JP2793585B2 - Hydraulic drive circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydraulic drive circuit for a hydrostatic transmission. (Prior Art) A hydrostatic pump that controls a traveling device driven by a motor by combining a hydraulic pump driven by an engine and a hydraulic motor rotated by the pump discharge oil to make the discharge amount of the pump variable. Transmission (hereinafter referred to as HST) control devices are known. The conventional HST control device guides the hydraulic pressure from the charge pump linked to the hydraulic pump to the servo cylinder of the hydraulic pump via the HST control valve, and controls the pump discharge direction and discharge amount according to the rotation speed and load. ing. (Problems to be Solved by the Invention) However, in this HST control device, since the hydraulic oil from the HST control valve is directly guided to the servo cylinder, the control accuracy of the servo cylinder is low and a stable running state is obtained. There was a problem that it was difficult. An object of the present invention is to solve such a problem. (Means for Solving the Problems) Accordingly, the present invention relates to a variable pump in a hydraulic drive circuit including a variable pump driven by an engine and a variable motor rotatably driven in accordance with the discharge amount of the variable pump. A regulator piston that guides a discharge pressure from a charge pump interlocked with a flow control regulator through a solenoid valve that switches according to forward and backward movements, and controls the flow control regulator to control the discharge amount of the variable pump; and a regulator piston. And a flow control valve for switching the supply of pressure oil for driving the variable pressure pump according to the discharge pressure from the charge pump, so that the discharge amount of the variable pump increases as the discharge pressure from the charge pump increases. The combined value of the load pressure of the variable pump and the discharge pressure from the charge pump is A horsepower control valve for controlling a discharge pressure from the charge pump led to the flow control regulator when the value exceeds a predetermined value is provided. Further, in the present invention, a high / low pressure selection valve that senses a pressure change and performs a switching operation is provided so that the charge pump discharge pressure is guided from the same direction even when the solenoid valve is switched with respect to the horsepower control valve. (Operation) Accordingly, the discharge pressure from the charge pump acts as the operating pressure of the flow control regulator, and the supply of the pressure oil to the regulator piston is controlled according to this pressure. The regulator piston controls a swash plate angle for adjusting the discharge amount of the variable pump. The operating pressure is controlled by the horsepower control valve in accordance with the pump load and the number of revolutions, so that the pump horsepower is controlled so as not to exceed the engine rated output. The working pressure is always guided to the horsepower control valve from the same direction via a high / low pressure selection valve. Therefore, even if the discharge direction of the variable pump changes, stable detection can be performed by automatically detecting the change. (Example) An example of the present invention will be described with reference to the drawings. In FIG. 1, a reversible variable pump 2 driven by an engine 1 and a main pump 3 and a charge pump 4 interlocked therewith are provided. The variable pump 2 rotates the motor 6 by supplying discharge oil to the reversible variable hydraulic motor 6 through the main pipes 5A and 5B. The main pump 3 supplies the discharge oil to auxiliary equipment and the like (not shown). Oil discharged from the charge pump 4 is guided to the HST control valve 7. The HST control valve 7 includes a solenoid valve 10 for controlling switching between forward rotation and reverse rotation of the variable pump 2, and a variable orifice connecting between the high pressure circuit 8 and the low pressure circuit 9.
11 comprises a variable orifice 12 having a relief valve and a fixed orifice 14. In addition, a variable orifice for short-circuiting the high voltage circuit 8 and the low voltage circuit 9 in conjunction with the inching pedal for braking during traveling.
13 is provided. When the forward / reverse selection pedal of the driver's seat is operated, the solenoid valve 10 is electromagnetically switched by a signal from a control circuit (not shown), and has a forward position, a reverse position, and a neutral position. Circuits 15 and 16 connected to the high-pressure circuit 8 and the low-pressure circuit 9 via a solenoid valve 10 communicate with left and right pressure chambers 18 and 19 of a flow control valve 20 of a flow control regulator 17. The flow control valve 20 performs a switching operation in accordance with the differential pressure between the pressure chambers 18 and 19, and introduces pressure-controlled pressure oil into the regulator piston 21. The regulator piston 21 controls the discharge amount and discharge direction of the variable pump 2, and this control amount is fed back to the flow control valve 20. A horsepower control valve 22 for adjusting the operating pressure of the circuits 15 and 16 to be transmitted to the flow control regulator 17 according to the load and the number of revolutions of the variable pump 2 is provided. High pressure (load pressure) extracted from the main lines 5A and 5B through the check valves 23A and 23B is supplied to the horsepower control valve 22.
Is transmitted by the circuit 24 and the high / low pressure selection valve 25
Thereby, the differential pressure between the high pressure via the circuit 26 and the low pressure via the circuit 27 is transmitted, the opening of the horsepower control valve 22 is controlled according to these pressure differences, and the circuits 15 and 16 are bypassed. The opening degree of the circuit 28 to be adjusted is adjusted. The high / low pressure selection valve 25 has a parallel position and an intersecting position so that the circuit 26 is always at a high pressure and the circuit 27 is at a low pressure, and performs switching operation according to the differential pressure between the circuits 15 and 16. Next, the specific configuration of the flow control valve 20 will be described in the second.
A specific configuration of the horsepower control valve 22 and the high / low pressure selection valve 25 will be described with reference to FIG. In FIG. 2, sleeves 32 and 33 are symmetrically arranged with a low-pressure opening 31 at the center of the body 30 interposed therebetween. A spool 34 is slidably inserted into the sleeve 32, and a plunger 35 is slidably inserted into the other sleeve 33. The end surface of the spool 34 is in contact with the end surface of the plunger 35. The spool 34 is urged toward the plunger 35 by a spring 37 interposed between the spool 34 and a nut 36 fitted to the end face of the sleeve 32. The sleeve 32 is formed with a high-pressure port 38 that communicates with the circuit 24 and constantly guides high pressure, and a control port 39 that communicates with the oil chamber 21A of the regulator piston 21. An annular groove 40 for selectively communicating the high pressure port 38 and the control port 39 on the outer periphery of the spool 34, and a low pressure passage
Annular grooves 42 selectively communicating with 41 are arranged in parallel. The low-pressure passage 41 penetrates through the inside of the spool 34 in the axial direction and communicates with the low-pressure opening (tank) 31. At the left end of the spool 34, a pressure chamber 18 for accommodating the spring 37 is formed.
Is conducted through circuit 16 and connection port 43. A pressure chamber 19 is formed at the right end of the plunger 35, and the pressure chamber 19 is always communicated with a port 44 formed in the sleeve 33, through a passage 45 formed in the plunger 35,
The pressure from the circuit 15 connected to the HST control valve 7 is led. The pressure chamber 19 is provided with a spring 46 for urging the plunger 35 toward the spool 34. The spool 34 and the plunger for the pressure chambers 18 and 19
The pressure receiving areas of 35 are set equal. In the opening 31, spring holders 47 and 48 are fitted to the respective steps of the spool 34 and the plunger 35, and between the central holder 49 fitted so as not to contact the plunger 35, respectively. Springs 50 and 51 are interposed in a pre-compressed state. The center holder 49 is interlocked with the regulator piston 21 and is displaced in parallel in accordance with the stroke of the regulator piston 21 to compress the spring 50 or 51. The oil chamber 21B having a small pressure receiving area of the regulator piston 21 communicates with the circuit 24, and high pressure from the main pipelines 5A and 5B is always introduced. High pressure in circuit 15 by HST control valve 7, circuit 1
Assuming that a low pressure is introduced to 6, the spool 34 held in the neutral state is displaced leftward in the figure due to the pressure difference between the pressure chambers 19 and 18. Spool 34 and plunger 35 are springs 37 and 46
And is kept neutral by the balance of 50 and 51,
When a pressure difference occurs between the pressure chambers 18 and 19, the spool 34 is displaced in this manner. When the spool 34 is displaced to the left, the high pressure port 38 communicates with the control port 39, pressure oil is sent into the oil chamber 21A of the regulator piston 21, the pressure rises, and the regulator piston 21 operates to the extension side. As a result, the tilt angle of the variable pump 2 increases, and the discharge flow rate increases. On the other hand, with the operation of the regulator piston 21, the central holder 49 moves in the same direction, and the compression force of the spring 51 increases.
Therefore, the force for pushing the plunger 35 back against the pressure in the pressure chamber 19 increases, and at a position where these are balanced, the spool 34 returns to the neutral state and stands still. In this way, the spool 34 is displaced in accordance with the pressure difference, and the displacement is feedback-controlled through the regulator piston 21. When the pressure relationship between the circuits 15 and 16 is reversed by the switching of the solenoid valve 10, the spool 34 is displaced in the opposite direction, that is, from the neutral state to the right side, whereby the control port
38 communicates with the low pressure passage 41, the pressure in the oil chamber 21A of the regulator piston 21 decreases, the regulator piston 21 operates to the contraction side, and the variable pump 2 increases the discharge amount in the opposite direction. Then, the center holder 49 compresses the spring 51 by the displacement of the regulator piston 21 and pushes back the spool 34, so that the spool 34 returns to the neutral state at a position where these are balanced. In this way, the forward and reverse discharge amounts of the variable pump 2 are controlled according to the operating pressure from the HST control valve 7. Next, the structure of the horsepower control valve 22 and the high / low pressure selection valve 25 for adjusting the operating pressure from the HST control valve 7 according to the pump speed and load will be described with reference to FIG. These two valves 22 and 25 are housed inside the same body 60, and first branched from the circuits 15 and 16 into pressure chambers 62 and 63 formed at both ends of the spool 61 of the high / low pressure selection valve 25. The circuits 15A and 15B communicate with each other, and the spool 61 is displaced according to the pressure difference between the two circuits 15A and 15B. That is, when one pressure chamber becomes high pressure and the other pressure chamber becomes low pressure, the spool 61 moves from the high pressure side to the low pressure side. Passages 64 and 65 are formed inside the spool 61 to communicate with the pressure chambers 62 and 63, respectively.
Is opened around the spool 61 through annular grooves 66 and 67. A high-pressure passage 68 is formed in the body 60 between the annular grooves 66 and 67, and low-pressure passages 69 and 70 are formed outside the annular grooves 66 and 67 and communicate with each other. When the pressure chamber on the high pressure side is connected to the high pressure passage 68 due to the displacement of 61, the other pressure chamber is always connected to the low pressure passage 69 or 70. A pressure chamber 73 into which a low pressure is introduced is formed at the left end of the spool 71 of the horsepower control valve 22, a first pressure chamber 74 into which a high pressure is introduced at the right end, and a second pressure into which a pressure from the circuit 24 is introduced. A chamber 75 is formed, and the spool 71 is displaced to a position where these and the spring 76 interposed in the pressure chamber 73 are balanced. Therefore, an internal passage 77 communicating with the low-pressure passage 69 is formed in the spool 71, and a side groove 78 communicating the high-pressure passage 68 with the first pressure chamber 74 is formed. A plunger 79 that is displaced together with the spool 71 is inserted into the second pressure chamber 75. An inclined groove 80 is formed around the spool 71 so as to always communicate with the high-pressure passage 68.
Communicates with the low-pressure passage 69. The degree of opening of the inclined groove 80 with respect to the low-pressure passage 69 changes according to the amount of displacement of the spool 71, and this communication short-circuits the circuits 15 and 16 and changes the pressure difference. The flow control valve is operated in accordance with the change in the pressure difference.
The opening of 20 is controlled. The high / low pressure selection valve 25 changes from the high pressure side to the low pressure side regardless of whether the circuit 15A or 15B becomes high pressure, and always connects the high pressure side to the high pressure passage 68 and connects the low pressure side to the low pressure passage.
Connect to 69. The high pressure in the high pressure passage 68 is guided to the first pressure chamber 74 at the right end of the spool 71 of the horsepower control valve 22, and presses the spool 71 leftward in opposition to the low pressure in the left end pressure chamber 73 and the spring 76. At the same time, the pressure from the circuit 24 of the second pressure chamber 75 also pushes the spool 71 to the left. As will be described later, the pressure in the first pressure chamber 74 is proportional to the pump rotation speed, and the pressure in the second pressure chamber 75 is proportional to the pump load. Therefore, as the rotation speed and the load increase, the pressure of the spool 71 increases. The displacement increases. When the spool 71 is displaced, the high-pressure passage 68 and the low-pressure passage 69 communicate with each other through the inclined groove 80, and the circuits 15 and 16 are short-circuited. This allows the flow control valve of the flow control regulator 17
The working pressure for controlling the opening degree of 20 is adjusted, and the discharge amount of the variable pump 2 is controlled. In this case, a circuit that is short-circuited between the high-pressure passage 68 and the low-pressure passage 69 via the inclined groove 80 corresponds to the bypass circuit 28 in FIG. With the above configuration, the overall operation will be described with reference to FIG. When moving the vehicle forward, use the HST control valve 7
Is switched to the forward side, and the variable orifice 13 linked to the inching pedal (brake pedal) is closed. In this state, the high voltage circuit 8 and the low voltage circuit 9 of the charge pump 4 communicate with the circuits 15 and 16. The discharge oil of the charge pump 4 escapes from the high-pressure circuit 8 to the low-pressure circuit 9 by the variable orifice 11 and the fixed orifice 14, and at this time, a pressure difference is generated according to the orifice opening. When the accelerator pedal is depressed, the rotation speed of the engine 1 increases, and the discharge amounts of the reversible variable pump 2 and the charge pump 4 increase accordingly. When the discharge amount of the charge pump 4 increases, the pressure difference (operating pressure) generated by the orifice also increases. These pressure differences (PH-PL) are passed through circuits 15 and 16 to the left and right pressure chambers 18 and 19 of the control valve 20 of the flow control regulator 17.
(Note that the pressure in the pressure chamber 18 is higher than that in the pressure chamber 19). When the pressure difference exceeds a predetermined value, the flow control valve
20 is switched from the neutral state, high pressure is introduced into the pressure chamber 21A of the regulator piston 21, and the regulator piston 21
Is displaced, and the swash plate of the variable pump 2 is inclined. As a result, the variable pump 2 starts the discharge operation, and the variable motor 6 starts rotating by receiving the pressure oil from the main pipeline 5A. The rotation speed of the variable motor 6 is proportional to the discharge amount of the variable pump 2. When the engine speed is increased by operating the accelerator pedal, the discharge amount of the charge pump 4 increases, and the operating pressure also increases in proportion thereto, and the discharge amount of the variable pump 2 increases via the regulator piston 21. I will do it. By the way, the regulator piston 21 of the flow control regulator 17 is displaced in accordance with the operating pressure. However, since this displacement is fed back to the flow control valve 20, the discharge amount of the variable pump 2 is Is controlled precisely. When the engine speed reaches a predetermined high speed range, the relief valve of the variable orifice 12 opens, and the maximum swash plate angle is regulated. By the way, an operating pressure corresponding to the engine speed from the HST control valve 7 and a pressure corresponding to the load of the variable pump 2 acting on the main pipelines 5A and 5B act on the horsepower control valve 22. When the combined value exceeds the predetermined value, the horsepower control valve 22 switches to short-circuit the circuits 15 and 16. The pressure escapes from the high pressure side to the low pressure side between the circuits 15 and 16 according to the opening degree of the horsepower control valve 22, and the flow control regulator
17 working pressure decreases. When the operating pressure decreases, the swash plate angle is adjusted by the regulator piston 21 via the flow control valve 20 in the direction in which the discharge amount of the variable pump 2 passes, thereby preventing the engine 1 from being overloaded. When the load on the variable motor 6 increases, the discharge pressure of the variable pump 2 increases, and the generated horsepower of the engine 1 that drives the variable pump 2 increases even if the pump discharge amount is the same. Therefore, if the load on the variable motor 6 increases when the engine speed is relatively high, the rated output of the engine may be exceeded. This also occurs when the engine speed is increased while the load on the variable motor 6 is large to some extent. In order to avoid such a phenomenon, when the product of the load and the number of revolutions exceeds a predetermined value by the horsepower control valve 22, the operating pressure of the flow rate control regulator 17 is reduced and the regulator piston 21 is returned to reduce the swash plate angle. Variable pump 2
To reduce the discharge amount. As a result, it is possible to control the pump consumption horsepower, which is the product of the discharge amount and the discharge pressure, so as not to exceed a predetermined maximum horsepower. When braking the vehicle, by opening the variable orifice 13 in conjunction with the inching pedal, the circuits 15 and 16 are short-circuited with each other, the operating pressure drops, and the flow control regulator
17 controls the swash plate angle of the variable pump 2 so that the discharge amount becomes zero. Next, when the vehicle moves backward, the solenoid valve 10 of the HST control valve 7 is switched to the reverse side.
The pressure relationship between the circuits 15 and 16 is reversed from that at the time of forward movement, the flow control valve 20 of the flow control regulator 17 is switched in the reverse direction, the pressure in the pressure chamber 21A of the regulator piston 21 decreases, and the inclination of the variable pump 2 The plate angle is inclined in the opposite direction from the neutral state. As a result, the discharge direction of the variable pump 2 is reversed from the above, pressure oil is sent from the main line 5B to the variable motor 6, and the motor 6 rotates in the reverse direction of the vehicle. Even in this case, the reverse of the pressure relationship between the circuits 15 and 16 is detected, and the high / low pressure selection valve 25 is switched to operate the horsepower control valve 22.
In this case, the high pressure and the low pressure are applied from the same direction as when the vehicle is moving forward, so that the horsepower control of the variable pump 2 is similarly performed stably. (Effects of the Invention) As described above, according to the present invention, a flow control regulator provided with a flow control valve that performs switching operation in accordance with the discharge pressure of a charge pump is provided, and the operating pressure of the flow control regulator is adjusted to the pump speed. And a horsepower control valve that corrects according to the load, the discharge amount of the variable pump can be controlled very accurately, and the stability of traveling control is significantly improved. In addition, the horsepower control valve always introduces the operating pressure from the same direction even if the discharge direction of the variable pump changes via the high / low pressure selection valve, so that it is automatically stabilized for both forward and backward travel. Control can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention, FIG. 2 is a sectional view of a flow control regulator, and FIG. 3 is a sectional view of a horsepower control valve and a high / low pressure selection valve. . 1 ... Engine, 2 ... Variable pump, 4 ... Charge pump, 5A, 5B ... Main pipeline, 6 ... Variable motor, 7 ...
… HST control valve, 10 …… Solenoid valve, 1
7 ... Flow control regulator, 20 ... Flow control valve, 2
1 ... Regulator piston, 22 ... Horse control valve, 2
5 ... High / low pressure selection valve.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F16H 61/42

Claims (1)

(57) [Claims] In a hydraulic drive circuit including a variable pump driven by an engine and a variable motor that is driven to rotate in accordance with the discharge amount of the variable pump, the discharge pressure from a charge pump interlocked with the variable pump is changed according to forward and reverse travel. And a regulator piston for controlling the discharge amount of the variable pump, and a supply of pressure oil for driving the regulator piston to a discharge pressure from the charge pump. And a flow control valve that switches in accordance with the flow rate. The discharge pressure of the variable pump increases as the discharge pressure of the charge pump increases, while the load pressure of the variable pump and the discharge pressure of the charge pump increase. When the combined value exceeds the predetermined value, it is guided to the flow control regulator. Hydraulic drive circuit characterized in that a horsepower control valve for limiting the discharge pressure from the charge pump that. 2. In a hydraulic drive circuit including a variable pump driven by an engine and a variable motor that is driven to rotate in accordance with the discharge amount of the variable pump, the discharge pressure from a charge pump interlocked with the variable pump is changed according to forward and reverse travel. And a regulator piston for controlling the discharge amount of the variable pump, and a supply of pressure oil for driving the regulator piston to a discharge pressure from the charge pump. And a flow control valve that switches in accordance with the flow rate. The discharge pressure of the variable pump increases as the discharge pressure of the charge pump increases, while the load pressure of the variable pump and the discharge pressure of the charge pump increase. When the combined value exceeds the predetermined value, it is guided to the flow control regulator. The horsepower control valve for limiting the discharge pressure from the charge pump is provided, the charge pump discharge pressure be switched the solenoid valve with respect to the horsepower control valve to direct from the same direction that,
A hydraulic drive circuit comprising a high / low pressure selection valve that performs a switching operation by sensing a pressure change.