Fuel injection pump

TECHNICAL FIELD

[0001] The present invention relates to a fuel injection pump that supplies fuel to an internal combustion engine, and 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

[0002] 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.

[0003] 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 constituting 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 constituting the axial bearing as a bearing plate, which 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 and a structure achieved by constituting the radial bearing as a cylindrical roller bearing provided within a bearing cover in a similar manner and constituting 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.

[0004] 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.

[0005] 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 necessitating the cam shaft to have a large length. This structure, too, achieves an advantage of supporting the cam shaft individually along the axial direction and along the radial direction.

[0006] 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, and 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 constituted 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 constituted as a separate member must be provided along the axis of the cam shaft, the length of the cam shaft along the axis cannot the reduced readily, 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.

DISCLOSURE OF THE INVENTION

[0007] 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 constituted as a separate member can be eliminated by regulating the position of the cam shaft along the axial direction with the existing component.

[0008] Namely, in the fuel injection pump according to the present invention having 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 projecting along the radial direction is provided at the cam shaft, 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 and 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.

[0009] 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 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 and, 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 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.

[0010] In this structure, the radial bearing at the cam shaft may be constituted of a cylindrical roller bearing which uses a cylindrical roller as a rolling element, or the radial bearing may be constituted of a plane bearing. In the latter case, the dimension of the cam shaft along the radial direction, too, can be reduced and, at the same time, the process for assembling the cam shaft is facilitated, thereby allowing the injection pump to be manufactured at low cost.

[0011] Furthermore, since the pump housing is normally constituted 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

[0012]
FIG. 1 is a partially notched sectional view of the fuel injection pump, according to the present invention;

[0013]
FIG. 2 shows in an enlargement of the cam shaft and the feed pump in the fuel injection pump shown in FIG. 1;

[0014]
FIG. 3 is a sectional view taken along A-A in FIG. 1 and FIG. 2;

[0015]
FIG. 4 is a perspective of the cam shaft and the feed pump employed in the fuel injection pump according to the present invention; and

[0016]
FIG. 5 is a system operation diagram of the fuel injection pump according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] The following is an explanation of an embodiment of the present invention, given in reference to the drawings. FIGS. 1 through 3 show a fuel injection pump constituted by assembling a supply pump 1, a fuel metering unit (FMU) 2 and a feed pump 3.

[0018] 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.

[0019] The pump housing 8 includes a housing member 8a having longitudinal holes 10 at which the plunger barrels 5 are fitted and housing members 8b and 8c that are secured to the housing member 8a with bolts or the like and rotatably hold the cam shaft 7 near the two ends thereof.

[0020] In this example, two longitudinal holes 10 are formed at the housing member 8a, and the plunger barrels 5 are each secured to the housing member 8a inside one of the longitudinal holes with the plungers 4 inserted at the plunger barrels 5 so as to move reciprocally within the plunger barrels.

[0021] In addition, the cam shaft 7 is supported by the housing members 8b and 8c near the two ends thereof via radial bearings 11 and 12 so as to allow play along the axial direction, with two drive cams 13 and 14 each provided for one of the plungers formed at the cam shaft 7 between the bearings at phases offset from each other.

[0022] 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 8a 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.

[0023] At the top of each plunger barrels 5, an IO valve (inlet/outlet valve) 20 mounted between the plunger barrels 5 and a delivery valve holder 19 is provided. A plunger chambers 21 is formed between the IO valve 20 and the plungers 4, and a fuel outlet 22 formed at the delivery valve holder 19 is set above the IO valve 20.

[0024] The IO valve 20 in this structure, which have a function of supplying the fuel fed from the fuel metering unit (FMU) 2 that is to be detailed later to the plunger chambers 21 and sending 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 valve bodies 23 mounted at an upper portion of the plunger barrels 5, inlet valves 25 having one end thereof communicating with the FMU 2 and the other end thereof opening/closing a fuel passage 24 that is formed at the valve bodies 23 communicating with the plunger chambers 21, the inlet valves 25 which impart 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 and outlet valves 27 having one end thereof communicating with the plunger chambers 21 and the other end thereof opening/closing a fuel passage 26 communicating with the fuel outlet 22, which 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 plungers 4 enter a descending process, the outlet valves 27 close, 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, whereas as the plungers 4 enter an ascending process, the pressurized fuel closes the inlet valves 25 to push up the outlet valves 27 thereby forcibly feeding the fuel through the fuel outlet 22.

[0025] In the fuel metering unit (FMU) 2, which has a function of feeding 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 is made to stop at the position at 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, the pressure at the pressure chamber 33 is adjusted by utilizing an electromagnetic valve 36 controlled by an electronic control unit (ECU) (not shown) and thus, the constriction of the fuel passage 31 is controlled to adjust the quantity of fuel supplied to the IO valve 20.

[0026] 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 8c 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 that is secured to the end of the cam shaft 7 on the opposite side from the end on the driven side 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 and, as the rotation of the cam shaft 7 causes the main gear 44 and the slave gear 45 to rotate, the gear pump constituted of the main gear 44 and the slave gear 45 draws in the fuel from the fuel tank 40 and thus, the fuel oil is supplied to the fuel metering unit (FMU) 2 via a fuel filter (46: shown in FIG. 5).

[0027] 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 plunger chambers 21 at the supply pump 1 is adjusted, then the fuel is supplied to the plungers chambers 21 via the IO valve to forcibly feed the fuel oil alternately pressurized by the two plungers 4 through the fuel outlet 22.

[0028] 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 at the cam shaft 7 so as to be allowed to slide against 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.

[0029] The means for axial position regulation is achieved by providing a flange part 52 projecting along the radial direction further frontward relative to the bearing surface 51 of the cam shaft 7 formed on the opposite side from the driven side, i.e., between the bearing surface 51 and the drive cam 14 and by holding the housing member 8c supporting the cam shaft 7 via the radial bearing 12 between the flange part 52 and the is internal gear 41 provided further toward the end relative to the bearing surface 51, i.e., the internal gear 41 secured to the end of the cam shaft 7 on the opposite side from the driven side, while assuring enough clearance so that the rotation of the cam shaft is not hindered.

[0030] In this structure, the width along the axial direction of the housing member 8c that is held in between the flange part and the internal gear roughly matches the width of the bearing surface 51 along the axial direction, and 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 52a placed in contact with the housing member 8c 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 41a 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 41b tightly secured to the end surface of the cam shaft 7 on the opposite side from the driven side by a bolt 53 and an end surface 41c of the bottom 41c which is in contact with the housing member 8c formed perpendicular to the axial center of the cam shaft 7.

[0031] Namely, this means for axial position regulation is characterized in that the axial position of the cam shaft 7 is regulated by slidably holding the housing member 8c between the end surface 52a of the flange part 52 formed at the cam shaft 7 and the end surface 41c 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, thereby eliminating the need to include a thrust bearing in the related art in the structure of the means for axial position regulation.

[0032] By adopting this structure, the cam shaft 7 becomes supported along the axial direction at the end on the opposite side from the end on the driven side, and 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 8c at the end on the side opposite from the driven side and 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 side, 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 8c, the support structure remains virtually unaffected by heat and, as a result, no play manifests along the axial direction.

[0033] 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.

[0034] Since the radial bearings 11 and 12 supporting the cam shaft along the radial direction are each constituted of a plane bearing in the structure explained above, the cam shaft can be mounted at the pump housing with ease, and since the dimensions of the support structure along the radial direction can be reduced, the injection pump can be miniaturized. In addition, the structure achieved in the present invention, in which the separate housing members 8b and 8c 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 and thus, the housing member 8c 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, does not necessitate any major design modification of the injection pump.

INDUSTRIAL APPLICABILITY

[0035] As described above, according to the present invention in which a flange part formed at a cam shaft of an injection pump and a power transmission member that is provided at the end of the cam shaft on the opposite side from the end on the driven side and transmits a motive force to the feed pump hold the portion supporting the cam shaft along the radial direction between them to regulate the axial position of the cam shaft, it is not necessary to provide a separate member for regulating the axial position and, 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.

[0036] 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 and, 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.

[0037] Moreover, by constituting radial bearings at the cam shaft with plane bearings, the dimensions of the support structure along the radial direction, too, can be reduced to achieve further miniaturization of the injection pump. The cam shaft assembly process is also facilitated by constituting the radial bearings with plane bearings, and consequently, the injection pump can be manufactured at low cost.

[0038] It is to be noted that since a portion that rotatably supports the cam shaft via a 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, and by adopting such a structure, it becomes unnecessary to greatly modify the design of the existing structural features.

Fuel injection pump

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