JPH09144649A - Piston pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a driving motor in a piston pump. SOLUTION: An elastic body 18 is eccentrically fixed to the shaft 15 of a motor 14, and a rotor 19 is also fixed concentrically to the elastic body 18. When the shaft 15 is rotated, a piston 28 is reciprocated to suck and discharge an operating fluid. The elastic deformation caused in the elastic body according to discharge pressure is differed between when the piston 28 is situated in the discharge side displaced end and when it is in the inlet side discharge end. Therefore, the stroke of the piston 28 is reduced according to discharge pressure. The discharge quantity is reduced according to the rise of discharge pressure, whereby the load of the motor is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston pump, and in particular, an object thereof is to provide a piston pump capable of miniaturizing a drive motor.

[0002]

2. Description of the Related Art Conventionally, a piston pump has been known as a pump for pumping a fluid. The piston pump has a cam, a piston, and a pump chamber. A drive motor is connected to the cam as a drive source. When the cam is rotated by the drive motor, the piston reciprocates in synchronization with the rotation. When the piston reciprocates, the pump chamber expands and contracts, and the fluid is sucked and discharged. As a piston pump having such a configuration, for example, a piston pump disclosed in Japanese Utility Model Laid-Open No. 62-64886 is known. The piston pump disclosed in Japanese Utility Model Laid-Open No. 62-64886 uses an eccentric cam to reciprocate the piston. Further, the piston pump described above includes an elastic body provided concentrically with the shaft between the shaft of the drive motor and the eccentric cam. When the elastic body is interposed between the eccentric cam and the shaft, the noise generated when the eccentric cam and the piston come into contact with each other is reduced, and the operation noise of the piston pump is reduced.

[0003]

By the way, in a vehicle brake system, for example, the amount of brake fluid to be supplied to the wheel cylinders decreases as the wheel cylinder pressure increases. Therefore, the discharge capacity required for the pump used to supply the brake fluid to the wheel cylinders becomes smaller as the discharge pressure increases.
On the other hand, in the conventional piston pump described above, the stroke of the piston is kept constant, so that the discharge amount per one rotation of the cam is constant regardless of the discharge pressure. Therefore, when the above conventional piston pump is applied to a hydraulic device such as a vehicle brake device in which a required discharge amount decreases in accordance with an increase in discharge pressure, the discharge amount of the pump is low even when the discharge pressure is high. It remains the same as before, causing the load of the drive motor to increase unnecessarily. In order to always smoothly drive the above-mentioned conventional piston pump, it is necessary to give the drive motor the ability to withstand such a load. Therefore, it is difficult to reduce the size of the motor in the above conventional configuration.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a piston pump capable of downsizing the motor by reducing the load on the cam drive motor when the discharge pressure is high. To aim.

[0005]

The above object is achieved by the present invention.
As described above, in a piston pump having a motor, a cam rotated by the motor, a piston reciprocated by the rotation of the cam, and a pump chamber expanded / contracted by the reciprocating motion of the piston, the pump comprising: This is achieved by a piston pump having a reciprocating amount reducing means for reducing the reciprocating amount of the piston according to the pressure in the chamber.

In the present invention, the reciprocating amount of the piston is reduced by the reciprocating amount reducing means according to the pressure in the pump chamber. When the reciprocating amount of the piston is reduced, the discharge amount of the pump per one rotation of the motor is reduced. The pressure in the pump chamber matches the pressure on the discharge side of the pump. Therefore, the discharge amount per one rotation of the motor is reduced according to the pressure on the discharge side of the pump. The load of the motor matches the product of the pressure on the discharge side of the pump and the discharge amount. Therefore, when the motor rotation speed is constant, the load on the motor is reduced according to the pressure in the pump chamber.

Further, the above object is the invention of claim 1, wherein the reciprocating motion reducing means includes an eccentric elastic body disposed between the cam and the shaft of the motor, and the cam is This is also achieved by a piston pump that can rotate around the outer circumference of the cam and that includes an annular body that abuts the piston.

In the present invention, the piston presses the cam with a force corresponding to the pressure in the pump chamber. The elastic body is provided between the cam and the shaft of the motor. Therefore, the elastic body is contracted and deformed in the radial direction by the pressing force of the piston. The elastic body is eccentric with respect to the shaft of the motor. Therefore, the amount of contraction and deformation of the elastic body changes depending on the rotation angle of the cam. Therefore, the contraction deformation amount differs depending on whether the piston is at the discharge side displacement end or at the suction side displacement end. The position of the piston is moved to the suction side according to the amount of contraction and deformation of the elastic body. Therefore, the amount of movement of the piston due to the contraction deformation of the elastic body differs between the position of the discharge side displacement end of the piston and the position of the suction side displacement end. As a result, the displacement amount between the discharge side displacement end and the suction side displacement end of the piston, that is, the reciprocating amount is changed.

The piston is in contact with the annular body. Due to the frictional force between the annular body and the piston, the relative sliding movement between the piston and the annular body is restricted. On the other hand, the annular body can rotate around the outer circumference of the eccentric cam. Therefore, when the cam rotates, a relative rotational movement occurs between the cam and the annular body, and the rotational movement of the annular body is restricted by the frictional force between the piston and the annular body. For this reason, the annular body undergoes movement such that its center rotates around the shaft of the motor while the relative sliding movement with respect to the piston is restricted. Therefore, only reciprocating motion with respect to the piston occurs in the annular body. As a result, the frictional force acting between the piston and the annular body is reduced.

[0010]

1 is a sectional view of a piston pump 10 which is an embodiment of the present invention. The housing 11 is a rectangular parallelepiped metal member, and includes a rotor receiving portion 12 and a cylinder portion 13. The rotor receiving portion 12 is provided by forming a cylindrical recess having two steps on one surface (the left surface in FIG. 1) of the housing 11, and the small-diameter portion in order from the bottom side (the right side in FIG. 1). 12a, medium diameter portion 12
b and a large diameter portion 12c.

The motor 14 has a flange portion 1 of the motor 14.
4 a is fitted into the large diameter portion 12 c of the rotor receiving portion 12 so that it is attached to the housing 11. Large diameter part 12
An oil seal 16 is attached to c. The oil seal 16 allows the flange portion 14a of the motor 14 and the large diameter portion 1
The sealing property with 2c is secured.

The shaft 15 of the motor 14 has a large diameter portion 15a.
And a small diameter portion 15b. The large diameter portion 15a is provided on the shaft 15 on the motor 14 side (left side in FIG. 1). The large diameter portion 15 a is fitted to the inner race of the bearing 17. The outer race of the bearing 17 is fitted to the medium diameter portion 12b of the rotor receiving portion 12.

An elastic body 18 is attached to the outer peripheral surface of the small diameter portion 15b of the shaft 15. The elastic body 18 is a cylindrical elastic member, and is fixed to the shaft 15 so that its central axis is eccentric by α with respect to the central axis of the shaft 15. A rotor 19 is mounted on the outer peripheral surface of the elastic body 18. The rotor 19 is a cylindrical rigid member, and the elastic body 1
It is fixed concentrically with 8. Therefore, the rotor 19 is eccentric with respect to the shaft 15 by α in the same direction as the eccentric direction of the elastic body 18 with respect to the shaft 15.

The cylinder portion 13 of the housing 11 has a small diameter portion 12a of the rotor receiving portion 12 at one end (upper end in FIG. 1).
It is provided so that the side surface opens to the lower part in FIG. 1 and the other end (the lower end in FIG. 1) opens to the bottom surface of the housing 11. A thread 13a is formed on the inner peripheral surface of the cylinder portion 13 near the opening to the bottom surface of the housing 11. Screw thread 13
A plug 22 is screwed on a. An oil seal 23 seals between the plug 22 and the cylinder portion 13. A cylinder base 2 is provided on the upper surface of the plug 22 in FIG.
4 are provided. In addition, the cylinder base 24 shown in FIG.
A piston 28 is arranged on the inner upper surface via a spring 26. The piston 28 is pressed toward the rotor 19 by the spring 26. A pump chamber 40 is formed between the cylinder base 24 and the piston 28 inside the cylinder portion 13.

FIG. 2 is a sectional view taken along the line II-II shown in FIG. As shown in FIG. 2, the housing 1
1, a suction part 42 and a discharge part 44 are formed to connect the cylinder part 13 and the left side surface and the right side surface of the housing 11 in FIG. 2, respectively. The suction part 42 is a cylindrical part. A small diameter portion 42a, a medium diameter portion 42b, and a large diameter portion 42c are formed in the suction portion 42 in order from the cylinder portion 13 side (right side in FIG. 2). The small diameter portion 42a is opened in the cylinder portion 13, and the large diameter portion 42c is opened in the left surface of the housing 11 in FIG. A thread 42d is formed on the inner peripheral surface of the large diameter portion 42c near the opening. A connector 45 is screwed onto the thread 42d. Connector 4
5 and the large diameter portion 42c of the suction portion 42 between the oil seal 4
6 sealed. A reservoir (not shown) is connected to a hose connection port (hereinafter referred to as a suction port) 45a of the connector 45 via an oil supply hose.

The seat 4 is attached to the medium diameter portion 42b of the suction portion 42.
7, balls 48, and springs 49 are arranged. The seat 47 is a cylindrical member and has one end (see FIG. 2).
The bottom surface on the left end side is arranged so as to contact the bottom surface of the connector 45. A ball engaging surface 47a is formed on the inner peripheral portion of the other end (the right end in FIG. 2) of the seat 47. A ball 48 is engaged with the ball engagement surface 47a. Ball 4
2, a spring 49 is arranged between the middle diameter portion 42b and the right end surface in FIG. Spring 49 is ball 48
Is urged toward the ball engaging surface 47a. Sheet 4
7, the ball 48, and the spring 49 are suction ports 45a.
The intake valve 50 is configured to allow only the flow from the direction toward the cylinder portion 13.

The discharge section 44 is a cylindrical portion. The discharge portion 44 is formed with a small diameter portion 44a, a medium diameter portion 44b, and a large diameter portion 44c in order from the cylinder portion 13 side (left side in FIG. 2). The small diameter portion 44a opens into the pump chamber 40,
The large diameter portion 44c is open on the right side surface of the housing 11 in FIG. A screw thread 44d is formed on the inner peripheral surface of the large diameter portion 44c near the opening to the surface of the housing 11. The connector 52 is screwed to the screw thread 44d. An oil seal 54 seals between the connector 52 and the large diameter portion 44c of the discharge portion 44. A hydraulic device (not shown) such as a wheel cylinder is connected to a hose connection port (hereinafter referred to as a discharge port) 52a of the connector 52 via a hose.

The sheet 5 is attached to the medium diameter portion 44b of the discharge portion 44.
6, balls 58, and springs 60 are provided. The seat 56 is a cylindrical member and has one end (see FIG. 2).
The bottom surface on the (middle left end) side is engaged with the left end surface of the middle diameter portion 44b in FIG. A ball engagement surface 56a is formed on the inner peripheral portion of the other end (the right end in FIG. 2) of the seat 56. A ball 58 is engaged with the ball engagement surface 56a. Ball 58
And a bottom surface of the connector 52, a spring 60 is disposed. The spring 60 biases the ball 58 toward the ball engaging surface 56a. The seat 56, the ball 58, and the spring 60 form a discharge valve 62 that allows only the flow in the direction from the cylinder portion 13 to the discharge port 52a.

According to the structure of the piston pump described above,
When the motor 14 is driven, the shaft 15 rotates. As described above, the rotor 19 is eccentrically fixed to the shaft 15 by α. When the shaft 15 rotates, the rotor 19 rotates while maintaining the eccentric state (hereinafter, such rotation is referred to as eccentric rotation). When such eccentric rotation occurs, the piston 28 reciprocates in the vertical direction in FIG.

FIG. 3 shows a state in which the piston is displaced farthest from the shaft 15 (position shown by a solid line in FIG. 3) and a state closest to the shaft 15 (position shown by a broken line in FIG. 3). Shows the state of displacement. Less than,
The position shown by the solid line in FIG. 3 is called the discharge side displacement end of the piston 28, and the position shown by the broken line in FIG. 3 is called the piston suction side displacement end. As shown in FIG. 3, the piston pump 1 of the present embodiment
At 0, the stroke of the piston 28 is twice the maximum eccentricity α of the rotor 19 at maximum.

When the piston 28 moves upward in FIG. 1, the pump chamber 40 is in a depressurized state. For this reason,
The suction valve 50 is opened and the discharge valve 62 is closed, so that the hydraulic fluid is sucked into the pump chamber 40 from the suction port 45a. Hereinafter, the operating state of the piston pump 10 will be referred to as a suction process. On the other hand, when the piston 28 moves downward in FIG. 1, the pump chamber 40 is in a pressurized state. Therefore, the discharge valve 62 is opened and the suction valve 51 is closed, so that the hydraulic fluid is discharged from the pump chamber 40 to the discharge port 52a.
Is discharged to Hereinafter, the operating state of the piston pump 10 will be referred to as a discharge process. The piston pump 10 alternately repeats the suction process and the discharge process by the reciprocating motion of the piston 28, thereby pumping the hydraulic fluid from the reservoir connected to the suction port 45a to the hydraulic device connected to the discharge port 52a.

As described above, the elastic body 18 is provided between the shaft 15 and the rotor 19. For this reason, the pressing force of the piston 28 against the rotor 19 causes the elastic body 18 to contract and deform in the radial direction. When the piston pump is in the process of discharging, the pressing force of the piston 28 on the rotor 19 changes in proportion to the internal pressure of the pump chamber 40. Pump room 40
Since the internal pressure of (1) matches the pressure of the hydraulic device connected to the discharge port 52a (hereinafter referred to as the discharge pressure), the pressing force on the rotor 19 is proportional to the discharge pressure. Due to the pressing force, elastic contraction deformation δ in the radial direction having a magnitude proportional to the pressing force is generated at the contact portion of the elastic body 18 with the piston 28. As a result, the position of the piston 28 moves toward the suction side displacement end side by δ as compared with the state in which the contraction deformation does not occur (hereinafter, referred to as a normal state).

The radial elastic contraction deformation of the elastic body 18 is more likely to occur as the thickness t of the elastic body 18 in the direction in which the pressing force acts becomes larger, and is less likely to occur as t becomes thinner. Since the rotor 19 and the elastic body 18 are provided concentrically, the piston 28
Is at the discharge side displacement end, the thickness t becomes maximum. Further, the thickness t is minimum when the piston 28 is at the suction side displacement end. Therefore, when the piston 28 is at the discharge side displacement end, the elastic body 18 has a larger elastic contraction deformation amount than the elastic contraction deformation amount δ2 generated in the elastic body 18 when the piston 28 is at the suction side displacement end. δ1 occurs. In this case, the stroke length when the piston 28 is displaced between the discharge side displacement end and the suction side displacement end is reduced by (δ1−δ2) compared to the normal state.

As described above, the amount of contraction and deformation of the elastic body 18 is proportional to the pressing force of the piston 28, that is, the discharge pressure of the piston cylinder 10. Therefore, the stroke reduction amount is proportional to the discharge pressure of the piston cylinder 10. The discharge amount per one rotation of the rotor 19 matches the product of the stroke of the piston 28 and the cross-sectional area of the cylinder portion 13. FIG.
Shows the relationship between the discharge pressure of the piston pump 28 and the discharge amount per one rotation of the rotor together with the case of the conventional piston pump. As shown by the broken line in FIG. 4, in the conventional piston pump, the discharge amount per one rotation of the rotor is maintained constant regardless of the change in the discharge pressure. On the other hand, in the piston pump 10 of the present embodiment, the stroke decreases as the discharge pressure rises as described above, so that as shown by the solid line in FIG. Therefore, the discharge amount of is reduced.

By the way, assuming that there is no friction loss in the sliding portion of the piston pump, the load of the motor matches the amount of work done by the piston pump. Therefore, the load of the motor matches the product of the discharge pressure and the discharge amount. In the conventional piston pump, since the stroke of the piston is always constant, the discharge amount per one rotation of the motor is constant regardless of the discharge pressure. Therefore, the load of the motor is proportional to the discharge pressure under normal operating conditions in which the rotation speed of the motor is kept constant. On the other hand, the piston pump 10 of the present embodiment
In the above, since the discharge amount is reduced as the discharge pressure increases as described above, the degree of increase in the motor load decreases as the discharge pressure increases. Figure 5 shows the piston pump 1
The relationship between the discharge pressure of 0 and the motor load is shown together with the case of the conventional piston pump. As shown by the solid line in FIG. 5, in the piston pump 10 of the present embodiment, the motor load when the discharge pressure becomes high is reduced as compared with the case of the conventional piston pump shown by the broken line in FIG. Has been done.

FIG. 6 shows the relationship between the hydraulic pressure in the wheel cylinder of the vehicle brake device and the amount of liquid consumed in the wheel cylinder until the hydraulic pressure is reached. FIG.
As shown in, since the amount of liquid consumption rapidly increases as the hydraulic pressure increases in the low hydraulic pressure region, it is necessary to supply a large amount of brake fluid to the wheel cylinders by the pump. On the other hand, in a region where the hydraulic pressure is high, the change in the amount of liquid consumption with respect to the increase in the hydraulic pressure becomes gradual, so the amount of brake fluid to be supplied by the pump decreases. Therefore, when the pump discharge pressure is low, a large discharge amount is required, whereas when the discharge pressure is high, only a small discharge amount is required.

Therefore, the piston pump 10 of this embodiment is
Is applied to a hydraulic device that requires only a small discharge amount when the discharge pressure is high, such as the above-described brake device, so that the load on the motor can be reduced as compared with the conventional piston pump. Therefore, according to the piston pump 10 of the present embodiment, it is possible to reduce the output of the motor, and thus to reduce the size of the motor.

The relationship of the discharge amount with respect to the discharge pressure of the piston pump 10 can be arbitrarily set by changing the diameter of the elastic body 18 or the elastic constant of its constituent material. Therefore, the effect of motor miniaturization is maximized by optimally setting the relationship between the discharge pressure and the discharge amount according to the hydraulic pressure-consumed liquid amount characteristic of the hydraulic device to which the piston cylinder 10 of the present embodiment is applied. Can be obtained.

By the way, generally, there is a relationship as shown in FIG. 7 between the torque of the motor and the rotational speed. In the conventional piston pump, when the motor load torque changes according to the change in the discharge pressure, the motor rotation speed changes according to the relationship shown in FIG. 7. When the motor speed changes, the pulsating frequency of the hydraulic pressure discharged from the piston pump also changes. Since the pulsation of hydraulic pressure adversely affects the operation of the hydraulic device, pulsation is removed by using a pulsation removing device such as an accumulator. In this case, since the pulsation removing device is designed according to the pulsation frequency, if the pulsation frequency varies as described above, the pulsation cannot be effectively removed.

On the other hand, in the piston pump 10 of the present embodiment, the discharge amount is reduced according to the discharge pressure, so that the fluctuation of the motor load torque when the discharge pressure changes is suppressed, and therefore the motor The fluctuation of the rotation speed is suppressed. Therefore, the fluctuation of the pulsation frequency of the hydraulic pressure discharged from the piston pump can be suppressed. As a result, according to the piston pump 10 of the present embodiment, it is possible to effectively remove the pulsation by the pulsation removing device.

The pressure in the pump chamber when the piston is at the discharge side displacement end is higher than when the piston is at the suction side displacement end. Therefore, even with the configuration in which the elastic body having a sufficient thickness is provided concentrically with the motor shaft, the amount of contraction of the elastic body varies depending on whether the piston is at the displacement end of the discharge side or at the displacement end of the suction side. It is possible to obtain the effect of reducing the discharge amount as the discharge pressure increases. However, when the elastic body is provided with a sufficiently large thickness, the rigidity of the rotor is lowered and the rotor is likely to vibrate. As a result, the rotation of the rotor becomes unstable and problems such as a delay in the rise of the discharge pressure occur.

On the other hand, in the piston pump 10 of this embodiment, since the elastic body 18 is eccentrically arranged with respect to the motor shaft, the discharge amount is reduced. It can be made smaller than in the case of a piston pump. Therefore, it is possible to prevent the rigidity of the rotor 19 from being lowered due to the arrangement of the elastic body. As a result, according to the piston pump 10 of the present embodiment, it is possible to prevent the problems such as the delay in the rise of the discharge pressure due to the instability of the rotor rotation as described above from occurring. In the above embodiment, the rotor 19 corresponds to the cam described above.

Next, a piston pump 80 which is a second embodiment of the present invention will be described with reference to FIG. FIG.
In Fig. 1, the same components as those of the piston pump 11 shown in Fig. 1 are designated by the same reference numerals and the description thereof will be omitted. The present embodiment is characterized in that the bearing 82 is used as the rotor to reduce the sliding friction between the rotor and the piston.

In FIG. 8, the inner race 84 of the bearing 82 is fitted on the outer peripheral surface of the elastic body 18. The piston 28 is pressed against the outer race 86 of the bearing 82 by the spring 26. When the shaft 15 rotates, the inner race 84 rotates eccentrically around the central axis of the shaft 15 together with the elastic body 18. On the other hand, in the outer race 86, the relative sliding movement on the contact surface with the piston 28 is restricted by the frictional force caused by the pressing force of the piston 28, and the center of the outer race 86 is the shaft 1.
A movement such as rotating around 5 occurs. As a result, the outer race 86 makes the piston 28 reciprocate in the vertical direction in FIG. 8 while performing rolling motion relative to the inner race 84. Due to the reciprocating motion of the piston, the piston pump 80 moves to the above-described first
The fluid is sucked and discharged in the same manner as the piston pump 10 of the embodiment. Then, due to the elastic deformation of the elastic body 18,
Similar to the piston pump 10 of the first embodiment described above,
It is possible to obtain the effect of reducing the discharge amount as the discharge pressure increases.

As described above, the piston pump 8 of this embodiment
At 0, no sliding occurs between the outer race 86 of the bearing 82 and the piston 28, and only relative rolling motion occurs. Therefore, the frictional force generated between the outer race 86 and the piston 28 is reduced. Therefore, according to the piston pump 80 of the present embodiment, the motor 1
By reducing the rotational resistance acting on the shaft 15 of No. 4, the motor load is reduced, and the motor can be downsized. Further, the outer race 86 and the piston 28
The wear on the contact surfaces of the parts is reduced, and the life of these parts can be improved.

In the second embodiment, the rotor 19 corresponds to the above-mentioned cam, and the outer race 86 of the bearing 82 corresponds to the annular body of claim 2.

[0037]

As described above, according to the first aspect of the present invention, the reciprocating amount of the piston is reduced according to the pressure of the pump chamber, so that the discharge amount is reduced according to the increase of the discharge pressure of the pump. be able to. As a result, the load on the motor can be reduced and the motor can be downsized.

According to the second aspect of the invention, the reciprocating amount reducing means can be realized by the elastic body eccentric to the shaft of the motor. Therefore, the effect of the invention described in claim 1 can be obtained with a simple structure. Furthermore, by bringing the piston into contact with the rotatable eccentric cam, the frictional force between the cam and the piston can be reduced. Therefore, the load on the motor can be reduced, and therefore the motor can be further downsized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a piston pump according to an embodiment of the present invention.

FIG. 2 shows a piston pump of the present embodiment along a straight line A shown in FIG.
It is sectional drawing at the time of cutting along -A.

FIG. 3 is a diagram illustrating a relationship between an eccentric amount of a rotor and a stroke of a piston.

FIG. 4 is a diagram showing the relationship between the discharge pressure and the discharge amount of the piston pump of the present embodiment, together with the case of a conventional piston pump.

FIG. 5 is a diagram showing the relationship between the discharge pressure of the piston pump of this embodiment and the motor load, together with the case of a conventional piston pump.

FIG. 6 is a diagram showing a relationship between a hydraulic pressure and a total liquid consumption in the brake device.

FIG. 7 is a diagram showing a relationship between load torque and rotation speed of a motor.

FIG. 8 is a sectional view of a piston pump according to a second embodiment of the present invention.

[Explanation of symbols]

 10, 80 Piston pump 14 Motor 15 Shaft 18 Elastic body 19 Rotor 28 Piston 40 Pump chamber 82 Bearing 84 Inner race 86 Outer race

Claims (2)

[Claims] 1. A piston pump comprising a motor, a cam rotated by the motor, a piston reciprocated by the rotation of the cam, and a pump chamber expanded / contracted by the reciprocating motion of the piston, A piston pump comprising reciprocating amount reducing means for reducing the reciprocating amount of the piston according to the pressure in the pump chamber. 2. The reciprocating amount reducing means includes an eccentric elastic body disposed between the cam and the shaft of the motor, and the cam can rotate around the outer circumference of the cam. The piston pump according to claim 1, further comprising an annular body that abuts on the piston.