WO2008102245A1

WO2008102245A1 - Plunger pump

Info

Publication number: WO2008102245A1
Application number: PCT/IB2008/000393
Authority: WO
Inventors: Masakuni Suzuki
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-02-23
Filing date: 2008-02-22
Publication date: 2008-08-28
Also published as: JP2008208750A; WO2008102245A9

Abstract

A plunger pump (1) pressurizes an operating fluid by converting the rotational motion of a cam drive shaft (12) to reciprocating motion of a piston (34). In the plunger pump (1), a linear gear (26) is interposed between a cam (18) and pistons (34). A plurality of balls (28) is disposed as rolling elements in the linear bearing (26) along the thrust direction.

Description

PLUNGER PUMP

BACKGROUND OF THE INVENTION

1. Field of the Invention [0001] The present invention relates to a plunger pump that pressurizes a fluid by causing reciprocating motion of a piston.

2. Description of the Related Art

[0002] The hydraulic circuit in vehicle brake systems generally has a hydraulic source that includes a plunger pump to draw operating fluid from a reservoir tank and pressurize the operating fluid, and an accumulator that stores the pressurized operating fluid. For example, according to Japanese Patent Application Publication No. 2005-337252 (hereinafter, referred to as "JP-A-2005-337252"), a plunger pump pressurizes to a fluid using an internal piston that is reciprocated by an eccentric cam. [0003] The plunger pump described in JP-A-2005-337252 includes a cylinder with a pressure chamber into which operating fluid is introduced; a cam drive shaft that is connected to a pump motor and is rotationally driven; a bearing provided on the eccentric portion of the cam drive shaft; and a piston that is reciprocally disposed within the cylinder and that has one end engaged to an outer peripheral surface of the bearing. When the pump motor is driven, the eccentric rotational motion of the bearing is converted to reciprocating motion of the piston, and thereby the operating fluid introduced into the pressure chamber becomes pressurized.

[0004] In a plunger pump such as this, a needle bearing (radial roller bearing) is generally used as the bearing. Because the needle bearing uses an elongated needle (roller) as a rolling element, it provides a large contact surface area with the rotating body to be supported. For this reason, the needle bearing may withstand a larger load than ball bearings having the same diameters. Therefore, needles with smaller diameters may be used in the needle bearing, and thereby enabling a compact overall bearing configuration.

[0005] In a plunger pump using such a needle bearing, however, there are problems of vibration of the plunger pump and the accompanying noise. The inventor attributed the vibration of the plunger pump to so-called "skew" of the needle with respect to the proper rotational axis. That is, when the rotational axis of the needle is skewed with respect to the axis of the bearing, the needle moves in the skewed direction, which generates a thrust load in the axial direction of the bearing.

This thrust load may cause vibrations in the axial direction. Therefore, the inventor conceived that suppression of the occurrence of the skew of the needle would lead to a reduction of the vibrations in the plunger pump.

SUMMARY OF THE INVENTION

[0006] The present invention provides a plunger pump whose vibration may be reliably suppressed. [0007] The plunger pump according to one aspect of the present invention includes; a housing inside of which is disposed a passage for an operating fluid; a cam drive shaft that is rotatably held in the housing; a cam that is eccentric with respect to the rotational axis of the cam drive shaft; a linear bearing, fitted outside the cam, in which a plurality of spherical rolling elements is arranged in a thrust direction of the linear bearing; a balancer that is mounted on the cam drive shaft, to balance out an eccentric weight of the cam; a cylinder, disposed in the housing, that forms a pressure chamber within the cylinder, and a piston that reciprocates within the cylinder with one end of the piston being engaged with an outer peripheral surface of an outer race of the linear bearing at substantially a right angle while the other end of the piston facing the pressure chamber. The operating fluid introduced into the pressure chamber is pressurized by the reciprocating motion of the piston.

[0008] The plunger pump may further include retention members that are provided on both ends of the linear bearing to restrict movement of the spherical rolling elements in the thrust direction.

[0009] The balancer may be disposed adjacent to the cam to restrict movement of the outer race of the linear bearing in the axial direction, and a surface treatment may be applied to a sliding surface of at least one of the outer race of the linear bearing and the balancer to reduce sliding resistance between the outer race of the linear bearing and the balancer.

[0010] The surface treatment may include baking a fluorine-based resin onto or polishing the sliding surface of at least one of the outer race of the linear bearing and the balancer. [0011] A wear-resistance treatment may be applied to the sliding surface of the balancer.

[0012] The wear-resistance treatment may include coating the sliding surface of the balancer.

[0013] Furthermore, the balancer may include a molded metal member in a resin body for adjusting the eccentric weight of the cam, and a portion of the resin body may form a sliding surface of the balancer that slides with the linear bearing.

[0014] Furthermore, the balancer may be made of a metallic material, and a resin member may be further interposed between the balancer and the linear bearing.

[0015] The resin member may be a resin ring. [0016] An inner race of the linear bearing may be provided and fitted over the outer peripheral surface of the cam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements, and wherein:

FIG. 1 shows the overall plunger pump according to a first embodiment of the present invention;

FIG. 2 shows an enlarged cross-sectional view of the main portion of a plunger pump according to a second embodiment of the present invention;

FIG. 3 shows an enlarged cross-sectional view of the main portion of a plunger pump according to a modification of the second embodiment of the present invention; FIG. 4 shows an enlarged cross-sectional view of the main portion of a plunger pump according to a third embodiment of the present invention; and

FIG. 5 shows an enlarged cross-sectional view of the main portion of a plunger pump according to a fourth embodiment of the present invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Embodiments of the present invention are described below, with reference to the accompanying drawings. As a convenience in the descriptions that follow, the positional relationship of components shown in drawings may be simply indicated with reference to up and down.

[0019] FIG. 1 shows the overall plunger pump according to the first embodiment of the present invention. The plunger pump 1 is provided in the hydraulic circuit of the vehicle brake system, in which operating fluid is drawn from a reservoir tank and pressurized. The pressurized operating fluid is stored in an accumulator. A pump motor (not shown) drives the plunger pump 1.

[0020] The plunger pump 1 includes a housing 2, inside of which a path for the operating fluid is formed; a first pump 3 and a second pump 4, provided within the housing 2, that pressurize the operating fluid; and an eccentric cam mechanism 5, rotatably held within the housing 2, that drives the first pump 3 and the second pump 4.

[0021] The housing 2 has a cam-housing portion 7 that is formed with a side opening toward the pump motor, and a pair of pump housing portions 8 that communicate up and down with the cam-housing portion 7. The eccentric cam mechanism 5, which is linked to the pump motor, is rotatably housed in the cam-housing portion 7. The first pump 3 and the second pump 4 are housed in the upper and lower pump housing portions 8. In the first embodiment, the first pump 3 and the second pump 4 have the same configuration and sandwich the eccentric cam mechanism 5 up and down.

[0022] The eccentric cam mechanism 5 has a cylindrical cam drive shaft 12 with a step, one end of which is linked to the output shaft of the pump motor via a linking member 9. The cam drive shaft 12 is rotatably supported by the ball bearings 14, 16 disposed at the rear side of the cam-housing portion 7 and the opening side of the cam-housing portion 7, respectively. A cam 18, which is eccentric with respect to the rotational axis of the cam drive shaft 12, is provided in the middle of the cam drive shaft 12. One end of the cam drive shaft 12 toward the pump motor is provided with an annular seal member 20. Additionally, balancers 22, 24 made of metal are respectively fixed to the cam drive shaft 12 and sandwich the cam 18 from both sides in the axial direction. The balancers 22, 24 adjust for the offset of the center-of-gravity of the cam 18, to suppress vibrations due to the rotation of the cam drive shaft 12. The balancer 22 is held between the cam 18 and the inner race of the ball bearing 14 while the balancer 24 is held between the cam 18 and the inner race of the ball bearing 16. When the ball bearing 14 and the ball bearing 16 are assembled into the cam-housing portion 7, the balancer 22, the cam 18, and the balancer 24 are held from both sides of the ball bearings 14, 16, and are restricted from moving in the axial direction.

[0023] A linear bearing 26 is fitted around the outside of the cam 18. The linear bearing 26 is formed with a plurality of spherical rolling elements, which are arranged in a thrust direction parallel to the rotational axis of the linear bearing 26. Specifically, the linear bearing 26 includes a plurality of balls 28 on the outer periphery of the cam 18, and an outer race 30 that rotates in contact with the outer surfaces of the balls 28. The linear bearing 26 according to the first embodiment does not have an inner race; instead the outer peripheral portion of the cam 18 fulfills the function as the inner race of the linear bearing 26. Retainers 31 are provided at both ends of the outer race 30, to restrict the movement of the balls 28 in the thrust direction. The retainers 31 may be regarded as "retention members" of the present invention.

[0024] The first pump 3 includes a cylinder 32 with a closed bottom; a cylindrical piston 34 that is inserted into the cylinder 32and reciprocates within the cylinder 32; and a pressure-chamber forming member 36 with a closed bottom, provided on the opposite side of the piston 34. [0025] The front end of the piston 34 is engaged with the outer peripheral surface of the outer race 30 of the linear bearing 26. A first spring 38 that biases the piston 34 toward the linear bearing 26 is provided between the rear end of the piston 34 and the base of the cylinder 32. A first communicating passage 40 provided in the piston 34 passes through from the vicinity of the front end of the piston 34 to the rear end of the piston 34. A first valve seat 44 is formed around the opening edge of the first communicating passage 40 on the rear end of the piston 34, and a detachable ball-shaped first valve body 46 is attached to the first valve seat 44. The first valve body 46 is supported by a cup-shaped valve-supporting member 48. A second spring 50 is interposed between the valve-supporting member 48 and the base of the cylinder 32. The first valve body 46 is biased toward the valve closing direction by the second spring 50 via the valve supporting member 48, but moves away from the first valve seat 44 when the front-to-rear pressure difference exceeds a prescribed value, thereby opening the valve.

[0026] A second communicating passage 42 is formed in the base of the cylinder 32. A second valve seat 52 is formed around the opening edge of the second communicating passage 42 on the rear end of the cylinder 32, and a detachable ball-shaped second valve body 54 is attached to the second valve seat 52. A cylindrical spring receiving member 56 is fitted to the rear portion of the cylinder 32, and a third spring 58 that biases the second valve body 54 toward the valve closing direction is interposed between the spring receiving member 56 and the second valve body 54. The spring receiving member 56 is disposed in a delivery chamber 66, which is surrounded by the pressure-chamber forming member 36 and the cylinder 32. A communicating hole through which the inside of the cylinder 32 is communicated with the outside of the cylinder 32 is formed on the side portion of the delivery chamber 66.

[0027] The space surrounded by the cylinder 32 and the piston 34 functions as a pressure chamber 64 into which low-pressure operating fluid is introduced from the reservoir tank (not shown). Specifically, when operating fluid is introduced from the reservoir tank into a space surrounded by the first pump 3 and the eccentric cam mechanism 5, the operating fluid is further introduced into the pressure chamber 64 through the first communicating passage 40. When the piston 34 reciprocates, the operating fluid is pressurized in the pressure chamber 64. The pressurized operating fluid is introduced into the delivery chamber 66 through the second communicating passage 42, and is further delivered toward an accumulator (not shown).

[0028] Because the second pump 4 has the same configuration as the first pump 3, corresponding elements therebetween are assigned the same reference numerals as the first pump 3, and the descriptions thereof will be omitted. The first pump 3 and the second pump 4 are disposed on diametrically opposite sides across the eccentric cam mechanism 5, with pressurization and delivery being performed alternatively. Thus, the operating fluid that is introduced into the plunger pump 1 is pressurized and delivered with good efficiency.

[0029] As described above, in the plunger pump 1 according to the first embodiment, the linear bearing 26 is interposed between the cam 18 and pistons 34. That is, because the linear bearing 26 employs balls 28 as the rolling elements, the skew of the rolling elements does not occur as compared to the needle bearing. For this reason, the behaviors of the rolling elements do not cause a thrust load on the linear bearing 26, and thereby vibrations of the plunger pump 1 may be suppressed. Also, because the plurality of balls 28 are arranged in the thrust direction of the linear bearing 26, a large contact surface area with the cam 18 may be ensured, thereby the linear bearing 26 to withstand a relatively large load, such as is the case with a needle bearing.

[0030] The second embodiment of the present invention will be described next. The plunger pump according to the second embodiment, with the exception of surface treatment to reduce the sliding resistance with the linear bearing, is the same as the first embodiment. For this reason, constituent elements that are substantially the same as in the first embodiment are assigned the same reference numerals and description of the corresponding elements will be omitted.

[0031] FIG. 2 shows an enlarged cross-sectional view of the main portion of the plunger pump according to the second embodiment. Similarly to the first embodiment, a linear bearing 226 is used in the plunger pump 201. [0032] When the balls are used as the rolling elements in the bearing, frictional force dose not act in the thrust direction. Therefore, if an external force is applied to the bearing in the thrust direction, the outer race of the bearing tends to be displaced in the thrust direction. For example, if the piston angle of contact with respect to the outer peripheral surface of the bearing is very slightly inclined from a right angle, the outer race is pressed by the piston and tends to move in the thrust direction.

[0033] Therefore, according to the plunger pump 201 of the second embodiment, the balancers 22, 24 are disposed in contact with the cam 18, to restrict the movement of the outer race 230 of the linear bearing 226 in the axial direction. For this reason, the balancers 22, 24 not only balance out the eccentric weight of the cam 18, but also contact the outer race 230 of the linear bearing 226 and thereby fulfill the function as restricting members that restrict the movement of the linear bearing 226 in the axial direction. [0034] Additionally, the sliding surface 251 of the outer race 230 that comes into contact with the balancers 22, 24 is subjected to the surface treatment such as baking a fluorine-based resin (refer to the black portion in the drawing), to reduce the sliding resistance. As a result, the contact noise between the linear gear 226 and the balancers 22, 24 may be suppressed.

[0035] FIG. 3 shows an enlarged cross-sectional view of the main portion of a plunger pump according to a modification of the second embodiment. As shown in FIG. 3, the sliding surfaces 252 of the balancers 222 and 224 may be subjected to the surface treatment such as baking a fluorine-based resin. Alternatively, the fluorine-based resin may be respectively baked onto the sliding surfaces 251, 252. Furthermore, any treatment such as polishing treatment that sufficiently reduces the sliding resistance may be used. Also, further surface treatments for reducing the sliding resistance may be done after polishing.

[0036] The sliding surfaces 252 of the balancers 222, 224 may be subjected to wear-resistance treatment. This wear-resistance treatment may be, for example, a nitriding treatment such as Toughtriding (registered trademark) or a film coating, such as DLC (diamond-like carbon). As a result, it is possible to reduce contact noise due to wear of the balancers, and also possible to maintain the long lifetime of the plunger pump. [0037] The above-described surface treatment and wear-resistance treatment may be performed over the entire sliding surface, or alternatively over a select portion thereof.

[0038] The third embodiment of the present invention will be described next. The plunger pump according to the third embodiment, with the exception of the difference in the structure of the balancers, is the same as the first embodiment. For this reason, constituent elements that are substantially the same as in the first embodiment are assigned the same reference numerals, and description of the corresponding elements will be omitted. [0039] FIG. 4 shows an enlarged cross-sectional view of the main portion of the plunger pump according to the third embodiment. Similarly to the first embodiment, a linear bearing 26 is used in the plunger pump 301. Additionally, balancers 322, 324 made of resin sandwich the linear bearing 26 from both sides in the axial direction.

[0040] Specifically, the balancers 322 and 324 are formed by injection molding of a resin material, with a metal member 351 molded therein at the time of molding at a location at which the density is to be increased. The metal member 351 may be buried inside the resin body, and may be exposed at a portion other than the sliding portion. The resin material portion therefore comes into contact with the linear bearing 26.

[0041] Because the bodies of the balancers are made of resin in this manner, it is possible to prevent adhesive wear between the balancers 322, 324 and the outer race 30 of the linear bearing 26. Also, because the weight bias of the balancer may be increased using the difference in density between the resin and the metal, the eccentric weight of the cam 18 may be efficiently adjusted. By doing this, it is possible to achieve compact balancers and, by extension, to reduce the size of the plunger pump.

[0042] The fourth embodiment of the present invention will be described next. The plunger pump according to the fourth embodiment, with the exception of a separate resin member disposed between the linear bearing and the balancer, is the same as the first embodiment. For this reason, constituent elements that are substantially the same as in the first embodiment are assigned the same reference numerals and description of the corresponding elements will be omitted.

[0043] FIG. 5 shows an enlarged cross-sectional view of the main portion of the plunger pump according to the fourth embodiment. Similarly to the first embodiment, a linear bearing 26 is used in the plunger pump 401. Additionally, a resin ring 451 is interposed between the balancers 22, 24 and the linear bearing 26.

According to this configuration, the occurrence of adhesive wear between the outer race of the linear bearing 26 and the balancers is prevented.

[0044] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, other combinations and configurations, including more, fewer, or only a single element, are also within the spirit and scope of the invention.

[0045] For example, although the cam 18 fulfills the function as the inner race of the linear bearing 26 in the above embodiments, a separate inner race of the linear bearing 26 may be provided and fitted over the outer peripheral surface of the cam 18.

Claims

1. A plunger pump comprising: a housing inside of which is disposed a passage for an operating fluid; a cam drive shaft that is rotatably held in the housing; a cam that is eccentric with respect to the rotational axis of the cam drive shaft; a linear bearing, fitted outside the cam, in which a plurality of spherical rolling elements is arranged in a thrust direction of the linear bearing; a balancer that is mounted on the cam drive shaft, to balance out an eccentric weight of the cam; a cylinder, disposed in the housing, a pressure chamber being formed within the cylinder; and a piston that reciprocates within the cylinder with one end of the piston being engaged with an outer peripheral surface of an outer race of the linear bearing at substantially a right angle while the other end of the piston faces the pressure chamber, the operating fluid introduced into the pressure chamber being pressurized by the reciprocating motion of the piston.

2. The plunger pump according to claim 1, further comprising retention members that are provided on both ends of the linear bearing to restrict movement of the spherical rolling elements in the thrust direction.

3. The plunger pump according to claim 1 or 2, wherein: the balancer is disposed adjacent to the cam to restrict movement of the outer race of the linear bearing in the axial direction; and a surface treatment is applied to a sliding surface of at least one of the outer race of the linear bearing and the balancer to reduce sliding resistance between the outer race of the linear bearing and the balancer.

4. The plunger pump according to claim 3, wherein the surface treatment includes baking a fluorine-based resin onto the sliding surface of at least one of the outer races of the linear bearing and the balancer.

5. The plunger pump according to claim 3, wherein the surface treatment includes polishing the sliding surface of at least one of the outer races of the linear bearing and the balancer.

6. The plunger pump according to any one of claims 1 to 3, wherein a wear-resistance treatment is applied to the sliding surface of the balancer.

7. The plunger pump according to claim 6, wherein the wear-resistance treatment includes coating the sliding surface of the balancer.

8. The plunger pump according to claim 1 , wherein: the balancer includes a metal member molded in a resin body for adjusting the eccentric weight of the cam; and a portion of the resin body forms a sliding surface of the balancer that slides with the linear bearing.

9. The plunger pump according to claim 1 , wherein: the balancer is made of a metallic material; and a resin member is further interposed between the balancer and the linear bearing.

10. The plunger pump according to claim 9, wherein the resin member is a resin ring.

11. The plunger pump according to any one of claims 1 to 10, wherein an inner race of the linear bearing is provided and fitted over the outer peripheral surface of the cam.