Transfer pump with several pistons

Description

This invention has as its object a pump of the type called a transfer pump, i.e., of the type that comprises a moving part that pumps an aggressive liquid such as automotive fuel, whereby this moving part is driven by an alternating movement by the oil that is pumped by a hydraulic pump.

It is known to use a hydraulic pump with a single piston, a so-called single-piston pump, to supply the injectors of an engine with fuel at high pressure.

A pump of this type is described in the patent U.S. Pat. No. 1,696,825 of Dec. 25, 1928, as well as in the patent application Ser. No. 06/02,594 of Mar. 24, 2006, in the name of the applicant.

The flow rate provided by a single-piston pump, however, has proven inadequate for high capacities.

Actually, in practice, it turns out that there is a maximum limit of the capacity of the single-piston pumps, a limit that is approximately a bit more than 1 cc per turn.

To increase this capacity, the travel of the piston should be increased or the diameter should be increased. If the travel is increased, the accelerations are high; if the diameter is increased, the force upon contact with the cam that drives the piston becomes too significant.

The use of two single-piston pumps is therefore proposed, but it then is necessary to double the electronic control means, which is suitable for a prototype but is not economically suitable for the very large-scale production (2,000 single-piston pumps with 2,000 electronic control means are necessary for 1,000 engines per day).

These electronic control means are in general solenoid valves that are controlled by the engine monitoring computer.

The transfer pump according to the invention is of the type in which the moving part for pumping is a metal bellows that is alternately filled with and emptied of hydraulic liquid at high pressure, whereby the amount of fuel allowed into the chamber in which said bellows moves is determined, upstream, by a solenoid valve that is driven by the computer for monitoring the engine, characterized by the fact that it comprises at least two pumping units (bellows/piston) that are supplied by a single intake system, common to the two units.

This invention can also comprise all or part of the following arrangements:

• • a. The conveyor circuit is common to pumping units;
  • b. The pump comprises two pistons, whereby each piston is actuated by a cam, whereby the two cams are carried in parallel by a camshaft and are angularly offset by 60°;
  • c. The pump comprises “n” pistons, whereby each piston is actuated by a cam, whereby the “n” cams are carried parallel to one another by a camshaft and are angularly offset;
  • d. The pump comprises a single cam and at least two pistons placed radially around the cam;
  • e. The pump comprises two pistons that are placed in a V at 60° C. from one another.

By way of nonlimiting examples and to facilitate the understanding of the invention, there have been shown in the accompanying drawings:

FIG. 1, a diagrammatic view of a first embodiment of the invention.

FIG. 2, a variant of FIG. 1.

FIG. 3, a perspective view illustrating a pump according to FIG. 1.

FIG. 4, a diagrammatic view of a variant embodiment of FIGS. 1 and 2 with “n” pistons.

FIG. 5, a diagrammatic view of a second embodiment of the invention.

By referring to FIGS. 1 and 2, it is seen that the pump according to the invention comprises two pistons 1a and 1b that are driven by two cams 2a and 2b that are parallel and carried by a shaft 3.

Each cam 2a and 2b comprises three lobes, placed at 120° C. from one another (as is shown in FIG. 3).

In a way that is known in the art, each piston 1a and 1b moves hydraulic liquid inside a bellows 4a, 4b, which extends and retracts in a chamber 5a, 5b. The inside of the bellows 4a, 4b receives hydraulic liquid that is put under high pressure when the piston 1 rises, high pressure that is communicated to the fuel that is found in the chambers 5a, 5b.

According to this invention, the fuel is allowed into the two chambers 5a, 5b by means of a single supply circuit 6 that comprises two branches 6a, 6b.

The supply circuit 6 is connected by the orifice 7 to the tank by way of a solenoid valve 8 that measures the amount of fuel that can be introduced into the chambers 5a and 5b.

Two nonreturn valves 7a, 7b allow the fuel that is fed via the hose 6 to penetrate the chambers 5a, 5b, and two nonreturn valves 9a, 9b allow the fuel that is fed at high pressure via the bellows 4a, 4b to flow into the single conveyor duct 10 toward the conveyor orifice 11.

Preferably, the cams 2a and 2b are offset angularly by 60°.

This arrangement provides the following advantages:

• • As there is a single supply and conveyor circuit, there are fewer components than with two standard single-piston pumps.
  • In particular, there is only a single solenoid valve 8 for monitoring the amount of fuel sent to the engine.
  • The force exerted by the pistons on the camshaft 3 is less than the equivalent capacity that would be present if there were a single piston.
  • The angular offset of the two cams 2 ensures better progressiveness of the pressurized flow toward the injection rail and makes it possible to reduce the variations of the torque on the camshaft.

In the embodiment shown in FIG. 1, the conveyor circuit is common to two pistons 1a and 1b, but the invention is not limited to this particular embodiment: it is possible to use a conveyor circuit 10a and 10b for each piston as is illustrated in FIG. 2 in which the same elements bear the same references.

FIG. 4 illustrates a variant embodiment in which the same elements bear the same references.

According to this variant, there are more than two pistons 1a, 1b . . . 1n each driven by a cam 2a, 2b . . . 2n, whereby these cams are parallel to one another and carried by the same camshaft 3.

There is a conveyor circuit 10 that is common to all “n” pistons, as in the case of FIG. 1; but it would be possible to use a conveyor circuit (10a, 10b . . . 10n) for each piston, as in the case of FIG. 2.

The only difference with the pump of FIG. 1 is that there is only a single cam 1 (whereby the camshaft 3 is drawn symbolically) to drive the two pistons 1a and 1b, but the latter are placed in a V, their axes being arranged at 60°.

The same advantages as in the example of FIG. 2 are obtained, whereby the unit is a bit more compact.

In this same FIG. 5, an additional piston 1m, . . . is shown symbolically by the branching 6m of the duct 6 and by being connected at 10m to the conveyor duct 10.

The purpose of this representation is to demonstrate that it is possible to use, in a radial manner, a number “m” of pistons, around the cam 2.

In all of the examples that are shown, the cams are cams with three lobes arranged at 120° from one another, but it is necessary to note that the invention is not limited to this particular example: the cam 2 can comprise one or more lobes.