GB2279706A

GB2279706A - Fuel injection pumping system

Info

Publication number: GB2279706A
Application number: GB9412430A
Authority: GB
Inventors: Jaroslaw Hlousek
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-06-22
Filing date: 1994-06-21
Publication date: 1995-01-11
Anticipated expiration: 2014-06-21
Also published as: KR100340741B1; DE4320620B4; GB2279706B; JP3574681B2; JPH0719140A; DE4320620A1; GB9412430D0; KR950001085A

Description

2279706

DESCRIPTION FUEL INJECTION DEVICES FOR INTERNAL COMBUSTION ENGINES

The invention relates to fuel injection devices for internal combustion engines.

In a fuel injection device, known from US-PS 4 387 686. a pump piston, axially guided in a cylindrical bore of a cylinder liner, is reciprocated by a cam drive against the force of a return spring. The end face of the pump piston delimits a pump working chamber in the cylindrical bore, which pump working chamber is connected to an injection valve extending into the combustion chamber of the internal combustion engine to be supplied, and may be filled with fuel from a fuel reservoir, or relieved of fuel, by way of a fuel line. A hydraulically operable slide valve is disposed in the fuel line, by way of which slide valve the connection between the pump working chamber and the fuel line may be closed for the purpose of controlling the high-pressure delivery in the pump working chamber.

The slide valve has a cylindrical valve member which is axially displaceable in a housing, one end face of which valve member is acted upon by a return spring, and the other end face of which valve member delimits a working chamber which is connected to a pressure medium line. Fuel passes through the open slide valve through recesses in the valve member which start from the spring-side end face permanently connected to the fuel line. and which. by way of an annular groove in the valve member, open into the region of a connected passage leading to the pump working chamber. The return spring holds the valve member in abutment against a stop when the valve is open, the annular groove in the valve member being in register with the connection passage leading to the pump working chamber when the valve is in this position, so that the fuel may flow into or out of the pump working chamber. If the slide valve is to close the connection between the pump working chamber and the fuel line, the working chamber at the end face is filled with a pressure medium by way of the pressure medium line, and the valve member is displaced against the force of the return spring into a closed position in which the outer surface of the cylindrical valve member closes the connection passage leading to the pump working chamber.

In the known fuel injection device, the pressure medium line filling the working chamber is controlled by means of a control edge on the pump piston and two solenoid valves which are disposed in parallel with one another and which connect the pressure medium line to a high-pressure circuit or to the fuel circuit, operating with low pressure, of the fuel line, wherein the pressure in the low-pressure circuit and in the highpressure circuit is controlled by way of a respective pressure valve.

The known fuel injection device has the disadvantage that the build-up of pressure in the pressure medium line connected to the high-pressure circuit is delayed at the commencement of the control, so that the instant of control of the pressure medium line does not coincide with the instant of control of the slide valve, which may result in inaccuracies of control at high rotational speeds and short control times. Furthermore, very short control times can be obtained with the known device only by the overlapping of the two parallel solenoid valves which, however, require increased costs with respect to installation and control.

In accordance with the present invention there is provided a fuel injection device for an internal combustion engine, having a pump piston which is guided in a cylindrical bore of a cylinder liner and which is axially moved by a cam drive and delimits in the cylindrical bore a pump working chamber which is connected by way of a high-pressure line to an injection valve adapted to extend into the combustion chamber of the internal combustion engine to be supplied and which may be filled with, and relieved of, fuel by way of a controlled fuel line, wherein the closing of the fuel line, controlling the highpressure delivery, relative to the pump working chamber is effected by means of a valve which is disposed in the fuel line and which is hydraulically operated against the force of a return spring and has a pressure surface which is axially directed in the closing direction and which is subjected to pressure medium by way of a pressure medium line fed from a reservoir by a feed pump, which valve is acted upon by pressure medium by controlling a relief line, leading from the pressure medium line, by means of a solenoid valve, and wherein the solenoid valve is disposed in the relief line, and a non-return valve opening towards the valve in the fuel line is disposed between the branching off point of the relief line from the pressure medium line and the feed pump.

This has the advantage that, by virtue of disposing a non-return valve in the pressure medium line, having pressure medium permanently flowing therethrough, leading to the valve in the fuel line between the feed pump and a solenoid valve connecting the pressure medium line to a relief line, a hammer line is formed between the solenoid valve and the non-return valve after the line has been closed by the solenoid valve. The nonreturn valve is also closed by a returning pressure wave after the closing of the solenoid valve, whereby the flow energy of the pressure medium is converted in the closed volume to a rapid pressure rise which puts the valve in the fuel line, against the force of the return spring, into its position closing the connection between the pump working chamber and the fuel line. In this manner, with only a low feed performance of the feed pump, the pressure increased in this way relative to the static feed pressure of the feed pump makes it possible to obtain a very rapid pressure rise in the pressure medium line, adequate for the closing operation of the valve in the fuel line, with the use of only one solenoid valve, thus resulting in low cost with respect to regulating technology as well as inexpensive manufacture. Furthermore, the fuel injection device in accordance with the invention does not require any additional hydraulic systems having a pressure level in excess of 10 bar in order to ensure the high control dynamics required, which also reduces the demands made on the construction of the system.

In this connection, the hammer line is advantageously designed in such a way that, upon an increase in the volume of the working chamber, connected to the line, in the valve as a result of the lifting movement of the valve member during closing, the static pressure remaining in the line is sufficient to hold the valve member reliably in its position closing the connection between the pump working chamber and the fuel line, especially since the valve member, when in its closed position, does not have a sealing surface directed in the adjusting direction of the closure member and subjected to the feed pressure of the fuel injection pump. Advantageously, the valve is a slide or seat valve having conical sealing surfaces, thus resulting in smaller demands on the accuracy of manufacture. Moreover. by virtue of the conical valve seat, the high closing pressure at the valve member is only required for closing the slide valve. since, when the slide valve is closed, the high pressure built up in the pump working chamber during the delivery stroke no longer acts upon the slide valve member in the adjusting direction, and the static pressure in the pressure medium line now only has to overcome the spring force and the feed pressure of the feed pump. On the other hand the seat valve makes it possible to terminate the high-pressure delivery very rapidly, since, upon pressure relief of the pressure medium line by way of the solenoid valve, the return movement of the slide valve is assisted by the high-pressure of the fuel acting upon the valve sealing surface, even when the slide valve is only slightly open. Furthermore, when the slide valve is open, the surface subjected to the pressure in the opening direction is larger than the surface of the valve member facing the closing direction.

A further advantage is obtained by fitting the cylindrical slide valve member from the outside into a guide bore in-the housing and by closing the guide bore by means of a closure screw, the end face of the closure screw extending into the guide bore being used as an abutment surface for the return spring of the slide valve. Thus, the prestressing force of the spring, and thus the restoring force in the opening direction of the slide valve, can be set by the depth to which the closure screw is screwed in.

Furthermore, the possibility of separating the pressure medium circuit, serving as a control circuit, from the fuel circuit leading to the injection valve makes it possible, in an advantageous manner, to use heavy oil as fuel, wherein contact between the heavy oil, heated up to 1800C in the operating state of the system, and the solenoid valve is avoided.

By way of example only specific embodiments of the invention will now be described, with reference to the accompanying drawings, in which- Figure I is a diagrammatic illustration of a first embodiment in which the fuel circuit and also the control circuit of the fuel injection device are fed from a common reservoir; and Figure 2 is a diagrammatic illustration of a second embodiment in which the control circuit is separated from the fuel circuit of the fuel injection device.

In the fuel injection shown diagrammatically in Figure 1, a pump piston 5 is guided in a cylindrical bore 1 provided in a pump housing 3 and is axially reciprocated by a cam drive (not further illustrated). The end face 7 of the pump piston 5 delimits a pump working chamber 9 in the cylindrical bore 1, which pump working chamber 9 is permanently connected by way of a connection passage 11 to a control chamber 13 from which a high-pressure line 17, containing a pressure-equalizing valve 15, leads to an injection valve 19 extending into the combustion chamber of the internal combustion engine to be supplied. In this connection, the pressure-equalizing valve 15 is formed by two non-return valves which open in opposite directions and by way of which a specific static pressure can be established in the high-pressure line 17.

Furthermore, a fuel line 23, closeable by way of a slide valve 21, leads from the control chamber 13 and opens into an inlet line 25 which is in turn filled with fuel from a fuel reservoir 31 by way of a feed line 29 containing a feed pump 27.

The slide valve 21, closing the connection between the control chamber 13, connected to the pump working chamber 9, and the fuel line 23, is formed by a piston-shaped slide valve member 33 which is axially displaceably guided in a guide bore 35, intersecting the control chamber 13, in the housing 3 and which has in the course of its outer surface a conical crosssectional reduction with which it forms a valve sealing surface 37. The valve sealing surface 37 cooperates with a conical valve seat surface 39 which leads from the control chamber 13 and which is formed by a crosssectional reduction of the guide bore 35 towards a region of smaller diameter, wherein the fuel line 23 opens into the reduced diameter portion of the guide 35 in such a way that it remains in register with an annular chamber 41, between the guide bore 35 and the slide valve member 33, in the smaller diameter portion of the guide bore. This annular chamber 41 is delimited at its side remote from the valve seat by renewed enlargement of the cross section of the slide valve member 33 and, when the slide valve member 33 is removed from the valve seat 39, allows fuel to pass from the fuel line 23 to the control chamber 13.

The end face of the slide valve member 33 facing the exit of the guide bore 35 from the pump housing 3 is acted upon by a return spring 43 whose other end is supported on the end face, extending into the guide bore 35, of a closure screw 45 -g- which seals the guide bore 35 externally. The return spring 43 holds the slide valve member 23 in its position raised from the valve sat when the slide valve member 33 is in its initial state, that is, when the slide valve 21 is open. The end face, remote from the return spring 43, of the portion of valve member 33 of larger diameter than the spring-side end delimits a working chamber 47 in the guide bore 35, which working chamber 47 is delimited at the other end by the end of the guide bore 35 having a shoulder 48, and is connected to a pressure medium line 49. In the first embodiment, this pressure medium line 49 is likewise connected to the inlet line 25 and has a non-return valve 51 opening towards the working chamber 47. Furthermore, a relief line 53 leads from the pressure medium line 49 between the nonreturn valve 51 and the working chamber 47, and opens into the fuel reservoir 31 and, together with the pressure medium line 49, forms a control circuit.

The relief line 53 is closeable relative to the pressure medium line 49 by way of a solenoid valve 55 which is disposed in the relief line 53 and which is controlled by an electrical control device which processes operating parameters of the internal combustion engine. The relieving outflow of the pressure medium from the pressure medium line 49 is abruptly prevented by the closing of the relief line 53 in conjunction with the non-return valve 51, so that the now closed pressure medium line acts like a hammer line in which the flow energy of the enclosed medium is converted to a pressure rise whose pressure achieved is higher than that otherwise available by virtue of the feed performance of the feed pump 27.

Furthermore, for the purpose of maintaining a constant pressure in the fuel line 23, a return line 61 containing a pressure valve 59 leads from the inlet line 25 and into the fuel reservoir 31, wherein the pressure valve 59 also maintains a specific static pressure in the fuel system in addition to a constant supply pressure in the fuel line 23.

The leakage fuel at the pump piston 5 and at the valve member'33 is collected by way of annular grooves therein and is returned to the fuel reservoir 31 by way of a leakage oil line 63.

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

When the solenoid valve 55 is open, the pressure in the working chamber 47 is too low to put the slide valve member 33 into its closed position. The pump working chamber 9 is filled during the suction stroke of the pump piston 5 when the slide valve 21 is open in such a way, wherein, for this purpose, the slide valve member 33 is held in abutment against the shoulder 48 by the return spring 41. so that the fuel may be delivered by means of the feed pump 27 from the fuel reservoir 31 and into the pump working chamber 9 by way of the feed line 29, the inlet line 25, the fuel line 23, the control chamber 13 and the connection passage 11.

During the subsequent delivery stroke of the pump piston 5. and in accordance with injection parameters, a portion of the fuel is first displaced again from the pump working chamber 9 and back into the fuel reservoir 31 by way of the fuel line 23. the inlet line 25 and the return line 61.

At the same time. the fuel delivered parallel to the fuel line 23 into the pressure medium line 49 is returned to the fuel reservoir 31 through the open solenoid valve 53 and by way of the relief line 53. so that the working chamber 47 of the slide valve 21 subjected to only a low pressure which is insufficient to overcome the force of the return spring 43. The high-pressure delivery in the pump working chamber 9 is initiated by the flow through the solenoid valve 55 controlled by the control device 57, as a result of which the solenoid valve 55. in the form of a two-port. two-position valve, closes the relief line 53.

The flowing medium located in the pressure medium line 49 is reflected at the solenoid valve 55. whereby a returning pressure wave is created and also closes the non-return valve 51 in the pressure medium line 48. At the same time. the flow energy in the closed volume of the pressure medium line 49 is converted to a pressure rise which continues into the working chamber 47 of the slide valve 21 where it brings the valve sealing surface 37 of the slide valve member 33 into abutment against the valve seat 39 by a pressure surge against the force of the return spring 43, so that the connection between the pump working chamber 9 and the fuel line 23 is closed by the slide valve 21. In this connection, the hammer line, formed by the volume enclosed in the pressure medium line 49, is dimensioned in such a way that, despite the increase in the volume of the working chamber 47. the static pressure remaining in the hammer line is sufficient to hold the side valve member 33 in abutment against the valve seat 39 against the force of the return spring 43. At the same time, this is assisted by the larger diameter of the portion of the valve member 33 at the working chamber end thereof compared with the smaller diameter of the portion of the valve member 33 at the spring chamber end thereof, so that the effective surface is larger in the closing direction.

As a result of the closing of the fuel line 23, a high pressure may build up in the working chamber 9 during the further delivery stroke movement of the pump piston 9 and, after the pressure-equalizing valve 15 has opened, it is transmitted by way of the high-pressure line 17 to the injection valve 19 where it leads, in a known manner, to the injection of fuel into the combustion chamber of the internal combustion engine to be supplied.

The termination of the high-pressure delivery and of the injection of fuel is initiated by the opening of the solenoid valve 55, as a result of which the pressure in the hammer line rapidly expands into the relief line 53. At the same time, the working chamber 47 is also relieved of pressure, and the return spring 43 again opens the slide valve 21, so that also the pressure in the pump working chamber 9 expands into the fuel line 23, wherein the pressure drop in the high-pressure line 17 leads to the closing of the injection valve 19. At the same time, the opening stroke of the valve member 33 is assisted by the high fuel pressure acting upon the valve member 33 in the opening direction.

The second embodiment shown in Figure 2 differs from the first embodiment in that, in the second embodiment, the control circuit formed by the pressure medium line 49 and the relief line 53 is separated from the fuel circuit formed by the fuel line 23.

Analogously to Figure 1, the fuel circuit comprises the fuel line 23 which is fed from the fuel reservoir 31 by the feed pump 27 and whose pressure is also adjustable by way of the pressure valve 59 in the return line 61 branching from the fuel line 23.

In Figure 2, the pressure medium line 49 is fed from a separate pressure medium reservoir 71 by way of a pressure medium feed pump 73 and an inlet passage 75, wherein the nonreturn valve 51 and the relief line 53 and the solenoid valve 55 are disposed analogously to those of Figure 1, and the relief line 53 opens into the pressure medium reservoir 71.

In the second embodiment, the supply pressure in the inlet passage 75 is controlled by means of a n adjustable throttle 77 in a return line leading into the pressure medium reservoir 71.

The mode of operation of the second embodiment described with reference to Figure 2 differs from the mode of operation of the first embodiment in that the fuel circuit filling the pump working chamber 9, and the control circuit acting upon the slide valve member 33, are fed from separate reservoirs 31. 71.

This separation-of the circuits makes it possible to-use heavy oil as fuel, since the heavy oil, heated up to 180C during operation of the fuel injection device, does not come into contact the solenoid valve 55 controlling the control circuit.

Claims

- CLAIMS -

1. A fuel injection device for an internal combustion engine, having a pump piston which is guided in a cylindrical bore of a cylinder liner and which is axially moved by a cam drive and delimits in the cylindrical bore a pump working chamber which is connected by way of a high-pressure line to an injection valve adapted to extend into the combustion chamber of the internal combustion engine to be supplied and which may be filled with, and relieved of, fuel by way of a controlled fuel line, wherein the closing of the fuel line, controlling the highpressure delivery, relative to the pump working chamber is effected by means of a valve which is disposed in the fuel line and which is hydraulically operated against the force of a return spring and has a pressure surface which is axially directed in the closing direction and which is subjected to pressure medium by way of a pressure medium line fed from a reservoir by a feed pump, which valve is acted upon by pressure medium by controlling relief line, leading from the pressure medium line, by means of solenoid valve, and wherein the solenoid valve is disposed in the relief line. and a non-return valve opening towards the valve in the fuel line is disposed between the branching-off point of the relief line from the pressure medium line and the feed pump.

2. A fuel injection device as claimed in claim 1, wherein the valve in the fuel line is a slide valve and has a valve member which has on its circumferential surface a cross- sectional reduction which forms a conical transition to the smaller cross section of a valve sealing surface which cooperates with a conical valve seat formed by a reduction in the diameter of the guide bore which guides the valve member, wherein the guide bore widens at one side of the valve seat into a control chamber of increased diameter which is a component part of the high-pressure line between the pump working chamber and the injection valve and which merges at the other side of the valve seat into a portion of the guide bore of smaller diameter where, together with an annular groove in the valve member delimits annular chamber connected tothe fuel line, in the smaller diameter portion of the guide bore in which a reduced diameter portion of the valve member slides.

3. A fuel injection device as claimed in claim 2, wherein the return spring abuts against the end face of the valve member remote from the pressure medium line, and its other end is supported on an externally adjustable closure screw of the guide bore.

4. A fuel injection device as claimed in claims 2 and 3, wherein the portion of the valve member delimiting the annular chamber faces the return spring and has a smaller cross section than the portion of the valve member facing the pressure medium line.

5. A fuel injection device as claimed in claim 1, wherein the pressure medium line and the fuel line line open into a common inlet line which is filled with fuel from the fuel reservoir by means of the feed pump and the pressure of which fuel in controllable by way of a pressure valve in a return line leading from the inlet line line into the fuel reservoir.

6. A fuel injection device as claimed in claim 1, wherein the pressure medium circuit controlling the valve in the fuel line, and the fuel circuit filling the pump working chamber, are separated from one another and each have a feed pump and a pressure-regulating device.

7., A fuel injection device as claimed in claim 6, wherein heavy oil is used as the fuel to be injected, and diesel fuel is used as the pressure medium.

8. A fuel injection device as claimed in claim 1, wherein the solenoid valve is controlled by an electrical control device which processes operating parameters of the internal combustion engine to the supplied.

9. A fuel injection device as claimed in claim 1, wherein a pressure-equalizing valve is disposed in the high pressure line between the pump working chamber and the injection valve.

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