Work vehicle

Abstract

To provide a work vehicle capable of improving fuel efficiency.SOLUTION: A work vehicle includes: a vehicle body; a work device attached to the vehicle body; an engine mounted on the vehicle body; a first generator and a second generator that generate electricity using a driving force of the engine; a traction motor that receives an electric power generated by the first generator and generates a driving force for driving wheels; at least one electric auxiliary machine that operates by receiving the electric power generated by the second generator; an automatic voltage regulator that controls an excitation current of the second generator in order to adjust a generated voltage of the second generator to a predetermined set voltage; and a control device that controls an engine rotation speed. The control device monitors the excitation current of the second generator, calculates a command speed according to the excitation current of the second generator, and controls the engine rotation speed so that the engine rotation speed becomes the command speed, increasing the engine rotation speed as the excitation current of the second generator becomes higher.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a work vehicle. [Background technology]

[0002] There is known a hybrid system that includes an engine, a secondary battery, a motor, a generator that generates electricity using power from the engine, an AVR (automatic voltage regulator) that adjusts the voltage generated by the generator, and a control device that can adjust the load sharing between the generator and the secondary battery by increasing or decreasing the voltage setting value of the AVR while the motor is running (see Patent Document 1). The control device described in Patent Document 1 switches the engine speed from the rated speed to an idle speed when the voltage setting value of the AVR falls below a predetermined setting value in order to reduce unnecessary fuel consumption. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-135686 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the control described in Patent Document 1, the engine speed is only switched between two speeds, the rated speed and the idle speed, and therefore there is room for improvement in terms of reducing fuel consumption.

[0005] An object of the present invention is to provide a work vehicle that is capable of achieving further improvement in fuel efficiency. [Means for solving the problem]

[0006] A work vehicle according to one aspect of the present invention includes a vehicle body, a working device attached to the vehicle body, an engine mounted on the vehicle body, a first generator and a second generator that generate electricity using the driving force of the engine, a travel motor that receives the electric power generated by the first generator to generate driving force for driving wheels, at least one electric accessory that operates by receiving the electric power generated by the second generator, an automatic voltage regulator that controls the excitation current of the second generator to adjust the generation voltage of the second generator to a predetermined set voltage, and a control device that controls the rotation speed of the engine. The control device monitors the excitation current of the second generator, calculates a command speed according to the excitation current of the second generator, controls the rotation speed of the engine so that the rotation speed of the engine becomes the command speed, and increases the rotation speed of the engine as the excitation current of the second generator becomes higher. Effect of the Invention

[0007] According to the present invention, a work vehicle capable of achieving further improvements in fuel efficiency can be provided. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a side view showing the appearance of a dump truck 100. As shown in FIG. [Diagram 2] FIG. 2 is a system configuration diagram of the dump truck 100. [Diagram 3] FIG. 3 is a diagram showing the hardware configuration of the main controller 120. As shown in FIG. [Figure 4] FIG. 4 is a functional block diagram of the main controller 120 according to the first embodiment. [Diagram 5] FIG. 5 is a flowchart showing an example of the flow of processing executed by the main controller 120 according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing an idle speed table according to the first embodiment. [Figure 7] FIG. 7 is a functional block diagram of the main controller 220 according to the second embodiment. [Figure 8] FIG. 8 is a flowchart showing an example of the flow of processing executed by the main controller 220 according to the second embodiment. [Figure 9] FIG. 9 is a functional block diagram of the main controller 320 according to the third embodiment. [Figure 10] FIG. 10 is a flowchart showing an example of the flow of processing executed by the main controller 320 according to the third embodiment. [Figure 11] FIG. 11 is a diagram showing an idle speed table according to the first modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A work vehicle according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a side view showing the appearance of a dump truck 100, which is an example of a work vehicle according to a first embodiment of the present invention. In the following description, the front of the driver's seat (the left direction in the figure) is the front of the vehicle body 101 unless otherwise specified.

[0010] The dump truck 100 shown in Fig. 1 is a large one that operates in mines and the like, and includes a vehicle body 101, a cab 103, a loading platform 104, front wheels 105, and rear wheels 106. The cab 103 is supported by a support base 102, and is located at the front and left side of the vehicle body 101. The cab 103 forms a cab where an operator of the dump truck 100 gets on and off, and inside the cab 103 are provided a driver's seat, an accelerator operation device 160 (see Fig. 2), a brake operation device, a steering handle, an operation device for the loading platform, and the like.

[0011] The loading platform 104 is mounted on the rear of the vehicle body 101 so as to be able to rise and fall. The loading platform 104 is rotatably supported on the rear side of the vehicle body 101 via a connecting pin, and moves up and down around the connecting pin as a fulcrum by the extension and contraction of a hoist cylinder (hydraulic actuator) 107. Excavated material (object to be transported) such as soil and sand excavated by a hydraulic excavator or the like is loaded onto the loading platform 104. The dump truck 100 transports the object to be transported from the work site of the hydraulic excavator to a predetermined location and releases the object at the predetermined location. In the release operation (earth dumping operation), the hoist cylinder 107 is extended, and the loading platform 104 is tilted. In this way, the loading platform 104 and the hoist cylinder 107 attached to the vehicle body 101 constitute a working device for carrying out the transport operation and the release operation.

[0012] The front wheels 105 are located on the left and right sides at the front of the vehicle body 101, and the rear wheels 106 are located on the left and right sides at the rear of the vehicle body 101, and support the vehicle body 101 so that the vehicle body 101 can travel. The front wheels 105 constitute steering wheels that are steered by the operator of the dump truck 100, and are steered in accordance with the extension and contraction of the left and right steering cylinders when the operator of the dump truck 100 operates a steering handle. The rear wheels 106 constitute driving wheels of the dump truck 100, and are rotationally driven by the traveling motor 31 (see FIG. 2).

[0013] Fig. 2 is a system configuration diagram of the dump truck 100. As shown in Fig. 2, the dump truck 100 is a series hybrid type work vehicle in which the traveling drive unit is electrified. The electric drive system of the dump truck 100 generates electricity by driving the main generator 11 with the engine 140, operates the traveling motor 31 with the electricity generated by the main generator 11, and rotates the rear wheels (drive wheels) 106 with the torque generated by the traveling motor 31.

[0014] The dump truck 100 is equipped with an engine 140 mounted on a vehicle body 101, a main generator (first generator) 11 that generates electricity using the driving force of the engine 140, an auxiliary generator (second generator) 12 that generates electricity using the driving force of the engine 140, a traction motor 31 that receives a supply of electricity generated by the main generator 11 to generate driving force for driving rear wheels (wheels) 106, at least one electric accessory 32 that operates using a supply of electricity generated by the auxiliary generator 12, an automatic voltage regulator (AVR) 170 that controls the excitation current of the auxiliary generator 12 to adjust the generation voltage of the auxiliary generator 12 to a predetermined set voltage, and a control device 180 that controls the rotational speed of the engine 140.

[0015] The engine 140 is configured by an internal combustion engine such as a diesel engine. The control device 180 includes a main controller 120 and an engine controller 130. The main controller 120 controls the engine 140 via the engine controller 130. The main controller 120, the engine controller 130, and the automatic voltage regulator 170 configure a control unit 181 of the dump truck 100.

[0016] The dump truck 100 is equipped with a main inverter (first inverter) 21 that converts DC power generated by the main generator 11 into three-phase AC power and outputs it to the traction motor 31, and an auxiliary inverter (second inverter) 22 that converts DC power generated by the auxiliary generator 12 into three-phase AC power and outputs it to the electric auxiliary machine 32.

[0017] The traveling motor 31 rotates by receiving a supply of three-phase AC power from the main inverter 21. The rotational driving force of the traveling motor 31 is transmitted to the rear wheels 106 via a reduction gear (not shown), causing the dump truck 100 to travel (accelerate).

[0018] The electric accessory 32 is, for example, a fan motor that serves as a drive source for a cooling fan that generates cooling air. The electric accessory 32 rotates upon receiving three-phase AC power from the auxiliary inverter 22, and rotates the cooling fan. The cooling air generated by the rotation of the cooling fan is used to cool the cooling water (hereinafter also referred to as engine cooling water) that cools the engine 140, the hydraulic oil that is supplied to the hoist cylinder 107, the refrigerant that cools the traveling motor 31, and the like. The main controller 120 monitors the temperatures of the engine cooling water, the hydraulic oil, and the refrigerant, and controls the rotation speed of the electric accessory (fan motor) 32 so that the temperatures do not rise above a predetermined temperature. For example, the main controller 120 increases the rotation speed of the electric accessory 32 as the temperature of the traveling motor 31 rises.

[0019] The automatic voltage regulator 170 controls the output of the auxiliary generator 12 for the purpose of stably driving the electric auxiliary machine 32. A voltage sensor 12a that detects the output voltage of the auxiliary generator 12 is connected to the automatic voltage regulator 170. The automatic voltage regulator 170 receives feedback of the output voltage of the auxiliary generator 12 from the voltage sensor 12a.

[0020] The automatic voltage regulator 170 controls the output of the auxiliary generator 12 so that the deviation between the output voltage detected by the voltage sensor 12a and a predetermined set voltage (e.g., 200V) becomes 0 (zero). The automatic voltage regulator 170 controls the excitation current of the auxiliary generator 12 so that the output voltage of the auxiliary generator 12 is always constant. The automatic voltage regulator 170 outputs a command value for controlling the excitation current (hereinafter also referred to as an excitation current command value) to the auxiliary generator 12.

[0021] In this way, the automatic voltage regulator 170 adjusts the output of the auxiliary generator 12 by controlling the excitation current. The excitation current of the auxiliary generator 12 refers to a current that magnetizes the rotor of the auxiliary generator 12. The auxiliary generator 12 is a known self-excited generator that uses its own generated power for excitation. The auxiliary generator 12 adjusts the excitation current so that the excitation current becomes the excitation current command value from the automatic voltage regulator 170. At start-up, the residual magnetism of the rotor winding rotates to generate an AC voltage in the stator winding, so excitation is possible without receiving power from the battery.

[0022] When the output of the auxiliary generator 12 is increased, the automatic voltage regulator 170 increases the excitation current. Here, if the excitation current is increased too much, the coil (rotor winding) of the auxiliary generator 12 becomes hot, which causes the auxiliary generator 12 to break down. The output of the auxiliary generator 12 is generally proportional to the product of the excitation current flowing through the rotor winding of the auxiliary generator 12 and the rotation speed of the rotor of the auxiliary generator 12. In other words, the output of the auxiliary generator 12 can also be increased by increasing the rotation speed of the engine 140. For this reason, when the control unit 181 of the dump truck 100 increases the output of the auxiliary generator 12, it increases the excitation current and increases the rotation speed of the engine 140. On the other hand, when the control unit 181 of the dump truck 100 decreases the output of the auxiliary generator 12, it decreases the excitation current and decreases the rotation speed of the engine 140.

[0023] An accelerator operation device 160 for instructing acceleration of the vehicle body 101 is connected to the main controller 120. The accelerator operation device 160 includes an accelerator pedal (operating member) 161 and an accelerator operation amount sensor 162 that detects the operation amount of the accelerator pedal 161 (hereinafter also referred to as accelerator operation amount). The accelerator operation amount sensor 162 outputs an accelerator signal indicating the operation amount (depression amount) of the accelerator pedal 161 to the main controller 120. The accelerator operation amount sensor 162 is, for example, a potentiometer that outputs a voltage according to the operation position of the accelerator pedal 161.

[0024] An engine rotation speed sensor 141 and a fuel injector 142 are connected to the engine controller 130. The engine rotation speed sensor 141 detects the rotation speed of the engine 140 and outputs a signal representing the detection result to the engine controller 130. The fuel injector 142 controls the amount of fuel injected into the engine 140 based on a fuel injection command from the engine controller 130.

[0025] The main controller 120 sets a target value for the rotation speed of the engine 140 (hereinafter also referred to as a command speed) based on the accelerator operation amount detected by the accelerator operation amount sensor 162. The command speed set by the main controller 120 is output to the engine controller 130. The engine controller 130 controls the fuel injector 142 so that the rotation speed of the engine 140 detected by the engine rotation speed sensor 141 becomes the command speed.

[0026] 3 is a hardware configuration diagram of the main controller 120. The main controller 120 is composed of a computer including a processing device 151 such as a central processing unit (CPU), a micro processing unit (MPU), or a digital signal processor (DSP), a non-volatile memory 152 such as a read only memory (ROM), a flash memory, or a hard disk drive, a volatile memory 153 called a random access memory (RAM), an input interface 154, an output interface 155, and other peripheral circuits. These hardware components work together to operate software and realize a plurality of functions. The main controller 120 may be composed of one computer or a plurality of computers. In addition, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like may be used as the processing device.

[0027] The non-volatile memory 152 stores programs capable of executing various calculations. In other words, the non-volatile memory 152 is a storage medium (storage device) capable of reading programs that realize the functions of this embodiment. The volatile memory 153 is a storage medium (storage device) that temporarily stores the results of calculations by the processing device 151 and signals input from the input interface 154. The processing device 151 is a calculation device that loads the programs stored in the non-volatile memory 152 into the volatile memory 153 and executes calculations, and performs predetermined calculation processing on data taken from the input interface 154, the non-volatile memory 152, and the volatile memory 153 in accordance with the programs.

[0028] The main controller 120 is connected to each of the engine controller 130, the accelerator operation amount sensor 162, and the automatic voltage regulator 170. The input interface 154 converts signals input from various devices (such as the accelerator operation amount sensor 162 and the automatic voltage regulator 170) into data that can be calculated by the processing device 151. In addition, the output interface 155 generates an output signal according to the calculation result by the processing device 151, and outputs the signal to the various devices (such as the engine controller 130).

[0029] Although not shown, the engine controller 130 and the automatic voltage regulator 170 also have the same hardware configuration as the main controller 120.

[0030] 2, an excitation current command value is input to the main controller 120 from the automatic voltage regulator 170. The main controller 120 monitors the excitation current of the auxiliary generator 12 by monitoring the input excitation current command value.

[0031] When the vehicle is in a running state in which the accelerator pedal 161 is not being operated, the main controller 120 outputs an idle operation command to the engine controller 130 to cause the engine controller 130 to perform idle operation. During idle operation, the main controller 120 calculates an idle speed Ni according to the excitation current of the auxiliary generator 12, and outputs the calculated idle speed Ni as a command speed to the engine controller 130. Examples of running states in which the accelerator pedal 161 is not being operated include a coasting state on flat ground and a coasting state on a downhill slope.

[0032] Fig. 4 is a functional block diagram of the main controller 120. As shown in Fig. 4, the main controller 120 functions as a rotation speed calculation unit 121 and a current difference value calculation unit 122 by executing a program stored in the non-volatile memory 152.

[0033] The rotation speed calculation unit 121 judges whether the accelerator operation device 160 is operated or not based on the detection result of the accelerator operation amount sensor 162. When the accelerator operation amount is equal to or less than the operation judgment threshold, the rotation speed calculation unit 121 judges that the accelerator operation device 160 is not operated. When the accelerator operation amount is greater than the operation judgment threshold, the rotation speed calculation unit 121 judges that the accelerator operation device 160 is operated. The operation judgment threshold is, for example, an arbitrary value in a dead band of the operation amount of the accelerator pedal 161, and is stored in advance in the non-volatile memory 152. When it is judged that the accelerator operation device 160 is not operated, the rotation speed calculation unit 121 calculates a command speed according to the excitation current of the auxiliary generator 12, and outputs it to the engine controller 130. When it is determined that the accelerator operation device 160 is being operated, the rotation speed calculation unit 121 calculates a command speed according to the operation of the accelerator operation device 160 regardless of the excitation current of the auxiliary generator 12, and outputs the command speed to the engine controller 130.

[0034] The method of calculating the command speed of engine 140 when accelerator operation device 160 is operated is, for example, as follows. Rotation speed calculation unit 121 refers to an engine speed table (not shown) and calculates the command speed of engine 140 based on the accelerator operation amount detected by accelerator operation amount sensor 162. The engine speed table is stored in non-volatile memory 152. The engine speed table is a data table that specifies the characteristic that the command speed of engine 140 increases as the accelerator operation amount increases.

[0035] The method of calculating the command speed of the engine 140 when the accelerator operation device 160 is operated is not limited to the above example. For example, the rotation speed calculation unit 121 may calculate the command speed of the engine 140 based on the rotation speed of the travel motor 31 (hereinafter also referred to as the motor speed) and the accelerator operation amount detected by the accelerator operation device 160. Specifically, the rotation speed calculation unit 121 calculates the required torque of the travel motor 31 based on the motor speed and the accelerator operation amount. The rotation speed calculation unit 121 calculates the required torque of the engine 140 based on the required torque of the travel motor 31. The rotation speed calculation unit 121 calculates the command speed of the engine 140 based on the required torque of the engine 140. The rotation speed calculation unit 121 calculates the command speed of the engine 140 based on at least the accelerator operation amount, similar to the above example.

[0036] A method for calculating the command speed of engine 140 when accelerator operation device 160 is not operated is, for example, as follows. This will be described in detail with reference to the flowchart in FIG. 5. FIG. 5 is a flowchart showing an example of the flow of processing executed by main controller 120. The flowchart shown in FIG. 5 is started, for example, when engine 140 is started by the ignition switch and the accelerator operation amount is equal to or less than the operation judgment threshold. The flowchart shown in FIG. 5 is also started when, during driving (engine operation), the accelerator operation amount transitions from a state where it is greater than the operation judgment threshold to a state where it is equal to or less than the operation judgment threshold.

[0037] In step S110, the rotation speed calculation unit 121 outputs an idle operation command to the engine controller 130. Upon receiving the idle operation command, the engine controller 130 starts the idle operation of the engine 140. The reference speed Ni0 is set as the initial value of the rotation speed of the engine 140 during idle operation. In other words, the process of step S110 corresponds to a process of outputting the reference speed Ni0 to the engine controller 130 as a command speed of the engine 140. When the idle operation command process (S110) is completed, the processes from steps S120 to S140 are executed in the next control cycle.

[0038] In step S120, the current difference value calculation unit 122 calculates a current difference value ΔI which is the difference between the excitation current command value (feedback value) I output from the automatic voltage regulator 170 and the current threshold value It. Since the excitation current of the auxiliary generator 12 is controlled by the excitation current command value, it can be said that the magnitude of the excitation current corresponds to the excitation current command value. The current difference value calculation unit 122 calculates the current difference value ΔI by dividing the excitation current command value I by the current threshold value It (ΔI=I-It).

[0039] The current threshold It is a predetermined arbitrary value and is stored in the non-volatile memory 152. The current threshold It is, for example, a value obtained by subtracting a predetermined value from the warning current value. The warning current value is a current value determined by the specifications of the auxiliary generator 12. When the excitation current command value (excitation current) I exceeds the warning current value, the main controller 120 causes an alarm device (not shown) to output an alarm. The alarm device is composed of a sound output device and a light emitting device. The warning current value corresponds to an excitation current value at which the auxiliary generator 12 will not break down even when the outside air temperature is the highest expected temperature.

[0040] In the next step S130, the rotation speed calculation unit 121 refers to an idle speed table and calculates the idle speed Ni based on the current difference value ΔI calculated by the current difference value calculation unit 122. The idle speed table is stored in the non-volatile memory 152. FIG. 6 is a diagram showing the idle speed table. As shown in FIG. 6, the idle speed table is a data table that specifies the characteristics that the idle speed Ni increases continuously as the current difference value ΔI increases from 0 (zero) and that the idle speed Ni decreases continuously as the current difference value ΔI decreases from 0 (zero). When the current difference value ΔI is 0 (zero), the idle speed Ni becomes the reference speed Ni0.

[0041] The lower limit value Nimin of the idle speed Ni is set to, for example, the minimum rotation speed (e.g., about 600 rpm) permitted by the engine 140. The upper limit value Nimax of the idle speed Ni is set to a rotation speed according to the maximum power consumption of the electric accessories 32. For example, the upper limit value Nimax corresponds to a rotation speed at which the power required to operate all of the electric accessories 32 can be supplied.

[0042] 5, when the calculation process (S130) of the idle speed Ni is completed, the process proceeds to the next step S140. In step S140, the rotation speed calculation unit 121 outputs the idle speed Ni calculated in step S130 as a command speed to the engine controller 130. Thereafter, the main controller 120 repeatedly executes the processes of steps S120 to S140 at a predetermined control period.

[0043] The engine controller 130 controls the rotation speed of the engine 140 so that the rotation speed of the engine 140 becomes the command speed output from the main controller 120. During idle operation, the engine controller 130 increases the rotation speed of the engine 140 as the excitation current of the auxiliary generator 12 increases.

[0044] An example of main operations of the control unit 181 of the dump truck 100 according to the first embodiment will be described. For example, when the rotation speed of the cooling fan increases while the vehicle is stopped or coasting downhill, the load on the electric auxiliary machine (fan motor) 32 increases. When the load on the electric auxiliary machine 32 increases, the output voltage of the auxiliary generator 12 decreases. The automatic voltage regulator 170 outputs an excitation current command value to the auxiliary generator 12 for setting the output voltage of the auxiliary generator 12 to a set voltage. The auxiliary generator 12 uses its own generated power to increase the excitation current flowing through the rotor winding to the excitation current command value. That is, the excitation current is strengthened. As the excitation current increases, the rotation speed of the engine 140 also increases (see Figs. 5 and 6). As the rotation speed of the engine 140 increases, the required excitation current is reduced, and the temperature rise of the auxiliary generator 12 can be suppressed.

[0045] According to the first embodiment, the following advantageous effects are achieved.

[0046] (1) The control device 180 includes the main controller 120 and the engine controller 130. The control device 180 monitors the excitation current of the auxiliary generator (second generator) 12. Specifically, the control device 180 acquires an excitation current command value of the automatic voltage regulator 170 and monitors the acquired excitation current command value to monitor the excitation current of the auxiliary generator 12. The control device 180 calculates an idle speed Ni according to the excitation current (excitation current command value) of the auxiliary generator 12 as a command speed. The control device 180 controls the rotation speed of the engine 140 so that the rotation speed of the engine 140 becomes the command speed. The control device 180 increases the rotation speed of the engine 140 as the excitation current (excitation current command value) of the auxiliary generator 12 increases. According to this configuration, when the excitation current of the auxiliary generator 12 increases with an increase in the load of the electric auxiliary machine 32, the rotation speed of the engine 140 can be increased according to the excitation current. That is, the control device 180 can control the rotation speed of the engine 140 to a rotation speed according to the electric power required for the electric accessory 32. When the excitation current is small, the speed of the engine 140 can also be reduced according to the excitation current, so that the fuel efficiency of the engine 140 can be improved. In addition, the noise and vibration of the engine 140 are also reduced. As a result, the discomfort felt by the operator can be reduced, and the riding comfort of the operator can be improved.

[0047] In this embodiment, for example, the control device 180 continuously increases the rotation speed of the engine 140 in response to an increase in the excitation current. This allows the rotation speed of the engine 140 to always be the minimum rotation speed relative to the power consumption of the electric accessory 32.

[0048] (2) The control device 180 determines whether or not the accelerator operation device 160 is being operated based on the detection result of the accelerator operation amount sensor 162. When the accelerator operation device 160 is not being operated, the control device 180 calculates a command speed according to the excitation current of the auxiliary generator 12. When the accelerator operation device 160 is being operated, the control device 180 calculates a command speed according to the operation of the accelerator operation device 160 regardless of the excitation current of the auxiliary generator 12. With this configuration, the rotation speed of the engine 140 during idling operation such as coasting is controlled according to the power consumption of the electric accessories 32, thereby reducing fuel consumption, noise, and vibration during idling operation.

[0049] (3) The control device 180 calculates a current difference value ΔI which is the difference between an excitation current command value (excitation current) I of the auxiliary generator 12 and a predetermined current threshold value It. The control device 180 calculates an idle speed Ni according to the calculated current difference value ΔI as a command speed of the engine 140. With this configuration, when the current difference value ΔI is larger than 0, the rotation speed of the engine 140 can be increased, and when the current difference value ΔI is smaller than 0, the rotation speed of the engine 140 can be decreased. Therefore, the fuel consumption, noise, and vibration of the engine 140 can be reduced while the auxiliary generator 12 generates the generated power required for the electric auxiliary device 32.

[0050] <Second embodiment> A dump truck 100 according to a second embodiment of the present invention will be described with reference to Fig. 7 and Fig. 8. Note that the same reference symbols are used for configurations that are the same as or equivalent to those described in the first embodiment, and differences will be mainly described.

[0051] Fig. 7 is a functional block diagram of the main controller 220 according to the second embodiment. As shown in Fig. 7, the main controller 220 includes a rotation speed calculation unit 221, a current difference value calculation unit 122, and a determination unit 223. Fig. 8 is a diagram similar to Fig. 5, and is a flowchart showing an example of processing executed by the main controller 220 according to the second embodiment. In the flowchart of Fig. 8, processing of steps S222, S224, and S226 is added after the processing of step S120 in the flowchart of Fig. 5.

[0052] 8, when the current difference value calculation process (S120) is completed, the process proceeds to step S222. In step S222, the determination unit 223 determines whether the current difference value ΔI calculated in step S120 is equal to or less than 0. If it is determined in step S222 that the current difference value ΔI is equal to or less than 0, the process proceeds to step S130, and if it is determined that the current difference value ΔI is greater than 0, the process proceeds to step S224.

[0053] In step S224, the determination unit 223 determines whether or not the state in which the current difference value ΔI calculated in step S120 is greater than 0 continues for a set time t1 [seconds] or more. The time is measured by a timer function of the main controller 220. The set time t1 is determined in advance and stored in the non-volatile memory 152.

[0054] If it is determined in step S224 that the state in which the current difference value ΔI is greater than 0 has not continued for the set time t1 [seconds] or more, the process proceeds to step S226. If it is determined in step S224 that the state in which the current difference value ΔI is greater than 0 has continued for the set time t1 [seconds] or more, the process proceeds to step S130.

[0055] In step S226, the rotation speed calculation unit 221 determines to maintain the current idle speed Ni, and proceeds to step S140. When the process proceeds from step S226 to step S140, the rotation speed calculation unit 221 outputs the current idle speed Ni as a command speed to the engine controller 130. In other words, the command speed is not changed.

[0056] An example of main operations of the control unit 181 of the dump truck 100 according to the second embodiment will be described. For example, when the rotation speed of the cooling fan increases while the vehicle is stopped or coasting downhill, the load on the electric accessory (fan motor) 32 increases. When the load on the electric accessory 32 increases, the output voltage of the auxiliary generator 12 decreases. The automatic voltage regulator 170 outputs an excitation current command value to the auxiliary generator 12 for setting the output voltage of the auxiliary generator 12 to a set voltage. The auxiliary generator 12 uses its own generated power to increase the excitation current flowing through the rotor winding to the excitation current command value. That is, the excitation current is strengthened.

[0057] In the first embodiment, when the excitation current I exceeds the current threshold It, the main controller 120 immediately increases the rotation speed (idle speed Ni) of the engine 140 (S120, S130, S140 in FIG. 5). In contrast, in the second embodiment, even if the excitation current I exceeds the current threshold It, if the time is shorter than a preset time t1, the main controller 120 does not increase the rotation speed of the engine 140, but maintains the current rotation speed (No in S222, No in S224, S226, S140 in FIG. 8).

[0058] Therefore, in the second embodiment, the frequency with which the rotation speed of the engine 140 increases can be reduced compared to the first embodiment. When the state in which the excitation current I exceeds the current threshold It continues for the set time t1, the rotation speed of the engine 140 increases according to the excitation current of the auxiliary generator 12 (Yes in S224 in FIG. 8, S130, S140). Since the required excitation current is reduced by increasing the rotation speed of the engine 140, the temperature rise of the auxiliary generator 12 can be suppressed.

[0059] The longer the set time t1, the more effective it is in terms of reducing fuel consumption. However, if the set time t1 is too long, the auxiliary generator 12 may be damaged due to an increase in temperature of the coil (rotor winding) of the auxiliary generator 12. For this reason, the set time t1 is set to a time that allows the excitation current to exceed the current threshold value. The set time t1 is determined by calculating the time until the auxiliary generator 12 reaches a predetermined temperature (for example, the maximum operating temperature) based on the specifications of the auxiliary generator 12 (such as the rate of increase in coil temperature [°C / sec] when the excitation current is at the upper limit value).

[0060] According to the second embodiment, in addition to the effects of the first embodiment, the following effects are achieved.

[0061] (1) When the excitation current command value (excitation current) I of the auxiliary generator 12 exceeds a predetermined current threshold value It, the control device 180 judges whether or not the state in which the excitation current command value (excitation current) I of the auxiliary generator 12 exceeds the current threshold value It has exceeded a predetermined set time t1 (No in S222, S224 in FIG. 8). When the state in which the excitation current command value (excitation current) I of the auxiliary generator 12 exceeds the current threshold value It has not exceeded the set time t1, the control device 180 does not increase the rotation speed of the engine 140 (No in S224, S226, S140 in FIG. 8). When the state in which the excitation current I of the auxiliary generator 12 exceeds the current threshold value It has exceeded the set time t1, the control device 180 increases the rotation speed of the engine 140 (Yes in S224, S130, S140 in FIG. 8). In this configuration, even if the excitation current I exceeds the current threshold It, the rotation speed of the engine 140 does not increase until the set time t1 has elapsed. Therefore, the fuel consumption, noise, and vibration of the engine 140 can be reduced more than in the first embodiment.

[0062] (2) When the excitation current command value (excitation current) I of the auxiliary generator 12 falls below the current threshold value It, the control device 180 immediately reduces the rotation speed of the engine 140 regardless of the elapsed time of the state in which the excitation current command value (excitation current) I of the auxiliary generator 12 falls below the current threshold value It (Yes in S222, S130, S140 in FIG. 8). Note that the time from when the excitation current I falls below the current threshold value It to when the rotation speed of the engine 140 is reduced is equal to or longer than the control period and shorter than the set time t1, and the shorter the better. This makes it possible to reduce fuel consumption, noise, and vibration of the engine 140 compared to when the rotation speed of the engine 140 is reduced after the excitation current I of the auxiliary generator 12 has been below the current threshold value It for a certain period of time.

[0063] <Third embodiment> A dump truck 100 according to a third embodiment of the present invention will be described with reference to Fig. 9 and Fig. 10. Note that the same reference symbols are used for configurations that are the same as or equivalent to those described in the second embodiment, and differences will be mainly described.

[0064] FIG. 9 is a functional block diagram of the main controller 320 according to the third embodiment. As shown in FIG. 9, the dump truck 100 according to the third embodiment includes a temperature sensor 12b that detects the temperature of the auxiliary generator 12. The temperature sensor 12b detects, for example, the temperature of a rotor winding (coil) of the auxiliary generator 12, and outputs a signal representing the detection result to the main controller 320. The main controller 320 includes a rotation speed calculation unit 321, a current difference value calculation unit 122, and a determination unit 323. FIG. 10 is a diagram similar to FIG. 8, and is a flowchart showing an example of processing executed by the main controller 320 according to the third embodiment. In the flowchart of FIG. 10, the processing of step S324 is executed instead of the processing of step S224 in the flowchart of FIG. 8.

[0065] As shown in FIG. 10, when it is determined in step S222 that the current difference value ΔI is greater than 0, the process proceeds to step S324. In step S324, the determination unit 323 determines whether or not the temperature Tm of the auxiliary motor 12 detected by the temperature sensor 12b is higher than the temperature threshold value Tt. The temperature threshold value Tt is determined in advance and stored in the non-volatile memory 152. The temperature threshold value Tt is a temperature at which the coil of the auxiliary generator 12 does not melt and the auxiliary generator 12 does not ignite even if the auxiliary generator 12 is operated for an infinite period of time at that temperature. The temperature threshold value Tt is determined according to the specifications of the auxiliary generator 12. In addition, the temperature threshold value Tt is set to a temperature that is a predetermined temperature lower than a temperature that may damage the auxiliary generator 12.

[0066] If it is determined in step S324 that the temperature Tm of the auxiliary motor 12 is equal to or lower than the temperature threshold value Tt, the process proceeds to step S226, and if it is determined that the temperature Tm of the auxiliary motor 12 is higher than the temperature threshold value Tt, the process proceeds to step S130.

[0067] An example of main operations of the control unit 181 of the dump truck 100 according to the third embodiment will be described. For example, when the rotation speed of the cooling fan increases while the vehicle is stopped or coasting downhill, the load on the electric accessory (fan motor) 32 increases. When the load on the electric accessory 32 increases, the output voltage of the auxiliary generator 12 decreases. The automatic voltage regulator 170 outputs an excitation current command value to the auxiliary generator 12 for setting the output voltage of the auxiliary generator 12 to a set voltage. The auxiliary generator 12 uses its own generated power to increase the excitation current flowing through the rotor winding to the excitation current command value. That is, the excitation current is strengthened.

[0068] In the first embodiment, when the excitation current I exceeds the current threshold It, the main controller 120 immediately increases the rotation speed (idle speed Ni) of the engine 140 (S120, S130, S140 in FIG. 5). In contrast, in the third embodiment, even if the excitation current I exceeds the current threshold It, if the temperature Tm of the auxiliary motor 12 is lower than the temperature threshold Tt, the main controller 120 does not increase the rotation speed of the engine 140, but maintains the current rotation speed (No in S222, No in S324, S226, S140 in FIG. 10).

[0069] Therefore, in the third embodiment, the frequency with which the rotation speed of the engine 140 increases can be reduced compared to the first embodiment. When the temperature Tm of the auxiliary motor 12 exceeds the temperature threshold value Tt due to the continued state in which the excitation current I exceeds the current threshold value It, the rotation speed of the engine 140 increases according to the excitation current of the auxiliary generator 12 (Yes in S324 in FIG. 10, S130, S140). Since the required excitation current is reduced by increasing the rotation speed of the engine 140, the temperature rise of the auxiliary generator 12 can be suppressed.

[0070] According to the third embodiment, in addition to the effects of the first embodiment, the following effects are achieved.

[0071] (1) When the excitation current command value (excitation current) I of the auxiliary generator 12 exceeds a predetermined current threshold It, the control device 180 judges whether or not the temperature Tm of the auxiliary generator 12 detected by the temperature sensor 12b exceeds a predetermined temperature threshold Tt (No in S222, S324 in FIG. 10). When the temperature of the auxiliary generator 12 does not exceed the temperature threshold Tt, the control device 180 does not increase the rotation speed of the engine 140 (No in S324, S226, S140 in FIG. 10). When the temperature of the auxiliary generator 12 exceeds the temperature threshold Tt, the control device 180 increases the rotation speed of the engine 140 (Yes in S324, S130, S140 in FIG. 10). In this configuration, even if the excitation current I exceeds the current threshold It, when the temperature Tm of the auxiliary generator 12 does not exceed the temperature threshold Tt, the rotation speed of the engine 140 does not increase. Therefore, it is possible to reduce fuel consumption, noise, and vibration of the engine 140 compared to the first embodiment. In a low-temperature environment such as a cold region or winter, the state in which the excitation current I exceeds the current threshold It can be maintained for a long time, so that the effects of reducing fuel consumption, noise, and vibration are particularly large.

[0072] (2) When the excitation current command value (excitation current) I of the auxiliary generator 12 falls below the current threshold It, the control device 180 immediately reduces the rotation speed of the engine 140 (Yes in S222 in FIG. 10, S130, S140), regardless of the temperature Tm of the auxiliary generator 12. This makes it possible to appropriately reduce the fuel consumption, noise, and vibration of the engine 140 in accordance with the reduction in the excitation current of the auxiliary generator 12.

[0073] The following modified examples are also within the scope of the present invention, and it is possible to combine the configurations shown in the modified examples with the configurations described in the above-mentioned embodiments, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0074] <Variation 1> In the above embodiment, an example in which the rotational speed of the engine 140 is continuously increased in response to an increase in the excitation current has been described (see FIG. 6). However, the method for controlling the rotational speed of the engine 140 is not limited to this. The control for continuously increasing the rotational speed of the engine 140 described in the above embodiment can be said to be optimal control from the viewpoint of fuel consumption reduction. However, when the frequency of fluctuations in the power consumption of the electric auxiliary machine (fan motor) 32 increases due to changes in the temperature of the traveling motor 31 or the like, the rotational speed of the engine 140 also fluctuates finely. As a result, due to the vibration and sound changes of the engine 140, there is a possibility that the riding comfort of the operator may deteriorate by giving discomfort to the operator. Therefore, in this modification, the rotational speed of the engine 140 is changed stepwise using the idle speed table shown in FIG. 11.

[0075] As shown in FIG. 11, the idle speed table is a data table that defines the characteristic that the idle speed Ni increases stepwise as the current difference value ΔI increases. The characteristics defined by the idle speed table are specifically as follows. In the range where the current difference value ΔI is equal to or greater than ΔI1 and less than ΔI2, the idle speed Ni becomes a low idle speed Ni1 that is smaller than the reference speed Ni0 by a predetermined value. In the range where the current difference value ΔI is equal to or greater than ΔI2 and less than ΔI3, the idle speed Ni becomes the reference speed Ni0. In the range where the current difference value ΔI is equal to or greater than ΔI3 and less than ΔI4, the idle speed Ni becomes a high idle speed Ni2 that is larger than the reference speed Ni0 by a predetermined value. The magnitude relationship of the current difference values ΔI1, ΔI2, ΔI3, and ΔI4 is ΔI1 < ΔI2 < 0 < ΔI3 < ΔI4. The low idle speed Ni1 is a value that is equal to or greater than the lower limit value Nimin of the idle speed Ni and less than the reference speed Ni0 (Nimin ≦ Ni1 < Ni0). The high idle speed Ni2 is a value that is larger than the reference speed Ni0 and equal to or less than the upper limit value Nimax of the idle speed (Ni0 < Ni2 ≦ Nimax).

[0076] The main controller 120 refers to an idle speed table shown in Fig. 11 and calculates an idle speed Ni based on the current difference value ΔI. The main controller 120 outputs the calculated idle speed Ni to the engine controller 130 as a command speed.

[0077] That is, the control device 180 according to this modification increases the rotation speed of the engine 140 stepwise as the excitation current I increases. In this modification, the engine rotation speed is not always the minimum speed relative to the power consumption of the electric accessory 32. However, since small fluctuations in the rotation speed of the engine 140 are suppressed, it is possible to prevent the ride comfort of the operator from becoming worse.

[0078] In this modification, an example has been described in which the idle speed Ni of the engine 140 changes in three stages according to the current difference value ΔI. However, the control device 180 may change the idle speed Ni in four or more stages according to the current difference value ΔI. When changing the idle speed Ni in stages, the control device 180 changes the idle speed Ni in at least three or more stages.

[0079] <Variation 2> In the above embodiment, an example has been described in which the electric accessory 32 is a fan motor. However, the example of the electric accessory 32 is not limited to this. For example, the electric accessory 32 may be a compressor motor for an air conditioner in a cab. Furthermore, there may be a plurality of electric accessories 32.

[0080] <Variation 3> In the above embodiment, an example has been described in which the rotation speed of the engine 140 is controlled according to the excitation current only when the accelerator operation device 160 is not operated. However, the present invention is not limited to this. When the accelerator operation device 160 is finely operated, the rotation speed of the engine 140 may be controlled based on the accelerator operation amount and the excitation current I. In this case, when the excitation current I exceeds the current threshold value It, the control device 180 calculates the command speed by adding a rotation speed correction value according to the excitation current I to the rotation speed of the engine 140 calculated based on the accelerator operation amount. Note that, when the excitation current I falls below the current threshold value It while the accelerator operation device 160 is finely operated, the control device 180 does not correct the rotation speed of the engine 140. This ensures driving operability during fine operation of the accelerator operation device 160.

[0081] <Variation 4> In the above embodiment, the dump truck 100 has been described as an example of a work vehicle, but the example of the work vehicle is not limited to this. The work vehicle may be, for example, a wheel loader having a work device including a lift arm and a bucket attached to a vehicle body.

[0082] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0083] 11...Main generator (first generator), 12...Auxiliary generator (second generator), 12a...Voltage sensor, 12b...Temperature sensor, 21...Main inverter (first inverter), 22...Auxiliary inverter (second inverter), 31...Travel motor, 32...Electric accessory (fan motor), 100...Dump truck (work vehicle), 101...Vehicle body, 104...Loading platform (working device), 105...Front wheels (wheels), 106...Rear wheels (wheels), 107...Hoist cylinder (working device, hydraulic actuator), 120...Main controller, 121...Rotational speed calculation unit, 122...Current difference value calculation unit, 130...Engine controller, 140...Engine, 141...Engine rotational speed sensor, 142...Fuel injection device, 151...Processing device, 15 2...Non-volatile memory (storage device), 153...Volatile memory (storage device), 160...Accelerator operation device, 162...Accelerator operation amount sensor, 170...Automatic voltage regulator, 180...Control device, 181...Control unit, 220...Main controller, 221...Rotational speed calculation unit, 223...Determination unit, 320...Main controller, 321...Rotational speed calculation unit, 323...Determination unit, I...Excitation current command value (excitation current), It...Current threshold, Ni...Idle speed, Ni0...Reference speed, Ni1...Low idle speed, Ni2...High idle speed, Nimax...Upper limit value of idle speed, Nimin...Lower limit value of idle speed, t1...Setting time, Tm...Temperature of auxiliary generator (second generator), Tt...Temperature threshold, ΔI...Current difference value

Claims

1. The car body and A working device attached to the vehicle body; An engine mounted on the vehicle body; a first generator and a second generator that generate electricity by the driving force of the engine; a traction motor that receives the electric power generated by the first generator and generates a driving force for driving wheels; at least one electric auxiliary machine that operates by receiving a supply of electric power generated by the second generator; an automatic voltage regulator that controls an excitation current of the second generator in order to regulate a generated voltage of the second generator to a predetermined set voltage; A control device for controlling a rotation speed of the engine; In a work vehicle equipped with The control device includes: monitoring an excitation current of the second generator; Calculating a command speed according to an excitation current of the second generator; Controlling the rotation speed of the engine so that the rotation speed of the engine becomes the command speed; The rotation speed of the engine is increased as the excitation current of the second generator increases. A work vehicle characterized by:

2. The work vehicle according to claim 1, An accelerator operating device; an accelerator operation amount sensor for detecting an operation amount of the accelerator operation device, The control device includes: determining whether the accelerator operation device is operated based on a detection result of the accelerator operation amount sensor; When the accelerator operation device is not operated, a command speed is calculated according to an excitation current of the second generator; When the accelerator operation device is operated, a command speed is calculated according to the operation of the accelerator operation device regardless of the excitation current of the second generator. A work vehicle characterized by:

3. The work vehicle according to claim 1, The control device includes: Calculating a current difference value that is a difference between the excitation current of the second generator and a predetermined current threshold value; The command speed is calculated according to the calculated current difference value. A work vehicle characterized by:

4. The work vehicle according to claim 1, The control device includes: When the excitation current of the second generator exceeds a predetermined current threshold, it is determined whether or not a state in which the excitation current of the second generator exceeds the current threshold has elapsed for a predetermined set time; When the state in which the excitation current of the second generator exceeds the current threshold has not elapsed for the set time, the rotation speed of the engine is not increased, When the state in which the excitation current of the second generator exceeds the current threshold value has elapsed for the set time, the rotation speed of the engine is increased. A work vehicle characterized by:

5. The work vehicle according to claim 4, When the excitation current of the second generator falls below the current threshold, the control device immediately reduces the rotation speed of the engine regardless of the elapsed time during which the excitation current of the second generator falls below the current threshold. A work vehicle characterized by:

6. The work vehicle according to claim 1, a temperature sensor for detecting a temperature of the second generator; The control device includes: When the excitation current of the second generator exceeds a predetermined current threshold, it is determined whether or not the temperature of the second generator detected by the temperature sensor exceeds a predetermined temperature threshold; if the temperature of the second generator does not exceed the temperature threshold, not increasing the rotational speed of the engine; increasing the rotational speed of the engine when the temperature of the second generator exceeds the temperature threshold. A work vehicle characterized by:

7. The work vehicle according to claim 6, When the excitation current of the second generator falls below the current threshold, the control device immediately reduces the rotation speed of the engine regardless of the temperature of the second generator. A work vehicle characterized by:

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