GB2042066A - A fuel injection pump for internal combustion engines - Google Patents

Abstract

A fuel injection pump for internal combustion engines having a pump housing (11) which is protected against cavitation and erosion caused by the jet of fuel emerging with high energy from a spill port (24) at the termination of injection. The fuel injection pump (10) includes a baffle rod (26) which is made from a round rod and which is fitted in the pump housing (11) in a plane at right angles to the axis of the pump piston and at a distance from the said axis and which is located opposite to the spill port (24). The baffle rod (26) incorporates pocket-like depressions (29) which intercept the emerging jet of fuel and which are provided with a return-flow passage for the spilled fuel and each pocket- like depression being defined above and below the spill port (24) by a respective web (26a) which arcuately surrounds the pump cylinder (12). <IMAGE>

Description

SPECIFICATION A fuel injection pump for internal combustion engines This invention concerns a fuel injection pump for internal combustion engines.

The invention depends from a fuel injection pump having at least one pump cylinder which is disposed in a pump housing and which receives a pump piston having a control edge for controlling the termination of injection, and in the wall of which pump cylinder is located a spill port, controlled by the control edge, for spilling fuel into the pump suction chamber under high pressure at the termination of injection.

A fuel injection pump, described in AT Patent Specification 251,976, has a baffle rod which comprises a sheet metal strip clamped in a bore which extends laterally along the row of cylinders and which acts as a fuel chamber, the sheet metal strip protecting the wall of the bore against cavitation damage by the fuel emerging from the spill port. Since the pump elements are turned through a limited angular range for the purpose of equalising the delivery quantities, and the jet of fuel also emerges obliquely from the port, the deflected jet of fuel destroys unprotected portions of the wall of the pump housing and particularly the reception bore for the pump cylinder in the pump housing. The same dmage also occurs in pumps in which the socalled baffle screws, acting as baffle means, are screwed into the wall of the pump housing (USA Patent Specification 2,797,644).

However, baffle screws of this kind have the disadvantage that they require a screw-in bore and the associated sealing and securing means for each pump cylinder.

According to the present invention there is provided a fuel injection pump for internal combustion engines, having at least one pump cylinder which is disposed in a pump housing and which receives a pump piston having a control edge for controlling the termination of injection, and in the wall of which pump cylinder is located a spill port, controlled by the control edge, for the fuel spilling into the pump suction chamber or back to the fuel tank under high pressure at the termination of injection, there being located opposite to the spill port a baffle rod which is fitted in the pump housing in a plane at right angles to the axis of the pump piston and at a distance from the said axis, and which is made from a round rod which incorporates a pocket-like depression which is located opposite the spill port and which is provided with a return-flow passage for the outflow of the spilled fuel, the or each pocket-like depression being defined above and below the spill port by a web portion which arcuately surround the pump cylinder.

The fuel injection pump in accordance with the invention has the advantage that the energy of the fuel jet emerging under very high pressure is reduced within the pocket-like depression in the baffle rod to the extent that damage is no longer caused by the spilling fuel emerging from the return-flow passage.

In particular, the reception bore and any seating surfaces for the pump cylinder are protected in a particularly reliable manner by the web portions which arcuately surround the pump cylinder above and below the spill port.

Advantageously by arranging for the pocket-like depression and the web portions surrounding the cylinder line to be formed as an arcuate groove both can be produced simultaneously in a single working operation by plunge-milling. Further when at least 60 of the circumference of the cylinder liner is embraced by the pocket-like depression, there is not risk of cavitation or erosion of the pump housing even in the case of a possible rotation of the pump cylinder of - 10" for the purpose of equalising the delivery quantities.

Advantageously the outflow side can be isolated from the suction side such that the return-flow surges no longer have a negative effect upon the suction behaviour of the pump and when the return passage is connected to a separate return line, satisfactory separation between the inflow side and the outflow side of the pump is achieved, so that differences in the charge can no longer occur as a result of the pressure waves which occur in the suction chamber when the pump is shut off.

With the simple construction of the baffle rod a reliable method of securing it is possible. In a fuel injection pump having a plurality of pump cylinders arranged in line and a single baffle rod arranged in the direction of the longitudinal axis of the pump a single baffle rod can be used which contains a number of depressions equal to the number of pump cylinders.

The present invention will now be described further by way of example only with reference to the accompanying drawings, in which: Figure 1 is a section through the first embodiment of a fuel injection pump equipped in accordance with the invention, taken on the line I-I of Fig. 2, Figure 2 is a section taken on the line !I-II of Fig. 1, and Figure 3 is a section, corresponding to Fig.

2, through the second embodiment.

Figures 1 and 2, illustrate a first emboo'- ment, of a fuel injection pump 10 which is provided with a separate drive from an engine camshaft and which is fitted in the engine housing. A pump cylinder 1 2 is secured in a pump housing 11 and receives a pump piston 14 having a control edge 1 3 which controls the termination of injection.The pump piston 14 is driven in a known manner by way of a rolier tappet 1 6 which is guided in the pump housing 11 and which is movable against the force of a tappet spring 15, and the pump cylinder 1 2 is clamped in its fitted position by means of a pipe connection member 1 8 by way of an interposed pressure valve 1 7. An annular shoulder 1 9 of the pump cylinder 1 2 abuts against a shoulder 21 in the pump housing 11.

An eccentric stud 22 is fitted in the pump housing 11 and has a pin 22a which engages a groove 23 in the pump cylinder 12, which eccentric stud acts as an auxiliary tool for rotating the pump cylinder when equalising the delivery quantities.

The wall of the pump cylinder 1 2 incorporates a control port 24 which is controlled by the control edge 1 3 of the pump piston 14 and which, in the present embodiment, at the same time acts as a suction and spill port.

Upon the termination of injection, fuel flows under high pressure from the control port 24 back into a pump suction chamber 25 which surrounds the upper portion of the pump cylinder 12.

In order to prevent the jet of fuel, emerging with high energy, from destroying that wall of the pump housing 11 which is located opposite the control port 24, a baffle rod 26 acting as baffle means is fitted in a blind bore 27 of the pump housing 11 and, when in its illustrated fitted position, is held by a closure member 28 which closes the bore 27 (see Fig. 2). As will be seen in Figs. 1 and 2, the blind bore 27 is incorporated in the pump housing 11 in a plane at right angles to the axis of the pump piston and at a distance from the said axis, and the distance of the longitudinal axis of the blind bore 27 from the axis of the pump piston corresponds, advantageously, to approximately half the diameter of the pump cylinder 12 in the region of the control port 24.

The baffle rod 26 is made from a round rod and incorporates pocket-like depressions 29 which correspond in number to the number of pump cylinders 1 2 contained in the injection pump 10, that is to say, in the present case, two pocket-like depressions, which are in the form of annular segment grooves which are concentric with the outer surface of the pump piston 1 2 and whose open sides 29a opening into the suction chamber 25 of the pump act as a return-flow passage for the fuel emerging from the spill port 24 at the termination of injection.In the present case, the pocket-like depression 29 embraces an approximately 1 20 wide sector of the pump cylinder 12, so that, even in the case of extreme angular adjustment of the pump cylinder adjustment of the pump cylinder 1 2 for basic setting of the delivery quantity, the jet of fuel emerging from the control port 24 always strikes the wall of the annular segmental groove 29 in the same manner, and the deflection of the jet of fuel causes the jet to lose a sufficient amount of energy to prevent the jet of fuel from causing damage in the suction chamber 25.

The configuration of the annular segmental groove 29 is chosen such that a respective web 26a of the baffle rod 26 closely surrounds the pump cylinder 1 2 in an arcuate manner above and below the control port 24.

The webs 26 a prevent erosion of the adjacent regions of the pump housing 1 1, particular destruction of the seat of the pump cylinder 12 which is located below the control port 24 and which is formed by the shoulder 21.

In the second embodiment of Fig. 3, the same parts are provided with the same reference numerals, and parts which differ slightly are additionally provided with an index mark.

The baffle rod fitted in the blind bore 27 of the pump housing 11' of the injection pump 10' is designated 26' in Fig. 3 and incorporates, as pocket-like depressions, two recesses 29' in the form of longitudinal grooves which are closed at both ends, the continuous rim of each recess abuts fully against the outer surface 12a' of a respective one of the pump cylinders 12'. The baffle rod 26' is held in its illustrated fitted position by means of a closure member 28' which is in the form of an annular bush, and the outwardly leading opening of the blind bore 27 is closed by means of a screw-threaded bush 31 which serves for the connection of a return line 32 (indicated by an arrow) for returning the fuel back to the fuel tank (not shown).The return line 32 is connected to the control ports 24 (acting only as spill ports in the present instance) of the two pump cylinders 12' by way of a return-flow passage 33 in the form of a longitudinal bore which interconnects the two longitudinal grooves 29' and which is bored concentrically into the baffle rod 26' from that end face thereof which is presented to the return line 32. A suction port 34 is bored in the wall of each pump cylinder 12' and is located opposite to, and preferably axially offset relative to, the respective control port 24 and enables fuel located in the suction chamber 25 to enter a pump working chamber 37 located above the pump piston 14.

Thus, in this fuel injection pump 10' with suction chamber scavenging the suction chamber 25 is separated from the spill chamber formed by the longitudinal grooves. 29' and the return-flow passage 33. Thus, the return-flow surges in the spill chamber do not affect the suction behaviour of this pump, whereby more uniform filling of the pump can be achieved.

This effect can also be obtained when the return-flow passage 33 communicates directly with the suction chamber 25, preferably by way of a throttle port 35 which is incorporated in the wall of the baffle rod 26', as is shown by broken lines in Fig. 3. in this case, as in Fig. 2, the open end of the blind bore 27 has to be sealed by means of a closure member 28.

In the baffle rod 26 of the first embodiment of Figs. 1 and 2, the pocket-like depressions in the form of annular segmental grooves 29, and the two associated webs, are defined by mutually concentric arcs, so that the pocketlike depressions 29 can be produced in a simple manner by plunge-milling, and thus the return-flow passages 29a, formed by the two open ends of the depressions 29, are also produced at the same time.

The fuel injection pump 10, described as a first embodiment with reference to Figs. 1 and 2, operates in the following manner.

When in its position illustrated in Fig. 1, the pump piston 14 is in its bottom end position. The control port 24 is then open and fuel flows from an inlet, indicated by an arrow 36, into the suction chamber and, by way of the pocket-like depression 29 in the baffle rod 26 and the control port 24 which also acts as a suction port in the present instance, into the pump working chamber 37 located above the pump piston 1 4. During the pressure stroke of the pump piston 14, a small quantity of fuel is first displaced back into the suction chamber 25 from the pump working chamber 37 through the control port 24 until the top end face of the pump piston 14 shuts off the control port 24.The effective pressure stroke commences at this instant and, during the pressure stroke, fuel is delivered through the valve 1 7 from the pump working chamber 37 to the injection nozzle on the cylinder (not illustrated) of the internal combustion engine.

The effective pressure stroke is terminated as soon as the oblique control edge 1 3 reaches the control port 24. The return-flowing fuel is injection under the very high pressure prevailing in the pump working chamber 37 through the gap which is very small in the first instance, and would strike against the interior wall of the suction chamber 25 in the pump housing 11 if it were not intercepted by the interior wall, acting as a baffle surface, of the pocket-like recess 29. Since the baffle rod 27 is made from hardened steel, the jet of the return-flowing fuel cannot destroy the baffle rod 26. As soon as the fuel in the pump working chamber 37 has expanded, fuel displaced during the further course of the pressure stroke is fed back into the suction chamber 25 without the formation of a strong jet.

In the second embodiment of Fig. 3, the return-flowing fuel does not flows into the suction chamber 25, but flows directly back to the tank by way of the return-flow passage 31 and the return line 32.

Claims (7)

1. A fuel injection pump for internal combustion engines, having at least one pump cylinder which is disposed in a pump housing and which receives a pump piston having a control edge for controlling the termination of injection, and in the wall of which pump cylinder is located a spill port, controlled by the control edge, for the fuel spilling into the pump suction chamber or back to the fuel tank under high pressure at the termination of injection, there being located opposite to the spill port a baffle rod which is fitted in the pump housing in a plane at right angles to the axis of the pump piston and at a distance from the said axis, and which is made from a round rod which incorporates a pocket-like depression which is located opposite the spill port and which is provided with a return-flow passage for the outflow of the spilled fuel, the or each pocket like depression being defined above and below the spill port by a web portion which arcuately surround the pump cylinder.

2. A fuel injection pump as claimed in claim 1, in which the pocket-like depression is formed by an annular groove portion which extends concentrically with the outer surface of the pump piston and whose ends open into the suction chamber of the pump and at the same time act as the return-flow passage.

3. A fuel injection pump as claimed in claim 1 or 2, in which the pocket-like depression embraces at least 60 of the pump cylinder circumference.

4. A fuel injection pump as claimed in one of the claims 1 or 3, in which the pocket-like depression is formed by a recess which is in the form of a longitudinal groove and which is closed at both ends and whose edge abuts fully against the outer surface of the pump cylinder, the longitudinal groove being connected to a return line or to the suction chamber of the pump by way of a longitudinal bore located in the baffle rod and acting as a return-flow passage.

5. A fuel injection pump as claimed in one of the claims 1 to 4, in which the baffle rod is fitted into a blind bore and is held in its fitted position by means of a closure member which seals the bore.

6. A fuel injection pump as claimed in any preceding claim having a plurality of pump cylinders arranged in line and a single baffle rod aligned in the direction of the longitudinal axis of the pump in which the baffle rod is provided with a plurality of depressions corresponding to the number of pump cylinders.

7. A fuel injection pump constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.