GB2570490A

GB2570490A - Fuel pump

Info

Publication number: GB2570490A
Application number: GB1801349.0A
Authority: GB
Inventors: J Pedley Toby; Buckley Paul; Tully Adam
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2018-01-26
Filing date: 2018-01-26
Publication date: 2019-07-31
Also published as: GB201801349D0

Abstract

A fuel pump 10 and method of manufacturing a pump are disclosed. The pump has a compression chamber 14 defined by a bore 22, a piston 24 and an outlet valve assembly 20 fixed in a recess 26 dug in an external face of the pump body12. The bottom of the hollow 26 defining an annular shoulder at the centre of which opens the hole 22. The valve assembly may be screwed into the recess or slid in and then held in place by a fixing nut. The fuel pump is produced by drilling the bore and recess into a blank casting. The valve assembly may be calibrated before arranging it in the recess. The pump and method allow for versatility and interchangeability whilst maintaining the required tolerances of the components.

Description

TECHNICAL FIELD

The present invention relates to a fuel pump and more particularly to the arrangement of the outlet valve assembly of said pump.

BACKGROUND OF THE INVENTION

Outlet or non-return valves in diesel fuel injection pumps are complex assemblies inserted as multiple separate components into the pump body or head of the pump.

Effective operation of the valve requires precision machining operations to obtain micron accuracy tolerances on a large and expensive component, namely the pump body or head. Achieving these tolerances will become more arduous and costly as the valve is required to seal effectively and repeatedly at ever increasing pump speeds and pressures.

Versatility and interchangeability are also compromised by fully integrated arrangements.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a fuel pump having a compression chamber defined by a bore, a piston and an outlet valve assembly fixed in a recess dug in an external face of the pump body, the bottom of the recess defining an annular shoulder at the centre of which opens the bore.

The outlet valve assembly may seal against said annular shoulder, said sealing being assured by a lip defining a knife edge, said lip rising above a face of the body of the valve assembly or above said shoulder.

The body of the outlet valve assembly may define a cartridge provided with an internal conduit wherein a valve member is urged against a seat toward a closed position of said conduit.

The control valve assembly may be screwed and tightened in the recess.

The control valve assembly may be slidably inserted in the recess and therein pressed and fixed by a nut.

In an embodiment the pumping bore and the recess may be coaxial.

The invention further extends to a method to manufacture a high pressure fuel pump as claimed in any one of the preceding claims the method comprising the following steps:

a) providing a blank casting for a pump body and,

b) drilling a recess in said blank, the recess opening on an outer face of the blank and defining a lateral face and a bottom face;

c) drilling in said blank a pumping bore that opens in the bottom face of said recess.

d) providing an outlet valve assembly forming a standalone assembly having a body provided with an inner conduit defining a seat against which a valve member is urged in a closed position by a spring compressed between said valve member and a retainer member fixed in the conduit and,

e) calibrating said outlet valve assembly in tuning the pressure to apply on the valve member to move it to an open position.

f) arranging said valve assembly in said recess of the pump body

g) screwing the valve assembly in the recess and,

h) tightening said valve assembly down to the bottom of the recess so a sealing lip, defining a knife edge, provided on the valve body is pressed a complementary deformed contact against the bottom face of the recess.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial section of an outlet valve as per the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fuel injection equipment of an internal combustion engine comprises a fuel pump 10, partially shown in the figure, receiving fuel at low pressure and delivering pressurised fuel to a HP reservoir, commonly known as a common rail, wherefrom said pressurised fuel is distributed to fuel injectors.

The pump 10 has a body 12 housing a compression chamber 14 wherein fuel at low pressure enters via an inlet conduit controlled by an inlet valve, not shown, and exits via an outlet conduit 18 controlled by an outlet valve assembly

20. The compression chamber 14 is defined at an end of a bore 22 provided in said body 12 and extending along a pumping axis XI. In use, the volume of said chamber 14 is cyclically varied by a piston 24 guided in said bore 22 and urged by a camshaft, or an eccentric or other means, not shown, to reciprocal displacements.

The pump body 12 is further provided with a recess 26 dug along a recess axis X2 in an outer face of the body, said recess defining a cylindrical hollow having a lateral face 28 and a bottom face wherein centrally opens the bore 22, said bottom face being then limited to a peripheral annular shoulder 30 defining a sealing face 30.

On the figure, the bore and the recess have coincident axes XI, X2 but, in alternative arrangements not shown, said axes XI, X2 may be angled, the recess not being aligned with the bore.

The outlet valve assembly 20 defines a cartridge extending along a valve axis X3 which, when arranged in the recess, is coincident with the recess axis X2. The valve assembly 20 has a tubular body 32 which inner channel is the outlet conduit 18, said body 32 having an outer peripheral face 34 extending between a lower face 36 that abuts against the sealing face 30 in the bottom of the recess and, an opposed upper annular face 38 protruding outside the recess. The recess 26 and the valve body 32 are complementary threaded enabling to engage, to screw and tighten the valve assembly 20. Moreover, to ensure a leak free arrangement a sealing system is provided between said male valve body 32 and female recess 26, said system comprising a “knife edge” arrangement 40 and an oring 42. The knife edge 40 comprises an annular sealing lip 44 raising from the valve body lower face 36 to a sharp edge which, when the valve assembly 20 is firmly tightened in the recess 26 complementary fits and slightly deforms and marks the sealing face 30. In use, the pressure in the compression chamber may raise to several thousands of bars and, should some very minor quantity of fuel still find a way to leak through said knife edge, the pressure of said leaks would drop immediately after the knife edge and, the fuel would enter in an annular chamber 46 between the recess and the valve body, the chamber 46 surrounding the valve. A return conduit 48 opening in said chamber 46 enables evacuation of the low pressure fuel. Opposite the knife edge 40, the chamber 46 is sealed by said o-ring 42 arranged between a groove provided in the valve body and the lateral face 28 of the recess, said o-ring 42 just having to seal against low pressure fuel. This is a preferred arrangement but it can be done successfully without the o-ring 42, chamber 46 and connection 48.

As shown on the figure, the valve assembly 20 is provided with a central channel axially X3 extending through the valve body 32 and opening at both ends in the lower face 36 and in the upper face 38. As said, said central channel defines the outlet conduit 18 and is in fluid continuity with the bore 22. In said conduit 18 is defined a valve seat 50 and, a ball 52 a spring 54 and a tubular retainer member 56 are arranged. The ball 52 is urged against the seat 50 in a closed position of the conduit by the spring 54 compressed between said ball and said tubular retainer 56 member that is press-fitted in the conduit 18. In use, the outlet conduit 18 is closed and, the piston 24 moving toward the Top Dead Center position raise the pressure in the compression chamber 14 generating an opening force on the ball 52. When said opening force overcomes the closing force of the spring 54 and the trapped pressure in conduit 18, the ball 52 lifts off the seat and opens a fluid passage for pressurised fuel to exit the compression chamber 14.

Alternatively, another valve member 52 such as a flat plate or the tip of a needle may be arranged in place of the ball. Moreover, the retainer 56 is fixed in the conduit 18 by press-fit interference but other known means of fixation such as welding, brazing, threaded may be utilised.

This outlet valve arrangement eases the manufacturing of the pump body, of the control valve and, the assembly of the pump 10. Indeed on the pump body 12, the machining of the recess 26 enables an easy drilling and finishing of the bore 22 as well as it enables to enlarge the positioning tolerances of the bore 22. In case of theoretically coincident axes a small offset between the pumping axis XI and the recess axis X2 would remain acceptable as long as the knife edge 40 seals against the sealing shoulder 30. In case of an embodiment with an angular arrangement, it would remain acceptable for said axes XI, X2 not to perfectly intersect.

Moreover, the valve assembly is arranged as a standalone cartridge comprising the body 32 and the internal components (ball, spring, retainer) so, a manufacturing error on the valve body 32 limits the scrap to said valve body and does not affect a pump body.

Calibration and functional tuning of the opening outlet pressure can be performed on the valve assembly 20 alone not requiring the complete pump 10.

In another alternative not shown, instead of being complementary threaded within the recess for being screwed and tightened, the valve assembly may be freely and fully inserted inside the recess then, being pressed to the bottom face by a nut tightened in the opening area of the recess.

LIST OF REFERENCES

XI pumping axis

X2 recess axis

X3 outlet valve axis pump body compression chamber outlet conduit outlet valve assembly bore piston recess lateral face annular shoulder - sealing face valve body peripheral face lower face upper face knife edge

O-ring lip chamber conduit seat ball spring retainer

Claims

CLAIMS:

1. Fuel pump (10) having a compression chamber (14) defined by a bore (22), a piston (24) and an outlet valve assembly (20) fixed in a recess (26) dug in an external face of the pump body(12), the bottom of the recess defining an annular shoulder at the center of which opens the bore (22).

2. Fuel pump (10) as claimed in the preceding claim wherein the outlet valve assembly (20) seals against said annular shoulder (30).

3. Fuel pump (10) as claimed as in claim 2 wherein the sealing is assured by a lip (44) defining a knife edge (40), said lip rising above a face of the body (32) of the valve assembly or above said shoulder (30).

4. Fuel pump (10) as claimed as in any one of the preceding claims wherein the body (32) of the outlet valve assembly defines a cartridge provided with an internal conduit (18) wherein a valve member (52) is urged against a seat (50) toward a closed position of said conduit (18).

5. Fuel pump (10) as claimed in any one of the preceding claims wherein the control valve assembly (20) is screwed and tightened in the recess (26).

6. Fuel pump (10) as claimed in any one of the claims 1 to 4 wherein the control valve assembly (20) is slidably inserted in the recess and therein pressed and fixed by a nut.

7. Fuel pump (10) as claimed in any one of the preceding claims wherein the pumping bore (22) and the recess (26) are coaxial.

8. Method (100) to manufacture a high pressure fuel pump (10) as claimed in any one of the preceding claims the method comprising the following steps:

a) providing a blank casting for a pump body (12) and,

b) drilling a recess (26) in said blank, the recess opening on an outer face of the blank and defining a lateral face and a bottom face;

c) drilling in said blank a pumping bore (22) that opens in the bottom face of said recess (26).

9. Method (100) as claimed in claim 8 further comprising the steps:

d) providing an outlet valve assembly (20) forming a standalone assembly having a body (32) provided with an inner conduit (18) defining a seat (50) against which a valve member (52) is urged in a closed position by a spring (54) compressed between said valve member (52) and a retainer member (56) fixed in the conduit (18) and,

e) calibrating said outlet valve assembly (20) in tuning the pressure to apply on the valve member (52) to move it to an open position.

f) arranging said valve assembly (20) in said recess (26) of the pump body.

10. Method (100) as claimed in claim 9 wherein the arranging step f) is done by:

g) screwing the valve assembly (20) in the recess (26) and,

h) tightening said valve assembly (20) down to the bottom of the recess so a sealing lip (44), defining a knife edge, provided on the valve body (32) is pressed a complementary deformed contact against the bottom face of the recess.