Wheel loader and method for controlling wheel loader

Abstract

A wheel loader according to the present invention comprises a vehicle body, an electric motor, a transmission, and a controller. The vehicle body includes a traveling body and a work machine. The electric motor is installed on the vehicle body. The transmission is installed on the vehicle body. The transmission can change a gear ratio at a plurality of speed stages. The transmission transmits drive force from the electric motor to the traveling body. The controller controls the transmission. The controller acquires a current work mode from among a plurality of work modes that correspond to types of work performed by the vehicle body. When the current work mode is cargo transport, the controller holds the gear ratio of the transmission at a prescribed speed stage and prohibits changes from the prescribed speed stage to other speed stages.

Description

Wheel loader and method for controlling a wheel loader

[0001] The present disclosure relates to a wheel loader and a method for controlling a wheel loader.

[0002] Some wheel loaders are equipped with a transmission that can change the gear ratio among multiple speed stages. For example, the wheel loader disclosed in Patent Document 1 is equipped with a shift operation member for setting the highest speed stage of the transmission. For example, when the operator operates the shift operation member to fourth speed, the highest speed stage of the transmission is set to fourth speed. The transmission changes the gear ratio between first speed stage and fourth speed stage according to the vehicle speed or engine rotation speed.

[0003] JP 2023-14108 A

[0004] Wheel loaders perform various tasks, such as excavation and load transport. For example, when transporting loads, the wheel loader scoops up the work object with its work equipment and travels with the work object held by the work equipment. The wheel loader travels to a transport vehicle, such as a truck, and loads the object onto it. By repeating the above operations, the wheel loader transports the object from a predetermined location onto the transport vehicle and loads it onto it.

[0005] As described above, when transporting a load, the wheel loader frequently stops and moves repeatedly. Therefore, as described above, if the transmission changes the gear ratio in accordance with the vehicle speed or engine rotation speed, the gear ratio will be changed frequently when transporting a load. When the gear ratio is changed, a gear shift shock occurs. Therefore, if the gear ratio is changed frequently when transporting a load, and gear shift shock occurs frequently, there is a concern that the load may spill from the work machine.

[0006] An object of the present disclosure is to suppress the occurrence of gear shift shock in a wheel loader when transporting a load.

[0007] A wheel loader according to one aspect of the present disclosure includes a vehicle body, an electric motor, a transmission, and a controller. The vehicle body includes a traveling body and a work machine. The electric motor is mounted on the vehicle body. The transmission is mounted on the vehicle body. The transmission is capable of changing the gear ratio among a plurality of speed stages. The transmission transmits driving force from the electric motor to the traveling body. The controller controls the transmission. The controller acquires a current work mode from a plurality of work modes corresponding to the type of work performed by the vehicle body. When the current work mode is load transportation, the controller maintains the gear ratio of the transmission at a predetermined speed stage and prohibits changing from the predetermined speed stage to another speed stage.

[0008] A method according to another aspect of the present disclosure is a method for controlling a wheel loader. The wheel loader includes a traveling body, a work implement, an electric motor, and a transmission. The transmission is capable of changing the gear ratio among a plurality of speed stages and transmits driving force from the electric motor to the traveling body. The method according to this aspect includes acquiring a current work mode from a plurality of work modes corresponding to the type of work performed by the wheel loader, and, if the current work mode is load transport, maintaining the gear ratio of the transmission at a predetermined speed stage and prohibiting a change to a speed stage other than the predetermined speed stage.

[0009] According to the present disclosure, when the current operation mode is cargo transport, the gear ratio of the transmission is maintained at a predetermined speed and shifting from the predetermined speed to another speed is prohibited, thereby suppressing the occurrence of gear shift shocks caused by the transmission.

[0010] Fig. 1 is a side view of a wheel loader according to an embodiment. Fig. 2 is a block diagram showing the configuration of a drive system mounted on the wheel loader. Fig. 3 is a diagram showing tractive force-vehicle speed characteristics for each of a plurality of speed stages of the transmission. Fig. 4 is a block diagram showing the configuration of a control system for the wheel loader. Fig. 5 is a flowchart showing the processing of transmission speed change control. Fig. 6 is a top view showing the operation of the wheel loader during V-shaped loading. Fig. 7 is a flowchart showing the processing of transmission speed change control according to a modified example.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a side view of a wheel loader 1 according to an embodiment of the present disclosure. As shown in Fig. 1, the wheel loader 1 includes a vehicle body 2. The vehicle body 2 includes a front vehicle body 3, a rear vehicle body 4, a work implement 5, and a traveling body 6.

[0012] The rear vehicle body 4 is connected to the front vehicle body 3 so as to be able to turn left and right. A driver's cab 7 is disposed in the rear vehicle body 4. A steering cylinder 15 is connected to the front vehicle body 3 and the rear vehicle body 4. The steering cylinder 15 is a hydraulic cylinder. The extension and contraction of the steering cylinder 15 causes the front vehicle body 3 to turn left and right relative to the rear vehicle body 4.

[0013] The work implement 5 is used for work such as excavation. The work implement 5 is attached to the front vehicle body 3. The work implement 5 includes a boom 11, a bucket 12, a boom cylinder 13, and a bucket cylinder 14. The boom cylinder 13 and the bucket cylinder 14 are hydraulic cylinders. The boom 11 moves when the boom cylinder 13 extends and retracts. The bucket 12 moves when the bucket cylinder 14 extends and retracts.

[0014] The running body 6 causes the wheel loader 1 to travel. Figure 2 is a block diagram showing the configuration of a drive system 8 mounted on the wheel loader 1. As shown in Figures 1 and 2, the running body 6 includes front wheels 16A, 16B and rear wheels 17A, 17B. The front wheels 16A, 16B are rotatably supported by the front vehicle body 3. The rear wheels 17A, 17B are rotatably supported by the rear vehicle body 4.

[0015] As shown in FIG. 2 , the drive system 8 includes a battery 21, a power control circuit 22, a work implement motor 23, and a travel motor 24. The work implement motor 23 and the travel motor 24 are electric motors. The battery 21 supplies power to the work implement motor 23 and the travel motor 24. The power control circuit 22 controls the power supplied to the work implement motor 23 and the travel motor 24. The power control circuit 22 includes, for example, an inverter. The work implement motor 23 generates drive power for driving the work implement 5. The travel motor 24 generates drive power for driving the travel body 6.

[0016] The drive system 8 includes a work implement pump 25 and a control valve 26. The work implement pump 25 is a variable displacement hydraulic pump. The work implement pump 25 is connected to the work implement motor 23. The work implement pump 25 is driven by the work implement motor 23 to supply hydraulic oil to the above-mentioned hydraulic cylinders 13-15. The control valve 26 is connected to the work implement pump 25 and the hydraulic cylinders 13-15 via a hydraulic circuit. The control valve 26 includes a plurality of valves. The control valve 26 controls the flow rate of hydraulic oil supplied from the work implement pump 25 to the hydraulic cylinders 13-15.

[0017] The drive system 8 includes a transmission 27, a front axle 28, and a rear axle 29. The front wheels 16A, 16B are connected to the transmission 27 via the front axle 28. The rear wheels 17A, 17B are connected to the transmission 27 via the rear axle 29. The transmission 27 is connected to the traction motor 24. The transmission 27 changes the speed of the driving force from the traction motor 24 and transmits it to the traveling body 6.

[0018] The transmission 27 includes a plurality of speed change gears 33 to 35. The transmission 27 transmits the driving force from the traveling motor 24 to the traveling body 6.

[0019] The multiple speed change gears 33-35 each have a different gear ratio. The transmission 27 has first to third speed change gears 33-35. Therefore, the transmission 27 can change the speed change ratio between a first speed stage, a second speed stage, and a third speed stage. Figure 3 is a diagram showing the tractive force-vehicle speed characteristics for each of the multiple speed stages. The tractive force-vehicle speed characteristics indicate the maximum tractive force of the wheel loader 1 at each vehicle speed.

[0020] In FIG. 3, L1 indicates the tractive force-vehicle speed characteristics in the first speed stage. L2 indicates the tractive force-vehicle speed characteristics in the second speed stage. In FIG. 3, L3 indicates the tractive force-vehicle speed characteristics in the third speed stage. As shown in FIG. 3, the maximum tractive force is the largest in the first speed stage and the smallest in the third speed stage. The maximum tractive force in the second speed stage is a value between the first and second speed stages. The maximum vehicle speed is the largest in the third speed stage and the smallest in the first speed stage. The maximum tractive force in the second speed stage is a value between the first and second speed stages.

[0021] Figure 4 is a block diagram showing the configuration of the control system 9 for the wheel loader 1. As shown in Figure 4, the control system 9 includes a motor speed sensor 41 and a vehicle speed sensor 42. The motor speed sensor 41 detects the output rotation speed of the travel motor 24. The vehicle speed sensor 42 detects the vehicle speed of the wheel loader 1.

[0022] The control system 9 includes a pump pressure sensor 43, a boom pressure sensor 44, and a bucket pressure sensor 50. The pump pressure sensor 43 detects the discharge pressure of the work implement pump 25. The boom pressure sensor 44 detects the bottom pressure of the boom cylinder 13. The bucket pressure sensor 50 detects the bottom pressure of the bucket cylinder 14.

[0023] The control system 9 includes a boom angle sensor 45 and a bucket angle sensor 46. The boom angle sensor 45 detects the boom angle. The boom angle is the angle of the boom 11 relative to the front vehicle body 3. The bucket angle sensor 46 detects the bucket angle. The bucket angle is the angle of the bucket 12 relative to the boom 11.

[0024] The control system 9 includes a controller 47. The controller 47 controls the wheel loader 1. The controller 47 includes a processor 48 and a storage device 49. The processor 48 is, for example, a CPU (central processing unit). The processor 48 executes processing for controlling the wheel loader 1 in accordance with a program. The storage device 49 includes a non-volatile memory such as a ROM and a volatile memory such as a RAM. The storage device 49 may include storage such as a hard disk or an SSD (Solid State Drive). The storage device 49 stores programs and data for controlling the wheel loader 1.

[0025] The controller 47 receives a signal indicating the output rotation speed of the travel motor 24 from the motor speed sensor 41. The controller 47 receives a signal indicating the vehicle speed from the vehicle speed sensor 42. The controller 47 receives a signal indicating the discharge pressure of the work implement pump 25 from the pump pressure sensor 43. The controller 47 receives a signal indicating the bottom pressure of the boom cylinder 13 from the boom pressure sensor 44. The controller 47 receives a signal indicating the bottom pressure of the bucket cylinder 14 from the bucket pressure sensor 50. The controller 47 receives a signal indicating the boom angle from the boom angle sensor 45. The controller 47 receives a signal indicating the bucket angle from the bucket angle sensor 46.

[0026] The control system 9 includes an accelerator operation device 51, an FR operation device 52, a steering operation device 53, a work implement operation device 54, a shift operation device 55, and an input device 56. The accelerator operation device 51, the FR operation device 52, the steering operation device 53, the work implement operation device 54, and the input device 56 can each be manually operated by the operator of the wheel loader 1.

[0027] The accelerator operating device 51 is operated to control the vehicle speed of the wheel loader 1. The accelerator operating device 51 includes, for example, an accelerator pedal. However, the accelerator operating device 51 may also include other members such as a lever or a switch.

[0028] The FR operating device 52 is operated to switch the wheel loader 1 between forward and reverse travel. The FR operating device 52 can be operated to an FNR position, which includes a forward position, a neutral position, and a reverse position. The FR traveling device includes, for example, an FR lever. However, the FR operating device 52 may also include other members, such as a switch.

[0029] The steering operation device 53 is operated to steer the hole loader. The steering operation device 53 includes, for example, a steering wheel. However, the steering operation device 53 may include other members such as a lever or a switch.

[0030] The work machine operating device 54 is operated to control the work machine 5. The work machine operating device 54 is, for example, a lever. However, the work machine operating device 54 may also be another member such as a switch or a pedal.

[0031] The shift operating device 55 is operated to change the gear ratio of the transmission 27. The shift operating device 55 is, for example, a switch. However, the shift operating device 55 may be another member such as a lever.

[0032] The input device 56 can be operated by an operator to set the control mode of the wheel loader 1. The input device 56 includes, for example, a switch. However, the input device 56 may also include other members such as a touch screen.

[0033] The controller 47 receives a signal indicating the accelerator operation amount from the accelerator operation device 51. The accelerator operation amount is the operation amount of the accelerator operation device 51. The controller 47 controls the power control circuit 22 so as to change the output rotation speed of the travel motor 24 in accordance with the accelerator operation amount.

[0034] The controller 47 receives a signal indicating the FNR position from the FR operation device 52. The controller 47 controls the rotation direction of the travel motor 24 so as to switch the drive direction of the traveling body 6 between a forward direction and a reverse direction according to the FNR position of the FR operation device 52. The controller 47 receives a signal indicating the operation position of the steering operation device 53 from the steering operation device 53. The controller 47 controls the steering cylinder 15 so that the wheel loader 1 is steered according to the operation position of the steering operation device 53.

[0035] The controller 47 receives a signal indicating the operation position of the work machine operation device 54 from the work machine operation device 54. The controller 47 controls the boom cylinder 13 and the bucket cylinder 14 so that the work machine 5 operates in accordance with the operation position of the work machine operation device 54.

[0036] The controller 47 receives a signal indicating the selected speed stage of the transmission 27 from the shift operation device 55. The controller 47 switches the gear ratio of the transmission 27 between the first speed stage and the selected speed stage in accordance with the vehicle speed and the output rotation speed of the traction motor 24.

[0037] The controller 47 receives a signal indicating the setting of the control mode of the wheel loader 1 from the input device 56. The controller 47 controls the wheel loader 1 in accordance with the control mode set by the input device 56. In particular, the operator can use the input device 56 to select a current work mode from a plurality of work modes executed by the wheel loader 1. When the current work mode is selected by the input device 56, the controller 47 controls the speed change of the transmission 27 in accordance with the current work mode. The speed change control of the transmission 27 in accordance with the current work mode will be described below.

[0038] 5 is a flowchart showing the process of shift control of the transmission 27. As shown in FIG. 5, in step S101, the controller 47 acquires the current work mode selected from a plurality of work modes by the input device 56.

[0039] The multiple work modes include heavy excavation, V-shaped loading, loading and transport, and low-load traveling. Heavy excavation is work in which the wheel loader 1 excavates a work object such as earth and sand using the work implement 5. V-shaped loading is work in which an object placed in a predetermined location is loaded onto a transport vehicle such as a dump truck. Figure 6 is a top view showing the operation of the wheel loader 1 during V-shaped loading.

[0040] As shown in Figure 6, the wheel loader 1 moves forward toward a pile 100 of objects placed in a predetermined location (arrow A1). The wheel loader 1 carries objects in the bucket 12 and moves backward, moving away from the pile 100 of objects (arrow A2). The wheel loader 1 moves forward toward the transport vehicle 200 while changing direction (arrow A3). The wheel loader 1 loads the objects onto the transport vehicle 200. The wheel loader 1 moves backward, moving away from the transport vehicle 200 (arrow A4). The wheel loader 1 then moves forward again toward the pile 100 of objects while changing direction (arrow A1). By repeating the above operations, the wheel loader 1 loads the objects onto the transport vehicle 200.

[0041] Similar to V-shaped loading, loading transport is an operation in which the wheel loader 1 travels with an object held in the bucket 12 and loads the object onto the transport vehicle 200. However, in loading transport, the wheel loader 1 travels a longer distance than in V-shaped loading. Low-load traveling is an operation in which the wheel loader 1 travels in a low-load state. For example, low-load traveling is an operation in which the wheel loader 1 travels a long distance in an empty state in which the bucket 12 is not holding an object.

[0042] In step S102, the controller 47 determines whether the current work mode is load transportation. If the current work mode is load transportation, in step S103, the controller 47 controls the transmission 27 to maintain the gear ratio at the second speed stage. The controller 47 also prohibits switching from the second speed stage to another speed stage. Therefore, while the current work mode is load transportation, the gear ratio of the transmission 27 is fixed at the second speed stage.

[0043] In the wheel loader 1 according to the present embodiment described above, when the current work mode is load transport, the gear ratio of the transmission 27 is maintained in the second speed stage, and changing from the second speed stage to another speed stage is prohibited. This reduces the occurrence of gear change shock by the transmission 27, thereby preventing the load from spilling out of the work implement 5 during load transport. Furthermore, maintaining the gear ratio in the second speed stage ensures maximum tractive force and maximum speed suitable for load transport.

[0044] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0045] The configuration of the wheel loader 1 is not limited to that of the above embodiment and may be modified. For example, the work implement pump 25 and the traveling body 6 may be driven by a common motor. The number of speed stages of the transmission 27 is not limited to three, and may be less than three or more than three. The wheel loader 1 may be operable remotely. In that case, the above-mentioned operating devices 51-55 and input device 56 may be arranged external to the wheel loader 1.

[0046] The processing by the controller 47 described above may be distributed and executed by multiple controllers. The speed change control of the transmission 27 is not limited to that in the above embodiment and may be changed. For example, when the current work mode is cargo transport, the controller 47 may maintain the gear ratio of the transmission 27 at a speed other than second speed.

[0047] The method of acquiring the current work mode is not limited to that of the above embodiment and may be modified. For example, Fig. 7 is a flowchart showing processing for speed change control of the transmission 27 according to a modified example. As shown in Fig. 7, in step S201, the controller 47 acquires running condition data. The running condition data indicates the running condition of the wheel loader 1. The running condition data includes, for example, the output rotation speed of the travel motor 24 and the vehicle speed.

[0048] In step S202, the controller 47 acquires load data of the work implement 5. The load data of the work implement 5 indicates the load on the work implement 5. The load data of the work implement 5 includes, for example, the discharge pressure of the work implement pump 25, the bottom pressure of the boom cylinder 13, and the bottom pressure of the bucket cylinder 14.

[0049] In step S203, the controller 47 acquires attitude data of the work implement 5. The attitude data of the work implement 5 indicates the attitude of the work implement 5. The attitude data of the work implement 5 includes, for example, a boom angle and a bucket angle.

[0050] In step S204, the controller 47 acquires operation status data. The operation status data indicates operations on the above-mentioned operation devices 51-55. The operation status data includes, for example, the accelerator operation amount, the FNR position, the operation position of the steering operation device 53, the operation position of the work machine operation device 54, and the selected gear ratio.

[0051] In step S205, the controller 47 determines the current work being performed by the wheel loader 1. The controller 47 determines the current work based on the above-mentioned traveling state data, load data of the work implement 5, attitude data of the work implement 5, and operation state data. The controller 47 determines the current work being performed by the wheel loader 1 from a plurality of works including heavy excavation, V-shaped loading, loading and transport, and low-load traveling.

[0052] For example, the controller 47 determines whether the bucket 12 is in an empty state based on the bottom pressure of the boom cylinder 13. The controller 47 determines that the bucket 12 has transitioned from an empty state to a loading and conveying state when the bottom pressure of the boom cylinder 13 becomes equal to or greater than a predetermined pressure and the boom angle becomes equal to or greater than horizontal and equal to or less than a predetermined angle. The controller 47 also determines that the work machine 1 has transitioned to a loading and conveying state when the traveling direction of the work machine 1 is changed from an excavating state to reverse. For example, the controller 47 determines that the work machine 1 is in an excavating state when the traveling direction is forward, the boom angle is equal to or less than horizontal, and the bottom pressure of the bucket cylinder 14 is equal to or greater than a predetermined pressure.

[0053] In step S206, the controller 47 determines the current work mode. The controller 47 determines the work mode according to the current work determined in step S205 as the current work mode.

[0054] In step S207, similar to step S102 described above, the controller 47 determines whether the current operation mode is cargo transport. If the current operation mode is cargo transport, in step S208, similar to step S103 described above, the controller 47 controls the transmission 27 to maintain the gear ratio at the second speed stage. In addition, the controller 47 prohibits switching from the second speed stage to another speed stage.

[0055] In the speed change control of the transmission 27 according to the modified example described above, as in the above-described embodiment, when the current work mode is load transport, the gear ratio of the transmission 27 is maintained in the second speed stage, and a change from the second speed stage to another speed stage is prohibited. This reduces the occurrence of gear change shock by the transmission 27, thereby preventing the load from spilling from the work implement 5 during load transport. Furthermore, maintaining the gear ratio in the second speed stage ensures maximum tractive force and maximum speed suitable for load transport.

[0056] According to the present disclosure, the occurrence of gear shift shocks can be reduced in a wheel loader when transporting a load.

[0057] 2: Vehicle body 5: Work machine 6: Running body 24: Running motor 27: Transmission 47: Controller 56: Input device

Claims

1. A wheel loader comprising: a vehicle body including a running body and a work machine; an electric motor mounted on the vehicle body; a transmission mounted on the vehicle body, the gear ratio of which can be changed among a plurality of speed stages, and which transmits driving force from the electric motor to the running body; and a controller controlling the transmission, wherein the controller obtains a current work mode from a plurality of work modes corresponding to the type of work performed by the vehicle body, and when the current work mode is load transportation, maintains the gear ratio of the transmission at a predetermined speed stage, and prohibits changing from the predetermined speed stage to another speed stage.

2. The wheel loader according to claim 1, further comprising an input device that is manually operable and that is used to select the current work mode from the plurality of work modes, and the controller acquires the work mode selected by the input device as the current work mode.

3. The wheel loader according to claim 1, wherein the controller determines a current operation being performed by the vehicle body, and determines an operation mode corresponding to the current operation as the current operation mode.

4. A method for controlling a wheel loader which includes a running body, a work machine, an electric motor, and a transmission, the transmission having a speed ratio that can be changed among a plurality of speed stages, and which transmits driving force from the electric motor to the running body, comprising: obtaining a current work mode from a plurality of work modes corresponding to the type of work performed by the wheel loader; and if the current work mode is load transportation, maintaining the gear ratio of the transmission at a predetermined speed stage, and prohibiting changing to a speed stage other than the predetermined speed stage.

5. The method of claim 4, comprising: receiving a signal from an input device, the input device being manually operable for selecting the current work mode from the plurality of work modes; and obtaining the work mode selected by the input device as the current work mode.

6. The method of claim 4, comprising: determining a current operation being performed by the wheel loader; and determining an operation mode corresponding to the current operation as the current operation mode.

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