JP3387506B2 - Low leakage plunger and barrel assembly for high pressure fluid systems - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plunger and barrel assembly for a fluid system that effectively minimizes leakage from the clearance between the plunger and barrel assembly.

BACKGROUND OF THE INVENTION Engine designers are constantly pursuing improvements in engine design that improve engine efficiency. One way to improve engine efficiency is to improve the operating efficiency of fluid systems. In particular, leakage of high pressure fuel in the fluid system represents energy loss that can reduce engine efficiency. High pressure fuel loss has become an ever-increasing problem as higher injection pressure levels have been attempted to improve fuel economy and reduce exhaust emissions in accordance with the requirements of recent and forthcoming legislation.

The undesired fuel leak is sized to fit reciprocally into a bore formed in the body and sized to form a close sliding fit with the inner surface of the body. It often occurs in fuel system components that have members, such as valve elements or fuel plungers, that form a partial fluid tight seal between the surfaces to be sewn.
As the fuel pressure increases, along the length of the seal,
That is, a pressure gradient is created along the clearance between the member and the opposing wall forming the bore. The leakage flow rate from the clearance depends mainly on the magnitude of the pressure gradient, the length of engagement, the magnitude of the operating clearance, and the viscosity of the fluid. The magnitude of the operational clearance is affected by the amount of fuel pressure induced expansion or deformation of the body forming the bore. One way to reduce leakage is to design the component to have a smaller clearance between the plunger and the barrel. However, if you try to make the tolerances smaller,
Manufacturing costs increase. Another way to reduce leakage is to design the body to counter pressure-induced expansion by increasing the size and / or strength of the body or housing forming the bore. However, this method is undesirable because it increases the size and weight of the components and thus the fuel system.

Many fuel systems used in modern engines include, for example, unitary fuel injectors such as those disclosed in U.S. Pat.No. 5,072,709, or fuel pump assemblies such as those disclosed in U.S. Pat. And a fuel pressurizing plunger incorporated for reciprocating movement. Each plunger typically operates mechanically or hydraulically to pressurize the fuel in the pressure chamber and inject it into the engine cylinder. For example, U.S. Pat.
And 5,441,027 disclose hydraulically actuated pressure intensifying plunger assemblies. However, these references do not suggest a reduction in leakage between the plunger and the adjacent bore wall and are therefore subject to the above-mentioned disadvantages.

Loegel, Sr. et al., U.S. Pat.No. 4,991,495, discloses a plunger mounted in a bore and a plurality of inserts arranged in series along the plunger to seal the space between the plunger and its housing. A pumping mechanism including is disclosed. The insert includes thrust and sealing rings that deform and expand radially in response to axial fluid-induced forces provided by adjacent inserts. However, this sealing assembly requires extra disks and other components that are complicated and expensive equipment that is costly and difficult to maintain. In addition, the device reseals two gaps, one on each side of the insert, during each pumping stroke of the plunger,
This is desirable because it increases the likelihood of subminimum leakage.

US Pat. No. 5,038,826 to Kabai et al. Discloses a three-way valve that includes a piston slidably disposed on a valve body. High-pressure fuel is fed into the valve through an alignment port formed in the valve body and the piston. The integral portion of the piston or valve body is activated by the fuel pressure supplied to reduce the clearance between the piston and the valve body, thereby reducing leakage between components. Deformation of the integral part tends to close the clearance and reduce leakage, but the resulting small tolerances result in wear of the valve body or piston or possibly scuffing due to wear.
fing) and excessive clearance may occur over time. In the case of the Kabai et al. Design, excessive wear ultimately requires replacement of the entire piston and / or valve disc, adding extra cost. Also, the integral part is disadvantageous because it only reduces the pressure gradient only in the localized part of the seal length which is not optimally minimized. Furthermore, the integral part is formed by machining the internal flow passage in the valve body or the piston, which increases the manufacturing time and cost.

Therefore, there is a need for an improved plunger and barrel assembly that effectively and optimally minimizes leakage of fluid from the plunger-barrel clearance while minimizing assembly cost and size.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved plunger and barrel assembly that overcomes the deficiencies of the prior art and allows for optimally minimizing fuel leakage between the plunger and barrel, thus increasing efficiency. Is to provide.

Another object of the present invention is applicable to either a valve or a pump, which effectively reduces fluid leakage between the pump or valve member and its body forming the bore, and an improved plunger and It is to provide a barrel assembly.

Yet another object of the present invention is to provide an improved plunger and barrel assembly applicable to a fuel pump including a unitary fuel injector and a reciprocating plunger type pump located upstream of the fuel injector in a high pressure fuel system. That is.

Yet another object of the present invention is to provide an improved plunger and barrel assembly in which the working clearance between the plunger and barrel decreases as fuel pressure increases.

Yet another object of the present invention is an improved plunger and barrel that includes an elastic section that allows the material of the elastic section to be selected independently of the barrel to meet component lubrication and structural requirements. It is to provide an assembly.

Yet another object of the present invention is to provide an improved plunger and barrel assembly which minimizes the cost of manufacturing a blind bore formed in the barrel.

Yet another object of the present invention is to provide a plunger bore.
It is an object of the present invention to provide an improved plunger and barrel assembly in which the r bore) is substantially unaffected by the strain effects of tightening or mounting loads on the assembly.

Yet another object of the present invention is to obtain a new bore-forming surface without replacing the barrel for easy and inexpensive refurbishment,
An object is to provide an improved plunger and barrel assembly.

Yet another object of the present invention is to provide an improved plunger and barrel assembly that includes a resilient sealing sleeve that removes the fluid tight feature from the barrel.

Yet another object of the present invention is to provide an improved plunger and barrel assembly that includes an easily replaceable elastic sealing sleeve.

Yet another object of the present invention is to allow the barrel to be designed and sized to limit operating stress, and instead of being sized to limit radial expansion, the radial direction of the barrel To provide an improved plunger and barrel assembly that includes an elastic sealing sleeve that allows for increased expansion of the.

Yet another object of the present invention is to provide an improved plunger and barrel assembly for a fuel pump that improves the efficiency of the fuel system and minimizes the required pump displacement.

These and other objects of the invention are directed to cavities.
y) and the device body including the high pressure flow circuit, the plunger arranged to reciprocate in the cavity, and the leakage flow reduction arranged in the cavity to reduce the leakage flow of fluid from the fluid circuit. And a fluid control device for a high-pressure fluid system.
The leak rate reducer is removably mounted between the plunger in the cavity and the body of the device, includes a bore for slidably receiving the plunger, and forms a ring-shaped gap between the plunger and the bore. Including sleeve. The sealing sleeve is designed to flex elastically against fluid pressure to reduce the annular gap and to minimize fluid leakage through the annular gap. The sealing sleeve may include an outer annular surface that is directly acted upon by fluid pressure to cause the sealing sleeve to flex radially inwardly to reduce the annular clearance. The sealing sleeve can also include an inner flexible portion and an outer portion that is rigidly attached to the device body. The outer portion may include an annular step for sealingly adjoining an annular land formed on the apparatus body. Axial clamping forces acting on the outer side can be used to hold the sealing sleeve firmly in place to press it against the annular land. The sealing sleeve can be press fit into the cavity to press it against the body of the device. The pressure of the fluid acting on the inner end of the sealing sleeve tends to bias the sleeve into abutting and tight sealing against the annular land such that the inner end of the sealing sleeve is spaced from the inner end of the cavity. Are arranged. Thus, the cavity can be formed in a one-piece device body and the sealing sleeve can be retained in the cavity by an axial clamping force, or alternatively, the device body can be divided into two parts. It can be made up of parts, so that when they are connected together, a cavity is formed which secures the sealing sleeve.

The present invention is incorporated into a fuel pump for a stroke high pressure fuel system such that the plunger moves in a periodic pumping stroke and is operable to pressurize fuel in a high pressure fuel chamber formed at the inner end of the cavity. Is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional view of a conventional plunger and barrel assembly used in prior art fuel pumps.

FIG. 2 is a partial cross-sectional view of a plunger and barrel assembly designed in accordance with the preferred embodiment of the present invention.

FIG. 3 is a partial cross-sectional view of a second embodiment of the plunger and barrel assembly of the present invention.

FIG. 4 is a graph showing the leakage reduction effect of the present invention as compared to the conventional assembly as disclosed in FIG.

FIG. 5 is a graph illustrating the radial displacement of the plunger and barrel of the plunger and barrel assembly of the present invention as well as the radial clearance of the gap along the length of the sealing sleeve.

FIG. 6 is a graph showing the pressure in the annular gap along the length of the sealing sleeve of the present invention.

Description of the Preferred Embodiments FIG. 1 clearly illustrates the advantages of incorporating the plunger and barrel assembly of the present invention into a fuel pump over other fuel pumps that use conventional plunger and barrel assemblies. To be presented for. FIG. 1 illustrates a prior art plunger and barrel assembly, generally designated 10, including a barrel 12 that includes a plunger bore 14 and a plunger 16 mounted for reciprocal movement within the bore 14.
The plunger 16 moves in forward and reverse strokes to operate to periodically pressurize a fluid or fuel within a high pressure chamber 18 formed at one end of the bore 14. The high-pressure fuel in the high-pressure chamber 18 is sent to the engine via the high-pressure flow circuit 20.
The plunger 16 and the bore 14 are sized relative to each other such that the plunger 16 forms a slip fit with the inner surface of the barrel 12 forming the bore 14 and forms a partial fluid seal in the annular gap formed between adjacent surfaces. Is formed. During the reciprocating movement of the plunger 16, an axial pressure gradient is created along the length of the engagement or sealing of the annular gap, and the high pressure chamber 18
There is a leakage flow from the outside. In addition, the high pressure chamber 18
As the fuel pressure within increases, the leakage flow rate increases. The pressure in the high pressure chamber 18 is often high enough to cause the barrel 12 to expand, i.e., elastically radially outwardly deform, increasing the size of the annular gap, and thus undesirably, causing leakage flow. Will increase. While it is desirable for this leak rate to function to lubricate the plunger 16, the leak rate also means a loss of energy that reduces the efficiency of the fuel system and increases the required pump delivery of the assembly. .

The plunger and barrel assembly of the present invention shown in FIGS. 2 and 3 functions to minimize leakage flow around the plunger, thus increasing the efficiency of the fuel system and reducing the required pump displacement. , Enables effective reciprocating movement of the plunger without increasing the size of the assembly. Referring to FIG. 2, there is shown a preferred embodiment of the plunger and barrel assembly of the present invention applied to a fuel pump generally indicated at 30.
The fuel pump 30 is a body or barrel having a cavity 34 formed therein.
32, a plunger mounted for reciprocating movement in cavity 34, and a leak rate reducer 38 mounted between plunger 36 in barrel 34 and barrel 32. The fuel pump 30 of the present invention can be incorporated into a variety of applications, such as one integrated with a single fuel injector, or a fuel pump in a high pressure fuel system located upstream of the fuel injector. The plunger and barrel assembly can also be incorporated into a hydraulically actuated pressure boost pump system. The plunger and barrel assembly of the present invention also includes a plunger 36
Can be incorporated into another type of fluid control device, such as a high pressure fuel valve that acts as a valve body for engaging a valve seat formed in the barrel.

Leakage reduction device 38 includes a sealing sleeve 40 disposed within cavity 34, which includes a bore 42 for receiving plunger 36. Sealing sleeve 40 is a barrel
An outer portion 44 including an annular step 46 for sealing adjacent an annular land 48 formed within 32 bores 34 is included.
The sealing sleeve 40 includes an annular step 46 and an annular land.
Numeral 48, provided by a mounting or clamping device (not shown) to maintain a seal adjacent to 48
It is held securely in place within the cavity 34 by an axial clamping force indicated by 50. Accordingly, the sealing sleeve 40 is designed to be removably disposed within the cavity 34. The axial clamping force 50 can be provided by an injector clamping device such as shown in U.S. Pat.No. 5,503,128, incorporated herein by reference, in which case the fuel pump 30 is integral to the injector and clamping The device also provides sufficient force to hold the fuel injector and barrel 32 in place in the injector mounting bore formed in the engine.

The sealing sleeve 40 also includes an inner flexible portion 52 integrally formed with the outer portion 44 and extending inwardly within the cavity 34. The inner end portion 54 of the inner flexible portion 52 ends at a distance from the inner end portion of the cavity 34. The plunger 36 is reciprocally mounted in the bore 42 to form a high pressure fluid chamber 56 at the inner end of the cavity 34. The high pressure fuel circuit 58 directs the supply fuel into the high pressure chamber 56 and injects a flow of high pressure fuel from the high pressure chamber 56 into the engine, for example, through a nozzle assembly of a fuel injector.

The inner flexible portion 52 is generally cylindrical and has an outer shape that is sufficiently smaller than the inner diameter of the cavity 34 so that the outer annular chamber 60 is formed. The outer annular chamber 60 is in continuous fluid communication with the high pressure chamber 56 via an end gap 61 formed between the inner end 54 of the inner flexible portion 52 and the inner end of the cavity 34. Therefore,
The fuel pressure in the outer annular chamber 60 is maintained during the movement of the plunger 36,
It is substantially the same as the fuel pressure in the high pressure chamber 56. Also, the outer shape of the plunger 36 and the inner diameter of the sealing sleeve 44 are such that a gap 62 is formed between the outer surface of the plunger 36 and the inner surface of the sealing sleeve 40 to form a sliding interference fit and a partial fluid seal. It becomes big. As a result, the fuel pressure in the outer annular chamber 60 becomes higher than the fuel pressure in at least a part of the annular gap 62, so that the inner flexible portion 52 bends inward, and the size of the gap 62 and the leakage flow rate from the gap decrease. .

During operation, when the plunger 36 retracts, the high pressure chamber 56 expands and the supply fuel flows from the circuit 58 into the high pressure chamber 56. High pressure chamber
At some point during the inward or forward stroke of the plunger 36 in the direction of 56, the fuel in the high pressure chamber 56 is compressed by the plunger 36, which similarly increases the fuel pressure in both the high pressure chamber 56 and the outer annular chamber 60. To do. Therefore, the high pressure fuel of the same pressure acts on both the inner surface of the flexible portion 52 adjacent to the high pressure chamber 56 and the outer annular surface of the inner flexible portion 52 forming the outer annular chamber 60. As a result, the inner end of the inner flexible portion 52 receives the same pressure, thereby avoiding fuel pressure induced expansion of the portion of the inner flexible portion 52 located adjacent to the high pressure chamber 56. Further, the partial fluid seal formed in the annular gap 62 between the plunger 36 and the inner flexible portion 52 tends to produce a throttling effect that reduces the pressure along the axial length of the annular gap 62. However, the fuel pressure in the outer annular chamber 60 located on the opposite side of the annular gap 62 is maintained at a high pressure level equal to the pressure in the high pressure chamber 56. Therefore, the portion of the inner flexible portion 52 that overlaps the plunger 36, i.e., located adjacent to the annular gap 62, receives fluid pressure on its outer surface, causing that portion of the sealing sleeve 40 to flex radially inward. That is, it tends to elastically deform. Accordingly, the fluid pressure induced deflection of the sealing sleeve 40 reduces the annular gap 62, which results in a reduced leakage flow rate from the annular gap 62.
High pressure fuel in the outer annular chamber 60 may cause fuel-induced expansion of the barrel 32, but the expansion does not adversely affect the seal between the plunger 36 and the sealing sleeve 40.

FIG. 3 illustrates a second embodiment of the plunger and barrel assembly of the present invention, here a leak flow reduction device 70.
Includes a generally cylindrical sealing sleeve 72 disposed between a two-piece barrel 74 and a plunger 75. The two-piece barrel 74 includes a first piece 76 and a second piece 78, each having a respective cavity 80, 82.
Form a complete cavity 84 when they are placed in line adjacent to the second piece 78. The second barrel piece 78 includes an upper annular land 86 and an annular recess 88, and the sealing sleeve 72 is press fit therein for securely connecting the sleeve 72 to the second barrel piece 78. The outer end of the sealing sleeve 72 is adjacent to the upper annular land 86, and the sealing sleeve 72 is axially disposed within the cavity 84. After the sealing sleeve 72 is pressed into the annular recess 88, the first
The barrel piece 76 may be threadedly engaged with the second barrel piece 78 in any conventional manner, such as with an outer retainer to provide a first barrel piece 78.
And by holding the second pieces 76, 78 in compression adjacent relationship, they can be connected to the second barrel piece 78. The sealing sleeve 72 includes an inner flexible portion 90 that is structurally and functionally the same as the inner flexible portion 52 of the previous example of FIG. The fuel pressure in the high pressure chamber 56 acts on the inner end portion 54 of the inner flexible portion 80 to bias the sealing sleeve 72 upward so as to be adjacent to the upper annular land 86, and the sealing sleeve 72 and the second
Helps seal the connection to and from the barrel piece 78. The clamping force shown at 92 serves to hold the fuel pump in place and is used to secure the first and second barrel pieces 76, 78 adjacent to one another.

The sealing sleeves 40, 72 are formed of an inner flexure thickness with a material that allows an optimal amount of radial deflection or displacement to achieve improved leakage flow reduction for any application. The desired radial displacement of the sleeves 40, 70 depends on the magnitude of the initial radial clearance of the gap 62 when unloaded and the fuel pressure within the high pressure chamber 56.

The low leak plunger and barrel assembly of the present invention provides significant advantages over conventional high pressure fluid control systems.
First, the leak rate reducer of the present invention effectively reduces fluid leakage between the pump or valve member and the body forming the member bore, improving the efficiency of the high pressure fluid system. In fuel pump applications, the present invention further functions to minimize the required pump delivery of the fuel pump. This advantage is shown in FIGS. As shown in FIG.
The sealing sleeve of the present invention reduces leakage by 90% compared to standard barrels and sleeves. The radial clearance of the annular gap 62 is preferably greater than the radial clearance of conventional gaps to allow pressure-induced radial offset of the sleeve. Needless to say, unlike the reverse reaction of the sealing sleeve of the present invention, which gradually diminishes as fuel pressure increases, resulting in an annular gap 62 that is smaller than the standard assembly, the fuel pressure increases. Increases due to fuel pressure induced expansion of the barrel. FIG. 5 shows the radial displacement of the barrel and the plunger and the radial clearance of the gap 62 along the length of the sealing sleeve 40.
As can be seen, the radial clearance of the gap 62 is significantly reduced in the region adjacent the outermost portion of the inner flexible portion 52. With reference to FIG. 6, it can be seen that the pressure in the gap 62 is significantly reduced in the region of minimal radial clearance. During operation, due to the pressure difference at the outermost part of the inner flexible portion 52 due to the partial fluid sealing of the gap, the outermost part is displaced inward in the radial direction or bends, and the size of the gap decreases as shown in FIG. The pressure is therefore reduced further. Needless to say, the pressure in the annular gap 62 at the position adjacent to the inner flexible portion 52 becomes the minimum at the position farthest from the high-pressure chamber 56, so the displacement of the inner flexible portion 52 occurs at the outermost part.

A second advantage of the present invention is the sealing sleeve of the present invention.
The 40, 72 can be easily removed and replaced with a new sealing sleeve, which allows for easy, quick and low cost maintenance. Third, the inner flexure
By forming 52, 80 as part of the sealing sleeve separately from the body or barrel, the leak rate reducer of the present invention allows the sealing sleeve to have its requirements or lubrication independent of the material selection of the barrel. , Wear resistance,
And can be made of materials that can better achieve elasticity. Thus, the sealing sleeves 40, 72 can be formed of any material that provides suitable flexibility and resilience to optimally minimize leakage flow, such as, for example, metal, non-metal, or composite materials. Fourth, the leak reduction device of the present invention reduces the working clearance between the plunger and barrel as the fuel pressure increases, unlike prior art devices where clearance increases at higher pressure levels. Function. Fifth, first
The sleeve of the present invention by comparing FIG. 2 with FIG.
It can be seen that the 40, 72 can increase the length of engagement between the plunger 36 and its complementary bore, thus further reducing leakage flow. Sixth, the present invention avoids the high manufacturing costs associated with forming blind bores with precise diameters due to the through bores formed in the sealing sleeve. Seventh, the present invention also removes the sealing function from the barrel so that fluid pressure induced expansion of the barrel does not affect the clearance seal of the plunger while designing the barrel to limit operating stress. , Is advantageous. Eighth, the plunger and barrel assembly of the present invention forms a plunger bore that is substantially unaffected by the strain effects often experienced by the clamping or mounting loads 50, 92 applied to the assembly. Since the inner flexible portions 52, 90 are not directly supported by the barrel and are surrounded by high pressure fuel, the strain effect of the mounting load is substantially isolated from this portion of the sealing sleeve.

INDUSTRIAL APPLICABILITY The plunger and barrel assembly including the leak rate reducer of the present invention is used in many high pressure fluid systems where it is desirable to effectively minimize the leak rate between the moveable plunger and the corresponding bore. can do. The invention is particularly advantageous for use in high-pressure fuel pumps arranged in high-pressure fuel systems of internal combustion engines, for example in motor vehicles and industrial equipment.

Continued Front Page (72) Inventor Carol, John Tee. The Sard United States 47201 Columbus Baywood Court, Indiana 915 (72) Inventor Benson, Donald J. United States 47203 Columbus Greenbrier Road, Indiana 3954 (56) Reference JP-A-3-43681 (JP, A) Jitsukaihei 3 -123984 (JP, U) Actually opened 58-161177 (JP, U) Actually opened 60-84775 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F04B 53/02 F02M 59/44

Claims (13)

(57) [Claims] 1. A device body including a cavity and a high pressure flow circuit, a plunger having a diameter range and arranged to reciprocate in the cavity, and a fluid leakage flow rate from the fluid circuit. A leakage flow reducing means disposed in the cavity for providing a leakage flow reducing means between the plunger and the device body, the sealing sleeve being removably mounted in the cavity. , The sealing sleeve includes an inner annular surface defining a bore for slidably receiving the plunger, the bore having a diameter range greater than a diameter range of the plunger, between the plunger and the inner annular surface. An annular gap is formed in the annular gap, and the sealing sleeve elastically flexes in response to fluid pressure to minimize the fluid leakage flow rate through the annular gap. Reducing, but maintaining the annular gap, the sealing sleeve including an outer annular surface, the fluid pressure acting directly on the outer annular surface to deflect the sealing sleeve radially inwardly, Includes an inner flexible portion and an outer portion fixedly attached to the apparatus body, the outer annular surface being formed in the inner flexible portion, and further being formed adjacent to the outer annular surface. The outer portion includes an annular step for abutting and sealing an annular land formed in the apparatus body so as to fluid-tightly seal one end of the outer annular chamber, and the sealing sleeve includes the outer portion. Is firmly held in a sealed position with respect to the annular land by the axial tightening force acting on the high pressure fluid chamber inside the free end of the inner flexible portion. A fluid control device for use in a high-pressure fluid system, comprising: 2. The sealing sleeve is press-fitted into the cavity so as to press it against the apparatus body, and fluid pressure acting on an inner end of the sealing sleeve displaces the sleeve in a sealingly adjacent state with the annular land. The fluid control device according to claim 1, wherein: 3. The fluid control device according to claim 1, wherein the sleeve is formed of a material having elasticity higher than that of a material forming the device main body. 4. The apparatus body includes a first portion and a second portion abutting the first portion, the cavity being formed in both the first and second portions, and the sealing sleeve. 3. The fluid control device of claim 2, wherein is press-fitted into the first portion and extends along the cavity at a distance from the second portion of the body to form the outer annular chamber. . 5. A barrel including a cavity and a high-pressure fuel circuit, a high-pressure fuel chamber arranged in the cavity, a reciprocating movement in the cavity, and adding fuel in the high-pressure fuel chamber. A plunger operative to move in a periodic pumping stroke to pressurize; a leak flow reducing means disposed in the cavity to reduce a fluid leak flow from the high pressure fuel chamber, the leak flow rate The reducing means includes a sealing sleeve removably mounted within the cavity between the plunger and the barrel, the sealing sleeve including an outer annular surface and a bore slidably receiving the plunger;
An annular gap is formed between the plunger and the bore and the sealing sleeve is elastically responsive to a fuel pressure inducing force acting on the outer annular surface to minimize fluid leakage flow within the annular gap. Flexing to reduce the annular gap, the sealing sleeve includes an inner flexible portion and an outer portion rigidly attached to the barrel, the inner flexible portion free of axial abutment with the barrel. A leak flow reducing means including a distal end and defining a fuel flow gap, wherein the high pressure fuel chamber is formed inside a free end of the inner flexible portion; Fuel pump. 6. The fuel pump of claim 5, wherein the fuel pressure acts directly on the outer annular surface to deflect the sealing sleeve radially inward. 7. The fuel pump according to claim 6, wherein the outer portion includes an annular step for abutting and sealing an annular land formed on the barrel. 8. The fuel pump according to claim 7, wherein the sealing sleeve is firmly held in place so as to be pressed against the annular land by an axial tightening force acting on the outer portion. 9. The sealing sleeve is press-fitted into the cavity so as to press it against the barrel, and fuel pressure acting on an inner end of the sealing sleeve displaces the sleeve into a sealing contact with the annular land. The fuel pump according to claim 7, wherein: 10. The fuel pump according to claim 5, wherein the sleeve is formed of a material having a higher elasticity than the material forming the barrel. 11. The barrel includes a first portion and a second portion abutting the first portion, the cavity being formed in both the first and second portions, and the sealing sleeve being formed in the sealing sleeve. The fuel pump of claim 9, wherein the fuel pump is press-fitted into the first portion and extends along the cavity at a distance from the second portion of the body to form an annular high pressure chamber. 12. A barrel including a cavity, a high pressure fuel chamber disposed within the cavity, a high pressure fuel circuit for providing flow to and from the high pressure fuel chamber, and reciprocating motion within the cavity. A leak flow reducing device used in a high pressure fuel pump including a plunger arranged to move in a periodic pumping stroke to pressurize fuel in the high pressure fuel chamber, and a fuel leak flow rate from the high pressure fuel chamber. A replaceable sealing sleeve removably mounted in the cavity between the plunger and the barrel to reduce the load, the replaceable sealing sleeve slidably receiving the outer annular surface and the plunger. A high-pressure fuel from the high-pressure fuel chamber acts on the outer annular surface to form a ring-shaped gap between the plunger and the bore, the fuel passing through the ring-shaped gap. Mounted on the barrel to prevent expansion of the replaceable sealing sleeve so as to prevent an increase in leak rate and to be radially unsupported over the entire circumference of the distal end. Leakage flow reduction constituted by a replaceable sealing sleeve, characterized in that it has an internal flexure including the possible distal end, the high pressure fuel chamber being formed inside the free end of the internal flexure. apparatus. 13. The replaceable sealing sleeve elastically flexes in response to a fuel pressure inducing force acting on the outer annular surface to reduce the annular gap, thereby reducing fuel leakage flow in the annular gap. 13. The leakage flow reduction device according to claim 12, wherein the leakage flow reduction device is provided.