Electric Work Vehicle

Abstract

To provide an electric work vehicle, which can make both protection of a motor of a work machine and improvement in work efficiency compatible.SOLUTION: An electric work vehicle includes: a travelling motor that drives a wheel; a motor of a work machine that drives the work machine; an operation part 32 that instructs a target rotation speed of the travelling motor and actuation of the work machine; a control part 100 that controls the travelling motor and the motor of the work machine, in accordance with operation of the operation part 32; and a temperature sensor 34 that detects a temperature of the motor of the work machine. The control part 100 maintains or changes a target torque range of the motor of the work machine in accordance with a detected temperature of the motor of the work machine, and maintains or changes a target rotation speed of the travelling motor so that a calculated value of output torque of the motor of the work machine is in the target torque range.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electric work vehicle that is equipped with a traction motor that drives wheels and a work implement motor that drives a work implement. [Background technology]

[0002] A work vehicle equipped with a working machine has been known for some time. For example, a lawnmower equipped with a lawnmower as a working machine driven to perform lawn mowing work has been known for some time. In addition, among such work vehicles, an electric work vehicle equipped with a travel motor, which is an electric motor that drives the wheels, and a working machine motor that drives the working machine has also been considered.

[0003] For example, Patent Documents 1 and 2 describe an electric work vehicle in which left and right electric motors, that is, traction motors, drive the wheels on the corresponding sides, and a blade motor (work machine motor) drives the rotating blade of a lawnmower unit (work machine).

[0004] In the vehicle described in Patent Document 1, a temperature sensor detects the temperature of the blade motor, and when the temperature detected by the temperature sensor is higher than a threshold value, an exception speed control unit drives the traveling motor so that the vehicle travels at an exception speed lower than the target traveling speed determined by the left and right steering levers. This is said to protect the blade motor.

[0005] On the other hand, in the vehicle described in Patent Document 2, the controller has a load evaluation unit that calculates a load evaluation value indicating the load on the blade motor, and when the load evaluated by the load evaluation unit is higher than a threshold value, the exception speed control unit drives the traveling motor so that the vehicle travels at an exception speed lower than the target traveling speed determined by the left and right steering levers. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6121213 [Patent Document 2] JP 2012-187026 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the configuration described in Patent Document 1, when the detected temperature of the working machine motor is high, the vehicle is driven at an exceptional speed. If the temperature is high, the vehicle speed may be excessively reduced regardless of the state of the work target of the working machine, such as no grass or little grass. This leaves room for improvement in terms of both protecting the working machine motor and improving work efficiency by extending the driving time at high vehicle speed. On the other hand, in the configuration described in Patent Document 2, although the state of the grass may be reflected to some extent in the driving control, there is a possibility that the vehicle speed may be reduced more than necessary when the temperature of the working machine motor is sufficiently higher than the allowable temperature even if the load on the working machine motor is high. In this case, too, there is room for improvement in terms of both protecting the working machine motor and improving work efficiency by extending the driving time at high vehicle speed.

[0008] An object of the present invention is to achieve both protection of a work implement motor and improvement of work efficiency in an electric work vehicle. [Means for solving the problem]

[0009] The electric work vehicle of the present invention is an electric work vehicle comprising a travel motor that drives wheels, a work machine motor that drives a work machine, an operation unit that instructs the target rotational speed of the travel motor and the operation of the work machine, a control unit that controls the travel motor and the work machine motor in accordance with the operation of the operation unit, and a temperature sensor that detects the temperature of the work machine motor, wherein the control unit maintains or changes the target torque range of the work machine motor in accordance with the detected temperature of the work machine motor, and maintains or changes the target rotational speed of the travel motor so that the calculated value of the output torque of the work machine motor falls within the target torque range.

[0010] According to the above electric work vehicle, when the detected temperature of the work equipment motor becomes high, the target torque range of the work equipment motor can be changed to a lower range accordingly, thereby protecting the work equipment motor. Also, unlike the case where the vehicle is always driven at an exceptional speed lower than normal when the detected temperature is high, the driving speed can be increased when the load of the work equipment is low, so that the driving time at high vehicle speed can be extended. Also, since the target torque range is changed according to the detected temperature of the work equipment motor, the work equipment motor can be protected more appropriately than when the target torque range is changed according to the load. This makes it possible to prevent the target rotation speed of the travel motor from decreasing excessively, and therefore it is possible to achieve both protection of the work equipment motor and improvement of work efficiency by extending the driving time at high vehicle speed.

[0011] In the electric work vehicle of the present invention, the control unit may have a second configuration in which it sets the target torque range of the work machine motor so that when the detected temperature of the work machine motor is equal to or higher than a predetermined first temperature, the work machine motor is driven in a low torque range, and when the detected temperature of the work machine motor is equal to or lower than a predetermined second temperature lower than the first temperature, the work machine motor is driven in a high torque range.

[0012] According to the second configuration, the work efficiency can be improved while protecting the work machine motor.

[0013] In the above second configuration, the control unit may be configured such that, after the detected temperature of the work machine motor becomes equal to or higher than the first temperature and the vehicle speed is reduced by driving the work machine motor in the low torque range, the detected temperature of the work machine motor becomes equal to or lower than the second temperature and the work machine motor is driven in the high torque range, and the absolute value of the vehicle acceleration when increasing the vehicle speed is smaller than the absolute value of the vehicle deceleration when the vehicle speed is reduced.

[0014] According to the above configuration, sudden acceleration can be prevented, and jerky vehicle speed can be suppressed.

[0015] In the above second configuration, the control unit may be configured to increase a rate of reduction in vehicle speed in accordance with a predetermined amount of reduction when a decrease in the measured value of the rotational speed of the work machine motor per predetermined time period becomes equal to or greater than a predetermined amount of reduction.

[0016] According to the above configuration, when the reduction in the rotation speed of the work machine motor is large due to a deterioration in the discharge of cut grass, etc., the load on the work machine motor can be reduced by increasing the reduction rate of the vehicle speed. This improves the durability of the work machine motor and the work accuracy, such as the mowing accuracy.

[0017] In the above second configuration, the control unit may be configured to increase a rate of reduction in vehicle speed in accordance with a predetermined rate of change of an increase in the calculated value of the output torque of the work machine motor when the rate of change of the increase is equal to or greater than a predetermined rate of change.

[0018] With the above configuration, when the load on the working machine motor increases suddenly due to a deterioration in the discharge of cut grass, etc., and the rate of increase in the output torque of the working machine motor increases, the rate of decrease in vehicle speed is increased to reduce the load on the working machine motor, thereby improving the durability of the working machine motor and the working accuracy, such as the mowing accuracy. Effect of the Invention

[0019] According to the electric work vehicle of the present invention, it is possible to protect the work implement motor while improving work efficiency. [Brief description of the drawings]

[0020] [Figure 1] 1 is a perspective view of an electric work vehicle according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic configuration diagram of the vehicle shown in FIG. [Diagram 3] FIG. 2 is a block diagram showing a control system for the vehicle of FIG. [Figure 4] FIG. 4 is a diagram showing the relationship between the temperature of a deck motor, which is a work machine motor, and a target torque range in an embodiment. [Diagram 5]4 is a flowchart showing a method for controlling a target rotation speed of a traveling motor in the embodiment. [Figure 6] FIG. 4 is a diagram showing an example of the torque of a deck motor and the traveling speed of a vehicle over time in an embodiment. [Figure 7] 13 is a diagram showing an example of the torque and rotation speed of a deck motor and the traveling speed of a vehicle over time in another example of an embodiment. FIG. [Figure 8] FIG. 11 is a diagram showing an example of the torque of a deck motor and the traveling speed of a vehicle over time in another example of an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following, a case where the electric work vehicle is a lawnmower vehicle will be described, but the electric work vehicle is not limited to this, and may be another work vehicle having a work machine that performs one or more of snow removal work, excavation work, civil engineering work, and agricultural work. In addition, in the following, a case where a left-right lever type operator having two operation levers on the left and right is used will be described, but this is an example, and the steering handle may be used as a turning instruction tool, and the accelerator pedal provided in front of the seat may be used as an acceleration instruction tool. The shapes, numbers, and arrangement of parts described below are examples for explanation, and can be appropriately changed according to the specifications of the electric work vehicle. In the following, the same symbols are used for similar elements in all drawings, and duplicate explanations are omitted or simplified.

[0022] An electric work vehicle 10 according to an embodiment will be described with reference to Fig. 1 to Fig. 6. Hereinafter, the electric work vehicle 10 will be referred to as vehicle 10. Fig. 1 is a perspective view of the vehicle 10. Fig. 2 is a schematic configuration diagram of the vehicle 10. Note that in the configuration of Figs. 1 to 6, a case will be described in which the left and right wheels 12, 13 are arranged on the rear side and the caster wheels 15, 16 are arranged on the front side, but the wheels may be on the front side and the caster wheels on the rear side.

[0023] The vehicle 10 is a self-propelled lawnmower suitable for mowing grass. The vehicle 10 is equipped with two left and right wheels, a left wheel 12 and a right wheel 13 (FIG. 2), caster wheels 15, 16, a lawnmower 18 as a working machine, a left traveling motor 30 and a right traveling motor 31 (FIG. 2), two left and right operation levers 22, 23 and a working machine start switch 33 (FIG. 3) constituting an operation unit 32, two left and right traveling inverters 84, 86, three deck inverters 88, and a control device 40 (FIG. 3) constituting a control unit 100, and three motor temperature sensors 34 (FIG. 3). The left traveling motor 30 and the right traveling motor 31 are each an electric motor.

[0024] The left wheel 12 and the right wheel 13 are rear wheels supported on both the left and right sides of the rear of a main frame 20, which is the vehicle body, and are also main drive wheels. The main frame 20 is formed into a beam structure or the like from metal such as steel. The main frame 20 includes side plate portions 20a, 20b extending in the approximately front-rear direction at both left and right ends, and a connecting portion 20c connecting the left and right side plate portions 20a, 20b. A driver's seat 21, where a driver sits, is fixed to the upper side between the rear ends of the left and right side plate portions 20a, 20b.

[0025] Two guide panels 26, 27 are fixed to the main frame 20 on both the left and right sides of the driver's seat 21, and two left and right operation levers 22, 23 are supported on the main frame 20 so as to protrude upward from each of the two guide panels 26, 27. The left operation lever 22 corresponds to an acceleration instruction part that instructs the acceleration of the left traveling motor 30, and the right operation lever 23 corresponds to an acceleration instruction part that instructs the acceleration of the right traveling motor 31. The tip of each operation lever 22, 23 is used by the driver to grip and instruct the rotation direction and rotation speed of the left wheel 12 and the right wheel 13. The left operation lever 22 is operated to instruct the drive and acceleration of the left wheel 12 by changing the instruction of the rotation speed of the left wheel 12 so that the rotation speed becomes higher. The right operation lever 23 is operated to instruct the drive and acceleration of the right wheel 13 by changing the instruction of the rotation speed of the right wheel 13 so that the rotation speed becomes higher. Each of the operating levers 22, 23 is substantially L-shaped, and has a grip portion 24 extending in the left-right direction at its upper end. The grip portion 24 is grasped by the driver to operate it. Each of the operating levers 22, 23 is capable of swinging about an axis along the left-right direction at its lower end. When each of the operating levers 22, 23 is tilted forward with respect to the N position, which is a neutral position close to the upright position, as a reference, the motor 30 (or 31) on the same side as the operating lever 22 (or 23) is rotated at a target number of rotations per unit time (sec ) as a target rotation speed corresponding to forward movement. -1 ), and the operating levers 22, 23 instruct the motor 30 (or 31) on the same side as the operating lever 22 (or 23) to be driven at a target rotation speed corresponding to reverse when the operating lever 22, 23 is tilted rearward with respect to the N position, and instruct the target rotation speed to be higher as the amount of tilt increases. In this way, each operating lever 22, 23 instructs the target rotation speed of the corresponding traveling motor 30, 31.

[0026] The swing positions of the two left and right operating levers 22, 23 in the front-rear direction are detected by a left lever sensor 50 and a right lever sensor 51 (FIG. 3) which are lever position sensors. Each of the lever sensors 50, 51 includes, for example, a potentiometer. The detection signals of each of the lever sensors 50, 51 are transmitted to the control device 40.

[0027] The two left and right caster wheels 15, 16 are steering wheels supported on the front end of the main frame 20 and are also front wheels. Each caster wheel 15, 16 is provided spaced apart from the left wheel 12 and the right wheel 13 in the front-rear direction of the vehicle 10. Each caster wheel 15, 16 can freely rotate 360 ​​degrees or more around an axis in the vertical direction (the up-down direction in FIG. 1). The number of caster wheels provided on the vehicle is not limited to two, and only one or three or more caster wheels may be provided on the vehicle.

[0028] 2, the left traveling motor 30 is connected to the left wheel 12 via a left reduction gear unit 58 supported on the rear side of the main frame 20. The right traveling motor 31 is connected to the right wheel 13 via a right reduction gear unit 59 supported on the rear side of the main frame 20. The left traveling motor 30 and the right traveling motor 31 are supported on the left and right sides, respectively, on the rear side of the main frame 20.

[0029] The left traveling motor 30 is connected to a battery 82 (FIG. 3) via a left traveling inverter 84 (FIG. 3), and is supplied with power from the battery 82. The right traveling motor 31 is connected to a battery 82 via a right traveling inverter 86 (FIG. 3), and is supplied with power from the battery 82. The left traveling motor 30 and the right traveling motor 31 are, for example, three-phase motors.

[0030] As shown in Figs. 1 and 2, the lawnmower 18 is supported on the lower side of the longitudinal middle part of the main frame 20. As a result, the lawnmower 18 is disposed between the caster wheels 15, 16 and the left and right wheels 12, 13 in the front-rear direction. The lawnmower 18 includes three lawnmower blades 18a, 18b, 18c (Fig. 2) which are lawnmower rotary tools disposed inside a mower deck 19 which is a cover. The upper sides of the lawnmower blades 18a, 18b, 18c are covered by the mower deck 19. Each of the lawnmower blades 18a, 18b, 18c has multiple blade elements which rotate around an axis which faces in the vertical direction (the front-rear direction of the paper in Fig. 2). As a result, the blade elements rotate to break and mow the grass. Of the three deck motors 60 which are working machine motors, a corresponding deck motor 60 is connected to each of the three lawnmower blades 18a, 18b, 18c. A battery 82 (FIG. 3) is connected to each deck motor 60 via a deck inverter 88 (FIG. 3) which is an inverter for the corresponding deck motor 60, and power is supplied from the battery 82. Each deck motor 60 is, for example, a three-phase motor. Furthermore, a motor temperature sensor 34 (FIG. 3) described below is attached to each deck motor 60. The motor temperature sensor 34 detects the temperature of the corresponding deck motor 60. The detected temperature is used to set a target torque range for the deck motor 60, as described below.

[0031] The lawnmower may be a rotary lawnmower tool having a function of cutting grass, for example, with a helical blade arranged on a rotating shaft parallel to the ground surface, and may be configured with a lawnmower reel driven by a deck motor.

[0032] FIG. 3 is a block diagram showing a control system 80 of the vehicle 10. The control device 40 is connected to a start switch 35, a working machine start switch 33, two left and right lever sensors 50, 51, two left and right travel inverters 84, 86, a deck inverter 88, and two left and right motor speed sensors 54, 55. The start switch 35 and the working machine start switch are provided on one of the guide panels 26 (or 27) that guide one of the two left and right operation levers 22, 23, or in the vicinity thereof. The start switch 35 is provided so as to be operable by a user, and based on the operation, power is supplied from a battery 82 to the control device 40 to start the control device 40. The working machine start switch 33 is provided so as to be operable by a user, and based on the operation, switches between operating and stopping the lawnmower 18. When the start of the lawnmower 18 is instructed by the working machine start switch 33, i.e., when it is turned on, the control device 40 controls a deck inverter 88 (described later) to operate the deck motor 60 so as to continue rotating at a predetermined target rotation speed.

[0033] The control system 80 includes a start switch 35, an operation unit 32 including a work machine start switch 33 and two left and right operation levers 22, 23, two left and right lever sensors 50, 51, two left and right travel motors 30, 31 and travel inverters 84, 86, two left and right motor speed sensors 54, 55, three deck motors 60 and a deck inverter 88, three deck motor speed sensors 52 and a motor temperature sensor 34, and a control device 40. In Fig. 3, only one deck motor 60, one deck inverter 88, one deck motor 60 speed sensor 52 and one motor temperature sensor 34 are shown, but in reality, three deck motors 60 are provided as shown in Fig. 2, and therefore, in the control system 80, three deck inverters 88, three deck motor speed sensors 52 and three motor temperature sensors 34 are provided correspondingly.

[0034] The left traveling inverter 84 drives the left traveling motor 30, and the right traveling inverter 86 drives the right traveling motor 31. Each of the traveling inverters 84, 86 has a traveling inverter circuit including, for example, three arms, each having two switching elements electrically connected in series, and a traveling inverter control device that controls the traveling inverter circuit.

[0035] The operation of each of the traveling inverters 84, 86 is controlled by the control device 40. As a result, the left traveling motor 30 is controlled by the control device 40 via the left traveling inverter 84. The right traveling motor 31 is controlled by the control device 40 via the right traveling inverter 86. Therefore, the left traveling motor 30 and the right traveling motor 31 are independently controlled by the control device 40 in terms of rotation direction and rotation speed. Therefore, the left traveling motor 30 and the right traveling motor 31 drive the left wheels 12 and the right wheels 13 independently in terms of rotation direction and rotation speed.

[0036] Each deck inverter 88 drives a corresponding deck motor 60. Like the travel inverter circuits and travel inverter controllers of each of the travel inverters 84, 86, each deck inverter 88 also has a deck inverter circuit and a deck inverter controller that controls the deck inverter circuit.

[0037] The operation of each deck inverter 88 is controlled by the control device 40. As a result, each deck motor 60 is controlled by the control device 40 via the deck inverter 88. As a result, each lawnmower blade 18a, 18b, 18c is rotated and driven by the corresponding deck motor 60. Each deck motor 60 is basically driven so as to maintain a predetermined target rotation speed. Grass cut by the lawnmower 18 is discharged to one left-right side of the vehicle 10 through a discharge duct 18d provided on one left-right side of the mower deck 19.

[0038] Furthermore, the deck inverter control device of each deck inverter 88 receives the rotation speed n (sec) of the deck motor 60 from the deck motor speed sensor 52 described later. -1) is input to the deck inverter control device. In addition, the deck inverter control device receives detection values ​​from a current sensor (not shown) that detects the output current from the deck inverter circuit to the deck motor 60, and a voltage sensor (not shown) that detects the phase-to-phase voltage of the deck motor 60. The deck inverter control device calculates the output power P (W) output to the deck motor 60 from the detected current value and voltage value. The deck inverter control device may calculate the voltage value of the deck motor 60 from the detected current value and the rotation speed detected by the deck motor speed sensor 52, and calculate the output power P based on these. The detected value of the rotation speed n of the deck motor 60 and the calculated value of the output power P for the deck motor 60 are output from each deck inverter 88 to the control device 40, and are used to calculate a calculated value Tr of the output torque of the deck motor 60, as described below.

[0039] Furthermore, a motor temperature sensor 34 is attached to each deck motor 60. Each motor temperature sensor 34 detects the temperature of the corresponding deck motor 60. The detected temperature of each motor temperature sensor 34 is output to the control device 40 via a signal line and the corresponding deck inverter 88. For example, each motor temperature sensor 34 detects the temperature of the part of each deck motor 60 that is most likely to become hot directly, or detects the temperature by estimation based on the temperature detection value of a part that is highly correlated with the temperature of that part.

[0040] Further, the two left and right motor speed sensors 54, 55 detect the rotation speed of each of the two left and right travel motors 30, 31. The detected rotation speed value of each motor speed sensor 54, 55 is output to the control device 40. Each deck motor speed sensor 52 detects the rotation speed of the corresponding deck motor 60. The detected rotation speed value of each deck motor speed sensor 52 is output to the control device 40 via the corresponding deck inverter 88. Note that in FIG. 3, the power supply path from the battery 83 is indicated by a thick solid line.

[0041] The control device 40 includes a calculation unit such as a CPU and a storage unit such as a memory, and is configured, for example, by a microcomputer. The control device 40 acquires the operation positions of the two control levers 22, 23 from the detection signals of the two left and right lever sensors 50, 51, and sets the target rotation speeds of the left traveling motor 30 and the right traveling motor 31 according to the operation positions of the respective control levers 22, 23.

[0042] The control device 40 can set the target rotation speeds of the two left and right travel motors 30, 31 according to the operating positions of the two left and right operating levers 22, 23, thereby enabling the vehicle to travel either straight ahead or in a turn.

[0043] Furthermore, when the working machine start switch 33 is turned on and the left and right operation levers 22, 23 are used to instruct the target rotation speed of each traveling motor 30, 31 to be equal to or higher than the predetermined speed, the control device 40 maintains or changes the target torque range of the corresponding deck motor 60 according to the detected temperature of each deck motor 60 or according to the detected temperature of a predetermined deck motor 60 (hereinafter, sometimes referred to as a predetermined deck motor 60). Then, the control device 40 maintains or changes the target rotation speed of each traveling motor 30, 31 so that the calculated value Tr of the output torque of each deck motor 60 or the predetermined deck motor 60 falls within the target torque range. This makes it possible to achieve both protection of each deck motor 60 and improvement of work efficiency by maintaining a high vehicle speed, as described later. Note that whether the detected temperature of each deck motor 60 or the detected temperature of the predetermined deck motor 60 is used to maintain or change the target rotation speed of the traveling motors 30, 31 can be set in advance by the control device 40. Generally, it is considered that the three deck motors 60 are often subjected to similar loads during lawn mowing work and therefore the temperatures change to the same extent, so the target rotation speeds of the traveling motors 30, 31 may be controlled using the detected temperature of only a specified deck motor 60. In this case, the temperature sensors of the other deck motors 60 may be omitted. The specified deck motor may be, for example, the central deck motor 60 of the three deck motors 60. The following mainly describes the case where the target rotation speeds of the traveling motors 30, 31 are controlled using the detected temperature of only the specified deck motor 60.

[0044] FIG. 4 shows the relationship between the temperature of the deck motor 60 and the target torque range in the embodiment. The target torque range of the deck motor 60 is set according to the temperature of the deck motor 60. In the example of FIG. 4, when the temperature of the deck motor 60 is equal to or higher than a predetermined first temperature d1, the target torque range of the deck motor 60 is a predetermined first range A1. The first range A1 corresponds to a low torque range, with a lower limit of torque T1 and an upper limit of torque T2. On the other hand, when the temperature of the deck motor 60 is lower than the first temperature d1 and higher than a predetermined second temperature d2 lower than the first temperature d1, the target torque range of the deck motor 60 is a predetermined second range A2. The second range A2 corresponds to an intermediate torque range, with a lower limit of torque T3 intermediate between torque T1 and torque T2 and an upper limit of torque T4 higher than torque T1. Also, when the temperature of the deck motor 60 is equal to or lower than the second temperature d2, the target torque range of the deck motor 60 is a predetermined third range A3. The third range A3 corresponds to a high torque range, with a lower limit being a torque T5 which is intermediate between the torque T3 and the torque T4, and an upper limit being a torque T6 which is higher than the torque T4.

[0045] Using the relationship in Figure 4, the control device 40 sets the target torque range of the deck motor 60 so that when the detected temperature of the deck motor 60 is equal to or higher than the first temperature d1, the deck motor 60 is driven at a target torque in the first range A1, and when the detected temperature of the deck motor 60 is equal to or lower than the second temperature d2, the deck motor 60 is driven at a target torque in the third range A3, which is higher than the first range A1.

[0046] The control device 40 maintains or changes the target rotation speed of each of the travel motors 30, 31 so that the calculated value Tr of the output torque of the deck motor 60 falls within the above-mentioned target torque range. Here, the calculated value Tr (N·m) of the output torque of the deck motor 60 is calculated by multiplying the calculated value of the output power P (W) output to the deck motor 60, which is obtained by the corresponding deck inverter as described above, by the rotation speed n (sec -1 ) and the detected value, using the following formula (1): Tr = P / (2n × n) (1)

[0047] The deck motor speed sensor 52 may detect the angular velocity ω (rad / sec) of the deck motor 60 instead of the rotation speed of the deck motor 60. In this case, the calculated value Tr (N m) of the output torque of the deck motor 60 is calculated using the following equation (2). Tr = P / ω (2)

[0048] When the calculated value Tr is lower than the lower limit of the target torque range, the target rotation speed of each traveling motor 30, 31 is increased linearly with time, or by a predetermined amount or a predetermined rate per predetermined time. On the other hand, when the calculated value Tr is higher than the upper limit of the target torque range, the target rotation speed of each traveling motor 30, 31 is decreased linearly with time, or by a predetermined amount or a predetermined rate per predetermined time. In this way, the vehicle speed is automatically adjusted so that the temperature of the deck motor 60 does not become too high and the driving time at a high vehicle speed can be extended.

[0049] Fig. 5 is a flowchart showing a method for controlling the target rotation speeds of the traveling motors 30, 31. In step S10 of Fig. 5, the control device 40 judges whether the work machine start switch 33 is turned on and whether a target rotation speed equal to or higher than a predetermined speed of each traveling motor 30, 31 is instructed by the left and right operating levers 22, 23. If the judgment in step S10 is positive (YES), in step S12, the control device 40 calculates the output torque of the corresponding deck motor 60 and causes the deck inverter 88 and the motor temperature sensor 34 to detect the temperature of the deck motor 60.

[0050] After the process of step S12, in step S14, the target torque range of the deck motor 60 is maintained or changed depending on the detected temperature of the corresponding deck motor 60. That is, the target torque range of the deck motor 60 is set using the relationship in FIG.

[0051] Then, in step S16, the control device 40 maintains or changes the target rotation speeds of the travel motors 30, 31 so that the calculated value Tr of the output torque of the deck motor 60 falls within the above-mentioned target torque range, and ends the process.

[0052] On the other hand, if the determination in step S10 is negative (NO), normal control is executed without performing drive control of the drive motors 30, 31 using the detected temperature of the deck motor 60, and the process ends.

[0053] According to the vehicle 10, when the detected temperature of the deck motor 60 becomes high, the target torque range of the deck motor 60 can be changed to a lower range accordingly, so that the deck motor 60 can be protected. Also, unlike the case where the vehicle is always driven at an exceptional speed lower than normal when the detected temperature is high, the driving speed can be increased when the load of the deck motor 60 is low, so that the driving time at a high vehicle speed can be extended. Also, since the target torque range is changed according to the detected temperature of the deck motor 60, the deck motor 60 can be protected more appropriately than when the target torque range is changed according to the load. This makes it possible to prevent the target rotation speed of the driving motors 30, 31 from being excessively reduced, so that it is possible to achieve both protection of the deck motor 60 and improvement of work efficiency by extending the driving time at a high vehicle speed.

[0054] Furthermore, the control unit 100 sets the target torque range of the deck motor 60 so that when the detected temperature of the deck motor 60 is equal to or higher than a first temperature d1, the deck motor 60 is driven in a first range A1 of a low torque range, and when the detected temperature of the deck motor 60 is equal to or lower than a second temperature d2 that is lower than the first temperature d1, the deck motor 60 is driven in a third range A3 of a high torque range. This makes it possible to improve the work efficiency while protecting the deck motor 60.

[0055] In Figure 4, a case has been described in which the target torque range switches between three ranges A1 to A3 depending on the temperature of the deck motor 60, but the target torque range may be switchable between only two ranges, or between four or more ranges.

[0056] Also, the speed of each of the traveling motors 30, 31 may be controlled using the detected temperatures of the three deck motors 60. In this case, the target rotation speed of each of the traveling motors 30, 31 may be maintained or changed so that the output torque calculation value of the corresponding deck motor 60 falls within a target torque range according to the detected temperature of each deck motor 60. In this case, if the target rotation speed of each of the traveling motors 30, 31 cannot be uniquely determined so that the output torque calculation value of the corresponding deck motor 60 falls within a target torque range according to the detected temperature of each deck motor 60, the control may be performed to maintain the previous target rotation speed.

[0057] In addition, when controlling the speed of each traveling motor 30, 31 using the detected temperature of each deck motor 60, the target torque range of each deck motor 60 may be set to the same using the maximum temperature or average temperature of the detected temperatures of the three deck motors 60, and the target rotation speed of each traveling motor 30, 31 may be set accordingly.

[0058] In step S10 of FIG. 5, the predetermined speed when the control device 40 determines whether the target rotation speed of each travel motor 30, 31 is equal to or higher than the predetermined speed can be set to the rotation speed of each travel motor 30, 31 when the torque of the deck motor 60 reaches or exceeds the lower limit torque T5 of the highest torque range (third range A3 in FIG. 4) when a predetermined amount of grass is mowed by the lawnmower 18. This prevents the rotation speed of each travel motor 30, 31 from automatically increasing beyond the target rotation speed of each travel motor 30, 31 specified by the user using the operation unit 32, and prevents the vehicle speed from automatically increasing, thereby preventing the user from feeling uncomfortable. Note that in step S10 of the flowchart in FIG. 5, the condition for moving to step S12 may exclude the target rotation speed of each travel motor 30, 31 being specified to be equal to or higher than the predetermined speed.

[0059] Figure 6 shows an example of the torque of the deck motor 60 and the traveling speed of the vehicle 10 over time in an embodiment. In Figure 6, the horizontal axis indicates time, and the vertical axis indicates the torque of the deck motor 60 and the traveling speed of the vehicle 10. The thick solid line a in Figure 6 indicates the traveling speed in this example. The upper part of the figure also shows the amount of grass to be cut by the lawnmower 18, with the increase in the number of vertical lines in the vertical direction indicating a greater amount of grass at that point in time.

[0060] FIG. 6 shows a case where the target rotation speed of each traveling motor 30, 31 instructed by the operation unit 32 is a constant speed equal to or higher than a predetermined speed, and the vehicle 10 moves straight forward. First, the speed of the vehicle 10 increases linearly, and at time t1 during the increase, grass mowing begins, and the torque of the deck motor 60 starts to increase from P1 as the traveling speed increases. In this case, the temperature of the deck motor 60 is low, so the target torque range is set to the third range A3. Then, at time t2, it is determined that the torque of the deck motor 60 is within the third range, and the traveling speed has reached a predetermined upper limit speed vM, so the traveling speed and the torque of the deck motor 60 are maintained constant. However, at time t3, the amount of grass increases, and the torque of the deck motor 60 increases and exceeds the upper limit of the third range A3, so the target rotation speed of each traveling motor 30, 31 decreases, and the traveling speed decreases from P2. This decrease in traveling speed reduces the amount of grass cut by the lawnmower 18, so the load on the deck motor 60 decreases and its torque decreases from P3.

[0061] Then, at time t4, the torque of the deck motor 60 returns to the third range A3, so the travel speed is maintained constant at a low speed from P4. Then, as the temperature of the deck motor 60 rises, the target torque range of the deck motor 60 is changed to the second range A2 at time t5. This causes the target rotation speed of each travel motor 30, 31 to decrease, so the travel speed also decreases. This travel speed decreases to the lower limit speed vL during work and is maintained constant. Then, as the amount of grass decreases, the load on the deck motor 60 decreases, and at time t6, when the torque of the deck motor 60 falls below the lower limit of the target torque range, the target rotation speed of each travel motor 30, 31 increases and the travel speed increases from P5. This travel speed is maintained constant when it reaches the upper limit speed vM at P6.

[0062] Then, as the amount of grass increases again, the load increases and the torque of the deck motor 60 increases, and from time t7 to t8, the torque of the deck motor 60 exceeds the upper limit of the second range A2, causing the target rotation speeds of the travel motors 30, 31 to decrease, and the torque of the deck motor 60 returns to the second range A2. Then, at time t9, the temperature of the deck motor 60 further increases, changing the target torque range to the first range A1. As a result, the target rotation speeds of the travel motors 30, 31 decrease to the lower limit speed vL and are maintained constant, but the temperature of the deck motor 60 decreases, changing the target torque range to the second range A2, and the target rotation speeds of the travel motors 30, 31 increase so that the torque of the deck motor 60 falls into the second range A2. This increases the travel speed.

[0063] As shown in FIG. 6, according to the configuration of this example, the torque of the deck motor 60 is controlled so as to fall within an appropriate target torque range according to the temperature of the deck motor 60, so that the deck motor 60 can be protected and the driving time at high vehicle speeds can be extended, thereby improving work efficiency.

[0064] In FIG. 6, the thin solid line b branching off from the thick solid line a indicating the travel speed of this embodiment indicates another example of the embodiment. In the configuration of the other example, the configuration before time t10 is the same as the embodiment indicated by the thick solid line a. In the configuration of the other example, the detected temperature of the deck motor 60 is equal to or higher than a predetermined first temperature d1 from time t8 to t10, so the target torque range of the deck motor 60 is the first range A1, and after time t10, the detected temperature of the deck motor 60 is equal to or lower than a predetermined second temperature lower than the first temperature d1, so the target torque range of the deck motor 60 is set to the second range A2. In this case, the first range A1 corresponds to the low torque range, and the second range A2 corresponds to the high torque range. Then, from time t8 to t9, the detected temperature of the deck motor 60 becomes equal to or higher than the first temperature d1, causing the deck motor 60 to be driven in the first range A1 to reduce the vehicle speed, and after time t10, the detected temperature of the deck motor 60 becomes equal to or lower than a temperature (second temperature) lower than the first temperature d1, causing the control unit 100 to drive the deck motor 60 in the second range A2 to increase the vehicle speed. The control unit 100 further makes the absolute value of the acceleration of the vehicle 10 at this time smaller than the absolute value of the deceleration of the vehicle 10 when the vehicle speed was reduced.

[0065] According to the configuration of the above-described alternative example, sudden acceleration when the vehicle speed of the vehicle 10 increases can be prevented, thereby suppressing jerky sensations in the vehicle speed.

[0066] FIG. 7 shows an example of the torque and rotational speed of the deck motor 60 and the traveling speed of the vehicle 10 over time in another embodiment. In FIG. 7, the thick solid line indicates the deck motor rotational speed and traveling speed in the configuration of this example. The rotational speed of the deck motor 60 is basically controlled to maintain the predetermined target rotational speed after rising to a predetermined target rotational speed during operation, but when the amount of grass to be cut increases, the discharge of the cut grass from the mower deck 19 becomes poor, and the grass accumulates in the mower deck 19, causing the deck motor 60 to become overloaded, the rotational speed of the deck motor 60 may decrease from time t1a as shown by b. In this example, when the decrease in the detected value of the rotational speed of the deck motor 60 per predetermined time is equal to or greater than a predetermined decrease, the control unit 100 increases the reduction rate of the vehicle speed in accordance with the decrease in the amount of decrease, as shown by c, compared to the configuration of FIGS. 1 to 6. For this purpose, the control device 40 uses the detection values ​​of the two left and right motor speed sensors 54, 55 (FIG. 3) to control the rotation speed of each of the traveling motors 30, 31 so as to increase the rate of decrease in the vehicle speed. As a result, as shown by d in FIG. 7, the rate of decrease in the traveling speed of the vehicle 10 increases, so the load on the deck motor 60 can be reduced. This improves the durability and mowing accuracy of the deck motor 60. Furthermore, since the load on the deck motor 60 is reduced by the decrease in the traveling speed, the rotation speed of the deck motor 60 is more likely to return to the predetermined target rotation speed between times t2a and t3a. In this example, other configurations and operations are similar to those of FIGS. 1 to 6.

[0067] FIG. 8 shows an example of the torque of the deck motor 60 and the traveling speed of the vehicle 10 over time in another example of the embodiment. In FIG. 8, the thick solid line indicates the deck motor torque and traveling speed in this example. During lawn mowing work, the load on the deck motor 60 may increase suddenly due to a deterioration in the discharge of cut grass, etc., and the rate of change of the increase in the motor torque over time may increase. In this case, the deck motor 60 may be in an overloaded state for a long time, which may lead to a deterioration in the durability and mowing accuracy of the deck motor 60. In the configuration of this example, when the rate of change of the increase in the calculated value of the output torque of the deck motor 60 is equal to or greater than a predetermined rate of change, the control unit 100 increases the rate of decrease in the vehicle speed according to the rate of change of the increase. Specifically, in the example shown in FIG. 8, when the rate of change of the increase in the calculated value of the output torque of the deck motor 60 becomes higher than the rate of change of the increase in the case shown by the thin line f1 at times t1b to t2b as shown by e, the control unit 100 increases the rate of decrease in the vehicle speed as shown by g, compared to the rate of decrease in the case shown by the thin line f2 corresponding to the thin line f1.

[0068] According to the configuration of this example, when the load on the deck motor 60 increases suddenly as described above and the rate of change in the output torque increases, the vehicle speed reduction rate is increased. This allows the load on the deck motor 60 to be reduced. This improves the durability and mowing accuracy of the deck motor 60. In addition, since the deceleration of the traveling speed starts when the output torque of the deck motor 60 exceeds the upper limit of the third range A3, the start of deceleration indicated by g can be made earlier than the start of deceleration t2b indicated by f2. This allows the load on the deck motor 60 to be reduced early, so that the output torque of the deck motor 60 can be suddenly reduced between times t2b and t3b. In this example, other configurations and operations are the same as those of the configurations of Figs. 1 to 6 or the configuration described using Fig. 7. [Explanation of symbols]

[0069] 10 Electric work vehicle (vehicle), 12 Left wheel, 13 Right wheel, 15, 16 Caster wheel, 18 Lawnmower, 18a-18c Lawnmower blade, 18d Exhaust duct, 19 Mower deck, 20 Main frame, 20a, 20b Side plate portion, 20c Connection portion, 21 Driver's seat, 22, 23 Operation lever, 24 Grip portion, 26, 27 Guide panel, 30 Left travel motor, 31 Right travel motor, 32 Operation portion, 33 Work machine start switch, 34 Motor temperature sensor, 35 Start switch, 40 Control device, 50 Left lever sensor, 51 Right lever sensor, 52 Deck motor speed sensor, 54 Left motor speed sensor, 55 Right motor speed sensor, 60 Deck motor, 80 Control system, 82 Battery, 84 Left travel inverter, 86 Right travel inverter, 88 Deck inverter, 90 Battery monitoring device, 100 control section.

Claims

1. A traction motor that drives the wheels; A work machine motor that drives the work machine; an operation unit for instructing a target rotation speed of the traveling motor and an operation of the working machine; A control unit that controls the travel motor and the work machine motor in accordance with an operation of the operation unit; A temperature sensor for detecting a temperature of the working machine motor, the control unit maintains or changes a target torque range of the work machine motor in accordance with a detected temperature of the work machine motor, and maintains or changes a target rotation speed of the travel motor so that a calculated value of an output torque of the work machine motor falls within the target torque range. Electric work vehicle.

2. The electric work vehicle according to claim 1, the control unit sets the target torque range of the work machine motor such that, when the detected temperature of the work machine motor is equal to or higher than a predetermined first temperature, the work machine motor is driven in a low torque range, and, when the detected temperature of the work machine motor is equal to or lower than a predetermined second temperature that is lower than the first temperature, the work machine motor is driven in a high torque range. Electric work vehicle.

3. The electric work vehicle according to claim 2, the control unit, after the detected temperature of the work machine motor becomes equal to or higher than the first temperature and the vehicle speed is reduced by driving the work machine motor in the low torque range, the control unit, after the detected temperature of the work machine motor becomes equal to or lower than the second temperature and drives the work machine motor in the high torque range and increases the vehicle speed, sets an absolute value of the vehicle acceleration to be smaller than an absolute value of the vehicle deceleration when the vehicle speed is reduced. Electric work vehicle.

4. The electric work vehicle according to claim 2, When a decrease in a detection value of the rotation speed of the work machine motor per predetermined time period is equal to or greater than a predetermined decrease, the control unit increases a rate of decrease in the vehicle speed in accordance with the decrease. Electric work vehicle.

5. The electric work vehicle according to claim 2, the control unit, when a rate of change of an increase in the calculated value of the output torque of the work machine motor becomes equal to or greater than a predetermined rate of change, increases a rate of decrease in the vehicle speed in accordance with the rate of change. Electric work vehicle.

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