Forklift truck and method for controlling forklift truck

Abstract

To suppress a sense of discomfort given to an operator of a forklift truck.SOLUTION: A controller multiplies an output ratio and a torque current curve together, thereby calculating a torque current command value. The controller converts the toque current command value into a command value for an inverter, thereby controlling a traveling motor so that a rotational speed of the traveling motor follows a target rotational speed. When torque at a current control cycle does not change across 0 from torque at a previous control cycle, the controller adds up a difference between the output ratio at the current control cycle and the output ratio at the previous control cycle as acceleration torque. When a rotational speed command at the current control cycle is 0, the controller sets, as the output ratio at the current control cycle, a value obtained by reducing only the acceleration torque of the output ratio at the previous control cycle by a predetermined value.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a forklift and a method for controlling the forklift. [Background technology]

[0002] The vehicle disclosed in Patent Document 1 includes a traveling motor, an inverter that drives the traveling motor, and a control device that controls the inverter. The control device drives the vehicle by powering the traveling motor. The control device brakes the vehicle by regenerating power from the traveling motor. The control device performs feedback control so that the rotation speed of the traveling motor follows a target rotation speed. The feedback control is performed so as to reduce the deviation between the rotation speed of the traveling motor and the target rotation speed. The feedback control is, for example, proportional-integral control. The forklift disclosed in Patent Document 2 includes a loading device. The loading device includes a fork and a mast. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-68596 A [Patent Document 2] JP 2023-46547 A Summary of the Invention [Problem to be solved by the invention]

[0004] A forklift may be subjected to a pushing operation. A pushing operation is an operation in which the forks are pushed against a load placed on the forklift. For example, a pushing operation is performed when moving a load to the base end of the forks to prevent the load from falling off the forks while the forklift is traveling. When a pushing operation is performed, the load comes into contact with the mast. Even if the accelerator member is operated in this state, the forklift will not travel due to the static friction force generated at the interface between the load and the place where the load is placed. In other words, when the accelerator member is operated, the deviation between the target rotation speed and the rotation speed of the travel motor becomes larger.

[0005] As disclosed in Patent Document 1, when feedback control is performed so that the rotation speed of the traveling motor follows the target rotation speed, the torque is increased as the deviation between the rotation speed of the traveling motor and the target rotation speed increases. Therefore, when a forklift is being pushed, the torque also increases as the deviation increases. When the pushing operation ends and the accelerator member is no longer operated, the deviation becomes 0. When the deviation becomes 0, the torque immediately before is maintained, resulting in a state in which torque is generated even though the accelerator member is not being operated. In this state, when the fork is raised, the load and the place where the load is placed are no longer in contact with each other, and the static friction force no longer acts. Then, the remaining torque may cause the forklift to move. This may cause the operator of the forklift to feel uncomfortable. [Means for solving the problem]

[0006] The forklift that solves the above problem includes an accelerator member, a traveling motor, an inverter that drives the traveling motor, and a control device that controls the inverter, wherein the control device obtains a rotation speed command corresponding to an operation amount of the accelerator member, calculates a target rotation speed based on the rotation speed command, an acceleration command, and a deceleration command, calculates a deviation between the rotation speed of the traveling motor and the target rotation speed, calculates an output ratio based on the deviation, a proportional gain, and an integral gain, calculates a torque current command value by multiplying the output ratio by a torque current curve, and controls the traveling motor so that the rotation speed of the traveling motor follows the target rotation speed by converting the torque current command value into a command value for the inverter, and sets a component of the output ratio that contributes to acceleration as an acceleration component and a component of the output ratio that contributes to braking as an acceleration component. When the torque in this control cycle is not changed from the torque in the previous control cycle by crossing 0, and a first condition that the absolute value of the output ratio in this control cycle is equal to or less than the absolute value of the output ratio in the previous control cycle or a second condition that the product of the rotation speed command and the output ratio in this control cycle is greater than 0 is satisfied, the difference between the output ratio in this control cycle and the output ratio in the previous control cycle is integrated as the acceleration component, and an acceleration output ratio up to a predetermined maximum number is calculated from the acceleration component and the output ratio in this control cycle, and when the rotation speed command in this control cycle is 0 and the acceleration output ratio is a value other than 0, a value obtained by reducing only the acceleration component of the output ratio in the previous control cycle by a predetermined value is used as the output ratio in the current control cycle.

[0007] The state where the rotation speed command in the current control cycle is 0 means that the accelerator member is not operated. In this case, the control device sets the output ratio in the current control cycle to a value obtained by reducing only the acceleration component of the output ratio in the previous control cycle by a predetermined value. The output ratio is reduced by reducing the acceleration component by a predetermined value. Therefore, when the rotation speed command becomes 0 with the end of the pushing operation, the torque is reduced by reducing the output ratio. When the load and the place where the load is placed are no longer in contact with each other and the static friction force no longer acts, the forklift is prevented from starting to travel even though the accelerator member is not being operated. This can prevent the forklift operator from feeling uncomfortable. In addition, by reducing only the acceleration component, the brake component that contributes to the braking of the forklift can remain in the output ratio. Therefore, when the output ratio is required to stop the forklift, such as when stopping the forklift on a slope, the forklift can be stopped by the brake component.

[0008] With regard to the forklift, when a pushing operation of the forklift is performed on a flat road, the output ratio in a previous control cycle may include only the acceleration component. With regard to the forklift, when the forklift is stopped on a slope, the output ratio in the previous control cycle may include only the brake component.

[0009] A method for controlling a forklift that solves the above-mentioned problems is a method for controlling a forklift that includes an accelerator member, a traveling motor, an inverter that drives the traveling motor, and a control device that controls the inverter, wherein the control device obtains a rotation speed command corresponding to an operation amount of the accelerator member, calculates a target rotation speed based on the rotation speed command, an acceleration command, and a deceleration command, calculates a deviation between the rotation speed of the traveling motor and the target rotation speed, calculates an output ratio based on the deviation, a proportional gain, and an integral gain, calculates a torque current command value by multiplying the output ratio by a torque current curve, and controls the traveling motor so that the rotation speed of the traveling motor follows the target rotation speed by converting the torque current command value into a command value for the inverter, and and when a component of the force ratio that contributes to braking is defined as a brake component, if a first condition is satisfied in which the absolute value of the output ratio in the current control cycle is equal to or less than the absolute value of the output ratio in the previous control cycle or a second condition is satisfied in which the product of the rotation speed command and the output ratio in the current control cycle is greater than 0, integrating a difference between the output ratio in the current control cycle and the output ratio in the previous control cycle as the acceleration component, calculating an acceleration output ratio up to a predetermined maximum number from the acceleration component and the output ratio in the current control cycle, and when the rotation speed command in the current control cycle is 0 and the acceleration output ratio is a value other than 0, reducing only the acceleration component of the output ratio in the previous control cycle by a predetermined value as the output ratio in the current control cycle.

[0010] When the rotation speed command becomes 0 as the pushing operation ends, the output ratio decreases, thereby reducing the torque. When the load and the place where the load is placed are no longer in contact and the static friction force no longer acts, the forklift is prevented from starting to move even though the accelerator member is not being operated. This makes it possible to prevent the forklift operator from feeling uncomfortable. Effect of the Invention

[0011] According to the present invention, it is possible to suppress a sense of discomfort felt by the operator of the forklift. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing a forklift. [Diagram 2] FIG. 2 is a schematic diagram of a forklift. [Diagram 3] FIG. 3 is a schematic diagram showing the function of the output ratio determination unit. [Figure 4] FIG. 4 is a flowchart showing the acceleration torque subtraction control. [Diagram 5] FIG. 5 is a flowchart showing the acceleration torque subtraction control. [Figure 6] FIG. 6 is a flowchart showing the acceleration torque calculation control. [Figure 7] FIG. 7 is a diagram showing an increase and decrease in torque. [Figure 8] FIG. 8 is a table showing the classification of acceleration torque and braking torque. [Figure 9] FIG. 9 is a diagram showing the rotation speed command, the output ratio, and the actual rotation speed of the forklift of the comparative example. [Figure 10] FIG. 10 is a diagram showing the rotation speed command, the output ratio, and the actual rotation speed of the forklift according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An embodiment of a forklift and a method for controlling the forklift will be described below. <Forklift> 1, the forklift 10 includes driving wheels 12 and steering wheels 13. The forklift 10 may be a counter type or a reach type.

[0014] The forklift 10 includes forks 14, a lift cylinder 15, and a mast 16. A load L is placed on the forks 14. The lift cylinder 15 is a hydraulic cylinder. The forks 14 are raised and lowered along the mast 16 by supplying and discharging hydraulic oil to the hydraulic cylinder.

[0015] As shown in Fig. 2, the forklift 10 includes a battery 21. The battery 21 is formed by connecting a plurality of power storage devices, for example. Any power storage device may be used as long as it is capable of charging and discharging. The power storage device may be, for example, a lead storage battery, a lithium ion secondary battery, or a nickel metal hydride storage battery.

[0016] The forklift 10 includes an inverter 22. The inverter 22 is, for example, a three-phase inverter that converts DC power into three-phase AC power. The inverter 22 is electrically connected to a battery 21. The inverter 22 converts DC power input from the battery 21 into AC power and outputs the AC power. The inverter 22 includes, for example, a switching element 23, and converts the DC power into AC power by the switching operation of the switching element 23.

[0017] The forklift 10 includes a traveling motor 24. The traveling motor 24 is, for example, a three-phase AC rotating electric machine. The traveling motor 24 is driven by an inverter 22. When power is supplied from the inverter 22, the traveling motor 24 operates as an electric motor to generate a rotational driving force. This rotational driving force is transmitted to the driving wheels 12 through the axles, causing the forklift 10 to travel. When the forklift 10 is braked, the traveling motor 24 operates as a generator to generate regenerative power. The power generated by the traveling motor 24 is supplied to the battery 21 through the inverter 22 as regenerative power. In this way, the traveling motor 24 is a motor generator that performs power running and regeneration.

[0018] The forklift 10 is braked by a regenerative braking force generated by the traveling motor 24. The forklift 10 does not include a mechanical brake such as a disk brake or a drum brake. Therefore, the forklift 10 includes only the traveling motor 24 as a braking device.

[0019] When the forklift 10 has a plurality of drive wheels 12, a travel motor 24 may be provided for each drive wheel 12. In this case, an inverter 22 may be provided for each travel motor 24. The forklift 10 is an electric forklift that travels by the travel motor 24.

[0020] The forklift 10 includes an accelerator member 25. The accelerator member 25 is a member that is operated when the forklift 10 is driven. If the forklift 10 is a counter-load forklift, the accelerator member 25 is, for example, an accelerator pedal. If the forklift 10 is a reach forklift, the accelerator member 25 is, for example, a direction lever.

[0021] The forklift 10 includes an accelerator sensor 26. The accelerator sensor 26 detects the amount of operation of the accelerator member 25. The accelerator sensor 26 outputs an electric signal according to the amount of operation of the accelerator member 25.

[0022] The forklift 10 includes a rotation speed sensor 27. The rotation speed sensor 27 outputs an electric signal corresponding to the rotation speed [rpm] of the traveling motor 24. The rotation speed sensor 27 is, for example, a resolver or an encoder.

[0023] The forklift 10 includes a phase current detection unit 28. The phase current detection unit 28 detects phase currents flowing through the traveling motor 24. The phase current detection unit 28 detects phase currents for at least two phases. It is also possible to detect phase currents for two of the three phases and calculate the phase current for the remaining phase from the phase currents for the two phases.

[0024] The forklift 10 includes a hydraulic mechanism 29. The hydraulic mechanism 29 supplies and discharges hydraulic oil to hydraulic devices included in the forklift 10. The hydraulic mechanism 29 includes, for example, a pump that discharges hydraulic oil, and a control valve that controls the supply amount and destination of the hydraulic oil. The hydraulic devices included in the forklift 10 include the lift cylinder 15.

[0025] The forklift 10 includes a control device 30. The control device 30 includes a processor and a storage unit. The processor is, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit includes a random access memory (RAM) and a read only memory (ROM). The storage unit stores a program for operating the forklift 10. The storage unit stores program code or instructions configured to cause the processor to execute processing. The storage unit, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control device 30 may be configured by a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control device 30, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0026] The control device 30 obtains an electrical signal from the accelerator sensor 26. The control device 30 recognizes the accelerator operation amount from the electrical signal obtained from the accelerator sensor 26. The control device 30 obtains an electrical signal from the rotation speed sensor 27. The control device 30 recognizes the rotation speed of the traveling motor 24 from the electrical signal obtained from the rotation speed sensor 27. The rotation speed of the traveling motor 24 recognized by the rotation speed sensor 27 is appropriately referred to as the actual rotation speed. The sign of the actual rotation speed [rpm] is reversed (+ or -) depending on the rotation direction of the traveling motor 24. For example, if the actual rotation speed is +, it is a forward rotation, and if the actual rotation speed is -, it is a reverse rotation.

[0027] The control device 30 controls the hydraulic mechanism 29. For example, the control device 30 controls the hydraulic mechanism 29 to raise and lower the forks 14. The control device 30 controls the inverter 22. The control device 30 includes an output ratio determination unit 41, a torque current command calculation unit 31, and a voltage command calculation unit 32. The output ratio determination unit 41, the torque current command calculation unit 31, and the voltage command calculation unit 32 are functional units that function as the control device 30 executes predetermined processing.

[0028] The output ratio determination unit 41 determines the output ratio [%]. The torque current command calculation unit 31 calculates a torque current command value. The torque current command value may also be referred to as a q-axis current command value. The torque current command calculation unit 31 calculates the torque current command value by multiplying the output ratio determined by the output ratio determination unit 41 by a torque current curve.

[0029] The voltage command calculation unit 32 calculates a voltage command value based on the deviation between the torque current command value and the torque current, and the deviation between the excitation current command value and the excitation current. The excitation current command value is calculated by the control device 30. The excitation current command value is sometimes referred to as a d-axis current command value. The torque current is a component of the current flowing through the traveling motor 24 that generates torque. The excitation current is a component of the current flowing through the traveling motor 24 that generates magnetic flux. The torque current and the excitation current can be calculated from the phase current. The voltage command calculation unit 32 calculates a voltage command value so that the deviation between the torque current command value and the torque current, and the deviation between the excitation current command value and the excitation current are reduced. The inverter 22 is controlled based on the voltage command value. The voltage command value is a command value for the inverter 22. In this way, the control device 30 converts the torque current command value into a command value for the inverter 22 to control the traveling motor 24 so that the rotation speed of the traveling motor 24 follows the target rotation speed.

[0030] As shown in FIG. 3, the output ratio determination unit 41 includes a target rotation speed calculation unit 42, a subtraction unit 43, an output ratio calculation unit 44, a proportional gain calculation unit 45, an integral gain calculation unit 46, and an output ratio correction unit 47.

[0031] The target rotation speed calculation unit 42 calculates the target rotation speed based on the rotation speed command, the acceleration command, and the deceleration command. The rotation speed command is calculated based on, for example, an accelerator operation amount. The target rotation speed calculation unit 42 may calculate the rotation speed command according to the accelerator operation amount. The target rotation speed calculation unit 42 may obtain the rotation speed command from a higher-level control device. The ± of the rotation speed command differs depending on, for example, whether the forklift 10 is instructed to move forward or backward. For example, when the direction lever instructs the forklift 10 to move forward, the rotation speed command is +. When the direction lever instructs the forklift 10 to move backward, the rotation speed command is -. The acceleration command is calculated based on, for example, a deviation between the target rotation speed and the actual rotation speed. The deceleration command is calculated based on, for example, a deviation between the target rotation speed and the actual rotation speed. The target rotation speed is a target value of the rotation speed that makes the actual rotation speed follow the acceleration instructed by the acceleration command or the deceleration instructed by the deceleration command.

[0032] The subtraction unit 43 calculates a speed deviation, which is the deviation between the target rotation speed and the actual rotation speed. The output ratio calculation unit 44 calculates the output ratio based on the speed deviation, the proportional gain, and the integral gain. The output ratio calculation unit 44 calculates the output ratio based on the proportional gain and the integral gain so that the speed deviation approaches 0. The output ratio determination unit 41 calculates the output ratio by proportional-integral control as feedback control.

[0033] When the traveling motor 24 is powered, the actual rotation speed and the output ratio are the same in sign. When the traveling motor 24 is regenerating, the actual rotation speed and the output ratio are different in sign. For example, when the traveling motor 24 is powered, if the actual rotation speed is a positive value, the output ratio is a positive value. When the traveling motor 24 is regenerating, if the actual rotation speed is a positive value, the output ratio is a negative value. For convenience, the output ratio calculated by the output ratio calculation unit 44 is referred to as the speed control output ratio.

[0034] The proportional gain calculation unit 45 calculates the proportional gain. The proportional gain is calculated based on, for example, the accelerator operation amount and the actual rotation speed of the travel motor 24. The integral gain calculation unit 46 calculates the integral gain. The integral gain is calculated based on, for example, the accelerator operation amount and the actual rotation speed of the travel motor 24.

[0035] The output rate correction unit 47 corrects the speed control output rate. Then, the output rate correction unit 47 outputs the output rate. The output rate determination unit 41 outputs the output rate at a predetermined control period.

[0036] The control device 30 has a boost mode. The boost mode is a mode in which the torque of the travel motor 24 is temporarily increased to a certain value. The control device 30 sets the boost mode when the rotation speed command is greater than a threshold value, the actual rotation speed is lower than the threshold value, the output ratio is 100[%], and these states continue for a predetermined time. In this state, even though the output ratio is 100[%], the deviation between the actual rotation speed and the rotation speed command is large. For this reason, control is performed so that the deviation between the actual rotation speed and the rotation speed command is reduced by temporarily increasing the torque. The threshold value and the predetermined time can be set arbitrarily. For convenience, the case in which the boost mode is not set is referred to as a normal mode.

[0037] The output rate correcting unit 47 executes the acceleration torque subtraction control and the acceleration torque calculation control, whereby the control method for the forklift 10 by the control device 30 is executed. <Acceleration torque subtraction control> The acceleration torque subtraction control performed by the output rate correcting section 47 will be described.

[0038] As shown in FIG. 4 and FIG. 5, in step S1, the output ratio correction unit 47 judges whether the rotation speed command is 0, the mode is normal, and the acceleration output ratio is a value different from 0. The rotation speed command is 0 when the accelerator member 25 is not operated. Therefore, by judging whether the rotation speed command is 0, it is possible to judge whether the accelerator member 25 is no longer operated or is still being operated. Since the normal mode is a case where the boost mode is not set, in step S1, it is judged whether the boost mode is set. The acceleration output ratio can take a value in the range of 0 to a predetermined maximum number. The predetermined maximum number is, for example, 10000. The acceleration output ratio is calculated by an acceleration torque calculation control to be described later. When the acceleration output ratio is 0, the acceleration torque is also 0. Therefore, in step S1, the output ratio correction unit 47 may judge whether the rotation speed command is 0, the mode is normal, and the acceleration torque is a value different from 0. In this case, the acceleration torque may be calculated in the same manner as in step S2 to be described later.

[0039] If the determination result of step S1 is negative, the output ratio correction unit 47 performs the process of step S30. In step S30, the output ratio correction unit 47 sets the current value output ratio as the speed control output ratio. The current value output ratio is the output ratio in the current control cycle. In other words, it is the output ratio output from the output ratio determination unit 41 to the torque current command calculation unit 31.

[0040] When the determination result of step S1 is positive, the output ratio correction unit 47 performs processing of step S2. In step S2, the output ratio correction unit 47 calculates acceleration torque. The output ratio includes an acceleration component that contributes to the acceleration of the forklift 10 and a brake component that contributes to the braking of the forklift 10. The acceleration torque is the acceleration component of the output ratio. The acceleration torque can be calculated by the previous value output ratio x acceleration output ratio / predetermined maximum number. Thereby, the acceleration torque can be expressed as a percentage like the output ratio. The previous value output ratio is the output ratio in the previous control cycle. The predetermined maximum number is the maximum number that the above-mentioned acceleration output ratio can take. A value obtained by subtracting the acceleration torque from the output ratio is the brake torque. The brake torque is the brake component of the output ratio. The output ratio correction unit 47 can also calculate the brake torque by subtracting the acceleration torque from the output ratio.

[0041] Next, in step S3, output ratio correction unit 47 determines whether the acceleration torque is greater than 0. The positive or negative sign of the acceleration torque is the same as the positive or negative sign of the previous value output ratio. Therefore, if the previous value output ratio is positive, the acceleration torque is positive. If the previous value output ratio is negative, the acceleration torque is negative. If the determination result in step S3 is positive, output ratio correction unit 47 performs the process of step S4.

[0042] In step S4, the output ratio correction unit 47 determines the post-subtraction acceleration torque as a value obtained by subtracting a fixed value [%] from the acceleration torque. The fixed value is set based on the target time required to make the acceleration torque 0. By performing step S4 for each control cycle, the post-subtraction acceleration torque approaches 0 by a fixed value for each control cycle. Therefore, the time required to make the acceleration torque 0 is determined by the interval of the control cycle and the fixed value. For example, the target time required to make the acceleration torque 0 is set to 300 [ms], and the interval of the control cycle is set to 4 [ms]. Then, assuming that the acceleration torque is to be made 0 in the target time from 100 [%], which is the maximum value that the acceleration torque can take, the fixed value is set to 1.33 [%].

[0043] Next, in step S5, the output ratio correction unit 47 determines whether the post-subtraction acceleration torque is less than 0. That is, the output ratio correction unit 47 determines whether the post-subtraction acceleration torque has become less than 0 by repeating the process of step S4. If the determination result of step S5 is negative, the output ratio correction unit 47 performs the process of step S7. If the determination result of step S5 is positive, the output ratio correction unit 47 performs the process of step S6.

[0044] In step S6, the output ratio corrector 47 sets the post-subtraction acceleration torque to 0 and performs the process of step S7. Even if the post-subtraction acceleration torque becomes a value less than 0, the post-subtraction acceleration torque is set to 0 in step S6. That is, the lower limit value of the post-subtraction acceleration torque is 0.

[0045] In step S7, output rate correction unit 47 calculates the post-subtraction output rate. The post-subtraction output rate can be calculated by: previous value output rate - (acceleration torque - post-subtraction acceleration torque). By calculating the difference between the acceleration torque and the post-deceleration acceleration torque, a value subtracted from the acceleration torque in steps S4 to S6 can be obtained. By subtracting this value from the previous value output rate, the post-subtraction output rate can be obtained. Since the post-subtraction acceleration torque is subtracted by a fixed value every control cycle, the post-subtraction output rate is also subtracted by a fixed value every control cycle. The fixed value is a predetermined value that is subtracted from the acceleration torque of the previous value output rate.

[0046] Next, in step S8, the output ratio correction unit 47 judges whether the post-subtraction output ratio is greater than the speed control output ratio. If the judgment result in step S8 is positive, the output ratio correction unit 47 performs processing in step S9. In step S9, the output ratio correction unit 47 sets the current value output ratio to the speed control output ratio. If the judgment result in step S8 is negative, the output ratio correction unit 47 performs processing in step S10. In step S10, the output ratio correction unit 47 sets the current value output ratio to the post-subtraction output ratio.

[0047] In steps S8 to S10, the output rate correction unit 47 sets the smaller one of the speed control output rate and the post-deceleration output rate as the current value output rate. If the determination result of step S3 is negative, output ratio correction unit 47 performs the process of step S20. In step S20, output ratio correction unit 47 determines whether or not the acceleration torque is less than 0. If the determination result of step S20 is negative, output ratio correction unit 47 performs the process of step S30. If the determination result of step S20 is positive, output ratio correction unit 47 performs the process of step S21.

[0048] In step S21, the output ratio correction unit 47 sets a value obtained by adding a fixed value [%] to the acceleration torque as the post-subtraction acceleration torque. The fixed value is the same value as the fixed value in step S4. Next, in step S22, the output ratio correction unit 47 determines whether the post-subtraction acceleration torque is greater than 0. That is, the output ratio correction unit 47 determines whether the post-subtraction acceleration torque has become greater than 0 by repeating the process of step S21. If the determination result of step S22 is negative, the output ratio correction unit 47 performs the process of step S24. If the determination result of step S22 is positive, the output ratio correction unit 47 performs the process of step S23.

[0049] In step S23, the output rate correcting unit 47 sets the post-subtraction acceleration torque to 0, and then performs the process of step S24. In step S24, the output rate correction unit 47 calculates the post-subtraction output rate. The post-subtraction output rate can be calculated by: previous value output rate-(post-subtraction acceleration torque-acceleration torque).

[0050] Next, in step S25, the output ratio correction unit 47 judges whether the post-subtraction output ratio is smaller than the speed control output ratio. If the judgment result in step S25 is positive, the output ratio correction unit 47 performs the processing of step S26. In step S26, the output ratio correction unit 47 sets the current value output ratio to the speed control output ratio. If the judgment result in step S25 is negative, the output ratio correction unit 47 performs the processing of step S27. In step S27, the output ratio correction unit 47 sets the current value output ratio to the post-subtraction output ratio.

[0051] In steps S25 to S27, the output rate correction unit 47 sets the larger of the speed control output rate and the post-deceleration output rate as the current value output rate. As described above, steps S4 to S10 are processes for reducing the acceleration torque and obtaining a current value output ratio with the reduced acceleration torque when the acceleration torque is positive. Steps S21 to S27 are processes for reducing the acceleration torque and obtaining a current value output ratio with the reduced acceleration torque when the acceleration torque is negative. That is, the process for reducing the acceleration torque is performed whether the acceleration torque is positive or negative. In the acceleration torque subtraction process, a value obtained by reducing the acceleration torque by a fixed value in one control period can be obtained. In the acceleration torque subtraction process, since the process for reducing the brake torque is not performed, only the acceleration torque is reduced. "Reducing the acceleration torque" means bringing the acceleration torque closer to 0, that is, reducing the absolute value of the acceleration torque.

[0052] <Acceleration torque calculation control> The acceleration torque calculation control performed by the output rate correcting section 47 will be described. As shown in FIG. 6, in step S41, output rate correction unit 47 calculates the output rate change amount, the previous value acceleration torque, and the product of the rotation speed command and the output rate. The output rate change amount can be calculated by: current value output rate - previous value output rate. The previous value acceleration torque can be calculated by: previous value output rate x previous value acceleration output rate / predetermined maximum number. The previous value acceleration torque is the acceleration torque in the previous control cycle. The previous value acceleration output rate is the acceleration output rate in the previous control cycle. The predetermined maximum number is the maximum number that the acceleration output rate mentioned above can take. The product of the rotation speed command and the output rate can be calculated by: rotation speed command x current value output rate.

[0053] Next, in step S42, output ratio correction unit 47 determines whether the current value output ratio is a value different from 0. If the determination result in step S42 is negative, output ratio correction unit 47 performs processing in step S60. In step S60, output ratio correction unit 47 sets the acceleration torque to 0. In addition, output ratio correction unit 47 sets the acceleration output ratio to 0. Since the acceleration torque is the ratio of the output ratio that contributes to acceleration, when the current value output ratio is 0, the acceleration torque and acceleration output ratio also become 0.

[0054] If the determination result in step S42 is positive, the output rate corrector 47 performs the process of step S43. In step S43, output ratio correction unit 47 determines whether the condition that the previous value output ratio is greater than 0 and the current value output ratio is equal to or greater than 0, or the condition that the previous value output ratio is less than 0 and the current value output ratio is equal to or less than 0 is satisfied. If either of the above two conditions is satisfied, the positive or negative output ratio has not changed during one control cycle. In other words, the torque in the current control cycle has not changed from the torque in the previous control cycle by straddling 0. The positive or negative output ratio and the positive or negative torque match. If the determination result in step S43 is positive, output ratio correction unit 47 performs the process of step S44.

[0055] In step S44, the output ratio correction unit 47 judges whether or not a first condition is satisfied, that is, the absolute value of the current value output ratio is equal to or less than the absolute value of the previous value output ratio, or a second condition is satisfied, that is, the product of the rotation speed command and the output ratio is greater than 0. If the absolute value of the current value output ratio is equal to or less than the absolute value of the previous value output ratio, the torque changes to approach 0 during one control cycle, or the torque does not change during one cycle. If the product of the rotation speed command and the output ratio is greater than 0, the positive and negative signs of the rotation speed command and the output ratio match. If the positive and negative signs of the rotation speed command and the output ratio match, the traveling motor 24 is powered in response to the operation of the accelerator member 25 by the operator of the forklift 10. If the judgment result in step S44 is negative, the output ratio correction unit 47 performs the process of step S49.

[0056] If the determination result of step S44 is positive, the output ratio correction unit 47 performs processing of step S45. In step S45, the output ratio correction unit 47 sets the acceleration torque to the previous value acceleration torque + the output ratio change amount. If the first condition is satisfied, the output ratio is decreased or maintained during one control cycle. If the output ratio is decreased during one control cycle, the output ratio change amount becomes a negative value, so the acceleration torque becomes small. If the output ratio is maintained during one control cycle, the output ratio change amount is 0, so the acceleration torque is maintained. If the first condition is not satisfied, the output ratio is increased. If the product of the rotation speed command and the output ratio is greater than 0, the traveling motor 24 is powered, so the increased output ratio in this case is the acceleration torque. If the product of the rotation speed command and the output ratio is less than 0, the traveling motor 24 is regenerating, so the increased output ratio in this case is the brake torque. If the second condition is satisfied, the output ratio change amount becomes a positive value, so the acceleration torque becomes large. In this way, when the torque in the current control cycle has not changed beyond 0 from the torque in the previous control cycle and the first condition or the second condition is satisfied, the output ratio correction unit 47 accumulates the difference between the output ratio in the current control cycle and the output ratio in the previous control cycle as the acceleration torque. Then, whether the acceleration torque increases or decreases depends on whether the first condition or the second condition is satisfied.

[0057] If the result of the determination in step S43 is negative, the output rate corrector 47 performs the process of step S46. In step S46, output ratio correction unit 47 judges whether the product of the rotation speed command and the output ratio is greater than 0. If the judgment result in step S46 is positive, output ratio correction unit 47 performs the processing of step S47. In step S47, output ratio correction unit 47 sets the current value output ratio as the acceleration torque and performs the processing of step S49. If the judgment result in step S46 is negative, output ratio correction unit 47 performs the processing of step S48. In step S48, output ratio correction unit 47 sets the acceleration torque to 0 and performs the processing of step S49.

[0058] In steps S43 to S48, the acceleration torque is determined. If the determination results of steps S43 and S44 are positive, the acceleration torque is the previous acceleration torque plus the output rate change amount. That is, the acceleration torque is integrated while the determination results of steps S43 and S44 remain positive. If the determination result of step S43 is negative and the determination result of step S46 is positive, the acceleration torque is the current output rate. If the determination results of steps S43 and S46 are negative, the acceleration torque is zero.

[0059] In step S49, the output ratio correction unit 47 determines whether either the condition that the current value output ratio is equal to or greater than 0 and the acceleration torque is less than 0, or the condition that the current value output ratio is equal to or less than 0 and the acceleration torque is greater than 0 is satisfied. If the determination result in step S49 is negative, the output ratio correction unit 47 performs processing in step S51. If the determination result in step S49 is positive, the output ratio correction unit 47 performs processing in step S50.

[0060] In step S50, the output rate correcting unit 47 sets the acceleration torque to 0, and then performs the process of step S51. In step S51, the output ratio correction unit 47 calculates the acceleration output ratio from the acceleration torque determined in step S45, step S47, step S48, or step S50, and the current value output ratio. That is, the output ratio correction unit 47 calculates the acceleration output ratio from the acceleration torque calculated using the output ratio change amount, the previous value acceleration torque, and the product of the rotation speed command and the output ratio, and the current value output ratio. The acceleration output ratio can be calculated by acceleration torque x predetermined maximum number / current value output ratio. The predetermined maximum number is the maximum number that the above-mentioned acceleration output ratio can take. The acceleration output ratio is a value obtained by converting the acceleration torque, which is a component of the output ratio that contributes to acceleration, into a numerical value with the predetermined maximum number as an upper limit. When the acceleration output ratio is calculated in step S51, the output ratio correction unit 47 ends the acceleration torque calculation control.

[0061] The above-mentioned acceleration torque calculation control can be expressed in FIG. 7 and FIG. As shown in Fig. 7, when the torque changes away from 0, it is considered that the torque is increasing. When the torque changes toward 0, it is considered that the torque is decreasing.

[0062] As shown in FIG. 8, the case where the positive and negative signs of the rotation speed command and the torque match is defined as an acceleration torque. The case where the positive and negative signs of the rotation speed command and the torque do not match is defined as a brake torque. The state where the positive and negative signs of the rotation speed command and the torque match includes a state where the forklift 10 moves forward as the operator of the forklift 10 operates the accelerator member 25 to move the forklift 10 forward. The state where the positive and negative signs of the rotation speed command and the torque match includes a state where the forklift 10 moves backward as the operator of the forklift 10 operates the accelerator member 25 to move the forklift 10 backward. The positive and negative signs of the torque are the positive and negative signs of the current value output ratio. Whether the positive and negative signs of the rotation speed command and the torque match can be determined by whether the product of the rotation speed command and the current value output ratio is greater than 0.

[0063] As shown in Figures 7 and 8, when the torque does not change beyond 0, the acceleration torque can be calculated by integrating the difference in the output ratio during one control cycle in response to the increase or decrease in torque.

[0064] When the forklift 10 is pushed on a flat road, the output ratio in the previous control cycle includes only the acceleration torque. This is because, on a flat road, there is no need to stop the forklift 10 by braking torque, and so only the acceleration torque increases due to the pushing operation. The pushing operation is an operation in which the forks 14 are pushed against the load L placed on the road.

[0065] When the forklift 10 is stopped on a slope, the output ratio in the previous control cycle includes only the brake torque. This is because when the forklift 10 is stopped on a slope, it is necessary to stop the forklift 10 by the brake torque. Also, when the forklift 10 is stopped, the acceleration torque is 0.

[0066] [Operation of this embodiment] 9 and 10 show the relationship between the rotation speed command, the output ratio, and the actual rotation speed. In Fig. 9 and Fig. 10, line L1 shows the rotation speed command, line L2 shows the output ratio, and line L3 shows the actual rotation speed.

[0067] FIG. 9 shows, as a comparative example, the relationship between the rotation speed command, the output ratio, and the actual rotation speed of a forklift in which the acceleration torque subtraction control and the acceleration torque calculation control are not performed. Assume that the forklift is pushed forward until time T1. When the forklift is pushed forward, the load L comes into contact with the mast 16. Even if the accelerator member 25 is operated in this state, the forklift 10 does not move due to the static friction generated at the interface between the load L and the place where the load L is placed. As a result, the deviation between the rotation speed command and the actual rotation speed increases. Accordingly, the output ratio, i.e., the torque of the traveling motor 24, also increases.

[0068] When the pushing operation is no longer performed at time T1, the accelerator member 25 is no longer operated, and the rotation speed command becomes 0. When the deviation between the rotation speed command and the actual rotation speed is 0, the deviation between the target rotation speed and the actual rotation speed is also 0. Feedback gains such as proportional gain and integral gain act on the deviation to reduce the deviation, so when the deviation is 0, the output ratio immediately before is maintained. When a pushing operation is performed, the output ratio when a pushing operation is performed is maintained.

[0069] When the forks 14 start to rise at time T2, the load L is raised by the forks 14. As a result, the load L is no longer in contact with the location where the load L is placed, and the static friction force no longer acts. Since the output ratio during the pushing operation is maintained, the forklift 10 starts to move due to the torque generated by this output ratio. When the forklift 10 starts to move, the output ratio changes so that the deviation between the rotation speed command and the actual rotation speed becomes large and the forklift 10 stops. As a result, although the forklift 10 stops, the operator of the forklift 10 may feel uncomfortable in operation.

[0070] FIG. 10 shows the relationship between the rotation speed command, the output ratio, and the actual rotation speed of the forklift 10 of this embodiment. Assume that the forklift 10 is pushed until time T1. As a result, the output ratio increases. As can be seen from Fig. 10, during the pushing operation, the positive and negative rotation speed command and the positive and negative output ratio match. Therefore, the acceleration torque is accumulated while the pushing operation continues.

[0071] When the pushing operation is no longer performed at time T1, the accelerator member 25 is no longer operated and the rotation speed command becomes 0. When the rotation speed command becomes 0, the acceleration torque is reduced from the previous output rate until the acceleration output rate becomes 0. In other words, a process is performed to reduce the output rate from the output rate at the time when the rotation speed command became 0, with the acceleration torque at that time as the upper limit. As a result, the output rate decreases from time T1. In the acceleration torque subtraction control, only the acceleration torque calculated in the acceleration torque calculation control is reduced. As a result, the brake torque remains in the output rate.

[0072] Even if the forks 14 start to rise at time T2 and the load L is no longer in contact with the place where the load L is placed, and the static friction force no longer acts, the acceleration torque is removed from the output ratio at this stage. This prevents the forklift 10 from starting to travel even if the accelerator member 25 is not being operated.

[0073] [Effects of this embodiment] (1) When the rotation speed command is 0, the control device 30 reduces the acceleration torque. When the rotation speed command becomes 0 as the pushing operation ends, the output ratio decreases, thereby reducing the torque. When the load L and the place where the load L is placed are no longer in contact with each other and the static friction force no longer acts, the forklift 10 is prevented from starting to travel even though the accelerator member 25 is not being operated. This makes it possible to prevent the operator of the forklift 10 from feeling uncomfortable.

[0074] Moreover, by reducing only the acceleration torque, it is possible to leave the brake torque that contributes to braking the forklift 10 out of the output ratio. Therefore, when the output ratio is required to stop the forklift 10, such as when stopping the forklift 10 on a slope, the forklift 10 can be stopped by the brake torque.

[0075] (2) When the forklift 10 is pushed on a flat road, the output ratio in the previous control cycle includes only the acceleration torque. Therefore, after the pushing operation is completed, the output ratio decreases. Since the acceleration torque decreases after the pushing operation is completed, the forklift 10 is prevented from starting to travel after the pushing operation is completed even if the accelerator member 25 is not operated.

[0076] (3) When stopping the forklift 10 on a slope, the output ratio in the previous control cycle includes only the brake torque. Since the brake torque is not reduced by the acceleration torque subtraction control, the forklift 10 can be stopped on a slope.

[0077] (4) The control device 30 subtracts a constant value from the acceleration torque for each control period, which makes it possible to prevent the acceleration torque from decreasing suddenly. [Example of change] The embodiment can be modified as follows: The embodiment and the following modified examples can be combined with each other to the extent that there is no technical contradiction.

[0078] The control device 30 may perform proportional-integral-derivative control as feedback control. The forklift 10 may be equipped with a mechanical brake. The predetermined value is not limited to a constant value. For example, the predetermined value may be a variable value that increases every control cycle, or a variable value that decreases every control cycle.

[0079] The control device 30 does not have to have the boost mode. [Explanation of symbols]

[0080] L...load, 10...forklift, 22...inverter, 24...travel motor, 25...accelerator member, 30...control device.

Claims

1. An accelerator member; A driving motor; An inverter that drives the traveling motor; A control device for controlling the inverter, The control device includes: Obtaining a rotation speed command corresponding to an operation amount of the accelerator member; Calculating a target rotation speed based on the rotation speed command, the acceleration command, and the deceleration command; Calculating a deviation between the rotation speed of the traveling motor and the target rotation speed; Calculating an output ratio based on the deviation, a proportional gain, and an integral gain; calculating a torque current command value by multiplying the output ratio by a torque current curve; converting the torque current command value into a command value for the inverter to control the traveling motor so that the rotation speed of the traveling motor follows the target rotation speed; When a component of the output ratio that contributes to acceleration is defined as an acceleration component and a component of the output ratio that contributes to braking is defined as a braking component, if the torque in this control cycle has not changed across 0 from the torque in the previous control cycle and a first condition is satisfied in which the absolute value of the output ratio in this control cycle is equal to or less than the absolute value of the output ratio in the previous control cycle or a second condition is satisfied in which the product of the rotation speed command and the output ratio in this control cycle is greater than 0, the difference between the output ratio in this control cycle and the output ratio in the previous control cycle is integrated as the acceleration component, Calculating an acceleration output ratio, the upper limit of which is a predetermined maximum number, from the acceleration component and the output ratio in the current control cycle; When the rotation speed command in the current control cycle is 0 and the acceleration output ratio is a value other than 0, a value obtained by reducing only the acceleration component of the output ratio in the previous control cycle by a predetermined value is set as the output ratio in the current control cycle.

2. The forklift according to claim 1 , wherein, when a pushing operation of the forklift is performed on a flat road, the output ratio in a previous control cycle includes only the acceleration component.

3. 3. The forklift according to claim 1, wherein when the forklift is stopped on a slope, the output ratio in a previous control cycle includes only the brake component.

4. An accelerator member; A travel motor; An inverter that drives the traveling motor; A control device for controlling the inverter. The control device, Obtaining a rotation speed command corresponding to an operation amount of the accelerator member; Calculating a target rotation speed based on the rotation speed command, the acceleration command, and the deceleration command; Calculating a deviation between a rotation speed of the traveling motor and the target rotation speed; calculating an output ratio based on the deviation, a proportional gain, and an integral gain; calculating a torque current command value by multiplying the output ratio by a torque current curve; converting the torque current command value into a command value for the inverter to control the traveling motor so that a rotation speed of the traveling motor follows the target rotation speed; a component of the output ratio that contributes to acceleration is defined as an acceleration component, and a component of the output ratio that contributes to braking is defined as a braking component. In a case where the torque in a current control cycle has not changed across 0 from the torque in a previous control cycle, and a first condition is satisfied in which the absolute value of the output ratio in the current control cycle is equal to or smaller than the absolute value of the output ratio in the previous control cycle, or a second condition is satisfied in which the product of the rotation speed command and the output ratio in the current control cycle is greater than 0, the difference between the output ratio in the current control cycle and the output ratio in the previous control cycle is integrated as the acceleration component; calculating an acceleration output ratio, the upper limit of which is a predetermined maximum number, from the acceleration component and the output ratio in the current control cycle; and when the rotation speed command in a current control cycle is 0 and the acceleration output ratio is a value other than 0, setting as the output ratio in a current control cycle a value obtained by reducing only the acceleration component of the output ratio in a previous control cycle by a predetermined value.

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