JP5791554B2 - Power converter for forklift traveling motor and forklift using the same - Google Patents

Description

  The present invention relates to a power converter for a forklift travel motor.

  One of the industrial vehicles is an electric forklift that uses a battery as a power source. An electric forklift (hereinafter simply referred to as a forklift) is a traveling motor that transmits power to a front wheel that is a traveling wheel (driving wheel) and a hydraulic pump that controls a turning angle (steering angle) of a rear wheel that is a steered wheel. Hydraulic actuator motor (steering motor) that transmits power, hydraulic actuator motor (loading motor) that transmits power to the hydraulic pump that controls the lifting body, and power conversion that drives each of the travel motor, steering motor, and cargo handling motor Equipment.

  The motor generates a torque corresponding to the power supplied from the power converter or rotates at a rotational speed corresponding to the power. The power conversion device includes an upper arm and a lower arm, each of which includes a P-line and an N-line to which a DC voltage from a battery is supplied, and a power transistor provided in series between the P-line and the N-line. Is provided. The gate drive circuit of the power converter switches the upper arm and the lower arm in a complementary manner, and controls the current supplied to the motor by controlling the switching duty ratio, thereby controlling the torque and the number of revolutions.

JP 2009-692553 A

  As a result of studying such a power converter, the present inventors have recognized the following problems.

  The present invention has been made in view of such a problem, and one of exemplary purposes of an embodiment thereof is to provide a forklift capable of reducing power loss.

  An aspect of the present invention relates to a power converter that receives battery voltage and supplies power to a traveling motor that transmits power to wheels of a forklift. The power conversion device receives a speed command value according to a user operation, generates a torque command value according to the speed command value, an inverter that supplies electric power according to the torque command value to the travel motor, And an output limiting circuit that changes at least one of (1) an upper limit value of the motor speed, (2) an upper limit value of the acceleration of the motor, and (3) a modulation method in accordance with a decrease in the battery voltage.

  The current supplied from the battery to the power converter can be reduced by reducing the upper limit value of the speed or acceleration of the motor or changing the modulation method. Therefore, by changing at least one of (1) the upper limit value of the motor speed, (2) the upper limit value of the acceleration of the motor, and (3) the modulation method as the battery voltage decreases, the power loss when the battery voltage decreases is reduced. Can be reduced.

The output limiting circuit is configured to change at least (1) the upper limit value of the motor speed and (3) the modulation method, and (1) before changing the upper limit value of the motor speed in accordance with a decrease in the battery voltage. (3) The modulation method may be switched.
Compared to changing the upper limit value of the motor speed, switching the modulation method causes less discomfort and stress to the user. Therefore, when the battery voltage decreases, the power loss can be reduced while suppressing the influence on the user's operational feeling by switching the modulation method first.

The output limiting circuit is configured to change at least (2) the upper limit value of the acceleration of the motor, and (3) change the modulation method, and (2) before changing the upper limit value of the acceleration of the motor according to the decrease in the battery voltage. (3) The modulation method may be switched.
Compared with the case where the upper limit value of the acceleration of the motor is changed, the switching of the modulation method causes less discomfort and stress to the user. Therefore, when the battery voltage decreases, the power loss can be reduced while suppressing the influence on the user's operational feeling by switching the modulation method first.

The output limiting circuit is configured to change (1) an upper limit value of the motor speed, (2) an upper limit value of the acceleration of the motor, and (3) a modulation method in accordance with a decrease in the battery voltage. Accordingly, (1) the modulation method may be switched before (1) the upper limit value of the motor speed and (2) the upper limit value of the motor acceleration are changed.
Compared to changing the upper limit values of the acceleration and speed of the motor, the switching of the modulation method causes less discomfort and stress to the user. Therefore, when the battery voltage decreases, the power loss can be reduced while suppressing the influence on the user's operational feeling by switching the modulation method first.

The switching of the modulation method may include switching between three-phase modulation and two-phase modulation.
By switching from three-phase modulation to two-phase modulation, circuit current can be reduced and power loss can be reduced.

The output limiting circuit is configured to change at least (1) an upper limit value of the motor speed and (2) an upper limit value of the acceleration of the motor, and (1) an upper limit value of the motor speed according to a decrease in the battery voltage. (2) The upper limit value of the acceleration of the motor may be changed before changing.
Compared with changing the upper limit value of the motor speed, changing the upper limit value of the acceleration of the motor causes less discomfort and stress to the user. Therefore, when the battery voltage decreases, the power loss can be reduced while suppressing the influence on the user's operational feeling by reducing the acceleration upper limit value before the speed upper limit value.

  Another aspect of the present invention relates to a forklift. The forklift may include a vehicle body, wheels that support the vehicle body, a travel motor that transmits power to the wheels, and the power conversion device according to any one of the above-described modes that drives the travel motor.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to the present invention, it is possible to reduce power loss when the battery voltage drops.

It is a perspective view which shows the external view of a forklift. It is a figure which shows an example of the control panel of a forklift. It is a block diagram which shows the structure of the electric system of a forklift, and a mechanical system. It is a block diagram which shows the structure of a 1st power converter device. It is a figure which shows an example of control of the upper limit of speed by the output limiting circuit, and the upper limit of acceleration. It is a wave form diagram which shows operation | movement of a forklift.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected to each other in addition to the case where the member A and the member B are physically directly connected. It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

  FIG. 1 is a perspective view showing an external view of a forklift. The forklift 600 includes a vehicle body (chassis) 602, a fork 604, a lifting body (lift) 606, a mast 608, and wheels 610 and 612. The mast 608 is provided in front of the vehicle body 602. The elevating body 606 is driven by a power source such as a hydraulic actuator (not shown in FIG. 1A, 116 in FIG. 3) and moves up and down along the mast 608. A fork 604 for supporting a load is attached to the elevating body 606.

  FIG. 2 is a view showing an example of a control panel 700 of a forklift. The control panel 700 includes an ignition switch 702, a steering wheel 704, a lift lever 706, an accelerator pedal 708, a brake pedal 710, a dashboard 714, and a forward / reverse lever 712.

  The ignition switch 702 is a switch for starting the forklift 600. The steering wheel 704 is an operation means for steering the forklift 600. The lift lever 706 is an operation means for moving the elevating body 606 up and down. The accelerator pedal 708 is an operating means that controls the rotation of the traveling wheels, and the travel of the forklift 600 is controlled by the user adjusting the amount of depression. When the user depresses the brake pedal 710, the brake is applied. The forward / reverse lever 712 is a lever for switching the traveling direction of the forklift 600 between forward and reverse. In addition, an inching pedal (not shown) may be provided.

  Next, the configuration of the forklift 600 will be described for traveling, cargo handling, and steering. FIG. 3 is a block diagram showing the configuration of the electrical system and the mechanical system of the forklift 600. The ECU (electronic control controller) 110 is a processor for controlling the forklift 600 as a whole.

(Running)
The ECU 110 receives a signal for instructing forward / reverse from the forward / reverse lever 712 and a signal indicating a travel operation amount corresponding to the depression amount from the accelerator pedal 708, and a signal (also referred to as travel operation amount) S1 corresponding thereto. Is output to the first power converter 200. The first power conversion device 200 controls the power supplied to the travel motor M1 according to the travel operation amount S1. The travel operation amount S1 has a correlation with a speed command value that indicates the target rotation speed of the travel motor M1. The front wheels 610 that are drive wheels are connected to the drive shaft 114. The gear box 112 and the drive shaft 114 transmit power from the travel motor M1 to the front wheels 610.

(Handling)
The vertical movement of the elevating body 606 is controlled by the inclination of the lift lever 706. The ECU 110 detects the tilt of the lift lever 706 and outputs a signal indicating the cargo handling operation amount S <b> 2 corresponding to the tilt to the second power conversion device 102. The second power converter 102 supplies power corresponding to the cargo handling operation amount S2 to the cargo handling motor M2, and controls its rotation. The elevating body 606 is connected to the hydraulic actuator 116. The hydraulic actuator 116 converts the rotary motion generated by the cargo handling motor M2 into a linear motion and controls the lifting body 606.

(steering)
The resolver 122 detects the rotation angle of the steering wheel 704 and outputs a signal indicating the rotation angle to the ECU 110. The ECU 110 outputs a control signal S3 corresponding to the rotation angle to the third power conversion device 104. The third power conversion device 104 supplies power corresponding to the control signal S3 to the steering motor M3, and controls the number of rotations thereof. A rear wheel 612 that is a steered wheel is connected to a gear box 124 via a tie rod 126. The rotational motion of the steering motor M3 is transmitted to the tie rod 126 via the hydraulic actuator 118 and the gear box 124, and the steering is controlled.

  The above is the description of the configuration of the forklift 600 as a whole. Then, the structure of the 1st power converter device 200 which concerns on embodiment is demonstrated.

FIG. 4 is a block diagram illustrating a configuration of the first power conversion device 200. The first power conversion device 200 includes a controller 202 and an inverter 220. The inverter 220 includes output stages 224U to 224W and gate drive circuits 222U to 222W. Each output stage 224, including upper and lower arms provided in series between the line P L _P and N lines L _N. The gate drive circuits 222U to W switch corresponding output stages 224U to 224W in response to the drive signal S7 from the controller 202, respectively.

The controller 202 includes a command value generation unit 203, a pulse modulator 210, and an output limiting circuit 250.
The command value generation unit 203 receives a signal (speed command value) indicating the travel operation amount S1 as a control command value from the ECU 110, and generates a torque command value S5 corresponding to the travel operation amount S1. The configuration of the command value generation unit 203 is not particularly limited. For example, the command value generation unit 203 includes a subtracter 204 and a PI (proportional / integration) control unit 206. The subtracter 204 is fed back with a detection signal S4 indicating the rotation state (the number of rotations) of the traveling motor M1. The subtractor 204 calculates a deviation between the travel operation amount S1 and the detection signal S4. The PI control unit 206 receives the deviation and outputs a torque command value S5 whose value is controlled so that the deviation becomes zero. The pulse modulator 210 generates a drive signal S7 that is pulse width modulated based on the torque command value S5.

The DC voltage generated by the battery (battery voltage V _BAT ) decreases with time. When the battery voltage V _BAT decreases, the voltage amplitude applied to the motor coil decreases, and the current required to supply the same power to the motor increases. When the circuit current increases, there is a problem that power loss at the wiring resistance increases and efficiency decreases.

  In order to solve this problem, the controller 202 according to the embodiment includes (1) an upper limit value of the speed (rotation speed) of the travel motor M1, (2) an upper limit value of the acceleration of the rotation speed of the travel motor M1, (3 ) The modulation system can be switched, and an output limiting circuit 250 is further provided.

The output limiting circuit 250 monitors the battery voltage _VBAT . Then, the output limiting circuit 250 has (1) an upper limit value of the speed (number of revolutions) of the traveling motor M1, (2) an upper limit value of the acceleration of the number of revolutions of the traveling motor M1, according to the degree of decrease in the battery voltage _VBAT . (3) Control the modulation method.

(1) Limiting speed (rotation speed) If the load torque is the same, the current flowing through the traveling motor M1 increases as the rotation speed increases. In other words, if the rotational speed of the traveling motor M1 is limited, the current flowing through the traveling motor M1 can be suppressed. Therefore, the output limiting circuit 250 suppresses the current to be supplied to the traveling motor M1 by reducing the upper limit value of the speed of the traveling motor M1 when the battery voltage _VBAT decreases, thereby reducing the power loss.

  A specific method for limiting the speed in the controller 202 is not particularly limited. For example, the speed command value S1 may be clamped at a predetermined upper limit value. Alternatively, the speed detection signal S4 is monitored, the torque command value S5 generated by the PI control unit 206 is controlled so that the speed detection signal S4 does not exceed the upper limit value, or the duty ratio of the pulse signal generated by the pulse modulator 210 May be controlled.

(2) Limitation of acceleration The current flowing through the traveling motor M1 increases as the acceleration increases. In other words, if the acceleration of the traveling motor M1 is limited, the current flowing through the traveling motor M1 can be suppressed. Therefore, the output limiting circuit 250 suppresses the current to be supplied to the traveling motor M1 by reducing the upper limit value of the acceleration of the traveling motor M1 when the battery voltage _VBAT decreases, thereby reducing the power loss.

The specific method for limiting the acceleration in the controller 202 is also not particularly limited. For example, based on the speed detection signal S4, the acceleration of the actual rotational speed of the traveling motor M1 is detected, and the torque command value S5 generated by the PI control unit 206 is controlled so that the detected acceleration does not exceed the upper limit value. Alternatively, the duty ratio of the pulse signal generated by the pulse modulator 210 may be controlled.
(Modulation control)
The current flowing through the traveling motor M1 can also be controlled by switching the modulation method. In the present embodiment, as an example, two-phase modulation and three-phase modulation are switched. By switching from the three-phase modulation to the two-phase modulation, the switching loss, that is, the circuit current is reduced.

  According to the first power conversion device 200, by combining the controls (1) to (3) by the output limiting circuit 250, the current is limited and the power loss is reduced while suppressing a sense of discomfort given to the user.

  The output limiting circuit 250 preferably changes the upper limit value and switches the modulation method in ascending order of discomfort given to the user.

When the present inventors examined, (1) the upper limit of speed, (2) the upper limit of acceleration, and (3) Among the modulation methods, the change of the modulation method tended to be most difficult for the user to perceive. Therefore, the output limiting circuit 250 first switches the modulation method from the three-phase modulation to the two-phase modulation when the battery voltage V _BAT starts to decrease. The output limiting circuit 250 outputs a control signal S21 that instructs the modulation method to the pulse modulator 210. When the battery voltage V _BAT is higher than the first threshold value V _TH1 , the output limiting circuit 250 instructs the pulse modulator 210 to perform three-phase modulation, and the battery voltage V _BAT is lower than the first threshold value V _TH1. At this time, it instructs the pulse modulator 210 to perform two-phase modulation.

  The inventors of the present invention also compared (1) a decrease in the upper limit of speed and (2) a decrease in the upper limit of acceleration. If the upper limit of the speed is lowered, the speed of the vehicle becomes slower, which directly affects the working time (working efficiency). On the other hand, when the upper limit of the acceleration is lowered, the followability to the accelerator operation is lowered and the operational feeling is impaired, but the work efficiency is not lowered as much as the upper limit of the speed is lowered.

Therefore, the output limiting circuit 250 reduces the upper limit value of the acceleration of the traveling motor M1 (2) before decreasing the upper limit value of the speed of the traveling motor M1 in accordance with the decrease in the battery voltage _VBAT .

The output limiting circuit 250 may change the speed and acceleration of the traveling motor M1 stepwise or continuously. FIG. 5 is a diagram illustrating an example of control of the upper limit value of the speed and the upper limit value of the acceleration by the output limiting circuit 250. The horizontal axis represents the battery voltage _VBAT , and the vertical axis represents the upper limit value (i) of the speed and the upper limit value (ii) of the acceleration.

Acceleration (ii) The battery voltage _{V BAT} is in the region higher than the second threshold value _{V TH2} takes a constant value, starts to decrease as the battery voltage _{V BAT} becomes lower than the second threshold value _{V TH2.} Likewise rate (i) is at high space than the battery voltage _{V BAT} third threshold _{V TH3} takes a constant value, starts to decrease as the battery voltage _{V BAT} becomes lower than the third threshold value _{V TH3.} From the relationship between work efficiency and operational feeling, it is desirable to _satisfy V _TH2 > V _TH3 .

The above is the configuration of the forklift 600. Next, the operation will be described.
FIG. 6 is a waveform diagram showing the operation of the forklift 600. When the user operates the forklift 600 and repeats the transportation and unloading of the load, the battery voltage _VBAT decreases with time. The current I _BAT is an operating current of the first power conversion device 200. (1) The upper limit value of the motor speed, (2) the upper limit value of the acceleration of the motor, (3) the operation when the modulation method is not controlled is indicated by a broken line, and the operation when the control is performed is indicated by a solid line.

When the control is not performed, the current I _BAT increases as the battery voltage V _BAT decreases. As a result, the loss in the internal resistance of the battery, the bus bar, other wiring, the on-resistance of the power transistor, and the DC resistance component of the motor coil increases. On the other hand, when (1) the upper limit value of the motor speed, (2) the upper limit value of the motor acceleration, and (3) the modulation method are controlled, the increase in the current I _BAT can be suppressed, and the loss can be reduced.

  In addition, by appropriately determining (1) the upper limit value of the motor speed, (2) the upper limit value of the motor acceleration, and (3) the order of changing the modulation method, the influence on the user's operational feeling and work efficiency is suppressed. it can.

  In the above, this invention was demonstrated based on the Example. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiment, and various design changes are possible, various modifications are possible, and such modifications are within the scope of the present invention. By the way. Hereinafter, such modifications will be described.

  In the embodiment, the technology for switching all of the acceleration, speed, and modulation method for the power conversion device for the travel motor has been described, but the present invention is not limited thereto. For example, only the acceleration, only the speed, and only the modulation method may be switched, or any combination thereof may be switched. Further, when controlling a plurality of parameters, the order of changing them is not limited to that in the embodiment, and may be changed based on the user's operational feeling and work efficiency.

  Further, in addition to or instead of the first power conversion device 200 that drives the traveling motor M1, the same technology is applied to the second power conversion device 102 that drives the cargo handling motor M2 and the power conversion device 104 that drives the steering motor M3. May be applied.

600 ... Forklift, 602 ... Car body, 604 ... Fork, 606 ... Elevator, 608 ... Mast, 610 ... Front wheel, 612 ... Rear wheel, 100 ... Battery, 200 ... First power converter, 102 ... Second power converter, DESCRIPTION OF SYMBOLS 104 ... 3rd power converter device, 110 ... ECU, 112 ... Gear box, 114 ... Drive shaft, 116, 118 ... Hydraulic actuator, 120 ... Steering shaft, 122 ... Resolver, 124 ... Gear box, 126 ... Tie rod, 202 ... Controller , 203 ... command value generation unit, 204 ... subtractor, 206 ... PI control unit, 210 ... pulse modulator, 220 ... inverter, 222 ... gate drive circuit, 224 ... output stage, 250 ... output limiting circuit, M1 ... travel motor , M2 ... cargo handling motor, M3 ... steering motor, 700 ... control panel, 7 2 ... ignition switch, 704 ... steering wheel, 706 ... lift lever, 708 ... accelerator pedal, 710 ... brake pedal, 712 ... forward-reverse lever 714 ... dashboard.

Claims (7)

A power conversion device that receives battery voltage and supplies power to a traveling motor that transmits power to wheels of a forklift,
A command value generation unit that receives a speed command value according to a user operation and generates a torque command value according to the speed command value;
An inverter for supplying electric power corresponding to the torque command value to the traveling motor;
An output limiting circuit that changes at least (1) an upper limit value of the speed of the motor and (3) a modulation method in response to a decrease in the battery voltage;
With
Wherein the output limiting circuit, with a decrease of the prior SL battery voltage, (1) before the change the upper limit value of the speed of the motor, (3) the modulation scheme you wherein power converter that switches the . A power conversion device that receives battery voltage and supplies power to a traveling motor that transmits power to wheels of a forklift,
A command value generation unit that receives a speed command value according to a user operation and generates a torque command value according to the speed command value;
An inverter for supplying electric power corresponding to the torque command value to the traveling motor;
An output limiting circuit that changes at least (2) an upper limit value of the acceleration of the motor and (3) a modulation method in response to a decrease in the battery voltage;
With
Wherein the output limiting circuit, with a decrease of the prior SL battery voltage, (2) before the change the upper limit value of the acceleration of the motor, (3) characterized by switching the modulation scheme power converter . A power conversion device that receives battery voltage and supplies power to a traveling motor that transmits power to wheels of a forklift,
A command value generation unit that receives a speed command value according to a user operation and generates a torque command value according to the speed command value;
An inverter for supplying electric power corresponding to the torque command value to the traveling motor;
An output limiting circuit that changes (1) an upper limit value of the speed of the motor, (2) an upper limit value of the acceleration of the motor, and (3) a modulation method in accordance with a decrease in the battery voltage;
With
Wherein the output limiting circuit, with a decrease of the prior SL battery voltage prior to change the (1) upper limit and (2) the upper limit value of the acceleration of the motor speed of the motor, and (3) the modulation scheme it characterized in that switched power converter. The power conversion device according to any one of claims 1 to 3 , wherein the modulation method switching includes switching between three-phase modulation and two-phase modulation.   A power conversion device that receives battery voltage and supplies power to a traveling motor that transmits power to wheels of a forklift,
  A command value generation unit that receives a speed command value according to a user operation and generates a torque command value according to the speed command value;
  An inverter for supplying electric power corresponding to the torque command value to the traveling motor;
  An output limiting circuit that changes at least (3) a modulation method in response to a decrease in the battery voltage;
  With
  The modulation method switching includes switching between three-phase modulation and two-phase modulation. A power conversion device that receives battery voltage and supplies power to a traveling motor that transmits power to wheels of a forklift,
A command value generation unit that receives a speed command value according to a user operation and generates a torque command value according to the speed command value;
An inverter for supplying electric power corresponding to the torque command value to the traveling motor;
An output limiting circuit that changes at least (1) an upper limit value of the speed of the motor and (2) an upper limit value of the acceleration of the motor in accordance with a decrease in the battery voltage;
With
Wherein the output limiting circuit, with a decrease of the prior SL battery voltage, (1) before the change the upper limit value of the speed of the motor, and characterized by changing the upper limit value of the acceleration of (2) the motor It is that power conversion device. The car body,
Wheels for supporting the vehicle body;
A travel motor for transmitting power to the wheels;
The power conversion device according to any one of claims 1 to 6, which drives the travel motor;
A forklift characterized by comprising:

Images