GB2252135A

GB2252135A - Fuel injection pump for supplying fuel and a further liquid to diesel engines

Info

Publication number: GB2252135A
Application number: GB9200591A
Authority: GB
Inventors: Dominique Buisson
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-01-14
Filing date: 1992-01-13
Publication date: 1992-07-29
Anticipated expiration: 2012-01-13
Also published as: DE4100832C2; GB9200591D0; BR9200059A; GB2252135B; DE4100832A1; JPH04301176A

Description

2252135 4

DESCRIPTION FUEL INJECTION PUMP FOR DIESEL ENGINES

The present invention relates to a fuel injection pump for diesel engines, such as a pumping nozzle, in which a working chamber of the pump piston is bounded by a displaceably guided separating piston disposed coaxially to the pump piston, the separating piston being driven hydraulically,by the pump piston by way of the volume of liquid enclosed in the working chamber of the pump piston for movement which extends in the same direction as the movement of the pump piston over portions of the stroke of the separating piston.

An injection pump of this kind is known from DEOS 37 00 357. In this known injection pump, only the fuel from the working chamber of the separating piston is delivered to the nozzle and injected, while the fuel delivered into the working chamber of the pump piston is used to drive the separating piston and to control the injection of the fuel from the working chamber of the separating piston.

It is an object of the present invention to use the arrangement of such a separating piston in order to feed a further liquid, such as water, to the engine, in addition to the fuel. The feeding of water into the working chamber of the engine has great -2advantages with respect to reducing the emission of toxic substances or the emission of nitrous oxides, and with respect to improving the combustion.

In accordance_with the present invention. there is provided a fuel injection pump for a diesel engine, in which a working chamber of a pump piston is bounded by a displaceably guided separating piston disposed coaxially to the pump piston, the separating piston being driven hydraulically by the pump piston by way of the volume of liquid enclosed in the working chamber of the pump piston for a movement which extends in the same direction as movement of the pump piston over portions of a stroke of the separating piston, and in which supply of liquid to the working chamber of the pump piston, shutting-off of the working chamber and overflow of liquid from the working chamber are controlled by a solenoid valve controlled in dependence upon at least one operating parameter of the engine, a mixing chamber is disposed outside an injection pump element housing a pump and an injection nozzle and contains an emulsion of fuel and a further liquid, and is connected to a working chamber of the separating piston by way of a device preventing a return flow from the working chamber of the separating piston, and the working chamber of the separating piston is connected to a pressure chamber -3upstream of the injection nozzle.

The operating parameter controlling the solenoid valve may be the load. The additional liquid may be water, possibly with the addition of an emulsifier.

The liquid contained in the working chamber of the pump piston only serves to effect the drive of the separating piston by the pump piston. The fuel to be injected is in the form of an emulsion only in the working chamber of the separating piston which is connected to the pressure chamber of the injection nozzle. By virtue of the fact that the supply of liquid to the working chamber of the pump piston, the shutting-off of this working chamber and the overflow of the liquid from the latter, that is, the relief of this working chamber, are controlled in dependence upon at least one operating parameter of the engine, the prevailing stroke of the separating piston is also controlled, and the injection quantity. the commencement of injection and the termination of injection are thus controlled in dependence upon the relevant operating parameter of the engine. By virtue of the fact that the emulsion of fuel and a further liquid or water is prepared outside the pumping nozzle or the like, a homogeneous emulsion is available for injection and, by virtue of the fact that the said device is provided between the mixing chamber and the working chamber of the separating piston for preventing a return flow from the working chamber of the separating piston, the required injection pressure may be built up during the pressure stroke of the separating piston.

Since the liquid from the working chamber of the pump piston is not injected, this liquid need not be fuel and, in accordance with a preferred embodiment of the present invention, a different liquid may be used, preferably a liquid of small compressibility. Constructively, it is simplest to use fuel as such a liquid, since fuel is available. In addition to the small compressibility, such a different liquid should also have other properties, namely the possibility of using a higher pressure, a lower sensitivity to clearance volumes, better efficiency and satisfactory operating capability at a low temperature. The viscosity of this liquid should also be largely independent of fluctuations in temperature. By way of example, water may be used as such a liquid, possibly with the addition of an anti-freezing agent.

Preferably, the mixing chamber is connected to the working chamber of the separating piston by way of a non-return valve opening towards the working chamber of the separating piston. However, an arrangement of this kind has the disadvantage that the non-return -5valve is subjected to high pressure during the injection operation, and therefore leakage losses can occur. Therefore, in accordance with the invention, the connection of the mixing chamber to the working chamber of the separating piston is preferably controlled by the pump piston. In accordance with the invention, a construction of this kind may be realised in an advantageous manner in that the mixing chamber is connected to the working chamber of the separating piston by way of a bore which intersects the guide bore of the pump piston and whose openings into the guide bore are located opposite one another and past which an annular groove of the pump piston slides in the region of the bottom dead centre position.

Advantageously, in order to prevent a dangerous pressure rise in the working chamber of the pump piston, that edge of the separating piston which faces the working chamber of the pump piston may, when the separating piston is in its top dead centre position, open a relief bore leading to a chamber of low pressure, and the stroke of the separating piston may be limited by a stop.

The return stroke of the separating piston may be effected in a simple manner by the pressure difference between the working chamber of the pump piston and the working chamber of the separating piston.

-6Alternatively, however, the separating piston may be loaded by a return spring acting in a direction towards the working chamber of the pump piston.

The mixing chamber should be disposed as near as possible to the working chamber of the separating piston in order to avoid separation of the water from the fuel.

Preferably a stroke sensor indicating the prevailing stroke of the separating piston may be provided. The cross section of the separating piston is invariable and the stroke of the separating piston therefore indicates the injection quantity.

The required quantity of water, which is to be added, differs under the differing operating conditions. The emulsion should contain a large quantity of water at full load. Only a small quantity of water is required at low load, and addition of water should be avoided during the braking operation. Therefore, in accordance with the present invention, the quantity of additional liquid, particularly water, added to the fuel in or upstream of the mixing chamber is preferably controlled in dependence upon at least one operating parameter of the engine, particularly the load on the engine.

By way of example only, specific embodiments of the present invention will now be described with -7reference to the accompanying drawings, in which:

Fig.1 is a schematic diagram of an embodiment of a pumping nozzle in accordance with the present invention; Fig.2 is a schematic diagram of a further embodiment of a pumping nozzle; Fig.3 shows a partial section of a pumping nozzle; Fig.4 shows a pumping nozzle, corresponding to Fig.2, in five different piston positions I to V. and Fig.5 shows a section of a further embodiment of the pumping nozzle modified upon that in Fig.4.

In the embodiment of Fig.1, a pump piston 3 driven by a camshaft, and a separating piston 4, are guided in a common guide bore 1 of the pumping nozzle 2, which has a working chamber 5 for the pump piston 3, and a working chamber 6 for the separating piston 4. A solenoid valve 8 is fitted in a bore 7 opening into the working chamber 5 and is controlled in dependence upon various operating parameters of the engine, such as by the load. Fuel is fed to the working chamber 5 by way of a line 9 and the solenoid valve 8. Fuel is introduced by way of a branch line 11, into a mixing chamber 10, disposed outside the pumping nozzle, and water, possibly with the addition of an emulsifier, is fed thereto by way of a line 12.

-8The mixing chamber 10 is connected to the working chamber 6 of the separating piston by way of a bore 13. A non-return valve 14 is fitted in the bore 13 and opens in the direction towards the working chamber 6. The emulsion of fuel and water is delivered from the working chamber 6 to the injection nozzle by way of a bore 15.

In this embodiment, fuel fed through the line 9 is used as liquid for transmitting the lifting movement of the pump piston 3 to the separating piston 4. Alternatively, however, a different liquid, such as water,, may be fed through the line 9. in this case, the connecting line 11 is omitted, and fuel and water may be fed commonly to the mixing chamber 10 through the line 12. In this embodiment of Fig.1, the non-return valve 14 is loaded by the high pressure occurring during injection.

In the embodiment of Fig.2, a liquid is fed to the working chamber 16 of the pump piston 17 by way of a solenoid valve 19 controlled by an engine operating parameter. The separating piston 20 is actuated by the pump piston 17 through the intermediary of this liquid volume. The separating piston 20 is guided in a guide bore 21 of the pumping nozzle 22, the diameter of the guide bore 21 being smaller than the diameter of the guide bore 23 in which the pump piston 17 is -gguided. In this manner, the force of the separating piston 20 is increased.

An emulsion of water and fuel is located in a mixing chamber 24 located outside the pumping nozzle 22, or is produced in the chamber 24. A bore 25 is connected to this mixing chamber 24 and intersects the guide bore 23 of the piston 17 at right angles thereto. When the pump piston 17 is in its bottom dead centre position, an annular groove 26 in the pump piston 17 connects the branch 25a to the branch 25b of the bore 25, and the emulsion of fuel and water flows into the working chamber 29 of the separating piston 20 by way of bores 27 and 28. The emulsion flows into the injection nozzle by way of a bore 30 during the pressure stroke of the separating piston 20.

A stroke sensor 31 may be provided in order to monitor the injection quantity and indicates the prevailing lift of the separating piston 30, and thus the volume injected.

The stroke of the separating piston 20 is limited by a stop 32. An arrangement as shown in Fig.3 may be provided in order to avoid damage to the pumping nozzle due to excessive pressure developing in the working chamber 16. As is shown in Fig.3, the guide bore 21 for the separating piston 20 opens into a bore 33 which leads to a chamber of low pressure. When the -10separating piston 20 is in its top dead centre position, the bore 33 is opened by the surface edge 34 of the separating piston 20 facing the working chamber 16 of the pump piston. and the working chamber 16 is relieved.

Fig.4 shows, diagrammatically, five piston positions I to V of the arrangement shown in Fig.2.

Position I: The bore 25 leading from the mixing chamber 24 is closed by the pump piston 17. The solenoid valve 19 is open and the working chamber 16 of the pump piston 17 is depressurised, and the separating piston 20 is located in its bottom dead centre position.

Position II: The solenoid valve 19 has been closed, and pressure thus builds up in the working chamber 16. The separating piston 20 is moved in the direction towards its top dead centre position, and injection is effected by way of the passage 30.

Position III: The pump piston 17 and the separating piston 20 have reached their top dead centre positions. The solenoid valve 19 is opened and the injection operation is terminated.

Position IV: The pump piston 17 is in the region of its bottom dead centre position. The annular groove 26 of the pump piston 17 opens the transverse bore 25. During its stroke in the direction towards -11its bottom dead centre position, the pump piston 17 draws in the separating piston 20. and the working chamber 29 of the separating piston 20 is filled with emulsion. The solenoid valve 19 is closed.

Position V: The separating piston 20 is located in its bottom dead centre position. The working chamber 29 of the separating piston 20 is therefore entirely filled with emulsion. The solenoid valve is opened, so that the working chamber 16 of the pump piston 17 is depressurised, and the solenoid valve 19 is only closed again when position II has been reached.

Fig.5 again shows, in a modified form, the position of the separating piston 20 corresponding to position V. In this case. a return spring 35 is provided in the working chamber 29 of the separating piston 20 and urges the separating piston 20 in the direction of its top dead centre position. In this case, it is unnecessary for the solenoid valve to be closed in the position IV, since, in view of the spring 35, the pump piston 17 does not have to draw in the separating piston 20.

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Claims

-12CLAIMS

1. A fuel injection pump for a diesel engine. in which a working chamber of a pump piston is bounded bya displaceably guided separating piston disposed coaxially to the pump piston, the separating piston being driven hydraulically by the pump piston by way of the-volume of liquid enclosed in the working chamber of the pump piston for a movement which extends in the same direction as movement of the pump piston over portions of a stroke of the separating piston, and in which supply of liquid to the working chamber of the pump piston, shutting-off of the working chamber and overflow of liquid from the working chamber are controlled by a solenoid valve controlled in dependence upon at least one operating parameter of the engine, a mixing chamber is disposed outside an injection pump element housing a pump and an injection nozzle and contains an emulsion of fuel and a further liquid, and is connected to a working chamber of the separating piston by way of a device preventing a return flow from the working chamber of the separating piston, and the working chamber is connected to a pressure chamber upstream of the injection nozzle.

2. An injection pump as claimed in claim 1, wherein the liquid fed to the working chamber of the i -13pump piston is fuel or another liquid, particularly one of low compressibility.

3. An injection pump as claimed in claim 1 or 2, wherein the mixing chamber is connected to the working chamber of the separating piston by way of a nonreturn valve opening in a direction towards the working chamber of the separating piston.

4. An injection pump as claimed in claim 1, 2 or 3. wherein the connection of the mixing chamber to the working chamber of the separating piston is controlled by the pump piston.

5. An injection pump as claimed in claim 4, wherein the mixing chamber is connected to the working chamber of the separating piston by way of a bore which intersects a guide bore of the pump piston and whose openings into the guide bore are located opposite one another, and an annular groove of the pump piston which is able to slide past said openings in the region of the bottom dead centre position of the separating piston in the working chamber of the separating piston.

6. An injection pump as claimed in any of claims 1 to 5, wherein, when the separating piston is in its top dead centre position, its edge facing the working chamber of the pump piston opens a relief bore leading i -14to a chamber at low pressure, and the stroke of the separating piston is limited by a stop.

7. An injection pump as claimed in any of the preceding claims, wherein the separating piston is loaded by a return spring acting in a direction towards the working chamber of the pump piston.

8. An injection pump as claimed in any of the preceding claims, wherein a stroke sensor indicating the prevailing stroke of the separating piston is provided.

9. An injection pump as claimed in any of the preceding claims, wherein the quantity of said further liquid added to the fuel in or upstream of the mixing chamber, is controlled in dependence upon at least one operating parameter of the engine.

10. An injection pump as claimed in any of the preceding claims, wherein the mixing chamber is disposed as near as possible to the working chamber of the separating piston.

11. An injection pump as claimed in any preceding claim, in which the engine operating parameter controlling the solenoid valve is load.

12. An injection pump as claimed in any preceding claim, which is a pumping nozzle.

13. A fuel injection pump as hereinbefore described with reference to and as illustrated in the accompanying drawings.