JP2005207499A - Hydraulic circuit of construction machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic circuit of a construction machine capable of preventing a rapid operation of an actuator for driving a motor capacity variable mechanism section in increasing the motor capacity. <P>SOLUTION: When a pressing force acting on a small diameter pressure receiving surface 24b becomes larger than a pressing force acting on a large diameter pressure receiving surface 24a, the motor capacity variable mechanism section 22 is driven by a piston 24 in the increasing direction of the motor capacity. A selector valve 50 comprises an initial position 51 for connecting a large diameter cylinder chamber 25 to a high pressure selection valve 37, a throttle position 52 for connecting the large diameter cylinder chamber 25 to a tank circuit 90 via a throttle 86, an intermediate position 53 for closing a large area side duct 39, a first pressure receiver 55 for receiving pressure selected by the high pressure selection valve 37 as a pilot pressure, a setting spring 54 for setting a working pressure, and a second pressure receiver 56 for receiving pressure between the large area side duct 39 and the throttle 86 from the same direction as that of energizing force of the setting spring 54. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a traveling hydraulic circuit for driving the wheels of a construction machine such as a wheel loader or a wheel excavator, the actuator is operated by the pressure on either the inflow side or the outflow side of the variable displacement hydraulic motor, The present invention relates to a hydraulic circuit of a construction machine that drives a motor capacity variable mechanism by this actuator.

  A traveling hydraulic circuit provided in a construction machine such as a wheel loader or a wheel excavator includes a variable displacement hydraulic motor and a main pump that discharges hydraulic oil supplied to the variable displacement hydraulic motor.

  The variable displacement hydraulic motor has a motor capacity varying mechanism that varies the motor flow rate per rotation (hereinafter referred to as “motor capacity”). This motor capacity variable mechanism unit increases or decreases the motor capacity by tilting a swash plate or a swash shaft (hereinafter referred to as “swash plate or the like”). This motor capacity variable mechanism is driven by an actuator that operates by receiving the higher pressure on the inflow side or the outflow side of the variable capacity hydraulic motor, that is, a motor tilt cylinder. This motor tilting cylinder has a pair of pressure receiving surfaces having different areas on both end faces, in other words, different diameters, that is, a large diameter pressure receiving surface and a small diameter pressure receiving surface, and is moved by pressure acting on these pressure receiving surfaces. The piston includes a large-diameter cylinder chamber in which the large-diameter side of the piston slides, and a small-diameter cylinder chamber in which the small-diameter side of the piston slides continuously with the large-diameter cylinder chamber.

  The swash plate or the like of the motor capacity variable mechanism section tilts in conjunction with the piston of the motor tilt cylinder, and thereby the motor capacity increases or decreases. In the conventional hydraulic circuit for traveling, when the piston moves to the large-diameter cylinder chamber side, the tilt angle of the swash plate or the like decreases and the motor capacity decreases. Conversely, when the piston moves to the small-diameter cylinder chamber side, The tilt angle of the plate or the like is increased and the motor capacity is increased.

  In addition, the conventional traveling hydraulic circuit includes a high pressure selection valve that selects and outputs the higher pressure on the inflow side or the outflow side of the variable displacement hydraulic motor, and a small diameter that connects the small diameter cylinder chamber to the high pressure selection valve. A side pipe and a large-diameter side pipe connected to the large-diameter cylinder chamber of the motor tilt cylinder are provided. The large-diameter side pipe line is provided with a switching valve that selectively connects the large-diameter cylinder chamber to the high-pressure selection valve and the hydraulic oil tank.

  The switching valve includes an initial position where the large-diameter cylinder chamber is connected to the hydraulic oil tank, an operating position where the large-diameter cylinder chamber is connected to the high pressure selection valve, and a pressure receiving portion that receives the pressure selected by the high pressure selection valve as a pilot pressure. And a setting spring for setting the pilot pressure (operating pressure) necessary for switching from the initial position to the operating position.

  In the conventional traveling hydraulic circuit configured as described above, a load is applied to the variable displacement hydraulic motor during acceleration or climbing, or a so-called break pressure is generated during deceleration. When either the inflow side or the outflow side of the variable displacement hydraulic motor becomes higher, the higher pressure on the inflow side or the outflow side of the variable displacement hydraulic motor is selected and output by the high pressure selection valve. The selected pressure is guided to the small-diameter cylinder chamber of the tilt cylinder for the motor through the small-diameter side pipe and is given to the small-diameter pressure receiving surface, and is also given to the pressure-receiving portion of the switching valve.

  In this way, when the pressure applied to the pressure receiving portion of the switching valve, that is, the pressure selected by the high pressure selection valve is smaller than the operating pressure of the switching valve, the switching valve is held at the initial position by the elastic force of the setting spring. Thus, the large-diameter cylinder chamber has a tank pressure. On the other hand, since the pressure selected by the high pressure selection valve is guided to the small diameter pressure receiving surface of the piston of the tilt cylinder for the motor, the piston is held at the limit position on the large cylinder chamber side, and accordingly, the variable for the motor is changed. The minimum tilt angle of the mechanism is maintained. As a result, the motor capacity is held at the minimum motor capacity. In this case, the motor rotation speed becomes higher than the flow rate of the hydraulic pressure supplied from the main pump, and, for example, high speed running is possible.

  When the pressure selected by the high pressure selection valve exceeds the operating pressure, the switching valve switches from the initial position to the operating position against the elastic force of the setting spring, and the large-diameter cylinder chamber turns the large-diameter side line and the switching valve. The pressure selected by the high pressure selection valve is applied to the large diameter pressure receiving surface of the piston. That is, the same pressure is applied to both of the pair of pressure receiving surfaces of the piston. At this time, in the piston, the pressing force applied to the large-diameter pressure receiving surface is larger than the pressing force applied to the small-diameter pressure receiving surface due to the area difference. As a result, the piston moves toward the small diameter cylinder chamber and stops at a position where the pressing force applied to the large diameter pressure receiving surface and the pressing force applied to the small diameter pressure receiving surface balance.

When the piston moves to the small-diameter cylinder chamber in this way, the tilt angle of the swash plate or the like of the motor capacity varying mechanism portion increases in conjunction with the movement of the piston, and the motor capacity increases. In this case, the driving torque of the motor increases with respect to the flow rate of the pressure oil supplied from the main pump, and for example, it is possible to climb a steep slope.
JP-A-2-261975 (FIG. 5)

  In the conventional traveling hydraulic circuit described above, when the higher pressure on the inflow side or the outflow side of the variable displacement hydraulic motor becomes equal to or higher than the operating pressure, the switching valve is activated and the large diameter of the motor tilt cylinder is increased. The state in which the cylinder chamber is connected to the hydraulic oil tank is switched to a state in which the cylinder chamber is connected to the high pressure selection valve. For this reason, the pressure applied to the large-diameter side pressure receiving surface of the tilt cylinder for motor suddenly increases, and the piston of the tilt cylinder for motor rapidly moves to the small-diameter cylinder chamber side. The tilt angle of the motor increases rapidly, and the motor capacity increases rapidly. As a result, there arises a problem that the rotational speed of the variable displacement hydraulic motor is abruptly lowered and the traveling operability is deteriorated.

  The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a hydraulic circuit for a construction machine that can prevent an abrupt operation of an actuator that drives a motor capacity variable mechanism section when the motor capacity is increased. Is to provide.

  In order to achieve the above-described object, the present invention provides a variable displacement hydraulic motor having a motor displacement variable mechanism that makes a motor displacement variable, and a main pump that discharges hydraulic fluid supplied to the variable displacement hydraulic motor. A high pressure selection valve that selects and outputs the higher pressure of the inflow side and the outflow side of the variable displacement hydraulic motor, and a pair of pressure receiving surfaces having different areas, and is applied to the pair of pressure receiving surfaces. An actuator that operates by the pressure applied to drive the motor capacity varying mechanism, and a small area side pipe that connects the pressure receiving surface side of the actuator that has a smaller area of the pair of pressure receiving surfaces to the high pressure selection valve A large-area side pipe connected to the larger pressure-receiving surface side of the pair of pressure-receiving surfaces of the actuator, and the large-area side pipe. In a hydraulic circuit of a construction machine including a switching valve that selectively connects the larger pressure receiving surface side of a rotor to the high pressure selection valve and a hydraulic oil tank, the pressing force acting on the smaller pressure receiving surface is The actuator and the motor capacity variable so that the motor capacity variable mechanism is driven in the direction of increasing the motor capacity by the operation of the actuator accompanying the increase in the pressing force acting on the larger pressure receiving surface. A mechanism portion is coupled, and the switching valve restricts the larger pressure-receiving surface side of the actuator to the high-pressure selection valve and the larger pressure-receiving surface side of the actuator to the hydraulic oil tank. The throttle position to be connected via the intermediate position, the intermediate position for closing the large area side pipe line, and the pressure selected by the high pressure selection valve as the pilot pressure. A first pressure receiving portion that receives the pressure, a setting spring that sets a magnitude of the pilot pressure necessary to switch to the throttle position, and a biasing force of the setting spring that applies a pressure between the large-area side pipe line and the throttle. And a second pressure receiving portion received from the same direction.

  In the present invention configured as described above, when the variable displacement hydraulic motor rotates, when a load is applied to the variable displacement hydraulic motor, or when brake pressure is generated during deceleration, the variable displacement hydraulic motor When either the inflow side or the outflow side becomes higher, the higher pressure on the inflow side or the outflow side of the variable displacement hydraulic motor is selected and output by the high pressure selection valve. This higher pressure is applied to the smaller pressure receiving surface of the actuator via the small area side conduit and also to the first pressure receiving portion of the switching valve.

  When the pressure applied to the first pressure receiving portion of the switching valve, that is, the pressing force by the pressure selected by the high pressure selection valve is lower than the biasing force of the setting spring, the switching valve is held at the initial position by the elastic force of the setting spring. Then, the larger pressure receiving surface side of the actuator is connected to the high pressure selection valve via the switching valve. That is, the same pressure is applied to both of the pair of pressure receiving surfaces of the actuator. At this time, since the pressing force applied to the pressure receiving surface having a larger area difference is larger than the pressing force applied to the smaller pressure receiving surface, the actuator is held at the limit position on the smaller pressure receiving surface. Thus, the motor capacity is kept at the minimum motor capacity.

  When the pressing force on the switching valve by the pressure selected by the high pressure selection valve becomes larger than the urging force of the setting spring, the valve position of the switching valve is switched to the throttle position via the intermediate position. At the intermediate position, the larger pressure-receiving surface side of the actuator is blocked, and the pressure at the time of blocking is held. Thereafter, the throttle position is reached, the larger pressure receiving surface side of the actuator is connected to the hydraulic oil tank via the large area side conduit and the switching valve, and only the smaller pressure receiving surface of the actuator is selected by the high pressure selection valve. Pressure is applied. At this time, the pressure on the larger pressure receiving surface side of the actuator is gradually reduced to the tank pressure by the throttle provided in the switching valve. For this reason, the actuator operates in the direction of gradually increasing the motor capacity while gradually pushing out the hydraulic oil on the larger pressure receiving surface side to the large area side conduit.

  In addition, while the hydraulic oil is being discharged to the hydraulic oil tank through the throttle, the pressure between the large area side pipe and the throttle acts to return the switching valve to the intermediate position and the initial position. This also limits the moving speed of the actuator.

  As described above, in the present invention, while the actuator operates in the direction of increasing the motor capacity, the flow rate of the hydraulic oil discharged from the larger pressure receiving surface side of the actuator to the hydraulic oil tank is limited by the restriction of the switching valve. In addition, the switching valve operates between the throttle position and the intermediate position according to the pressure between the large-area side pipe line and the throttle, and is discharged from the larger pressure receiving surface side of the actuator to the hydraulic oil tank. Since the flow rate of the hydraulic oil is adjusted, it is possible to prevent a rapid operation of the actuator when the motor capacity is increased.

  As described above, according to the present invention, it is possible to prevent a rapid operation of the actuator when the motor capacity is increased. As a result, it is possible to prevent the rotational speed of the variable displacement hydraulic motor from rapidly decreasing, and to ensure good traveling operability.

  Hereinafter, an embodiment of a hydraulic circuit for a construction machine according to the present invention will be described with reference to the drawings.

  The present embodiment is intended for a construction machine that runs on wheels such as a wheel loader and a wheel excavator.

  1 is a travel hydraulic circuit diagram, FIG. 2 is a cross-sectional view of the switching valve 50 shown in FIG. 1, and FIG. 3 is a constant horsepower control curve and an engine horsepower curve of a variable displacement hydraulic pump 2 provided in this embodiment. FIG. 4 is a diagram showing the relationship between the driving pressure and the motor capacity during the constant pressure control of the variable displacement hydraulic motor 19 provided in the present embodiment.

  As shown in FIG. 1, the traveling hydraulic circuit 1 includes a variable displacement hydraulic motor 19 connected to a wheel (not shown) and a main pump 2 driven by an engine (not shown).

  The main pump 2 is a variable displacement hydraulic pump for both tilts, and has a pump displacement variable mechanism 3 that makes the displacement of the pump 2 (hereinafter also referred to as “pump displacement”) variable. The variable pump capacity mechanism 3 increases or decreases the pump capacity by tilting a swash plate or the like. The pump displacement variable mechanism 3 is driven by a pump tilt cylinder 5 that operates by receiving the discharge pressure from the constant displacement hydraulic pump 4. The tilting cylinder 5 for pump has a pair of pressure receiving surfaces 6a and 6b having the same area on both end surfaces, and a piston 6 that moves by pressure acting on the pair of pressure receiving surfaces 6a and 6b, and the piston 6 slides. It has a cylinder chamber 7 that can be arranged, and a pair of return springs 8 and 9 that urge the piston 6 toward the neutral position.

  The pump tilting cylinder 5 is connected to a forward / reverse direction switching valve 10 on both sides of the pair of pressure receiving surfaces 6a, 6b of the piston 6. The direction switching valve 10 is a mechanical direction switching valve mechanically connected to an operation lever 11 that instructs forward or reverse. The direction switching valve 10 is hydraulic fluid discharged from the constant displacement hydraulic pump 4. It controls the direction of flow. In addition, the direction switching valve 10 includes a first position 10a that connects the constant displacement hydraulic pump 4 to one side of the pump tilt cylinder 5 and the other side to the hydraulic oil tank 30, and a constant displacement hydraulic pressure. A second position 10b is connected from the pump 4 to the other side of the pump tilt cylinder 5 and one side is connected to the hydraulic oil tank 30, and a neutral position where both sides of the pump tilt cylinder 5 are connected to the hydraulic oil tank 30. 10c and a pair of return springs 10d and 10e for urging the spool in the neutral position 10c direction.

  A pressure reducing valve 12 for reducing the discharge pressure of the constant capacity hydraulic pump 4 is provided between the constant capacity hydraulic pump 4 and the direction switching valve 10. An operation pedal 13 is connected to the pressure reducing valve 12, and a pilot pressure for driving the piston 6 of the pump tilting cylinder 5 is output in accordance with the depression amount of the operation pedal 13.

  Restrictions 16 and 17 are provided in each of the pair of pipes 14 and 15 that connect the direction switching valve 10 and both sides of the pump tilt cylinder 6. These throttles 16 and 17 are used for abrupt changes in pressure acting on the piston 6 of the tilting cylinder 5 for pump, in other words, rapid movement of the piston 6, and in other words, tilt angles of the pump displacement variable mechanism section 3. It is provided in order to prevent sudden changes.

  The variable displacement hydraulic motor 19 is connected to the main pump 2 in a closed circuit via a pair of pipes, that is, first and second pipes 20 and 21. The variable displacement hydraulic motor 19 has a motor displacement variable mechanism 22 that makes the motor displacement variable. The motor capacity varying mechanism 22 increases or decreases the motor capacity by tilting a swash plate or the like. The motor capacity varying mechanism 22 is driven by an actuator that operates by receiving the higher pressure on the inflow side or the outflow side of the variable capacity hydraulic motor 19, that is, the motor tilt cylinder 23. is there. The motor tilting cylinder 23 has a pair of pressure receiving surfaces having different areas, in other words, different diameters, that is, a large diameter pressure receiving surface 24a and a small diameter pressure receiving surface 24b, and acts on these pressure receiving surfaces 24a and 24b. A piston 24 that is moved by the pressure applied, a large-diameter cylinder chamber 25 in which the large-diameter side of the piston 24 slides, and a small-diameter cylinder chamber 26 that is continuous with the large-diameter cylinder chamber 25 and in which the small-diameter side of the piston 24 slides. Yes.

  Further, in the present embodiment, the high pressure selection valve 37 that selects and outputs the higher one of the inflow side pressure and the outflow side pressure of the variable displacement hydraulic motor 19, and the small diameter cylinder chamber of the motor tilt cylinder 23. 26 is provided with a small-diameter side pipe line 38 for connecting 26 to the high-pressure selection valve 37, and a large-diameter side pipe line 39 connected to the large-diameter cylinder chamber 25. The large diameter side pipe line 39 is provided with a switching valve 50 for selectively connecting the large diameter cylinder chamber 25 to the high pressure selection valve 37 and the tank circuit 90.

  In particular, in the present embodiment, the motor displacement variable mechanism 22 is caused by the movement of the piston 24 due to the pressing force acting on the small diameter pressure receiving surface 24b of the piston 24 becoming larger than the pressing force acting on the large diameter pressure receiving surface 24a. The piston 24 and the motor capacity variable mechanism 22 are connected so as to drive in the direction of increasing the motor capacity. That is, as the piston 24 moves to the small-diameter cylinder chamber 26 side, the tilt angle of the swash plate or the like of the motor capacity variable mechanism portion 22 decreases, and the motor capacity decreases. Along with the movement to the cylinder chamber side 25, the tilt angle of the swash plate or the like is increased and the motor capacity is increased.

  Further, particularly in the present embodiment, the switching valve 50 includes the initial position 51 where the high-diameter cylinder chamber 25 of the motor tilt cylinder 23 is connected to the high-pressure selection valve 37, and the large-diameter cylinder chamber 25 via the throttle 86. A throttle position 52 connected to the circuit 90 and an intermediate position 53 for closing the large diameter side pipe 39 are provided.

  The switching valve 50 includes a first pressure receiving portion 55 that receives a pressure selected by the high pressure selection valve 37 as a pilot pressure for switching from the initial position 51 to the throttle position 52, and a switch from the initial position 51 to the throttle position 52. A setting spring 54 that sets the magnitude of the pilot pressure (operating pressure) necessary for the change, and a second pressure receiving pressure that receives the pressure between the large-diameter side conduit 39 and the throttle 86 in the same direction as the urging force of the setting spring 54. A portion 56 is provided.

  Here, the structure of the switching valve 50 will be described with reference to FIG.

  As shown in FIG. 2, the switching valve 50 includes a spool 60 and a spool chamber 70 in which the spool 60 slides. The spool 60 is a member having a cylindrical shape as a basic shape, and includes a large-diameter sliding portion 61, a small-diameter sliding portion 62 having a smaller diameter than the large-diameter sliding portion 61, a large-diameter sliding portion 61, and a small-diameter. It has a neck portion 63 that is provided between the sliding portion 62 and has a diameter smaller than that of the small diameter sliding portion 62. The large diameter sliding portion 61, the small diameter sliding portion 61, and the neck portion 63 are integrally formed. Is. The spool chamber 70 includes a large-diameter sliding chamber 71 in which the large-diameter sliding portion 61 slides and a small-diameter sliding chamber 72 in which the small-diameter sliding portion 62 slides.

  The space surrounded by the one end surface 61a of the large-diameter sliding portion 61, the outer peripheral surface of the neck portion 63, and the one end surface 71a of the large-diameter sliding chamber 71 is filled with hydraulic oil introduced by the high-pressure selection valve 37. Port portion 80 is provided. The first pressure receiving surface 55 is a part of one end surface 61 a of the large diameter sliding portion 61 facing the first port portion 80, and the pressure receiving area is a circle obtained from the diameter of the large diameter sliding portion 61. This is the difference between the area and the area of the circle determined from the inner diameter of the small-diameter sliding chamber 72. (Almost equivalent to the difference between the cross-sectional area of the large-diameter sliding portion 61 and the cross-sectional area of the small-diameter sliding portion 62) The other end surface 71b of the large-diameter sliding chamber 71 and the other end surface 61b of the large-diameter sliding portion 61 The setting spring 54 is disposed between them.

  The small-diameter sliding chamber 72 is provided with a second port portion 81 connected to the large-diameter cylinder chamber 25 via the large-diameter side conduit 39. The second port portion 81 is configured to wrap the small diameter sliding portion 62 of the spool 60. An oil passage 82 is formed between the wall surface of the small diameter sliding chamber 72 and the neck portion 63.

  The spool 60 includes a first oil passage 84 that penetrates the spool 60 in the axial direction, and a second oil passage 85 that is continuous with the first oil passage 84 and penetrates the spool 60 in the radial direction. The throttle 86 is provided at one end of the first oil passage 84. The first oil passage 84 is communicated with the tank port portion 87 via the throttle 86.

  Further, the other end of the first oil passage 84 is open to the sliding hole 88. A rod 89 is provided in the sliding hole 88, and the spool 60 is slidable with respect to the rod 89. The second pressure receiving portion 56 is a pressure receiving portion of the sliding hole 88.

  Further, in the present embodiment, as shown in FIG. 3, the main pump 2 is controlled according to the horsepower constant control curve 41 set in a range not exceeding the engine horsepower curve 40, that is, the horsepower constant control is performed. . In this constant horsepower control, the maximum discharge flow rate Qp = Qpmax can be obtained when the state of the main pump 2 is the discharge pressure Pp = P. Therefore, by making the pressures of the first pipe line 20 and the second pipe line 21 connecting the variable displacement hydraulic motor 19 and the main pump 2 near P, the variable displacement hydraulic pressure can be effectively used while using the engine output effectively. The control range of the rotation speed and driving force of the motor 19 can be widened.

  Therefore, in the present embodiment, when the pressure applied to the small diameter pressure receiving surface 24b of the piston 24 of the motor tilt cylinder 23, that is, the load pressure applied to the variable displacement hydraulic motor 19 becomes higher than the discharge pressure P. The large diameter pressure receiving surface 24a and the small diameter pressure receiving surface of the piston 24 so that the piston 24 moves to the small diameter cylinder chamber 26 side when the piston 24 moves to the large diameter cylinder chamber 25 side and becomes lower than the discharge pressure P. Each area of 24b is set.

  The present embodiment configured as described above operates as follows.

<Drive of variable displacement hydraulic motor>
When the operator advances the construction machine, the operator first operates the operation lever 11 to switch the direction switching valve 10 from the neutral position 10c shown in FIG. 1 to the first position 10a. At this time, one side of the pump tilt cylinder 5 is connected to the pressure reducing valve 12 via the conduit 14 and the direction switching valve 10, and the other side is connected to the hydraulic oil tank 30 via the conduit 15 and the direction switching valve 10. Is done.

  Next, the operator depresses the operation pedal 13 to operate the pressure reducing valve 12. At this time, when the operation pedal 13 is fully depressed and the amount of depression reaches the maximum amount of depression, the pitoro pressure corresponding to the maximum amount of depression, that is, the maximum pilot pressure is output from the pressure reducing valve 12, and the direction switching valve 10 and the pipe line 14 are output. Is led to one side of the pump tilting cylinder 5. At this time, in the tilting cylinder 5 for the pump, since the maximum pilot pressure is applied to one pressure receiving surface 6a of the piston 6 with the other side connected to the hydraulic oil tank 30, the piston 6 is shown in FIG. It moves from the neutral position shown to the limit position in the right direction, and in conjunction with this, the tilt angle of the pump displacement variable mechanism section 3 becomes the maximum tilt angle. That is, the main pump 2 discharges the hydraulic oil having the discharge pressure P at the maximum discharge flow rate Qpmax.

  Then, the hydraulic oil discharged from the main pump 2 is guided by the first pipe 20 and flows into the variable displacement hydraulic motor 19, whereby the variable displacement hydraulic motor 19 is driven. The hydraulic fluid that has flowed out of the variable displacement hydraulic motor 19 returns to the main pump 2 via the second pipeline 21, is discharged from the main pump 2 to the first pipeline 20 again, and flows into the variable displacement hydraulic motor 19. . That is, the circulation of hydraulic oil is repeated between the main pump 2 and the variable displacement hydraulic motor 19, and the variable displacement hydraulic motor 19 continues to be driven. As a result, the wheels connected to the variable displacement hydraulic motor 19 are driven, and the construction machine moves forward.

<Constant pressure control>
When the variable displacement hydraulic motor 19 rotates, when a load is applied to the variable displacement hydraulic motor 19 or when a brake pressure is generated during deceleration, the inflow side and the outflow side of the variable displacement hydraulic motor 19 When any pressure increases, that is, when any pressure in the first pipe line 20 and the second pipe line 21 increases, the pressure in the first pipe line 20 and the second pipe line are increased by the high pressure selection valve 37. The higher one of the pressures in 21 is selected and output. The selected pressure is guided to the small-diameter cylinder chamber 26 of the motor tilt cylinder 24 via the small-diameter side pipe 38 and is given to the small-diameter pressure receiving surface 24b of the piston 24, and the first port of the switching valve 50 is provided. Guided to the portion 80 and applied to the first pressure receiving portion 55.

  When the pressure applied to the first pressure receiving portion of the switching valve 50, that is, the pressing force by the pressure selected by the high pressure selection valve 37 is smaller than the biasing force defined by the setting spring 54, the spool 60 of the switching valve 50 is The initial position 51, that is, as shown in FIG. 2, is held at the limit position on the small-diameter sliding chamber 72 side.

  In this position, the second port portion 81 and the oil passage 82 communicate with each other, and the pressure selected by the high pressure selection valve 37 is applied to the first port portion 80, the oil passage 82, the second port portion 81, and the large-diameter side pipe. It is guided to the large-diameter cylinder chamber 25 of the motor tilt cylinder 23 via the path 39. As a result, the pressure selected by the high pressure selection valve 37 is applied to the large diameter pressure receiving surface 24a. That is, when the pressure selected by the high pressure selection valve 37 is smaller than the operating pressure of the switching valve 50 defined by the setting spring 54, both the large diameter pressure receiving surface 24a and the small diameter pressure receiving surface 24b of the piston 24 have the same size. Pressure is given.

  As described above, when the same pressure is applied to both the large-diameter pressure receiving surface 24a and the small-diameter pressure receiving surface 24b of the piston 24, the large-diameter pressure receiving surface 24a is given due to the area difference between the two pressure-receiving surfaces 24a and 24b. The pressing force is larger than the pressing force applied to the small diameter side pressure receiving surface 24b. Thereby, the piston 24 is held at the limit position on the small-diameter cylinder chamber 24b side, and accordingly, the swash plate and the like of the motor variable mechanism 22 are held at the minimum tilt angle. As a result, the motor capacity Qm = Qmmim (minimum motor capacity) is maintained.

  Further, for example, when the load applied to the variable displacement hydraulic motor 19 increases and the pressure selected by the high pressure selection valve 37 becomes equal to or higher than the operating pressure of the switching valve 50, the pressure applied to the first pressure receiving surface 55 of the spool 60 is increased. The pressing force that presses the spool 60 toward the large-diameter sliding chamber 71 is larger than the urging force of the setting spring 54. As a result, the spool 60 of the switching valve 50 moves from the initial position 51, that is, the limit position on the small-diameter sliding chamber 72 side, through the intermediate position 53 to the throttle position 52, for example, the limit position on the large-diameter sliding chamber 71 side. .

  Furthermore, at the throttle position 52, the spool 60 has moved greatly in the left direction in the figure, so the second port 81 and the second oil passage 85 communicate with each other, and the large-diameter cylinder chamber 25 of the motor tilt cylinder 23 is The hydraulic oil tank 30 is connected via the output port portion 81, the second oil passage 85, the first oil passage 84, the throttle 86, the tank port 87, and the tank circuit 90. Along with this, the piston 24 moves to the large-diameter cylinder chamber 25 side while pushing out the hydraulic oil in the large-diameter cylinder chamber 25 by the pressure acting on the small-diameter pressure receiving surface 24b, and in conjunction with this, the motor capacity variable mechanism The tilt angle of the portion 22 is increased. As a result, the motor capacity Qm increases.

  In the present embodiment, the piston 24 and the switching valve 50 of the motor tilt cylinder 23 operate as described above, so that the variable displacement hydraulic pump 2 is driven with the discharge pressure Pp = P and the discharge flow rate Qp = Qpmax. 3, the discharge pressure P of the main pump 2 is set as the drive pressure Pm of the variable displacement hydraulic motor 19 and the drive pressure Pm = P is maintained as shown in a diagram portion 42a of the diagram 42 shown in FIG. The motor capacity Qm ranges from the minimum motor capacity Qmmin to the maximum motor capacity Qmmax according to the change in pressure selected by the high pressure selection valve 37, that is, according to the change in load pressure applied to the variable displacement hydraulic motor 19. It is controlled by. As a result, the driving force of the variable displacement hydraulic motor 19 is controlled according to the load.

  Further, at the intermediate position 53 of the switching valve 50 described above, the spool 60 shown in FIG. 2 moves to the left in the figure, the second port 81 and the oil passage 82 are shut off by the small-diameter sliding portion 62, and the second The port 81 and the second oil passage 85 are blocked. Therefore, the pressure in the large-diameter cylinder chamber 25 of the motor tilt cylinder 23 is maintained as it is at the time of interruption. For this reason, even if the pressure oil from the high pressure selection valve 37 is supplied only to the small-diameter cylinder chamber 26, the piston 24 does not rapidly move to the large tilt side. Further, while the switching valve 50 moves from the intermediate position 53 to the throttle position 52 where the maximum tilt angle is reached, the hydraulic oil pushed out from the large-diameter side cylinder chamber 25 to the large-diameter side conduit 39 is transferred to the switching valve 50. The flow rate discharged to the hydraulic oil tank 30 is restricted by the throttle 86. That is, the moving speed of the piston 24 toward the large-diameter cylinder chamber 25 during this period is limited.

  In addition, the pressure oil flowing out from the large-diameter cylinder chamber 25 is guided to the sliding hole 88 via the second port 81, the second oil passage 85, and the first oil passage 84 shown in FIG. A pressing force in the right direction in the figure is applied to the second pressure receiving portion 56 formed in the above. Therefore, the speed at which the spool 60 moves to the left in the figure is limited, and as a result, the speed at which the piston 24 moves to the large-diameter cylinder chamber 25 is further limited.

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

  In the present embodiment, the flow rate of the hydraulic oil discharged from the large-diameter cylinder chamber 25 to the hydraulic oil tank 30 is limited by the throttle 86 of the switching valve 50 while the piston 24 moves in the direction of increasing the motor capacity. In addition, the spool 60 of the switching valve 50 moves between the throttle position 52 and the intermediate position 53 in accordance with the pressure between the large area side pipe 39 and the throttle 86, so that the hydraulic oil tank is moved from the large diameter cylinder chamber 25. Since the flow rate of the hydraulic oil discharged to 30 is adjusted, rapid movement of the piston 24 when the motor capacity is increased can be prevented. Thereby, it is possible to prevent the rotational speed of the variable displacement hydraulic motor 19 from rapidly decreasing, and to ensure good traveling operability.

  In the present embodiment, the spool 60 of the switching valve 50 moves between the throttle position 52 and the intermediate position 53 in accordance with the pressure between the large area side conduit 39 and the throttle 86, so that the large-diameter cylinder chamber 25. The flow rate of the hydraulic oil discharged from the hydraulic oil tank 30 to the hydraulic oil tank 30 is adjusted. Thereby, the flow rate of the hydraulic oil discharged from the large-diameter cylinder chamber 25 to the hydraulic oil tank 30 can be effectively limited without making the throttle 86 extremely small. As a result, dust clogging with respect to the diaphragm 86 can be reduced.

  In the present embodiment, the variable displacement hydraulic motor 19 and the main pump 2 are connected in a closed circuit, but the present invention is not limited to this. That is, a directional switching valve may be interposed between the first and second pipelines 20 and 21 and the main pump 2 so that the suction side of the main pump 2 is connected to the hydraulic oil tank 30.

It is a hydraulic circuit diagram for driving. It is sectional drawing of the switching valve 50 shown in FIG. It is a PQ diagram which shows the relationship between the horsepower constant control curve and engine horsepower curve of the variable displacement hydraulic pump 2 provided in this embodiment. It is a diagram which shows the relationship between the drive pressure and the motor capacity | capacitance at the time of the fixed pressure control of the variable displacement hydraulic motor 19 with which this embodiment is equipped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic circuit for driving | running | working 2 Main pump 19 Variable displacement type hydraulic motor 22 Motor capacity variable mechanism part 23 Tilt cylinder (actuator) for motors
24 Piston 24a Large diameter pressure receiving surface (larger pressure receiving surface)
24b Small diameter pressure receiving surface (smaller pressure receiving surface)
25 Large-diameter cylinder chamber (larger pressure-receiving surface side)
26 Small-diameter cylinder chamber (smaller pressure-receiving surface side)
30 Hydraulic oil tank 37 High pressure selection valve 38 Small diameter side pipe (small area side pipe)
39 Large diameter side pipe (Large area side pipe)

Claims (1)

A variable displacement hydraulic motor having a motor displacement variable mechanism that makes the motor displacement variable; a main pump that discharges hydraulic fluid supplied to the variable displacement hydraulic motor; the inflow side of the variable displacement hydraulic motor; A high-pressure selection valve that selects and outputs the higher pressure on the outflow side, and a pair of pressure-receiving surfaces having different areas, and operates by the pressure applied to the pair of pressure-receiving surfaces. An actuator to be driven, a small-area side pipe connecting the pressure-receiving surface side of the pair of pressure-receiving surfaces of the actuator, which has a smaller area, to the high-pressure selection valve, and of the pair of pressure-receiving surfaces of the actuator A large-area side pipe connected to the larger pressure-receiving surface side, and the large-area side pipe connected to the larger pressure-receiving surface side of the actuator. In the hydraulic circuit for a construction machine and a switching valve for selectively connecting to a hydraulic oil tank and the high pressure selection valve,
Direction in which the motor capacity variable mechanism section increases the motor capacity due to the operation of the actuator due to the pressing force acting on the smaller pressure receiving surface becoming larger than the pressing force acting on the larger pressure receiving surface The actuator and the motor capacity variable mechanism unit are coupled to each other,
An initial position where the switching valve connects the larger pressure-receiving surface side of the actuator to the high-pressure selection valve, and a throttle that connects the larger pressure-receiving surface side of the actuator to the hydraulic oil tank via a throttle Position, an intermediate position for closing the large area side conduit, a first pressure receiving portion that receives a pressure selected by the high pressure selection valve as a pilot pressure, and a magnitude of the pilot pressure required to switch to the throttle position A hydraulic circuit for a construction machine, comprising: a setting spring for setting a height; and a second pressure receiving portion that receives a pressure between the large-area-side pipe line and the throttle in the same direction as an urging force of the setting spring. .

Images