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Title:
PLUNGER PUMP AND CONTACT MATING STRUCTURE USED IN THE SAME
Document Type and Number:
WIPO Patent Application WO/2019/201640
Kind Code:
A1
Abstract:
The present application discloses a contact mating structure between a cam (201, 202) and a tappet assembly (500) and a plunger pump using the contact mating structure, wherein the cam (201, 202) is formed in a rotatable shaft, the tappet assembly (500) is movable perpendicularly relative to the rotatable shaft, the contact mating structure comprises a cam follower (800) pivotally provided at one end of the tappet assembly (500), and the cam follower (800) has a contact side (820) for contacting the profile of the cam (201, 202), wherein viewed in a cross-section perpendicular to a central axis of rotation of the rotatable shaft, the contact side (820) is concaved towards the cam (201, 202).

Inventors:
SHI, Kai (17 Xinhua Road New District, Wuxi, Jiangsu 8, 214028, CN)
Application Number:
EP2019/058784
Publication Date:
October 24, 2019
Filing Date:
April 08, 2019
Export Citation:
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Assignee:
ROBERT BOSCH GMBH (Postfach 30 02 20, Stuttgart, 70442, DE)
International Classes:
F04B1/04; F02M59/10
Foreign References:
DE102004048714A12006-04-13
DE102012024924A12014-06-26
US20140202325A12014-07-24
DE102006057246A12008-06-12
DE102012007125A12013-10-10
DE3505176C11986-04-24
JP2010001828A2010-01-07
Other References:
None
Download PDF:
Claims:
CLAIMS

1. A contact mating structure between a cam (201, 202) and a tappet assembly (500), the cam (201, 202) being formed in a rotatable shaft, the tappet assembly (500) being movable perpendicularly relative to the rotatable shaft, the contact mating structure comprising a cam follower (800) pivotally provided at one end of the tappet assembly (500), and the cam follower (800) having a contact side (820) for contacting a profile of the cam (201, 202), wherein viewed in a cross-section perpendicular to a central axis of rotation of the rotatable shaft, the contact side (820) is concaved towards the cam (201, 202).

2. The contact mating structure as recited in claim 1, wherein the contact side (820) has a curvature radius which is greater than or equal to the maximum surface curvature radius of the profile of the cam (201, 202).

3. The contact mating structure as recited in claim 1 or 2, wherein viewed in the cross-section perpendicular to the central axis of rotation of the rotatable shaft, the profile of the cam (201, 202) is in the form of a circle, and wherein the contact side (820) is an arc-shaped side whose radius is equal to the circle’s radius.

4. The contact mating structure as recited in claim 1 or 2, wherein viewed in the cross-section perpendicular to the central axis of rotation of the rotatable shaft, the profile of the cam (201, 202) is in the form of an oval, and wherein the curvature radius of the contact side (820) is greater than or equal to the maximum curvature radius of the oval.

5. The contact mating structure as recited in claim 3, wherein a through-hole (810) is formed in the cam follower (800) for defining its pivotal axis.

6. The contact mating structure as recited in claim 1 or 2, wherein the rotatable shaft and/or the cam (201, 202) is at least partially immersed in lubricant oil.

7. The contact mating structure as recited in claim 1 or 2, wherein the tappet assembly (500) is coupled to a plunger at the other end, and the plunger is slidable in a plunger sleeve (300).

8. A plunger pump, comprising: a rotatable cam shaft (200) in which a cam (201, 202) is formed; a plunger cavity in which a tappet assembly (500) is installed so as to be moveable linearly therein, wherein a cam follower (800) is pivotally provided at one end of the tappet assembly (500), and the cam follower (800) has a contact side (820) for contacting the profile of the cam (201, 202), and wherein viewed in a cross-section perpendicular to a central axis (O) of rotation of the rotatable shaft, the contact side (820) is concaved towards the cam (201, 202).

9. The plunger pump as recited in claim 8, wherein the contact side (820) has a curvature radius which is greater than or equal to the maximum surface curvature radius of the profile of the cam (201, 202).

10. The plunger pump as recited in claim 8 or 9, wherein viewed in the cross-section perpendicular to the central axis (O) of rotation of the rotatable shaft, the profile of the cam (201, 202) is in the form of a circle, and wherein the contact side (820) is an arc-shaped side whose radius is equal to the circle’s radius.

11. The plunger pump as recited in claim 8 or 9, wherein wherein viewed in the cross-section perpendicular to the central axis (O) of rotation of the rotatable shaft, the profile of the cam (201, 202) is in the form of an oval, and wherein the curvature radius of the contact side (820) is greater than or equal to the maximum curvature radius of the oval.

12. The plunger pump as recited in claim 8 or 9, wherein the cam follower (800) is pivotally installed to the tappet assembly (500) by a pin shaft (700).

13. The plunger pump as recited in claim 12, wherein a through-hole (810) is formed in the cam follower (800) to enable the pin shaft (700) to pass throughthere.

14. The plunger pump as recited in claim 12, wherein the pin shaft (700) defines a pivotal axis (O') of the cam follower (800), and the pivotal axis (O') and the central axis (O) of rotation are always parallel to each other and in the same plane.

15. The plunger pump as recited in claim 8 or 9, wherein the rotatable shaft and/or the cam (201, 202) is at least partially immersed in lubricant oil.

16. The plunger pump as recited in claim 8 or 9, wherein the tappet assembly (500) is coupled to a plunger at the other end.

Description:
Plunger Pump and Contact Mating Structure Used in the Same

Field

The present application relates to a plunger pump used to supply fuel to a high-pressure common rail in a diesel vehicle, and to a contact mating structure applied between a cam and a tappet assembly of the plunger pump.

Background

High-pressure common rail technology has been widely used in diesel vehicles. Fuel is pressurized by a booster pump and supplied to a common rail in which the fuel is stored, such that the fuel can be ejected into a diesel engine. For example, the booster pump is in the form of a plunger pump, comprising a housing. A cam shaft is rotatably provided in the housing. Several cams are provided in the cam shaft. The plunger pump also comprises a plunger sleeve connected to the housing. A plunger is slidably provided in the plunger sleeve. The plunger is operatively coupled to a cam via a tappet such that when the cam shaft is being rotated, the plunger is driven to reciprocate in the plunger sleeve. In this way, the fuel can be pressurized and supplied to the high-pressure common rail.

In the housing of the plunger pump, the cam shaft is at least partially immersed in lubricant oil. The tappet is provided with a freely-pivotal cam follower, for instance a cam follower roll, thereon such that the tappet is in contact with the cam’s profile via the cam follower roll.

For a conventional plunger pump, the contact between the cam follower roll and the profile of the cam is a linear contact having a small contact area. In high-speed and heavy-loaded applications in which the fuel need be pressurized, it is very hard to establish a lubricant film between the cam follower roll and the profile of the cam so as to enduringly transfer heavy loads between them.

Summary

The present application is aimed at proposing an improved plunger pump to solve those already-mentioned technical issues.

According to one aspect of the present application, a contact mating structure between a cam and a tappet assembly is proposed, wherein the cam is formed in a rotatable shaft, the tappet assembly is movable perpendicularly relative to the rotatable shaft, the contact mating structure comprises a cam follower pivotally provided at one end of the tappet assembly, and the cam follower has a contact side for contacting the cam’s profile, wherein viewed in a cross-section perpendicular to a central axis of rotation of the rotatable shaft, the contact side is concaved towards the cam.

According to another aspect of the present application, a plunger pump is proposed, comprising: a rotatable cam shaft in which a cam is formed; a plunger cavity in which a tappet assembly is installed so as to be moveable linearly therein, wherein a cam follower is pivotally provided at one end of the tappet assembly, and the cam follower has a contact side for contacting the cam’s profile, wherein viewed in a cross-section perpendicular to the central axis of rotation of the rotatable shaft, the contact side is concaved towards the cam.

Using the inventive technical means mentioned above, greater loads can be transmitted between the cam and the tappet assembly and the cam follower has good fatigue resistance after long-term use. Furthermore, a sufficient lubricant oil film can be readily established between the cam follower and the profile of the cam, resulting in less friction therebetween, during rotation of the cam shaft.

Brief description of the drawings

The forgoing and other aspects of the present application will be well understood by the following detailed explanation with reference to the drawings. It shall be noted that although the drawings may be given in different scales, which shall not be thought to affect understanding to the present application. In the drawings:

Fig. 1 is a partially cross-sectional and perspective view schematically illustrating a plunger pump according to the prior art.

Fig. 2 is a perspective view schematically illustrating a part of a tappet assembly of Fig. 1.

Fig. 3 schematically shows how a cam follower according to one embodiment of the present application cooperates with a cam shaft.

Fig. 4 schematically shows the cam follower of Fig. 3. Figs. 5a and 5b each schematically shows how the cam follower according to the embodiment of the present application is moved as the cam shaft is rotated.

Detailed description

In the drawings of the present application, those features having the same configuration or similar functions are represented by the same reference numerals.

It should be understood by one ordinary person in the art that although the present application’s technical solutions will be explained by referring to a plunger pump, use of the present application is not limited to the plunger pump.

Fig. 1 is a partially cross-sectional and perspective view schematically illustrating a conventional plunger pump. The plunger pump generally comprises a housing 100. One cam shaft 200 is rotatably supported in the housing 100. Two cams 201 and 202 are integrally formed in the cam shaft 200. For instance, viewed in a cross-section, the two cams 201 and 202 are in the form of two circles which are eccentric relative to a central axis of rotation of the cam shaft 200.

The plunger pump also comprises a plunger sleeve 300 connected to the housing 100. Two plunger cavities are separately defined in the plunger sleeve 300 to communicate with an interior space of the housing 100. Either plunger cavity of the plunger sleeve 300 is provided with a slidable plunger (invisible in the drawings) therein.

One plunger is coupled to one tappet assembly 500. As shown by Fig. 2, either tappet assembly 500 has a receiving end 510 which is hollow. In either receiving end 510, one cam follower 600 is pivotally installed by a pin shaft 700. In Fig. 2, the cam follower 600 is in the form of a hollow roll through which the pin shaft 700 passes. As such, one spring 400 is provided for either tappet assembly 500. The spring 400 is securely installed relative to the plunger sleeve at one end and bears against the responding tappet assembly 500 at the other end in such a way that the cam follower 600 is always pressed to be in contact with a profile of the cam 201 or 202. In this way, as the cam shaft 200 is rotated, the cam followers 600 is driven by the profile of the cam 201 or 202 to move upwards and downwards, such that the plunger is driven by the tappet assembly 600 to reciprocate in the plunger cavity. In the context of the present application,“the profile of the cam” refers to a side of the cam contacting the cam follower in operation.

Usually, lubricant oil is contained within the housing 100, for example in a bottom part of the housing 100, such that the cam shaft 200 and/or the cams 201 and 202 formed therein are at least partially immersed in the lubricant oil. Because there exists a linear contact between the cam follower 600 and the profile of the cam 201 or 202, it is difficult to establish a sufficient oil film between the cam follower 600 and the profile when the cam shaft 200 is rotated at high speed, which results in poor lubrication between the cam follower and the profile. Furthermore, the linear contact leads to a very small contact area between the cam follower 600 and the profile of the cam 201 or 202, and thus under long-term and heavy load condition fatigue break may occur in the cam follower 600 so as to damage the plunger pump.

In order to solve those issues, Fig. 3 schematically illustrates a partial view of a plunger pump equipped with a cam follower 800 according to one embodiment of the present application. The plunger pump of Fig. 3 is distinguished from that of Fig. 1 only by the cam follower 800. Therefore, other elements of the plunger pump of Fig. 3 can refer to the above explanation to Fig. 1.

Further, as shown by Fig. 4, the cam follower 800 comprises a through-hole 810 through which the pin shaft 700 shown by Figs. 2 and 3 can pass. As such, the cam follower 800 is pivotally installed at the receiving end 510 of the tappet assembly 500. The cam follower 800 also comprises a contact side 820 which is arc-shaped. In case that the cam follower 800 is in contact with the cam 201 or 202, the arc-shaped side extends following the circular profile of the cam 201 or 202. When the cam 201 or 202 is an eccentric circular cam, the contact side 820 of the cam follower 800 has a surface curvature radius which is the same as that of the circular shape of the cam 201 or 202.

Further as shown by Figs. 5a and 5b, they illustrate that viewed in a cross-section, the cam 201 is respectively in one position and the other position which is rotated by 90 degrees along a direction R about the central axis O of rotation of the cam shaft 200. In the position illustrated by Fig. 5a, because the surface curvature radius of the contact side 820 of the cam follower 800 is the same as that of the profile of the cam 201, there exists an areal contact between the contact side 820 and the profile of the cam 201. As the cam shaft 200 is rotated along the direction R about the central axis O of rotation, the cam follower 800 is also rotated along a direction R' about a pivotal axis O' of the pin shaft 700 while the areal contact is maintained between the contact side 820 and the profile of the cam 201, and at the same time the cam follower 800 is moved along a downward direction S. No matter how the cam 201 is rotated, the pivotal axis O' of the pin shaft 700 and the central axis O of rotation of the cam shaft 200 are always parallel to each other and in the same plane. In the context of the present application, the term “in the same plane” means that no matter how the cam is rotated and the cam follower is moved, the pivotal axis O' and the central axis O of rotation are always and remain unchanged in a straight line in a cross-section perpendicular to them. As such, as shown by Figs. 5a and 5b, as the cam 201 is rotated, the cam follower 800 is driven to linearly move upwards and downwards with wobbling leftwards and rightwards. Because the cam follower 800 is configured such that it can wobble at a small angle leftwards and rightwards, wobbling will not affect load transfer between the cam follower 800 and the cam 201, such that a sufficient driving force can be transmitted to the plunger via the cam follower 800 and the tappet assembly 500. In this way, the plunger can be driven to reciprocate in the respective plunger sleeve.

Although in the already-described embodiments the cam 201 or the 202 provided in the cam shaft 200 is in the form of the eccentric circular cam, the ordinary person in the art shall appreciate that the present application can apply to a case that the cam shaft 200 is provided with an oval-shaped cam. For instance, in an alternative embodiment, at least one oval-shaped cam is provided in the cam shaft 200. In this case, the contact side 820 of the cam follower 800, after being installed in place, is concaved towards the cam. In the context of the present application, the term“be concaved towards the cam” means that the curved side of the contact side 820 follows a direction along which the profile of the cam extends. Furthermore, in the alternative embodiment, viewed in a cross-section perpendicular to the cam shaft 200, the curvature radius of the contact side 820 is greater than or equal to the maximum surface curvature radius of the profile of the oval-shaped cam. As such, although in the alternative embodiment the cam is not a perfectly circular cam, an approximate areal contact, which is at least superior to the linear contact between the roll and the cam, is almost established between the contact side 820 and the profile of the oval-shaped cam, in operation, due to the existence of minute contact deformation therebetween. This is because the contact side 820 is concaved towards the cam and the curvature radius of the contact side is greater than or equal to the maximum surface curvature radius of the cam. Furthermore, due to the design of the areal or approximate areal contact, much more lubricant oil can be held between the contact side 820 and the profile of the cam, resulting in a better lubricating effect.

Moreover, in an alternative embodiment, viewed in the cross-section perpendicular to the cam shaft 200, it is also possible that the curvature radius of the contact side 820 can be less that the maximum surface curvature radius of the profile of the cam. As such, although viewed in the cross-section the contact side 820 may be in linear-contact with the profile of the cam at two circumferential ends, much more lubricant oil can be held in a region between the linear contacts, between the contact side 820 and the profile of the cam, also resulting in a better lubricating effect.

In conclusion, the present application provides a contact mating structure between a cam and a tappet assembly, the cam being formed in a rotatable shaft, the tappet assembly being movable perpendicularly relative to the rotatable shaft, the contact mating structure comprising a cam follower pivotally provided at one end of the tappet assembly, and the cam follower having a contact side for contacting a profile of the cam, wherein viewed in a cross-section perpendicular to a central axis of rotation of the rotatable shaft, the contact side is concaved towards the cam.

The present application also provides a plunger pump, comprising: a rotatable cam shaft in which a cam is formed; a plunger cavity in which a tappet assembly is installed so as to be moveable linearly therein, a cam follower being pivotally provided at one end of the tappet assembly, and the cam follower having a contact side for contacting a profile of the cam, wherein viewed in a cross-section perpendicular to the central axis of rotation of the rotatable shaft, the contact side is concaved towards the cam.

According to the embodiments of the present application, because the areal or approximate areal contact is established between the cam follower and the cam, great load can be transmitted from the cam to the tappet assembly and the cam follower has good fatigue resistance after long-term use. Further, because the contact area becomes greater, a sufficient lubricant oil film can be established between the cam follower and the profile of the cam, causing less friction therebetween, during rotation of the cam shaft. Further, because the contact area becomes greater, a sufficient lubricant oil film can be established between the cam follower and the profile of the cam, causing less friction therebetween, during rotation of the cam shaft.

Although the specific embodiments of the present application have been described here, they are given for explanatory purposes only and shall not been deemed restraining the scope of the present application. Furthermore, it should be understood by the ordinary person in the art that the embodiments described in the description can be arbitrarily combined with each other. Without departing from the spirit and scope of the present application, various alternations, modifications and changes can be thought out.