GB2139296A

GB2139296A - A fuel injection pump for a reciprocating-piston internal combustion engine

Info

Publication number: GB2139296A
Application number: GB08408132A
Authority: GB
Inventors: Max Matzen
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1983-04-13
Filing date: 1984-03-29
Publication date: 1984-11-07
Also published as: DE3313322C2; FR2544395A1; DE3313322A1; GB2139296B; GB8408132D0

Abstract

A fuel injection pump for use in injecting preheated heavy oil fuel into a reciprocating-piston internal combustion engine, the pump having a piston 1 reciprocable in a bore provided with a leak-oil stop groove (5) through which flows oil under pressure. The groove (5) is fed with oil by a pump (8) and is discharged through a line (11, 12) and a pressure relief valve (9). <IMAGE>

Description

SPECIFICATION A fuel injection pump for a reciprocating piston internal combustion engine This invention relates to a fuel injection pump for a reciprocating- piston internal combustion engine which is operated by a pre-heated heavy oil fuel, the pump elements comprising a pump piston and a pump casing, in which an internal surface of the pump casing is provided with a circumferential groove into which oil under pressure is admitted from a radially extending feed duct of the pump when the latter is in use.

If heavy oil is used as fuel for operating a reciprocating-piston internal combustion engine, pre-heating of the heavy oil to a temperature of substantially 1 70 degrees Centigrade is indispensible for the purpose of achieving a viscosity suitable for operating the engine. It has also been found to be essential, if an engine is operated by heavy oil, to provide the injection pump with a leak-oil stop for preventing the fuel from corroding the working surfaces of the pump elements or from impairing their lubrication.The oil supply, in the case of previously proposed leak-oil stops, remains under pressure within an annular space around the pump piston; although it moistens the cylindrical surface of the longitudinally displaceable pump piston, this does not lead to any appreciable consumption nor any appreciable flow in the circumferential duct.

As a result, the oil contained in the leak-oil stop is heated to the high temperature of the pre-heated heavy fuel since the latter heats the pump elements. It has been found that at these temperatures the oil of the leak-oil stop becomes overheated. It is known that the oil for the leak-oil stop is taken from the compressed oil in the lubricating oil circuit of the internal combustion engine and is suitable, therefore, for temperatures which, on average, fluctuate around 100 degrees Centigrade. If the temperatures are higher the lubricating oil is subjected to increasingly rapid ageing until it finally becomes unusable. The consequence of overheating is decomposition of the additives in the lubricating oil including sedimentation in the oil groove and incrustation of the super-finished sliding surfaces of the pump piston and pump casing resulting in breakdowns.

Figure 1 shows a radial sectional view of a fuel injection pump with a leak-oil stop of a previously proposed construction. The pump comprises a pump piston 1 and a pump casing 2 into which an injection duct 3 is screwed. An interior surface of the pump casing 2 is provided with a first circumferential groove 4 through which leak fuel can flow back to the suction side of the pump piston 1.

Oil under pressure is fed from the lubricating-oil system through a radial feed duct 6 to a second circumferential groove 5. The oil under pressure moistens the sliding surface of the pump piston 1 and spreads over this surface and thus prevents the fuel from advancing over the super-finished sliding surfaces. A reservoir 7, an oil feed pump 8, a pressure-relief valve 9 and a pressure gauge 10 are parts of the lubricating-oil system.

Since the pump piston uses only very little lubricating oil on its sliding surface and since, moreover, hardly any oil creeps along the sliding surfaces of the piston and the casing to the circumferential groove 4, the oil in the circumferential groove 5 remains motionless.

As a result, the temperature of the oil rises to that of the pump elements 1 and 2 which, bearing in mind that the fuel is pre-heated to substantially 1 70 degrees Centigrade, may render the lubricating oil unusable and may cause the injection pump to break down.

It is an aim of the invention to reduce or completely eradicate overheating of the stop oil in the leak-oilstop of an injection pump for pre-heated heavy oil.

Accordingly, the present invention is directed to a fuel injection pump of the construction set out in the opening paragraph of this specification, in which an oil outlet duct opens into the circumferential groove at a position which is substantially opposite the opening of the feed duct into the circumferential groove and through which the oil under pressure is returned to an oil circulation system when the injection is in use.

As a result, oil of a temperature lower than that of the pump elements can flow continuously through the leak-oil stop. The flow velocity brought about by the pressure inhibits heating of the stop oil to the critical temperature range so that sedimentation is avoided or at least reduced.

A pressure-relief valve may be arranged in the outlet duct. As a result, a predetermined pressure is maintained which inhibits the fuel from entering the gap between the pump piston and the pump casing.

An example of a fuel injection pump made in accordance with the present invention is drammatically illustrated in Fig. 2 of the acaccompanying drawing, which shows an axial sectional view of the pump. Parts of the pump illustrated in Fig. 2 which correspond to those of the pump shown in Fig. 1 bear the same reference numerals. Thus the pump shown in Fig. 2 has a piston 1 and a casing 2 similar to those illustrated in Fig. 1, but differing therefrom by a radial oil outlet duct 11 opening into a return duct 1 2 connected to the lubricating-oil system. The outlet duct 11 opens into the circumferential groove 5 at a position which is disposed substantially opposite the opening of the feed duct 6 into the circumferential groove 5. The pressure-relief valve 9 in the Fig. 2 pump is arranged in the duct 1 2 which ensures that a predetermined pressure prevails in the leak-oil stop. With the outlet duct 11, the lubricating-oil system may now cause lubricating oil of a temperature lower than that of the pump elements 1 and 2 to flow through the circumferential groove 5. As a result, the pump elements in the region of the ducts are locally slightly cooled and the heating of the lubricating oil with all its consequences is inhibited.

Claims

1. A fuel injection pump for a reciprocating-piston internal combustion engine which is operated by a pre-heated heavy oil fuei, the pump elements comprising a pump piston and a pump casing, in which an internal surface of the pump casing is provided with a circumferential groove into which oil under pressure is admitted from a radially extending feed duct of the pump when the latter is in use, and in which an oil outlet duct opens into the circumferential groove at a position which is substantially opposite the opening of the feed duct into the circumferential groove and through which the oil under pressure is returned to an oil circulation system when the injection pump is in use.

2. A fuel injection pump according to claim 1, in which a pressure-relief valve is arranged downstream of the oil outlet duct.

3. A fuel injection pump substantially as described herein with reference to Fig. 2 of the accompanying drawing.

4. A reciprocating-piston internal combustion engine provided with a fuel injection pump connected to an oil circulation system substantially as described herein with reference to Fig. 2 of the accompanying drawing.