GB2543500A

GB2543500A - High pressure fuel pump

Info

Publication number: GB2543500A
Application number: GB1518423.7A
Authority: GB
Inventors: Ivan De Saram Ruwantha
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-10-19
Filing date: 2015-10-19
Publication date: 2017-04-26
Anticipated expiration: 2035-10-19
Also published as: GB201518423D0; GB2543500B

Abstract

A high pressure diesel fuel pump comprising a pumping assembly and a drivetrain assembly 20; the pumping assembly comprises a plunger extending from a pump head along a pumping axis (A-A). The drivetrain assembly 20 comprises a drive shaft and a cam 80 mounted thereon within a cambox 22 of a housing, a shoe 50 for contact with a lower end of the plunger, a roller 70 mounted within a cavity 52 of the shoe 50 for contact with the cam 80, and a shoe guide 60 mounted within a guide chamber 24 of the housing substantially between the cam 80 and the plunger and adapted to receive the shoe 50 and roller 70 within a bore 62 thereof. The shoe 50 comprises at least one hollow 59a, 59b in at least a side face 57a, 57b thereof. The arrangement is intended to supply diesel or lubricant to a thrust interface between the shoe and its guide bore, which would otherwise be starved due to the direction of rotation of the driving cam.

Description

HIGH PRESSURE FUEL PUMP BACKGROUND Technical Field

The present invention relates generally to the field of high pressure fuel pumps. More particularly, but not exclusively, the present invention concerns an adapted shoe for high pressure diesel fuel pumps.

Description of the Related Art

As shown in Figures la and lb, a typical high pressure diesel fuel pump adopting a roller-shoe arrangement as part of the drivetrain, comprises a plunger 2 extending from a hydraulic head 1 along a pumping axis A-A'. A plunger return spring 3 is seated around the head 1 and extends to the top of a spring seat 4 fixed near a lower end 2a of the plunger 2. The lower end 2a of the plunger 2 contacts an upper face 5a of a shoe 5. The shoe 5 slides within an axial bore 6a (disposed along the pumping axis A-A') of a shoe guide 6. A roller 7 is mounted and retained within an aperture provided at a lower end of the shoe 5 and slides within the bore 6a with the shoe 5. The roller 7 contacts a surface of a cam 8, which is driven to rotate in direction D by a rotating driveshaft (not shown) to provide upward sliding motion along the pumping axis A-A'.

As the shoe 5 is lifted and dropped within the bore 6a of the shoe guide 6 at a high speeds, one 'leading' or 'trust' side face 5d of the shoe 5 is constantly biased towards a corresponding internal 'leading' or 'trust' side face 6d of the bore 6a of the shoe guide 6 caused by the direction of rotation D of the cam 8. Accordingly, this side face 5d and the internal face 6d are starved of fuel and therefore, lubrication. Fuel starvation between two such 'leading' or 'trust' faces 5d, 6d causes cavitation of the faces 5d, 6d which deteriorates the smooth running of the shoe 5 within the bore 6a and causes inefficiencies and possible failures in the entire fuel system, including pump and injector failure.

In order to prevent such inefficiencies and failures as a result of the fuel starvation, it is necessary to increase the lubrication to these 'leading' or 'trust' side faces 5d, 6d.

It is an object of the present invention to address one or more of the problems of known designs, particularly, but not exclusively high pressure pumps.

Therefore, it is now desired to provide an improved drivetrain arrangement for a high pressure fuel pump that is capable of delivering increased lubrication to 'leading' or 'trust' side faces of the shoe and corresponding 'leading' or 'trust' side face of the shoe guide bore. More particularly, it is desired to provide an improved shoe for a drivetrain arrangement of a high pressure fuel pump.

SUMMARY OF THE INVENTION

In a first aspect of the present invention there is provided a high pressure diesel fuel pump comprising a pumping assembly and a drivetrain assembly, the pumping assembly comprising a plunger extending from a pump head along a pumping axis, the drivetrain assembly comprising a drive shaft and a cam mounted thereon within a cambox of a housing, a shoe for contact with a lower end of the plunger, a roller mounted within a cavity of the shoe for contact with the cam, and a shoe guide mounted within a guide chamber of the housing substantially between the cam and the plunger and adapted to receive the shoe and roller within a bore thereof, wherein the plunger is arranged for reciprocating linear movement along the pumping axis within a pumping chamber of the housing upon rotation of the cam, characterised in that the shoe comprises at least one hollow in at least a side face thereof.

With this arrangement, the hollow in the side face functions to continuously transfer fuel from a front and back of the shoe to the 'starving' interface between the side face of the shoe and the corresponding face of the shoe guide bore as it reciprocates within the bore. In a further advantage of the invention, the hollow(s) reduce(s) the reciprocating mass of the shoe, which allows for a less stiff plunger return spring and/ or spring seat and reduces torque and ultimately C02 emissions.

By 'side face', what is meant is a 'leading' or 'trust' side face of the shoe that is prone to cavitation as a result of being biased or thrust towards a corresponding internal side face of the bore of the shoe guide caused by the direction of rotation of the cam, e.g. not a face open to said roller.

By 'hollow', what is meant is a concave depression in the side face of the shoe, which is closed to an upper and/or lower face of the shoe, e.g. does not breach the upper and/ or lower face of the shoe.

Preferably, the hollow comprises a substantially lateral groove in said side face.

By 'substantially lateral groove', what is meant is a hollow extending generally across the side face of the shoe either horizontally, or on an angle.

The lateral groove may extend across a part of the side face, e.g. with zero or one open end. Most preferably, the lateral groove extends across the entire side face to be open to adjacent end faces of the shoe. By 'end face' we mean faces open to the roller.

Alternatively, the, or each hollow may comprise a depression open to the bore from the side face only, e.g. closed except to the side face. In this case, the, or each hollow may comprise a bowl, or other shaped depression, such as closed-ended channel or groove.

Preferably, there is a single hollow or lateral groove in said side face. The single hollow or lateral groove preferably covers at least approximately 25% of the depth of the side face from a top end of said shoe to a bottom end of said shoe. More preferably, the single hollow or lateral groove preferably covers between approximately 25% and approximately 75% of the depth of the side face from a top end of said shoe to a bottom end of said shoe. Most preferably, the single hollow or lateral groove preferably covers approximately 50% of the depth of the side face from a top end of said shoe to a bottom end of said shoe.

Alternatively, there may be multiple hollows and/or lateral grooves in said side face. The, or each hollow/ lateral groove may be the same in profile. The, or each hollow/ lateral groove may be arranged in an organised pattern in said side face to optimise fuel delivery. The, or each hollow/ lateral groove may together cover at least approximately 25% of the depth of the side face from a top end of said shoe to a bottom end of said shoe, more preferably, the between approximately 25% and approximately 75% of the depth of the side face, most preferably, approximately 50% of the depth of the side face from a top end of said shoe to a bottom end of said shoe.

Preferably, the, or each hollow/ lateral groove comprises a smooth transition with the side face. This removes the possibility for sharp edges which would increase the wear on the side face, internal face of the bore.

Preferably, the shoe further comprises at least one hollow in each of two opposing side faces (one being said 'leading' or 'trust' side face in use and the other being the 'anti-trust' side face). Preferably, the hollows are the same in number, shape and arrangement in both side faces. This not only brings balance to the shoe and further reduces the reciprocating mass of the shoe, but also enables the shoe to be used in two different orientations within the bore of the shoe guide.

Preferably, the shoe comprises a chamfered upper end. Preferably, the chamfered upper end comprises at least two opposing sloped portions extending between a flat plunger-engaging surface and respective side walls of the shoe. The chamfered upper end may be presented at an angle of between approximately 95° and approximately 130° relative to the plunger axis, preferably, between approximately 100° and approximately 120°, most preferably, approximately 110°.

Preferably, the pump is a diesel pump.

In a second aspect of the present invention there is provided a drivetrain assembly for a high pressure fuel pump comprising a drive shaft and a cam mounted thereon within a cambox of a housing, a shoe for contact with a lower end of the plunger, a roller mounted within a cavity of the shoe for contact with the cam, and a shoe guide mounted within a guide chamber of the housing substantially between the cam and the plunger and adapted to receive the shoe and roller within a bore thereof, wherein the plunger is arranged for reciprocating linear movement along the pumping axis within a pumping chamber of the housing upon rotation of the cam, characterised in that the shoe comprises at least one hollow in at least a side face thereof.

It will be appreciated that the preferred features described in relation to the first aspect of the invention also apply to the second aspect of the invention.

In a third aspect of the present invention there is provided a shoe for a drivetrain assembly of a high pressure fuel pump comprising a cavity for a roller to be mounted therein, characterised in that the shoe comprises at least one hollow in at least a side face thereof.

It will be appreciated that the preferred features described in relation to the first aspect of the invention also apply to the third aspect of the invention.

In a fourth aspect of the present invention there is provided a shoe for a drivetrain assembly of a high pressure fuel pump comprising a cavity for a roller to be mounted therein, characterised in that the shoe comprises a chamfered upper end.

It will be appreciated that the preferred features described in relation to the first aspect of the invention also apply to the fourth aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how exemplary embodiments may be carried into effect, reference will now be made to the accompanying drawings in which:

Figure la is a cross-sectional partial view of a prior art pumping assembly and drivetrain assembly of a high pressure diesel fuel pump at bottom dead centre (BDC);

Figure lb is cross-sectional partial view of a prior art shoe guide, shoe and roller as part of the drivetrain assembly.

Figure 2 is a schematic perspective front view of a shoe for a drivetrain assembly of a high pressure fuel pump according to an embodiment of the invention; and

Figure 3 is a schematic cross-sectional front view of the shoe of Figure 2 in use.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

An embodiment of the invention is shown in Figures 2 and 3. A high pressure diesel fuel pump comprises a pumping assembly (not shown) and a drivetrain assembly 20, the pumping assembly comprising a plunger (not shown) extending from a pump head (not shown) along a pumping axis A-A', the drivetrain assembly 20 comprising a drive shaft (not shown) and a cam 80 mounted thereon within a cambox 22 of a housing (not shown), a shoe 50 for contact with a lower end of the plunger, a roller 70 mounted within a cavity 52 of the shoe 50 for contact with the cam 80, and a shoe guide 60 mounted within a guide chamber 24 of the housing substantially between the cam 80 and the plunger and adapted to receive the shoe 50 and roller 70 within a bore 62 thereof, wherein the plunger is arranged for reciprocating linear movement along the pumping axis A-A' within a pumping chamber (not shown) of the housing upon rotation of the cam 80, characterised in that the shoe 50 comprises at least one hollow 59a, 59b in at least a side face 57a, 57b thereof.

The shoe 50 comprises a body 51 with an upper face 53 and a lower face 54. The cavity 52 for the roller 70 is provided in the bottom face 54, whilst a plunger contact surface 55 is provided by the upper face 53. Between the upper face 53 and the lower face 54 are a pair of opposing end faces 56 and a pair of opposing side faces 57a, 57b. The cavity 52 for the roller 70 extends between the pair of end faces 56 and is open to both end faces 56. The side faces 57a, 57b are closed to the cavity 52.

Since a 'leading' or 'trust' side face is characterised by the direction D of rotation of the cam 80 (as the side face of the shoe 50 that is biased or thrust towards a corresponding internal side wall of the bore 62 of the shoe guide 60 during rotation), in the Figures, the side face has been designated as side face 57a and the internal side wall as 66d where the direction D is clockwise. However, it is to be appreciated that either of said side faces 57a, 57b may comprise the 'leading' or 'trust' side face of the shoe 50 and either of said walls 66c, 66d of the guide 60 may comprise the corresponding 'leading' or 'trust' side internal wall, with the remaining opposing side face 57a, 57b/ wall 66c, 66d taking on the function of an 'anti-trust' side face/ 'anti-trust' side wall. Accordingly, in the event that the rotation of the cam 80 was reversed, side face 57b would be the 'leading' or 'trust' side face and wall 66c would be the 'anti-trust' side internal wall.

The body 51 of the shoe 50 is generally cuboidal, with side faces 57a, 57b being elongate compared with the end faces 56. At the junction between the side faces 57a, 57b and the end faces 56, the body 51 comprises blunted corners 58. The body 51 of the shoe 50 is sized to fit snugly between two pairs of retaining walls 66a/b (66b not shown), 66c/d of the bore 62 of the shoe guide 60. The cavity 52 provided within the body 51 comprises a half-cylindrical open-ended aperture sized to accommodate the rotating roller 70.

The side faces 57a, 57b of the shoe 50 each comprise a laterally disposed groove to provide the hollow 59a, 59b. The grooves 59a, 59b extend across the entire width of the respective side face 57a, 57b and reaching into the blunted corners 58.

Each lateral groove 59a, 59b covers at covers approximately 50% of the depth of the side face 57a, 57b from the upper face 53 of said shoe 50 to the lower end 54. However, it is to be appreciated that to have an advantageous effect, each lateral groove 59a, 59b can cover between approximately 25% and approximately 75% of the depth of the side face 57a, 57b from the upper face 53 of said shoe 50 to the lower end 54.

The grooves 59a, 59b comprise a uniform depth profile thereacross. The profile of each groove 59a, 59b takes the form of a concave channel of shallow bowl-shape in cross-section. Where each groove 59a, 59b re-joins the respective side face 57a, 57b of the shoe 50 at either side, the transition comprises a smooth curved section 59c, 59d (best seen in Figure 2) of large radii in order to avoid a sharp edge.

The upper face 53 of the shoe 50 comprises the substantially flat plunger contact face 55 centrally thereon. Opposing downwardly sloping sections 53a, 53b as part of the upper face 53 extend from the contact face 55 to meet the side faces 57a, 57b. Accordingly, the side faces 57a, 57b are shorter between the upper face 53 and the lower face 54 compared with the end walls 56. The sloping sections 53a, 53b provide the upper face 53 with a chamfer which reduces the mass of the body 51. The plunger contact face 55 need only be marginally larger than the intended plunger, allowing the sloping sections 53a, 53b to remove a significant proportion of the mass of the upper part of the shoe 50.

The shoe guide 60 comprises a body, which in this case is substantially cylindrical in shape in order to fit directly (press-fit) within a cylindrical aperture within the guide chamber 24 of the housing. It is, however, to be appreciated that the body of the guide 60 may be of any suitable external shape to correspond with either the internal shape of a guide chamber 24, or an adapter which may sit inside such a chamber 24. The bore 62 is substantially centrally located and extends between lower and upper ends 61, 63, respectively The bore 62 is adapted to provide guided sliding contact with the shoe 50 with the pairs of internal walls 66a/b, 66c/d. Accordingly, the bore 62 comprises a shape that substantially corresponds with the external shape of the largest outer peripheral boundary of the shoe 50. In this case, the shape of the bore 62 is substantially cuboidal to correspond to that of the shoe 50.

The bore 62 further comprises a plurality of flow passages in the form of four concavely curved channels 65 cut into the corners of the bore 62 and extending between the two ends 61, 63 of the body. Accordingly, the sliding relationship with the shoe 50 is dependent on the two pairs of internal walls 66a, 66b that are disposed between the corner channels 65.

During assembly, the shoe 50 is disposed in the bore 62 such that the end faces 56 of the shoe 50 contact the internal walls 66a/b and the side faces 57a, 57b of the shoe 50 contact the internal walls 66c/d. The blunted corners 58 of the shoe 50 substantially span across the corner channels 65 of the bore 62 to provide large flow passages around each corner of the shoe 50. Therefore, the lateral grooves 59a, 59b span across an entire width of the internal walls 66c, 66d respectively and into the corner channels 65 of the bore 62.

In the described embodiment, since both side faces 57a, 57b incorporate such a groove 59a, 59b, the 'leading' or 'trust' side face 57a and the 'anti-trust' side face 57b or vice versa, are both continuously lubricated. This means that the shoe 50 can be used in either of two orientations and still function as intended, which minimises assembly issues. However, only one such side face 57a, 57b may be provided with a groove 59a, 59b in which case the shoe 50 should be assembled so as to provide the 'leading' or 'trust' side face 57a with the groove 59a on the side that would be prone to cavitation. The smooth transitional sections 59c, 59d of the grooves 59a, 59b, form a smooth contact with the respective internal wall 66c, 66d of the bore 62.

In a further advantage of the invention, the grooves 59a, 59b reduce the reciprocating mass of the shoe 50, which allows for a less stiff plunger return spring and/ or spring seat and reduces torque and ultimately C02 emissions. The further reduction in mass of the shoe 50 contributed by the sloping sections 53a, 53b provides a further advantage.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

Claims

1. A high pressure diesel fuel pump comprising a pumping assembly and a drivetrain assembly (20), the pumping assembly comprising a plunger extending from a pump head along a pumping axis (A-A'), the drivetrain assembly (20) comprising a drive shaft and a cam (80) mounted thereon within a cambox (22) of a housing, a shoe (50) for contact with a lower end (54) of the plunger, a roller (70) mounted within a cavity (52) of the shoe (50) for contact with the cam (80), and a shoe guide (60) mounted within a guide chamber (24) of the housing substantially between the cam (80) and the plunger and adapted to receive the shoe (50) and roller (70) within a bore (62) thereof, wherein the plunger is arranged for reciprocating linear movement along the pumping axis (A-A') within a pumping chamber of the housing upon rotation of the cam (80), characterised in that the shoe (50) comprises at least one hollow (59a, 59b) in at least a side face (57a, 57b) thereof.

2. The pump according to claim 1, wherein the hollow (59a, 59b) comprises a substantially lateral groove (59a, 59b) in said side face (57a, 57b).

3. The pump according to claim 2, wherein the lateral groove (59a, 59b) extends across the entire said side face (57a, 57b) to be open to adjacent end faces (56) of the shoe (50).

4. The pump according to claim 1, wherein the, or each hollow (59a, 59b) comprises a depression open to the bore (62) from the side face (57a, 57b) only.

5. The pump according to any one of claims 1 or 4, wherein the, or each hollow (59a, 59b) comprises a shaped depression, such as closed-ended channel or groove.

6. The pump according to any one of claims 1 to 5, wherein there is a single hollow (59a, 59b) or lateral groove (59a, 59b) in the side face (57a, 57b).

7. The pump according to claim 6, wherein the single hollow (59a, 59b) or lateral groove (59a, 59b) covers between approximately 25% and approximately 75% of the depth of the side face (57a, 57b) from an upper end (53) of said shoe (50) to a lower end (54) of said shoe (50).

8. The pump according to any one of claims 1 to 5, wherein there are multiple hollows (59a, 59b) and/or lateral grooves (59a, 59b) in said side face (57a, 57b).

9. The pump according to any one of claims 1 to 8, wherein the, or each hollow (59a, 59b)/ lateral groove (59a, 59b) comprises a smooth transition with the side face (57a, 57b).

10. The pump according to any one of claims 1 to 9, wherein the shoe (50) comprises at least one hollow (59a, 59b) in two opposing side faces (57a, 57b), one being said 'leading' or 'trust' side face (57a, 57b) in use.

11. The pump according to claim 10, wherein the hollows (59a, 59b) are the same in number, shape and arrangement in both side faces (57a, 57b).

12. The pump according to any one of claims 1 to 11, wherein the shoe (50) comprises a chamfered upper end (53).

13. The pump according to claim 12, wherein the chamfered upper end (53) comprises at least two opposing sloped portions extending between a flat plunger-engaging surface (55) and respective side walls (57a, 57b) of the shoe (50).

14. A drivetrain assembly (20) for a high pressure fuel pump comprising a drive shaft and a cam (80) mounted thereon within a cambox (22) of a housing, a shoe (50) for contact with a lower end (54) of the plunger, a roller (70) mounted within a cavity (52) of the shoe (50) for contact with the cam (80), and a shoe guide (60) mounted within a guide chamber (24) of the housing substantially between the cam (80) and the plunger and adapted to receive the shoe (50) and roller (70) within a bore (62) thereof, wherein the plunger is arranged for reciprocating linear movement along the pumping axis (A-A') within a pumping chamber of the housing upon rotation of the cam (80), characterised in that the shoe (50) comprises at least one hollow (59a, 59b) in at least a side face (57a, 57b) thereof.

15. A shoe (50) for a drivetrain assembly (20) of a high pressure fuel pump comprising a cavity (52) for a roller (70) to be mounted therein, characterised in that the shoe (50) comprises at least one hollow (59a, 59b) in at least a side face (57a, 57b) thereof.