Engine fuel pump mounting structure

A rocker shaft holder that supports a rocker shaft and a camshaft holder that supports an intake camshaft and an exhaust camshaft in association with the rocker shaft holder are superimposed and connected to each other on the upper surface of a cylinder head, and a fuel pump that supplies fuel at high pressure to an injector is driven by a journal on a shaft end of the exhaust camshaft. The fuel pump is fastened to the cylinder head by means of a bolt; to the integral type camshaft holder, in which a plurality of bearings are integrally connected together via connecting parts, by means of a bolt; and to the rocker shaft holder by means of bolts, and the rigidity of that parts on which the fuel pump is mounted is thereby enhanced to reliably support the camshaft and the rocker shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an engine fuel pump mounting structure in which a camshaft holder that supports a camshaft is fixed to the upper surface of a cylinder head, and a fuel pump is mounted on a shaft end of the camshaft.

2. Description of the Related Art

With regard to an engine in which a fuel pump that supplies fuel at high pressure to an injector is driven by a shaft end of a camshaft, one in which a pump housing of the fuel pump is bolted so as to extend over both a cylinder head and a camshaft holder is known in Japanese Patent Application Laid-open No. 11-82159.

In general, when a pump housing of a fuel pump that is driven by a camshaft is bolted to a cylinder head and a camshaft holder, since the rigidity of the camshaft holder, which is a comparatively small member that is provided so as to support each of the journals of the camshaft, is insufficient, there is a possibility that the heavy fuel pump might not be reliably supported.

SUMMARY OF THE INVENTION

The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to enhance the rigidity with which a fuel pump that is driven by a camshaft is supported.

In order to achieve the above-mentioned object, in accordance with a first aspect of the present invention, there is proposed an engine fuel pump mounting structure in which a camshaft holder that supports a camshaft is fixed to an upper surface of a cylinder head and a fuel pump is mounted on a shaft end of the camshaft, wherein the camshaft holder is formed by integrally connecting together a plurality of bearings that support the camshaft via connecting parts, and the fuel pump is fastened to the camshaft holder by a bolt.

In accordance with the above-mentioned arrangement, since the camshaft holder to which the fuel pump is fastened by the bolt has a highly rigid integral structure in which the plurality of bearings that support the camshaft are integrally connected together via the connecting parts, both the rigidity with which the camshaft is supported and the rigidity with which the fuel pump is supported by the camshaft holder can be enhanced.

Furthermore, in accordance with a second aspect of the present invention, there is proposed an engine fuel pump mounting structure in which a rocker shaft holder that supports a rocker shaft and a camshaft holder that supports a camshaft alone, or in association with the rocker shaft holder, are superimposed on the upper surface of a cylinder head and a fuel pump is mounted on a shaft end of the camshaft, wherein the camshaft holder is formed by integrally connecting together a plurality of bearings that support the camshaft via connecting parts and the fuel pump is fastened to each of the cylinder head, the rocker shaft holder and the camshaft holder by a bolt.

In accordance with the above-mentioned arrangement, since the fuel pump is fastened by a bolt to each of the three members consisting of the cylinder head, the rocker shaft holder and the camshaft holder, the rigidity of these three members can be enhanced effectively by a pump housing of the fuel pump, and the camshaft and the rocker shaft can be supported reliably. In particular, since the camshaft holder has an integral structure in which the plurality of bearings that support the camshaft are connected integrally together via the connecting parts, the rigidity of the camshaft holder is further increased, and, as a result, the camshaft can be supported more reliably while enhancing the rigidity with which the fuel pump is supported.

In accordance with a third aspect of the present invention, there is proposed an engine fuel pump mounting structure in which a camshaft holder that supports a camshaft is fixed to the upper surface of a cylinder head and a fuel pump is mounted on a shaft end of the camshaft, wherein a bearing provided on the camshaft holder and a fuel pump mounting boss provided on the camshaft holder are connected to each other via a reinforcing rib.

In accordance with the above-mentioned arrangement, since the bearing provided on the camshaft holder and the fuel pump mounting boss provided on the camshaft holder are connected to each other via the reinforcing rib, the rigidity with which the fuel pump is supported can be enhanced by the integral connection of the bearing and the fuel pump mounting boss on the camshaft holder.

In addition to any one of the above-mentioned first to third aspects, a fuel pump mounting boss formed on the cylinder head and an outer wall of an EGR gas passage formed in the cylinder head are connected to each other via a reinforcing rib, and the rigidity of the fuel pump mounting boss can thereby be enhanced so supporting the fuel pump yet more reliably.

In addition to either one of the above-mentioned first aspect or second aspect, a reinforcing rib extending in the direction toward where the fuel pump is mounted is provided on a reverse surface of a fuel pump mounting boss formed on the camshaft holder, and it is thereby possible to suppress downward movement of the camshaft holder due to the weight of the fuel pump and enhance the rigidity with which the fuel pump and the camshaft are supported.

In addition to the above-mentioned third aspect, the reinforcing rib that connects the bearing of the camshaft holder to the fuel pump mounting boss is extended from the reverse side of the fuel pump mounting boss in the direction toward where the fuel pump is mounted, and it is thereby possible to suppress downward movement of the camshaft holder due to the weight of the fuel pump and enhance the rigidity with which the fuel pump and the camshaft are supported.

The above-mentioned objects, and other objects, characteristics and advantages of the present invention will become apparent from explanation of a preferred embodiment that will be described in detail below by reference to the attached drawings.

DESCRIPTION OF PREFERRED EMBODIMENT

The embodiment of the present invention is explained below by reference to the attached drawings.

FIG. 1is a cross section of an in-line four cylinder engine E. A cylinder head12is connected to the upper surface of a cylinder block11, and a head cover13is connected to the upper surface of the cylinder head12. A piston15is supported in a cylinder14formed in the cylinder block11in a slidable manner, and a conical form of combustion chamber16formed on the lower surface of the cylinder head12faces the top surface of the piston15. A pair of intake ports17and a pair of exhaust ports18open inside the combustion chamber16. The intake ports17are opened and closed by a pair of intake valves20, which are forced in the closing direction by means of valve springs19. The exhaust ports18are opened and closed by a pair of exhaust valves22, which are forced in the closing direction by means of valve springs21.

An ignition plug insertion tube12ais formed in the cylinder head12on the exhaust side so as to make an angle to the cylinder axis, and the tip of an ignition plug23mounted within the insertion tube12afaces the combustion chamber16. The cylinder head12includes a cylinder head side wall12bon the intake side and a cylinder head side wall12con the exhaust side. An extension pipe24, which is press-fitted into the ignition plug insertion tube12a, extends outward from the cylinder head side wall12con the exhaust side. A valve operation cam chamber25is formed between the cylinder head12and the head cover13. A boss-form injector mounting base12eis formed on a valve operation cam chamber deck surface12dforming the base of the valve operation cam chamber25so as to surround the cylinder axis. An injector27is housed within an injector pipe26, which is press-fitted into the injector mounting base12e, and the lower end of the injector27provided in the injector mounting base12efaces the top part of the combustion chamber16.

As is clear by referring additionally toFIGS. 2to4, a valve operating mechanism housed within the valve operation cam chamber25, which is surrounded by the head cover13, includes a rocker shaft holder28and an integral type camshaft holder29. The rocker shaft holder28and the integral type camshaft holder29are superimposed on the upper surface of the cylinder head12and fixed by means of bolts30. An intake rocker shaft31and an exhaust rocker shaft32are fixed in the rocker shaft holder28. An intake camshaft33and an exhaust camshaft34are rotatably supported between the rocker shaft holder28and the integral type camshaft holder29. The intake camshaft33and the exhaust camshaft34are driven by a crankshaft via an endless chain.

The integral type camshaft holder29connected to the upper surface of the rocker shaft holder28and supporting the intake camshaft33and the exhaust camshaft34has five bearings29athat each support one of five journals of each of the intake camshaft33and the exhaust camshaft34, and four connecting parts29bthat integrally connect these bearings29a. Injector insertion openings29d, through which injector pipes26run, are formed in the central parts of the four connecting parts29bof the integral type camshaft holder29, and the gaps between the outer peripheries of the injector pipes26and the inner peripheries of the injector insertion openings29dare sealed with sealing members35.

A recess13aextending in the direction in which the cylinders are arranged is formed downward in the center of the head cover13. Oil separating chambers13band13care formed with partitions36on the intake side and the exhaust side, respectively, on either side of the recess13a. The outer periphery of the lower surface of the head cover13is supported on the outer periphery of the upper surface of the cylinder head12via a first sealing member37. The inner periphery of the lower surface of the head cover13, that is, the lower edge of the recess13a, is supported on the upper surface of the integral type camshaft holder29via a second sealing member38. The valve operation cam chamber25is thus sealed from the outside air via the first sealing member37and the second sealing member38, and the integral type camshaft holder29forms a part of the roof of the valve operation cam chamber25.

A fuel pipeline39is housed within the recess13aof the cylinder head13and fixed by means of four bolts40to the upper ends of the four injectors27projecting into the recess13afrom the injector insertion openings29dof the integral type camshaft holder29. On one end surface of the engine E, the rocker shaft holder28and the integral type camshaft holder29are exposed outside the head cover13, and a journal33aat the shaft end of the intake camshaft33and a journal34aat the shaft end of the exhaust camshaft34are rotatably supported in both the rocker shaft holder28and the bearing29aof the integral type camshaft holder29. In order to supply fuel at high pressure to the injectors27via the fuel pipeline39, the fuel pump41, which is driven by the shaft end of the exhaust camshaft34, is mounted so as to extend over the three members consisting of the cylinder head11, the rocker shaft holder28and the integral type camshaft holder29.

That is, the fuel pump41, which is an axial plunger pump, has a pump housing42, and four bolt holes42bto42eare formed in a mounting flange42aof the pump housing42. A bolt43that runs through the first bolt hole42bat the lowest position is tightened into a bolt hole12hof a fuel pump mounting boss12gformed on the end surface of the cylinder head12. A bolt44that runs through the second bolt hole42cat the highest position is tightened into a bolt hole29fof a fuel pump mounting boss29ethat projects upward from the bearing29aof the integral type camshaft holder29. Bolts45and46that run through the third bolt hole42dand the fourth bolt hole42epositioned between the highest and lowest positions are tightened into bolt holes28cand28dof fuel pump mounting bosses28aand28bof the rocker shaft holder28. A pump shaft47of the fuel pump41thus fixed by means of the four bolts43to46is fitted coaxially to the shaft end of the exhaust camshaft34and joined to it by means of a pin48.

An EGR gas passage49extends from the cylinder head side wall12con the exhaust side into the interior of the cylinder head12. An outer wall of the EGR gas passage49and the fuel pump mounting boss12gof the cylinder head12are connected to each other via a reinforcing rib12i(FIGS.3and4). A reverse surface of the fuel pump mounting boss29eof the integral type camshaft holder29and the upper surface of the bearing29aare connected to each other via a reinforcing rib29gthat extends in the direction toward where the fuel pump41is mounted (FIGS.3and4).

As shown inFIGS. 5to8, a variable valve operating characteristic mechanism V for changing the valve lift and opening angle of the intake valves20in two stages is provided in the valve operation cam chamber25.

On the intake camshaft33a pair of low speed cams61and a high speed cam62interposed between the two low speed cams61are provided so as to correspond to each of the cylinders14. A first intake rocker arm63, a second intake rocker arm64and a third intake rocker arm65are swingably supported on the intake rocker shaft31, which is fixed beneath and parallel to the intake camshaft33, so as to correspond to the low speed cam61, the high speed cam62and the low speed cam61, respectively.

The pair of low speed cams61have base circles61band elevations61athat project by a comparatively small amount in the radial direction of the intake camshaft33. The high speed cam62has a base circle62band an elevation62athat projects by a larger amount and over a wider angle than that of the projection of the elevations61aof the low speed cams61.

Flanges20bare provided on the upper ends of valve stems20aof the intake valves20. The intake valves20are forced in the closing direction by the valve springs19that are installed between the cylinder head12and the flanges20bin a compressed state. The first and third rocker arms63and65are swingably supported around the intake rocker shaft31at one of their ends, have rollers67that are supported within their cut-outs63aand65bvia needle bearings66and are in contact with the pair of low speed cams61, and have tappet screws68that are in freely movable contact with the upper ends of the valve stems20aof the intake valves20at the other of their ends.

The second intake rocker arm64, which is disposed between the pair of intake valves20and is swingably supported around the intake rocker shaft31at one end, has a force applied to it by a compressed lost motion spring69mounted in a spring seat12fformed in the cylinder head12and has a roller71that is supported in a cut-out64avia a needle bearing70and is in contact with the high speed cam62.

As is clear fromFIG. 8, a connection switch-over mechanism72for switching over the state of connection between the first, second and third intake rocker arms63to65has a first switch-over pin73that can provide a connection between the first intake rocker arm63and the second intake rocker arm64, a second switch-over pin74that can provide a connection between the second intake rocker arm64and the third intake rocker arm65, and a third switch-over pin75that restrains the movement of the first switch-over pin73and the second switch-over pin74. The switch-over pins73to75are slidably supported within sleeves76to78that are press-fitted into the respective intake rocker arms63to65. The sleeves76to78form the support shafts for the rollers67and71. The third switch-over pin75is made in the form of a cup and is forced toward the first and second switch-over pins73and74by means of a return spring80that is disposed between the third switch-over pin75and a spring seat79fixed to the sleeve78.

An oil chamber63bis formed within the first intake rocker arm63, and one end of the first switch-over pin73faces the oil chamber63b. A communicating passage63cthat communicates with the oil chamber63bis formed in the first intake rocker arm63, and a hydraulic pressure supply passage31ais formed in the intake rocker shaft31. The communicating passage63cand the hydraulic pressure supply passage31acommunicate with each other all the time via a communicating passage31bformed in the side wall of the intake rocker shaft31regardless of the swinging state of the first intake rocker arm63.

When the hydraulic pressure supplied to the oil chamber63bis released, the first to third switch-over pins73to75move to the disconnected side due to the resilient force of the return spring80, and the third switch-over pin75stops at a position where it is in contact with the stopper81. At this point, since the plane on which the second switch-over pin74and the third switch-over pin75are in contact with each other is between the second intake rocker arm64and the third intake rocker arm65and the plane on which the first switch-over pin73and the second switch-over pin74are in contact with each other is between the first intake rocker arm63and the second intake rocker arm64, the first to third intake rocker arms63to65are in a non-connected state. When a hydraulic pressure is supplied to the oil chamber63b, the first to third switch-over pins73to75move to the connected side against the resilient force of the return spring80, the first switch-over pin73of the first intake rocker arm63engages with the second intake rocker arm64and the second switch-over pin74of the second intake rocker arm64engages with the third intake rocker arm65, and the first to third intake rocker arms63to65are thus connected integrally.

As shown inFIG. 1, one end of the exhaust rocker arm82is swingably supported around the exhaust rocker shaft32. The other, forked, end of the exhaust rocker arm82is in contact with the upper end of the valve stem of the exhaust valve22, and a roller83that is provided in the middle section of the exhaust rocker arm82is in contact with an exhaust cam84that is provided on the exhaust camshaft34.

The action of the embodiment of the present invention is now explained.

When the variable valve operating characteristic mechanism V establishes a low speed valve timing, no hydraulic pressure is applied to the oil chamber63bthat communicates with the hydraulic pressure supply passage31awithin the intake rocker shaft31and the first to third switch-over pins73to75move to the disconnected positions shown inFIG. 8due to the resilient force of the return spring80. As a result, the first to third intake rocker arms63to65are isolated from each other, and the two intake valves20are operated so as to open and close by the first and third intake rocker arms63and65whose rollers67are in contact with the two low speed cams61. In this case, the second intake rocker arm64whose roller71is in contact with the high speed cam62moves independently of the action of the intake valves20and without effect.

When a hydraulic pressure is applied to the oil chamber63bin order to establish a high speed valve timing, the first to third switch-over pins73to75move to the connected positions against the resilient force of the return spring80. Since the first and second switch-over pins73and74make the first to third intake rocker arms63to65connect integrally together, the swinging action of the second intake rocker arm64whose roller71is in contact with the high speed cam62having the high and wide-angled elevation62ais transmitted to the first and third intake rocker arms63and65that are integrally connected to the second intake rocker arm64thereby operating the two intake valves20so as to open and close them. In this case, the elevations61aof the low speed cams61are detached from the rollers67of the first and third intake rocker arms63and65and move without effect.

As hereinbefore described, when the variable valve operating characteristic mechanism V establishes the low speed valve timing, the intake valves20are operated with a low valve lift and a small opening angle. When the high speed valve timing is established, the intake valves20are operated with a high valve lift and a large opening angle.

The exhaust valves22are operated so as to open and close with constant valve lift and opening angle via the exhaust rocker arm82by the exhaust cam84provided around the exhaust camshaft34.

When the fuel pump41connected to the shaft end of the exhaust camshaft34, which rotates accompanying the operation of the engine E, is operated, fuel at high pressure supplied via the fuel pipeline39is injected into the interiors of the cylinders14via the respective injectors27. Not only is the fuel pump41heavy, it also receives a driving torque from the exhaust camshaft34and, as a result, a large load is applied to the attachment points of the fuel pump41. When this load causes any deformation in the end of the integral type camshaft holder29, it becomes particularly difficult to support the journal34aon the shaft end of the exhaust camshaft34in a stable manner thereby causing a possibility that abnormal wear, etc. might occur.

However, since the mounting flange42aof the fuel pump41is fastened to the three members consisting of the cylinder head12, the rocker shaft bolder28and the integral type camshaft holder29by means of the four bolts43to46in the present embodiment, the rigidity of the parts on which the fuel pump41is mounted is enhanced thereby preventing any deformation of the integral type camshaft holder29and the rocker shaft bolder28. Not only can the intake camshaft33, the exhaust camshaft34, the intake rocker shaft31and the exhaust rocker shaft32be supported reliably, but also the rigidity with which the fuel pump41itself is supported can be enhanced. Moreover, since the integral type camshaft holder29has a structure in which the plurality of bearings29athat extend in a direction perpendicular to the direction in which the cylinders are arranged are connected integrally together by the plurality of connecting parts29bin the direction in which the cylinders are arranged, the rigidity of the integral type camshaft holder29is further enhanced thereby contributing to an increase in the rigidity with which the fuel pump41is supported.

Furthermore, since the outer wall of the EGR gas passage49, which is formed in a tube shape and has high rigidity, is connected to the fuel pump mounting boss12gof the cylinder head12via the reinforcing rib12i, the fuel pump mounting boss12gis reinforced, thus further enhancing the rigidity with which the fuel pump41is supported. Furthermore, since the reverse surface of the fuel pump mounting boss29eof the integral type camshaft holder29is connected to the upper surface of the bearing29avia the reinforcing rib29g, it becomes possible to suppress downward movement of the integral type camshaft holder29due to the weight of the fuel pump41, and the rigidity with which the fuel pump41, the intake camshaft33and the exhaust camshaft34are supported can be further enhanced. In particular, since the reinforcing rib29gof the reverse surface of the fuel pump mounting boss29eextends to the bearing29aof the integral type camshaft holder29, the effect of enhancing the rigidity can be further increased.

Although an embodiment of the present invention has been explained in detail above, the present invention can be modified in a variety of ways without departing from the spirit and scope of the present invention.

For example, the present invention can also be applied to an engine having no variable valve operating characteristic mechanism V and to an in-line engine or a V-type engine other than a four cylinder type. Furthermore, a DOHC type engine has been illustrated in the present embodiment, but the present invention can be applied to an SOHC type engine.

Furthermore, the rocker shafts31and32are supported in the rocker shaft holder28and the camshafts33and34are supported between the rocker shaft holder28and the integral type camshaft holder29in the embodiment, but while supporting the rocker shafts31and32in the rocker shaft holder28, the camshafts33and34can be supported in the integral type camshaft holder29, or the rocker shafts31and32can be supported between the rocker shaft holder28and the integral type camshaft holder29while supporting the camshafts33and34in the integral type camshaft holder29. Moreover, although the fuel pump41is driven by the exhaust camshaft34in the embodiment, it can be driven by the intake camshaft33.