Continuously variable speed power transmission device for work vehicle and work vehicle

Abstract

To provide a continuously variable speed power transmission technology for suppressing a changeover shock that occurs at the switching of a shift change of a planetary gear device from a preceding shift stage to a succeeding shift stage due to work load or the like.SOLUTION: A continuously variable speed power transmission device for a working vehicle comprises a shift control unit 50 for controlling a change gear ratio of a static hydraulic continuously variable transmission 28 and a shift stage of a planetary transmission 31 on the basis of a gear change operation command. The shift control unit 50 comprises: a continuously variable speed control unit 52 for generating a control signal to adjust a gear ratio of the static hydraulic continuously variable transmission 28; a planetary clutch control unit 53 for generating a clutch control signal to change a shift stage of a planetary clutch mechanism 32; and a changeover timing change unit 55 for changing the changeover timing of the shift stage by the planetary clutch control unit 53 on the basis of a power traveling speed transmitted to running devices 1, 2, and a hydraulic pressure of the static hydraulic continuously variable transmission 28 detected by a pressure detection unit 97.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a continuously variable speed power transmission device for a work vehicle that transmits engine power from an engine to a traveling device, and to a work vehicle equipped with such a continuously variable speed power transmission device for a work vehicle. [Background technology]

[0002] Patent Document 1 discloses a travel transmission device that transmits engine power to front and rear wheels that constitute a travel device. In this travel transmission device, power from the engine is branched to a hydraulic pump of a hydrostatic continuously variable transmission (HST) and a planetary transmission. Continuously variable speed output from a hydraulic motor shaft of the hydrostatic continuously variable transmission and power from the engine are input to the planetary transmission, and the output from the planetary transmission is transmitted to the travel device. The planetary transmission has multiple gears that are switched by a planetary clutch mechanism. In vehicle speed control using tilting operation of the HST swash plate, if the vehicle speed range of the currently used gear is exceeded, a shift from the original gear to the next gear is performed. The shift point from the original gear to the next gear is a fixed value determined by design and set in advance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-96208 Summary of the Invention [Problem to be solved by the invention]

[0004] In the continuously variable power transmission device described in Patent Document 1, when the vehicle speed value at the original gear reaches a fixed value, the gear is switched to the next gear. However, if the volumetric efficiency of the HST changes due to changes in the internal pressure of the HST closed circuit based on the workload, etc., when the gear is switched to the next gear at the fixed value, the originally planned speed value does not appear, and a large switching shock occurs.

[0005] An object of the present invention is to provide a continuously variable speed power transmission technology that suppresses the shift shock that occurs when a planetary transmission shifts from an original gear to a next gear due to a work load or the like. [Means for solving the problem]

[0006] The continuously variable speed power transmission device for a work vehicle according to the present invention is a device that transmits engine power from an engine to a traveling device, a hydrostatic continuously variable transmission that receives engine power and outputs continuously variable speed power; a planetary transmission that receives engine power and the continuously variable speed power and outputs planetary power; a pressure detection unit that detects oil pressure in a closed circuit in the hydrostatic continuously variable transmission; a planetary clutch mechanism that selects a gear position of the planetary transmission; and a transmission control unit that controls the hydrostatic continuously variable transmission and the planetary clutch mechanism based on a transmission operation command, The transmission control unit The vehicle is equipped with a continuously variable transmission control unit that generates a control signal to adjust the gear ratio of the hydrostatic continuously variable transmission device, a planetary clutch control unit that generates a clutch control signal to change the gear stage of the planetary transmission device, and a switch timing change unit that changes the timing of the gear stage change by the planetary clutch control unit based on the traveling speed of the power transmitted to the traveling device and the oil pressure detected by the pressure detection unit.

[0007] With this configuration, the timing of the planetary clutch mechanism to switch from the original gear to the next gear is determined in real time based on the traveling speed of the power transmitted to the travel device and the detected hydraulic pressure of the closed circuit in the hydrostatic continuously variable transmission, rather than a fixed value. In other words, because the gear is switched based on the gear change environment at each time, switching shock caused by the work load, etc., when the planetary transmission is switched from the original gear to the next gear at a fixed value is suppressed.

[0008] The shift timing determined based on the traveling speed (the speed of power sent to the traveling device) and the detected hydraulic pressure is used as the shift point for switching gears. However, if the output of the hydrostatic continuously variable transmission fluctuates near this shift point, the traveling speed will fluctuate, resulting in the inconvenience of repeated clutch shifting of the planetary clutch mechanism. To prevent this inconvenience, it is preferable to provide a threshold value for the shift timing so that slight fluctuations in the traveling speed do not cause clutch shifting of the planetary clutch mechanism. In particular, it is advantageous to use a threshold characteristic for the shift timing that differs between when the traveling speed changes from one side and when the traveling speed changes from the other side, i.e., a first threshold value is used for one direction of change and a second threshold value is used for the other direction of change. For this reason, in the present invention, the shift timing change unit is configured to provide a threshold characteristic for the shift timing that differs between when the traveling speed changes from one side and when the traveling speed changes from the other side, thereby preventing the vehicle from shifting back to the original gear immediately after switching from the original gear to the next gear.

[0009] In the present invention, the switching timing changing unit includes a switching timing table that derives the switching timing from at least the detected hydraulic pressure. When the switching timing table is based on various switching timing derivation formulas defined by various shift conditions for shift-up and shift-down environments, an ideal switching point can be obtained by selecting an optimal switching timing derivation formula (switching timing table) from the multiple switching timing derivation formulas.

[0010] For example, fluctuations in output from a hydrostatic continuously variable transmission are caused by factors such as the oil temperature in the closed circuit, the detected oil pressure, which is the HST effective pressure, which is the pressure difference between the high-pressure side and the low-pressure side of the closed circuit, and engine speed. For this reason, in the present invention, the switching timing table is configured to derive the switching timing from the detected oil pressure, the oil temperature in the closed circuit, and the current gear position of the planetary transmission. This switching timing table is created by referring to experiments using an actual machine and simulation results using a simulator.

[0011] The present application also covers a work vehicle equipped with the above-described continuously variable speed power transmission device for a work vehicle. Such a work vehicle has the functions and effects of the above-described continuously variable speed power transmission device for a work vehicle. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. [Figure 2] FIG. 1 is a schematic diagram of a continuously variable speed power transmission device. [Figure 3] FIG. [Figure 4] FIG. 2 is a block diagram showing input / output devices in the transmission control unit. [Figure 5] FIG. 2 is a control function block diagram of the continuously variable speed power transmission device. [Figure 6] FIG. 2 is a hydraulic circuit diagram showing a continuously variable transmission and an operating structure of the continuously variable transmission. [Figure 7] FIG. 4 is an explanatory diagram of a vehicle speed change in the speed change control unit. [Figure 8] 1 is a diagram showing a clutch shift process. [Figure 9] 1 is a diagram showing a clutch shift process. [Figure 10] 1 is a diagram showing a clutch shift process. [Figure 11] 1 is a diagram showing a clutch shift process. [Figure 12] 10A and 10B are diagrams showing a group of graphs showing a plurality of switching timing derivation formulas that form the basis of the switching timing table; [Figure 13] 1 is a diagram showing a clutch switching process including a region showing threshold characteristics in which the thresholds differ when changing from one side and when changing from the other side. [Figure 14] 10 is a table showing values ​​specifying threshold characteristics in which the thresholds differ when the change occurs from one side and when the change occurs from the other side. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. In the following explanation, with respect to the running body of a tractor (an example of a "work vehicle"), the direction of arrow F shown in Figure 1 will be referred to as the "front side of the body," the direction of arrow B shown in Figure 1 will be referred to as the "rear side of the body," the direction of arrow U shown in Figure 1 will be referred to as the "upper side of the body," the direction of arrow D shown in Figure 1 will be referred to as the "lower side of the body," the direction toward the front of the page in Figure 1 will be referred to as the "left side of the body," and the direction toward the back of the page in Figure 1 will be referred to as the "right side of the body."

[0014] [Overall tractor] FIG. 1 shows a tractor. This tractor has a traveling body 3 supported by a pair of steerable and drivable front wheels 1 (traveling gear) on the left and right, and a pair of drivable rear wheels 2 (traveling gear). A prime mover 5 equipped with an engine 4 is provided at the front of the traveling body 3. A driver's section 6, where a driver sits and operates the vehicle, and a link mechanism 7, which connects a work implement such as a rotary tiller so that the implement can be raised and lowered, are provided at the rear of the traveling body 3. The driver's section 6 is equipped with a driver's seat 8, a steering wheel 9 for steer- ing the front wheels 1, and a cabin 10 that covers the riding space. A body frame 11 of the traveling body 3 is composed of the engine 4, a transmission case 12 whose front portion is connected to the rear of the engine 4, a front wheel support frame 13 connected to the bottom of the engine 4, and the like. A power takeoff shaft 14 is provided at the rear of the transmission case 12, which extracts and transmits power from the engine 4 to the work implement connected by the link mechanism 7.

[0015] [Power transmission device for driving] 2, a power transmission device 15 for driving, which transmits power (engine power) from the engine 4 to the front wheels 1 and the rear wheels 2, includes a transmission 18 that changes the speed of the power from the engine 4 and transmits it to a rear wheel differential mechanism 16 and a front wheel differential mechanism 17. The transmission 18 is housed in a transmission case 12.

[0016] As shown in FIG. 2, the transmission 18 is provided with: an input shaft 20 that is provided in the front part of the transmission case 12 and to which the power of the output shaft 4 a of the engine 4 is transmitted; a main transmission unit 21 that receives the power of the input shaft 20, changes the speed of the input power, and outputs it; a forward / reverse switching device 23 that receives the output of the main transmission unit 21; a gear mechanism 24 that transmits the output of the forward / reverse switching device 23 to the input shaft 16 a of the rear wheel differential mechanism 16; and a front wheel transmission unit 25 that receives the output of the forward / reverse switching device 23, changes the speed of the input power, and outputs it to the front wheel differential mechanism 17.

[0017] [Main transmission section] As shown in FIG. 2, the main transmission section 21 includes a hydrostatic continuously variable transmission 28 to which the power of the input shaft 20 is input, a planetary transmission 31 to which the power of the input shaft 20 and the output of the continuously variable transmission 28 are input, and a planetary clutch mechanism 37 that selects the gear stage of the planetary transmission 31.

[0018] As shown in FIG. 2 , the hydrostatic continuously variable transmission 28 includes a variable displacement hydraulic pump P connected to a pump shaft 28a serving as a continuously variable transmission input shaft via a first gear mechanism 27 connected to the rear end of a rotary shaft 26 connected to the rear end of the input shaft 20, and a hydraulic motor M driven by pressurized oil from the hydraulic pump P. By changing the swash plate angle of the hydraulic pump P, the power from the input shaft 20 is converted into forward rotation power or reverse rotation power, and the rotation speed of the forward rotation power and reverse rotation power is continuously changed. The hydrostatic continuously variable transmission 28 outputs power from a motor shaft 28b serving as a continuously variable transmission output shaft at a predetermined speed ratio (predetermined swash plate angle) and is referred to as an HST (hydraulic static transmission). Hereinafter, the hydrostatic continuously variable transmission 28 will be simply referred to as the continuously variable transmission 28.

[0019] Planetary transmission 31 has a planetary transmission section 31A to which the power of input shaft 20 and the output of continuously variable transmission 28 are input. Planetary clutch mechanism 37 functions as output section 31B of planetary transmission 31, and outputs the output of planetary transmission section 31A in stages across four speed ranges.

[0020] 2 and 3, the planetary transmission unit 31A is provided with a first planetary transmission unit 32 having a first sun gear 32a, a first planetary gear 32b meshing with the first sun gear 32a, and a first ring gear 32c with internal teeth meshing with the first planetary gear 32b. The planetary transmission unit 31A is provided with a second planetary transmission unit 33 located rearward of the first planetary transmission unit 32 and having a second sun gear 33a, a second planetary gear 33b meshing with the second sun gear 33a, a second ring gear 33c with internal teeth meshing with the second planetary gear 33b, and a second carrier 33d supporting the second planetary gear 33b.

[0021] As shown in Fig. 2, a second gear mechanism 30 is provided between the first sun gear 32a and the motor shaft 28b of the continuously variable transmission 28, and the output of the continuously variable transmission 28 is input to the first sun gear 32a via the second gear mechanism 30. A third gear mechanism 29 is provided between the first ring gear 32c and the input shaft 20, and the power of the input shaft 20 is input to the first ring gear 32c via the third gear mechanism 29. As shown in Figs. 2 and 3, the first planetary transmission unit 32 is provided with an interlocking gear 32d that meshes with the first planetary gear 32b, and the interlocking gear 32d and the second planetary gear 33b are interlocked and connected by a connecting member 33e. The first planetary transmission unit 32 and the second planetary transmission unit 33 constitute a so-called compound planetary transmission unit.

[0022] As shown in Figures 2 and 3, the planetary clutch mechanism 37 includes a triple-shaft structure of a first input shaft 34a, a second input shaft 34b, and a third input shaft 34c, and an output shaft 35 positioned parallel to the first input shaft 34a. The first input shaft 34a is connected to the second ring gear 33c, the second input shaft 34b is connected to the second carrier 33d, and the third input shaft 34c is connected to the second sun gear 33a. A first range gear mechanism 36a is connected to the first input shaft 34a, and a first clutch CL1 is provided between the first range gear mechanism 36a and the output shaft 35. A second range gear mechanism 36b is connected to the third input shaft 34c, and a second clutch CL2 is provided between the second range gear mechanism 36b and the output shaft 35. A third range gear mechanism 36c is connected to the second input shaft 34b, and a third clutch CL3 is provided between the third range gear mechanism 36c and the output shaft 35. A fourth range gear mechanism 36d is connected to the third input shaft 34c, and a fourth clutch CL4 is provided between the fourth range gear mechanism 36d and the output shaft 35.

[0023] In the main transmission unit 21, power from the engine 4 is input to the hydraulic pump P via the input shaft 20, the rotating shaft 26, and the first gear mechanism 27, and the power is changed in speed by the continuously variable transmission 28 to forward rotation power and reverse rotation power and output from the motor shaft 28b, and the rotation speed of the output forward rotation power and reverse rotation power is changed continuously. The output of the continuously variable transmission 28 is input to the first sun gear 32a of the first planetary transmission unit 32 via the second gear mechanism 30, and the power from the engine 4 is input to the first ring gear 32c of the first planetary transmission unit 32 via the input shaft 20 and the third gear mechanism 29. The input power from the continuously variable transmission 28 and the power from the engine 4 are combined by the first planetary transmission unit 32 and the second planetary transmission unit 33 of the planetary transmission unit 31A, and the combined power is transmitted from the second planetary transmission unit 33 to the output unit 31B and output from the output shaft 35.

[0024] In main transmission section 21, when continuously variable transmission device 28 is operated to change speeds with first clutch CL1 engaged, the combined power generated by planetary transmission section 31A is transmitted from second ring gear 33c to first input shaft 34a of output section 31B. Continuously variable transmission power in the first speed range is output from output shaft 35 via first range gear mechanism 36a and first clutch CL1 in output section 31B.

[0025] When the continuously variable transmission 28 is operated to change speeds with the second clutch CL2 engaged, the combined power generated by the planetary transmission unit 31A is transmitted from the second sun gear 33a to the third input shaft 34c of the output unit 31B. The continuously variable transmission power in the second speed range is output from the output shaft 35 via the second range gear mechanism 36b and the second clutch CL2 in the output unit 31B.

[0026] When continuously variable transmission 28 is operated to change speeds with third clutch CL3 engaged, the combined power generated by planetary transmission unit 31A is transmitted from second carrier 33d to second input shaft 34b of output unit 31B. Continuously variable transmission power in the third speed range is output from output shaft 35 via third range gear mechanism 36c and third clutch CL3 in output unit 31B.

[0027] When the continuously variable transmission 28 is operated to change speeds with the fourth clutch CL4 engaged, the combined power generated by the planetary transmission unit 31A is transmitted from the second sun gear 33a to the third input shaft 34c of the output unit 31B. The continuously variable transmission power in the fourth speed range is output from the output shaft 35 via the fourth range gear mechanism 36d and the fourth clutch CL4 in the output unit 31B.

[0028] [Forward / forward switching device] 2, the forward / reverse switching device 23 includes an input shaft 23a connected to the output shaft 35 of the planetary transmission 31, and an output shaft 23b provided in parallel to the input shaft 23a. A forward clutch CLF and a reverse clutch CLR are provided on the input shaft 23a. A forward gear interlock mechanism 23c is provided between the forward clutch CLF and the output shaft 23b, and a reverse gear interlock mechanism 23d is provided between the reverse clutch CLR and the output shaft 23b.

[0029] When the forward clutch CLF is engaged, it connects the input shaft 23a to the forward gear interlock mechanism 23c, creating a forward transmission state in which the power of the input shaft 23a is transmitted to the output shaft 23b via the forward gear interlock mechanism 23c. When the reverse clutch CLR is engaged, it connects the input shaft 23a to the reverse gear interlock mechanism 23d, creating a reverse transmission state in which the power of the input shaft 23a is transmitted to the output shaft 23b via the reverse gear interlock mechanism 23d.

[0030] In the forward / reverse switching device 23, the output of the planetary transmission 31 is input to the input shaft 23a, and when the forward clutch CLF is engaged, the power of the input shaft 23a is converted into forward power by the forward clutch CLF and the forward gear interlock mechanism 23c and transmitted to the output shaft 23b. When the reverse clutch CLR is engaged, the power of the input shaft 23a is converted into reverse power by the reverse clutch CLR and the reverse gear interlock mechanism 23d and transmitted to the output shaft 23b. The forward power and reverse power of the output shaft 23b are transmitted to the rear wheel differential mechanism 16 and the front wheel transmission part 25 by the gear mechanism 24.

[0031] In the rear wheel differential mechanism 16, the forward or reverse power transmitted from the forward / reverse switching device 23 is transmitted from the left and right output shafts 16b to the left and right rear wheels 2. The power of the left output shaft 16b is transmitted to the left rear wheel 2 via a planetary reduction mechanism 38B. A steering brake 38A is provided on the left output shaft 16b. Although not shown, the transmission system from the right output shaft 16b to the right rear wheel 2 is provided with a planetary reduction mechanism 38B and a steering brake 38A, similar to the transmission system to the left rear wheel 2.

[0032] [Front wheel transmission section] As shown in Fig. 2, the front wheel transmission unit 25 includes an input shaft 25a connected to the output shaft 24a of the gear mechanism 24, and an output shaft 25b positioned parallel to the input shaft 25a. A constant speed clutch CLT and an accelerating clutch CLH positioned rearward of the constant speed clutch CLT are provided on the input shaft 25a. A constant speed gear mechanism 40 is provided between the constant speed clutch CLT and the output shaft 25b. A accelerating gear mechanism 41 is provided between the accelerating clutch CLH and the output shaft 25b. A parking brake 39 is provided on the output shaft 24a of the gear mechanism 24.

[0033] In the front wheel transmission unit 25, when the constant speed clutch CLT is engaged, the power of the input shaft 25a is transmitted to the output shaft 25b by the constant speed clutch CLT and the constant speed gear mechanism 40, a constant speed transmission state is created by the constant speed gear mechanism 40, and power for driving the front wheels 1 is output from the output shaft 25b in a state in which the peripheral speed of the front wheels 1 is the same as the peripheral speed of the rear wheels 2. When the speed-up clutch CLH is engaged, the power of the input shaft 25a is transmitted to the output shaft 25b by the speed-up clutch CLH and the speed-up gear mechanism 41, and a front wheel speed-up transmission state is created by the speed-up gear mechanism 41, and power for driving the front wheels 1 is output from the output shaft 25b in a state in which the peripheral speed of the front wheels 1 is faster than the peripheral speed of the rear wheels 2. The output from the output shaft 25b is input to the front wheel differential mechanism 17 via a rotary shaft 42 that connects the output shaft 25b to the input shaft 17a of the front wheel differential mechanism 17.

[0034] When the constant velocity clutch CLT is engaged, the traveling vehicle body 3 enters a four-wheel drive state in which the front wheels 1 and rear wheels 2 are driven in a state in which the average peripheral speed of the left and right front wheels 1 is the same as the average peripheral speed of the left and right rear wheels 2, and when the speed-up clutch CLH is engaged, the traveling vehicle body 3 enters a four-wheel drive state in which the front wheels 1 and rear wheels 2 are driven in a state in which the average peripheral speed of the left and right front wheels 1 is faster than the average peripheral speed of the left and right rear wheels 2. As a result, when the speed-up clutch CLH is engaged, the traveling vehicle body 3 can turn with a turning radius that is smaller than the turning radius when the constant velocity clutch CLT is engaged.

[0035] [Regarding the rotation detector group] The power transmission device 15 is provided with a group of rotation detectors 70 that detects the engine rotation speed, which is the rotation speed of the output power of the engine 4, the continuously variable transmission rotation speed, which is the rotation speed of the continuously variable transmission power (output of the continuously variable transmission 28), the planetary rotation speed, which is the rotation speed of the planetary power (output of the planetary transmission 31), and the traveling rotation speed, which is the rotation speed of the forward power (output of the forward / reverse travel switching device 23). The group of rotation detectors 70 is made up of a plurality of rotation detectors arranged at appropriate locations, and includes an engine rotation detector that detects the engine rotation speed, a continuously variable transmission rotation detector that detects the continuously variable transmission rotation speed, a main planetary rotation detector that detects the planetary rotation speed, and a traveling rotation detector that detects the traveling rotation speed.

[0036] [About the gear change control unit] Shift control in this continuously variable transmission device is performed by a shift control unit 50 shown in Figures 4 and 5. Shift operations by the driver are performed using a shift pedal 46 and a forward / reverse lever 47 provided in the driving section 6 as a shift operation device 45. The amount of operation of the shift pedal 46 and the forward / reverse lever 47 is input to the shift control unit 50 as a shift operation command. A detection signal (number of rotations) from the rotation detector group 70 is also input to the shift control unit 50. The shift control unit 50 generates control signals for hydraulically controlling the operation of the continuously variable transmission 28, planetary clutch mechanism 37, forward / reverse switching device 23, etc.

[0037] The hydraulic circuit of the continuously variable transmission 28 is shown in FIG. 6. A hydraulic cylinder 90 is connected to the swash plate Psp of the hydraulic pump P of the continuously variable transmission 28, and a speed change operation valve 92 is connected to the hydraulic cylinder 90 via an operation oil passage 91. A hydraulic pump 94 is connected to the speed change operation valve 92 via an oil supply passage 93. By switching the port of the speed change operation valve 92, hydraulic oil supplied by the hydraulic pump 94 enters one or the other of two oil chambers of the hydraulic cylinder 90, actuating the hydraulic cylinder 90. By stopping the supply of hydraulic oil to the hydraulic cylinder 90, the hydraulic cylinder 90 maintains its position. The continuously variable transmission 28 tilts the swash plate Psp in the forward or reverse direction by switching the port of the speed change operation valve 92. This tilting causes the continuously variable transmission 28 to change gears. Specifically, the speed change operation valve 92 is configured as an electromagnetically operated valve, and the operation of a solenoid 92a of the speed change operation valve 92 is controlled by the speed change control unit 50. An emergency relief valve 96 is connected to a closed circuit 95 that connects the hydraulic pump P and hydraulic motor M of the continuously variable transmission 28. Furthermore, a pressure sensor 97 serving as a pressure detection unit that detects the hydraulic pressure of the closed circuit 95 is provided in the first drive oil line and the second drive circuit that make up this closed circuit 95. The differential pressure generated between the first drive oil line and the second drive circuit is called the HST effective pressure, and is found from the detection value of the pressure sensor 97.

[0038] As shown in FIG. 5, the transmission control unit 50 includes a transmission control section 51, a rotation speed acquisition section 61, an operation amount acquisition section 62, and a pressure acquisition section 63.

[0039] The transmission control unit 51 includes a continuously variable transmission control unit 52, a planetary clutch control unit 53, a forward / reverse clutch control unit 54, and a switching timing change unit 55. The continuously variable transmission control unit 52 generates a control signal that adjusts the swash plate angle of the continuously variable transmission 28. The planetary clutch control unit 53 generates a clutch control signal that controls the ON (connection) / OFF (disconnection) of the four hydraulic clutches of the planetary clutch mechanism 37, namely, the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4. The forward / reverse clutch control unit 54 generates a clutch control signal that controls the ON (connection) / OFF (disconnection) of the two hydraulic clutches of the forward / reverse switching device 23, namely, the forward clutch CLF and the reverse clutch CLR. The switching timing change unit 55 changes the timing of switching the gears (switching timing of the hydraulic clutch) by the planetary clutch control unit 53 based on the speed of the power transmitted to the front wheels 1 and the rear wheels 2 (traveling speed: number of travel revolutions), the detected oil pressure detected by the pressure sensor 97 (more specifically, the HST effective pressure of the continuously variable transmission control unit 52), etc. The switching timing change unit 55 is provided with a switching timing table 55a that derives the switching timing from at least the detected oil pressure.

[0040] The rotation speed acquisition unit 61 receives detection signals from the rotation detector group 70, calculates the engine rotation speed, continuously variable transmission rotation speed, planetary rotation speed, and travel rotation speed (rotation speed here has the same meaning as speed), and provides these to the transmission control unit 51. The operation amount acquisition unit 62 receives operation signals from the transmission operating device 45, such as the speed change pedal 46 or forward / reverse lever 47, converts them into a transmission operation amount, and provides these to the transmission control unit 51. The pressure acquisition unit 63 receives detection signals from the pressure sensor 97, calculates the hydraulic pressures of the first drive circuit and the second drive circuit that make up the hydraulic closed circuit 95 in the continuously variable transmission control unit 52, and the differential pressure therebetween, and provides these to the transmission control unit 51.

[0041] FIG. 7 is an explanatory diagram of vehicle speed changes performed by the gear change control unit 51. The vertical axis of FIG. 7 represents the gear ratio G, which is the ratio (traveling RPM / engine RPM) between the engine RPM and the traveling RPM (traveling speed: vehicle speed), which is the rotational speed of the input shaft 16a to the traveling device corresponding to the vehicle speed. In other words, the gear ratio G is a numerical value corresponding to the traveling RPM. The vertical axis also represents the traveling RPM (vehicle speed): V of the input shaft 16a. The horizontal axis of FIG. 7 represents the speed change state of the continuously variable transmission 28, with [N] representing the neutral state and [-MAX] representing the speed change state in which reverse power is output at the highest speed. [+MAX] representing the speed change state in which forward power is output at the highest speed. [-K] represents the speed change state for switching the clutch on the reverse side (the speed change state just before [-MAX]), and [+K] represents the speed change state for switching the clutch on the forward side (the speed change state just before [+MAX]). [G1], [G2], [G3], and [G4] are preset gear ratios: G. The transmission control unit 51 performs transmission control of the traveling rotation speed: V of the input shaft 16a by switching between the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4 based on the gear ratio: G and the speed change state of the continuously variable transmission 28.

[0042] That is, with first clutch CL1 engaged, continuously variable transmission 28 is shifted from [-MAX] toward [+MAX], and thus traveling speed V increases continuously from zero speed [0] in the first gear range. When continuously variable transmission 28 reaches [+K] and the gear ratio G reaches [G1], transmission control unit 51 switches first clutch CL1 off and second clutch CL2 on. With second clutch CL2 engaged, continuously variable transmission 28 is shifted toward [-MAX], and thus traveling speed V increases continuously in the second gear range. When continuously variable transmission 28 reaches [-K] and the gear ratio G reaches [G2], transmission control unit 51 switches second clutch CL2 off and third clutch CL3 on. When continuously variable transmission 28 is operated to change gears toward [+MAX] with third clutch CL3 engaged, traveling speed: V increases steplessly in the third-speed range. When continuously variable transmission 28 reaches [+K] and gear ratio: G reaches [G3], transmission control unit 51 switches third clutch CL3 off and switches fourth clutch CL4 on. With fourth clutch CL4 engaged, continuously variable transmission 28 is shifted toward [-MAX], and traveling speed: V increases steplessly in the fourth-speed range.

[0043] [Planetary clutch switching timing] Next, the planetary clutch switching timing (gear stage switching timing: gear stage switching point) of the planetary clutch mechanism 37 by the planetary clutch control unit 53 and the switching timing change unit 55 will be described with reference to Figs. 8 to 11. The planetary clutch mechanism 37 is equipped with four planetary clutches, but Figs. 8 to 11 show clutch switching between two of these clutches, namely, the first clutch CL1 and the second clutch CL2. The numerical value showing the gear ratio on the vertical axis is (travel speed / engine speed) x 10,000. The horizontal axis represents the inclination (swash plate angle) of the swash plate Psp of the hydraulic pump P of the continuously variable transmission control unit 52.

[0044] 8 shows the ideal process of clutch shifting from the first clutch CL1 to the second clutch CL2. The clutch shifting point (design shifting point: fixed point or set point) that is set by design is the point at which the gear ratio (vehicle speed) becomes "G1." If the continuously variable transmission 28 is in an unloaded state, when the clutch is shifted from the first clutch CL1 to the second clutch CL2 at the design shifting point, a smooth shift is achieved in which the gear ratio (which can be thought of as vehicle speed) continuously increases during the transition from the first gear achieved by the first clutch CL1 to the second gear achieved by the second clutch CL2.

[0045] When a work vehicle is traveling, continuously variable transmission 28 is rarely in an unloaded state. When a load is applied to continuously variable transmission 28, the volumetric efficiency of continuously variable transmission 28 changes. For this reason, as shown in FIG. 9, when accelerating toward the design switching point, clutch switching occurs when the gear ratio (vehicle speed) reaches "G1," and as shown by the thick arrow in FIG. 9, the gear ratio temporarily decreases, and then acceleration occurs. In FIG. 9, "G1-α" indicates the gear ratio decreased by a certain value α from "G1." This means that the gear ratio, i.e., the vehicle speed, fluctuates discontinuously when shifting from the first gear achieved by first clutch CL1 to the second gear achieved by second clutch CL2, resulting in an unnatural shift.

[0046] To address this issue, the clutch-switching timing change unit 55 calculates the clutch-switching timing (calculated switching point) based on the HST effective pressure of the continuously variable transmission control unit 52, and the planetary clutch control unit 53 performs clutch switching at the calculated clutch-switching timing. In other words, as shown in FIG. 10 , by performing clutch switching at a calculated switching point that keeps the gear ratio (vehicle speed) as constant as possible before and after clutch switching, the double clutch engagement period shortens the period during which the gear ratio, i.e., the vehicle speed, returns to "G1," thereby achieving substantially smooth acceleration. While FIG. 10 illustrates the process during an upshift, performing clutch switching at the clutch-switching timing (calculated switching point) during a downshift also results in the clutch-switching process shown in FIG. 11, thereby achieving substantially smooth deceleration. In FIG. 10 , "G1-α" indicates the gear ratio that is lowered by a certain value α from "G1," and in FIG. 11 , "G1+β" indicates the gear ratio that is higher by a certain value β from "G1."

[0047] [About the switching timing table] To calculate the appropriate clutch shift timing, input parameters include the oil temperature and HST effective pressure of the continuously variable transmission control unit 52, engine speed, the original gear position, and the next gear position. A lookup table that assigns clutch shift timing as an output value to input parameters as input values ​​is a convenient program structure for deriving the appropriate clutch shift timing using these input parameters. This lookup table is the shift timing table 55a. As an example, as shown in FIG. 11, such a shift timing table 55a can be created based on multiple relational expressions between the HST effective pressure and the gear ratio that are generated by performing simulations or the like while selecting values ​​for each input parameter. While FIG. 12 shows these relational expressions as linear expressions, they may, of course, be expressed as quadratic expressions or other multidimensional polynomial expressions.

[0048] To prevent frequent clutch switching around the clutch switching point, the switching timing change unit 55 provides threshold characteristics for upshifting and downshifting, with different thresholds for shifting from one side to the other. In other words, this threshold characteristic uses a first threshold for shifting from a higher gear ratio (vehicle speed) to a lower gear ratio, and a second threshold for shifting from a lower gear ratio to a higher gear ratio (vehicle speed). This results in a control behavior similar to that of a hysteresis comparator. An example of a clutch switching process using such threshold characteristics is described below with reference to FIGS. 13 and 14. In FIG. 13, the area showing this threshold characteristic is enclosed by a rectangle. The example in FIG. 13 shows the threshold characteristic for upshifting from the first clutch CL1 (first gear) to the second clutch CL2 (second gear), but the threshold characteristic for upshifting may be similar or identical. Furthermore, the constants α1, α2, α3, β1, β2, β3, γ1, γ2, and γ3 indicating the gear ratios (vehicle speeds) in FIG. 14 are determined experimentally, empirically, and by design.

[0049] (1) When the target gear ratio (target vehicle speed) and current gear ratio (current vehicle speed) in the first gear stage are traveling at a value (first value) significantly lower than "G1," the calculation switching point calculated based on the HST effective pressure is set to a value slightly lower than "G1" (second value higher than the first value). (2) When the target gear ratio from the operation amount acquisition unit 62 becomes a value (third value) higher than “G1” which exceeds the calculated switching point, the target gear ratio is set to the second value, clutch switching is performed from the first clutch CL1 to the second clutch CL2, and the second value is recorded as the switching point for shifting up. (3) After the clutch switching is completed, the point at which the downshift is performed from the second clutch CL2 to the first clutch CL1 is calculated as a fourth value that is higher than the third value. (4) The upper limit value of the threshold characteristic region (the shaded rectangle in FIG. 13) here is “G1+α1” as shown in the table in FIG. 14, and since the target gear ratio is the third value, the downshift calculation switching point is overwritten with the previously recorded second value. (5) As a result, the target gear ratio is the third value and the downshift calculation switch point is the second value, which is lower than the third value, so no downshift is performed and the gear ratio is maintained at the third value. (6) After that, once the target gear ratio exceeds the upper limit value "G1+α1" of the threshold characteristic region, the data is not overwritten with the second value as described in (4). As a result, if the downshift calculation switching point is a fourth value that is lower than the upper limit value "G1+α1," the downshift clutch is switched when the target gear ratio falls below the fourth value. (7) After (4), if the target gear ratio falls to a fifth value lower than the second value without exceeding the upper limit value "G1 + α1" of the threshold characteristic region, a downshift is performed when the target gear ratio falls below the second value, which is the overwritten calculation switching point, and the gear ratio at that time is recorded. (8) Next, after the clutch switching from the first clutch CL1 to the second clutch CL2 is completed, it is assumed that the switching point for this upshift is a sixth value that is lower than the fifth value. (9) The lower limit value of the threshold characteristic region (the hatched rectangle in FIG. 13) between the first and second gears is “G1-α2,” as shown in the table in FIG. 14. If the target gear ratio is a fifth value that is higher than “G1-α2,” the shift-up calculation switch point is overwritten with the previously recorded second value. (10) After that, whether to overwrite or not is determined depending on whether the vehicle leaves this threshold characteristic area or returns to the original gear position, and clutch switching is performed based on the shift-up or shift-down switching point.

[0050] The above example shows a clutch switching process in which upshifting and downshifting immediately return to the original gear. In normal acceleration and deceleration, the threshold characteristic region is passed within a certain time, so it is probabilistic that the control behavior at this threshold characteristic is rarely maintained.

[0051] [Another embodiment] (1) The types and arrangement of the rotation detectors constituting the rotation detector group 70 are not limited to those in the above-described embodiment. Any type of rotation detector that can detect substantially the same number of rotations can be used, and the arrangement of the rotation detectors can be freely determined as long as they can detect substantially the same number of rotations. (2) The control function section included in the transmission control unit 50 may be integrated with other control function sections or may be divided into multiple sections. In addition, a specific control function section may be implemented in a control unit (ECU) other than the transmission control unit 50. (3) In the above-described embodiment, the planetary transmission 31 is configured to have four gear stages, but it may also be configured to have three or fewer or five or more gear stages.

[0052] (4) In the above-described embodiment, an example was shown in which the vehicle was equipped with front wheels 1 and rear wheels 2, but the running device may also be a crawler running device or a combination of a mini crawler and wheels.

[0053] (5) In the above embodiment, an example was shown in which the speed change pedal 46 was provided, but this is not limiting, and a speed change lever may be used as the speed change operating device 45.

[0054] (6) In the above embodiment, an example was shown in which the forward / reverse lever 47 was provided, but this is not limiting, and a forward / reverse pedal may be used as the speed change operating device 45.

[0055] (7) The switching timing table 55a, which derives the timing for switching the gear stage of the planetary transmission 31 from the detected oil pressure, may be prepared in multiple types to suit the type of work performed by the work vehicle and the characteristics of the driver, and may be selectable as desired.

[0056] The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0057] The present invention can be applied to a continuously variable speed power transmission device for a work vehicle that includes a continuously variable speed device and a planetary speed device, and to various work vehicles that include this continuously variable speed power transmission device for a work vehicle. can be applied to. [Explanation of symbols]

[0058] 1: Front wheels (running gear) 2: Rear wheels (running gear) 4: Engine 16: Rear wheel differential mechanism 16a: Input shaft 16b: Output shaft 18: Transmission 20: Input shaft 23: Forward / forward switching device 28: Hydrostatic continuously variable transmission (continuously variable transmission) 28a: Pump shaft 28b: Motor shaft 31: Planetary transmission 31A: Planetary transmission 31B: Output section 37: Planetary clutch mechanism 45: Gear shifter 46: Gear shift pedal 47: Forward / reverse lever 50: Transmission control unit 51: Transmission control section 52: Continuously variable transmission control unit 53: Planetary clutch control unit 54: Forward / reverse clutch control unit 55: Switching timing change section 55a: Switching timing table 95 :Closed circuit 97: Pressure sensor M: Hydraulic motor P: Hydraulic pump Psp: Swash plate

Claims

1. A continuously variable speed power transmission device for a work vehicle that transmits engine power from an engine to a traveling device, a hydrostatic continuously variable transmission that receives the engine power and outputs continuously variable transmission power; a planetary transmission that receives the engine power and the continuously variable transmission power as inputs and outputs planetary power; a pressure detection unit that detects the oil pressure of a closed circuit in the hydrostatic continuously variable transmission; a planetary clutch mechanism for selecting a gear stage of the planetary transmission; a speed change control unit that controls the hydrostatic continuously variable transmission and the planetary clutch mechanism based on a speed change operation command, The transmission control unit a continuously variable transmission control unit that generates a control signal for adjusting the speed ratio of the hydrostatic continuously variable transmission device; a planetary clutch control unit that generates a clutch control signal for changing a gear position of the planetary transmission; a switching timing change unit that changes the timing of switching the gear position by the planetary clutch control unit based on the traveling speed of the power transmitted to the traveling device and the oil pressure detected by the pressure detection unit; A continuously variable speed power transmission device for a work vehicle.

2. 2. The continuously variable speed power transmission device for a work vehicle according to claim 1, wherein the switch timing change unit provides the switch timing with threshold characteristics that differ between when the switch timing changes from one side and when the switch timing changes from the other side, thereby preventing the shift from the original gear stage to the next gear stage immediately after switching from the original gear stage to the next gear stage.

3. 2. The continuously variable speed power transmission device for a work vehicle according to claim 1, wherein the switching timing change unit includes a switching timing table that derives the switching timing from at least the detected hydraulic pressure.

4. 4. The continuously variable transmission device for a work vehicle according to claim 3, wherein the switching timing table derives the switching timing from the detected oil pressure, the oil temperature in the closed circuit, and the current gear position of the planetary transmission device.

5. A work vehicle comprising the continuously variable speed power transmission device for a work vehicle according to any one of claims 1 to 4.

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