Electric transport vehicle

Abstract

To provide an electric transportation vehicle that can surely determine a starting impossible state caused by contacting of the vehicle with a vehicle stop when the vehicle starts.SOLUTION: An electric transportation vehicle 1 runs by driving force of an electric motor 11 that is driven by electric power supply from an electric power generator 13 that is driven by an engine 12. A controller 30 that controls the electric motor has: an engine rotation speed determining part 42 that determines whether an engine rotation speed Ne that is a detected value by a rotation speed sensor 23 is equal to a rotation speed threshold Nth or higher when an instruction for making the vehicle start; an elapsed-time determining part 43 that determines whether a first elapsed time Ta measured after a time at which the detected value Ne is determined to be the rotation speed threshold or higher is equal to a time threshold Tth; and a start determining part 44 that determines whether a vehicle speed Vs that is a detected value by a speed sensor 24 is equal to the speed threshold Vth or higher after the first elapsed time is determined to be equal to the time threshold. The electric transportation vehicle stops the electric motor when the detected value by the speed sensor is determined to be less than the speed threshold.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a transport vehicle such as a dump truck for transporting ores and earth and sand excavated in mines and the like. More specifically, the present invention relates to an electric transport vehicle that runs by the driving force of an electric motor driven by power supplied from a generator mechanically connected to an engine.

Background Art

[0002] In open-pit mines, transport vehicles such as dump trucks transport excavated ores and earth and sand. Generally, a transport vehicle loads the transported material onto the loading platform at the loading site where the minerals are being excavated, travels on the transport route with the transported material loaded, and discharges (dumps) the transported material at the dumping site. The transport vehicle with an empty loading platform after discharging the transported material travels on the transport route again to return to the loading site and loads the transported material onto the loading platform again. The transport vehicle performs such operations of loading and dumping repeatedly many times.

[0003] As a method for a transport vehicle to dump the transported material at the dumping site, there are the following methods. First, the transport vehicle retreats to the target position while gradually changing its position on a wide flat ground and directly dumps the material onto the ground. Second, the transport vehicle retreats to the inlet called a hopper or just before the cliff and dumps the material into the hopper or under the cliff.

[0004] When using the second method, there is an advantage that the dumping can be performed from approximately the same fixed location each time. However, there is a concern that the transport vehicle may fall into the hopper or under the cliff by overshooting when retreating to the dumping position. Therefore, in front of the hopper or the cliff, a vehicle stop such as an embankment is installed to prevent the vehicle from falling. Even if the transport vehicle is about to overshoot the dumping position, its running is suppressed by the running resistance of the vehicle stop.

[0005] In the transport vehicles described above, electrification has been progressing in recent years with the aim of reducing maintenance costs by eliminating mechanical parts such as transmissions. Electric transport vehicles generally generate electricity using a generator mechanically connected to the engine, and the electricity generated by the generator is supplied to an electric motor mounted on the rear wheel (drive wheel), so that the electric motor is the driving source for propulsion.

[0006] In electric transport vehicles that use an electric motor as their driving source, if the electric motor continues to output power even when the vehicle is immobilized due to contact with a wheel stop, the energy of the electric motor (driving source) is wasted, and the load on the drive mechanism increases, leading to a decrease in energy efficiency. Furthermore, in autonomous transport vehicles that have recently begun to be introduced in mines and other areas, if the vehicle remains immobilized due to contact with a wheel stop despite a start command being issued, there is a concern that the start command will not be completed, resulting in a deadlock where the vehicle cannot proceed to the next command. For these reasons, it is desirable for electric transport vehicles to determine whether they are immobilized due to contact with a wheel stop, and to stop the vehicle's driving source if it is determined that they are immobilized.

[0007] A technology described in Patent Document 1 has been proposed for determining whether a vehicle's wheels are in contact with a wheel stop and the vehicle is unable to move. The driving assistance device described in Patent Document 1 calculates the degree of discrepancy between the longitudinal acceleration of the vehicle, estimated based on the braking force (combined force of braking force and driving force) generated by the driving operation detected by the braking force detection unit, and the longitudinal acceleration of the vehicle detected by the acceleration detection unit, and determines whether the vehicle has come into contact with a wheel stop based on the calculated degree of discrepancy. This driving assistance device is intended for installation in mass-produced vehicles such as automobiles. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2012-116360 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] When using the technology described in Patent Document 1 to determine whether or not a vehicle makes contact with a wheel stop when starting, it is necessary to accurately estimate the acceleration of the vehicle by sequentially detecting the braking and driving forces generated by the driving operation with high precision. In the case of electric vehicles, the driving force among the braking and driving forces generated by the driving operation is calculated based on the output torque value of the electric motor, so it is necessary to detect the output torque of the electric motor with high precision.

[0010] Incidentally, large electric transport vehicles used in mines require large electric motors as their driving source, so induction motors are generally used instead of the permanent magnet synchronous motors used in electric vehicles for general passenger use. This is because induction motors can be manufactured in larger sizes than permanent magnet types by using wound field magnets, and they can also withstand harsh environments such as vibration, shock, and high temperatures.

[0011] In induction motors, due to the principle of rotational force generation, it is difficult to accurately detect the motor's output torque during vehicle startup. An induction motor generates torque (rotational force) through the interaction between a rotating magnetic field, which is generated by exciting the coils of the stator on the housing side, and an induced current, which is generated in the coils of the rotor on the output shaft side. The induced current is generated by the difference (slip) between the rotational speed of the rotating magnetic field and the rotational speed of the rotor. The output torque of an induction motor can be calculated using the motor rotation speed detected by a sensor. However, during vehicle startup, the rotor of the induction motor is almost stationary and its rotation speed is extremely low, making it very difficult to accurately measure the rotation speed of the induction motor (rotor) with a sensor.

[0012] Thus, when an induction motor is used as the driving source for a vehicle, it is difficult to detect the motor's output torque with high accuracy. For this reason, if the technology described in Patent Document 1 is used to determine whether or not the vehicle has made contact with the wheel stop when the vehicle starts moving, it may be difficult to accurately estimate the vehicle's acceleration, and a normal determination may not be possible.

[0013] The present invention was made to solve the above-mentioned problems, and its objective is to provide an electric transport vehicle that can reliably determine whether or not the vehicle is unable to start due to contact with a wheel stop when starting, even when an induction motor is used as the vehicle's driving source. [Means for solving the problem]

[0014] The present invention includes multiple means for solving the above problems. To give one example, in an electric transport vehicle that transports cargo by moving with the driving force of the electric motor, the electric transport vehicle includes an engine, a generator mechanically driven by the engine, an electric motor driven by power supplied from the generator, a rotation speed sensor for detecting the rotation speed of the engine, a speed sensor for detecting the vehicle speed, and a controller for controlling the drive of the electric motor, the controller is characterized in that when an instruction to start the vehicle is input, the detected value of the rotation speed sensor is equal to or greater than a rotation speed threshold, the controller has an engine rotation speed determination unit that determines whether the detected value of the rotation speed sensor is equal to or greater than a rotation speed threshold, the first elapsed time from the time when the engine rotation speed determination unit determines that the detected value of the rotation speed sensor is equal to or greater than the rotation speed threshold, and the first elapsed time determination unit that determines whether the first elapsed time has reached a time threshold, and after the elapsed time determination unit determines that the first elapsed time has reached the time threshold, the controller has a start determination unit that determines whether the detected value of the speed sensor is equal to or greater than a speed threshold, and the start determination unit stops the electric motor when it determines that the detected value of the speed sensor is less than the speed threshold. [Effects of the Invention]

[0015] According to the present invention, by determining whether the vehicle speed reaches the speed threshold after the first elapsed time from the moment the engine speed reaches the rotational speed threshold has reached the time threshold, it becomes possible to determine whether the electric transport vehicle is in a state where it cannot start due to contact with a wheel stop, taking into account the acceleration time from when the vehicle starts moving until it reaches a driving state that can be detected by the speed sensor, thereby preventing errors in the determination. In other words, it is possible to reliably determine whether the vehicle is in a state where it cannot start due to contact with a wheel stop when the vehicle starts. Other issues, configurations, and effects will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0016] [Figure 1] This is an external view showing a dump truck as an electric transport vehicle according to the first embodiment of the present invention. [Figure 2] This is a block diagram showing the schematic configuration of the electric drive system in an electric transport vehicle according to the first embodiment and the control controller for the electric drive system. [Figure 3] Figure 2 is a flowchart showing an example of the control procedure for the controller of the electric transport vehicle according to the first embodiment. [Figure 4] This is a time chart showing the time progression of engine speed and vehicle speed at startup in an electric transport vehicle according to the first embodiment. [Figure 5] This is a block diagram showing the schematic configuration of the electric drive system in an electric transport vehicle according to a second embodiment of the present invention, and a control controller for the electric drive system. [Figure 6] Figure 5 is a flowchart showing an example of the control procedure for the controller of the electric transport vehicle according to the second embodiment. [Figure 7] This is a block diagram showing the schematic configuration of the electric drive system and the control controller of the electric drive system in an electric transport vehicle according to a modified example of the second embodiment. [Figure 8]It is a block diagram showing a schematic configuration of an electric drive system in an electric industrial vehicle according to a third embodiment of the present invention and a controller for controlling the electric drive system. [Figure 9] It is a flowchart showing an example of a control procedure of a controller of an electric industrial vehicle according to a third embodiment shown in FIG. 8. [Figure 10] It is a block diagram showing a schematic configuration of an electric drive system in an electric industrial vehicle according to a first modification of the third embodiment and a controller for controlling the electric drive system. [Figure 11] It is a block diagram showing a schematic configuration of an electric drive system in an electric industrial vehicle according to a second modification of the third embodiment and a controller for controlling the electric drive system. [Figure 12] It is a flowchart showing an example of a control procedure of a controller of an electric industrial vehicle according to a second modification of the third embodiment shown in FIG. 11.

MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, embodiments of the electric industrial vehicle of the present invention will be described with reference to the drawings. In the present embodiment, as an example of an electric industrial vehicle, a dump truck will be described as an example. Note that the front-back, left-right directions described in this specification indicate the directions as viewed from an operator on board the electric industrial vehicle.

[0018] [First Embodiment] First, a schematic configuration of a dump truck as an electric industrial vehicle according to a first embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is an external view showing a dump truck as an electric industrial vehicle according to a first embodiment of the present invention.

[0019] In Figure 1, the dump truck 1, as an electric transport vehicle, is used to transport cargo W such as ore and soil excavated from a mine, and is driven by the power of an electric motor 11, which will be described later. The dump truck 1 comprises a body frame 2, which is a support structure extending in the front-rear direction (left-right direction in Figure 1); front wheels 3 and rear wheels 4, which are rotatably mounted on the left and right sides of the front and rear of the body frame 2, respectively; a cabin 5 installed at the front of the body frame 2; and a cargo bed 6 mounted on the body frame 2 so as to be able to tilt (unravel). An engine 12, a generator 13, an inverter 14 (see Figure 2, described later), etc., are mounted at the front of the body frame 2 to supply power to the electric motor 11.

[0020] The front wheels 3 are steering wheels, for example, steered by an operator. The rear wheels 4 are drive wheels, rotationally driven by an electric motor 11. Between the front of the vehicle frame 2 and the front wheels 3, there is a front suspension 7 that absorbs vibrations received from the road surface during driving and mitigates impacts to the vehicle frame 2. Between the rear of the vehicle frame 2 and the rear wheels 4, there is a rear suspension 8 that absorbs vibrations received from the road surface during driving and mitigates impacts to the vehicle frame 2. The front suspension 7 and the rear suspension 8 include, for example, a suspension cylinder filled with compressible oil and have a mechanism that uses the compression of the oil by a piston as a spring.

[0021] Cabin 5 is the section where the operator sits and drives the vehicle. Cabin 5 is equipped with various operating devices for the operator to operate the dump truck 1, including a driver's seat (not shown) where the operator sits, operating pedals 21 for driving the dump truck 1 (see Figure 2 below), a steering wheel (not shown) for steering the front wheels 3, and an operating unit (not shown) for controlling the elevation of the cargo bed 6.

[0022] The cargo bed 6 is for loading the cargo W, and its rear end is rotatably attached to the rear end of the vehicle frame 2 via a pivot pin 2a. A hoist cylinder 9 for raising and lowering the cargo bed 6 is provided between the vehicle frame 2 and the cargo bed 6. The cargo bed 6 is configured to tilt relative to the vehicle frame 2 between a transport rotation position (solid line), which is the position for loading and transporting the cargo W onto the cargo bed 6, and a soil release rotation position (dash-dot line), which is the position for releasing the cargo W from the cargo bed 6, by the extension and retraction of the hoist cylinder 9.

[0023] The dump truck 1 has a rotation speed sensor 23 (see Figure 2 below) for detecting the rotation speed of the engine 12, a vehicle speed sensor 24 for detecting the vehicle speed (speed of the dump truck 1), an acceleration sensor 26 for detecting the vehicle acceleration (acceleration of the dump truck 1), and a load sensor 25 for detecting the load weight of the cargo W. The vehicle speed sensor 24 is, for example, a speed sensor for detecting the rotation speed of the rear wheels 4. The load sensor 25 is, for example, a pressure sensor for detecting the pressure in the suspension cylinders of the front suspension 7 and the rear suspension 8. In addition to the pressure sensor, the load sensor can also be configured to use a sensor capable of detecting the force acting on the front suspension 7 and the rear suspension 8. Furthermore, the load sensor can also be configured to be a weight sensor installed on the seating portion of the cargo bed 6.

[0024] In this configuration, the dump truck 1 has its cargo W (transported material), such as soil and sand, loaded onto its bed 6 at the loading area using loading machinery such as a shovel or wheel loader. With the transported material W loaded on its bed 6, the dump truck 1 travels along the transport path by rotating its rear wheels 4 with the driving force of an electric motor 11. At the unloading area, the dump truck 1 tilts its bed 6 from the transport rotation position (solid line in Figure 1) to the unloading rotation position (dash-dot line in Figure 1) by extending the hoist cylinder 9 at the operator's command, and the transported material W loaded on the bed 6 is discharged (unloaded) from the rear end of the bed 6. With the transported material W discharged and the bed 6 empty, the dump truck 1 departs from the unloading area and travels along the transport path back to the loading area. Dump truck 1 repeatedly loads at the loading area, drives from the loading area to the unloading area or from the unloading area to the loading area, and unloads at the unloading area.

[0025] For example, the dump truck 1 reverses and stops just before the loading opening called a hopper or the bottom of a cliff (neither shown) at the unloading site, and unloads the material W on its cargo bed 6 into the hopper or the bottom of the cliff. In this case, a wheel stop 100 made of earth or the like is installed in front of the hopper or cliff at the unloading site to prevent the dump truck 1 from going past its stopping position when reversing. When the dump truck 1 is about to go past its stopping position, the wheel stop 100 provides resistance to the dump truck 1, restricting its movement.

[0026] Next, the schematic configuration of the electric drive system in the electric transport vehicle according to the first embodiment, and the hardware and functions of the controller that controls the electric drive system, will be described with reference to Figure 2. Figure 2 is a block diagram showing the schematic configuration of the electric drive system in the electric transport vehicle according to the first embodiment shown in Figure 1, and the controller that controls the electric drive system.

[0027] The electric drive system of the dump truck 1 includes an electric motor 11 that rotates the rear wheels 4, a generator 13 that supplies power to the electric motor 11, an engine 12 that drives the generator 13, and an inverter 14 that adjusts the power supplied from the generator 13 to the electric motor 11. The electric motor 11 is an induction motor. The generator 13 is mechanically connected to the engine 12 and is driven by the engine 12 to generate electricity. The engine 12 is configured so that its rotational speed increases when the vehicle starts and during acceleration. The engine 12 has an engine control unit (not shown) that controls the engine speed in response to commands from the controller 30 described later. The engine 12 is equipped with the aforementioned rotational speed sensor 23 that detects the rotational speed of the engine 12. The engine 12 (engine control unit) outputs the detected value (engine speed Ne) from the rotational speed sensor 23 to the controller 30 described later. The inverter 14 controls the torque and rotational speed of the electric motor 11 in response to commands from the controller 30 described later. In the case of electric drive systems, mechanical elements such as transmission gears that make up mechanical drive systems are unnecessary, so maintenance costs such as lubrication oil management and equipment overhaul can be reduced.

[0028] The controller 30 controls the electric drive system of the dump truck 1 based on the operation signal Pi input from the operation pedal 21 and information (such as engine speed Ne) input from the engine 12 (engine control unit). The controller 30 is configured to control the drive of the engine 12 of the electric drive system via the engine control unit, and to control the drive of the electric motor 11 of the electric drive system via the inverter 14. Furthermore, in the case of an autonomous driving type dump truck 1 that drives without operation by an operator in the cabin 5 (see Figure 1), the controller 30 is configured to control the electric drive system of the dump truck 1 in response to autonomous driving instructions Si from the control station 60.

[0029] Here, we consider a scenario where dump truck 1 is unable to start because it has come into contact with the wheel stop 100 (see Figure 1) at the time of departure. If the electric motor 11 continues to output driving force despite being unable to start, the power (energy) supplied to the electric motor 11 will be wasted, reducing energy efficiency. Furthermore, if dump truck 1 is an autonomous vehicle, and it remains unable to start due to contact with the wheel stop 100 despite a start command being issued from the control station 60, there is a concern that the start command will not be completed, leading to a deadlock where the system cannot proceed to the next command.

[0030] Therefore, the controller 30 of the dump truck 1 according to this embodiment is configured to determine whether the dump truck 1 is immobilized due to contact between the front wheels 3 or rear wheels 4 (wheels) and the wheel stop 100 at the time of starting, and to stop the electric motor 11 if it is determined that the dump truck 1 is immobilized. This prevents the waste of power (energy) supplied to the electric motor 11. In addition, if the dump truck 1 is an autonomous driving type, it prevents it from getting stuck in a deadlock in response to a starting command.

[0031] Specifically, the controller 30 includes, as a hardware configuration, a storage device 31 consisting of, for example, RAM or ROM, and an arithmetic processing unit 32 consisting of a CPU or MPU including a timer capable of measuring time. The storage device 31 pre-stores programs and various information necessary for controlling the electric drive system when the dump truck 1 starts. The arithmetic processing unit 32 reads programs and various information from the storage device 31 as appropriate and executes processing according to the programs to realize various functions, including the following functions. The controller 30 has a drive torque command unit 41, an engine speed determination unit 42, an elapsed time determination unit 43, and a start determination unit 44 as functions executed by the arithmetic processing unit 32 when the dump truck 1 starts.

[0032] The drive torque command unit 41 receives an operation signal Pi corresponding to the amount of operation of the operation pedal 21 or an autonomous driving instruction Si (such as an acceleration instruction or deceleration instruction) from the control station 60, and calculates a command value for the drive torque that the electric motor (induction motor) 11 applies to the wheels (rear wheels 4) based on the received operation signal Pi or autonomous driving instruction Si. Basically, it outputs a command value Ci for the supply current to the electric motor (induction motor) 11 corresponding to the calculated drive torque command value to the inverter 14. In this way, the controller 30 controls the driving of the electric motor (induction motor) 11 (vehicle movement) via the inverter 14. However, if the start determination unit 44 receives a determination result of inability to start as described later, it outputs a command with a supply current value of "0", which is a command to stop the electric motor 11, instead of a command for the supply current value calculated based on the operation signal Pi of the operation pedal 21 or the autonomous driving instruction Si from the control station 60. Furthermore, the stop command for the electric motor 11 can also be a command that gradually reduces the supplied current value (driving torque) until it becomes "0".

[0033] The induction motor 11 is capable of outputting forward or backward torque depending on the rotation direction (forward or reverse) of the rotating magnetic field. Furthermore, the induction motor 11 is capable of outputting torque to accelerate the vehicle or torque to decelerate the vehicle through regenerative braking, depending on the relationship between the rotation speed of the rotating magnetic field and the rotation speed of the wheels (rear wheels 4). The operating pedal 21 is composed of two pedals, for example, an accelerator pedal for acceleration and a retard pedal for deceleration, and the direction of the output torque of the induction motor 11 can be switched by operating either the accelerator pedal or the retard pedal.

[0034] Therefore, the drive torque command unit 41 can express command values ​​corresponding to all forward and reverse movement and acceleration / deceleration of the vehicle by assigning positive and negative signs to the calculated drive torque command value according to the direction of application of the output torque of the induction motor 11. For example, as the sign of the drive torque command value, acceleration during forward movement is set to positive and braking to negative, and conversely, braking during reverse movement is set to positive and acceleration to negative. When the vehicle is reversing, such as when approaching the earth-discharge position, the drive torque command unit 41 increases the drive torque command value in the negative direction as the amount of operation of the accelerator pedal, which constitutes the operating pedal 21, increases. On the other hand, when the amount of operation of the retard pedal, which constitutes the operating pedal 21, increases, the drive torque command value increases in the positive direction.

[0035] The engine speed determination unit 42 monitors the engine speed when the start operation of the vehicle is input and determines whether the engine speed is equal to or greater than the rotation speed threshold Nth. Specifically, it takes in the engine speed Ne, which is the value detected by the rotation speed sensor 23 output from the engine control unit of the engine 12, and determines whether the engine speed Ne is equal to or greater than the rotation speed threshold Nth. The rotation speed threshold Nth is an indicator used to determine whether the generator 13 is in a state where it can supply sufficient power to the electric motor 11 for starting the dump truck 1.

[0036] In the case of large electric transport vehicles, such as those used in mines, the engine 12 is also large, so it takes a certain amount of time for the engine speed to increase during starting. Moreover, the torque of the engine 12 is used not only to increase the rotational speed of the engine 12 itself, but also to drive the generator 13. For this reason, depending on the starting load of the electric transport vehicle, it may take even longer for the engine speed to increase. For this reason, the elapsed time from the start of the starting operation cannot be used as an indicator to determine whether the generator 13 is able to supply sufficient power for starting the vehicle.

[0037] Therefore, the controller 30 uses the engine speed Ne as an indicator of the power generated by the generator 13. Since the power generated by the generator 13, which is driven by the engine 12, increases as the rotational speed of the engine 12 increases, if the engine speed Ne is equal to or greater than the rotational speed threshold Nth, it can be considered that the generator 13 is in a state where it can generate enough power to start the dump truck 1. The rotational speed threshold Nth is stored in the memory device 31 in advance, for example.

[0038] The elapsed time determination unit 43 measures the elapsed time Ta from the time the engine speed determination unit 42 made its determination when the engine speed determination unit 42 determined that the engine speed Ne, which is the value detected by the rotation speed sensor 23, is equal to or greater than the rotation speed threshold Nth, and determines whether the measured elapsed time Ta has reached the time threshold Tth. The time threshold Tth is an indicator for determining whether enough time has elapsed to accelerate from the start of movement of the dump truck 1 until it reaches a driving state. The time threshold Tth is stored in the storage device 31 in advance, for example.

[0039] The starting determination unit 44 determines whether the dump truck 1 has started moving when the elapsed time determination unit 43 determines that the measured elapsed time Ta has reached the time threshold Tth. Specifically, when the elapsed time determination unit 43 determines that the elapsed time Ta has reached the time threshold Tth, the starting determination unit 44 takes in the vehicle speed Vs, which is the value detected by the vehicle speed sensor 24, and determines whether the vehicle speed Vs is equal to or greater than the speed threshold Vth. If it is determined that the vehicle speed Vs is lower than the speed threshold Vth, it is considered that the dump truck 1 is unable to start because either the front wheels 3 or the rear wheels 4 have come into contact with the wheel stop 100 at the time of starting, and outputs the determination result Df of being unable to start to the drive torque command unit 41.

[0040] The speed threshold Vth is set to a speed that the vehicle speed sensor 24 can reliably detect and that reliably confirms that the dump truck 1 is in a driving state without contacting the wheel stop 100. If the dump truck 1 is unable to start because either the front wheels 3 or the rear wheels 4 are in contact with the wheel stop 100 at the time of starting, the vehicle speed Vs will not reach the speed threshold Vth. On the other hand, if the front wheels 3 or the rear wheels 4 are not in contact with the wheel stop 100 at the time of starting, after a time threshold Tth has elapsed from the state in which the dump truck 1 is able to start, the vehicle speed Vs will rise and reach the speed threshold Vth. Therefore, it is possible to determine whether the dump truck 1 has started or not based on whether the vehicle speed Vs has reached the speed threshold Vth. The speed threshold Vth can be set to a constant value that is pre-stored in the storage device 31. In addition, the speed threshold Vth can be set to change according to the amount of operation of the starting operation pedal 21 or the target speed of the starting instruction from the control station 60.

[0041] Next, the vehicle start control procedure of the controller for the electric transport vehicle according to the first embodiment will be explained using Figure 3. Figure 3 is a flowchart showing an example of the vehicle start control procedure of the controller for the electric transport vehicle according to the first embodiment shown in Figure 2.

[0042] In Figure 3, the controller 30 shown in Figure 2 determines whether or not a starting instruction for the dump truck 1 has been input (step S10). If it is determined that a starting instruction for the dump truck 1 has been input, the process proceeds to step S20; otherwise, the control flow is terminated. For example, if the detected value Vs of the vehicle speed sensor 24 is 0, and an operation signal indicating an acceleration instruction from the operation pedal 21 (accelerator pedal operation signal) or an acceleration instruction from the control station 60 is input, it is determined that a starting instruction for the dump truck 1 has been input. Otherwise, it is determined that no starting instruction has been input.

[0043] If step S10 determines YES (input of a start command), the drive torque command unit 41 of the controller 30 outputs a drive torque command value for the electric motor 11, calculated based on the acceleration command from the operating pedal 21 or the control station 60, to the inverter 14 (step S20). Specifically, the drive torque command value for the electric motor 11 is calculated based on the acceleration command from the operating pedal 21 or the control station 60, and the calculated drive torque command value is output to the inverter 14 as a supply current command value Ci, which is the current value supplied from the generator 13 to the electric motor 11. As a result, the inverter 14 supplies the power generated by the generator 13 driven by the engine 12 to the electric motor 11 according to the supply current command value (drive torque command value). Note that this output of the drive torque command value by the controller 30 to the inverter 14 continues even while steps from step S20 onward are being executed.

[0044] Next, the controller 30 determines whether the engine speed Ne detected by the rotation speed sensor 23 is equal to or greater than the rotation speed threshold Nth (step S30). Specifically, the engine speed determination unit 42 determines this by comparing the engine speed Ne detected by the rotation speed sensor 23 with the rotation speed threshold Nth pre-stored in the storage device 31. If the engine speed Ne is lower than the rotation speed threshold Nth (NO), the process returns to step S30, and the determination in step S30 is repeated until the engine speed Ne is equal to or greater than the rotation speed threshold Nth (YES).

[0045] If the answer in step S30 is YES, the controller 30 starts measuring the elapsed time Ta from the point in time when the engine speed determination unit 42 determined that the engine speed Ne is equal to or greater than the speed threshold Nth (YES), and determines whether the measured elapsed time Ta has exceeded the time threshold Tth (step S40). Specifically, the elapsed time determination unit 43 makes this determination by comparing the measured elapsed time Ta with the time threshold Tth that is pre-stored in the storage device 31. If the elapsed time Ta has not elapsed longer than the time threshold Tth (if NO), the process returns to step S40, and the determination in step S40 is repeated until the elapsed time Ta exceeds the time threshold Tth (becomes YES).

[0046] If the answer in step S40 is YES, the controller 30 determines whether the vehicle speed Vs detected by the vehicle speed sensor 24 is equal to or greater than the speed threshold Vth (step S50). Specifically, the start determination unit 44 makes this determination by comparing the vehicle speed Vs detected by the vehicle speed sensor 24 with the speed threshold Vth pre-stored in the storage device 31. If the vehicle speed Vs is higher than the speed threshold Vth (if YES), it is determined that the start is complete and the control flow ends. On the other hand, if the vehicle speed Vs is lower than the speed threshold Vth (if NO), the process proceeds to step S60.

[0047] If the result in step S50 is NO, that is, if the vehicle speed Vs is lower than the speed threshold Vth, the drive torque command unit 41 outputs a stop command to the inverter 14 to stop the electric motor 11 (step S60). Specifically, the start determination unit 44 outputs the determination result Df of "NO" in step S50, which is the determination result of being unable to start, to the drive torque command unit 41. Upon receiving the determination result Df of being unable to start, the drive torque command unit 41 changes the drive torque command value from the calculated value corresponding to the acceleration instruction from the operating pedal 21 or the control station 60 in step S20 to "0", which is the stop command.

[0048] These processes, when a vehicle start command is input, first determine whether the generator 13 has reached a state where it can supply sufficient power for the electric motor 11 to output the driving force for starting the vehicle, and then determine whether the vehicle has started moving and accelerated to a speed detectable by the vehicle speed sensor 24. These determinations make it possible to reliably determine whether the dump truck 1 has started moving without contacting the wheel stop 100 or whether it has come into contact with the wheel stop 100 and is unable to start, without detecting the driving torque of the induction motor 11.

[0049] Next, the operation of the electric transport vehicle according to the first embodiment of the present invention will be explained using Figures 2 to 4. Figure 4 is a time chart showing the time progression of engine speed and vehicle speed at the time of starting in the electric transport vehicle according to the first embodiment.

[0050] In Figure 4, the upper panel shows the time progression of the amount of operation of the accelerator pedal, which is the starting command for the operating pedal 21. The middle panel shows the time progression of the engine speed Ne in response to the starting command for the operating pedal 21 shown in the upper panel. The lower panel shows the time progression of the vehicle speed Vs in response to the starting command for the operating pedal 21 shown in the upper panel.

[0051] As shown in the upper diagram of Figure 4, the case where a start command is input from the operating pedal 21 at time T1 will be explained. In response to the start command from the operating pedal 21, the controller 30 shown in Figure 2 increases the engine speed Ne from the idle speed Ni to a target speed corresponding to the amount of operation of the operating pedal 21 via the engine control unit of the engine 12. However, the torque of the engine 12 is used not only to increase the rotational speed of the engine 12 itself, but also to drive the generator 13. For this reason, it takes a certain amount of time for the engine speed Ne to increase from the idle speed Ni to the target speed. For this reason, as shown in the middle diagram of Figure 4, the engine speed Ne gradually increases from the idle speed Ni at time T1 and finally reaches the target speed.

[0052] When a start command is input from the operating pedal 21 at time T1, the controller 30 of this embodiment determines whether the engine speed Ne is equal to or greater than the rotational speed threshold Nth (step S30 shown in Figure 3). For a short period of time since time T1, the engine speed Ne does not reach the rotational speed threshold Nth, as shown in the middle diagram of Figure 4.

[0053] When the engine speed Ne reaches the rotational speed threshold Nth at time T2, the controller 30 determines that the engine speed Ne is equal to or greater than the rotational speed threshold Nth and measures the elapsed time Ta from the time of this determination (i.e., time T2) (step S40 shown in Figure 3). When the measured elapsed time Ta exceeds the time threshold Tth, that is, when it reaches time T3 (T3-T2=Tth) in the lower diagram of Figure 4, the controller 30 determines the vehicle speed Vs(V) at time T3 when the time threshold Tth has elapsed. T3 It is determined whether the speed threshold Vth is exceeded (step S50 shown in Figure 3).

[0054] Furthermore, when a start command is input to the controller 30 at time T1, it outputs a drive torque command for the electric motor 11 calculated based on the amount of operation of the operating pedal 21 to the inverter 14 (step S20 shown in Figure 3). As a result, the power generated by the generator 13 driven by the engine 12 is supplied to the electric motor 11 via the inverter 14. The electric motor 11 attempts to rotate the rear wheels 4 with its drive torque. However, for a short period of time since time T1, as shown in the middle diagram of Figure 2, the engine speed Ne is not high, so the power generated by the generator 13 has not reached a level where it can rotate the rear wheels 4. For this reason, as shown in the lower diagram of Figure 4, the driving speed (vehicle speed Vs) of the dump truck 1 remains stationary (speed 0) for a while from time T1. After that, as time passes from time T1, the engine speed Ne gradually increases, and the power generated by the generator 13 reaches a level where it can rotate the rear wheels 4, causing the dump truck 1 to start moving.

[0055] At this time, if the front wheels 3 or rear wheels 4 of the dump truck 1 are not in contact with the wheel stop 100, the dump truck 1 that has started to move will be accelerated by the driving torque of the electric motor 11, so the vehicle speed Vs will gradually increase. In the lower part of Figure 4, the vehicle speed Vs at time T3 is V T3 It has reached this point. In this case, the controller 30 determines the vehicle speed Vs(V) at time T3. T3 It is determined that the speed threshold Vth is greater than or equal to (YES in step S50 shown in Figure 3). In this case, the output of a drive torque command to the inverter 14 corresponding to the amount of operation of the operating pedal 21 continues.

[0056] On the other hand, if the front wheels 3 or rear wheels 4 of the dump truck 1 are in contact with the wheel stop 100, the dump truck 1 will be unable to start due to the wheel stop 100. Therefore, the vehicle speed Vs of the dump truck 1 will be "0" or close to it, meaning that it will be unable to start even after time has elapsed since time T1. That is, at time T3, the vehicle speed Vs is "0" or close to it. In this case, the controller 30 will determine the vehicle speed Vs(V) at time T3. T3 The controller determines that the torque is lower than the speed threshold Vth (NO in step S50 shown in Figure 3). In this case, the controller 30 outputs a command to the inverter 14 with a drive torque of "0" as a stop command for the electric motor 11, regardless of the amount operated on the operating pedal 21.

[0057] As described above, in this embodiment, the controller 30 determines whether the vehicle speed Vs is equal to or greater than the speed threshold Vth when the elapsed time Ta from the point in time when the engine speed Ne is determined to be equal to or greater than the rotational speed threshold Nth has elapsed to a time threshold Tth. The time threshold Tth takes into account the acceleration time from when the dump truck 1 starts moving until it reaches a driving state. If the dump truck 1 is unable to start because its front wheels 3 or rear wheels 4 are in contact with the wheel stop 100, the vehicle speed Vs will not exceed the speed threshold Vth. On the other hand, if the dump truck 1 starts moving without contacting the wheel stop 100, the dump truck 1 will reach a driving state where its vehicle speed Vs exceeds the speed threshold Vth after the time threshold Tth has elapsed. Therefore, the controller 30 can determine whether the dump truck 1 is unable to start because it is in contact with the wheel stop 100 by the above determination without detecting the driving torque of the electric motor 11.

[0058] Furthermore, in this embodiment, the controller 30 is configured to stop the electric motor 11 when it determines that the vehicle speed Vs does not exceed the speed threshold Vth when the elapsed time Ta has exceeded the time threshold Tth. This prevents the electric motor 11 from continuing to output when it is unable to move due to contact with the wheel stop 100, thereby suppressing energy waste of the electric motor 11. In addition, it prevents a deadlock from occurring when the vehicle is unable to move due to contact with the wheel stop 100 during autonomous driving, where the start command cannot be completed and the vehicle cannot proceed to the next command.

[0059] As described above, the dump truck 1 (electric transport vehicle) according to the first embodiment includes an engine 12, a generator 13 mechanically driven by the engine 12, an electric motor 11 driven by electricity supplied from the generator 13, a rotation speed sensor 23 for detecting the rotation speed Ne of the engine 12, a vehicle speed sensor 24 (speed sensor) for detecting the vehicle speed Vs, and a controller 30 for controlling the drive of the electric motor 11, and transports cargo W by moving using the driving force of the electric motor 11. The controller 30 includes an engine speed determination unit 42 that determines whether the detected value Ne of the rotation speed sensor 23 is greater than or equal to the rotation speed threshold Nth when a vehicle start command is input, an elapsed time determination unit 43 that measures the elapsed time Ta (first elapsed time) from the time the engine speed determination unit 42 determines that the detected value Ne of the rotation speed sensor 23 is greater than or equal to the rotation speed threshold Nth, and determines whether the elapsed time Ta (first elapsed time) has reached the time threshold Tth, and a start determination unit 44 that determines whether the detected value Vs of the vehicle speed sensor 24 (speed sensor) is greater than or equal to the speed threshold Vth after the elapsed time determination unit 43 has determined that the elapsed time Ta (first elapsed time) has reached the time threshold Tth, and is configured to stop the electric motor 11 if the start determination unit 44 determines that the detected value Vs of the vehicle speed sensor 24 (speed sensor) is less than the speed threshold Vth.

[0060] With this configuration, by determining whether the vehicle speed Vs reaches the speed threshold Vth after the elapsed time Ta (first elapsed time) from the moment the engine speed Ne reaches the rotational speed threshold Nth reaches the time threshold Tth, it becomes possible to determine whether the dump truck 1 (electric transport vehicle) is in a state where it cannot start due to contact with the wheel stop 100, taking into account the acceleration time from when the dump truck 1 (electric transport vehicle) starts moving until it reaches a driving state that can be detected by the vehicle speed sensor 24 (speed sensor). This prevents errors in the determination. In other words, it is possible to reliably determine whether the dump truck 1 (electric transport vehicle) is in a state where it cannot start due to contact with the wheel stop 100 when the vehicle starts.

[0061] [Second Embodiment] Next, an electric transport vehicle according to a second embodiment of the present invention will be described with reference to Figures 5 and 6. In Figures 5 and 6, parts with the same reference numerals as those shown in Figures 1 to 4 are similar parts, so a detailed explanation of them will be omitted. Figure 5 is a block diagram showing the schematic configuration of the electric drive system in the electric transport vehicle according to the second embodiment and the controller that controls the electric drive system.

[0062] The differences between the electric transport vehicle according to the second embodiment shown in Figure 5 and the first embodiment are as follows. In the controller 30 according to the first embodiment, the engine speed determination unit 42 is configured to make a determination using a predetermined value, which is the rotation speed threshold Nth. In contrast, in the controller 30A according to the second embodiment, the engine speed determination unit 42A is configured to change the setting of the rotation speed threshold Nth, which is the determination index, according to the load weight W of the dump truck 1.

[0063] The total weight of dump truck 1 changes significantly depending on whether or not it is loaded with cargo W. The greater the total weight of dump truck 1, the greater the power generated by the generator 13 required to start dump truck 1. The rotational speed threshold Nth, which is the judgment index of the engine rotational speed determination unit 42A, is used as an indicator of whether or not the power generated by the generator 13 has reached the power required to start dump truck 1. For this reason, it is preferable to change the rotational speed threshold Nth according to the change in the total weight of dump truck 1 (the load weight of cargo W) rather than setting it to a fixed value.

[0064] Specifically, the engine speed determination unit 42A takes in the cylinder pressure Ps of the suspensions 7 and 8, which is the detected value of the pressure sensor 25 that functions as a load sensor for detecting the load weight of the cargo W, and calculates the total weight of the dump truck 1, including the weight of the cargo W, based on the detected pressure Ps of the pressure sensor 25. Based on the calculated total weight of the dump truck 1, it calculates the power (energy) required to start the dump truck 1, and sets the rotation speed threshold Nth according to the magnitude of the calculated power (energy). In other words, the engine speed determination unit 42A sets the rotation speed threshold Nth to increase as the load weight of the cargo W increases. In this embodiment, the drive torque command unit 41, elapsed time determination unit 43, and start determination unit 44, other than the engine speed determination unit 42A, are the same as in the first embodiment.

[0065] Next, the control procedure for vehicle starting of the electric transport vehicle controller according to the second embodiment will be explained with reference to Figure 6. Figure 6 is a flowchart showing an example of the control procedure for starting of the electric transport vehicle controller according to the second embodiment shown in Figure 5.

[0066] The control procedure of the controller 30A in the second embodiment shown in Figure 6 differs from the control procedure of the controller 30 in the first embodiment (see Figure 3) in the following respects. When a start command for the dump truck 1 is input, after step S20, in which a drive torque command corresponding to the acceleration command from the operating pedal 21 or the control station 60 is output to the inverter 14, the engine speed determination unit 42A sets a rotation speed threshold Nth according to the load weight of the cargo W (step S25). As a result, the rotation speed threshold Nth is set to increase as the load weight of the cargo W increases. Furthermore, the engine speed determination unit 42A determines whether the engine speed Ne, which is the detected value of the rotation speed sensor 23, exceeds the rotation speed threshold Nth set in step S25 (step S30A). In this case, since the rotation speed threshold Nth is set to increase as the load weight of the cargo W increases, it is possible to accurately determine whether the power generated by the generator 13 has reached the power required to start the dump truck 1 based on the engine speed Ne. The processing from step S30A onward (steps S40 to S60) is the same as in the first embodiment.

[0067] According to the second embodiment described above, similar to the first embodiment described above, by determining whether the vehicle speed Vs reaches the speed threshold Vth after the elapsed time Ta (first elapsed time) from the moment the engine speed Ne reaches the rotational speed threshold Nth reaches the time threshold Tth, it becomes possible to determine whether the dump truck 1 (electric transport vehicle) is in a state where it cannot start due to contact with the wheel stop 100, taking into account the acceleration time from when the dump truck 1 (electric transport vehicle) starts moving until it reaches a driving state that can be detected by the vehicle speed sensor 24 (speed sensor), thereby preventing errors in the determination. In other words, it is possible to reliably determine whether the dump truck 1 (electric transport vehicle) is in a state where it cannot start due to contact with the wheel stop 100 when the vehicle starts.

[0068] Furthermore, the dump truck 1 (electric transport vehicle) according to this embodiment is further equipped with a pressure sensor 25 as a load capacity sensor for detecting the load weight of the cargo W. In addition, the rotation speed threshold Nth is set to increase as the detected value of the pressure sensor 25 increases.

[0069] With this configuration, the rotational speed threshold Nth is set according to the load weight of the cargo W, rather than a predetermined value. Therefore, the rotational speed threshold Nth becomes an appropriate value that takes into account the influence of the load weight of the cargo W, serving as an indicator for determining whether the power generated by the generator 13 has reached the power required to start the dump truck 1. Consequently, it is possible to reliably determine whether the dump truck 1 (electric transport vehicle) is unable to start due to contact with the wheel stop 100 when the vehicle is starting.

[0070] [Modified version of the second embodiment] Next, an electric transport vehicle according to a modified example of the second embodiment of the present invention will be described with reference to Figure 7. Figure 7 is a block diagram showing the schematic configuration of the electric drive system and the controller that controls the electric drive system in an electric transport vehicle according to a modified example of the second embodiment. In Figure 7, parts with the same reference numerals as those shown in Figures 1 to 6 are similar parts, so their detailed explanation will be omitted.

[0071] The differences between the modified electric transport vehicle of the second embodiment shown in Figure 7 and the second embodiment are as follows. In the second embodiment, the engine speed determination unit 42A of the controller 30A is configured to set the rotation speed threshold Nth according to the load weight (detection value of the pressure sensor 25) of the dump truck 1's cargo W. In contrast, the engine speed determination unit 42B of the modified controller 30B of the second embodiment is configured to set the rotation speed threshold Nth according to the inclination state (road surface gradient) at the starting position of the dump truck 1.

[0072] If the road surface gradient at the starting position of the dump truck 1 is uphill relative to the direction of travel, it is considered that the power generated by the generator 13 required for the dump truck 1 to start will increase by the amount the dump truck 1 climbs. The rotational speed threshold Nth, which is the judgment index of the engine rotational speed determination unit 42B, is used as an indicator of whether or not the power generated by the generator 13 has reached the power required for the dump truck 1 to start. For this reason, it is preferable to set the rotational speed threshold Nth according to the magnitude of the road surface gradient at the starting position rather than a predetermined value.

[0073] In electric transport vehicles, control functions to prevent wheel slippage are widespread. To realize this control function, most electric transport vehicles are equipped with acceleration sensors. The dump truck 1 in this embodiment also has an acceleration sensor 26.

[0074] The acceleration sensor 26 detects acceleration, including gravitational acceleration, in a coordinate system fixed to the vehicle (dump truck 1), and can detect the tilt of the vehicle relative to the horizontal plane by detecting the direction of gravity acting on the vehicle when the vehicle is stationary. In other words, by detecting the tilt of the vehicle relative to the horizontal plane, the acceleration sensor 26 functions as a tilt sensor capable of detecting the road surface gradient at the starting position of the dump truck 1. The tilt sensor can also be made up of sensors other than the acceleration sensor 26, as long as it is capable of detecting the road surface gradient at the starting position of the dump truck 1.

[0075] In this embodiment, the engine speed determination unit 42B of the controller 30B acquires the inclination of the dump truck 1 relative to the horizontal plane (road surface gradient), which is the detected value As of the acceleration sensor 26, and sets the rotation speed threshold Nth according to the magnitude of the detected value As (road surface gradient) of the acceleration sensor 26. In other words, when the direction of travel of the dump truck 1 instructed to start the vehicle is uphill, the engine speed determination unit 42B sets the rotation speed threshold Nth to increase as the road surface gradient, which is the detected value As of the acceleration sensor 26, increases. Therefore, it is possible to accurately determine whether or not the power required for starting the dump truck 1 has been reached, given the road surface gradient conditions at the time of starting the dump truck 1, based on the engine speed Ne.

[0076] In this embodiment, the controller 30B, other than the engine speed determination unit 42B, has the same functional units as in the second embodiment: the drive torque command unit 41, the elapsed time determination unit 43, and the start determination unit 44. Furthermore, the control procedure of the modified controller 30B of the second embodiment is the same as the control procedure of the controller 30A of the second embodiment shown in Figure 6, except that in step S25, the engine speed determination unit 42B sets the rotation speed threshold Nth according to the road surface gradient of the dump truck 1's starting position.

[0077] According to the modified version of the second embodiment described above, similar to the second embodiment described above, it is possible to reliably determine whether or not the dump truck 1 (electric transport vehicle) is unable to start due to contact with the wheel stop 100 when the vehicle starts.

[0078] Furthermore, the dump truck 1 (electric transport vehicle) according to this embodiment is further equipped with an acceleration sensor 26 as a tilt sensor capable of detecting the road surface gradient. In addition, the rotation speed threshold Nth is set to increase as the detected value As of the acceleration sensor 26 increases when the direction of travel of the vehicle when instructed to start the vehicle is in the uphill direction.

[0079] With this configuration, the rotational speed threshold Nth is set according to the road surface gradient when climbing, rather than being a predetermined value. Therefore, the rotational speed threshold Nth becomes an appropriate value that takes into account the effect of the road surface gradient when climbing, serving as an indicator for determining whether the power generated by the generator 13 has reached the power required to start the dump truck 1. Consequently, it is possible to reliably determine whether or not the vehicle is unable to start due to contact with the wheel stop 100 when starting the vehicle.

[0080] [Third Embodiment] Next, an electric transport vehicle according to a third embodiment of the present invention will be described with reference to Figures 8 and 9. In Figures 8 and 9, parts with the same reference numerals as those in Figures 1 to 7 are similar, so a detailed explanation of them will be omitted. Figure 8 is a block diagram showing the schematic configuration of the electric drive system in the electric transport vehicle according to the third embodiment and the controller that controls the electric drive system.

[0081] The differences between the electric transport vehicle according to the third embodiment shown in Figure 8 and the first embodiment are as follows. In the controller 30 according to the first embodiment, the elapsed time determination unit 43 makes a determination using a predetermined time threshold Tth that is set in advance. In contrast, in the controller 30C according to the third embodiment, the elapsed time determination unit 43C changes the setting of the time threshold Tth, which is the determination index, according to the load weight W of the dump truck 1.

[0082] The total weight of the dump truck 1 changes significantly depending on whether or not it is loaded with cargo W. If the total weight of the dump truck 1 is different, even if the electric motor 11 applies the same driving torque to the rear wheels 4, the time it takes for the vehicle speed Vs of the dump truck 1 to reach the speed threshold Vth will change. It is known that when the driving torque of the electric motor 11 is constant, i.e., when the vehicle acceleration is constant, the time it takes to reach a predetermined speed is proportional to the total weight of the vehicle. In other words, the more the total weight of the dump truck 1 (the load weight of cargo W) increases, the longer it takes for the vehicle speed Vs of the dump truck 1 to reach the speed threshold Vth. Therefore, it is preferable to set the time threshold Tth according to the change in the total weight of the dump truck 1 (the load weight of cargo W) rather than a predetermined value.

[0083] Specifically, the elapsed time determination unit 43C acquires the cylinder pressure Ps of the suspensions 7 and 8, which is the detected value of the pressure sensor 25 that functions as a load sensor, and calculates the load weight of the cargo W or the total weight of the dump truck 1 including the load weight of the cargo W based on the detected value Ps of the pressure sensor 25. A time threshold Tth is set according to the magnitude of the calculated load weight of the cargo W or the total weight of the dump truck 1. In other words, the elapsed time determination unit 43C sets the time threshold Tth to increase as the load weight of the cargo W increases. In this embodiment, the controller 30C, other than the elapsed time determination unit 43C, has the same functions as in the first embodiment: the drive torque command unit 41, the engine speed determination unit 42, and the start determination unit 44.

[0084] Next, the control procedure for the controller of the electric transport vehicle according to the third embodiment when the vehicle starts will be explained with reference to Figure 9. Figure 9 is a flowchart showing an example of the control procedure for the controller of the electric transport vehicle according to the third embodiment shown in Figure 8 when the vehicle starts.

[0085] The control procedure of the controller 30C in the third embodiment shown in Figure 9 differs from the control procedure of the controller 30 in the first embodiment (see Figure 3) in the following respects. When a starting command for the dump truck 1 is input, after it is determined that the engine speed Ne is equal to or greater than the speed threshold Nth (after the determination of YES in step S30), the elapsed time determination unit 43C sets a time threshold Tth according to the load weight of the cargo W or the total weight of the dump truck 1 (step S35). As a result, the time threshold Tth is set to increase as the load weight of the cargo W increases. Furthermore, the elapsed time determination unit 43C determines whether the measured elapsed time Ta exceeds the time threshold Tth set in step S35 (step S40C). In this case, since the time threshold Tth is set to increase as the load weight of the cargo W increases, it is possible to determine whether or not there is contact with the wheel stop 100 after considering the time required for the vehicle speed Vs of the dump truck 1 to accelerate until it reaches the speed threshold. Note that steps other than steps S35 and S40C (steps S10 to S30 and S50 to S60) are the same as in the first embodiment.

[0086] According to the third embodiment described above, similar to the first embodiment described above, by determining whether the vehicle speed Vs reaches the speed threshold Vth after the elapsed time Ta (first elapsed time) from the moment the engine speed Ne reaches the rotational speed threshold Nth reaches the time threshold Tth, it becomes possible to determine whether the dump truck 1 (electric transport vehicle) is in a state where it cannot start due to contact with the wheel stop 100, taking into account the acceleration time from when the dump truck 1 (electric transport vehicle) starts moving until it reaches a driving state that can be detected by the vehicle speed sensor 24 (speed sensor), thereby preventing errors in the determination. In other words, it is possible to reliably determine whether the dump truck 1 (electric transport vehicle) is in a state where it cannot start due to contact with the wheel stop 100 when the vehicle starts.

[0087] Furthermore, the dump truck 1 (electric transport vehicle) according to this embodiment is further equipped with a pressure sensor 25 as a load capacity sensor for detecting the load weight of the cargo W. In addition, the time threshold Tth is set to increase as the detected value of the pressure sensor 25 increases.

[0088] With this configuration, the time threshold Tth is set according to the load weight of the cargo W, so the time threshold Tth becomes an appropriate value that takes into account the influence of the load weight of the cargo W, as an indicator of the acceleration time from when the vehicle starts moving until it reaches a driving state detectable by the vehicle speed sensor 24. Therefore, it is possible to reliably determine whether or not the vehicle is unable to start due to contact with the wheel stop 100 when the vehicle starts moving.

[0089] [First modified example of the third embodiment] Next, an electric transport vehicle according to the first modified example of the third embodiment of the present invention will be described with reference to Figure 10. In Figure 10, parts with the same reference numerals as those in Figures 1 to 9 are similar parts, so a detailed explanation of them will be omitted. Figure 10 is a block diagram showing the schematic configuration of the electric drive system and the controller that controls the electric drive system in an electric transport vehicle according to the first modified example of the third embodiment of the present invention.

[0090] The differences between the electric transport vehicle according to the first modified example of the third embodiment shown in Figure 10 and the third embodiment are as follows. The elapsed time determination unit 43C of the controller 30C according to the third embodiment sets a time threshold Tth according to the load weight W of the dump truck 1 or the total weight of the dump truck 1 (the detected value Ps of the pressure sensor 25 as a load sensor) (see Figure 8). In contrast, the elapsed time determination unit 43D of the controller 30D according to the first modified example of the third embodiment changes the setting of the time threshold Tth according to the difference in road surface driving resistance at the starting position of the dump truck 1.

[0091] If the road surface resistance at the dump truck 1's starting position differs, even if the electric motor 11 applies the same driving torque to the rear wheels 4, the time it takes for the dump truck 1's vehicle speed Vs to reach the speed threshold Vth will change. In other words, the greater the road surface resistance, the longer it takes for the dump truck 1's vehicle speed Vs to reach the speed threshold Vth. Therefore, in order to accurately determine whether or not the dump truck 1 is unable to start due to contact with the wheel stop 100, it is preferable to set the time threshold Tth that defines the time of such determination according to the difference in road surface resistance rather than a predetermined value. Examples of road resistance include, firstly, when the road surface gradient at the dump truck 1's starting position is uphill relative to the direction of travel. Secondly, when the road surface is softened by mud, the resistance to pushing away the mud when the wheels are moving increases.

[0092] Therefore, the elapsed time determination unit 43D takes in, for example, the inclination (road surface gradient) of the dump truck 1 relative to the horizontal plane, which is the detected value As of the acceleration sensor 26 that functions as a tilt sensor, calculates the gradient resistance as the driving resistance of the road surface according to the magnitude of the detected value As (road surface gradient) of the acceleration sensor 26, and sets a time threshold Tth based on the calculated gradient resistance. Furthermore, regarding the magnitude of driving resistance due to road surface conditions such as the resistance of pushing aside muddy roads, it is conceivable to obtain information Sr regarding the road surface conditions at the work site, such as the amount of rainfall at the site or image data of the road surface conditions, from the control station 60. The elapsed time determination unit 43D can also calculate the driving resistance of the road surface conditions based on the information Sr regarding road surface conditions input from the control station 60, and set a time threshold Tth according to the calculated driving resistance of the road surface conditions. It is also possible to set a time threshold Tth according to the driving resistance due to the road surface gradient calculated based on the detected value of the acceleration sensor 26 and the driving resistance of the road surface conditions calculated based on the information Sr regarding road surface conditions input from the control station 60. This makes it possible to accurately determine whether or not the dump truck 1 is unable to start due to contact with the wheel stop 100, depending on the magnitude of the road surface resistance when the dump truck 1 starts.

[0093] In this embodiment, the controller 30D, other than the elapsed time determination unit 43D, the drive torque command unit 41, the engine speed determination unit 42, and the start determination unit 44, are the same as in the third embodiment. Furthermore, the vehicle start control procedure of the controller 30D of the first modified example of the third embodiment is the same as the control procedure of the controller 30C of the third embodiment shown in Figure 9, except that in step S35, the elapsed time determination unit 43D sets a time threshold Tth according to the driving resistance at the starting position of the dump truck 1.

[0094] According to the first modified example of the third embodiment described above, similar to the third embodiment described above, it is possible to reliably determine whether or not the dump truck 1 (electric transport vehicle) is unable to start due to contact with the wheel stop 100 when the vehicle starts.

[0095] Furthermore, in this modified example, the time threshold Tth is set to increase as the road surface resistance increases.

[0096] With this configuration, the time threshold Tth is set according to the road surface resistance, so the time threshold Tth becomes an appropriate value that takes into account the influence of road surface resistance as an indicator of the acceleration time from when the vehicle starts moving until it reaches a driving state detectable by the vehicle speed sensor 24. Therefore, it is possible to reliably determine whether or not the vehicle is unable to start due to contact with the wheel stop 100 when the vehicle starts moving.

[0097] Furthermore, the dump truck 1 (electric transport vehicle) according to this modified example is further equipped with an acceleration sensor 26 as a tilt sensor capable of detecting the road surface gradient. The driving resistance on this road surface is the driving resistance corresponding to the road surface gradient, which is calculated based on the road surface gradient detected by the acceleration sensor 26 as a tilt sensor.

[0098] With this configuration, the time threshold Tth becomes an appropriate value that takes into account the effect of driving resistance according to the road surface gradient, as an indicator of the acceleration time from when the vehicle starts moving until it reaches a driving state detectable by the vehicle speed sensor 24.

[0099] Furthermore, in this modified example, the driving resistance of the road surface is the driving resistance corresponding to the road surface condition, calculated based on the road surface condition information Sr input from the control station 60 (external).

[0100] With this configuration, the time threshold Tth becomes an appropriate value that takes into account the influence of driving resistance depending on the road surface conditions, such as muddy roads, as an indicator of the acceleration time from when the vehicle starts moving until it reaches a driving state detectable by the vehicle speed sensor 24.

[0101] [Second variation of the third embodiment] Next, an electric transport vehicle according to a second modified example of the third embodiment of the present invention will be described with reference to Figures 11 and 12. In Figures 11 and 12, parts with the same reference numerals as those in Figures 1 to 10 are similar parts, so a detailed explanation of them will be omitted. Figure 11 is a block diagram showing the schematic configuration of the electric drive system and the controller that controls the electric drive system in an electric transport vehicle according to a second modified example of the third embodiment.

[0102] The differences between the electric transport vehicle according to the second modification of the third embodiment shown in Figure 11 and the third embodiment are as follows. The elapsed time determination unit 43C of the controller 30C according to the third embodiment sets a time threshold Tth according to the load weight W of the dump truck 1 or the total weight of the dump truck 1 (detection value Ps of the pressure sensor 25) (see Figure 8). In contrast, the elapsed time determination unit 43E of the controller 30E according to the second modification of the third embodiment changes the setting of the time threshold Tth according to the length of elapsed time Te taken from when a start command is input until the engine speed Ne reaches the rotation speed threshold Nth.

[0103] The torque of engine 12 is used not only to increase the rotational speed of engine 12 itself, but also to drive the generator 13 (generating power). For this reason, depending on the magnitude of the starting load of the dump truck 1, it may take a long time for the engine speed to increase. As mentioned above, the driving force required of the electric motor 11 increases depending on the weight of the load W and the amount of driving resistance on uphill slopes and muddy roads. When the driving force required of the electric motor 11 for starting the vehicle increases, the amount of power required to be generated by the generator 13 also increases. In this case, the magnitude of the torque of engine 12 to drive the generator 13 inevitably increases, and as a result, the engine speed Ne tends to increase more slowly, and the time it takes to reach a predetermined value tends to be relatively longer.

[0104] Therefore, the elapsed time determination unit 43E of the controller 30E in this modified example measures the elapsed time Te taken from the time a start command is input until the engine speed Ne reaches the speed threshold Nth, and sets the time threshold Tth based on the measured elapsed time Te. This makes it possible to set the time threshold Tth, which affects the determination of whether or not the vehicle starts, without taking in the detected value Ps of the pressure sensor 25, the detected value As of the acceleration sensor 26, and the information Sr regarding the road surface condition and driving resistance from the control station 60.

[0105] Next, the control procedure for the controller of the electric transport vehicle according to the second modified example of the third embodiment when the vehicle starts will be explained with reference to Figure 12. Figure 12 is a flowchart showing an example of the control procedure for the controller of the electric transport vehicle according to the second modified example of the third embodiment shown in Figure 11 when the vehicle starts.

[0106] The control procedure of the controller 30E according to the second modified example of the third embodiment shown in Figure 12 differs from the control procedure of the controller 30C of the third embodiment (see Figure 9) in the following respects. When a start command for the dump truck 1 is input, after step S20, in which a drive torque command corresponding to the acceleration command from the operating pedal 21 or the control station 60 is output to the inverter 14, the elapsed time determination unit 43E starts measuring the elapsed time Te of the increase in engine speed Ne (step S27). Furthermore, the elapsed time determination unit 43E measures the elapsed time Te up to the point in time when it is determined that the engine speed Ne has risen to the rotation speed threshold Nth (YES in step S30), and sets the time threshold Tth based on the measured elapsed time Te (the elapsed time from the time of input of the start command until the engine speed Ne reaches the rotation speed threshold Nth) (step S35E). As a result, the time threshold Tth is set to be longer as the elapsed time Te taken for the engine speed Ne to rise to the rotation speed threshold Nth increases. In this case, since the time threshold Tth is set according to the load weight and driving resistance of the cargo W, it is possible to accurately determine whether or not the dump truck 1 is unable to start due to contact with the wheel stop 100. Note that the processes other than steps S27 and S35E (steps S10 to S20, S30, S40 to S60) are the same as in the third embodiment.

[0107] According to the second modification of the third embodiment described above, similar to the third embodiment described above, it is possible to reliably determine whether or not the dump truck 1 (electric transport vehicle) is unable to start due to contact with the wheel stop 100 when the vehicle starts.

[0108] Furthermore, in this modified example, the elapsed time determination unit 43E is configured to measure the elapsed time Te (second elapsed time) from the time the instruction to start the vehicle is input until the time when the engine speed determination unit 42 determines that the detected value Ne of the rotation speed sensor 23 is equal to or greater than the rotation speed threshold Nth. The above time threshold Tth is set to increase as the measured elapsed time Te (second elapsed time) increases.

[0109] With this configuration, the time threshold Tth is set according to the elapsed time Te that takes for the engine speed Ne to rise to the rotational speed threshold Nth. Therefore, without using sensors that detect the load weight of the cargo W or the road surface gradient, such as the pressure sensor 25 as a tilt sensor in the third embodiment or the acceleration sensor 26 in the first modified example of the third embodiment, the time threshold Tth, which serves as an indicator of the acceleration time from when the vehicle starts moving until it reaches a driving state detectable by the vehicle speed sensor 24, can be set to an appropriate value.

[0110] [Other embodiments] It should be noted that the present invention is not limited to the first to third embodiments and their variations described above, but includes various variations. The above embodiments are described in detail for the purpose of explaining the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. For example, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0111] For example, it is possible to combine the configurations of the second embodiment and its modified form described above. In other words, it is also possible to configure the engine speed determination unit of the controller to change the setting of the rotation speed threshold Nth according to two conditions: the load weight of the cargo W of the dump truck 1 and the inclination state (road surface gradient) at the starting position of the dump truck 1.

[0112] Furthermore, it is possible to combine the configurations of the third embodiment and its first modified form described above. In other words, the elapsed time determination unit of the controller can be configured to change the setting of the time threshold Tth according to two conditions: the load weight of the cargo W of the dump truck 1 and the road surface driving resistance at the starting position of the dump truck 1.

[0113] Furthermore, it is possible to combine the configuration of the second embodiment or its modified form described above with the configuration of the third embodiment or its first modified form. In other words, it is also possible to configure the controller's engine speed determination unit to change the rotation speed threshold Nth according to at least one of two conditions: the load weight of the cargo W of the dump truck 1 and the inclination state (road surface gradient) at the starting position of the dump truck 1, and to configure the controller's elapsed time determination unit to change the time threshold Tth according to at least one of two conditions: the load weight of the cargo W of the dump truck 1 and the road surface driving resistance at the starting position of the dump truck 1.

[0114] Furthermore, it is possible to combine the configuration of the second embodiment or its modified form described above with the configuration of the second modified form of the third embodiment. In other words, the engine speed determination unit of the controller can be configured to change the rotation speed threshold Nth setting according to at least one of two conditions: the load weight of the cargo W of the dump truck 1 and the inclination state (road surface gradient) at the starting position of the dump truck 1. The elapsed time determination unit of the controller can also be configured to change the time threshold Tth setting according to the length of the elapsed time Te that takes for the engine speed Ne to reach the rotation speed threshold Nth.

[0115] Furthermore, some or all of the functions of controllers 30, 30A, 30B, 30C, 30D, and 30E in the above-described embodiment may be implemented in hardware, for example, by designing them as integrated circuits.

[0116] Furthermore, in the above-described embodiment, an example was shown in which the electric motor 11 is an induction motor. However, the present invention can also be applied even if the electric motor 11 is a synchronous motor. [Explanation of Symbols]

[0117] 1…Dump truck (electric transport vehicle), 11…Electric motor, 12…Engine, 13…Generator, 23…Rotation speed sensor, 24…Vehicle speed sensor (speed sensor), 25…Pressure sensor (load sensor), 26…Accelerometer (tilt sensor), 30, 30A, 30B, 30C, 30D, 30E…Controller, 42, 42A, 42B…Engine rotation speed determination unit, 43, 43C, 43D, 43E…Elapsed time determination unit, 44…Starting determination unit, 60…Control station (external), W…Cargo, Nth…Rotation speed threshold, Tth…Time threshold, Vth…Speed ​​threshold, Ta…Elapsed time (1st elapsed time), Te…Elapsed time (2nd elapsed time)

Claims

1. The engine and A generator mechanically driven by the aforementioned engine, An electric motor driven by power supplied from the aforementioned generator, A rotational speed sensor for detecting the rotational speed of the engine, A speed sensor that detects vehicle speed, The system includes a controller that controls the drive of the electric motor, In an electric transport vehicle that transports cargo by moving using the driving force of the aforementioned electric motor, The aforementioned controller, An engine speed determination unit that determines whether the value detected by the rotation speed sensor is equal to or greater than a rotation speed threshold when a vehicle start command is input, A time-elapsed unit measures a first elapsed time from the point in time when the engine speed determination unit determines that the detected value of the rotation speed sensor is equal to or greater than the rotation speed threshold, and determines whether the first elapsed time has reached the time threshold. The system includes a start determination unit that determines whether the detected value of the speed sensor is equal to or greater than the speed threshold after the elapsed time determination unit has determined that the first elapsed time has reached the time threshold, If the starting determination unit determines that the value detected by the speed sensor is less than the speed threshold, the electric motor is stopped. An electric transport vehicle characterized by the following features.

2. In the electric transport vehicle according to claim 1, The system further includes a load sensor for detecting the load weight of the aforementioned cargo, The rotation speed threshold is set to increase as the value detected by the load sensor increases. An electric transport vehicle characterized by the following features.

3. In the electric transport vehicle according to claim 1, It is further equipped with a tilt sensor capable of detecting the road surface gradient, The rotational speed threshold is set to increase as the detected value of the tilt sensor increases when the vehicle's direction of travel in the vehicle starting instruction is uphill. An electric transport vehicle characterized by the following features.

4. In the electric transport vehicle according to claim 1, The system further includes a load sensor for detecting the load weight of the aforementioned cargo, The aforementioned time threshold is set to increase as the detected value of the load sensor increases. An electric transport vehicle characterized by the following features.

5. In the electric transport vehicle according to claim 1, The aforementioned time threshold is set to increase as the road surface resistance increases. An electric transport vehicle characterized by the following features.

6. In the electric transport vehicle according to claim 5, It is further equipped with a tilt sensor capable of detecting the road surface gradient, The road surface driving resistance is calculated based on the road surface gradient detected by the tilt sensor. An electric transport vehicle characterized by the following features.

7. In the electric transport vehicle according to claim 5, The aforementioned road surface driving resistance is a driving resistance calculated based on information about the road surface condition input from an external source. An electric transport vehicle characterized by the following features.

8. In the electric transport vehicle according to claim 1, The elapsed time determination unit is further configured to measure a second elapsed time from the time the instruction to start the vehicle is input until the time when it is determined that the value detected by the rotation speed sensor is equal to or greater than the rotation speed threshold. The aforementioned time threshold is set to increase as the measured second elapsed time increases. An electric transport vehicle characterized by the following features.

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