Title :

"HIGH PRESSURE PUMP FOR SUPPLYING FUEL, PREFERABLY DIESEL, TO AN INTERNAL COMBUSTION ENGINE"

The present invention relates to a high pressure pump for supplying fuel from a low pressure hydraulic circuit to an internal combustion engine.

Generally, a high pressure pump comprises a pump body; at least one piston movable in reciprocating motion along a first axis for pumping fuel to the internal combustion engine; an operating unit for the piston capable of moving the piston along the first axis; a shoe located between the piston operating unit and the piston to operatively couple them; and in which the shoe is in abutment with the piston.

One disadvantage of the known art is that the abutment coupling between the piston and the shoe gives rise to stresses on the piston which can cause malfunctions. This leads to the useful life, reliability and efficiency of the pump being critical parameters.

An object of the present invention is to create a high pressure pump which reduces the disadvantages of the known art .

According to the present invention a high pressure pump is created to supply fuel, preferably diesel, to an internal combustion engine; the pump comprising:

a pump body;

a piston movable along a first axis for pumping fuel;

an operating unit for the piston capable of moving the piston along the first axis; a shoe located between the piston operating unit and the piston to operatively couple them;

and wherein the shoe and the piston are in abutment with each other along a first contact surface of the shoe and along a second contact surface of the piston; the first contact surface being concave.

Thanks to the present invention, the useful life, reliability and efficiency of the pump are greater than in the case of the known art, because the forces radial to the axis of the piston and bearing on the piston itself are smaller. Furthermore, thanks to the present invention, the relative movements between the shoe and the piston are smaller, thus causing a reduction in wear along the first and second contact surfaces and improving the operation and the useful life of the piston. Furthermore, thanks to the present invention, the abutment coupling between the first and second contact surfaces causes a reduction in misalignments between the piston and the shoe. Another advantage of the present invention is the increase in efficiency of the pump thanks to the reduction in the overheating of the piston; this increase in efficiency is due to the reduction in the reaction forces on the piston which develop along a cylinder in which the piston slides.

According to a preferred embodiment of the present invention, the first contact surface has a first radius of curvature smaller than 450 mm.

According to another preferred embodiment of the present invention, the first contact surface has a first radius of curvature greater than 350 mm.

According to another preferred embodiment of the present invention, the first contact surface has a first radius of curvature equal to 400 mm. According to another preferred embodiment of the present invention, the second contact surface is convex.

Thanks to the present invention there is an abutment coupling between a convex surface and a concave surface which makes it possible to limit the forces radial with respect to the axis of the piston and the relative movements between the piston and the shoe. This causes a reduction in wear and improves the operation and useful life of the pump.

According to another preferred embodiment of the present invention, the second contact surface has a second radius of curvature greater than 250 mm.

According to another preferred embodiment of the present invention, the second contact surface has a second radius of curvature smaller than 350 mm.

According to another preferred embodiment of the present invention, the second contact surface has a first radius of curvature equal to 300 mm.

According to another preferred embodiment of the present invention, wherein the first contact surface has a first radius of curvature and the second contact surface has a second radius of curvature and wherein a ratio between the second radius of curvature and the first radius of curvature is comprised between 0.60 and 0.90, in particular the ratio is equal to 0.75.

According to another preferred embodiment of the present invention, the piston comprises a rod and a foot, the foot being in contact with the shoe along the second contact surface .

According to another preferred embodiment of the present invention, the pump comprises a cup which in turn comprises the shoe and a cylindrical wall which slides along a cylinder of the piston.

The present invention will now be described with reference to the annexed drawings, which illustrate a non-limiting embodiment of the invention, in which:

figure 1 is a view in section, with parts removed for clarity and not in scale, of a high pressure pump created according to the present invention; and

figure 2 is an enlarged view and not in scale of a detail of High pressure pump of figure 1.

In figure 1, no. 1 indicates, in its entirety, a high pressure pump for supplying fuel from a low pressure hydraulic circuit to an internal combustion engine (not illustrated in the annexed drawings) , in particular a Diesel cycle engine fitted to a motor vehicle.

Pump 1 is a piston pump and comprises, in this instance, a pump body 2 and a piston 3 arranged radially and movable in reciprocating motion along an axis Al under the thrust of an operating unit 4 of the piston 3.

In particular, the pump body 2 comprises a central body 5, inside which is formed a cylindrical housing 6 having an axis A2 transverse to axis Al and accommodating, with the interposition of two bearings 8, a drive shaft 9, which is part of the operating unit 4 of the piston 3 and features, at a free end thereof external to the central body 5, a conical portion 10 for attachment to an output of an engine (not illustrated) . The drive shaft 9 has an enlarged intermediate portion, which is housed inside a chamber 11 of the central body 5 and forms a cam 12 for operating the piston 3.

The cam 12 has the form of a solid of substantially elliptical section (not visible in the annexed drawings) , featuring two lobes (not visible in the annexed drawings) arranged symmetrically on opposite segments of axis A2.

Besides the central body 5, the pump body 2 comprises a head 14 formed of a metal block assembled to the central body 5 and having a compression chamber 15 and a cylinder 16 coaxial with axis Al and housing the piston 3 in axially slidable manner.

The head 14 houses, furthermore, a supply duct (not illustrated) for supplying fuel, in use, through an inlet valve to the compression chamber 15 through an inlet valve (not illustrated) ; an outlet duct 18 for supplying fuel, in use, to the internal combustion engine (not illustrated) through a high pressure control valve (not illustrated) .

The operating unit 4 comprises, furthermore, a tappet, which is coupled to the cam 12 in order, in use, to convert the rotary motion of the cam 12 into the reciprocating motion of the piston 3 and is movable, with piston 3 itself, along axis Al .

The pump 1 comprises a socket 23 which in turn comprises a shoe 22 and a cylindrical wall 24, which extends along axis Al, and is slidably housed along axis Al in a respective cylindrical housing 25 formed in the central body 5 in a position coaxial with axis Al . Furthermore, the cylindrical wall 24 forms, in the housing 25, a housing for accommodating the shoe 22 and the piston 3 and for an elastic system 26. The shoe 22 and the cylindrical wall 24 are assembled with an interference fit and are integral with each other.

The tappet is formed of a roller 19, which has an axis (not illustrated in the annexed drawing) parallel to axis A2 and perpendicular to axis Al and is housed, in angularly free manner, in a semicylindrical housing formed in the shoe 22 of the socket 23. The elastic system 26 comprises a helical spring 27 and a disc 28. The spring 27, at one end, is housed on the disc 28, while at the other end it is in abutment with the head 14. Consequently, the spring 27 is compressed between the head 14 and the disc 28.

The disc 28 on one side houses the spring 26, and on the other side houses a foot 29 of piston 3.

In use, with reference to figures 1 and 2, the foot 29 of the piston 3 is in abutment with the shoe 22 of the socket 23, in particular along a contact surface 30 of shoe 22 and along a contact surface 32 of the foot 29 of the piston 3. In use, thanks to the effect of the spring 27, the foot 29 of the piston 3 is maintained in constant contact with the shoe 22, the shoe 22 is in constant contact with the roller 19, and the roller 19 in constant contact with the cam 12.

With reference to figures 1 and 2, the piston 3 comprises the foot 29 and a rod 36; the rod 36 is housed in the cylinder 16. The rod 36 and the foot 29 have a radial dimension D. In a preferred and non-limiting embodiment of the present invention the radial dimension D is 6.5 mm.

The contact surface 30 of the shoe 22 is concave. In particular, the contact surface 30 has a spherical shape having a radius of curvature Rl comprised between 350 mm and 450 mm. Furthermore, in a preferred embodiment, the contact surface 30 has radius of curvature Rl equal to 400 mm.

The contact surface 32 of the foot 29 of the piston 3 is convex. In particular, the contact surface 32 has a spherical shape having a radius of curvature R2 comprised between 250 mm and 350 mm. Furthermore, in a preferred embodiment, the contact surface 32 has radius of curvature R2 equal to 300 mm. Furthermore, the radii of curvature Rl and R2 are in proportion to each other, in particular the ratio between radius of curvature R2 and radius of curvature Rl is comprised between the values 0.60 and 0.90. In a preferred embodiment, the ratio between radius of curvature R2 and radius of curvature Rl is equal to 0.75.

In use, the foot 29 and the shoe 22 form an abutment coupling between first contact surface 30 which is concave and second contact surface 32 which is convex. Said abutment coupling reduces the forces radial to the piston compared with the known art, thus increasing the useful life, the reliability and the efficiency of the pump. Furthermore, the relative movements between the shoe and the piston are smaller, thus causing a reduction in wear along the first and the second contact surfaces 30 and 32 and improving the operation and the useful life of the pump 1 and reducing wear. Furthermore, thanks to the present invention, the abutment coupling between the first and the second contact services 30 and 32 causes a reduction in misalignments between the piston 3 and the shoe 22. Another advantage of the present invention is the increase in efficiency of the pump 1 thanks to the reduction in the overheating of the piston 3; this increase in efficiency is due to the reduction in the reaction forces of the piston 3 which develop along the cylinder 16.

In an alternative embodiment of the present invention, the radial dimension D is equal to 5.5 mm and the radii of curvature Rl and R2 are in proportion to each other, in particular the ratio between the radius of curvature R2 and the radius of curvature Rl is comprised between the values 0.60 and 0.90. In a preferred embodiment, the ratio between the radius of curvature R2 and the radius of curvature Rl is equal to 0.75.

In another embodiment of the present invention, the radial dimension D is equal to 7.35 mm and the radii of curvature Rl and R2 are in proportion to each other, in particular the ratio between the radius of curvature R2 and the radius of curvature Rl is comprised between the values 0.60 and 0.90. In a preferred embodiment, the ratio between radius of curvature R2 and radius of curvature Rl is equal to 0.75.

It is furthermore obvious that the present invention also covers embodiments not described in the detailed description and equivalent embodiments which come into the protective scope of the annexed claims.