear part of the vehicle body. Some car models do not have caster wheels 8. The caster wheel 8 is rotatably attached while supporting the vehicle load. A vehicle speed lever (not shown) of the driver's seat 5 is operated to set the vehicle speed.
Steering is not mechanically connected to the steering wheel 9 disposed in the driver's seat 5 and the steering shaft of the tire 7, but is performed via a controller. As a method for controlling the steering angle of the tire 7, when the operator rotates the handle 9, the steering angular velocity of the tire 7 is controlled according to the rotation angular velocity, and when the rotation of the handle 9 is stopped, the steering is also stopped. . This is a steering control method in which steering angle detection is not performed by a steering angle detector and there is no steering angle feedback. At this time, the controller 21 shown in FIG. 6 outputs a PWM signal S having a duty corresponding to the handle operation angular velocity signal θhd from the handle operation angular velocity detector 41 attached in the vicinity of the handle 9 to the drive circuit 22. . The PWM signal is a signal that controls the pulse width of the on / off time, and is called 100% duty when the on pulse width is 100%, and zero% duty when the on pulse width is zero%. The drive circuit 22 controls the current value Im output to the steering motor (hereinafter referred to as the motor 15) by turning on and off the semiconductor switching elements in the drive circuit 22 at high speed based on the duty of the PWM signal.
[0003]
[Problems to be solved by the invention]
However, in the reach fork 1 described above, there is a problem that even if the steering angle of the tire 7 is changed by an obstacle during traveling, the changed steering angle cannot be corrected because there is no feedback of the steering angle. Therefore, as a control method for solving this problem, when the steering angle is changed by an obstacle, for example, in the clockwise direction when the steering wheel is not operated, voltage detection provided between the armature terminals of the DC motor 15 is detected. It is conceivable to prevent the steering angle from being changed by an obstacle by rotating the motor counterclockwise based on an electromotive voltage signal corresponding to the rotational angular velocity of the motor 15 detected by the device.
[0004]
However, this technique has the following problems.
When the steering wheel is operated when the vehicle is stopped (hereinafter referred to as stationary), the frictional resistance torque between the road surface in the steering angle direction and the tire 7 is larger than that during traveling. The twist angle in the steering direction is larger than the twist angle during travel. This twist angle is a magnitude corresponding to the frictional resistance between the road surface and the tire 7.
When the steering wheel operating angular velocity is set to zero after the tire 7 is fixed, that is, when the steering wheel operation is stopped, the motor 15 is electrically free. Therefore, the angle of the motor 15 is set to the tire by the twisting torque having the twisting angle. It is twisted back slightly to approach the angle of 7. At this time, since a voltage is generated in the motor 15, a PWM signal having a duty corresponding to the electromotive voltage value detected by the voltage detector is output to the motor 15, and the angle at which the motor 15 completes the steering operation. Go back in the direction. Then, when the motor output torque corresponding to the current value controlled by the duty of the outputted PWM signal becomes equal to the torsion torque of the tire, the rotation of the motor 15 is stopped. At this time, the duty of the PWM signal to all the switches of the drive circuit 22 that drives the motor 15 becomes zero% duty, and the motor 15 becomes electrically free again. Therefore, the motor is driven by the twisting torque having a twisting angle. The angle of 15 is slightly twisted back to approach the angle of the tire 7. By repeating the operation as described above, the motor 15 continuously vibrates, and the motor 15 is always in an operating state. For this reason, the consumption of the battery (not shown) and the wear of the motor brush increase, and the maintenance of the battery and the motor 15 takes much cost and time. For this reason, there is a strong demand for a steering control device in which the motor 15 does not continuously vibrate in free electric power steering control in which the steering angular velocity is controlled according to the steering operation angular velocity as described above.
[0005]
The present invention has been made paying attention to the above-mentioned problem, and in free electric power steering control for controlling the steering angular velocity according to the steering operation angular velocity, the motor and the continuous vibration at the time of stationary are prevented, and the battery and An object of the present invention is to provide a forklift steering control device capable of reducing the maintenance cost of a motor.
[0006]
[Means, actions and effects for solving the problems]
In the first invention, a handle (9), a handle operation angular velocity detector (41) for detecting an operation angular velocity (θhd) of the handle (9), and a signal indicating the handle operation angular velocity (θhd) are inputted, and a motor ( 15) Calculates and outputs signals (S1, S2, S3, S4) for driving, and rotates according to signals (S1, S2, S3, S4) output from the controller (21) A forklift steering control device comprising: a motor (15) for driving and a steered wheel (7) steered according to the rotation of the motor (15);
Speed detector (60) for detecting vehicle speed (V)
Is provided,
The controller (21)
While inputting the signal which shows the speed (V) of a vehicle, the calculation value (V2) according to the rotation direction and rotation speed of a motor (15) is calculated,
When the vehicle speed (V) is not zero and the steering wheel operating angular velocity (θhd) is zero , the motor (15) is rotated in the direction opposite to the rotation direction indicated by the calculation value (V2). Calculate and output signals (V3, S1, S2, S3, S4),
When the vehicle speed (V) is zero and the steering wheel operating angular velocity (θhd) is zero, the calculated value (V2) continues to change over a predetermined vibration duration (Tj). As a condition, a signal (V3, S1, S2, S3, S4) for making the motor (15) electrically free during a predetermined motor off time (ΔT) is calculated and output. The second invention is the steering control device for the same forklift,
Speed detector (60) for detecting vehicle speed (V)
Is provided,
The controller (21)
While inputting the signal which shows the speed (V) of a vehicle, the calculation value (V2) according to the rotation direction and rotation speed of a motor (15) is calculated,
When the vehicle speed (V) is not zero and the steering wheel operating angular velocity (θhd) is zero , the motor (15) is rotated in the direction opposite to the rotation direction indicated by the calculation value (V2). Calculate and output signals (V3, S1, S2, S3, S4),
When the vehicle speed (V) is zero and the steering wheel operating angular velocity (θhd) is zero , the motor (15) is brought into an electrically free state for a predetermined motor off time (ΔT). Signal (V3, S1, S2, S3, S4) is calculated and output.
[0007]
According to the first invention, when the vehicle is stopped and the steering wheel operating angular velocity becomes zero, the current command value of zero is output to the steering motor for a predetermined time, and the steering motor is electrically Make it free. As a result, the torsional torque generated between the steering motor and the steered wheels at the time of the stationary operation causes the steering motor to be twisted back to the position of the steered wheels, and the torsion angle becomes zero, so the torsional torque and the motor output torque The vibration of the steering motor, which occurs due to repeated balance, is stopped. This electrically free processing may be executed after it is determined that the output value of the voltage detector has continued to change for a predetermined time, or may be executed immediately after the steering operation. As a result, it is possible to obtain a forklift steering control device that does not sustain motor vibration during steering operation when the vehicle is stopped, and that can prevent battery consumption and motor brush wear.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a hardware configuration diagram of the present embodiment. The same components as those shown in FIGS. 5 and 6 will be described with the same reference numerals. A first sprocket 11 is attached to the shaft end of the handle shaft 10 extending from the center of the handle 9, and a second sprocket 12 is provided in the vicinity of the first sprocket 11. A chain 13 is wound around the first sprocket 11 and the second sprocket 12 to transmit the handle operating angle θh to the second sprocket 12. A handle operation angular velocity detector 41 for detecting a handle operation angular velocity θhd is attached to the center of the second sprocket 12. A first gear 16 is attached to a shaft end of a DC motor 15 that controls steering, and a second gear 17 is engaged with the first gear 16. A bracket 20 for transmitting the rotation of the second gear 17 to the tire 7 is fixed from the second gear 17, and the tire 7 is rotatably attached to an end portion of the bracket 20.
[0009]
The controller 21 includes a handle operation angular velocity θhd from the handle operation angular velocity detector 41, a first voltage value C1 of the first armature terminal A of the motor 15, a second voltage value C2 of the second armature terminal B, and the vehicle A speed V signal is input. The speed V of the vehicle is detected by a speed detector 60 attached in the vicinity of the axle (not shown) of the tire 7.
[0010]
The controller 21 includes a calculation unit 24, a determination unit 45, a signal generation unit 46, and a voltage detector 47. The voltage detector 47 is composed of, for example, an input / output insulation type differential amplifier. The calculation unit 24 calculates the first calculation value V1 according to the input handle operation angular velocity θhd. The first calculation value V <b> 1 is a speed command value for the motor 15. The voltage detector 47 receives the first voltage value C1 and the second voltage value C2, and based on the difference value between these voltage values, that is, the electromotive voltage value of the motor 15, according to the rotation direction and the rotation angular velocity of the motor 15. The second calculated value V2 is calculated. The determination unit 45 calculates the third calculation value V3 based on the calculated first calculation value V1, the second calculation value V2, and the input vehicle speed V, and outputs the third calculation value V3 to the signal generation unit 46. The signal generation unit 46 outputs a PWM signal to a semiconductor switching element (hereinafter referred to as a switch) in the drive circuit 22 to be described later according to the input third calculation value.
[0011]
Next, the drive circuit 22 will be described.
The drive circuit 22 has four switches, for example, first, second, third, and fourth switches 48, 49, 50, and 51. A parallel circuit of a series circuit of first and fourth switches 48 and 51 and a series circuit of third and second switches 50 and 49 is connected between the positive electrode and the negative electrode of the battery 52. A third terminal C between the first switch 48 and the fourth switch 51 and the first armature terminal A of the motor 15 are connected. The fourth terminal D between the third switch 50 and the second switch 49 and the second armature terminal B of the motor 15 are connected. That is, the drive circuit 22 constitutes an H-type bridge circuit centered on the motor 15. The first, second, third, and fourth switches 48, 49, 50, and 51 are turned on and off by the duty of the first, second, third, and fourth PWM signals S1, S2, S3, and S4 output from the signal generation unit 46 of the controller 21, respectively. . The duty of the first, second, third, and fourth PWM signals S1, S2, S3, and S4 is defined as a first duty S1D, a second duty S2D, a third duty S3D, and a fourth duty S4D.
When the first and second PWM signals S1 and S2 are output to the first and second switches 48 and 49 and the third and fourth switches 50 and 51 are off, the third terminal C, the first armature terminal A, It is assumed that a current flows through the path of the second armature terminal B and the fourth terminal D, and the motor 15 rotates in the clockwise direction. When a duty other than zero% is output to the first and second switches 48 and 49, either the first or second duty S1D or S2D is set to 100% duty, and the remaining duty is controlled to control the motor. There are cases where a method of controlling the rotational speed in the clockwise direction of 15 is employed. Here, it is assumed that the first duty S1D is set to 100% duty. Next, when the third and fourth PWM signals S3 and S4 are output to the third and fourth switches 50 and 51 and the first and second switches 48 and 49 are OFF, the fourth terminal D and the second armature terminal B A current flows through the path of the first armature terminal A and the third terminal C, and the motor 15 rotates counterclockwise. When a duty other than zero% is output to the third and fourth switches 50 and 51, either the third or fourth duty S3D or S4D is set to 100% duty, and the remaining duty is controlled to control the motor. A method of controlling the rotational speed of 15 counterclockwise directions may be used. Here, it is assumed that the third duty S3D is set to 100% duty.
As shown in FIG. 2, when the motor 15 is rotated by an external force, the voltage detector 47 is positive when the motor 15 is rotating clockwise and negative when the motor 15 is rotating counterclockwise. The second calculation value V2 is output.
[0012]
Next, the processing procedure of the determination unit 45 will be described with reference to the flowchart shown in FIG. In the description of FIG. 3, each processing step number is indicated with S.
In S1, it is determined whether or not the vehicle speed V is zero. If it is not a zero value, the first duty S1D, the second duty S2D, the third duty S3D, and the fourth duty S4D output to the first, second, third, and fourth switches 48, 49, 50, and 51, respectively, at S8. Is output to the signal generator 46 as a third calculation value V3 for setting a duty corresponding to the steering operation angular velocity θhd based on the first calculation value V1. That is, when the first calculated value V1 commanding the clockwise rotation, the first and second duties S1D and S2D of the first and second switches 48 and 49 are controlled, and the third and fourth switches 50 and 51 are controlled. The 3 and 4 duties S3D and S4D are set to zero% duty. In addition, when the first calculation value V1 commands rotation in the counterclockwise direction, the third and fourth duties S3D and S4D of the third and fourth switches 50 and 51 are controlled, and the first and second switches 48 and 49 1, 2 duty S1D, S2D is set to zero% duty. If it is determined in S1 that the vehicle speed V is a zero value, it is determined in S2 whether or not the first calculation value V1 is a zero value. If it is not zero, the process of S8 is executed. If the value is zero, it is determined in S3 whether or not the second calculation value V2 continues to change for a predetermined vibration duration Tj seconds or more. If the vibration duration continues to change for Tj seconds or more, in S4, the third calculation value V3 that sets the duty of all PWM signals to zero% duty for a predetermined motor off time ΔT seconds is given to the signal generator 46. Output. If the vibration duration has not changed for more than Tj seconds, it is determined in S5 whether or not the second calculation value V2 is greater than the zero value. When larger than the zero value, in S6, the first duty S1D and the second duty S2D are set to zero% duty, the third duty S3D is set to 100% duty, and the fourth duty S4D is set to the absolute value of the second calculated value V2. The third calculation value V3 set for each duty is output to the signal generator 46. When the second calculated value V2 is less than or equal to zero, in S7, the first duty S1D is set to 100% duty, the second duty S2D is set to a duty corresponding to the absolute value of the second calculated value V2, and the third duty S3D is set. The fourth duty S4D is set to zero% duty, and the third calculation value V3 that is set is output to the signal generator 46.
[0013]
Next, the effect | action by the above structure is demonstrated.
In FIG. 4, when the vehicle speed V is zero and the time t is zero, for example, the steering operation angular velocity θhd is increased stepwise from the zero value in a clockwise direction, that is, rotated at a constant speed, and zero at time Ts. Assuming that the values are returned in steps, the time change of the state quantities such as the steering operation angular velocity θhd, the steering angle, that is, the motor angle θm, and the tire angle θ at this time is shown. The tire angle θt changes following the motor angle θm while generating a twist angle Δθ between the motor angles θm due to the spring constant in the steering angle direction of the tire 7. In the temporal change of the state quantity shown in FIG. 4, the processing operation executed in the flowchart shown in FIG. 3 varies with the passage of time, so the time corresponding to the step number of FIG. Shown in the area.
[0014]
When the steering wheel operation angular velocity θhd increases stepwise in the clockwise direction, the calculation unit 24 calculates the first calculation value V1 according to the steering wheel operation angular velocity θhd. In the flowchart of FIG. 3, the vehicle speed V is zero. However, since the steering wheel operation angular velocity θhd is not zero, the process of S8 is executed. That is, the first switch 48 has a first PWM signal S1 having a first duty S1D of 100% duty, and the second switch has a second PWM signal S2 having a second duty S2D corresponding to the absolute value of the first calculation value V1. Each is output. Further, third and fourth PWM signals S3 and S4 having zero% duty are output to the third and fourth switches 50 and 51, and the motor 15 rotates in the clockwise direction. At this time, the tire 7 follows the motor angle θm with a twist angle Δθ that generates a torque equal to the frictional resistance torque in the steering angle direction between the road surface and the tire 7.
[0015]
When the steering operation angular velocity θhd is set to zero at the time Ts, the first calculation value V1 becomes zero. Therefore, the third calculation value V3 that sets the duty of all the PWM signals output to all the switches to zero% duty. The determination unit outputs. As a result, the motor becomes electrically free, and the torsional torque of the tire tends to be twisted back so that the motor angle approaches the tire angle θt from the point P1.
[0016]
The motor that has been rotating in the clockwise direction so far starts to rotate counterclockwise from the point P1 due to the torsional torque of the tire, so that the second calculated value V2 outputs a negative value as shown in FIG. To do. At this time, in the flowchart of FIG. 3, since the steering wheel operation angular velocity is zero, it is determined in S3 whether or not the second calculation value V2 continues to change for Tj seconds or more. If the second calculated value V2 has not changed for more than Tj seconds, it is determined in S5 whether the second calculated value V2 is greater than or equal to a zero value. At this time, since the second calculation value V2 is smaller than the zero value, the processing operation of S7 is executed. That is, the first PWM signal S1 having a first duty S1D of 100% duty is applied to the first switch 48, and the second PWM having a second duty S2D having a duty corresponding to the absolute value of the second calculated value V2 is applied to the second switch 49. A signal S2 is output, and third and fourth PWM signals S3D and S4D having a 0% duty are output to the third and fourth switches 50 and 51, and the motor 15 has a point P2 in the clockwise direction from the counterclockwise direction. Invert. Then, when the motor 15 rotates clockwise to the point P3 and the motor angle θm is a balance between the output torque of the motor 15 and the torsional torque, the second calculated value V2 becomes a zero value. Then, since the motor 15 is in an electrically free state, the motor 15 continues to vibrate in an attempt to rotate counterclockwise with the twisting torque of the tire 7 again.
[0017]
If it is determined in S3 of FIG. 3 that the second calculated value V2 continues to change for Tj seconds or more, that is, the continuous vibration of the motor continues for Tj seconds or more, the process proceeds to S4 and a predetermined motor off time ΔT. For a second, the third calculation value V3 that sets the duty of the PWM signal to all the switches of the drive circuit 22 to zero% duty is output to the signal generation unit. Since the motor 15 is in an electrically free state for only the motor off time ΔT seconds, the motor angle θm settles to an angle that matches the tire angle θt by the torsional torque and stops the continuous vibration.
[0018]
Next, the effect of this embodiment will be described.
After determining that the steering is stationary in S1 of the flowchart shown in FIG. 3 of the determination unit 45 and determining that the steering wheel operating angular velocity θhd is a zero value in S2, the first detection from the voltage detector 47 is performed in S3. 2. It is determined whether or not the calculated value V2 continues to change for a predetermined vibration duration Tj seconds or more. It can be seen that the motor 15 is continuously oscillating by determining that the vibration duration has continued to change for at least Tj seconds. The condition that the vibration duration is Tj seconds or more is set to prevent erroneous detection due to the influence of noise or the like. When it is detected that the motor 15 is continuously oscillating, the duty of the PWM signal to all the switches of the drive circuit 22 that drives the motor 15 is set to zero% duty for a predetermined motor off time ΔT seconds, and the motor 15 is Make it electrically free. When the motor 15 is in an electrically free state, the motor angle θm is twisted back to the tire angle θt by the torsional torque of the tire 7 in the steering angle direction, and the continuous vibration is stopped. To do. Note that the motor-off time ΔT during which the motor 15 is electrically free is a time during which the motor 15 sufficiently approaches the tire angle θt. As a result, the forklift steering control device can be obtained in which the motor does not continue to vibrate at the time of stationary and can prevent battery consumption and motor brush wear.
[0019]
According to the present embodiment, when it is determined that the motor electromotive voltage detected by the voltage detector continues to change for more than the vibration duration Tj seconds after the handle operation, the duty to all switches is set to zero% duty. Although set, this process of electrically freeing the motor 15 may be executed immediately after the steering wheel operation. Further, when the vehicle is stopped, a process of periodically making the motor 15 electrically free may be performed.
Further, according to the present embodiment, the drive circuit 22 of the motor 15 is an H-type bridge circuit using four semiconductor switching elements, and the rotational speed and direction of the motor 15 are controlled by the PWM signal. For example, a drive circuit using two semiconductor switching elements or another normal motor drive circuit may be used.
[0020]
As described above, the steering control device according to the present invention calculates the current command value based on the steering operation angular velocity detected by the steering operation angular velocity detector, outputs the current command value to the steering motor, and steers the steering motor angle or the steering motor angular velocity signal value. This is a steering control device that prevents continuous vibration of the motor in a steering control system without any feedback. That is, in order to prevent the steering angle from being changed by an external force, a voltage detector provided between the armatures of the motor is used to detect the rotational direction and rotational speed of the motor caused by the external force. In accordance with the output, a control circuit is provided to rotate the motor in the direction opposite to the steering angle changed by the external force. This control circuit is a steering control device for preventing the continuous vibration of the motor that has been induced when the steering wheel is closed.
The command current value output to the motor for a predetermined time after the steering wheel operating angular velocity becomes zero is set to zero. As a result, the motor is in an electrically free state, so that the motor angle is twisted back to the tire angle and settled by the torsion torque of the tire in the steering angle direction, and continuous vibration occurs. do not do. As a result, battery consumption and motor brush wear can be prevented, so that maintenance costs can be reduced.
[Brief description of the drawings]
FIG. 1 is a hardware configuration diagram according to the present invention.
FIG. 2 is an explanatory diagram of output characteristics of a voltage detector.
FIG. 3 is a flowchart of a determination unit.
FIG. 4 is an explanatory diagram showing temporal changes in handle operating angular velocity, motor angle, and tire angle.
FIG. 5 is an explanatory diagram of a reach fork as a forklift that is a subject of the present invention.
FIG. 6 is an explanatory diagram of a steering control device in which a steered wheel is not mechanically connected to a handle, which is a subject of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reach fork, 2 ... Reach leg, 3 ... Fork, 5 ... Driver's seat, 6 ... Front wheel, 7 ... Tire, 8 ... Caster wheel, 9 ... Handle, 14 ... Handle operation angle detector, 15 ... Motor, 21 ... Controller, 22 ... Drive circuit, 24 ... Calculation unit, 45 ... Judgment unit, 46 ... Signal generation unit, 47 ... Voltage detector, 48 ... First switch, 49 ... Second switch, 50 ... Third switch, 51 ... First 4 switches, 52, battery, θhd, steering wheel angular velocity, θm, motor angle, θt, tire angle, S1, first PWM signal, S2, second PWM signal, S3, third PWM signal, S4, fourth PWM signal, V1, second 1 calculated value, V2 ... 2nd calculated value, V3 ... 3rd calculated value, Tj ... vibration duration, ΔT ... motor off time.

Claims (2)

The handle (9), a handle operation angular velocity detector (41) for detecting the operation angular velocity (θhd) of the handle (9), and a signal indicating the handle operation angular velocity (θhd) are input to drive the motor (15). Controller (21) for calculating and outputting signals (S1, S2, S3, S4) for the purpose, and a motor (15) rotating in accordance with signals (S1, S2, S3, S4) output from the controller (21) And a steering control device for a forklift comprising a steering wheel (7) steered according to the rotation of the motor (15),
Speed detector (60) for detecting vehicle speed (V)
Is provided,
The controller (21)
While inputting the signal which shows the speed (V) of a vehicle, the calculation value (V2) according to the rotation direction and rotation speed of a motor (15) is calculated,
When the vehicle speed (V) is not zero and the steering wheel operating angular velocity (θhd) is zero , the motor (15) is rotated in the direction opposite to the rotation direction indicated by the calculation value (V2). Calculate and output signals (V3, S1, S2, S3, S4),
When the vehicle speed (V) is zero and the steering wheel operating angular velocity (θhd) is zero, the calculated value (V2) continues to change over a predetermined vibration duration (Tj). As a condition, a signal (V3, S1, S2, S3, S4) for making the motor (15) electrically free for a predetermined motor off time (ΔT) is calculated and output. Steering control device. The handle (9), a handle operation angular velocity detector (41) for detecting the operation angular velocity (θhd) of the handle (9), and a signal indicating the handle operation angular velocity (θhd) are input to drive the motor (15). Controller (21) for calculating and outputting signals (S1, S2, S3, S4) for the purpose, and a motor (15) rotating in accordance with signals (S1, S2, S3, S4) output from the controller (21) And a steering control device for a forklift comprising a steering wheel (7) steered according to the rotation of the motor (15),
Speed detector (60) for detecting vehicle speed (V)
Is provided,
The controller (21)
While inputting the signal which shows the speed (V) of a vehicle, the calculation value (V2) according to the rotation direction and rotation speed of a motor (15) is calculated,
When the vehicle speed (V) is not zero and the steering wheel operating angular velocity (θhd) is zero , the motor (15) is rotated in the direction opposite to the rotation direction indicated by the calculation value (V2). Calculate and output signals (V3, S1, S2, S3, S4),
When the vehicle speed (V) is zero and the steering wheel operating angular velocity (θhd) is zero , the motor (15) is brought into an electrically free state for a predetermined motor off time (ΔT). A forklift steering control device characterized by calculating and outputting signals (V3, S1, S2, S3, S4) for output.

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