The present invention relates to a variable capacity piston pump.
As a variable capacity piston pump in the related art, for example, as described in Patent Literature 1 (Japanese Unexamined Patent Publication No. 2006-348911), a variable capacity piston pump which is used as a hydraulic pressure generation source of a hydraulic circuit and changes a discharge capacity by adjusting the inclination of a swashplate is known.
The variable capacity piston pump described in Patent Literature 1 includes a control piston which presses the swashplate and a swashplate return spring which biases the swashplate from a side opposite to the control piston. As the control pressure of the control piston is changed, the magnitude of a pressing force exerted on the swashplate is changed. By controlling the magnitude of the pressing force, the inclination of the swashplate is adjusted. Specifically, when the pressing force of the control piston is decreased, the inclination of the swashplate is increased by the biasing force of the swashplate return spring. When the pressing force of the control piston is increased, the inclination of the swashplate is decreased. When the inclination is changed, the swashplate turns about a certain turning center.
The inventors found that when the inclination of the swashplate is changed, the distance between the pressing force of the control piston and the turning center (that is, the length of a moment arm of the pressing force of the control piston about the turning center) is changed, resulting in deterioration in controllability over the inclination of the swashplate.
For example, when the control piston presses the swashplate to decrease the inclination of the swashplate, in a case where the length of the moment arm is shortened as the inclination of the swashplate is decreased, the moment of the pressing force of the control piston about the turning center is decreased, and it becomes difficult for the swashplate to rotate. In this case, the responsiveness of the inclination of the swashplate to the pressing force of the control piston deteriorates (for example, the response speed becomes slow), and inappropriate control over the inclination of the swashplate may be incurred.
In contrast, when the control piston presses the swashplate to decrease the inclination of the swashplate, in a case where the length of the moment arm is lengthened as the inclination of the swashplate is decreased, the moment of the pressing force of the control piston about the turning center is increased, and the swashplate more easily rotates. In this case, the response of the inclination of the swashplate to the pressing force of the control piston becomes excessively sensitive (for example, the response speed becomes excessively fast), and inappropriate control over the inclination of the swashplate may be incurred.
An object of various aspects of the present invention is to provide a variable capacity piston pump which achieves an improvement in controllability over the inclination of a swashplate.
According to an aspect of the present invention, there is provided a variable capacity piston pump performing suction and discharge of a hydraulic fluid by reciprocation of a piston in a cylinder block rotating integrally with a rotating shaft, the stroke of the reciprocation of the piston depending on an inclination of a swashplate, wherein the swashplate includes a sliding contact surface contacting slidably with one end portion of the piston via a shoe, the swashplate being disposed to enable to turn about a turning center to change the inclination that defines the stroke of the piston, the variable capacity piston pump comprising: a pressing portion disposed on one side with respect to the sliding contact surface of the swashplate, the pressing portion causing a pressing force to act along one direction by pressing a pressed portion of the swashplate to adjust the inclination of the swashplate between a maximum inclination and a minimum inclination, wherein a discharge capacity of the hydraulic fluid is maximized at the maximum inclination and the discharge capacity of the hydraulic fluid is minimized at the minimum inclination, and a swashplate return spring disposed on the other side with respect to the sliding contact surface of the swashplate, the swashplate return spring biasing the pressed portion of the swashplate toward the one side of the sliding contact surface, wherein the pressed portion is capable of taking a first action position and a second action position, wherein the first action position is a position at which the pressing force of the pressing portion acts when the inclination of the swashplate is the maximum inclination and the second action position is a position at which the pressing force of the pressing portion acts when the inclination of the swashplate is the minimum inclination, and wherein there is a positional relationship in which a vertical reference line passes between the first action position and the second action position, the vertical reference line being a straight line perpendicular to a parallel reference line and passing through the turning center of the swashplate, the parallel reference line being a straight line parallel to a direction in which the pressing force of the pressing portion acts and passing through the turning center of the swashplate.
In the variable capacity piston pump described above, there is a positional relationship in which the vertical reference line passes between the first action position which is the position at which the pressing force of the pressing portion acts on the pressed portion when the inclination of the swashplate is the maximum inclination and the second action position which is the position at which the pressing force of the pressing portion acts on the pressed portion when the inclination of the swashplate is the minimum inclination. When the position at which the pressing force of the pressing portion acts on the pressed portion is on the vertical reference line or near the vertical reference line, the length of a moment arm of the pressing force due to the pressing portion barely changes. In the variable capacity piston pump described above, since the first action position and the second action position are positioned with the vertical reference line interposed therebetween, the position at which the pressing force of the pressing portion acts on the pressed portion is on the vertical reference line or near the vertical reference line. Therefore, even when the inclination of the swashplate changes from the maximum inclination to the minimum inclination, the length of the moment arm of the pressing force barely changes. Accordingly, the amount of variation in the moment of the pressing force can be suppressed regardless of the inclination of the swashplate. As a result, controllability over the inclination of the swashplate can be improved.
According to another aspect of the present invention, in the variable capacity piston pump, there may be a positional relationship in which the vertical reference line passes through a midpoint between the first action position and the second action position. In this case, the length of the moment arm when the inclination of the swashplate is the maximum inclination and the length of the moment arm when the inclination of the swashplate is the minimum inclination can be equal to each other. Therefore, the amount of a change in the length of the moment arm of the pressing force while the inclination of the swashplate displaces from the maximum inclination to the minimum inclination can be minimized. Accordingly, the amount of variation of the moment of the pressing force due to the displacement of the inclination of the swashplate can be suppressed to the maximum degree. As a result, controllability over the inclination of the swashplate can be further improved.
According to another aspect of the present invention, in the variable capacity piston pump, the pressing portion may be disposed in parallel to the rotating shaft. In this case, design of the variable capacity piston pump can be facilitated.
According to the various aspects of the present invention, a variable capacity piston pump which achieves an improvement in controllability over the inclination of a swashplate is provided.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the description, like elements which are the same or having the same function are denoted by like reference numerals, and overlapping description thereof will be omitted.
First, a variable capacity piston pump (hereinafter, “a pump”) according to the embodiment will be described with reference to
The pump housing 10 is configured by bonding a front housing 10a, a center housing 10b, and a rear housing 10c together, and has a crank chamber 12 therein.
Most of the rotating shaft 20 is accommodated in the crank chamber 12 of the pump housing 10, and only one end portion thereof protrudes from the pump housing 10. The rotating shaft 20 is rotatably held in the crank chamber 12 by a bearing. The end portion of the rotating shaft 20 protruding from the pump housing 10 is connected to a power take-off (not illustrated) such that the entirety of the rotating shaft 20 is driven to rotate by an engine.
The cylinder block 14 is also accommodated in the crank chamber 12 of the pump housing 10. The cylinder block 14 is spline-fitted to the rotating shaft 20 so as to rotate integrally with the rotating shaft 20. In the cylinder block 14, a plurality of cylinder bores 14a, each including an opening on a side of the protruding end portion of the rotating shaft 20, are provided, and the plurality of cylinder bores 14a are disposed with intervals therebetween at a predetermined angle around the rotating shaft 20 in the cylinder block 14. In addition, in each of the plurality of cylinder bores 14a, a piston 16a having a head protruding toward the side of the protruding end portion of the rotating shaft 20 is accommodated.
A swashplate 30 is further accommodated in the crank chamber 12 of the pump housing 10. Hereinafter, the configuration of the swashplate 30 will be described with reference to
As illustrated in
The body portion 31 has a substantially plate shape, and the center portion thereof is provided with a through-hole 31a through which the above-described rotating shaft 20 is inserted. The pair of sliding portions 32 are provided at positions with the body portion 31 interposed therebetween to be integrated with the body portion 31.
The rear surface side of the body portion 31 and the sliding portions 32 become a flat surface 30a as illustrated in
In addition, in the body portion 31, the pressed portion 33 which extends upward from the body portion 31 is provided. On the rear surface side in the pressed portion 33, an accommodation hole 33a is formed, and a cylindrical member 33b, which will be described later, is disposed in the accommodation hole 33a. In addition, the cylindrical member 33b may be disposed in a fixed state so as not to be turned, or may be disposed so as to be turned. In addition, on the front surface side in the pressed portion 33, at a position biased by the tip end portion of a swashplate return spring 60, a protruding portion 33c and a planar portion 33d with which the tip end portion of the swashplate return spring 60 is engaged are formed.
Returning to
The swashplate 30 is disposed so as to turn about the turning center X and change the inclination that defines the stroke of the piston 16. For example, the inclination can be defined as an angle with respect to a straight line perpendicular to the axial line of the rotating shaft 20. In the embodiment, the inclination is defined as an angle of the sliding contact surface 30a with respect to the straight line perpendicular to the axial line of the rotating shaft 20.
The sliding contact surface 30a on the rear surface side of the swashplate 30 faces the cylinder block 14 side. The head (one end portion) of each piston 16 protruding from the cylinder block 14 comes into sliding contact with the sliding contact surface 30a via a shoe 36. The shoe 36 to which the head of the piston 16 attached is held in a disk-shaped retainer 35 having a hole into which the shoe 36 is inserted. When the cylinder block 14 is rotated along with the rotating shaft 20, each piston 16 rotates about the rotating shaft 20 while sliding on the sliding contact surface 30a via the shoe 36.
As the swashplate 30 is turned and inclined about the turning center X, the end portion of the head side (the left end portion in
In addition, as the cylinder block 14 and the rotating shaft 20 rotate integrally with each other, the stroke of each piston 16 defined by the inclination of the swashplate 30 is reciprocated, and the cylinder bore 14a alternately communicates with a suction port 40a and a discharge port 40b forming an arc shape, which are provided to penetrate through the valve plate 40. Accordingly, hydraulic oil is suctioned into the cylinder bore 14a from the suction port 40a, and the hydraulic oil in the cylinder bore 14a is discharged from the discharge port 40b due to a pump action. In addition, a suction passage 10d and a discharge passage 10e are formed in the rear housing 10c to respectively communicate with the suction port 40a and the discharge port 40b.
The pump 1 is further provided with a control piston 50 provided on the rear surface side of the swashplate 30, that is, on the cylinder block 14 side. The control piston 50 is provided at a side portion of the center housing 10b of the pump housing 10, and includes a housing 52 that communicates with the crank chamber 12 and a piston portion 58 that reciprocates in the housing 52. The housing 52 has a substantially cylindrical shape extending in a direction inclined with respect to the rotating shaft 20 so as to cause the piston portion 58 to face the pressed portion 33 of the swashplate 30.
One opening of the openings of the housing 52 distant from the swashplate 30 is blocked by a screw 54. Accordingly, a piston accommodation chamber 56 is defined in the housing 52, and the piston portion 58 is accommodated in the piston accommodation chamber 56.
The piston portion 58 has a columnar external shape. The diameter of the piston portion 58 is designed such that there is no gap from the inner wall surface of the piston accommodation chamber 56 and the piston portion 58 slides in the piston accommodation chamber 56. The end surface of the piston portion 58 on the swashplate 30 is a planar shape and can move to a position that comes into contact with the cylindrical member 33b in the pressed portion 33 of the swashplate 30. As illustrated in
A space between the piston portion 58 and the screw 54 in the piston accommodation chamber 56 functions as a control chamber 56a into which the hydraulic oil flows. The pressure in the control chamber 56a (hereinafter, referred to as control pressure) is changed due to the inflow of the hydraulic oil. The control piston 50 causes the piston portion 58 to slide due to a change in the control pressure and press the swashplate 30 from the cylinder block 14 side. Accordingly, the control piston 50 adjusts the inclination of the swashplate 30 between the maximum inclination, at which the discharge capacity of the hydraulic oil is maximized, and the minimum inclination, at which the discharge capacity of the hydraulic oil is minimized.
The pump 1 further includes the swashplate return spring 60 which is a cylindrical spiral shape (coil spring) extending in one direction on the front surface side of the swashplate 30. That is, the swashplate return spring 60 is disposed on the side opposite to the control piston 50 with respect to the sliding contact surface 30a of the swashplate 30. Specifically, the base end portion of the swashplate return spring 60 is accommodated in a spring chamber 70 formed in the front housing 10a of the pump housing 10.
In the embodiment, the spring chamber 70 is formed in parallel to the rotating shaft 20, and the swashplate return spring 60 extends toward the swashplate 30 from the spring chamber 70. As a result, the swashplate return spring 60 is disposed so that the axial direction thereof is parallel to the rotating shaft 20. The tip end portion of the swashplate return spring 60 abuts the front surface of the pressed portion 33 of the swashplate 30 described above and is engaged with the protruding portion 33c and the planar portion 33d formed on the front surface. The swashplate return spring 60 is not fixed to the spring chamber 70 and the swashplate 30 and the position and posture thereof are held in a state of being interposed between the spring chamber 70 and the pressed portion 33.
In other words, regarding the seat surfaces (spring end surfaces) of the swashplate return spring 60, a seat surface 60a of the base end portion abuts the bottom wall of the spring chamber 70, and a seat surface 60b of the tip end portion abuts the pressed portion 33 of the swashplate 30. Accordingly, the swashplate return spring 60 is compressed such that the swashplate 30 is biased toward the cylinder block side with respect to the sliding contact surface 30a. In addition, the swashplate return spring 60 is a wire spring formed by processing a metallic wire rod such as SWP-B.
Next, with reference to
First, references such as the turning center X, the vertical reference line and the parallel reference line for the action position of the pressing force of the piston portion 58 will be described.
As illustrated in
The parallel reference line Y is a straight line which is parallel to a direction in which the pressing force of the piston portion 58 acts and passes through the turning center X. A straight line that is perpendicular to the parallel reference line Y and passes through the turning center X is defined as the vertical reference line Z.
In
As indicated by the double-headed arrow A of
In a case where the first action position A1, the second action position A2, and the vertical reference line Z have this positional relationship, as illustrated in
As described above, while the inclination of the swashplate 30 moves from the maximum inclination to the minimum inclination, the action position of the pressing force F barely displaces in the directions of the vertical reference line Z. Therefore, the distance between the pressing force F and the turning center X when the inclination of the swashplate 30 is the maximum inclination (that is, the length of a moment arm of the pressing force F about the turning center X) La1 and the distance between the pressing force F and the turning center X when the inclination of the swashplate 30 is the minimum inclination La2 barely change. That is, even when the inclination of the swashplate 30 moves from the maximum inclination to the minimum inclination, the length of the moment arm of the pressing force F about the turning center X barely changes. Therefore, the amount of variation in the moment of the pressing force F about the turning center X due to a change in the inclination of the swashplate 30 can be suppressed.
The double-headed arrow B indicates variation in the action position of the pressing force F in a case where both a first action position B1 and a second action position B2 are positioned on the swashplate return spring 60 side in relation to the vertical reference line Z. As illustrated in
As described above, when the length of the moment arm of the pressing force F is shortened as the inclination of the swashplate 30 is decreased, the moment of the pressing force F is decreased, and it is difficult for the swashplate 30 to rotate. Therefore, the responsiveness of the inclination of the swashplate 30 to the pressing force F of the piston portion 58 deteriorates (for example, the response speed becomes slow), and the inclination of the swashplate 30 is not appropriately controlled.
The double-headed arrow C indicates variation in the action position of the pressing force F in a case where both a first action position C1 and a second action position C2 are positioned on the control piston 50 side in relation to the vertical reference line Z. As illustrated in
As described above, when the length of the moment arm of the pressing force F is lengthened as the inclination of the swashplate 30 is decreased, the moment of the pressing force F is increased, and the swashplate 30 more easily rotate. Therefore, the response of the inclination of the swashplate 30 to the pressing force F of the piston portion 58 becomes excessively sensitive (for example, the response speed becomes excessively fast), and the inclination of the swashplate 30 is also not appropriately controlled.
As described above, in the pump 1 according to the embodiment, since the first action position A1 and the second action position A2 are positioned with the vertical reference line Z interposed therebetween, the position at which the pressing force F of the piston portion 58 of the control piston 50 acts on the cylindrical member 33b of the pressed portion 33 is on the vertical reference line Z or near the vertical reference line Z. Therefore, even when the inclination of the swashplate 30 displaces from the maximum inclination to the minimum inclination, the length of the moment arm of the pressing force F barely changes, and the amount of variation in the moment of the pressing force F due to the displacement of the inclination of the swashplate 30 can be suppressed. As a result, controllability over the inclination of the swashplate 30 can be improved.
In addition, the positional relationship in which the vertical reference line Z passes between the first action position A1 and the second action position A2, that is, the positional relationship in which the vertical reference line Z is interposed between the first action position A1 and the second action position A2 includes a positional relationship in which the vertical reference line Z overlaps the first action position A1 or the second action position A2.
In addition, as indicated by the double-headed arrow A of
At this time, the length La1 of the moment arm when the inclination of the swashplate 30 is the maximum inclination and the length La2 of the moment arm when the inclination of the swashplate 30 is the minimum inclination can be equal to each other. That is, the length of the moment arm does not excessively increases in any of cases where the inclination of the swashplate 30 is the maximum inclination or the minimum inclination. Therefore, the amount of variation of the moment due to the displacement of the inclination of the swashplate 30 can be minimized. Accordingly, controllability over the inclination of the swashplate 30 can be further improved.
While various embodiments of the present invention have been described, the present invention is not limited to the embodiments, and includes modifications without departing from the gist described in the appended claims and applications to other forms.
The swashplate 30 is not limited to that in the embodiment. For example, instead of the swashplate 30, a swashplate 130 having a shape illustrated in
The swashplate 130 includes a pair of rotating shaft portions 132 instead of the pair of sliding portions 32 of the swashplate 30. The above-described swashplate 30 has a form that oscillates about the turning center X by cooperation between the sliding portions 32 and the swashplate receiving member 34. However, the swashplate 130 can oscillate about the turning center X since the pair of rotating shaft portions 132 having a columnar shape extending along the turning center X are rotatably held in the crank chamber 12. The swashplate 130 also includes a disk-shaped body portion 131 having the same function as that of the body portion 31 of the swashplate 30 described above. The body portion 131 includes a sliding contact surface 130a, which is the same as the sliding contact surface 30a, on the rear surface side thereof and further includes a pressed portion 133 which is the same as the pressed portion 33 at the upper portion thereof. The swashplate 130 illustrated in
In addition,
As illustrated in
In addition, in the case where the control piston 50 is disposed obliquely with respect to the rotating shaft 20 as in the above-described embodiment, the dimensions (diameter dimension) of the center housing 10b are greater than those of the front housing 10a or the rear housing 10c. In the case where the piston portion 58 of the control piston 50 is disposed in parallel to the rotating shaft 20, an increase in the dimensions is suppressed. As a result, miniaturization of the variable capacity piston pump can be realized.
Number | Date | Country | Kind |
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2014-145926 | Jul 2014 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2015/069135 | 7/2/2015 | WO | 00 |