EP3191704B1

EP3191704B1 - Fuel pump

Info

Publication number: EP3191704B1
Application number: EP15753637.6A
Authority: EP
Inventors: Toby Pedley; Paul Garland
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2014-09-12
Filing date: 2015-08-05
Publication date: 2018-12-05
Anticipated expiration: 2035-08-05
Also published as: KR102327787B1; KR20170053628A; GB201416109D0; CN107076124B; CN107076124A; EP3191704A1; WO2016037771A1

Description

TECHNICAL FIELD

The present invention relates to a fuel pump for supplying high-pressure fuel to a common rail fuel injection system of an internal combustion engine. The present invention has particular application in compression ignition (diesel) engines.

BACKGROUND

High-pressure fuel pumps for common rail fuel injection systems typically comprise one or more hydraulic pump heads where fuel is pressurised in a pumping chamber by the reciprocating movement of a plunger. Typically, low-pressure fuel is fed to the pump heads from a fuel supply, such as a vehicle fuel tank. Once pressurised, the high-pressure fuel is fed from the pumping chamber to the common rail. DE102008041176 A , JPS6314863U and US 2007/128058 A1 disclose high-pressure fuel pumps. A known high-pressure fuel pump 1 comprising a hydraulic pump head 2 is shown in Figures 1 and 2. The pump head 2 includes a pump head housing 3 having a housing body region 5 and a housing projection 7. A pumping plunger 9 is arranged to reciprocate within a bore 11 defined partly within the housing body region 5 and partly within the housing projection 7.
The pumping plunger 9 comprises a low-pressure end 13 which is driven by a rotating cam (not shown) mounted to a drive shaft (not shown) located in a cam box (not shown). A pumping chamber 15 is defined within the housing body region 5, at an end of the bore 11.
Low-pressure fuel is supplied to the pumping chamber 15 along an entry drilling 17 in the housing body region 5. Fuel is pressurised within the pumping chamber 15 by the reciprocating movement of the pumping plunger 9 within the bore 11. As the drive shaft rotates, the cam imparts an axial force on the low-pressure end 13, causing the plunger 9 to reciprocate within the bore 11 between a top dead centre position (i.e. the uppermost position of the plunger 9 within the bore 11), as represented in Figure 1, and a bottom dead centre position (i.e. the lowermost position of the plunger 9 within the bore 11), as represented in Figure 2. The plunger 9 performs a pumping cycle consisting of an intake stroke, during which the plunger 9 is moved from the top dead centre to the bottom dead centre position and low-pressure fuel is introduced into the pumping chamber 15, and a pumping stroke, during which the plunger 9 is moved from the bottom dead centre position to the top dead centre position and fuel is pressurised in the pumping chamber 15. The pressurised fuel is pumped from the pumping chamber 15 along an exit drilling 19 to the common rail.
During the pumping cycle, dynamic leakage past the plunger 9 can occur and reduce hydraulic (volumetric) efficiency of the pump 1, in particular at low speeds. This problem is exacerbated when the pump 1 operates at high pressures, for example in excess of 2,000 bar or 2,500 bar, where the dimensions of the bore 11 and the plunger 9 can undergo geometric variations which may increase dynamic leakage past the plunger 9.
At least in certain embodiments, the present invention sets out to overcome or ameliorate at least some of the problems associated with known pump heads. In particular, at least in certain embodiments, the present invention sets out to provide a fuel pump having an enhanced hydraulic efficiency and in which dynamic leakage past the plunger may be reduced.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a fuel pump for supplying high-pressure fuel to a common rail fuel injection system of an internal combustion engine according to the claims. According to a further aspect of the present invention, there is provided a pump for supplying high-pressure fuel to a common rail fuel injection system, the pump comprising:

an elongated aperture forming a pumping chamber and a pressurisation chamber;
a pumping element configured to reciprocate within the elongated aperture to pump fuel from the pumping chamber; and
pressurisation means for pressurising fuel in the pressurisation chamber;
wherein the pressurisation chamber extends at least partially around the circumference of the pumping element to reduce leakage from the pumping chamber. The fuel pressure in the pressurisation chamber increases to reduce hydraulic leakage past the pumping element during a pumping operation. By establishing an intermediate pressurised region in the pressurisation chamber, a non-uniform or stepped pressure profile is established along the length of the pumping element. The gradient of the pressure profile proximal to the pumping chamber can be reduced and this can reduce dynamic fuel leakage from the pumping chamber past the pumping element. At least in certain embodiments, the hydraulic efficiency of the fuel pump can be improved.

The elongated aperture comprises a first region defining the pumping chamber and a second region defining the pressurisation chamber, and the second region can be offset from the first region along a longitudinal axis of the pumping element. The first and second regions can be substantially cylindrical. The first region can have a first diameter and the second region can have a second diameter, the second diameter being larger than the first diameter. The second region can comprise a tapered section. The tapered section can be configured to cooperate with the pressurisation means. For example, the tapered section in said second region can cooperate with a tapered section in the pressurisation means.
The pressurisation means can be configured to seal the pressurisation chamber. In an example not being part of the invention, the pressurisation means can comprise an annular projection formed on the pumping element, for example in the form of an annular shoulder having an enlarged radius. The annular projection can be arranged to pressurise fuel in the pressurisation chamber when the pumping element advances. The annular projection can extend about the circumference of the pumping element. In an example not being part of the invention, the annular projection can be formed integrally with the pumping element. In an example not being part of the invention, the annular projection can be an annular step.
According to the invention, the pressurisation means can comprise an annular sleeve extending about the pumping element. The annular sleeve can be arranged to form a seal with a sidewall of the pressurisation chamber. The pumping element can be substantially cylindrical, and the annular sleeve can extend about the circumference of the pumping element. The annular sleeve can be coupled to the pumping element. An annular clearance is formed between the annular sleeve and the pumping element. In use, a radial width of the annular clearance decreases due to radial expansion of the pumping element when the pumping element is under load. When fuel in the pumping chamber is pressurised, at least a portion of the pumping element can undergo radial expansion which reduces the annular clearance between the pumping element and the annular sleeve. Thus, the fuel pressure in the pressurisation chamber increases only when the fuel pressure in the pumping chamber increases. At least in certain embodiments, this arrangement helps control fuel pressure within the pressurisation chamber in dependence on the fuel pressure within the pumping chamber, and allows the pressurisation chamber to avoid wasting energy pressurising fuel in the pressurisation chamber when it is not required. The radial expansion of the pumping element is elastic deformation. The elastic deformation of the pumping element is due to the Poisson effect and is determined by the Poisson's ratio. The radial expansion of the pumping element occurs at least at a low-pressure end of the pumping element. The radial expansion of the pumping element can occur along the entire length of the pumping element. In particular, the radial expansion of the pumping element can occur at a high-pressure end of the pumping element; however, the radial expansion of the high-pressure end can be restrained by the hydraulic pressure proximate to the high-pressure end. The annular clearance can be sized such that it substantially closes due to the radial expansion of the pumping element under axial load.
The annular sleeve can comprise a bottom wall, the bottom wall can comprise at least one vent groove, and the at least one vent groove can be in fluid communication with the annular clearance. The pumping element can comprise an annular flange for drivingly engaging the annular sleeve.
The pressurisation chamber can comprise at least one fuel inlet for allowing fuel flow into the pressurisation chamber. The at least one fuel inlet can be open when the pumping element is in a bottom dead centre position and closed when the pumping element is displaced towards a top dead centre position. The at least one fuel inlet can comprise an inlet port formed in a sidewall of the elongated aperture. Each inlet port can extend radially through the sidewall of the elongated aperture. Each inlet port can be in the form of an aperture, such as a hole or a slot, formed in the sidewall. The fuel inlet can comprise a plurality of inlet ports.
In a variant, the pressurisation means can be retracted out of the pressurisation chamber when the pumping element is in a bottom dead centre position to enable fuel to enter the pressurisation chamber.
Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:

Figure 1 is a schematic cross-sectional view of a pump head of a known high-pressure fuel pump for use in a fuel injection system, the plunger being in a top dead centre position;
Figure 2 is a schematic cross-sectional view of the pump head of Figure 1, the plunger being in a bottom dead centre position;
Figure 3 is a cross-sectional view of a high-pressure fuel pump according to an example, not being part of the invention;
Figure 4 is a schematic cross-sectional view of a pump head of the high-pressure fuel pump of Figure 3, the plunger being in the top dead centre position;
Figure 5 is a schematic cross-sectional view of the pump head of Figure 3, the plunger being in the bottom dead centre position;
Figure 6 is a schematic cross-sectional view of a pump head according to a first variant of example, not being part of the invention, the plunger being in the top dead centre position;
Figure 7 is a schematic cross-sectional view of the pump head of Figure 6, the plunger being in the bottom dead centre position;
Figure 8 is a schematic cross-sectional view of a pump head according to a second variant of the example, not being part of the invention, the plunger being in the bottom dead centre position;
Figure 9 is a schematic cross-sectional view of a pump head according to a first embodiment of the present invention, the plunger being in the top dead centre position;
Figure 10 is a schematic cross-sectional view of the pump head of Figure 9, the plunger being in the bottom dead centre position; and
Figure 11 is a perspective view of an annular sleeve for use in the pump head of Figures 9 and 10.

DETAILED DESCRIPTION

A high-pressure fuel pump 100 in accordance with a first example, not being part of the invention, will now be described with reference to Figures 3 to 5. The fuel pump 100 is intended for pumping diesel fuel to a common rail of an internal combustion engine.
The pump 100 comprises a pump head 101 (shown in detail in Figures 4 and 5). The pump head 101 comprises a pump head housing 103 including a housing body portion 105 and a housing cylindrical projection 107, also known as a turret portion. The cylindrical projection 107 projects from the housing body portion 105. The pump head housing 103 comprises an elongated aperture 109 extending into the housing body portion 105 and through the cylindrical projection 107. The aperture 109 defines a pumping chamber 111 and a pressurisation chamber 119. A plunger 113 having a longitudinal axis X is slidably received within the aperture 109 and is configured to pressurise fuel in the pumping chamber 111.
The pump head 101 is arranged in fluid communication with a low-pressure inlet line 115 and a high-pressure outlet line 116.
The low-pressure inlet line 115 is in fluid communication with a low-pressure fuel reservoir (not shown) for supplying low-pressure fuel to the pumping chamber 111. An inlet valve 117 is provided in the low-pressure inlet line 115 to inhibit the return of fuel from the pumping chamber 111 to the low-pressure inlet line 115.
The high-pressure outlet line 116 is in fluid communication with a fuel common rail (not shown). An outlet valve 118 comprising an outlet valve member 120 biased by an outlet spring 122 is provided in the high-pressure outlet line 116 to inhibit the return of fuel from the high-pressure outlet line 116 to the pumping chamber 111. The force applied by the outlet spring 122 on the valve member 120 and the fuel pressure in the common rail determines the fuel pressure which must be exceeded in the pumping chamber 111 to pump fuel out of the pumping chamber 111.
The plunger 113 comprises a first cylindrical member 121 and a second cylindrical member 123. The second cylindrical member 123 has a larger diameter than the first cylindrical member 121. The plunger 113 comprises a high-pressure end 125 (the upper end of the plunger 113 in the orientation shown in Figures 3 to 5) and a low-pressure end 127 (the lower end of the plunger 113 in the orientation shown in Figures 3 to 5) disposed opposite to the high-pressure end 125. As shown in Figure 3, the low-pressure end 127 is driven by drive means in the form of a cam arrangement 128. The low-pressure end 127 cooperates with a follower 130 driven by a rotating cam 132 mounted on a drive shaft 134 located in a cam box 136. As the drive shaft 134 rotates, the cam 132 imparts an axial force on the low-pressure end 127, causing the plunger 113 to reciprocate within the aperture 109 between a top dead centre position (i.e. the uppermost position of the plunger 113 within the aperture 109), as represented in Figure 4, and a bottom dead centre position (i.e. the lowermost position of the plunger 113 within the aperture 109), as represented in Figure 3 and 5.
The plunger 113 is configured to perform a pumping cycle consisting of an intake stroke and a pumping stroke. During the intake stroke, the plunger 113 is moved from the top dead centre to the bottom dead centre position by a return spring 138 (shown in Figure 3) to draw fuel from the low-pressure inlet line 115 into the pumping chamber 111. During the pumping stroke, the plunger 113 is moved from the bottom dead centre position to the top dead centre position by the rotating cam 132 to pressurise the fuel in the pumping chamber 111.
The second cylindrical member 123 of the plunger 113 defines pressurisation means in the form of an annular shoulder 129 of enlarged radius. As described herein, the annular shoulder 129 is configured to pressurise fuel in the pressurisation chamber 119.
The aperture 109 comprises a first region 135 delimited by a first sidewall 131a, and a second region 137 delimited by the second sidewall 131b. The first region 135 defines the pumping chamber 111, and the second region 137 defines the pressurisation chamber 119. The first and second regions 135, 137 are right cylindrical. The first region has a first diameter D1 and the second region has a second diameter D2. The second diameter D2 is larger than the first diameter D1. The first and second regions 135, 137 are arranged to slidingly receive the first and second cylindrical members 121, 123 respectively of the plunger 113. An opening 133 is formed at the lower end of the aperture 109. The first and second regions 135, 137 are formed respectively by first and second drilling operations to form the first and second regions 135, 137. Finishing operations, such as honing or grinding operations, can be performed in the first and second regions 135, 137 after the drilling operations. The second region 137 comprises first and second fuel inlet ports 141 extending radially in the second sidewall 131b. The first and second inlet ports 141 in the present example, not being part of the invention, are diametrically opposed to each other in the second sidewall 131b.
The pressurisation chamber 119 is offset from the pumping chamber 111 along the longitudinal axis X. The pressurisation chamber 119 is defined by the second sidewall 131b of the aperture 109, the plunger 113 and the annular shoulder 129 of the plunger 113. The plunger 113 and the second sidewall 131b are configured to seal the pressurisation chamber 119. When the plunger 113 is in the bottom dead centre position, the pressurisation chamber 119 is in fluid communication with the inlet ports 141 (i.e. the pressurisation chamber 119 is open) so that fuel can flow into the pressurisation chamber 119 through the inlet ports 141. When the plunger 113 is in the top dead centre position, the inlet ports 141 are obstructed by the second cylindrical member 123 of the plunger 113, thereby closing the pressurisation chamber 119. As described herein, the pressurisation chamber 119 is configured to establish a pressurised region within the aperture 109 between the pumping chamber 111 and the cam arrangement 128.
The operation of the pump 100 in accordance with the first example, not being part of the invention, will now be described. As the drive shaft 134 rotates, the cam 132 and the return spring 138 cause the plunger 113 to reciprocate within the aperture 109 to perform the intake stroke and the pumping stroke. During the intake stroke, low-pressure fuel is fed from the fuel reservoir to the pumping chamber 111 through the inlet valve 117. Fuel in the pumping chamber 111 is then pressurised during the pumping stroke. Once the fuel pressure in the pumping chamber 111 exceeds the force applied by the outlet spring 122 and the fuel pressure in the common rail on the valve member 120, the valve member 120 is displaced and pressurised fuel is pumped through the high-pressure outlet line 116.
As the plunger 113 moves from the bottom dead centre position to the top dead centre position, the second cylindrical member 123 of the plunger 113 closes the inlet ports 141, thereby closing the pressurisation chamber 119. While the second cylindrical member 123 advances in the pressurisation chamber 119, the volume of the pressurisation chamber 119 decreases, and the fuel within the pressurisation chamber 119 is pressurised. The peak fuel pressure within the pressurisation chamber 119 is determined by the volume of the pressurisation chamber 119 when the plunger 113 is in the top dead centre position. By establishing an intermediate pressurised region in the pressurisation chamber 119, a non-uniform or stepped pressure profile is established between the pumping chamber 111 and the cam box 136. The gradient of the pressure profile between the pumping chamber 111 and the pressurisation chamber 119 is less than the gradient of the pressure profile between the pressurisation chamber 119 and the cam box 136. The reduced pressure gradient proximal to the pumping chamber 111 can reduce dynamic fuel leakage from the pumping chamber 111 past the plunger 113, thereby improving the hydraulic efficiency of the fuel pump 100. It will be appreciated that the pressure differential between the pumping chamber 111 and the cam box 136 is substantially unaffected by the pressurisation chamber 119.
In a first variant, not being part of the invention, represented in Figures 6 and 7, a female tapered section 143 is provided between the first and second regions 135, 137 of the aperture 109. The diameter of the female tapered section 143 decreases towards the first region 135. The first and second cylindrical members 121, 123 of the plunger 113 are connected via a male tapered section 145 which substantially matches the female tapered section 143. The pressurisation chamber 119 is therefore defined by the second sidewall 131b of the aperture 109, by the plunger 113 and by the female and male tapered sections 143, 145. The female and male tapered sections 143, 145 help reduce stress concentration in the pressurisation chamber 119 during the pumping cycle. It will be appreciated that the operation of the first variant is unchanged from that of the pump with the first example, not being part of the invention.
In a second variant, not being part of the invention, represented in Figure 8, the inlet ports 141 are omitted. In use, when the plunger 113 is in the bottom dead centre position, the second cylindrical member 123 of the plunger 113 is retracted out of the second region 137 of the aperture 109 so that fuel can flow through the opening 133 into the pressurisation chamber 119. The first cylindrical member 121 of the plunger 113 is guided by the first region 135 of the aperture 109 to allow the second cylindrical member 123 to re-engage the second region 137 during the pumping stroke. When the plunger 113 is moved from the bottom dead centre position to the top dead centre position, the second cylindrical member 123 of the plunger 113 closes the opening 133, thereby closing the pressurisation chamber 119. As the second cylindrical member 123 advances in the pressurisation chamber 119, the volume of the pressurisation chamber 119 decreases and the fuel within the pressurisation chamber 119 is pressurised. As with the first example, not being part of the invention, described above, the increased fuel pressure within the pressurisation chamber 119 forms a pressurised region in the aperture 109, between the pumping chamber 111 and the cam arrangement 128, which helps reduce dynamic leakage of fuel from the pumping chamber 111 past the plunger 113.
A pump head 201 of a fuel pump 200 according to a first embodiment of the present invention is shown in Figures 9 to 11. The first embodiment corresponds closely to the first example, not being part of the invention, and like reference numerals have been used for like components, albeit incremented by 100 for clarity. Only the differences in relation to the first embodiment are described below.
In the first embodiment, the first and second cylindrical members 221, 223 of the plunger 213 have the same diameter. The pressurisation means is in the form of an annular sleeve 247 mounted to the second cylindrical member 223 and extending about the circumference of the second cylindrical member 223. The annular sleeve 247 and the second cylindrical member 223 are arranged concentrically. An annular clearance C is provided between the annular sleeve 247 and the second cylindrical member 223. A seal is formed between the annular sleeve 247 and the second sidewall 231b of the aperture 209. The annular sleeve 247 is configured to pressurise fuel in the pressurisation chamber 219. Moreover, the annular sleeve 247 is configured to control the fuel pressure within the pressurisation chamber 219 in dependence on the fuel pressure in the pumping chamber 211 during the pumping cycle.
The annular sleeve 247 comprises an inner wall 249, a top wall 251 and a bottom wall 253. The top wall 251 is substantially perpendicular to the longitudinal axis X. In a variant, the top wall 251 is inclined relative to the longitudinal axis X to form a tapered top wall 251. The bottom wall 253 abuts against an annular flange 255 of the low-pressure end 227 of the plunger 113. As shown in Figure 11, the bottom wall 253 is provided with first, second, third and fourth vent grooves 257. In the present embodiment the vent grooves 257 extend radially outwardly and are regularly distributed in the bottom wall 253. The vent grooves 257 provide a fuel path between the bottom wall 253 of the annular sleeve 247 and the annular flange 255 of the plunger 113. Thus, the vent grooves 257 maintain fluid communication between the annular clearance C and the cam box 136.
In the first embodiment, the pressurisation chamber 219 is defined by the second sidewall 231b of the aperture 209, by the plunger 213 and by the top wall 251 of the annular sleeve 247.
The first embodiment has particular application in a pump 200 comprising an inlet metering valve (not shown) operable to meter the quantity of fuel introduced into the pumping chamber 211. The inlet metering valve thereby controls the quantity of fuel pressurised in the pumping chamber 211 and delivered to the common rail. In the present arrangement, the inlet metering valve is provided in the low-pressure inlet line 215 upstream of the inlet valve 217. The inlet metering valve is therefore distinct from, and operable independently of, the inlet valve 217. In a variant, the inlet valve 217 can be an inlet metering valve operable to meter the volume of fuel introduced into the pumping chamber 211. In use, the inlet metering valve is operable to control the pumping of fuel from the pump 200, for example during light or partial load conditions.
It will be appreciated that elastic radial deformation of the low-pressure end 227 of the plunger 213 occurs only when the plunger 213 is under axial load. The annular clearance C is therefore dependent on the fuel pressure in the pumping chamber 211 and, depending on the volume of fuel in the pumping chamber 211, may remain substantially unchanged during part or all of the pumping stroke. The axial load applied to the plunger 213, and accordingly the radial expansion of the plunger 213, increases with the fuel pressure in the pumping chamber 211. Thus, the size of the annular clearance C is inversely proportional to the pressure in the pumping chamber 211. The pressure in the pressurisation chamber 219 increases in conjunction with the pressure in the pumping chamber 211. The pump 200 is operative to control the fuel pressure within the pressurisation chamber 219 in dependence on the fuel pressure in the pumping chamber 211 during the pumping cycle. Thus, unnecessary pressurisation of the fuel in the pressurisation chamber 219 can be reduced or avoided. The operation of the pump 200 in accordance with the first embodiment of the present invention will now be described.
When fuel is to be delivered to the fuel common rail, the inlet metering valve is opened during the intake stroke to introduce fuel into the pumping chamber 211 through the inlet valve 117. During the subsequent pumping stroke, the plunger 213 moves from bottom dead centre to its top dead centre. The annular flange 255 of the plunger 113 engages the bottom wall 253 of the annular sleeve 247 causing the annular sleeve 247 to be displaced with the plunger 213 and the inlet ports 241 to be closed. The axial load applied to the plunger 213 by the cam 232 as the fuel in the pumping chamber 211 is pressurised causes the plunger 213 to be compressed axially. There is a corresponding radial expansion of the plunger 213 (which may be more pronounced at the low-pressure end 227 thereof) which causes a corresponding reduction in the size of the annular clearance C between the plunger 213 and the annular sleeve 247. The annular clearance C is thereby partially or fully closed when the plunger 213 is under load. The flow of fuel from the pressurisation chamber 219 through the annular clearance C is thereby partially or completely restricted, and the pressurisation chamber 219 is at least partially sealed. The continued movement of the plunger 213 and the annular sleeve 247 towards top dead centre causes the fuel pressure in the pressurisation chamber 219 to increase. An intermediate pressurised region is thereby established between the pumping chamber 211 and the cam box 236. The pressurised region reduces the pressure differential along the length of the plunger 213, which can help to reduce dynamic leakage from the pumping chamber 211 past the plunger 213.
The inlet metering valve can be opened during only a portion of the intake stroke to introduce a metered volume of fuel into the pumping chamber 211. In this operating mode, the axial load applied to the plunger 213 during the pumping stroke is reduced, at least during an initial portion of the stroke. Thus, the radial expansion of the plunger 213 is reduced and the annular clearance C remains open during at least the initial portion of the pumping stroke. The fuel in the pressurisation chamber 219 can thereby exit through the annular clearance C and enter the cam box 236 through the vent grooves 257. Only when the plunger 213 comes under sufficient axial load to cause radial expansion is the annular clearance C reduced. It will be appreciated, therefore, that the pressurisation chamber 219 is pressurised only during a portion of the pumping stroke. Moreover, the peak pressure in the pressurisation chamber 219 during the pumping stroke can be reduced.
The inlet metering valve can remain closed during an intake stroke to inhibit the introduction of the fuel into the pumping chamber 211. During the subsequent pumping stroke, the plunger 213 is under reduced axial load with the result that little or no radial expansion occurs. The annular clearance C remains substantially unchanged during the pumping stroke, allowing fuel to exit the pressurisation chamber 219 through the annular clearance C and the vent grooves 257. Thus, peak pressure in the pressurisation chamber 219 during the pumping stroke is further reduced. Indeed, in certain arrangements, the pressurisation chamber 219 may remain substantially un-pressurised during the pumping stroke.
It will be appreciated that various changes and modifications can be made to the pump described herein without departing from the scope of the present invention, as set out in the appended claims.
In a variant (not shown) of the first embodiment, the top wall 251 could be inclined relative to the longitudinal axis X to form a taper, and the first and second regions 235, 237 of the aperture 209 could be connected via a matching tapered intermediate connecting section. This configuration can help reduce stress concentration in the pressurisation chamber 219 during the pumping cycle.
In a further variant (not shown) of the first embodiment, the inlet ports 241 could be omitted. In use, the annular sleeve 247 could be configured to disengage from the second region 237 of the aperture 209 so that fuel could flow into the pressurisation chamber 219 through the opening 233 of the cylindrical projection 207.

Claims

A pump (100, 200) for supplying high-pressure fuel to a common rail fuel injection system, the pump comprising:
an elongated aperture (109, 209) forming a pumping chamber (111, 211) and a pressurisation chamber (119, 219);

a pumping element (113, 213) configured to reciprocate within the elongated aperture (109, 209) to pump fuel from the pumping chamber (111, 211); and

pressurisation means (129, 249) for pressurising fuel in the pressurisation chamber;

wherein the pressurisation chamber (119, 219) extends at least partially around the circumference of the pumping element (113, 213) to reduce leakage from the pumping chamber (111, 211) and,

wherein the pressurisation means comprises an annular sleeve (247) extending about the pumping element (213) and,

and wherein the pump (100, 200) comprises an annular clearance (C) formed between the annular sleeve (247) and the pumping element (213); wherein, in use, the annular clearance (C) decreases in size due to radial expansion of the pumping element (213) when the pumping element (213) is under load.
A pump (100, 200) as claimed in claim 1, wherein the elongated aperture (109, 209) comprises a first region (135, 235) defining the pumping chamber (111, 211) and a second region (137, 237) defining the pressurisation chamber (119, 219), the second region (137, 237) being offset from the first region (135, 235) along a longitudinal axis of the pumping element (113, 213).
A pump (100, 200) as claimed in claim 2, wherein the first region (135, 235) has a first diameter and the second region (137, 237) has a second diameter, the second diameter being larger than the first diameter.
A pump (100, 200) as claimed in claim 2 or claim 3, wherein the second region (137, 237) comprises a tapered section.
A pump (100, 200) as claimed in any one of the preceding claims comprising drive means (129) for driving the pumping element (113, 213), wherein the pressurisation chamber (119, 229) is configured to establish a pressurised region between the pumping chamber (111, 211) and the drive means (129).
A pump (100, 200) as claimed in any one of the preceding claims, wherein the pressurisation chamber (119, 229) is an annular chamber.
A pump (100, 200) as claimed in any one of the preceding claims, wherein the pressurisation means (129, 247) is configured to seal the pressurisation chamber (119, 229).
A pump (100, 200) as claimed in any one of the preceding claims, wherein the pressurisation means comprises an annular projection (129) located on the pumping element (113, 213).
A pump (100, 200) as claimed in claim 1, wherein the pumping element (213) and the annular sleeve (247) are sized such that, in use, the annular clearance (C) at least substantially closes due to radial expansion of the pumping element (247) under axial load.
A pump (100, 200) as claimed in claim 1 or claim 9, the annular sleeve (247) comprising a bottom wall (254), wherein the bottom wall (254) comprises at least one vent groove (257), the at least one vent groove (257) being in fluid communication with the annular clearance (C).
A pump (100, 200) as claimed in any one of claims 1, 9 and 10, wherein the pumping element (213) comprises an annular flange (255) for drivingly engaging the annular sleeve (247).
A pump (100, 200) as claimed in any one of the preceding claims, wherein the pressurisation chamber (119, 219) comprises at least one fuel inlet (241) for allowing fuel flow into the pressurisation chamber (119, 219).
A pump (100, 200) as claimed in any one of claims 1 to 11, wherein the pressurisation means (129, 247) is retracted out of the pressurisation chamber (119, 219) when the pumping element (113, 213) is in a bottom dead centre position to enable fuel to enter the pressurisation chamber (119, 219).