GB2305221A

GB2305221A - Fuel-injection pump for internal combustion engines

Info

Publication number: GB2305221A
Application number: GB9616066A
Authority: GB
Inventors: Otto Hagenauer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-09-15
Filing date: 1996-07-31
Publication date: 1997-04-02
Anticipated expiration: 2016-07-31
Also published as: DE19534286A1; GB2305221B; FR2738875B1; FR2738875A1; GB9616066D0

Description

2305221

DESCRIPTION

FUEL-INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES Prior Art

The invention relates to a fuel-injection pump for internal combustion engines according to the generic type of claim 1. In the case of this type of fuel-injection pump disclosed by DE-OS 40 30 951 a pump piston is guided in an axial manner in a cylinder bore of a cylinder liner. The pump piston, which is driven axially in a reciprocating manner by a cam, defines with its one end face a pump working chamber in the cylinder liner into which pump working chamber issues a control bore, which exits from a fuel-filled low pressure chamber and can be controlled by the pump piston, and from which pump working chamber an injection line leads to an injection site on the internal combustion engine which is to be supplied.

In the region of the piston arrangement the known fuel-injection pump comprises three annular grooves in the wall of the cylinder bore, of which a first upper annular groove, which lies closest to the pump working chamber, serves to collect any leakage from the fuel being delivered. This upper annular groove, the so-called fuel leakage groove, is connected for this purpose by means of a fuel leakage bore, which leads therefrom, to the low pressure chamber of the injection pump to which low pressure chamber the fuel collected is returned.

At the lower end of the piston arrangement a lower, so-called blocking oil groove is provided in the cylinder bore wall which blocking oil groove is connected by way of a supply duct to the lubricating oil circuit of the injection pump or of the internal combustion engine being supplied and said blocking oil groove serves to lubricate the narrow passage between the pump piston shaft and the cylinder bore. Furthermore, any fuel leakage through to the spring chamber is prevented. Moreover, for the purpose of discharging any fuel and lubricating oil which leaks through, a socalled mixture groove is disposed between the upper fuel leakage groove and the lower blocking groove in the wall of the cylinder bore, which mixture groove is connected by way of a discharge bore to a collecting chamber outside the pump, wherein the mixture of fuel and lubricating oil collected is discharged into the said collecting chamber.

During the operation of the injection pump, in particular when using heavy oil as the fuel which is to be supplied, high temperatures of up to 180c can occur in the injection pump. In order to prevent the blocking oil, formed from the lubricating oil supplied, from dwelling too long in the heat exposed oil-groove, which can otherwise lead to paint/varnish- type deposits and carbonisation, a recess is provided on the pump piston in the case of the known fuel-injection pump, which recess connects the blocking oil groove at least in the region of the top dead centre of the pump piston stroke movement to a spring chamber of the injection pump, so that the lubricating oil can flow out of the blocking oil groove continuously and a specific circuit can be constructed on the blocking oil groove which prevents the lubricating oil from dwelling too long in the blocking oil groove which is exposed to extreme heat, which would otherwise cause the disadvantages mentioned.

However, the known fuelinjection pump has the disadvantage that there is a continuously open connection from the lubricating oil circuit into the spring chamber of the fuel injection pump in the event that the internal combustion engine and thus the pump piston are idle and the lubricating pump is running in certain or all pump piston positions, which results in an unacceptable throughput of lubricating oil and moreover an unacceptable accumulation of oil in the spring chamber.

Advantages of the invention In contrast thereto, the fuel-injection pump for internal combustion engines in accordance with the invention comprising the characterising features of claim 1, has the advantage that a continuous connection of the blocking oil groove to the spring chamber of the injection pump with the resulting disadvantages, is reliably avoided without impairing substantially the lubricating oil circuit in the blocking oil groove. The "portioned" discharging of lubricating oil from the blocking oil groove in accordance with the invention ensures that lubricating oil is discharged in sufficient quantities in a pulsating manner only during the operation of the injection pump.

This is achieved in an advantageous manner by providing a recess in the pump piston wall whose axial extension is smaller than the distance between the blocking oil groove in the cylinder bore wall and the edge of the cylinder bore which lies adjacent to the spring chamber, and which recess overlaps the blocking oil groove in the region of the top dead centre position of the piston movement and protrudes into the spring chamber in the region of the bottom dead centre position of the pump piston stroke. By dimensioning the length and the reception volume of the recess which is closed in a middle position, the quantity of lubricating oil delivered into the spring chamber can be adjusted in such a way that a sufficient throughflow is attained at the blocking oil groove without drawing off an unacceptably large quantity of lubricating oil from the lubricating oil circuit of the internal combustion engine. The recess in the pump piston can be formed as one or more, preferably two substantially oblong pockets or as an annular groove, wherein, alternatively, other forms for the recess are also possible.

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

Drawing An exemplified embodiment of the fuel-injection pump for internal combustion engines in accordance with the invention is illustrated in the drawing and explained further in the description hereinunder. Figure 1 shows a longitudinal sectional view through the fuel-injection pump and figure 2 shows an enlarged sectional view of figure 1, which illustrates the position and the arrangement on the pump piston of the recess which cooperates with the blocking oil groove.

Description of the exemplified embodiment

The fuel-injection pump for internal combustion engines in accordance with the invention, illustrated as an enlarged sectional view in figure 1 and figure 2, comprises a cylinder liner 3, fitted into a pump housing 1, in the cylinder bore 5 of which cylinder liner a pump piston 7 is guided in an axially sliding manner. The pump piston 7, which is driven axially in a reciprocating manner by a cam drive 9 and can be rotated in a conventional manner for the purpose of adjusting the delivery quantity, defines with its one end face 11 remote from the cam drive 9 a pump working chamber 13 from which an injection line 15 leads to an injection site [not illustrated in detail] on the internal combustion engine to be supplied, wherein a pressure valve can be inserted in a known manner in to the injection line 15. Fuel is supplied to the pump working chamber 13 and surplus, controlled fuel is discharged therefrom by way of two radial control bores 17 in the wall of cylinder liner 3 which issue at the wall of the cylinder bore 5 starting from a fuelfilled low pressure chamber 19 which surrounds the cylinder liner 3 and which two radial control bores can be controlled in the progression of the pump.piston stroke by virtue of the outer surface of the pump piston 7. In order to regulate the delivery quantity the pump piston 7 comprises, moreover, two chamfered grooves 21, which are continuously connected to the pump working chamber 13 and cooperate in a known manner with the control bores 17 for the purpose of terminating the high pressure delivery.

The cylinder liner 3 protrudes with its end remote from the pump working chamber 13 into a spring chamber 22 of the injection pump, wherein a restoring spring 24 is disposed which holds the pump piston 7 in position on the cam drive 9.

In the exemplified embodiment three annular grooves are provided in the wall of the cylinder bore 5 for the purpose of lubricating thoroughly the running surface of the pump piston 7 which is guided in the cylinder bore 5 with a small amount of play. An upper annular groove, which lies closest to the pump working chamber 13, forms a fuel leakage groove 23, from which leads a fuel leakage return bore 25 which issues into the low pressure chamber 19 and by way of which fuel leakage groove fuel, which leaks along at the shaft of the pump piston 7, is collected from the pump working chamber 13.

In the wall of the cylinder bore 5 a lower annular groove, which lies furthest from the pump working chamber 13, forms a blocking oil groove 27 which is connected by way of a supply duct 29 to the lubricating oil circuit of the injection pump and of the internal combustion engine and thereby is filled continuously with lubricating oil which is transferred during the pump piston stroke movement as a lubricating film to the shaft of the pump piston 7 which transmits the blocking oil groove 27. [sic] In the wall of the cylinder bore 5, a third annular groove, disposed between the fuel leakage groove 23 and the blocking oil groove 27, is formed as a mixture groove 31 from which leads off a discharge bore 33, which issues into a collecting chamber [not illustrated] outside the injection pump and which mixture groove collects any remaining residual leakage of fuel and lubricating oil, which is discharged from the cylinder bore 5.

moreover, in order to discharge the lubricating oil from the blocking oil groove 27 at least one recess is provided in the outer periphery of the pump piston 7 which recess is formed in the exemplified embodiment illustrated by two substantially oblong pockets 35 whose extension in the axis direction of the pump piston 7 is smaller than the distance between the blocking oil groove 27 and an annular edge 37 which defines the cylinder bore 5 at its spring chamber side end.

The pockets 35 are disposed on the pump piston 7 in such a manner that they overlap the blocking oil groove 27 in the top dead centre of the pump piston (see figure 1) and protrude into the spring chamber 22 in the bottom dead centre position of the pump piston In an intermediate position during the pump piston stroke movement the pockets 35 are completely sealed by virtue of the wall of the cylinder bore 5. The fuel-injection pump in accordance with the invention functions in the following manner.

During the operation of the internal combustion engine which is being supplied, the pump piston 7 is driven axially in a reciprocating manner by the cam drive 9 in conjunction with the restoring spring 24. During the piston downwards stroke movement, fuel is drawn off from the low pressure chamber 19 and into the pump working chamber 13 by way of the control bores 17 During the subsequent delivery stroke movement of the pump piston 7 in the direction of the top dead centre fuel is initially urged from the pump working chamber 13 into the control bores 17. The high pressure delivery commences in the pump working chamber 13 once the pump piston 7 has travelled over the control bores 17, wherein, as a consequence of the delivery stroke movement, the pressure of the fuel enclosed in the pump working chamber 13 increases to the injection pressure and the fuel is injected in a known manner by way of an injection valve, which is provided at the injection site, into the combustion chamber of the internal combustion engine being supplied. The end of the high pressure injection process is instigated by virtue of the fact that the chamfered grooves 21 travel over the control bores 17 and as a consequence the fuel which is subjected to high pressure is released from the pump working chamber 13 into the control bore-s17, so that the pressure in the pump working chamber and in the injection line 15 drops once again below the required injection pressure and the injection valve closes.

The pump piston 7 is lubricated by means of the lubricating oil of the lubricating oil circuit of the internal combustion engine which is delivered into the blocking oil groove 27 and is distributed during the course of the piston stroke by way of the portion of the pump piston shaft which travels over the blocking oil groove 27.

The quantity of lubricating oil is exchanged in a cyclic and "portioned" manner in the blocking oil groove 27 by virtue of the pockets 35. When the pockets 35 overlap in the region of the top dead centre position of the pump piston 7, the quantity of lubricating oil located in the blocking oil groove 27 flows very rapidly into the pockets 35 due to the fall in pressure. In this manner the blocking oil groove 27 is momentarily almost completely emptied, followed by the said blocking oil groove 27 being immediately refilled, wherein this almost complete exchange of lubricating oil prevents carbonisation of the lubricating oil located in the blocking oil groove even at high operating temperatures at the injection pump. In the event that the pump piston moves in the direction of the bottom dead centre, which follows the movement to the top dead centre position, the pockets 35 pass through an intermediate region, wherein they are completely sealed by the wall of the cylinder bore 5. It is only after the pockets 35 have been received -11into the spring chamber 22 that the quantity of lubricating oil collected in the pockets is released into the spring chamber 22 and flows off from this site by way of a return line.

This type of lubricating oil discharge from the blocking oil groove 27 by means of controllable pockets 35 or, alternatively, recesses formed on the pump piston 7, prevents a continuous or long-term direct connection between the blocking oil groove 27 and the spring chamber 22, so that as little as possible lubricating oil can flow from the lubricating oil circuit of the internal combustion engine into the spring chamber 22 of the injection PUMP.

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Claims

1. Fuel-injection pump for internal combustion engines comprising a pump piston, which is driven axially in a reciprocating manner in a cylinder bore of a cylinder liner and defines with its one end face a pump working chamber which can be connected to a fuel-filled low pressure chamber and to an injection site, and comprising at least one annular groove, disposed in the region of the piston arrangement, in the wall of the cylinder bore which annular groove is filled with lubricating oil by way of a supply duct and is connected during a portion of the pump piston stroke to a recess on the pump piston by way of which recess said annular groove is emptied at least indirectly into a spring chamber which receives a restoring spring of the pump piston, characterised in that the extension of the recess in the pump piston, aligned in the axis direction with respect to the pump piston, is smaller in design than the distance between the annular groove in the cylinder bore and a lower annular edge which defines the cylinder bore at its end which protrudes into the spring chamber.

2. Fuel-injection pump according to claim 1, characterised in that a plurality of recesses, are provided on the outer periphery of the pump piston.

3. Fuel-injection pump according to claim 2, -13characterised in that two recesses are provided on the outer periphery of the pump piston.

4. Fuel-injection pump according to any one of claims 1 to 3, characterised in that the recesses are formed substantially as oblong pockets which are disposed on the pump piston in the angular position in an offset manner to each other.

5. Fuel-injection pump according to claim 1, characterised in that the recess on the pump piston is formed as an annular groove.

6. Fuel-injection pump according to claim 1, characterised in that the recess in the pump piston, when the pump piston is at its top dead centre position, overlaps the annular groove, which is filled with lubricating oil, and in the bottom dead centre position of the pump piston said recess is received into the spring chamber.

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