System and method for controlling work machine having continuously variable transmission

Abstract

A system according to one aspect of the present disclosure is a system for controlling a work machine having a continuously variable transmission. The system according to the aspect comprises a shift operation member and a controller. The shift operation member can be operated by an operator. The controller shifts up the virtual gear ratio of the continuously variable transmission at a predetermined increase rate in response to a first shift-up operation on the shift operation member. The controller shifts up the virtual gear ratio of the continuously variable transmission to a preset gear ratio determined in advance in response to a second shift-up operation on the shift operation member.

Description

System and method for controlling a work machine having a continuously variable transmission

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to systems and methods for controlling a work machine having a continuously variable transmission.

[0002] Conventionally, there are known work machines in which the virtual gear ratio of a continuously variable transmission can be shifted by operating an operating member. For example, a bulldozer disclosed in Patent Document 1 is equipped with a shift mode selector switch, a shift-up switch, and a shift-down switch. The shift mode selector switch is operated to switch between a quick shift mode and a continuously variable shift mode.

[0003] In quick shift mode, the controller shifts up one gear when the upshift switch is pressed, and shifts down one gear when the downshift switch is pressed. In continuously variable shift mode, the gears are set more precisely than in quick shift mode. In continuously variable shift mode, the controller shifts up one gear for the duration that the upshift switch is pressed, and shifts down one gear for the duration that the downshift switch is pressed.

[0004] Patent No. 4956001

[0005] In the above-described work machine, the quick shift mode and the continuously variable shift mode make it easy to change gears in the continuously variable transmission. However, there is a demand for making the gear change operation of the continuously variable transmission even easier. An object of the present disclosure is to make the gear change operation of the continuously variable transmission easier.

[0006] A system according to one aspect of the present disclosure is a system for controlling a work machine having a continuously variable transmission. The system according to this aspect includes a shift operation member and a controller. The shift operation member is operable by an operator. The controller upshifts a virtual gear ratio of the continuously variable transmission at a predetermined increase rate in response to a first upshift operation of the shift operation member. The controller upshifts the virtual gear ratio of the continuously variable transmission to a predetermined preset gear ratio in response to a second upshift operation of the shift operation member.

[0007] A method according to another aspect of the present disclosure is a method for controlling a work machine having a continuously variable transmission, the method including receiving an operation signal indicative of an operation of a shift operating member operable by an operator, upshifting a virtual gear ratio of the continuously variable transmission at a predetermined increase rate in response to a first upshift operation of the shift operating member, and upshifting the virtual gear ratio of the continuously variable transmission to a predetermined preset gear ratio in response to a second upshift operation of the shift operating member.

[0008] According to the present disclosure, a first upshift operation of the shift operating member allows for fine upshifts of the virtual gear ratio at a predetermined rate of increase, and a second upshift operation of the shift operating member allows for quick upshifts to a predetermined preset gear ratio, thereby facilitating gear shifting operations of the continuously variable transmission.

[0009] 1 is a side view showing a work machine according to an embodiment. FIG. 2 is a block diagram showing the configuration of a drive system and a control system of the work machine. FIG. 3 is a perspective view of a travel operation device. FIG. 4 is a diagram showing an example of set vehicle speed data. FIG. 5 is an enlarged view of a shift operation member. FIG. 6 is a diagram showing the relationship between the stroke amount of the shift operation member and the operation reaction force. FIG. 7 is a diagram showing changes in the shift display when upshifting in the first shift mode. FIG. 8 is a diagram showing changes in the shift display when upshifting in the first shift mode. FIG. 9 is a diagram showing changes in the shift display when upshifting in the first shift mode. FIG. 10 is a diagram showing changes in the shift display when upshifting in the second shift mode. FIG. 11 is a diagram showing changes in the shift display when upshifting in the second shift mode. FIG. 12 is a diagram showing changes in the shift display when downshifting in the first shift mode. FIG. 13 is a diagram showing changes in the shift display when downshifting in the first shift mode. FIG. 14 is a diagram showing changes in the shift display when downshifting in the second shift mode. FIG. 15 is a diagram showing changes in the shift display when downshifting in the second shift mode. FIG. 16 is a diagram showing changes in the shift display when downshifting in the second shift mode. FIG. 17 is a diagram showing changes in the shift display when downshifting in the second shift mode. FIG. 10 is a diagram showing a change in the shift display when upshifting in the second shift mode after changing the preset gear ratio; FIG. 11 is a diagram showing a change in the shift display when upshifting in the second shift mode after changing the preset gear ratio; FIG. 12 is a diagram showing a change in the shift display when upshifting in the second shift mode after changing the preset gear ratio; FIG. 13 is a diagram showing a change in the shift display when downshifting in the second shift mode after changing the preset gear ratio; FIG. 14 is a diagram showing a change in the shift display when downshifting in the second shift mode after changing the preset gear ratio;

[0010] A work machine according to an embodiment will be described below with reference to the drawings. Figure 1 is a side view showing a work machine 1 according to an embodiment. The work machine 1 according to this embodiment is a bulldozer. The work machine 1 comprises a vehicle body 11 and a work implement 12.

[0011] The vehicle body 11 includes a cab 13 and a traveling device 15. A driver's seat (not shown) is disposed in the cab 13. The traveling device 15 is provided on the lower part of the vehicle body 11. The traveling device 15 includes a pair of left and right tracks 16. Note that only the left track 16 is shown in FIG. 1. The work machine 1 travels as the tracks 16 rotate.

[0012] The work machine 12 is attached to the vehicle body 11. The work machine 12 has a lift frame 17, a blade 18, and a lift actuator 19. The lift frame 17 is supported on the vehicle body 11 so as to be able to rotate up and down. The blade 18 is supported by the lift frame 17. The lift actuator 19 is a hydraulic cylinder. The blade 18 moves up and down as the lift actuator 19 extends and retracts.

[0013] Figure 2 is a block diagram showing the configuration of the drive system 2 and control system 3 of the work machine 1. As shown in Figure 2, the drive system 2 includes a drive source 22, a hydraulic pump 23, and a continuously variable transmission 24. The drive source 22 includes, for example, an internal combustion engine. The drive source 22 may also include an electric motor. The hydraulic pump 23 is driven by the drive source 22 and discharges hydraulic oil. The hydraulic oil discharged from the hydraulic pump 23 is supplied to the lift actuator 19 via a control valve 25. Note that although Figure 2 shows one hydraulic pump 23, multiple hydraulic pumps may be provided.

[0014] The continuously variable transmission 24 transmits the driving force of the drive source 22 to the traveling device 15. The continuously variable transmission 24 is capable of continuously and infinitely changing the gear ratio. The continuously variable transmission 24 is, for example, an HST (Hydro Static Transmission). The continuously variable transmission 24 includes a hydraulic pump 26 and a hydraulic motor 27. The hydraulic pump 26 is driven by the drive source 22 and discharges hydraulic oil. The hydraulic motor 27 is driven by the hydraulic oil discharged from the hydraulic pump 26. The hydraulic motor 27 is connected to the traveling device 15. The hydraulic motor 27 drives the traveling device 15, causing the work machine 1 to travel. The gear ratio of the continuously variable transmission 24 is continuously and infinitely changed by changing the capacity of the hydraulic pump 26 and the capacity of the hydraulic motor 27.

[0015] The control system 3 includes a controller 30. The controller 30 is programmed to control the work machine 1 based on the acquired data. The controller 30 includes a storage device 31 and a processor 32. The processor 32 includes, for example, a CPU. The storage device 31 includes, for example, a memory and an auxiliary storage device. The storage device 31 may be, for example, a RAM or a ROM. The storage device 31 may be, for example, a semiconductor memory or a hard disk. The storage device 31 stores computer instructions that are executable by the processor 32 and are used to control the work machine 1.

[0016] The control system 3 includes an input device 33 and a display 34. The input device 33 can be operated by an operator to make control settings for the work machine 1. The input device 33 may be a touch screen. Alternatively, the input device 33 may include other devices such as switches. The input device 33 outputs an input signal indicating an operation by the operator to the controller 30. The display 34 displays an image according to an image signal from the controller 30.

[0017] The control system 3 includes a work implement operating device 35 and a travel operating device 36. The work implement operating device 35 can be operated by an operator to operate the work implement 12. The work implement operating device 35 includes, for example, a work implement lever. However, the work implement operating device 35 may include other components such as a switch. The work implement operating device 35 outputs a work command in response to the operator's operation to the controller 30. The controller 30 controls the control valve 25 in response to the work command from the work implement operating device 35 so as to operate the work implement 12. As a result, the work implement 12 moves up and down in response to the operator's operation of the work implement operating device 35.

[0018] Figure 3 is a perspective view of the travel operation device 36. As shown in Figure 3, the travel operation device 36 includes a travel lever 37 and a shift operation member 38. The travel lever 37 can be operated by the operator to control the forward and reverse movement of the work machine 1. The travel operation device 36 outputs a travel command to the controller 30 in response to the operation of the travel lever 37 by the operator. The controller 30 controls the drive source 22 and the continuously variable transmission 24 in response to the travel command from the travel operation device 36 so as to cause the work machine 1 to travel. As a result, the work machine 1 moves forward or reverse in response to the operation of the travel operation device 36 by the operator. The travel operation device 36 may also include a brake pedal (not shown).

[0019] The shift operating member 38 is operable to change the virtual gear ratio of the continuously variable transmission 24. The travel operating device 36 outputs a gear shift signal in response to the operator's operation of the shift operating member 38. The controller 30 receives the gear shift signal. The controller 30 changes the virtual gear ratio of the continuously variable transmission 24 among a plurality of virtual gear ratios in response to the gear shift signal from the travel operating device 36. As a result, the continuously variable transmission 24 changes its virtual gear ratio in response to the operator's operation of the shift operating member 38.

[0020] The virtual gear ratio is a gear ratio set by the controller 30. For example, the controller 30 sets a plurality of virtual gear ratios including 1.0, 2.0, and 3.0. The controller 30 controls the vehicle speed of the work machine 1 according to the virtual gear ratio set by operating the shift operating member 38. For example, FIG. 4 is a diagram showing an example of set vehicle speed data that defines the relationship between the set virtual gear ratio and the vehicle speed of the work machine 1. The set vehicle speed is the vehicle speed obtained at a specified engine rotation speed (e.g., high idle rotation speed) under a specified traveling load state. The specified traveling condition is, for example, a state in which the work machine 1 is traveling on a flat road surface with hard, compacted soil and no incline, and the work implement 12 is not performing earthwork, towing, or the like. The operator can travel the work machine 1 at a desired vehicle speed by selecting a virtual gear ratio. The controller 30 references the set vehicle speed data and sets the vehicle speed of the work machine 1 based on the set virtual gear ratio. The controller 30 controls the gear ratio of the continuously variable transmission 24 based on the set vehicle speed.

[0021] As shown in FIG. 4 , the controller 30 stores virtual gear ratios that change at a predetermined rate between 0 speed (neutral) and 3.0 speed. In this embodiment, the predetermined rate is 0.1. For example, the controller 30 stores multiple virtual gear ratios that change in increments of 0.1 between 0 speed and 3.0 speed. In this embodiment, the number of virtual gear ratios is 30, ranging from 0.1 speed to 3.0 speed.

[0022] The controller 30 performs shift control of the virtual gear ratio of the continuously variable transmission 24 in a plurality of modes in response to operation of the shift operating member 38. The plurality of modes include a first shift mode and a second shift mode. In the first shift mode, the controller 30 shifts the virtual gear ratio of the continuously variable transmission 24 at the predetermined change rate (0.1) described above. In the second shift mode, the controller 30 shifts the virtual gear ratio of the continuously variable transmission 24 to a preset gear ratio. The preset gear ratio is a pre-set virtual gear ratio that can be adjusted by an operator operating the input device 33. Note that, as will be described in detail later, in this embodiment, 0.1, 1.0, 2.0, and 3.0 are pre-stored in the controller 30 as initial values ​​of the preset gear ratios.

[0023] The following describes shift control of the virtual gear ratio of the continuously variable transmission 24 in response to operation of the shift operating member 38. FIG. 5 is an enlarged view of the shift operating member 38. The shift operating member 38 is rotatably attached to the travel lever 37. The shift operating member 38 is movable in an upshift direction and a downshift direction from a neutral position N1. The shift operating member 38 is a momentary switch. That is, when not operated, the shift operating member 38 returns to the neutral position N1. As shown in FIG. 3, the shift operating member 38 can be operated with the fingertip (thumb tip) of an operator with their hand on the travel lever 37.

[0024] The shift operating member 38 can be operated between a neutral range, a first range, a second range, a third range, and a fourth range. The neutral range is a range that includes the neutral position N1. The first range is a range in which the stroke amount in the upshift direction is greater than that of the neutral range. The second range is a range in which the stroke amount in the upshift direction is greater than that of the first range. The third range is a range in which the stroke amount in the downshift direction is greater than that of the neutral range. The fourth range is a range in which the stroke amount in the downshift direction is greater than that of the third range.

[0025] The shift operating member 38 is biased by a biasing member (not shown) to generate an actuation reaction force corresponding to the stroke amount. FIG. 6 is a diagram illustrating the relationship between the stroke amount of the shift operating member 38 and the actuation reaction force. As shown in FIG. 6 , when the stroke amount of the shift operating member 38 in the upshift direction increases from the neutral range to a first stroke amount S1 within a first range, the actuation reaction force increases at a first increasing rate. When the stroke amount of the shift operating member 38 in the upshift direction increases from the first stroke amount S1 to a second stroke amount S2 within the first range, the actuation reaction force increases at a second increasing rate. The second increasing rate is greater than the first increasing rate. After the stroke amount of the shift operating member 38 in the upshift direction exceeds the second stroke amount S2, the actuation reaction force increases at a third increasing rate. The third increasing rate is smaller than the second increasing rate. The third increasing rate is greater than the first increasing rate.

[0026] Therefore, when the operator operates the shift operating member 38 in the upshift direction, the operator feels a greater resistance due to an increase in the rate of increase in the operation reaction force when the shift operating member 38 is operated from the neutral range to the first range. Then, when the shift operating member 38 is operated beyond the first range to the second range, the operator feels a change in resistance due to a decrease in the rate of increase in the operation reaction force. This allows the operator to easily distinguish between the first range and the second range when operating the shift operating member 38 in the upshift direction.

[0027] Additionally, when the stroke amount of the shift operating member 38 in the downshift direction is from the neutral range to a third stroke amount S3 within the third range, the operation reaction force increases at a first increasing rate. When the stroke amount of the shift operating member 38 in the downshift direction is from the third stroke amount S3 to a fourth stroke amount S4 within the third range, the operation reaction force increases at a second increasing rate. After the stroke amount of the shift operating member 38 in the downshift direction exceeds the fourth stroke amount S4, the operation reaction force increases at a third increasing rate.

[0028] Therefore, when the operator operates the shift operating member 38 in the downshift direction, the operator feels a greater resistance due to an increase in the rate of increase in the operation reaction force when the shift operating member 38 is operated from the neutral range to the third range. Then, when the shift operating member 38 is operated beyond the third range to the fourth range, the operator feels a change in resistance due to a decrease in the rate of increase in the operation reaction force. This allows the operator to easily distinguish between the third range and the fourth range when operating the shift operating member 38 in the downshift direction.

[0029] The controller 30 performs shift control in a first shift mode or a second shift mode depending on the stroke amount of the shift operating member 38. Figures 7A to 7C and 8A to 8C are diagrams showing a shift indicator 40 displayed on the display 34 by the controller 30. Figures 7A to 7C and 8A to 8C show the shift indicator 40 when moving forward. As shown in Figures 7A to 7C and 8A to 8C, the shift indicator 40 includes preset indicators 41A-41D, a first shift indicator 42, and a second shift indicator 43.

[0030] The preset displays 41A-41D indicate preset gear ratios. The preset gear ratios are pre-set virtual gear ratios that can be adjusted by the operator operating the input device 33. In this embodiment, the preset gear ratios include a first preset gear ratio, a second preset gear ratio, a third preset gear ratio, and a fourth preset gear ratio. In this embodiment, the initial values ​​of the first to fourth preset gear ratios are set to 0.1, 1.0, 2.0, and 3.0, respectively. The preset displays 41A-41D include first to fourth preset displays 41A-41D. The first preset display 41A indicates the first preset gear ratio. The second preset display 41B indicates the second preset gear ratio. The third preset display 41C indicates the third preset gear ratio. The fourth preset display 41D indicates the fourth preset gear ratio. 7A to 7C and 8A to 8C, the first preset display 41A shows 0.1 speed as the initial value of the first preset gear ratio. The second preset display 41B shows 1.0 speed as the initial value of the second preset gear ratio. The third preset display 41C shows 2.0 speed as the initial value of the third preset gear ratio. The fourth preset display 41D shows 3.0 speed as the initial value of the fourth preset gear ratio. Note that in this embodiment, the controller 30 stores four preset gear ratios, but the number of preset gear ratios is not limited to four. The number of preset gear ratios may be more or less than four.

[0031] The first shift indicator 42 and the second shift indicator 43 indicate the current virtual gear ratio of the continuously variable transmission 24. The first shift indicator 42 includes a plurality of indicators 44. Note that in the drawings, only one of the plurality of indicators 44 is denoted by the reference numeral 44, and the reference numerals of the other indicators 44 are omitted.

[0032] One of the indicators 44 indicates a predetermined rate of change of the virtual gear ratio described above. That is, in this embodiment, one of the indicators 44 indicates a rate of change of 0.1 of the virtual gear ratio. The number of indicators 44 corresponds to the number of virtual gear ratios. The first shift indicator 42 indicates the current virtual gear ratio by the number of indicators displayed. The second shift indicator 43 indicates the current virtual gear ratio numerically. In the example shown in FIG. 7A , the current virtual gear ratio is 1.0.

[0033] 7A to 7C show the change in the shift indicator 40 when a gear shift is performed in the first shift mode during forward travel. The letter "F" in the displays in FIGS. 7A to 7C indicates forward travel, and "R" is displayed instead of "F" during reverse travel. When the shift operating member 38 is operated from the neutral range to the first range (hereinafter referred to as the first upshift operation), the controller 30 upshifts the virtual gear ratio of the continuously variable transmission 24 at a predetermined rate of increase in the first shift mode. The predetermined rate of increase is equal to the aforementioned rate of change of 0.1. Therefore, when the first upshift operation is performed on the shift operating member 38, the controller 30 increases the virtual gear ratio by 0.1. For example, when the shift operating member 38 returns from the first range to the neutral range after the first upshift operation, the controller 30 upshifts the virtual gear ratio at the predetermined rate of increase. Alternatively, the controller 30 upshifts the virtual gear ratio at a predetermined rate when the shift operating member 38 is held in the first range for a predetermined time after a first upshift operation is performed on the shift operating member 38. The controller 30 increments the indicator 44 displayed on the first shift indicator 42 by one in response to the upshift of the virtual gear ratio.

[0034] For example, as shown in Fig. 7A , if a first upshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 1.0, the controller 30 upshifts the virtual gear ratio to 1.1, as shown in Fig. 7B . If a first upshift operation is performed on the shift operating member 38 when the virtual gear ratio is 1.1, as shown in Fig. 7B , the controller 30 upshifts the virtual gear ratio to 1.2, as shown in Fig. 7C . Similarly, each time a first upshift operation is performed on the shift operating member 38, the controller 30 increases the virtual gear ratio by 0.1 until it reaches the maximum virtual gear ratio of 3.0.

[0035] Although not shown, when the virtual gear ratio is between the first preset gear ratio and the second preset gear ratio, the controller 30 similarly increases the virtual gear ratio by 0.1 each time a first upshift operation is performed on the shift operating member 38. Similarly, when the virtual gear ratio is between the third preset gear ratio and the fourth preset gear ratio, the controller 30 similarly increases the virtual gear ratio by 0.1 each time a first upshift operation is performed on the shift operating member 38.

[0036] 8A to 8C show changes in the shift display 40 in the second shift mode. When the shift operating member 38 is operated into the second range (hereinafter referred to as a second upshift operation), the controller 30 upshifts the virtual gear ratio of the continuously variable transmission 24 to a higher preset gear ratio in the second shift mode. The higher preset gear ratio is a preset gear ratio that is closest to the current virtual gear ratio and is greater than the current virtual gear ratio.

[0037] For example, as shown in Fig. 8A, if a second upshift operation is performed on the shift operating member 38 when the current virtual gear ratio is the second preset gear ratio or between the second and third preset gear ratios, the controller 30 upshifts the virtual gear ratio to the third preset gear ratio, which is a higher preset gear ratio, as shown in Fig. 8B. Specifically, as shown in Fig. 8A, if a second upshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 1.2, the controller 30 upshifts the virtual gear ratio to 2.0 as shown in Fig. 8B.

[0038] As shown in Fig. 8B, when a second upshift operation is performed on the shift operating member 38 while the current virtual gear ratio is the third preset gear ratio or between the third and fourth preset gear ratios, the controller 30 upshifts the virtual gear ratio to the fourth preset gear ratio, which is a higher preset gear ratio, as shown in Fig. 8C. Specifically, as shown in Fig. 8B, when a second upshift operation is performed on the shift operating member 38 while the current virtual gear ratio is 2.0, the controller 30 upshifts the virtual gear ratio to 3.0 as shown in Fig. 8C.

[0039] Although not shown, even when the virtual gear ratio is the first preset gear ratio or between the first and second preset gear ratios, if a second upshift operation is performed on the shift operating member 38, the controller 30 will upshift the virtual gear ratio to the second preset gear ratio in the same manner as described above. In other words, if the virtual gear ratio is between 0.1 and 0.9 speeds and a second upshift operation is performed on the shift operating member 38, the controller 30 will upshift the virtual gear ratio to 1.0 speed.

[0040] Next, a downshift operation will be described. When the shift operating member 38 is operated from the neutral range to the third range (hereinafter referred to as a first downshift operation), the controller 30 downshifts the virtual gear ratio of the continuously variable transmission 24 at a predetermined rate of decrease in the first shift mode. The predetermined rate of decrease is equal to the rate of change described above. Therefore, when a first downshift operation is performed on the shift operating member 38, the controller 30 decreases the virtual gear ratio by 0.1. For example, the controller 30 downshifts the virtual gear ratio at a predetermined rate of decrease when the shift operating member 38 returns from the third range to the neutral range after a first downshift operation is performed on the shift operating member 38. Alternatively, the controller 30 downshifts the virtual gear ratio at a predetermined rate of decrease when the shift operating member 38 is held in the third range for a predetermined time after a first downshift operation is performed on the shift operating member 38. The controller 30 decreases the indicator displayed on the first shift indicator 42 by one in response to the downshift of the virtual gear ratio.

[0041] For example, as shown in Fig. 9A , when the current virtual gear ratio is 3.0 and a first downshift operation is performed with the shift operating member 38, the controller 30 downshifts the virtual gear ratio to 2.9, as shown in Fig. 9B . When the virtual gear ratio is 2.9 and a first downshift operation is performed with the shift operating member 38, as shown in Fig. 9B , the controller 30 downshifts the virtual gear ratio to 2.8, as shown in Fig. 9C . Similarly, the controller 30 decreases the virtual gear ratio by 0.1 each time a first downshift operation is performed with the shift operating member 38.

[0042] Although not shown, similarly, between the third preset gear ratio and the second preset gear ratio, the controller 30 decreases the virtual gear ratio by 0.1 each time a first downshift operation is performed on the shift operating member 38. Similarly, when the virtual gear ratio is between the second preset gear ratio and the first preset gear ratio, the controller 30 decreases the virtual gear ratio by 0.1 each time a first downshift operation is performed on the shift operating member 38, until the virtual gear ratio reaches 0.1 speed, which is the minimum virtual gear ratio.

[0043] 10A to 10C show changes in the shift display 40 in the second shift mode. When the shift operating member 38 is operated into the fourth range (hereinafter referred to as a second downshift operation), the controller 30 downshifts the virtual gear ratio of the continuously variable transmission 24 to a lower preset gear ratio in the second shift mode. The lower preset gear ratio is a preset gear ratio that is closest to the current virtual gear ratio and is smaller than the current virtual gear ratio.

[0044] For example, as shown in Fig. 10A, if a second downshift operation is performed on the shift operating member 38 when the current virtual gear ratio is the fourth preset gear ratio or between the fourth preset gear ratio and the third preset gear ratio, the controller 30 downshifts the virtual gear ratio to the third preset gear ratio, which is a lower preset gear ratio, as shown in Fig. 10B. Specifically, as shown in Fig. 10A, if a second downshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 2.8 speed, the controller 30 downshifts the virtual gear ratio to 2.0 speed, as shown in Fig. 10B.

[0045] As shown in Fig. 10B , when a second downshift operation is performed on the shift operating member 38 while the current virtual gear ratio is the third preset gear ratio or between the third preset gear ratio and the second preset gear ratio, the controller 30 downshifts the virtual gear ratio to the second preset gear ratio, which is a lower preset gear ratio, as shown in Fig. 10C . Specifically, as shown in Fig. 10B , when a second downshift operation is performed on the shift operating member 38 while the current virtual gear ratio is 2.0, the controller 30 downshifts the virtual gear ratio to 1.0 as shown in Fig. 10C .

[0046] Although not shown, if a second downshift operation is performed on the shift operating member 38 when the current virtual gear ratio is the second preset gear ratio or between the second preset gear ratio and the first preset gear ratio, the controller 30 downshifts the virtual gear ratio to the first preset gear ratio. In other words, if a second downshift operation is performed on the shift operating member 38 when the current virtual gear ratio is between 0.2 and 1.0, the controller 30 downshifts the virtual gear ratio to 0.1. While the shift control during forward travel has been described above, the controller 30 also performs the same shift control during reverse travel.

[0047] As described above, the initial values ​​of the preset gear ratios in the second shift mode are 0.1, 1.0, 2.0, and 3.0, but these values ​​can be changed. That is, the preset gear ratios can be changed by the operator operating the input device 33. Figure 11 is a diagram showing a preset gear ratio setting screen 50. The controller 30 displays the preset gear ratio setting screen 50 on the display 34.

[0048] As shown in FIG. 11 , the preset gear ratio setting screen 50 includes a shift range display 51, preset displays 52A-52D, and gear displays 53A-53D. The shift range display 51 shows the entire range of virtual gear ratios of the continuously variable transmission 24. The shift range display 51 includes multiple indicators 54. The number of the multiple indicators 54 corresponds to the number of virtual gear ratios. One of the multiple indicators 54 indicates a predetermined rate of change of the virtual gear ratio described above. That is, in this embodiment, one of the multiple indicators 54 indicates a rate of change of 0.1 of the virtual gear ratio. In this embodiment, 30 indicators 54 are displayed corresponding to the 30 virtual gear ratios.

[0049] The preset displays 52A-52D indicate preset gear ratios. The preset displays 52A-52D are indicated by icons. The positions of the preset displays 52A-52D relative to the shift range display 51 indicate the preset gear ratio that has been set. The preset displays 52A-52D include first to fourth preset displays 52A-52D. The first preset display 52A indicates the first preset gear ratio. The second preset display 52B indicates the second preset gear ratio. The third preset display 52C indicates the third preset gear ratio. The fourth preset display 52D indicates the fourth preset gear ratio.

[0050] The preset gear ratios can be changed within a variable range set for each preset gear ratio. In FIG. 11, arrows 55A-55D indicate the variable range set for each preset gear ratio. The operator sets each preset gear ratio by operating the input device 33 to move the preset indicators 52A-52D on the setting screen 50 within the variable range 55A-55D.

[0051] The gear displays 53A-53D indicate each preset gear ratio that has been set as a numerical value. The gear displays 53A-53D include a first gear display 53A, a second gear display 53B, a third gear display 53C, and a fourth gear display 53D. The first gear display 53A indicates the first preset gear ratio as a numerical value. The second gear display 53B indicates the second preset gear ratio as a numerical value. The third gear display 53C indicates the third preset gear ratio as a numerical value. The fourth gear display 53D indicates the fourth preset gear ratio as a numerical value.

[0052] The shift range display 51, preset displays 52A-52D, gear displays 53A-53D, and variable ranges 55A-55D of the preset gear ratio setting screen 50 described above are displays for forward travel. The preset gear ratio setting screen 50 also includes a shift range display 56, preset displays 57A-57D, gear displays 58A-58D, and variable ranges 59A-59D for reverse travel. The shift range display 56, preset displays 57A-57D, gear displays 58A-58D, and variable ranges 59A-59D for reverse travel are similar to the shift range display 51, preset displays 52A-52D, gear displays 53A-53D, and variable ranges 55A-55D for forward travel, respectively, and therefore detailed description thereof will be omitted.

[0053] For example, as shown in Fig. 12, the operator operates the input device 33 to move the third preset indicator 52C. In this way, the operator changes the third preset gear ratio. For example, the operator changes the third preset gear ratio from the initial value of 2.0 speed shown in Fig. 11 to 1.7 speed shown in Fig. 12. In this case, the position of the third preset indicator 41C on the shift indicator 40 is changed as shown in Figs. 13A to 13C.

[0054] The controller 30 performs shift control in the second shift mode described above based on the changed preset gear ratio. For example, as shown in FIG. 13A , if a second upshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 1.0 or between 1.0 and 1.6, the controller 30 upshifts the virtual gear ratio to 1.7 as shown in FIG. 13B . Also, as shown in FIG. 13C , if a second upshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 1.7 or between 1.7 and 3.0, the controller 30 upshifts the virtual gear ratio to 3.0.

[0055] Similarly, for downshifts, the controller 30 performs shift control in the second shift mode described above based on the changed preset gear ratio. For example, as shown in FIG. 14 , if a second downshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 3.0 or between 1.7 and 3.0, the controller 30 downshifts the virtual gear ratio to 1.7 as shown in FIG. 14B . Also, if a second downshift operation is performed on the shift operating member 38 when the current virtual gear ratio is 1.7 or between 1.0 and 1.7, the controller 30 downshifts the virtual gear ratio to 1.0 as shown in FIG. 14C .

[0056] In the work machine 1 according to the present embodiment described above, the virtual gear ratio increases by a predetermined increase rate with a first upshift operation to the shift operating member 38. Therefore, the operator can finely upshift the virtual gear ratio at the predetermined increase rate by repeating the first upshift operation to the shift operating member 38. Furthermore, the virtual gear ratio jumps up to the preset gear ratio with a second upshift operation to the shift operating member 38. Therefore, the operator can quickly upshift to the preset gear ratio with the second upshift operation to the shift operating member 38. This makes it easier to change gears in the continuously variable transmission 24.

[0057] A first downshift operation of the shift operating member 38 decreases the virtual gear ratio by a predetermined decrease rate. Therefore, by repeating the first downshift operation of the shift operating member 38, the operator can finely downshift the virtual gear ratio at the predetermined decrease rate. Furthermore, a second downshift operation of the shift operating member 38 causes the virtual gear ratio to jump up to the preset gear ratio. Therefore, the operator can quickly downshift to the preset gear ratio by the second downshift operation of the shift operating member 38. This makes it easier to perform gear changes in the continuously variable transmission 24.

[0058] 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.

[0059] The work machine 1 is not limited to a bulldozer, and may be other vehicles such as a wheel loader or a motor grader. The work machine 1 may be remotely operable. In that case, the operation devices 35, 36, the input device 33, and the display 34 may be located outside the work machine 1. The work machine 1 may have multiple controllers that are separate from each other. The processing by the controller 30 described above may be distributed and executed by multiple controllers. The continuously variable transmission 24 is not limited to an HST, and may be another transmission such as an HMT (Hydro Mechanical Transmission) or an EMT (Electric-Mechanical Transmission). Alternatively, the continuously variable transmission 24 may be a combination of a generator and an electric motor.

[0060] The structure of the shift operating member 38 is not limited to that of the above embodiment and may be modified. For example, the shift operating member 38 may be slidably attached to the travel lever 37. The shift operating member 38 may also be provided separately from the travel lever 37.

[0061] The shift control process by the controller 30 is not limited to that of the above embodiment and may be modified. For example, the predetermined rate of change is not limited to 0.1 as in the above embodiment and may be modified. The upper limit of the virtual gear ratio of the continuously variable transmission 24 is not limited to 3.0 speed and may be greater than or equal to 3.0 speed. The lower limit of the virtual gear ratio is not limited to 0.1 speed and may be 0.0 speed (i.e., vehicle speed 0).

[0062] According to the present disclosure, the gear shifting operation of a continuously variable transmission can be easily performed.

[0063] 1: Work machine, 24: Continuously variable transmission, 30: Controller, 33: Input device, 38: Shift operation member

Claims

1. A system for controlling a work machine having a continuously variable transmission, comprising: a shift operation member operable by an operator; and a controller that, in response to a first upshift operation to the shift operation member, upshifts a virtual gear ratio of the continuously variable transmission at a predetermined increase rate, and, in response to a second upshift operation to the shift operation member, upshifts the virtual gear ratio of the continuously variable transmission to a predetermined preset gear ratio.

2. The system according to claim 1, wherein the controller distinguishes between the first up-shifting operation and the second up-shifting operation based on a stroke amount of the shift operating member.

3. The system described in claim 2, wherein the shift operating member is operable between a neutral range, a first range in which the stroke amount is larger than that of the neutral range in a predetermined upshift direction, and a second range in which the stroke amount is larger than that of the first range in the upshift direction, the first upshift operation being an operation of the shift operating member from the neutral range to the first range, and the second upshift operation being an operation of the shift operating member to the second range.

4. The system described in claim 1, wherein the controller upshifts the virtual gear ratio of the continuously variable transmission between a first preset gear ratio and a second preset gear ratio at the increasing rate in response to the first upshift operation of the shift operation member, and upshifts the virtual gear ratio of the continuously variable transmission from between the first preset gear ratio and the second preset gear ratio to the second preset gear ratio in response to the second upshift operation of the shift operation member.

5. The system of claim 1, further comprising an input device operable by an operator, wherein the preset gear ratio can be changed by operating the input device.

6. The system according to claim 1, wherein the controller downshifts the virtual gear ratio of the continuously variable transmission at a predetermined rate of decrease in response to a first downshift operation to the shift operation member, and downshifts the virtual gear ratio of the continuously variable transmission to the preset gear ratio in response to a second downshift operation to the shift operation member.

7. The system according to claim 6, wherein the controller distinguishes between the first downshift operation and the second downshift operation based on a stroke amount of the shift operation member.

8. The system described in claim 7, wherein the shift operation member is operable between a neutral range, a third range in which the stroke amount is greater in a predetermined downshift direction than the neutral range, and a fourth range in which the stroke amount is greater in the downshift direction than the third range, the first downshift operation being an operation of the shift operation member from the neutral range to the third range, and the second downshift operation being an operation of the shift operation member to the fourth range.

9. The system described in claim 6, wherein the controller downshifts the virtual gear ratio of the continuously variable transmission between a first preset gear ratio and a second preset gear ratio at the reduction rate in response to the first downshift operation of the shift operating member, and downshifts the virtual gear ratio of the continuously variable transmission from between the first preset gear ratio and the second preset gear ratio to the first preset gear ratio in response to the second downshift operation of the shift operating member.

10. A method for controlling a work machine having a continuously variable transmission, comprising: receiving an operation signal indicative of an operation to a shift operating member operable by an operator; upshifting a virtual gear ratio of the continuously variable transmission at a predetermined increase rate in response to a first upshift operation to the shift operating member; and upshifting the virtual gear ratio of the continuously variable transmission to a predetermined preset gear ratio in response to a second upshift operation to the shift operating member.

11. The method according to claim 10, further comprising distinguishing between the first up-shifting operation and the second up-shifting operation based on a stroke amount of the shift operating member.

12. The method of claim 11, wherein the shift operating member is operable between a neutral range, a first range in which the stroke amount is greater than the neutral range in a predetermined upshift direction, and a second range in which the stroke amount is greater than the first range in the upshift direction, the first upshift operation being an operation of the shift operating member into the first range, and the second upshift operation being an operation of the shift operating member into the second range.

13. The method according to claim 10, comprising: upshifting a virtual gear ratio of the continuously variable transmission between a first preset gear ratio and a second preset gear ratio at the increasing rate in response to the first upshift operation of the shift operating member; and upshifting a virtual gear ratio of the continuously variable transmission from between the first preset gear ratio and the second preset gear ratio to the second preset gear ratio in response to the second upshift operation of the shift operating member.

14. The method of claim 10, comprising changing the preset gear ratio in response to an operation on an operator-operable input device.

15. The method according to claim 10, comprising: downshifting the virtual gear ratio of the continuously variable transmission at a predetermined rate of decrease in response to a first downshift operation on the shift operating member; and downshifting the virtual gear ratio of the continuously variable transmission to the preset gear ratio in response to a second downshift operation on the shift operating member.

16. The method according to claim 15, further comprising distinguishing between the first downshift operation and the second downshift operation based on a stroke amount of the shift operating member.

17. The method of claim 16, wherein the shift operating member is operable between a neutral range, a third range in which the stroke amount is greater in a predetermined downshift direction than the neutral range, and a fourth range in which the stroke amount is greater in the downshift direction than the third range, the first downshift operation being an operation of the shift operating member to the third range, and the second downshift operation being an operation of the shift operating member to the fourth range.

18. The method of claim 15, comprising: downshifting a virtual gear ratio of the continuously variable transmission between a first preset gear ratio and a second preset gear ratio at the decreasing rate in response to the first downshift operation on the shift operating member; and downshifting a virtual gear ratio of the continuously variable transmission from between the first preset gear ratio and the second preset gear ratio to the first preset gear ratio in response to the second downshift operation on the shift operating member.

Images