The present invention relates to a gasket adapted to seal a front plate of a high pressure fuel pump.

BACKGROUND OF THE INVENTION

In high pressure fuel pump a camshaft rotates between two aligned bearings, defining a main axis, and imparts to a plunger to perform a pumping cycle. One bearing is arranged in a bore of the pump body and, the other bearing is arranged in a front plate that is fixed to the body by three screws unevenly distributed about said main axis. Sealing is ensured by a metallic gasket compressed between said front plate and the body, the gasket being a metal sheet of about 0.3 mm thickness. It is substantially a circular disc with a central opening, further provided with three screw holes, for fixation of the front plate onto the body, and also with another aperture enabling fluid communication of a return low pressure circuit. To accommodate various pump embodiments, said another aperture may be square, rectangular, circular, oblong, straight, curved or to have a kidney shape... Also, the edges surrounding the central opening and said another aperture are shaped so as to be slightly raised by few tenth of mm above the level of a disc front face.

Despite great care provided during manufacturing and assembly processes, because of the rising edges, only one being centred, a slight misalignment of the bearings, superior to allowable tolerances, has be observed and should be annealed or at least diminished.

Furthermore, an external circular face of the front plate guides the pump when being mounted on the engine. Due to uneven placement of the screw holes on the pump body and, of the kidney feature on the gasket, said front plate guiding face slightly distorts to a non-circular shape resulting in making difficult, or even impossible, said mounting of the pump. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a gasket made out of a metallic sheet having a thickness and adapted be arranged between a front plate and a body of a high pressure fuel pump. The gasket has a disc-like shape with a front face and an opposed rear face radially extending about a main axis from a peripheral outer edge to an inner edge surrounding a central opening provided for the passage of a cylindrical portion of the front plate. The inner edge is shaped so as to be slightly raised above the level of a front face. The gasket is further provided with a first screw hole, a second screw hole and a third screw hole adapted to provide passage to tightening screws, all three holes being centred on a circle concentric to the main axis and radially arranged substantially half way between the inner edge and the outer edge.

The gasket is also provided with a fourth aperture adapted to enable, in use, fluid communication within a fluid circuit of the pump, said fourth aperture being arranged radially between the inner edge and the outer edge and, angularly between the first and the third screw hole, substantially opposite to the second screw hole, the edge surrounding said fourth aperture also being shaped so as to be raised above the level of the front face.

Advantageously, the gasket is further provided with a first protrusion, a second protrusion and a third protrusion rising above the level of the front face to a similar height as the inner edge and the surrounding edge of the fourth aperture.

Also, the first protrusion is arranged in close vicinity to the first screw hole and, the second protrusion is arranged in close vicinity to the second screw hole and, the third protrusion is arranged in close vicinity to the third screw hole.

Also, the first screw hole is between the fourth aperture and the first protrusion and, the third screw hole is between the fourth aperture and the third protrusion.

Also, the fourth aperture is substantially rectangular or circular or it has a curved oblong shape, such as a kidney shape.

Also, the gasket may comprise more than three screw holes.

The invention further extends to a high pressure fuel pump having a body on which is screwed a front plate defining an axis and, having a gasket as described above, said gasket being compressed between the body of the pump and the front plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a section of a high pressure pump.

Figure 2 is a 3D view presenting the body of the pump and a gasket as per the invention.

Figure 3 is a view of the gasket as per the invention.

Figures 4, 5 and 6 and three section of the gasket of figure 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to figure 1 is now described a diesel high pressure pump 10 wherein a camshaft 12 rotating about a main axis X between two aligned bearings 14, 16 imparts a piston 18, via a cam-follower 20, to reciprocal displacements of a pumping cycle thus, varying the volume of a compression chamber 22 wherein fuel is pressurized prior to be delivered to fuel injectors. The bearings are known as a rear bearing 14 arranged in a recess of the body 24 of the pump and drawn on the right of figure 1 and, a front bearing 16 arranged in a bore 26 of a front plate 28 bolted to the body 24 and, on the left of the figure.

The front plate 28 comprises a cylindrical tubular portion 30 provided with the bore 26 and also, a thick disc portion 32 radially outwardly extending from the cylindrical portion 30. The disc portion 32 has a rear flat face 34 perpendicular to the axis of the bore 26, said rear flat face 34 being bolted via three screws 36 and pressed in sealing contact against a complementary flat face 38 of the body. The pump 10 also defines a return circuit 40 for non-pressurized fuel to flow back toward a low pressure tank, a portion of said return circuit 40 emerging in a recess of the flat face 38 of the body.

To ensure sealing, a gasket 42 is arranged between the rear flat face 34 of the front plate and the flat face 38 of the body.

Concentricity of the rear 14 and front 16 bearings requires to ensure tight manufacturing tolerances in flatness of said faces 34, 38 of the body and of the front plate, tight perpendicularity of the rear face 34 of the front plate and of the axis of the bore 26 and, radial positioning of the front plate onto the body.

An embodiment of said gasket 42 is now presented on figures 2 to 6. The gasket 42, made out of a flat metal sheet of thickness T, has a flat disc-shape with a rear face 44 lying against the body and, an opposed front face 46 against the front plate, said front face 46 being visible on figure 2. The disc-shape gasket 42 radially extends about the main axis X between a peripheral outer edge 48 and a circular inner edge 50 surrounding a central opening 52 adapted to engage over the cylindrical portion 30 of the front plate and, in said annular disc are arranged a first hole 54, a second hole 56 and a third hole 58 for enabling passage of the tightening screws 36 and also, a fourth aperture 60 that has, in the exemplary embodiment of the figures, a curved oblong shape for enabling fluid connection of said return circuit 40. By curved-oblong is meant that the fourth aperture 60 has two circular concentric sides joined at their ends by small semi-circular end sides.

The three screw holes 54, 56, 58 and the fourth aperture 60 are substantially radially equidistant from the main axis X and, they are angularly distributed so that said fourth aperture 60 is between the first 54 and third 58 screw holes, substantially opposite to the second screw hole 56.

The "curved oblong" shape of the fourth aperture 60 should not be considered a limitation to the invention as other shapes circular, rectangular, moon-like or others are also possible.

Furthermore, as shown on figures 3, 4, 5 and 6, the inner edge 50 that entirely surrounds the central opening 52 is shaped and has a Z-like profile 62 so as to be slightly raised above the level of a front face 46 of the gasket and similarly, the surrounding edge 64 of the fourth opening is also shaped in a Z-like profile 62 so as to be slightly raised above the level of a front face 46. To the contrary, the surroundings of the screw holes 54, 56, 58 are flat, and so are the surroundings of other holes shown on the embodiment of figure 2 that are provided to ensure either fuel passage of manufacturing key.

As visible on the figures, the screws 36 are not evenly distributed 120° apart from each other. Consequently when the screws 36 are being tightened, the forces applied onto the thick disc plate 32 are not equal and generate a small bias. In addition, the Z-like profiles 62 also add imbalance to the whole. To ensure balance of the forces when tightening the screws 36 for fixing the front plate, the gasket 42 is further provided with a first protrusion 66, a second protrusion 68 and a third protrusion 70, all three protrusions rising above the level of the front face 46 of the gasket.

In the embodiment shown, the three protrusions are cylindrical dome having a flat top and, said three protrusions as well as the Z-like profiles of the inner edge 50 and of the surrounding edge 64 of the fourth opening equally rise above the level of the front face 46 of the gasket.

The first protrusion 66 is arranged in the near vicinity to the first screw hole 54, said first screw hole 54 being between the first protrusion 66 and the fourth aperture 60. Similarly, the third protrusion 70 is arranged in the near vicinity to the third screw hole 58, said third screw hole 58 being between the third protrusion 70 and the fourth aperture 60.

When placed in position against the body face 38, the gasket 42 is parallel and between remains stable protrusions and Z-like edges in contact with said flat face 38 of the body and, when the front plate 28 is approached and tightened, the gasket 42 remains in parallel since the protrusions and raised edges are substantially angularly distributed about the gasket.

Conclusive tests have been performed with a gasket having a thickness T of 0.25mm and a rising level of the protrusions and raised edges of about 0.35mm.

main axis

thickness high pressure pump

camshaft

rear bearing

front bearing

piston

cam- follower

compression chamber

body of the pump

bore

front plate

cylindrical portion of the front plate thick disc plate of the front plate rear face of the disc portion

screw

body flat face

return circuit - fluid circuit

gasket

rear face of the gasket

front face of the gasket

outer edge of the gasket

inner edge of the gasket

central opening

first screw hole

second screw hole

third screw hole

fourth aperture

Z-like profile

surrounding edge of the fourth aperture first protrusion

second protrusion

third protrusion