EP1323919B1

EP1323919B1 - Fuel pump

Info

Publication number: EP1323919B1
Application number: EP20020026932
Authority: EP
Inventors: Naoki Yamamoto
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2001-12-28
Filing date: 2002-12-03
Publication date: 2009-11-04
Anticipated expiration: 2022-12-03
Also published as: JP2003201934A; EP1323919A3; EP1323919A2; DE60234240D1; JP3815324B2

Description

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates in general to fuel pressure pumps of internal combustion engines, and more particularly to the fuel pressure pumps of a type that allows a sealing member installed therein to exhibit an excellent performance against a fuel leakage.

2. Description of Related Art

In fuel injection type internal combustion engines wherein fuel is directly injected into cylinders, it is necessary to increase the pressure of fuel to a sufficiently high level (viz., 5 to 15Mpa) before it is led to each injection valve (viz., fuel injector). For this purpose, a mechanical type fuel pressure pump connected to a camshaft has been hitherto used widely. In this fuel pressure pump, a pump driving cam is mounted on the camshaft to reciprocate a corresponding plunger that is slidably received in a cylinder to provide an end of the cylinder with a pressure chamber. That is, upon movement of the plunger in the cylinder in a direction to reduce the volume of the pressure chamber, a fuel in the pressure chamber is pressurized and led into injection valves of the engine. In the fuel pressure pumps of this type, there are employed a sealing member for suppressing a fuel leakage and a fuel return passage for returning a surplus fuel back to a fuel pump. Furthermore, in order to suppress the seal member from being directly affected by a pressure fluctuation produced during exhaust stroke of the pump, there is usually employed a fuel by-pass system through which a fuel holding space formed near the seal member and the fuel return passage are connectable. That is, upon production of excessive pressure fluctuation, the fuel by-pass system becomes opened to relieve the pressure from the pressure chamber.
Laid-open Japanese Patent Application (Tokkal) 2000-110685 shows a fuel pressure pump of a so-called return-less type that has no means corresponding to the above-mentloned fuel return passage.
However, it has been revealed that the fuel pressure pump of the application fails to exhibit a satisfied performance. That is, it often happens that a seal member used therein shows a non-negligible deterioration In a short period of time.
US-A-2 372 694 according to the preamble of claim 1, discloses a high pressure fluid pump for use in fuel injection systems for internal combustion engines, comprising a plunger bore in which a plunger is slidably received. At the upper end of the plunger bore, a pressure chamber is defined for pressing the fluid when the plunger is moved in the upper direction. A low pressure fluid passage communicating with communication passages is provided for supplying fluid through a passage inside the plunger to the pressure chamber. A seal member is provided to seal a leakage recess defining a fluid holding space. The communicating passage connects the leakage recess to the low pressure fluid passage.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fuel pressure pump of an internal combustion engine, which is superior to the fuel pressure pump proposed by the above-mentioned application.
This object is solved by the features of claim 1.
That is, according to the present invention, there is provided a fuel pressure pump of an internal combustion engine, which exhibits an excellent fuel leakage suppression performance irrespective of employment of the return-less type.
Further improvements are laid down in the subclaims.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a schematic view of a fuel supply system to which a fuel pressure pump of the present invention is practically applied;
Fig. 2 is a sectional view of a fuel pressure pump of the present invention;
Figs. 3A, 3B and 3C are sectional views showing three examples of a second fuel holding space possessed by the fuel pressure pump of the present invention;
Fig. 4 is a graph showing a fuel pressure appearing at various portions in the fuel pressure pump of the present invention;
Fig. 5 is a view similar to Fig. 2, but showing a first fuel holding space that is larger than that of Fig. 2;
Fig. 6 is a view also similar to Fig. 2, but showing a plurality of second fuel holding spaces possessed by the fuel pressure pump of the invention; and
Fig. 7 is a view also similar to Fig. 6, but showing that a volume of the second fuel holding spaces gradually increases with increase of distance from a pressure chamber.

DETAILED DESCRIPTION OF INVENTION

In the following, a fuel pressure pump of the present invention will be described in detail with reference to the accompanying drawings.
Referring to Fig. 1, there is shown a fuel supply system 1 to which a fuel pressure pump 4A of a first embodiment of the invention is practically applied.
As shown, fuel supply system 1 generally comprises a fuel tank 2, a low pressure fuel pump unit 3, a fuel pressure pump 4A, injectors 5 and an engine control unit 6. Low pressure fuel pump unit 3 and fuel pressure pump 4A are connected through a low pressure fuel passage 7, and fuel pressure pump 4A and injectors 5 are connected through a high pressure fuel passage 8.
Low pressure fuel pump unit 3 is installed in fuel tank 2 and comprises a fuel feed pump 31, a fuel filter 32 and a low pressure regulator 33.
Feed pump 31 functions to discharge fuel from fuel tank 2, and fuel filter 32 functions to filtrate fuel discharged from fuel tank 2. As shown, low pressure regulator 33 is arranged to bypass the line including feed pump 31 and fuel filter 32 and functions to regulate the fuel pressure to a fixed lower pressure.
As is seen from Figs. 1 and 2, fuel pressure pump 4A comprises a pump proper 41, an electromagnetic valve 42 and a discharge check valve 43.
As is seen from Fig. 2, pump proper 41 comprises a pump housing 44 mounted on a cylinder head or the like of an engine. Pump housing 44 is provided with a cylinder 441.
Within cylinder 441, there is slidably received a cylindrical plunger 45. Thus, there is defined a pressure chamber 442 between a closed upper end of cylinder 441 and a top surface 45a of cylindrical plunger 45. A tappet 46 is connected to a lower end of plunger 45. A return spring 47 is compressed between tappet 46 and pump housing 44 to constantly bias cylindrical plunger 45 downward in Fig. 2. Below tappet 46, there is arranged a camshaft 9 which has a pump driving cam 9a that can abut against tappet 46. Thus, upon rotation of camshaft 9, plunger 45 is forced to make a reciprocating movement in directions (Y-Y') to pressurize fuel in pressure chamber 442. More specifically, pressurizing of fuel in pressure chamber 442 is achieved when plunger 45 is lifted upward to reduce the volume of pressure chamber 442.
Pump housing 44 is formed with both a first fuel supply passage 443 that is connected to low pressure fuel passage 7 and a second fuel supply passage 444 that is connected to high pressure fuel passage 8. First fuel supply passage 443 is connected to pressure chamber 442 through a fuel inlet passage 445, while, second fuel supply passage 444 is connected to pressure chamber 442 through a fuel outlet passage 446.
Fuel inlet passage 445 through which first fuel supply passage 443 and pressure chamber 442 are connected is selectively opened and closed by electromagnetic valve 42. This electromagnetic valve 42 comprises a valve head 421 that faces fuel inlet passage 445, a return spring 423 that biases valve head 421 in a direction to close fuel inlet passage 445 and a solenoid 422 that, when energized, pushes valve head 421 in a direction to open fuel inlet passage 445 against force of return spring 423.
Within second fuel supply passage 444, there is installed discharge check valve 43 that selectively opens and closes fuel outlet passage 446 that connects second fuel supply passage 444 and pressure chamber 442. That is, when the fuel pressure in pressure chamber 442 becomes higher than that appearing in high pressure fuel passage 8, discharge check valve 43 is forced to open fuel outlet passage 446.
In a lower portion of pump housing 44, there is formed an auxiliary cylindrical chamber 447 that is merged and coaxial with a chamber of cylinder 441. As shown, this auxiliary cylindrical chamber 447 is larger in diameter than the chamber of cylinder 441.
Within auxiliary cylindrical chamber 447, there is arranged a seal member 48. Seal member 48 comprises generally paired sealing lips 48a that are made of a rubber material and a supporting piece 48b that is fixed to the inner surface of auxiliary cylindrical chamber 447 to support the paired sealing lips 48a. As shown, tips of sealing lips 48a are elastically pressed against a cylindrical outer surface of cylindrical plunger 45 to achieve a hermetical sealing between the cylindrical inner surface of auxiliary cylindrical chamber 447 and the cylindrical outer surface of cylindrical plunger 45. With this sealing, pressurized fuel in pressure chamber 442 is suppressed from being leaked to the outside and at the same time, lubrication oil lubricating camshaft 9 is suppressed from being led into the chamber of cylinder 441.
As is seen from Fig. 2, in pump housing 44, there is formed a first fuel holding space 448 that is defined essentially by the cylindrical inner surface of cylinder 441, the cylindrical outer surface of plunger 45 and seal member 48. More specifically, first fuel holding space 448 is defined by an inner surface of auxiliary cylindrical chamber 447, an outer surface of cylindrical plunger 45 and seal member 48.
Furthermore, at a mutually contacting area between the cylindrical inner surface of cylinder 441 and the cylindrical outer surface of plunger 45, there is defined a second fuel holding space 449 that is arranged to extend around cylindrical plunger 45, as shown.
Figs. 3A, 3B and 3C show three examples of the second fuel holding space 449, respectively. In the first example of Fig. 3A, the second space 449 is defined by an annular groove 441a that is formed in the cylindrical inner surface of cylinder 441. In the second example of Fig. 3B, the second space 449 is defined by an annular groove 45a that is formed around cylindrical plunger 45, and in the example of Fig. 3C, the second space 449 is defined by both an annular groove 441a formed in the cylindrical inner surface of cylinder 441 and an annular groove 45a formed around cylindrical plunger 45.
Referring back to Fig. 2, in pump housing 44, there are further formed a first connection passage 450 that connects first fuel holding space 448 and first fuel supply passage 443 and a second connection passage 451 that connects second fuel holding space 449 and first fuel supply passage 443.
As is seen from Fig. 1, injectors 5 are connected to respective cylinders of the engine, and each injector 5 is controlled to assume an open position upon receiving a pulse signal that is applied thereto at a given injection timing. During open period, each injector 5 injects a pressure-controlled pressurized fuel into a combustion chamber of the corresponding cylinder. Remaining fuel that is not injected is returned to fuel tank 2 through a relief passage 10 and a relief valve 11.
Engine control unit 6 carries out various operation controls for engine, such as fuel injection control and the like by processing various information signals fed thereto from various sensors such as a fuel pressure sensor 13 connected to high pressure fuel passage 8. That is, fuel feed pump 31, electromagnet valve 42 and injectors 5 are all controlled by instruction signals issued from engine control unit 6.
In the following, operation of fuel pressure pump 4A will be described with the aid of Figs. 1 and 2.
As is seen from Fig. 1, fuel in fuel tank 2 is controlled to have a given lower pressure and led into low pressure fuel passage 7 by low pressure fuel pump unit 3.
As is seen from Fig. 2, in an intake stroke of pressure pump 4A wherein cylindrical plunger 45 is moved down (viz., in the direction of arrow Y') due to escape of pump driving cam 9a from tappet 46, electromagnetic valve 42 is controlled to assume its open position so that the lower pressure fuel is led into pressure chamber 442 through first fuel supply passage 443. Under this condition, the fuel pressure in high pressure fuel passage 8 (see Fig. 1) is kept higher than that led into pressure chamber 442, and thus discharge check valve 43 assumes a close position.
In discharge stroke of pressure pump 4A wherein plunger 45 is moved upward (viz., in the direction of arrow Y) due to work of pump driving cam 9a, electromagnetic valve 42 is controlled to assume its close position. That is, solenoid of valve 42 is de-energized. It is to be noted that a fuel feeding rate of pressure pump 4A is controlled by controlling a valve open timing of electromagnetic valve 42.
After electromagnetic valve 42 assumes its close position, fuel in pressure chamber 442 is pressurized due to upward movement of plunger 45. Thus, when the pressure in pressure chamber 442 comes to a certain high value, discharge check valve 43 is forced to open and thus highly pressurized fuel is discharged toward injectors 5 through high pressure fuel passage 8.
In this discharge stroke, the pressure produced in pressure chamber 442 shows such a characteristic as shown in the graph of Fig. 4. That is, as is seen from this graph and Fig. 2, the fuel pressure in pressure chamber 442 is inevitably leaked to the first fuel holding space 448 of seal member 48 through a clearance that is defined between the cylindrical inner surface of cylinder 441 and the cylindrical outer surface of plunger 45 while being attenuated.
In the graph of Fig. 4, reference P1 denotes the fuel pressure appearing in an inlet portion of first fuel supply passage 443 (see Fig. 2), P2 denotes the fuel pressure appearing in pressure chamber 442, P3 denotes the fuel pressure appearing in a mutually contacting portion between cylinder 441 and plunger 45 at a position nearer to pressure chamber 442 than second fuel holding space 449, P4 denotes the fuel pressure appearing in a mutually contacting portion between cylinder 441 and plunger 45 at a position nearer to camshaft 9 than second fuel holding space 449, and P5 denotes the fuel pressure appearing in first fuel holding space 448.
As has been mentioned hereinabove, first fuel holding space 448 and first fuel supply passage 443 are connected through first connection passage 450. Thus, the pressure (viz., pressure wave) appearing in pressure chamber 442 is inevitably exposed or led to first fuel supply passage 443, so that much higher pressure reduction effect (viz., P4 ⇒ P5) is carried out as compared with a case (viz., P4' ⇒ P5') wherein there is no means corresponding to first connection passage 450, that is, first fuel holding space 448 has a closed end.
Thus, seal member 48 is suppressed or at least minimized from being affected by a pressure fluctuation produced in pressure chamber 422, and thus, durability of seal member 48 is increased.
If first fuel holding space 448 is constructed to have a sufficiently large volume, damping effect is much effectively made, which brings about a much effective pressure reduction effect.
That is, as is shown in Fig. 5 that shows a second embodiment of the present invention, the diameter "D" of first fuel holding space 448 is greater than the outer diameter "Ds" of seal member 48. With this measure for increasing the volume of first fuel holding space 448, the mutually contacting portion between cylinder 441 and plunger 45 can have a sufficient length "L" and thus undesirable inclination of plunger 45 relative to cylinder 441 is suppressed and thus a so-called one-sided wearing therebetween is suppressed or at least minimized.
Furthermore, in this case, the fuel in first fuel holding space 448 can smoothly circulate through the passage without gathering therein, and thus, seal member 48 is suppressed from being heated. That is, sealing lips 48a of seal member 48 are protected from a thermal deterioration.
Furthermore, in this case, there is provided, at the mutually contacting portion between cylinder 441 and plunger 45, second connection passage 451 that connects second fuel holding space 449 and first fuel supply passage 443. Accordingly, the second connection passage 451 functions to expose the pressure wave to first fuel supply passage 443. Accordingly, much higher pressure reduction effect (P3 ⇒ P4) is carried out as compared with a case (P3 ⇒ P4') wherein there is no means corresponding to second connection passage 451.
For the reasons as have been mentioned hereinabove, the seal member 48 is suppressed from being affected by the pressure fluctuation and thus, the seal member 48 can have a longer life.
In the above-mentioned fuel pressure pump 4A, there is provided second fuel holding space 449 at the mutually contacting portion between cylinder 441 and plunger 45, in addition to first fuel holding space 448 that is defined by cylinder 441, plunger 45 and seal member 48.
However, if possible, as is seen from Fig. 6 which shows a third embodiment 4C of the invention, a plurality of second fuel holding spaces 449a, 449b and 449c may be provided in place of the single second fuel holding space 449. In this case, respective connection passages 451a, 451b and 451c are provided for connecting the spaces 449a, 449b and 449c with first fuel supply passage 443, as shown.
Due to provision of such plurality of fuel holding spaces 449a, 449b and 449c, the pressure reduction effect is much effectively achieved. Furthermore, because of the same reason, heat radiation area of pump housing 44 against fuel in the housing 44 is increased and thus cooling effect of the engine onto which the housing 44 is mounted is increased. Thus, durability of seal member 48 is increased.
Furthermore, if possible, as is seen from Fig. 7 which shows a fourth embodiment 4D of the invention, the volume of the three second fuel holding spaces 449'a, 449'b and 449'c may gradually increase with increase of distance from pressure chamber 442. In this disclosed embodiment 4D, the depth "d" of annular grooves 441a formed in the cylindrical inner surface of cylinder 441 increases with increase of distance from pressure chamber 442. However, if possible, the width "w" of annular grooves 441a may increase with increase of distance from pressure chamber 442, or such grooves may be provided in the cylindrical outer surface of plunger 45.

Claims

A fuel pressure pump (4A, 4B, 4C, 4D) for use with an internal combustion engine, comprising:
a cylinder (441);

a plunger (45) slidably received in the cylinder to define at one end of the cylinder (441) a pressure chamber (442), the pressure chamber (442) pressing a fuel therein when the plunger (45) moves in a direction to reduce a volume of the pressure chamber (442);

a fuel supply passage (443) through which the fuel is led to the pressure chamber (442);

a seal member (48) provided at a position other than a position where an inner surface of the cylinder (441) and an outer surface of the plunger (45) are slidably engaged, the seal member (48) achieving a hermetical sealing between the inner surface of the cylinder (441) and the outer surface of the plunger (45); and

a first fuel holding space (448) defined by the inner surface of the cylinder (441), the outer surface of the plunger (45) and the seal member (48), and

a first connection passage (450) that connects the first fuel holding space (448) and the fuel supply passage (443),
characterized by

a fuel inlet passage (445) through which the fuel supply passage (443) and the pressure chamber (442) are directly connected; and

an electromagnetic valve (42) having a valve head (421), the valve head (421) being arranged to selectively close and open the fuel inlet passage (445).
A fuel pressure pump as claimed in claim 1, characterized by a second fuel holding space (449) defined at the position where the inner surface of the cylinder (441) and the outer surface of the plunger (45) are slidably engaged, the second fuel holding space (449) being larger in volume than a space defined between the inner surface of the cylinder (441) and the outer surface of the plunger (45); and
a second connection passage (451) that connects the second fuel holding space (449) and the fuel supply passage (443).
A fuel pressure pump as claimed in claim 2, characterized in that the second fuel holding space (449) comprises a plurality of holding spaces (449a, 449b, 449c) that are arranged around at axially different portions of the plunger (45) respectively, each holding space (449a, 449b, 449c) being connected to the fuel supply passage (443) through a corresponding connection passage (451 a, 451 b, 451 c).
A fuel pressure pump as claimed in claim 3, characterized in that a volume of the plurality of holding spaces (449a, 449b, 449c) increases with increase of distance from the pressure chamber (442).
A fuel pressure pump as claimed in one of claims 1-4, characterized in that the inner surface of the cylinder (441) is cylindrical in shape and the outer surface of the plunger is cylindrical in shape, so that the first and second holding spaces (448, 449) are annular in shape.
A fuel pressure pump as claimed in claim 5, characterized in that the seal member (48) is annular in shape, and the first fuel holding space (448) has an outer diameter (D) that is greater than an outer diameter (Ds) of the annular seal member (48).
A fuel pressure pump as claimed in claim 1 or 2, characterized in that the second fuel holding space (449) is defined by a groove (441 a) that is formed in the inner surface of the cylinder (441).
A fuel pressure pump as claimed in claim 1 or 2, characterized in that the second fuel holding space (449) is defined by a groove (45a) that is formed in the outer surface of the plunger (45).
A fuel pressure pump as claimed in claim 1 or 2, characterized in that the second fuel holding space (449) is defined by:
a groove (441a) that is formed in the inner surface of the cylinder (441); and

a groove (45a) that is formed in the outer surface of the plunger (45).
A fuel pressure pump as claimed in one of claims 1-9, characterized by a fuel outlet passage (446) through which the pressure chamber (442) is connected to fuel injectors (5) of the engine; and
a check valve (43) arranged to selectively close and open the fuel outlet passage (446), the check valve (43) being biased in a direction to close the fuel outlet passage (446) against a fuel pressure produced in the pressure chamber (442).
A fuel pressure pump as claimed in one of claims 1-10, characterized by a tappet (46) connected to the plunger (45) to move therewith;
a spring (47) incorporated with the plunger (45) to bias the plunger (45) in a direction to increase the volume of the pressure chamber (442); and
a pump driving cam (9a) disposed on a camshaft (9) of the engine, the driving cam (9a) being able to push the tappet (46) in a direction to reduce the volume of the pressure chamber (442) when the camshaft (9) rotates.