JP2013256988A - Hydraulic control device for traveling of working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a vehicle speed at similar decelerations in both of a case where a command by a forward/backward change-over command device is changed from a forward position to a neutral position and the command is maintained and a case where a command by the forward/backward change-over command device is changed from a backward position to the neutral position and the command is maintained, and to suppress rapid deceleration of a vehicle speed.SOLUTION: A controller 100 includes: a means 102 for determining, in a predetermined cycle, whether a command by a forward/backward change-over lever device 90 (forward/backward change-over command device) designates a forward, backward or neutral position; a means 105 for comparing the latest determination result to the determination result previous by one cycle by the means 102; and a means 106 for controlling a two-position valve 73 via a change-over valve 85 based on the result of comparison by the means 105. When the latest command designates the neutral position while the command previous by one cycle designates the forward position, the controller maintains a valve position of the two-position valve 73 to a first valve position 74 that is the same position as that in the command previous by one cycle designating the forward position, and when the latest command designates the neutral position while the command previous by one cycle designates the backward position, the controller maintains a valve position of the two-position valve 73 to a second valve position 75 that is the same position as that in the command previous by one cycle designating the backward position.

Description

  The present invention relates to a traveling hydraulic control device for a work vehicle applied to a wheel loader, a rolling machine, an agricultural vehicle, and the like.

  2. Description of the Related Art Conventionally, a traveling hydraulic control device for a work vehicle has a pair of a swash plate type variable displacement hydraulic pump capable of reversing a suction port and a discharge port and a traveling motor composed of an oblique axis type variable displacement hydraulic motor. A traveling HST circuit connected to a closed circuit via a first conduit and a second conduit, and a forward / reverse switching lever device that commands forward, reverse, and neutral in a device that commands a travel direction. A forward / reverse switching command device), a pump control hydraulic circuit for controlling the discharge direction of the variable displacement hydraulic pump based on a command from the forward / reverse switching command device, and the pressure in the first pipe or the second pipe A motor control hydraulic circuit that controls the capacity of the traveling motor in accordance with the pressure in the road.

  The pump control hydraulic circuit controls the variable displacement hydraulic pump so that the hydraulic oil is sucked from the second pipe and discharged to the first pipe when forward movement is commanded by the forward / reverse switching command device. When the reverse movement is commanded by the forward / reverse switching command device, the variable displacement hydraulic pump is controlled so as to suck the hydraulic oil from the first pipe and discharge it to the second pipe, When the neutral is instructed, the discharge amount of the variable displacement hydraulic pump is controlled to 0, which is the minimum discharge amount. When the variable displacement hydraulic pump sucks hydraulic oil from the second pipe and discharges it to the first pipe, the travel motor rotates in a direction to advance the wheel loader. When the variable displacement hydraulic pump sucks hydraulic oil from the first pipe and discharges it to the second pipe, the travel motor rotates in the direction of moving the wheel loader backward.

  The motor control hydraulic circuit is a hydraulically driven motor servo piston that operates the oblique axis of the variable displacement hydraulic pump, and a hydraulic pilot type spring return that controls the flow of pressure oil supplied to the motor servo piston. A pilot pressure that gives one of the pressure in the first pipe line and the pressure in the second pipe line to the motor capacity control valve based on the command of the motor capacity control valve of the type and the forward / reverse switching command device And a 2-position valve (switching valve) to be selected.

  The valve position of the two-position valve is controlled to the first valve position when forward movement is commanded by the forward / reverse switching command device, whereby the pressure in the first pipe is selected as the pilot pressure of the motor capacity control valve Is done. When reverse movement is commanded by the forward / reverse switching command device, the valve position of the two-position valve is controlled to the second valve position, so that the pressure in the second pipe is used as the pilot pressure of the motor capacity control valve. Selected. Further, when neutral is commanded by the forward / reverse switching command device, the valve position of the two-position valve is controlled to the second valve position in the same way as when reverse is commanded. Is selected as the pilot pressure of the motor displacement control valve.

  When the pilot pressure of the motor capacity control valve (the pressure in the first pipe line or the pressure in the second pipe line) is lower than the starting pressure of the motor capacity control valve, the motor servo piston has a capacity of the travel motor. The minimum capacity is maintained. Also, the capacity of the traveling motor increases when the pilot pressure of the motor capacity control valve is higher than the starting pressure, and the capacity of the traveling motor decreases when the pilot pressure of the motor capacity control valve is lower than the starting pressure. Is equal to the starting pressure, the capacity of the traveling motor is constant.

  A hydraulic control device for traveling of this type of work vehicle is disclosed in Patent Document 1, for example.

JP 2010-38203 A

  In the traveling hydraulic control device described above, the two-position valve (switching valve) controls the motor capacity of the pressure in the first pipe line when the forward movement is commanded by the forward / reverse switching lever device (forward / backward switching command device). It is controlled to select as the pilot pressure of the valve, and is controlled to select the pressure in the second pipe line as the pilot pressure of the motor displacement control valve when reverse and neutral are commanded by the forward / reverse switching lever device. . For this reason, the vehicle speed is decelerated between when the command from the forward / reverse switching lever device is switched and maintained from forward to neutral, and when the command from the forward / backward switching lever device is switched and maintained from reverse to neutral. There is a risk that the operator will feel uncomfortable. This will be described in detail below with reference to FIGS.

  First, the relationship between the pilot pressure of the motor capacity control valve and the capacity of the travel motor will be described with reference to FIG.

  As shown in FIG. 7, when the pilot pressure Pm of the motor capacity control valve is lower than the starting pressure Pm1, the capacity C of the traveling motor becomes the minimum capacity Cmin. Further, the traveling motor capacity C increases when the pilot pressure Pm is higher than the starting pressure Pm1 (state where Pm> Pm1), and travels when the pilot pressure Pm is lower than the starting pressure Pm1 (state where Pm <Pm1). The capacity C of the motor decreases, and the capacity C of the traveling motor becomes constant in a state where the pilot pressure Pm is equal to the starting pressure Pm1 (Pm = Pm1 state).

  Next, FIG. 8 is used for the relationship between the content of the command by the forward / reverse switching command and the pipeline (first pipeline or second pipeline) selected as the hydraulic pressure source of the pilot pressure of the motor displacement control valve. I will explain.

  As shown in FIG. 8, when neutral is commanded by the forward / reverse switching lever device, the second pipe is selected as the hydraulic pressure source of the pilot pressure Pm of the motor displacement control valve, and the forward / backward switching lever device commands the forward movement. If the first pipe is selected as the hydraulic pressure source of the pilot pressure Pm and the reverse movement is commanded by the forward / reverse switching lever device, the second pipe is piloted in the same manner as when the neutral is commanded. It is selected as a hydraulic pressure source of the pressure Pm.

  Next, deceleration of the vehicle speed when the command from the forward / reverse switching lever device is switched from forward to neutral and maintained will be described with reference to FIG.

  As shown in FIG. 9 (a), in the state where the forward movement is commanded by the forward / reverse switching lever device, the two-position valve is used as a hydraulic pressure source for the pilot pressure Pm of the motor displacement control valve as shown in FIG. 9 (b). 1 pipeline is selected. Further, since the variable displacement hydraulic pump is controlled so as to suck in hydraulic fluid from the second pipe and discharge it to the first pipe, the inside of the first pipe as shown in FIG. The pressure Pa (solid line) is higher than the pressure Pb (broken line) in the second pipe line. And the capacity | capacitance C of a traveling motor is controlled according to the pressure Pa in the 1st pipe line. For example, when the pressure Pa in the first pipe line is maintained lower than the starting pressure Pm1 of the motor capacity control valve, the capacity C of the travel motor is the minimum capacity as shown in FIG. 9 (d). Cmin is maintained. As a result, the work vehicle moves forward at the vehicle speed V1 as shown in FIG.

  In a state where the work vehicle is moving forward at the speed V1, the command by the forward / reverse switching lever device is switched from forward to neutral as shown at time t1 in FIG. 9A, and thereafter the neutral command is maintained. In this case, the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump are decreased and finally controlled to zero. During this time, the rotation of the travel motor is not immediately decelerated as the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump decrease, but is maintained by inertia, so that the travel motor has a pump action. That is, while the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump are decreasing, the traveling motor continues to rotate so as to maintain the flow of hydraulic oil from the first pipe line to the second pipe line due to inertia. Thus, the hydraulic oil is sucked from the first pipe and discharged to the second pipe. For this reason, as shown in FIG.9 (c), the pressure Pa (solid line) in a 1st pipe line falls, and the pressure Pb (dashed line) in a 2nd pipe line rises. At this time, since the pressure Pb in the second pipe line becomes a brake pressure that brakes the rotation of the travel motor, the vehicle speed V decreases from V1 as shown in FIG. 9 (e).

  On the other hand, based on the fact that the command by the forward / reverse switching lever device is neutral, the two-position valve has a second pipe as a hydraulic pressure source of the pilot pressure Pm of the motor displacement control valve, as shown in FIG. The road is controlled to be selected. For this reason, the capacity | capacitance C of a traveling motor is controlled according to the brake pressure which arose in the 2nd pipe line. As shown in FIG. 9 (c), when the pressure Pb (brake pressure) in the second pipe becomes equal to or higher than the starting pressure Pm1 of the motor capacity control valve, the travel motor is shown in FIG. 9 (d). Capacity C increases to C1. This increase in the capacity C of the travel motor increases the braking force against the rotation of the travel motor.

  That is, when the command from the forward / reverse switching lever device is switched from forward to neutral and maintained, the vehicle speed is reduced by the braking force due to the braking pressure and the braking force due to the increase in the capacity C of the traveling motor. It is made by the action. As a result, for example, as shown in FIG. 9E, the work vehicle moving forward at the vehicle speed V1 stops after the deceleration time Tf from the start of deceleration.

  Next, the deceleration of the vehicle speed when the command from the forward / reverse switching lever device is switched and maintained from reverse to neutral will be described with reference to FIG.

  As shown in FIG. 10 (a), in the state in which reverse movement is commanded by the forward / reverse switching lever device, the two-position valve is used as a hydraulic pressure source for the pilot pressure Pm of the motor displacement control valve as shown in FIG. 10 (b). 2 pipelines are selected. In addition, since the variable displacement hydraulic pump is controlled so as to suck hydraulic oil from the first pipe and discharge it to the second pipe, the inside of the second pipe as shown in FIG. The pressure Pb (broken line) is higher than the pressure Pa (solid line) in the first pipeline. And the capacity | capacitance C of a traveling motor is controlled according to the pressure Pb in the 2nd pipe line. For example, when the pressure Pa in the first pipe line is maintained in a state lower than the starting pressure Pm1 of the motor capacity control valve, the capacity C of the travel motor is minimum as shown in FIG. 10 (d). The capacity is maintained at Cmin. As a result, the work vehicle moves backward at the vehicle speed V1 as shown in FIG.

  In this state where the work vehicle is moving backward at the speed V1, the command by the forward / reverse switching lever device is switched from reverse to neutral as shown at time t2 in FIG. 10A, and thereafter the neutral command Is maintained, the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump are decreased and finally controlled to zero. During this time, the traveling motor continues to rotate so as to maintain the flow of the hydraulic oil from the second pipe line to the first pipe line due to inertia, thereby sucking the hydraulic oil from the second pipe line and As shown in FIG. 10C, the pressure Pb (broken line) in the second pipe line decreases, and the pressure Pb (solid line) in the first pipe line increases. At this time, the pressure Pa in the first pipe line becomes a brake pressure that brakes the rotation of the traveling motor, so the vehicle speed V is decelerated from V1 as shown in FIG.

  On the other hand, based on the fact that the command by the forward / reverse switching lever device is neutral, the two-position valve continues to drive the second pipe line from the time when the command is reverse as shown in FIG. The state is controlled to be selected as a hydraulic pressure source of the pilot pressure Pm of the capacity control valve. For this reason, the capacity C of the travel motor is controlled according to the pressure Pb in the second pipe, not the pressure Pa in the first pipe that is the brake pressure. Since the pressure Pb in the second pipe line is lower than the starting pressure Pm1 of the motor capacity control valve, the capacity C of the travel motor continues from the time when the command by the forward / reverse switching lever device is reverse, and the minimum capacity Cmin Maintained.

  That is, when the command by the forward / reverse switching lever device is switched from reverse to neutral and maintained, the vehicle speed is reduced because the braking force due to the increase in the capacity C of the traveling motor does not act on the rotation of the traveling motor. This is done only by the braking force due to the brake pressure acting on the rotation of the motor. Thus, for example, as shown in FIG. 10 (e), the work vehicle moving backward at the vehicle speed V1 is stopped after the deceleration time Tr longer than the deceleration time Tf (see FIG. 9 (e)) from the start of deceleration. To do.

  In this way, when the command from the forward / reverse switching lever device is switched from forward to neutral and maintained, the braking force against the rotation of the traveling motor increases as the traveling motor capacity increases more than the braking force of only the brake pressure. Therefore, the deceleration of the vehicle speed when the command by the forward / reverse switching lever device is switched and maintained from forward to neutral is the same as when the command by the forward / backward switching lever device is switched and maintained from reverse to neutral. It becomes larger than the deceleration of the vehicle speed. Therefore, when the command by the forward / reverse switching lever device is switched and maintained from forward to neutral, the vehicle speed is reduced at the same deceleration as when the command by the forward / backward switching lever device is switched and maintained from reverse to neutral. If the operator is convinced, the vehicle speed will be decelerated with a rapid deceleration against the operator's will, which may cause discomfort to the operator.

  The present invention has been made in consideration of the above-described circumstances. The purpose of the present invention is to maintain a case where the command by the forward / reverse switching command device is maintained by switching from forward to neutral, and when the command by the forward / reverse switching command device is reverse. An object of the present invention is to provide a traveling hydraulic control device for a work vehicle that can reduce the vehicle speed at the same deceleration as when the vehicle is switched from the neutral position to the neutral position, and can suppress the rapid deceleration of the vehicle speed.

  In order to achieve the above-described object, the hydraulic control apparatus for traveling a work vehicle according to the present invention is configured as follows.

[1] In the traveling hydraulic control apparatus for a work vehicle according to the present invention, the variable displacement hydraulic pump capable of reversing the suction port and the discharge port and the traveling motor including the variable displacement hydraulic motor are a pair of first motors. A traveling HST circuit connected to a closed circuit via a pipeline and a second pipeline, and a device for commanding the traveling direction of the work vehicle, and a forward / reverse switching command device for commanding forward, reverse and neutral A pump control means for controlling the discharge direction of the variable displacement hydraulic pump based on a command from the forward / reverse switching command device; and a capacity of the travel motor to determine a pressure in the first pipe or the second pipe. Motor control means for controlling the pressure in accordance with the pressure in the passage, wherein the pump control means causes the variable displacement hydraulic pump to be connected to the second pipe line when forward movement is commanded by the forward / reverse switching command device. Before sucking hydraulic oil from Control is made to discharge to the first pipeline, and when the reverse movement is commanded by the forward / reverse switching command device, the variable displacement hydraulic pump sucks hydraulic oil from the first pipeline and The discharge amount of the variable displacement hydraulic pump is controlled to the minimum discharge amount when neutral is instructed by the forward / reverse switching command device, and the motor control means Includes a servo piston that operates a variable mechanism that changes the capacity of the variable displacement hydraulic motor, a hydraulic pilot motor capacity control valve that controls the flow of pressure oil supplied to the servo piston, A hydraulic control apparatus for traveling a work vehicle, comprising: a two-position valve that selects one of a pressure in one pipe line and a pressure in the second pipe line as a pilot pressure applied to the motor capacity control valve smell The motor control means is configured to switch the command by the forward / reverse switching command device from reverse to neutral when the vehicle speed is decelerated when the command by the forward / reverse switching command device is switched from forward to neutral. When the vehicle speed is reduced, the pressure in the pipe on the opposite side of the pipe in which the brake pressure is generated in the first pipe and the second pipe is selected as the pilot pressure. The valve position is provided with deceleration control means for controlling the valve position of the two-position valve.

  In the traveling hydraulic control apparatus according to the present invention described in “[1]”, the deceleration control means of the motor control means is configured to control the vehicle speed associated with the command from the forward / reverse switching command device being switched from forward to neutral. Brake pressure is generated in the first pipe line and the second pipe line during deceleration and when the vehicle speed is decelerated when the command from the forward / reverse switching command device is switched from reverse to neutral. The valve position of the two-position valve is controlled so that the pressure in the pipe line opposite to the pipe line is selected as the pilot pressure of the motor capacity control valve. As a result, when the vehicle speed decelerates when the command by the forward / reverse switching command device is switched from forward to neutral, and when the vehicle speed decelerates when the command by the forward / backward switch command device is switched from reverse to neutral In any of these cases, the motor capacity control valve is not operated by the brake pressure, so that the capacity of the travel motor does not increase, and the braking force against the rotation of the travel motor is only the braking force by the brake pressure. . Therefore, when the command from the forward / reverse switching command device is switched and maintained from forward to neutral, and when the command from the forward / backward switching command device is switched and maintained from reverse to neutral, the vehicle speed is reduced at the same deceleration. Can be decelerated, and sudden deceleration of the vehicle speed can be suppressed.

[2] The travel hydraulic control device for a work vehicle according to the present invention is the travel hydraulic control device according to [1], wherein the deceleration control means is configured such that the command by the forward / reverse switching command device is neutral from forward. The two-position valve position is maintained at the same valve position as when the command is forward, and the command by the forward / reverse switching command device is switched from reverse to neutral, The valve position of the two-position valve is maintained at the same valve position as when the command is reverse.

  The traveling hydraulic control device according to the present invention described in “[2]” includes the forward / reverse switching command device when the vehicle speed is reduced when the command from the forward / reverse switching command device is switched from forward to neutral. Of the first pipe and the second pipe in the pipe opposite to the pipe where the brake pressure is generated when the vehicle speed is reduced due to the switch from reverse to neutral. The pressure can be reliably selected as the pilot pressure of the motor capacity control valve.

[3] The travel hydraulic control device for a work vehicle according to the present invention is the travel hydraulic control device according to “[2]”, wherein the deceleration control means is configured such that the command by the forward / reverse switching command device is forward or reverse. A determination means for determining which is neutral in a predetermined cycle, and a comparison means for comparing the latest and the determination results of one cycle before by the determination means, and as a result of the comparison by the comparison means, When the result is that the latest command is neutral and the command one cycle before is forward, the valve position of the two-position valve is maintained at the same valve position as one cycle before the command was forward; As a result of the comparison by the comparison means, when the result that the latest command is neutral and the command one cycle before is reverse is obtained, the valve position of the two-position valve is changed to one cycle when the command is reverse. It is characterized by maintaining the same valve position as before .

  The traveling hydraulic control device according to the present invention described in “[3]” is a two-position valve when the latest command by the forward / reverse switching command device is neutral and the command one cycle before is forward. If the valve position is maintained at the same valve position as one cycle before the command was forward, and the latest command by the forward / reverse switching command device is neutral and the command one cycle before is reverse, the two-position valve The valve position is maintained at the same valve position as one cycle before when the command was reverse. Thus, when the command by the forward / reverse switching command device is switched from forward to neutral, the valve position of the two-position valve can be maintained at the same valve position as when the command is forward, When the command by the switching command device is switched from reverse to neutral, the valve position of the two-position valve can be maintained at the same valve position as when the command is reverse.

  As described above, the hydraulic control device for a traveling vehicle for a work vehicle according to the present invention includes a case where the command by the forward / reverse switching command device is maintained by being switched from forward to neutral, and a case where the command by the forward / reverse switching command device is neutral from the reverse. The vehicle speed can be decelerated with the same deceleration as in the case where it is switched and maintained, and a sudden deceleration of the vehicle speed can be suppressed. Thereby, sudden deceleration contrary to the will of the operator can be prevented, and the operator can be prevented from feeling uncomfortable.

1 is a left side view of an example (wheel loader) of a work vehicle to which a traveling hydraulic control device according to an embodiment of the present invention is applied. The hydraulic circuit diagram which shows the hydraulic control apparatus for driving | running | working of the working vehicle which concerns on one Embodiment of this invention. It is a flowchart which shows the flow of the process for control of the 2 position valve performed by the controller shown in FIG. It is a time chart which shows an example of transition of the pipe line (the 1st pipe line or the 2nd pipe line) selected as a hydraulic pressure source of the pilot pressure of a motor capacity control valve. When the command from the forward / reverse switching lever device is switched from forward to neutral and maintained, the hydraulic pressure source of the pilot pressure of the motor displacement control valve, the pressure in the first line, and the pressure in the second line, It is a time chart which shows an example of each transition of the capacity | capacitance of a traveling motor, and a vehicle speed. When the command by the forward / reverse switching lever device is maintained by switching from reverse to neutral, the hydraulic source of pilot pressure of the motor capacity control valve, the pressure in the first pipe, and the pressure in the second pipe, It is a time chart which shows an example of each transition of the capacity | capacitance of a traveling motor, and a vehicle speed. FIG. 5 is a characteristic diagram showing a relationship between a pilot pressure of a motor capacity control valve and a capacity of a variable displacement hydraulic motor in a conventional hydraulic control device for a working vehicle according to the present invention. 6 is a time chart showing an example of transition of a pipeline (first pipeline or second pipeline) selected as a hydraulic pressure source of pilot pressure of a motor displacement control valve in a conventional hydraulic control device for a work vehicle. is there. In the conventional hydraulic control device for a work vehicle, when the command by the forward / reverse switching lever device is switched from forward to neutral and maintained, the hydraulic pressure source of the pilot pressure of the motor capacity control valve, in the first pipeline It is a time chart which shows an example of each transition of the pressure of this, the pressure in a 2nd pipe line, the capacity | capacitance of a traveling motor, and a vehicle speed. In a conventional hydraulic control device for a working vehicle, when the command by the forward / reverse switching command device is switched and maintained from reverse to neutral, the hydraulic pressure source for the pilot pressure of the motor capacity control valve, in the first pipeline It is a time chart which shows an example of each transition of the pressure of this, the pressure in a 2nd pipe line, the capacity | capacitance of a traveling motor, and a vehicle speed.

  A traveling hydraulic control device for a work vehicle according to an embodiment of the present invention will be described with reference to FIGS.

  A work vehicle to which a traveling hydraulic control device according to an embodiment of the present invention is applied is, for example, a wheel loader 1 shown in FIG. 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 traveling hydraulic control apparatus according to the present embodiment is the traveling hydraulic control apparatus 10 shown in FIG. The travel hydraulic control device 10 includes a variable displacement hydraulic pump 30 capable of reversing the suction port and the discharge port, and a variable displacement hydraulic motor, and is a travel motor connected to the front wheels 4 and the rear wheels 5 so as to be capable of transmission. 40 is connected to a closed circuit via a pair of first and second pipes 51 and 52, and a pump control for controlling the discharge amount of the variable displacement hydraulic pump 30. The hydraulic circuit 60 for a motor and the hydraulic circuit 70 for motor control which controls the capacity | capacitance of the traveling motor 40 are provided.

  The variable displacement hydraulic pump 30 includes a bi-tilting and swash plate type variable mechanism 31 so that the discharge amount (push-off volume) is variable. The hydraulic circuit 60 for pump control discharges the hydraulic pressure pump servo piston 61 that operates the swash plate of the variable mechanism 31 of the variable displacement hydraulic pump 30 and the hydraulic pressure used to drive the pump servo piston 61. A constant displacement hydraulic pump 64 and a directional control valve 65 for controlling the flow of pressure oil supplied from the constant displacement hydraulic pump 64 to the pump servo piston 61 are provided.

  The pump servo piston 61 is displaceable in two opposite directions (F direction and R direction) from the neutral position (position shown in FIG. 2) defined by the return springs 62 and 63. The direction control valve 65 is an electromagnetic valve, and is a spring center type three-position valve. The direction switching valve 65 has a central position 66 for controlling the pump servo piston 61 to a neutral position, an operating position 67 for displacing the pump servo piston 61 in the F direction from the neutral position, and a pump servo piston 61. Can be switched from the neutral position to the operating position 68 for displacing in the R direction.

  In the state where the pump servo piston 61 is located at the neutral position (the state shown in FIG. 2), the discharge amount of the variable displacement hydraulic pump 30 is controlled to 0, which is the minimum discharge amount. In a state where the pump servo piston 61 is displaced in the F direction from the neutral position, the variable displacement hydraulic pump 30 is controlled so as to suck in hydraulic oil from the second pipe 52 and discharge it to the first pipe 51. In a state where the pump servo piston 61 is displaced in the R direction from the neutral position, the variable displacement hydraulic pump 30 is controlled so as to suck in hydraulic fluid from the first pipe 51 and discharge it to the second pipe 52. When the variable displacement hydraulic pump 30 sucks hydraulic oil from the second pipe 52 and discharges it to the first pipe 51, the traveling motor 40 rotates in the direction in which the wheel loader 1 moves forward. When the variable displacement hydraulic pump 30 sucks the hydraulic oil from the first pipe 51 and discharges it to the second pipe 52, the traveling motor 40 rotates in the direction in which the wheel loader 1 moves backward.

  The traveling hydraulic control device 10 is a device that commands the traveling direction of the wheel loader 1 in the form of an electric signal, and a forward / reverse switching lever device 90 (forward / reverse switching command device) that commands forward, reverse, and neutral; And a controller 100 that performs a predetermined process based on a command from the forward / reverse switching lever device 90.

  The forward / reverse switching lever device 90 includes an operation lever 91 that can be selectively operated at a position Fp for commanding forward, a position Rp for commanding reverse, and a position Np for commanding neutrality, and corresponds to the position of the operation lever 91. A command signal (electrical signal) is output.

  The controller 100 performs processing using a CPU, RAM, and ROM, and includes a reading unit 101, a determining unit 102, and a pump control processing unit 103, which are units set by a computer program.

  The reading means 101 reads a command from the forward / reverse switching lever device 90 at a predetermined cycle. The determination unit 102 determines whether the command read by the reading unit 101 is forward, neutral, or reverse.

  The pump control processing unit 103 controls the valve position of the direction control valve 65 to the operating position 67 by applying the driving power Wf to the direction control valve 65 when the determination result by the determination unit 102 is forward, and the determination unit When the determination result by 102 is reverse, the valve position of the direction control valve 65 is controlled to the operating position 68 by applying the driving power Wr to the direction control valve 65, and the determination result by the determination means 102 is neutral. In this case, the valve position of the direction control valve 65 is controlled to the central position 66 by not applying any of the driving power Wf and Wr to the direction control valve 65.

  When the valve position of the directional control valve 65 is switched from the central position 66 to the operating position 67, the pump servo piston 61 is displaced in the F direction from the neutral position, whereby the variable displacement hydraulic pump 30 is moved to the second pipeline. The hydraulic oil is sucked from 52 and controlled to be discharged to the first pipe 51. When the valve position of the direction control valve 65 is switched from the central position 66 to the operating position 68, the pump servo piston 61 is displaced in the R direction from the neutral position, whereby the variable displacement hydraulic pump 30 is moved to the first pipe line. The hydraulic fluid is controlled to be sucked from 51 and discharged to the second pipe 52. In a state where the valve position of the direction control valve 65 is maintained at the central position 66, the pump servo piston 61 stops at the neutral position, whereby the discharge amount of the variable displacement hydraulic pump 30 is the minimum flow rate. Maintained at 0.

  The pump control hydraulic circuit 60, the reading means 101, the determination means 102, and the pump control processing means 103 constitute the pump control means of the present invention. As can be understood from the above description of the pump control hydraulic circuit 60, the reading means 101, the determination means 102, and the pump control processing means 103, this pump control means is based on a forward / reverse switching lever device 90 (forward / reverse switching command device). The discharge direction of the variable displacement hydraulic pump 30 is controlled based on the command. More specifically, the pump control means sucks in the hydraulic fluid from the variable displacement hydraulic pump 30 through the second pipe 52 when the forward movement is commanded by the forward / reverse switching lever device 90, and the first pipe 51 When the reverse movement is instructed by the forward / reverse switching lever device 90, the variable displacement hydraulic pump 30 sucks hydraulic oil from the first pipe 51 and discharges it to the second pipe 52. When the neutral is instructed by the forward / reverse switching lever device 90, the discharge amount of the variable displacement hydraulic pump 30 is controlled to 0 which is the minimum discharge amount.

  The travel motor 40 is provided with an oblique shaft type variable mechanism 41 so that the capacity is variable. The motor control hydraulic circuit 70 includes a motor servo piston 71 that operates the oblique axis of the variable mechanism 41 and a hydraulic pilot motor capacity control valve 72 that controls the flow of pressure oil supplied to the motor servo piston 71. And a two-position valve 73 that selects one of the pressure Pa in the first pipe 51 and the pressure Pb in the second pipe 52 as the pilot pressure Pm applied to the motor capacity control valve 72. Prepare.

  As shown in FIG. 7, the pilot pressure Pm (pressure Pa in the first pipe 51 or pressure Pb in the second pipe 52) applied to the motor capacity control valve 72 is the starting pressure of the motor capacity control valve 72. In a state lower than Pm1, the capacity C of the traveling motor 40 is maintained at the minimum capacity Cmin. Further, when the pilot pressure Pm is higher than the starting pressure Pm1 (Pm> Pm1 state), the capacity C of the traveling motor 40 increases, and when the pilot pressure Pm is lower than the starting pressure Pm1 (Pm <Pm1 state). The capacity C of the traveling motor 40 decreases, and the capacity C of the traveling motor 40 is constant in a state where the pilot pressure Pm is equal to the starting pressure Pm1 (a state where Pm = Pm1).

  The two-position valve 73 is a spring return type hydraulic pilot type valve. When the valve position of the two-position valve 73 is controlled to the first valve position 74 (normal position), the pressure Pa in the first pipe 51 is selected as the pilot pressure Pm of the motor capacity control valve 72. When the valve position of the two-position valve 73 is controlled to the second valve position 75 (operating position), the pressure Pb in the second pipe 52 is selected as the pilot pressure Pm of the motor capacity control valve 72.

  The motor control hydraulic circuit 70 includes a flushing circuit 80, and the two-position valve 73 is operated using pressure oil introduced into the flushing circuit 80. The flushing circuit 80 is introduced by a low-pressure selection valve 81 that introduces pressure oil into the flushing circuit 80 from the low-pressure side of the first pipeline 51 and the second pipeline 52, and the low-pressure selection valve 81. A flushing relief valve 83 is provided for guiding the pressurized oil to the hydraulic oil tank 82 when the pressure of the pressurized oil exceeds a preset flushing pressure. The motor control hydraulic circuit 70 includes a switching valve 85 that can set the pressure in the pipe 84 that guides the pressure oil from the low pressure selection valve 81 to the flushing relief valve 83 as the pilot pressure of the two-position valve 73. . This switching valve 85 is a spring return type electrically operated two-position valve. When the valve position of the switching valve 85 is the normal position 86, no pilot pressure is applied to the two-position valve 73. When the position is the operating position 87, the pilot pressure is applied to the two-position valve 73.

  The controller 100 described above includes tractive force control processing means 104, comparison means 105, and deceleration control processing means 106, which are means set by a computer program.

  When the result of determination by the determination unit 102 is that the command is forward, the traction force control processing unit 104 sets the valve position of the switching valve 85 to the normal position by not applying the driving power W to the switching valve 85. 86, and when the result of determination by the determination means 102 is that the command is reverse, the drive position W is applied to the switching valve 85 to control the valve position of the switching valve 85 to the operating position 87. To do.

  The state in which the valve position of the switching valve 85 is controlled to the normal position 86 by the traction force control processing means 104 is not a state in which the pressure in the pipe 84 in the flushing circuit 80 acts on the two-position valve 73 as a pilot pressure. The valve position of the two-position valve 73 is controlled to the first valve position 74. As a result, the two-position valve 73 is in a state of selecting the pressure Pa in the first pipe line 51 as the pilot pressure Pm of the motor capacity control valve 72. In this state, the capacity C of the travel motor 40 is controlled according to the pressure Pa in the first pipe line 51, and thereby the traction force when the wheel loader 1 moves forward is controlled.

  The state in which the valve position of the switching valve 85 is controlled to the operating position 87 by the traction force control processing means 104 is a state in which the pressure in the conduit 84 in the flushing circuit 80 acts on the two-position valve 73 as a pilot pressure. The valve position of the two-position valve 73 is controlled to the second valve position 75. As a result, the two-position valve 73 is in a state of selecting the pressure Pb in the second conduit 52 as the pilot pressure Pm of the motor capacity control valve 72. In this state, the capacity C of the travel motor 40 is controlled in accordance with the pressure Pb in the second pipe line 52, whereby the traction force when the wheel loader 1 moves backward is controlled.

  The comparison unit 105 stores the determination result of the previous cycle by the determination unit 102 in the RAM of the controller 100, and when the latest determination result by the determination unit 102 is neutral, the neutral result that is the latest determination result is obtained. And the determination result of the previous cycle by the determination unit 102 stored in the RAM of the controller 100 is compared. Since the data stored in the RAM of the controller 100 is erased when the controller 100 is shut down, the determination unit 102 does not have a determination result one cycle before immediately after the controller 100 is started. Therefore, the comparison unit 105 is set to perform the processing on the assumption that the result of the determination of one cycle before by the determination unit 102 is neutral at the first comparison performed after the activation of the controller 100.

  The deceleration control processing unit 106 outputs two positions by not outputting the driving power W when the comparison result that the latest command is neutral and the command one cycle before is forward is obtained by the comparison by the comparison unit 105. Contrast that the valve position of the valve 73 is maintained at the first valve position 74, which is the same valve position as one cycle before the command was forward, and the latest command is neutral and the command one cycle before is reverse. When the result is obtained by the comparison means 105, the second electric valve position 75, which is the same valve position as the previous one cycle when the command was reverse, is output by outputting the driving electric power W. To maintain.

  The controller 100 performs the processing shown in FIG. 3 at a predetermined cycle by the reading means 101, the determination means 102, the traction force control processing means 104, the comparison means 105, and the deceleration control processing means 106, thereby controlling the two-position valve 73. To do. The process flow will be described next.

  First, the controller 100 reads a command from the forward / reverse switching lever device 90 by the reading means 101 (step S1). Next, the controller 100 determines whether the command from the forward / reverse switching lever device 90 is forward, neutral, or reverse by the determination means 102 (step S2).

  When the command by the forward / reverse switching lever device 90 is forward as a result of the determination by the determination unit 102 in step S2, the traction force control processing unit 104 does not output the driving power W, thereby the valve of the switching valve 85. The position is controlled to the normal position 86 (step S2 → step S3). Further, as a result of the determination by the determination means 102 in step S2, when the command by the forward / reverse switching lever device 90 is reverse, the valve position of the switching valve 85 is controlled to the operating position 87 by outputting the driving power W. (Step S2 → Step S4).

  Further, if the instruction by the forward / reverse switching lever device 90 is neutral as a result of the determination by the determination means 102 in step S2, the comparison means 105 is the latest (current) determination result (neutral) by the determination means 102. Is compared with the result of the determination one cycle before (previous) (step S2 → step S5).

  As a result of the comparison by the comparison unit 105 in step S5, the latest (current) determination result by the determination unit 102 is neutral, whereas the determination result of one cycle before (previous) by the determination unit 102 is forward. In this case, the deceleration control processing means 106 does not output the driving power W (Step S5 → Step S6). Thereby, the valve position of the switching valve 85 is controlled to the normal position 86, and accordingly, the valve position of the two-position valve 73 is controlled to the first valve position 74. As a result, the pressure Pa in the first pipe 51 is selected as the pilot pressure Pm of the motor capacity control valve 72.

  As a result of the comparison by the comparison unit 105 in step S5, the latest (current) determination result by the determination unit 102 is neutral, whereas the determination result of one cycle before (previous) by the determination unit 102 is backward. If this is the case, the deceleration control processing means 106 outputs the drive power W (step S5 → step S7). Thereby, the valve position of the switching valve 85 is controlled to the operating position 87, and accordingly, the valve position of the two-position valve 73 is controlled to the second valve position 75. As a result, the pressure Pb in the second pipeline 52 is selected as the pilot pressure Pm of the motor capacity control valve 72.

  When the comparison result by the comparison means 105 in step S5 shows that both the latest (current) determination result by the determination means 102 and the previous one (previous) determination result are neutral, the deceleration control processing means 106 does not output the driving power W (step S5 → step S6). Thereby, the valve position of the switching valve 85 is controlled to the normal position 86, and accordingly, the valve position of the two-position valve 73 is controlled to the first valve position 74. As a result, the pressure Pa in the first pipe 51 is selected as the pilot pressure Pm of the motor capacity control valve 72.

  Since the process shown in FIG. 3 is performed by the controller 100 as described above, a pipe line (first line) selected as a hydraulic pressure source for the pilot pressure Pm of the motor displacement control valve in response to a change in the command by the forward / reverse switching lever device 90. For example, the pipe 51 or the second pipe 52) changes as shown in FIG. FIG. 4 shows an example in which the command by the forward / reverse switching lever device 90 changes in the order of neutral, forward, neutral, reverse, neutral, forward, and neutral after the controller 100 is activated.

  In the example shown in FIG. 4, first, the first pipeline 51 is selected as a hydraulic pressure source for the pilot pressure Pm of the motor displacement control valve 72 based on the neutral command. Next, when the command is switched from neutral to forward, the first pipe 51 is continuously selected as the hydraulic pressure source of the pilot pressure Pm. Next, when the command is switched from forward to neutral, the first pipe 51 is continuously selected as the hydraulic pressure source of the pilot pressure Pm. That is, when the command from the forward / reverse switching lever device 90 is switched from forward to neutral, the hydraulic pressure source of the pilot pressure Pm is maintained in the same first pipeline 51 as when the command is forward.

  Next, when the command is switched from neutral to reverse, the second pipeline 52 is selected as the hydraulic pressure source of the pilot pressure Pm. Next, when the command is switched from reverse to neutral, the second pipe 52 is continuously selected as the hydraulic pressure source of the pilot pressure Pm. That is, when the command by the forward / reverse switching lever device 90 is switched from reverse to neutral, the hydraulic pressure source of the pilot pressure Pm is maintained in the same second pipeline 52 as when the command is reverse.

  Next, when the command is switched from neutral to forward, the first pipeline 51 is selected as the hydraulic pressure source of the pilot pressure Pm. Next, when the command is switched from forward to neutral, the state where the first pipeline 51 is continuously selected as the hydraulic pressure source of the pilot pressure Pm is maintained.

  The motor control hydraulic circuit 70, the reading means 101, the determination means 102, the traction force control processing means 104, the comparison means 105, and the deceleration control processing means 106 constitute the motor control means of the present invention. As can be seen from the above description of the motor control hydraulic circuit 70, the reading means 101, the determination means 102, and the traction force control processing means 104, this motor control means is used when a forward movement is instructed by the forward / reverse switching lever device 90. The valve position of the two-position valve 73 is controlled to a first valve position 74 where the pressure Pa in the first pipe 51 is selected as the pilot pressure Pm of the motor capacity control valve 72, and the forward / reverse switching lever device 90 When reverse travel is commanded, the valve position of the two-position valve 73 is controlled to a second valve position 75 where the pressure Pb in the second pipe 52 is selected as the pilot pressure Pm.

  The motor control hydraulic circuit 70, the reading means 101, the determination means 102, the comparison means 105, and the deceleration control processing means 106 constitute a deceleration control means of the present invention. As can be seen from the description of the motor control hydraulic circuit 70, the reading means 101, the determination means 102, the comparison means 105, and the deceleration control processing means 106, this deceleration control means is the latest as a result of the comparison by the comparison means 105. When the command is neutral and the result that the command one cycle before is forward is obtained, the valve position of the two-position valve 73 is set to the first valve position that is the same as the one cycle before the command is forward. When the valve position 74 is maintained, and the result of the comparison by the comparison means 105 is that the latest command is neutral and the previous command is reverse, the valve position of the two-position valve 73 is Is maintained at the second valve position 75, which is the same valve position as one cycle before the reverse. Thereby, the deceleration control means has the same valve position as that when the command is forward when the command by the forward / reverse switching lever device 90 is switched from forward to neutral when the command is forward. When the command by the forward / reverse switching lever device 90 can be switched from reverse to neutral, the valve position of the two-position valve 73 is the same as when the command is reverse. The second valve position 75, which is the valve position, can be maintained. That is, when the vehicle speed is decelerated when the command from the forward / reverse switching lever device 90 is switched from forward to neutral, and when the command from the forward / reverse switching lever device 90 is switched from reverse to neutral, Sometimes, the pressure in the pipe on the opposite side of the pipe in which the brake pressure is generated in the first pipe 51 and the second pipe 52 is selected as the pilot pressure Pm of the motor capacity control valve 72. The valve position of the two-position valve 73 can be controlled to the valve position.

  Next, deceleration of the vehicle speed when the command from the forward / reverse switching lever device 90 is switched from forward to neutral will be described with reference to the drawings.

  As shown in FIG. 5A, in the state where the forward movement is commanded by the forward / reverse switching lever device 90, the two-position valve 73 has a hydraulic pressure of the pilot pressure Pm of the motor displacement control valve 72 as shown in FIG. The first pipeline 51 is selected as the source. Further, since the variable displacement hydraulic pump 30 is controlled so as to suck the hydraulic oil from the second pipe 52 and discharge it to the first pipe 51, the first variable pump as shown in FIG. The pressure Pa (solid line) in the pipe line 51 is higher than the pressure Pb (dashed line) in the second pipe line 52. And the capacity | capacitance C of the traveling motor 40 is controlled according to the pressure Pa in the 1st pipe line 51. FIG. For example, when the pressure Pa in the first pipe line is maintained lower than the starting pressure Pm1 of the motor capacity control valve, the capacity C of the travel motor is minimum as shown in FIG. The capacity is maintained at Cmin. As a result, the vehicle moves forward at the vehicle speed V1 of the wheel loader 1 as shown in FIG.

  In a state in which the wheel loader 1 is moving forward at the speed V1, the command by the forward / reverse switching lever device 90 is switched from forward to neutral as shown at time t1 in FIG. 5A, and then the neutral command is When maintained, the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump 30 are controlled to be finally reduced to zero. During this time, the rotation of the travel motor 40 is not immediately decelerated as the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump 30 decrease, but is maintained by inertia, so that the travel motor 40 has a pumping action. That is, while the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump 30 are decreasing, the traveling motor 40 maintains the flow of hydraulic oil from the first pipeline 51 to the second pipeline 52 due to inertia. By continuing the rotation as described above, the hydraulic oil is sucked from the first pipe 51 and discharged to the second pipe 52, and therefore, as shown in FIG. 5C, the pressure Pa ( (Solid line) decreases, and the pressure Pb (broken line) in the second pipeline 52 increases. At this time, the pressure Pb in the second pipeline 52 becomes a brake pressure that brakes the rotation of the travel motor 40, so that the vehicle speed V decreases from V1 as shown in FIG.

  On the other hand, since the two-position valve 73 is controlled by the deceleration control processing means 106 via the switching valve 85, as shown in FIG. 5B, the command by the forward / reverse switching lever device 90 is forward. The first pipeline 51 has been selected as the hydraulic pressure source for the pilot pressure Pm of the motor capacity control valve 72 since the occurrence. For this reason, the capacity C of the travel motor 40 is controlled according to the pressure Pa in the first pipeline 51. Since the pressure Pa in the first pipe 51 is not the brake pressure but lower than the starting pressure Pm1 of the motor capacity control valve 72, the capacity C of the travel motor 40 is determined to be forward by a command from the forward / reverse switching lever device 90. The minimum capacity Cmin is continuously maintained from that time.

  That is, when the command from the forward / reverse switching lever device 90 is switched from forward to neutral and maintained, the braking speed due to the increase in the capacity C of the traveling motor 40 does not act on the rotation of the traveling motor 40 in the deceleration of the vehicle speed. Therefore, only the braking force due to the brake pressure acts on the rotation of the traveling motor 40. Thus, for example, as shown in FIG. 5 (e), the wheel loader 1 moving forward at the vehicle speed V1 stops after the deceleration time Tf from the start of deceleration.

  Next, the deceleration of the vehicle speed when the command from the forward / reverse switching lever device 90 is switched from the reverse to the neutral and maintained will be described with reference to FIG.

  As shown in FIG. 6 (a), in the state where the reverse movement is instructed by the forward / reverse switching lever device 90, the two-position valve 73 has a hydraulic pressure of the pilot pressure Pm of the motor displacement control valve 72 as shown in FIG. 6 (b). The second conduit 52 is selected as the source. Further, since the variable displacement hydraulic pump 30 is controlled so as to suck the hydraulic oil from the first pipe 51 and discharge it to the second pipe 52, the second hydraulic pump 30 is operated as shown in FIG. The pressure Pb (broken line) in the pipe line 52 is higher than the pressure Pa (solid line) in the first pipe line 51. And the capacity | capacitance C of the traveling motor 40 is controlled according to the pressure Pb in the 2nd pipe line 52. FIG. For example, when the pressure Pb in the second pipe line is maintained lower than the starting pressure Pm1 of the motor capacity control valve, the capacity C of the travel motor 40 is as shown in FIG. 6 (d). The minimum capacity Cmin is maintained. As a result, as shown in FIG. 6E, the wheel loader 1 moves backward at the vehicle speed V1.

  In the state where the wheel loader 1 is moving backward at the speed V1, the command by the forward / reverse switching lever device 90 is switched from backward to neutral as shown at time t2 in FIG. 6 (a), and then the neutral command is issued. When maintained, the suction flow rate and the discharge flow rate of the variable displacement hydraulic pump 30 are controlled to be finally reduced to zero. During this time, the traveling motor 40 continues to rotate so as to maintain the flow of hydraulic fluid from the second pipeline 52 to the first pipeline 51 due to inertia, thereby sucking hydraulic fluid from the second pipeline 52 and As shown in FIG. 6C, the pressure Pb (broken line) in the second pipe 52 is lowered and the pressure Pa (solid line) in the first pipe 51 is reduced. To rise. At this time, the pressure Pa in the first pipe line 51 becomes a brake pressure that brakes the rotation of the travel motor 40, so that the vehicle speed V decreases from V1 as shown in FIG. 6 (e).

  On the other hand, since the two-position valve 73 is controlled by the deceleration control processing means 106 via the switching valve 85, the command by the forward / reverse switching lever device 90 is reverse as shown in FIG. In this state, the second pipeline 52 is continuously selected as the hydraulic pressure source for the pilot pressure Pm of the motor capacity control valve 72. For this reason, the capacity C of the traveling motor 40 is controlled according to the pressure Pb in the second conduit 52. Since the pressure Pb in the second pipe line 52 is not the brake pressure but lower than the starting pressure Pm1 of the motor capacity control valve 72, the command by the forward / reverse switching lever device 90 indicates that the capacity C of the travel motor 40 is forward. The minimum capacity Cmin is continuously maintained from that time.

  That is, even when the command by the forward / reverse switching lever device 90 is switched from reverse to neutral and maintained, the braking force due to the increase in the capacity C of the traveling motor 40 acts on the rotation of the traveling motor 40 to reduce the vehicle speed. Therefore, only the braking force by the brake pressure acts on the rotation of the traveling motor 40. Thus, for example, as shown in FIG. 6 (e), the wheel loader 1 moving backward at the vehicle speed V1 stops after the deceleration time Tr from the start of deceleration. The deceleration time Tr is the same length as the deceleration time Tf shown in FIG.

  According to the traveling hydraulic control apparatus 10 according to the present embodiment, the following effects can be obtained.

  In the traveling hydraulic control apparatus 10 according to the present embodiment, the deceleration control means configured by the motor control hydraulic circuit 70, the reading means 101, the determination means 102, the comparison means 105, and the deceleration control processing means 106 is a forward / reverse drive. When the vehicle speed is reduced when the command by the switching lever device 90 is switched from forward to neutral, and when the vehicle speed is reduced when the command by the forward / reverse switching command device is switched from reverse to neutral, Two positions are selected such that the pressure in the pipe 51 and the pipe 52 on the opposite side of the pipe where the brake pressure is generated is selected as the pilot pressure Pm of the motor capacity control valve 72. The valve position of the valve 73 is controlled. As a result, the vehicle speed is reduced when the vehicle speed is reduced when the command by the forward / reverse switching lever device 90 is switched from forward to neutral, and when the command by the forward / backward switching lever device 90 is switched from reverse to neutral. Since the motor capacity control valve 72 is not operated by the brake pressure at any time during deceleration, there is no situation where the capacity of the travel motor 40 increases, and the braking force against the rotation of the travel motor 40 depends on the brake pressure. Only braking force. Accordingly, the deceleration is the same between when the command from the forward / reverse switching lever device 90 is switched and maintained from forward to neutral and when the command from the forward / backward switching lever device 90 is switched and maintained from backward to neutral. Thus, the vehicle speed can be decelerated, and a sudden deceleration of the vehicle speed can be suppressed. Thereby, sudden deceleration contrary to the will of the operator can be prevented, and the operator can be prevented from feeling uncomfortable.

  In the traveling hydraulic control device 10 according to the present embodiment, as described above, when the vehicle speed is decelerated when the command from the forward / reverse switching lever device 90 is switched from forward to neutral, and the forward / backward switching lever device. The situation that the capacity of the traveling motor 40 increases does not occur at any time of deceleration of the vehicle speed due to the change of the command by 90 from reverse to neutral. Therefore, it is possible to prevent cavitation in the suction side pipe line (first pipe line 51 or second pipe line 52) of the traveling motor 40 in which the pump action has occurred, and to prevent erosion and noise caused by the cavitation.

  The traveling hydraulic control apparatus 10 according to the present embodiment is configured so that one of the pressure Pa in the first pipe 51 and the pressure Pb in the second pipe 52 is supplied to the motor capacity control valve 72 as a pilot pressure. A spring return type two-position valve 73 is provided as a valve to be selected as Pm, and the valve position of the two-position valve 73 is set to the first valve position 74 (normal position) when the switching valve 85 is not supplied with driving power W. ) To select the pressure Pa in the first pipeline 51 as the pilot pressure Pm of the motor capacity control valve 72. As a result, the traction force during the forward movement of the wheel loader 1 can be controlled even when the driving power W cannot be applied to the switching valve 85 due to a malfunction of the electrical system.

  The travel hydraulic control apparatus 10 according to the present embodiment uses one of the pressure Pa in the first pipe 51 and the pressure Pb in the second pipe 52 as the pilot pressure Pm of the motor capacity control valve 72. A two-position valve 73 is provided as a valve to be selected, and when the command from the forward / reverse switching lever device 90 is forward or neutral, the pressure Pa in the first pipe 51 is set to the two-position valve 73 as the pilot pressure Pm. When the command is reverse, the pressure Pb in the second pipe 52 is set to the pilot pressure Pm, and the pressure Pb in the second pipe 52 is selected by the two-position valve 73. On the other hand, when a three-position valve is used instead of the two-position valve 73, the valve position at which the pressure Pa in the first pipe 51 is selected as the pilot pressure Pm, and the second pipe 52 The second valve position in which the internal pressure Pb is selected as the pilot pressure Pm, and the pressure Pa in the first pipe 51 and the pressure Pb in the second pipe 52 are not selected as the pilot pressure Pm. The valve position of the 3-position valve can be switched to the valve position of 3, and when the command is forward, the valve position of the 3-position valve is controlled to the first valve position, and when the command is reverse, the 3-position valve The object of the present invention is achieved by controlling the valve position of the three position valve to the second valve position and controlling the valve position of the three position valve to the third valve position when the command is neutral. However, the adoption of a three-position valve is not preferable because it leads to a more complicated hydraulic circuit and higher cost than the adoption of a two-position valve. That is, the traveling hydraulic control apparatus 10 according to the present embodiment employs the 2-position valve 73 to realize a traveling hydraulic control apparatus that has a simpler and less expensive hydraulic circuit configuration than the case of employing the 3-position valve. it can.

  In the traveling hydraulic control apparatus 10 according to the above-described embodiment, the two-position valve 73 of the motor control means is a hydraulic pilot type valve, and the pressure oil introduced into the flushing circuit 80 is supplied through the switching valve 85. However, the two-position valve of the present invention is not limited to this. The switching valve 85 may be omitted so that the two-position valve 73 is an electromagnetic valve and the driving power W is directly supplied to the two-position valve 73.

  The traveling hydraulic control device 10 according to the above-described embodiment has the forward / reverse switching except when the command by the forward / reverse switching lever device 90 is switched from reverse to neutral and when the command is switched from forward to neutral. When the command by the lever device 90 is neutral, the two-position valve 73 is controlled so that the pressure Pa in the first pipe 51 is selected as the pilot pressure Pm of the motor capacity control valve 72. The pressure Pb in the pipe line 52 may be selected as the pilot pressure Pm.

  Although the traveling hydraulic control device 10 according to the above-described embodiment is applied to the wheel loader 1, the traveling hydraulic control device 10 may be applied to a work vehicle other than the wheel loader (such as a rolling machine or an agricultural vehicle).

DESCRIPTION OF SYMBOLS 1 Wheel loader 10 Traveling hydraulic control apparatus 20 Traveling HST circuit 30 Variable displacement hydraulic pump 31 Variable mechanism section 40 Traveling motor 41 Variable mechanism section 51 First pipeline 52 Second pipeline 60 Pump control hydraulic circuit 61 Pump servo pistons 62, 63 Return spring 64 Constant displacement hydraulic pump 65 Directional control valve 66 Central position 67 Operating position 68 Operating position 70 Motor control hydraulic circuit 71 Motor servo piston 72 Motor capacity control valve 73 Two-position valve 74 1 valve position 75 second valve position 80 flushing circuit 81 low pressure selection valve 82 hydraulic oil tank 83 flushing relief valve 84 conduit 85 switching valve 86 normal position 87 operating position 90 forward / reverse switching lever device 91 operating lever 100 controller 101 reading Means 102 Determination means 103 Pump control processing Means 104 Traction force control processing means 105 Contrast means 106 Deceleration control processing means

Claims (3)

A variable displacement hydraulic pump capable of reversing the suction port and the discharge port and a travel motor composed of a variable displacement hydraulic motor are connected to a closed circuit via a pair of first and second pipes. And a forward / reverse switching command device for commanding forward, reverse, and neutral, and the variable capacity type based on a command from the forward / reverse switching command device. Pump control means for controlling the discharge direction of the hydraulic pump, and motor control means for controlling the capacity of the traveling motor in accordance with the pressure in the first pipe line or the pressure in the second pipe line,
The pump control means is a state in which when the forward movement is commanded by the forward / reverse switching command device, the variable displacement hydraulic pump sucks hydraulic oil from the second pipe and discharges it to the first pipe And when the reverse is commanded by the forward / reverse switching command device, the variable displacement hydraulic pump is controlled so as to suck in hydraulic oil from the first pipe and discharge it to the second pipe. When the neutral is commanded by the forward / reverse switching command device, the discharge amount of the variable displacement hydraulic pump is controlled to the minimum discharge amount,
The motor control means includes a servo piston that operates a variable mechanism that makes the capacity of the variable displacement hydraulic motor variable, and a hydraulic pilot motor capacity control valve that controls the flow of pressure oil supplied to the servo piston. And a two-position valve that selects one of the pressure in the first pipe line and the pressure in the second pipe line as a pilot pressure applied to the motor capacity control valve. Hydraulic control device for
The motor control means is configured to reduce the vehicle speed when the command from the forward / reverse switching command device is switched from forward to neutral, and when the command from the forward / backward switching command device is switched from reverse to neutral. A valve in which the pressure in the pipe on the opposite side of the pipe in which the brake pressure is generated in the first pipe and the second pipe is selected as the pilot pressure when the vehicle speed is reduced. A hydraulic control apparatus for traveling a work vehicle, comprising a deceleration control means for controlling a valve position of the two-position valve at a position. The hydraulic control device for traveling a work vehicle according to claim 1,
The deceleration control means maintains the valve position of the two-position valve at the same valve position as when the command was forward when the command by the forward / reverse switching command device is switched from forward to neutral, When the command by the forward / reverse switching command device is switched from reverse to neutral, the valve position of the two-position valve is maintained at the same valve position as when the command is reverse. Hydraulic control device for traveling. The hydraulic control device for traveling a work vehicle according to claim 2,
The deceleration control means includes determination means for determining whether the command from the forward / reverse switching command device is forward, reverse, or neutral at a predetermined cycle, and the result of the latest and one cycle previous determination by the determination device. And when the result of the comparison by the comparison means is that the latest command is neutral and the previous command is forward, the valve position of the two-position valve Is maintained at the same valve position as one cycle before the command is forward, and as a result of the comparison by the comparison means, the latest command is neutral and the command one cycle before is reverse And a valve position of the two-position valve is maintained at the same valve position as one cycle before the command was reverse.

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