Vehicle power transmission device

Abstract

A transmission device (21) as a vehicle power transmission device includes an input shaft (22), an output shaft (23), and a planetary continuously variable transmission mechanism (31). The planetary continuously variable transmission mechanism (31) includes a planetary gear mechanism (32), a pump-side clutch (33), a hydraulic pump (36), a hydraulic motor (38), and a motor-side clutch (40). The hydraulic pump (36) and the hydraulic motor (38) are connected via a pair of main pipes (37A, 37B). When switching from a driving state to a neutral state, at least one of the clutches (33, 40) of the pump-side clutch (33) and the motor-side clutch (40) is released.

Description

Technical Field

[0001] The present invention relates to a vehicle power transmission device that is mounted on, for example, a wheel loader and that can obtain a travel speed and a driving force that are optimal for various working conditions. Background Art

[0002] Wheel loaders repeatedly perform a "V-cycle" operation, primarily loading the bucket, or a "Load & Haul" operation, primarily pouring material into the hopper. The "V-cycle" involves loading excavated soil and other materials into the bucket. The "Load & Haul" operation involves transporting excavated soil and other materials (loaded travel), pouring them into the hopper, and returning them (unloaded travel). During these various operations, including excavation, transporting, loading, and returning, wheel loaders frequently switch gears to optimize travel speed and driving force.

[0003] Wheel loader drive systems are typically categorized into three types: a transmission with a torque converter, a hydrostatic continuously variable transmission (HST), and a hydraulic mechanical continuously variable transmission (HMT). Vehicles equipped with a torque converter (hereinafter referred to as a torque converter) (hereinafter referred to as torque converter vehicles) typically employ a lock-up torque converter that allows for mechanical engagement for improved efficiency.

[0004] Torque converter vehicles utilize torque amplification in the low-speed range, effectively exploiting this effect in torque-requiring operations such as vehicle launch and excavation. However, this torque amplification process causes torque converter slippage, reducing efficiency. Specifically, while efficiency increases with increasing speed ratios, it reaches a maximum at a certain speed ratio and then declines. Therefore, torque converter vehicles tend to experience a decrease in efficiency at high speeds. However, torque converter vehicles utilize a locking mechanism that mechanically connects the engine output shaft to the transmission output shaft, thereby improving power transmission efficiency.

[0005] In vehicles equipped with a hydrostatic continuously variable transmission (CVT), either or both the hydraulic pump and motor within the CVT are variable capacity. By controlling the tilt of the variable capacity hydraulic pump or motor, CVT vehicles can control vehicle speed and traction by varying the capacity. Efficiency is calculated as the product of the mechanical efficiency and volumetric efficiency of the CVT. CVT vehicles operate at high efficiencies of approximately 70-80% at high speeds and also achieve higher efficiency than torque converter vehicles at low speeds.

[0006] A hydraulic mechanical continuously variable transmission (CVT) combines a hydraulic power transmission mechanism based on the hydraulic unit of a hydrostatic continuously variable transmission (HPVT) with a mechanical power transmission mechanism based on gears (Patent Document 1). Power input from the engine to the CVT is split into hydraulic and mechanical power transmissions, which are then combined and input. The mechanism responsible for splitting and combining this power is a planetary gear mechanism. In a vehicle equipped with a CVT, the proportion of mechanical power transmission (higher transmission efficiency) increases as vehicle speed increases, thanks to the planetary gear mechanism. This structure mitigates the low efficiency caused by torque converter slip at low speeds, a drawback of torque converter vehicles, and enables higher transmission efficiency at high speeds than vehicles equipped with hydrostatic continuously variable transmissions. Furthermore, a CVT vehicle can control vehicle speed and traction by varying the volume of the hydraulic power transmission mechanism through tilt control. Therefore, the hydraulic mechanical continuously variable transmission-equipped vehicle can control the distribution of power input from the engine between the loading and unloading machine and the drive system.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application No. 2010-540866 (Japanese Patent No. 5190513) Summary of the Invention

[0010] Summary of the Invention

[0011] When transporting cargo at low speeds (5-10 km / h), vehicles equipped with a hydraulic mechanical continuously variable transmission (CMVT) achieve high efficiency through continuously variable transmission. However, when transporting cargo at high speeds (10-20 km / h), CMVT vehicles distribute power to the hydraulic pressure, potentially leading to lower transmission efficiency compared to torque converter vehicles with a lockup mechanism. Similarly, when returning (10-40 km / h), CMVT vehicles distribute power to the hydraulic pressure, potentially leading to lower transmission efficiency compared to torque converter vehicles with a lockup mechanism. For example, at 0-5 km / h, the efficiency difference between CMVT vehicles and torque converter vehicles is close to zero. In contrast, at 5-10 km / h, CMVT vehicles are more efficient than torque converter vehicles. Meanwhile, at 10-40 km / h, torque converter vehicles with a lockup mechanism are more efficient than CMVT vehicles.

[0012] Therefore, in order to achieve high efficiency, the following transmission is considered: when traveling at low speeds and during excavation and loading operations, the power is transmitted through a hydraulic mechanical continuously variable transmission using oil pressure, which has high transmission efficiency and excellent operability at low speeds; when traveling at high speeds such as returning and transporting, the power route is switched to a direct connection mechanism with high transmission efficiency at high speeds. Specifically, consider the following vehicle power transmission device, which includes: an input shaft rotated by a power machine mounted on the vehicle; an output shaft that outputs rotation to a travel device of the vehicle; a planetary continuously variable transmission mechanism provided between the input shaft and the output shaft, which changes the speed of rotation on the input shaft side and transmits it to the output shaft side; a direct-connection mechanism that transmits the rotation on the input shaft side to the output shaft side bypassing the planetary continuously variable transmission mechanism; an idler element that mechanically couples the output side of the planetary continuously variable transmission mechanism and the output side of the direct-connection mechanism; and a direct-connection clutch provided between the input shaft and the idler element in the direct-connection mechanism, the planetary continuously variable transmission mechanism including: a planetary gear mechanism connected to the input shaft side; a pump-side clutch (first clutch) provided on a first output side of the planetary gear mechanism; a hydraulic pump connected to the output side of the planetary gear mechanism via the pump-side clutch; a hydraulic motor connected to the hydraulic pump via a pair of main lines; a motor-side clutch (second clutch) provided between the hydraulic motor and the idler element or the output shaft; and a component mechanically coupled to the idler element on the second output side of the planetary gear mechanism.

[0013] In such a configuration, for example, if both the pump-side clutch and the motor-side clutch are engaged during a neutral state, which cuts off or limits the transmission of power from the power machine to the travel device, there is a possibility of significant energy loss. The neutral state is necessary when stopping the vehicle while keeping the engine, which serves as the power machine, running (rotating).

[0014] An object of the present invention is to provide a vehicle power transmission device that can reduce energy loss in a neutral state by providing a clutch on the output side of a planetary gear mechanism and the output side of a hydraulic motor.

[0015] The present invention is a vehicle power transmission device, which includes: an input shaft, which is rotated by a power machine mounted on the vehicle; an output shaft, which outputs the rotation to the travel device of the above-mentioned vehicle; and a planetary continuously variable transmission mechanism, which is arranged between the above-mentioned input shaft and the above-mentioned output shaft, and changes the speed of the rotation on the above-mentioned input shaft side and transmits it to the above-mentioned output shaft side. The above-mentioned planetary continuously variable transmission mechanism includes: a planetary gear mechanism connected to the above-mentioned input shaft side; a first clutch arranged on the output side of the above-mentioned planetary gear mechanism; a hydraulic pump connected to the output side of the above-mentioned planetary gear mechanism via the above-mentioned first clutch; a hydraulic motor connected to the above-mentioned hydraulic pump via a pair of main pipelines; a second clutch arranged between the above-mentioned hydraulic motor and the above-mentioned output shaft side; and a controller for controlling the connection and release of the above-mentioned first clutch and the above-mentioned second clutch, wherein the above-mentioned controller releases at least one of the first clutch and the above-mentioned second clutch when switching from a driving state in which the power from the above-mentioned power machine can be transmitted to the above-mentioned travel device to a neutral state in which the power from the above-mentioned power machine is cut off or restricted from being transmitted to the above-mentioned travel device.

[0016] According to the present invention, by providing the first clutch between the planetary gear mechanism and the hydraulic pump and providing the second clutch on the output side of the hydraulic motor, energy loss in the neutral state can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a left side view showing a wheel loader equipped with the vehicle power transmission device according to the embodiment.

[0018] Figure 2 Yes Figure 1 A partially cutaway side view of a transmission (power transmission device for a vehicle) in FIG.

[0019] Figure 3 This is a structural diagram showing the power transmission path of a wheel loader together with the controller.

[0020] Figure 4 It will Figure 3 A block diagram showing the controller together with a communication valve (electromagnetic on-off valve), etc.

[0021] Figure 5 This is a flowchart showing the processing of the controller when the pump-side clutch (first clutch) and the motor-side clutch (second clutch) are connected.

[0022] Figure 6 This is a flowchart showing the processing of the controller when the pump-side clutch (first clutch) and the motor-side clutch (second clutch) are released.

[0023] Figure 7 Yes Figure 1A partially cutaway perspective view of the interior of a driver's cab of a wheel loader.

[0024] Figure 8 This is a configuration diagram showing a power transmission path of a wheel loader equipped with the vehicle power transmission device according to the first modified example, together with a controller.

[0025] Figure 9 This is a configuration diagram showing a power transmission path of a wheel loader equipped with a vehicle power transmission device according to a second modified example, together with a controller. DETAILED DESCRIPTION

[0026] Hereinafter, the case where the vehicle power transmission device according to the embodiment of the present invention is applied to a wheel loader will be described as an example, with reference to the attached drawings. Figure 1 In addition, Figure 5 and Figure 6 Each step in the flowchart shown is denoted by an "S" (for example, step 1 is set to "S1").

[0027] Figures 1 to 7 An embodiment is shown. Figure 1 In the figure, wheel loader 1 is a representative example of a vehicle (work vehicle). Wheel loader 1 is constructed as an articulated work vehicle, namely, 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 are connected so as to bend leftward and rightward. In other words, the front body 3 and the rear body 5 constitute the body of 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. The front body 3 and the rear body 5 bend leftward and rightward around the central hinge 6 by extending and contracting the steering cylinder. This allows the wheel loader 1 to be steered while driving.

[0028] A working mechanism 7, also known as a loading and unloading mechanism, is mounted on the front body 3 of the wheel loader 1 so as to be capable of pitching and tilting. The working mechanism 7 includes a loading bucket 7A. Meanwhile, a cab 8 (with a driver's cab inside), an engine 9, a hydraulic pump 10, and a transmission 21 are mounted on the rear body 5 of the wheel loader 1.

[0029] like Figure 7As shown, the driver's cab 8 is provided with a driver's seat 8A, a steering wheel 8B, an accelerator pedal 8C, a brake pedal 8D, an FNR lever 8E, a parking brake switch, and the like. The FNR lever 8E is operated by the operator to switch the wheel loader 1 between forward and reverse directions and to switch the gear stage. When the wheel loader 1 is moved forward, the operator switches the FNR lever 8E to the forward position (F). When the wheel loader 1 is moved backward, the operator switches the FNR lever 8E to the reverse position (R). When the wheel loader 1 is stopped without moving, the operator switches the FNR lever 8E to the neutral position (N). When switching the gear stage, the operator rotates the FNR lever 8E around the lever axis.

[0030] The engine 9 is the power source (power machine) of the wheel loader 1. The power source (power machine) may be composed not only of the engine 9 alone, which is an internal combustion engine, but also of an engine and an electric motor, or of an electric motor alone. A hydraulic pump 10 is connected to the engine 9. The hydraulic pump 10 is the hydraulic source for operating the working mechanism 7.

[0031] A front axle 12 extending leftward and rightward is provided below the front vehicle body 3. Left and right front wheels 2 are mounted on both ends of the front axle 12. Meanwhile, a rear axle 13 extending leftward and rightward is provided below the rear vehicle body 5. Left and right rear wheels 4 are mounted on both ends of the rear axle 13.

[0032] 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 reduces the speed of the engine 9 and transmits it to the front drive shaft 14 and the rear drive shaft 15. In other words, the power from the engine 9 is transmitted to the transmission 21 coupled to the engine 9.

[0033] The power from the engine 9 is adjusted in speed and direction by the transmission 21, and then transmitted from the front and rear output shafts 23A and 23B of the transmission 21 to the front axle 12 and the rear axle 13 via the front drive shaft 14 and the rear drive shaft 15. Figure 2 As shown, the transmission 21 includes an input shaft 22 connected to the engine 9, an output shaft 23A connected to the front side of the front drive shaft 14, and an output shaft 23B connected to the rear side of the rear drive shaft 15. The transmission 21 changes speed and switches forward and reverse rotation between the input shaft 22 and the output shafts 23A and 23B by switching the power transmission path within the transmission 21.

[0034] Next, in Figure 1 and Figure 2 Based on this, we also refer to Figures 3 to 6 , the speed change device 21 of the embodiment will be described. Figure 3In order to avoid complexity in the drawing, the output shaft 23 of the transmission 21 is simply represented as a common output shaft 23 (= output shafts 23A, 23B) that transmits power to both the front axle 12 and the rear axle 13. Figure 3 In the figure, the structure for dividing the power into the front output shaft 23A and the rear output shaft 23B via, for example, a center differential mechanism is omitted.

[0035] The transmission 21, which serves as a vehicle power transmission device, includes an input shaft 22, an output shaft 23, a planetary continuously variable transmission mechanism 31, and a controller 43. Furthermore, the transmission 21 includes a speed change mechanism 25, which serves as a stepped speed change mechanism, a direct-connection mechanism 27, a transmission shaft 28, and an idler gear 29, which serves as an idler element.

[0036] The input shaft 22 is rotated by the engine 9, which serves as a power machine, mounted on the vehicle. That is, the engine 9 (its drive shaft) is connected to the input shaft 22. Conversely, the output shaft 23 outputs rotation to the front axle 12 and / or rear axle 13, which serve as the vehicle's travel devices. Specifically, the power of the engine 9 is output from the output shaft 23 via the speed change device 21, which serves as a transmission. 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. In other words, the power of the output shaft 23 is transmitted to the front axle 12 and / or rear axle 13, which serve as the travel devices.

[0037] The power input from the input shaft 22 to the transmission 21 is transmitted to the idler gear 29 via the planetary continuously variable transmission mechanism 31 or the direct-connection mechanism 27. The power transmitted to the idler gear 29 is output from the output shaft 23 via the speed change mechanism 25. The planetary continuously variable transmission mechanism 31 is disposed between the input shaft 22 and the output shaft 23. The planetary continuously variable transmission mechanism 31 changes the speed of rotation on the input shaft 22 side and transmits it to the output shaft 23 side. The input side of the planetary continuously variable transmission mechanism 31 is connected to the input shaft 22, which is provided with the input-side gear 27A of the direct-connection mechanism 27. The output side of the planetary continuously variable transmission mechanism 31 is connected to the transmission shaft 28, which is provided with the idler gear 29.

[0038] The speed change mechanism 25 is arranged 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 speed change mechanism 25 also changes the speed of the rotation on the input shaft 22 side and transmits it to the output shaft 23 side. In this case, the speed change mechanism 25 is arranged between the intermediate gear 26 that meshes with the idler gear 29 and the output shaft 23. In other words, the input side of the speed change mechanism 25 is connected to the intermediate gear 26. The output side of the speed change mechanism 25 is connected to the output shaft 23. The speed change mechanism 25 is configured as a multi-stage stepped speed change mechanism, for example. The speed change mechanism 25 is configured to include multiple transmission shafts, multiple gears, and multiple clutches. In this case, the speed change mechanism 25 can be configured as a speed change mechanism (DCT: Dual Clutch Transmission) that includes 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. For example, when the FNR lever 8E of the operator's cab 8 is in the forward position (F), the forward clutch 25A is engaged. When the FNR lever 8E of the operator's cab 8 is in the reverse position (R), the reverse clutch 25B is engaged. Furthermore, the speed change mechanism 25 may be omitted. That is, the intermediate gear 26 and the output shaft 23 may be directly connected without the speed change mechanism 25.

[0039] The direct-connection mechanism 27 transmits the rotation of the input shaft 22 to the output shaft 23, bypassing the planetary continuously variable transmission mechanism 31. In other words, the direct-connection mechanism 27 transmits the rotation of the input shaft 22 directly to the speed change mechanism 25, without passing through the planetary continuously variable transmission mechanism 31. The direct-connection 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-connection clutch 30 serving as a third clutch. The rotation of the output-side gear 27B is transmitted to the transmission shaft 28 via the direct-connection clutch 30. In the embodiment, the input-side gear 27A is provided on the input shaft 22. The output-side gear 27B is provided on a rotating shaft 27B1 coaxially arranged with the transmission shaft 28. The direct-connection clutch 30 is coaxially arranged between the transmission shaft 28 and the rotating shaft 27B1.

[0040] The transmission shaft 28 corresponds to the output shaft of the direct-connection mechanism 27 and also to the output shaft of the planetary continuously variable transmission mechanism 31. In this case, the transmission shaft 28 is arranged coaxially with the rotating shaft 27B1 of the direct-connection mechanism 27 and coaxially with the motor shaft 39 of the planetary continuously variable transmission mechanism 31. The transmission shaft 28 is connected to the rotating shaft 27B1 of the direct-connection mechanism 27 via the direct-connection clutch 30. When the direct-connection clutch 30 is engaged, the rotation of the output-side gear 27B of the direct-connection mechanism 27 is transmitted to the transmission shaft 28. The transmission shaft 28 is connected to the hydraulic motor 38 of the planetary continuously variable transmission mechanism 31 via the motor-side clutch 40. When the motor-side clutch 40 is engaged, the rotation of the hydraulic motor 38 of the planetary continuously variable transmission mechanism 31 is transmitted to the transmission shaft 28. Furthermore, the transmission shaft 28 is connected to the planetary output gear 32B of the planetary continuously variable transmission mechanism 31 via the idler gear 29.

[0041] An idler gear 29, serving as an idler element, is provided on the transmission shaft 28. The idler gear 29 mechanically connects the output side of the planetary continuously variable transmission mechanism 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 continuously variable transmission mechanism 31. The idler gear 29 meshes with the intermediate gear 26. The rotation of the idler gear 29 is transmitted to the speed change mechanism 25 via the intermediate gear 26. Specifically, the power input from the input shaft 22 of the speed change device 21 is transmitted to the idler gear 29 via the planetary continuously variable transmission mechanism 31 or the direct-connection mechanism 27. The power transmitted to the idler gear 29 is output from the output shaft 23 via the speed change mechanism 25.

[0042] A direct-connection clutch 30 is provided within the direct-connection mechanism 27, which is 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-side 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" (engaged state), in which rotation (torque, rotational force, power) is transmitted between the direct-connection mechanism 27 (rotating shaft 27B1) and the idler gear 29 (transmission shaft 28), and a "disconnected state" (disconnected state), in which rotation transmission is interrupted. When the direct-connection clutch 30 is in the connected state, the rotation of the output-side 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 disengaged state, the rotation of the output-side gear 27B (rotating shaft 27B1) is not transmitted to the transmission shaft 28. The engagement and release of the direct clutch 30 are controlled based on a command (command signal C1 ) from the controller 43 .

[0043] Next, the planetary continuously variable transmission mechanism 31 will be described.

[0044] The planetary continuously variable transmission mechanism 31 includes a planetary gear mechanism 32, a pump-side clutch 33 serving as a first clutch, a hydrostatic continuously variable transmission mechanism 34, a motor-side clutch 4 serving as a second clutch, and a controller 43. The hydrostatic continuously variable transmission mechanism 34 includes a pump shaft 35, a hydraulic pump 3, a pair of main lines 37A and 37B, a hydraulic motor 38, a motor shaft 39, an electromagnetic on-off valve 41, and a connecting line 42.

[0045] The planetary gear mechanism 32 is connected to the input shaft 22 side. Specifically, the planetary gear mechanism 32 is connected to the input shaft 22. The planetary gear mechanism 32 is composed of a planetary gear device (not shown) of one or more stages, a planetary output shaft 32A, and a planetary output gear 32B. The planetary gear device includes, for example, a sun gear, a ring gear, and a planetary carrier that supports planetary gears that mesh with these sun gears and ring gears. For example, the input shaft 22 is connected to any one of the sun gear, the ring gear, and the planetary carrier. The planetary output shaft 32A is connected to the sun gear, the ring gear, and the planetary carrier except the part connected to the input shaft 22. The planetary output gear 32B is connected to the remaining parts of the sun gear, the ring gear, and the planetary carrier. The planetary output shaft 32A is connected to the pump shaft 35 (hydraulic pump 36) of the hydrostatic continuously variable transmission mechanism 34 via the pump-side clutch 33. The rotation of the planetary output shaft 32A is transmitted to the pump shaft 35 (hydraulic pump 36) of the hydrostatic continuously variable transmission mechanism 34 via the pump-side clutch 33. 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.

[0046] The pump-side clutch 33 is provided on the output side of the planetary gear mechanism 32. Specifically, it is provided between the planetary output shaft 32A of the planetary gear mechanism 32 and the pump shaft 35 (hydraulic pump 36) of the hydrostatic continuously variable transmission mechanism 34. The pump-side clutch 33 can switch between a "connected state" (engaged state), in which rotation is transmitted between the planetary gear mechanism 32 (planetary output shaft 32A) and the hydraulic pump 36 (pump shaft 35) of the hydrostatic continuously variable transmission mechanism 34, and a "disconnected state" (disconnected state), in which rotation transmission is cut off. When the pump-side clutch 33 is in the connected state, rotation of the planetary output shaft 32A of the planetary gear mechanism 32 is transmitted to the hydraulic pump 36 via the pump shaft 35 of the hydrostatic continuously variable transmission mechanism 34. When the pump-side clutch 33 is in the disengaged state, rotation of the planetary output shaft 32A is not transmitted to the pump shaft 35. The connection and disengagement of the pump-side clutch 33 are controlled based on a command (command signal C2) from the controller 43.

[0047] The pump shaft 35 of the hydrostatic continuously variable transmission mechanism 34 corresponds to the input shaft of the hydrostatic continuously variable transmission mechanism 34. The pump shaft 35 is connected to the rotating shaft (input shaft) of the hydraulic pump 36. Alternatively, the pump shaft 35 is equivalent to the rotating shaft (input shaft) of the hydraulic pump 36. The hydraulic pump 36 is connected to the output side of the planetary gear mechanism 32, that is, the planetary output shaft 32A of the planetary gear mechanism 32, via the pump side clutch 33. The hydraulic pump 36 is driven to rotate by the pump shaft 35, so that the pressure oil flows in a pair of main lines 37A and 37B. The hydraulic pump 36 is composed of, for example, a variable capacity and inclined plate type hydraulic pump. The hydraulic pump 36 has a regulator 36A for adjusting the pump capacity. The regulator 36A of the hydraulic pump 36 is based on an instruction (instruction signal W) from the controller 43. P A pair of main conduits 37A and 37B connects a pair of supply and discharge ports of the hydraulic pump 36 and a pair of supply and discharge ports of the hydraulic motor 38.

[0048] The hydraulic motor 38 is connected to the hydraulic pump 36 via a pair of main pipes 37A and 37B. The hydraulic motor 38 is rotated by the pressurized oil supplied from the hydraulic pump 36. The hydraulic motor 38 is, for example, a variable displacement type and swash plate type hydraulic motor. The hydraulic motor 38 includes a regulator 38A for adjusting the motor capacity. The regulator 38A of the hydraulic motor 38 is controlled by a command (command signal W) from the controller 43. M ) is variably controlled. The motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 corresponds to the output shaft of the hydrostatic continuously variable transmission mechanism 34. The motor shaft 39 is connected to the rotating shaft (output shaft) of the hydraulic motor 38. Alternatively, the motor shaft 39 corresponds to the rotating shaft (output shaft) of the hydraulic motor 38.

[0049] The motor-side clutch 40 is provided between the hydraulic motor 38 and the output shaft 23. Specifically, the motor-side clutch 40 is provided between the hydraulic motor 38 and the idler gear 29. This connects the hydraulic motor 38 to the idler gear 29 via the motor-side clutch 40. In this case, the motor-side clutch 40 is provided between the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 and the transmission shaft 28 on which the idler gear 29 is provided. The motor-side clutch 40 can switch between a "connected state" (engaged state) in which rotation is transmitted between the idler gear 29 (transmission shaft 28) and the hydraulic motor 38 (motor shaft 39) of the hydrostatic continuously variable transmission mechanism 34, and a "disconnected state" (disconnected state) in which rotation is disconnected. When the motor-side clutch 40 is in the connected state, the rotation of the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 (=the rotation of the hydraulic motor 38) is transmitted to the idler gear 29 via the transmission shaft 28. When the motor-side clutch 40 is in the released state, the rotation of the motor shaft 39 is not transmitted to the transmission shaft 28. The connection and release of the motor-side clutch 40 are controlled based on a command (command signal C3) from the controller 43.

[0050] In the embodiment, it is possible to arbitrarily select whether the power input from the input shaft 22 of the transmission 21 is transmitted to the speed change mechanism 25 via the planetary continuously variable transmission mechanism 31 or via the direct connection mechanism 27. Thus, under conditions where the planetary continuously variable transmission mechanism 31 operates appropriately, the planetary continuously variable transmission mechanism 31 can be utilized. On the other hand, under conditions where the speed change by the direct connection mechanism 27 is appropriate, power transmission can be performed via the direct connection mechanism 27.

[0051] When power is transmitted to the variator 25 via the planetary continuously variable transmission mechanism 31, the direct clutch 30 is released, and the pump-side clutch 33 and the motor-side clutch 40 are connected. In this case, the power flow can be divided into two types: one in which the power is distributed to the variator 25 via the planetary gear mechanism 32 and the hydrostatic continuously variable transmission mechanism 34, and the other in which the power is transmitted to the variator 25 without being transmitted to the hydrostatic continuously variable transmission mechanism 34 by setting the rotation speed of the hydraulic pump 36 to zero.

[0052] The state in which the direct-connect clutch 30 is released, the pump-side clutch 33 and the motor-side clutch 40 are connected, and power is not transmitted to the hydrostatic continuously variable transmission 34 but is transmitted to the variator 25 is referred to as an internal direct connection. On the other hand, the state in which the direct-connect clutch 30 is released, the pump-side clutch 33 and the motor-side clutch 40 are connected, and power is transmitted to the hydrostatic continuously variable transmission 34 but is transmitted to the variator 25 is referred to as a continuously variable transmission state. During internal direct connection, the displacement (discharge capacity) of the hydraulic pump 36 is increased to a predetermined value, and the displacement of the hydraulic motor 38 is neutralized. This acts as a brake within the hydrostatic continuously variable transmission 34, reducing the rotational speed of the hydraulic pump 36 to zero. This allows power from the engine 9 to be transmitted to the variator 25. In reality, due to oil leakage from the hydraulic pump 36 and the hydraulic motor 38, the rotational speed of the hydraulic pump 36 does not reach zero, but the majority of the power from the engine 9 can be distributed to the variator 25. On the other hand, when power is transmitted to the speed change mechanism 25 via the direct connection mechanism 27 , the direct connection clutch 30 is engaged, and the pump-side clutch 33 and the motor-side clutch 40 are released.

[0053] Here, the direct-connect clutch 30, the pump-side clutch 33, and the motor-side clutch 40 can be a wet multi-plate clutch or a synchromesh clutch. A wet multi-plate clutch generates transmission torque by pressing friction plates together. A synchromesh clutch transmits torque by meshing small teeth on the end face of a hub fixed to a shaft. Because a synchromesh clutch transmits torque by meshing small teeth, it is smaller and has a larger torque transmission capacity than a friction plate clutch. Furthermore, the drag torque when the synchromesh clutch is disengaged (released) is small, so the heat generated by the linked rotation is less than that of a wet multi-plate clutch.

[0054] Therefore, in the embodiment, to reduce losses, the pump-side clutch 33 and the motor-side clutch 40 are meshing clutches that transmit rotation through the engagement (meshing) of claws, i.e., synchromesh clutches. The direct-connect clutch 30 is a wet multi-plate clutch. However, if the pump-side clutch 33 and the motor-side clutch 40 are configured as synchromesh clutches, engaging and disengaging the pump-side clutch 33 and the motor-side clutch 40 becomes difficult unless the load on the hydraulic pump 36 and the hydraulic motor 38 of the hydrostatic continuously variable transmission 34 is reduced.

[0055] Therefore, in the embodiment, the hydrostatic continuously variable transmission mechanism 34 is provided with an electromagnetic on-off valve 41 serving as a connecting valve. That is, the pair of main lines 37A and 37B of the hydrostatic continuously variable transmission mechanism 34 are connected by a connecting line 42. Moreover, an electromagnetic on-off valve 41 is provided midway in the connecting line 42. Thus, an electromagnetic on-off valve 41 capable of switching between the pair of main lines 37A and 37B is provided between the pair of main lines 37A and 37B and capable of switching between the pair of main lines 37A and 37B to a connected state and a disconnected state. The electromagnetic on-off valve 41 is capable of switching between an open position (A) corresponding to the connected state and a closed position (B) corresponding to the disconnected state. The switching of the electromagnetic on-off valve 41 is controlled based on a command (command signal W) from a controller 43. When power is transmitted through the planetary continuously variable transmission mechanism 31, the electromagnetic on-off valve 41 is in a closed position (B) that disconnects the pair of main lines 37A and 37B. On the other hand, when switching the power transmission path between the planetary continuously variable transmission mechanism 31 and the direct-connection mechanism 27, the electromagnetic on-off valve 41 is switched to the open position (A), connecting the pair of main lines 37A and 37B. This connection between the pair of main lines 37A and 37B allows the pump-side clutch 33 and the motor-side clutch 40 to be engaged and disengaged while briefly interrupting the power transmission based on the hydraulic pressure within the hydraulic circuit of the planetary continuously variable transmission mechanism 31. This allows switching between the planetary continuously variable transmission mechanism 31 and the direct-connection mechanism 27, as well as switching from the direct-connection mechanism 27 to the planetary continuously variable transmission mechanism 31.

[0056] Next, let's consider the neutral state, that is, the neutral state in which the power from the engine 9 as a power machine is prevented from being transmitted to the front axle 12 and / or the rear axle 13 as the travel device via the output shaft 23 of the speed change device 21. The neutral state is necessary when the wheel loader 1 is stopped while the engine 9 is kept in operation (rotating). Here, the neutral state corresponds to a state in which the power from the engine 9 is "cut off" or "restricted" from being transmitted to the front axle 12 and / or the rear axle 13 (hereinafter also referred to as the travel device 12, 13). The state of "cutting off" the power from the engine 9 to the travel device 12, 13 corresponds to a state in which the forward clutch 25A and the reverse clutch 25B of the speed change mechanism 25 are released, for example, by switching the FNR lever 8E to the neutral position (N).

[0057] The state in which the transmission of power from the engine 9 to the travel devices 12 and 13 is "restricted" corresponds to a state in which the forward clutch 25A or reverse clutch 25B of the transmission mechanism 25 is engaged, but the operator has no intention to drive. This state in which the operator has no intention to drive corresponds, for example, to a state in which the vehicle speed is below V1 (V1: 0 to 1 km / h, essentially 0 km / h) and the acceleration indication is 0 (the accelerator pedal 8C is depressed to zero). More specifically, this corresponds to a state in which the FNR lever 8E is switched to the forward position (F) or reverse position (R), but the wheel loader 1 is stopped and the operator is depressing the brake pedal 8D. In this neutral state, in which the transmission of power from the engine 9 to the travel devices 12 and 13 is prevented (disconnected or restricted), if both the pump-side clutch 33 and the motor-side clutch 40 are engaged, there is a possibility that, for example, the hydraulic pump 36 will continue to rotate, increasing energy loss.

[0058] Therefore, in the embodiment, in the neutral state, at least one of the pump-side clutch 33 and the motor-side clutch 40 is released. More specifically, in the neutral state, both the pump-side clutch 33 and the motor-side clutch 40 are released. This can reduce energy loss caused by the rotation of the hydraulic pump 36 in the neutral state.

[0059] Based on this, in the embodiment, in the neutral state, the electromagnetic on-off valve 41 switches from the closed position (B) to the open position (A). That is, the electromagnetic on-off valve 41 is in the closed position (B) when the planetary continuously variable transmission mechanism 31 is the power transmission path. In other words, the electromagnetic on-off valve 41 is in the closed position (B) during the driving state, when the power from the engine 9 can be transmitted to the travel devices 12 and 13 via the planetary continuously variable transmission mechanism 31 and the output shaft 23. In contrast, in the neutral state, the electromagnetic on-off valve 41 switches from the closed position (B) to the open position (A). That is, in the neutral state, the electromagnetic on-off valve 41 is in the open position (A). Therefore, by connecting the pair of main lines 37A and 37B, the power transmission based on the oil pressure within the hydraulic circuit of the planetary continuously variable transmission mechanism 31 can be cut off, thereby reducing energy loss in the neutral state. Moreover, when the power transmission is cut off, the pump-side clutch 33 and the motor-side clutch 40 can be released. This also enables the pump-side clutch 33 and the motor-side clutch 40 to be released stably.

[0060] Furthermore, in the embodiment, when switching from the driving state to the neutral state, the tilting of the hydraulic pump 36 is minimized, and then the pump-side clutch 33 and the motor-side clutch 40 are released. This allows the pump-side clutch 33 and the motor-side clutch 40 to be released smoothly while the load on the hydraulic pump 36 is reduced. Specifically, in the embodiment, when switching from the driving state to the neutral state, the pump-side clutch 33 and the motor-side clutch 40 are released. Furthermore, when switching from the driving state to the neutral state, the electromagnetic on-off valve 41 is switched from the closed position (B) to the open position (A).

[0061] Next, refer to Figure 3 and Figure 4 , the controller 43 of the speed change device 21 will be described. Here, Figure 4 It is a block diagram showing the details of the controller 43 .

[0062] 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, and the third pressure detector 48. The output side of the controller 43 is connected to the electromagnetic on-off valve 41, the direct clutch 30, the pump-side clutch 33, the motor-side clutch 40, the regulator 36A of the hydraulic pump 36 of the planetary continuously variable transmission mechanism 31, and the regulator 38A of the hydraulic motor 38 of the planetary continuously variable transmission mechanism 31. The controller 43 is configured, for example, to include a microcomputer having a computing circuit (CPU), a memory, etc., and the memory stores information for executing the operations described below. Figure 5 and Figure 6The processing procedure of the processing flow shown is a processing flow for switching control processing for connecting and disconnecting the pump-side clutch 33 and the motor-side clutch 40, and the like.

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

[0064] The first pressure detector 46 is provided in one main line 37A. The first pressure detector 46 is a pressure sensor that detects the hydraulic pressure (pressure) of the one main line 37A. The first pressure detector 46 is connected to the hydraulic pressure P of the one main line 37A. A The corresponding detection signal is output to the controller 43. The second pressure detector 47 is provided in the other main line 37B. The second pressure detector 47 is a pressure sensor that detects the hydraulic pressure (pressure) of the other main line 37B. The second pressure detector 47 is connected to the hydraulic pressure P of the other main line 37B. B The corresponding detection signal is output to the controller 43. The third pressure detector 48 is provided in the direct-connection clutch 30. The third pressure detector 48 is a pressure sensor that detects the clutch pressure (pressure) of the direct-connection clutch 30. The third pressure detector 48 is connected to the clutch pressure P of the direct-connection clutch 30. C The corresponding detection signal is output to the controller 43 .

[0065] The controller 43 controls the connection and release of the direct-connect clutch 30, the pump-side clutch 33, and the motor-side clutch 40. When transmitting power to the speed change mechanism 25 via the direct-connect mechanism 27, the controller 43 connects the direct-connect clutch 30 and releases the pump-side clutch 33 and the motor-side clutch 40. This corresponds to, for example, a high-speed mode, enabling the wheel loader 1 to travel at high speed. When transmitting power to the speed change mechanism 25 via the planetary continuously variable transmission mechanism 31, the controller 43 releases the direct-connect clutch 30 and connects the pump-side clutch 33 and the motor-side clutch 40. This corresponds to, for example, a low-speed mode, enabling the wheel loader 1 to start and travel at low speed. When in neutral, the controller 43 releases the direct-connect clutch 30 and releases both the pump-side clutch 33 and the motor-side clutch 40.

[0066] In addition to controlling the direct-connect clutch 30, the pump-side clutch 33, and the motor-side clutch 40, the controller 43 also controls the connection and disconnection of the electromagnetic on-off valve 41. Here, the first state (driving state) is defined as the state in which the direct-connect clutch 30 is disengaged and both the pump-side clutch 33 and the motor-side clutch 40 are connected, i.e., the state in which power can be transmitted to the travel devices 12 and 13 via the planetary continuously variable transmission mechanism 31 and the output shaft 23. Conversely, the second state (neutral state) is defined as the state in which the direct-connect clutch 30 is disengaged and both the pump-side clutch 33 and the motor-side clutch 40 are disengaged, i.e., the state in which power transmission to the travel devices 12 and 13 via the output shaft 23 is cut off or limited.

[0067] In this case, when switching from the first state to the second state, the controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A), and then releases the pump-side clutch 33 and the motor-side clutch 40. On the other hand, when switching from the second state to the first state, the controller 43 connects the pump-side clutch 33 and the motor-side clutch 40, and then switches the electromagnetic on-off valve 41 from the open position (A) to the closed position (B). In other words, when switching from the first state to the second state, the controller 43 releases the pump-side clutch 33 and the motor-side clutch 40. Furthermore, when switching from the first state to the second state, the controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A).

[0068] Furthermore, the controller 43 switches the electromagnetic on-off valve 41 based on the detection values of the first pressure detector 46 and the second pressure detector 47. The first pressure detector 46 and the second pressure detector 47 correspond to pressure detectors that detect the pressure difference between the pair of main lines 37A and 37B. The controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A) when the detection values of the first pressure detector 46 and the second pressure detector 47 fall below a threshold value. More specifically, the controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A) when the difference between the detection values of the first pressure detector 46 and the second pressure detector 47, i.e., the pressure difference (differential pressure) between the pair of main lines 37A and 37B, falls below a threshold value. Alternatively, the pressure difference can be detected using a differential pressure gauge (differential pressure detector) that directly detects the pressure difference. The pressure difference threshold can be set, for example, to a value that suppresses pressure fluctuations when switching the electromagnetic on-off valve 41 from the closed position (B) to the open position (A).

[0069] In addition to controlling the direct clutch 30, the pump-side clutch 33, and the motor-side clutch 40, the controller 43 also controls the tilting of the hydraulic pump 36 and the hydraulic motor 38 of the hydrostatic continuously variable transmission 34 (adjusting the pump and motor capacities). Specifically, the controller 43 controls the regulator 36A of the hydraulic pump 36 and the regulator 38A of the hydraulic motor 38. In this case, when shifting from the driving state to the neutral state, the controller 43 minimizes the tilting of the hydraulic pump 36 and then releases the pump-side clutch 33 and the motor-side clutch 40.

[0070] like Figure 4 As shown, the controller 43 includes an engine speed detection unit 43A, a vehicle speed determination unit 43B, a pressure detection unit 43C, a command operation unit 43D, a communication valve command unit 43E, a clutch command unit 43F, and a tilt control command unit 43G. The engine speed V is input to the engine speed detection unit 43A from the first speed detector 44. in The engine speed detection unit 43A calculates the engine speed V in The output speed V is input from the second speed detector 45 to the vehicle speed determination unit 43B. out The vehicle speed determination unit 43B determines the output rotation speed V corresponding to the vehicle speed. out The hydraulic pressure P is input to the pressure detection unit 43C 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 pressure detection unit 43C compares the hydraulic pressure PA with the hydraulic pressure P B The pressure difference (=the pressure difference between a pair of main lines 37A and 37B) and the clutch pressure P C Output to the instruction operation unit 43D.

[0071] The controller 43 also includes a timer 43H for measuring time and a tilt detector 43J for detecting the tilt of the controller 43 relative to a horizontal plane. The timer 43H measures, for example, the time the wheel loader 1 is parked (parking duration). Specifically, the timer 43H measures, for example, the output speed V detected by the second speed detector 45. out When the vehicle speed is below the vehicle speed threshold V1, the time T during which the state below the vehicle speed threshold V1 continues is measured. The vehicle speed threshold V1 is a determination value for determining whether the wheel loader 1 is stopped and can be set, for example, to V1 = 0 to 1 km / h (substantially 0 km / h). The timer 43H outputs the measured time T to the command operation unit 43D. The tilt detector 43J is a tilt sensor (inclination sensor) that detects the tilt angle θ of the wheel loader 1 relative to the horizontal plane. The tilt detector 43J outputs the tilt angle θ to the command operation unit 43D.

[0072] Based on inputs from the engine speed detector 43A, the vehicle speed determination unit 43B, the pressure detector 43C, the timer 43H, and the tilt detector 43J, the command calculation unit 43D calculates a command for the electromagnetic on-off valve 41 (a solenoid valve command), a command for the clutches 30, 33, and 40 (a clutch command), a command for the regulator 36A of the hydraulic pump 36 (a pump command), and a command for the regulator 38A of the hydraulic motor 38 (a motor command). The command calculation unit 43D outputs the solenoid valve command to the communication valve command unit 43E, the clutch command to the clutch command unit 43F, and the pump and motor commands to the tilt control command unit 43G.

[0073] The communication valve command unit 43E receives an electromagnetic valve command from the command calculation unit 43D. The communication valve command unit 43E outputs a control command related to the opening and closing operation of the electromagnetic on-off valve 41 to the electromagnetic on-off valve 41 in accordance with the electromagnetic valve command from the command calculation unit 43D. Specifically, the communication valve command unit 43E outputs an on / off (disconnection) signal W to the electromagnetic on-off valve 41. In this case, on / off corresponds to the open position (A) of the electromagnetic on-off valve 41, and off / disconnect corresponds to the closed position (B) of the electromagnetic on-off valve 41. The clutch command unit 43F receives a clutch command from the command calculation unit 43D. Based on the clutch command from the command calculation unit 43D, the clutch command unit 43F outputs a control command related to the connection and release of the clutches 30, 33, and 40 to the clutches 30, 33, and 40. Specifically, the clutch command unit 43F outputs on / off (disconnection) signals C1, C2, and C3 to the clutches 30, 33, and 40. In this case, a signal C1 is output to the direct clutch 30 , a signal C2 is output to the pump-side clutch 33 , and a signal C3 is output to the motor-side clutch 40 .

[0074] The tilt control command unit 43G receives a pump command and a motor command from the command operation unit 43D. Based on the pump command and the motor command from the command operation unit 43D, the tilt control command unit 43G outputs a control command related to the tilting operation of the hydraulic pump 36 and the hydraulic motor 38 to the regulator 36A of the hydraulic pump 36 and the regulator 38A of the hydraulic motor 38. In other words, the tilt control command unit 43G outputs a tilting command signal W for the swash plate or the swash axis to the regulator 36A of the hydraulic pump 36 and the regulator 38A of the hydraulic motor 38. P 、W M In this case, the tilting command signal W is output to the regulator 36A of the hydraulic pump 36. P , outputs a tilting command signal W to the regulator 38A of the hydraulic motor 38 MThe hydraulic pump 36 and hydraulic motor 38 within the hydrostatic continuously variable transmission 34 are variable capacity. The discharge capacity of the hydraulic pump 36 and hydraulic motor 38 is adjusted by changing the tilt angle of the swash plate or swash shaft. The hydraulic pump 36 and hydraulic motor 38 can tilt in either one or two directions.

[0075] Next, a description will be given of a specific control process for connecting and disconnecting the pump-side clutch 33 and the motor-side clutch 40 by the controller 43. The direct clutch 30 is disconnected.

[0076] Figure 5 The following shows a specific process flow executed by the controller 43 when the pump-side clutch 33 and the motor-side clutch 40 are connected, that is, a control process (determination process) when the pump-side clutch 33 and the motor-side clutch 40 are released from the connected state. Figure 5 The control process is repeatedly executed in a predetermined control cycle, for example, while the pump-side clutch 33 and the motor-side clutch 40 are connected, in other words, while power can be transmitted through the planetary continuously variable transmission mechanism 31.

[0077] For example, through the following Figure 6 If the pump side clutch 33 and the motor side clutch 40 are connected in the process of S12, the Figure 5 processing flow. Figure 5 In S1, it is determined whether the acceleration instruction is disconnected. For example, in S1, it is determined whether the accelerator pedal 8C is disconnected. In addition, in S1, it is also possible to determine whether the acceleration instruction is disconnected by whether the brake pedal 8D is stepped on. When S1 determines as "yes", that is, when the acceleration instruction is disconnected (the accelerator pedal 8C is not stepped on), enter S3. On the other hand, when S1 determines as "no" and the acceleration instruction is connected (the accelerator pedal 8C is stepped on), enter S2. In S2, the connection of the pump side clutch 33 and the motor side clutch 40 is maintained, and return is made. That is, by returning, it returns to the beginning and repeats the processing below S1.

[0078] In S3, it is determined whether the vehicle speed V of the wheel loader 1 is below the vehicle speed threshold value V1. The vehicle speed V corresponds to the actual speed (actual speed) of the wheel loader 1 detected by the second speed detector 45. The vehicle speed threshold value V1 is a threshold value for determining whether the wheel loader 1 is parked, for example, V1 = 0 to 1 km / h. If S3 determines "No", that is, if the vehicle speed V exceeds the threshold value V1, the process proceeds to S2. If S3 determines "Yes", that is, if the vehicle speed V is below the threshold value V1, the process proceeds to S4. In S4, it is determined whether the parking brake switch provided in the operator's cab 8 is OFF. If S4 determines "No", that is, if the parking brake switch is ON (brake applied), the process proceeds to S5.

[0079] In S5, the service brake is turned on and the parking brake is turned on. The service brake is provided in the travel device 12, 13 by, for example, a wet multi-plate disc brake. The service brake imparts braking force by supplying pressurized oil. The parking brake imparts braking force by releasing the supply of pressurized oil using, for example, a reverse brake provided between the speed change mechanism 25 and the travel device 12, 13. In the following S6, the electromagnetic on-off valve 41 is switched from the closed position (B) to the open position (A). At this time, the tilt of the hydraulic pump 36 is minimized. In the following S7, the pump side clutch 33 and the motor side clutch 40 are released. After the pump side clutch 33 and the motor side clutch 40 are released in S7, the vehicle starts Figure 6 processing.

[0080] On the other hand, if S4 is determined to be "Yes", that is, if the parking brake switch is off, the process proceeds to S8. In S8, it is determined whether the tilt angle θ of the wheel loader 1 is less than the tilt threshold value θ1. The tilt angle θ of the wheel loader 1 corresponds to the actual tilt angle of the wheel loader 1 detected by the tilt detector 43J. The tilt threshold value θ1 is a reference (threshold) for determining the tilt angle at which the wheel loader 1 can be maintained stationary even if the pump-side clutch 33 and the motor-side clutch 40 are released. The tilt threshold value θ1 can be calculated based on the weight of the wheel loader 1 (vehicle weight) and the friction between the wheel loader 1 and the road surface when the wheel loader 1 is parked on a slope. If S8 is determined to be "No", that is, if the tilt angle θ of the wheel loader 1 is greater than θ1, the process proceeds to S2. On the other hand, if S8 is determined to be "Yes", that is, if the tilt angle θ of the wheel loader 1 is less than θ1, the process proceeds to S9.

[0081] In S9, it is determined whether the FNR lever 8E is in the neutral position (N). If S9 determines to be "yes", that is, if the FNR lever 8E is in the neutral position (N), the process proceeds to S5. On the other hand, if S9 determines to be "no", that is, if the FNR lever 8E is not in the neutral position (N), the process proceeds to S10. In S10, it is determined whether the vehicle speed V has been below V1 for more than T1 time. The time elapsed since the vehicle speed V was below V1 is measured by the timer 43H. The threshold value T1 as the determination time can be set to determine whether the loading operation of the working device 7 of the wheel loader 1 is stopped or the state of temporary parking during the loading operation. For example, while the working device 7 is loading the dump truck, the service brake is actuated with the FNR lever 8E in the forward position (F), and the vehicle stops for about 2 to 6 seconds. On the other hand, when waiting for the dump truck with the FNR lever 8E in the forward position (F), the vehicle stops for about 10 to 180 seconds.

[0082] Therefore, threshold T1 can be set, for example, between 3 and 60 seconds. Thus, using timer 43H, controller 43 can determine whether the loading operation is stopped or temporarily stopped during the loading operation based on the difference in stopping time. If the determination in S10 is "Yes," meaning the vehicle speed V has remained below V1 for a period of time exceeding T1, the process proceeds to S5. Conversely, if the determination in S10 is "No," meaning the vehicle speed V has not remained below V1 for a period of time exceeding T1, the process proceeds to S2.

[0083] Figure 6 The following shows a specific process flow executed by the controller 43 when the pump-side clutch 33 and the motor-side clutch 40 are released, that is, a control process (determination process) when the pump-side clutch 33 and the motor-side clutch 40 are connected from the released state. Figure 6 The control process is repeatedly executed in a predetermined control cycle while the pump-side clutch 33 and the motor-side clutch 40 are released, for example.

[0084] For example, through the above Figure 5 When the pump side clutch 33 and the motor side clutch 40 are released, the process of S7 starts. Figure 6 The processing flow. Figure 6 In S11, it is determined whether the vehicle speed V of the wheel loader 1 is below the vehicle speed threshold value V1. If S11 determines to be "No", that is, if the vehicle speed V exceeds the threshold value V1, the process proceeds to S12. In S12, the pump side clutch 33 and the motor side clutch 40 are connected. In the following S13, the electromagnetic on-off valve 41 is switched from the open position (A) to the closed position (B). In the following S14, the service brake is set to be disconnected, and the parking brake is set to be disconnected. After the service brake and the parking brake are set to be disconnected in S14, the process starts. Figure 5 processing.

[0085] On the other hand, if S11 determines "yes", that is, if the vehicle speed V is below the threshold value V1, the process proceeds to S15. In S15, it is determined whether the parking brake switch is off. If S15 determines "no", that is, if the parking brake switch is not on, the process proceeds to S16. In S16, the pump-side clutch 33 and the motor-side clutch 40 are continuously released, and the process returns. That is, the process returns to the beginning via the return, and the process after S11 is repeated. On the other hand, if S15 determines "yes", that is, if the parking brake switch is off, the process proceeds to S17. In S17, it is determined whether the FNR lever 8E is in the neutral position (N). If S17 determines "yes", that is, if the FNR lever 8E is in the neutral position (N), the process proceeds to S16. On the other hand, if S17 determines "no", that is, if the FNR lever 8E is not in the neutral position (N), the process proceeds to S18.

[0086] In S18, it is determined whether the FNR lever 8E has been operated from the neutral position (N) to the forward position (F). If the determination in S18 is "Yes," meaning the FNR lever 8E has been operated to the forward position (F), the process proceeds to S12. Conversely, if the determination in S18 is "No," meaning the FNR lever 8E has not been operated to the forward position (F), the process proceeds to S19. In S19, it is determined whether the FNR lever 8E has been operated from the neutral position (N) to the reverse position (R). If the determination in S19 is "Yes," meaning the FNR lever 8E has been operated to the reverse position (R), the process proceeds to S12. Conversely, if the determination in S19 is "No," meaning the FNR lever 8E has not been operated to the reverse position (R), the process proceeds to S16.

[0087] As described above, according to the embodiment, a pump-side clutch 33 (first clutch) is provided on the output side of the planetary gear mechanism 32 (between the planetary gear mechanism 32 and the hydraulic pump 36). Furthermore, a motor-side clutch 40 (second clutch) is provided on the output side of the hydraulic motor 38 (between the hydraulic motor 38 and the idler gear 29). Furthermore, in the neutral state, which cuts off or limits the transmission of power from the engine 9 to the travel devices 12 and 13, the controller 43 disengages both the pump-side clutch 33 and the motor-side clutch 40. This reduces energy loss in the neutral state.

[0088] For example, when the FNR lever 8E is switched to the neutral position (N) and the forward clutch 25A and reverse clutch 25B of the speed change mechanism 25 are released (power-off neutral state), both the pump-side clutch 33 and the motor-side clutch 40 are released. Therefore, power is not transmitted to the hydraulic pump 36 or the hydraulic motor 38. This reduces energy loss caused by the rotation (idling) of the hydraulic pump 36 or the hydraulic motor 38. Furthermore, for example, when the FNR lever 8E is switched to the forward position (F) or the reverse position (R), and the forward clutch 25A or the reverse clutch 25B of the speed change mechanism 25 is connected, but the operator has no intention of driving (power-limited neutral state), both the pump-side clutch 33 and the motor-side clutch 40 are released. Therefore, power is not transmitted to the hydraulic pump 36 or the hydraulic motor 38. This also reduces energy loss in this situation. Furthermore, in this case, when the operator's intention to drive is detected, for example, by the accelerator pedal 8C being stepped on, the wheel loader 1 can be started directly simply by engaging both the pump-side clutch 33 and the motor-side clutch 40. Therefore, it is possible to achieve both reduced energy loss in the neutral state and improved responsiveness when starting the wheel loader 1.

[0089] According to the embodiment, when switching from a driving state in which power from the engine 9 can be transmitted to the driving devices 12 and 13 to a neutral state, the tilting of the hydraulic pump 36 is minimized, and then both the pump-side clutch 33 and the motor-side clutch 40 are released. Therefore, the pump-side clutch 33 and the motor-side clutch 40 can be released smoothly while reducing the load on the hydraulic pump 36. Thus, according to the embodiment, when switching from a driving state to a neutral state, both the pump-side clutch 33 and the motor-side clutch 40 are released.

[0090] According to the embodiment, a solenoid on-off valve 41 serving as a communication valve is provided between the pair of main lines 37A and 37B connecting the hydraulic pump 36 and the hydraulic motor 38. Furthermore, the solenoid on-off valve 41 is in the open position (A), which serves as the communication position, in the neutral state. That is, the controller 43 sets the solenoid on-off valve 41 to the open position (A) in the neutral state. Therefore, power transmission via the hydraulic pressure within the hydraulic circuit of the planetary continuously variable transmission mechanism 31 (hydrostatic continuously variable transmission mechanism 34) can be cut off in the neutral state, thereby reducing energy loss. Furthermore, by setting the solenoid on-off valve 41 to the open position (A), the pump-side clutch 33 and the motor-side clutch 40 can be released while power transmission within the hydraulic circuit is cut off. This allows for stable release of the pump-side clutch 33 and the motor-side clutch 40. In particular, in the embodiment, the pump-side clutch 33 and the motor-side clutch 40 are configured as synchromesh clutches. Therefore, by connecting the hydraulic pump 36 and the hydraulic motor 38 via the electromagnetic on-off valve 41, the synchromesh clutch can be stably engaged and disengaged while quickly shutting off the power generated by the rotation of the hydraulic pump 36 and the hydraulic motor 38. As a result, a synchromesh clutch having a low drag torque when the pump-side clutch 33 and the motor-side clutch 40 are disengaged can be used, thereby reducing power loss in the vehicle and providing a transmission 21 (transmission) with high transmission efficiency.

[0091] According to the embodiment, when releasing both the pump-side clutch 33 and the motor-side clutch 40 from a connected state (driving state), the controller 43 switches the electromagnetic on-off valve 41 from a closed position (B), which serves as a disconnecting position, to an open position (A), which serves as a connecting position, before releasing both the pump-side clutch 33 and the motor-side clutch 40. This allows the pump-side clutch 33 and the motor-side clutch 40 to be released smoothly while quickly shutting off power transmission by the hydraulic pressure within the hydraulic circuit of the planetary continuously variable transmission mechanism 31 (hydrostatic continuously variable transmission mechanism 34). Thus, in the embodiment, when switching from the driving state to the neutral state, the electromagnetic on-off valve 41 is switched from the closed position (B), which serves as a disconnecting position, to the open position (A), which serves as a connecting position.

[0092] According to the embodiment, when connecting the pump-side clutch 33 and the motor-side clutch 40 from a state where both are released (neutral state), the controller 43 switches the electromagnetic on-off valve 41 from the open position (A) to the closed position (B) after connecting the pump-side clutch 33 and the motor-side clutch 40. This reduces pressure fluctuations when connecting the pump-side clutch 33 and the motor-side clutch 40, allowing for smooth connection of the pump-side clutch 33 and the motor-side clutch 40.

[0093] According to the embodiment, the controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A) when the pressure difference between the pair of main conduits 37A and 37B detected by the pressure detectors 46 and 47 falls below a threshold value. Therefore, by switching the electromagnetic on-off valve 41 from the closed position (B) to the open position (A), it is possible to suppress sudden pressure fluctuations when the pair of main conduits 37A and 37B are connected.

[0094] According to the embodiment, a second speed detector 45 for detecting the rotational speed of the output shaft 23 and a timer 43H for measuring time are provided. Furthermore, when the controller 43 determines, based on the second speed detector 45 and the timer 43H, that the wheel loader 1 has been stopped for a duration T (the duration during which the vehicle speed V is below V1) for a predetermined time period T1 or longer, it disengages the pump-side clutch 33 and the motor-side clutch 40. Specifically, the controller 43 determines that the loading operation is not a temporary stop due to the duration T (T1) exceeding the predetermined time period (T1), interrupting the operation and disengaging the pump-side clutch 33 and the motor-side clutch 40. This allows the pump-side clutch 33 and the motor-side clutch 40 to be disengaged at the appropriate time, thereby reducing energy loss.

[0095] Furthermore, according to the embodiment, an FNR lever 8E is provided. The controller 43 releases the pump-side clutch 33 and the motor-side clutch 40 when the FNR lever 8E is in the neutral position (N). Furthermore, even when the FNR lever 8E is in the forward position (F) or reverse position (R), the controller 43 releases the pump-side clutch 33 and the motor-side clutch 40 when the vehicle speed V remains below V1 for a predetermined time (T1 time) or longer. Furthermore, when the parking brake is applied, the controller 43 releases the pump-side clutch 33 and the motor-side clutch 40. This allows the operator to release the pump-side clutch 33 and the motor-side clutch 40 even when the operator does not intend to drive.

[0096] According to the embodiment, when the vehicle speed V of the wheel loader 1 exceeds V1, the controller 43 connects the pump-side clutch 33 and the motor-side clutch 40. Therefore, when power from the engine 9 should be transmitted to the travel devices 12 and 13, it can be transmitted to the travel devices 12 and 13. Furthermore, when the tilt angle θ detected by the tilt detector 43J exceeds the tilt threshold θ1, the controller 43 maintains the connection of the pump-side clutch 33 and the motor-side clutch 40. Therefore, when the wheel loader 1 is parked on a sloped road, the pump-side clutch 33 and the motor-side clutch 40 remain connected, allowing the vehicle to remain parked.

[0097] According to the embodiment, the communication valve that connects and disconnects the pair of main lines 37A and 37B is an electromagnetic on-off valve 41. Therefore, by switching the electromagnetic on-off valve 41 from its closed position (B), which serves as a disconnection position, to its open position (A), which serves as a connection position, the pair of main lines 37A and 37B can be switched from a disconnected state to a connected state. Conversely, by switching the electromagnetic on-off valve 41 from its open position (A) to its closed position (B), the pair of main lines 37A and 37B can be switched from a connected state to a disconnected state.

[0098] In the embodiment, the pump-side clutch 33 and the motor-side clutch 40 are described as synchronized meshing clutches. However, this is not limiting. For example, the pump-side clutch (first clutch) and the motor-side clutch (second clutch) may be dog clutches or wet multi-plate clutches.

[0099] In the embodiment, the electromagnetic on-off valve 41 is used as the communication valve for connecting and disconnecting a pair of main lines 37A and 37B. However, the invention is not limited thereto. For example, Figure 8 As shown in the first modified example, the connecting valves that switch the pair of main lines 37A and 37B between connected and disconnected states are electromagnetic relief valves 51A and 51B, each capable of changing the set pressure (relief set pressure, relief start pressure). Here, one-way valves 52 and 53, which serve as check valves, are installed in the connecting line 42 connecting the pair of main lines 37A and 37B. One-way valve 52 allows pressurized oil to flow from one main line 37A to the other main line 37B, while preventing it from flowing in the opposite direction. The other-way valve 53 allows pressurized oil to flow from the other main line 37B to one main line 37A, while preventing it from flowing in the opposite direction. Connected to the connecting line 42 are bypass lines 54 and 55 that bypass the respective one-way valves 52 and 53. The electromagnetic relief valves 51A and 51B are located midway in the bypass lines 54 and 55.

[0100] The electromagnetic relief valves 51A and 51B are electrically variable relief valves that vary their valve opening pressure (relief pressure) based on a command signal (command signal W) from the controller 43. The setting pressures (relief setting pressure, relief start pressure) of the electromagnetic relief valves 51A and 51B are controlled based on the command signal (command signal W) from the controller 43. The electromagnetic relief valves 51A and 51B are placed in a blocked state, isolating the pair of main conduits 37A and 37B, by increasing the setting pressures. They are placed in a connected state, connecting the pair of main conduits 37A and 37B, by decreasing the setting pressures.

[0101] Thus, in the first modified example, electromagnetic relief valves 51A and 51B, which serve as variable relief valves, are used as a mechanism for shutting off the power transmission by the hydraulic pressure within the hydrostatic continuously variable transmission mechanism 34. The electromagnetic relief valves 51A and 51B normally set the relief pressure to a predetermined value on the high-pressure side (e.g., 35 MPa to 50 MPa). Furthermore, in the neutral state, the controller 43 changes the relief pressure of the electromagnetic relief valves 51A and 51B to a predetermined value on the low-pressure side (e.g., the minimum value). In other words, the electromagnetic relief valves 51A and 51B release pressure between the pair of main lines 37A and 37B. Furthermore, when switching from the first state (driving state) in which both the pump-side clutch 33 and the motor-side clutch 40 are connected to the second state (neutral state) in which both the pump-side clutch 33 and the motor-side clutch 40 are released, the controller 43 changes the relief pressure of the electromagnetic relief valves 51A and 51B to a predetermined low-pressure value (minimum value) before releasing the pump-side clutch 33 and the motor-side clutch 40. Conversely, when switching from the second state (neutral state) in which both the pump-side clutch 33 and the motor-side clutch 40 are released to the first state (driving state) in which both the pump-side clutch 33 and the motor-side clutch 40 are connected, the controller 43 changes the relief pressure of the electromagnetic relief valves 51A and 51B to a predetermined high-pressure value after connecting the pump-side clutch 33 and the motor-side clutch 40. This allows the pump-side clutch 33 and the motor-side clutch 40 to be connected and released while power transmission by the hydraulic pressure within the hydrostatic continuously variable transmission mechanism 34 is cut off.

[0102] Alternatively, a configuration may be employed in which both the electromagnetic on-off valve 41 and the electromagnetic relief valves 51A and 51B are provided as the communication valve. Specifically, the communication valve comprises the electromagnetic on-off valve 41, which can switch between an open position (A) and a closed position (B), and the electromagnetic relief valves 51A and 51B, which can change the set pressure. Furthermore, the electromagnetic on-off valve 41 and the electromagnetic relief valves 51A and 51B are provided in parallel between the pair of main lines 37A and 37B. In this case, when switching from a first state (driving state) in which both the pump-side clutch 33 and the motor-side clutch 40 are connected, to a second state (neutral state) in which both the pump-side clutch 33 and the motor-side clutch 40 are released, the controller 43 changes the relief pressure of the electromagnetic relief valves 51A and 51B to a predetermined low-pressure value (minimum value), then switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A), thereby releasing the pump-side clutch 33 and the motor-side clutch 40. On the other hand, when the controller 43 switches from the second state (neutral state) in which both the pump side clutch 33 and the motor side clutch 40 are released to the first state (driving state) in which both the pump side clutch 33 and the motor side clutch 40 are connected, after connecting the pump side clutch 33 and the motor side clutch 40, the electromagnetic on-off valve 41 is switched from the open position (A) to the closed position (B), and the overflow pressure of the electromagnetic overflow valves 51A and 51B is changed to a predetermined value on the high-pressure side.

[0103] In the embodiment, the case where the motor side clutch 40 as the second clutch is provided between the hydraulic motor 38 and the idler gear 29 of the planetary continuously variable transmission mechanism 31 is described as an example. However, the present invention is not limited thereto. For example, Figure 9 As shown in the second modified example, a motor-side clutch 40 is provided between the hydraulic motor 38 of the planetary continuously variable transmission mechanism 31 and the output shaft 23. Specifically, an output shaft gear 61 is provided on the output shaft 23 connected to the output side of the transmission mechanism 25. A transmission gear 63 is provided on the output-side transmission shaft 62, which meshes with the output shaft gear 61 of the output shaft 23 directly or via a plurality of gears (not shown).

[0104] The motor-side clutch 40 is provided between the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 and the output-side transmission shaft 62. The motor-side clutch 40 can switch between a "connected state" (engaged state) in which rotation is transmitted between the output shaft 23 and the hydrostatic continuously variable transmission mechanism 34 (the motor shaft 39 of the hydraulic motor 38), and a "disconnected state" (disconnected state) in which rotation transmission is cut off. When the motor-side clutch 40 is in the connected state, the rotation of the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 (= the rotation of the hydraulic motor 38) is transmitted to the output shaft 23 via the output-side transmission shaft 62, the transmission gear 63, and the output gear 61. When the motor-side clutch 40 is in the disengaged state, the rotation of the motor shaft 39 is not transmitted to the output-side transmission shaft 62. According to this second modified example, the transmission mechanism 25 can be constructed in a compact size.

[0105] In the embodiment, an example is given in which the operator operates the FNR lever 8E to switch between forward (F), reverse (R), and neutral (N). When the FNR lever 8E is in the neutral (N) position, Figure 5 S9 and Figure 6 In the case where the determination in S17 is "Yes". However, the present invention is not limited thereto, and the operating member may be, for example, an FNR switch. Alternatively, the operating member may be, for example, an FR lever and an N switch. Furthermore, the operating member may be, for example, an FR switch and an N switch.

[0106] In the embodiment, the transmission 21 is described as including a direct-connection mechanism 27, a transmission shaft 28, an idler gear 29, a direct-connection clutch 30 serving as a third clutch, and a third pressure detector 48. However, this is not limiting; for example, these components, specifically those related to the direct-connection mechanism, may be omitted. In the embodiment, the electromagnetic on-off valve 41 is set to the open position (A) in the neutral state. However, this is not limiting; the electromagnetic on-off valve 41 may be maintained in the closed position (B) rather than the open position (A) in the neutral state. In the embodiment, the electromagnetic on-off valve 41 is switched before and after the pump-side clutch 33 and the motor-side clutch 40 are connected and released. However, this is not limiting; the electromagnetic on-off valve 41 may not be switched before and after the pump-side clutch 33 and the motor-side clutch 40 are connected and released. The same applies to the electromagnetic relief valves 51A and 51B.

[0107] In the embodiment, the controller 43 is described as releasing both the pump-side clutch 33 and the motor-side clutch 40 in the neutral state. However, this is not limiting. For example, the pump-side clutch 33 may be released in the neutral state while the motor-side clutch 40 remains connected. Alternatively, the motor-side clutch 40 may be released in the neutral state while the pump-side clutch 33 remains connected. That is, the controller releases at least one of the first clutch (pump-side clutch) and the second clutch (motor-side clutch) in the neutral state, which cuts off or limits the transmission of power from the power machine to the travel device. Preferably, at least the first clutch (pump-side clutch) of the first clutch (pump-side clutch) and the second clutch (motor-side clutch) is released in the neutral state. In other words, in the embodiment, the controller 43 is described as releasing both the pump-side clutch 33 and the motor-side clutch 40 when switching from the driving state to the neutral state. However, this is not limiting. For example, the pump-side clutch 33 may be released while the motor-side clutch 40 remains connected when switching from the driving state to the neutral state. Alternatively, when switching from the driving state to the neutral state, the motor-side clutch 40 may be released while the pump-side clutch 33 remains connected. Specifically, when switching from the driving state, in which power from the power machine can be transmitted to the driving device, to the neutral state, the controller releases at least one of the first clutch (the pump-side clutch) and the second clutch (the motor-side clutch). Preferably, when switching from the driving state to the neutral state, at least the first clutch (the pump-side clutch) of the first clutch (the pump-side clutch) and the second clutch (the motor-side clutch) is released.

[0108] In the embodiment, the transmission 21 as a vehicle power transmission device is described as being mounted on a wheel loader 1 as a work vehicle. However, the present invention is not limited thereto and can be widely used as a power transmission device for various vehicles, such as construction vehicles such as wheel excavators, transport vehicles such as lift trucks, and agricultural vehicles such as tractors.

[0109] Explanation of symbols

[0110] 1—Wheel loader (vehicle), 9—Engine (power machine), 12—Front axle (travel device), 13—Rear axle (travel device), 21—Speed transmission (vehicle power transmission device), 22—Input shaft, 23, 23A, 23B—Output shaft, 31—Planetary continuously variable transmission mechanism, 32—Planetary gear mechanism, 33—Pump-side clutch (first clutch), 36—Hydraulic pump, 37A, 37B—Main line, 38—Hydraulic motor, 40—Motor-side clutch (second clutch), 41—Electromagnetic on-off valve (communication valve), 43—Controller, 51A, 51B—Electromagnetic overflow valve (communication valve).

Claims

1. A power transmission device for a vehicle, characterized in that: have: an input shaft that is rotated by a power machine mounted on the vehicle; an output shaft that outputs rotation to a travel device of the vehicle; and A planetary continuously variable transmission mechanism is provided between the input shaft and the output shaft, which changes the speed of the rotation on the input shaft side and transmits it to the output shaft side. The planetary continuously variable transmission mechanism has: a planetary gear mechanism connected to the input shaft; a first clutch provided on the output side of the planetary gear mechanism; a hydraulic pump connected to the output side of the planetary gear mechanism via the first clutch; a hydraulic motor connected to the hydraulic pump via a pair of main pipes; a second clutch provided between the hydraulic motor and the output shaft; a communication valve provided between the pair of main conduits and capable of switching the pair of main conduits between a communication state and a shutoff state; and a controller for controlling the connection and release of the first clutch and the second clutch, and the connection and disconnection of the communication valve; The communication valve is an electromagnetic relief valve capable of changing the set pressure. It is in a shutoff state when the set pressure is increased, and in a communicating state when the set pressure is decreased. When the controller switches from a driving state in which power from the power machine can be transmitted to the driving device to a neutral state in which power transmission from the power machine to the driving device is cut off or restricted in order to stop the vehicle while keeping the power machine in motion, the controller releases at least one of the first clutch and the second clutch, and switches the electromagnetic relief valve from the cut-off state to the connected state.

2. The vehicle power transmission device according to claim 1, wherein: In addition to controlling the first clutch, the second clutch, and the electromagnetic relief valve, the controller also controls the tilting of the hydraulic pump. The controller minimizes the tilt of the hydraulic pump and then releases at least one of the first clutch and the second clutch when the vehicle is switched from the driving state to the neutral state.

3. The vehicle power transmission device according to claim 1, wherein: When the controller releases at least one of the first clutch and the second clutch from a state in which both the first clutch and the second clutch are connected, the controller releases at least one of the first clutch and the second clutch after switching the electromagnetic relief valve from a disconnected state to a connected state.

4. The vehicle power transmission device according to claim 1, wherein: The controller connects both the first clutch and the second clutch from a state in which at least one of the first clutch and the second clutch is released, and switches the electromagnetic relief valve from a connected state to a disconnected state after connecting both the first clutch and the second clutch.

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