WO2012065566A1

WO2012065566A1 - High-pressure fuel pump

Info

Publication number: WO2012065566A1
Application number: PCT/CN2011/082397
Authority: WO
Inventors: Zhaohui Tang; Jianxin Zhang; Guanqun Hua
Original assignee: Robert Bosch Gmbh
Priority date: 2010-11-18
Filing date: 2011-11-18
Publication date: 2012-05-24
Also published as: CN201851241U

Abstract

A high-pressure fuel pump comprises a high-pressure assembly (2) for receiving fuel from a fuel tank and pressurizing the fuel, and a driving shaft (3) comprising a cam (50) for driving the high-pressure assembly (2). The high-pressure assembly (2) comprises a plunger sleeve (20), a plunger (22) to be moved in the plunger sleeve (20) back and forth, and a check valve assembly (24). A pressurizing chamber (26) is defined between the front end of the plunger (22) and the check valve assembly (24) in the plunger sleeve (20). The plunger sleeve (20) is formed with a fuel feeding hole (30) through which the fuel is drawn into the pressurizing chamber (26), and a leakage discharging passage (34a,34b) for returning leaked fuel from the pressurizing chamber (26) through a gap between the plunger (22) and the plunger sleeve (20) back to the fuel tank completely. High-temperature leaked fuel is returned back to the fuel tank completely, which prevents temperature increasing and velocity decreasing of the fuel in the pressurizing chamber.

Description

HIGH-PRESSURE FUEL PUMP

Technical Field

The invention relates to a high-pressure fuel pump and, in particular, to a high-pressure pump for a common rail of an internal combustion engine (such as a diesel engine), wherein a high-pressure assembly of the high-pressure pump is provided with an individual leakage returning passage for returning the fuel leaked from the interior of the high-pressure assembly back to a fuel tank completely.

Background Art

In a fuel injection system for a vehicle or other fuel consuming equipments, a high-pressure pump is generally used for feeding high-pressure fuel to an internal combustion engine. The high-pressure pump comprises a feeding pump and a high-pressure assembly, which are integrated together. The feeding pump feeds fuel from a fuel tank to the high-pressure assembly, and the high-pressure assembly pressurizes the fuel and supplies it to the internal combustion engine.

Common rail techniques become more and more popular today. In a common rail type fuel injection system, establishing fuel pressure and injecting the fuel are performed independently from each other. The fuel is supplied by the high-pressure pump at a certain high pressure and is then stored in a common rail. The common rail is connected in braches to fuel injectors which are controlled by an electronic control unit. Each injector comprises a precisely machined injection nozzle and a plunger driven by a solenoid. The electronic control unit controls the operation of the solenoids to control the injection of fuel into cylinders of the internal combustion engine.

Figure 1 shows schematically a plunger type high-pressure assembly 2 of a high-pressure pump according to prior art. The high-pressure assembly 2 is mounted in a casing 5 of the high-pressure pump and mainly comprises: a plunger sleeve 20 fixed in the casing 5 and defining a valve accommodating chamber and a plunger chamber, which are in communication with each other, in the plunger sleeve, a plunger 22 movable back and forth in the plunger chamber, a check valve assembly 24 mounted in the valve accommodating chamber for defining a pressurizing chamber 26 in the plunger chamber between a front end of the plunger 22 and the check valve assembly 24, and a cam follower 28 driven by a cam shaft (not shown) for moving the plunger back and forth.

The plunger sleeve 20 is formed with a fuel feeding hole 30, the fuel feeding hole having opposite ends in communication with the check valve assembly 24 and a fuel feeding passage (not shown) in the casing respectively.

The check valve assembly 24, on one hand, allows the fuel in the fuel feeding hole 30 to flow into the pressurizing chamber 26, while prevents the fuel in the pressurizing chamber 26 from flowing back to the fuel feeding hole 30. On the other hand, the check valve assembly 24 allows the fuel in the pressurizing chamber 26 to be discharged in the direction shown by the arrow F in Figure 1 and be supplied to an internal combustion engine or a common rail, while prevents the discharged fuel from flowing back to the pressurizing chamber 26.

Low pressure fuel fed from a feeding pump (not shown) is supplied to a fuel feeding passage through a fuel feeding line (not shown), and is then supplied to the fuel feeding hole 30 through the fuel feeding passage. When the plunger 22 is moved backwards (in a direction away from the check valve assembly 24), the fuel in the fuel feeding hole 30 is drawn into the pressurizing chamber 26. When the plunger 22 is moved forwards (in a direction towards the check valve assembly 24), the fuel in the pressurizing chamber 26 is pressurized by the plunger 22 and is then discharged through the check valve assembly 24 in the direction shown by the arrow F.

When the plunger 22 is moved forwards to pressurize the fuel in the pressurizing chamber 26, the fuel pressure in the pressurizing chamber 26 is very high, and thus a small amount of fuel is leaked in a backward direction through a gap between an outer surface of the plunger 22 and an inner wall of the plunger chamber. For collecting the leaked fuel, the plunger sleeve 20 is formed with a ring shaped collecting socket 32, which surrounds the plunger 22, in the substantially middle portion of the plunger chamber and a leakage discharging passage 34 extending from the collecting socket 32 to the outer periphery of the plunger sleeve 20. The leakage discharging passage 34 is in communication with a corresponding leaking fuel circulation passage 36 which is formed in the casing 5 and extends to the fuel feeding passage. In this way, the fuel leaked along the outer surface of the plunger 22 is collected in the collecting socket 32. When the plunger 22 is moved backwards, the pressure in the pressurizing chamber 26 is decreased, so that the leaked fuel flows to the fuel feeding hole 30 through the leakage discharging passage 34, the leaking fuel circulation passage 36 and the fuel feeding passage and is mixed with the fuel fed by the feeding pump. In this way, the leaked fuel returns back to the pressurizing chamber 26. Thus, there is a circulation process for the leaked fuel in the high-pressure assembly 2, in which process the fuel leaked from the pressurizing chamber 26 flows through the collecting socket 32, the leakage discharging passage 34, the leaking fuel circulation passage 36, the fuel feeding passage and the fuel feeding hole 30 in sequence so as to return to the pressurizing chamber 26.

In an existing high-pressure pump having a high-pressure assembly 2 constructed as above, the temperature of the leaked fuel is very high because of the fuel pressurizing process in the pressurizing chamber 26. The circulation process of the leaked high-temperature fuel causes temperature increasing and velocity decreasing of the fuel in the pressurizing chamber 26, as a result of which, fuel leakage amount is increased and thus a worse operation situation is formed. When the existing high-pressure pump is used for supplying fuel to an internal combustion engine or a common rail at high pressure, such as 1800 bar, fuel leakage will result in significant decreasing of the efficiency of the high-pressure pump, and thus some operation requirements cannot be met.

Thus, it is desired to account for the fuel leakage in the plunger chamber to avoid efficiency decreasing of the high-pressure pump.

Summary of the Invention

An object of the invention is to provide a high-pressure pump, in particular a high-pressure pump for a common rail of an internal combustion engine (such as a diesel engine), to avoid efficiency decreasing of the high-pressure pump caused by fuel leakage in the plunger chamber of the high-pressure assembly of the high-pressure pump.

For this end, the invention in one aspect provides a high-pressure fuel pump comprising at least one high-pressure assembly configured for receiving fuel (such as diesel fuel) from a fuel tank and pressurizing the fuel to a high pressure, and a driving shaft comprising at least one cam for operatively driving the high-pressure assembly. The high-pressure assembly comprises a plunger sleeve, a plunger configured to be moved in the plunger back and forth reciprocatingly, and a check valve assembly mounted in the plunger sleeve to define a pressurizing chamber between a front end of the plunger and the check valve assembly in the plunger sleeve. The plunger sleeve is formed with a fuel feeding hole, the fuel received from the fuel tank being drawn into the pressurizing chamber through the fuel feeding hole. The plunger sleeve is further formed with a leakage discharging passage configured for returning leaked fuel, which is leaked from the pressurizing chamber through a gap between the plunger and the plunger sleeve, back to the fuel tank completely.

The high-pressure assembly may comprise a cam follower which is driven by the cam on the driving shaft to move the plunger back and forth reciprocatingly.

According to a preferred embodiment of the invention, the high-pressure pump further comprises a feeding pump for drawing fuel from the fuel tank and supplying the fuel to the high-pressure assembly.

According to a preferred embodiment of the invention, the feeding pump is also driven by the driving shaft. The feeding pump may be a vane pump or a gear pump.

According to a preferred embodiment of the invention, the at least one high-pressure assembly comprises two or more high-pressure assemblies, and the driving shaft comprises the same number of cams. In this condition, each cam may comprise at least one cam lobe, the cam lobe on each cam being displaced around the driving shaft with respect to the cam lobes of other cams.

According to a preferred embodiment of the invention, the fuel feeding hole in the plunger sleeve of the high-pressure assembly is connected to a branch feeding passage formed in a corresponding location in a casing of high-pressure fuel pump, and the branch feeding passage is connected to a common main feeding passage formed in the casing.

According to a preferred embodiment of the invention, the leakage discharging passage in the plunger sleeve of the high-pressure assembly is connected to a branch returning passage formed in a corresponding location in the casing.

According to a preferred embodiment of the invention, the plunger sleeve is provided with a ring like collecting socket which surrounds the outer periphery of the plunger, the branch returning passage having one end connected to the corresponding collecting socket and another end connected to a common main returning passage which is formed in the casing and is in communication with the fuel tank.

According to a preferred embodiment of the invention, the fuel feeding hole, the branch feeding passage and the main feeding passage are disposed in one side of the high-pressure assembly, and the leakage discharging passage, the branch returning passage and the main returning passage are disposed in the opposite side of the high-pressure assembly.

According to a preferred embodiment of the invention, the main returning passage is in communication with the fuel tank via a duct formed inside the casing.

According to a preferred embodiment of the invention, the main returning passage is in communication with the fuel tank via a pipe line disposed outside the casing.

According to a preferred embodiment of the invention, the main returning passage is connected with the pipe line by a fuel returning valve.

The high-pressure fuel pump of the invention is preferably a high-pressure pump for a diesel engine. For a diesel engine equipped with a common rail, the high-pressure assembly is connected with the common rail.

According to the invention, an individual leakage returning passage is provided in the high-pressure assembly of the high-pressure pump, for returning high-temperature fuel leaked in the high-pressure assembly back to the fuel tank completely, rather than circulating it to the pressurizing chamber as in the prior art. Thus, the leaked fuel cannot result in temperature increasing and velocity decreasing of the fuel in the pressurizing chamber, and the fuel leakage amount will not be increased. Thus, the efficiency of the high-pressure pump will not be negatively affected.

Brief Description of the Drawings

The above and other aspects of the invention will be understood more comprehensively through the detailed description with reference to the drawings in which:

Figure 1 is a partial sectional view of a high-pressure assembly of a high-pressure fuel pump according to prior art;

Figure 2 is a front sectional view of a high-pressure fuel pump according to an embodiment of the invention;

Figure 3 is a sectional view of the high-pressure fuel pump taken in the direction A-A of Figure 2;

Figure 4 is a schematic sectional view of a plunger sleeve according to the prior art;

Figure 5 is a schematic sectional view of a plunger sleeve according to the invention;

Figure 6 is a sectional view of a casing of the invention taken in the direction B-B of Figure 2;

Figure 7 is a sectional view taken in a plane through a branch returning passages in the casing;

Figure 8 is a sectional view taken in a plane through the branch feeding passages in the casing; and

Figure 9 is a sectional view of the casing of the invention taken in the direction A' -A' of Figure 2.

Detailed Description of Preferred Embodiments

Figures 2 and 3 show the overall arrangement of a high-pressure fuel pump of an embodiment of the invention. The high-pressure fuel pump can be used for supplying high-pressure fuel to an internal combustion engine of a vehicle or other fuel consuming equipments. For example, the high-pressure fuel pump may form a component of a common rail system of the internal combustion engine, for supplying high-pressure fuel to a common rail (not shown), and the common rail in turn supplies the fuel to an internal combustion engine (not shown) by means of injectors.

It can be seen that the high-pressure pump mainly comprises a casing 5, and a feeding pump 1 , high-pressure assemblies 2 and 2' , a driving shaft 3 and the like supported by the casing 5.

The casing 5 is preferably a cast casing which can be formed integrally into a single piece or be formed by assembling of separate components. The feeding pump 1 is mounted to the casing 5, for drawing fuel (such as diesel fuel) from a fuel tank (not shown) and supplying it to a main feeding passage 35 (see Figures 6, 8 and 9) formed in the casing. The fuel flows from an inlet valve (not shown), which is mounted in an inlet valve accommodating bore 33 (see Figure 8) formed in an initial end of the main feeding passage 35, into the main feeding passage 35, then flows into a branch feeding passage 31 corresponding to each high-pressure assembly, and is then supplied to each of the high-pressure assemblies 2 and 2' through a respective fuel feeding hole 30 of the high-pressure assembly which is connected with the corresponding branch feeding passage 31. The fuel fed from the feeding pump 1 may be supplied to the main feeding passage 35 either through an internal duct (not shown) formed inside the casing 5, or through an outside pipe line (not shown), connected outside the casing 5, via a fuel inlet 40 (see Figure 2) of the high-pressure assembly.

The feeding pump 1 is fixed to the casing 5 and is coupled with a distal end of the driving shaft 3 so as to be driven by the driving shaft 3. The feeding pump 1 may have a traditional structure. For example, it may be a traditional vane pump, gear pump or the like.

The high-pressure assemblies are configured for pressurizing the fuel fed by the feeding pump 1 and supplying it to an internal combustion engine or a common rail. In a simplest embodiment, only one high-pressure assembly is provided. However, two or more high-pressure assemblies are preferable for reducing the fluctuation of the fuel supplying pressure. Two high-pressure assemblies 2 and 2' are provided in the illustrated embodiment.

The driving shaft 3 extends through the casing 5, and are supported at its opposite ends by the casing 5 via corresponding bearings.

The driving shaft 3 drives both the feeding pump 1 and the high-pressure assemblies 2 and 2' . For this end, the distal end of the driving shaft 3 is adapted for driving the feeding pump 1 , and a middle portion of the driving shaft 3 is provided with cams 50 for driving plunger type high-pressure assemblies 2 and 2' . The high-pressure assemblies are disposed along an axial direction of the driving shaft.

A proximal end 54 of the driving shaft 3, as a power inputting end of the high-pressure fuel pump, extends to the outside of the casing 5 and is driven to rotate by the output power of the internal combustion engine, preferably via a transmission mechanism.

According to the illustrated embodiment, each of the high-pressure assemblies 2 and 2' is a plunger type high-pressure assembly, and the high-pressure assemblies are mounted in-line to the casing 5. In the illustrated embodiment, the two high-pressure assemblies have substantially the same structure, and thus only the high-pressure assembly 2 is described in details. In an alternative embodiment, the high-pressure assemblies 2 and 2' may have structures different from each other.

The high-pressure assembly 2 mainly comprises a plunger sleeve 20 fixed in a high-pressure assembly mounting bore 55 (see Figures 6 and 9) formed in the casing 5 and comprising inside it a valve accommodating chamber and a plunger chamber which are in communication with each other, a plunger 22 configured to be able to move back and forth in the plunger chamber, a check valve assembly 24 mounted in the valve accommodating chamber for defining a pressurizing chamber 26 in the plunger chamber between a front end of the plunger 22 and the check valve assembly 24, a cam follower 28 driven by a cam 50 on the driving shaft 3 and in turn moving the plunger 22 back and forth, and a outputting joint 23 mounted to the outer side of the check valve assembly 24 for outputting high-pressure fuel from the high-pressure assembly through the check valve assembly 24.

The plunger sleeve 20 is formed with a fuel feeding hole 30 having opposite ends connected to the check valve assembly 24 and the branch feeding passage 31 in the casing respectively.

The check valve assembly 24 is composed of two check valves, wherein one of the check valves allows the fuel in the fuel feeding hole 30 to flow into the pressurizing chamber 26, while prevents the fuel in the pressurizing chamber 26 from flowing back to the fuel feeding hole 30. The other check valve allows the fuel in the pressurizing chamber 26 to be discharged to the internal combustion engine or the common rail, while prevents the discharged fuel from flowing back to the pressurizing chamber 26. The check valve assembly having such functions is known in the art, and can be designed to have various structures. Thus, the detailed description to it is omitted.

The cam follower 28 is a roller type cam follower which is biased against a cam surface of the cam 50 by a spring 56, so that a roller of the cam follower is always in rolling contact with the cam surface of the cam 50. When the driving shaft 3 is rotated, a cam lobe 52 formed on the cam surface of the cam 50 pushes up the cam follower 28 which in turn drives the plunger 22 to move forwards in the plunger chamber. When the cam lobe 52 is rotated away from the cam follower 28, the spring 56 pushes the cam follower 28 down towards a recessed portion on the cam surface, so that the plunger 22 is moved backwards in the plunger chamber. In this way, the cam drives the plunger 22 to move back and forth reciprocatingly in the plunger chamber.

Each high-pressure assembly is a plunger pump driven by a corresponding cam 50 on the driving shaft 3. The number of the high-pressure assemblies equal to that of the cams 50. In the embodiment shown in Figure 2, two high-pressure assemblies 2 and 2' are provided and are driven by two cams 50 on the driving shaft 3 respectively. The two cams 50 are formed in axial locations on the driving shaft 3 corresponding to the high-pressure assemblies 2 and 2' respectively, and are displaced from each other by a regular angle in a circumferential direction around the central axis of the driving shaft 3. The cam surface of each cam 50 may have at least one cam lobe 52, and there are three cam lobs arranged in an equal angular distance in the illustrated embodiment. In the illustrated condition, once the driving shaft 3 is rotated by one turn, each cam 50 drives the high-pressure assembly to operate three times by means of its cam lobes 52. Meanwhile, when one of the high-pressure assemblies operates to draw fuel, the other high-pressure assembly operates to discharge fuel, as described below in details. In the condition shown in Figure 2, the plunger 22 of the high-pressure assembly 2 is at its upper dead point within its travel, and the pressurizing chamber of the high-pressure assembly 2 has a minimum volume; meanwhile, the plunger 22 of the high-pressure assembly 2' is at its lower dead point within its travel, and the pressurizing chamber of the high-pressure assembly 2' has a maximum volume. The high-pressure assemblies displaced in such a manner provide operation cycles which can advantageously suppress fluctuation of the pressure of the fuel supplied to the internal combustion engine or the common rail.

The cam 50 may be either formed integrally with the driving shaft 3 or formed separately and then mounted to the driving shaft 3. During the operation of the high-pressure pump, low pressure fuel is supplied to the main feeding passage 35 from the feeding pump 1 , and flows into the branch feeding passage 31 from the main feeding passage 35. Then the fuel is supplied to the fuel feeding hole 30 from the branch feeding passage 31. When the plunger 22 is moved backwards (in a direction away from the check valve assembly 24, or in a direction which results in increasing of the volume of the pressurizing chamber 26), the fuel in the fuel feeding hole 30 is drawn into the pressurizing chamber 26. When the plunger 22 is moved forwards (towards the check valve assembly 24, or in a direction which results in decreasing of the volume of the pressurizing chamber 26), the fuel in the pressurizing chamber 26 is pressurized by the plunger 22 and is discharged from the high-pressure pump through the check valve assembly 24.

When the plunger 22 is moved forwards to pressurize the fuel in the pressurizing chamber 26, the pressure in the pressurizing chamber 26 becomes very high, and thus a small amount of fuel will be leaked in a backward direction through a gap between an outer surface of the plunger 22 and an inner wall of the plunger chamber. For collecting this leaked fuel, the plunger sleeve 20 is formed in it with a ring shaped collecting socket 32 which is formed in a substantially middle portion of the plunger chamber around the plunger 22, and leakage discharging passage 34a and 34b which extend to the outer periphery of the plunger sleeve 20 from the collecting socket 32.

The discharging passages 34a and 34b are connected to each other and form an angle between them, for facilitating the machining process of them. However, a single linear leakage discharging passage can be provided according to the structure of the plunger sleeve 20 if possible.

The leakage discharging passages 34a and 34b are in communication with corresponding branch returning passages 60 formed in the casing 5 respectively, and the branch returning passages 60 are in communication with a common main returning passage 65 (see Figures 6 and 7). The main returning passage 65 is in communication with the fuel tank. In this way, high-temperature fuel leaked along the outer surface of the plunger 22 is collected in the collecting socket 32, and all the leaked fuel returns back to the fuel tank through the leakage discharging passages 34a and 34b, the branch returning passages 60 and the main returning passage 65, rather than be circulated to the pressurizing chamber as in the prior art.

The main returning passage 65 may be in communication with the fuel tank either through an internal duct (not shown) formed in the casing or through an outside pipe line (not shown) connected outside the casing.

Further, a fuel returning valve accommodating bore 62 (see Figure 6) may be formed in a downstream end of the main returning passage 65 for mounting a fuel returning valve (not shown) for controlling the flow of the leaked fuel.

Furthermore, for preventing the temperature of the leaked high-temperature fuel from being transferred to the feeding fuel, as shown in Figures 6 and 9, the fuel feeding holes, the branch feeding passages and the main feeding passage are disposed in one side of the high-pressure assembly, and the leakage discharging passages, the branch returning passages and the main returning passage are disposed in the opposite side of the high-pressure assembly.

The schematic sectional views of Figure 4 and Figure 5 show the difference in the structure of the plunger sleeve 20 and the flow path of the leaked fuel between the high-pressure assembly of the high-pressure pump of the prior art and that of the invention.

As shown in Figure 4, in the plunger sleeve 20 of the high-pressure assembly of the high-pressure pump according to the prior art, the collecting socket 32 receiving the leaked fuel is in communication with the fuel feeding hole 30 via the leakage discharging passage 34, and thus the leaked fuel is circulated to the fuel feeding hole 30 along the path indicated by the arrow in Figure 4, is then mixed with the fuel fed by the feeding pump, and then enters into the pressurizing chamber 26. Thus, A problem that the leaked high-temperature fuel is circulated back to the pressurizing chamber 26 occurs in the prior art.

In contrary, as shown in Figure 5, in the plunger sleeve 20 of the high-pressure assembly of the high-pressure pump according to the invention, the collecting socket 32 for receiving the leaked fuel is in communication with the branch returning passage in the casing via the leakage discharging passages 34a and 34b, and thus the leaked fuel returns back to the fuel tank through the branch returning passage and the main returning passage along the path indicated by the arrow in Figure 5. The leaked fuel has a high temperature because the temperature of fuel is increased by being pressurized in the pressurizing chamber 26. However, the leaked high-temperature fuel returns back to fuel tank completely through the individually provided branch returning passages and main returning passage, thus there is not any leaked high-temperature fuel to be circulated to the pressurizing chamber, and the problem existed in the prior art, i.e., increasing of temperature of the fuel resulted by the leaked high-temperature fuel which is mixed with the fuel fed by the feeding pump and enters into the pressurizing chamber, is avoided. Thus, according to the invention, the fuel velocity is not reduced and the fuel leakage amount is not increased. Even if the high-pressure pump according to the invention is used for supplying fuel to an internal combustion engine or a common rail at a very high pressure such as 1800 bar or more, the efficiency of the high-pressure pump is not decreased, and thus operation requirements can always be met.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the invention.

Claims

CLAIMS:

1. A high-pressure fuel pump comprising: at least one high-pressure assembly configured for receiving fuel from a fuel tank and pressurizing the fuel to a high pressure; and a driving shaft comprising at least one cam for operatively driving the high-pressure assembly; wherein the high-pressure assembly comprises a plunger sleeve, a plunger configured to be moved in the plunger back and forth reciprocatingly, and a check valve assembly mounted in the plunger sleeve to define a pressurizing chamber between a front end of the plunger and the check valve assembly in the plunger sleeve; wherein the plunger sleeve is formed with a fuel feeding hole, the fuel received from the fuel tank being drawn into the pressurizing chamber through the fuel feeding hole; and wherein the plunger sleeve is further formed with a leakage discharging passage configured for returning leaked fuel, which is leaked from the pressurizing chamber through a gap between the plunger and the plunger sleeve, back to the fuel tank completely.

2. The high-pressure fuel pump of claim 1 , wherein the at least one high-pressure assembly comprises two or more high-pressure assemblies, and the driving shaft comprises the same number of cams.

3. The high-pressure fuel pump of claim 1 or 2, wherein the fuel feeding hole in the plunger sleeve of the high-pressure assembly is connected to a branch feeding passage formed in a corresponding location in a casing of high-pressure fuel pump, and the branch feeding passage is connected to a common main feeding passage formed in the casing.

4. The high-pressure fuel pump of any one of claims 1 to 3, wherein the leakage discharging passage in the plunger sleeve of the high-pressure assembly is connected to a branch returning passage formed in a corresponding location in the casing.

5. The high-pressure fuel pump of claim 4, wherein the plunger sleeve is provided with a ring like collecting socket which surrounds the outer periphery of the plunger, the branch returning passage having one end connected to the corresponding collecting socket and another end connected to a common main returning passage which is formed in the casing and is in communication with the fuel tank.

6. The high-pressure fuel pump of claim 5, wherein the fuel feeding hole, the branch feeding passage and the main feeding passage are disposed in one side of the high-pressure assembly, and the leakage discharging passage, the branch returning passage and the main returning passage are disposed in the opposite side of the high-pressure assembly.

7. The high-pressure fuel pump of claim 5 or 6, wherein the main returning passage is in communication with the fuel tank via a duct formed inside the casing.

8. The high-pressure fuel pump of claim 5 or 6, wherein the main returning passage is in communication with the fuel tank via a pipe line disposed outside the casing, the main returning passage being connected with the pipe line by a fuel returning valve.

9. The high-pressure fuel pump of any one of claims 1 to 8, wherein the high-pressure fuel pump is a high-pressure pump for a diesel engine.

10. The high-pressure fuel pump of claim 9, wherein the high-pressure assembly is connected with a common rail for the diesel engine.