JP2013087690A - Variable displacement piston pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable displacement piston pump which has increased pump efficiency by more approximating pump output: H=P×q to an ideal fixed output line.SOLUTION: A pressure reducing valve 37 attached to a body 11 includes: a valve body 45 which is integrally attached to the body 11 by a bolt member (that is not illustrated); a sleeve 46 which is screwed to the valve body 45 while being opposed to a cylinder 32 coaxially with the cylinder 32; a spool 47 which is freely slidable fitted into the sleeve 46; a spring holder 48 which is provided adjacently to the sleeve 46 and mounted to a housing 11 and the valve body 45; and a spring member 50 which is inserted between the spring holder 48 and a spring guide 49 screwed to an axial end (right end in Fig.2) of a rod 35.

Description

  The present invention relates to a variable displacement piston pump capable of approximating a pump output to an ideal constant output in a constant output variable displacement piston pump widely used as a hydraulic pump for construction machinery.

  In this type of variable displacement piston pump, the arm length: l, which decreases the tilt angle of the swash plate by the resultant force of multiple plungers, varies with the tilt angle of the swash plate: α. The present applicant has proposed a technique capable of obtaining a constant horsepower characteristic in order to keep the moment opposite to approximately constant (see, for example, Patent Document 1).

JP 2010-53854 A

  In general, as shown in FIG. 4, the constant output variable displacement piston pump for construction machinery is controlled by the characteristic curve A so that the pump output: H = P × q is constant (where P: (Discharge pressure, q: represents the discharge capacity per one rotation of the pump). As a result, as shown in FIG. 5, the pump input torque: T is controlled to be constant as shown by the characteristic line B, and T is substantially matched within a range not exceeding the rated output of the prime mover, thereby preventing the stall of the prime mover. The output can be used relatively effectively.

In a general variable displacement piston pump, the pump displacement: q is proportional to the swash plate angle: α, and has a relationship of q∝α.
Further, the arm length of the moment due to the resultant force of the plunger: l is proportional to the swash plate angle: α, and has a relationship of α∝l. The moment of clockwise rotation in FIG. 1 (clockwise in FIG. 1) due to the ranger resultant force shown in Patent Document 1 is represented by P × l, and P × l∝P × α∝P × q = H.

  The counterclockwise moment by the control piston that counters this is almost constant regardless of the swash plate angle because the secondary pressure of the pressure reducing valve that drives the control piston is constant. In the invention, H = P × q∝P × α∝P × l = C (C: constant) to l = C / P, that is, when the arm length of moment by the resultant force of the plunger: l and the discharge pressure: P have a hyperbolic relationship, the pump output : H can be kept constant.

  Here, the length of the arm of moment due to the resultant force of the plunger: l slightly changes depending on various conditions such as the rotational speed of the pump input shaft, oil temperature, hydraulic oil viscosity, and so on, so that l = C / P. When the dimensions are determined, the control characteristics with a constant output change depending on various conditions such as the number of revolutions of the pump input shaft, oil temperature, and hydraulic oil viscosity, which cannot be put to practical use.

  In order to solve this, it is necessary to reduce the influence of the change of l, that is, to design the length of l to be long. As a result, as the swash plate angle becomes smaller, it should become smaller in a hyperbolic relationship with respect to P. Since the length l of the moment arm due to the resultant force of the plunger is larger than ideal, the output characteristic is as shown in FIG. 6, and deviates from the ideal constant output characteristic, for example, the hyperbola A (shown by the chain line) in FIG. As the pressure increases, the actual discharge capacity becomes smaller than the ideal discharge capacity with a constant output. For this reason, as shown in FIG. 7, it becomes like the characteristic curve C, and the ratio of the pump output to the rated output of the prime mover decreases.

  The present invention has been made in connection with the variable displacement piston pump according to the present applicant, and the pump output: H = P × q can be approximated to an ideal constant output line to increase the pump efficiency. An object of the present invention is to provide a variable displacement piston pump.

In order to solve the above problems, the invention according to claim 1 is a shaft;
A cylinder block coupled to the shaft by a spline and rotating in synchronization with the shaft;
A plurality of pistons fitted in the cylinder block in the axial direction;
The piston has a rotation axis perpendicular to the shaft, and the rotation axis is located on the side opposite to the plunger on the plane where the piston slides, and the tilting angle of the swash plate is reduced in the direction in which the tilting force of the piston decreases. A control cylinder located at a right angle to the rotation axis of the swash plate so that a tilting moment of the swash plate acts, and provided in a direction to increase the tilt angle of the swash plate;
In a piston pump with
A pressure reducing valve that controls the control pressure to increase as the tilt angle of the swash plate decreases due to the resultant force of the piston,
The internal pressure of the control cylinder is adjusted to a constant pressure by the pressure reducing valve so that the internal pressure of the control cylinder changes according to the inclination angle of the swash plate, and the discharge pressure-discharge flow rate curve is approximated to an ideal line.

The pressure reducing valve is
A valve body attached to the body;
A sleeve screwed to the valve body and provided coaxially with the control cylinder;
A spool slidably inserted into the sleeve;
A spring member mounted between a spring member guide fastened to the rod of the control cylinder and a spring member holder engaged with the spool end;
With
The valve body is provided with a first oil passage connected to the control cylinder and a second oil passage connected to an external hydraulic source,
The sleeve is provided with radial communication passages communicating with the first and second oil passages at intervals in the axial direction,
The spool has first and second small-diameter shaft portions provided at both ends, and first and second large-diameter shaft portions provided in connection with the first and second small-diameter shaft portions, respectively. , First and second annular grooves provided in the longitudinal direction of the outer peripheral surface of the first and second large-diameter shaft portions, respectively, and lands provided between the first and second annular grooves, ,
A first communication path communicating with the tank in a substantially axial direction and communicating with the first annular groove;
A second communication path provided opposite to the first communication path in a substantially axial direction and communicating with one chamber of the spool and the second annular groove;
With
The pressure of the control cylinder is applied to one of the spools, and the elastic force of the spring member is urged to the other of the spools, and the elastic force of the spring member that changes according to the tilt angle of the swash plate and the spool The spool is displaced and the pressure acting on the control cylinder is controlled to be constant by the balance with the pressure of the control cylinder acting on the cross-sectional area of the shaft portion.

  Since the present invention has the characteristic that the secondary pressure of the pressure reducing valve increases with a decrease in the tilt angle of the swash plate, the pump output: H = P × q can be approximated to an ideal line with a constant output. It is possible to provide a variable displacement piston pump capable of increasing the pump efficiency with respect to the rated output.

1 is a schematic longitudinal sectional view showing a schematic structure of a variable displacement piston pump according to an embodiment of the present invention. It is a principal part expanded schematic longitudinal cross-sectional view of the pressure-reduction valve shown in FIG. It is explanatory drawing which shows the relationship between a swash plate, a control cylinder, and a pressure reducing valve. It is a diagram which shows the relationship between the discharge pressure and discharge capacity of an ideal constant output pump. It is a diagram which shows the relationship between the discharge pressure of an ideal constant output pump, and input torque. It is a diagram which shows the relationship between the discharge pressure and discharge capacity of an actual constant output pump. It is a diagram which shows the relationship between the discharge pressure of an actual constant output pump, and input torque. It is a diagram which shows the relationship between the pump swash plate angle | corner and secondary pressure of the pressure-reduction valve used for the variable displacement piston pump which concerns on embodiment of this invention. It is a diagram which shows the relationship between the discharge pressure implement | achieved with the variable displacement type piston pump which concerns on embodiment of this invention, and discharge capacity. It is a diagram which shows the relationship between the discharge pressure implement | achieved with the variable displacement piston pump which concerns on embodiment of this invention, and input torque.

A fixed output variable displacement piston pump (hereinafter referred to as a piston pump) according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view showing a schematic structure of the piston pump 10.
As shown in FIG. 1, the body 11 and the case 12 of the piston pump 10 are formed by a screw member (not shown), and a body 13 is formed. The body 11 and the case 12 are rotatably supported by a roller bearing 14 and a needle bearing 15. A shaft 16 is mounted. A spline groove 19 formed on the inner peripheral surface of the cylinder block 18 is coupled to the spline 17 formed on the shaft 16, and the cylinder block 18 rotates together with the shaft 16.

  A plurality of bores 20 are formed on the same circumference around the rotation axis of the cylinder block 18, and a plurality of pistons 21 are slidably inserted into the bore 20. A head portion 22 which is one end portion of the piston 21 protrudes from the opening of the bore 20 and is slidably brought into contact with the surface of the swash plate 24 via a shoe 23 and a shoe holder 23a.

The piston 21 is in sliding contact with the swash plate 24 having a rotation axis 25 perpendicular to the shaft 16, and strokes in the axial direction of the shaft 16 when the shaft 16 rotates once. The piston pump 10 that discharges fluid is configured by switching the suction process and the discharge process by the change in the volume of the bore 20 due to the reciprocation of the piston 21 in the axial direction and the valve plate 26 that is in sliding contact with the cylinder block 18. Yes.
The rotation shaft 25 of the swash plate 24 is located on the side opposite to the plunger of the flat surface 30 of the swash plate 24 with which the piston 21 is slidably contacted.

  The center of the resultant force of the plurality of pistons 21 due to the internal pressure of the bore 20 is substantially at the intersection 29 of the straight line 28 passing through the spherical center 27 of the piston 21 and the shaft 16 in FIG. Acting perpendicularly to the plane 30. Therefore, the arm length: l that reduces the tilt angle of the swash plate 24 by the resultant force 30 a of the plurality of pistons 21 varies depending on the tilt angle α of the swash plate 24.

A control cylinder 31 provided in parallel with the shaft 16 is disposed in opposition to the moment of decreasing the tilt angle α of the swash plate 24.
The control cylinder 31 is, for example, a cylinder 32 fastened to the body 11 by a screw mechanism (not shown), a control piston 33 slidably fitted in the cylinder 32, and the cylinder 32 and a control piston 33, and a rod 35 that moves in the axial direction of the cylinder 32 due to the elastic force of the spring member 34. Inside the control cylinder 31, A secondary pressure 38 of the pressure reducing valve 37 is guided.
One end (right end in FIG. 1) of the spring member 34 is engaged with a bottom surface (right wall surface in FIG. 1) of the cylinder 32, and the other end (left end in FIG. 1) is bottom surface (left side in FIG. 1) of the control piston 33. It is engaged with a stepped disk-shaped spring member guide 36 mounted on the wall surface. The spring member guide 36 is screwed to one end (left end in FIG. 1) of the rod 35.

As shown in FIG. 2, the pressure reducing valve 37 attached to the body 11 has a valve body 45 integrally attached to the body 11 by a bolt member (not shown), and is opposed to the cylinder 32 coaxially with the cylinder 32. The sleeve 46 screwed into the circular hole of the valve body 45, the spool 47 slidably fitted into the sleeve 46, and the small diameter hole of the valve body 45 provided adjacent to the sleeve 46. A spring holder 48 mounted on the portion 45a, and a spring member 50 fitted between the spring holder 48 and a spring guide 49 screwed to the shaft end (right end in FIG. 2) of the rod 35. .

A sleeve 46 screwed to the valve body 45 is fixed to the valve body 45 by a nut 51, and a spool 47 slidably fitted into the sleeve 46 is inserted into the spool 47 by a plug 52 in the axial direction. The position of the side (the right end in FIG. 2) is regulated.
The valve body 45 has a stepped circular hole, and a small-diameter hole 45a, a medium-diameter hole 45b, and a large-diameter hole 45c are continuously formed from a position close to the body 11, and An oil passage (first oil passage) 53a communicating with the control piston 33 is connected to the diameter hole portion 45b, and an oil passage (second oil passage) communicating to an external hydraulic power source (not shown) is connected to the large diameter hole portion 45c. 53b is formed.

The sleeve 46 has a stepped cylindrical shape, and a small diameter shaft portion 46a and a medium diameter shaft portion that are slidably fitted into the small diameter hole portion 45a, the medium diameter hole portion 45b, and the large diameter hole portion 45c of the valve body 45, respectively. 46b and a large diameter shaft portion 46c.
An oil passage 53a is provided between the small diameter shaft portion 46a and the medium diameter shaft portion 46b, and a communication passage 54 and a communication passage 55 are provided between the medium diameter shaft portion 46b and the large diameter shaft portion 46c. Are drilled in the radial direction at intervals.
Both ends of the spool 47 slidably fitted into the sleeve 46 form a first small diameter shaft portion 56a and a second small diameter shaft portion 56b, and the small diameter hole portion 45a and the medium hole diameter portion of the valve body 45. The first annular groove 57a and the second annular groove 57b are formed in the longitudinal direction of the outer peripheral surface at a position (range) corresponding to 45b, and a land is formed between the first annular groove 57a and the second annular groove 57b. 58 is formed. Further, a large diameter shaft portion 59a is formed between the second small diameter shaft portion 56a and the first annular groove 57a, and a large diameter shaft is formed between the second small diameter shaft portion 56b and the second annular groove 57b. A portion 59b is formed.

  Further, in the substantially axial direction of the spool 47, a communication path (first communication path) 60a is drilled from the small diameter shaft portion 56a side to a position corresponding to the first annular groove 57a, and the second small diameter shaft portion 56b. A communication path (second communication path) 60b is formed from the side to a position corresponding to the second annular groove 57b. The communication passage 60a is formed with channels 61a and 61b communicating with the first small-diameter shaft portion 56a and the first annular groove 57a in the radial direction, and the communication passage 60b is formed with the second small-diameter shaft in the radial direction. Channels 62a and 62b communicating with the portion 56b and the second annular groove 57b are formed.

The piston pump 10 according to the embodiment of the present invention is basically configured as described above. Next, the operation will be described.
When the engine (not shown) is started and the shaft 16 is driven, hydraulic pumping of the hydraulic oil is started from the piston pump 10. At the same time, as the shaft 16 rotates, the constant discharge pump 40 is driven to start feeding hydraulic oil.
In the piston pump 10 according to the embodiment of the present invention, the constant discharge pump 40 is tandemly coupled to the piston pump 10 via the shaft 16, and the discharge pressure 41 of the constant discharge pump 40 is controlled by the control cylinder of the swash plate 24. The control cylinder 31 acting on the swash plate 24 according to the discharge pressure 41 of the constant discharge pump 40 is guided to the piston chamber 43 of the piston 42 provided on the opposite side to the surface on which the load 31 (not shown) acts. The moment of increasing the discharge amount due to the load is reduced, the output of the piston pump 10 is decreased, and the outputs of the piston pump 10 and the constant discharge pump 40 are made constant.

FIG. 3 is an explanatory diagram showing the relationship between the swash plate 24, the control cylinder 31 acting on the swash plate 24, and the pressure reducing valve 37 connected to the control cylinder 31, and in FIG. The same components are denoted by the same reference numerals.
In FIG. 3, when the swash plate 24 tilts in the direction of arrow A or B with the rotation shaft 25 as a fulcrum, the pump discharge amount of the piston pump 10 (see FIG. 1) changes, and the control piston 33 of the control cylinder 31 moves to the arrow. In accordance with this displacement, the length L of the spring member 50 of the pressure reducing valve 37 changes, and the elasticity of the spring member 50 changes accordingly.

For example, when the swash plate 24 tilts in the direction of the arrow B, the control piston 33 moves in the direction of the arrow Y, the length L of the spring member 50 is shortened, the elasticity of the spring member 50 is increased, and the pressure reducing valve The secondary pressure 38 of 37 (see FIG. 1) increases.
On the contrary, when the swash plate 24 tilts in the direction of arrow A, the control piston 33 moves in the direction of arrow X, the length L of the spring member 50 becomes longer, the elastic force of the spring member 50 decreases, and the pressure is reduced. The secondary pressure 38 of the valve 37 decreases.

Therefore, in the piston pump 10 shown in FIG. 1, the elastic force of the spring member 50 of the pressure reducing valve 37 is configured to change in accordance with the pump swash plate angle α. As shown in FIG. When the angle α is small, the secondary pressure 38 of the pressure reducing valve 37 increases.
As a result, since the control piston 33 is driven by the secondary pressure 38 of the pressure reducing valve 37, the moment due to the counterclockwise control piston 33 in FIG. 1 can be increased as the pump swash plate angle α decreases. It is.

  As a result, even if the length of the arm of the moment due to the resultant force 30a of the piston 21 that should be reduced in a hyperbolic relationship with the discharge pressure P as the pump swash plate angle α decreases, By determining the characteristics of the secondary pressure 38 (see FIG. 8) of the pressure reducing valve 37 so as to correct, the output of the pump≈input torque is approximated to a substantially constant ideal line as shown in FIGS. Can do.

DESCRIPTION OF SYMBOLS 10 Variable capacity type piston pump 11 Body 12 Case 13 Main body 14, 15 Bearing 16 Shaft 18 Cylinder block 20 Bore 21 Piston 24 Swash plate 25 Rotating shaft 26 Valve plate 27 Ball center 31 Control cylinder 32 Cylinder 33 Control piston 34, 44 Spring member 35 Rod 36, 43, 50 Spring member guide 51 Nut 52 Plug 53a, 53b Oil passage 54, 55, 60a, 60b Communication passage 56a, 56b Small diameter shaft portion 57a, 57b Annular groove 58 Land 59a, 59b Large diameter shaft portion 61a, 61b, 61a, 61b flow path

Claims (2)

A shaft,
A cylinder block coupled to the shaft by a spline and rotating in synchronization with the shaft;
A plurality of pistons fitted in the cylinder block in the axial direction;
The piston has a rotation axis perpendicular to the shaft, and the rotation axis is located on the side opposite to the plunger on the plane where the piston slides, and the tilting angle of the swash plate is reduced in the direction in which the tilting force of the piston decreases. A controller cylinder disposed at a right angle to the rotation axis of the swash plate so that a tilting moment of the swash plate acts, and provided in a direction to increase the tilt angle of the swash plate;
In a piston pump with
A pressure reducing valve that controls the control pressure to increase as the tilt angle of the swash plate decreases due to the resultant force of the piston,
A variable displacement piston pump characterized in that the internal pressure of the control cylinder is adjusted to a constant pressure by the pressure reducing valve so that the internal pressure of the control cylinder changes according to the inclination angle of the swash plate, and the discharge pressure-discharge flow rate curve is approximated to an ideal line. . The pressure reducing valve is
A valve body attached to the body;
A sleeve screwed to the valve body and provided coaxially with the control cylinder;
A spool slidably inserted into the sleeve;
A spring member mounted between a spring member guide fastened to the rod of the control cylinder and a spring member holder engaged with the spool end;
With
The valve body is provided with a first oil passage connected to the control cylinder and a second oil passage connected to an external hydraulic source,
The sleeve is provided with radial communication passages communicating with the first and second oil passages at intervals in the axial direction,
The spool has first and second small-diameter shaft portions provided at both ends, and first and second large-diameter shaft portions provided in connection with the first and second small-diameter shaft portions, respectively. , First and second annular grooves provided in the longitudinal direction of the outer peripheral surface of the first and second large-diameter shaft portions, respectively, and lands provided between the first and second annular grooves, ,
A first communication path communicating with the tank in a substantially axial direction and communicating with the first annular groove;
A second communication path provided opposite to the first communication path in a substantially axial direction and communicating with one chamber of the spool and the second annular groove;
With
The pressure of the control cylinder acts on one of the spools, and the spring force of the spring member is urged on the other side of the spool, and the spring force of the spring member that changes according to the tilt angle of the pump swash plate and the spool 2. The variable displacement piston according to claim 1, wherein the spool is displaced and the pressure acting on the control cylinder is controlled to be constant by the balance with the pressure of the control cylinder acting on the cross-sectional area of the shaft portion of the shaft. pump.

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