Drive system for work vehicle and work vehicle

Abstract

To provide an electric work vehicle that does not cause structural complexity due to addition of a transmission or the like.SOLUTION: A drive system 50 drives a work vehicle 100 provided with a work device 4 and a travel device 6. The drive system comprises a first electric motor 20 that drives the travel device 6, a second electric motor 21 that drives the work device 4 and the travel device 6, a power switching mechanism 23 that switches between a first state in which power from the second electric motor 21 is transmitted to a hydraulic pump 4h that supplies hydraulic oil to the work device 4 without transmitting power to the travel device 6, and a second state in which power from the second electric motor 21 is transmitted to the hydraulic pump 4h and the travel device 6, and a control device 24 that controls the power switching mechanism 23. When a travel speed of the work vehicle 100 exceeds a first threshold value, the control device 24 switches the power switching mechanism 23 to the second state.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a drive system for a work vehicle and a work vehicle. [Background technology]

[0002] In recent years, there has been a growing trend toward energy conservation in industrial products due to environmental issues and rising crude oil prices. Until now, construction vehicles, transport vehicles, and other work vehicles have mainly used mechanical drive systems with diesel engines, but electrification is leading to increased efficiency and energy savings.

[0003] When electrifying a work vehicle, it is conceivable to provide a battery instead of an engine as a power source, and to configure the traveling device and the work device to be driven by an electric motor.

[0004] For example, Patent Document 1 discloses an electric drive system having two electric motors EM1 and EM2. The system disclosed in Patent Document 1 includes clutches C1 and C2 between the electric motor EM2 and the transmission TM, and between the electric motor EM2 and the hydraulic pump. The system disclosed in Patent Document 1 selectively controls whether the power of the electric motor EM2 is transmitted to the transmission TM on the traveling device side or to the hydraulic pump on the working device side by operating the opening and closing of the clutches C1 and C2.

[0005] Furthermore, Patent Document 2 discloses a drive system in which an automatic transmission is provided between a PTO (power take off) motor and a travel drive shaft, and when the rotational load on the rear wheels increases and there is power available on the PTO side, the rotation of the output shaft of the automatic transmission is controlled to match the rotation of the travel device side, thereby transmitting part of the power on the PTO side to the travel device side. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent Application Publication No. 3750733 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-136970 Summary of the Invention [Problem to be solved by the invention]

[0007] In the system disclosed in Patent Document 1, the power of the electric motor EM2 cannot be transmitted to both the working device and the traveling device simultaneously, and a transmission on the traveling device side is an essential component. The system disclosed in Patent Document 2 also requires an automatic transmission to be provided between the PTO motor and the traveling drive shaft. In other words, in the systems disclosed in Patent Documents 1 and 2, when electrifying a work vehicle, it is necessary to add a transmission or the like to the traveling device, which results in a complex configuration.

[0008] The present invention has been made in view of the above, and has an object to provide an electric work vehicle that does not require the addition of a transmission or the like to complicate the structure. [Means for solving the problem]

[0009] In order to solve the above problems, the drive system for a work vehicle of the present invention is a drive system for a work vehicle equipped with a work device and a traveling device, and comprises: a first electric motor that drives the traveling device; a second electric motor that drives the work device and the traveling device; a power switching mechanism that switches between a first state in which power from the second electric motor is transmitted to a hydraulic pump that supplies pressurized oil to the work device without being transmitted to the traveling device, and a second state in which power from the second electric motor is transmitted to the hydraulic pump and the traveling device; and a control device that controls the power switching mechanism, wherein the control device controls the power switching mechanism to switch to the second state when the traveling speed of the work vehicle exceeds a first threshold. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an electric work vehicle that does not require the addition of a transmission or the like to complicate the structure. Other problems, components, and advantages will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the external configuration of a work vehicle. [Figure 2] FIG. 1 is a diagram illustrating a work vehicle equipped with a conventional drive system. [Figure 3] FIG. 3 is a diagram illustrating a typical example in which the work vehicle shown in FIG. 2 is electrified. [Figure 4] FIG. 1 is a diagram illustrating a V-shaped excavation operation performed by a basic operation of a wheel loader. [Figure 5] FIG. 1 is a diagram showing the NT characteristics required for an electric motor that drives the traveling device of a wheel loader. [Figure 6] 1 is a diagram showing the configuration of a drive system of a work vehicle according to an embodiment of the present invention; [Figure 7] FIG. 3 is a conceptual diagram of power distribution between a first electric motor and a second electric motor. [Figure 8] 4A and 4B are diagrams showing the states of the power switching mechanism with respect to basic operations of the wheel loader. [Figure 9] FIG. 3 is a diagram illustrating a switching determination unit of the control device. [Figure 10] FIG. 4 is a diagram illustrating a power command for a second electric motor. [Figure 11] FIG. 3 is a diagram illustrating a tilt command unit of the control device. [Figure 12] FIG. 2 is a diagram showing the relationship between the functions of the control device. [Figure 13] FIG. 2 is a diagram showing the configuration of a drive system according to the present embodiment that uses a power distribution mechanism. [Figure 14] FIG. 2 is a diagram showing the configuration of a drive system according to the present embodiment that uses a power interruption mechanism. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that components with the same reference numerals in each embodiment have similar components in each embodiment unless otherwise specified, and description thereof will be omitted.

[0013] Fig. 1 is a diagram showing the external configuration of a work vehicle 100. Fig. 2 is a diagram illustrating a work vehicle 100 equipped with a conventional drive system. Fig. 3 is a diagram illustrating a typical example in which the work vehicle 100 shown in Fig. 2 has been electrified.

[0014] The work vehicle 100 is a work machine, such as a wheel loader or hydraulic excavator, that is equipped with a work device 4 for performing excavation and the like, and a self-propelled traveling device 6. In this embodiment, the work vehicle 100 will be described using a wheel loader as an example.

[0015] The work vehicle 100 shown in FIG. 1 is a wheel loader that travels on four-wheel drive wheels 6f, 6r and has an articulated steering mechanism. Attached to the front of the work vehicle 100 are work implements 4a-4d, including a bucket 4a for scooping up earth and other objects. The body of the work vehicle 100 is made up of a front frame 5f that has the work implements 4a-4d and front wheels 6f, and a rear frame 5r that has rear wheels 6r, a cab 7, and an engine 1. The front frame 5f and rear frame 5r are connected by a center hinge 5c so that they can bend left and right, and the bending angle can be changed by a pair of steering cylinders 4g provided on the left and right of the center hinge 5c. The work vehicle 100 is steered by extending and retracting the steering cylinders 4g while traveling to change the angle (bending angle) of the front frame 5f relative to the rear frame 5r.

[0016] The work implements 4a to 4d each have a lift arm 4b rotatably connected to the front frame 5f, a bucket 4a rotatably connected to the lift arm 4b, and a bell crank 4c and a push rod 4d that connect the bucket 4a to the bucket cylinder 4e.

[0017] The lift arm 4b is connected to a lift arm cylinder 4f. The lift arm cylinder 4f is connected to the front frame 5f so that the front frame 5f can support the weight of the bucket 4a connected to the lift arm 4b. The lift arm cylinder 4f performs a lift-up function, which rotates the lift arm 4b upward to increase the height of the bucket 4a, and a lift-down function, which rotates the lift arm 4b downward to decrease the height of the bucket 4a.

[0018] The bucket 4a is connected to a bucket cylinder 4e via a bell crank 4c and a push rod 4d so that the angle of the bucket 4a relative to the lift arm 4b can be changed. The bucket cylinder 4e is connected to a front frame 5f. The height of the bucket 4a can be changed by extending and retracting the lift arm cylinder 4f. The angle of the bucket 4a can be changed by extending and retracting the bucket cylinder 4e.

[0019] The hydraulic actuators 4e to 4g, such as the bucket cylinder 4e, the lift arm cylinder 4f, and the steering cylinder 4g, are operated by pressure oil supplied from a hydraulic pump 4h via a control valve 4i.

[0020] As shown in Fig. 2, a conventional work vehicle 100 performs work such as excavation while traveling by using an engine 1 to drive a traveling device 6 and a working device 4. Specifically, the conventional work vehicle 100 travels by transmitting power from the engine 1 to a drive shaft 13 of the traveling device 6 and wheels 6f, 6r via a torque converter (hereinafter also referred to as "torcon") 2 and a transmission (hereinafter also referred to as "TM") 3. The conventional work vehicle 100 performs work by using power from the engine 1 to drive a hydraulic pump 4h that supplies pressure oil to the working device 4, and operating hydraulic actuators 4e, 4f to move working equipment 4a to 4d.

[0021] When the work vehicle 100 shown in Fig. 2 is electrified, a battery 10 is provided as a power source in place of the engine 1, as shown in Fig. 3, for example. Then, electric motors 11, 12 and inverters 14, 15 are often provided in place of the torque converter 2 and transmission 3 described above. The electric motor 11 is a motor that drives the hydraulic pump 4h to drive the work device 4. The electric motor 12 is a motor that drives the traveling device 6. The torque, power and rotation speed of the electric motor 11 are controlled by the inverter 14. The torque, power and rotation speed of the electric motor 12 are controlled by the inverter 15. Overall control of the work vehicle 100, including commands to the inverters 14, 15, is performed in an integrated manner by a control device (not shown).

[0022] Here, we will explain the basic operation of a wheel loader, which is an example of the work vehicle 100. Figure 4 is a diagram explaining the V-shaped excavation work performed by the basic operation of the wheel loader.

[0023] The basic operations of a wheel loader include an "excavation operation" in which an object is excavated using the bucket 4a, a "loading operation" in which the excavated object is held in the bucket 4a while being moved and loaded onto a loading machine such as a dump truck, and a "transportation operation" in which the object is held in the bucket 4a while being traveled a longer distance than during the loading operation.

[0024] The transport traveling operation is an operation in which the bucket 4a holds an object and travels at a relatively high traveling speed of about 20 to 40 km / h in a mine, quarry, etc. Therefore, in the transport traveling operation, the electric motor 12 that drives the traveling device 6 needs to have characteristics that enable it to generate the torque required for traveling in the medium to high speed rotation range.

[0025] The excavation operation and the loading operation are repeatedly performed in the V-shaped excavation operation shown in FIG. 4. As shown in FIG. 4, the wheel loader first moves forward toward the excavation target, such as a pile of earth and sand, and loads the object, such as earth and sand, into the bucket 4a by plunging into the excavation target (excavation operation). The wheel loader then moves backward to return to its original position, and moves forward toward the machine to be loaded while operating the steering and raising the bucket 4a (loading operation). After loading the object into the machine to be loaded (discharging the object from the bucket 4a), the wheel loader moves backward again to return to its original position. This series of operations is repeated while tracing a V-shaped trajectory as shown in FIG. 4, and is therefore called V-shaped excavation operation. V-shaped excavation operation takes up the majority of the wheel loader's working time.

[0026] In V-shaped excavation work, the wheel loader excavates the object at an extremely slow travel speed, almost at a standstill, so the electric motor 12 that drives the traveling device 6 needs to have the ability to generate large torque in the low rotation speed range in addition to the characteristics required for the transport travel operation described above. Therefore, the electric motor 12 that drives the traveling device 6 needs to be able to generate both large torque in the low rotation speed range and torque in the medium to high rotation speed range, and is required to have a wide range of NT characteristics (motor rotation speed-torque characteristics).

[0027] FIG. 5 is a diagram showing the NT characteristics required for the electric motor 12 that drives the traveling device 6 of the wheel loader.

[0028] Generally, an electric motor having a wide NT characteristic such as that shown in FIG. 5 is quite large. It is not practical to actually install such a large electric motor in a wheel loader. Therefore, to obtain the NT characteristic shown in FIG. 5, it is usually considered to install two different types of electric motors in the wheel loader: a low-speed, high-torque electric motor capable of generating large torque in the low-speed rotation range, and a high-speed electric motor capable of generating the torque required for traveling in the medium- to high-speed rotation range. Alternatively, it is considered to expand the NT characteristic with a single electric motor by adding a transmission 3, which is also used in conventional work vehicles 100 (vehicles equipped with torque converters 2), to the wheel loader. In other words, when electrifying a work vehicle 100 that performs work such as a wheel loader, a design change is required, such as installing multiple electric motors 12 that drive the traveling gear 6 and / or installing a new transmission 3. As a result, electrifying the work vehicle 100 tends to complicate the configuration of the work vehicle 100. Therefore, the work vehicle 100 of this embodiment has a configuration as shown in FIG. 6.

[0029] FIG. 6 is a diagram showing the configuration of a drive system 50 of a work vehicle 100 according to this embodiment.

[0030] The drive system 50 of this embodiment is a system that drives a work vehicle 100 that includes a working device 4 and a traveling device 6. The drive system 50 of this embodiment includes a first electric motor 20 that drives the traveling device 6, a second electric motor 21 that drives the working device 4 and the traveling device 6, an inverter 25 that controls the torque, power, and rotation speed of the first electric motor 20, an inverter 26 that controls the power and rotation speed of the second electric motor 21, and a control device 24 that controls the inverter 25 and the inverter 26. Note that although the battery 10 is not shown in FIG. 6, the drive system 50 of this embodiment includes the battery 10. The battery 10 is connected to the inverter 25 and the inverter 26, as in FIG. 3.

[0031] The first electric motor 20 is connected to the drive shaft 13 of the traveling device 6 via a gear 27. The first electric motor 20 rotates the drive shaft 13 to rotate the wheels 6f, 6r. The second electric motor 21 is connected to a hydraulic pump 4h that supplies pressure oil to the working device 4. The second electric motor 21 drives the hydraulic pump 4h to operate the hydraulic actuators 4e to 4g of the working device 4. This moves the working implements 4a to 4d of the working device 4.

[0032] Furthermore, the drive system 50 of this embodiment includes a power switching mechanism 23 provided between the second electric motor 21 and the traveling device 6. The power switching mechanism 23 may be configured with a clutch. The power switching mechanism 23 is connected to the output shaft 22 of the second electric motor 21 and is also connected to the drive shaft 13 of the traveling device 6 via a gear 28. The power switching mechanism 23 is switchable between a first state in which power from the second electric motor 21 is transmitted to the hydraulic pump 4h without being transmitted to the traveling device 6, and a second state in which power from the second electric motor 21 is transmitted to the hydraulic pump 4h and the traveling device 6. The states of the power switching mechanism 23 are switched and controlled by a control device 24.

[0033] When the power switching mechanism 23 is controlled to the first state by the control device 24, it mechanically blocks the power transmission path between the output shaft 22 of the second electric motor 21 and the drive shaft 13 of the traveling device 6 so that power from the second electric motor 21 is not transmitted to the traveling device 6. In this state, power from the second electric motor 21 is transmitted only to the hydraulic pump 4h, which operates the hydraulic actuators 4e to 4g of the working device 4. In other words, when the power switching mechanism 23 is controlled to the first state, the second electric motor 21 can drive only the working device 4.

[0034] On the other hand, when the power switching mechanism 23 is controlled to the second state by the control device 24, it mechanically opens the power transmission path between the output shaft 22 of the second electric motor 21 and the drive shaft 13 of the traveling device 6 so that power from the second electric motor 21 is also transmitted to the traveling device 6. In this state, power from the second electric motor 21 is transmitted not only to the hydraulic pump 4h but also to the drive shaft 13 of the traveling device 6. Therefore, in this state, the power from the second electric motor 21 can not only operate the hydraulic actuators 4e to 4g of the working device 4, but also rotate the wheels 6f, 6r. In other words, when the power switching mechanism 23 is controlled to the second state, the second electric motor 21 can drive the working device 4 and the traveling device 6 simultaneously.

[0035] As a result, the drive system 50 can use the second electric motor 21 that drives the working device 4 also to drive the traveling device 6, eliminating the need to add a new electric motor for driving the traveling device 6 or to add a transmission 3. The drive system 50 can electrify the work vehicle 100 without adding a transmission 3 or the like. Therefore, the drive system 50 can provide an electric work vehicle 100 that does not incur the complicated configuration that would accompany the addition of a transmission 3 or the like. Moreover, because the power switching mechanism 23 is configured using a clutch, the drive system 50 can realize the power switching mechanism 23 with a simple configuration, making it possible to provide an electric work vehicle 100 with a simple configuration.

[0036] 7 is a conceptual diagram of power distribution between the first electric motor 20 and the second electric motor 21. In FIG. 7, the concept of power distribution between the first electric motor 20 and the second electric motor 21 is superimposed on the NT characteristics shown in FIG.

[0037] In the drive system 50, the first electric motor 20 is configured to mainly provide large torque in the low rotation speed range, and the second electric motor 21 is configured to mainly provide torque in the high rotation speed range. In other words, the first electric motor 20 is configured as a low-speed, large-torque electric motor capable of generating large torque in the low rotation speed range, and the second electric motor 21 is configured as a high-speed electric motor capable of generating torque required for driving in the medium to high rotation speed range.

[0038] The purpose of this power distribution is to utilize the second electric motor 21 in the medium to high speed rotation range. As described above, the second electric motor 21 is originally a motor that drives the hydraulic pump 4h, which is the power source for the hydraulic actuators 4e to 4g and the work machines 4a to 4d of the working device 4. Since the second electric motor 21 needs to generate a flow rate and pressure of hydraulic oil sufficient to operate the hydraulic actuators 4e to 4g, it is naturally preferable to employ a high rotation speed electric motor.

[0039] The low-speed rotation range refers to the range of motor rotation speeds when the travel speed of the work vehicle 100 is equal to or lower than a first threshold. The medium- to high-speed rotation range refers to the range of motor rotation speeds when the travel speed of the work vehicle 100 exceeds the first threshold. The high-speed rotation range refers to the range of motor rotation speeds when the travel speed of the work vehicle 100 exceeds a second threshold that is greater than the first threshold. The motor rotation speed corresponding to the first threshold distinguishes whether or not the electric motors 20, 21 are operating in the low-speed rotation range. The motor rotation speed corresponding to the second threshold distinguishes whether or not the electric motors 20, 21 are operating in the high-speed rotation range. In Figure 7, the motor rotation speed corresponding to the first threshold is represented as Nt1, and the motor rotation speed corresponding to the second threshold is represented as Nt2.

[0040] In the drive system 50, the first electric motor 20 is configured as a low-speed, high-torque electric motor, and by distributing the power of the electric motors 20, 21 as shown in Figure 7, the second electric motor 21 can simultaneously drive the working device 4 and the traveling device 6, and the wide range of NT characteristics shown in Figure 5 can be met. Therefore, the drive system 50 can meet the wide range of NT characteristics shown in Figure 5 without adding a new electric motor or transmission 3 for driving the traveling device 6, and the work vehicle 100 can be reliably electrified. Therefore, the drive system 50 can provide an electric work vehicle 100 while reliably minimizing the complexity of the configuration that would otherwise accompany the addition of a transmission 3, etc.

[0041] The reason why the second electric motor 21 simultaneously drives the working implement 4 and the traveling implement 6 in the medium to high speed rotation range is that there are occasions when the steering cylinder 4g operates for steering the work vehicle 100 even in the medium to high speed rotation range, so the hydraulic pump 4h needs to be driven at all times. However, the power required for the hydraulic pump 4h in the medium to high speed rotation range is smaller than in the low speed rotation range where excavation operations are performed, so the second electric motor 21 has sufficient capacity to simultaneously drive the working implement 4 and the traveling implement 6.

[0042] FIG. 8 is a diagram showing the state of the power switching mechanism 23 for the basic operation of the wheel loader.

[0043] As explained with reference to FIG. 4, the basic operations of a wheel loader include excavation, loading, and transport travel (combining excavation and loading results in the V-shaped excavation work described above). During excavation and loading, the travel speed is low, and the electric motors 20, 21 operate in a low rotation speed range. The power required for the hydraulic pump 4h is medium to high. Therefore, during excavation and loading, the power required is not matched with the high-speed second electric motor 21, and the control device 24 controls the power switching mechanism 23 to the first state (shut-off state).

[0044] In contrast, during transport travel, the travel speed is high and the electric motors 20, 21 operate in a high-speed rotation range. The hydraulic pump 4h only requires a small amount of power. Therefore, during transport travel, the control device 24 controls the power switching mechanism 23 to the second state (open state).

[0045] As a result, the drive system 50 can appropriately distribute power between the first electric motor 20 and the second electric motor 21 in accordance with each operation of the work vehicle 100. Therefore, the drive system 50 can reliably electrify the work vehicle 100 without interfering with each operation of the work vehicle 100, even without adding a new electric motor or transmission 3 for driving the traveling device 6. Therefore, the drive system 50 can provide an electric work vehicle 100 while reliably minimizing the complexity of the configuration that would accompany the addition of a transmission 3, etc.

[0046] The above is a description of the overall configuration and operation of the drive system 50 of this embodiment. Below, a detailed configuration and operation of the control device 24 that controls the power switching mechanism 23 will be described with reference to Figures 9 to 12. Note that each function of the control device 24 is realized by a processor included in the control device 24 executing a program stored in a memory.

[0047] The control device 24 controls the power switching mechanism 23 in accordance with the power distribution shown in FIG.

[0048] FIG. 9 is a diagram illustrating the switching determination unit 30 of the control device 24. As shown in FIG.

[0049] The switching determination unit 30 is a function of the control device 24 that determines whether to control the power switching mechanism 23 to the first state or the second state. Signals indicating the rotation speed of the drive shaft 13 of the traveling device 6, the rotation speed of the second electric motor 21, and the required power of the traveling device 6 (hereinafter also referred to as "required traveling power") are input to the switching determination unit 30. The switching determination unit 30 determines the state of the power switching mechanism 23 based on these input signals and outputs a power switching signal. The power switching signal may be, for example, an ON / OFF signal that is OFF when specifying the first state as the state of the power switching mechanism 23 and ON when specifying the second state. The state of the power switching mechanism 23 is switched to the first state or the second state in accordance with the power switching signal.

[0050] When the traveling speed of the work vehicle 100 is equal to or less than a first threshold, the switching determination unit 30 turns the power switching signal OFF to control the power switching mechanism 23 to the first state. When the traveling speed of the work vehicle 100 exceeds the first threshold, the switching determination unit 30 turns the power switching signal ON to control the power switching mechanism 23 to the second state. The traveling speed of the work vehicle 100 is converted into the rotation speed of the drive shaft 13 and input to the switching determination unit 30. The switching determination unit 30 determines whether the traveling speed exceeds the first threshold by determining whether the rotation speed of the drive shaft 13 exceeds the rotation speed corresponding to the first threshold.

[0051] The switching determination unit 30 can control the power switching mechanism 23 to the second state when the traveling speed of the work vehicle 100 exceeds the first threshold value and the difference between the rotation speed of the drive shaft 13 calculated from the traveling speed and the rotation speed of the second electric motor 21 falls within an allowable range. In other words, the switching determination unit 30 does not immediately turn on the power switching signal to control the power switching mechanism 23 to the second state, but turns on the power switching signal when the difference between the rotation speed of the drive shaft 13 and the rotation speed of the second electric motor 21 falls within the allowable range.

[0052] As a result, the drive system 50 can reduce the impact or vibration that occurs when the power switching mechanism 23 switches from the first state to the second state, for example, the impact or vibration that occurs when the power transmission path between the output shaft 22 of the second electric motor 21 and the drive shaft 13 is opened. Therefore, the drive system 50 can provide an electric work vehicle 100 that can suppress a decrease in driving performance without incurring a complicated configuration that would otherwise accompany the addition of a transmission 3 or the like.

[0053] In the above description, the switching determination unit 30 controls the state of the power switching mechanism 23 by inputting the rotation speed of the drive shaft 13, the rotation speed of the second electric motor 21, and the required traveling power. The switching determination unit 30 may also control the state of the power switching mechanism 23 by adding the required power of the hydraulic pump 4h associated with the work implement 4 (hereinafter also referred to as "required work power") as a determination condition. For example, even if the traveling speed of the work vehicle 100 exceeds a first threshold, the switching determination unit 30 may control the power switching mechanism 23 to the first state if the required work power is greater than a predetermined value.

[0054] As a result, the drive system 50 can avoid a situation in which the hydraulic pump 4h associated with the working implement 4 is unable to obtain the necessary power due to the second electric motor 21 simultaneously driving the working implement 4 and the traveling device 6, despite the large power required of the hydraulic pump 4h associated with the working implement 4. Therefore, the drive system 50 can provide an electric work vehicle 100 that is capable of suppressing a decline in work performance without incurring a complicated configuration that would otherwise accompany the addition of a transmission 3 or the like.

[0055] FIG. 10 is a diagram illustrating a power command for the second electric motor 21. In FIG.

[0056] When the power switching mechanism 23 is controlled to the first state, the second electric motor 21 provides power for the working device 4. In this case, the control device 24 generates a power command for the second electric motor 21 so that the required work power is output from the second electric motor 21. On the other hand, when the power switching mechanism 23 is controlled to the second state, the second electric motor 21 provides power for both the working device 4 and the traveling device 6. In this case, as shown in FIG. 10 , the control device 24 generates a power command for the second electric motor 21 so that the second electric motor 21 outputs power that is the sum of the required work power and the portion of the required traveling power that is provided by the second electric motor 21.

[0057] FIG. 11 is a diagram illustrating the tilt command unit 31 of the control device 24. As shown in FIG.

[0058] The hydraulic pump 4h of the working device 4 may be configured as a variable displacement swash plate type axial piston pump. This type of hydraulic pump 4h can control the power of the hydraulic pump 4h by controlling the tilt angle of the swash plate.

[0059] The tilt command unit 31 is a function of the control device 24 that generates a tilt command to control the tilt angle of the swash plate of the hydraulic pump 4h. In order for the hydraulic pump 4h to output power according to the required work power, signals indicating the required work power, the rotation speed of the second electric motor 21, and the pressure of the hydraulic pump 4h are input to the tilt command unit 31. The tilt command unit 31 calculates the tilt angle of the swash plate based on these input signals and generates a tilt command. As a result, the power output from the second electric motor 21 minus the required work power is transmitted to the traveling device 6 as power for the traveling device 6.

[0060] Fig. 12 is a diagram showing the relationship between the functions of the control device 24. Note that Fig. 12 shows only the functions of the control device 24 that are related to this embodiment, and does not show all of the functions of the control device 24 that control the work vehicle 100.

[0061] As shown in Fig. 12, in the control device 24, signals indicating the accelerator, brake, and traveling speed are input to a traveling power requirement calculation unit 32. The traveling power requirement calculation unit 32 calculates the traveling power requirement based on these input signals. The traveling power requirement calculated by the traveling power requirement calculation unit 32 is input to the switching determination unit 30, and is used to control the power switching mechanism 23, as described using Fig. 9.

[0062] Furthermore, a signal indicating the operation amount of the control lever of the bucket 4a and a signal indicating the operation amount of the control lever of the lift arm 4b are input to the work required power calculation unit 33. The work required power calculation unit 33 calculates the work required power based on these input signals. The work required power calculated by the work required power calculation unit 33 is used to generate a power command for the second electric motor 21, as described using FIG. 10. Furthermore, the work required power calculated by the work required power calculation unit 33 is input to the tilt command unit 31, as described using FIG. 11, and is used to control the hydraulic pump 4h. In this way, the power to be transmitted from the second electric motor 21 to the traveling device 6 is determined.

[0063] 13 is a diagram showing the configuration of a drive system 50 of this embodiment that uses a power distribution mechanism 35. Note that, in FIG. 13, similar to FIG. 6, the battery 10 is not shown.

[0064] In the drive system 50 shown in Fig. 6, the power switching mechanism 23 is configured by a clutch. However, in the drive system 50 of this embodiment, the power switching mechanism 23 may be configured by a mechanism other than a clutch. For example, in the drive system 50 shown in Fig. 13, the power switching mechanism 23 is configured by a power distribution mechanism 35.

[0065] The power distribution mechanism 35 is a mechanism configured using planetary gears and has an input shaft 35a connected to the output shaft 22 of the second electric motor 21, a first output shaft 35b connected to the hydraulic pump 4h, and a second output shaft 35c connected to the drive shaft 13 of the traveling device 6 via a gear 36.

[0066] When the power distribution mechanism 35 is controlled to the first state by the control device 24, it transmits the power transmitted from the output shaft 22 of the second electric motor 21 to the input shaft 35a from the first output shaft 35b to the hydraulic pump 4h.

[0067] On the other hand, when the power distribution mechanism 35 is controlled to the second state by the control device 24, it transmits the power transmitted from the output shaft 22 of the second electric motor 21 to the input shaft 35a from the first output shaft 35b to the hydraulic pump 4h and from the second output shaft 35c to the drive shaft 13. At this time, the control device 24 generates a power command for the second electric motor 21 so that the second electric motor 21 outputs power that is the sum of both the required traveling power and the required work power.

[0068] 13, the second electric motor 21 that drives the work implement 4 can also be used to drive the traveling implement 6, making it possible to electrify the work vehicle 100 without adding a transmission 3 or the like. Therefore, the drive system 50 can provide an electric work vehicle 100 that does not incur the complicated configuration that would accompany the addition of a transmission 3 or the like.

[0069] 14 is a diagram showing the configuration of a drive system 50 of this embodiment that uses a power interruption mechanism 37. Note that in FIG. 14, similar to FIGS. 6 and 13, the battery 10 is not shown.

[0070] The drive system 50 shown in FIGS. 6 and 13 is based on the assumption that the first electric motor 20, a low-speed, high-torque type, is configured as an induction motor. When the traveling speed is high, the traveling device 6 shown in FIGS. 6 and 13 is driven only by the second electric motor 21. However, because the drive shaft 13 is connected to the first electric motor 20, the first electric motor 20 is in an idle state. This embodiment also applies when the first electric motor 20 is configured as a permanent magnet motor. However, when the first electric motor 20 is in an idle state as described above, an induced voltage is generated due to changes in the magnetic flux of the permanent magnet incorporated in the motor rotor. If the traveling device 6 is driven while an induced voltage is generated, a large current may be generated in the first electric motor 20. Furthermore, if the motor terminals are short-circuited, a large braking force may be generated in the first electric motor 20.

[0071] Therefore, in the drive system 50 shown in FIG. 14 , a power interrupting mechanism 37 is provided between the first electric motor 20 and the traveling device 6. The power interrupting mechanism 37 may be configured with a clutch. The power switching mechanism 23 is connected to the output shaft 20a of the first electric motor 20, and is also connected to the drive shaft 13 of the traveling device 6 via a gear 38. The power interrupting mechanism 37 is switchable between a first state in which power from the first electric motor 20 is not transmitted to the traveling device 6, and a second state in which power from the first electric motor 20 is transmitted to the traveling device 6. The state of the power interrupting mechanism 37 is switched and controlled by the control device 24.

[0072] When controlled to the first state by the control device 24, the power interrupting mechanism 37 mechanically interrupts the power transmission path between the output shaft 20a of the first electric motor 20 and the drive shaft 13 of the traveling device 6 so that power from the first electric motor 20 is not transmitted to the traveling device 6. When controlled to the second state by the control device 24, the power interrupting mechanism 37 mechanically opens the power transmission path between the output shaft 20a of the first electric motor 20 and the drive shaft 13 of the traveling device 6 so that power from the first electric motor 20 is transmitted to the traveling device 6.

[0073] When the traveling speed of the work vehicle 100 exceeds the second threshold value, the control device 24 controls the power interruption mechanism 37 to the first state so that power from the first electric motor 20 is not transmitted to the traveling device 6. In other words, when the traveling speed of the work vehicle 100 is high, the control device 24 mechanically interrupts the power transmission path between the output shaft 20a of the first electric motor 20 and the drive shaft 13 of the traveling device 6.

[0074] 14 can thereby disconnect the first electric motor 20 from the drive shaft 13 when the work vehicle 100 is traveling at high speeds, thereby preventing the first electric motor 20 from entering the above-mentioned free-spinning state. Therefore, because the drive system 50 can prevent the generation of induced voltage that causes the above-mentioned problems, the first electric motor 20 can be configured as a permanent magnet motor, allowing various models of work vehicles 100 to be electrified with a high degree of design freedom.

[0075] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the components described. Furthermore, some of the components of one embodiment can be replaced with components of another embodiment, and components of another embodiment can be added to components of one embodiment. Furthermore, some of the components of each embodiment can be added, deleted, or replaced with other components.

[0076] Furthermore, the above-described components, functions, processing units, or processing means may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described components or functions may also be implemented in software, with a processor interpreting and executing a program that implements each function. Information such as the programs, tables, or files that implement each function may be stored in a storage device such as a memory, a hard disk, or an SSD (solid state drive), or in a storage medium such as an IC card, SD card, or DVD.

[0077] In addition, the control lines and information lines shown are those that are considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected. [Explanation of symbols]

[0078] 4...working device, 4a to 4d...working machine, 4e to 4g...hydraulic actuator, 4h...hydraulic pump, 6...traveling device, 13...drive shaft, 20...first electric motor, 20a...output shaft, 21...second electric motor, 22...output shaft, 23...power switching mechanism, 24...control device, 35...power distribution mechanism, 35a...input shaft, 35b...first output shaft, 35c...second output shaft, 37...power cut-off mechanism, 50...drive system, 100...working vehicle

Claims

1. A drive system for a work vehicle equipped with a work implement and a traveling implement, a first electric motor that drives the traveling device; a second electric motor that drives the working device and the traveling device; a power switching mechanism that switches between a first state in which power from the second electric motor is transmitted to a hydraulic pump that supplies pressure oil to the working device without being transmitted to the traveling device, and a second state in which power from the second electric motor is transmitted to the hydraulic pump and the traveling device; a control device that controls the power switching mechanism, The control device controls the power switching mechanism to switch to the second state when the traveling speed of the work vehicle exceeds a first threshold value. A drive system for a work vehicle.

2. The power switching mechanism is a clutch, connected to an output shaft of the second electric motor and connected to a drive shaft of the traveling device; When the control device controls the vehicle to the first state, a power transmission path between the output shaft of the second electric motor and the drive shaft of the traveling device is interrupted, When the control device controls the second state, the power transmission path between the output shaft of the second electric motor and the drive shaft of the traveling device is opened.

2. A drive system for a work vehicle according to claim 1.

3. The first electric motor is a low-speed, large-torque electric motor capable of generating a large torque in a low-speed rotation range that indicates a range of motor rotation speeds when the traveling speed is equal to or less than the first threshold value.

2. A drive system for a work vehicle according to claim 1.

4. The control device controls the power switching mechanism to the second state when the traveling speed exceeds the first threshold value and a difference between the rotation speed of the drive shaft of the traveling device calculated from the traveling speed and the rotation speed of the second electric motor falls within an allowable range.

2. A drive system for a work vehicle according to claim 1.

5. The control device controls the power switching mechanism to the first state when the required power of the working device is greater than a predetermined value even when the traveling speed exceeds the first threshold value.

2. A drive system for a work vehicle according to claim 1.

6. the working device is configured to include a working machine and a hydraulic actuator that moves the working machine using the pressure oil supplied from the hydraulic pump, the second electric motor drives the hydraulic pump to operate the hydraulic actuator; The power switching mechanism is a power distribution mechanism having an input shaft connected to the output shaft of the second electric motor, a first output shaft connected to the hydraulic pump, and a second output shaft connected to a drive shaft of the traveling device, When the control device is controlled to the first state, power transmitted from the output shaft to the input shaft of the second electric motor is transmitted from the first output shaft to the hydraulic pump, When controlled to the second state by the control device, the power transmitted from the output shaft to the input shaft of the second electric motor is transmitted from the first output shaft to the hydraulic pump and from the second output shaft to the drive shaft of the traveling device.

2. A drive system for a work vehicle according to claim 1.

7. a power interruption mechanism that switches between a first state in which power from the first electric motor is not transmitted to the traveling device and a second state in which power from the first electric motor is transmitted to the traveling device, When the traveling speed exceeds a second threshold value that is greater than the first threshold value, the control device controls the power interruption mechanism to switch to the first state so that power from the first electric motor is not transmitted to the traveling device.

2. A drive system for a work vehicle according to claim 1.

8. The work vehicle is a wheel loader that performs an excavation operation to excavate an object, a loading operation to move while holding the excavated object and load it onto a loaded machine, and a transport traveling operation to travel a longer distance than the loading operation while holding the object, The control device During the excavation operation and the loading operation, the power switching mechanism is controlled to the first state, During the transport traveling operation, the power switching mechanism is controlled to the second state.

2. A drive system for a work vehicle according to claim 1.

9. Equipped with a drive system according to any one of claims 1 to 8 A work vehicle characterized by:

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