GB2303411A

GB2303411A - Fuel-injection pumping device for internal combustion engines

Info

Publication number: GB2303411A
Application number: GB9613784A
Authority: GB
Inventors: Juergen Kirschner; Sandro Soccol
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-07-21
Filing date: 1996-07-01
Publication date: 1997-02-19
Anticipated expiration: 2016-07-01
Also published as: GB9613784D0; JPH0932690A; DE19526692A1; GB2303411B

Description

ú 1 I R. 29222 19.07.95 DgALm ROBERT BOSCH GMBH; 70442 STUTTGART

Fuel-iniection device for Internal Combustion Engines

Prior Art

2303411 The invention relates to a fuel-injection device for internal combustion engines according to the generic type of claim 1. EP-O 261 156 discloses a fuel-injection device of this type in which a pump piston is guided in an axial manner in a cylinder bore of a cylinder liner and is driven in a reciprocating manner by a cam drive. The pump piston defines a pump working chamber in the cylinder liner with its end face remote from the cam drive and comprises on its peripheral surface two control recesses, disposed diametrically opposite to one another, which are connected by way of a transverse bore to an axial blind bore which issues into the pump working chamber. The control recesses are designed as inclined grooves which cooperate, for the purpose of controlling the high pressure delivery in the pump working chamber, with an annular slide valve disposed in an axially displaceable manner on the pump piston. To this end the annular slide valve comprises an axial piston bore and a radial control bore which intersects said piston bore and cooperates with the inclined grooves of the pump piston and by way of which radial control bore the fuel subjected to high pressure in the pump working chamber is pressure released into a low pressure chamber surrounding the annular slide valve for the purpose of discontinuing the high pressure delivery, as the said annular slide valve travels beyond the inclined grooves in the progression of the delivery t 1 2 stroke of the pump piston.

The pump working chamber formed in the cylinder bore is defined on its side remote from the pump piston by a pressure valve assembly which is fitted into the cylinder liner and clamped thereto, and at the other side thereof an injection line is connected to the injection valve which protrudes into the internal combustion engine to be supplied.

However, the known fuel-injection device has the disadvantage that during the high pressure delivery phase the high injection pressure is transmitted by way of the control recesses at the pump piston in a nonuniform manner to the wall surface of the piston bore of the annular slide valve. This nonuniform manner in which the pressure acts upon the wall surface of the piston bore of the annular slide valve results in an increase in the diameter of the piston bore in the region which lies perpendicular to the control bores and subsequently results in a reduction in diameter of the piston bore in the region above the control bores. An approximately oval cross section of the piston bore develops in the upper end of the annular slide valve facing the pump working chamber, wherein the extent to which the area having a reduced cross section increases in the surface direction is determined in particular by means of the shape of the piston control recess (inclined groove) and the outer contour of the annular slide valve.

During the operation of the known fuel-injection device the constricted region of the piston bore of the annular slide valve at this point causes, between the peripheral surface of the pump piston and the wall of the piston bore in the annular slide valve, an increased surface pressure which is restricted moreover to a small localised region so that the lubricating film between the pump piston and the piston bore may tear off causing increased wear by friction (fretting). This increased wear by friction reduces considerably the serviceable life of the fuel-injection device and can lead to the fuel-injection device failing completely.

3 The described effect of increasing wear by friction occurs in particular in fuel-injection devices which operate at very high injection pressures (above 1000 bar) so that they can no longer satisfy the high demands.

Advantages of the Invention In contrast thereto, the fuel-injection device in accordance with the invention comprising the characterising features of claim I has the advantage that the arrangement of an increase in cross section (widening in a curve) in the region of the reduction in area, Le at the upper end of the piston bore in the annular slide valve facing the pump working chamber, can reliably prevent the lubricating film from tearing off as a result of an increased surface pressure between pump piston and annular slide valve.

The reduction in area or reduction in diameter of the piston bore is counteracted effectively in that the endangered region is enlarged by virtue of the increase in cross section in the diameter in such a way, that a reduction in area does not arise even when the annular slide valve deforms under the high pressure loading on the piston bore wall, but the deformation of the piston bore wall overlies merely the extent of the widening in the curve. A uniform diametrical progression without reduction in area is adjusted under the high compressive stress of the inner wall of the annular slide valve by way of the annular slide valve elevation. In this manner the danger of the lubricating film tearing off between the annular slide valve and piston, or that of wear increasing by friction, is reduced considerably.

The increase in cross section is preferably conical in shape, wherein the diameter of the piston bore in the annular slide valve increases preferably from the axis of the control bores axially in the direction of the end face of the annular slide valve facing the pump working chamber a h 4 by up to approx. 20 lim.

Further advantages and advantageous embodiments of the subject matter of the invention are evident from the description, the drawing and the claims.

Drawing An exemplified embodiment of the fuel-injection device invention for internal combustion engines in accordance with the invention is illustrated in the drawing and is explained further in the description hereinunder.

Figure 1 shows a longitudinal sectional view through a cylinder liner which receives the pump piston and the annular slide valve.

Figure 2 shows a developed view of the peripheral surface of the pump piston in the region of the control recesses and Figures 3 and 4, respectively, show an axial sectional view through the annular slide valve in two planes which extend in a perpendicular manner to one another.

Description of the exemplified embodiment

In the case of the exemplified embodiment of the fuel-injection device in accordance with the invention illustrated in Figure 1 with only those components essential to the invention, a pump piston 1 is guided in a known manner axially in a cylinder bore 3 of a cylinder liner 5 fitted into a housing [not illustrated]. The pump piston 1 is driven in a known manner axially in a reciprocating manner by a cam drive [likewise not illustrated] and defines with its end face 7 remote from the cam drive a pump working chamber 9 in the cylinder bore 3 and an injection line connects the said pump working chamber at the other it a side to the internal combustion engine to be supplied. The pump piston 1 comprises on its peripheral surface two control recesses lying diametrically opposite in the forrri of inclined grooves 11 which are connected continuously to the pump working chamber 9 by way of a radial bore 13 and a blind bore 15, which intersects said radial bore and exits from the end face 7, in the pump piston 1.

For the purpose of controlling the high pressure fuel delivery, an annular slide valve 17, axially displaceable on the pump piston 1 by means of an adjusting mechanism [not illustrated], cooperates with these inclined grooves 11 which annular slide valve comprises a radial control bore 19 (see Figure 2) which serves as a control port, which intersects in a perpendicular manner an axial piston bore 20 in the annular slide valve 17 which piston bore receives the pump piston 1. The lower edge of the annular slide valve 17 remote from the pump working chamber 9 forms a control edge 21 which cooperates with the inclined grooves The annular slide valve 17 is disposed in a low pressure chamber 23 formed by virtue of a recess in the cylinder liner 5, which low pressure chamber is filled continuously with fuel by way of a fuel line [not illustrated].

For the purpose of illustrating more effectively, a developed view of the peripheral surface of the pump piston 1 in the region of the inclined grooves 11 is shown in Figure 2. Moreover, transverse bores 25, for the purpose of controlling the commencement of delivery of the high pressure delivery, are disposed on the lower end of the inclined grooves 11 remote from the pump working chamber 9. The control bores 19 of the annular slide valve 17 are illustrated using broken lines in order to show their position with respect to the inclined grooves 11.

In order to counteract the effect (described more precisely in the introduction of the

6 description) of a reduction in area of the piston bore 20 of the annular slide valve 17 at its upper end facing the pump working chamber 9 as a result of the high pressure acting on one side on the wall surface of the piston bore 20, the piston bore 20 (broken line) of the annular slide valve 17 comprises a widening in cross section 27 at its upper end facing the pump working chamber 9, as shown in Figures 3 and 4.

In the exemplified embodiment this widening in cross section 27 extends from the axis of the control bore 19 to the upper end face 29, wherein the diameter of the piston bore 20 increases in size in a conical manner in the direction of the end face 29 over the total circumference by up to 20gm.

This widening in cross section 27 (widening in a curve) at the upper end of the piston bore 20 of the annular slide valve 17 ensures that the deformation of the piston bore 20, illustrated as a continuous line, caused by the high fuel pressure does not result in a localised reduction in area on the wall surface.

It is evident from the various sectional views of Figures 3 and 4 that the radial widening of the piston bore 20 perpendicular to the control bores 19 is larger than in the axial plane of the control bores 19. The dimension of the widening in cross section 27 must be selected in such a way that the maximum localised reduction in diameter in the region of the control bores 19 is only so large as to prevent an effective reduction in diameter and/or a reduction in area of the piston bore 20, which otherwise could cause the lubricating film to tear off. The fuel- injection device in accordance with the invention functions in the following manner. Firstly during the intake stroke of the pump piston 1 the pump working chamber 9 is filled with fuel from the low pressure chamber 23 by way of the inclined grooves 11, the radial bore 13 and blind bore 15. In the subsequent delivery stroke of the pump piston 1 a portion of fuel initially flows back from the pump working chamber 9 into the low pressure chamber 1 7 23 until the inclined grooves 11 and the transverse bores 25 are completely immersed in the annular slide valve 17 or in other words the lower control edge 21 on the annular slide valve 17 has moved beyond the said inclined grooves and transverse bores and the said annular slide valve thus seals said inclined grooves and transverse bores, so that a high pressure fuel is built up in the pump working chamber 9 during a subsequent delivery stroke, and once a predetermined fuel-injection pressure has been achieved this high fuel pressure continues into the injection line to the injection valve where it triggers the fuel injection into the combustion chamber of the internal combustion engine. The high pressure injection process is terminated when the inclined grooves 11 travel beyond the control bore 19 in the annular slide valve 17 (see Figure 2), wherein the fuel subjected to high pressure is pressure released from the pump working chamber 9 into the low pressure chamber 23 by way of the blind bore 15, the radial bore 13, the inclined grooves I I and the control bore 19. The pressure in the pump working chamber 9 falls below the injection pressure causing the injection valve to close so that the injection process is terminated. The timing of the commencement of the high pressure delivery can be controlled in a known manner by way of the stroke position of the annular slide valve 17, the timing of the termination of the delivery by way of the torsional position of the pump piston I and/or the relative position of the inclined grooves I I with respect to the control bore 19.

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Claims

1. Fuel-injection device for internal combyStion engines having a pump piston which is guided in an axial manner in a cylinder bore of a cylinder liner and driven in a reciprocating manner by a cam drive, which pump piston defines with its one end face a pump working chamber in the cylinder bore and comprises on its peripheral surface at least one control recess connected to the pump working chamber and having an annular slide valve disposed within a fuel-filled low pressure chamber formed by a recess in the cylinder liner, which annular slide valve is guided in an axial displaceable manner by means of an axial piston bore on the pump piston and comprises radial control bores in its peripheral surface, characterised in that piston bore provided in the annular slide valve comprises on its upper end facing the pump working chamber a widening in cross section.

2. Fuel-injection device according to claim 1, characterised in that the widening in cross section of the piston bore in the annular slide valve extends beyond its total diameter starting from the axis of the radial control bores in an axial direction as far as the upper end face of the annular slide valve facing the pump working chamber.

3. Fuel-injection device according to claim 2, characterised in that the widening in cross section of the piston bore is designed as a cone, whose cross section increases in size in a uniform manner in the direction of the upper end face of the annular slide valve.

4. Fuel-injection device according to claim 1, characterised in that the diameter of the piston bore in the annular slide valve increases in size by a maximum of 20,Urn in the region of the increase in cross section.

5. Fuel-injection device constructed and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.