JP6258593B2 - Automatic transmission for work vehicle - Google Patents

Description

  The present invention relates to an automatic transmission for a work vehicle.

  In some work vehicles such as wheel loaders, the rotation output of the hydraulic motor of the HST circuit is shifted by a transmission, and the rotation output after the shift is transmitted to a tire by an axle or the like to travel. In such a working vehicle, there is a traveling device for the working vehicle that reduces the motor tilt angle to a predetermined value when the transmission is switched in order to reduce a shift shock when the transmission is switched from high to low (for example, Patent Document 1).

JP 2012-52580 A

  By the way, the excavation work of the wheel loader is generally performed by moving the vehicle body toward an object to be excavated such as crushed rocks and earth and sand, and by operating the bucket and the arm after the bucket enters the object to be excavated by this traveling operation. Is done.

  Here, before the bucket enters the excavation object, it is necessary to increase the vehicle body speed, so the operator of the wheel loader operates the transmission at a high position. After the bucket has entered the object to be excavated, it is necessary to increase the driving force in order to enter the bucket deeper into the object to be excavated, so the wheel loader operator switches the transmission to the low position.

  According to the above-described prior art, it may be possible to reduce a shift shock at the time of switching the transmission. However, since it is the operator who determines the transmission switching timing, an experienced operator can appropriately determine the transmission switching timing to improve the efficiency of excavation work. In the case of a low operator, it is not possible to appropriately determine the transmission switching timing, and the efficiency of excavation work may be reduced.

  In the excavation work of a wheel loader, such a transmission switching operation is indispensable. However, since this operation is troublesome for the operator, there is little shift shock at the time of transmission switching, and the automatic operation of a work vehicle that can automatically shift gears. A transmission was desired.

  The present invention has been made based on the above-described matters, and an object of the present invention is to provide an automatic transmission device for a work vehicle that can automatically perform a shift-down operation of a transmission during excavation with a small shift shock by a simple control method. It is to provide.

In order to achieve the above object, a first invention is an automatic transmission device for a work vehicle having a bucket and a lift arm provided at a front portion, and is variable to a main pump comprising a variable capacity hydraulic pump that can be reversed. A travel HST circuit in which a travel motor composed of a capacitive hydraulic motor is connected in a closed circuit via a pair of main hydraulic lines, a motor regulator that controls the motor capacity of the travel motor, and the travel motor and wheels A transmission having a plurality of speed stages for shifting and outputting rotational power input from the travel motor, and controlling the position of the bucket by driving the lift arm, and excavating reaction force of the bucket A lift arm cylinder in which the pressure in the bottom side chamber increases, a pressure sensor for detecting the pressure in the bottom side chamber of the lift arm cylinder, An excavation determination unit for reading the pressure in the bottom side chamber of the lift arm cylinder by the pressure sensor and determining that the excavation state by the bucket is when the pressure in the bottom side chamber is equal to or higher than a predetermined determination pressure; A motor capacity increase control unit that outputs a command to increase the capacity of the travel motor to the motor regulator at a higher speed than the command increase rate during normal travel of the work vehicle in response to a command received from the unit; A shift down control unit for controlling the downshift from the high speed stage to the minimum speed stage of the transmission when the capacity of the traveling motor exceeds a preset motor capacity in accordance with a command received from the determination unit; it is assumed that the example Bei the.

In addition , a second invention includes an HST driving pressure sensor that detects an HST driving pressure that is a pressure of the main hydraulic pipe line in the first invention, and the motor capacity increase control unit includes the HST driving pressure sensor. The detected HST driving pressure is read, and when the HST driving pressure is equal to or higher than a preset set pressure, the command increasing speed for increasing the capacity of the traveling motor output to the motor regulator is set to a higher speed. It is characterized by that.

Furthermore, the third invention, the first or second inventions in Oite, comprising an operating lever for operating the lift arm, and an operation amount sensor for detecting an operation amount of the operating lever, the excavation determination unit Reads the operation amount of the operation lever detected by the operation amount sensor, and changes the determination pressure according to the operation amount of the operation lever.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the stroke sensor that detects the maximum stroke position of the piston rod of the lift arm cylinder is provided, and the excavation determination unit is detected by the stroke sensor. The excavation determination is not performed when the maximum stroke position of the piston rod of the lift arm cylinder is read.

Furthermore, in a fifth aspect based on any one of the first to fourth aspects, the motor capacity increase control unit is configured to control the motor based on the pressure in the bottom side chamber of the lift arm cylinder by the pressure sensor during excavation. An increase speed of a command for increasing the capacity of the traveling motor to be output to the regulator is set.

  According to the present invention, since the shift down operation of the transmission is controlled according to the pressure of the bottom side chamber of the lift arm cylinder interlocked with the load of the work vehicle and the change of the motor capacity of the traveling motor, Thus, it is possible to provide an automatic transmission device for a work vehicle that can automatically perform a shift-down operation of the transmission with a small shift shock. As a result, the manual switching operation of the transmission during excavation of the work vehicle is unnecessary, and the work efficiency is improved.

1 is a left side view showing a wheel loader to which an embodiment of an automatic transmission for a work vehicle according to the present invention is applied. 1 is a schematic diagram showing a power transmission system of a wheel loader to which an embodiment of an automatic transmission for a work vehicle according to the present invention is applied. 1 is a side view showing a working machine of a wheel loader to which an embodiment of an automatic transmission device for a work vehicle according to the present invention is applied. 1 is a hydraulic circuit diagram showing a power transmission device including a traveling HST circuit and a multi-stage transmission which is an embodiment of an automatic transmission for a work vehicle according to the present invention. It is a characteristic view which shows the control concept of the motor capacity | capacitance control part of the controller which comprises one Embodiment of the automatic transmission apparatus of the working vehicle of this invention. FIG. 3 is a characteristic diagram showing the relationship between the driving force and the vehicle speed of a work vehicle including a traveling HST circuit and a multi-stage transmission that is an embodiment of the automatic transmission for a work vehicle of the present invention. It is a characteristic view which shows the control concept of the downshift control part of the controller which comprises one Embodiment of the automatic transmission apparatus of the working vehicle of this invention. It is a characteristic figure explaining the control concept of the motor capacity increase control part of the comparative example compared with the present invention. It is a flowchart figure which shows the flow of the downshift control at the time of excavation of the controller which comprises one Embodiment of the automatic transmission apparatus of the working vehicle of this invention. It is a flowchart figure which shows the flow of excavation state determination of the controller which comprises one Embodiment of the automatic transmission of the working vehicle of this invention. It is a flowchart figure which shows the flow of the motor capacity increase control of the controller which comprises one Embodiment of the automatic transmission apparatus of the working vehicle of this invention. It is a characteristic view which shows an example of operation | movement in one Embodiment of the automatic transmission of the working vehicle of this invention. It is a characteristic view which shows the other example of operation | movement in one Embodiment of the automatic transmission of the working vehicle of this invention.

  Embodiments of an automatic transmission for a work vehicle according to the present invention will be described below with reference to the drawings.

  An embodiment of an automatic transmission for a work vehicle according to the present invention will be described with reference to FIGS. FIG. 1 is a left side view showing a wheel loader to which an embodiment of an automatic transmission device for a work vehicle according to the present invention is applied. FIG. 2 is an embodiment of an automatic transmission device for a work vehicle according to the present invention. FIG. 3 is a schematic view showing a power transmission system of a wheel loader, FIG. 3 is a side view showing a working machine of a wheel loader to which an embodiment of an automatic transmission for a work vehicle of the present invention is applied, and FIG. 4 is a work vehicle of the present invention. FIG. 5 is a hydraulic circuit diagram showing a power transmission device including a traveling HST circuit and a multi-stage transmission, which is an embodiment of the automatic transmission of the present invention. FIG. 5 shows an embodiment of the automatic transmission of a work vehicle according to the present invention. FIG. 6 is a characteristic diagram showing the control concept of the motor capacity control unit of the controller that constitutes, FIG. 6 is a diagram of a working vehicle equipped with a traveling HST circuit and a multi-stage transmission, which is an embodiment of an automatic transmission device for a working vehicle of the present invention Driving FIG. 7 is a characteristic diagram showing the relationship between force and vehicle speed, FIG. 7 is a characteristic diagram showing the control concept of the downshift control unit of the controller constituting one embodiment of the automatic transmission for a working vehicle of the present invention, and FIG. It is a characteristic figure explaining the control concept of the motor capacity increase control part of the comparative example to compare.

  In FIG. 1, the wheel loader 1 includes a cab 2, a work machine 3 used for excavation work and the like, and front wheels 4 and rear wheels 5.

  The wheel loader 1 includes a power transmission system shown in FIG. The power output from the engine 6 is transmitted to the transmission 7 by the traveling HST circuit 20 including the main pump 21 and the traveling motor 22, and further transmitted from the transmission 7 to the drive shaft 8. The drive shaft 8 drives the front axle 9 and the rear axle 10, and the front axle 9 transmits power to the front wheels 4, and the rear axle 10 transmits power to the rear wheels 5.

  As shown in FIG. 3, the work machine 3 includes a lift arm 11 that is coupled to the front portion of the wheel loader 1 so as to be pivotable in the vertical direction, and a bucket 12 that is pivotally coupled to a tip portion of the lift arm 11. It has. The lift arm 11 is driven by a lift arm cylinder 13 that is a hydraulic cylinder. The bucket 13 is driven by transmitting the operation of the bucket cylinder 14, which is a hydraulic cylinder, via the bell crank 15.

Next, a power transmission device including a traveling HST circuit and a multi-stage transmission, which is an embodiment of an automatic transmission for a work vehicle according to the present invention, will be described with reference to FIG.
As shown in FIG. 4, in the present embodiment, the power transmission device includes a traveling HST circuit 20 and a traveling HST circuit 20 interposed between the traveling HST circuit 20 and the front wheels 4 and the rear wheels 5. A transmission 7 that shifts and outputs the rotational power output from the traveling motor 22, a controller 80 that controls the traveling HST circuit 20 and the transmission 7, and a forward / reverse travel that instructs the controller 80 on the traveling direction of the wheel loader 1. A switching device 62 and a lift arm operation lever 61 for operating the lift arm 11 up and down are provided.

Power from the engine 6 is transmitted to the transmission 7 via the traveling HST circuit 20. In the traveling HST circuit 20, a main pump 21 and a traveling motor 22 are connected in a closed circuit via a pair of main hydraulic lines 30A and 30B. The output shaft of the traveling motor 22 is connected to the transmission input shaft 40 of the transmission 7. The power transmitted to the transmission 7 is output from the transmission output shaft 41. The main hydraulic lines 30A and 30B are provided with pressure sensors 31A and 31B capable of detecting the respective line pressures. Pipe pressure signals P _A and P _B of the main hydraulic lines 30A and 30B detected by the pressure sensors 31A and 31B are input to the controller 80, respectively.

  The main pump 21 is a variable displacement hydraulic pump that can reverse the suction port and the discharge port. The main pump 21 is a pump regulator 23 that switches the circulation direction of the hydraulic oil in the main hydraulic lines 30A and 30B in accordance with a switching command for the forward position Fp and the reverse position Rp of the forward / reverse switching device 62 provided in the cab 2. It has. When the wheel loader 1 travels forward, the main pump 21 draws hydraulic oil from the main hydraulic line 30B and discharges pressure oil to the main hydraulic line 30A. Conversely, when the wheel loader 1 travels backward, the main pump 21 draws hydraulic oil from the main hydraulic line 30A and discharges pressure oil to the main hydraulic line 30B.

  The traveling motor 22 includes a motor regulator 24 that makes the motor capacity variable. The motor regulator 24 changes the capacity Q of the travel motor 22 in proportion to the drive power W from the controller 80.

The transmission 7 includes two power transmission systems, a high-speed transmission system 42 and a low-speed transmission system 43. The high-speed transmission system 42 is a power transmission system with a reduction ratio R _{Hi that} includes a high-speed clutch 44, a high-speed drive gear 45, and a high-speed driven gear 46. The low speed transmission system 43 is a power transmission system having a reduction ratio R _{Lo including} a low speed clutch 47, a low speed drive gear 48, and a low speed driven gear 49. Here, these reduction ratios have a relationship of R _Lo > R _Hi .

  The two power transmission systems are selected by connecting one clutch and disconnecting the other clutch. When power transmission is performed by the high-speed transmission system 42, the transmission output shaft 41 outputs high rotation / small torque rotation, and when power transmission is performed by the low-speed transmission system 43, the transmission output shaft 41 outputs low rotation / large torque rotation. To do. In the work vehicle, the former state has high speed and small driving force, and the latter state has low speed and large driving force.

The connection / disconnection control of the high-speed clutch 44 and the low-speed clutch 47 is hydraulic. The clutch is connected by applying a clutch pressure, and the clutch is disconnected by not applying the clutch pressure. The clutch pressure P _Hi of the high speed clutch 44 and the clutch pressure P _Lo of the low speed clutch 47 are controlled by the high speed clutch control valve 50 and the low speed clutch control valve 51, respectively. These clutch control valves 50 and 51 are proportional solenoid valve systems, and output clutch pressures P _Hi and P _Lo proportional to drive powers W _Hi and W _Lo supplied from the controller 80 to the solenoids 52. The clutch pressure primary pressure supplied to the primary side of the clutch control valves 50, 51 is supplied from the charge pump 25 that is attached to the main pump 21 and driven by the engine 6.

  Expansion and contraction of the piston rod of the lift arm cylinder 13 that drives the lift arm 11 is performed by operating a lift arm operation lever 61 provided in the cab 2. Specifically, the operating portion of the lift arm control valve 63 that controls the direction and flow rate of the pressure oil flowing into the port 16A of the bottom side chamber 13A of the lift arm cylinder 13 and the port 16B of the rod side chamber 13B is a lift arm operating lever 61. Because it is directly connected to. The primary pressure of the work implement supplied to the lift arm control valve 63 is supplied from the work implement pump 26 that is provided in the main pump 21 and driven by the engine 6.

The lift arm operation lever 61 includes a lift arm operation amount detection device 65 capable of detecting the lever operation amount. In addition, a pressure sensor 64 is provided in the pipe connected to the bottom side port 16 </ b> A that detects the pressure in the bottom side chamber 13 </ b> A of the lift arm cylinder 13. On the piston rod side of the lift arm cylinder 16, a lift arm cylinder maximum stroke position detection sensor 66 that can detect that the piston rod is at the maximum stroke position is provided. Lever operation amount signal the lift arm operation amount detecting device 65 detects the signal P _C of the bottom side port pressure the bottom side port pressure sensor 64 has _detected, and the maximum stroke of the lift arm cylinder maximum stroke position detecting sensor 66 detects Each signal S is input to the controller 80.

  The controller 80 is a device that includes an arithmetic processing unit constituted by a CPU, a RAM, a ROM, and the like and operates according to a computer program, and electronically controls the motor regulator 24, the high-speed clutch control valve 50, the low-speed clutch control valve 51, and the like. The arithmetic processing unit includes a motor capacity control unit 81, a shift down control unit 82, an excavation determination unit 83, and a motor capacity increase control unit 84, which will be described in detail later.

The controller 80 detects the pressure values P _A and P _{B of} the main hydraulic lines 30A and 30B detected by the pressure sensors 31A and 31B and the pressure in the bottom side chamber 13A of the lift arm cylinder 13 detected by the pressure sensor 64. enter a value P _C, the driving power W to the motor regulator 24, the driving power to the solenoid 52 of the high-speed clutch control valve 50 and the low-speed clutch control valve 51 W _Hi, W _Lo to be to supply output respectively, the motor The capacity Q and the clutch pressures P _Hi and P _Lo are controlled.

  In addition, the controller 80 inputs switching commands for the forward position Fp, the neutral position Np, and the reverse position Rp detected by the forward / reverse switching device 62. Further, an operation amount of the lift arm operation lever 61 detected by the lift arm operation amount detection device 65 and a signal indicating whether or not the lift arm cylinder 13 detected by the lift arm cylinder maximum stroke position detection sensor 66 is at the maximum stroke position are also provided. You are typing.

Motor displacement controller 81 of the controller 80, the pressure sensor 31A, read from 31B pressure value _P A, of _{P B,} the discharge-side pipe line pressure of the main pump 21 (hereinafter, referred to as HST driving pressure _{P D)} in accordance with the Perform motor capacity control. Since the discharge direction of the main pump 21 is switched by the forward-reverse switching device 62, the pressure P _A of the forward-reverse switching device 62 is a main hydraulic line 30A is the case of the forward command (Fp) is, in the case of backward command (Rp) is the pressure _{P B} of the main hydraulic line 30B is read into the controller 80 as HST driving pressure _{P D.} Also, read opposite the main pump suction side pipe of the pressure P _R is the same time HST driving pressure P _D.

In the present embodiment, as shown in FIG. 5, there is the motor displacement control to match the HST driving pressure P _D target pressure is set to P _T, the so-called constant pressure control is performed. Specifically, when the HST driving pressure P _D is larger than the set target pressure P _T, the driving power W to increase the motor capacity Q is supplied from the controller 80 to the motor regulator 24. Thus, the motor capacity is changed, it operates to HST driving pressure P _D is equal to the adjusted target pressure P _T. Further, since the motor capacity Q and the drive power W are in a proportional relationship, the controller 80 can calculate the motor capacity Q from the output drive power W. The change speed of the motor capacity Q is determined in advance by the lamp control parameters of the difference deviation between the PID control of the set change speed or HST driving pressure P _D and the target pressure P _T in the function or the like or the like.

  By the way, the work vehicle including the row HST circuit and the multi-stage transmission in the present embodiment has a driving force-vehicle speed characteristic as shown in FIG. In FIG. 6, the solid line indicates the traveling HST circuit shift characteristic at the time of transmission high-speed transmission, and the broken line indicates the traveling HST circuit shift characteristic at the time of transmission low-speed transmission.

  According to the traveling HST circuit, continuously variable transmission is possible by changing the motor capacity Q. Specifically, by setting the motor capacity of the traveling motor 22 to a small capacity, a state of high speed and small driving force is obtained, and by setting the motor capacity of the traveling motor 22 to a large capacity, a state of low speed and large driving force is obtained. become. As shown by a solid line and a broken line in FIG. 6, a shift in a wide region is possible by combining a multi-stage transmission and a variable displacement travel motor 22.

The downshift control unit 82 of the controller 80 controls the transmission 7 by controlling the drive powers W _Hi and W _Lo supplied to the solenoids 52 of the high speed clutch control valve 50 and the low speed clutch control valve 51, respectively. Shift down control will be described with reference to FIGS. 4 and 7. In FIG. 7, the horizontal axis indicates time, and the vertical axes (a) to (c) indicate the motor capacity Q, the clutch pressure P _CL , and the gear ratio R in order from the top. Time T _SD is the shift down control start time, and time T _LO is the shift down control completion time. Note that the solid line _PCL-Hi in (b) indicates the clutch pressure on the high speed clutch side, and the broken line _PCL-LO indicates the clutch pressure on the low speed clutch side. In (c), the solid line R _Total indicates the total gear ratio, the broken line R _HST indicates the travel motor speed ratio, and the dotted line R _TM indicates the transmission speed ratio.

When the high-speed transmission system 42 is selected, the controller 80 supplies the driving power W _Hi to the solenoid 52 of the high-speed clutch control valve 50 and puts the clutch pressure on the high-speed clutch 44 side (P _CL-Hi ). On the other hand, the controller 80 does not supply the drive power W _Lo to the solenoid 52 of the low speed clutch control valve 51 and does not apply the clutch pressure to the low speed clutch 47 side (P _CL-LO ). As a result, the high speed clutch 44 is connected and the low speed clutch 47 is disconnected.

Prior to time T _{SD in} FIG. 7, the high-speed transmission system 42 is selected, and the motor capacity Q gradually increases toward a preset shift-down start setting capacity Q _SD . An increase in the motor capacity Q indicates that the traveling motor 22 is required to have a low speed and a large driving force.

In the shift-down control start time T _SD, the motor capacity Q reaches the downshift start setting capacity Q _SD, the controller 80 starts the shift-down control.

In the shift-down control, between the down-shifting control start time T _SD shift down control completion time T _LO, transmission gear ratio by switching from the high-speed transmission system 42 to the low-speed transmission system 43 of the power transmission system of the transmission 7 R _TM As shown in (C) of FIG. 7, the motor capacity Q is controlled to decrease as shown in (a) of FIG. As a result, the travel motor speed ratio R _HST is changed to the opposite side of the increase in the transmission speed ratio R _TM , so that the total speed ratio R _Total , which is the product of the transmission speed ratio R _TM and the travel motor speed ratio R _HST , is smoothed. Can be changed.

The controller 80 changes the motor capacity Q, the high-speed clutch pressure (P _CL-Hi ), and the low-speed clutch pressure (P _CL-LO ) by changing the drive power W, W _Hi , W _Lo associated with the shift control. Shift down control is performed. First, as shown in FIG. 7B, the high _- speed clutch 44 shown in FIG. 4 is disconnected by reducing the high-speed clutch pressure (P _CL-Hi ).

At this time, the rotational speed of the transmission input shaft 40 that is the input side of the low-speed clutch 47 is R _Lo / R _Hi times (R _Lo / R _Hi > 1) the rotational speed of the low-speed drive gear 48 that is the output side. Yes. Therefore, the rotational speed of the transmission input shaft 40 is increased by reducing the travel motor speed ratio R _HST by the reciprocal of the speed ratio R _Lo / R _Hi of the low speed transmission system 43 and the high speed transmission system 42. As a result, the rotational speed difference from the rotational speed of the low-speed drive gear 48 is absorbed, and in this state, the low-speed clutch pressure (P _CL-LO ) is increased and the low-speed clutch 47 is connected. As a result, an automatic downshift operation with little shift shock is realized.

The maximum motor capacity Qmax and the minimum motor capacity Qmin are set so that Qmax / Qmin ≧ R _Lo / R _Hi so that the travel motor speed ratio R _HST can be changed by the reciprocal of the transmission speed ratio R _TM . The shift down start set capacity Q _SD is set so that Q _SD / Qmin ≧ R _Lo / R _Hi, and a necessary motor capacity change ratio (= R _Lo / R _Hi ) is secured. As a result, it is possible to absorb a shift shock during downshifting. When the downshift control is completed, the low speed transmission system 43 is selected, and the driving force F of the work vehicle increases.

The excavation determination unit 83 of the controller 80 includes a lever operation amount signal detected by the lift arm operation amount detection device 65, a pressure signal P _C in the bottom side chamber 13A of the lift arm cylinder 13 detected by the pressure sensor 64, and the lift arm. The excavation state of the wheel loader 1 is determined based on the maximum stroke signal S detected by the cylinder maximum stroke position detection sensor 66. Specifically, it is determined that the following conditions are satisfied that excavation starts or is excavating.
(1) The piston rod of the lift arm cylinder 13 detected by the lift arm cylinder maximum stroke position detection sensor 66 is not at the maximum stroke position.
(2) that the pressure signal P _C of the detected bottom chamber 13A of the pressure sensor 64, is calculated drilled initiated determination pressure P _EX more.

The signal P _C of the pressure of the bottom side chamber 13A of the lift arm cylinder 13, since it increases with the lever operation amount of the lift arm cylinder 13, the drilling start determination pressure P _EX is the lift arm operation amount detecting device 65 indicates the lever operation amount signal α (for example, the lever angle) and when the lift arm is not operated (for example, when the lift arm control valve 63 is in the neutral position and the primary pressure of the work implement supplied from the work implement pump 26). Is calculated by the following equation (1) using the signal P _EX0 of the pressure in the bottom side chamber 13A (when is closed).
P _EX = P _EX0 + kα (1)
Here, k represents a proportionality constant.

Signal P _C of the pressure in the bottom chamber 13A has been detected by the pressure sensor 64, that is calculated drilled initiated determination pressure P _EX above, the reaction force from the drilling material in the lift arm cylinder 13 is operated It shows that. Therefore, in this case, it can be determined that excavation has started (during excavation). The excavation determination value of the wheel loader 1 determined by the excavation determination unit 83 is used in an excavation shift down control calculation described later.

Next, the necessity of the motor capacity increase control will be described with reference to FIG. 4 and FIG. In FIG. 8, the horizontal axis indicates time, and the vertical axes (a) and (b) indicate the driving pressure P _D and the motor capacity Q in order from the top. Time T _EX is the time when the wheel loader 1 enters the excavated material (such as gravel mountain), and time T ₁ indicates the time when the excavation start motor capacity Q starts increasing capacity. Time _TSD indicates the shift down control start time.

First, the wheel loader 1 enters an excavated object (such as a gravel mountain) when the transmission high-speed transmission system 42 is selected (time T _EX ). Thus, the wheel loader 1 are also subject to the reaction force from the drilling thereof, HST driving pressure P _D is increased. Then, the motor capacity Q have begun to increase when the HST driving pressure P _D exceeds the target pressure P _T.

Thus, in the case of only normal motor capacity control, the time T _EX when the wheel loader 1 enters the excavated material (such as a gravel mountain) and the time T ₁ when the excavation start motor capacity Q starts increasing the capacity. There is a time difference that cannot be ignored. This reaction force from the drilling material is caused by a response delay up to appear as HST driving pressure P _D at the traveling HST circuit 20.

Also, in the case of normal motor displacement control only, HST motor capacity increase rate of the by detecting the driving pressure P _D, the setting values of the setting pressure constant control by the matching such as the operation feeling during the vehicle normal driving From the time T _EX when the wheel loader 1 enters the excavated material (such as gravel mountain), the motor capacity Q reaches a shift down start time T _{SD at} which the motor capacity Q reaches the shift down start set capacity Q _SD . Time is needed.

In such a motor capacity increasing operation, the driving force F increases too slowly with respect to a sudden load increase during excavation, so that work efficiency is deteriorated. Further, when the downshift operation of the transmission 7 is performed before the motor capacity Q reaches the downshift start setting capacity Q _SD, can not absorb the rotational speed difference of the clutch, a large shift shock occurs, discomfort to the operator Will be given. Therefore, the detection of the drilling operation is started, it is necessary to increase control until downshift start setting capacity Q _SD of rapid motor capacity Q.

Therefore, the motor capacity increase control unit 84 of the controller 80 detects the pressure signal P _C in the bottom chamber 13A of the lift arm cylinder 13 detected by the pressure sensor 64 and the pressure values P _A and P read from the pressure sensors 31A and 31B. based on the HST driving pressure P _D is a discharge-side pipe line pressure of the main pump 21 of the _B, and calculates the motor capacity increase amount dQ, performed promptly motor capacity increase control for increasing the motor capacity Q.

Specifically, first, the bottom chamber preset bottom chamber pressure maximum value signal P _Cmax (time controller start signal P _C of the pressure in 13A of the lift arm cylinder 13 the pressure sensor 64 has detected at the start excavation compares the pressure signal P _EX0) of the bottom-side chamber 13A during the lift arm inoperative, the pressure in the bottom chamber 13A signal P _C is preset in the bottom side chamber pressure maximum value signal P _Cmax exceeded If selects the signal P _C of the pressure in the bottom-side chamber 13A, otherwise, selects a preset bottom chamber pressure maximum value signal P _Cmax.

Next, based on the selected signal (which is defined as _PCmax ), the first motor capacity increase amount dQ1 is calculated by the following equation (2). The first motor capacity increase amount dQ1 is a capacity increase amount in the motor capacity control interval dt of the controller 80. When the increase amount is a constant value, the motor capacity Q changes in capacity at a constant speed.
dQ1 = K × P _Cmax (2)
Here, K represents a proportionality constant.

Further, when the motor capacity increase amount during normal running is dQ0, the motor capacity Q is increased faster than during normal running by setting so that the following equation (3) is satisfied.
dQ1 = K × P _Cmax ≧ K × P _EX0 ≧ dQ0 (3)
However, at this time, if the value of the first motor capacity increase amount dQ1 is too large, the wheel loader 1 decelerates rapidly regardless of the excavation load. For this reason, it is necessary to appropriately set the proportionality constant K so that the vehicle body deceleration due to the excavation load and the vehicle body deceleration due to the increase in motor capacity are approximately the same by performing vehicle body matching or the like.

Then, by comparing the HST driving pressure P _D is a discharge-side pipe line pressure of the main pump 21, and increase start setting pressure P _SD which is set in advance, it increases start setting the HST driving pressure P _D is set in advance If it is less than pressure P _SD selects the first motor capacity increase amount dQ1 above as the motor capacity increase amount dQ. In other cases, a value obtained by adding a second motor capacity increase amount dQ2, which is a predetermined constant value, to the first motor capacity increase amount dQ1 is selected as the motor capacity increase amount dQ.

Here, the increase start set pressure _PSD is set to the value of the target pressure _PT of the motor capacity control unit 81, for example. Further, a product of the target pressure _PT and a constant coefficient (for example, P _SD = P _T × 0.9) or a subtraction value of the constant pressure from the target pressure _PT (for example, P _SD = P _T −0). .5 MPa) may be used.

  The case where the motor capacity increase amount dQ = dQ1 + dQ2 is selected is a case where it is determined that a large load that reaches the traveling load of the wheel loader 1 is necessary. In this case, the motor capacity increase speed is further increased. ing.

  After the motor capacity increase amount dQ is calculated as described above, the controller 80 drives the motor regulator 24 so that the motor capacity becomes a value Q + dQ obtained by adding the motor capacity increase amount dQ to the current motor capacity Q. W is controlled.

  Next, the excavation downshift control calculation procedure of the controller 80 will be described with reference to FIGS. FIG. 9 is a flowchart showing a flow of downshift control during excavation of a controller constituting one embodiment of an automatic transmission for a work vehicle according to the present invention, and FIG. 10 shows an embodiment of the automatic transmission for a work vehicle according to the present invention. FIG. 11 is a flowchart showing a flow of motor capacity increase control of a controller constituting an embodiment of an automatic transmission device for a work vehicle according to the present invention. . 9 to 11, the same reference numerals as those shown in FIGS. 1 to 8 are the same parts, and thus detailed description thereof is omitted.

In FIG. 9, the controller 80 reads which power transmission system selection is selected from among a plurality of stages of power transmission systems of the transmission 7 (step S1). Specifically, the output signals of the drive powers W _Hi and W _Lo are read.

The controller 80 determines whether or not the current transmission power transmission system is the high-speed transmission system 42 selection (step S2). Specifically, when the driving power W _Hi is supplied to the solenoid 52 of the high speed clutch control valve 50 and the driving power W _Lo is not supplied to the solenoid 52 of the low speed clutch control valve 51, the high speed transmission system 42 is selected. Is determined. If the high-speed transmission system 42 is selected, the process proceeds to (Step S3), and otherwise (including the state during switching of the power transmission system), the process proceeds to (Step S12).

  The controller 80 reads the excavation determination value, which will be described later, and the bottom port pressure Pc of the lift arm cylinder 13 (step S3). Here, the pressure Pc in the bottom side chamber 13A of the lift arm cylinder 13 is read because the excavation reaction force received by the bucket 12 acts on the lift arm cylinder 13 when the wheel loader 1 enters the excavation. This is to determine later whether it is in the excavation state or the other state.

  The controller 80 determines whether or not the excavation determination value is during excavation (step S4). If it is during excavation, it will progress to (step S5), otherwise it will progress to (step S9).

  The controller 80 reads the motor capacity Q (step S5). Specifically, the motor capacity Q is calculated from the output drive power W.

Controller 80, the motor capacity Q read in (step S5) is either downshift start setting capacity _{Q SD} above, determines whether (step S6). If the motor capacity Q is, downshift start setting capacity _{Q SD} above, it proceeds to (step S7) the process proceeds to, otherwise (step S11). The shift-down start setting capacity _QSD is set as described above.

  The controller 80 performs downshift control for reducing the shift shock by the cooperation of the transmission 7 and the traveling motor 22 described above (step S7). Specifically, the shift down control unit 82 described above controls. Upon completion of the downshift control, the low speed transmission system 43 is selected.

The controller 80 sets the excavation determination value in the excavation determination unit 83 to normal, and sets the maximum bottom side pressure _PCmax in the motor capacity increase control unit 84 as the excavation start determination pressure P _EXO when the lift arm is not operated ( Step S8). After completion of (Step S8), the calculation of the controller 80 returns to (Step S1) and starts the next calculation cycle.

  In (step S4), when the excavation determination value is not excavation, the controller performs an excavation start determination calculation described later (step S9). Specifically, the excavation determination unit 83 described above determines.

  The controller 80 determines whether or not the excavation determination value is during excavation (step S10). If it is during excavation, it will progress to (step S5), otherwise it will progress to (step S12).

In (step S6), and the motor capacity Q read in (step S5) is, if not downshift start setting capacity _{Q SD} above, the controller 80 makes the motor capacity increase control described later (step S11). Specifically, the motor capacity increase control unit 84 described above controls to increase the motor capacity Q.

(Step S11) After execution or in (Step S2), if the current transmission power transmission system is not the high-speed transmission system 42 selection, or if the excavation determination value is not excavation in (Step S10), the controller 80 The current transmission transmission system selection state read in (Step S1) is held (Step S12). After the end of (Step S12), the operation of the controller 80 returns to (Step S1) and starts the next operation cycle. In addition, the value used in the calculation is used in the next cycle as the excavation determination value in the excavation determination unit 83 and the value of the bottom side pressure maximum value _{PCmax in} the motor capacity increase control unit 84.

Next, a calculation procedure for excavation state determination in the above-described excavation shift down control calculation procedure will be described with reference to FIG. The following calculation procedure is executed by the excavation determination unit 83 described above.
The controller 80 reads the position information of the piston rod of the lift arm cylinder 13 from the lift arm cylinder maximum stroke position detection sensor 66 (step S21).

  The controller 80 determines whether or not the piston rod of the lift arm cylinder 13 has the maximum stroke (step S22). Specifically, if the maximum stroke signal S detected by the lift arm cylinder maximum stroke position detection sensor 66 is 1, the maximum stroke is determined. If it is the maximum stroke, the process proceeds to (Step S27), and otherwise, the process proceeds to (Step S23).

  The controller 80 reads the lever operation amount from the lift arm operation amount detection device 65 (step S23).

The controller 80 calculates the excavation start determination pressure P _EX based on the lever operation amount read in (Step S23) (Step S24). Specifically, the signal α (for example, lever angle) of the lever operation amount detected by the lift arm operation amount detection device 65 and when the lift arm is not operated (for example, when the lift arm control valve 63 is in the neutral position, It is calculated using the signal P _EX0 of the bottom port pressure (when the primary pressure of the work _implement supplied from the pump 26 is cut off).

The controller 80 determines whether or not the pressure Pc in the bottom side chamber 13A of the lift arm cylinder 13 read in (step S3) in the downshift control calculation procedure during excavation is _equal to or greater than the excavation start determination pressure PEX ( Step S25). The pressure Pc in the bottom chamber 13A is equal to or excavation start determination pressure _{P EX} above, the process proceeds to the process proceeds to (step S26), otherwise (step S27).

  The controller 80 sets the excavation determination value as being excavated (step S26). (Step S26) After the end, the excavation state determination calculation of the controller 80 ends, and the process proceeds to (Step S10) of the excavation downshift control calculation procedure.

In (step S22), if the piston rod of the lift arm cylinder 13 has the maximum stroke, or in (step S25), the pressure Pc in the bottom side chamber 13A is less than the excavation start determination pressure _PEX , the controller 80 sets the excavation determination value to normal (step S27). (Step S27) After the completion, the excavation state determination calculation of the controller 80 ends, and the process proceeds to (Step S10) of the excavation downshift control calculation procedure.

Next, a calculation procedure of motor capacity increase control in the above-described excavation shift down control calculation procedure will be described with reference to FIG. The following calculation procedure is executed by the motor capacity increase control unit 84 described above.
The controller 80 determines that the pressure Pc in the bottom side chamber 13A of the lift arm cylinder 13 read in (step S3) of the downshift control calculation procedure during excavation is a preset bottom side indoor pressure maximum value signal _PCmax (controller start-up). When the lift arm is not operated, it is determined whether or not the pressure signal P _EX0 ) in the bottom side chamber 13A is exceeded (step S31). If the pressure Pc in the bottom side chamber 13A exceeds the bottom side indoor pressure maximum signal _PCmax , the process proceeds to (Step S32), and otherwise the process proceeds to (Step S33).

The controller 80 sets the value of the preset bottom side indoor pressure maximum value signal _{PCmax to} the value of the pressure Pc in the bottom side chamber 13A of the lift arm cylinder 13 read in (Step S3) (Step S32). The value of the bottom-side chamber pressure maximum value signal P _Cmax at controller startup as described above, is set to a value of the signal P _EX0 pressure bottom-side chamber 13A during the lift arm inoperative.

After the execution of (Step S32) or in (Step S31), if the pressure Pc in the bottom side chamber 13A of the lift arm cylinder 13 does not exceed the preset bottom side chamber pressure maximum value signal _PCmax , the controller 80 Then, the first motor capacity increase amount dQ1 is calculated (step S33).

The controller 80 reads the driving pressure _{P D} of the traveling HST circuit 20 (step S34). Specifically, the pressure sensor 31A, read from 31B pressure value _P A, of _{P B,} reads the HST driving pressure _{P D} is a discharge-side pipe line pressure of the main pump 21.

The controller 80, the driving pressure _{P D} of (step S34) in the loaded travel HST circuit 20 is either increased start setting pressure _{P SD} above, determines whether (step S35). Drive pressure _{P D} of the traveling HST circuit 20, if the increase start setting pressure _{P SD} above, the process proceeds to the process proceeds to (step S36), otherwise (step S37).

  The controller 80 sets the motor capacity increase amount as dQ = dQ1 + dQ2 (step S36). Here, the second motor capacity increase amount dQ2 is a predetermined constant value.

(Step S35), the driving pressure _{P D} of the traveling HST circuit 20, if not increase start setting pressure _{P SD} above, the controller 80 sets the motor capacity increase amount dQ = dQ1 (step S37).

  The controller 80 sets the drive power W for driving the motor regulator 24 so that the motor capacity becomes a current capacity Q + dQ1 obtained by adding the motor capacity increase dQ set in (Step S36) or (Step S37) to the current motor capacity Q. Control. (Step S37) After the end, the motor capacity increase control calculation of the controller 80 ends, and the process proceeds to (Step 12) of the excavation shift down control calculation procedure.

  Next, the operation in one embodiment of the automatic transmission for a work vehicle according to the present invention will be described with reference to FIGS. FIG. 12 is a characteristic diagram showing an example of an operation in an embodiment of an automatic transmission device for a work vehicle according to the present invention. FIG. 13 is another example of an operation in an embodiment of an automatic transmission device for a work vehicle according to the present invention. FIG. 12 and 13, the same reference numerals as those shown in FIGS. 1 to 11 are the same parts, and the detailed description thereof will be omitted.

12 and 13, the horizontal axis indicates time, and the vertical axes (a) to (c) indicate the bottom pressure signal P _C , HST drive pressure P _D , and motor capacity of the lift arm cylinder 13 from the top. Q is shown. The time T _EX is the time when the wheel loader 1 enters the excavated material (such as gravel mountain), the time T ₁ is the time when the excavation start motor capacity Q starts increasing, and the time T ₂ is the bottom the time at which the signal _{P C} of the pressure in side chamber 13A has reached the bottom-side chamber pressure maximum value signal _{P Cmax,} the time _{T 3} is the time at which the HST driving pressure _{P D} is increased starting set pressure _{P SD} more thereof Yes. Further, the time _TSD indicates the shift down control start time. In FIG. 6C, the alternate long and short dash line characteristic line X indicates the increase characteristic of the motor capacity Q at the capacity increase speed during normal driving, and the alternate long and two short dashes line characteristic line Y indicates the capacity increase by the first motor capacity increase amount dQ1. The increase characteristics of the motor capacity Q in speed are shown respectively.

First, as shown in FIG. 12, when the wheel loader 1 enters the excavated material (such as a gravel mountain) at time T _EX , the excavation reaction force received by the bucket 12 acts on the lift arm cylinder 13 and the inside of the bottom side chamber 13A. pressure _{P C} is increased in a short time. At time T ₁ the pressure P _C in the bottom chamber 13A is therefore reaches the above excavation start determination pressure P _EX, the controller 80 determines that the wheel loader 1 has started the drilling. Thus, the controller 80 starts to increase also shown in (b) HST driving pressure P _D is a state does not reach the target pressure P _T, the capacity Q of the traveling motor 22.

Motor capacity increase rate, the bottom side port pressure _{P C} on the basis of the motor capacity increase amount dQ = dQ1 = K × _{P Cmax} continues to increase until the maximum, the bottom side port pressure maximum value signal time _{T 2,} after _{the P Cmax} is determined Becomes a constant value. The motor capacity Q at this time also has a larger increase speed than the capacity increase speed during normal running, but the wheel loader 1 is a value that maintains an appropriate deceleration that does not brake suddenly regardless of the excavation load. Is set.

Next, at time _{T SD,} motor capacity Q reaches the downshift start setting capacity _{Q SD.} At this time, a sufficient motor capacity change ratio (Q _SD / Qmin) that can absorb a shift shock at the time of downshifting can be ensured, so that the controller 80 performs cooperative control of the transmission 7 and the traveling motor 22. Start downshift control by.

As described above, in the present embodiment, since the excavation determination unit 83 and the motor capacity increase control unit 84 are provided, the downshift control is performed from the time T _EX when the wheel loader 1 enters the excavated material (such as a gravel mountain). it is possible to shorten the time required to start time T _SD. This can improve work efficiency.

  Next, the operation when a large traveling load is generated in the above-described process of changing the motor capacity during excavation will be described with reference to FIG.

13, operation up to time T _2, the bottom side port pressure maximum value signal P _Cmax is determined, a characteristic diagram showing an example of the operation in the embodiment of the automatic transmission for a working vehicle of the present invention in FIG. 12 It is the same. At time _{T 3,} as shown in (b), HST driving pressure _{P D} reaches the increase start setting pressure _{P SD} (FIG. _13, is set to _{P SD} = target pressure _{P T).}

  The controller 80 determines that a large load that covers the traveling load of the wheel loader 1 is necessary, and dQ = dQ1 + dQ2 that is a value obtained by adding the motor capacity increase amount dQ to the first motor capacity increase amount dQ1 and the second motor capacity increase amount dQ2. And set. As a result, the motor capacity increasing speed is further increased.

According to an embodiment of the automatic transmission for a working vehicle of the present invention described above, the lift arm pressure P _C and the traveling motor 22 in the bottom-side chamber 13A of the cylinder 13 in conjunction with the load of the wheel loader 1 is a work vehicle Since the downshifting operation of the transmission 7 is controlled in accordance with the change in the motor capacity Q, the automatic transmission device for a work vehicle that can automatically execute the downshifting operation of the transmission 7 during excavation with a small shift shock by a simple control method. Can be provided. As a result, the manual switching operation of the transmission 7 during excavation of the wheel loader 1 that is a work vehicle becomes unnecessary, and the work efficiency is improved.

In addition, according to the above-described embodiment of the automatic transmission device for a work vehicle of the present invention, a sufficient motor capacity change ratio (Q _SD / Qmin) for absorbing a shift shock generated during the downshift operation can be ensured. Therefore, occurrence of a shift shock can be avoided. This can reduce discomfort for the operator and improve the work environment.

Also, according to an embodiment of the automatic transmission for a working vehicle of the present invention described above, for performing the determination of the excavation state according to the pressure P _C in the bottom chamber 13A of the lift arm cylinder 13 by excavation reaction force, It is not necessary to newly add an angle sensor or the like, and cost increase can be suppressed. In addition, the excavation state determination is possible only by a simple control program without requiring a complicated program such as a control map for the excavation state determination. As a result, work efficiency can be improved without complicating the structure and increasing costs.

Further, according to the embodiment of the automatic transmission for a work vehicle of the present invention described above, when the operation of the lift arm cylinder 13 is detected, the value of the excavation start determination pressure P _EX is changed according to the operation amount. Therefore, it is possible to avoid the erroneous determination of the excavation start due to the operation of the lift arm cylinder 13. Further, since the maximum stroke position of the lift arm cylinder 13 is detected and taken into control, it is possible to avoid erroneous determination of excavation start due to shock pressure when the lift arm cylinder 13 reaches the maximum stroke. From these things, the reliability of control improves.

  According to the embodiment of the automatic transmission for a work vehicle of the present invention described above, the motor capacity increasing speed is set to be larger than the capacity increasing speed set by the constant pressure control during normal traveling. Therefore, the motor capacity Q can be changed at an appropriate deceleration without applying sudden braking that does not depend on the excavation load. As a result, it is possible to shorten the time until the start of the shift-down operation of the transmission 7 without deteriorating the operation feeling.

Also, according to an embodiment of the automatic transmission for a working vehicle of the present invention described above, the signal P _Cmax maximum value of the pressure P _C in the bottom chamber 13A of the motor capacity increase rate of drilling when the lift arm cylinder 13 Therefore, the motor capacity increase speed can be changed according to the load state of the work machine 3. As a result, the time until the start of the shift down operation of the transmission 7 can be shortened.

Also, when according to an embodiment of the automatic transmission for a working vehicle of the present invention described above, the HST driving pressure P _D of the traveling HST circuit 20 after the start drilling, became increased starting set pressure P _SD or By further increasing the motor capacity increasing speed, the motor capacity increasing speed is changed in accordance with the traveling load state of the wheel loader 1. As a result, the time required to start the shift-down operation of the transmission 7 can be further reduced.

  In the above-described embodiment, the motor regulator 24 is described as an example of the electronic control type by the controller 80, but a mechanical control type including a switching valve and a hydraulic pilot type valve may be used.

  In the above-described embodiment, the case where the constant pressure control is used for the capacity control of the traveling motor 22 is described as an example. However, this is not intended to limit the motor capacity control in the present invention to the constant pressure control. Absent.

Further, in the present embodiment described above, the main hydraulic two pressure sensors 31A to detect the HST driving pressure P _D, has been described as an example the case of using a 31B, in conjunction with the forward-reverse switching device 62 select HST driving pressure P _D by Kanro圧selection valve, which may be a method of reading a single pressure sensor.

  In the above-described embodiment, the case where the two-stage transmission 7 is used has been described as an example. However, this does not limit the automatic transmission according to the present invention to the two-stage transmission.

Further, in the present embodiment described above, the lift arm has been described as an example the case of performing digging determination based on the pressure P _C in the bottom-side chamber 13A of the cylinder 13, the pressure and the bucket cylinder 14 in the rod side chamber 13B A determination method using a pressure acting on the liquid crystal may be used.

  In the above-described embodiment, the lift arm control valve 63 is described as an example of the direct acting type from the lift arm operation lever 61. However, the lift arm control valve 63 may be a hydraulic pilot type and acts on the lift arm control valve 63. Alternatively, the pilot pressure may be used for detecting lift arm operation.

  Further, in the above-described embodiment, the wheel loader 1 is described as an example of a work vehicle, but this is not intended to limit the automatic transmission of the present invention to that provided in the wheel loader 1. The automatic transmission according to the present invention may be provided in a work vehicle including an HST circuit and a multi-stage transmission such as an agricultural vehicle.

1 Wheel loader (work vehicle)
2 cab 3 work implement 4 front wheel 5 rear wheel 6 engine 7 transmission 8 drive shaft 9 front axle 10 rear axle 11 lift arm 12 bucket 13 lift arm cylinder 13A bottom side chamber 14 bucket cylinder 15 bell crank 20 HST circuit 21 main pump 22 traveling Motor 23 Pump regulator 24 Motor regulator 31A Pressure sensor 31B Pressure sensor 61 Lift arm operation lever 62 Forward / reverse switching device 63 Lift arm control valve 64 Pressure sensor (in the bottom side chamber 13A)
65 Lift arm operation position detection device 66 Lift arm cylinder maximum stroke position detection sensor 80 Controller 81 Motor capacity control unit 82 Shift down control unit 83 Excavation determination unit 84 Motor capacity increase control unit

Claims (5)

An automatic transmission for a work vehicle having a bucket and a lift arm at the front,
A traveling HST circuit in which a traveling motor composed of a variable displacement hydraulic motor is connected to a main pump composed of a variable displacement hydraulic pump capable of reversing in a closed circuit via a pair of main hydraulic lines;
A motor regulator for controlling the motor capacity of the travel motor;
A transmission having a plurality of speed stages, which are interposed between the travel motor and the wheels and shift and output rotational power input from the travel motor;
A lift arm cylinder that drives the lift arm to control the position of the bucket, and the pressure in the bottom side chamber increases by the excavation reaction force of the bucket;
A pressure sensor for detecting the pressure in the bottom side chamber of the lift arm cylinder;
An excavation determination unit that reads the pressure in the bottom side chamber of the lift arm cylinder by the pressure sensor and determines that the excavation state by the bucket is when the pressure in the bottom side chamber is equal to or higher than a predetermined determination pressure;
A motor capacity increase control unit for outputting a command for increasing the capacity of the travel motor to the motor regulator at a higher speed than the command increase rate during normal travel of the work vehicle according to a command received from the excavation determination unit; ,
Shift down control for controlling the downshift from the high speed stage to the lowest speed stage of the transmission when the capacity of the travel motor exceeds a preset motor capacity in accordance with a command received from the excavation determination unit automatic transmission for a working vehicle, characterized in that example Bei and parts. The automatic transmission for a work vehicle according to claim 1,
An HST driving pressure sensor for detecting an HST driving pressure which is a pressure of the main hydraulic line;
The motor capacity increase control unit reads the HST driving pressure detected by the HST driving pressure sensor, and outputs the driving motor output to the motor regulator when the HST driving pressure is equal to or higher than a preset set pressure . An automatic transmission for a work vehicle, wherein an increase speed of a command for increasing a capacity is set to a higher speed. The automatic transmission for a work vehicle according to claim 1 or 2,
An operating lever for operating the lift arm;
An operation amount sensor for detecting an operation amount of the operation lever;
The excavation determination unit reads the operation amount of the operation lever detected by the operation amount sensor, and changes the determination pressure according to the operation amount of the operation lever. The automatic transmission device for a work vehicle according to any one of claims 1 to 3,
A stroke sensor for detecting the maximum stroke position of the piston rod of the lift arm cylinder;
The excavation determination unit does not perform excavation determination when the maximum stroke position of the piston rod of the lift arm cylinder detected by the stroke sensor is read. The automatic transmission for a work vehicle according to any one of claims 1 to 4,
The motor capacity increase control unit sets an increase speed of a command for increasing the capacity of the traveling motor to be output to the motor regulator based on the pressure in the bottom side chamber of the lift arm cylinder by the pressure sensor during excavation. An automatic transmission for a work vehicle.

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