Power transmission system for work vehicles and work vehicles

Abstract

To provide a power transmission device for work vehicles that can reduce power loss during high-speed driving. [Solution] The power transmission device 10 for the work vehicle 100 comprises a transmission 11 having an input shaft 20 rotated by a prime mover 103, a continuously variable transmission 30, a planetary gear mechanism 40, and a plurality of transmission gears 50, wherein the first planetary gear mechanism 41 has a first ring gear 41R, a first sun gear 41S, and a first planetary gear 41P, and the second planetary gear mechanism 42 has a second ring gear 42 The first planetary gear 41P has a second sun gear 42S and a second planetary gear 42P, and the first planetary gear 41P further has a third planetary gear 43P that meshes with the second planetary gear 42P, the outer diameter RS1 of the first sun gear 41S is larger than the outer diameter RS2 of the second sun gear 42S, and the inner diameter RR2 of the second ring gear 42R is larger than the inner diameter RR1 of the first ring gear 41R.

Description

Technical Field

[0004] ,

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[0001] The present invention relates to a power transmission device for a work vehicle and a work vehicle equipped with the same.

Background Art

[0002] Conventionally, a power transmission device for a work vehicle including a continuously variable transmission and a planetary gear mechanism has been known (see Patent Document 1). The power transmission device directly inputs the power from the prime mover (engine) to the planetary gear mechanism and also inputs the power from the prime mover via the continuously variable transmission. The power transmission device outputs power from any one of the sun gear, ring gear, and planetary carrier of the planetary gear mechanism according to the selected gear stage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the proportion of the power input to the planetary gear mechanism through the continuously variable transmission increases among the power input to the planetary gear mechanism, the output loss due to frictional resistance (hereinafter also referred to as power loss) increases. Conventionally, a work vehicle equipped with the power transmission device increases the swash plate angle of the continuously variable transmission when performing high-speed travel. Therefore, in the conventional work vehicle during high-speed travel, the proportion of the power passing through the continuously variable transmission increases, resulting in an increase in power loss.

[0005] Therefore, an object of the present disclosure is to provide a power transmission device for a work vehicle capable of reducing power loss during high-speed travel.

Means for Solving the Problems

[0006] The power transmission device for a work vehicle according to the present disclosure is a power transmission device for a work vehicle comprising a transmission having an input shaft rotationally driven by a prime mover, a first gear mechanism and a second gear mechanism driven by the input shaft, a continuously variable transmission having a hydraulic pump driven by the first gear mechanism and a hydraulic motor driven by the hydraulic pump, a planetary gear mechanism driven by the second gear mechanism and the hydraulic motor, and a plurality of transmission gears to which the output of the planetary gear mechanism is transmitted, wherein the plurality The transmission gear includes a first transmission gear corresponding to the lowest speed 1st gear range, a second transmission gear corresponding to the 2nd gear range which is faster than the 1st gear range, a third transmission gear corresponding to the 3rd gear range which is faster than the 2nd gear range, and a fourth transmission gear corresponding to the highest speed 4th gear range, and the planetary gear mechanism includes a first planetary gear mechanism and a second planetary gear mechanism which are coaxial with the input shaft and are arranged in the axial direction of the input shaft, and the first planetary gear mechanism and the second planetary gear mechanism have a common planetary carrier, and the first The planetary gear mechanism includes a first ring gear driven by the second gear mechanism, a first sun gear driven by the hydraulic motor, and a first planetary gear that meshes with the first ring gear and the first sun gear. The second planetary gear mechanism includes a second ring gear that transmits rotation to the first transmission gear, a second sun gear that transmits rotation to the second transmission gear and the fourth transmission gear, and a second planetary gear that meshes with the second ring gear, the second sun gear, and the first planetary gear. The planetary gear has an extended portion that extends in the axial direction to the second planetary gear mechanism, and has a third planetary gear that meshes with the second planetary gear in the extended portion, the planetary carrier rotatably supports the first planetary gear and the second planetary gear and transmits rotation to the third transmission gear, the outer diameter of the first sun gear is larger than the outer diameter of the second sun gear, and the inner diameter of the second ring gear is larger than the inner diameter of the first ring gear. [Effects of the Invention]

[0007] The power transmission device for work vehicles described herein can reduce power loss during high-speed driving. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a side view showing an example of a work vehicle. [Figure 2] Figure 2 is a skeleton diagram showing the power transmission system for a work vehicle. [Figure 3] Figure 3 is a partially enlarged skeleton diagram of the planetary gear mechanism shown in Figure 2. [Figure 4] Figure 4 is a partial cross-sectional view of a planetary gear mechanism. [Figure 5] Figure 5 is a control block diagram of the power transmission system. [Figure 6] Figure 6 is a partial skeleton diagram of a planetary gear mechanism that constitutes a conventional power transmission system. [Figure 7] Figure 7 is a partial cross-sectional view of a conventional planetary gear mechanism. [Figure 8] Figure 8 shows the relationship between the swashplate position and vehicle speed of a continuously variable transmission in a work vehicle. [Figure 9] Figure 9 shows the relationship between power loss and vehicle speed in the power transmission system of a work vehicle. [Modes for carrying out the invention]

[0009] <Summary of the embodiments of this disclosure> The embodiments of this disclosure are outlined below. (1) The power transmission device for a work vehicle of this embodiment includes a transmission having an input shaft rotationally driven by a prime mover, a first gear mechanism and a second gear mechanism driven by the input shaft, a hydraulic pump driven by the first gear mechanism and a hydraulic motor driven by the hydraulic pump, a planetary gear mechanism driven by the second gear mechanism and the hydraulic motor, and a plurality of transmission gears to which the output of the planetary gear mechanism is transmitted. The plurality of transmission gears include a first transmission gear corresponding to the lowest speed 1st gear range, a second transmission gear corresponding to a 2nd gear range that is faster than the 1st gear range, a third transmission gear corresponding to a 3rd gear range that is faster than the 2nd gear range, and a fourth transmission gear corresponding to the highest speed 4th gear range. The planetary gear mechanism is coaxial with the input shaft and includes a first planetary gear mechanism and a second planetary gear mechanism that are arranged in the axial direction of the input shaft. The first planetary gear mechanism and the second planetary gear mechanism have a common planetary carrier. The first planetary gear mechanism includes a first ring gear driven by the second gear mechanism, a first sun gear driven by the hydraulic motor, and a first planetary gear that meshes with the first ring gear and the first sun gear. The second planetary gear mechanism includes a second ring gear that transmits rotation to the first transmission gear, a second sun gear that transmits rotation to the second transmission gear and the fourth transmission gear, and a second planetary gear that meshes with the second ring gear, the second sun gear, and the first planetary gear. The first planetary gear has an extended portion that extends in the axial direction to the second planetary gear mechanism, and has a third planetary gear that meshes with the second planetary gear in the extended portion. The planetary carrier rotatably supports the first planetary gear and the second planetary gear and transmits rotation to the third transmission gear. In the power transmission device for a work vehicle according to the present disclosure, the outer diameter of the first sun gear is larger than the outer diameter of the second sun gear, and the inner diameter of the second ring gear is larger than the inner diameter of the first ring gear.

[0010] In this embodiment, the power transmission device for a work vehicle has a second ring gear with a larger internal diameter than the first ring gear. In this case, the internal diameter of the second ring gear can be made larger. In this embodiment, the power transmission device for a work vehicle has a first sun gear with a larger outer diameter than the second sun gear. In this case, the outer diameter of the first sun gear can be made smaller. With this configuration, the reduction ratio in the first gear range can be increased, and the reduction ratio in the fourth gear range can be decreased. This improves the maximum traction force when driving at low speeds by selecting the first gear range, and reduces power loss when driving at high speeds by selecting the fourth gear range. The power transmission device for a work vehicle in this embodiment can reduce power loss during high-speed driving.

[0011] (2) In the power transmission device for the work vehicle described in (1) above, the continuously variable transmission further has a swash plate, and the rotational speed and rotational direction of the hydraulic motor can be changed according to the angle of the swash plate, and when the angle of the swash plate is in the neutral range, it reaches an output that allows the work vehicle to travel at its maximum speed. The power transmission system for work vehicles in this embodiment allows the work vehicle to travel at its maximum speed when the angle of the swash plate of the continuously variable transmission is set to the neutral range. This reduces power loss during high-speed travel. Furthermore, by selecting the 4th gear range with the swash plate angle in the neutral range, travel at the maximum speed becomes possible.

[0012] (3) The power transmission device for the work vehicle described in (1) or (2) further comprises an output shaft that is rotationally driven by the planetary gear mechanism, and a clutch mechanism that engages any one of the first transmission gear, the second transmission gear, the third transmission gear, and the fourth transmission gear with the output shaft. The power transmission system for the work vehicle in this embodiment allows the driver to select any of the 1st to 4th gear ranges as the gear ratio using a clutch mechanism.

[0013] (4) In the power transmission device for any one of the working vehicles (1) to (3) above, the number of teeth of the second sun gear is smaller than that of the first sun gear. In the power transmission device for the working vehicle of the present embodiment, by reducing the number of teeth of the second sun gear, the reduction ratio of the four-speed range can be reduced. And by reducing the reduction ratio of the four-speed range, it is possible to suppress the speed reduction of the working vehicle, and it becomes possible to travel at the maximum speed in a state where the position of the swash plate is in the neutral range. As a result, it is possible to reduce the power loss when selecting the four-speed range and traveling at high speed.

[0014] (5) In the power transmission device for any one of the working vehicles (1) to (4) above, the number of teeth of the second ring gear is larger than that of the first ring gear. In the power transmission device for the working vehicle of the present embodiment, by increasing the number of teeth of the second ring gear, it becomes possible to arrange the meshing portions of the second planetary gear and the third planetary gear inside the second ring gear. As a result, the number of teeth of the first sun gear can be increased. And by increasing the number of teeth of the first sun gear, the reduction ratio of the second sun gear can be further reduced. Therefore, the reduction ratio between the continuously variable transmission and the first sun gear can be made larger than before. In this case, the torque input to the first sun gear can be increased. As a result, the maximum traction force when selecting the first-speed range and traveling at low speed can be improved.

[0015] (6) The power transmission device for any one of the working vehicles (1) to (5) above has a gear ratio of the second sun gear to the first sun gear less than 1.0, and a gear ratio of the second ring gear to the first ring gear greater than 1.0. In the power transmission device for the working vehicle of the present embodiment, the reduction ratio of the four-speed range is reduced, and the reduction ratio of the first-speed range is increased. As a result, it is possible to reduce the power loss when selecting the four-speed range and traveling at high speed, and to improve the maximum traction force when selecting the first-speed range and traveling at low speed.

[0016] (7) The work vehicle of this embodiment includes the power transmission device according to any one of the aspects (1) to (6). The work vehicle of this embodiment can reduce the power loss during high-speed travel.

[0017] <Details of Embodiments of the Present Disclosure> Hereinafter, details of embodiments of the present disclosure will be described with reference to the drawings. Note that at least a part of the embodiments described below may be arbitrarily combined.

[0018] 〔Regarding the work vehicle〕 FIG. 1 is a side view showing an example of a work vehicle. In FIG. 1, a work vehicle 100 which is an example of a work vehicle equipped with the power transmission device of the present disclosure is shown. The work vehicle 100 shown in FIG. 1 is a tractor 101, which is a vehicle for agricultural work. The tractor 101 has a vehicle body 102, a prime mover (engine) 103, a traveling device 104, a steering device 105, and a work device 106. The work device 106 is connected to the vehicle body 102 of the tractor 101. The tractor 101 travels on a work site such as a farm field, and the work device 106 performs work on that work site.

[0019] The vehicle body 102 has a chassis 121 that serves as the skeleton of the vehicle, a body 122 that serves as the exterior, a cabin 123, a driver's seat 124, and a coupling mechanism 125. The coupling mechanism 125 is mounted at the rear of the chassis 121 and connects the work device 106 to the chassis 121 (vehicle body 102).

[0020] The work vehicle 100 (tractor 101) further has a shift pedal 107 and a shift lever 108 inside the cabin 123. The tractor 101 can adjust the vehicle speed (traveling speed) of the work vehicle 100 (tractor 101) by a combination of operations of the shift pedal 107 and the shift lever 108.

[0021] The prime mover 103 is a power machine that generates the driving power for the tractor 101. The tractor 101 moves by driving the drive wheels of the running gear 104 with the prime mover 103. In this embodiment, the prime mover 103 is a diesel engine. However, the prime mover 103 may also be an electric motor, or a combination of an engine and an electric motor may be used.

[0022] The running gear 104 has front wheels 104a and rear wheels 104b. In this embodiment, the tractor 101 has front wheels 104a as steering wheels, and the direction of travel of the vehicle body 102 is changed by changing the rolling direction of the front wheels 104a using the steering gear 105. The front wheels 104a and rear wheels 104b may be of the tire type or the crawler type.

[0023] (Power transmission device) Figure 2 is a skeleton diagram showing a power transmission device for a work vehicle. As shown in Figure 1, the tractor 101 further has a power transmission device 10. The power transmission device 10 transmits power from the prime mover 103 to the front wheels 104a, rear wheels 104b, and work equipment 106, etc., when the tractor 101 is running. The power transmission device 10 is supported by the chassis 121 and mounted on the vehicle body 102. Note that the work vehicle 100 to which the power transmission device 10 of this disclosure is applied is not limited to the tractor 101, but may be other work vehicles (for example, a combine harvester, etc.).

[0024] (transmission) As shown in Figure 2, the power transmission device 10 has a transmission 11. The transmission 11 transmits power from the prime mover 103 by changing the speed. The transmission 11 is housed in a transmission case 12. The transmission 11 has an input shaft 20, a continuously variable transmission 30, a planetary gear mechanism 40, a transmission gear 50, a clutch mechanism 60, and a forward / reverse switching mechanism 70.

[0025] The power transmission device 10 further includes a rear-wheel differential mechanism 15, a front-wheel transmission mechanism 25, and a PTO mechanism 26. The rear-wheel differential mechanism 15 transmits power from the transmission 11 to the rear wheels 104b. The front-wheel transmission mechanism 25 transmits power from the transmission 11 to the front wheels 104a. The PTO mechanism 26 transmits power from the transmission 11 to the PTO shaft 126.

[0026] In the following explanation, the side of the input shaft 20 that connects to the prime mover 103 in the axial direction is defined as the front side of the power transmission device 10, and the opposite side is defined as the rear side. In the following explanation, the front side is also referred to as the axial side, and the rear side is also referred to as the other axial side.

[0027] In the transmission 11, the input shaft 20 is connected to the output shaft 103a of the prime mover 103. Power from the prime mover 103 is input to the input shaft 20 via the output shaft 103a. The transmission 11 has a rotary shaft 22 connected to the rear end of the input shaft 20.

[0028] (Gear shifting section) The transmission 11 has a gear shifting unit 21 that changes the speed of the power (rotation) input to the input shaft 20 and the rotating shaft 22 and outputs it. As shown in Figure 2, the gear shifting unit 21 includes a continuously variable transmission 30, a planetary gear mechanism 40, and a clutch mechanism 60. In the gear shifting unit 21, the continuously variable transmission 30 receives power from the input shaft 20, and the planetary gear mechanism 40 receives power from the input shaft 20 and the output from the continuously variable transmission 30. The clutch mechanism 60 selects the gear (speed range) for the output from the planetary gear mechanism 40.

[0029] (Continuously Variable Transmission) The continuously variable transmission 30 of this embodiment is a hydrostatic continuously variable transmission called an HST (Hydraulic Static Transmission). The continuously variable transmission 30 has a hydraulic pump 31 and a hydraulic motor 32. The hydraulic pump 31 is a variable displacement hydraulic pump and has a swash plate 33. The hydraulic motor 32 is driven by the hydraulic fluid supplied from the hydraulic pump 31. In the continuously variable transmission 30, the pump shaft 31a of the hydraulic pump 31 is connected to the input shaft 20 via a first gear mechanism G1. By changing the angle of the swash plate 33 of the hydraulic pump 31 (hereinafter also referred to as the swash plate position), the continuously variable transmission 30 switches the rotation direction of the power from the input shaft 20 to the forward or reverse side, and continuously changes the rotation speed, outputting it from the motor shaft 32a of the hydraulic motor 32.

[0030] In the continuously variable transmission 30, the swash plate 33 is configured to be rotatable by a predetermined angle (A°) in the forward direction f and also by a predetermined angle (A°) in the reverse direction r, relative to the neutral position N where the rotation angle of the swash plate 33 is 0°. In this embodiment, the angle of the swash plate 33 is expressed as the swash plate position (in %). For example, when the swash plate 33 is rotated a° in the forward direction f from the neutral position N (when the rotation angle is a°), the swash plate position is calculated by the formula a / A × 100 (%). Also, when the swash plate 33 is rotated a° in the reverse direction r from the neutral position N (when the rotation angle is -a°), the swash plate position is calculated by the formula -a / A × 100 (%). In other words, in this embodiment, the position of the swash plate 33 is expressed as the ratio of the actual rotation angle of the swash plate 33 to the range of angles in which the swash plate 33 can rotate (+A° to -A°).

[0031] When the swash plate 33 is in the neutral position N (swash plate position 0% (i.e., rotation angle 0°)), the power (rotation) output from the motor shaft 32a becomes "0". In this description, the range of swash plate positions of the swash plate 33 that includes the neutral position N is referred to as the "neutral region". In the continuously variable transmission 30 of this embodiment, the neutral region is defined as the swash plate position within 20 (%) of the forward direction f and within 20 (%) of the reverse direction r from the neutral position N.

[0032] (Planetary gear mechanism) Figure 3 is a partially enlarged skeleton diagram of the planetary gear mechanism in Figure 2. Figure 4 is a partial cross-sectional view of the planetary gear mechanism. The planetary gear mechanism 40 receives power (rotation) from the input shaft 20 and the output of the continuously variable transmission 30, and combines these to produce an output. As shown in Figures 2 to 4, the planetary gear mechanism 40 is composed of a first planetary gear mechanism 41 and a second planetary gear mechanism 42, which are arranged in the axial direction of the input shaft 20. In other words, the planetary gear mechanism 40 is a so-called composite planetary gear mechanism. The first planetary gear mechanism 41 is located on one axial side (front side), and the second planetary gear mechanism 42 is located on the other axial side (rear side). In the planetary gear mechanism 40, the first planetary gear mechanism 41 functions as the power input section, and the second planetary gear mechanism 42 functions as the power output section.

[0033] As shown in Figures 2 to 4, the first planetary gear mechanism 41 has a first ring gear 41R, a first sun gear 41S, and a first planetary gear 41P. The second planetary gear mechanism 42 has a second ring gear 42R, a second sun gear 42S, and a second planetary gear 42P.

[0034] The planetary gear mechanism 40 further includes a planetary carrier 40C provided in the axial direction of the rotating shaft 22 (input shaft 20) extending across the first planetary gear mechanism 41 and the second planetary gear mechanism 42. The planetary carrier 40C rotatably supports the first planetary gear 41P and the second planetary gear 42P.

[0035] In the first planetary gear mechanism 41, the first planetary gear 41P meshes with the first sun gear 41S and the first ring gear 41R, revolves around the rotation axis 22, and rotates on its own axis.

[0036] In the first planetary gear mechanism 41, the first planetary gear 41P has an extended portion 43 that extends axially to the other side to the position where the second planetary gear mechanism 42 is located. The first planetary gear 41P has a third planetary gear 43P in the extended portion 43. The third planetary gear 43P meshes with the second planetary gear 42P of the second planetary gear mechanism 42 (see dotted line in Figure 3).

[0037] In the second planetary gear mechanism 42, the second planetary gear 42P meshes with the second sun gear 42S and the second ring gear 42R, revolves around the rotation axis 22, and rotates on its own axis. As mentioned above, the second planetary gear 42P is also meshed with the third planetary gear 43P.

[0038] As shown in Figures 2 and 3, the first sun gear 41S is connected to the motor shaft 32a via the third gear mechanism G3. Therefore, the output from the continuously variable transmission 30 is transmitted to the first sun gear 41S of the first planetary gear mechanism 41 of the planetary gear mechanism 40.

[0039] Furthermore, the first ring gear 41R is connected to the input shaft 20 via the second gear mechanism G2. Therefore, power from the input shaft 20 is transmitted to the first ring gear 41R of the first planetary gear mechanism 41 of the planetary gear mechanism 40.

[0040] The first planetary gear mechanism 41 combines the power input to the first sun gear 41S and the first ring gear 41R. The first planetary gear mechanism 41 transmits this combined power to the second planetary gear mechanism 42 via the first planetary gear 41P and the third planetary gear 43P.

[0041] The second planetary gear mechanism 42 receives power combined by the first planetary gear mechanism 41 via the third planetary gear 43P to the second sun gear 42S and the second ring gear 42R. The second planetary gear mechanism 42 outputs this input power from one of the second sun gear 42S, the second ring gear 42R, and the planetary carrier 40C.

[0042] In the planetary gear mechanism 40, the power output from the second planetary gear mechanism 42 is a combined power from the power from the input shaft 20 and the power from the continuously variable transmission 30.

[0043] As shown in Figure 4, the planetary gear mechanism 40 is equipped with an oil passage 45. The oil passage 45 supplies lubricating oil to each part of the planetary gear mechanism 40. In the power transmission device 10 of this disclosure, the planetary gear mechanism 40 is supplied with lubricating oil by the oil passage 45 from the other axial side (rear side) to the one axial side (front side).

[0044] (Clutch mechanism) As shown in Figure 2, the clutch mechanism 60 includes a first transmission shaft 55, a second transmission shaft 56, a third transmission shaft 57, an output shaft 65, a first clutch CL1, a second clutch CL2, a third clutch CL3, and a fourth clutch CL4. The first transmission shaft 55, the second transmission shaft 56, and the third transmission shaft 57 are arranged coaxially with each other, forming a triple-shaft structure. The output shaft 65 is arranged parallel to each of the transmission shafts 55, 56, and 57.

[0045] The clutch mechanism 60 selects one of the four clutches CL1 to CL4 and outputs the output from the planetary gear mechanism 40 in four speed ranges. The first clutch CL1 corresponds to the first speed range (hereinafter referred to as the 1st speed range), the second clutch CL2 corresponds to the second speed range (hereinafter referred to as the 2nd speed range), the third clutch CL3 corresponds to the third speed range (hereinafter referred to as the 3rd speed range), and the fourth clutch CL4 corresponds to the fourth speed range (hereinafter referred to as the 4th speed range). In the power transmission device 10 of this disclosure, the 1st speed range is the lowest speed range, the 2nd speed range is a speed range higher than the 1st speed range, the 3rd speed range is a speed range higher than the 2nd speed range, and the 4th speed range is the highest speed range. When the 4th range is selected, the tractor 101 (see Figure 1) can travel at the maximum speed specified in the design specifications.

[0046] In the clutch mechanism 60, the first transmission shaft 55 is connected to the second ring gear 42R, the second transmission shaft 56 is connected to the planetary carrier 40C, and the third transmission shaft 57 is connected to the second sun gear 42S.

[0047] The transmission gear 50 includes a plurality of gears, including a first transmission gear 51, a second transmission gear 52, a third transmission gear 53, and a fourth transmission gear 54. The first transmission gear 51 is mounted coaxially with respect to the first transmission shaft 55. The first transmission gear 51 is connected to the output shaft 65 of the clutch mechanism 60 via a first range gear 61 and a first clutch CL1. The second transmission gear 52 is mounted coaxially with respect to the third transmission shaft 57. The second transmission gear 52 is connected to the output shaft 65 of the clutch mechanism 60 via a second range gear 62 and a second clutch CL2. The third transmission gear 53 is mounted coaxially with respect to the second transmission shaft 56. The third transmission gear 53 is connected to the output shaft 65 of the clutch mechanism 60 via a third range gear 63 and a third clutch CL3. The fourth transmission gear 54 is mounted coaxially with respect to the third transmission shaft 57. The fourth transmission gear 54 is connected to the output shaft 65 of the clutch mechanism 60 via the fourth range gear 64 and the fourth clutch CL4.

[0048] (Regarding the switching of speed ranges in the gear shifting mechanism) Here, we will explain the power transmission situation in the gear shifting unit 21 with reference to Figure 2. In the transmission unit 21, a portion of the power from the prime mover 103 is input to the pump shaft 31a via the input shaft 20, the rotating shaft 22, and the first gear mechanism G1, and is rotated forward or backward by the continuously variable transmission 30, and then output from the motor shaft 32a. The power output from the motor shaft 32a is further input to the first sun gear 41S of the first planetary gear mechanism 41 via the third gear mechanism G3.

[0049] In the transmission unit 21, the remaining power from the prime mover 103 (power other than a portion of the aforementioned power) is input to the first ring gear 41R of the first planetary gear mechanism 41 via the input shaft 20 and the second gear mechanism G2.

[0050] The transmission unit 21 combines power from the continuously variable transmission 30 and power from the prime mover 103 using the first planetary gear mechanism 41 and the second planetary gear mechanism 42. The power combined by the planetary gear mechanism 40 is transmitted to one of the first transmission shaft 55, the second transmission shaft 56, and the third transmission shaft 57.

[0051] When the first clutch CL1 is engaged, power from the planetary gear mechanism 40 is transmitted from the second ring gear 42R to the first transmission shaft 55, and output from the output shaft 65 via the first transmission gear 51, the first range gear 61, and the first clutch CL1. In this case, the continuously variable transmission 30 and the planetary gear mechanism 40 output power in the first gear range.

[0052] When the second clutch CL2 is engaged, power from the planetary gear mechanism 40 is transmitted from the second sun gear 42S to the third transmission shaft 57, and output from the output shaft 65 via the second transmission gear 52, the second range gear 62, and the second clutch CL2. In this case, the continuously variable transmission 30 and the planetary gear mechanism 40 output power in the second gear range.

[0053] When the third clutch CL3 is engaged, power from the planetary gear mechanism 40 is transmitted from the planetary carrier 40C to the second transmission shaft 56, and output from the output shaft 65 via the third transmission gear 53, the third range gear 63, and the third clutch CL3. In this case, the continuously variable transmission 30 and the planetary gear mechanism 40 output power in the third range.

[0054] When the fourth clutch CL4 is engaged, power from the planetary gear mechanism 40 is transmitted from the second sun gear 42S to the third transmission shaft 57, and output from the output shaft 65 via the fourth transmission gear 54, the fourth range gear 64, and the fourth clutch CL4. In this case, the continuously variable transmission 30 and the planetary gear mechanism 40 output power in the fourth range.

[0055] As described above, the power transmission device 10 of this embodiment includes an output shaft 65 that is rotationally driven by a planetary gear mechanism 40, and a clutch mechanism 60 that engages one of the first transmission gear 51, second transmission gear 52, third transmission gear 53, and fourth transmission gear 54 with the output shaft 65. With a power transmission device 10 configured in this way, it is possible to select any of the 1st gear range to 4th gear range as the gear ratio.

[0056] (Forward / forward switching mechanism) The forward / reverse switching mechanism 70 switches the power from the planetary gear mechanism 40 to either forward or reverse power and outputs it. As shown in Figure 2, the forward / reverse switching mechanism 70 has an input shaft 71 connected to the output shaft 65 of the clutch mechanism 60, and an output shaft 72 arranged parallel to the input shaft 71. The forward / reverse switching mechanism 70 further has a forward clutch CLF and a reverse clutch CLR provided on the input shaft 71. The forward clutch CLF is connected to the output shaft 72 via a forward gear mechanism 73. The reverse clutch CLR is connected to the output shaft 72 via a reverse gear mechanism 74.

[0057] When the forward clutch CLF is engaged, the input shaft 71 is connected to the forward gear mechanism 73. At this time, power from the input shaft 71 is transmitted to the output shaft 72 via the forward gear mechanism 73. In this case, the work vehicle 100 becomes capable of moving forward. When the reverse clutch CLR is engaged, the input shaft 71 is connected to the reverse gear mechanism 74. At this time, power from the input shaft 71 is transmitted to the output shaft 72 via the reverse gear mechanism 74. In this case, the work vehicle 100 becomes capable of moving in reverse.

[0058] The forward / reverse switching mechanism 70 receives the output of the planetary gear mechanism 40 via the clutch mechanism 60 to the input shaft 71. When the forward clutch CLF is "on", the power of the input shaft 71 is converted into forward power by the forward clutch CLF and the forward gear mechanism 73 and transmitted to the output shaft 72. When the reverse clutch CLR is "on", the power of the input shaft 71 is converted into reverse power by the reverse clutch CLR and the reverse gear mechanism 74 and transmitted to the output shaft 72.

[0059] The forward / reverse switching mechanism 70 further includes a gear mechanism 75. The gear mechanism 75 transmits power from the forward / reverse switching mechanism 70 to the rear wheel differential mechanism 15 and the front wheel transmission mechanism 25. Forward and reverse power from the output shaft 72 is transmitted to the rear wheel differential mechanism 15 and the front wheel transmission mechanism 25 by the gear mechanism 75.

[0060] (Rear wheel differential mechanism) As shown in Figure 2, the rear wheel differential mechanism 15 has an input shaft 15a and an output shaft 15b. Power from the output shaft 72 in the forward or reverse direction is transmitted to the input shaft 15a of the rear wheel differential mechanism 15. The rear wheel differential mechanism 15 transmits the power transmitted to the input shaft 15a to the left and right rear wheels 104b via the left and right output shafts 15b.

[0061] (Front wheel transmission mechanism) As shown in Figure 2, the front wheel transmission mechanism 25 has an input shaft 25a connected to the output shaft 76 of the gear mechanism 75, and an output shaft 25b located parallel to the input shaft 25a. The front wheel transmission mechanism 25 transmits the power transmitted to the input shaft 25a to the output shaft 25b via a constant-velocity clutch (not shown). The output shaft 25b is connected to the input shaft 28a of the front wheel differential mechanism 28 via a rotating shaft 27. The front wheel transmission mechanism 25 transmits the power transmitted to the output shaft 25b to the front wheel differential mechanism 28 (input shaft 28a) via the rotating shaft 27.

[0062] (Control device) Figure 5 is a control block diagram of the power transmission system. As shown in Figure 5, the work vehicle 100 (tractor 101) of this embodiment further includes a control device 80. In the work vehicle 100 (tractor 101) of this disclosure, the driver performs gear shifting operations using a gear shift pedal 107 and a gear shift lever 108 located in the cabin 123.

[0063] The control device 80 is connected to the gear shift pedal 107 and the gear shift lever 108, and receives operation signals related to the amount of operation of each part 107 and 108. Based on the operation signals received from the gear shift pedal 107 and the gear shift lever 108, the control device 80 outputs signals to the continuously variable transmission 30, the clutch mechanism 60, and the forward / reverse switching mechanism 70 to control their operation.

[0064] The control device 80 outputs a signal to the continuously variable transmission 30 to control the angle (swash plate position) of the swash plate 33. The control device 80 outputs a signal to the clutch mechanism 60 to turn each clutch (first clutch CL1, second clutch CL2, third clutch CL3, and fourth clutch CL4) ON (connected) or OFF (disconnected). The control device 80 outputs a signal to the forward / reverse switching mechanism 70 to turn each clutch (forward clutch CLF and reverse clutch CLR) ON (connected) or OFF (disconnected).

[0065] (Regarding conventional planetary gear mechanisms) This section describes conventional planetary gear mechanisms.

[0066] Figure 6 is a partial skeleton diagram of a planetary gear mechanism constituting a conventional power transmission device. Figure 7 is a partial cross-sectional view of a conventional planetary gear mechanism. Figures 6 and 7 show a conventional planetary gear mechanism 140. The conventional planetary gear mechanism 140 is an example of a planetary gear mechanism constituting a conventional power transmission device (not shown). In the following description, the conventional planetary gear mechanism 140 will also be referred to as the power transmission device relating to the "comparative example".

[0067] As shown in Figures 6 and 7, the conventional planetary gear mechanism 140, like the planetary gear mechanism 40 of this embodiment (see Figure 5), is a mechanism that receives power (rotation) from the input shaft 20 and the output of the continuously variable transmission 30, and combines them to produce an output. The planetary gear mechanism 140 is composed of a first planetary gear mechanism 141 and a second planetary gear mechanism 142 that are arranged in the axial direction of the input shaft 20. Here, the configuration of each part connected to one axial side and the other axial side of the planetary gear mechanism 140 (for example, the input shaft 20, the rotating shaft 22, the transmission gear 50, the clutch mechanism 60, etc.) will be described as being common to the planetary gear mechanism 40 (see Figures 3 and 4).

[0068] The first planetary gear mechanism 141 includes a first ring gear 141R, a first sun gear 141S, and a first planetary gear 141P. The second planetary gear mechanism 142 includes a second ring gear 142R, a second sun gear 142S, and a second planetary gear 142P. The planetary gear mechanism 140 includes a planetary carrier 140C that extends across the first planetary gear mechanism 41 and the second planetary gear mechanism 42 in the axial direction of the input shaft 20. The planetary carrier 140C rotatably supports the first planetary gear 141P and the second planetary gear 142P.

[0069] In the first planetary gear mechanism 141, the first planetary gear 141P meshes with the first sun gear 141S and the first ring gear 141R, revolves around the input shaft 20, and rotates on its own axis.

[0070] In the second planetary gear mechanism 142, the second planetary gear 142P meshes with the second sun gear 142S and the second ring gear 142R, revolves around the input shaft 20, and rotates on its own axis.

[0071] In the second planetary gear mechanism 142, the second planetary gear 142P further has an extension portion 143 that extends axially to the position where the first planetary gear mechanism 141 is located. The second planetary gear 142P has a third planetary gear 143P in the extension portion 143. The third planetary gear 143P meshes with the first planetary gear 141P of the first planetary gear mechanism 141 (see dotted line in Figure 6).

[0072] In the conventional planetary gear mechanism 140 configured in this way, the power transmitted to the first planetary gear 141P is transmitted to the second planetary gear 142P by meshing the first planetary gear 141P and the third planetary gear 143P in the first planetary gear mechanism 141 on one axial side.

[0073] As shown in Figure 7, the conventional planetary gear mechanism 140 is equipped with an oil passage 145. The oil passage 145 supplies lubricating oil to each part of the planetary gear mechanism 140. In the conventional planetary gear mechanism 140, lubricating oil is supplied by the oil passage 145 from one axial side (front side) to the other axial side (rear side).

[0074] (Regarding the comparison of the diameters of sun gears and ring gears) As shown in Figure 7, in the conventional planetary gear mechanism 140, the third planetary gear 143P is positioned on the side of the first planetary gear mechanism 141 (one side in the axial direction). In this case, the internal space of the planetary gear mechanism 140 is limited due to the size constraints of the planetary gear mechanism 140 itself. Therefore, the planetary gear mechanism 140 is forced to reduce the outer diameter dimension rs1 of the first sun gear 141S. For this reason, in the conventional planetary gear mechanism 140, the outer diameter dimension rs1 of the first sun gear 141S is smaller than the outer diameter dimension rs2 of the second sun gear 142S (rs1 <rs2)。

[0075] Furthermore, in this case, the conventional planetary gear mechanism 140 faces an additional challenge: due to internal space constraints, the inner diameter dimension rr1 of the first ring gear 141R in the first planetary gear mechanism 141 must be increased. As a result, in the conventional planetary gear mechanism 140, the inner diameter dimension rr1 of the first ring gear 141R is larger than the inner diameter dimension rr2 of the second ring gear 142R (rr1>rr2).

[0076] In other words, in a planetary gear mechanism 140 in which the third planetary gear 143P is positioned on the side of the first planetary gear mechanism 141 (one side in the axial direction), the outer diameter dimension rs1 of the first sun gear 141S is smaller than the outer diameter dimension rs2 of the second sun gear 142S, and the inner diameter dimension rr1 of the first ring gear 141R is larger than the inner diameter dimension rr2 of the second ring gear 142R.

[0077] Conventional planetary gear mechanisms 140 with this configuration tend to have a larger outer diameter rs2 of the second sun gear 142S. As a result, the gear ratio of the fourth transmission gear 54 to the second sun gear 142S is large in conventional planetary gear mechanisms 140. Consequently, in conventional power transmission devices (not shown) having a planetary gear mechanism 140, it becomes difficult to increase the rotational speed of the power in the 4th range output from the 4th range gear 64 via the 4th transmission gear 54 and the 4th clutch CL4.

[0078] Furthermore, conventional planetary gear mechanisms 140 with such a configuration tend to have a larger inner diameter dimension rr2 of the second ring gear 142R. As a result, the gear ratio of the first transmission gear 51 to the second ring gear 142R is small in conventional planetary gear mechanisms 140. Consequently, conventional power transmission devices (not shown) having a planetary gear mechanism 140 have difficulty increasing the traction force for the first gear range power output from the first range gear 61 via the first transmission gear 51 and the first clutch CL1.

[0079] On the other hand, in the planetary gear mechanism 40 of this disclosure shown in Figures 3 and 5, the third planetary gear 43P is provided on the second planetary gear mechanism 42 side. Therefore, the planetary gear mechanism 40 of this disclosure allows the outer diameter dimension RS1 of the first sun gear 41S in the first planetary gear mechanism 41 to be larger than in the conventional (see outer diameter dimension rs1 in Figure 7). Therefore, in the planetary gear mechanism 40 of this disclosure, the outer diameter dimension RS1 of the first sun gear 41S is larger than the outer diameter dimension RS2 of the second sun gear 42S (RS1 > RS2).

[0080] Furthermore, in the planetary gear mechanism 40 in which the third planetary gear 43P is provided on the second planetary gear mechanism 42 side, the inner diameter dimension RR1 of the first ring gear 41R in the first planetary gear mechanism 41 can be made smaller than in the conventional (see inner diameter dimension rr1 in Figure 7). For this reason, in the planetary gear mechanism 40 of this disclosure, the inner diameter dimension RR1 of the first ring gear 41R is smaller than the inner diameter dimension RR2 of the second ring gear 42R (RR1 <RR2)。

[0081] In other words, in the planetary gear mechanism 40 of this disclosure, the outer diameter dimension RS1 of the first sun gear 41S is larger than the outer diameter dimension RS2 of the second sun gear 42S, and the inner diameter dimension RR1 of the first ring gear 41R is smaller than the inner diameter dimension RR2 of the second ring gear 42R.

[0082] The planetary gear mechanism 40 with this configuration allows the outer diameter dimension RS2 of the second sun gear 42S to be smaller than in the conventional design. As a result, the power transmission device 10 having the planetary gear mechanism 40 can have a larger gear ratio of the fourth transmission gear 54 to the second sun gear 42S. Therefore, the power transmission device 10 of this disclosure can increase the rotational speed of the power in the 4th range output from the fourth range gear 64 via the fourth transmission gear 54 and the fourth clutch CL4. In this embodiment, the outer diameters of the first sun gear 41S and the second sun gear 42S are compared, but for example, the reference circle diameters may be compared.

[0083] Furthermore, the planetary gear mechanism 40 with this configuration allows for a larger inner diameter dimension RR2 of the second ring gear 42R compared to conventional designs. As a result, the power transmission device 10 having the planetary gear mechanism 40 can reduce the gear ratio of the first transmission gear 51 to the second ring gear 42R. Therefore, the power transmission device 10 of this disclosure can increase the traction force for the first gear range power output from the first range gear 61 via the first transmission gear 51 and the first clutch CL1. In this embodiment, the inner diameters of the first ring gear 41R and the second ring gear 42R are compared, but for example, the reference circle diameters may be compared.

[0084] (Regarding the relationship between the number of teeth on gears) In the transmission 11 of this embodiment, the relative number of teeth of each gear constituting the planetary gear mechanism 40 is as follows:

[0085] In the planetary gear mechanism 40, the number of teeth of the first sun gear 41S is greater than the number of teeth of the second sun gear 42S, and the number of teeth of the first ring gear 41R is less than the number of teeth of the second ring gear 42R.

[0086] Therefore, in the power transmission device 10 of this disclosure, the gear ratio GR1 of the second sun gear 42S relative to the first sun gear 41S is less than 1.0, and the gear ratio GR2 of the second ring gear 42R relative to the first ring gear 41R is greater than 1.0.

[0087] On the other hand, in the conventional planetary gear mechanism 140 shown in Figures 6 and 7, the relative number of teeth of each gear is as follows.

[0088] In the conventional planetary gear mechanism 140, the number of teeth of the first sun gear 141S is fewer than the number of teeth of the second sun gear 142S, and the number of teeth of the first ring gear 141R is more than the number of teeth of the second ring gear 142R.

[0089] Therefore, in conventional power transmission systems, the gear ratio GR1 of the second sun gear 142S relative to the first sun gear 141S is greater than 1.0, and the gear ratio GR2 of the second ring gear 142R relative to the first ring gear 141R is less than 1.0.

[0090] As described above, in the power transmission device 10 of this embodiment, the number of teeth of the second sun gear 42S is less than the number of teeth of the first sun gear 41S. In contrast, in the conventional planetary gear mechanism 140, the number of teeth of the second sun gear 142S is greater than the number of teeth of the first sun gear 141S. With this configuration, the power transmission device 10 can reduce the reduction ratio in the 4th gear range by further reducing the number of teeth of the second sun gear 42S. Therefore, the power transmission device 10 of this embodiment can reduce power loss when selecting the 4th gear range for high-speed driving.

[0091] Furthermore, in the power transmission device 10 of this embodiment, the number of teeth of the second ring gear 42R is greater than the number of teeth of the first ring gear 41R. In contrast, in the conventional planetary gear mechanism 140, the number of teeth of the second ring gear 142R is less than the number of teeth of the first ring gear 141R. With this configuration, the power transmission device 10 can increase the reduction ratio in the first gear range by increasing the number of teeth of the second ring gear 42R. Therefore, according to the power transmission device 10 of this embodiment, the maximum traction force can be improved when the first gear range is selected for low-speed driving.

[0092] Furthermore, in the power transmission device 10 of this embodiment, the gear ratio of the second sun gear 42S to the first sun gear 41S is less than 1.0, and the gear ratio of the second ring gear 42R to the first ring gear 41R is greater than 1.0. In contrast, in the conventional planetary gear mechanism 140, the gear ratio of the second sun gear 142S to the first sun gear 141S is greater than 1.0, and the gear ratio of the second ring gear 142R to the first ring gear 141R is less than 1.0. A power transmission device 10 with such a configuration can reduce the reduction ratio in the 4th gear range and increase the reduction ratio in the 1st gear range. Therefore, according to the power transmission device 10 of this embodiment, the maximum traction force when driving at low speed by selecting the 1st gear range can be improved, and power loss when driving at high speed by selecting the 4th gear range can be reduced.

[0093] (Regarding the maximum speed when work vehicles are in motion) Figure 8 shows the relationship between the swash plate position and vehicle speed in a continuously variable transmission (CVT) of a work vehicle. Figure 8 shows the experimental results confirming the relationship between the swash plate position of the swash plate 33 and vehicle speed (travel speed) for a tractor 101 (hereinafter also referred to as the "Example") equipped with a power transmission device 10 including a planetary gear mechanism 40, and a tractor (hereinafter also referred to as the "Comparative Example") equipped with a conventional power transmission device including a planetary gear mechanism 140. Each tractor used in this experiment is set to a desired maximum speed A in the 4th gear range. The maximum speed A in this experiment is approximately 40 to 60 km / h. Furthermore, this experiment was conducted with the rotational speed of the prime mover (engine) 103 set to its rated rotational speed.

[0094] As shown in Figure 8, in the case of the (comparative example), the desired maximum speed A in the 4th gear range was obtained when the swash plate position of the swash plate 33 was set to 75%. On the other hand, in the case of the (example), the desired maximum speed A in the 4th gear range was obtained when the swash plate position of the swash plate 33 was in the neutral range.

[0095] Thus, in this embodiment, the work vehicle 100 (tractor 101) can achieve the desired maximum speed A in the 4th gear range with the swash plate 33 in the neutral position. In other words, the work vehicle 100 can travel at high speed with the swash plate 33 in the neutral position.

[0096] In the power transmission device 10 of this disclosure, the continuously variable transmission 30 has a swash plate 33, and the rotational speed and rotational direction of the hydraulic motor 32 can be changed according to the position of the swash plate 33. Furthermore, in the power transmission device 10 of this disclosure, the planetary gear mechanism 40 is configured such that the rotational speed of the second sun gear 42S is maximized when the swash plate 33 is in the neutral range (a range of -20% or more and +20% or less) when the 4th gear range is selected. At this time, the rotational speed of the fourth transmission gear 54 is also maximized, and the rotational speed of the fourth range gear 64 is also maximized. Therefore, in the work vehicle 100 (tractor 101) of this embodiment, the desired maximum speed A can be achieved in the 4th gear range with the swash plate 33 in the neutral range.

[0097] According to the power transmission device 10 of this disclosure, when selecting the 4th gear range for high-speed driving, setting the swash plate 33 to the neutral position enables driving at the maximum speed A. Furthermore, when the swash plate 33 is positioned in the neutral position, power loss in the continuously variable transmission 30 can be reduced. Thus, the power transmission device 10 of this disclosure can achieve a reduction in power loss during high-speed driving.

[0098] The reason why the power transmission device 10 of this disclosure can achieve both an improvement in maximum traction force and travel at the maximum speed in the swashplate neutral zone will be explained. In this embodiment, the planetary gear mechanism 40 has a reduced number of teeth on the second sun gear 42S in order to reduce the reduction ratio of the planetary gear mechanism 40. In this embodiment, the planetary gear mechanism 40 has a reduced number of teeth on the first sun gear 41S in order to reduce the number of teeth on the second sun gear 42S. In other words, in this embodiment, the planetary gear mechanism 40 has a reduced reduction ratio in the 4th gear range (and 2nd gear range) by increasing the number of teeth on the first sun gear 41S and decreasing the number of teeth on the second sun gear 42S. In this case, the reduction ratio in the 1st gear range of the planetary gear mechanism 40 becomes larger.

[0099] Furthermore, the planetary gear mechanism 40 of this embodiment increases the reduction ratio between the continuously variable transmission 30 and the first sun gear 41S compared to conventional designs by increasing the number of teeth of the first sun gear 41S. In this case, the torque input to the first sun gear 41S increases. However, when the torque input to the first sun gear 41S increases, the reduction ratio in the first clutch CL1 to the fourth clutch CL4 increases, leading to a problem of reduced speed. The planetary gear mechanism 40 of this embodiment suppresses the increase in the reduction ratio in the first clutch CL1 to the fourth clutch CL4 by reducing the number of teeth of the second sun gear 42S, thereby suppressing the reduction in speed and enabling travel at the maximum speed A when the swash plate 33 is in the neutral position. Increasing the reduction ratio from the continuously variable transmission 30 to the first sun gear 41S reduces the adjustment range of the rotational speed of each gear constituting the planetary gear mechanism 40, making it difficult to achieve continuously variable speed control. However, with the planetary gear mechanism 40 of this embodiment, it is possible to set the gear ratio to one which enables continuously variable speed control.

[0100] In other words, compared to the conventional planetary gear mechanism 140, the planetary gear mechanism 40 of this embodiment achieves both improved maximum traction and operation at the maximum speed A when the swash plate 33 is in the neutral position by reversing the relative sizes of the outer diameters of the first sun gear 41S and the second sun gear 42S, and the relative sizes of the inner diameters of the first ring gear 41R and the second ring gear 42R.

[0101] [Regarding power loss during operation of work vehicles] Figure 9 shows the relationship between power loss and vehicle speed in the power transmission system of a work vehicle. Figure 9 shows experimental results confirming the relationship between vehicle speed and power loss for a tractor 101 (example) equipped with a power transmission system 10 including a planetary gear mechanism 40, and a tractor (comparative example) equipped with a conventional power transmission system including a planetary gear mechanism 140 (not shown).

[0102] Comparing the power loss at maximum speed A (4th gear range) for both the (Example) and the (Comparative Example), the work vehicle 100 (tractor 101) according to the (Example) shows reduced power loss at maximum speed A compared to the work vehicle according to the (Comparative Example).

[0103] The following reasons are presumed to be the reasons why the power transmission device 10 of this disclosure can reduce power loss. The work vehicle 100 (tractor 101) according to the (Example) is capable of high-speed travel at the maximum speed A with the swash plate 33 in the neutral position. When the swash plate 33 is in the neutral position, the power (rotation) output from the continuously variable transmission 30 is near "0". In this case, the ratio of power input from the input shaft 20 via the third gear mechanism G3 to the power input from the continuously variable transmission 30 via the third gear mechanism G3 becomes larger for the planetary gear mechanism 40. As the proportion of power input to the planetary gear mechanism 40 via the continuously variable transmission 30 increases, the power loss due to frictional resistance increases. The power transmission device 10 of this disclosure can set the swash plate position of the continuously variable transmission 30 to the neutral position when traveling at high speed. Therefore, a work vehicle 100 equipped with the power transmission device 10 of this disclosure can reduce the proportion of power transmitted via the continuously variable transmission 30 during high-speed travel, thereby reducing power loss. For this reason, the work vehicle 100 (tractor 101) according to the (embodiment) is configured such that the proportion of power input to the planetary gear mechanism 40 via the continuously variable transmission 30 becomes smaller when traveling in the 4th gear range, thereby reducing power loss during high-speed travel.

[0104] As described above, the power transmission device 10 for the work vehicle 100 (tractor 101) of this embodiment includes a transmission 11 having an input shaft 20 rotationally driven by a prime mover 103, a continuously variable transmission 30 having a first gear mechanism G1 and a second gear mechanism G2 driven by the input shaft 20, a hydraulic pump 31 driven by the first gear mechanism G1, and a hydraulic motor 32 driven by the hydraulic pump 31, a planetary gear mechanism 40 driven by the second gear mechanism G2 and the hydraulic motor 32, and a plurality of transmission gears 50 to which the output of the planetary gear mechanism 40 is transmitted. The plurality of transmission gears 50 include a first transmission gear 51 corresponding to the lowest speed 1st gear range, a second transmission gear 52 corresponding to the 2nd gear range which is faster than the 1st gear range, a third transmission gear 53 corresponding to the 3rd gear range which is faster than the 2nd gear range, and a fourth transmission gear 54 corresponding to the highest speed 4th gear range. The planetary gear mechanism 40 is coaxial with the input shaft 20 and includes a first planetary gear mechanism 41 and a second planetary gear mechanism 42 that are arranged in the axial direction of the input shaft 20. The first planetary gear mechanism 41 and the second planetary gear mechanism 42 have a common planetary carrier 40C. The first planetary gear mechanism 41 includes a first ring gear 41R driven by a second gear mechanism G2, a first sun gear 41S driven by a hydraulic motor 32, and a first planetary gear 41P that meshes with the first ring gear 41R and the first sun gear 41S. The second planetary gear mechanism 42 includes a second ring gear 42R that transmits rotation to the first transmission gear 51, a second sun gear 42S that transmits rotation to the second transmission gear 52 and the fourth transmission gear 54, and a second planetary gear 42P. The first planetary gear 41P has an extended portion 43 that extends axially to the second planetary gear mechanism 42, and has a third planetary gear 43P that meshes with the second planetary gear 42P at the extended portion 43. The planetary carrier 40C rotatably supports the first planetary gear 41P and the second planetary gear 42P and transmits rotation to the third transmission gear 53.In a power transmission device 10 with this configuration, the outer diameter dimension RS1 of the first sun gear 41S is larger than the outer diameter dimension RS2 of the second sun gear 42S (RS1 > RS2), and the inner diameter dimension RR2 of the second ring gear 42R is larger than the inner diameter dimension RR1 of the first ring gear 41R (RR2 > RR1).

[0105] In the power transmission device 10 for the work vehicle 100 (tractor 101) having such a configuration, the inner diameter dimension RR2 of the second ring gear 42R is larger than the inner diameter dimension RR1 of the first ring gear 41R. In this case, the inner diameter dimension RR2 of the second ring gear 42R can be made larger. Furthermore, in the power transmission device 10, the outer diameter dimension RS1 of the first sun gear 41S is larger than the outer diameter dimension RS2 of the second sun gear 42S. In this case, the outer diameter dimension RS1 of the first sun gear 41S can be made smaller. With this configuration, the power transmission device 10 can increase the reduction ratio in the 1st gear range and decrease the reduction ratio in the 4th gear range. With a power transmission system 10 for a work vehicle 100 (tractor 101) configured in this way, it is possible to improve the maximum traction force when driving at low speeds by selecting the 1st gear range, and to reduce power loss when driving at high speeds by selecting the 4th gear range.

[0106] The embodiments described above are illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than by the embodiments, and includes all modifications within the scope equivalent to the configurations described in the claims. [Explanation of Symbols]

[0107] 10 Power transmission device 11 Transmission 20 Input axes 30 Continuously Variable Transmission 31 Hydraulic pump 32 Hydraulic motor 33 Swash plate 40 Planetary gear mechanism 40C Planetary Carrier 41. First planetary gear mechanism 41S First Sun Gear 41R 1st Ring Gear 41P First Planetary Gear 42. Second planetary gear mechanism 42S Second Sun Gear 42R 2nd Ring Gear 42P Second Planetarium Gear 43 Extension part 43P Third Planetary Gear 50 transmission gears 51 First transmission gear 52 Second transmission gear 53 Third transmission gear 54 Fourth transmission gear 60 Clutch mechanism 65 Output shaft G1 First gear mechanism G2 Second gear mechanism 100 work vehicles 101 Tractor (work vehicle) RR1 (Inner diameter dimension of the first ring gear) RR2 (Second Ring Gear) Inner Diameter Dimension RS1 (Outer diameter of the first sun gear) RS2 (outer diameter of the second sun gear)

Claims

1. An input shaft that is driven to rotate by a prime mover, A first gear mechanism and a second gear mechanism driven by the aforementioned input shaft, A continuously variable transmission having a hydraulic pump driven by the first gear mechanism and a hydraulic motor driven by the hydraulic pump, The planetary gear mechanism driven by the second gear mechanism and the hydraulic motor, A power transmission device for a work vehicle, comprising a transmission having a plurality of transmission gears on which the output of the planetary gear mechanism is transmitted, The plurality of transmission gears include a first transmission gear corresponding to the lowest speed 1st gear range, a second transmission gear corresponding to the 2nd gear range which is faster than the 1st gear range, a third transmission gear corresponding to the 3rd gear range which is faster than the 2nd gear range, and a fourth transmission gear corresponding to the highest speed 4th gear range. The planetary gear mechanism is coaxial with the input shaft and includes a first planetary gear mechanism and a second planetary gear mechanism that are arranged in the axial direction of the input shaft. The first planetary gear mechanism and the second planetary gear mechanism have a common planetary carrier. The first planetary gear mechanism includes a first ring gear driven by the second gear mechanism, a first sun gear driven by the hydraulic motor, and a first planetary gear that meshes with the first ring gear and the first sun gear. The second planetary gear mechanism includes a second ring gear that transmits rotation to the first transmission gear, a second sun gear that transmits rotation to the second transmission gear and the fourth transmission gear, and a second planetary gear that meshes with the second ring gear, the second sun gear, and the first planetary gear. The first planetary gear has an extended portion that extends in the axial direction to the second planetary gear mechanism, and has a third planetary gear that meshes with the second planetary gear in the extended portion. The planetary carrier rotatably supports the first planetary gear and the second planetary gear, and transmits rotation to the third transmission gear. The outer diameter of the first sun gear is larger than the outer diameter of the second sun gear, A power transmission device for a work vehicle, wherein the inner diameter of the second ring gear is larger than the inner diameter of the first ring gear.

2. The continuously variable transmission further includes a swash plate, and the rotational speed and rotational direction of the hydraulic motor can be changed according to the angle of the swash plate. The power transmission device for a work vehicle according to claim 1, wherein the output is such that the work vehicle can travel at its maximum speed when the angle of the swash plate is in the neutral range.

3. The output shaft is rotationally driven by the aforementioned planetary gear mechanism, A clutch mechanism that engages any one of the first transmission gear, the second transmission gear, the third transmission gear, and the fourth transmission gear with the output shaft, A power transmission device for a work vehicle according to claim 1 or claim 2, further comprising:

4. The power transmission device for a work vehicle according to claim 1 or claim 2, wherein the second sun gear has fewer teeth than the first sun gear.

5. The power transmission device for a work vehicle according to claim 1 or claim 2, wherein the second ring gear has more teeth than the first ring gear.

6. The gear ratio of the second sun gear to the first sun gear is less than 1.0, and The power transmission device for a work vehicle according to claim 1 or claim 2, wherein the gear ratio of the second ring gear to the first ring gear is greater than 1.

0.

7. A work vehicle comprising the power transmission device according to claim 1 or claim 2.

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