JP2006336673A - Work vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a work vehicle capable of always supplementing a stable charge pressure oil to a closed circuit. <P>SOLUTION: A pressure oil from a variable displacement hydraulic pump 11 is fed to a charge valve 12 through a pressure-compensating valve 13. The charge pressure oil with a predetermined pressure or higher is always output from the charge valve 12 to a charge pressure oil passage 39. The charge pressure oil passage 39 is connected to the oil passages 31 and 32 of an HST circuit through check valves 23a and 23b. When a solenoid proportional valve 18 is controlled by a controller 30, a pilot pressure output from the solenoid proportional valve 18 is controlled to control a charged flow amount output from the charge valve 12. A charged flow amount required in the HST circuit can be supplemented from the charge pressure oil passage 39. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a work vehicle including a closed circuit that connects a hydraulic pump and a hydraulic motor driven by the hydraulic pump, and more particularly, to a work vehicle that can replenish charge pressure oil in the closed circuit.

  Conventionally, in work vehicles, a driving hydraulic pump, a working hydraulic pump, and the like are driven by a prime mover engine. The traveling motor is rotated by the pressure oil discharged from the traveling hydraulic pump to drive the drive wheels, thereby causing the vehicle to travel. Further, the working machine actuator is operated by the discharge hydraulic oil from the working hydraulic pump. This hydraulic circuit is known as an HST (Hydro Static Transmission) circuit and an HST circuit for work machines.

  In such a closed circuit, if the pressure oil is not charged in the closed circuit, the flow rate of the pressure oil in the closed circuit decreases due to the oil leaking from the hydraulic pump or the hydraulic motor.

  For this reason, it is assumed that the required amount of charge pressure oil can be charged in the closed circuit, using a work vehicle (see Patent Document 1) directly connected to the engine and provided with a charge pump, or a charge valve. There has been proposed a working machine (see Patent Document 2) that can charge a closed circuit using return pressure oil from an actuator as charge pressure oil.

  FIG. 5 shows an HST circuit diagram of a work vehicle described in Patent Document 1 as Prior Art 1 of the present invention. As shown in FIG. 5, the drive shaft of the engine 50 includes a variable displacement hydraulic pump 51 for traveling, a charge pump 55, a working machine hydraulic pressure that supplies pressure oil to the bucket cylinder 56 and the lift cylinder 57 of the front working machine. A hydraulic pump 61 used only for driving the pump 60 and the hydraulic motor 58 and a brake hydraulic pump 62 are connected.

  The traveling variable displacement hydraulic pump 51 and the variable displacement hydraulic motor 54 constitute a closed circuit as an HST circuit by a pair of main pipelines 52 and 53. The wheels 63 can be rotated by the rotation of the variable displacement hydraulic motor 54. When the pressure oil is discharged from the variable displacement hydraulic pump 51 to the main pipeline 52, if the wheel 63 rotates forward and the work vehicle moves forward, the pressure oil is supplied from the variable displacement hydraulic pump 51 to the main pipeline 53. By discharging, the wheel 63 can be rotated backward to move the work vehicle backward.

  The discharge pressure oil from the charge pump 55 can be replenished to the main pipelines 52 and 53 through the check valve 59 as charge pressure oil, respectively. When pressure oil is discharged from the variable displacement hydraulic pump 51 to the main pipeline 52 and the wheel 63 is rotating forward, the return hydraulic pressure from the variable displacement hydraulic motor 54 flows through the main pipeline 53 to form a low pressure circuit. When the oil pressure in the main line 53 becomes lower than the oil pressure on the upstream side of the check valve 59, the discharge pressure oil from the charge pump 55 can be replenished to the main line 53.

  Conversely, when pressure oil is discharged from the variable displacement hydraulic pump 51 to the main pipeline 53 and the wheel 63 rotates backward, the return hydraulic pressure from the variable displacement hydraulic motor 54 flows through the main pipeline 52 and the low pressure circuit. Become. When the oil pressure in the main line 52 becomes lower than the oil pressure on the upstream side of the check valve 59, the discharge pressure oil from the charge pump 55 can be replenished to the main line 52.

  FIG. 6 shows an HST circuit diagram of a working machine described in Patent Document 2 as the prior art 2 of the present invention. As shown in FIG. 6, the HST circuit 70 includes a variable displacement hydraulic pump 76 and a hydraulic motor 77 to form a closed circuit. A variable displacement hydraulic pump 76 and a hydraulic pump 71 are driven by an engine 81. The hydraulic oil discharged from the hydraulic pump 71 is supplied to the hydraulic power steering device 75 and the hydraulic cylinder 80 that moves the working device up and down.

  When hydraulic oil from the hydraulic pump 71 is supplied to the lift cylinder chamber 72 a via the hydraulic power steering device 75, return pressure is discharged from the non-lift cylinder chamber 72 b to the hydraulic oil supply / discharge passage 73. The return pressure oil discharged to the hydraulic oil supply / discharge path 73 can be replenished as charge pressure oil to the HST circuit 70 via the check valve 78.

  The charge pressure oil is controlled by the relief valve 79 so as to be in a predetermined pressure state. When the pressure in the low pressure circuit of the HST circuit 70 becomes lower than the pressure upstream of the check valve 78, that is, when the pressure in the low pressure circuit of the HST circuit 70 becomes lower than the pressure oil pressure in the hydraulic oil supply / discharge passage 73. The charge pressure oil can be replenished to the low pressure circuit through the check valve 78.

  Further, when the raising / lowering valve 74 is operated to the neutral position to stop the supply of the working oil to the raising / lowering cylinder chamber 72 a, the working oil discharged from the hydraulic pump 71 passes through the hydraulic power steering device 75 and then the raising / lowering valve 74. The charge pressure oil for the HST circuit 70 can be replenished as it is.

Therefore, while the hydraulic cylinder 80 is operating, the hydraulic cylinder 80 also functions as a charge pump for the HST circuit 70. For this reason, it is the structure which does not need to provide a charge pump separately.
JP 2001-173025 A JP 2004-332850 A

  In the work vehicle described in Patent Document 1, it is necessary to provide hydraulic pumps for traveling systems, working machines, charging, and the like. In addition, since each hydraulic pump is arranged in series with the drive shaft of the engine 50, there is a problem that the space is increased. In addition, the number of hydraulic pumps has increased, leading to an increase in manufacturing price.

  In the working machine described in Patent Document 2, it is not necessary to provide a charge pump by the lift valve 74. However, during the operation of the work implement, the charge pressure oil that is replenished to the HST circuit 70 is the return oil from the hydraulic power steering device 75 and the hydraulic cylinder 80 that has completed all operations. For this reason, the pump pressure of the hydraulic pump 71 is a pressure obtained by adding the relief pressure of the work implement and the relief pressure of the power steering to the pressure of the charge relief valve 79. Therefore, there arises a problem that the discharge pressure from the hydraulic pump 71 must be increased.

  An object of the present invention is to solve these problems and to provide a work vehicle that can always supply a stable charge pressure oil to a closed circuit.

The object of the present invention can be achieved by the inventions described in claims 1 to 3.
That is, according to the present invention, as described in claim 1, a closed circuit connecting a hydraulic pump and a hydraulic motor driven by the hydraulic pump, a variable displacement hydraulic pump, and pressure oil from the variable displacement hydraulic pump A load-sensitive control valve that supplies a plurality of actuators to each other, a charge valve that replenishes the closed circuit with pressure oil from the variable displacement hydraulic pump as charge pressure oil, An oil passage configured as a load-sensitive control valve, having one end connected to the charge valve and the other end branched and connected to the high-pressure circuit and the low-pressure circuit of the closed circuit, and the branch portion on the oil passage Each having a check valve disposed on the downstream side, and the main feature is that the low pressure circuit of the closed circuit is supplemented with charge pressure oil from the charge valve. .

  In the present invention, as described in claims 2 and 3, the main feature is that the configuration for operating the charge valve is specified.

  In the present invention, charge pressure oil can be supplemented to the closed circuit without providing a dedicated charge pump. Moreover, the pressure oil from the variable displacement hydraulic pump supplied to each actuator can be replenished directly as charge pressure oil via the charge valve. For this reason, like the working machine described in Patent Document 2, the pressure oil from the variable displacement hydraulic pump is always closed in a closed circuit without using the pressure oil after being used in the working machine. Can be replenished.

  As in claims 2 and 3 of the present application, the charge valve can be operated using an operating means operated based on a detection signal from a sensor for detecting the state of the work vehicle. Thereby, mode switching according to the vehicle state of the work vehicle becomes possible, and the replenishment efficiency of the charge pressure oil that replenishes the closed circuit can be improved.

Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. As the hydraulic circuit configuration in the work vehicle of the present invention, in addition to the shapes and arrangement configurations described below, those shapes and arrangement configurations are adopted as long as they can solve the problems of the present invention. It is something that can be done. For this reason, this invention is not limited to the Example demonstrated below, A various change is possible.
Moreover, as a closed circuit which can replenish charge pressure oil, it can apply with respect to various closed circuits used in work vehicles, such as an HST circuit.

  FIG. 1 is a hydraulic circuit diagram of a work vehicle according to an embodiment of the present invention. The hydraulic circuit includes a circuit for driving the two work machines 5 and 8 and a charge circuit for replenishing charge pressure oil to the HST circuit 1 and the HST circuit 1. Although the number of working machines disposed is not limited to two, in the illustrated example, the two working machines 5 and 8 are exemplarily shown.

  As the hydraulic pump, a variable displacement hydraulic pump 2 for the HST circuit and a variable displacement hydraulic pump 11 for the work machine and the charge circuit are disposed. Both of the two variable displacement hydraulic pumps 2 and 11 are rotationally driven by the drive shaft 4 a of the engine 4. The variable displacement hydraulic pump 2 and the variable displacement motor 3 are connected by oil passages 31 and 32 to form a closed circuit. The output from the variable displacement motor 3 is taken out by the output shaft 3a, and a wheel or the like (not shown) can be driven to rotate.

  The oil passages 31 and 32 are provided with pressure sensors 26a and 26b for detecting the pressure in the oil passage, respectively. The output shaft 3a is provided with a rotation sensor 27 that detects the rotation speed of the output shaft 3a. Detection signals from the pressure sensors 26 a and 26 b and the rotation sensor 27 are input to the controller 30.

  The pressure oil discharged from the variable displacement hydraulic pump 11 for the work machine and the charge circuit is supplied to the work machine 5 and the work machine 8 through the oil passage 33, the oil passage 34, and the like. Further, the pressure oil that has passed through the oil passage 37 branched from the oil passage 33 is supplied to the tilt cylinder 21 that controls the angle of the swash plate 20 in the variable displacement hydraulic pump 11. The pressure oil passing through the oil passage 37 is supplied to the switching valve 22 that controls the tilt cylinder 21, and is also supplied to the switching valve 22 as a pilot pressure for the switching valve 22.

  The work machine 5 is supplied with the discharge pressure oil from the variable displacement hydraulic pump 11 through the oil passage 33, the oil passage 34, and the pressure compensation valve 7 and the direction switching valve 6. The working machine 8 passes through an oil passage 34 from the oil passage 33 and an oil passage 34 b branched from the oil passage 34, and discharge pressure oil from the variable displacement hydraulic pump 11 passes through the pressure compensation valve 10 and the direction switching valve 9. Supplied. Further, the discharge pressure oil from the variable displacement hydraulic pump 11 is supplied to the charge valve 12 via the pressure compensation valve 13 through the oil passage 34 from the oil passage 33 and the oil passage 34d branched from the oil passage 34. .

  The oil passage 33 sets the maximum pressure value of the pressure oil that can be supplied to the pressure compensating valves 7, 10, 13 by the relief valve 16. The oil passage 34 branched from the oil passage 33 is connected to the electromagnetic proportional valve 18. The electromagnetic proportional valve 18 is switched and controlled by a control signal from the controller 30, and the pressure oil output from the electromagnetic proportional valve 18 is supplied to the charge valve 12 as a pilot pressure.

  The pilot pressure output from the electromagnetic proportional valve 18 to the pilot pressure oil passage 46 can be continuously variably controlled in accordance with the control current value input from the controller 30 to the electromagnetic proportional valve 18. In addition, the charge valve 12 can be continuously switched by supplying a control current directly to the solenoid of the charge valve 12.

  The pressure compensation valve 7 has hydraulic pilot portions 7a to 7d. The downstream pressure of the direction switching valve 6 is supplied as a pilot pressure to the hydraulic pilot portion 7a. The pilot section 7b is supplied with the upstream pressure of the pressure compensation valve 7 as a pilot pressure through a pilot oil passage 34a branched from the oil passage 34. The pilot section 7c is supplied with the downstream pressure of the pressure compensation valve 7 as a pilot pressure. The highest pressure among the load pressure of the work machine 5, the load pressure of the work machine 6, and the output pressure from the charge valve 12 is supplied to the pilot unit 7d as a pilot pressure.

  The direction switching valve 6 can be switched to three positions (A) to (C) and has five ports 6a to 6e. The port 6 a is connected to the tank 24, and the port 6 b is connected to the output port of the pressure compensation valve 7. The port 6 c and the port 6 e are respectively connected to the hydraulic chambers in the actuator of the work machine 5. By switching the direction switching valve 6, the port 6c and the port 6e function as an output port for pressure oil to the actuator of the work machine 5 and a drain port for return oil from the actuator, respectively.

  The port 6 d communicates with the output port of the direction switching valve 6 that supplies pressure oil to the work machine 5, and the load pressure in the work machine 5 can be taken out. The port 6d is connected to a pilot oil passage 47 communicating with the pilot portion 7a of the pressure compensation valve 7 and the check valve 46a.

  The direction switching valve 6 can switch the valve position to three positions (A) to (C) by operation control using a controller or an operation lever. At the position (A), the port 6 c is an output port for the actuator of the work machine 5, and the port 6 e is a drain port for return pressure oil from the actuator of the work machine 5. At this time, the port 6e communicates with the tank 24, and the port 6d communicates with the port 6c that is an output port.

  At the position (B), the port 6d is in communication with the tank 24, and the ports 6b, 6c, 6d are closed. At the position (C), the port 6 d is an output port for the actuator of the work machine 5, and the port 6 c is a drain port for return pressure oil from the actuator of the work machine 5. At this time, the port 6c communicates with the tank 24, and the port 6d communicates with the port 6d that is an output port.

  Next, the pressure compensation valve 10 has the same configuration as the two-port switching valve 6. That is, it has hydraulic pilot portions 10a to 10d. The hydraulic pilot unit 10a supplies the downstream pressure of the direction switching valve 9 as a pilot pressure. The pilot section 10b is supplied with the upstream pressure of the pressure compensation valve 10 as a pilot pressure through a pilot oil passage 34c connected to an oil passage 34b branched from the oil passage 34. The pilot section 10c is supplied with the downstream pressure of the pressure compensation valve 10 as a pilot pressure. The highest pressure among the load pressure of the work machine 5, the load pressure of the work machine 8, and the output pressure from the charge valve 12 is supplied to the pilot unit 10d as a pilot pressure.

  The direction switching valve 9 has the same configuration as the direction switching valve 6. That is, it can be switched to three positions (D) to (F), and has five ports 9a to 9e. The port 9 a is connected to the tank 24, and the port 9 b is connected to the output port of the pressure compensation valve 10. The port 9 c and the port 9 e are respectively connected to the hydraulic chambers in the actuator of the work machine 8. By switching the direction switching valve 9, the port 9c and the port 9e function as an output port for pressure oil to the actuator of the work machine 8 and a drain port for return oil from the actuator, respectively.

  The port 9 d communicates with the output port of the direction switching valve 9 that supplies pressure oil to the work machine 8, and can extract the load pressure in the work machine 8. The port 9d is connected to a pilot oil passage 48 communicating with the pilot portion 10a of the pressure compensation valve 10 and the check valve 46b.

  The direction switching valve 9 can switch the valve position to three positions (D) to (F) by operation control using a controller or an operation lever. At the position (D), the port 9 c is an output port for the actuator of the work machine 8, and the port 9 e is a drain port for return pressure oil from the actuator of the work machine 8. At this time, the port 9e communicates with the tank 24, and the port 9d communicates with the port 9c that is an output port.

  At the position (E), the port 9d is in communication with the tank 24, and the ports 9b, 9c, 9d are closed. At the position (F), the port 9 d is an output port for the actuator of the work machine 8, and the port 9 c is a drain port for return pressure oil from the actuator of the work machine 8. At this time, the port 9c communicates with the tank 24, and the port 9d communicates with the port 9d that is an output port.

  Furthermore, the pressure compensation valve 13 has the same configuration as the two-port switching valves 6 and 10. That is, it has hydraulic pilot parts 13a-13d. The downstream pressure of the charge valve 12 is supplied as a pilot pressure to the hydraulic pilot unit 13a. The pilot section 13 b is supplied with the upstream pressure of the pressure compensation valve 13 as a pilot pressure through a pilot oil path 34 e branched from the oil path 34. The pilot section 13c is supplied with the downstream pressure of the pressure compensation valve 13 as a pilot pressure. The highest pressure among the load pressure of the work machine 5, the load pressure of the work machine 8, and the output pressure from the charge valve 12 is supplied as a pilot pressure to the pilot unit 13d.

  The charge valve 12 can be switched to three positions (G), (H), and (I) and has three ports 12a to 12c. The charge valve 12 is switched to the three positions (G), (H), and (I) by the pilot pressure in which the discharge pressure oil from the variable displacement hydraulic pump 11 is controlled by the electromagnetic proportional valve 18. The port 12 a is connected to the output port of the pressure compensation valve 13. The port 12 b is connected to the charge pressure oil passage 39. The port 12c that communicates with the port 12b is connected to a pilot oil passage 49 that communicates with the pilot portion 13a of the pressure compensation valve 13 and the check valve 46c.

  The pilot oil passage 35 is connected to the check valves 46 a to 46 c, and the highest pressure among the load pressure of the work machine 5, the load pressure of the work machine 8 and the output pressure from the charge valve 12 is used as the pilot pressure. It can be taken out. The pilot oil passage 35 is connected to the pilot portions 7d, 10d, and 13d of the pressure compensation valves 7, 10, and 13, respectively. Moreover, it connects with the switching valve 22 as a pilot oil path with respect to the switching valve 22 which controls the tilt cylinder 21. FIG.

  The charge pressure oil output from the charge valve 12 is output to the charge pressure oil passage 39. The charge pressure oil passage 39 is bifurcated in the middle, and one of the branched oil passages 40 communicates with the oil passage 31 in the HST circuit 1 via the check valve 23a. The other branched oil passage 41 communicates with the oil passage 32 in the HST circuit 1 via the check valve 23b. The charge pressure oil passage 39 is provided with an oil temperature sensor 28 that detects the temperature of the charge pressure oil, that is, the temperature of the working pressure oil discharged from the variable displacement hydraulic pump 11. A detection signal from the oil temperature sensor 28 is input to the controller 30.

  When the pressure on the upstream side of the check valves 23a and 23b is higher than the pressure on the downstream side, the charge pressure oil from the charge pressure oil passage 39 can be replenished to the oil passage 31 or the oil passage 32. .

  For example, when the discharge pressure oil from the variable displacement hydraulic pump 2 is supplied to the variable displacement motor 3 through the oil passage 31, the oil passage 31 becomes a high pressure circuit and the oil passage 32 becomes a low pressure circuit. . At this time, when the pressure in the oil passage 32 on the low pressure circuit side becomes lower than the pressure in the charge pressure oil passage 39, the charge pressure oil is replenished from the charge pressure oil passage 39 to the oil passage 32 on the low pressure circuit side. become.

  The charge pressure oil passage 39 is connected to the tank 24 via the charge relief valve 14. The charge relief valve 14 controls the pressure in the charge pressure oil passage 39 so that it does not exceed the pressure specified by the charge relief valve 14.

  Next, the operation of the pressure compensation valves 7, 10 and 13, the direction switching valves 6 and 9 and the charge valve 12 will be described. Since the pressure compensation valves 7, 10, and 13 are configured to have the same configuration and the same action, the description of the pressure compensation valves 10 and 13 is omitted in the description of the pressure compensation valve 7 to be described below. To do.

  The pressure compensation valve 7 includes a pressure obtained by adding the discharge pressure from the variable displacement hydraulic pump 11 and the load pressure of the work machine 5 downstream of the direction switching valve 6, the pressure upstream of the direction control valve 6, and the pilot oil passage. The valve position is controlled to a position where the maximum load pressure is balanced among the load pressures at 35. As a result, the pressure difference before and after the direction switching valve 6 is controlled to be constant, and a flow rate proportional to the opening area of the direction switching valve 6 is supplied to the work implement. In the pressure compensation valve 13, the output pressure of the charge valve 12 is used instead of the load pressure of the work machine 5.

  Next, since the direction switching valve 6 and the direction switching valve 9 have the same configuration, the description of the direction switching valve 9 will be omitted in the description of the direction switching valve 6 to be described below. The direction switching valve 6 has three valve positions (A), (B: neutral position), and (C). Further, the valve position of the direction switching valve 6 is controlled by pilot signals 29a and 29b.

  For example, the valve position (A) can be the lowered position of the work machine 5, and the valve position (C) can be the raised position of the work machine 5. In addition, the valve position of the direction switching valve 6 changes continuously, and the opening area can also change continuously.

  As a pilot signal 29a for the direction switching valve 6, when the pilot pressure or the direction switching valve 6 is an electromagnetic direction control valve, when a current signal is input by operating the controller 30 or an operation lever, the input pilot signal According to 29a, the opening area of the direction switching valve 6 changes, and the direction switching valve 6 can be switched to the valve position (A). When the discharge pressure oil of the variable displacement hydraulic pump 11 is supplied from the port 6b, a flow rate corresponding to the opening area can be supplied from the port 6c to the actuator of the work machine 5.

  The return pressure oil from the actuator of the work machine 5 is discharged from the port 6e to the tank 24. At this time, since the port 6 c and the port 6 d are in communication with each other, the pressure downstream of the direction switching valve 6 is output to the pilot port 7 a of the pressure compensation valve 7 through the pilot oil passage 47.

  When the pilot signal 29b is input to the direction switching valve 6, the opening area of the direction switching valve 6 changes according to the input pilot signal 29b, and the direction switching valve 6 is switched to the valve position (C). be able to. When pilot signals 29a and 29b are not input to the direction switching valve 6, the direction switching valve 6 is positioned at the valve position (B) which is the neutral position.

  The charge valve 12 can be switched to three positions (G), (H), and (I). The charge valve 12 is controlled by the pilot pressure from the electromagnetic proportional valve 18. When the pilot pressure from the electromagnetic proportional valve 18 is not supplied, the charge valve 12 is positioned at the position (G), and the charge pressure oil of a predetermined pressure can be output to the charge pressure oil passage 39.

  When the pilot pressure from the electromagnetic proportional valve 18 becomes a little larger than the spring force acting on the charge valve 12, the charge valve 12 can be switched to the position (H) side. At this time, the output pressure output from the charge valve 12 is controlled according to the position where the pilot pressure from the electromagnetic proportional valve 18 and the spring force acting on the charge valve 12 are balanced. Further, when the pilot pressure from the electromagnetic proportional valve 18 becomes larger than the spring force acting on the charge valve 12, the charge valve 12 can be switched to the position (H) side. At this time, the pressure oil output from the pressure compensation valve 13 can be output as it is from the charge valve 12.

  The output pressure output from the charge valve 12 is supplied from the charge pressure oil passage 39 via the check valves 23a and 23b. Further, it is supplied as a source pressure of the check valve 46 c through the pilot oil passage 49. The highest pressure among the load pressures of the working machines 5 and 6 supplied as the original pressure of the check valves 46a and 46b and the output pressure from the charge valve 12 supplied as the original pressure of the check valve 46c, It is output to the pilot oil passage 35.

  The maximum load pressure in the pilot oil passage 35 acts on the switching valve 22 as a pilot pressure for the switching valve 22. The switching valve 22 is controlled to a position where the resultant pressure of the pilot pressure from the pilot oil passage 35 and the spring force acting on the switching valve 22 and the discharge pressure from the variable displacement hydraulic pump 11 are balanced.

  As shown in FIG. 1, by supplying pilot pressure from the pilot oil passage 35 to the switching valve 22, the position of the illustrated example for discharging the pressure oil from the oil chamber 21a of the tilt cylinder 21 and the oil chamber 21a It is possible to switch to a position where the discharge pressure from the variable displacement hydraulic pump 11 is supplied. When the switching valve 22 is in a position for discharging the pressure oil from the oil chamber 21 a of the tilting cylinder 21, the discharge amount from the variable displacement hydraulic pump 11 can be increased or decreased according to the load pressure in the oil passage 37.

  When the pilot pressure acting on the switching valve 22 from the oil passage 42 through the oil passage 37 becomes larger than the pilot pressure acting on the switching valve 22 from the pilot oil passage 35 and the spring force acting on the switching valve 2, the switching valve 22 (L) Switch to position. At this time, the pump flow rate from the oil passage 37 can be supplied to the oil chamber 21 a from the oil passage 43 through the oil passage 42 and the switching valve 22. Accordingly, the piston of the tilting cylinder 21 moves to the right in FIG. 1 and acts to reduce the capacity of the variable displacement hydraulic pump 11.

  When the pilot pressure acting on the switching valve 22 from the oil passage 42 through the oil passage 37 is smaller than the pilot pressure acting on the switching valve 22 from the pilot oil passage 35 and the spring force acting on the switching valve 2, the switching valve 22 switches to the (M) position. At this time, the oil chamber 21 a is connected to the tank 24 via the oil passage 43 and the switching valve 22. Accordingly, the piston of the tilting cylinder 21 moves to the left side in FIG. 1 and acts to increase the capacity of the variable displacement hydraulic pump 11.

  The flow rate output from the charge valve 12 will be described with reference to FIGS. 2 and 3 show examples of the shape of the spool in the charge valve 12. FIG. 2 shows a spool in which the opening area of the spool is switched in multiple stages, and FIG. 3 shows a spool in which the opening area is switched in a stepless manner.

  2 and 3, the positive direction on the vertical axis indicates the opening area of the charge valve 12, and the positive direction downward indicates the charge flow rate from the charge valve 12. The horizontal axis indicates the pilot pressure output from the electromagnetic proportional valve 18 or the current value supplied to the solenoid of the electromagnetic proportional valve 18.

  As shown in FIG. 2, the opening area of the charge valve 12 can be configured in multiple stages. Moreover, as shown in FIG. 3, the opening area of the charge valve 12 can be configured as a variable area that continuously changes.

  As shown in FIG. 2, when the vehicle state is mode M1, pilot pressure is not output from the electromagnetic proportional valve 18 shown in FIG. At this time, the opening area of the charge valve 12 is A1, and the charge flow rate is Q1. That is, the charge valve 12 is in the position (G) in FIG. 1, and a preset charge flow rate Q 1 can be output to the charge pressure oil passage 39.

  When the vehicle state is mode M2, the spool moves to a position where the pilot pressure output from the electromagnetic proportional valve 18 shown in FIG. 1 and the spring force acting on the charge valve 12 are balanced, and the charge valve 12 is in position (H). Thus, the opening area is A2. The charge flow rate at this time is Q2, and the charge flow rate Q2 is output to the charge pressure oil passage 39.

  As a result, in mode 2, the charge flow rate Q2 can be increased more than in mode M1, and the charge flow rate to be further supplemented to the HST circuit 1 can be increased.

  When the vehicle state is mode M3, the charge valve 12 is in the position (I) by the pilot pressure output from the electromagnetic proportional valve 18 shown in FIG. 1, and its opening area is A3. The charge flow rate at this time is Q3. A charge flow rate Q3 is output to the charge pressure oil passage 39.

  Accordingly, a large amount of charge flow rate Q3 can be output to the charge pressure oil passage 39 in the mode M3. In particular, when it is necessary to supply pressure oil to the HST circuit, such as when the work vehicle is moving forward in a heavy load state, the mode M3 can be set. Thereby, a large amount of charge flow can be replenished to the HST circuit 1.

  As shown in FIG. 3, the opening area of the charge valve 12 can be continuously variably controlled. At this time, the spool of the charge valve 12 is moved according to the pilot pressure output from the electromagnetic proportional valve 18 shown in FIG. 1 so that the opening area of the charge valve 12 is in the states of A1, A2, A3, for example. Can be controlled. By controlling the opening area of the charge valve 12 to be in the respective states A1, A2, and A3, the charge flow rate output from the charge valve 12 to the charge pressure oil passage 39 is controlled as Q1, Q2, and Q3. be able to.

Thereby, when the vehicle state is set to the modes M1 to M3, the charge flow rates Q1 to Q3 corresponding to the modes M1 to M3 can be output to the charge pressure oil passage 39.
In addition, the opening area of the charge valve 12 can be continuously changed by continuously changing and controlling the pressure oil from the electromagnetic proportional valve 18.
Explanation about each mode M1-M3 in a vehicle state shall be given in description of FIG. 4 mentioned later.

  The case where the pressure in the low pressure circuit of the HST circuit 1 is lower than the pressure of the charge pressure oil in the charge pressure oil passage 39 will be described. At this time, it is assumed that the discharge pressure from the variable displacement hydraulic pump 2 is supplied to the oil passage 31. When the pressure in the low pressure side oil passage 32 serving as a return circuit from the variable displacement hydraulic motor 3 becomes lower than the pressure in the charge pressure oil passage 39, the charge pressure oil is supplied to the oil passage 32 via the check valve 23b. To be replenished. Thereby, the shortage of pressure oil in the HST circuit 1 can be compensated. The remaining charge pressure oil that is not replenished flows into the tank 24 from the charge relief valve 14.

  Modes M1 to M3 can be selected based on conditions preset by the controller 30 according to the vehicle state of the work vehicle from the pressure sensors 26a and 26b, the rotation sensor 27, the oil temperature sensor 28, and the like. The relationship between the various sensors and the modes M1 to M3 can also be understood as a relationship as shown in FIG. Further, the relationship between the various sensors and the modes M1 to M3 can be appropriately set according to the use conditions of the work vehicle, the type of the work vehicle, and the like.

  The relationship between the vehicle state and the modes M1 to M3 will be described using a typical example with reference to FIG. The relationship between the vehicle state and the modes M1 to M3 shown in FIG. 4 is an exemplification, and can be appropriately set according to various work conditions, the type of work vehicle, and the like in an actual work vehicle.

  With respect to the detection signal from the rotation sensor 27 in FIG. 4, when the controller 30 determines that it is time to start running based on the detection signal, the mode M <b> 1 can be set to compensate for the torcross associated with running. Further, in the normal rotation region, as the mode M2, the charge flow rate can be made larger than that in the mode M1.

  When the controller 30 determines that the HST circuit 1 is in the normal load state based on the detection signals from the pressure sensors 26a and 26b, the mode M2 state can be set. In a heavy load state or a stall state that requires a large amount of charge pressure oil, the mode can be set to M3, and a large amount of charge flow can be replenished to the HST circuit 1.

  When the pressure oil of the working oil is in a low temperature state as detected by the oil temperature sensor 28, for example, when the engine is started in a cold region, the mode M1 can be set. When the temperature of the operating pressure oil becomes high, the mode is set to M3 from the viewpoint of lowering the temperature of the operating pressure oil, and a large amount of charge flow rate can be supplemented to the HST circuit 1.

  Thus, the charge flow rate required by the HST circuit 1 can be supplemented, and the charge flow rate can be supplemented without providing a charge pump. The charge flow rate can be set to an optimum flow rate according to the vehicle state of the work vehicle. For this reason, it is possible to efficiently replenish the charge flow rate without wastefully discharging the charge flow rate.

  Sensors for controlling the flow rate of charge pressure oil include: a rotation sensor that detects engine rotation, a pressure sensor that detects pressure oil pressure in a closed circuit, a pressure sensor that detects charge pressure oil pressure, and an operation Various sensors such as a temperature sensor that detects the temperature of the pressure oil and a speed sensor that detects the traveling speed of the work vehicle can be used.

  For example, the replenishment flow rate of the charge pressure oil can be controlled in order to eliminate the torque cross at the start of traveling by detecting the engine speed by the rotation sensor. In the case where the pressure sensor for detecting the pressure oil pressure in the closed circuit is provided in the closed circuit of the traveling system, for example, when the work vehicle is traveling in a heavy load state, the charge pressure It can be controlled to replenish a large amount of oil into the HST circuit.

  In the temperature sensor, for example, the flow rate of the charge pressure oil to be replenished in the closed circuit can be controlled according to the oil temperature state such as when the engine is started in a cold region or when the oil temperature is in a high temperature state. In addition, the flow rate of the charge pressure oil to be replenished to the closed circuit can be appropriately controlled according to detection signals from the respective sensors that detect the state of the work vehicle.

  Further, by variably operating the opening area of the charge valve 12, the mode switching according to the vehicle state of the work vehicle can be performed more finely. In addition, since the amount of charge pressure oil to be replenished to the closed circuit can be variably changed according to each mode, the replenishment efficiency of charge pressure oil to be replenished to the closed circuit can be further improved.

  Furthermore, it becomes unnecessary to provide a charge pump independently. For this reason, usually, a plurality of hydraulic pumps are arranged in the axial direction in a closed circuit. For this reason, since the dedicated charge pump becomes unnecessary, the space occupied by the charge pump can be shortened. Therefore, the space in the work vehicle can be secured, and the dedicated charge pump is not necessary, so that the pump cost can be reduced.

  The present invention can apply the technical idea of the present invention to an apparatus or the like to which the technical idea of the present invention can be applied.

It is a hydraulic circuit diagram. (Example) It is a figure which shows the relationship between the opening area of a charge valve, a charge flow rate, and the pilot pressure to a charge valve. (Example) FIG. 6 is a modified view showing the relationship between the opening area of the charge valve, the charge flow rate, and the pilot pressure to the charge valve. (It is a figure. (Example) It is a figure which shows the relationship between a vehicle state and the mode which prescribes | regulates a charge flow rate. (Example) It is a hydraulic circuit diagram. (Conventional example 1) It is a hydraulic circuit diagram. (Conventional example 2)

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... HST circuit, 2 ... Variable displacement type hydraulic pump, 3 ... Variable displacement type hydraulic motor, 5 ... Working machine, 6 ... Direction switching valve, 7 ... Pressure compensation valve, DESCRIPTION OF SYMBOLS 8 ... Work implement, 9 ... Direction switching valve, 10 ... Pressure compensation valve, 11 ... Variable displacement hydraulic pump, 12 ... Charge valve, 13 ... Pressure compensation valve, 18. .. Proportional solenoid valve, 26a, 26b ... Pressure switch, 27 ... Rotary switch, 28 ... Oil temperature sensor, 39 ... Charge pressure oil passage, 50 ... Engine, 51 ... Variable Displacement type hydraulic pump, 54 ... variable displacement type hydraulic motor, 55 ... charge pump, 58 ... hydraulic motor, 60 ... hydraulic pump for work implement, 61 ... hydraulic pump, 70 ... HST circuit, 71 ... hydraulic pump, 74 ... Lift valve, 75 ... hydraulic power steering apparatus, 76 ... variable displacement hydraulic pump, 77 ... hydraulic motor.

Claims (3)

A closed circuit connecting the hydraulic pump and a hydraulic motor driven by the hydraulic pump;
A variable displacement hydraulic pump;
A load-sensitive control valve that supplies pressure oil from the variable displacement hydraulic pump to each of a plurality of actuators;
In a work vehicle equipped with
A charge valve that replenishes the closed circuit with pressure oil from the variable displacement hydraulic pump as charge pressure oil is configured as the load-sensitive control valve,
An oil passage having one end connected to the charge valve and the other end branched and connected to the high-pressure circuit and the low-pressure circuit of the closed circuit;
A check valve disposed on the downstream side of the branch portion on the oil passage;
With
A work vehicle, wherein charge pressure oil from the charge valve is supplemented to the low-pressure circuit of the closed circuit. Operating means for operating the charge valve;
One or more sensors for detecting the state of the work vehicle;
With
The work vehicle according to claim 1, wherein the operation means is operated based on a detection signal from the sensor.   The work vehicle according to claim 1 or 2, wherein an opening area of the charge valve is variably operated by the operation means.

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