JP7282647B2 - Variable displacement hydraulic pump - Google Patents

Description

The present invention relates to a variable displacement hydraulic pump, and more particularly to a technique for optimizing hydraulic characteristics.

2. Description of the Related Art Axial piston hydraulic pumps (hereinafter also simply referred to as hydraulic pumps) mounted on a wheel loader equipped with wheels, which is one of working machines, include types such as a single tilting pump and a double tilting pump. The uni-tilt pump can adjust the discharge flow rate by changing the tilt angle (tilt angle) of the swash plate with respect to the direction in which the cylinder extends. By stopping the reciprocating motion of the pistons with the plate in a vertical position, the stop state in which the discharge of hydraulic oil from the discharge port is stopped, or by increasing the tilt angle of the swash plate (the swash plate relative to the piston). It is possible to switch to the first flow state in which the hydraulic oil is discharged in one direction by increasing the angle of inclination.

Further, in the double-tilting pump, the discharge port and the suction port in the first flow state are reversed by tilting the swash plate from the stop state to the side opposite to the first flow state with respect to the uni-tilt pump. It is also possible to switch to a second flow state in which the hydraulic fluid is discharged in the opposite direction.

By the way, a wheel loader (body) equipped with such a hydraulic pump is equipped with an engine, and the engine drives a bi-tilting hydraulic pump to discharge hydraulic oil. In addition, the fuselage is equipped with a fixed displacement type hydraulic motor that has a structure similar to that of a hydraulic pump and in which the tilting angle of the swash plate is fixed, and this hydraulic motor drives the wheels. The tilting pump and the hydraulic motor are connected in a closed circuit (so-called HST circuit), and the hydraulic motor is supplied with hydraulic oil discharged from the hydraulic pump to rotate forward and backward.

This double tilting pump serves as the hydraulic oil discharge side when the hydraulic motor is rotated forward, and serves as the hydraulic oil suction side when the hydraulic motor is reversed, and serves as the hydraulic oil discharge side when the hydraulic motor is reversed. The hydraulic pump has a B port that becomes the suction side when rotating in the forward direction, and when the hydraulic pump is accelerating or decelerating due to the forward rotation of the hydraulic motor, when an external force such as running resistance is applied to the wheels, the A port and B port A differential pressure is created between the ports.

When a differential pressure is generated between the A port and the B port in this way, resistance (flow resistance) to the flow of hydraulic oil occurs between the A port and the B port when the aircraft is accelerating, and when the aircraft is decelerating, the A port on the discharge side The pressure drops and the pressure at the B port on the suction side rises, causing a so-called hydraulic pump motor action to be driven.

Therefore, when the A port and the B port begin to communicate with each other due to the flow resistance of the hydraulic oil and the motor action of the hydraulic pump, the internal pressure fluctuates, which may cause pulsation in the hydraulic circuit.

Therefore, in the unilateral tilting pump, each switching land is provided with a discharge hole (13) and a preload introduction hole (14), and when the pressure of the discharge hole is lower than the pressure of the preload introduction hole, hydraulic fluid flows between them. A technique has been developed to reduce the pulsation due to the pressure difference as described above by providing a check valve that shuts off the pressure (Patent Document 1).

JP 2015-218618 A

The technology disclosed in Patent Document 1 can be applied to a pump such as a single-tilt pump in which the suction-side port and the discharge-side port are not switched. can be switched, the suction side and the discharge side of the A port and B port are switched, so it is necessary to switch the roles of the discharge hole and the preload introduction hole, and a check valve that closes only in one direction The problem is that it cannot be used.

In addition, in a double tilting pump, pressure fluctuations are particularly large when the A port and B port are switched from the suction side to the discharge side, and pulsation due to the differential pressure tends to increase. It is necessary to take measures against

The present invention has been made in view of such problems, and its object is to change the cylinder port from one port (one of A port and B port) to the other port (A port and B port). To provide a double tilt type variable displacement hydraulic pump capable of reducing pulsation that occurs when switching to either one of the two.

In order to achieve the above object, the variable displacement hydraulic pump of the present invention includes a drive shaft member driven by a drive device, and a plurality of drive shaft members rotating in conjunction with the drive shaft member and extending in the axial direction of the drive shaft member. a cylinder block having cylinders; a plurality of pistons reciprocatingly inserted into the respective cylinders of the cylinder block; a plate, a guide member for guiding the pistons to rotate along the swash plate, and a guide member located on the opposite side of the swash plate with the cylinder block interposed therebetween in the axial direction. A double-tilt type variable displacement hydraulic pump having an intermittently communicating A port and a B port formed with a pair of switching lands interposed therebetween, and a valve plate in sliding contact with the cylinder block, wherein the switching land a flow hole for circulating hydraulic oil into the cylinder when communicating with the cylinder; a discharge passage capable of discharging the hydraulic oil in the cylinder to a hydraulic oil tank; a supply position connecting the circulation hole and the supply passage; and the circulation hole and the discharge passage. and an on-off valve that is switched between the supply position and the discharge position, and the on-off valve switches between the supply position and the discharge position according to the differential pressure between the A port and the B port. Hydraulic oil in the supply passage is supplied into the cylinder through the flow hole when switched to the supply position, and the cylinder is switched to the discharge position when switched to the discharge position. Hydraulic oil inside is discharged to the discharge passage through the circulation hole, and the flow rate of the hydraulic oil switched to the supply position and circulated in the supply passage is switched to the discharge position and discharged. The opening is adjusted according to the differential pressure between the A port and the B port by increasing the flow rate of the hydraulic fluid that flows through the flow path .

As a result, when the on-off valve is in the discharge position, the hydraulic oil in the cylinder is discharged to the hydraulic oil tank to increase the flow rate of the circulating hydraulic oil compared to when it is in the supply position. Since the opening is adjusted accordingly, it is possible to positively reduce pressure fluctuations when the cylinder port is switched from one of the A port and the B port to the other port .

According to the variable displacement hydraulic pump of the present invention, the on-off valve that can be switched between the supply position and the discharge position by closing one of the supply channel and the discharge channel while opening the other is provided at the discharge position. Occasionally, the hydraulic oil in the cylinder is discharged to the hydraulic oil tank to increase the flow rate of the circulating hydraulic oil compared to when it is in the supply position. It is possible to actively reduce pressure fluctuations when switching to the other port of the A port and B port, which serve as suction ports, and reduce pulsation occurring in the A port and B port. Occasionally, it is possible to suppress rotational fluctuations of the cylinder block and the drive shaft member due to a rapid increase in the internal pressure in the cylinder due to hydraulic oil supplied to the cylinder from the supply passage. Furthermore, since the opening degree of the on-off valve is adjusted according to the differential pressure between the A port and the B port, the A Pressure fluctuations in the ports A and B can be reduced, and pulsations occurring in the ports A and B can be reduced.

1 is a side view of an airframe equipped with a variable displacement hydraulic pump according to the present invention; FIG. It is a hydraulic circuit diagram of a hydraulic system. Fig. 3 is a cross-sectional view of a pump body of the variable displacement hydraulic pump; It is a front view of a valve plate. 4 is a graph showing the correlation between the degree of opening of the switching valve and the port pressure difference; FIG. 4 is a circuit diagram of a traveling hydraulic circuit when the machine body is accelerating forward; FIG. 10 is an explanatory diagram in which a side view of the swash plate and pistons and a front view of the valve plate are arranged side by side when the cylinder ports are positioned so as not to communicate with the ports A and B while the aircraft is accelerating forward; 4 is a graph showing cylinder internal pressure while the cylinder moves from point 1 to point 3; 5 is a graph showing cylinder internal pressure while the cylinder moves from point 4 to point 6; FIG. 4 is a circuit diagram of a travel hydraulic circuit when the machine body is accelerating backward; FIG. 10 is an explanatory diagram in which a side view of the swash plate and pistons and a front view of the valve plate are arranged side by side when the cylinder ports are positioned so as not to communicate with the ports A and B while the aircraft is accelerating rearward; FIG. 10 is a circuit diagram of a travel hydraulic circuit when decelerating a body moving forward; FIG. 10 is an explanatory drawing in which a side view of the swash plate and the piston and a front view of the valve plate are arranged side by side when the piston moves to the bottom dead center and the top dead center when the fuselage moving forward is decelerated; It is a front view of the valve plate in another Example.

An embodiment of the present invention will be described below with reference to the drawings.
Referring to FIG. 1, there is shown a side view of a fuselage 1 equipped with a variable displacement hydraulic pump 41 according to the present invention. The airframe 1 is a wheel loader equipped with a front attachment 7 , an engine (driving device) 9 and a hydraulic device 11 . The machine body 1 can run by driving the wheels 3a provided on the front and rear sides, and can perform work such as excavation work by operating the front attachment 7. As shown in FIG.

The wheels 3a and the front attachments 7 (hereinafter also referred to as various devices) are driven by the hydraulic pressure generated by the hydraulic system 11 driven by the engine 9.

The engine 9 is housed in the machine room of the fuselage 1 and drives the hydraulic system 11 by the engine 9 .

FIG. 2 is a hydraulic circuit diagram of the hydraulic device 11. As shown in FIG. The hydraulic system 11 includes a working hydraulic circuit 21 and a traveling hydraulic circuit 23 .

The work hydraulic circuit 21 is an open circuit including a unilateral tilting pump 31 , a hydraulic cylinder 33 for driving the front attachment 7 , and an operating lever 35 . The uni-tilting pump 31 is driven by the engine 9, and swings the swash plate 31a to adjust the discharge flow rate.

The hydraulic cylinder 33 controls the direction and flow rate of the hydraulic oil supplied by the switching valve 33a, thereby controlling the expansion and contraction and the operating speed.

The operation lever 35 is a lever provided in the operator's seat 8 (see FIG. 1), and can be operated by the operator to operate the hydraulic cylinder 33 . More specifically, the operation lever 35 is operated to guide the pilot pressure discharged from the pilot pump 35a to a pilot oil chamber (not shown) of the switching valve 33a, thereby switching the switching valve 33a in a desired direction by a desired amount. It guides to a control unit (not shown) of the swash plate 31a of the tilting pump, controls the amount of tilting of the swash plate 31a, and controls the discharge flow rate of the unilateral tilting pump 31. FIG.

With such a configuration, the working hydraulic circuit 21 can adjust the flow rate of hydraulic oil supplied from the unilateral tilting pump 31 to the hydraulic cylinder 33 according to the amount of operation of the operating lever 35 by the operator. The operation of the front attachment 7 can be controlled.

The travel hydraulic circuit 23 is a closed circuit including a variable displacement hydraulic pump 41 , a travel motor 43 , a first flow path 45 and a second flow path 47 . The variable displacement hydraulic pump 41 is a bi-tilt type variable displacement hydraulic pump that is driven by utilizing the driving force transmitted from the engine 9. It is possible to adjust and switch the flow rate and the direction of flow of hydraulic fluid flowing through the travel hydraulic circuit 23 . The structure of the variable displacement hydraulic pump 41 will be described later.

The traveling motor 43 is a hydraulic motor that serves as a driving force for the wheels 3a. The travel motor 43 is connected to the variable displacement hydraulic pump 41 via a first flow path 45 and a second flow path 47 so as to be able to circulate hydraulic oil, and is variable according to the operation of a travel pedal (not shown) or the like. The flow rate and flow direction of the hydraulic oil supplied from the positive displacement hydraulic pump 41 are controlled, and it is possible to drive by this.

FIG. 3 is a cross-sectional view of the pump body 51 of the variable displacement hydraulic pump 41. As shown in FIG. 4 is a front view of the valve plate 71. FIG.

The variable displacement hydraulic pump 41 includes a pump body 51 , a first pressure reducing circuit 53 and a second pressure reducing circuit 55 . The pump body 51 includes a drive shaft (drive shaft member) 61 , a cylinder block 63 , a plurality of pistons 65 , a swash plate 67 , a case 69 , a tilt actuator 70 and a valve plate (valve plate) 71 .

The drive shaft 61 is a shaft member that rotates around the drive shaft C when driving force is transmitted from the engine 9 . The cylinder block 63 is a member spline-fastened to the drive shaft 61 and rotates in conjunction with the drive shaft 61 . The cylinder block 63 has a plurality of (e.g., eight) cylinders 63a extending in the direction in which the drive shaft C extends (hereinafter referred to as the axial direction) and circumferentially spaced around the drive shaft C at regular intervals.

A plurality of (for example, eight) pistons 65 are inserted into a plurality of cylinders 63a formed in the cylinder block 63 so as to be reciprocable. As a result, when the drive shaft 61 rotates, the cylinder block 63 and the plurality of cylinders 63a rotate together, so that the plurality of pistons 65 also rotate around the drive shaft C. As shown in FIG. For convenience of explanation, the plurality of cylinders 63a and the plurality of pistons 65 are eight, but the number may be increased or decreased, or may be an odd number.

The swash plate 67 is a member that is tiltably provided on the end side of the plurality of pistons 65 projecting from each cylinder 63a. Here, a shoe (guide member) 65a is provided at the end (protruding end side) of the piston 65, and each piston is pushed by a swash plate 67 via a shoe holder (guide member) 67a. 65 is guided to rotate along the swash plate 67 . Further, the swash plate 67 swings around the tilt axis S by being pressed by a tilt actuator 70 provided on the case 69, for example. The tilting axis S is formed so as to be positioned at the center of an arc of a cylinder 67b formed on the side of a case body 69b, which will be described later, when viewed in the axial direction of the swash plate 67. As shown in FIG.

As a result, the piston 65 rotates along the swash plate 67 when rotating in conjunction with the drive shaft 61 . In other words, the piston 65 rotates around the drive shaft C while changing the sliding distance in the axial direction according to the tilt angle of the swash plate 67 that is pushed by the tilt actuator 70 and tilted.

The case 69 includes a front case 69a, a case main body 69b and a rear case 69c. The case 69 has a cylinder block 63, a plurality of pistons 65, a swash plate 67, a tilt actuator 70 and a valve plate 71 inside a case body 69b, and is sealed with a front case 69a and a rear case 69c. Further, the drive shaft 61 rotatably penetrates the front case 69a.

The valve plate 71 is an annular member disposed on the rear case 69c located axially opposite to the swash plate 67 with the cylinder block 63 interposed therebetween, and is in sliding contact with the cylinder block 63 . The valve plate 71 and the rear case 69c are provided with a pair of ports 81A and 81B (hereinafter also referred to as A port 81A and B port 81B, respectively) that intermittently communicate with each cylinder 63a via each cylinder port 89, which will be described later. Flow holes 83A and 83B (hereinafter also referred to as first flow hole 83A and second flow hole 83B, respectively) are formed. The cylinder block 63 also has a cylinder port 89 extending from each cylinder 63 a toward the valve plate 71 .

According to FIG. 4, the A port 81A is an elongated hole formed along the annular valve plate 71, and a notch 82A is formed at the end opposite to the rotation direction of the cylinder 63a. Similarly to the A port 81A, the B port 81B is an elongated hole formed along the annular valve plate 71, and a notch 82B is formed at the end on the side opposite to the rotational direction of the cylinder 63a. ing. The B port 81B and the A port 81A are located so as to be symmetrical with respect to the drive shaft C. As shown in FIG. In addition, the A port 81A connects the first flow path 45 and hydraulic fluid so as to flow therethrough, and the B port 81B connects the second flow path 47 and the hydraulic fluid so as to flow therethrough (see FIG. 2).

The cylinder port 89 is an elongated hole having a shape corresponding to the ports 81A and 81B and formed to be shorter than the ports 81A and 81B. When the cylinder block 63 rotates around the drive shaft C, the cylinder port 89 rotates along the ports 81A and 81B. Therefore, while the cylinder port 89 communicates with the ports 81A, 81B, the hydraulic oil in the cylinder 63a is discharged to the ports 81A, 81B or sucked from the ports 81A, 81B.

The first flow hole 83A and the second flow hole 83B are oil passages respectively formed in a pair of switching lands 85A and 85B sandwiched between the A port 81A and the B port 81B. The first communication hole 83A and the second communication hole 83B are closed when the cylinder port 89 is switched from a position at least partially facing the A port 81A and the B port 81B to a position facing only the switching lands 85A and 85B. 89 to allow hydraulic fluid to flow through the cylinder port 89 to the cylinder 63a.

Thereby, the cylinder port 89 communicates with the first communication hole 83A and the switching land 85A, the notch 82A, the A port 81A, the second communication hole 83B and the switching land 85B, the notch 82B and the B port 81B in this order.

With such a configuration, the pump body 51 rotates the cylinder block 63 in conjunction with the drive shaft 61 driven by the engine 9, and the piston 65 slides in the axial direction according to the inclination angle of the swash plate 67. . Here, when the piston 65 slides, it slides along the cylinder 63a. Therefore, after the piston 65 is farthest away from the cylinder port 89 (bottom dead center), as the piston 65 approaches the cylinder port 89, the cylinder Hydraulic oil in 63 a is discharged to cylinder port 89 . Similarly, after the piston 65 comes closest to the cylinder port 89 (top dead center), the hydraulic oil in the cylinder port 89 is sucked into the cylinder 63a as the piston 65 moves away from the cylinder port 89.

Here, when the piston 65 is at the bottom dead center, the cylinder port 89 corresponds to either one of the switching lands 85A and 85B. It is positioned so as to correspond to the other of the switching land 85A and the switching land 85B.

As a result, when the swash plate 67 inclines, the piston 65 rotates about the drive shaft C so that the cylinder port 89 moves from one of the switching lands 85A and 85B to the other. to the bottom dead center or from the bottom dead center to the top dead center, hydraulic oil can be sucked from either the A port 81A or the B port 81B and discharged from the other.

Further, as described above, the A port 81A is connected to the first flow path 45 so as to allow the hydraulic fluid to flow therethrough, and the B port 81B is connected to the second flow path 47 so as to be able to flow the hydraulic fluid therethrough. Hydraulic oil can be supplied to the travel motor 43 from either the flow path 45 or the second flow path 47, and the hydraulic oil can be sucked from the travel motor 43 by the other of the first flow path 45 and the second flow path 47. It is possible.

The first pressure reducing circuit 53 includes a switching valve (on-off valve) 91, an A flow path 93 connected to the A port 81A, a B flow path 95 connected to the B port 81B, and a communication flow connected to the first flow hole 83A. Hydraulic circuit with passage 97. FIG. The switching valve 91 has a valve element 101 formed to be switchable between three positions, a supply position 101a, a discharge position 101b, and a neutral position 101n. A second port 91b connected to the A flow path 93 via 93a and a third port 91c connected to the hydraulic oil tank 25 via a discharge flow path 95a are provided so as to allow the flow of hydraulic oil, The pressure in the A channel 93 and the pressure in the B channel 95 are introduced as switching pressures. The switching valve 91 is switched to the supply position 101a side as the pressure in the A channel 93 increases, and is switched to the discharge position 101b side as the pressure in the B channel 95 increases.

At the supply position 101a, the switching valve 91 communicates between the first port 91a and the second port 91b and communicates between the A port 81A and the first flow hole 83A. All of the second port 91b and the third port 91c are closed, and at the discharge position 101b, the first port 91a and the third port 91c are communicated to communicate the first flow hole 83A and the hydraulic oil tank 25 with each other. Further, the switching valve 91 includes an A spring (supply limiting biasing member) 102a and a B spring (discharging limited biasing member) 102a that biases toward the neutral position 101n when the valve body 101 is at the supply position 101a or the discharge position 101b. force member) 102b.

FIG. 5 is a graph showing the correlation between the degree of opening of the switching valve 91 (vertical axis) and the difference in pressure between the A port 81A and the B port 81B (port pressure difference, horizontal axis). According to this graph, when the pressure of the A port 81A is higher than the pressure of the B port 81B, the port pressure difference becomes closer to the A port (right side of the graph) and the switching valve 91 switches to the supply position 101a. On the other hand, when the pressure of the B port 81B is higher than the pressure of the A port 81A, the port pressure difference becomes closer to the B port (left side of the graph), and the switching valve 91 switches to the discharge position 101b.

At this time, since the opening area of the discharge position 101b is larger than that of the supply position 101a, assuming that the absolute value of the port pressure difference is the same, the discharge position 101b opens more than the supply position 101a. do. It should be noted that the opening areas of the supply position 101a and the discharge position 101b are changed by making the spools (not shown) of the valve body 101 have different shapes and numbers of notches. It should be bigger.

Therefore, when the switching valve 91 is opened, it switches between the supply passage 93a and the discharge passage 95a according to the differential pressure between the A port 81A and the B port 81B, and adjusts the degree of opening. can be done. Further, when the discharge passage 95a is opened, the flow rate of hydraulic oil flowing through the discharge passage 95a can be increased more than the flow rate of hydraulic oil flowing through the supply passage 93a when the supply passage 93a is opened.

The second pressure reducing circuit 55 is a hydraulic circuit including a switching valve 91 , an A flow path 93 , a B flow path 95 and a communication flow path 97 like the first pressure reducing circuit 53 . The second pressure reducing circuit 55 is arranged point-symmetrically with respect to the first pressure reducing circuit 53 with the drive axis C as a reference. Since the configuration of the second pressure reducing circuit 55 is the same by replacing the connection of the A port 81A and the B port 81B in the first pressure reducing circuit 53, the description here is omitted. , A flow path 93 connected to the B port 81B, a B flow path 95 connected to the A port 81A, and a communication flow path 97 connected to the second flow hole 83B.

The operation and effect of the variable displacement hydraulic pump according to the present invention when driven will be described below. FIG. 6 shows a circuit diagram of the travel hydraulic circuit 23 when the machine body 1 is accelerating forward.

FIG. 7 is a side view of the swash plate 67 and the piston 65 when the cylinder port 89 is not in communication with the A port 81A and the B port 81B while the machine body 1 is accelerating forward. It is explanatory drawing which arranged the front view of the valve plate 71. FIG. For convenience of explanation, the piston 65 and cylinder port 89 on the left side in FIG. 7 are also referred to as piston 65A and cylinder port 89A, and the piston 65 and cylinder port 89 on the right side are also referred to as piston 65B and cylinder port 89B.

According to FIG. 6, when the machine body 1 is moved forward, hydraulic fluid discharged from the A port 81A is sucked into the B port 81B via the traveling motor 43. As shown in FIG. In other words, as shown in FIG. 7, when the swash plate 67 is tilted toward the switching land 85B, the piston 65 is at the bottom dead center at the position communicating with the switching land 85A, and at the position communicating with the switching land 85B. top dead center.

Accordingly, the piston 65 can discharge hydraulic oil to the first flow path 45 by moving from the bottom dead center to the top dead center when the cylinder port 89 communicates with the A port 81A. Similarly, the piston 65 can suck hydraulic oil from the second flow path 47 by moving from the top dead center to the bottom dead center when the cylinder port 89 communicates with the B port 81B.

Here, when the body 1 is accelerating forward, a high pressure is generated on the first flow path 45 side due to the load for driving the wheels 3a. That is, since the A port 81A becomes high pressure and the B port 81B becomes low pressure, the switching valve 91 of the first pressure reducing circuit 53 is switched to the supply position 101a. As a result, the piston 65A and the cylinder port 89A move toward the bottom dead center while hydraulic oil is supplied from the first flow hole 83A.

FIG. 8 shows the movement (cylinder position , vertical axis) in the cylinder 63a (cylinder internal pressure, horizontal axis). In this graph, the internal pressure in the cylinder 63a when it is assumed that there is no first communication hole 83A is also indicated by a dashed line as an example (hereinafter referred to as example 1).

According to example 1, after the cylinder port 89A passes point 1, the cylinder internal pressure decreases as the piston 65 moves toward the bottom dead center. After that, when the cylinder port 89A moves to a position (hereinafter referred to as point 2) where the cylinder port 89A begins to communicate with the notch 82A, high-pressure hydraulic oil begins to flow into the cylinder 63a from the A port 81A. Furthermore, after that, as the cylinder port 89A moves from the point 2 to the point 3, the cylinder internal pressure rises.

When the cylinder internal pressure abruptly changes from low pressure (points 1 to 2) to high pressure (points 2 to 3) as in example 1, the internal pressure in the A port 81A rises sharply. Such a sudden increase in the internal pressure in the A port 81A may cause so-called pulsation that instantaneously changes the pressure balance of the entire travel hydraulic circuit 23 .

Therefore, by providing the first communication hole 83A in the switching land 85A, from the point 1 to the point 2, from the A port 81A through the A channel 93, the supply position 101a, the communication channel 97 and the cylinder port 89A Hydraulic oil can be supplied to the cylinder 63a. By increasing the cylinder internal pressure in advance while the cylinder port 89A is moving from point 1 to point 2, a sudden increase in the cylinder internal pressure can be reduced and pulsation can be suppressed.

FIG. 9 shows the time (cylinder position, vertical axis) when the cylinder port 89B moves from the position where the cylinder port 89B stops communicating with the A port 81A (hereinafter referred to as point 4) to the position where communication with the B port 81B starts (hereinafter referred to as point 6). is a graph showing the internal pressure (cylinder internal pressure, horizontal axis) in the cylinder 63a at . In this graph, the internal pressure in the cylinder 63a when it is assumed that there is no second communication hole 83B is also indicated by a dashed line as an example (hereinafter referred to as example 2).

According to Example 2, after the cylinder port 89B passes point 4, the cylinder internal pressure increases as the piston 65 moves toward the top dead center. After that, when the cylinder port 89B moves to the position where it starts communicating with the notch 82B (hereinafter referred to as point 5), hydraulic oil starts to flow from the cylinder 63a into the B port 81B. Furthermore, after that, as the cylinder port 89B moves from point 5 to point 6, the cylinder internal pressure decreases.

When the cylinder internal pressure abruptly changes from a high pressure (points 4 to 5) to a low pressure (points 5 to 6) as in example 2, the internal pressure in the B port 81B drops abruptly. Such a sudden drop in the internal pressure in the B port 81B may cause pulsation in the entire traveling hydraulic circuit 23, as in the first example.

Therefore, by providing the second communication hole 83B in the switching land 85B, from the point 4 to the point 5, from the cylinder 63a to the hydraulic oil tank 25 via the communication passage 97, the discharge position 101b and the discharge passage 95a. Oil can be drained. As a result, when the cylinder port 89B is positioned at the point 5, it is possible to reduce the sudden drop in the cylinder internal pressure and suppress the occurrence of pulsation.

By the way, as described above, when the cylinder port 89A moves from the point 1 to the point 2, hydraulic oil is supplied from the A port 81A to the cylinder 63a. On the other hand, when the cylinder port 89B moves from point 4 to point 5, hydraulic oil is discharged from the cylinder 63a to the hydraulic oil tank 25. As shown in FIG. That is, when the cylinder port 89B moves from the point 4 to the point 5, the working oil in the cylinder 63a is discharged from the travel hydraulic circuit 23, which is a closed circuit.

In this case, as shown in FIG. 5 above, the discharge position 101b opens wider than the supply position 101a, and the hydraulic oil is discharged to the hydraulic oil tank 25 without communicating with the A port 81A and the B port 81B. Therefore, the influence of changes in the cylinder internal pressure on pulsation can be suppressed only between points 1 and 2 rather than between points 4 and 5. Thereby, the amplitude of the pulsation of the A port 81A and the B port 81B can be reduced.

FIG. 10 is a circuit diagram of the travel hydraulic circuit 23 when the machine body 1 is accelerating rearward. 11 is a side view of the swash plate 67 and the piston 65 and the valve plate 71 when the cylinder port 89 is in a position where it does not communicate with the ports 81A and 81B while the airframe 1 is accelerating backward. is an explanatory diagram in which the front views of are arranged.

According to FIG. 10, when the machine body 1 is accelerated backward, hydraulic oil discharged from the B port 81B is sucked into the A port 81A via the travel motor 43. As shown in FIG. In other words, as shown in FIG. 11, when the swash plate 67 is tilted toward the switching land 85A, the piston 65 is at the bottom dead center at the position communicating with the switching land 85B, and at the position communicating with the switching land 85A. top dead center.

In other words, the piston 65 moves from the bottom dead center to the top dead center when the cylinder port 89 communicates with the B port 81B, which is the opposite of when the airframe 1 is accelerated forward, thereby pushing the hydraulic oil to the second position. It can be discharged to the channel 47 . Further, the piston 65 can suck hydraulic oil from the first flow path 45 by moving from the top dead center to the bottom dead center when the cylinder port 89 communicates with the A port 81A.

Here, when the airframe 1 is accelerating rearward, the B port 81B becomes high pressure and the A port 81A becomes low pressure, contrary to when the airframe 1 is accelerated forward. The switching valve 91 of the decompression circuit 53 switches to the discharge position 101b.

As described above, the second pressure reducing circuit 55 is arranged point-symmetrically with respect to the first pressure reducing circuit 53 with the drive axis C as a reference. Therefore, the switching valve 91 of the second pressure reducing circuit 55 is switched to the supply position 101a. That is, in the variable displacement hydraulic pump 41, even if the swash plate 67 can be tilted to either the switching land 85A side or the switching land 85B side like the pump main body 51, the cylinder internal pressure rapidly increases and decreases. pulsation can be suppressed.

FIG. 12 is a circuit diagram of the travel hydraulic circuit 23 when decelerating the machine body 1 moving forward. FIG. 13 is a side view of the swash plate 67 and the piston 65 and the valve plate 71 when the piston 65 has moved to the bottom dead center and the top dead center when the airframe 1 moving forward is decelerated. is an explanatory diagram in which the front views of are arranged.

According to FIG. 12, when the machine body 1 decelerates, the traveling motor 43 is driven by the wheels 3a to suck hydraulic oil from the first flow path 45 and discharge it to the second flow path 47 (pump action). When such a pumping action occurs in the travel motor 43, the pressure level in the travel hydraulic circuit 23 is opposite to that when the hydraulic oil accelerates the airframe 1 forward (see FIGS. 6 and 7). ). As a result, the variable displacement hydraulic pump 41 discharges low-pressure hydraulic fluid to the first flow path 45 and sucks high-pressure hydraulic fluid from the second flow path 47 (motor action).

According to FIG. 13, the A port 81A becomes low pressure and the B port 81B becomes high pressure, contrary to when the airframe 1 is accelerated forward. On the other hand, regarding the top dead center and the bottom dead center, the bottom dead center is located on the switching land 85A and the top dead center is located on the switching land 85B, similarly to when the aircraft 1 is accelerated forward.

In addition, since the A port 81A has a low pressure and the B port 81B has a high pressure, the switching valve 91 of the first pressure reducing circuit 53 is set to the discharge position 101b and the second pressure reducing circuit 55 switching valves 91 are respectively switched to the supply position 101a.

13, before the cylinder port 89A communicates with the notch 82A, the hydraulic fluid is discharged from the cylinder 63a to the hydraulic fluid tank 25, so that when the cylinder port 89A communicates with the notch 82A, the cylinder port 89A By reducing the differential pressure with the A port 81A, the working oil in the cylinder 63a can suppress an increase in pulsation in the A port 81A.

Similarly, by supplying hydraulic oil from the B port 81B to the cylinder 63a before the cylinder port 89B communicates with the notch 82B, the difference between the cylinder port 89B and the B port 81B when the cylinder port 89B communicates with the notch 82B is By reducing the pressure, the piston 65 can suppress an increase in pulsation in the B port 81B.

FIG. 14 is a front view of a valve plate in another embodiment. The neutral position 201n of the valve body 201 in another embodiment opens the first flow holes 83A, 83B and the A flow path 93 and the first flow holes 83A, 83B and the B flow path 95 so that the hydraulic fluid can flow. ing.

As a result, when the valve body 201 in another embodiment is in the neutral position 201n, the hydraulic oil is supplied from the A port 81A or the B port 81B to the cylinder 63a, and the hydraulic oil is discharged from the cylinder 63a to the hydraulic oil tank 25. Therefore, even when the valve body 201 is in the neutral position 201n, it is possible to reduce the sudden rise and fall of the cylinder internal pressure, and to suppress the occurrence of pulsation satisfactorily.

As described above, the variable displacement hydraulic pump 41 according to the present invention includes the drive shaft 61 rotated by the engine 9 and a plurality of cylinders rotating in conjunction with the drive shaft 61 and extending in the axial direction of the drive shaft 61. 63a, a plurality of pistons 65 reciprocally inserted into each cylinder 63a of the cylinder block 63, and an end portion of each piston 65 projecting from each cylinder 63a on the side opposite to the cylinder 63a. A swash plate 67 tiltably provided on the side of the swash plate 67, a shoe 65a and a shoe retainer 67a for guiding the pistons 65 to rotate along the swash plate 67, and a cylinder block 63 interposed between the swash plate 67 and the shaft. An A port 81A and a B port 81B, which are located on the opposite sides of the direction and intermittently communicate with each cylinder 63a, are formed with a pair of switching lands 85A and 85B interposed therebetween, and the valve plate is in sliding contact with the cylinder block 63. 71 and.

Further, in the variable displacement hydraulic pump 41, first flow holes 83A and 83B are formed in the switching lands 85A and 85B and allow hydraulic oil to flow into the cylinder 63a when communicating with the cylinder 63a. A supply passage 93a that supplies oil, a discharge passage 95a that discharges hydraulic oil in the cylinder 63a, a supply position 101a that connects the first flow holes 83A, 83B and the supply passage 93a, and the first flow holes 83A, 83B. and a discharge passage 95a, and has a switching valve 91 that can be switched between the supply position 101a and the discharge position 101b.

In the variable displacement hydraulic pump 41, when the switching valve 91 is switched to the supply position 101a, the hydraulic oil in the supply passage 93a is supplied into the cylinder 63a through the first flow holes 83A and 83B, and the switching valve 91 is in the discharge position. 101b, the hydraulic oil in the cylinder 63a is discharged to the discharge passage 95a through the first flow holes 83A and 83B, and the flow rate of the hydraulic oil that is switched to the supply position 101a and circulated in the supply passage 93a Also, it is switched to the discharge position 101b to increase the flow rate of the hydraulic oil circulated in the discharge passage 95a.

Therefore, when the switching valve 91 is at the discharge position 101b, the flow rate of the hydraulic oil flowing through it is increased more than when it is at the supply position 101a. It is possible to positively reduce the pressure fluctuation when switching from the port to the other of the A port 81A or the B port 81B serving as the suction port.

Further, since the switching valve 91 is provided, which can be switched between the supply position 101a and the discharge position 101b, in which one of the supply passage 93a and the discharge passage 95a is closed while the other is opened, the hydraulic oil is supplied to the cylinder 63a. to increase the internal pressure in the cylinder 63a, and then communicate with the A port 81A or B port 81B to reduce the internal pressure fluctuations in the A port 81A or B port 81B, and supply to the cylinder 63a from the supply passage 93a. It is possible to suppress the occurrence of rotational fluctuations in the cylinder block 63 and the drive shaft 61 due to a rapid increase in the internal pressure in the cylinder 63a due to the working oil.

Since the switching valve 91 has a larger opening area at the discharge position 101b than the opening area at the supply position 101a, the structure is simple, and the flow rate of the hydraulic oil supplied through the supply passage 93a and discharged through the discharge passage 95a is reduced. The flow rate of hydraulic oil to be applied can be specified in the switching valve 91 .

Since the discharge passage 95a is connected to the hydraulic oil tank 25 that stores the hydraulic oil so that the hydraulic oil can flow, the pressure inside the A port 81A and the B port 81B when the internal pressure of the cylinder port 89 is reduced is reduced. It is possible to suppress the occurrence of internal pressure fluctuations.

Since the supply passage 93a connects the hydraulic fluid to the A port 81A and the B port 81B so that the hydraulic fluid can flow, The amount of leakage to the outside of the circuit 23 can be reduced.

When the switching valve 91 switches between the supply position 101a and the discharge position 101b, the switching valve 91 selects a flow path that opens to either the supply passage 93a or the discharge passage 95a according to the differential pressure between the A port 81A and the B port 81B. Since the switching and the opening degree are adjusted, for example, the suction port and the discharge port of the A port 81A and the B port 81B can be changed by switching the tilting direction of the swash plate 67 or by causing a motor action to occur in the pump body 51. Even when the roles of the ports are switched, it is possible to switch between the supply passage 93a and the discharge passage 95a according to the internal pressure fluctuations of the A port 81A and the B port 81B.

As described above, the present invention is not limited to the above embodiments, and can be modified without departing from the gist of the invention.
For example, in the present embodiment, the variable displacement hydraulic pump 41 mounted on a wheel loader has been described, but it may be mounted on a road paving machine such as a tire roller.

Further, in the present embodiment, the switch valve 91 is used as the on-off valve, and the differential pressure between the A port 81A and the B port 81B is used to switch the position of the valve body 101. Alternatively, a pressure sensor may be used to determine the differential pressure between the A port 81A and the B port 81B to switch.

1 airframe 9 engine (driving device)
25 hydraulic oil tank 41 variable displacement hydraulic pump 61 drive shaft (drive shaft member)
63 cylinder block 63a cylinder 65 piston 65a shoe (guide member)
67 swash plate 67a shoe retainer (guide member)
71 valve plate
81A A port 81B B port 91 Switching valve (open/close valve)
93a supply passage (supply channel)
95a discharge passage (discharge channel)
101 valve element 101a supply position 101b discharge position 102a A spring (supply limit biasing member)
102b B spring (emission limit biasing member)
83A first circulation hole 83B second circulation hole 85A, 85B switching land

Claims (1)

a drive shaft member driven by a drive;
a cylinder block rotating in conjunction with the drive shaft member and having a plurality of cylinders extending in the axial direction of the drive shaft member;
a plurality of pistons reciprocally fitted in each cylinder of the cylinder block;
a swash plate tiltably provided on a protruding end side of each of the pistons protruding from each of the cylinders;
a guide member for guiding each piston to rotate along the swash plate;
An A port and a B port are provided on the opposite side of the swash plate with respect to the cylinder block in the axial direction and intermittently communicate with the cylinders, and are formed with a pair of switching lands interposed therebetween. A double-tilt type variable displacement hydraulic pump comprising a valve plate in sliding contact with a cylinder block,
a circulation hole formed in the switching land for circulating hydraulic oil into the cylinder when communicating with the cylinder;
a supply passage connected to the A port or the B port so as to allow the hydraulic fluid to flow therein, and supplying the hydraulic fluid to the cylinder;
a discharge passage capable of discharging hydraulic oil in the cylinder to a hydraulic oil tank;
It includes a supply position connecting the flow hole and the supply channel, and a discharge position connecting the flow hole and the discharge flow channel, and has an on-off valve that can be switched between the supply position and the discharge position. ,
The on-off valve switches between the supply position and the discharge position according to the differential pressure between the A port and the B port, and when switched to the supply position, the hydraulic oil in the supply passage is Hydraulic oil is supplied into the cylinder through the circulation hole, and when the hydraulic oil is switched to the discharge position, the hydraulic oil in the cylinder is discharged to the discharge passage through the circulation hole and switched to the supply position. is switched to the discharge position to increase the flow rate of the hydraulic oil circulated in the discharge passage than the flow rate of the hydraulic oil circulated in the supply passage, and according to the differential pressure between the A port and the B port A double-tilt type variable displacement hydraulic pump characterized by adjusting the degree of opening.

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