GB2033959A

GB2033959A - Fuel Injection Pump

Info

Publication number: GB2033959A
Application number: GB7933126A
Authority: GB
Original assignee: Cav Rotodiesel SA; CAV Rotodiesel SA
Current assignee: Cav Rotodiesel SA; CAV Rotodiesel SA
Priority date: 1978-09-29
Filing date: 1979-09-25
Publication date: 1980-05-29
Also published as: FR2437502B1; IT1119189B; DE2939142A1; IT7968881A0; JPS5549569A; FR2437502A1

Abstract

A fuel injection pump for internal combustion engines is provided which comprises a rotary distributor (1) having two axially spaced transverse bores (10, 10') each accommodating a pair of pistons (11; 11'). An axially extending delivery passage (6) is formed in the distributor to connect the pumping chambers defined between the respective pairs of pistons to a fuel inlet (5) and to outlets (9) connected to respective injection nozzles of the engine. A cam ring or rings (14) surrounding the distributor actuate all of the pistons (11, 11') in unison so that each pair of pistons displaces fuel towards the engine via the delivery passage (6) irrespective of the operating conditions of the engine. <IMAGE>

Description

SPECIFICATION Fuel Injection Pump The present invention relates to improvements in fuel injection pumps for internal combustion engines, and particularly for diesel engines.

Heretofore known types of injection pumps comprise a housing, a rotary distributor mounted in the housing, a transverse bore formed in the distributor, a pair of pistons mounted in said bore, a cam ring surrounding the distributor, which ring comprises on its inner periphery a plurality of cam lobes arranged to move the pistons inwardly as the distributor rotates, an axially extending delivery passage provided in the rotary distributor and connecting the pumping chamber defined between the pistons, on the one hand to fuel inlets formed in the housing and, on the other hand, to an outlet passage whose opening is successively brought, as the distributor rotates, into coincidence with outlet ports formed in the housing and respectively connected to the injection nozzles of the associated engine, said cam lobes engaging rollers carried by shoes in contact with the respective pistons, respective stop members being provided to limit the outward movement of the pistons due to fuel under pressure supplied to the pumping chamber.

In injection pumps of this type, the rolling motion of the rollers on the cam lobes produces compression strains, called Hertz strains. These strains produce an elastic deformation of the metal and, when a relative movement is produced between the parts in contact, the successive deformations lead to a degradation of the metal, or fatigue, which occurs all the more quickly as the strains are higher.

These strains are, on the one hand, proportional to the effort applied to the parts, i.e.

in the present case to the effort produced by the injection pressure acting on the section of the pistons and, on the other hand, they increase when the curvature radii of the parts in contact decrease.

In order to reduce the Hertz strains, it may therefore be contemplated to reduce the section of the pistons, but this would lead to a decrease in the injection pressure which would be detrimental to the engine performances.

To reduce these stresses without modifying the injection pressure, an arrangement has been proposed which comprises two intersecting bores of which the axes are located in the same plane, each bore receiving two opposite pistons, both pairs of pistons being actuated by one single cam ring with the same width as in the conventional pump of the above-specified type. This arrangement effectively makes it possible, for a given injection pressure, to divide the Hertz strains by two since the section of each piston may be divided by two, but the number of passages of the rollers on a given cam lobe is multiplied by two, which makes the stress reduction thus obtained less attractive.

It is therefore an object of the present invention to provide an injection pump in which the Hertz strains are reduced without decrease in the injection pressure and without increase in the number of passages of the rollers on the same cam lobe.

To this end, in the injection pump according to the invention, there is provided at least a further pair of pistons received in a further transverse bore formed in the distributor, the two bores having their axes in parallel planes, said further pistons being actuated by a further cam ring via respective rollers, both cam rings being mutualiy secured for rotation and arranged so that all the pistons are moved in unison, the pumping chamber defined within said further bore being in communication with said axially extending delivery passage, whereby each pair of pistons provides a part of the fuel amount delivered to the engine whatever be the operating conditions.

In the arrangement according to the invention, including a cam ring for each pair of pistons, the generatrices of the cam profile taken as a whole has a length twice that in the conventional pump.

The active cam surface is increased accordingly and the purposes of the invention are achieved.

Furthermore it is important that for a satisfactory operation of the pump that one roller be associated with each of the pistons. A single roller for two pistons would not correctly follow the cam profile, in view of the fact that the generatrices of the cam profile are twice longer than in the conventional arrangement.

French Patent Application 2,349,038 discloses an injection pump comprising, in addition to the main bore, a second bore receiving a second pair of pistons, but the arrangement is such that the inward movement of the second pistons occurs in advance with respect to that of the first pistons to produce a pilot injection.

French Patent 2,328,117 discloses an injection pump having two pairs of pistons actuated in unison, but the fuel amount delivered by one of the pairs of pistons is supplied to the engine only on starting and in normal operation, all the fuel amount is supplied by the other pair of pistons.

US Patent 2,765,741 and French Patent 2,166,746 disclose an injection pump having two axially spaced, diametrical bores in which the respective cam rings are angularly adjustable with respect to one another, with a view to allowing adjustment of the rate flow and the duration of injection.

The invention will be more readily understood on reading the following description with reference to the accompanying drawings, in which Fig. 1 is a schematic axial section of a pump according to the invention, and Fig. 2 is a transverse section of a modified embodiment.

Fig. 1 shows an injection pump which comprises a rotary distributor 1 mounted in a housing 2 and driven in timed relationship with the engine which is to be supplied with fuel. One end of the rotary distributor 1 is coupled to the rotating part of a feed pump 3 of which the outlet 4 is connected via a metering member (not shown) to an inlet port 5 which opens out on the periphery of the rotary distributor. The outlet pressure of the feed pump 3 is regulated, in known manner, by means (not shown) so as to vary in accordance with the speed of the engine.

The rotary distributor 1 comprises an axially extending delivery passage 6 which communicates with a plurality of inlet passages 7 formed in the rotary distributor in equi-angular arrangement, which are in turn brought into coincidence with the inlet port 5 as the rotary distributor rotates. On the other hand, the delivery passage 6 communicates with an outlet passage 8 which opens out on the periphery of the rotary distributor and is successively brought in register, as the rotary distributor rotates with a plurality of outlets 9 formed in the housing 2 and connected to respective injection nozzles mounted on the associated engine.

The delivery passage 6 communicates at its other end with two transverse bores 10, 1 0' formed in the rotary distributor with their axes in two parallel planes. Each of these bores receives a pair of opposed pistons 11, 1 1' respectively, which define therebetween pumping chambers.

The pistons 11 and 11' are identical.

Pistons 11,11 r respectively are engaged at their outer ends with respective shoes 12, 12' carrying rollers 1 3, 1 3' respectively. A cam ring 14, fixed to the housing 2, has formed on its inner periphery cam lobes which engage the rollers 13, 13' respectively as the rotary distributor rotates to produce an inward movement of the pistons 11,11 and therefore the displacement of fuel present in the pumping chamber towards the outlet passage 8.

The cam lobes are conventionally disposed in diametrically opposed pairs and their number depends on the number of cylinders of the associated engine.

On the other hand, the outward movement of the pistons 11,11 under the action of the pressurised fuel present in the pumping chambers is limited by respective stop members engageable with the shoes. The stop members are constituted, as disclosed in French Patent 2,165,220, by flexible blades secured by screws to the rotary distributor. The flexion of the blades may be varied by means of the screws, this enabling the stroke of the pistons, and therefore the maximum fuel amount which may be supplied by the pump, to be adjusted.

It will be noted, on this subject, that, in the pump according to the invention, the arrangement of the shoes described in above cited French Patent 2,165,220 may be used, which enables the maximum fuel amount to be varied as a function of the operational parameters of the engine due to the axial mobility of the shoes.

The angular position of the cam ring 14 is conventionally adjustable by means of a piston 1 5 subjected to a control pressure which is generally varied in accordance with the speed of the engine, the piston 1 5 being extended by a peg 16 attached to the cam ring 14. This enables the timing of injection to be varied according to the speed of the engine.

It should be emphasized that the cam lobes which act respectively on the rollers 13 and 13' are arranged so that the pistons 11 and 11' are moved inwardly perfectly in unison. The pistons 11 and 11' thus perform exactly the same role, insofar as pumping is concerned.

The advantage of such an arrangement with respect to a conventional injection pump having one bore receiving a pair of pistons is that, for a given injection pressure, the section of the pistons is divided by two since their number is multiplied by two. Taking in account that the active cam surface is twice that in the conventional construction, a corresponding decrease of the Hertz strains is achieved and accordingly a substantial improvement in the reliability of the pump.

Fig. 2 shows a modified embodiment in which, instead of the bore 10 of Fig. 1, there is provided a pair of bores 1 Oa, 1 Ob of which the axes are in the same plane perpendicular to the axis of the rotary distributor. The bore 10' of Fig. 1 is likewise replaced by a pair of bores.

A pair of pistons 11 a, 11 b, each provided with a roller 13a,13b, respectively and a shoe 12a, 1 2b respectively, is associated with each bore 10aor 10b.

There are therefore eight pistons instead of two in the conventional pump. The reduction in Hertz strains thus achieved is still greater.

It is clear that the invention is not limited to the embodiments described. More than two bores may thus be provided in the same plane, for example three intersecting bores. More than two diametrical bores whose axes are in different planes may also be provided, for example three bores.

Claims

1. A fuel injection pump for supplying fuel to an internal combustion engine, comprising a housing, a rotary distributor mounted in the housing, a transverse bore formed in the distributor, a pair of pistons mounted in said bore, a cam ring surrounding the distributor, which ring comprises on its inner periphery a plurality of cam lobes arranged to move the pistons inwardly as the distributor rotates, an axially extending delivery passage provided in the rotary distributor and connecting the pumping chamber defined between the pistons, on the one hand, to fuel inlets formed in the housing and, on the other hand, to an outlet passage whose opening is successively brought, as the distributor rotates, into coincidence with outlet ports formed in the housing and respectively connected to the injection nozzles of the associated engine, said cam lobes engaging rollers carried by shoes in contact with the respective pistons, respective stop members being provided to limit the outward movement of the pistons due to fuel under pressure supplied to the pumping chamber, wherein there is provided at least a further pair of pistons received in a further transverse bore formed in the distributor, the two bores having their axes in parallel planes, said further pistons being actuated by a further cam ring via respective rollers, both cam rings being mutually secured for rotation and arranged so that all the pistons are moved in unison, the pumping chamber defined within said further bore being in communication with said axially extending delivery passage, whereby each pair of pistons provides a part of the fuel amount delivered to the engine whatever be the operating conditions.

2. A pump as claimed in Claim 1 wherein the respective cam rings are made in the form of a single cam ring.

3. A pump as claimed in Claim 1, comprising at least two bores with axes in the same plane.

4. A fuel injection pump for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

5. A fuel injection pump for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figure 1 as modified by Figure 2 of the accompanying drawings.