Abstract:
The present invention provides an axial plunger pump which does not need bellows by restricting fuel to a cylinder bore configuring a pump portion and by lubricating the other portion with oil. The high pressure fuel pump comprises a plunger reciprocating according to a shaking movement of a swash plate, a cylinder block forming a pump chamber together with the plunger, and a sealing member provided between the plunger and a cylinder bore for sealing oil leaked from the pump chamber to a chamber surrounding the pump chamber, wherein oil in the oil chamber is supplied from the outside of the high pressure fuel pump.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a fuel pump for supplying fuel to an internal combustion engine, particularly relates to a high pressure fuel pump used in a fuel injection system of so-called in-cylinder direct injection type of an internal combustion engine, the system directly injects fuel into a fuel chamber through a fuel injection valve attached to the fuel chamber. 
     DESCRIPTION OF THE PRIOR ART 
     A type of system which directly injects fuel to a combustion chamber of an internal combustion engine requires a high pressure fuel pump for increasing a pressure of fuel to be supplied to a fuel injection valve up to the pressure of 3 MPa or higher. 
     Such a high pressure pump has been known from JP-A- 9-236080  as an axial plunger pump. Conventionally, such a high pressure pump is configured so as to part a driving mechanism part lubricated with oil from a pump chamber compressing and discharging fuel by metal bellows. 
     Another conventional high pressure fuel pump is described in JP-A- 9-250447 . The pump is configured so as to circulate fuel up to the sliding part of the driving mechanism part, in the other word, lubricate the driving mechanism part with fuel. In this prior art, the sliding part is lubricated with fuel. 
     Such types of conventional high pressure pump have problems as follows; 
     (1) As for the former pump, the pomp has a large sized shape by using the metal bellows. In addition, the pump needs a sealing part at a mounting part of the bellows. Because of these points, the pump has a problem that it is difficult to miniaturize the pump. 
     (2) As for the latter pump, the bellows is not necessary. However, a lubricating condition of the driving mechanism part is hard since the sliding part is lubricated with fuel of a low viscosity. 
     The object of the present invention is to provide an axial plunger pump which does not need bellows and lubricates the driving mechanism part sufficiently. 
     Another object of the present invention is to allow the pump to use a rolling bearing for the driving mechanism. 
     SUMMARY OF THE INVENTION 
     In order to solve the problems, the present invention provides a high pressure fuel pump comprising a cup-shaped body; a cylinder block engaged with the cup-shaped body so as to close the opening side of the cup-shaped body; a rotation shaft supported at the bottom of the cup-shaped body and rotated by a driving source; a swash plate disposed in a driving mechanism chamber inside the cup-shaped body, which converts a rotating movement to a shaking movement; a plunger reciprocated in a cylinder bore formed in the cylinder block according to the shaking movement of the swash plate; a sealing element provided between the inside wall of the cylinder bore and the plunger; and an oil supply mechanism which supplies oil to the driving mechanism chamber. 
     According to further aspect of the present invention, it provides a high pressure fuel pump comprising: a cup-shaped body; a cylinder block engaged with the cup-shaped body so as to close the opening side of the cup-shaped body; a rotation shaft supported at the bottom of the cup-shaped body and rotated by a driving source; a swash plate disposed in a driving mechanism chamber inside the cup-shaped body, which converts a rotating movement to a shaking movement; a plunger reciprocated in a cylinder bore formed in the cylinder block according to the shaking movement of the swash plate; a sealing element provided between the inside wall of the cylinder bore and the plunger; an oil supply mechanism which supplies oil to the driving mechanism chamber; a low pressure side fuel passage formed in the cylinder block; and a low pressure fuel introducing passage formed in the plunger, which connects the low pressure side fuel passage with a pump chamber formed in the cylinder bore, the pump chamber varying its capacity according to the plunger reciprocating in the cylinder bore. 
     Moreover, the high pressure fuel pump may comprise a valve mechanism disposed between the low pressure side fuel passage and the pump chamber, which shut off the connection between the low pressure side fuel passage and the pump chamber when a pressure of the pump chamber is more than a defined pressure so that the sealing element is adopted to be acted by a pressure of the upper stream of the valve mechanism. 
     According to another aspect of the present invention, it provides 9 a high pressure fuel pump comprising: a shaft for transmitting a driving force from the outside; a cam converting a rotating movement of the shaft to a reciprocating movement; a plunger reciprocated by the cam; a cylinder bore formed in a cylinder block; a pump chamber formed by putting the plunger into the cylinder bore; a sealing element sealing a apace between the cylinder bore and the plunger; and an oil supply mechanism which supplies oil to the cam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a longitudinal section of a pump of a first embodiment according to the present invention; 
     FIG. 2 shows a structure of passages in a rear body of the first embodiment; 
     FIG. 3 is an explanation figure of strokes; 
     FIG. 4 shows an engine oil passage of the first embodiment; and 
     FIG. 5 shows an oil passage of a second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment is shown in FIGS. 1-4. 
     A coupling  2  for transmitting a driving force transmitted by a cam shaft of an engine connects with a shaft  1  through a pin  3 . The shaft  1  is integrated with a swash plate  9  which extends in the radial direction and has an end surface forming a slope. A slipper  10  contacts with the swash plate  9 . The slipper  10  is provided with a taper at its outer circumference portion in the swash plate  9  side for helping formation of an oil layer between the swash plate  9  and the slipper  10 . A hole  50  opening in the center of the slipper  10  connects the swash plate  9  side with the other side of the slipper  10  and forms a space for holding oil. The swash plate  9  takes a role to supply oil scraped by the swash plate  9  from the swash plate  9  side to the other side of the slipper  10 . The slipper  10  has a spherical shape in the other side thereof and is supported by a sphere formed on a plunger  11  which slides in a cylinder bore  13 . The rotating swash plate  9  causes a shaking movement which is converted to a reciprocating movement of the plunger  11 . 
     In the pump having the above described structure, suction and discharge of fuel are performed as follows. 
     A plurality of pump chambers  14  are formed in a cylinder block  12  by the cylinder bores  13  and the plungers  11 . An intake space  15  connected to respective plungers  11  is provided in the center of the cylinder block  12  to supply fuel to the pump chamber  14 . In order to introduce fuel to the intake space  15 , a fuel piping from the outside of the pump is connected to a rear body  20  so as to connect with the intake space  15  provided in the cylinder block  12  thorough an intake passage  43  of the rear body  20  and an intake chamber  30  in the center of the rear body  20 . 
     In the plunger  11 , an intake valve  24  (a check valve) is formed by a ball  21 , a spring  22 , and a stopper  23  supporting the spring  22 . A plunger spring  25  is installed to press always the plunger  11  toward the swash plate  9  side in order to allow the slipper  10  and the plunger  11  to follow the swash plate  9 . 
     A connecting passage A  16  toward an intake valve  24  in the plunger  11  is formed as the connecting passage between a spot facing  51  made in the cylinder bore and the intake space  15 . The spot facing  51  has a diameter larger than that of the cylinder bore  13  and is formed up to a depth allowing the spot facing  51  to connect with an introducing hole  19  for always introducing fuel to the inside of the plunger  11  even if the pump chamber  14  becomes fully smaller (when the plunger position is at a top dead center). 
     FIG. 3 is an illustrated figure of strokes and an enlarged figure of the plunger  11 . In an intake stroke (a stroke in which the plunger  11  moving in a direction to increase a space of the pump chamber  14 ), the intake valve  24  installed in the plunger  11  is opened to introduce fuel into the pump chamber  14  when a pressure inside the pump chamber  14  installed in the plunger  11  reduces up to a pressure below a defined pressure. In this structure, when a discharge stroke (a stroke in which the plunger  11  moving in a direction to decrease the space of the pump chamber  14 ) has been started, fuel introduced into the pump chamber  14  during the intake stroke is sent out from the pump chamber  14  to a discharge chamber  29  installed in the rear body  20  by opening a discharge valve  28  comprising a ball  26  and a spring  27  at the time that a pressure of the pump chamber  14  comes to a defined pressure, as well as the intake valve  24 . An intake chamber  30  and the discharge chamber  29  which are installed in the rear body  20  are partitioned with an  0 -ring  31 , and the intake chamber  30  is installed nearer the center than the discharge chamber  29  so as to make the structure of the passage of the pump itself compact. 
     In the description stated before, a pressure of the discharge chamber  29  can be regulated to an optimal pressure with a pressure regulating valve  40  (a pressure regulator: hereafter stated as P/Reg) installed in a passage connected to the discharge chamber  29 . The purpose for regulating the discharge pressure is to regulate an additional pressure applied to an injector (not illustrated) installed in the downstream of the discharge side. A high pressure fuel passed from a high pressure chamber of the rear body  20  to P/Reg  40  is passed through a ball valve  41  installed in P/Reg  40  and passed through connecting passage B  42  installed in the rear body  20  to return to the intake chamber  30 . An intake passage  43 , the intake chamber  30 , the intake space  15 , and the connecting passage A  16  form a passage for supplying fuel from a fuel source to respective cylinders. 
     As described above, a pressure inside the pump chamber  14  also changes from a intake pressure (generally, from 0.2 MPa to 0.5 MPa) to a pressure of the high pressure chamber (generally, from 3 MPa to 20 Mpa). A load generated by a fuel pressure of the pump chamber is transmitted to the swash plate  9  of the shaft  1  via the plunger  14  and the slipper  10 . This means that the resultant of force loads of a plurality of the plungers  11  acts on the swash plate  9 . The resultant of forces acts as a radial load according to a load in the direction of the shaft and an angle of the swash plate. The present invention has the structure that the shaft  1  is engaged with a radial bearing  7  and the thrust bearing  8  to support its load by the body  5  for supporting these loads and achieving a smoothed rotation. 
     Parts (slipper  10 /swash plate surface  9 , slipper  10 /plunger sphere, and bearing parts) supporting these loads are the parts supporting a relative speed and loads by rotation, and sliding wear can be reduced by oil lubrication. For this purpose, the structure is required to trap oil by a swash plate chamber  38  formed between the body  5  and the cylinder  12 . 
     In this embodiment, a shaft seal  17  for sealing fuel and oil during reciprocating movement of the plunger  11  is installed in the cylinder  12 . This shaft seal  17  seals a gap between the plunger  11  and the cylinder bore  13 . The shaft seal A  17  seals fuel and oil. The present embodiment has a structure in which a pressure acting on the shaft seal A  17  is always the intake pressure of a low pressure to allow no application of a pressure of the high pressure chamber against the shaft seal  17  because an intake passage  43  exists between the shaft seal  17  and the pump chamber  14 . By this reason, durability and reliability of the shaft seal  17  increase. 
     The following is an explanation of a circulation passage and a circulation method of oil. The structure of the example is that a shaft  1  through which a shaft seal  35  and a coupling  2  are penetrated is engaged with a coupling engaging part  33  of the engine cam  6  which is provided with an oil passage  34  in its shaft center, so that oil is introduced from an engine through a connecting passage  4  to the swash plate chamber  38  installed in the center of the shaft  1 . The shaft seal  35  seals oil incompletely in a degree to allow necessary minimum flow from the engine side to a swash plate chamber  38 . By this, an eccentric load on the driving shaft via the shaft seal  35 , which is caused by a distance of centers of the shaft  1  and the engine cam  6 , can be suppressed in a maximum degree, so that durability of the radial bearing  7  is improved. In addition, since oil flowing into the swash plate chamber  38  is controlled as the necessarily minimized flow, rise of temperature of the swash plate chamber  38  is suppressed and oil diluted with fuel leaked to the swash plate chamber  38  from the shaft seal  17  is replaced. Further, since the purpose is accomplished by introducing oil from the center of the shaft  1  without installation of a new oil passage in the engine side, fitness to the engine and miniaturization of the engine are accomplished. 
     In this embodiment, oil is introduced from a connecting passage  4  installed in the center of the shaft. Notwithstanding, the place is not restrictive if the passage for introducing oil is installed to connect the source of an oil pressure of the engine to the swash plate chamber  38  of the pump. 
     The following is a description of a passage to return oil, which is supplied from the engine to the swash plate chamber  38 , to the engine. This passage comprises a return passage  36  from the swash plate chamber  38  to the engine cam chamber  39 . The return passage  36  is installed in a coupling  2  side of the surface of a flange  37  installed in the body  5  of the pump to be attached to the engine. By this, oil in the swash plate chamber  38  can be returned to the engine without installing a special passage in the engine side. The return passage  36  is installed in a level higher than a sliding surface between the swash plate  9  and the slipper  10 . By this, if vapor occurs, the vapor is discharged from the return passage  36  to the engine cam chamber  39  to lubricate always the sliding surface with oil. The diameter of the return passage  36  is set larger than that of the connecting passage C 4  for introducing oil. By this, the quantity of oil flowing out from the swash plate chamber  38  does not become lower than the quantity of oil flowing in, and the pressure of the inside of the swash plate chamber  38  does not rise, so that reliability of the shaft seal  17  is increased. 
     The pressure of the inside of the swash plate chamber  38  does not rise to become always lower than an intake pressure of fuel. By this, leak of oil to the fuel side can be prevented. As well, the plunger  11  received always a force toward the swash plate so as to reduce a load on the plunger spring  25 . The relations between pressures of respective parts are thus expressed by the following equation. 
     
       
         Intake fuel pressure≧oil chamber pressure; 
       
     
     and 
     
       
         oil pressure supplied from engine≧oil chamber pressure. 
       
     
     FIG. 5 shows a second embodiment in which an oil introducing passage  44  is installed to introduce oil positively from the engine. The oil introducing passage  44  is installed in the body  5  and a constriction  45  is installed in the middle thereof. The pressure of oil-introducing side has been increased than that of the swash plate chamber  38 . Installing the constriction  45  suppresses an excessive oil flow with a high temperature to prevent heating of fuel. Besides, a return passage  46  is installed in the body  5  to return oil from the swash plate chamber  38  to the engine cam chamber  39 . The return passage  46  is installed in a level higher than a sliding surface between the swash plate  9  and the slipper  10 . By this, if vapor occurs, the vapor is discharged from the return passage  46  to the engine cam chamber  39  to always lubricate the sliding surface with oil to increase reliability. 
     According to the features described above, the main body of the pump can be miniaturized since the pump requires no member such as bellows for insulating an oil circulating part from a fuel circulating part, and no sealing member installed at a part to which bellows is attached. Further, because the sliding part is lubricated with oil, a rolling bearing can be used as a bearing. Thus, a friction resistance is reduced, so that a driving torque can be decreased. 
     Furthermore, because an existing oil passage of an engine can be used since an oil-introducing passage is installed on an axis of a cam shaft, no exclusive passage is required. Therefore, fitness to the engine is improved and also the miniaturization of the pump can be accomplished.