GB2082266A

GB2082266A - Driving mechanism for fuel injection pumps

Info

Publication number: GB2082266A
Application number: GB8123385A
Authority: GB
Original assignee: Friedmann and Maier AG
Current assignee: Friedmann and Maier AG
Priority date: 1980-07-31
Filing date: 1981-07-30
Publication date: 1982-03-03
Also published as: DE3129317A1; GB2082266B; ATA398780A; AT367172B

Abstract

The driving mechanism comprises a rocker arm (4) for actuating, via a tappet 12 a piston rod and piston of the pump. The rocker is mounted on an eccentric shaft (7) which is rotatable by a special drive (not shown) for the purpose of adjusting the timing of the injection pump. The pump is operated by a camshaft (3) driven by the engine and has in addition to a fuel injection cam lobe (2) one or more auxiliary cam lobes (13, 14) which merely give the rocker arm (4) a slight swivelling movement but do not cause fuel injection. Normally a large torque is required to rotate the eccentric shaft (7) to adjust the pump timing in operation but the addition of the auxiliary cam lobes (13 14) give a continuous swivelling movement to the rocker arm (4) during the adjusting process so that only sliding friction between the arm (4) and the eccentric shaft (7) has to be overcome, thus reducing the torque required for adjustment. The height of the auxiliary cam lobe is not more than one fifth of the height of fuel injection cam lobe. <IMAGE>

Description

SPECIFICATION Driving mechanism for fuel injection pumps The present invention relates to a driving mechanism for single or multi-cylinder fuel injection pumps of internal combustion engines.

The invention is especially concerned with driving mechanisms of the kind comprising a camshaft adapted to be driven by the internal combustion engine and which are provided with a fuel injection cam for the or each cylinder of the fuel injection pump. The or each injection cam cooperates in use with a two armed rocker lever.

One end of one arm of the lever carries a cam follower, the central part of the lever is supported by an eccentric shaft and the end of the other arm is operatively connected to the piston of the pump.

The eccentric shaft is rotatable by a special drive mechanism. In this type of driving mechanism the eccentric shaft serves for adjusting the injection timing.

Similar driving mechanisms to that referred to above of a known type suffer from the disadvantage of necessitating a relatively large torque for turning the eccentric shaft on account of the friction in the various bearings of the eccentric shaft and the rocker levers. This disadvantage is particularly felt during the periods of fuel injection. In many cases this means that the eccentric shaft can be adjusted only when no fuel is injected whereas during periods of fuel injection the eccentric shaft does not move at all.

It is the object f the present invention to eliminate the above-mentioned disadvantages or at least to reduce them as far as possible and to provide a driving mechanism of the aforementioned type which will require less torque for turning the eccentric shaft, thus guaranteeing continuous movement of the eccentric shaft during the adjusting process even in periods of injection, without an increase of driving power.

The present invention consists in a driving mechanism for single or multi-cylinder fuel injection pumps used on internal combustion engines, said mechanism comprising a camshaft adapted to be driven by the internal combustion engine and having a fuel injection cam for the or each cylinder of the fuel injection pump, the or each injection cam being co-operable with a twoarmed rocker lever, one end of one arm of the lever carrying a cam follower, the central part of the lever being supported by an eccentric shaft and the end of the other arm being operatively connected to the piston of the pump, wherein the eccentric shaft is rotatable by a special drive and at least one auxiliary cam is positioned on the camshaft at an angular distance from the fuel injection cam or any cam used for fuel injection, the height of the auxiliary cam, as taken from the base circle of the camshaft cross-section, being a fraction of and in no case exceeding one fifth of the height of the fuel injection cam.

Preferably, the cam follower is a roller follower mounted on one arm of the rocker lever. The auxiliary cam - or auxiliary cams, as there may be several -will cause a slight additional swivelling motion of the rocker lever in that region of rotation in which, in known actuating devices utilizing a roller follower, the follower rolls aiong the cylindrical surface remote from the injection cam.

This swivelling motion causes a reduction in friction in the various bearings of the eccentric shaft; it is therefore no longer static friction which will have to be overcome, but the substantially lesser sliding friction.

In another variant of the invention the auxiliary cam or the first of the auxiliary cams can be positioned immediately behind, when considered in the direction of rotation, the corresponding fuel injection cam. This will permit better use of that part of the cam shaft which is not occupied by the injection cam, or - if desired -- placement of two or more auxiliary cams.

For a multi-cylinder injection pump the invention finally specifies that the nose of the auxiliary cam or of the first of the auxiliary cams should be positioned on the camshaft at an angular distance from the point at which the corresponding fuel injection cam runs out which equals a full angle of rotation (360 degrees) divided by the number of pump cylinders. If applicable, the nose of the second auxiliary cam can be placed at the same angular distance from the nose of the first auxiliary cam. This arrangement will influence the torque necessary for driving the eccentric shaft in a most favourable manner.

An embodiment of the invention will now be described in more detail by way of example with reference to accompanying drawings wherein: Figure 1 is a partial section of the exemplary embodiment of the invention representing a side view of the driving mechanism; Figure 2 is a diagram showing as a function of the angle of rotation the strokes of the injection cams and of the auxiliary cams in a six-cylinder injection pump during one rotation of the camshaft; Figure 3 is a diagram showing as a function of the angle of rotation the torque necessary for turning the eccentric shaft from an early to a late injection position at an engine speed of 450 r.p.m.;; Figures 4 and 5 are diagrams for a six-cylinder injection pump, showing as a function of the angle of rotation the torque necessary for the adjustment of the eccentric shaft position from "late injection" to "early injection" at an engine speed of 4500 r.p.m. and 1000 r.p.m., respectively; Figure 6 is a diagram showing as a function of the angle of rotation the torque necessary for turning the eccentric shaft of a six-cylinder injection pump from an early to a late injection position at an engine speed of 1000 r.p.m.

The driving mechanism represented in Figure 1 has a camshaft 3 driven by an internal combustion engine, not shown, carrying actuating devices 1 placed axially along the camshaft 3. The number of actuating devices 1 on the camshaft corresponds to the number of cylinders of the injection pump.

Each of these actuating devices 1 comprises a fuel injection cam 2 and auxiliary cams or cam portions 13, 14. In operation each actuating device 1 is brought into operative engagement with one end 5 of a two-armed rocker lever 4, which carries a roller follower 6. The rocker lever 4 is supported by the eccentric journai 8 of an eccentric shaft 7 which is, for example, supported by bearing blocks mounted on the engine housing and coupled to a drive (not shown).

The other end 9 of the rocker lever 4 is provided with a blind bore 10 having a cone shaped endwali which serves as a bearing for a tappet 12.

The axis of bore 10 lies in a plane normal to the axis of the eccentric shaft. This blind bore 10, which has a cylindrical mouth portion of larger diameter than the tappet 12, seats one end 11 of the tappet 12. The other end 11' of the tappet is seated in a similar blind bore in the piston rod (not shown) of the pump piston. Both ends 11, 11' of the tappet 12 have a hemispherical shape so as to allow swivelling movement of the tappet 12 relative to the rocker lever 4 or to the piston rod in order to adjust the stroke of the pump.

The auxiliary cams 13, 14 are positioned on the camshaft 3 with an angular spacing from the injection cam 2. The height 1 6 of the auxiliary cams 13, 14 is a fraction of the height of the injection cam 2, as taken from the base circle 1 5 of the cross-section of the actuating device 1, and in no case does it exceed one fifth.

If the shaft 3 is rotated in the direction of the arrow 18, cam 2 will cause the injection pump (not shown) to operate. Subsequently, the rocker lever 4 is twice given a slight swivelling movement by the two auxiliary cams 13 and 14, without causing fuel injection. This will enable the torque necessary for turning the eccentric shaft 7 to be reduced as only sliding friction will have to be overcome.

The diagram in Figure 2 shows as a function of time the strokes of the inejection cams 2 and of the auxiliary cams 13, 14 in a six-cylinder injection pump during one revolution of the shaft 3. The extents of the stroke curve corresponding to cams 2 and auxiliary cams 13, 14, respectively, are labelled 2' and 13', 14', respectively. The curves of the individual actuating devices 1 for each cylinder are drawn one below the other and have the numbers I to VI. For all actuating devices 1 the reference number 20 is used to mark the injection period.

Figure 3 is a diagram showing as a function of the angle of rotation, the torque necessary for turning the eccentric shaft 7 at an engine speed of 4500 r.p.m. In this case the shaft is turned from the "early injection" position to the position for "late injection". The figures on the abscissa indicate the rotation angle of the shaft 3 while those on the ordinate indicate the corresponding torque in Nm. On the right hand side curve 30 shows the torque for actuating devices with auxiliary cams 13, 14, and curve 31 that for actuating devices without any auxiliary cams.

From the shape of these two curves 30, 31 it can be seen that in the area marked by the double ended arrow 32 which corresponds to a rotation angle of some 25 degrees, the torque required for turning the eccentric shaft 7 is substantially reduced in the case of the use of actuating devices' 1 including the auxiliary cams 13,14, as compared with the use of actuating devices 1 without any auxiliary cams. The hatched area marked 33 is a measure of the energy saved by the use of auxiliary cams 13, 14.

Figures 4 and 5 are two diagrams representing the driving torque for the eccentric shaft for a sixcylinder fuel injection pump. The engine speed is 4500 r.p.m. in Figure 4 and 1000 r.p.m. in Figure 5. For a better comparison of the performance of the actuating devices 1 designed according to the invention and those without any auxiliary cams, both figures contain analogous curves 41 and 51 for conventional actuating devices in addition to the torque curves for actuating devices (40 and 50) in a mechanism according to the present invention. In Figure 4 the area of special interest has the reference 42 and covers a rotation angle of 42 degrees. In Figure 5 this area has the reference 52 and covers a rotation angle of 21 degress only. In both figures the hatched areas 43 and 53 are measures of the respective energy saved.

Figure 6 is a diagram showing the torque required for turning the eccentric shaft 7 of a sixcylinder injection pump, if the engine speed is 1000 r.p.m. and the eccentric shaft is turned from the "early injection" to the "late injection" position. The curve referring to the actuating device 1 arranged according to the present invention has the reference 60 while the one referring to a conventional device is marked 61.

The area of interest indicated by the arrow has the reference number 62 and covers a rotation angle of 20 degrees. Again, the hatched area 63 is a measure of the energy saved by an actuating device arranged according to present invention.

The invention is in no way restricted to the example in Figure 1. Design modifications such as driving mechanisms comprising actuating devices with more than two auxiliary cams, are possible and within the scope of the present invention.

Claims

1. A driving mechanism for single or multicylinder fuel injection pumps used on internal combustion engines, said mechanism comprising a camshaft adapted to be driven by the internal combustion engine and having a fuel injection cam for the or each cylinder of the fuel injection pump, the or each injection cam being cooperable with a two-armed rocker lever, one end, of one arm of the lever carrying a cam follower, the central part of the lever being supported by an eccentric shaft and the end of the other arm being operatively connected to the piston of the pump, wherein the eccentric shaft is rotatable by a special drive and at least one auxiliary cam is positioned on the camshaft at an angular distance from the fuel injection cam or any cam used for fuel injection, the height of the auxiliary cam, as taken from the base circle of the camshaft crosssection, being a fraction of and in no case exceeding one fifth of the height of the fuel injection cam.

2. A driving mechanism as claimed in Claim 1, wherein the cam follower is a roller follower.

3. A driving mechanism as claimed in Claim 1 or Claim 2, wherein the auxiliary cam or the first of the auxiliary cams is placed immediately behind the corresponding fuel injection cam.

4. A driving mechanism as in any preceding claim, for a multi-cylinder injection pump, wherein the nose of the auxiliary cam or of the first of the auxiliary cams is positioned on the camshaft at an angular distance from the point at which the corresponding fuel injection cam runs out, equalling a full angle of rotation (360 degrees) divided by the number of pump cylinders.

5. A driving mechanism as claimed in Claim 4, wherein the nose of a second auxiliary cam is positioned the same angular distance from the nose of the first auxiliary cam as said first auxiliary cam is from the injection cam.

6. A driving mechanism for single or multicylinder fuel injection pumps for use on internal combustion engines substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

7. In an internal combustion engine having a fuel injection system, a driving mechanism for a single or multi-cylinder fuel injection pump substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.