JP2013170377A - Wheel type work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wheel type work vehicle capable of preventing an operation of a cutoff valve by the brake pressure when a traveling speed is reduced by the brake pressure.SOLUTION: On the basis of a pressure of a main pipeline 15 detected by a first pressure detector 101, a pressure of a main pipeline 16 detected by a second pressure detector 102, and a traveling direction commanded by a forward and backward movement switching lever device 100, brake pressure determination means 112 for determining whether or not a brake pressure is generated in one or the other of the pair of main pipelines 15 and 16 makes a determination. When the brake pressure is generated, pressure discharge control means 113 controls a pressure control valve 71, and sets the pressure of the main pipeline 15 or the main pipeline 16 on a high pressure side needed for the operation of a cutoff valve 61 higher than the brake pressure.

Description

  The present invention relates to a wheeled work vehicle including an HST circuit for traveling.

  As a conventional traveling HST circuit provided in a wheeled work vehicle, there is one disclosed in Patent Document 1. The conventional HST circuit for traveling includes an engine (prime motor), a variable displacement pump (traveling pump) driven by transmission of the engine output, a hydraulic motor, a variable displacement pump, and a hydraulic motor in a closed circuit. When the discharge pressure of a pair of oil passages (main pipelines) connected to and the variable displacement pump exceeds the specified pressure, the inclination angle (tilt angle) of the swash plate of the variable displacement pump is reduced to travel A cut-off valve that regulates the traction force of the wheel-type work vehicle by lowering the discharge pressure of the pump.

  In this traveling HST circuit, the cut-off valve operates with the pressure of the oil passage on the high pressure side of the pair of oil passages as a pilot pressure.

Japanese Patent No. 4222842

  By the way, in the traveling HST circuit disclosed in Patent Document 1, the oil path on the discharge side of the variable capacity pump (traveling pump) of the pair of oil paths (main conduits) and the pair of oil paths If the oil path on the high-pressure side matches, the cut-off valve is activated using the pressure on the oil path on the discharge side as the pilot pressure, thereby regulating the traction force of the wheeled work vehicle. The cut-off valve achieves the purpose of.

  However, if the discharge flow rate of the variable displacement pump decreases due to a decrease in the rotational speed of the variable displacement pump (traveling pump) accompanying a decrease in the rotational speed of the engine (motor), the hydraulic motor (traveling motor) Since the rotation speed of the hydraulic motor is maintained higher than the rotation speed corresponding to the discharge flow rate of the variable displacement pump, the pressure of the hydraulic oil returning from the hydraulic motor to the variable displacement pump increases, that is, the return pressure increases. As a result, a brake pressure against the rotation of the hydraulic motor is generated, whereby the hydraulic oil is returned from the hydraulic motor to the variable displacement pump in the pair of oil passages (the opposite side from the discharge side of the variable displacement pump). The oil passage is an oil passage on the high pressure side. In this case, when the cut-off valve is operated using the pressure (brake pressure) of the oil passage on the high pressure side as a pilot pressure, the discharge flow rate of the variable displacement pump is further reduced and the brake pressure is further increased. The increase in the brake pressure causes unnecessary high pressure to act on the hydraulic equipment, and causes a sudden deceleration of the traveling speed, thereby deteriorating the operation feeling.

  The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a wheeled work vehicle that can prevent the operation of a cut-off valve due to the brake pressure when the traveling speed is reduced by the brake pressure. There is to do.

  In order to achieve the above object, the wheel type work vehicle of the present invention is configured as follows.

[1] A wheel-type work vehicle of the present invention includes a prime mover and a variable displacement hydraulic pump capable of discharging pressure oil in two opposite directions, and a traveling pump driven by being transmitted with the output of the prime mover. A traveling motor composed of a hydraulic motor rotatable in two directions, a pair of main pipes connecting the traveling pump and the traveling motor to a closed circuit, traveling direction command means for commanding the traveling direction, and the traveling The discharge direction control means for controlling the discharge direction of the traveling pump based on the command of the traveling direction by the direction command means, and the pressure of the main line on the high pressure side of the pair of main lines as a pilot pressure, A wheel-type work vehicle comprising: a cut-off valve that operates in a direction that reduces the displacement of the travel pump; and braking on one or the other of the pair of main pipes A brake pressure detecting means for detecting occurrence of the pressure, and when the generation of the brake pressure is detected by the brake pressure detecting means, the pressure of the main line on the high pressure side required for the operation of the cut-off valve is set to be higher than the brake pressure. And a high operating pressure control means.

  In the wheeled work vehicle described in “[1]”, when the travel direction command means commands forward or reverse as the travel direction, the discharge direction control means controls the discharge direction of the travel pump based on the command. As a result, the traveling pump in a state driven by the output of the prime mover discharges hydraulic oil to the main conduit on the side corresponding to the traveling direction command of the pair of main conduits. As a result, the circulation of the working oil “travel pump → one or other of the pair of main pipes → travel motor → the other or one of the pair of main lines → the travel pump” is the travel pump and the travel motor. Occurs between.

  During the circulation of the hydraulic oil between the travel pump and the travel motor, the state in which the oil discharged from the travel pump drives the travel motor is a state in which the wheel work vehicle is moving forward or backward, and a pair of The main pipeline on the discharge side of the traveling pump in the main pipeline and the high-pressure main pipeline in the pair of main pipelines coincide with each other. In this state, the brake pressure detecting means does not detect the occurrence of the brake pressure in one or the other of the pair of main pipes, so that the operating pressure control means is the high-pressure side main pipe required for operating the cut-off valve. The pressure of the road is not set higher than the brake pressure. Therefore, the cut-off valve can be operated by the pressure of the main line on the high-pressure side of the pair of main lines (discharge pressure of the traveling pump). It is in a state. And when a cut-off valve act | operates, the tractive force of a wheel type work vehicle is controlled.

  On the other hand, when the discharge flow rate of the travel pump decreases due to a decrease in the rotation speed of the travel pump accompanying a decrease in the rotational speed of the prime mover, the travel motor rotates due to inertial force, and the travel motor rotation speed Since the rotational speed corresponding to the flow rate is maintained higher than the number of revolutions, the pressure of the hydraulic oil returning from the traveling motor to the traveling pump increases, that is, the return pressure increases, and a brake pressure is generated against the rotation of the traveling motor. Thus, the main line on the side (reverse to the discharge side of the traveling pump) that returns the hydraulic oil from the traveling motor to the traveling pump among the pair of main conduits becomes the high pressure side main conduit.

  In this case, the brake pressure detecting means detects that the brake pressure is generated in one or the other of the pair of main pipelines. Then, the operating pressure control means sets the pressure of the main line on the high pressure side required for operating the cutoff valve to be higher than the brake pressure. Thereby, when the traveling speed is reduced by the brake pressure, the wheeled work vehicle described in “[1]” can prevent the operation of the cutoff valve by the brake pressure.

[2] The wheeled work vehicle according to the present invention is the wheeled work vehicle described in “[1]”, wherein the brake pressure detecting means detects a pressure of one of the pair of main pipes. A pressure detector, a second pressure detector for detecting the pressure of the other of the pair of main pipes, a pressure detected by the first pressure detector, and a pressure detected by the second pressure detector Brake pressure determining means for determining whether brake pressure is generated in one or the other of the pair of main pipes based on the pressure and the travel direction commanded by the travel direction command means; It is characterized by providing.

  In the wheeled work vehicle described in “[2]”, for example, one main pipe of the pair of main pipes becomes the discharge side of the traveling pump when moving forward, and the other main pipe becomes the discharge side when moving backward. In the case where the brake pressure is not generated, the pressure in one main pipeline is on the high pressure side when the vehicle is moving forward. On the high pressure side. On the other hand, the pressure of the other main pipeline is on the high pressure side when the vehicle is traveling backward without brake pressure being generated, but the pressure of the one main pipeline is on the high pressure side when traveling backward with the brake pressure being generated. It becomes. That is, in the case where the brake pressure is not generated, the main line on the discharge side of the traveling pump and the main line on the high pressure side do not match. From this, the brake pressure determination means of the brake pressure detection means is configured to detect the pressure detected by the first pressure detector, the pressure detected by the second pressure detector, and the travel direction commanded by the travel direction command means. Based on this, it is possible to determine whether or not the brake pressure is generated in one or the other of the pair of main pipelines.

[3] The wheeled work vehicle according to the present invention is the wheeled work vehicle described in “[1]”, wherein the brake pressure detecting means determines that the number of revolutions of the prime mover is decreased by a predetermined number or more. It is detected as occurrence of this.

  In the wheeled work vehicle described in “[3]”, when the rotational speed of the prime mover decreases, the rotational speed of the traveling pump decreases, and accordingly, the discharge flow rate of the traveling pump decreases. Accordingly, as described above, a brake pressure is generated in one or the other of the pair of main pipes. Therefore, the brake pressure detecting means indirectly detects the generation of the brake pressure by detecting that the rotational speed of the prime mover is decreased by a predetermined rotational speed or more. Note that the predetermined rotational speed that serves as a criterion for determination in the brake pressure detecting means is set to a value that exceeds the range in which the rotational speed decreases with normal work performed by the wheeled work vehicle. .

[4] The wheeled work vehicle according to the present invention is the wheeled work vehicle according to “[3]”, wherein the brake pressure detecting means includes a rotational speed detector for detecting the rotational speed of the prime mover, and the rotational speed detection. And a rotational speed determining means for determining whether or not the rotational speed of the prime mover detected by the device has decreased by a predetermined rotational speed or more.

  In the wheeled work vehicle described in “[4]”, the brake pressure detecting means directly detects the number of revolutions of the prime mover with a revolution number detector, and whether or not the number of revolutions of the prime mover has decreased by a predetermined number or more. This determination is performed by the rotation speed determination means, so that a decrease in the discharge flow rate of the traveling pump accompanying a decrease in the rotation speed of the prime mover can be indirectly detected. As a result, the generation of the brake pressure can be indirectly detected. .

[5] The wheeled work vehicle according to the present invention is the wheeled work vehicle according to [3], further comprising an accelerator pedal for instructing an increase / decrease in the number of rotations of the prime mover according to a depression amount. The pressure detection means detects the depression amount of the accelerator pedal, and determines whether or not the depression amount detected by the depression amount detector has decreased by a predetermined depression amount or more. And a stepping amount determining means for determining whether or not the rotational speed of the prime mover has decreased by the predetermined rotational speed or more.

  In the wheeled work vehicle described in “[5]”, the brake pressure detecting means detects the depression amount of the accelerator pedal by a depression amount detector, and determines whether or not the depression amount has decreased by a predetermined depression amount or more. By performing the determination by the stepping amount determination means, it is indirectly determined whether or not the rotational speed of the prime mover has decreased by a predetermined rotational speed or more, and thereby the generation of the brake pressure can be indirectly detected. It should be noted that the predetermined depression amount used as a determination criterion in the depression amount determination means is a depression amount larger than the variation range of the depression amount due to vibration generated in the wheeled work vehicle during traveling, that is, the depression amount determined by the operator's intention. It is set with the intention of detecting a decrease.

[6] The wheeled work vehicle according to the present invention is the wheeled work vehicle according to “[1]”, wherein the inching pedal and a direction in which the displacement of the traveling pump is decreased in accordance with an increase in the amount of depression of the inching pedal. An inching valve that operates, wherein the brake pressure detecting means detects a depression amount detector that detects a depression amount of the inching pedal, and a depression amount detected by the depression amount detector increases by a predetermined depression amount or more. And a stepping amount determination means for detecting the occurrence of brake pressure by determining whether or not it has been performed.

  In the wheeled work vehicle described in “[6]”, the brake pressure detecting means detects the depression amount of the inching pedal by a depression amount detector, and determines whether or not the depression amount has decreased by a predetermined depression amount or more. By performing the determination by the depression amount determination means, it is indirectly determined whether or not the displacement of the travel pump has decreased, that is, whether or not the discharge flow rate of the travel pump has decreased, and thus the brake The generation of pressure can be indirectly detected. It should be noted that the predetermined depression amount used as a determination criterion in the depression amount determination means is a depression amount larger than the variation range of the depression amount due to vibration generated by the wheeled work vehicle during traveling, that is, the depression amount determined by the operator's intention. It was set with the intention of detecting an increase.

[7] The wheeled work vehicle according to the present invention is the wheeled work vehicle according to “[1]”, wherein the travel direction command means selectively commands one of forward, reverse, and neutral. The discharge direction control means controls the discharge flow rate of the travel pump to zero when the travel direction command by the travel direction command means is neutral, and the brake pressure detection means It is detected as occurrence of brake pressure that the command of the travel direction by the means has been switched from forward to neutral, and that the command of the travel direction by the travel direction command means has been switched from reverse to neutral. To do.

  In the wheeled work vehicle described in “[7]”, the discharge direction control means controls the discharge flow rate of the travel pump to zero when the travel direction command by the travel direction command means is neutral. When the travel direction command by the travel direction command means switches from forward to neutral, and when the travel direction command by the travel direction command means switches from reverse to neutral, the discharge flow rate of the travel pump decreases. . Therefore, the brake pressure detecting means detects when the traveling direction command by the traveling direction command means is switched from forward to neutral and when the traveling direction command by the traveling direction command means is switched from reverse to neutral. As a result, a decrease in the discharge flow rate of the traveling pump is indirectly detected, and this indirectly detects the generation of the brake pressure.

  As described above, the wheeled work vehicle of the present invention can prevent the cut-off valve from being actuated by the brake pressure when the traveling speed is reduced by the brake pressure. As a result, it is possible to prevent unnecessary high pressure from acting on the hydraulic equipment, and it is possible to prevent the operation feeling from being deteriorated due to the sudden deceleration of the traveling speed due to the brake pressure.

It is a side view of the wheel loader which is a 1st embodiment of the wheel type work vehicle of the present invention. It is a figure which shows the hydraulic drive device mounted in the wheel loader shown in FIG. It is a figure which shows the hydraulic drive device mounted in the wheel loader of the 2nd Embodiment of this invention. It is a figure which shows the hydraulic drive device mounted in the wheel loader of the 3rd Embodiment of this invention. It is a figure which shows the hydraulic drive device mounted in the wheel loader of the 4th Embodiment of this invention. It is a figure which shows the hydraulic drive device mounted in the wheel loader of the 5th Embodiment of this invention.

  First to fifth embodiments of the wheeled work vehicle of the present invention will be described.

[First embodiment]
A first embodiment will be described with reference to FIGS.

  The first embodiment is a wheel loader 1 shown in FIG. The wheel loader 1 includes a cab 3, a main body 2 provided with a pair of left and right front wheels 4, and a pair of left and right rear wheels 5, and a work device 6 provided at the front of the main body 2. Prepare.

  The working device 6 includes a lift arm 7 coupled to the main body 2 so as to be rotatable in the vertical direction, and a bucket 8 coupled to the lift arm 7 so as to be rotatable in the vertical direction. The working device 6 is driven by a lift arm cylinder 7a and a bucket cylinder 8a.

  One end of the lift arm cylinder 7 a is rotatably coupled to the main body 2. The other end of the lift arm cylinder 7a is rotatably coupled to the lift arm 7. The lift arm 7 rotates upward with respect to the main body 2 by extension of the lift arm cylinder 7a, and rotates downward with respect to the main body 2 by contraction of the lift arm cylinder 7a. One end of the bucket cylinder 8a is rotatably coupled to the lift arm 7. The other end of the bucket cylinder 8a is coupled to the bucket 8 via a link mechanism 8b. The bucket 8 rotates upward with respect to the lift arm 7 by extension of the bucket cylinder 8a, and rotates downward with respect to the lift arm 7 by contraction of the bucket cylinder 8a.

  The wheel loader 1 shown in FIG. 1 is equipped with a hydraulic drive device 10 shown in FIG. The hydraulic drive device 10 includes a traveling HST circuit 11. The HST circuit 11 includes a diesel engine 12 that is a prime mover, and a variable displacement hydraulic pump that can discharge pressure oil in two opposite directions, and a travel pump 13 that is driven by transmission of the output of the diesel engine 12; The traveling motor 17 is composed of a hydraulic motor that can rotate in two opposite directions and is connected to the rear wheel 5 of the wheel loader 1 via a power transmission mechanism 18 including a speed reducer, and the traveling pump 13 and the traveling motor 17 are closed. And a pair of main lines 15 and 16 for traveling connected to the circuit.

  The diesel engine 12 is electronically controlled by the engine controller 82 based on the depression amount detection signal (electric signal) output from the depression amount detector 81 according to the depression amount of the accelerator pedal 80. It has become. The accelerator pedal 80 is provided in the cab 3 and is operated by an operator.

  The traveling pump 13 includes a pair of inlets / outlets 13a and 13b that serve as a suction port or a discharge port for hydraulic oil, a variable mechanism unit 14 that varies a displacement volume, and a regulator 20 that drives the variable mechanism unit 14. Prepare.

  The variable mechanism section 14 can change the tilt angle of the swash plate from a neutral angle (an angle shown in FIG. 2) at which the displacement volume becomes zero to two opposite directions (F direction and B direction). is there. When the variable mechanism portion 14 is tilted from the neutral angle in the F direction, the traveling pump 13 sucks the hydraulic oil in the main pipeline 16 from the inlet / outlet 13b and discharges it from the inlet / outlet 13a to the main pipeline 15; This causes a circulation of hydraulic oil between the traveling pump 13 and the traveling motor 17 such as “traveling pump 13 → main pipeline 15 → traveling motor 17 → main conduit 16 → traveling pump 13”. When the traveling motor 17 is driven by the discharged oil, the wheel loader 1 moves forward. On the contrary, when the variable mechanism portion 14 is tilted in the B direction from the neutral angle, the traveling pump 13 sucks the hydraulic oil in the main pipe line 15 from the inlet / outlet port 13a and enters the main pipe line 16 from the inlet / outlet port 13b. As a result, the hydraulic oil circulates between the traveling pump 13 and the traveling motor 17 as “traveling pump 13 → main pipeline 16 → traveling motor 17 → main conduit 15 → traveling pump 13”. When the traveling motor 17 is driven by the oil discharged from the traveling pump 13, the wheel loader 1 moves backward.

  The regulator 20 includes a servo piston 21 having a pair of pressure receiving portions 22 and 23 that receive the tilt control pressure, a pair of tilt control pressure chambers 24 and 25 that introduce the tilt control pressure, and a neutral position of the servo piston 21. And a pair of return springs 26 and 27 that define a position (position shown in FIG. 2). When the servo piston 21 is in the neutral position, the tilt of the variable mechanism portion 14 of the traveling pump 13 is controlled to a neutral angle, and the servo piston 21 is displaced in the F direction from the neutral position, whereby the variable mechanism portion of the traveling pump 13 is. The tilt angle of 14 changes from the neutral angle to the F direction (forward direction), and the servo piston 21 is displaced from the neutral position in the B direction, whereby the tilt angle of the variable mechanism portion 14 of the traveling pump 13 is changed from the neutral angle. It changes in the B direction (backward direction).

  The HST circuit 11 further includes a charge pump 31 composed of a constant displacement hydraulic pump driven by the diesel engine 12, a relief valve 32 that regulates the discharge pressure of the charge pump 31, and a tilt that drives the servo piston 21 of the regulator 20. A tilt control pressure generating unit 33 that generates the roll control pressure using the discharge pressure of the charge pump 31 as a primary pressure, and the direction of the tilt control pressure supplied from the tilt control pressure generating unit 33 to the regulator 20 is controlled. And a traveling control valve 34 (direction control valve).

  The control valve 34 is an electromagnetic spring center type three-position valve, and can switch the valve position to a neutral position 35, a first operating position 36, and a second operating position 37.

  The neutral position 35 is a valve position that controls the tilt angle of the variable mechanism 14 of the traveling pump 13 to a neutral angle. More specifically, both the tilt control pressure chamber 24 (the pressure receiving portion 22 side of the servo piston 21) of the regulator 20 and the tilt control pressure chamber 25 (the pressure receiving portion 23 side of the servo piston 21) communicate with the hydraulic oil tank 38. This is the valve position for controlling the servo piston 21 to the neutral position, thereby controlling the tilt angle of the variable mechanism portion 14 of the traveling pump 13 to the neutral angle.

  The first operating position 36 is a valve position for controlling the tilt angle of the variable mechanism portion 14 of the traveling pump 13 from the neutral angle to the F direction (direction corresponding to the forward movement of the wheel loader 1). More specifically, the tilt control pressure from the tilt control pressure generating portion 33 is guided to one tilt control pressure chamber 24, and the other tilt control pressure chamber 25 is communicated with the hydraulic oil tank 38, so that the servo piston 21 is a valve position in which 21 is displaced from the neutral position in the F direction, thereby changing the tilt angle of the variable mechanism portion 14 of the traveling pump 13 from the neutral angle to the F direction.

  The second operating position 37 is a valve position that controls the tilt angle of the variable mechanism portion 14 of the traveling pump 13 from the neutral angle to the B direction (the direction corresponding to the backward movement of the wheel loader 1). More specifically, the tilt control pressure from the tilt control pressure generator 33 is guided to the other tilt control pressure chamber 25, and the one tilt control pressure chamber 24 is communicated with the hydraulic oil tank 38, so that the servo piston. 21 is a valve position where 21 is displaced from the neutral position in the B direction, thereby changing the tilt angle of the variable mechanism portion 14 of the traveling pump 13 from the neutral angle to the B direction.

  The HST circuit 11 further includes a charge circuit 40 that replenishes hydraulic oil that circulates between the traveling pump 13 and the traveling motor 80. The charge circuit 40 includes the above-described charge pump 31, a check valve 41 that guides the discharge oil of the charge pump 31 to the main line 15, and a check valve 42 that guides the discharge oil of the charge pump 31 to the main line 16. .

  The HST circuit 11 further includes a cutoff valve 61. The cut-off valve 61 is a hydraulic pilot type two-position valve. The cut-off valve 61 has a valve body 62, an initial position 64 (the valve position on the left side in FIG. 2) and a starting pressure (minimum pilot pressure required for operation) of the valve body 62. A return spring 63 to be defined, and a first pilot port 66 and a second pilot port 67 for introducing a pilot pressure acting on the valve body 62 are provided. The valve body 62 includes a first pressure receiving portion 68 to which the pilot pressure introduced from the first pilot port 66 acts, and a second pressure receiving portion 69 to which the pilot pressure introduced from the second pilot port 67 acts. . Both the first and second pressure receiving portions 68 and 69 of the cut-off valve 61 are provided at positions where pilot pressure in a direction against the pressing direction of the valve body 62 by the return spring 63 acts.

  The pressure of the main line on the high pressure side of the main lines 15 and 16 is selected by the high pressure selection type shuttle valve 70 and guided to the first pilot port 66 of the cutoff valve 61. In addition, the discharge pressure of the charge pump 31 is guided to the second pilot port 67 of the cut-off valve 61. The pressure guided from the charge pump 31 to the second pilot port 67 can be adjusted by a pressure control valve 71 (detailed later). In other words, the cutoff valve 61 uses the pressure of the main line on the high pressure side of the main lines 15 and 16 and the discharge pressure of the charge pump 31 that has passed through the pressure control valve 71 as a pilot pressure. It comes to work.

  When the cutoff valve 61 is operated in a state where the valve position of the control valve 34 is controlled to the first operating position 36 or the second operating position 37, the valve body 62 of the cutoff valve 61 is moved to the initial position 64 (closed position). ) To the operating position 65 (open position), the difference between the pressure acting on the pressure receiving portion 22 and the pressure acting on the pressure receiving portion 23 in the servo piston 21 becomes smaller. The return spring 27 or the return spring 26 is displaced in the direction of the neutral position from the forward side position or the reverse side position. Thereby, the tilt angle of the variable mechanism part 14 of the traveling pump 13 approaches the neutral angle from the forward tilt angle or the reverse tilt angle, and as a result, the discharge flow rate of the travel pump 13 decreases.

  The hydraulic drive device 10 further includes a work pump 50 including a constant displacement hydraulic pump that is driven by the output of the diesel engine 12, and a lift arm cylinder 7a and a bucket cylinder 8a that are driven by oil discharged from the work pump 50. And a hydraulic control circuit 51 for the working device connected to a working main pipeline 52 extending from the working pump 50. The hydraulic control circuit 51 for the working device includes a lift arm control valve (not shown) provided between the lift arm cylinder 7a and the work pump 50, and between the work pump 50 and the bucket cylinder 8a. It includes a control valve (not shown) for the bucket provided interposed. The lift arm control valve operates in response to an operation of a lift arm operating device (not shown) provided in the cab 3, and the flow of pressure oil supplied from the work pump 50 to the lift arm cylinder 7a. That is, the operation direction of the lift arm 7 is controlled. The bucket control valve operates in response to an operation of a bucket operating device (not shown) provided in the cab 3, and the direction of the flow of pressure oil supplied from the work pump 50 to the bucket cylinder 8a, That is, the operation direction of the bucket 8 is controlled.

  Since the traveling pump 13 and the work pump 50 are driven by the same diesel engine 12, a forward / reverse switching lever device 100 described later and at least one of an operating device for a lift arm and an operating device for a bucket are provided. When operated at the same time, a so-called composite operation is performed in which the traveling motor 80 and at least one of the lift arm cylinder 7a and the bucket cylinder 8a operate in parallel.

  The hydraulic drive device 10 further includes an inching pedal 90 and an inching valve 91 that operates in a direction to decrease the tilt angle of the traveling pump 13 in accordance with an increase in the depression amount of the inching pedal 90. The inching pedal 90 is provided in the cab 3 and is operated by an operator. The inching valve 91 lowers the tilt control pressure by discharging part or all of the tilt control pressure to the hydraulic oil tank 38, and the tilt control pressure is increased as the amount of depression of the inching pedal 90 increases. It is designed to work down. When the tilt control pressure decreases due to the operation of the inching valve 91, the F-direction force that presses the pressure receiving portion 22 against the return spring 27 in the servo piston 21 or the pressure receiving portion 23 against the return spring 26 is pressed. The B direction force is reduced. As a result, the servo piston 21 is displaced from the forward side position or the reverse side position toward the neutral position, and accordingly, the tilt angle of the variable mechanism portion 14 of the traveling pump 13 is changed to the forward side tilt angle or the reverse side. As a result, the displacement angle of the traveling pump 13, that is, the discharge flow rate decreases.

  The inching valve 91 is activated when the output of the diesel engine 12 is preferentially assigned to the drive of the work device 6 rather than traveling, such as when the work device 6 lifts a load such as earth and sand and loads it on a dump truck. is there.

  The hydraulic drive device 10 further includes a forward / reverse switching lever device 100 which is a travel direction command means for commanding the travel direction of the wheel loader 1 and the pressure of one of the pair of main conduits 15, 16, that is, the main conduit The first pressure detector 101 that detects the pressure of 15 and outputs a pressure detection signal Sp1 (electric signal) corresponding to the pressure, and the other pressure of the pair of main pipes 15 and 16, that is, the main A second pressure detector 102 that detects the pressure in the pipe 16 and outputs a pressure detection signal Sp2 (electric signal) corresponding to the pressure, a command from the forward / reverse switching lever device 100, and a first pressure detection A controller 110 that performs a predetermined process related to traveling of the wheel loader 1 based on the pressure detected by the device 101 and the pressure detected by the second pressure detector 102. That.

  The forward / reverse switching lever device 100 is provided in the cab 3 and includes a forward position for commanding forward, a reverse position for commanding reverse, and a neutral position that commands neither forward nor reverse Is provided with an operation lever 100a that can be switched and outputs a command signal (electrical signal) corresponding to the position of the operation lever 100a. More specifically, the forward / reverse switching lever device 100 outputs a neutral command signal Sn when the operation lever 100a is in the neutral position, and a forward command signal Sf when the operation lever 100a is in the forward position. When the position is the reverse position, the reverse command signal Sb is output.

  The controller 110 is a microcomputer including a CPU, a ROM, and a RAM, and includes a tilt control unit 111, a brake pressure determination unit 112, and a pressure discharge control unit 113 set by a computer program.

  The tilt control means 111 receives the command signals (neutral command signal Sn, forward command signal Sf, reverse command signal Sb) output from the forward / reverse switching lever device 100, and controls the valve of the control valve 34 based on the command signals. The position is controlled. Specifically, the tilt control means 111 controls the valve position of the control valve 34 to the neutral position by not giving a control signal to the control valve 34 when the neutral command signal Sn is input, and the forward command signal Sf. Is input to the control valve 34 to control the valve position of the control valve 34 to the first operating position 36 (forward operating position), and the reverse command signal Sb is input. Gives a reverse control signal Cb to the control valve 34 to control the valve position of the control valve 34 to the second operating position 37 (backward operating position).

  The tilt control means 111, the tilt control pressure generator 33, the control valve 34, and the regulator 20 constitute a discharge direction control means in the present invention.

  The brake pressure determination means 112 includes a pressure detection signal Sp1 corresponding to the pressure detected by the first pressure detector 101, a pressure detection signal Sp2 corresponding to the pressure detected by the second pressure detector 102, and the front and rear Based on a travel command signal (forward command signal Sf or reverse command signal Sb) corresponding to the travel direction command from the forward / reverse switching lever device 100, the brake pressure is applied to one or the other of the pair of main pipelines 15 and 16. It is determined whether or not the above has occurred. In the first embodiment, one main pipeline 15 of the pair of main pipelines 15 and 16 becomes the discharge side of the traveling pump 13 when moving forward, and the other main pipeline 16 becomes the discharge side when moving backward. For this reason, the pressure of one main pipe line 15 is on the high pressure side when moving forward while no brake pressure is generated, but the pressure of the other main pipe line 16 is high when moving forward while the brake pressure is generated. On the side. On the other hand, the pressure of the other main pipe line 16 is on the high pressure side when the vehicle is traveling backward without brake pressure being generated, but the pressure of the one main line 15 is on the high pressure side when traveling backward with the brake pressure being generated. It becomes. That is, in the case where the brake pressure is not generated, the main line on the discharge side does not match the main line on the high pressure side. Therefore, the brake pressure determination means 112 is based on the pressure detected by the first pressure detector, the pressure detected by the second pressure detector, and the traveling direction command from the forward / reverse switching lever device 100. Thus, it is determined whether or not the brake pressure is generated in one or the other of the pair of main pipelines 15 and 16.

  The first pressure detector 101, the second pressure detector 102, and the brake pressure determination means 112 constitute a brake pressure detection means in the present invention.

  When the result of determination by the brake pressure determination unit 112 is a result that “brake pressure has been generated”, that is, when the brake pressure detection unit detects the generation of brake pressure, the pressure discharge control unit 113 is electromagnetic. By giving a control signal Cp to the pressure control valve 71, the pressure of the high-pressure side main pipeline required for the operation of the cutoff valve 61 is set higher than the pressure (brake pressure) of the high-pressure side main pipeline. The pressure control valve 71 is operated. The pressure discharge control means 113 determines the signal value of the control signal Cp based on the pressure detection signal indicating the pressure of the main line on the high pressure side of the pressure detection signal Sp1 or Sp2. The signal value of the control signal Cp determined by the pressure discharge control means 113 is such that the pressure of the high-pressure side main pipe required for the operation of the cutoff valve 61 is higher than the pressure (brake pressure) of the high-pressure side main pipe. Is a value that increases by the value of.

  Further, when the result of the determination by the brake pressure determination unit 112 is a result that “the brake pressure is not generated”, the pressure discharge control unit 113 does not apply the control signal Cp to the pressure control valve 71 to thereby reduce the pressure. The control valve 71 is not operated, that is, the pressure of the high-pressure side main pipeline required for the operation of the cut-off valve 61 is not set higher than the pressure of the high-pressure side main pipeline at that time. ing.

  The pressure control valve 71 is a valve capable of adjusting the discharge amount of the discharge pressure of the charge pump 31 to the hydraulic oil tank 38, for example, a proportional electromagnetic relief pressure reducing valve. Since the discharge pressure of the charge pump 31 is controlled to be constant by the relief valve 32, a part of the discharge pressure of the charge pump 31 guided to the second pilot port 67 of the cutoff valve 61 by the operation of the pressure control valve 71 or When all of the pressure is discharged, that is, when the pilot pressure acting on the second pressure receiving portion 69 of the valve body 62 of the cut-off valve 61 is reduced, the pressure of the main line on the high pressure side required for the operation of the cut-off valve 61 is increased. Will rise.

  The pressure control valve 71 and the pressure discharge control means 113 constitute an operating pressure control means in the present invention.

  The hydraulic drive apparatus 10 according to the first embodiment configured as described above operates as follows.

  When the wheel loader 1 is moved forward, the operation lever 100a of the forward / reverse switching lever device 100 is operated to the forward position, and accordingly, the forward / backward switching lever device 100 outputs a forward command signal Sf. The controller 110 inputs the forward command signal Sf, and in this controller 110, the discharge direction control means 111 gives a control signal Cf to the control valve 34, whereby the valve position of the control valve 34 is set to the first operating position 36 ( The forward operation position).

  Accordingly, the tilt control pressure is guided to the tilt control pressure chamber 24 of the regulator 20 through the control valve 34 with the valve position in the first operating position 36, and acts on the pressure receiving portion 22 of the servo piston 21. As a result, the servo piston 21 is displaced in the F direction against the return spring 27, whereby the tilt angle of the variable mechanism portion 14 of the traveling pump 13 is set to the forward tilt angle. As a result, the traveling pump 13 sucks the hydraulic oil in the main line 16 from the inlet / outlet 13b and discharges it from the inlet / outlet 13a to the main line 15, thereby "traveling pump 13 → main line 15 → traveling motor 17 → The circulation of the hydraulic oil called “main pipe line 16” occurs between the traveling pump 13 and the traveling motor 17, and the traveling motor 17 is driven by the oil discharged from the traveling pump 13, so that the wheel loader 1 starts moving forward. At this time, the main line on the high pressure side of the main lines 15 and 16 becomes the main line 15.

  Thus, in a state where the main pipe line 15 becomes the high-pressure side main pipe line, the first pressure detector 101 detects the pressure of the main pipe line 15 and outputs a pressure detection signal Sp1 corresponding to the pressure. The second pressure detector 102 detects the pressure in the main pipe line 16 and outputs a pressure detection signal Sp2 corresponding to the pressure. The controller 110 inputs these pressure detection signals Sp1 and Sp2, and the brake pressure determination means 112 in the controller 110 receives the forward command signal Sf from the forward / reverse switching lever device 100 and the first pressure detector 101. Based on the pressure detection signal Sp1 and the pressure detection signal Sp2 from the second pressure detector 102, it is determined that no brake pressure is generated. For this reason, the pressure discharge control means 113 in the controller 110 does not give the control signal Cp to the pressure control valve 71, and therefore, the discharge pressure of the charge pump 31 introduced into the second pilot port 67 of the cutoff valve 61. That is, the pilot pressure acting on the second pressure receiving portion 69 of the valve body 62 of the cut-off valve 61 is maintained at the pressure defined by the relief valve 32.

  When the wheel loader 1 is accelerated while moving forward, the load of the traveling motor 17 increases, and the discharge pressure of the traveling pump 13, that is, the pressure of the main line 15 increases. Along with this, the pressure by which the pressure of the main pipe line 15 presses the first pressure receiving portion 67 of the valve body 62 of the cutoff valve 61 and the discharge pressure of the charge pump 31 are the second pressure receiving portion 68 of the valve body 62. When the sum of the force and the force that presses exceeds the force that the return spring 63 presses the valve body 62, the cut-off valve 61 operates. As a result, the tilt control pressure decreases and the discharge flow rate of the travel pump 13 decreases, and as a result, the discharge pressure of the travel pump 13 presses the first pressure receiving portion 67 of the valve body 62 of the cutoff valve 61. And the discharge pressure of the traveling pump 13 until the sum of the discharge pressure of the charge pump 31 and the force pressing the second pressure receiving portion 68 of the valve body 62 becomes equal to the force of the return spring 63 pressing the valve body 62. descend. That is, the traction force of the wheel loader 1 is regulated by the operation of the cutoff valve 61.

  When decelerating the wheel loader 1 while moving forward, the amount of depression of the accelerator pedal 80 is decreased, the amount of depression of the inching pedal 90 is increased, or the operation lever 100a of the forward / reverse switching lever device 100 is neutralized from the forward position. Switching to the position is performed, and the discharge flow rate of the traveling pump 13 is reduced. At this time, the rotational speed of the traveling motor 17 is maintained higher than the rotational speed corresponding to the discharge flow rate of the traveling pump 13 by the inertial force acting on the traveling motor 17. As a result, the pressure of the hydraulic oil that returns from the traveling motor 17 to the traveling pump 13 through the main pipeline 16, that is, the return pressure rises, and this return pressure becomes a brake pressure against the rotation of the traveling motor 17. In a state where the brake pressure is generated, the main line 16 for returning the hydraulic oil from the traveling motor 17 to the traveling pump 13 among the pair of main lines 15 and 16 becomes a high-pressure side main line due to the brake pressure. .

  In this way, in the state where the main line 16 becomes a high-pressure side main line due to the brake pressure, the first pressure detector 101 detects the pressure in the main line 15 and a pressure detection signal corresponding to the pressure. Sp1 is output, and the second pressure detector 102 detects the pressure in the main pipe line 16, and outputs a pressure detection signal Sp2 corresponding to the pressure. The controller 110 inputs these pressure detection signals Sp1 and Sp2, and the brake pressure determination means 112 in the controller 110 receives the forward command signal Sf from the forward / reverse switching lever device 100 and the first pressure detector 101. Based on the pressure detection signal Sp1 and the pressure detection signal Sp2 from the second pressure detector 102, it is determined that the brake pressure has been generated.

  Accordingly, in the controller 110, the pressure discharge control means 113 determines a signal value according to the higher pressure indicated by the pressure detection signals Sp1 and Sp2, that is, the brake pressure, and the control signal Cp of this signal value is pressure-controlled. The valve 71 is given. As a result, the pressure control valve 71 increases the discharge amount of the discharge pressure of the charge pump 31 as the brake pressure increases. As a result, the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 is higher than the brake pressure. The value rises by a predetermined value.

  The operation of the hydraulic drive device 10 when the wheel loader 1 moves backward is that the operation lever 100a of the forward / reverse switching lever device 100 is operated to the reverse position, and the valve position of the control valve 34 is the second operating position 37 ( The operation position on the reverse side) is different from the forward direction in that the main line 15 of the pair of main lines 15 and 16 becomes the main line on the brake pressure side. Since the operation is the same as that of the hydraulic drive device 10 during forward movement, the description thereof is omitted.

  According to the first embodiment, the following effects can be obtained.

  In the first embodiment, the first pressure detector 101, the second pressure detector 102 and the brake pressure determining means 112 of the controller 110, that is, the brake pressure detecting means, When the generation of the brake pressure in one or the other of them is detected, the pressure discharge control means 113 of the controller 110 operates the pressure control valve 71 to guide it from the charge pump 31 to the second pilot port 67 of the cutoff valve 61. The pressure applied is reduced, and the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 is set higher than the brake pressure. Thereby, the operation of the cutoff valve 61 due to the brake pressure can be prevented when the traveling speed is reduced by the brake pressure. As a result, it is possible to prevent an unnecessary high pressure from being applied to the hydraulic device, and it is possible to prevent a sudden deceleration of the traveling speed and a deterioration in the operation feeling.

[Second Embodiment]
A second embodiment will be described with reference to FIG.

  The second embodiment does not include the first pressure detector 101, the second pressure detector 102, the brake pressure determination unit 112, and the pressure discharge control unit 113 in the first embodiment. Instead of these, the engine is provided with a rotation speed detector 201 that detects the rotation speed (rotation speed) of the diesel engine 12 and outputs a rotation speed detection signal Sr (electric signal) corresponding to the rotation speed. The signal Sr is input to the controller 110, and the controller 110 also includes a rotation speed determination unit 202 and a pressure discharge control unit that controls the pressure control valve 71 based on the determination result by the rotation speed determination unit 202. 203.

  The rotational speed determination means 202 is a means set by a computer program, and whether or not the rotational speed of the diesel engine 12 has decreased by a predetermined rotational speed or more based on the rotational speed detection signal Sr corresponding to the rotational speed of the diesel engine 12. This is a judgment. When the rotational speed of the diesel engine 12 decreases, the rotational speed of the traveling pump 13 decreases, so the discharge flow rate of the traveling pump 13 decreases. Accordingly, as described above, a brake pressure is generated in one or the other of the pair of main pipes 15 and 16. Therefore, the rotational speed determination means 202 indirectly detects the generation of the brake pressure by determining whether or not the rotational speed of the diesel engine 12 has decreased by a predetermined rotational speed or more. It should be noted that the predetermined rotational speed that is a determination criterion in the rotational speed determination means 202 is set with a value that exceeds the range in which the rotational speed decreases with normal work performed by the wheel loader.

  The rotation speed detector 201 and the rotation speed determination means 202 constitute the brake pressure detection means in the present invention.

  When the result of determination by the rotation speed determination means 202 is a result of “decrease by more than a predetermined rotation speed”, that is, when the brake pressure detection means detects the brake pressure, the pressure discharge control means 203 By giving the control signal Cp to the pressure control valve 71, the pressure is set so that the pressure of the high-pressure side main pipeline required for the operation of the cutoff valve 61 is set higher than the pressure (brake pressure) of the high-pressure side main pipeline. The control valve 71 is operated. In the second embodiment, the signal value of the control signal Cp is a predetermined constant value, which is higher than the maximum brake pressure that can be generated in the pair of main pipes 15 and 16 and required for the operation of the cutoff valve 61. For example, the pilot pressure that acts on the second pressure receiving portion 69 on the valve body 62 of the cutoff valve 61 is the lowest value (tank). Pressure).

  The pressure control valve 71 and the pressure discharge control means 203 constitute an operating pressure control means in the present invention.

  According to the second embodiment, the following effects can be obtained.

  In the second embodiment, the brake pressure is generated in one or the other of the pair of main pipes 15 and 16 by the rotation speed detector 201 and the rotation speed determination means 202 of the controller 110, that is, by the brake pressure detection means. Is indirectly detected based on a decrease in the rotational speed of the diesel engine 12 over a predetermined rotational speed, the pressure discharge control means 203 of the controller 110 operates the pressure control valve 71 to cut off from the charge pump 31. The pressure guided to the second pilot port 67 of the valve 61 is reduced, and the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 is set higher than the brake pressure. Thus, the operation of the cutoff valve 61 due to the brake pressure can be prevented only when the traveling speed is reduced by the brake pressure as the rotational speed of the diesel engine 12 decreases. As a result, it is possible to prevent an unnecessary high pressure from being applied to the hydraulic device, and it is possible to prevent a sudden deceleration of the traveling speed and a deterioration in the operation feeling.

  In the second embodiment, the rotational speed determination means 202 of the controller 110 detects the occurrence of brake pressure by determining whether or not the rotational speed of the diesel engine 12 has decreased by a predetermined rotational speed or more. The calculation process for performing the determination is simpler than the calculation process in the determination by the brake pressure determination unit 112 in the first embodiment, and only the rotational speed of the diesel engine 12 is necessary for the determination. It is less than in the case of the first embodiment (command of traveling direction, pressure of main pipes 15 and 16). That is, in the second embodiment, the computer program for detecting the occurrence of brake pressure can be made simpler than the first embodiment, and the number of detectors necessary for detecting the occurrence of brake pressure can be reduced. This can be less than in the first embodiment. In general, since the hydraulic drive device includes a rotation speed detector that detects the rotation speed of the diesel engine 12, the rotation speed detector can be used as the rotation speed detector 201.

[Third Embodiment]
The third embodiment does not include the first pressure detector 101, the second pressure detector 102, the brake pressure determination unit 112, and the pressure discharge control unit 113 in the first embodiment. Instead of this, a depression amount detection signal Sa output by the depression amount detector 81 of the accelerator pedal 80 is input to the controller 110. The controller 110 also includes a depression amount determination means 301 and the depression amount. Pressure discharge control means 302 for controlling the pressure control valve 71 based on the result of determination by the determination means 301.

  The depression amount determination means 301 is a means set by a computer program, and whether or not the depression amount of the accelerator pedal 80 has decreased by a predetermined depression amount or more based on the depression amount detection signal Sa corresponding to the depression amount of the accelerator pedal 80. By making this determination, it is indirectly determined whether or not the rotational speed of the diesel engine 12 has decreased by a predetermined rotational speed or more. When the rotational speed of the diesel engine 12 decreases as the amount of depression of the accelerator pedal 80 decreases, the rotational speed of the traveling pump 13 decreases, so the discharge flow rate of the traveling pump 13 decreases. Accordingly, as described above, a brake pressure is generated in one or the other of the pair of main pipes 15 and 16. Therefore, the depression amount determination means 301 indirectly detects the generation of the brake pressure by determining whether or not the depression amount of the accelerator pedal 80 has decreased by a predetermined depression amount or more. It should be noted that the predetermined depression amount used as a determination criterion in the depression amount determination unit 301 is a depression amount larger than the variation range of the depression amount due to vibration generated in the wheel loader during traveling, that is, a reduction in the depression amount due to the operator's intention. It is set with the intention of detecting this.

  The stepping amount detector 81 and the stepping amount determination means 301 constitute a brake pressure detection means in the present invention.

  When the determination result by the stepping amount determination unit 301 is a result of “decrease by more than a predetermined stepping amount”, that is, when the brake pressure detection unit detects the brake pressure, the pressure discharge control unit 302 By providing the control signal Cp to the pressure control valve 71, the pressure control valve is set so that the pressure of the high-pressure main line required for the operation of the cut-off valve 61 becomes higher than the pressure (brake pressure) of the high-pressure main line. 71 is operated. In the third embodiment, the signal value of the control signal Cp is a predetermined constant value, which is higher than the highest brake pressure that can be generated in the pair of main pipes 15 and 16 and required for the operation of the cutoff valve 61. For example, the pilot pressure that acts on the second pressure receiving portion 69 on the valve body 62 of the cutoff valve 61 is the lowest value (tank). Pressure).

  The pressure control valve 71 and the pressure discharge control means 302 constitute the operating pressure control means in the present invention.

  According to the third embodiment, the following effects can be obtained.

  In the third embodiment, the brake pressure is generated in one or the other of the pair of main pipes 15 and 16 by the depression amount detector 81 and the depression amount determination means 301 of the controller 110, that is, by the brake pressure detection means. Is indirectly detected based on the amount of depression of the accelerator pedal 80, the pressure discharge control means 302 of the controller 110 operates the pressure control valve 71, so that the second pilot port of the cut-off valve 61 from the charge pump 31 is operated. The pressure guided to 67 is reduced, and the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 is set higher than the brake pressure. Thus, the operation of the cutoff valve 61 due to the brake pressure can be prevented only when the traveling speed is reduced by the brake pressure as the rotational speed of the diesel engine 12 decreases. As a result, it is possible to prevent an unnecessary high pressure from being applied to the hydraulic device, and it is possible to prevent a sudden deceleration of the traveling speed and a deterioration in the operation feeling.

  In the third embodiment, the depression amount determination means 301 of the controller 110 detects the occurrence of brake pressure by determining whether or not the depression amount of the accelerator pedal 80 has decreased by a predetermined depression amount or more. The calculation process for performing the determination is simpler than the calculation process in the determination by the brake pressure determination unit 112 in the first embodiment, and only the amount of depression of the accelerator pedal 80 is necessary for the determination. It is less than in the case of the first embodiment (command of traveling direction, pressure of main pipes 15 and 16). That is, in the third embodiment, the computer program for detecting the occurrence of brake pressure can be made simpler than the first embodiment, and the number of detectors necessary for detecting the occurrence of brake pressure can be reduced. This can be less than in the first embodiment.

[Fourth Embodiment]
The fourth embodiment does not include the first pressure detector 101, the second pressure detector 102, the brake pressure determination unit 112, and the pressure discharge control unit 113 in the first embodiment. Instead of this, a depression amount detector 401 that detects the depression amount of the inching pedal 90 and outputs a depression amount detection signal Si corresponding to the depression amount is provided, and the depression amount detection signal Si is input to the controller 110. In addition, the controller 110 includes a depression amount determination unit 402 and a pressure discharge control unit 403 that controls the pressure control valve 71 based on the determination result by the depression amount determination unit 402.

  The depression amount determination means 402 is a means set by a computer program, and whether or not the depression amount of the inching pedal 90 has increased by a predetermined depression amount or more based on the depression amount detection signal Si corresponding to the depression amount of the inching pedal 90. This is a judgment. When the discharge flow rate of the traveling pump 13 decreases as the amount of depression of the inching pedal 90 increases, brake pressure is generated in one or the other of the pair of main pipes 15 and 16. Therefore, the depression amount determination means 402 indirectly detects the generation of the brake pressure by determining whether or not the depression amount of the inching pedal 90 has increased by a predetermined depression amount or more. It should be noted that the predetermined depression amount used as a determination criterion in the depression amount determination means 402 is a depression amount larger than the fluctuation range of the depression amount due to vibration generated in the wheel loader during traveling, that is, an increase in the depression amount due to the operator's intention. It is set with the intention of detecting this.

  The depression amount detector 401 and the depression amount determination means 402 constitute a brake pressure detection means in the present invention.

  The pressure discharge control unit 403 determines whether the determination result by the depression amount determination unit 402 is a result that “the predetermined depression amount has increased”, that is, when the brake pressure detection unit detects the brake pressure. By providing the control signal Cp to the pressure control valve 71, the pressure control valve is set so that the pressure of the high-pressure main line required for the operation of the cut-off valve 61 becomes higher than the pressure (brake pressure) of the high-pressure main line. 71 is operated. In the fourth embodiment, the signal value of the control signal Cp is a predetermined constant value, which is higher than the maximum brake pressure that can be generated in the pair of main pipes 15 and 16 and required for the operation of the cutoff valve 61. For example, the pilot pressure that acts on the second pressure receiving portion 69 on the valve body 62 of the cutoff valve 61 is the lowest value (tank). Pressure).

  The pressure control valve 71 and the pressure discharge control means 403 constitute an operating pressure control means in the present invention.

  According to the fourth embodiment, the following effects can be obtained.

  In the fourth embodiment, the brake pressure is generated in one or the other of the pair of main pipes 15 and 16 by the depression amount detector 401 and the depression amount determination means 402 of the controller 110, that is, by the brake pressure detection means. Is indirectly detected based on the depression amount of the inching pedal 90, the pressure discharge control means 403 of the controller 110 operates the pressure control valve 71, whereby the second pilot port of the cut-off valve 61 from the charge pump 31 is operated. The pressure guided to 67 is reduced, and the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 is set higher than the brake pressure. As a result, the operation of the cut-off valve 61 due to the brake pressure can be prevented only when the traveling speed is reduced by the brake pressure as the inching pedal 90 is depressed. As a result, it is possible to prevent an unnecessary high pressure from being applied to the hydraulic device, and it is possible to prevent a sudden deceleration of the traveling speed and a deterioration in the operation feeling.

  In the fourth embodiment, the depression amount determination means 402 of the controller 110 detects the occurrence of brake pressure by determining whether or not the depression amount of the inching pedal 90 has increased by a predetermined depression amount or more. The calculation process for performing the determination is simpler than the calculation process in the determination by the brake pressure determination unit 112 in the first embodiment, and only the amount of depression of the inching pedal 90 is necessary for the determination. It is less than in the case of the first embodiment (command of traveling direction, pressure of main pipes 15 and 16). That is, in the fourth embodiment, the computer program for detecting the occurrence of brake pressure can be made simpler than in the first embodiment, and the number of detectors necessary for detecting the occurrence of brake pressure can be reduced. This can be less than in the first embodiment.

[Fifth Embodiment]
The fifth embodiment does not include the first pressure detector 101, the second pressure detector 102, the brake pressure determination unit 112, and the pressure discharge control unit 113 in the first embodiment. Instead of these, the controller 110 determines whether or not the traveling direction command by the forward / reverse switching lever device 100 (traveling direction command means) has been switched from forward to neutral, and whether or not the backward direction has been switched to neutral. Command determining means 501 to perform, and pressure discharge control means 502 for controlling the pressure control valve 71 based on the result of determination by the command determining means 501.

  The command determination unit 501 is specifically a unit set by a computer program. The command signal from the forward / reverse switching lever device 100 receives the neutral command signal Sn from the state in which the controller 110 inputs the forward command signal Sf. The controller 110 determines whether or not the controller 110 has switched to a state in which the controller 110 has switched to the state in which the controller 110 has input the reverse command signal Sb to the state in which the neutral command signal Sn has been input.

  As the operating position of the operating lever 100a of the forward / reverse switching lever device 100 is switched from the forward position to the neutral position, the valve position of the control valve 34 is changed from the first operating position 36 (forward operating position) to the neutral position 35. And when the operating position of the operating lever 100a of the forward / reverse switching lever device 100 is switched from the reverse position to the neutral position, the valve position of the control valve 34 is changed to the second operating position 37 (reverse side). ), The tilt control pressure acting on the servo piston 21 is discharged to the hydraulic oil tank 38, so that the tilt angle of the variable mechanism portion 14 of the traveling pump 13 is increased. It becomes a neutral angle, that is, the discharge flow rate of the traveling pump 13 decreases to zero. Accordingly, a brake pressure is generated in one or the other of the pair of main pipelines 15 and 16. Therefore, the command determination unit 501 indirectly detects the generation of the brake pressure by determining whether or not the command in the traveling direction has been switched from forward to neutral and from reverse to neutral.

  The command determination means 501 is a brake pressure detection means in the present invention.

  The pressure discharge control unit 502 determines whether the result of determination by the command determination unit 501 is a result of “switching from forward to neutral” or a result of “switching from backward to neutral”, that is, braking. When the pressure detecting means detects the brake pressure, the control signal Cp is given to the electromagnetic pressure control valve 71 so that the pressure of the high-pressure main line required for the operation of the cut-off valve 61 is increased. The pressure control valve 71 is operated to be higher than the road pressure (brake pressure). In the fifth embodiment, the signal value of the control signal Cp is a predetermined constant value, which is higher than the highest brake pressure that can be generated in the pair of main pipes 15 and 16, and is higher than that required for the operation of the cutoff valve 61. For example, the pilot pressure that acts on the second pressure receiving portion 69 on the valve body 62 of the cutoff valve 61 is the lowest value (tank). Pressure).

  The pressure control valve 71 and the pressure discharge control means 502 constitute an operating pressure control means in the present invention.

  According to the fifth embodiment, the following effects can be obtained.

  In the fifth embodiment, the command determination means 501 (brake pressure detection means) of the controller 110 determines whether or not the brake pressure is generated in one or the other of the pair of main pipelines 15 and 16 by changing the forward / reverse switching lever device 100 ( Indirectly detected by detecting that the command from the travel command means) has been switched from forward to neutral, or that the command from the forward / reverse switching lever device 100 (travel command means) has been switched from forward to neutral. Then, the pressure discharge control means 502 of the controller 110 operates the pressure control valve 71 to reduce the pressure led from the charge pump 31 to the second pilot port 67 of the cut-off valve 61, and the operation of the cut-off valve 61. Is set higher than the brake pressure. As a result, when the command from the forward / reverse switching lever device 100 is switched from forward to neutral, or the command from the forward / backward switching lever device 100 is switched from reverse to neutral, the vehicle travels by brake pressure. The operation of the cutoff valve 61 due to the brake pressure can be prevented only when the speed is reduced. As a result, it is possible to prevent an unnecessary high pressure from being applied to the hydraulic device, and it is possible to prevent a sudden deceleration of the traveling speed and a deterioration in the operation feeling.

  In the first to fifth embodiments described above, the second pressure receiving portion 69 of the valve body 62 of the cutoff valve 61 is a position where a pilot pressure in a direction against the pressing direction of the valve body 62 by the return spring 63 acts. And the pressure control valve 71 increases the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 by reducing the pilot pressure acting on the second pressure receiving portion 69. However, the configuration for increasing the pressure of the main line on the high pressure side required for the operation of the cutoff valve 61 is not limited to this. Instead of this other configuration, a second pressure receiving portion 69 is provided at a position where the valve body 62 of the cut-off valve 61 is pressed in the same direction as the return spring 63, and a pilot pressure acting on the second pressure receiving portion 69 is provided. The pressure of the main line on the high pressure side required for the operation of the cut-off valve 61 may be increased by providing a pressure control valve for increasing the pressure.

  In the first to fifth embodiments described above, the pressure control valve 71 reduces the pilot pressure acting on the second pressure receiving portion 69 of the valve body 62 of the cut-off valve 61. The pilot pressure acting on the first pressure receiving portion 68 of 62 may be reduced.

  In the first to fifth embodiments described above, the high-pressure selective shuttle valve 70 is provided between the first pilot port 66 of the cutoff valve 61 and the main pipelines 15 and 16. Both the main pipelines 15 and 16 may be connected to the first pilot port 66 without providing the high-pressure selective shuttle valve 70.

  In the second and third embodiments, the cut-off valve 61 is operated by the brake pressure only when the traveling speed is reduced by the brake pressure as the rotational speed of the diesel engine 12 decreases. In the fourth embodiment, the operation of the cut-off valve 61 due to the brake pressure can be prevented only when the traveling speed is reduced by the brake pressure as the inching pedal 90 is depressed. In the fifth embodiment, the cut-off valve 61 based on the brake pressure is limited only to the case where the traveling speed is reduced by the brake pressure when the command from the forward / reverse switching lever device 100 is switched from reverse to neutral. However, the present invention is a combination of two or more of the second embodiment, the fourth embodiment, and the fifth embodiment. The third embodiment and the fourth embodiment and the fifth embodiment may be any two or more thereof.

1 Wheel loader (wheel-type work vehicle)
10 Hydraulic Drive 11 HST Circuit 12 Diesel Engine (Prime Motor)
13 Traveling pumps 15 and 16 Traveling main pipeline 17 Traveling motor 20 Regulator (discharge direction control means)
33 Tilt control pressure generator (discharge direction control means)
34 Control valve for travel (discharge direction control means)
61 Cut-off valve 71 Pressure control valve (working pressure control means)
80 Accelerator pedal 81 Depression amount detector (brake pressure detection means)
90 inching pedal 91 inching valve 100 forward / reverse switching lever device (traveling direction command means)
101 1st pressure detector (brake pressure detection means)
102 Second pressure detector (brake pressure detecting means)
111 Tilt control means (discharge direction control means)
112 Brake pressure determination means (brake pressure detection means)
113 Pressure discharge control means (working pressure control means)
201 Rotational speed detector (brake pressure detection means)
202 Rotational speed determination means (brake pressure detection means)
203 Pressure discharge control means (working pressure control means)
301 Depression amount determining means (brake pressure detecting means)
302 Pressure discharge control means (working pressure control means)
401 Depression amount detector (brake pressure detection means)
402 Depression amount determination means (brake pressure detection means)
403 Pressure discharge control means (working pressure control means)
501 Command determination means (brake pressure detection means)
502 Pressure discharge control means (working pressure control means)

Claims (7)

A travel comprising a prime mover, a variable displacement hydraulic pump capable of discharging pressure oil in two opposite directions, a drive pump driven by transmitting the output of the prime mover, and a hydraulic motor rotatable in two opposite directions A motor, a pair of main pipes that connect the travel pump and the travel motor to a closed circuit, travel direction command means for commanding the travel direction, and the travel direction command means based on the travel direction command The discharge direction control means for controlling the discharge direction of the traveling pump, and the pressure of the high-pressure side main conduit of the pair of main conduits is used as a pilot pressure to operate in a direction to reduce the displacement volume of the traveling pump. In a wheeled work vehicle comprising a cut-off valve,
Brake pressure detecting means for detecting the occurrence of brake pressure in one or the other of the pair of main pipes, and when the generation of brake pressure is detected by the brake pressure detecting means, A wheel-type work vehicle comprising: an operating pressure control means for setting a pressure of the main line on the high pressure side required for operation to be higher than a brake pressure. In the wheel type work vehicle according to claim 1,
The brake pressure detecting means includes a first pressure detector that detects the pressure of one of the pair of main pipes, and a second pressure detection that detects the pressure of the other of the pair of main pipes. And the pair of main pipes based on the pressure detected by the first pressure detector, the pressure detected by the second pressure detector, and the travel direction commanded by the travel direction command means And a brake pressure determining means for determining whether or not a brake pressure is generated on one or the other of the roads. In the wheel type work vehicle according to claim 1,
The wheel-type work vehicle, wherein the brake pressure detecting means detects that the number of revolutions of the prime mover is reduced by a predetermined number of revolutions or more as generation of brake pressure. In the wheel type work vehicle according to claim 3,
The brake pressure detecting means determines a rotational speed detector that detects the rotational speed of the prime mover and whether or not the rotational speed of the prime mover detected by the rotational speed detector has decreased by a predetermined rotational speed or more. A wheel-type work vehicle comprising: a rotation speed determination unit. In the wheel type work vehicle according to claim 3,
An accelerator pedal for commanding increase / decrease in the number of rotations of the prime mover according to the depression amount;
The brake pressure detecting means is configured to detect a depression amount detector that detects a depression amount of the accelerator pedal, and to determine whether or not the depression amount detected by the depression amount detector has decreased by a predetermined depression amount or more. And a stepping amount determining means for determining whether or not the rotational speed of the prime mover has decreased by more than the predetermined rotational speed. In the wheel type work vehicle according to claim 1,
An inching pedal, and an inching valve that operates in a direction to reduce the displacement of the traveling pump in accordance with an increase in the amount of depression of the inching pedal,
The brake pressure detecting means is configured to detect a depression amount detector that detects a depression amount of the inching pedal, and determine whether or not the depression amount detected by the depression amount detector has increased by a predetermined depression amount or more. And a stepping amount determining means for detecting the occurrence of brake pressure. In the wheel type work vehicle according to claim 1,
The travel direction command means selectively commands one of forward, reverse and neutral,
The discharge direction control means controls the discharge flow rate of the travel pump to zero when the travel direction command by the travel direction command means is neutral,
The brake pressure detection means, the travel direction command by the travel direction command means has been switched from forward to neutral, and the travel direction command by the travel direction command means has been switched from reverse to neutral, A wheeled work vehicle characterized by detecting the occurrence of brake pressure.

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