Patent Document

TECHNICAL FIELD 
     The present invention relates to a fuel injection pump that supplies fuel to an internal combustion engines. More specifically, it relates to a fuel injection pump having plungers and a cam shaft which is rotatably supported via radial bearings and drives the plungers, with a feed pump for delivering the fuel having been pressurized by the plungers installed therein. 
     BACKGROUND ART 
     The cam shaft of a fuel injection pump in the related art is supported at a bearing housing secured at a pump housing by utilizing a tapered roller bearing having a tapered roller constituting the rolling element or the like, so as to enable an accurate shim adjustment to set the clearance along the axial direction. Normally, the housing is constituted of an aluminum alloy to achieve a reduction in weight, and the cam shaft is constituted of steel to achieve good wear resistance. For this reason, when the cam shaft and the housing become heated, the difference between their coefficients of thermal expansion results in an increase in the clearance along the direction of the axis of the cam shaft, which, in turn, causes play when force is applied along the axial direction. Such play gives rise to problems of failure to achieve accurate injection characteristics and noise. Japanese Unexamined Patent Publication No. S 62-26372 and Japanese Unexamined Patent Publication No. H 2-42173, for instance, propose cam shaft supporting structures addressing these problems. 
     The first publication discloses a structure having a thrust bearing for the cam shaft formed as a fixed bearing that functions along the two axes, and a radial bearing formed as a movable bearing. More specifically, it discloses a structure achieved by forming the radial bearing as a cylindrical roller bearing provided inside a bearing cover so as to allow play of the cam shaft along the axial direction and by forming the axial bearing as a bearing plate. The axial bearing, together with a bearing cover, is tightly secured to the pump housing with screws with its internal circumferential edge connected inside a ring groove formed at the cam shaft. Another structure is achieved by forming the radial bearing as a cylindrical roller bearing provided within a bearing cover in a similar manner, and forming the bearing as a bearing having a bearing cover connected in a ring groove formed by the gap between an end surface of the cam shaft and a nut that screws into the end surface via a bearing plate. 
     These structures allow the cam shaft to be supported individually along the axial direction and along the radial direction so as to eliminate the need to use a tapered roller bearing. 
     In addition, the second publication discloses a structure achieved by providing a thrust bearing secured to the housing between two cams so as to achieve an accurate support while minimizing the wear of the bearings in a pump having a large number of cylinders requiring that the cam shaft has a large length. This structure, too, achieves an advantage of supporting the cam shaft individually along the axial direction and along the radial direction. 
     However, in the structures disclosed in the first publication, the position of the cam shaft along the axial direction is regulated by connecting the race member of the thrust bearing in the ring groove of the cam shaft on one side and linking the race member to the pump housing on the other side so as not to allow any movement of the race member on the other side. In the structure disclosed in the second publication, the axial position is adjusted by providing a thrust slide bearing secured to the housing. Since the position of the cam shaft along the axial direction is regulated by providing a slide bearing formed as a separate member in any of these structures, the number of required parts is bound to be large and, at the same time, the clearance along the axial direction must be adjusted in conformance to the extent to which the thrust bearing has become worn. In addition, since the slide bearing formed as a separate member must be provided along the axis of the cam shaft, the length of the cam shaft along the axis cannot readily be reduced, which presents a hindrance to achieving miniaturization of the injection pump. Accordingly, an object of the present invention is to provide a fuel injection pump that facilitates the assembly process, achieves a reduction in the number of required parts, and allows miniaturization by utilizing an existing member mounted at the pump instead of a separate bearing member for regulating the position of the cam shaft along the axial direction and eliminating the need for adjusting the gap along the axial direction which would otherwise be required to be adjusted in conformance to the extent to which the bearing has become worn. 
     SUMMARY OF THE INVENTION 
     An adoption of the present invention in practical application is realized as a result of the research and development conducted by the inventor based upon the concept that since a standard fuel injection pump includes a feed pump for feeding fuel pressurized by the plungers as an integrated part of the fuel injection pump assembly and the feed pump is driven by the cam shaft, the axial bearing formed as a separate member can be eliminated by regulating the position of the cam shaft along the axial direction with the existing component. 
     Namely, the fuel injection pump according to the present invention has plungers and a cam shaft that is rotatably supported via a radial bearing along the radial direction and drives the plungers with a feed pump for feeding fuel pressurized by the plungers installed therein. A flange part projects along the radial direction at the cam shaft, and a power transmission member that transmits a motive force to the feed pump is provided at an end of the cam shaft on a side opposite from the end of the cam shaft which is driven. The portion that rotatably supports the cam shaft via the radial bearing is held between the flange part and the power transmission member to adjust the axial position of the cam shaft. 
     Since the portion that supports the cam shaft along the radial direction is held between the flange part formed at the cam shaft and the power transmission member that is provided at the end on the opposite side from the end on the driven side and transmits the motive force to the feed pump, and since the axial position of the cam shaft is adjusted through this structure, the need for providing a special member for regulating the axial position is eliminated. As a result, since the axial position adjustment can be achieved without having to employ a thrust bearing, it becomes unnecessary to adjust the clearance in conformance to the extent of wear of the thrust bearing. At the same time, as the axial position of the cam shaft is regulated in reference to the portion held between the flange part and the power transmission member, an accurate support is achieved along the axial direction at all times and is unaffected by any changes in the temperature. In addition, since the axial position is regulated by utilizing the existing member provided to drive the feed pump instead of providing a special member along the axial direction, the absence of such a special member along the axial direction allows the dimension along the axial dimension to be reduced. 
     In this structure, the radial bearing at the cam shaft may be formed of a cylindrical roller bearing which uses a cylindrical roller as a rolling element, or the radial bearing may be formed of a plane bearing. In the latter case, the dimension of the cam shaft along the radial direction, too, can be reduced. At the same time, the process for assembling the cam shaft is facilitated, thereby allowing the injection pump to be manufactured at low cost. 
     Furthermore, since the pump housing is normally formed of a separate housing member, this housing member may be used as the portion that rotatably supports the cam shaft via the radial bearing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially notched sectional view of the fuel injection pump, according to the present invention; 
     FIG. 2 is an enlarged sectional view of the cam shaft and the feed pump in the fuel injection pump shown in FIG. 1; 
     FIG. 3 is a sectional view taken along A—A in FIG.  1  and FIG. 2; 
     FIG. 4 is a perspective view of the cam shaft and the feed pump employed in the fuel injection pump according to the present invention; and 
     FIG. 5 is a system operation diagram of the fuel injection pump according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following is an explanation of an embodiment of the present invention, given with reference to the drawings. FIGS. 1 through 3 show a fuel injection pump formed by assembling a supply pump  1 , a fuel metering unit (FMU)  2  and a feed pump  3 . 
     The supply pump  1  comprises plungers  4 , plunger barrels  5 , tappets  6  and a cam shaft  7 , with the cam shaft  7  supported at a pump housing  8  and one end of the cam shaft projecting out through the pump housing  8  to receive drive torque from an engine (not shown) so that the cam shaft  7  rotates in synchronization with the engine. 
     The pump housing  8  includes a housing member  8   a  having longitudinal holes  10  in which the plunger barrels  5  are fitted, and housing members  8   b  and  8   c  that are secured to the housing member  8   a  with bolts or the like and that rotatably hold the cam shaft  7  near the two ends thereof. 
     In this example, two longitudinal holes  10  are formed in the housing member  8   a , and the plunger barrels  5  are each secured to the housing member  8   a  inside one of the longitudinal holes with the plungers  4  inserted in the plunger barrels  5  so as to move reciprocally within the plunger barrels. 
     In addition, the cam shaft  7  is supported by the housing members  8   b  and  8   c  near the two ends thereof via radial bearings  11  and  12  so as to allow play along the axial direction, and two drive cams  13  and  14  each provided for one of the plungers are formed on the cam shaft  7  between the radial bearings at phases offset from each other. 
     The lower ends of the plungers  4  are placed in contact with the drive cams  13  and  14  formed at the cam shaft  7  via the tappets  6 , and springs  17  are each mounted between a spring receptacle  15  provided at the housing member  8   a  and a spring receptacle  16  provided at the bottom of the corresponding plunger  4  so that when the cam shaft  7  rotates, the plungers  4  are allowed to engage in reciprocal movement along the contours of the drive cams  13  and  14  in cooperation with the springs  17 . 
     At the top of each of the plunger barrels  5 , an IO valve (inlet) /outlet valve)  20  mounted between the plunger barrel  5  and a delivery valve holder  19  is provided. A plunger chamber  21  is formed between the IO valve  20  and each of the plungers  4 , and a fuel outlet  22  formed at the delivery valve holder  19  is set above the IO valve  20 . 
     Each IO valve  20  in this structure, which supplies the fuel fed from the fuel metering unit (FMU)  2  that is to be detailed later to the plunger chambers  21  and sends out the fuel having been compressed by the plungers  4  through the fuel outlet  22  so that the fuel does not flow back to the FMU  2 , includes a valve body  23  mounted at an upper portion of the plunger barrels  5 , an inlet valve  25  having a first end communicating with the FMU  2  while the other (second) end thereof opens/closes a fuel passage  24  that in formed at the valve body  23  and communicates with the plunger chambers  21 . The inlet valve  25  imparts a constant force to hold the fuel passage  24  closed by utilizing the force applied by the FMU  2  in resistance against the fuel pressure. Outlet valve  27  has a first end communicating with the plunger chamber  21  while the other (second) end thereof opens/closes a fuel passage  26  communicating with the fuel outlet  22 , and imparts a constant force to hold the fuel passage  26  closed by utilizing the force applied from the plunger chambers  21  in resistance against the fuel pressure. As the plunger  4  descends, the outlet valve  27  closes, thereby allowing the fuel from the FMU  2  to push up the inlet valves  25  and thus causing the fuel to flow into the plunger chambers  21 . As the plunger  4  ascends, the pressurized fuel closes the inlet valve  25  to push up the outlet valve  27  thereby forcibly feeding the fuel through the fuel outlet  22 . 
     In the fuel metering unit (FMU)  2 , which feeds the fuel fed from the feed pump  3  that is to be detailed later to the IO valve  20  after adjusting the quantity of the fuel so as to achieve the fuel pressure level required by the engine, throttle valves  32  are each provided in the middle of a fuel passage  31  through which the fuel fed from the feed pump  3  is guided to the IO valve  20  from a fuel inlet  30 . The fuel fed from the feed pump  3  is supplied via an orifice  34  to a pressure chamber  33  provided at one end of the throttle valve  32 . The throttle valve  32  stops at the position in which the pressure at the pressure chamber  33  and the spring force of a spring  35  provided at the other end of the throttle valve  32  are in balance, and the pressure in the pressure chamber  33  is adjusted by utilizing an electromagnetic valve  36  controlled by an electronic control unit (ECU) (not shown). Thus, the constriction of the fuel passage  31  is controlled to adjust the quantity of fuel supplied to the IO valve  20 . 
     The feed pump  3 , which feeds the fuel drawn up from a fuel tank  40  to the fuel metering unit (FMU)  2 , is mounted with a bolt or the like so as to close off the opening of the housing member  8   c  constituting the pump housing  8 . As shown in FIG. 4, the feed pump is an external gear pump to which a motive force is transmitted from an internal gear  41 , which is secured to the end of the cam shaft  7  opposite from the driven end of the cam shaft  7 , and rotates together with the cam shaft  7 . Namely, the feed pump  3  comprises a drive gear  42  which interlocks with the internal gear  41 , a main gear  44  which is linked to the drive gear  42  by a shaft  43 , and a slave gear  45  that interlocks with the main gear. As the rotation of the cam shaft  7  causes the main gear  44  and the slave gear  45  to rotate, the gear pump formed of the main gear  44  and the slave gear  45  draws in the fuel from the fuel tank  40 . Thus, the fuel oil is supplied to the fuel metering unit (FMU)  2  via a fuel filter ( 46 : shown in FIG.  5 ). 
     Thus, the fuel injection pump described above assumes an overall structure illustrated in FIG. 5, in which the fuel is supplied from the fuel tank  40  through the feed pump  3  to the fuel metering unit (FMU)  2  where the quantity of fuel oil to be supplied to each of the plunger chambers  21  of the supply pump  1  is adjusted. Then the fuel is supplied to the plunger chambers  21  via the IO valve to forcibly feed the fuel oil alternately pressurized by the two plungers  4  through the fuel outlet  22 . 
     In this fuel injection pump, the radial position of the cam shaft is regulated by the radial bearings  11  and  12 , which are each constituted as a cylindrical plane bearing externally fitted on the cam shaft  7  so as to be allowed to slide against (i.e., with respect to) the cam shaft  7 . At the circumferential surface of the cam shaft  7 , bearing surfaces  50  and  51  are formed as plane bearing receptacles over the ranges in which the plane bearings are set. The axial position of the cam shaft  7  is regulated by a means for axial position regulation described below. 
     The means for axial position regulation is achieved by providing a flange part  52  projecting in the radial direction (with respect to cam shaft  7 ) further frontward relative to the bearing surface  51  of the cam shaft  7  formed on the end opposite from the driven end. In other words, the flange part  52  is located between the bearing surface  51  and the drive cam  14 . In addition, the housing member  8   c  supporting the cam shaft  7  via the radial bearing  12  is held between the flange part  52  and the internal gear  41  provided further toward the end relative to the bearing surface  51 . In other words, the internal gear  41  is secured to the end of the cam shaft  7  on the opposite end from the driven end (i.e., the free end), while assuring enough clearance so that the rotation of the cam shaft is not hindered. 
     In this structure, the width along the axial direction of the housing member  8   c  that is held between the flange part and the internal gear roughly matches the width of the bearing surface  51  located along the axial direction. Thus, it also roughly matches the width of the radial bearing  12  along the axial direction. Since this width is very small compared to the entire length of the cam shaft  7 , it remains virtually unaffected by thermal expansion. In addition, the flange part  52  in this example is formed as an integrated part of the external circumferential surface of the cam shaft  7  over the entire circumference, and an end surface  52   a  placed in contact with the housing member  8   c  is formed perpendicular to the axial center of the cam shaft  7 . The internal gear  41  secured to the cam shaft  7  to transmit the motive force to the feed pump  3 , on the other hand, assumes a cylindrical shape with a bottom, with teeth formed at the inner surface of a cylindrical portion  41   a  along the circumferential direction so as to set the curved surfaces of the tips of the teeth further inward relative to the curved surfaces of the bases of the teeth by turning the opening side toward the feed pump. The bottom  41   b  is tightly secured to the end surface of the cam shaft  7  on the opposite end from the driven end by a bolt  53  and an end surface  41   c  of the bottom  41   c  which is in contact with the housing member  8   c  formed perpendicular to the axial center of the cam shaft  7 . 
     Namely, the axial position of the cam shaft  7  is regulated by slidably holding the housing member  8   c  between the end surface  52   a  of the flange part  52  formed on the cam shaft  7  and the end surface  41   c  of the power transmission member ( 41 ) that transmits motive force to the feed pump  3 , instead of regulating the position of the cam shaft  7  along the thrust direction by providing a thrust bearing in the related art such as a slide bearing between the cam shaft  7  and the housing. Thus, the need to include a thrust bearing in the related art in the structure of the means for axial position regulation is eliminated. 
     By adopting this structure, the cam shaft  7  is supported along the axial direction at the free end opposite from the driven end on the driven driven. In addition, since its axial position is adjusted in reference to the supported end, play in the cam shaft along the axial direction is minimized. In other words, as the pump housing  8  and the cam shaft  7  expand to different degrees along the axis of the cam shaft  7  due to the difference between their coefficients of thermal expansion when the cam shaft  7  and the pump housing  8  become heated, the cam shaft  7  is supported by holding the housing member  8   c  at the free end opposite from the driven end. Thus, a relative shift occurring with regard to the positions of the housing and the cam shaft  7  as a result of thermal expansion is absorbed by the radial bearing  11  provided at the cam shaft  7  on the driven end, which tolerates play in the cam shaft  7  along the axial direction. In addition, since the axial position of the cam shaft itself is regulated by holding the portion that supports the cam shaft along the radial direction via the radial bearing  12  (i.e., by holding the housing member  8   c ), the support structure remains virtually unaffected by heat and, as a result, no play manifests along the axial direction. 
     Consequently, no heat-induced play occurs along the axis of the cam shaft  7  to result in a failure to achieve accurate injection characteristics or noise. In addition, the internal gear  41  and the drive gear  42  are allowed to interlock with each other with a high degree of accuracy at all times. Furthermore, since the thrust bearing employed in the related art is not utilized, it is not necessary to adjust the gap along the axial direction in conformance to the extent of wear of the thrust bearing, and a reduction in the number of parts constituting the injection pump is achieved. Moreover, the absence of any thrust bearing allows the length of the cam shaft  7  along the axial direction to be reduced, to achieve miniaturization of the injection pump. 
     Since the radial bearings  11  and  12  supporting the cam shaft along the radial direction are each formed of a plane bearing in the structure explained above, the cam shaft can be mounted at the pump housing with ease. Since the dimensions of the support structure along the radial direction can be reduced, the injection pump can be miniaturized. In addition, in the structure achieved in the present invention, the separate housing members  8   b  and  8   c  constituting the pump housing  8  are used as members for rotatably supporting the cam shaft  7  via the radial bearings  11  and  12  under normal circumstances. Thus, the housing member  8   c  is held between the flange part  52  and the power transmission member (the internal gear  41 ) which transmits the motive force to the feed pump  3 , so that no major design modification of the injection pump is necessary. 
     Industrial Applicability 
     As described above, according to the present invention in which a flange part is formed at a cam shaft of an injection pump and a power transmission member is provided at the free end of the cam shaft opposite from the driven end on the driven side and transmits a motive force to the feed pump, and in which the portion supporting the cam shaft along the radial direction is held between the flange part and the power transmission member to regulate the axial position of the cam shaft, it is not necessary to provide a separate member for regulating the axial position. Since no thrust bearing is present, the need to adjust the clearance in conformance to the extent of wear of the thrust bearing is eliminated. Thus, as it is not necessary to implement a special process for positioning the cam shaft along the axial direction, the assembly process is simplified and a reduction in the production cost is achieved. 
     In addition, since the axial position of the cam shaft can be set in reference to the portion held between the flange part and the power transmission member without having to employ an axial bearing, the cam shaft is supported along the axial direction without readily becoming affected by heat to achieve an accurate support along the axial direction. Furthermore, instead of regulating the axial position by providing a special member, the existing member that transmits a motive force to the feed pump is utilized. As a result, the absence of a special member along the axial direction allows the length along the axial direction to be reduced, which, in turn, allows the injection pump to be miniaturized. 
     Moreover, by forming radial bearings at the cam shaft as plane bearings, the dimensions of the support structure along the radial can also be reduced to achieve further miniaturization of the injection pump. The cam shaft assembly process is also facilitated by forming the radial bearings as plane bearings, so that the injection pump can be manufactured at low cost. 
     It is to be noted that since a portion that rotatably supports the cam shaft via radial bearings is normally constituted of a separate housing member that constitutes the pump housing, this housing member may be held between the flange part formed at the cam shaft and the power transmission member that transmits a motive force to the feed pump. By adopting such a structure, it becomes unnecessary to greatly modify the design of the existing structural features.

Technology Category: f