Power transmission device for vehicle

Abstract

The first variable spill valve 51A is in a cut-off state in which the flow of the working oil from the first main line 37A to the second main line 37B is shut off when the pressure of the first main line 37A is below a first pressure, and is in a communication state in which the flow of the working oil is allowed when the pressure exceeds the first pressure. The second variable spill valve 51B is in a cut-off state in which the flow of the working oil from the second main line 37B to the first main line 37A is shut off when the pressure of the second main line 37B is below a second pressure, and is in a communication state in which the flow of the working oil is allowed when the pressure exceeds the second pressure. By setting the first pressure of the first variable spill valve 51A higher than the second pressure of the second variable spill valve 51B, the "power transmission capacity from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and the "power transmission capacity from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" are made different from each other.

Description

Technical Field

[0001] This disclosure relates to a vehicle power transmission device mounted on a vehicle (operating vehicle) such as a wheel loader. Background Technology

[0002] Wheel loaders and similar work vehicles typically lack a suspension system to cushion the impact, resulting in significant swaying (pitching) as the vehicle rotates in its direction of travel. Therefore, for example, when bulldozing (or dumping), it is difficult for the operator to maintain a consistent accelerator pedal input while the vehicle is traveling at a certain speed, making operation challenging. Furthermore, the poor ride comfort and the potential for operator fatigue are also issues.

[0003] Here, the greater the combined mass of the "front working machine, which consists of the bucket, boom, and lifting cylinder of the work vehicle" and the "cargo such as sand supported by the front working machine," the greater the pitching or rebounding of the work vehicle while it is in motion. Therefore, when traveling with the bucket fully loaded with sand or the like, there is a tendency for poor riding comfort. To solve this problem, for example, Patent Document 1 describes a work vehicle equipped with a riding vibration suppression device called a riding control device.

[0004] The riding control device is constructed by connecting a hydraulic accumulator to the hydraulic circuit of the lifting cylinder, which supplies working oil to the lifting cylinder, via a control valve. By opening the control valve, the riding control device allows working oil to flow between the lifting cylinder and the hydraulic accumulator, enabling the hydraulic accumulator to absorb the pressure fluctuations at the bottom of the lifting cylinder as the vehicle moves up and down, thereby reducing the overall impact on the vehicle body.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2018 / 199301 Summary of the Invention

[0008] Summary of the invention

[0009] However, according to the prior art described in Patent Document 1, the vibration suppression effect of the ride control device is limited by the accumulator capacity. Therefore, if the vibration is large, the accumulator capacity may be insufficient, and it may not be able to suppress the vibration adequately. Furthermore, if the front work machine is operated while the ride control device is functioning, the damping effect of the accumulator acts on the front work machine, and the operation of the front work machine may become unstable. Moreover, even if the front work machine stops operating due to the damping effect of the accumulator, the front work machine will still move slightly, thus potentially deteriorating the positioning accuracy of the front work machine or reducing its operability. Therefore, it is preferable to suppress vibrations during travel without using an accumulator.

[0010] The purpose of this invention is to provide a power transmission device for vehicles that does not use an accumulator and can improve the effect of suppressing vibrations during driving.

[0011] One embodiment of the present invention is a power transmission device for a vehicle, characterized by comprising: an input shaft that rotates via a prime mover mounted on the vehicle; an output shaft that outputs rotation to the vehicle's drive mechanism; and a continuously variable transmission (CVT) mechanism disposed between the input shaft and the output shaft, which transmits rotational speed changes from the input shaft side to the output shaft side, the CVT mechanism comprising: a first hydraulic pump motor disposed on the input shaft side; a second hydraulic pump motor connected to the first hydraulic pump motor via a pair of main lines, namely a first main line and a second main line; and a first relief valve that allows working oil to flow from the first main line to the second main line when the pressure in the first main line is below a first set pressure. The system comprises a cut-off state and a connected state when the pressure exceeds the first set pressure; and a second relief valve, which cuts off the flow of working oil from the second main pipeline to the first main pipeline when the pressure in the second main pipeline is below the second set pressure, and connects when the pressure exceeds the second set pressure. The first hydraulic pump motor and the second hydraulic pump motor are connected between them via the pair of main pipelines. By setting the first set pressure of the first relief valve higher than the second set pressure of the second relief valve, the power transmitted from the first hydraulic pump motor to the second hydraulic pump motor and the power transmitted from the second hydraulic pump motor to the first hydraulic pump motor are of different magnitudes.

[0012] Another embodiment of the present invention is a power transmission device for a vehicle, characterized by comprising: an input shaft that rotates via a prime mover mounted on the vehicle; an output shaft that outputs rotation to the vehicle's driving mechanism; and a continuously variable transmission (CVT) mechanism disposed between the input shaft and the output shaft, which enables speed change of rotation on the input shaft side and transmits it to the output shaft side. The CVT mechanism comprises: a first electric generator disposed on the input shaft side; a controller connected to the first electric generator via a first wire; and a second electric generator connected to the controller via a second wire. The first wire is configured to transmit power between the first electric generator and the controller, and the second wire is configured to transmit power between the second electric generator and the controller. The controller ensures that the power transmitted from the first electric generator to the second electric generator and the power transmitted from the second electric generator to the first electric generator are of different magnitudes.

[0013] According to one embodiment of the present invention, the effect of suppressing vibration during driving can be improved even without using an accumulator. Attached Figure Description

[0014] Figure 1 This is a left-side view of a wheel loader equipped with a vehicle power transmission device according to the embodiment.

[0015] Figure 2 It means Figure 1 A side view of a partial fracture of the transmission device (power transmission device for vehicles).

[0016] Figure 3 It is a structural diagram that, together with the controller, represents the power transmission path of a wheel loader.

[0017] Figure 4 This is a characteristic curve diagram representing an example of the time-varying changes in vehicle speed and output torque.

[0018] Figure 5 This is a characteristic curve diagram representing an example of the time-dependent pressure change at the start of overflow.

[0019] Figure 6 This is a characteristic curve diagram representing an example of the time-varying change in the amount of accelerator pedal operation.

[0020] Figure 7 This is a characteristic curve diagram representing an example of the time-varying amount of a hydraulic pump motor tilt.

[0021] Figure 8 It is equivalent to Figure 4 Characteristic curve of the output torque in section (VIII).

[0022] Figure 9 This is a structural diagram showing the power transmission path of the first variant, together with the controller.

[0023] Figure 10 This is a structural diagram showing the power transmission path of the second variation, together with the controller.

[0024] Figure 11 This is a structural diagram showing the power transmission path of the third variation, together with the controller.

[0025] Figure 12 This is a structural diagram showing the power transmission path of the fourth variation, together with the controller.

[0026] Figure 13 This is a structural diagram showing the power transmission path of the fifth variation, together with the controller.

[0027] Figure 14 This is a structural diagram showing the power transmission path of the sixth variation, together with the controller.

[0028] Figure 15 This is a structural diagram representing the power transmission path of the seventh variation. Detailed Implementation

[0029] Hereinafter, a detailed description will be given with reference to the accompanying drawings, taking the application of the vehicle power transmission device according to the embodiments of the present invention to a wheel loader as a vehicle as an example.

[0030] Figures 1 to 8 Indicates the implementation method. In Figure 1 In this example, the wheel loader 1 is a representative vehicle (operating vehicle). The wheel loader 1 is configured as an articulated operating vehicle, with a front body 3 equipped with left and right front wheels 2 and a rear body 5 equipped with left and right rear wheels 4 connected in a manner that allows it to bend to the left and right. That is, the front body 3 and the rear body 5 constitute the body of the wheel loader 1. A central hinge 6 and a steering cylinder (not shown) are provided between the front body 3 and the rear body 5. By extending / retracting the steering cylinder, the front body 3 and the rear body 5 bend to the left and right around the central hinge 6. Thus, the wheel loader 1 can be operated while driving.

[0031] A working device 7, referred to as a loading and unloading machine or front working machine, is installed at the front of the wheel loader 1, capable of pitching. The working device 7 has a loader bucket 7A. On the other hand, a driver's cab 8, which serves as the cab, an engine 9, a hydraulic pump 10, and a transmission device 21, which functions as a gearbox, are located at the rear of the wheel loader 1. The driver's cab 8 is equipped with an accelerator pedal 8A, which is an operating component for accelerating the vehicle, and a forward / reverse shift lever 8B (hereinafter referred to as the FNR lever 8B), which switches between forward, reverse, and gear shifting. In addition, although the mounting is omitted, the driver's cab 8 is equipped with a driver's seat, a steering wheel, a brake pedal, and a parking brake switch.

[0032] An operation amount detector 8C is installed on the accelerator pedal 8A to detect the operation amount θ of the accelerator pedal 8A. The FNR lever 8B is operated by the operator to switch the wheel loader 1 between forward and reverse, and to change gears. The operator switches the FNR lever 8B to the forward position (F) when moving the wheel loader 1 forward. The operator switches the FNR lever 8B to the reverse position (R) when moving the wheel loader 1 backward. The operator switches the FNR lever 8B to the neutral position (N) when the wheel loader 1 remains stationary or when the operator wants to stop while moving. The operator rotates the FNR lever 8B about its axis when changing gears.

[0033] Engine 9 is the power source (prime mover) of wheel loader 1. The power source (prime mover) can be composed solely of engine 9 as an internal combustion engine, or it can be composed of an engine and an electric motor, or an electric motor alone. Hydraulic pump 10 is connected to engine 9. Hydraulic pump 10 is the hydraulic source used to operate the working device 7.

[0034] A front axle 12 extending in the left and right directions is provided on the lower side of the front vehicle body 3. Left and right front wheels 2 are installed on both ends of the front axle 12. On the other hand, a rear axle 13 extending in the left and right directions is provided on the lower side of the rear vehicle body 5. Left and right rear wheels 4 are installed on both ends of the rear axle 13.

[0035] The front axle 12 is connected to the transmission 21 via the front drive shaft 14. The rear axle 13 is connected to the transmission 21 via the rear drive shaft 15. The transmission 21 changes (reduces) the rotational speed of the engine 9 and transmits it to the front drive shaft 14 and the rear drive shaft 15. That is, the power from the engine 9 is transmitted to the transmission 21 connected to the engine 9.

[0036] The power from engine 9, after its speed and direction of rotation are adjusted by transmission 21, is transmitted from the front and rear output shafts 23A and 23B of transmission 21 to the front axle 12 and rear axle 13 via front transmission shaft 14 and rear transmission shaft 15. That is, as... Figure 2 As shown, the transmission device 21 includes an input shaft 22 connected to the engine 9, a front output shaft 23A connected to the front transmission shaft 14, and a rear output shaft 23B connected to the rear transmission shaft 15. The transmission device 21 performs speed changes and forward / reverse switching between the input shaft 22 and the output shafts 23A and 23B by switching the power transmission path within the transmission device 21.

[0037] Next, besides Figure 1 and Figure 2 In addition, refer to Figures 3 to 8 The speed change device 21 of the embodiment will be described. Additionally, in Figure 3 In order to avoid complicating the diagram, the output shaft 23 of the transmission device 21 is simplified as a common output shaft 23 (=output shafts 23A, 23B) that transmits power to both the front axle 12 and the rear axle 13. That is, in Figure 3 The structure that divides the power into the front output shaft 23A and the rear output shaft 23B via a center differential mechanism is omitted.

[0038] The transmission device 21, serving as a power transmission device for a vehicle, includes an input shaft 22, an output shaft 23, and a planetary continuously variable transmission (CVT) mechanism 31. Additionally, the transmission device 21 includes a idling gear 29, a transmission mechanism 25 (a stepped transmission mechanism), a direct-drive mechanism 27, and a transmission shaft 28. The transmission device 21 also includes a controller 43, a first pressure detector 46, a second pressure detector 47, a third pressure detector 48, a first speed detector 44, and a second speed detector 45.

[0039] The input shaft 22 is rotated by the prime mover (engine 9) mounted on the vehicle (wheel loader 1). That is, the drive shaft of the engine 9 is connected to the input shaft 22. In contrast, the output shaft 23 outputs rotation to the vehicle's running gear (front axle 12 and / or rear axle 13). That is, the power of the engine 9 is output from the output shaft 23 via the transmission, i.e., the gear shifting device 21. The output shaft 23 outputs rotation to the front wheels 2 and / or rear wheels 4 via the front axle 12 and / or rear axle 13 of the wheel loader 1.

[0040] Power input from input shaft 22 to transmission device 21 is transmitted to idler gear 29 via planetary continuously variable transmission mechanism 31 or direct connection mechanism 27. Power transmitted to idler gear 29 is output from output shaft 23 via transmission mechanism 25. Planetary continuously variable transmission mechanism 31 is disposed between input shaft 22 and output shaft 23. Planetary continuously variable transmission mechanism 31 changes the rotational speed on the input shaft 22 side and transmits it to the output shaft 23 side. The input side of planetary continuously variable transmission mechanism 31 is connected to input shaft 22 with input gear 27A provided with direct connection mechanism 27. The output side of planetary continuously variable transmission mechanism 31 is connected to transmission shaft 28 with idler gear 29 provided.

[0041] The transmission mechanism 25 is connected in series with the planetary continuously variable transmission mechanism 31 and the direct connection mechanism 27 between the input shaft 22 and the output shaft 23. The transmission mechanism 25 also changes the rotational speed on the input shaft 22 side and transmits it to the output shaft 23 side. In this case, the transmission mechanism 25 is positioned between the intermediate gear 26, which meshes with the idler gear 29, and the output shaft 23. That is, the input side of the transmission mechanism 25 is connected to the intermediate gear 26. The output side of the transmission mechanism 25 is connected to the output shaft 23. The transmission mechanism 25 can be configured, for example, as a multi-stage stepped transmission mechanism.

[0042] The transmission mechanism 25 is configured, for example, to include multiple transmission shafts, multiple gears, and multiple clutches. In this case, the transmission mechanism 25 can be configured as a dual-clutch transmission (DCT) having a forward clutch 25A connected when the wheel loader 1 is moving forward and a reverse clutch 25B connected when the wheel loader 1 is moving backward. Alternatively, the transmission mechanism 25 can be omitted. That is, the intermediate gear 26 and the output shaft 23 can be directly connected without passing through the transmission mechanism 25.

[0043] The direct-connect mechanism 27 bypasses the planetary continuously variable transmission (CVT) 31 to transmit rotation from the input shaft 22 to the output shaft 23. That is, the direct-connect mechanism 27 directly transmits rotation from the input shaft 22 to the transmission mechanism 25 without going through the planetary CVT 31. The direct-connect mechanism 27 includes an input-side gear 27A connected to the input shaft 22, an output-side gear 27B meshing with the input-side gear 27A, a rotating shaft 27B1 coaxially arranged with the transmission shaft 28, and a direct-connect clutch 30. Rotation of the output-side gear 27B is transmitted to the transmission shaft 28 via the direct-connect clutch 30. In this embodiment, the input-side gear 27A is located on the input shaft 22. The output-side gear 27B is located on the rotating shaft 27B1 coaxially arranged with the transmission shaft 28. The direct-connect clutch 30 is located between the rotating shaft 27B1 and the transmission shaft 28.

[0044] The transmission shaft 28 is the output shaft of the direct-connection mechanism 27 and also the output shaft of the planetary continuously variable transmission (CVT) 31. In this case, the transmission shaft 28 is configured to be coaxial with the rotating shaft 27B1 of the direct-connection mechanism 27 and coaxial with the second rotating shaft 39 of the planetary CVT 31. The transmission shaft 28 is connected to the rotating shaft 27B1 of the direct-connection mechanism 27 via a direct-connection clutch 30. When the direct-connection clutch 30 is engaged, the rotation of the output gear 27B of the direct-connection mechanism 27 is transmitted to the transmission shaft 28. The transmission shaft 28 is connected to the second hydraulic pump motor 38 of the planetary CVT 31 via a second clutch 40. When the second clutch 40 is engaged, the rotation of the second hydraulic pump motor 38 of the planetary CVT 31 is transmitted to the transmission shaft 28. In addition, the transmission shaft 28 is connected to the planetary output gear 32B of the planetary CVT 31 via an idler gear 29.

[0045] An idler gear 29, serving as an idler component, is mounted on the transmission shaft 28. The idler gear 29 mechanically engages with both the output side of the planetary continuously variable transmission (CVT) 31 and the output side of the direct connection mechanism 27. The idler gear 29 meshes with the planetary output gear 32B of the planetary gear mechanism 32 that constitutes the planetary CVT 31. The idler gear 29 also meshes with the intermediate gear 26. The rotation of the idler gear 29 is transmitted to the transmission mechanism 25 via the intermediate gear 26. That is, the power input from the input shaft 22 of the transmission device 21 is transmitted to the idler gear 29 via the planetary CVT 31 or the direct connection mechanism 27. The power transmitted to the idler gear 29 is output from the output shaft 23 through the transmission mechanism 25.

[0046] A direct connection clutch 30 is provided within the direct connection mechanism 27 located between the input shaft 22 and the idler gear 29. Specifically, the direct connection clutch 30 is located between the rotating shaft 27B1 of the output gear 27B within the direct connection mechanism 27 and the transmission shaft 28 on which the idler gear 29 is located. The direct connection clutch 30 can switch between a "connected state (connected state)" where rotational (torque, rotational force, power) transmission occurs between the direct connection mechanism 27 (rotating shaft 27B1) and the idler gear 29 (transmission shaft 28), and a "disconnected state (released state)" where rotational transmission is interrupted. When the direct connection clutch 30 is in the connected state, for example, the rotation of the output gear 27B (rotating shaft 27B1) of the direct connection mechanism 27 is transmitted to the idler gear 29 via the transmission shaft 28. When the direct connection clutch 30 is in the released state, for example, the rotation of the output gear 27B (rotating shaft 27B1) is not transmitted to the transmission shaft 28. The engagement / disengagement of the direct-connect clutch 30 is controlled based on instructions (instruction signal C3) from the controller 43.

[0047] Next, the planetary continuously variable transmission mechanism 31 will be described.

[0048] The planetary continuously variable transmission (CVT) 31 includes a planetary gear mechanism 32, a first clutch 33, a hydrostatic CVT 34, and a second clutch 40. The hydrostatic CVT 34 includes a first rotating shaft 35, a first hydraulic pump motor 36, a pair of main pipelines 37A and 37B (first main pipeline 37A and second main pipeline 37B), a second hydraulic pump motor 38, a second rotating shaft 39, variable relief valves 51A and 5B (first variable relief valve 51A as the first relief valve and second variable relief valve 51B as the second relief valve), and a connecting pipeline 42.

[0049] The planetary gear mechanism 32 is connected to the input shaft 22 (the drive shaft of the engine 9). Specifically, the planetary gear mechanism 32 is connected to the input shaft 22. The planetary gear mechanism 32 consists of a single-stage or multi-stage planetary gear assembly (not shown), a planetary output shaft 32A, and a planetary output gear 32B. The planetary gear assembly includes, for example, a sun gear, a ring gear, and a gear carrier supporting the planetary gears meshing with these sun gears and ring gears. For example, the input shaft 22 is connected to any one of the sun gear, ring gear, and gear carrier. The planetary output shaft 32A is connected to the sun gear, ring gear, and gear carrier other than the component connected to the input shaft 22. The planetary output gear 32B is connected to the remaining components of the sun gear, ring gear, and gear carrier. The planetary output shaft 32A is connected to the first rotating shaft 35 (first hydraulic pump motor 36) of the hydrostatic continuously variable transmission mechanism 34 via a first clutch 33. The rotation of the planetary output shaft 32A is transmitted via the first clutch 33 to the first rotating shaft 35 (first hydraulic pump motor 36) of the hydrostatic continuously variable transmission 34. The planetary output gear 32B meshes with the idler gear 29. The rotation of the planetary output gear 32B is transmitted to the idler gear 29.

[0050] The first clutch 33 is located on the output side of the planetary gear mechanism 32. Specifically, the first clutch 33 is located between the planetary output shaft 32A of the planetary gear mechanism 32 and the first rotating shaft 35 (first hydraulic pump motor 36) of the hydrostatic continuously variable transmission 34. The first clutch 33 can switch between a "connected state" (engaged state) where rotational transmission occurs between the planetary gear mechanism 32 (planetary output shaft 32A) and the first hydraulic pump motor 36 (first rotating shaft 35) of the hydrostatic continuously variable transmission 34, and a "disconnected state" (released state) where rotational transmission is interrupted. When the first clutch 33 is in the connected state, for example, the rotation of the planetary output shaft 32A of the planetary gear mechanism 32 is transmitted to the first hydraulic pump motor 36 via the first rotating shaft 35 of the hydrostatic continuously variable transmission 34. When the first clutch 33 is in the released state, for example, the rotation of the planetary output shaft 32A is not transmitted to the first rotating shaft 35. The engagement / disengagement of the first clutch 33 is controlled based on commands (command signal C1) from the controller 43.

[0051] The first rotating shaft 35 of the hydrostatic continuously variable transmission (CVT) 34 is equivalent to the input shaft of the hydrostatic CVT 34. The first rotating shaft 35 is connected to the rotating shaft of the first hydraulic pump motor 36, and is also equivalent to the rotating shaft of the first hydraulic pump motor 36. The first hydraulic pump motor 36 is connected to the output side of the planetary gear mechanism 32, i.e., the planetary output shaft 32A of the planetary gear mechanism 32, via the first clutch 33.

[0052] The first hydraulic pump motor 36 is located on the output side of the planetary gear mechanism 32, i.e., on the input shaft 22 side. The first hydraulic pump motor 36 drives the first rotating shaft 35 by rotation, causing pressurized oil to circulate within a pair of main pipelines 37A and 37B. The first hydraulic pump motor 36 is, for example, a variable-capacity, swashplate type hydraulic pump motor. The first hydraulic pump motor 36 is a hydraulic device (hydraulic pump or hydraulic motor) that functions as a hydraulic pump when power is input from the first rotating shaft 35 and as a hydraulic motor when power is output to the first rotating shaft 35. The first hydraulic pump motor 36 has a regulator 36A for adjusting the pump capacity (motor capacity). The regulator 36A variably controls the first hydraulic pump motor 36 based on commands (command signal Wp) from the controller 43. The pair of main pipelines 37A and 37B connect a pair of feed ports of the first hydraulic pump motor 36 and a pair of feed ports of the second hydraulic pump motor 38.

[0053] The second hydraulic pump motor 38 is connected to the first hydraulic pump motor 36 via a pair of main lines 37A and 37B, namely the first main line 37A and the second main line 37B. The second hydraulic pump motor 38 rotates using pressurized oil supplied from the first hydraulic pump motor 36. The second hydraulic pump motor 38 is, for example, a variable capacity, swashplate type hydraulic pump motor. The second hydraulic pump motor 38 functions as a hydraulic motor when outputting power to the second rotating shaft 39 and as a hydraulic pump when inputting power from the second rotating shaft 39. The second hydraulic pump motor 38 has a regulator 38A for adjusting the motor capacity (pump capacity). This is based on commands (command signal W) from the controller 43. M A regulator 38A variably controls the second hydraulic pump motor 38. The second rotating shaft 39 of the hydrostatic continuously variable transmission 34 corresponds to the output shaft of the hydrostatic continuously variable transmission 34. The second rotating shaft 39 is connected to the rotating shaft of the second hydraulic pump motor 38. Alternatively, the second rotating shaft 39 is equivalent to the rotating shaft of the second hydraulic pump motor 38.

[0054] The second clutch 40 is disposed between the second hydraulic pump motor 38 and the idler gear 29. Thus, the second hydraulic pump motor 38 is connected to the idler gear 29 via the second clutch 40. The second clutch 40 is disposed between the second rotating shaft 39 of the hydrostatic continuously variable transmission 34 and the transmission shaft 28 on which the idler gear 29 is disposed. The second clutch 40 can switch between a "connected state" (engaged state) where rotational transmission occurs between the idler gear 29 (transmission shaft 28) and the second hydraulic pump motor 38 (second rotating shaft 39) of the hydrostatic continuously variable transmission 34, and a "disconnected state" (released state) where rotational transmission is interrupted. When the second clutch 40 is in the connected state, for example, the rotation of the second rotating shaft 39 of the hydrostatic continuously variable transmission 34 (= the rotation of the second hydraulic pump motor 38) is transmitted to the idler gear 29 via the transmission shaft 28. When the second clutch 40 is in the released state, for example, the rotation of the second rotating shaft 39 is not transmitted to the transmission shaft 28. The second clutch 40 is engaged / disengaged based on instructions (instruction signal C2) from the controller 43.

[0055] In this embodiment, the power input from the input shaft 22 of the transmission device 21 can be arbitrarily selected to be transmitted to the transmission mechanism 25 via the planetary continuously variable transmission mechanism 31 or via the direct connection mechanism 27. Therefore, the planetary continuously variable transmission mechanism 31 can be used under conditions suitable for its operation, such as high-load conditions requiring high torque, like excavation. On the other hand, power transmission can be performed via the direct connection mechanism 27 when speed changes are suitable, such as under low load conditions involving long-distance travel at a certain speed within the work site.

[0056] When power is transmitted to the transmission mechanism 25 via the planetary continuously variable transmission (CVT) 31, the direct-connect clutch 30 is released, and the first clutch 33 and the second clutch 40 are engaged. In this case, the power flow can be either distributed to the transmission mechanism 25 via the planetary gear mechanism 32 and the hydrostatic CVT 34, or transmitted to the transmission mechanism 25 by setting the speed of the first hydraulic pump motor 36 to 0, thus not transmitting power to the hydrostatic CVT 34.

[0057] The state in which the direct-connection clutch 30 is released, the first clutch 33 and the second clutch 40 are connected, and power is transmitted to the hydrostatic continuously variable transmission mechanism 34 and to the transmission mechanism 25 is called the continuously variable transmission state. The state in which the direct-connection clutch 30 is released, the first clutch 33 and the second clutch 40 are connected, and power is transmitted to the transmission mechanism 25 without transmitting power to the hydrostatic continuously variable transmission mechanism 34 is called the internal direct connection. In this internal direct connection, the tilt (discharge capacity) of the first hydraulic pump motor 36 is raised above a specified value, and the tilt of the second hydraulic pump motor 38 is neutralized, thereby applying braking action within the hydrostatic continuously variable transmission mechanism 34 and reducing the speed of the first hydraulic pump motor 36 to 0.

[0058] Therefore, in the internally directly connected state, power from the engine 9 is transmitted to the transmission mechanism 25. In reality, due to oil leakage in the first hydraulic pump motor 36 and the second hydraulic pump motor 38, the speed of the first hydraulic pump motor 36 will not be zero, but most of the power from the engine 9 can be distributed to the transmission mechanism 25. In the internally directly connected state, the second clutch 40 may not be engaged. On the other hand, when power is transmitted to the transmission mechanism 25 via the direct connection mechanism 27, the direct connection clutch 30 is engaged, and the first clutch 33 and the second clutch 40 are released. The direct connection clutch 30, the first clutch 33, and the second clutch 40 can be wet multi-plate clutches or synchronous mesh clutches.

[0059] In this embodiment, the hydrostatic continuously variable transmission (CVT) 34 includes variable relief valves 51A and 51B capable of changing the set pressure (overflow set pressure, overflow start pressure), and check valves 52 and 53 that allow unidirectional flow of pressurized oil and prevent reverse flow of pressurized oil. Specifically, the first main pipeline 37A and the second main pipeline 37B of the hydrostatic CVT 34 are connected via a connecting pipeline 42. Here, the first hydraulic pump motor 36 and the second hydraulic pump motor 38 transmit power through working oil flowing between them via a pair of main pipelines 37A and 37B. When the rotational speed is changed on the input shaft 22 side and transmitted to the output shaft 23 side, the pressure in the first main pipeline 37A is higher than that in the second main pipeline 37B. Conversely, when the rotational speed is changed on the output shaft 23 side and transmitted to the input shaft 22 side, the pressure in the second main pipeline 37B is higher than that in the first main pipeline 37A. A pair of check valves 52 and 53 are provided in the connecting pipeline 42 connecting the first main pipeline 37A and the second main pipeline 37B.

[0060] One check valve 52 (hereinafter also referred to as the first check valve 52) allows pressurized oil to flow from the second main pipeline 37B side to the first main pipeline 37A side, and prevents pressurized oil from flowing in the opposite direction. That is, the first check valve 52 enables the flow of working oil from the second main pipeline 37B to the first main pipeline 37A, and cuts off the flow of working oil from the first main pipeline 37A to the second main pipeline 37B. The other check valve 53 (hereinafter also referred to as the second check valve 53) allows pressurized oil to flow from the first main pipeline 37A side to the second main pipeline 37B side, and prevents pressurized oil from flowing in the opposite direction. That is, the second check valve 53 enables the flow of working oil from the first main pipeline 37A to the second main pipeline 37B, and cuts off the flow of working oil from the second main pipeline 37B to the first main pipeline 37A.

[0061] Bypass lines 54 and 55 are connected to the connecting line 42, bypassing the various check valves 52 and 53. The first bypass line 54 branches off from the connecting line 42 and bypasses the first check valve 52 before connecting to the connecting line 42. The second bypass line 55 branches off from the connecting line 42 and bypasses the second check valve 53 before connecting to the connecting line 42. Variable relief valves 51A and 51B are located midway through the bypass lines 54 and 55.

[0062] Specifically, the first variable relief valve 51A is located midway through the first bypass line 54. When the pressure in the first main line 37A is below a specified pressure (first pressure, fourth pressure), the first variable relief valve 51A cuts off the flow of working oil from the first main line 37A to the second main line 37B, and opens the flow when the pressure exceeds the specified pressure (first pressure, fourth pressure). The second variable relief valve 51B is located midway through the second bypass line 55. When the pressure in the second main line 37B is below a specified pressure (first pressure, second pressure, third pressure), the second variable relief valve 51B cuts off the flow of working oil from the second main line 37B to the first main line 37A, and opens the flow when the pressure exceeds the specified pressure (first pressure, second pressure, third pressure). The variable relief valves 51A and 51B are controlled by a command signal (command signal W) from the controller 43. A W B This is a electrically operated relief valve (e.g., a solenoid relief valve) that changes the opening pressure (relief pressure). That is, the change in the set pressure of the variable relief valves 51A and 51B is based on a command signal (command signal W) from the controller 43. A W B )conduct.

[0063] A first speed detector 44 is installed on the input shaft 22 of the transmission 21. The first speed detector 44 is a rotational sensor that detects the rotational speed and direction of rotation of the input shaft 22. The rotational speed of the input shaft 22 corresponds to the rotational speed of the engine 9 (hereinafter referred to as engine speed Vin). The first speed detector 44 outputs a detection signal corresponding to the engine speed Vin to the controller 43. A second speed detector 45 is installed on the output shaft 23 of the transmission 21. The second speed detector 45 is a rotational sensor that detects the rotational speed (hereinafter referred to as output speed Vout) and direction of rotation of the output shaft 23. The output speed Vout corresponds to the vehicle speed. The second speed detector 45 outputs a detection signal corresponding to the output speed Vout and direction of rotation to the controller 43.

[0064] A first pressure detector 46 is installed in the first main pipeline 37A. The first pressure detector 46 is a pressure sensor that detects the hydraulic pressure of the first main pipeline 37A. The first pressure detector 46 outputs the hydraulic pressure P of the first main pipeline 37A to the controller 43. A The corresponding detection signal. A second pressure detector 47 is installed in the second main pipeline 37B. The second pressure detector 47 is a pressure sensor that detects the hydraulic pressure of the second main pipeline 37B. The second pressure detector 47 outputs a signal to the controller 43 corresponding to the hydraulic pressure P of the second main pipeline 37B. B The corresponding detection signal.

[0065] The third pressure detector 48 is installed on the direct-connect clutch 30. The third pressure detector 48 is a pressure sensor that detects the clutch pressure (pressure) of the direct-connect clutch 30. The third pressure detector 48 outputs the clutch pressure P of the direct-connect clutch 30 to the controller 43. C The corresponding detection signal. Operation quantity detector 8C (reference) Figure 1 The operation amount detector 8C is installed on the accelerator pedal 8A. It is a sensor that detects the operation amount θ of the accelerator pedal 8A. The operation amount detector 8C outputs a detection signal corresponding to the operation amount θ of the accelerator pedal 8A to the controller 43.

[0066] Next, the controller 43, which controls the switching of the power transmission path of the speed change device 21 and the setting pressure change of the variable relief valves 51A and 51B, will be described.

[0067] The input side of the controller 43 is connected to the first speed detector 44, the second speed detector 45, the first pressure detector 46, the second pressure detector 47, the third pressure detector 48, and the operation quantity detector 8C. On the other hand, the output side of the controller 43 is connected to the regulator 36A of the direct-connection clutch 30, the first clutch 33, the second clutch 40, the regulator 38A of the first hydraulic pump motor 36 of the planetary continuously variable transmission mechanism 31, the regulator 38A of the second hydraulic pump motor 38 of the planetary continuously variable transmission mechanism 31, and the variable relief valves 51A and 51B.

[0068] The controller 43 is configured as, for example, a microcomputer including an arithmetic circuit (CPU), memory, etc. The memory stores processing programs for switching control of the power transmission path of the transmission device 21, processing programs for changing the set pressure of the variable relief valves 51A and 51B, etc. That is, the controller 43 controls the adjustment of pump capacity and motor capacity, the connection / disconnection of the direct-connection clutch 30, the first clutch 33 and the second clutch 40, and the set pressure of the variable relief valves 51A and 51B.

[0069] The controller 43 receives engine speed Vin from the first speed detector 44, output speed Vout from the second speed detector 45, and hydraulic pressure P from the first pressure detector 46, the second pressure detector 47, and the third pressure detector 48. A P B and clutch pressure P C The operation quantity θ is input from the operation quantity detector 8C. The controller 43 calculates the commands to clutches 30, 33, 40 (clutch commands), the commands to variable relief valves 51A, 51B (relief pressure commands), the commands to the regulator 36A of the first hydraulic pump motor 36 (pump commands, motor commands), and the commands to the regulator 38A of the second hydraulic pump motor 38 (motor commands, pump commands) based on these inputs.

[0070] Based on the calculation results, controller 43 outputs overflow pressure command signal W to variable overflow valves 51A and 51B. A W B In this case, the output signal W A The first variable relief valve 51A outputs signal W. B The signal is directed to the second variable relief valve 51B. Additionally, the controller 43 outputs ON (connect) / OFF (release) signals C1, C2, and C3 to the clutches 30, 33, and 40 based on the calculation results. In this case, signal C1 is output to the first clutch 33, signal C2 is output to the second clutch 40, and signal C3 is output to the direct-connect clutch 30.

[0071] Furthermore, based on the calculation results, the controller 43 outputs tilt command signals Wp and W' to the regulator 36A of the first hydraulic pump motor 36 and the regulator 38A of the second hydraulic pump motor 38, indicating the tilt of the swashplate or swashplate. M In this case, a tilt command signal Wp is output to the regulator 36A of the first hydraulic pump motor 36, and a tilt command signal W is output to the regulator 38A of the second hydraulic pump motor 38. M The hydraulic pump motors 36 and 38 within the hydrostatic continuously variable transmission mechanism 34 are variable capacity type. The discharge capacity of the hydraulic pump motors 36 and 38 is changed by altering the tilt angle of the swashplate or swashplate. The hydraulic pump motors 36 and 38 can be single-tilt or double-tilt.

[0072] Regardless, the controller 43 has an input section (receiving section), an arithmetic section, a storage section, and an output section. The controller 43 performs actions such as "engaging / releasing the first clutch 33," "operating the regulator 36A of the first hydraulic pump motor 36 (tilt adjustment)," "operating the regulator 38A of the second hydraulic pump motor 38 (tilt adjustment)," "engaging / releasing the second clutch 40," "engaging / releasing the direct-connection clutch 30," and "changing the set pressure of the variable relief valves 51A and 51B." These controls are achieved by the processor (arithmetic section) of the controller 43 performing arithmetic processing based on a program stored in the controller 43's storage section (e.g., non-volatile memory).

[0073] However, according to the aforementioned prior art, since the vibration suppression effect of the riding control device is limited by the capacity of the accumulator, it may not be able to sufficiently suppress the vibration of the working vehicle. Furthermore, due to the damping effect of the accumulator, the movement of the front working machine becomes unstable, potentially leading to a deterioration in the positioning accuracy of the front working machine or a reduction in its operability. In contrast, in this embodiment, an accumulator is not used to suppress vibration during travel. In this case, in this embodiment, vibration suppression during travel is achieved through the transmission device 21. Referring to... Figures 3 to 8 The operation and function of the transmission device 21, which can suppress vibration during driving, will be explained.

[0074] The controller 43 determines whether the wheel loader 1 is in motion based on information detected by the onboard sensors corresponding to the state of the wheel loader 1. For example, the controller 43 determines whether the FNR lever 8B is in the F or R position. When the FNR lever 8B is in the F or R position, the controller 43 determines that the wheel loader 1 is in motion. Alternatively, other conditions can be used in determining whether the loader is in motion.

[0075] When the controller 43 determines that the wheel loader 1 is stationary, it disconnects the vibration suppression control of the transmission 21. Conversely, when the controller 43 determines that the wheel loader 1 is moving, it activates the vibration suppression control of the transmission 21. Thus, the transmission 21 is configured such that, under the control of the controller 43, it can switch between the vibration suppression control disconnect state (hereinafter also referred to as the vibration damping control disconnect state) and the vibration suppression control activation state (hereinafter also referred to as the vibration damping control activation state) according to the movement of the wheel loader 1.

[0076] In the "vibration damping control off state," the overflow initiation pressure of the variable relief valves 51A and 51B becomes high (e.g., the first set pressure P1). That is, in the "vibration damping control off state," because the overflow initiation pressure of the variable relief valves 51A and 51B is high, the bypass lines 54 and 55 are not connected. Therefore, a state is formed in which power can be transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 and from the second hydraulic pump motor 38 to the first hydraulic pump motor 36. In addition, the first set pressure P1 can be set, for example, to the maximum overflow pressure that can be changed by the variable relief valves 51A and 51B.

[0077] When traveling in the forward direction in continuously variable transmission mode (i.e., when FNR lever 8B is switched to F), the system switches from "damping control off state" to "damping control on state". Figures 4 to 7 At time t0, the controller 43 sets the overflow start pressure of the second variable overflow valve 51B to a low state (e.g., the second set pressure P2). At this time, the overflow start pressure of the first variable overflow valve 51A is the first set pressure P1. Starting from time t0, the accelerator pedal 8A is operated to start driving. In addition, the second set pressure P2 can be set, for example, to the minimum overflow pressure that can be changed by the second variable overflow valve 51B.

[0078] The operator increases the operational input (command signal θ) by pressing the accelerator pedal 8A until the target vehicle speed is reached. At this time, the overflow pressure of the first variable relief valve 51A is maintained at the first set pressure P1. Thus, power is transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38. Figure 4 and Figure 6 As shown, the vehicle speed increases in response to the amount of input to the accelerator pedal 8A. When the vehicle speed reaches the operator's target speed ( Figures 4 to 7 At time t1, reduce the amount of operation of the accelerator pedal 8A to keep the amount of operation of the accelerator pedal 8A constant in order to maintain the vehicle speed. The amount of operation of the accelerator pedal 8A increases as the speed of the wheel loader 1 increases.

[0079] Explain the "vibration damping control off state" during the interval from time t1 to time t2 while traveling at a constant speed. In this case, as... Figure 8 As shown by the dashed line, the output torque of the transmission 21 (hereinafter also referred to as the "output torque of the transmission") changes. That is, in the continuously variable transmission (CVT) state, the "power acting in the direction of reducing vehicle speed" input from wheels 2 and 4 is transmitted to the second hydraulic pump motor 38 via the idler gear 29. At this time, viewed from the second clutch 40 side, the rotation of the rotating shaft (= second rotating shaft 39) of the second hydraulic pump motor 38 is counterclockwise, and the "power acting in the direction of reducing vehicle speed" is applied to the rotating shaft (= second rotating shaft 39) of the second hydraulic pump motor 38. The working oil (working fluid) discharged from the second hydraulic pump motor 38 flows to the first hydraulic pump motor 36 through the second main pipeline 37B. Power is transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 and absorbed by the engine 9 via the planetary gear mechanism 32. Thus, the output torque of the transmission is generated in the unintended direction (the direction of reducing vehicle speed). Figure 8 (This generates negative output torque).

[0080] In contrast, when the "damping control is on," the overflow start pressure of the second variable relief valve 51B is set to a second set pressure P2, which is lower than the first set pressure P1. Therefore, even when high-pressure working oil is discharged from the second hydraulic pump motor 38, the pressure in the second main pipeline 37B remains at the second set pressure P2. Thus, in the "damping control on" state, compared to the "damping control off" state, the proportion of "power acting in the direction of reducing vehicle speed" transmitted to the engine 9 can be reduced. As a result, braking torque can be reduced, and the output torque of the transmission in the unintended direction (the direction of reducing vehicle speed) can be reduced. That is, as... Figure 8 As shown by a solid line or double-dotted line, compared to a dashed line, it can reduce the output torque of the transmission in the non-intended direction (the direction that reduces vehicle speed) (the output torque on the negative side) (it can eliminate the slanted part on the negative side).

[0081] Additionally, at time t1, the controller 43 reads the vehicle speed based on the constant operation of the accelerator pedal 8A and calculates the required transmission output torque for that speed. With the tilt angles of the first hydraulic pump motor 36 and the second hydraulic pump motor 38 fixed, the transmission output torque is determined by the pressure difference between the first main line 37A and the second main line 37B. The controller 43 reduces the overflow initiation pressure of the first variable relief valve 51A (e.g., the fourth set pressure P4) and adjusts the value (pressure) of the first main line 37A so that the transmission output torque becomes the result of the calculation. Thus, the first main line 37A remains at the overflow initiation pressure (fourth set pressure P4) of the first variable relief valve 51A, and the transmission output torque does not rise above the required level.

[0082] The "power acting in the direction of increasing vehicle speed" input from wheels 2 and 4 is transmitted to the idler gear 29. At this time, viewed from the second clutch 40 side, the rotation of the rotating shaft (=second rotating shaft 39) of the second hydraulic pump motor 38 is counterclockwise, and the "power acting in the direction of increasing vehicle speed" is applied to the rotating shaft (=second rotating shaft 39) of the second hydraulic pump motor 38. That is, the rotating shaft (=second rotating shaft 39) of the second hydraulic pump motor 38 is pulled by the idler gear 29, and the "power acting in the direction of increasing vehicle speed" acts on the rotating shaft (=second rotating shaft 39) of the second hydraulic pump motor 38, so as to increase the output torque of the second hydraulic pump motor 38. However, since the overflow start pressure of the first variable overflow valve 51A is set to the fourth set pressure P4, the differential pressure between the first main line 37A and the second main line 37B does not increase. Therefore, the output torque of the transmission does not increase, and the output torque of the transmission in the intended direction (the direction of increasing vehicle speed) can be limited. That is, as Figure 8 As shown by a solid line or double-dotted line, compared to a dashed line, it can limit the output torque of the transmission in the intended direction (the direction of increasing vehicle speed) (the output torque on the positive side) (it can eliminate the slanted part on the positive side).

[0083] Here, controlling the tilt angle of the first hydraulic pump motor 36 or the tilt angle of the second hydraulic pump motor 38 can also control the output torque of the transmission. However, the responsiveness of the variable relief valves 51A and 51B is generally better than that of the hydraulic pump motors 36 and 38. Therefore, in this embodiment, the variable relief valves 51A and 51B are preferred for control.

[0084] Here, the output torque of the transmission only needs to be equal to the average value of the processed output torque. The output torque of the transmission can be calculated, for example, based on the measurements from pressure gauges (first pressure detector 46, second pressure detector 47) installed on the first main line 37A and the second main line 37B, respectively. Furthermore, the output torque of the transmission can also be calculated based on measurements of the rotation angle (pitch angle), speed, rotational acceleration, or rotational jerk of the wheel loader 1, with a horizontal axis (e.g., pitch axis) orthogonal to the direction of travel of the wheel loader 1 as the center of rotation. In other words, the output torque of the transmission can also be calculated based on the forward tilting posture of the wheel loader 1 during deceleration and the backward tilting posture of the wheel loader 1 during acceleration. Additionally, the output torque of the transmission can also be calculated based on the hydraulic pressure that moves the working device 7, which serves as the loading / unloading device.

[0085] To maximize the damping effect, it suffices to set the second set pressure P2 to the minimum relief pressure (e.g., 0). In this case, the second main pipeline 37B and the first main pipeline 37A are brought into communication. That is, power transmission from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 is cut off. Therefore, the "power acting in the direction of reducing vehicle speed" is not transmitted to the engine 9, and no engine braking is generated. Accordingly, the output torque of the transmission in the unintended direction can be reduced to zero. In this case, since the output torque of the transmission in the unintended direction becomes zero, the fourth set pressure P4 can be set to a low value. Accordingly, the proportion of the ramp portion of the transmission output torque in the intended direction can be increased.

[0086] In any case, when traveling in the "damping control ON state", as Figure 8 illustrated, the ramp portion of the output torque of the transmission can be reduced, and fluctuations in the output torque can be reduced. Accordingly, the amplitude of the output torque is reduced, and vibration during traveling can be suppressed.

[0087] In addition, as Figure 8 illustrated, the controller 43 can set the relief starting pressures of the variable relief valves 51A and 51B such that the output torque of the transmission can take any value between the "damping control OFF state" and the "damping control ON state (maximum damping effect)". When switching from the "damping control OFF state" to the "damping control ON state (maximum damping effect)", the wheel loader 1 may experience shock. Therefore, by providing a state with an intermediate value as described above, such shock can be suppressed. Accordingly, riding comfort can be improved.

[0088] Next, a description will be given of the case where the wheel loader 1 decelerates and stops, that is, after time t2 in Figures 4 to 7 . An operator reduces the operation amount of the accelerator pedal 8A at time t2. When a predetermined period of time (e.g., 0.1 to 1 second) has elapsed after the operation amount of the accelerator pedal 8A has dropped below a first operation amount (e.g., 0), the controller 43 gradually increases the relief starting pressure of the second variable relief valve 51B from the second set pressure P2 to a third set pressure P3 that is higher than the second set pressure P2 (P2<P3). Accordingly, power is gradually transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36. This power is absorbed by the engine 9 from the first hydraulic pump motor 36 via the planetary gear mechanism 32 (engine braking).

[0089] Therefore, applying engine braking can decelerate the vehicle. This allows the engine brake to activate when the operator intends to operate it. Furthermore, the first operating amount can be set, for example, to the amount of operation for switching between acceleration and deceleration of the wheel loader 1. The first operating amount can be set to increase as the vehicle speed increases. On the other hand, the third set pressure P3 can be set, for example, to the overflow pressure that achieves the desired engine braking. In this case, the third set pressure P3 can be set, for example, to a pressure higher than the second set pressure P2 and lower than the first set pressure P1 (P2... <P3<P1)。

[0090] Furthermore, by increasing the tilt angle of the second hydraulic pump motor 38, the pressure of the second main pipeline 37B is made higher than the third set pressure P3, causing the second variable relief valve 51B to actuate. That is, the overflow initiation pressure of the second variable relief valve 51B is increased (e.g., to the third set pressure P3), and the tilt angle of the second hydraulic pump motor 37 is controlled to be greater than the tilt angle of the first hydraulic pump motor 36. This results in a high pressure in the second main pipeline 37B. Then, by making the pressure in the second main pipeline 37B higher than the overflow initiation pressure of the second variable relief valve 51B (e.g., the third set pressure P3), the second variable relief valve 51B responds, and the working oil in the second main pipeline 37B is released while maintaining a high overflow initiation pressure. This results in energy loss (pressure loss), causing the vehicle speed to decrease. This series of actions is called CVT braking.

[0091] Thus, by actuating the second variable relief valve 51B as intended, losses can be generated, thereby reducing vehicle speed (CVT braking). After time t2, as the working oil flows from the second hydraulic pump motor 38 to the first hydraulic pump motor 36, the pressure in the second main pipeline 37B increases by decreasing the tilt angle of the first hydraulic pump motor 36 and increasing the tilt angle of the second hydraulic pump motor 38. Therefore, by applying not only engine braking but also CVT braking, the vehicle deceleration can be greater. By utilizing both engine braking and CVT braking, the load on auxiliary braking can be reduced. Figure 4 In the middle, at time t3, auxiliary braking is used to bring the vehicle to a stop at a speed of 0 km / h.

[0092] When the system is switched to "vibration damping control engaged," the output torque fluctuations of the transmission are absorbed within the hydrostatic continuously variable transmission (CVT) mechanism 34. This reduces output torque fluctuations and suppresses vibrations during operation, even when external forces are applied to the wheel loader 1 as a working vehicle due to road or vehicle vibrations. Because the power is absorbed within the hydrostatic CVT mechanism 34, it is not transmitted to the planetary gear mechanism 32, thus reducing gear losses. Furthermore, torque fluctuations are reduced even when there is no large vibration due to capacity limitations, unlike with an accumulator. This improves ride comfort during operation. Additionally, since vibrations are suppressed not only by the working device 7 but also by the vehicle body, instability in the operation of the working device 7 can be prevented even when operating it while in motion.

[0093] When the operator reduces the amount of pressure applied to the accelerator pedal 8A, engine braking can be applied to decelerate the vehicle by setting it to the "damping control off state". In this case, by gradually increasing the overflow initiation pressure of the second variable overflow valve 51B, a sharp increase in braking torque can be suppressed, achieving deceleration with minimal load on the operator. This also improves ride comfort during driving. Furthermore, by using both engine braking and CVT braking, the load on the auxiliary braking system can be reduced.

[0094] When the power flow direction of the transmission device 21 is in the internal direct connection state, the same control as in the continuously variable transmission (CVT) state is performed. The control in the internal direct connection state will be explained focusing on the differences from the CVT state. In the internal direct connection state, by raising the tilt (discharge capacity) of the first hydraulic pump motor 36 above a predetermined value, the tilt of the second hydraulic pump motor 38 is neutralized, thereby applying braking action within the hydrostatic CVT mechanism 34 and reducing the speed of the first hydraulic pump motor 36 to 0. The internal direct connection state described below involves the second clutch 40 being in the released state.

[0095] During the interval from time t1 to time t2 while traveling at a constant speed, the "power acting in the direction of reducing vehicle speed" input from wheels 2 and 4 is transmitted to the first hydraulic pump motor 36 via the idler gear 29 and the planetary gear mechanism 32. At this time, the planetary output shaft 32A, which serves as the output shaft of the planetary gear mechanism 32, rotates counterclockwise, and the working oil discharged from the first hydraulic pump motor 36 flows to the first main pipeline 37A via the second main pipeline 37B, the connecting pipeline 42, and the second variable relief valve 51B. That is, the overflow pressure of the second variable relief valve 51B is low (e.g., the second set pressure P2), and the power transmission from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 is cut off. As a result, the "power acting in the direction of reducing vehicle speed" input from wheels 2 and 4 is partially or completely absorbed in the hydrostatic continuously variable transmission mechanism 34. Consequently, the transmission of "power acting in the direction of reducing vehicle speed" to the engine 9 can be suppressed, and the generation of engine braking can be reduced. When performing this control, the speed of the first hydraulic pump motor 36 is not 0 for the time being, which can reduce the output torque of the transmission in the unintended direction (and eliminate the negative side of the diagonal section).

[0096] Additionally, the "power acting in the direction of increasing vehicle speed" input from wheels 2 and 4 is also transmitted to the first hydraulic pump motor 36 via the idler gear 29 and planetary gear mechanism 32. At this time, the planetary output shaft 32A, which serves as the output shaft of the planetary gear mechanism 32, rotates clockwise, and the working oil discharged from the first hydraulic pump motor 36 flows to the second hydraulic pump motor 38 via the first main pipeline 37A. The controller 43 reduces the overflow start pressure (fourth set pressure P4) of the first variable relief valve 51A and adjusts the value (pressure) of the first main pipeline 37A so that the output torque of the transmission becomes the result of the calculation process. The power output from the engine 9 and the "power acting in the direction of increasing vehicle speed" input from wheels 2 and 4 are input to the first hydraulic pump motor 36, but the first main pipeline 37A does not exceed the overflow start pressure (fourth set pressure P4) of the first variable relief valve 51A, and the output torque of the transmission does not increase to the required level. Thus, the output torque of the transmission in the intended direction can be limited (the diagonal portion on the positive side can be eliminated).

[0097] Thus, in this embodiment, the first pressure (first set pressure P1) of the first variable relief valve 51A is set higher than the second pressure (second set pressure P2) of the second variable relief valve 51B (P1>P2). Therefore, in this embodiment, the "power transmission capability from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" is different from the "power transmission capability from the second hydraulic pump motor 38 to the first hydraulic pump motor 36". In this case, according to the embodiment, the first variable relief valve 51B is a variable relief valve whose set pressure can be changed by the controller 43. Furthermore, the controller 43 sets the set pressure of the second variable relief valve 51B to a second pressure (second set pressure P2) that is lower than the first pressure (first set pressure P1) during vehicle operation, thereby making the power transmission capabilities between the "power transmission capability from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and the "power transmission capability from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" different. In other words, the power transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 and the power transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 are different magnitudes.

[0098] Therefore, when the pressure in the second main pipeline 37B exceeds the second pressure (second set pressure P2), the second variable relief valve 51B becomes in an overflow state (connected state), thereby allowing working oil to flow from the second main pipeline 37B to the first main pipeline 37A. This reduces the power transmission between the first hydraulic pump motor 36 and the second hydraulic pump motor 38 via the second main pipeline 37B, and absorbs torque variations (variations in the transmission's output torque) within the planetary continuously variable transmission 31 (more specifically, the hydrostatic continuously variable transmission 34).

[0099] Therefore, even when external forces are applied to the wheel loader 1 due to vehicle vibrations caused by uneven road surfaces, the fluctuations in the output torque of the transmission associated with these forces can be reduced. As a result, vibrations during driving can be suppressed, and ride comfort during driving can be improved. Furthermore, since torque fluctuations are absorbed within the planetary continuously variable transmission 31 (more specifically, the hydrostatic continuously variable transmission 34), its capacity is not limited like that of an accumulator. Therefore, even in the event of large vibrations, torque fluctuations can be reduced. Additionally, since vibrations are suppressed within the planetary continuously variable transmission 31 (more specifically, the hydrostatic continuously variable transmission 34), even when the working device 7 is operated while in motion, instability in the operation of the working device 7 can be prevented.

[0100] In this embodiment, the second pressure (second set pressure P2) is the minimum relief pressure that can be changed by the second variable relief valve 51B. Therefore, the power transmission capacity between the first hydraulic pump motor 36 and the second hydraulic pump motor 38 via the second main pipeline 37B can be minimized to the greatest extent possible. That is, the absorption (reduction) effect of torque variation based on the flow of working oil from the second main pipeline 37B to the first main pipeline 37A can be maximized.

[0101] In this embodiment, when the operating amount θ of the accelerator pedal 8A, which is an operating component for accelerating the vehicle, is reduced to below the first operating amount for switching between acceleration and deceleration, the controller 43 increases the power transmission capability from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 by changing the overflow start pressure of the second variable overflow valve 51B from a second pressure (second set pressure P2) to a third pressure (third set pressure P3) that is higher than the second pressure. Therefore, when the operator reduces the operating amount of the accelerator pedal 8A, engine braking can be applied to decelerate the vehicle.

[0102] Furthermore, by gradually increasing the overflow initiation pressure of the second variable relief valve 51B to the third pressure (third set pressure P3), a sharp increase in braking torque can be suppressed. This allows for deceleration with less operator load and improves ride comfort during driving. Additionally, as needed, by increasing the tilt angle of the second hydraulic pump motor 38, the pressure in the second main pipeline 37B is increased, and through active overflow by the second variable relief valve 51B, both engine braking and CVT braking can be used. This reduces the load on auxiliary braking.

[0103] Furthermore, the first operating amount, which serves as the threshold for the operating amount θ of the accelerator pedal 8A, can be set to increase as the vehicle speed increases. In this case, traction and vehicle speed can be controlled using only the accelerator pedal 8A (one operating component). That is, acceleration and deceleration can be performed using only the accelerator pedal 8A. This improves operability.

[0104] In this embodiment, the first variable relief valve 51A is a variable relief valve whose set pressure can be changed by the controller 43. Furthermore, the controller 43 changes the set pressure of the first variable relief valve 51A according to the vehicle's state during vehicle operation, thereby changing the ratio of "power transmission capacity from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" to "power transmission capacity from the second hydraulic pump motor 38 to the first hydraulic pump motor 36". In this case, for example, when the accelerator pedal 8A operation is constant, the controller 43 changes the overflow initiation pressure of the first variable relief valve 51A from a first pressure (first set pressure P1) to a fourth pressure (fourth set pressure P4) that is lower than the first and third pressures (third set pressure P3) and higher than the second pressure (second set pressure P2) (P1, P3>P4>P2). This prevents the transmission output torque from rising above the required level.

[0105] Here, the controller 43 reads the vehicle speed based on the constant operation amount θ of the accelerator pedal 8A, calculates the required transmission output torque for that speed, and calculates the fourth pressure (fourth set pressure P4) as a result of this calculation. In this case, the controller 43 can calculate the fourth pressure (fourth set pressure P4) based on the rotational force used for vehicle travel, the theoretical discharge volume of the first hydraulic pump motor 36, and the theoretical discharge volume of the second hydraulic pump motor 38. Additionally, the controller 43 can calculate the fourth pressure (fourth set pressure P4) based on measurements of the vehicle's rotation angle, rotational speed, rotational acceleration, and rotational jerk, centered on an axis orthogonal to the vehicle's direction of travel, and / or measurements from a pressure measuring device (first pressure detector 46) mounted on the first main pipeline 37A. Furthermore, the controller 43 can calculate the fourth pressure (fourth set pressure P4) based on the pressure of the hydraulic fluid that moves the working device 7. In either case, the controller 43 sends a signal to cause the first variable relief valve 51A to begin overflowing at a fourth pressure (fourth set pressure P4) corresponding to the vehicle's state, thereby changing the ratio of "power transmission capability from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 during vehicle operation" to "power transmission capability from the second hydraulic pump motor 38 to the first hydraulic pump motor 36". This prevents the transmission's output torque from rising above the required level.

[0106] Furthermore, in this embodiment, an example is given where the first variable relief valve 51A, serving as the first relief valve, and the second variable relief valve 51B, serving as the second relief valve, are both electrically operated relief valves whose set pressure can be changed via the controller 43. However, this is not a limitation; for example, a set pressure fixed relief valve with a fixed set pressure can also be used. That is, Figure 9This represents a first modification. In this first modification, a first fixed relief valve 61A is configured with a first set pressure fixed at a first pressure (e.g., a first set pressure P1), and a second fixed relief valve 61B is configured with a second set pressure fixed at a second pressure (e.g., a second set pressure P2). In this case, the first pressure of the first fixed relief valve 61A is set higher than the second pressure of the second fixed relief valve 61B, thereby making the "power transmission capacity from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and the "power transmission capacity from the second hydraulic pump motor 38 to the first hydraulic pump motor 26" different. In other words, the "power transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and the "power transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" are different magnitudes. As a result, the power transmission between the first hydraulic pump motor 36 and the second hydraulic pump motor 38 via the second main pipeline 37B can be reduced (absorbed), and vibrations during operation can be suppressed.

[0107] Alternatively, for example, it can also be like Figure 10 As shown in the second variation, the first relief valve is a fixed relief valve 61A with a set pressure fixed at a first pressure (e.g., a first set pressure P1), and the second relief valve is a variable relief valve 51B with a set pressure that can be changed by the controller 43. In this case, the controller 43 sets the set pressure of the second variable relief valve 51B to a second pressure (second set pressure P2) during vehicle operation, making the power transmission capabilities between "the power transmission capability from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and "the power transmission capability from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" different. In other words, the power transmitted from "the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and "the power transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" are different magnitudes.

[0108] Alternatively, for example, it can also be like Figure 11As shown in the third variation, the first relief valve is omitted. In this third variation, the hydrostatic continuously variable transmission 34 includes a second fixed relief valve 61B with a set pressure fixed to a second pressure (e.g., a second set pressure P2) and a pair of check valves 52 and 53. That is, in the third variation, the first relief valve is omitted, and a first check valve 52 is provided, which allows the flow of working oil from the second main pipeline 37B to the first main pipeline 37A to be open, and cuts off the flow of working oil from the first main pipeline 37A to the second main pipeline 37B. In this case, the flow of working oil from the first main pipeline 37A to the second main pipeline 37B is kept cut off (in other words, it is equivalent to a structure with a first relief valve having an infinitely high relief start pressure), and the second fixed relief valve 61B is set to the second pressure (e.g., the second set pressure P2). Therefore, the power transmission capabilities between "the power transmission capability from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and "the power transmission capability from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" are different. In other words, the power transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 and the power transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 are of different magnitudes.

[0109] Alternatively, for example, it can also be like Figure 12 As shown in the fourth variation example, in order to... Figure 11 In the third variation shown, the second fixed relief valve 61B is replaced with a second variable relief valve 51B. In this case, the controller 43 sets the set pressure of the second variable relief valve 51B to a second pressure (second set pressure P2) during vehicle operation, making the power transmission capabilities from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 and from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 different. In other words, the power transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38 and the power transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36 are different magnitudes.

[0110] Alternatively, for example, it can also be like Figure 13As shown in the fifth variation, the first relief valve is a first variable relief valve 51A, and the second relief valve is a second fixed relief valve 61B. In this case, the controller 43 changes the set pressure of the first variable relief valve 51A while the vehicle is in motion (according to the vehicle state quantity), thereby making the "power transmission capacity from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and the "power transmission capacity from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" different (changing the ratio of power transmission capacity). In other words, the "power transmitted from the first hydraulic pump motor 36 to the second hydraulic pump motor 38" and the "power transmitted from the second hydraulic pump motor 38 to the first hydraulic pump motor 36" are different magnitudes.

[0111] Furthermore, in the embodiments and the first to fifth modifications, the structure in which the second hydraulic pump motor 38 is connected to the idler gear 29 via the second clutch 40 was described as an example. However, it is not limited to this, and for example, it can also be as follows: Figure 14 As shown in the sixth variation, it can be a structure in which the second hydraulic pump motor 38 is connected via the second clutch 40 to a transmission gear 71 that meshes with the input side gear 27A of the direct connection mechanism 27.

[0112] Furthermore, in this embodiment, an example is given of a hydrostatic continuously variable transmission (CVT) 34 configured by connecting a first hydraulic pump motor 36 and a second hydraulic pump motor 38 via a pair of main pipelines 37A and 37B between the first clutch 33 and the second clutch 40. However, it is not limited to this; for example, it may also be configured as follows: Figure 15 As shown in the seventh variation, an electric continuously variable transmission (CVT) mechanism 81 can be provided between the first clutch 33 and the second clutch 40. That is, the transmission of the CVT mechanism can be a hydraulic pump motor or an electric generator.

[0113] exist Figure 15 In the seventh variation shown, the electric continuously variable transmission (CVT) 81 includes a first electric generator 82 disposed on the input shaft 22 side, a controller 84 connected to the first electric generator 82 via a first wire 83, and a second electric generator 86 connected to the controller 84 via a second wire 85. The first wire 83 transmits power between the first electric generator 82 and the controller 84. The second wire 85 transmits power between the second electric generator 86 and the controller 84. During the operation of the wheel loader 1, the controller 84 controls the "power transmitted from the first electric generator 82 to the second electric generator 86" and the "power transmitted from the second electric generator 86 to the first electric generator 82" to be of different values.

[0114] The controller 84 may be configured to include, for example, a battery (power storage source). The controller 84 controls the "power transmitted from the first electric generator 82 to the second electric generator 86" and the "power transmitted from the second electric generator 86 to the first electric generator 82" to be different values, for example, by receiving and discharging power from the battery. In this case, the controller 84 sets the "power transmitted from the first electric generator 82 to the second electric generator 86" to be higher than the "power transmitted from the second electric generator 86 to the first electric generator 82" during the operation of the wheel loader 1. In this seventh variation, by absorbing torque-based power fluctuations between the first electric generator 82 and the second electric generator 86, vibrations during operation can be suppressed.

[0115] Furthermore, the above structure can be appropriately modified, deleted, or added within the scope of this invention. For example, in this embodiment, the case where the transmission device 21 has a structure including a transmission mechanism 25 as a stepped transmission mechanism (multi-stage transmission mechanism) and a direct connection mechanism 27 is described as an example. However, it is not limited to this, for example, the direct connection mechanism 27 and / or the transmission mechanism 25 may be deleted (omitted).

[0116] Furthermore, in this embodiment, the case where the transmission device 21 has a planetary gear mechanism 32 is described as an example. That is, in this embodiment, the planetary continuously variable transmission (CVT) mechanism 31 is described as an example. However, it is not limited to this, for example, the planetary gear mechanism 32 may be omitted. In other words, the CVT mechanism may have a structure that includes a planetary gear mechanism 32 and a hydrostatic CVT mechanism 34 (or an electric CVT mechanism 81), or the planetary gear mechanism 32 may be omitted and it may be composed of a hydrostatic CVT mechanism 34 (or an electric CVT mechanism 81).

[0117] In this embodiment, the example described is a case where the transmission device 21, which serves as a power transmission device for a vehicle, is mounted on a wheeled loader 1, which serves as a vehicle (work vehicle). However, it is not limited to this, and can be widely used as a power transmission device for various vehicles, such as construction vehicles like wheeled excavators, transport vehicles like lift trucks, and agricultural vehicles like tractors.

[0118] Symbol Explanation

[0119] 1: Wheel loader (vehicle)

[0120] 8A: Accelerator pedal (operating component)

[0121] 9: Engine (Prime Mobility Unit)

[0122] 12: Front axle (running mechanism)

[0123] 13: Rear axle (running mechanism)

[0124] 21: Transmission system (power transmission system for vehicles)

[0125] 22: Input axis

[0126] 23: Output shaft

[0127] 31: Planetary continuously variable transmission (CVT)

[0128] 36: First hydraulic pump motor

[0129] 37A, 37B: Main road

[0130] 38: Second hydraulic pump motor

[0131] 43: Controller

[0132] 51A: First variable relief valve (first relief valve)

[0133] 51B: Second Variable Relief Valve (Second Relief Valve)

[0134] 52: First check valve (check valve)

[0135] 61A: First fixed relief valve (first relief valve)

[0136] 61B: Second fixed relief valve (second relief valve)

[0137] 82: First electric generator

[0138] 83: First Electric Wire

[0139] 84: Controller

[0140] 85: Second wire

[0141] 86: Second electric generator

Claims

1. A power transmission device for a vehicle, characterized in that, have: The input shaft rotates via a prime mover mounted on the vehicle; An output shaft that outputs rotation to the vehicle's driving mechanism; and A continuously variable transmission (CVT) mechanism is disposed between the input shaft and the output shaft, enabling speed changes in rotation on the input shaft side and transmitting the speed to the output shaft side. The continuously variable transmission mechanism has the following features: The first hydraulic pump motor is installed on the input shaft side; The second hydraulic pump motor is connected to the first hydraulic pump motor via a pair of main lines, namely the first main line and the second main line; The first relief valve cuts off the flow of working oil from the first main pipeline to the second main pipeline when the pressure in the first main pipeline is below the first set pressure, and opens the flow when the pressure exceeds the first set pressure. as well as The second relief valve, when the pressure in the second main pipeline is below the second set pressure, cuts off the flow of working oil from the second main pipeline to the first main pipeline; when the pressure exceeds the second set pressure, it opens the pipeline. The second relief valve is a variable relief valve whose set pressure can be changed via a controller. The controller sets the set pressure of the second relief valve to a second set pressure that is lower than the first set pressure, thereby ensuring that the power transmitted from the first hydraulic pump motor to the second hydraulic pump motor and the power transmitted from the second hydraulic pump motor to the first hydraulic pump motor are of different magnitudes. When the amount of operation of the operating component that accelerates the vehicle is reduced to below the first amount of operation for switching between acceleration and deceleration, the controller increases the power transmission capability from the second hydraulic pump motor to the first hydraulic pump motor by changing the overflow start pressure of the second overflow valve from the second set pressure to a third set pressure that is higher than the second set pressure.

2. The vehicle power transmission device according to claim 1, characterized in that, The second set pressure is the minimum overflow pressure that can be changed by the second overflow valve.

3. The vehicle power transmission device according to claim 1, characterized in that, The first operating amount of the operating component is set to increase as the vehicle speed increases.

4. The vehicle power transmission device according to claim 1, characterized in that, A check valve is provided to replace the first relief valve, which enables the flow of working oil from the second main pipeline to the first main pipeline and cuts off the flow of working oil from the first main pipeline to the second main pipeline.

5. The vehicle power transmission device according to claim 1, characterized in that, The first relief valve is a variable relief valve whose first set pressure can be changed by the controller. The controller changes the first set pressure of the first relief valve according to the state of the vehicle, thereby changing the ratio of the power transmission capacity from the first hydraulic pump motor to the second hydraulic pump motor to the power transmission capacity from the second hydraulic pump motor to the first hydraulic pump motor.

6. The vehicle power transmission device according to claim 1, characterized in that, The continuously variable transmission mechanism also includes a planetary gear mechanism connected to the input shaft. The first hydraulic pump motor is located on the output side of the planetary gear mechanism.

Images