JP2013124735A - Hydraulic drive device of wheel type working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an appropriate travel drive force and a travel speed.SOLUTION: A travel pump pressure control means 60 controls a capacity of a travel pump 11 to be smaller by a cutoff valve 61 as operating pump pressure Pf is higher when the total pressure of a travel pump pressure Pt and the operating pump pressure Pf is higher than predetermined pump reference pressure Pp to decrease the travel pump pressure Pt. A motor capacity control means 100 controls a capacity of the travel motor 80 to be a minimum capacity by a switching valve 110 when the total pressure is lower than predetermined motor reference pressure Pm, and controls the capacity of the travel motor 80 to be a maximum capacity by the switching valve 110 when the total pressure is equal to or higher than the motor reference pressure Pm. A maximum value Ptmax2 of the travel pump pressure Pt accounting for the motor reference pressure Pm is set to be a value between a maximum value Ptmax1 and a minimum value Ptmin1 of the travel pump pressure Pt accounting for reference pressure Pp, and a minimum value Ptmin2 of the travel pump pressure Pt accounting for in the motor reference pressure Pm is set to be a value lower than a minimum value Ptmin1 of the travel pump pressure Pt accounting for the pump reference pressure Pp.

Description

  The present invention includes a travel pump that discharges pressure oil for driving a travel motor and a work pump that discharges pressure oil for driving a work device, and the travel pump and the work pump are driven by the same prime mover. The present invention relates to a hydraulic drive device for a wheel type work machine.

  2. Description of the Related Art Conventionally, a hydraulic drive device for a wheel-type work vehicle includes a prime mover, a travel pump including a variable displacement hydraulic pump driven by transmission of the output of the prime mover, and a variable displacement hydraulic motor. A traveling motor, a working pump that is driven by the output of the same prime mover as the prime mover for driving the traveling pump, and a hydraulic actuator that is driven by the discharge oil of the working pump and is a composite of the traveling motor And a work actuator that can be operated. In this hydraulic drive device, since the traveling pump and the work pump are driven by transmitting the output of the same prime mover, when the wheeled work vehicle performs the operation of the working device and the traveling in parallel, The relationship between the driving force for driving the work device (work driving force) within the range of the output of the prime mover and the driving force for driving the wheeled work vehicle (traveling drive force) is set.

  A hydraulic drive device for this type of wheel-type work vehicle includes travel pump pressure control means for controlling the discharge pressure of the travel pump with a cut-off valve, and motor capacity control means for controlling the capacity of the travel motor with a switching valve.

  The cut-off valve is a valve that operates using the travel pump discharge pressure (travel pump pressure) and the work pump discharge pressure (work pump pressure) as pilot pressure, and the total pressure of the travel pump pressure and the work pump pressure is predetermined. When the pump reference pressure is exceeded, the pressure acting on the servo piston of the traveling pump is controlled so as to reduce the capacity of the traveling pump, thereby reducing the discharge pressure of the traveling pump. Thereby, traveling driving force is suppressed, so that work driving force is large.

  The switching valve is a valve that operates using the traveling pump pressure as a pilot pressure. When the traveling pump pressure is lower than a predetermined motor reference pressure, the switching valve is connected to the servo piston of the traveling motor so that the traveling motor has a predetermined small capacity. The pressure that acts on the servo piston of the travel motor is controlled so that the travel motor has a predetermined large capacity set higher than the small capacity when the travel pump pressure is equal to or higher than the motor reference pressure. It is something to control.

  The hydraulic drive device for a wheeled work vehicle described here is disclosed in, for example, Patent Document 1.

Japanese Patent No. 2818474 (first page, right column to second page, right column, FIG. 6)

  In the above-described conventional hydraulic drive device, the pump reference pressure is the starting pressure (minimum pilot pressure required for operation) of the cutoff valve. The traveling pump pressure occupying the pump reference pressure is a linear function with the working pump pressure as a variable, and decreases as the working pump pressure increases. In other words, the higher the working pump pressure, the lower the travel pump pressure (travel pump pressure occupying the pump reference pressure) required for operating the cut-off valve. On the other hand, the motor reference pressure is the starting pressure of the switching valve, and is a constant value that is not affected by fluctuations in the working pump pressure. For this reason, there exists a possibility that the subject of following "(A)"-"(C)" may arise.

(A) In FIG. 6, a characteristic line 200 indicates the characteristic of the pump reference pressure Pp, and shows the relationship between the working pump pressure Pf and the traveling pump pressure Pt in the pump reference pressure Pp. Specifically, when the working pump pressure Pf is the lowest value (= 0), the traveling pump pressure Pt occupying the pump reference pressure Pp is set to the highest value Ptmax1. When the working pump pressure Pf is the maximum value Pfmax, the traveling pump pressure Pt occupying the pump reference pressure Pp is set to the minimum value Ptmin1 (> 0). When the working pump pressure Pf varies within the range of “0 <Pf <Pfmax”, the traveling pump pressure Pt occupying the pump reference pressure Pp is set lower as the working pump pressure Pf is higher.

  The motor reference pressure Pm1 is set to be higher than the minimum value Ptmin1 of the traveling pump pressure Pt and lower than the maximum value Ptmax1 with respect to the pump reference pressure Pp defined by the characteristic line 200. In this case, the traveling pump pressure Pt occupying the pump reference pressure Pp is equal to or higher than the motor reference pressure Pm1 in the range of “0 ≦ Pf ≦ Pf1” in the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the working pump pressure Pf. Set to pressure. Thus, in the state where the traveling pump pressure Pt occupying the pump reference pressure Pp is set to a pressure equal to or higher than the motor reference pressure Pm1, a pilot pressure higher than the motor reference pressure Pm1 is always applied to the switching valve, thereby The capacity of the motor is always maintained at a predetermined large capacity.

  As a result, as shown in FIG. 7, in the range of “0 ≦ Pf ≦ Pf1” of the work pump pressure Pf, the travel drive force F (traction force) increases as the work pump pressure Pf increases (the work drive force increases). It is possible to achieve both suppression and securing the necessary travel driving force F.

  On the other hand, the traveling pump pressure Pt occupying the pump reference pressure Pp is lower than the motor reference pressure Pm1 in the range of “Pf1 <Pf” in the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the working pump pressure Pf. Is set. In this way, when the traveling pump pressure Pt occupying the pump reference pressure Pp is set to a pressure lower than the motor reference pressure Pm1, the traveling pump pressure Pt is maintained lower than the motor reference pressure Pm1 by the cut-off valve. Therefore, the minimum pilot pressure (motor reference pressure Pm1) required for the operation of the switching valve is not generated, so that the capacity of the traveling motor is unnecessarily maintained at a small capacity.

  As a result, as shown in FIG. 7, between the driving force F that can be secured in the range of “0 ≦ Pf ≦ Pf1” of the working pump pressure Pf and the driving force F that can be secured in the range of “Pf1 <Pf”. There is a possibility that a drop G occurs and the required driving force F cannot be secured.

(B) In order to solve the problem described in “(A)”, in FIG. 8, the motor reference pressure Pm2 (<Pm1) is a pressure lower than the minimum value Ptmin1 of the traveling pump pressure Pt occupying the pump reference pressure Pp. Is set to In this case, the traveling pump pressure Pt occupying the pump reference pressure Pp is higher than the motor reference pressure Pm2 in the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the working pump pressure Pf. Therefore, when the traveling pump pressure Pt is equal to or higher than Ptmin, a pilot pressure higher than the motor reference pressure Pm2 acts on the switching valve, and the displacement of the traveling motor is maintained at a large capacity.

  As a result, as shown in FIG. 9, in the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the work pump pressure Pf, the travel drive force F is suppressed as the work pump pressure Pf increases, that is, the work drive force increases. It is possible to achieve both necessary driving force F.

  However, in FIG. 8, the difference (Pt−Pm2) between the traveling pump pressure Pt occupying the pump reference pressure Pp and the motor reference pressure Pm2 increases when the traveling pump pressure Pt occupying the pump reference pressure Pp is the maximum value Ptmax1. Thus, the capacity of the traveling motor is unnecessarily controlled to a large capacity. For this reason, there is a possibility that the wheeled work vehicle cannot be driven at the maximum speed when climbing uphill.

(C) In order to solve the problem described in “(B)”, in FIG. 10, the motor reference pressure Pm3 is higher than the motor reference pressure Pm2 shown in FIG. 8, and the running pump pressure occupies the pump reference pressure Pp. The pressure is set close to the maximum value Ptmax1 of Pt. That is, the motor reference pressure Pm3 is shown in FIG. 8 so that the difference from the traveling pump pressure Pt occupied in the pump reference pressure Pp does not become too large when the traveling pump pressure Pt occupied in the pump reference pressure Pp is the maximum value Ptmax1. It is set to a pressure higher than the motor reference pressure Pm2. Further, in order to solve the problem described in “(A)”, the characteristic line 500 of the pump reference pressure Pp in FIG. 10 indicates the traveling pump pressure Pt in the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the working pump pressure Pf. Is set to a pressure higher than the motor reference pressure Pm3 so that the travel pump pressure Pt occupying the pump reference pressure Pp does not become a pressure lower than the motor reference pressure Pm3.

  As a result, when the traveling pump pressure Pt occupying the pump reference pressure Pp is the maximum value Ptmax1, it is possible to prevent the traveling motor capacity from being unnecessarily controlled to a large capacity, and accordingly, the wheel type work vehicle can be moved to the maximum speed when climbing up. It can be run with.

  However, in the characteristic line 500, the difference between the maximum value Ptmax1 and the minimum value Ptmin1 of the traveling pump pressure Pt in the pump reference pressure Pp is too small. That is, as shown in FIG. 11, the traveling driving force F obtained from the characteristic line 500 is larger than the traveling driving force shown in FIG. 9 in the range of “0 <Pf ≦ Pfmax” of the work pump pressure Pf. There is a possibility that the traveling driving force is too large with respect to the work driving force.

  For example, when the wheel-type work vehicle is a wheel loader, the wheel loader operation in which the operation of the work device and the traveling are performed in parallel is to move forward while penetrating the bucket into the embankment such as earth and sand and lifting the bucket to remove the earth and sand. There is an excavation operation of scooping up. If the traveling drive force F is too large with respect to the work drive force during the excavation operation, the wheel slips and the work efficiency of the wheel loader decreases.

  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 drive device for a wheel type work vehicle capable of obtaining an appropriate travel drive force and travel speed.

  In order to achieve the above object, a hydraulic drive device for a wheeled work vehicle according to the present invention is configured as follows.

  A hydraulic drive device for a wheeled work vehicle according to the present invention comprises a prime mover, a travel pump comprising a variable displacement hydraulic pump driven by being transmitted with the output of the prime mover, and a variable displacement hydraulic motor. A travel motor composed of a variable displacement hydraulic motor connected in a closed circuit, a work pump driven by transmission of the output of the prime mover, and a hydraulic actuator driven by oil discharged from the work pump, the travel motor A hydraulic drive device for a wheel-type work vehicle, comprising: a work actuator capable of performing a combined operation; a travel pump pressure control unit that controls a discharge pressure of the travel pump; and a motor capacity control unit that controls a capacity of the travel motor. The traveling pump pressure control means is configured so that a total pressure of the discharge pressure of the traveling pump and the discharge pressure of the work pump is a predetermined pump. When the pressure is equal to or higher than the reference pressure, the discharge pressure of the traveling pump is decreased by controlling the displacement of the traveling pump so that the discharge pressure of the working pump is high. When the pressure is less than a predetermined motor reference pressure, the capacity of the traveling motor is controlled to a predetermined small capacity, and when the total pressure is equal to or higher than the motor reference pressure, the capacity of the traveling motor is less than the small capacity. The maximum value of the travel pump discharge pressure occupying the motor reference pressure is between the maximum value and the minimum value of the travel pump discharge pressure occupying the pump reference pressure. The minimum value of the travel pump discharge pressure occupying the motor reference pressure is set to a value lower than the minimum value of the travel pump occupying the pump reference pressure. And butterflies.

  In the hydraulic drive device for a wheeled work vehicle according to the present invention configured as described above, the travel pump pressure (travel pump discharge pressure) occupying the pump reference pressure is a variable of the work pump pressure (work pump discharge pressure). Is a linear function that decreases as the working pump pressure increases. The traveling pump pressure occupying the motor reference pressure is also a linear function with the work pump pressure (work pump discharge pressure) as a variable, and decreases as the work pump pressure increases. Therefore, the traveling pump pressure occupying the pump reference pressure when the working pump pressure is the lowest value and the traveling pump pressure occupying the motor reference pressure are both the highest values, and occupy the pump reference pressure when the working pump pressure is the highest value. Both the travel pump pressure and the travel pump pressure occupying the motor reference pressure are minimum values. The maximum value of the traveling pump pressure occupying the motor reference pressure is set to a value between the maximum value and the minimum value of the traveling pump pressure occupying the pump reference pressure. The value is set to a value lower than the minimum value of the traveling pump pressure occupying the pump reference pressure.

  Since the motor reference pressure is set with respect to the pump reference pressure in this way, the motor reference pressure is lower than the pump reference pressure in the entire fluctuation range of the discharge pressure of the work pump. As a result, the above-mentioned problem “(A)”, that is, the problem that the travel motor capacity is unnecessarily controlled to a small capacity and the required travel drive force cannot be secured can be solved, and the discharge of the work pump can be solved. In the entire pressure fluctuation range, it is possible to achieve both the suppression of the travel driving force as the discharge pressure of the work pump increases (as the work drive force increases) and the necessary travel drive force.

  In the hydraulic drive system for a wheeled work vehicle according to the present invention, the maximum value of the traveling pump pressure in the motor reference pressure is between the maximum value and the minimum value of the traveling pump pressure in the pump reference pressure as described above. Is set to the value of As a result, the hydraulic drive device for the wheeled work vehicle according to the present invention can solve the above-described problem in “(B)”, that is, the problem that the capacity of the travel motor is unnecessarily controlled to a large capacity. Sometimes a wheeled work vehicle can run at maximum speed.

  Further, in the hydraulic drive device for a wheel type work vehicle according to the present invention, the discharge pressure of the traveling pump occupying the motor reference pressure becomes lower as the discharge pressure of the work pump becomes higher as described above. As a result, the hydraulic drive device for the wheeled work vehicle according to the present invention is such that the driving reference force is so large that the travel drive force is too large relative to the work drive force as described in “(C)”. There is no need to set a high minimum pressure.

  For these reasons, the hydraulic drive device according to the wheeled work vehicle described in “[1]” can obtain an appropriate travel drive force and travel speed.

  The hydraulic drive device for a wheeled work vehicle according to the present invention is the above-described hydraulic drive device for a wheeled work vehicle, wherein the travel pump includes a variable mechanism for a pump that makes the displacement of the travel pump variable, and the pump A pump servo piston for driving the variable mechanism, and the traveling pump pressure control means includes a cut-off valve for controlling a pressure acting on the pump servo piston. When the pressure is higher than the pump reference pressure, the pressure acting on the pump servo piston is controlled so that the capacity of the traveling pump decreases as the discharge pressure of the working pump increases. A variable mechanism portion for the motor that makes the capacity of the travel motor variable, and a servo piston for the motor that drives the variable mechanism portion for the motor, The motor capacity control means includes a switching valve that controls a pressure acting on the servo piston for the motor, and the switching valve has a capacity of the traveling motor that is small when the total pressure is less than the motor reference pressure. The pressure acting on the motor servo piston is controlled so as to have a capacity, and the motor servo is controlled so that the capacity of the traveling motor becomes the large capacity when the total pressure is equal to or higher than the motor reference pressure. It is preferable to control the pressure acting on the piston.

  As described above, the hydraulic drive device for a wheeled work vehicle according to the present invention can obtain an appropriate travel drive force and travel speed.

1 is a side view of a wheeled work vehicle (wheel loader) on which a hydraulic drive device for a wheeled work vehicle according to a first embodiment of the present invention is mounted. 1 is a hydraulic circuit diagram of a hydraulic drive device according to a first embodiment of the present invention. It is a figure which shows the relationship between the pump reference pressure in the hydraulic drive apparatus shown in FIG. 2, and a motor reference pressure. It is a figure which shows the relationship between the working pump pressure obtained by the relationship between the pump reference pressure shown in FIG. 3, and a motor reference pressure, and driving | running | working driving force. FIG. 5 is a hydraulic circuit diagram of a hydraulic drive device according to a second embodiment of the present invention. It is a figure which shows an example of the relationship between a pump reference pressure and a motor reference pressure in case a motor reference pressure consists only of traveling pump pressure. It is a figure which shows the relationship between the working pump pressure obtained from the relationship between the pump reference pressure shown in FIG. 6, and a motor reference pressure, and driving | running | working driving force. It is a figure which shows another example of the relationship between a pump reference pressure and a motor reference pressure in case a motor reference pressure consists only of traveling pump pressure, and FIG. It is a figure which shows the relationship between the working pump pressure obtained from the relationship between the pump reference pressure shown in FIG. 8, and a motor reference pressure, and driving | running | working driving force. It is a figure which shows an example different from FIG. 5, FIG. 6 of the relationship between a pump reference pressure and a motor reference pressure in case a motor reference pressure consists only of traveling pump pressure. It is a figure which shows the relationship between the working pump pressure obtained from the relationship between the pump reference pressure shown in FIG. 10, and a motor reference pressure, and driving | running | working driving force.

  A hydraulic drive device for a wheeled work vehicle according to first and second embodiments of the present invention will be described.

[First Embodiment]
A hydraulic drive device for a wheeled work vehicle according to a first embodiment of the present invention will be described with reference to FIGS.

  The hydraulic drive device according to the first embodiment of the present invention is mounted on 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 working device 6 provided at the front of the main body 2. .

  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 work actuators (hydraulic actuators) that drive the work device 6 are 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.

  As shown in FIG. 2, the hydraulic drive apparatus according to the first embodiment includes a diesel engine 10 that is a prime mover, and a travel pump 11 that includes a variable displacement hydraulic pump that is driven by transmission of the output of the diesel engine 10. The travel pump 11 and a travel motor 80 composed of a variable displacement hydraulic motor connected in a closed circuit by a pair of travel drive lines 12 and 13 are provided.

  The traveling pump 11 includes a pair of inlet / outlet ports 11a and 11b that serve as a suction port or a discharge port for hydraulic oil, a bi-tilt type pump variable mechanism unit 14 that makes the displacement volume variable, and the pump variable mechanism unit. And a pump regulator 20 for driving the motor 14. The wheel loader 1 moves forward when the traveling pump 11 draws hydraulic oil from the inlet / outlet 11b and discharges it from the inlet / outlet 11a. Conversely, when the traveling pump 11 draws hydraulic oil from the inlet / outlet 11a and discharges it from the inlet / outlet 11b, the wheel loader 1 moves backward.

  The pump regulator 20 includes a pump servo piston 21 having a pair of pressure receiving portions 22 and 23 for receiving a pump control pressure, a pair of pump control pressure chambers 24 and 25 for introducing the pump control pressure, and a pump servo piston. And a pair of return springs 26 and 27 for urging 21 in a direction in which the capacity (pushing displacement) of the traveling pump 11 decreases. The pressure receiving areas of the pair of pressure receiving portions 22 and 23 of the pump servo piston 21 and the set load of the pair of return springs 26 and 27 are pumps when the pressure acting on the pair of pressure receiving portions 22 and 23 is the same pressure. The servo piston 21 is set to be held at a position where the capacity is minimized, that is, a position where the capacity of the traveling pump 11 is zero.

  The travel motor 80 is a reversible 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 (not shown).

  The hydraulic drive apparatus according to the first embodiment is a pilot pump 31 composed of a constant displacement hydraulic pump driven by a diesel engine 10 and a pump control that is a hydraulic circuit connected to the pilot pump 31 via a pipe 32. A pressure generation unit 33 and a traveling direction control valve 34 provided between the pump control pressure generation unit 33 and the pump regulator 20 are provided.

  The pump control pressure generator 33 generates a pump control pressure proportional to the amount of depression of an accelerator pedal (not shown) provided in the cab 3 with the discharge pressure of the pilot pump 31 as the primary pressure.

  The traveling direction control valve 34 is a spring center type three-position valve, and the valve position can be switched to a neutral position 35, a first operating position 36, and a second operating position 37. The neutral position 35 operates both the pump control pressure chamber 24 (the pressure receiving portion 22 side of the pump servo piston 21) and the pump control pressure chamber 25 (the pressure receiving portion 23 side of the pump servo piston 21) of the pump regulator 20. This is a valve position for communicating with the tank 38, that is, a valve position for setting the capacity (pushing capacity) of the traveling pump 11 to the minimum capacity (= 0). The first operating position 36 is a valve position that guides the pump control pressure from the pump control pressure generating unit 33 to one pump control pressure chamber 24 and communicates the other pump control pressure chamber 25 to the hydraulic oil tank 38, that is, the pump This is the valve position at which the pump servo piston 21 of the regulator 20 is driven in the F direction and the traveling pump 11 discharges the pressure oil for advancing the wheel loader 1. The second operating position 37 is a valve position for guiding the pump control pressure from the pump control pressure generating unit 33 to the other pump control pressure chamber 25 and communicating one pump control pressure chamber 24 to the hydraulic oil tank 38, that is, the pump The valve position is such that the pump servo piston 21 of the regulator 20 is driven in the B direction and the traveling pump 11 discharges the pressure oil in the direction in which the wheel loader 1 moves backward. The valve position of the traveling direction control valve 34 is controlled based on an operation of a forward / reverse switching lever (not shown) provided in the cab 3.

  The hydraulic drive device according to the first embodiment includes a charge circuit 40 that replenishes hydraulic oil that circulates between the traveling pump 11 and the traveling motor 80. The charge circuit 40 includes a pilot pump 31, a relief valve 41 that defines an upper limit of the discharge pressure of the pilot pump 31, a check valve 42 that guides the discharge oil of the pilot pump 31 to the traveling drive line 12, and a pilot pump And a check valve 43 that guides the discharged oil 31 to the driving drive line 13.

  The hydraulic drive device according to the first embodiment includes a work pump 50 including a constant displacement hydraulic pump that is driven by being transmitted with the output of a diesel engine 10 that is the same prime mover as the prime mover that drives the traveling pump 11, and the work pump. The lift arm cylinder 7a (working actuator) and bucket cylinder 8a (working actuator) driven by 50 discharged oil, and the work device hydraulic control circuit 51 connected to the work device drive line 52 extending from the work pump 50. With. The work device hydraulic control circuit 51 includes a lift arm control direction 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 bucket directional control valve (not shown) provided therebetween. The lift arm directional control valve operates in response to an operation of a lift arm operating device (not shown) provided in the cab 3 and controls the flow of pressure oil supplied from the work pump 50 to the lift arm cylinder 7a. The direction, that is, the operation direction of the lift arm 7 is controlled. The bucket direction control valve operates in response to an operation of a bucket operation 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. When at least one of the lift arm operating device and the bucket operating device and the accelerator pedal are operated at the same time, at least one of the lift arm cylinder 7a and the bucket cylinder 8a and the travel motor 80 operate in parallel. In other words, a so-called composite operation is performed.

  The hydraulic drive device according to the first embodiment includes travel pump pressure control means 60 that controls travel pump pressure Pt (discharge pressure of the travel pump 11). The traveling pump control means 60 is configured such that when the total pressure (Pt + Pf) of the traveling pump pressure Pt and the working pump pressure Pf (the discharge pressure of the working pump 50) is equal to or higher than a predetermined pump reference pressure Pp, the working pump pressure Pf is The higher the value is, the smaller the travel pump 11 volume (push-away volume) is controlled to lower the travel pump pressure Pt.

  Specifically, the traveling pump pressure control means 60 includes a cutoff valve 61 that controls the pressure acting on the pump servo piston 60. The cut-off valve 61 is a hydraulic pilot type two-position valve, and includes a return spring 63 that defines an initial position 64 (the valve position on the left side in FIG. 2) of the valve body 62 and a starting pressure (minimum pilot pressure required for operation). And first and second pilot ports 66 and 67 for introducing pilot pressure to be applied to the valve body 62. 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.

  The traveling pump pressure control means 60 further includes a high pressure selection type shuttle valve 77 that selects a pressure in the traveling drive line 12 and a pressure on the high pressure side in the traveling drive line 13, and the high pressure selection type shuttle valve. And a first pilot line 74 that guides the pressure selected by 77 to the first pilot port 66 of the cut-off valve 61. The high-pressure side pressure selected by the high-pressure selection type shuttle valve 77 is equal to the traveling pump pressure Pt. The traveling pump pressure control means 60 includes a second pilot line 75 that branches from the work device drive line 52 and guides the work pump pressure Pf to the second pilot port 67 of the cut-off valve 61. Both the first and second pressure receiving portions 68 and 69 of the cut-off valve 61 are provided so that a pilot pressure in a direction against the pressing direction of the valve body 62 by the return spring 63 acts. In other words, the cutoff valve 61 uses the total pressure (Pt + Pf) of the traveling pump pressure Pt and the working pump pressure Pf as a pilot pressure, and the total pressure (Pt + Pf) is regulated by the return spring 63 that is equal to or higher than the predetermined pump reference pressure Pp. When the pressure is equal to or higher than the set starting pressure (minimum pilot pressure required for operation), the operation is started.

  The cut-off valve 61 has a first inlet / outlet port 72 and a second inlet / outlet port 73, and the first inlet / outlet port 72 and the second inlet / outlet port 73 are blocked when the valve body 62 is at the initial position 64. The cross section of the flow path formed between the first inlet / outlet port 72 and the second inlet / outlet port 73 becomes larger as the valve body 62 is displaced in the direction from the initial position 64 to the operating position 65. The first inlet / outlet port 72 communicates with one pump control pressure chamber 24 of the pump regulator 20, and the second inlet / outlet port 73 communicates with the other pump control pressure chamber 25 of the pump regulator 20.

  When the cutoff valve 61 is activated, the pump servo piston 21 causes the pressure receiving portion 22 to move as the valve body 62 of the cutoff valve 61 is displaced from the initial position 64 (closed position) to the operating position 65 (open position). The difference between the pressure acting on the pressure receiving portion 23 and the pressure acting on the pressure receiving portion 23 decreases, and accordingly, the pump servo piston 21 reduces the displacement (pushing displacement volume) of the traveling pump 11 by the return spring 26 or the return spring 27. It will be pushed. That is, the cutoff valve 61 operates when the total pressure (Pt + Pf) of the traveling pump pressure Pt and the working pump pressure Pf is equal to or higher than a predetermined pump reference pressure Pp, that is, equal to or higher than the starting pressure regulated by the return spring 63. The pressure acting on the pump servo piston 21 is controlled so that the capacity (push-out volume) of the traveling pump 11 decreases as the pump pressure Pf increases.

  When the cutoff valve 61 is not in operation (when the valve position is the initial position 64 (closed position)), the pump regulator 20 acts on the pair of pressure receiving portions 22 and 23 of the pump servo piston 21. The pressure to be controlled is controlled by the traveling direction control valve 34.

  The travel motor 80 includes a pair of inlet / outlet ports 80 a and 80 b, a motor variable mechanism 81 that varies the displacement volume, and a motor regulator 90 that drives the motor variable mechanism 81. The motor regulator 90 includes a motor servo piston 91 having a small diameter pressure receiving portion 92 at one end and a large diameter pressure receiving portion 93 having a larger pressure receiving area than the small diameter pressure receiving portion 92 at one end, a small diameter pressure receiving portion 92, and a large diameter. A small-diameter control pressure chamber 94 and a large-diameter control pressure chamber 95 for introducing a motor control pressure to be applied to each of the pressure receiving portions 93 are provided.

  The hydraulic drive apparatus according to the first embodiment includes motor capacity control means 100 that controls the capacity of the travel motor 80. In the motor capacity control means 100, the total pressure (Pt + Pf) of the travel pump pressure Pt (discharge pressure of the travel pump 11) and the work pump pressure Pf (discharge pressure of the work pump 50) is less than a predetermined motor reference pressure Pm. In this case, the capacity of the traveling motor 80 is controlled to a predetermined small capacity (for example, the minimum capacity), and when the total pressure (Pt + Pf) is equal to or higher than the predetermined motor reference pressure Pm, the capacity of the traveling motor 80 is less than the predetermined small capacity. Is controlled to a large predetermined large capacity (for example, maximum capacity).

  Specifically, the motor capacity control means 100 includes a motor control pressure line 101 that branches from the first pilot line 74 and guides the traveling pump pressure Pt to the small diameter control pressure chamber 94 of the motor regulator 90, and a motor servo piston. And a switching valve 110 for controlling the pressure acting on 91.

  The switching valve 110 is a hydraulic pilot type two-position valve, and a return spring 114 that defines an initial position 112 (lower valve position in FIG. 2) and a starting pressure (minimum pilot pressure required for operation) of the valve body 111; First and second pilot ports 115 and 116 for introducing pilot pressure to be applied to the valve body 111 are provided. The valve body 111 includes a first pressure receiving portion 117 to which the pilot pressure introduced from the first pilot port 115 acts, and a second pressure receiving portion 118 to which the pilot pressure introduced from the second pilot port 116 acts. The first pilot port 115 is a port for introducing the pressure in the motor control pressure line 101, that is, the traveling pump pressure Pt as a pilot pressure, and the second pilot port 116 is the pressure in the second pilot line 75, that is, work. This is a port for introducing the pump pressure Pf as a pilot pressure. Both the first and second pressure receiving portions 117 and 118 of the switching valve 110 are provided so that a pilot pressure in a direction against the pressing direction of the valve body 111 by the return spring 114 acts. That is, the switching valve 110 is regulated by the return spring 114, with the total pressure (Pt + Pf) of the traveling pump pressure Pt and the working pump pressure Pf being a pilot pressure, and the total pressure (Pt + Pf) being equal to or higher than the predetermined motor reference pressure Pm. It operates when it is higher than the starting pressure (minimum pilot pressure required for operation).

  The initial position 112 (the lower valve position in FIG. 2) of the switching valve 110 is a valve position at which the large-diameter control pressure chamber 95 communicates with the hydraulic oil tank 38. Therefore, when the switching valve 110 is not actuated (when the valve position is maintained at the initial position 112), the motor servo piston 91 is lowered to the limit by the traveling pump pressure Pt acting on the small diameter pressure receiving portion 92. Will be displaced. As a result, the capacity (push-away volume) of the travel motor 80 is controlled to the minimum capacity.

  On the other hand, the operation position 113 (the valve position on the upper side in FIG. 2) of the switching valve 110 is a valve position that guides the pressure in the motor control pressure line 101 to the large-diameter control pressure chamber 95, that is, the traveling pump pressure Pt. Therefore, when the switching valve 110 is actuated (when the valve position is displaced to the actuated position 113), the traveling pump pressure Pt acts on both the small-diameter pressure receiving portion 92 and the large-diameter pressure receiving portion 93 of the motor servo piston 91. Since the pressure receiving area of the diameter pressure receiving portion 93 is larger than the pressure receiving area of the small diameter pressure receiving portion 92, the motor servo piston 91 increases the capacity (pushing capacity) of the traveling motor 80 by pressing the traveling pump pressure Pt against the large diameter pressure receiving portion 93. It will be displaced in the increasing direction (arrow I direction). As a result, the capacity of the traveling motor 80 is set to a predetermined large capacity (the maximum capacity in the first embodiment) larger than the minimum capacity.

  That is, the switching valve 110 is configured so that the traveling motor pressure Pt and the working pump pressure Pf (Pt + Pf) is less than the predetermined motor reference pressure Pm, that is, less than the starting pressure regulated by the return spring 114. The pressure acting on the motor servo piston 91 is controlled so that the capacity of 80 becomes the minimum capacity, and when the total pressure (Pt + Pf) is equal to or higher than a predetermined motor reference pressure Pm, the capacity of the traveling motor 80 is The pressure acting on the servo piston 91 for the motor is controlled so as to reach the maximum capacity.

  In FIG. 3, as indicated by the characteristic line 200 of the pump reference pressure Pp, the traveling pump pressure Pt occupying the pump reference pressure Pp is a linear function with the work pump pressure Pf as a variable, and decreases as the work pump pressure Pf increases. Become. Further, as indicated by the characteristic line 300 of the motor reference pressure Pm, the traveling pump pressure Pt occupying the motor reference pressure Pm is also a linear function with the work pump pressure Pf as a variable, and decreases as the work pump pressure Pf increases. Therefore, when the working pump pressure Pf is the lowest value Pfmin (= 0), the traveling pump pressure Pt occupying the pump reference pressure Pp and the traveling pump pressure Pt occupying the motor reference pressure Pm are both the highest values (Ptmax1, Ptmax2). When the working pump pressure Pf is the highest value, the traveling pump pressure Pt indicated by the pump reference pressure Pp and the traveling pump pressure Pt occupying the motor reference pressure Pm are both the lowest values (Ptmin1, Ptmin2). The maximum value Ptmax2 of the traveling pump pressure Pt occupying the motor reference pressure Pm is set to a value between the maximum value Ptmax1 and the minimum value Ptmin1 of the traveling pump pressure Pt occupying the pump reference pressure Pp. The minimum value Ptmin2 of the traveling pump pressure Pt occupied is set to a value lower than the minimum value Ptmin1 of the traveling pump pressure Pt occupied in the pump reference pressure Pp.

  Since the motor reference pressure Pm is set with respect to the pump reference pressure Pp as described above, the traveling pump pressure Pt occupying the motor reference pressure Pm is within the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the working pump pressure Pf. The traveling pump pressure Pt occupies the pump reference pressure Pp. Thereby, in the wheel type work vehicle according to the first embodiment, the traveling driving force F is the same as in the case of the combination of the characteristic line 200 of the pump reference pressure Pp and the motor reference pressure Pm1 shown in FIG. The drop G shown in FIG. 4 does not occur, and as shown in FIG. 4, the work pump pressure Pf increases in the entire fluctuation range (0 ≦ Pf ≦ Pfmax) of the work pump pressure Pf, that is, the work driving force increases. Along with this, it decreases at a constant rate of change. As a result, in the hydraulic drive device according to the first embodiment, the travel drive force F increases as the work pump pressure Pf increases (the work drive force increases) in the entire variation range (0 ≦ Pf ≦ Pfmax) of the work pump pressure Pf. It is possible to satisfy both of the above and ensuring the required driving force F.

  Further, in the hydraulic drive device for the wheel type work vehicle according to the first embodiment, the maximum value Ptmax1 and the minimum value of the traveling pump pressure Pt that the maximum value Ptmax2 of the traveling pump pressure Pt occupies in the motor reference pressure Pm occupies the pump reference pressure Pp. Unlike the combination of the characteristic line 200 of the pump reference pressure Pp and the motor reference pressure Pm2 shown in FIG. 8, the capacity of the travel motor 80 is unnecessarily increased to the maximum capacity by setting the value between Ptmin1. It is possible to avoid falling into a controlled situation, so that the wheeled work vehicle can run at the maximum speed when climbing.

  Further, in the hydraulic drive system for the wheel type work vehicle according to the first embodiment, the travel pump pressure Pt occupying the motor reference pressure Pp decreases as the work pump pressure Pf increases. Therefore, the pump reference pressure Pp shown in FIG. It is not necessary to set the minimum value Ptmin of the traveling pump pressure Pt occupying the pump reference pressure Pp as shown by the characteristic line 500 so high that the traveling driving force becomes too large with respect to the work driving force. Thereby, the hydraulic drive device according to the first embodiment can prevent the rear wheel 5 from slipping during the excavation operation of the wheel loader.

  From these things, the hydraulic drive device which concerns on the wheel type work vehicle which concerns on 1st Embodiment can obtain suitable traveling drive force and traveling speed.

[Second Embodiment]
A hydraulic drive system for a wheeled work vehicle according to a second embodiment of the present invention will be described with reference to FIG. Among the components shown in FIG. 5, the same components as those shown in FIG. 2 are denoted by the same reference numerals as those shown in FIG.

  As shown in FIG. 5, in the hydraulic drive device according to the second embodiment, unlike the hydraulic drive device according to the first embodiment, an electrically controllable cutoff valve 310 (electromagnetic valve), A control valve 320 (solenoid valve) that can be controlled, a travel pump pressure sensor 321 that converts the travel pump pressure Pt into a detection signal St (electric signal) and outputs it, and a work pump pressure Pf as a detection signal Sf (electric signal). And a work pump pressure sensor 322 that converts the output into the output, and a CPU, a ROM, and a RAM. Based on the detection signal St from the traveling pump pressure sensor 321 and the detection signal Sf from the work pump pressure sensor 322, the cutoff valve 310 and The controller 400 (microcomputer) which performs electronic control of the switching valve 320 is provided.

  The controller 400 includes pump control processing means 401 and motor control processing means 402 which are means set by a control program and data stored in a ROM.

  The pump control processing unit 401 stores in advance the relationship between the characteristic line 200 of the pump reference pressure Pp described above, the detection signal St from the traveling pump pressure sensor 321 and the detection signal Sf from the work pump pressure sensor 322, and the traveling When the total pressure (Pt + Pf) of the pump pressure Pt and the work pump pressure Pf is equal to or higher than the pump reference pressure Pp, that is, equal to or higher than the starting pressure regulated by the return spring 63, the higher the work pump pressure Pf, A control signal Cp for decreasing the capacity (push-off volume) is given to the solenoid 310a of the cut-off valve 310. In addition, the pump control processing unit 401 causes the return spring 63 to hold the valve position of the cutoff valve 310 at the initial position 64 when the total pressure (Pt + Pf) is less than the pump reference pressure Pp.

  The motor control processing unit 402 stores in advance the relationship between the characteristic line 300 of the motor reference pressure Pm described above, the detection signal St from the traveling pump pressure sensor 321 and the detection signal Sf from the work pump pressure sensor 322. When the total pressure (Pt + Pf) of the pump pressure Pt and the working pump pressure Pf is not less than the motor reference pressure Pm, that is, not less than the starting pressure regulated by the return spring 114, the control signal Cm is given to the solenoid 320a of the switching valve 320. The valve position of the switching valve 320 is switched to the operating position 113. Further, when the total pressure (Pt + Pf) is less than the motor reference pressure Pm, the motor control processing unit 402 causes the return spring 114 to hold the valve position of the switching valve 320 at the initial position 113.

  That is, in the hydraulic drive device according to the second embodiment, the pump pressure control means of the present invention is configured to include the cutoff valve 310, the traveling pump pressure sensor 321, and the pump control processing means 401 of the controller 400. The motor capacity control means of the present invention comprises a switching valve 320, a work pump pressure sensor 322, and a motor control processing means 402 of the controller 400.

  The hydraulic drive device according to the second embodiment configured as described above can also obtain an appropriate travel drive force and travel speed, similarly to the hydraulic drive device according to the first embodiment.

1 Wheel loader (wheel-type work vehicle)
6 Working device 7 Lift arm 7a Lift arm cylinder (work actuator)
8 Bucket 8a Bucket cylinder (work actuator)
10 Diesel engine (motor)
DESCRIPTION OF SYMBOLS 11 Traveling pumps 12 and 13 Traveling drive line 14 Pump variable mechanism part 21 Pump servo piston 50 Working pump 60 Traveling pump pressure control means 61 Cut-off valve 80 Traveling motor 81 Motor variable mechanism 91 Motor servo piston 100 Motor capacity control means 110 Switching valve 310 Cutoff valve 320 Switching valve 321 Traveling pump pressure sensor 322 Work pump pressure sensor 400 Controller 401 Pump control processing means 402 Motor control processing means

Claims (2)

A traveling motor comprising a prime mover, a traveling pump comprising a variable displacement hydraulic pump driven by transmission of the output of the prime mover, and a variable displacement hydraulic motor comprising a variable displacement hydraulic motor and connected in a closed circuit with the traveling pump. A work pump that is driven by being transmitted with the output of the prime mover, a hydraulic actuator that is driven by the discharge oil of the work pump and that can be combined with the travel motor, and A hydraulic drive device for a wheeled work vehicle comprising: a traveling pump pressure control unit that controls a discharge pressure; and a motor capacity control unit that controls a capacity of the traveling motor,
When the total pressure of the travel pump discharge pressure and the work pump discharge pressure is equal to or higher than a predetermined pump reference pressure, the travel pump pressure control means increases the work pump discharge pressure as the discharge pressure of the travel pump increases. The discharge pressure of the traveling pump is reduced by controlling the capacity to be small,
The motor capacity control means controls the capacity of the travel motor to a predetermined small capacity when the total pressure is less than a predetermined motor reference pressure, and the travel when the total pressure is equal to or greater than the motor reference pressure. The motor capacity is controlled to a predetermined large capacity larger than the small capacity,
The maximum value of the travel pump discharge pressure occupying the motor reference pressure is set to a value between the maximum value and the minimum value of the travel pump discharge pressure occupying the pump reference pressure. The hydraulic drive device for a wheeled work vehicle, wherein the minimum value of the discharge pressure of the traveling pump is set to a value lower than the minimum value of the traveling pump that occupies the pump reference pressure. In the hydraulic drive device of the wheel type work vehicle according to claim 1,
The traveling pump includes a pump variable mechanism that makes the capacity of the traveling pump variable, and a pump servo piston that drives the pump variable mechanism.
The traveling pump pressure control means includes a cut-off valve that controls a pressure acting on the pump servo piston, and the cut-off valve is configured so that when the total pressure is equal to or higher than the pump reference pressure, The pressure acting on the pump servo piston is controlled so that the capacity of the traveling pump decreases as the discharge pressure increases.
The travel motor includes a motor variable mechanism that makes the capacity of the travel motor variable, and a motor servo piston that drives the motor variable mechanism.
The motor capacity control means includes a switching valve that controls a pressure acting on the servo piston for the motor, and the switching valve has a capacity of the traveling motor that is small when the total pressure is less than the motor reference pressure. The pressure acting on the motor servo piston is controlled so as to have a capacity, and the motor servo is controlled so that the capacity of the traveling motor becomes the large capacity when the total pressure is equal to or higher than the motor reference pressure. A hydraulic drive device for a work machine, which controls pressure acting on a piston.

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