GB2554036A

GB2554036A - High pressure fuel pumps

Info

Publication number: GB2554036A
Application number: GB1607233.2A
Authority: GB
Inventors: T D Mchattie James; John Mccrindle Christopher
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2016-04-26
Filing date: 2016-04-26
Publication date: 2018-03-28

Abstract

A pressure regulator 20 comprising a housing 21 with a chamber 22 having an inlet 23 and a closed end 24, a plunger 26 arranged within the chamber 22; The plunger 26 has a first portion 33 comprising a head 33b having a front end 33a oriented toward the inlet 23 of the chamber and a substantially hollow part 33c thereafter and, a second portion 34 comprising a rear end 34a oriented towards the closed end 24 of the chamber 22; The first portion 33 comprises a hole 33d extending through the head 33b of the plunger creating a permanent fluid pathway through the plunger 26 between the inlet 23 and the hollow part 33c. The front end 33a of the first portion may have a larger surface area than the rear end 34a of the second portion. The clearance 35 between the plunger 26 and the wall of the chamber 22 may allow for a continuous leakage of fuel between the inlet 23 and a return fuel line via a first orifice 27.

Description

(54) Title of the Invention: High pressure fuel pumps

Abstract Title: Pressure regulator for a high pressure pump (57) A pressure regulator 20 comprising a housing 21 with a chamber 22 having an inlet 23 and a closed end 24, a plunger 26 arranged within the chamber 22; The plunger 26 has a first portion 33 comprising a head 33b having a front end 33a oriented toward the inlet 23 of the chamber and a substantially hollow part 33c thereafter and, a second portion 34 comprising a rear end 34a oriented towards the closed end 24 of the chamber 22; The first portion 33 comprises a hole 33d extending through the head 33b of the plunger creating a permanent fluid pathway through the plunger 26 between the inlet 23 and the hollow part 33c. The front end 33a of the first portion may have a larger surface area than the rear end 34a of the second portion. The clearance 35 between the plunger 26 and the wall of the chamber 22 may allow for a continuous leakage of fuel between the inlet 23 and a return fuel line via a first orifice 27.

1/4

Fig-1 prior a^rt

2/4

1502 18

Fig. 5

3/4

1502 18

Fig. 6

Fig.7

4/4

ν εο 5 ν

HIGH PRESSURE FUEL PUMPS

Technical Field

The present invention relates generally to the field of high pressure fuel pumps. More particularly, but not exclusively, the present invention concerns a pressure regulator arrangement for a high pressure fuel pump.

Description of the Related Art

As it is well known in the art, diesel internal combustion engines comprise a lowpressure fuel pump in order to feed fuel from a fuel tank to a high pressure fuel pump, which in turn delivers high pressure fuel to the common rail connected to a set of fuel injectors.

The high pressure fuel pump typically comprises one or a plurality of pumping units disposed about a rotating driveshaft with a cam. Each of the pumping units comprises a plunger and the cam drives the plungers along respective pumping axes. The driveshaft and cam are located within a cambox of a pump housing. A low pressure fuel pump supplies fuel through a low pressure fuel line at low pressure into the cambox. The fuel serves as a lubricant and essentially a cool flow of fuel for front and rear bearings of the rotating drive shaft, as well as supplying fuel to pumping chambers and pumping head. The pumping head sends the fuel at high pressure down a high pressure fuel line to the common rail and fuel injectors. The fuel pressure in the cambox may be regulated by means of a low pressure regulator typically arranged in a wall of the cambox.

A typical low pressure regulator 1 is shown in Figure 1 and comprises a housing 2 for mounting in a bore in said wall of a cambox. The housing 2 comprises an axially reciprocating plunger 3 located in an axial chamber 4. The plunger 3 is biased towards an inlet 5 by a spring 6 thereby closing said inlet 5. The housing 2 further comprises one or more standard outlets 7 arranged at a bottom end of the chamber 4 near the inlet 5. When the pressure in the cambox acting on the plunger 3 exceeds the force of the spring 6, the exceeding pressure pushes the plunger 3 back from the inlet 5, thereby opening the inlet 5 and allowing fuel to flow through to the outlets 7 to be returned to the fuel tank.

The disadvantage of such known low pressure regulators 1 is that, they are typically open or shut, without the ability for a low-level of continuous leakage.

Some pressure regulators do provide a small diameter orifice (approximately 0.5 mm) to overcome this issue, but this orifice requires filtering to prevent blockage, which can damage the pump. These small orifices are unresponsive to temperature differences, which are indicative of pressure in the system, since they instead provide a similar flow irrespective of the temperature and therefore, the viscosity of the fuel passing through.

It is an object of the present invention to address one or more of the problems of known arrangements.

Therefore, it is now desired to provide an improved pressure limiting arrangement or pressure regulator that is capable of optimising the flow rate of fuel back to the tank depending on the running temperature of the pump. In particular, it is desired to provide a pressure limiting arrangement or pressure regulator capable of providing viscosity-controlled leakage.

SUMMARY OF THE INVENTION

In a first aspect of the present invention there is provided a pressure regulator adapted to be in fluid communication with a cambox of a high pressure pump. The pressure regulator comprises a housing with a chamber having an inlet and a closed end. A plunger is arranged within the chamber and adapted therein to reciprocal displacements along a plunger axis. A spring compressed in the chamber between the plunger and the closed end of the chamber, biases the plunger towards the inlet, the housing further comprising a first orifice disposed proximal to said inlet linking the chamber with a return fuel line.

The plunger advantageously has a first portion comprising a head having a front end oriented toward the inlet of the chamber and a substantially hollow part thereafter and, a second portion comprising a rear end oriented towards the closed end of the chamber.

The first portion also comprises a hole extending through the head of the plunger from the front end to the hollow part, this hole creating a permanent fluid pathway through the plunger between the inlet and and the hollow part.

The front end of the first portion of the plunger has a larger surface area than the rear end of the second portion.

Also, the first portion has a diameter 5% to 15% larger than the diameter of the second portion.

Also, the front end of said head is substantially flat and, the rear end of the second portion is substantially annular and open.

Furthermore, the second portion of the plunger is substantially hollow and said hollow part of the second portion extends from the substantially hollow part of the first portion toward the rear end.

Also, the first portion of the plunger comprises substantially a front half of the plunger and, the second portion of the plunger comprises substantially a rear half of the plunger.

Also, the first portion of the plunger is configured to sit within a first sub-chamber and the second portion of the plunger is configured to sit within a second sub-chamber of the chamber.

The first sub-chamber extends from the inlet beyond the first orifice.

The second portion of the plunger comprises an exterior circumferential groove located adjacent to the first portion of the plunger.

In another embodiment said hole comprises a restriction.

Also, the pressure regulator defines a first clearance between the plunger and a wall of said chamber, said first clearance being greater than a functional clearance sufficient to just allow sliding so that, said first clearance behaves in use, as an orifice allowing a continuous leakage of fuel between the inlet and the return fuel line via the first orifice.

Also, the pressure regulator defines a second clearance between the plunger and a wall of said chamber, said second clearance being greater than a functional clearance sufficient to just allow sliding so that, said second clearance behaves in use, as an orifice allowing a continuous leakage of fuel between from the chamber and the return fuel line.

Also, said first clearance is arranged around the first portion of the plunger and, said second clearance is arranged around the second portion of the plunger.

And, at least one of the first or second clearances comprises a width of gap of between approximately 10 microns to 40 microns.

Also, at least one of the first clearance or the second clearance comprises a length of gap of at least 3 mm.

In yet another embodiment, the pressure regulator further comprises a second orifice disposed between the inlet and the closed end linking the chamber with the return fuel line.

The first sub-chamber extends from the inlet up to and including the second orifice and the second sub-chamber extends from the second orifice to the closed end.

Specifically, the hollow part of the first portion and the hollow part of the second portion of the plunger respectively, together form a spring chamber within the plunger, with a seat for the spring being located against the head of the first portion.

The invention further extends to a high pressure fuel pump comprising a pressure regulator communicable with a cambox, the pressure regulator being as described above.

With this arrangement, the first and second clearances between the plunger and the wall of the chamber allow for continuous leakage therebetween, that provide cooling flow. The rate of leakage is controlled by the viscosity of the fuel, which in turn depends upon the temperature of the fuel. Therefore, when the temperature of the fuel is high, the viscosity is lower, allowing a greater rate of cooling flow through the specific clearance than when the temperature of the fuel is low with a greater viscosity. In low pressure scenarios, a much lower rate of continuous leakage is provided, since it is necessary to maintain fuel in the pump to assist with cold start scenarios.

The first and second clearances are also referred as 'specific clearance' and, what is meant is a greater amount of space than would be considered to be a standard clearance, by increasing a width of a gap between an outer wall of the moving plunger and the wall of the chamber and/or by increasing a length of a gap between an outer wall of the moving plunger and the wall of the chamber.

By comparison, 'standard clearance' is intended to refer to a standard amount of space between an outer wall of the moving plunger and the wall of the chamber sufficient to allow the plunger to slide freely. This is expected to be an engineering fit with high precision and narrow tolerance (allowance), including those defined as category RC4 (Close Running Fits for accurate machinery with moderate surface speed, bearing pressures, and journal pressures where accurate location and minimum play are desired) to RC6 (Medium Running Fits for machines running at higher running speeds, considerable bearing pressures, and heavy journal pressure).

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 1 is a schematic cross-sectional side view of a PRIOR ART low pressure regulator;

Figure 2 is a schematic cross-sectional perspective side view of a pressure regulator for a high pressure fuel pump according to a first embodiment of the invention in a first position;

Figure 3 is a schematic side view of the pressure regulator of Figure 2;

Figure 4 is a schematic cross-sectional side view of the pressure regulator of Figure 2 in the first position;

Figure 5 is a schematic cross-sectional side view of the pressure regulator of Figure 2 in a second position;

Figure 6 is a schematic cross-sectional side view of the pressure regulator of Figure 2 in a third position; and

Figure 7 is a schematic cross-sectional side view of the pressure regulator of Figure 2 in a fourth position.

Figure 8 is a schematic cross-sectional side view of the pressure regulator as per a second embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

As shown in the Figures 1 to 7, a first embodiment of the invention relates to a pressure regulator 20 of a high pressure fuel pump (not shown). In use, the pressure regulator 20 is communicable with a cambox (not shown). The pressure regulator 20 comprises a housing 21 defining a chamber 22 comprising an inlet 23 and a closed end 24. A spring 25 is arranged in the chamber 22 and compressed between the closed end 24 and an plunger 26 slidably arranged in the chamber 22. The spring 25 is configured to provide axially reciprocating movement of the plunger 26 along a plunger axis A-A' towards the inlet 23. The housing 21 comprises a first orifice Tl disposed proximal to said inlet 23 linking the chamber 22 with a return fuel line (not shown), and a second orifice 28 disposed between the inlet 23 and the closed end 24 linking the chamber 22 with the return fuel line. The pressure regulator 20 further defines a 'specific' clearance 35, 36 between the plunger 26 and a wall of said chamber 22.

Throughout this description, clearances that are referred as being 'specific clearance' meaning they define a larger, or greater, amout of space between the plunger and the wall of the chamber, than what would be considered to be a 'standard clearance' having an amount of space just sufficient to allow the plunger to slide freely.

This increase in amout of space is achieved by increasing a width of a gap between an outer wall of the moving plunger and the wall of the chamber and, or, by increasing a length of a gap between an outer wall of the moving plunger and the wall of the chamber.

By comparison, 'standard clearance' is intended to refer to a standard amount of space between an outer wall of the moving plunger and the wall of the chamber sufficient to allow the plunger to slide freely. This is expected to be an engineering fit with high precision and narrow tolerance, or allowance, including those defined as category RC4 (Close Running Fits for accurate machinery with moderate surface speed, bearing pressures, and journal pressures where accurate location and minimum play are desired) to RC6 (Medium Running Fits for machines running at higher running speeds, considerable bearing pressures, and heavy journal pressure).

The housing 21 of the pressure regulator 20 is substantially cylindrical in shape and is adapted for installation in a bore (not shown) in a wall of the cambox of the high pressure fuel pump of a diesel internal combustion engine or, in any wall portion of the cambox. The bore is fluidly connected to both the cambox via a fluid inlet port (not shown), and to a return fuel line via a fluid outlet port (not shown). The housing 21 is retained in the bore via two O-ring seals 30.

The chamber 22 comprises a first sub-chambers 31 and a second sub-chamber 32 of different diameter, the first sub-chamber 31 having a slightly larger diameter that the second sub-chamber 32. Both sub-chambers 31, 32 are cylindrical in shape and are arranged end-toend and concentrically with one another, each make up approximately half of the length of the chamber 22.

The first sub-chamber 31 extends from the inlet 23 and includes the first orifice 27 and the second orifice 28 and, the second sub-chamber 32 extends from the second orifice 28 to the closed end 24.

The plunger 26 comprises a first portions 33 and a second portion 34 of different diameter, the first portion 33 having a slightly larger diameter than the second portion 34. Both first and second portions 33, 34, are substantially cylindrical in shape and are arranged end-to-end and concentrically with one another, each making up approximately half of the length of the plunger 26.

The first portion 33 of the plunger 26 is shaped for a sliding fit with the wider first sub-chamber 31 and comprises a length that almost exactly spans the distance from the first orifice 27, including the first orifice Y1, up to, and including, the second orifice 28. The first portion 33 accommodates approximately 60% of the length of the first sub-chamber 31 and, said first portion 33 comprises a substantially flat driven end 33a as part of a head 33b and, a substantially hollow part 33c thereafter. A hole 33d, approximately 2 mm in diameter, is provided substantially centrally through the head 33b from the flat driven end 33a to the hollow part 33c. This hole 33d creates a permanent fluid pathway through the plunger 26 between the inlet 23 and the hollow part 33c.

The second portion 34 of the plunger 26 is shaped for a sliding fit with the narrower second sub-chamber 32 and comprises a length that spans approximately 80% of the length of the second sub-chamber 32. The second portion 34 of the plunger 26 is a substantially hollow part 34b that continues from the substantially hollow part 33c of the first portion 33. Accordingly, the hollow part 33c of the first portion 33 and the hollow part 34b of the second portion 34 together form a spring chamber within the plunger 26, with a seat for the spring 25 being located against the head 33b of the first portion 33. The second portion 34 of the plunger 26 thereby presents a narrow end wall 34a at a free end thereof. The second portion 34 of the plunger 26 further comprises an exterior circumferential groove 34c located adjacent to the first portion 33 of the plunger 26. The distance between the driven end 33a to the start of the circumferential groove 34c is substantially the same as the distance between the inlet-side of the first orifice Y1 up to, but not including, the second orifice 28.

Overall, the plunger 26 has been increased in total length, relative to a plunger of the prior art, by providing a spring chamber within the plunger 26. By adding the second portion 34 with the hollow part 34b and adapting the first portion 33 to provide a substantially hollow part 33c at a rear end thereof, the plunger can be increased by at least 50% up to three times its original length. In the described embodiment, the plunger 26 is substantially twice the length of a standard plunger of the prior art.

The spring 25 is seated at the closed end 24 of the housing 21 at one end, fixed end, and seated against the head 33b of the first portion 33 within the spring chamber defined by the hollow parts 33c, 34b provided by the plunger 26.

The driven end 33a of the plunger 26 also has a larger surface area than the narrow end wall 34a disposed at an opposite end thereof. This creates a differential effort between the two ends 33a, 34a, so that despite the same pressure acting on said driven end 33a on one side and on the sum of said end wall 34a and spring seat area of the head 33b,, the pressure will have a greater impact at the larger driven end 33a, resulting in the plunger 26 being moved back against the action of the spring 25 from the inlet 23 towards the closed end 24.

The first orifice Y1 is approximately 2 mm in diameter and is disposed approximately 3 mm from the inlet 23. The first orifice Y1 provides regulating flow as a result of increasing pressure in the cambox when opened.

The second orifice 28 is approximately 1.5 mm in diameter and is disposed approximately 8 mm from the first orifice 2J. The second orifice 28 provides for cooling flow through the specific clearances 35, 36 when opened.

As mentioned and defined previously, the plunger 26 and chamber 22 together define the first 'specific' clearance 35 provided between the first portion 33 of the plunger 26 and the wall of the first sub-chamber 31. The second 'specific' clearance 36 is defined between the second portion 34 of the plunger 26 and the wall of the second sub-chamber 32. Each 'specific' clearance 35, 36 provides a gap of approximately 30 microns around the relevant portions 33, 34 of the plunger 26 and,, each clearance 35, 36 also extends substantially the full length of the relevant portions 33, 34 of the plunger 26, but in any event, are at least 3 mm in length.

In use, the 'specific' clearances 35, 36 between the plunger 26 and the wall of the chamber 22 behave as an orifice that allows a continuous leakage of fuel therebetween to pass through the second orifice 28 and to the return fuel line. When the fuel has a low viscosity, thin, due to high temperatures in the cambox, the 'specific' clearances 35, 36 allow a greater rate of flow of that thin fuel, which is required due to the high pressures. In contrast, when the fuel has a high viscosity, thick, due to low temperatures in the cambox, the specific clearances 35, 36 allow a much lower rate of flow of that thick fuel, which is not required due to the low pressures in the cambox. Accordingly, the specific clearances 35, 36 provide viscositycontrolled leakage of fuel through the pressure limiter 20. Since the specific clearances 35, 36 are small, no filtering is required.

The hole 33d through the head 33b of the first portion 33 of the plunger 26 links the first sub-chamber 31 of the housing 21 at the inlet side 23 of the plunger 26, with the spring chamber provided by the plunger 26 and the second sub-chamber 32 of the housing 21. Accordingly, not only can fuel leak from the second sub-chamber 32 through the specific clearance 36 to the second orifice 28, but the pressure across the two areas 31/33c/34b/32 can be balanced, which prevents shuttling, bouncing, of the plunger 26 in the chamber 22. However, due to the greater effect of the pressure on the larger surface area of the driven end 33a of the plunger 26 at the inlet 23 when compared with the effect of the same pressure on the smaller surface area of the narrow end 33a, the plunger 26 is still driven back to overcome the force of the spring 25, when the pressure is high enough at the inlet 23. This opens the first orifice 27 to allow normal cambox pressure limitation. For the same reason, since there are no enclosed volumes within the pressure limiter 20, pressure limiter hardening, where the plunger 26 is stuck closed, is not possible.

When the plunger 26 is moved back from the inlet 23 to open the first orifice 27, even partially at cracking point, due to the presence of the circumferential groove 34c that is then positioned opposite the second orifice 28, the second orifice 28 is opened to allow leakage flow passing through the first and second specific clearances 35, 36 to pass out to the return fuel line.

Finally, the entire arrangement is simple to clear or flush to remove debris by simply increasing pressure at the inlet 23, which pushes the plunger 26 back, opening both orifices 27, 28 and allowing flow through both orifices 27, 28 and leakage through both specific clearances 35, 36.

It will be appreciated that where a thinner fuel is to be used, a specific clearance on the smaller side of the range provided is preferable in order to provide a useful viscositycontrolled leakage.

In addition, if a greater difference in diameter is provided between the first portion 33 and the second portion 34, a greater surface area differential will be achievable between the driven end 33a and the narrow end 34a. Accordingly, a stiffer spring 25 could be used, since the pressure acting on the driven end 33a will overwhelm the spring 25 and the same pressure acting on the narrow end 34a.

Although the above embodiments are shown and have been described in relation to a fuel combustion engine, it is to be appreciated that the invention may be applied to other fuel consuming devices.

In reference to figure 8, a second embodiment of the pressure regulator 20 is now described by ways of differences relative to the first embodiment of figures 2 to 7.

The main differences are that in the second embodiment the housing 21 only comprises the first orifice Y1 and not the second orifice and, the hole 33d comprises a restriction 40 between the inlet and the rear face.

Otherwise, the plunger 26 is slidably guided along the plunger axis thanks to a front guiding means and to a rear guiding means. The front guiding means is provided toward the inlet 23 and is defined by the outer face of the head 33b of the plunger arranged against the wall of the first sub-chamber 31, said two front faces defining between them the first 'specific' clearance 35 and, the rear guiding means is provided toward the rear end and is defined by the outer face of the second portion 34 of the plunger arranged against the wall of the second subchamber 32, said two rear faces defining between them the second 'specific' clearance 36.

The spring, 25, instead of being engaged inside the hollow portion of the plunger is, in this second embodiment, complementary arranged around the rear end of the plunger. The spring is compressed between the end of the chamber 22 and a back shoulder face of the rear guiding means.

In operation, pressure variations on the inlet side will generate minor axial movements of the plunger, some fuel leaking through the first clearance 35. A rearward displacement of the plunger, toward the right on the figure, will generate a leak of the fuel contained in the chamber 22 through the second clearance 36 toward the first orifice 2J. A frontward displacement of the plunger will generate an entry of fuel in the chamber 22 through the hole 33d and the restriction 40. In this second embodiment the regulator may further act as a damper amortizing pressure pulsations travelling in the fuel.

Claims

CLAIMS:

1. A pressure regulator (20) adapted to be in fluid communication with a cambox of a high pressure pump, the pressure regulator (20) comprising a housing (21) with a chamber (22) having an inlet (23) and a closed end (24), a plunger (26) arranged within the chamber (22) and adapted therein to reciprocal displacements along a plunger (26) axis (A-A'), a spring (25) compressed in the chamber between the plunger (26) and the closed end (24) of the chamber, said spring (25) biasing the plunger towards the inlet (23), the housing (21) further comprising a first orifice (27) disposed proximal to said inlet (23) linking the chamber (22) with a return fuel line, characterised in that the plunger (26) has a first portion (33) comprising a head (33b) having a front end (33a) oriented toward the inlet (23) of the chamber and a substantially hollow part (33c) thereafter and, a second portion (34) comprising a rear end (34a) oriented towards the closed end (24) of the chamber (22) and wherein, the first portion (33) comprises a hole (33d) extending through the head (33b) of the plunger from the front end (33a) to the hollow part (33c), this hole creating a permanent fluid pathway through the plunger (26) between the inlet (23) and the hollow part (33c).

2. Pressure regulator (20) as claimed in the preceding claim wherein, the front end (33a) of the first portion (33) of the plunger (26) has a larger surface area than the rear end (34a) of the second portion (34).

3. Pressure regulator (20) as claimed claim 2 wherein, the first portion (33) has a diameter 5% to 15% larger than the diameter of the second portion (34).

4. Pressure regulator (20) as claimed in any one of the claims 2 or 3 wherein, the front end (33a) of said head (33b) is substantially flat and, the rear end (34a) of the second portion (34) is substantially annular and open.

5. Pressure regulator (20) as claimed in any one of the claims 2 to 4 wherein, the second portion (34) of the plunger is substantially hollow and said hollow part (34b) of the second portion (34) extends from the substantially hollow part (33c) of the first portion (33) toward the rear end (34a).

6. Pressure regulator (20) as claimed in any one of the preceding claims wherein, the first portion (33) of the plunger (26) comprises substantially a front half of the plunger (26) and, the second portion (34) of the plunger (26) comprises substantially a rear half of the plunger (26).

7. Pressure regulator (20) as claimed in any one of the preceding claims wherein, the first portion (33) of the plunger (26) is configured to sit within a first sub-chamber (31) and the second portion (34) of the plunger (26) is configured to sit within a second sub-chamber (32) of the chamber (22).

8. Pressure regulator (20) as claimed in claim 6 wherein, the first sub-chamber (31) extends from the inlet (23) beyond the first orifice (27).

9. Pressure regulator (20) as claimed in any one of the preceding claims wherein, the second portion (34) of the plunger (26) comprises an exterior circumferential groove (34c) located adjacent to the first portion (33) of the plunger (26).

10. Pressure regulator (20) as claimed in any one of the preceding claims wherein, said hole (33d) comprises a restriction (40).

11. Pressure regulator (20) as claimed in any one of the claims 1 to 9 wherein, the pressure regulator (20) defines a first clearance (35) between the plunger (26) and a wall of said chamber (22), said first clearance (35) being greater than a functional clearance sufficient to just allow sliding so that, said first clearance (35) behaves in use, as an orifice allowing a continuous leakage of fuel between the inlet (23) and the return fuel line via the first orifice (27).

12. A pressure regulator (20) as claimed claim 11 wherein, the pressure regulator (20) defines a second clearance (36) between the plunger (26) and a wall of said chamber (22), said second clearance (36) being greater than a functional clearance sufficient to just allow sliding so that, said second clearance (36) behaves in use, as an orifice allowing a continuous leakage of fuel between from the chamber (22) and the return fuel line.

13. Pressure regulator (20) as claimed in any one of the claims 11 or 12 wherein, said first clearance (35) is arranged around the first portion (33) of the plunger and, said second clearance (34) is arranged around the second portion (34) of the plunger.

14. Pressure regulator (20) as claimed in any one of the claims 11 to 13 wherein, at least one of the first or second clearances (35, 36) comprises a width of gap of between approximately 10 microns to 40 microns.

15. Pressure regulator (20) as claimed in any one of the claims 11 to 14 wherein, at least one of the first clearance (35) or the second clearance (36) comprises a length of gap of at least 3 mm.

16. A pressure regulator (20) as claimed in any one of the preceding claims further comprising a second orifice (28) disposed between the inlet (23) and the closed end (24) linking the chamber (22) with the return fuel line.

17. Pressure regulator (20) as claimed in claim 16 wherein, the first sub-chamber (31) extends from the inlet (23) up to and including the second orifice (28) and the second subchamber (32) extends from the second orifice (28) to the closed end (24).

18. Pressure regulator (20) as claimed in any one of the claims 16 or 17 taken in combination with claim 5 wherein the hollow part (33c) of the first portion (33) and the hollow part (34b) of the second portion (34) of the plunger (26) respectively, together form a spring chamber within the plunger (26), with a seat for the spring (25) being located against the head (33b) of the first portion (33).

19. High pressure fuel pump comprising a pressure regulator (20) communicable with a cambox characterized in that the pressure regulator (20) is as claimed in any one of the preceding claims.

Intellectual

Property

Office

Application No: GB1607233.2