GB2188103A - Fuel injection for an internal combustion engine - Google Patents

Abstract

A fuel injection pump for internal combustion engines has a control spool (5) displaceable on a pump piston (3) and in a recess (4) provided in a cylinder sleeve (2), the sleeve being made of one piece and provided radially on one side only with an opening. The recess has parallel side walls (23) as seen from the opening, so that the walls which surround the recess radially can absorb the maximum compressive and bending stresses acting on the cylinder sleeve. <IMAGE>

Description

SPECIFICATION Fuel injection pump for an internal combustion engine The invention relates to afuel injection pumpforan internal combustion engine.

In a known fuel injection pump, (German Offenlegungsschrift No. 3428174), a recess is a pump cylinder in the form of an opening which penetrates radiallythrough the pump cylinder sleeve, so that there are only two iateral connection members, and axial or radial forces can only be transmitted byway of these relatively weak pieces. Pump cylinder sleeves of this type are thus considerably weakened by the recess provided to accommodate a control spool.This weakness can have a particularly disadvantageous effect if the pump cylinder sleeve is clamped, following adjustment, by screws acting on aflange on the pump cylinder sleeve, and its lower section is axially supported on a step ofthe pump housing or is radially supported by the wall ofthe housing bore accommodating the pump cylinder sleeve. If the cylinder is not strong enough, slight axial or radial tolerance errors can be sufficient to result in deformation ofthe cylinder sleeve when clamped, such that the pump piston, which is sealingly guided both above and below the recess, is subjected to additional frictional forces in the cylinder bore, which is no longer in exact alignment, which forces can iead to premature wear and leaks.

In another known fuel injection pump of this type (EP-A-01 81402, Figure 4), the pump cylinder sleeve is formed by two parts, the recess being obtained by axial boring (from above with pump stationary). The upper part of the cylinder sleeve, which is provided with the flange, is inserted into this bore and a radial opening to the bore is obtained byway of a milled-out portion. The two parts are connected to one another either by shrinking or hard-soldering.

The recess formed in this way, is, as a result ofthe milled-out portion, open on the side facing the direction of adjustment of the control spool, so that, on the one hand, the control spool can be inserted and, on the other hand, it is accessible forthe purposes of adjustment. Although the niche-like form of the recess provides a relatively large degree of stability with respect to alignment and distortion errors, manufacture is complex and hence expensive, as the two parts of the pump cylinder sleeve must be precisely aligned when joined together. Hence, additional working operations and expensive tools are required, although alignment errors still cannot be ruled out.

In accordance with the present invention there is provided a fuel injection pump for an internal combustion engine, comprising at least one pump element whose pump cylinder, which is in the form of a cylinder sleeve, can be somewhat rotated and fixed in a corresponding bore in the pump housing to adjust the quantity of fuel, the pump cylinder being provided with a pump piston which isdrivableto effect a reciprocating working stroke and rotatable to control the fuel, and at least one control spool which is in a recess in the pump cylinder and which is axially displaceable on the pump piston to control fuel, the pump cylinder sleeve being made in one piece,the recess provided for accommodating the control spool in the pump cylinder sleeve having a hole on one side onlywhich is radially disposed with respect two the cylinder axis and through which the control spool is insertable and the recess, as seen from the hole, having substantially parallel side walls.

In contrasttothe prior art, thefuel injection pump according to the present invention has the advantage that, despite its surprisingly simple manufacture, alignment errors are largely eliminated, which results, above all, in the pump having a long working life. There was a prejudice in the field regarding this design of pump cylinder sleeve, as it was assumed that, in the heattreatment of parts which are not exactly symmetrical, alignment errors will occur as a result of a one-sided accumulation of material. For this reason, the cylinder sleeve of one of the known fuel injection pumps is made of two parts.The parallel side walls ensure above all that the remaining side wall thickness is such that, as in the case of the known cylinder sleeves having onlytwo supports, is as close as possible to the control spool, that is, almost touching it. As a result, greater rigidity and a correspondingly increased moment of inertia against bending stresses due to assymmetrical driving forces are obtained.

According to an advantageous embodiment of the invention,the recess is formed by machining. It is possible to carry out such mechanical machining at low cost and without the risk of distortions or changes in position which could lead to alignment errors.

According to a further advantageous embodiment of the invention,the rearwall of the recess, as seen from the opening, has a stepped form which is an approximation of the external form of the cylinder and is intended to achieve maximum thickness of the wall ofthe cylinder sleeve. Inthisway,an end-milling cutter can be used to make the recess as large as the radial dimensions of the control spool will allow, sothatthe remaining wall isableto absorb the maximum possible forces.

According to an alternative advantageous embodiment of the invention,the rear wall of the recess as seen from the opening, is made cylindrical by machining using a spherical cutter. This also allows a greater approximation between the inside wall of the recess and the external surface of the control spool, and hence improves stability.

According to afurther advantageous embodiment ofthe invention, a slot-shaped hole having parallel walls and running in the axial direction ofthe pump is provided in the rearwall ofthe recess to guidethe control spool torsionally, so that the angular position of the control spool with respect to the pump piston can be fixed during basic adjustment, and the hole can be made using an end-milling cutter in the same operation together with the recess.

According to yet another embodiment ofthe invention, the recess can be made by casting the pump cylinder, the bore accommodating the piston and the outer cylinder wall being subsequently machined.

Byway of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: Figure lisa partial section through a partof afirst embodiment of fuel injection pump, containing a pump cylinder sleeve in accordance with the invention; Figure2 is a cross-section through the pump cylinderonlyalongthe line ll-ll in Figure 1; Figure 3 is a partial view of the pump cylinder only along the arrow Ill in Figure 1; Figure 4 is a longitudinal section through part of a second embodiment of fuel injection pump, containing a pump cylinder sleeve in accordance with the invention; Figure 5is a cross-section along the line V-V in Figure4; and Figure 6 is a partial view along the arrow VI in Figure 4.

In the first embodiment shown in Figures 1 to3, Figure 1 shows a cylinder sleeve 2 in a pump housing 1 (only part of which is shown) of a fuel injection pump. In such cylinder sleeves 2, which are in series in the pump housing 1, pump pistons 3 operate which are axially driven by a cam shaft (not shown).

A recess 4 in the form of a blind hole is provided in the cylinder sleeve 2 and accommodates a control spool Swhich is axially displaceable on the pump piston.

The control spool 5 can be axially displaced by a pivotally mounted lever 6, for which purpose the head 7 of said lever engages in a transverse groove 8 in the control spool 5.

The pump piston 3 can be rotated through a particularanglebya a bushing 9, in that the bushing 9 engages in a flattened region 10 in the pump piston 3, but does not impede the stroke movement of said pump piston. The upper section of the bushing 9 is provided with a toothed ring into which a toothed rack 11 acting as a control rack projects. Of course, any other device may serve as the rotating means.

The pump piston 3 is pressed byway of a spring 12, which rests on a spring plate 13, against the cams of a camshaft byway of a tappet (not shown).

Axiallysymmetrical oblique grooves 15 are disposed in the outer surface of the pump piston 3 and their upper ends 16 open into longitudinal grooves 17. The upper ends of the longitudinal grooves 17 are connected to one another by a radially running transverse bore 18, into which a blind bore 19, which runs centrally in the pump piston 3, opens and which terminates on the end face 21 ofthe pump piston3definingthe pumpworking chamber 20. The transverse bore 18 and the blind bore 19 form a connection between the oblique groove 15 and the pump working chamber 20.

Two radial discharge bores 22 are provided in the control spool 5 and co-operate with the oblique grooves 15 and longitudinal grooves 17to determine the quantity of fuel injected. The longitudinal grooves 17 are provided at the bottom and top with sharp control edges 24 and 25, which co-operate with the upper and lower end faces 26 and 27 of the control spool 5, which end faces also form control edges.

As can beseen in particularfromFigure2,the transition 30 from the sidewalls 23 to the rear wall 28 of the recess 4 has a stepped shape. These steps are the result of machining using so-called end-milling cutters, whereby it is attempted to approach the outer surface 29 of the cylinder sleeve 2 only as closely as is necessary to obtain a sufficiently rigid wall thickness, despite the gap required with respect to the control spool 5.

The dash-dotted line in Figure 3 indicates the diameters 31 ofthe cutters used to produce this recess 4. The radiuses 2 which remain on the transition from the side walls 23 to the upper and lower boundary walls 33 ofthe recess 4 do not cause interference, because the control spool 5 is also provided with corresponding radiuses or broken edges, or the overall height of the recess 4 is made correspondingly largerthan is required by the overall height and stroke of the control spool 5.

In the second embodiment shown in Figures 4to 6, the recess 104 has approximately the same form as in the first embodiment. The transitions 130 between the sidewalls 103 and the rearwall 128arerounded off, that is, they have radiuses 132, so that it is possible to obtain better adaptation to the form of the control spool. The wall thickness is substantially uniform, at least atthe rear wail 128 and the radiuses 132 towards the outer surface 129. As there are no steps, it is possible to make the control spool (not shown) even closerto the inner walk of the recess 104, so that a further optimization ofthe measured proportions can be obtained, with a corresponding improvement in the rigidity of the cylinder sleeve 2.

Such a rounded transition is obtained either by machining with a spherical cutter 34 as shown by the dash-dotted lines in Figures 4 and 5, or by casting the whole cylinder sleeve.

A slot-like hole 35 having parallel walls 36 is provided in the rearwall 128 of the recess 104, into which hole a guide device of the control spool can engage, so thatthe control spool can perform an axial movement but is prevented from rotating.

The fuel injection pump according to the invention operates, as explained with reference to Figure 1, as follows. When the pump piston 3 moves into the bottom dead centre position as shown in Figure 1, the longitudinal grooves 17 are exposed bythe control spool 5, so that fuel can flow in a substantially unthrottled manner by way of the passage formed by the transverse bore 18 and blind bore 19 into the pump working chamber 20. As soon as the delivery stroke of the pump piston 3 commences, the longitudinal groove 17 plunges into the control spool at an earlier or later point depending on the axial position of the control spool 5. As soon as the lower control edge 24 of the longitudinal groove 17 passes the lower end face 26 ofthe control spool 5, the pressure necessaryfor injection can be built up in the pump working chamber 20, and fuel delivery to the engine, that is injection, can commence. This injection continues to take place until the discharge bore 22 of the control spool 5 is opened by the oblique groove 15 and delivery to the engine is interrupted. As the stroke of the pum piston 3 continues, fuel flows from the pump working chamber 20 back to the suction side ofthe pump. From a particular axial position ofthe control spool 5 onwards, the longitudinal groove 17 emerges at the top from the cntrol spool 5, with the uppermost end face 27 partially exposing the longitudinal groove 17.

All the features mentioned in the above description, together with those which can be taken from the drawings only, are, as further embodiments, integral parts of the invention, even if they are not particularly emphasized or mentioned in the claims appended hereto.

Claims (7)

1. Afuel injection pumpforan internal combustion engine, comprising at least one pump element whose pump cylinder, which is in the form of a cylinder sleeve, is located in a corresponding bore in the pump housing, the pump cylinder being provided with a pump piston which isdrivableto effect a reciprocating working stroke and rotatable to control the fuel, and at least one control spool which is in a recess in the pump cylinder and which is axially displaceable on the pump piston to control fuel, the pump cylinder sleeve being made in one piece, the recess provided for accommodating the control spool in the pump cylinder sleeve having a hole on one side only which is radially disposed with respect two the cylinder axis and through which the control spool is insertable, and the recess, as seen from the hole, having substantially parallel side walls.

2. Afuel injection pump as claimed in claim 1, wherein the recess is formed by machining.

3. Afuel injection pump as claimed in claim 2, wherein the rearwall of the recess, as seen from the hole, has a stepped form in approximation of the outercylinderform and to obtain maximumwail thickness of the cylinder sleeve.

4. Afuel injection pump as claimed in claim 2, wherein the rearwall of the recess, as seen from the hole, is made substantially semi-cylindrical by machining with a spherical cutter.

5. Afuel injection pump as claimed in any of claims 1 to 4, wherein a slot-type hole having parallel walls running in the axial direction of the pump is provided inthe rearwall of the recess to guide the control spool torsionally.

6. Afuel injection pump as claimed in any of claims 1 to 5, wherein the recess is formed by casting the cylinder sleeve.

7. Afuel injection pumpforan internal combustion engine, substantially as herein described, with reference to, and as illustrated in, Figures 1 to 3 or Figures 4to 6 of the accompanying drawings.