GB2577081A

GB2577081A - Fuel pump and plunger therefor

Info

Publication number: GB2577081A
Application number: GB1814849.4A
Authority: GB
Inventors: Guerrato Diego
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2018-09-12
Filing date: 2018-09-12
Publication date: 2020-03-18
Anticipated expiration: 2038-09-12
Also published as: GB201814849D0; GB2577081B

Abstract

A plunger assembly 14 suitable for a high pressure fuel pump is disclosed. The piston assembly 14 comprises a pumping element 48 with a concentric bore 52 extending into a chamber 86 so to form a shoulder. A filler element 50 is located in the cavity 52; having a smaller diameter such that an annular channel 88 is formed. A fastening assembly 70 comprising a retaining ring is pushed against the shoulder by a biasing means, preventing relative movement between the filler and the pumping elements. The hole 50 may be sloped and the filler tapered to match. The biasing means may be a helical or cup spring. A fuel pump and method of manufacturing the assembly, by attaching the ring to the filler element before fitting them to the pumping element, are also disclosed. In use high pressure flows in the annular channel to prevent the plunger contracting thus preventing fuel leakage around the plunger and maintaining volumetric efficiency.

Description

(54) Title of the Invention: Fuel pump and plunger therefor Abstract Title: Fuel pump plunger with filler element (57) A plunger assembly 14 suitable for a high pressure fuel pump is disclosed. The piston assembly 14 comprises a pumping element 48 with a concentric bore 52 extending into a chamber 86 so to form a shoulder. A filler element 50 is located in the cavity 52; having a smaller diameter such that an annular channel 88 is formed. A fastening assembly 70 comprising a retaining ring is pushed against the shoulder by a biasing means, preventing relative movement between the filler and the pumping elements. The hole 50 may be sloped and the filler tapered to match. The biasing means may be a helical or cup spring.

A fuel pump and method of manufacturing the assembly, by attaching the ring to the filler element before fitting them to the pumping element, are also disclosed. In use high pressure flows in the annular channel to prevent the plunger contracting thus preventing fuel leakage around the plunger and maintaining volumetric efficiency.

FIG. 4

1/6

FIG. 1

2/6

FIG. 2

3/6

FIG. 3

4/8

FIG. 4

5/6

FIG. 5

6/6

FIG. 6

FUEL PUMP AND PLUNGER THEREFOR

FIELD OF THE INVENTION

This invention relates to pumping plunger for a fuel pump and in particular to a fuel pump for delivering pressurised fuel to a common rail fuel volume.

BACKGROUND

A fuel pump used for delivering fuel to a common rail fuel volume of a compression-ignition internal combustion engine is required to pressurise fuel to more than 2,000 bar. Such pressure causes, amongst other things, the plunger of the fuel pump to contract, reducing the diameter of the plunger. This, in turn, increases the clearance between the outer radial surface of the plunger and the bore in which it reciprocates, opening up a larger surface area for pressurised fuel to leak past the plunger. This reduces the volumetric efficiency of the fuel pump.

Plunger designs to reduce this effect have been proposed but often their manufacturability and/ or durability does not allow them to be taken forward.

It is against this background that the invention has been devised.

STATEMENTS OF INVENTION

According to a first aspect of the invention, there is provided a pumping plunger assembly for a high-pressure fuel pump, the pumping plunger assembly comprising: a pumping element comprising a concentric bore and a chamber, wherein the bore expands into the chamber forming a shoulder element therebetween; a cylindrical filler element located in the bore and extending from the bore into the chamber, wherein the diameter of the filler element is less that the diameter of the bore forming an annular flow channel extending between an outer radial surface of the filler element and a radial surface of the bore into the chamber; and, a fastening assembly secured to a lower section of the filler element within the chamber, the fastening assembly comprising a retaining ring and a biasing means, wherein the biasing means is configured to push the retaining ring against the shoulder element thereby preventing relative movement between the pumping element and the filler element.

Preferably, a diameter of the bore decreases towards the chamber and filler element comprises a tapered section complementing the decreasing diameter of the bore.

Preferably, the filler element comprises a circumferential groove adjacent a bottom end of the filler element for receiving the retaining ring.

Preferably, the pumping plunger assembly further comprises a collar radially extending from the filler element, wherein an upper surface of the collar defines the circumferential groove.

Preferably, the retaining ring comprises a break defining a gap in the retaining ring.

Preferably, a wall of the retaining ring diverges from its lower end meaning that the diameter of the retaining ring at its lower end is smaller than the diameter at its upper end.

Preferably, the pumping plunger assembly further comprises a circumferential groove in an outer radial surface of the pumping element positioned adjacent to at least part of the chamber.

Preferably, the biasing means comprises a helical spring or a cup spring.

According to a second aspect of the invention, there is provided a pump comprising a pumping plunger assembly according to the first aspect.

According to a third aspect of the invention, there is provided a method of assembling a pumping plunger according to any preceding claim, the method comprising: pushing the fastening assembly over the lower end of the filler element to secure the fastening assembly to the filler element; and, pushing the filler element with the fastening assembly into the bore of the pumping element until the fastening element is received in the chamber of the pumping element.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a simplified view of a common rail fuel pump assembly having a pumping plunger assembly in accordance with an embodiment of the invention;

Figure 2 is an exploded view of the pumping plunger assembly in Figure 1;

Figure 3 is a detailed view of the pumping assembly in Figure 1 showing a fastening assembly;

Figure 4 is a cross sectional view of the pumping assembly in Figure 1;

Figure 5 is a detailed cross sectional view of the pumping assembly in Figure 1 showing the fastening assembly in a chamber of the pumping assembly;

Figure 6 is a detailed cross sectional view of the pumping assembly in Figure 1 showing an alternative fastening assembly in the chamber of the pumping assembly.

In the drawings, like features are denoted by like reference signs.

SPECIFIC DESCRIPTION

The following description refers to accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilised and structural changes may be made without departing from the scope of the invention as defined in the appended claims. Moreover, references in the following description to “upper”, “lower” or any other terms having an implied orientation are not intended to be limiting and refer only to the orientation of the features as shown in the accompanying drawings.

Figure 1 shows an embodiment of a common rail fuel pump assembly, generally designated as 2, for a compression-ignition internal combustion engine in accordance with the invention. The common rail fuel pump assembly 2 (hereinafter, “the pump 2”) comprises a pump head 4 having a centrally located blind bore 6 that is circular in cross section. The bore 6 opens at a lower face 8 of the pump head 4 and extends upwardly to define a blind end 10 in the proximity of an upper face 12 of the pump head 4. A pumping plunger assembly 14 (hereinafter, “the pumping plunger 14”) is provided in the form of an elongate, generally cylindrical, hardened steel rod arranged to slide back and forth within the bore 6 along its longitudinal axis. An inner end 16 or “pumping face” of the pumping plunger 14 defines a pumping chamber 18 with the blind end 10 of the bore 6.

At this point it should be noted that the term “pumping plunger” is used herein in its accepted engineering sense of an elongate pumping member having a length which is significantly greater than its diameter. It is this characteristic that is commonly relied upon to provide a sealing function in a pump in high pressure pumping applications. A plunger is to be distinguished from a piston which is typically of discoid form having a length less than or generally comparable to its diameter and which provides no direct sealing function.

A lower end 20 of the pumping plunger 14 extends from the pump head 4 and cooperates with a rotating drive arrangement, generally designated as 22, in the form of a rotatable cam member 24, having a base circle 23 and a cam lobe 25. The drive arrangement 22 is arranged to drive the pumping plunger 14 in a reciprocating manner between a bottom-dead-centre position (hereinafter, “BDC position”) and a top-dead-centre position (hereinafter, “TDC position”), defining a pumping stroke, and between the TDC position and the BDC position, defining a return stroke, as described in further detail below.

A tappet member, generally designated as 26, is affixed to the lower end 20 of the pumping plunger 14, positioned between the cam member 24 and the pumping plunger 14. The tappet member 26 includes a tappet base 28, which provides a relatively large contact face for the cam member 24 to act on the pumping plunger 14. The tappet member 26 is generally in the shape of a bucket and includes a side wall 29 upwardly extending from the tappet base 28 towards the pump head 4, defining a central chamber 30. The central chamber 30 houses a helical compression spring 32 (hereinafter, “the spring 32”) extending between the tappet base 28 and the lower face 8, or underside, of the pump head 4. The spring 32 acts on the tappet member 26, and so on the pumping plunger 14, to ensure that the pumping plunger 14 is biased outwardly from the bore 6, effecting the return stroke as permitted by rotation of the cam member 24.

The pump head 4 further comprises a first fuel passage 34 constituting an inlet to the pumping chamber 18 and a second fuel passage 36 constituting an outlet from the pumping chamber 18. Each fuel passage incorporates an associated spring-biased non-return valve 38, 40 (hereinafter, “the valves 38, 40”) to ensure that fuel can only flow through the first fuel passage 34 or the second fuel passage 36 into or out of the pumping chamber 18 respectively. The precise configuration of the valves 38, 40 is not central to the invention, and so will not be described in detail. Instead, it is sufficient for present purposes that the valves 38, 40 are considered to be conventional in that they both comprise a valve member that, in the absence of a pressure drop across the valve member, is held against a valve seat under the force of a spring. Moreover, it will be appreciated by the skilled reader that the pump 2, as shown in Figure 1, is greatly simplified for present purposes and that, in practice, it would include many components in addition to the principle features shown and described herein.

The pump 2 operates as follows. In the initial position shown in Figure 1, the tappet member 26 rests on the base circle 23 of the cam member 24 and, therefore, the pumping plunger 14 resides in the BDC position. At this position, the volume of the pumping chamber 18 it at a maximum. Note that at this initial condition, the pumping chamber 18 is filled with fuel.

The cam member 24 rotates in the direction of the arrow A' such that the tappet member 26 rides up the surface of the cam lobe 25 which drives the pumping plunger 14 along the bore 6 to perform the pumping stroke, during which the volume of the pumping chamber 18 is reduced, pressurising the fuel in the pumping chamber 18. The valve 40 is arranged to open when the fuel pressure has reached a predetermined pressure, allowing the pressurised fuel to evacuate the pumping chamber 18 through the second fuel passage 36. Although not shown in Figure 1, the pressurised fuel would be directed to a suitable load such as a common rail fuel volume connected, via suitable pipe work, to an outlet connector 42 of the pump 2. In practice, the fuel in the pumping chamber 18 is compressed to a pressure of at least 2,000 bar (200 MPa) before being displaced from the pumping chamber 18.

Following the pumping stoke, continued rotation of the cam member 24 results in the tappet member 26 riding down the back of the cam lobe 25, allowing the spring 32 to outwardly draw the pumping plunger 14 from the bore 6 to perform the return stroke. During the return stroke, the volume of the pumping chamber 18 increases, which decreases the pressure in the pumping chamber 18, establishing a pressure drop across the valve 38 associated with the first fuel passage 34. The pressure drop causes the valve 38 to open to permit fuel to enter the pumping chamber 18. Note that although not shown in Figure 1, in practice a low pressure fuel supply is connected via appropriate pipe work to an inlet connector 44 of the pump 2 to provide fuel for filling of the pumping chamber 18 during the return stroke.

An annular clearance 46 is provided between a radial surface of the bore 6 and an outer radial surface of the pumping plunger 14 to enable reciprocating movement of the pumping plunger 14 within the bore 6. During the pumping stroke, fuel in the pumping chamber 18 is pressurised to a high level, which can be up to 3,000 bar (300 MPa). Such a pressure causes pressurised fuel to leak into the annular clearance 46 from the pumping chamber 18, exerting radially inward and outward forces on the outer radial surface of the pumping plunger 14 and the radial surface of the bore 6 respectively. This has the effect of dilating the bore 6 and compressing the pumping plunger 14 slightly, which increases the size of the annular clearance 46. This increases the leakage of pressurised fuel past the pumping plunger 14 during the pumping stroke, and so reduces the volumetric efficiency of the pump 2. In order to reduce the leakage of fuel, the pumping plunger 14 is configured to radially expand during the pumping stroke, as will now be described in detail.

Figure 2 shows an exploded view of an embodiment of the pumping plunger 14 in accordance with the invention. The pumping plunger 14 comprises a pumping element 48 and a filler element 50 arranged to be received in a concentric blind bore 52 of the pumping element 48. The pumping element 48 comprises an upper section 56 and a lower section 58 separated from the upper section 56 by a circumferential groove 54 in the outer radial surface of the pumping element 48. The bore 52 opens at an upper face of the pumping element 48 and extends downwardly to define a blind end in the proximity of the circumferential groove 54. The filler element 50 includes three sections concentrically arranged with respect to each other comprising a cylindrical upper section 60 and a tapered middle section 62 downwardly tapering from the upper section 60. The lower end of the middle section 62 has a stepped profile, stepping down to a cylindrical lower section 64. The cylindrical lower section 64 comprises a collar 66 radially extending therefrom. The collar 66 comprises an upper surface 67 of which defines, together with the lower end of the middle section 62, a circumferential groove 68 for holding a fastening assembly, generally designated by 70.

With reference to Figure 3, , which is an enlargement of detail ‘A’ shown in Figure 2, the fastening assembly 70 comprises a deformable retaining ring 72 and a biasing means in the form of a helical spring 74, extending downwardly from and secured to a lower end 90 of the retaining ring 72. The retaining ring 72 comprises a discontinuous circular wall section 76 with two free ends 78 defining a gap 80 therebetween. That is, the circular wall section 76 comprises a break defining the gap 80. The gap 80 allows the diameter of the retaining ring 72 to change during the assembly of the pumping plunger 14.

Figure 4 is an assembled view of pumping plunger 14 with the filler element 50 located in the bore 52 of the pumping element 48. The bore 52 comprises three regions, the first two of which are configured to substantially correspond with the shape of the upper and middle sections 60, 62 of the filler element 50. That is, the bore 52 comprises a cylindrical upper region 82, corresponding to the shape of the cylindrical upper section 60 of the filler element 50, and a conical middle region 84, corresponding to the tapered middle section 62 of the filler element 50. The lower end of middle region 84 radially expands into a chamber 86, defining the lower region of the bore 52, configured to receive the lower section 64 of the filler element 50 and the fastening assembly 70. The chamber 86 fluidicallycommunicates with the inner end 16 of the pumping plunger 14 via an annular flow channel 88 formed between the outer radial surfaces of the upper and middle sections 60, 62 of the filler element 50 and the radial surfaces of the upper and middle regions 82, 84 of the bore 52. The gap 80 provides a means for connecting the annular flow channel 88 and the chamber 86 to enable pressure equalization around the filler element 50. The filler element 50 may also include a channel (not shown) connecting the pumping chamber 18 and the chamber 86 to facilitate pressure equalization around the filler element 50. The circumferential groove 54 in the outer radial surface of the pumping element 48 is longitudinally positioned to surround at least part of the chamber 86.

With reference to Figure 5, the inner diameter at the lower end 90 of the retaining ring 72 is less that the outer diameter of the collar 66, meaning that, when the fastening assembly 70 is held in the retaining groove 68, the lower end 90 of the retaining ring 72 abuts the upper surface 67 of the collar 66, preventing downward movement of the fastening assembly 70 relative to the filler element 50. The circular wall section 76 of the retaining ring 72 is configured to outwardly flare or diverge slightly from its lower end 90, meaning that the diameter of the retaining ring 72 at its lower end 90 is less than the diameter at its upper end 92. This widening of the retaining ring 72 aligns its upper end 92 with a circumferential shoulder element 94 defined by the radial expansion of the middle region 84 of the bore 52 into the chamber 86. The helical spring 74 acts on the collar 66 to bias the upper end 92 of the retaining ring 72 into engagement with the shoulder element 94, preventing downward movement of the filler element 50 relative to the pumping element 48. Accordingly, the fastening assembly 70 functions to connect indirectly the pumping element 48 and the filler element 50. This avoids the need for direct connections between these two components 48, 50, providing two significant advantages over pumping plungers comprising direct connections between their pumping elements and fillers. Firstly, direct connections can generate structural weaknesses within the pumping plunger 14, decreasing its durability. Secondly, direct connections would most likely be made using welding, press fitting or similar techniques, but these techniques have the disadvantage of making manufacturing the pumping plungers cumbersome. In contrast, assembly of the present pumping plunger 14 is straightforward and can be completed with few steps. Firstly, the filler element 50 is held upside down, so that its lower section 64 is uppermost. Secondly, the retaining ring 72 is pushed over the collar 66 into the retaining groove 68. Thirdly, the helical spring 74 is placed over the end of the lower section 64 to sit on a lower surface 96 of the collar 66. Fourthly, the pumping element 48, also orientated upside down, is pushed onto the filler element 50 carrying the retaining ring 72 and the helical spring 74. During this step, the diameter of the retaining ring 74 decreases, as permitted by the gap 80, as it travels along the conical middle region 84 of the bore 52 to the chamber 86. Once it reaches the chamber 86, the retaining ring 74 expands to its original dimensions, causing the upper end 92 of the retaining ring 72 to engage with the circumferential shoulder, preventing the filler element 50 from being withdrawn from the pumping element 48.

During the pumping stroke, pressurised fuel is forced from the pumping chamber 18 into the annular flow channel 88 via the inner end 16 of the pumping plunger 14. From there, the pressurised fuel enters the chamber 86 and generates forces upwardly acting on the lower section 64 of the filler element 50 and on the retaining ring 72 to counteract the pressure in the pumping chamber 18 downwardly acting on the upper face of the filler element 50. This prevents the filler element 50 from moving downwards with respect to the pumping element 48. The pressurised fuel in the chamber 86 and the annular flow channel 88 also generates forces outwardly acting on the radial surfaces of the bore 52 of the pumping element 48. During the pumping stroke, pressurised fuel leaks from the pumping chamber 18 into the annular clearance 46 between the radial surface of the bore 6 and the outer radial surface of the pumping plunger 14. As the fuel progresses along the annular clearance 46, it losses pressure until it reaches the groove 54, at which point its pressure is less than 5 bar (0.5 MPa), possibly even as low as atmospheric pressure. On the other hand, the pressure of the fuel within the annular flow channel 88 and the chamber 86 is substantially the same as the pressure of the fuel in the pumping chamber 18. That is, the pressurised fuel moving from the pumping chamber 18 to the chamber 86 does not experience a significant pressure drop. This a large pressure difference across the pumping element 48, forcing the pumping element 48 to expand radially towards the radial surface of the bore 6. This effect grows as the pressure within the pumping chamber 18 increases, which minimises fuel leakages through the annular clearance 46 to maintain the volumetric efficiency of the pump 2 at all running conditions.

It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms to that described herein, without departing from the scope of the appended claims. For example, with reference to Figure 6, in an alternative embodiment, the biasing means comprises a cup spring 98, which is alternative to and functions substantially the same as the helical spring 74 described above. The presence of the cup spring 98 reduces the volume of chamber 86 to increase the volumetric efficiency of the pump 2.

References used:

Pump 2

Pump head 4

Blind bore 6

Pump head lower face 8

Bore blind end 10

Pump head upper face 12

Pumping plunger 14

Pumping plunger inner end 16

Pumping chamber 18

Pumping plunger lower end 20

Drive arrangement 22

Base circle 23

Cam member 24

Cam lobe 25

Tappet member 26

Tappet base 28

Central chamber 30

Helical compression spring 32

First fuel passage 34

Second fuel passage 36

Non-return valves 38, 40

Outlet connector 42

Inlet connector 44

Annular clearance 46

Pumping element 48

Filler element 50

Bore 52 of the pumping element 48

Groove 54

Upper section 56 of the pumping element 48

Lower section 58 of the pumping element 48

Upper section 60 of the filler element 50

Middle section 62 of the filler element 50

Lower section 64 of the filler element 50

Collar 66

Upper surface 67 of the collar 66

Retaining groove 68

Fastening assembly 70

Retaining ring 72

Helical spring 74

Circular wall section 76

Free ends 78

Gap 80

Upper region 82 of the bore 52

Middle region 84 of the bore 52

Chamber 86

Annular flow channel 88

Lower end 90 of the retaining ring 72

Upper end 92 of the retaining ring 72

Shoulder element 94

Lower surface 96 of the collar 66

Cup spring 98

Claims

CLAIMS:

1. A pumping plunger assembly (14) for a high-pressure fuel pump (2), the pumping plunger assembly (14) comprising:

a pumping element (48) comprising a concentric bore (52) and a chamber (86), wherein the bore (52) expands into the chamber (86) forming a shoulder element (94) therebetween;

a cylindrical filler element (50) located in the bore (52) and extending from the bore (52) into the chamber (86), wherein the diameter of the filler element (50) is less that the diameter of the bore (52) forming an annular flow channel (88) extending between an outer radial surface of the filler element (50) and a radial surface of the bore (52) into the chamber (86); and, a fastening assembly (70) secured to a lower section (64) of the filler element (50) within the chamber (86), the fastening assembly (70) comprising a retaining ring (72) and a biasing means (74, 98), wherein the biasing means (74, 98) is configured to push the retaining ring (72) against the shoulder element (94) thereby preventing relative movement between the pumping element (48) and the filler element (50).

2. A pumping plunger assembly (14) according to claim 1, wherein a diameter of the bore (52) decreases towards the chamber (86) and filler element (50) comprises a tapered section (62) complementing the decreasing diameter of the bore (52).

3. A pumping plunger assembly (14) according to claim 1 or 2, wherein the filler element (50) comprises a circumferential groove (68) adjacent a bottom end of the filler element (50) for receiving the retaining ring (72).

4. A pumping plunger assembly (14) according to claim 3, further comprising a collar (66) radially extending from the filler element (50), wherein an upper surface (67) of the collar (66) defines the circumferential groove (68).

5. A pumping plunger assembly (14) according to claim 3 or 4, wherein the retaining ring (72) comprises a break defining a gap (80) in the retaining ring (72).

6. A pumping plunger assembly (14) according to claim 5, wherein a wall (76) of the retaining ring (72) diverges from its lower end (90) meaning that the diameter of the retaining ring (72) at its lower end (90) is less than the diameter at its upper end (92).

7. A pumping plunger assembly (14) according to any preceding claim, further comprising a circumferential groove (54) in an outer radial surface of the pumping element (48) positioned adjacent to at least part of the chamber (86).

8. A pumping plunger assembly (14) according to any preceding claim, wherein the biasing means (74, 98) comprises a helical spring (74) or a cup spring (98).

9. A pump (2) comprising a pumping plunger assembly (14) according to any preceding claim.

10. A method of assembling a pumping plunger (14) according to any preceding claim, the method comprising:

pushing the fastening assembly (70) over the lower end of the filler element (50) to secure the fastening assembly (70) to the filler element (50); and, pushing the filler element (50) with the fastening assembly (70) into the bore (52) of the pumping element (48) until the fastening assembly (70) is received in the chamber (86) of the pumping element (48).

Intellectual

Property

Office

Application No: GB1814849.4