EP0687812B1 - High pressure pump for feeding fuel injectors for internal combustion engines - Google Patents

Description

It is known to use injectors in engines with explosion. However, to supply such injectors, it high pressure pumps (about 140 bar) are required and is very difficult to realize such pumps because the essence has a viscosity and a very greasy power low and the result is that these pumps are expensive.

Hydraulic axial piston pumps driven in one reciprocating movement through a bias plate are known for a long time. In particular in the patent 1,519,694 of February 3, 1967 a pump has been described bias against the inclined face of which lie a plurality of hollow pistons each supported by a spring. Each hollow piston is provided with a spherical head resting in the conical housing of a stud, also hollow which slides on the inclined face of the bias plate. On this inclined face is engraved a curved groove in the shape of a lunula of such so that when a skate passes over the lunula, the hydraulic communication is established between the chamber, filled with oil, in which the bias plate swings and the interior of the corresponding hollow piston; what achieves the hydraulic fluid intake phase in the piston. In the part of the skate stroke that corresponds to displacement movement of the piston, this communication is interrupted and the liquid is discharged at high pressure at through a non-return valve placed on the opposite side of the piston.

This arrangement does not allow pumping at high pressure liquids such as unleaded petrol because it immediately produces seizures and leaks.

The present invention relates to such a pump which has the considerable advantage of being very simple and therefore very good market while not seizing up despite the fact that petrol has practically no lubricating power, in particular unleaded gasoline.

The pump according to the present invention is a pump bias and axial piston platter of the type in which said axial pistons are hollow and each have a head partially spherical which rests on a stud sliding on the surface of the bias plate which turns in a room inlet filled with liquid to be pumped and has a curved bezel allowing suction through the studs and the heads of the pistons, characterized in that the pump body is in one piece and is in two parts, the first part with a cylindrical bore in which are arranged the pump shaft and the bearings who wear it; while the second part has a another bore in which are arranged: a bias plate secured to the pump shaft; a cylindrical core, whose faces are parallel, crossed by a series through bores intended to receive the pistons; a second core with the flat front face applied the rear flat face of the first core, this second core carrying non-return valves opposite each bore opening and the rear part of which has a shoulder circular; and a screw cap at the end of said second bore and bearing on the shoulder of the second core so as to keep the two cores tight one against the other pressing against a circular stop formed in the second part of the pump body at the level of the front face of the first core; the two parts of the pump body being separated from each other by a seal sealing so that only the second pieces part are in contact with the gasoline to be injected.

As an example and to facilitate the understanding of the invention, there is shown in the accompanying drawing a view in longitudinal section of an embodiment of the invention.

Referring to this figure, we see that the body 1 of the pump is in two parts 1a and 1b, the bore of the part 1a may have a diameter different from that of part 1b and these two parts being separated one of the other by a seal 2.

The first part 1a is also closed by another seal 3 and between the two seals 2 and 3, are arranged bearings 4 which carry the shaft 5 of the pump. A cap 6 allows a quantity of lubricant housed in the free space between the seals 2 and 3.

The internal bore of part 1b has a crown circular 7 intended to constitute a support stop.

On the side of the stop 7 facing part 1a is arranged a chamber 8, called the intake chamber, in which struggles a bias plate 9, integral with the tree 5 and having, in the example shown, a diameter close to that of the tree 5.

Between the bias plate 9 and the shaft 5 is disposed a cylindrical ring 10, which serves as a bearing surface for the seal sealing 2.

On the other side of the stop 7 is disposed a core cylindrical 11. This cylindrical core 11 has two faces parallel planes 11a and 11b. This nucleus is crossed by a plurality of through bores 12, which are 3 in the example shown.

In each bore 12 is disposed a hollow piston 13, of which the head 14 is a portion of a sphere which rests in the conical housing of a support pad 15 which slides on the surface 9a of the bias plate 9.

In a manner known per se, the surface 9a of the bias plate 9 has a curved lunula which allows the liquid to finding in chamber 8 to cross the stud 15 and the head 14 to penetrate inside the piston 13. The chamber 8 has an inlet 8a.

In abutment against the rear face 11b of the core 11 is the front face of a second core 16 which carries a plurality of non-return valves 17, each opposite each bore 12 (three in the example shown).

At its rear part, this core 16 has a shoulder 18. A plug 19, screwed into the internal bore of part 1b comes to bear on the shoulder 18 of the core 16 and thus keeps the two cores 16 and 11 tight against each other the other pressing against the circular stop 7. A pawn of blocking 20 ensures correct positioning of the two cores 11 and 16 relative to each other.

The pump shaft 5 is made of alloy steel and treated to have a Rockwell hardness of 62HRC. Face 9a of bias plate undergoes a succession of operations of grinding, lapping and polishing with dough to have a surface condition which corresponds to a roughness index Ra (Arithmetic roughness) less than 0.2 micron.

The studs 15 are made of bronze; their flat face is lapped at Ra = 2 microns. The conical housing of each of the studs 15, in which the spherical head 14 of the piston rests is all first polished so as to have a surface finish corresponding to the standard Ra = 0.2 micron; and then we traces on this surface a multiplicity of scratches crossed less than a hundredth of a millimeters. This allows a film of liquid to be maintained to the cone / sphere contact circle even when the pump is at standstill and prevents seizure during startup.

The pistons 13 are made of alloy steel treated to have a Rockwell hardness of 62 HRC. The sphere of each piston is ground in stone for a surface finish Ra = 0.1 micron. Lapping is followed by polishing with a paste of so as to obtain a "mirror polish". The core 11 is made of bearing type steel, treated for hardness Rockwell at the heart of 60 HRC.

The fact that the bores 12 are through bores allows machining their surface with the same high precision as that of the pistons so as to give them the same condition of surface.

The finish of the rear face 11b of the body 11 is rectified, then lapped and final polishing on marble allows to obtain a "lapped-glazed" surface finish of roughness Ra less than 0.2 micron.

The non-return valves 17 are made of steel with high mechanical characteristics, treated to have a breaking strength of 1.800 N / mm ² . After this treatment, the valves undergo a plane running-in to obtain a surface condition Ra = 0.2 micron, then an icing on polishing marble with a flatness less than a "fringe", the fringe being a unit of measurement of flatness. A high quality of the seal 11b / valves 17 is thus obtained.

The nut 19 makes it possible to carry out a prestress on the cores 11 and 16 which are pressed against each other at a force greater than the maximum separation force at which they will be submitted during operation.

These two cores are preferably provided with seals sealing 21 and 22. But again, the fact that the internal bore of part 1b is a bore opening out and the fact that the outer walls of the cores 11 and 16 are cylinders to obtain a state of perfect surface of these walls and therefore sealing by metal to metal contact such that seals 21 and 22 do not are practically unsolicited and thus have a excellent resistance over time.

In the example shown, the slope of the bias plate is determined so that the value of the tangent is 0.2, which gives an angle of 11.2 °. It is better that this angle is between 10 ° and 15 °. For values the radial component of the forces acting on the pistons becomes too large and this can cause a scratch between the pistons and their bores.

The particular structure of the pump allows two separate parts separated from each other by the joint sealing 2, the part 1a which supports the largest efforts being isolated from the essence and bathed in a lubricant, only the second part 1b is bathed in gasoline.

All of these provisions result in that it is possible to make a bias plate pump which pumps not a hydraulic fluid with good viscosity (200 centiStokes) but petrol having a viscosity 400 times lower (0.5 centiStoke), which never could be obtained before.

Claims (12)

1. A high-pressure pump for feeding fuel injectors of the type having a bias plate (9) and axial pistons, said pistons (13) being hollow and each resting by means of their spherical heads (14) against a sliding contact piece (15) which slides on the bias plate (9) which moves within an admission chamber (8) filled in particular with unleaded fuel and comprises a crescent permitting the intake of the fuel into the pistons (13) through the contact pieces (15) and the piston heads (14), characterised by the fact that the body (1) of the pump is monobloc and in two parts, the first part (la) comprising a cylindrical bore in which are arranged the shaft (5) of the pump and its bearings (4); whilst the second part (1b) comprises a different bore in which there are arranged: a bias plate (9) integral with the shaft (5) of the pump; a cylindrical core (11), the faces (11a, 11b) of which are parallel, through which a plurality of opening bores (12) pass which are intended to receive the pistons (13); a second cylindrical core (16) having a plane front face which is applied against the rear face (11b) of the first, this second core (16) bearing non-return valves (17) opposite each bore (12) and the rear part of which comprises a circular shoulder (18); and a plug (19) screwed to the end of the internal bore of the second part (16) or the pump body (1), said plug (19) bearing on the shoulder (18) of the second core (16) so as to keep the two cores (11, 16) pressed tightly against one another, bearing against a circular stop (7) provided in the second part (1b) of the pump body (1), the internal bores of the two parts (la, 1b) of the pump body being separated from each other by a gasket (2) such that only the parts located in the second part (1b) are in contact with the fuel to be injected.
2. A pump according to Claim 1, in which the internal bore of the first part (1a) of the pump body (1) is provided with a second gasket (3) such that the space in which the bearings are arranged is impermeable and filled with a lubricant of metered capacity.
3. A pump according to Claim 1, in which the bias plate (9) has a slope which is preferably between 10° and 15°.
4. A pump according to Claim 3, in which the bias plate (9) has a slope of 11.2°.
5. A pump according to Claim 1, in which the sliding contact pieces (15) are made of bronze, the conical housings of these contact pieces receiving the spherical heads (14) of the hollow pistons (13) being firstly polished so as to have a surface condition of Ra = 0.2 microns; this surface then being provided with crossed scores of an average depth of less than one-hundredth of a millimetre.
6. A pump according to Claim 1, in which the core (11) in which the bores (12) receiving the hollow pistons (13) are provided is made of bearing-type steel treated for a Rockwell core hardness of 60 HRC, said pistons (13) being of alloyed steel treated to have a Rockwell hardness of 62 HRC.
7. A pump according to Claim 6, in which the spherical head (14) of each piston (13) is honed for a surface condition of Ra = 0.1 micron, and then is polished using paste until it is "mirror-finished".
8. A pump according to Claim 1, in which the rear face (11b) of the core (11) in which the bores (12) for the hollow pistons (13) are made is polished, ground, honed then polished on marble so as to have a honed-mirror-finished surface condition of a roughness Ra of less than 0.2 microns.
9. A pump according to Claim 1, in which the face (9a) of the bias plate (9) is ground, honed and polished so as to have a surface condition of roughness Ra of less than 0.2 microns.
10. A pump according to Claim 1, in which the cores (11) and (16) are prestressed by means of the plug (19) so as to be held tightly against one another with a force which is at least slightly greater than the maximum separation stress to which they may be subjected during operation.
11. A pump according to Claim 8, in which the correct positioning of the cores (11) and (16) relative to each other is obtained by a pin (20).
12. A pump according to Claim 1, in which the cores (11 and 16) are provided with gaskets (21 and 22).

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