GB2269209A

GB2269209A - Fuel injection pumps for internal combustion engines

Info

Publication number: GB2269209A
Application number: GB9315764A
Authority: GB
Inventors: Anton Pischinger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-07-31
Filing date: 1993-07-30
Publication date: 1994-02-02
Anticipated expiration: 2013-07-30
Also published as: JPH06159195A; JP3302457B2; GB2269209B; DE4225302A1; DE4225302C2; GB9315764D0

Abstract

A fuel injection pump comprises a pump piston (7) reciprocated in a cylindrical bore (5) of a cylinder liner (3), a pump working chamber (11) supplied with fuel through control ports (31, 33) in the liner, a constant pressure valve (15), and a connection piece (17) holding the constant-pressure valve (15) in abutment against the cylinder liner (3). The valve (15) includes a valve body (39) having axial ends in the form of cylindrical hollow spigots (51, 53). The spigots are located in the cylindrical bore (5) and a bore (55) of the connection piece (17) to define therewith sealing surfaces (72). Radial expansion of the spigots (51, 53), caused by the pressure medium flowing through the body (39), causes the relatively thin walls of the spigots to be pressed against the surrounding wall of the cylinder liner (3) and the connection piece (17), respectively, thereby to improve the sealing. <IMAGE>

Description

2269209

DESCRIPTION "FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES"

The invention relates to fuel injection pumps'-for internal combustion engines.

A fuel injection pump is known from DE-OS 27 05 489, in which a cam drive axially reciprocates a pump piston in the cylindrical bore of a cylinder'llner fitted in a pump housing. The end face of the pump piston remote from the cam drive defines a pump working chamber which is supplied with fuel by way of two control ports and which is connected to an injection point by way of a pressure line. A constant-pressure valve is fitted in the pressure line and the end of its valve body contiguous to the pump working chamber is fitted into the cylindrical bore of the cylinder liner and thus tightly closes the pump working chamber at this end. The end face of the constant-pressure valve remote from the pump working chamber is contiguous to a connection piece having a part of the pressure line and which, by way of a flange clamped to the pump housing# clamps a flange-side end of the valve body between itself and the end face of the cylinder liner, and which has at the end remote from the pressure valve an external screw thread onto which the injection line is screwed.

The known fuel injection pump at the same time has the disadvantage that the seal at the point of'fit between the pressure-valve body and the cylinder liner and between the end face of the pressure-valve body and the connection piece, is not adequately ensured at high injection pressures. Furthermore# these sealing problems at the pressure valve are increased when there is a considerable difference between the expansion of the parts to be sealed, thus resulting in wear at the sealing surfaces. These differences in expansion may be conditional upon pressure or temperature and occur particularly in the region of the cylindrical bore and the contact surface on the connection piece. Thus, the seal, in the known fuel injection pump, between the pressure valve and the cylinder liner or the connection piece is insufficient to ensure a reliable seal at high injection pressures.

It is an object of the invention to overcome or alleviate the above disadvantages.

In accordance with the present invention there is provided a fuel injection pump for internal combustion engines, having a pump piston which is guided in a cylindrical bore of a cylinder liner inserted into a pump housing and which is axially reciprocated by a cam drive and whose end face remote from the cam drive delimits a pump working chamber which is connected to an injection point by way of a high-pressure line in which a pressure valve is disposed, wherein the pressure valve has a valve body comprising a spigotshaped part which is inserted into the cylindrical bore and which is located opposite the pump piston and also delimits the pump working chamber, and a flangeshaped part which overlaps the end face of the cylinder liner and is pressed thereagainst by means of a connection part of the pressure line. and wherein the spigot-shaped part has an axial blind bore starting from the end face at the pump working chamber side and forms a thin-walled hollow cylinder from which the pressure line enters the valve body.

This has the advantage that. even at high pressures in the pump working chamber, reliable sealing of the pump working chamber between the valve body and the cylinder liner is ensured. This is achieved in an advantageous manner in that the spigotshaped part of the pressure-valve body entering the cylinder liner is of a hollow construction and that, when subjected to high pressure, it is stressed in the sense of pressing the outer wall of the hollow spigot part against the inside wall of the cylinder liner, thus improving the sealing effect between the spigot and the cylinder liner.

This "breathing" effect of the spigot is particularly perceptible at very high pressures, so that. in contrast to the prior art. the sealing action in the design in accordance with the invention increases as the injection pressures increase.

Advantageously, the pump piston also has on its end face defining the pump working chamber a spigotshaped extension for reducing the dead- volume space, which extension, during the course of the delivery stroke, extends into the hollow space of the spigot facing the pump working chamber and thus rapidly reduces the large clearance volume formed by the hollow space, so that a negative influence of the hollow spaces on the build-up of pressure in the pump working chamber and in the entire injection system may be avoided.

By way of example only a specific embodiment of the present.invention will now be described with reference to the accompanying drawing. which is a sectional view illustrating the seal between the valve body of the pressure valve and the cylinder liner or the connection piece by the sealing surfaces on the spigots of the valve body.

In the embodiment of the fuel injection pump in accordance with the invention. which is shown only in its region material to the invention in Fig. 1. a cylinder liner 3 having a cylindrical bore 5, in which -5a pump piston 7 is axially guided, is fitted in a pump housing 1. The pump piston 7 is reciprocated by acam drive (not illustrated) and its end face 9 remote from the cam drive defines a pump working chamber 11 in the cylindrical bore 5, a pressure line 13 being connected to the pump working chamber 11. The pressure line 13 is formed by a pressure valve in the form of a constant-pressure valve 15 contiguous to the pump working chamber 11. a connection piece 17 contiguous to the constant-pressure valve 15, and an injection line 19 which is screwed onto the connection piece 17 by way of a thread and which opens into an injection valve 21 extending into the combustion chamber of the internal combustion engine to be supplied. The pump piston 7 has two control recesses 23 which, together with the outer surface of the pump piston 7. form two oblique control edges and communicate with the pump working chamber 11 by way of a longitudinal groove 29. A first control edge 25 is at a greater distance from the end face 9 than a second control edge 27. For the purpose of supplying the pump working chamber 11 with fuel and for the purpose of relieving pressure at the end of the delivery stroke, two radial control ports, axially offset relative to one another, are disposed in the cylinder liner 3, a first control port 31 of which cooperates with the first control edge 25 on the -6pump piston 7 and is at a greater-distance from the constant-pressure valve 15 than a second control port 33 which cooperates with the second control edge 27. In this manner, it is ensured that the second control port 33 is the last to be closed upon the closing of the control ports by the pump piston 7 and is the first to be opened upon the opening of the control ports by the control recesses. Pressure valves are disposed at the control ports 31, 33 for the purpose of reducing cavitation damage, wherein the pressure valve located at the lower, first control port 31 serving as an inlet line opens as auction valve 35 opening towards the pump working chamber 11, and the pressure valve 37 disposed at the second, upper control port 33 serving as relief line opens away from the pump working chamber 11.

The constant-pressure valve 15, disposed between the pump working chamber 11 and the connection piece 17, comprises a valve body 39 with two nonreturn valves which are disposed parallel to one another and open in opposite directions, a first non-return valve 43 of which opens towards the injection line 19 and is disposed in a stepped bore 41r forming a part of the pressure line 13. which is located in the pressurevalve body 39 and which extends parallel to the axis of the pump piston, and a second non-return valve 45 -7which opens in the opposite direction and, like the first, has a spring- loaded ball as a valve closure member, is located in a by-pass line 47 which branches from the stepped bore 41 and which opens into the pump working chamber 11. The bypass line 47 accommodating the second valve 45 comprises a stepped, radial bore 86 which extends from a flange-like part 88 on the outer circumference of the valve body 39, where it is closed by a closure member 84, and opens downstream into the stepped bore 41 of the first valve 43. The bore 86 accommodates the second valve 45 and is connected to the pump working chamber 11 upstream of the second valve 45. wherein the second valve 45 opens towards the pump working chamber 11 against the force of a valve spring 49 supported on the closure member 84. The opening pressures of the non-return valves 43, 45 are in case adjustable by way of the initial stress of the valve springs of the non- return valves 43, 45. wherein the first non-return valve 43 determines the opening pressure to the injection valve 21, and the second non-return valve 45 determines the residual pressure in the pressure passage 13. Here, a further possible variant of the embodiment of the constant- pressure valve 15 would be the known form of the constant-pressure valve with a valve body having a conical valve seat against which a valve closure member is held in abutment by a valve spring, the valve having a pressure valve which opens in the opposite direction to the opening direction of the valve closure member.

In order to obtain a reliable seal at the constant-pressure valve 15, even at high injection pressures, each axial end of the valve body 15 has a blind bore and a spigot-shaped part projecting from a flange-shaped part, wherein the spigot 51 facing the pump working chamber 11 projects into the cylindrical bore 5 in the region of the pump working chamber 11. The oppositely located second spigot 63 projects from the end of the valve body 39 remote from the spigotshaped part 51 and extends into a corresponding bore 55 in the connection piece 17. The outer surfaces of the spigots 51, 53 acting as sealing surfaces, and the surfaces of the bores 5, 55 cooperating with the spigots, are ground very finely, preferably lapped, so that a high sealing effect is obtained even in a pressureless state. If the constant-pressure valve 15 is subjected to the high pressure of the fuel during operation of the fuel injection pump, and a pressure builds up in its interior, the outer walls of the hollow spigots 51, 53 are pressed against the inside wall of the cylinder liner 3 or ol the connection piece 17, whereby the seal between the constant- -gpressure valve 15 and the cylinder liner 3 or the connection piece 17 is improved, wherein, by way of the dimensioning of the remaining wall thickness of the spigots 51, 53. the latter may be designed in such a way that, in dependence upon the operating parameters of the fuel injection pump. they ensure reliable sealing without increased wear as a result of too high a stress on the components. In order to assist this pressing operation, the wall thickness of the constant-pressure valve 15 in the region of the spigots 51, 53 is greatly reduced by increasing the internal diameter of the stepped bore 41, this larger clearance volume created in a blind bore 52 defining the pump working chamber 11 in turn being cancelled by a spigot-shaped extension 57 on the end face 9 of the pump piston 7 which thus avoids a delayed build-up of pressure in the entire injection system caused by the additional clearance volume.

The additional clearance volume in the region of the second spigot 53 is reduced by an insert part 54 which has a through bore and is inserted into this portion of the stepped bore 41, wherein the insert part 54 also serves as an abutment for the valve spring 49 of the first valve 43 in the constantpressure valve 15.

In order to discharge a quantity of leakage oil -10which nevertheless occurs, cavities 61 are provided contiguously to the spigots 51, 53 in the region of the end faces 59 of the flange-shaped part of the constant-pressure valve 15 and may be incorporated in the constant-pressure valve 15 and also in the walls, contiguous thereto. of the connection piece 17 or of the pump housing 1. and are connected to the gap between the pump housing 1 and the cylinder liner 3 by way of a discharge passage 63 in the form of, for example, a longitudinal groove and a transverse groove.

In the embodiment, the connection piece 17 pressing the constant-pressure valve 15 against the cylinder liner 17 is clamped directly and axially to the pump housing 1 by way of tie rods 65 and clamping nuts 66. one end face 67 of the connection piece 17 being located approximately on a level with the first spigot 51. so that the connection piece 17 guides the valve body 39 axially and also radially.

In order to press the end face 67 of the flangeshaped part 88 of the valve body 39 tightly against the end face of the cylinder liner 3, the connection piece 17 has in its cylindrical wall a shoulder by which the connection piece 17 presses the flange-shaped part 88 against the cylinder liner 3 by way of the clamping nuts 66.

In order to reduce a notch effect caused at the transition from the flange-shaped part 88 to the spigot 51 by the high contact pressures and the high pressures. this transition is of conical configuration.

The fuel injection pump in accordance with the invention operates in the following manner.

The fuel flows into the pump working chamber 11 by way of the first control port 31 during the auction stroke of the pump piston 7 towards bottom dead centre. the suction valve 35 being opened by the vacuum prevailing in the pump working chamber relative to the supply line, and by the fuel pressure prevailing in the supply line. During the subsequent delivery stroke of the pump piston 7 towards top dead centre. a portion of the volume of fuel located in the pump working chamber is first displaced out of the pump working chamber by way of the second control port 33. The pressure valve 37 in the second control port 33 is at the same time opened, while the suction valve 35 in the fist control port 31 prevents the fuel located in the pump working chamber from flowing off by way of the control port 31. After the end face 9 of the pump piston 7 has travelled across the second control port 33 during the course of the further stroke of the pump piston, the fuel located in the -12pump working chamber 11 is compressed, attains the injection pressure, opens the first non-return valve 43 in the constant-pressure valve 13 and flows by way of the pressure passage 13 and the injection valve 31 for injection into the combustion chamber of the internal combustion engine to be supplied. The highpressure delivery is terminated by the travelling of the second control edge 27 across the second control port 33. the fuel under high pressure in the pump working chamber 11 and in the pressure passage 13 being relieved into the second control port 33 by way of the longitudinal groove 29 and the control recess. The pressure in the pump working chamber at the same time drops below the injection pressure# so that the first non-return valve 43 closes. and the fuel under high pressure flows off from the pressure passage 13 by way of the by-pass line 47 and the second nonreturn valve 45 into the pump working chamber 11 and then into the second control port 33. The second nonreturn valve 45 closes at a specific residual pressure in the pressure passage 13. The control port 31 leading to the inlet passage is opened by the control edge 25 when the pump piston 7 is in its top dead centre position, so that fuel may be drawn in by way of the control port 31 during the subsequent suction stroke of the pump piston 7. The quantity of fuel -13delivered is controlled in a known manner by the position of the oblique control edge 27 which is variable by the rotation of the pump piston 7.

It is thereby possible, by means of the fuel injection pump in accordance with the invention, to ensure reliable sealing in the region of the constantpressure valve even at high injection pressures. and to reduce the leakage oil loss at this location.

z= - - - 1 1

Claims

1. A fuel injection pump for internal combustion engines, having a pump piston which is guided in a cylindrical bore of a cylinder liner inserted into a pump housing and which is axially reciprocated by a cam drive and whose end face remote from the cam drive delimits a pump working chamber which is connected to an injection point by way of a high-pressure line in which a pressure valve is disposedy wherein the pressure valve has a valve body comprising a spigotshaped part which is inserted into the cylindrical bore and which is located opposite the pump piston and also delimits the pump working chamber, and a flangeshaped part which overlaps the end face of the cylinder liner and is pressed thereagainst by means of a connection part of the pressure line, and wherein the spigot-shaped part has an axial blind bore starting from the end face at the pump working chamber side and forms a thin-walled hollow cylinder from which the pressure line enters the valve body.

2. A fuel injection pump as claimed in claim 1, wherein the pump piston has on its end face defining the pump working chamber a spigot-shaped extension which enters the blind bore when the pump piston is in its top dead centre position.

3. A fuel injection pump as claimed in claim 1 or 2, wherein the valve body has on its side remotb from the pump working chamber a second spigot which starts from the flange-like part and which is fitted Into an axial bore of the connection part and at which the pressure line leading out of the pressure valve opens, which pressure line extends through the connection part from an axial stepped bore.

4. A fuel injection pump as claimed in claim 3, wherein the second spigot also has an axial blind bore which enters from its end face and forms a thin-walled hollow cylinder.

5. A fuel injection pump as claimed in claim 4, wherein the connection part has a cylindrical wall which is contiguous to the end face acting upon the flange-shaped part of the valve body and on which the cylindrical outer circumference of the flange-shaped part is guided.

6. A fuel injection pump as claimed in claim 5, wherein the cylindrical wall of the connection part embraces the outer circumference of a part of the cylinder liner extending out of the pump housing, a seal being inserted between the said part of the cylinder liner and the cylindrical wall.

7. A fuel injection pump as claimed in any preceding claim, wherein a conical part is disposed at -16the transition from the spigot-shaped part to the flange-shaped part of the connection partf and the end of the cylinder liner at the end face is of funnelshaped construction adapted to the frustum-shaped part.

8. A fuel injection pump as claimed in any preceding claim, wherein the pressure valve is in the form of a constant-pressure valve.

9. A fuel injection pump as claimed in claim 8, wherein a first valve is disposed in the pressurevalve body and comprises a spring-loaded valve member inserted into a part of a stepped bore parallel to the axis of the pump piston and passing through the pressure valve from the blind bore forming a hollow space. the seat of which valve member is formed by a reduction in diameter and the valve member opens towards the injection valve, and there is disposed in the pressure-valve body a second valve guided in a stepped bore which starts from the flange-shaped part of the outer circumference of the valve body, where the stepped bore is closed by a closure member, and the stepped bore opens into the stepped bore downstream of the valve member of the first valve and is connected to the pump working chamber upstream of the valve member of the second valve, the valve member of the second valve likewise opens towards the pump -17working chamber against the force of a valve spring.

10. A fuel injection pump constructed and adapted to operate substantially as described herein with reference to, and as illustrated in the accompanying drawings.

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