GB2610401A

GB2610401A - Pump assembly for a fuel pump

Info

Publication number: GB2610401A
Application number: GB2112504.2A
Authority: GB
Inventors: Aziz Abdul
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2023-03-08
Anticipated expiration: 2041-09-02
Also published as: GB2610401B; GB202112504D0

Abstract

A fuel pump assembly for an internal combustion engine comprising a plunger 10 located within a plunger bore 12 to pressurise fuel within a pump chamber 6, a fuel supply line 26 for supplying fuel from a low pressure source, a seal 36 through which the plunger is slidingly received, a flushing inlet line 46 to deliver a flow of fuel to the seal (e.g. a top surface of the seal) to flush debris from the seal and a flushing return line 48 to return the flushed fuel to the low pressure source. The flushing return line may be comprise a restriction 54. The flushing inlet line may be defined by a groove or flute (fig.3, 56) on the inner/outer surface of the plunger, or a hole through the body of the plunger. The plunger may be driven by a rotating cam 4. There may be a filter in the return line.

Description

PUMP ASSEMBLY FOR A FUEL PUMP

FIELD OF THE INVENTION

This invention relates to a pump assembly for a fuel pump. In particular, but not exclusively, the invention relates to a pump assembly for use in a fuel pump for delivering fuel to an internal combustion engine. Aspects of the invention also relate to a method of flushing a seal for a pump assembly of a fuel pump.

BACKGROUND OF THE INVENTION

Fuel injection systems are used to introduce high pressure fuel into the combustion chambers of an internal combustion engine, such as a diesel engine. In a popular arrangement, the fuel injection system delivers fuel to the engine via a set of fuel injectors that are supplied with fuel from a pressurised accumulator, known as a common rail. The fuel in the common rail is typically pressurised by a high pressure reciprocating pump, which includes a plunger that is driven in a reciprocating linear motion inside a compression chamber, repeating successive pumping and filling strokes. The reciprocating motion of the plunger is driven by the rotation of an abutting camshaft that features a suitably shaped cam for displacing the plunger in a reciprocating motion as the camshaft rotates. A low pressure pump feeds the high pressure pump with fuel that is elevated, above drain pressure, by around 5-10 bar before it is supplied to the high pressure pump.

In such systems, a stationary plunger seal is provided where the plunger slides into and out of the bottom of the compression chamber. The seal provides the advantage that it prevents fuel from leaking out, mixing with oil that is used to lubricate the rotating camshaft and causing a pressure drop in the chamber. However, a common problem with these systems is that fuel in the compression chamber deposits debris which collects on top of and subsequently damages the plunger seal.

Known arrangements flush the deposited debris on the plunger seal by providing a controlled flow of fuel to the end of the seal, remote from the compression chamber, which then recirculates to the inlet of the compression chamber. By flushing the fuel back to the inlet in this way, losses in the system are minimised and the demand on the low pressure pump can be well managed.

However, one problem with the arrangement is that it can lead to debris being carried to the common rail and eventually to the engine.

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

SUMMARY OF THE INVENTION

According to a first aspect of the present disclosure, a pump assembly for pressurising fuel in a fuel system of an internal combustion engine is provided. The pump assembly comprises a plunger which undergoes reciprocating motion within a plunger bore to pressurise fuel within a pump chamber to a relatively high level; a fuel supply line for supplying relatively low pressure fuel from a low pressure source to the pump chamber for pressurisation; and a seal through which the plunger is slidingly received which serves to limit fuel leakage through the plunger bore. The pump assembly further comprises a flushing inlet line configured to deliver a flow of fuel to the seal to flush debris from the seal; and a flushing return line through which flushed fuel is returned to the low pressure source.

This arrangement beneficially allows for debris to be removed from the fuel, for example via a sump or filter, before recirculating the fuel to the lower pressure source and back through the system.

The seal may include an upper surface which is proximal to the pump chamber and a lower surface which is distal from the pump chamber, and wherein the flushing inlet line is configured to deliver a flow of fuel to the upper surface of the seal where debris is prone to collect.

The flushing return line may include a restriction or control orifice which serves to restrict the rate of flow of fuel which is returned to the low-pressure source. Advantageously, the restriction effects a pressure differential across the surface of the seal and thereby minimises the volume of fuel required to flush the debris from seal. The benefit of the restriction is that the rate of flow of fuel to the low pressure sump is controlled. Accordingly, the orifice beneficially minimises the volume of fuel required to flush the debris from the top surface of the seal.

The control orifice may also service to deaerate the fuel in the compression chamber.

In embodiments including a restriction, the flushing return line may be defined, at least in part, by a drilling formed in a pump housing and the restriction may be an orifice formed in the drilling.

In other embodiments, the flushing inlet line may be defined, at least in part, by a groove or flute formed on an outer surface of the plunger. In addition, or alternatively, the flushing inlet line may be defined, at least in part, by an internal surface of the plunger bore or by a hole provided through the plunger body.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of non-limiting example, with reference to the following figures, in which: Figure 1 is a schematic view of a known pump assembly of a fuel system of an internal combustion engine; Figure 2 is a schematic view of a pump assembly in accordance with an embodiment of the invention; and Figure 3 is a schematic view of a pump assembly in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

To provide context for the invention. Figure 1 shows a portion of a pump assembly 2 for a fuel system in simplified schematic form. The pump assembly 2 is configured to deliver a supply of pressurised fuel to an accumulator of the fuel system, such as a common fuel rail (not shown). Typically, the fuel system delivers pressured fuel to the engine cylinders of a compression ignition internal combustion engine via fuel injection equipment which receives pressurised fuel from the common rail.

The pump assembly 2 takes the form of a reciprocating pump assembly 2 operated by the rotation of an abutting camshaft 4, which may be driven by connection to an engine driveshaft, for example. The reciprocating pump 2 comprises an elongate compression chambers formed within a main housing 8 of the pump assembly 2 and a correspondingly shaped plunger arrangement 10 configured to move within the compression chamber 6 in a reciprocating linear motion. The plunger arrangement includes a plunger 10 which reciprocates within a plunger bore 12 defined within the main pump housing 8 with the compression chamber 6 being defined at one end 14 of the plunger bore 12.

Accordingly, the compression chamber 6 is configured to receive the plunger arrangement 10 via the bore 12 in the main housing 8, the bore 12 extending from one end 14 of the compression chamber 6 to a cavity 16 in which the rotating camshaft 4 resides. When the pump 2 is assembled, the plunger arrangement 10 extends from the abutting camshaft 4, through the bore 12, and into the compression chamber 6.

For the purpose of achieving reciprocating motion, the plunger arrangement comprises an intermediate drive member 18 in the form of a roller-tappet assembly, also known as a lifter, at one end for interfacing with the rotating camshaft 4. The roller tappet 18 assembly is configured to ride a cam member 20 of the camshaft 4 as the camshaft 4 rotates about the longitudinal axis in the manner shown by arrow A. In this manner, the rotational motion of the camshaft 4 is converted into reciprocating linear motion of the plunger arrangement 10 wherein the plunger arrangement 10 is urged in alternating first 22 and second 24 directions out of and into the compression chamber 6 via the bore 12.

In other embodiments, an intermediate drive member 18 of alternative form may be used, for example including a shoe instead of the tappet. Specifically, during a filling stroke, the plunger 10 is moved in a first direction 22 out of the compression chamber 6, thereby expanding the internal volume of the compression chamber 6 available to receive fuel. Accordingly, the pressure in the compression chamber 6 drops and fuel is drawn into the compression chamber 6 from an inlet supply line 26 via an inlet valve 28. Conversely, during a pumping stroke, the plunger arrangement 10 is moved in a second direction 24 into the compression chamber 6, thereby pressurising the volume of fuel inside the compression chamber 6 and forcing it through an outlet valve 30 to the accumulator via an outlet supply line 31. The second direction 24 is opposed to the first direction 22 along a common axis (i.e. the plunger axis). In accordance with known arrangements, the plunger 10 is shaped and dimensioned to achieve a close tolerance clearance fit within the compression chamber 6. While most of the fuel in the compression chamber 6 is pushed through the outlet valve 30 during the pumping stroke, some typically leaks between the walls 32 of the compression chamber 6 and the plunger 10. To avoid a build-up of fuel in this region, a drain or return line 34 is provided which is configured to guide any leaked fuel out of the compression chamber 6 for recirculation to the low pressure source or fuel tank.

The plunger 10 extends through a seal assembly. The seal assembly takes the form of an annular seal assembly and includes a first seal 36 provided in the bore 12, the first seal 36 configured to prevent fuel from leaking through the bore 12 and out of the compression chamber 6. In the example shown in Figure 15 the seal assembly also includes a second seal 38 provided in the bore 12, axially below the first seal 36, the second deal 38 configured to prevent lubricating oil applied to the camshaft 4 and rolling tappet assembly 18 from leaking into the compression chamber 6 via the bore 12. Accordingly, each seal 36, 38 extends fully around the outer surface of the plunger 10 so as to fill the gap between the plunger 10 and the bore 12. As such, each seal 36, 38 may be annular depending on the shape of the plunger 10 and bore 12. In some embodiments the first seal 36 and the second seal 38 may be formed together to form one elongate seal.

In use, fuel at relatively low pressure is supplied to the compression chamber 6 for pressurisation as the plunger 10 reciprocates. The fuel is suppled to the compression chamber 6 at relatively low pressure from a low pressure fuel source. Typically, the fuel is supplied through the inlet supply line 26 provided in the main pump housing 8. The inlet valve 28 may take the form of an inlet metering valve which may be used to control the volume of fuel that is supplied to the compression chamber 6 for pressurisation in a given pump cycle. Once fuel is pressurised to a relatively high level within the compression chamber 6, it is supplied through the outlet supply line 31 to the downstream parts of the fuel system and the common rail.

As described above, debris carried by the fuel may be deposited within the compression chamber 6 and will tend to accumulate at the bottom of the chamber 6 where it may abrade and damage the first seal 36 provided at the bore.

Figure 2 shows a cross-sectional view of a pump assembly 2 according to a first embodiment of the invention comprising a seal flushing system 39 for removing accumulated debris from a top surface 40 of the first seal 36. The system 39 comprises first 42 and second 44 flow paths or conduits configured to direct fuel to and from, respectively, the top surface 40 of the seal 36. The first conduit 42 defines a flushing inlet line 46 and the second conduit 44 defines a flushing outlet line 48. In the embodiment shown, the flushing inlet line 46 is formed in the main pump housing 8 and extends from the inlet supply line 26 to the top surface 40 of the seal 36. The flushing outlet line 48 is similarly formed in the main pump housing Sand extends from the top surface 40 of the seal 36 to the return line 34 configured to direct fuel away from the pump 2 to the fuel tank or sump. The flushing inlet line 46 provides a flow path for delivering fuel to the seal 36 which is separate and distinct from the flow path provided by the fuel supply line 26 which delivers fuel to the compression chamber 6 for pressurisation. Likewise, the flushing outlet line 48 provides a flow path for delivering fuel to the drain 34 that is separate and distinct from the flow path provided by outlet supply line 31 for delivering pressurised fuel to the common rail. In practice, the inlet supply line 26 and the flushing inlet line 46 draw fuel from the same low pressure fuel source, but the separate flushing inlet line 46 is provided by a distinct flow path specifically provided for the purpose of delivering fuel to the seal 36.

As the plunger 10 reciprocates and fuel is drawn into the compression chamber 6 via the inlet supply line 26, some fuel is diverted through the flushing inlet line 46 under low pressure conditions to be expelled over the top surface 40 of the seal 36. In this manner, the flushing inlet line 46 acts as a branch line from the inlet supply line 26. The flow of fuel over the top surface 40 of the seal 36 collects any accumulated debris and carries it along the flushing outlet line 48 to the return line 34. The return line 34 may then be in communication with a fuel filter configured to remove the debris from the fuel before recirculating the fuel to the inlet supply line 26 via the fuel tank.

The flushing outlet line 48 includes a seal end 50, at the end of the line closest to the seal 36, and a drain end 52, at the end of the line closest to the return line 34. A control orifice 54 is provided towards the seal end 50 of the flushing outlet line 48 and is configured to restrict the rate at which fuel enters the flushing outlet line 48 from the top surface 40 of the seal 36. Equally, the control orifice 54 is configured to encourage positive flow over the seal 36 and to prevent an excessive increase in pressure in the seal region. That is to say, the orifice 54 is optimally shaped and dimensioned to achieve a suitable flow rate over the top surface 40 of the seal 36 while minimising any additional demand on the low pressure pump which drives the inlet supply line 26. Accordingly, the orifice 54 beneficially minimises the volume of fuel required to flush the debris from the top surface 40 of the seal 36.

It should be appreciated that the control orifice 54 may also act to deaerate the fuel in the compression chamber 6.

Figure 3 shows another embodiment of a pump assembly 2 according to the invention. As shown, the pump 2 comprises a seal flushing system 39 as described above comprising flushing inlet 46 and outlet lines 48 configured to direct fuel to and from, respectively, the top surface 40 of the seal 36. In this embodiment, the flushing inlet line 46 is a channel, groove or flute 56 formed in an outer surface 58 of the plunger 10 which is configured to guide fuel which has leaked between the plunger 10 and the walls 32 of the compression chamber 6 towards the top surface 40 of the seal 36. That is to say, the channel 56 extends along a length of the plunger surface 58 so as to guide fuel towards the seal 36 at the bottom of the compression chamber 6. In this way, leaked fuel is redirected via the top surface of the seal 36 and along the flushing outlet line 48 so as to flush debris to the return line 34.

Additionally, in providing an outlet for the leaked fuel, this embodiment of the seal flushing system 39 further serves to relieve excess pressure from between the plunger 10 and the walls 32 of the compression chamber 6.

The compression chamber 6 may comprise a collection annulus 58, formed as a groove in the walls 32 of the compression chamber 6, which collects leaked fuel for delivery to the channel 56. The collection annulus 58 may be formed as a groove that extends circumferentially around the walls 32 of the compression chamber 6. As described above, the channel 56 is configured to guide the leaked fuel from the collection annulus 58, which leaks between the plunger 10 and the plunger bore 12, towards the upper surface 40 of the seal 36 where it may be removed from the compression chamber 6 via the flushing outlet line 48. In this way, the channel 56 serves to drain excess fuel from between the walls 32 of the compression chamber 6 and the plunger 10 and thereby prevents the build-up of excess upstream pressure.

The flow rate through the channel 56 is dependent on the running conditions of the pump 2 whereby the temperature and pressure in the compression chamber 6 influence the viscosity of the leakage flow between the plunger and the plunger bore and, hence, through the channel 56. In turn, the viscosity influences the flow rate through the channel 56. This differs from the embodiment in Figure 1 where the flushing inlet line 56 receives fuel directly from the low pressure drain or reservoir.

In another embodiment, the wall of the bore 12 may be provided with a groove, channel or flute to define the inlet flushing line (in addition or alternatively to a channel on the plunger). The extent of any groove(s) in the plunger 10 or in the wall of the plunger bore 12 must be sized to ensure that the guidance of the plunger 10 in cooperating with the plunger bore 12 is not prejudiced. In still further embodiments, the plunger may be provided with a hole through the plunger body to route fuel which leaks between the plunger 10 and the plunger bore 12 to the upper surface of the seal 36.

It will be appreciated that various modifications may be made to the aforementioned embodiments without departing from the scope of the invention as set out in the accompanying claims.

Claims

CLAIMS: 1. A pump assembly (2) for pressurising fuel in a fuel system of an internal combustion engine, the pump assembly (2) comprising; a plunger (10) which undergoes reciprocating motion within a plunger bore (12) to pressurise fuel within a pump chamber (6) to a relatively high level; a fuel supply line (26) for supplying relatively low pressure fuel from a low pressure source to the pump chamber (6) for pressurisation, a seal (36) through which the plunger (10) is slidingly received which serves to limit fuel leakage through the plunger bore (12); a flushing inlet line (46) configured to deliver a flow of fuel to the seal (36) to flush debris from the seal (36); and a flushing return line (48) through which flushed fuel is returned to the low pressure source.
2. The pump assembly (2) as claimed in claim 1, wherein the seal (36) includes an upper surface (40) which is proximal to the pump chamber (6) and a lower surface which is distal from the pump chamber (6), and wherein the flushing inlet line (46) is configured to deliver a flow of fuel to the upper surface (40) of the seal (36).
3. The pump assembly (2) as claimed in claim 1 or claim 2, wherein the flushing return line (48) includes a restriction (54) which serves to restrict the rate of flow of fuel which is returned to the low pressure source.
4. The pump assembly (2) as claimed in claim 3, wherein the flushing return line (48) is defined, at least in part, by a drilling formed in a pump housing (8) and wherein the restriction (54) is an orifice formed in the drilling.
5. The pump assembly (2) as claimed in claim 1 or claim 2, wherein the flushing inlet line (46) is defined, at least in part, by a groove or flute (56) formed on an outer surface (58) of the plunger (10).
6. The pump assembly (2) as claimed in claim 1, 2 or 5, wherein the flushing inlet line (46) is defined, at least in part, by the groove or flute (56) and an internal surface of the plunger bore (12).
7. The pump assembly (2) as claimed in any of claims 1, 2, 5 or 6, wherein the flushing inlet line (46) is defined, at least in part, by a hole provided through the body of the plunger (10).