GB2142388A

GB2142388A - Fuel injection pump for an internal combustion engine

Info

Publication number: GB2142388A
Application number: GB08413328A
Authority: GB
Inventors: Karl Konrath
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1983-07-01
Filing date: 1984-05-24
Publication date: 1985-01-16
Also published as: JPS6019955A; DE3323761A1; GB2142388B; DE3323761C2; GB8413328D0; JPH0536632B2

Abstract

A fuel injection pump for an internal combustion engine is proposed, whose pump working chamber (3) is connectible to a quiet-idle device (14) having an extraction chamber (17) which is defined by a damping piston (16) and which is connectible to a line (9) connected to the pump working chamber (3) by a passage in the damping piston (16), the latter being in the form of a rotary slide valve. Communication between the extraction chamber (17) and the pump working chamber (3) can be interrupted by rotating the damping piston, and hence the quiet-idle device can be shut off. A device (24, 25, 30, 29, 39) is provided for turning the damping piston (16). The device can be mounted directly coaxially of, and contiguous to, the pump working chamber (3) of the fuel injection pump. <IMAGE>

Description

SPECIFICATION Fuel injection pump for an internal combustion engine The invention relates to a fuel injection pump for an internal combustion engine.

In a fuel injection pump described in Ger man Patent Specification No. 18 07 554, a pump piston reciprocates in a pump cylinder and defines a pump working chamber. The pump working chamber is connectible to a fuel injection line during at least a portion of the delivery stroke of the pump piston and is also connectible by way of a throttle and a fuel reception line to a fuel reception chamber or fuel accumulator.

The reception line leads coaxially of the axis of the pump piston from the pump working chamber to the reception chamber upstream of a displaceable piston which defines the reception chamber and which is also located coaxially of the pump piston. A drainage line from the reception chamber incorporates a rotary valve whose axis extends at right angles to a drainage passage and which is operable by a linkage on the fuel injection pump.

Devices of this kind serve to soften the combustion operation and, particularly in selfigniting internal combustion engines in which the fuel is injected directly into the combustion chamber, to prevent too large a quantity of fuel from accumulating in the combustion chamber up to the expiry of the ignition delay from the commencement of the first injection operation and then burning abruptly. Such abrupt combustion leads to a steep pressure rise and hence to the development of a considerable amount of noise during combustion.

The device mentioned initially has the disadvantage that an accurately guided and sealingly fitted shaft additionally has to be provided for actuating the valve in the drainage line.

Furthermore, the known solution has the disadvantage that the transverse shaft takes up a considerable amount of space, and that an expensive linkage has to be provided for actuating this shaft.

It is an object of the present invention to provide a fuel injection pump for an internal combustion engine which substantially overcomes the above disadvantages.

In accordance with the invention there is provided a fuel injection pump for an internal combustion engine, having a pump piston which reciprocates -in a pump cylinder and which defines a pump working'chamber, the latter being connectible to a fuel injection line during at least a portion of the delivery stroke of the pump piston and also connectible by way of a throttle and a fuel reception line to a fuel.reception chamber upstream of a springloaded displaceable piston which is guided in a cylinder and which is in the form of a rotary valve in.the said fuel reception jine;; for which purpose the outer surface of the displaceable piston incorporates a control port which is permanently connected to the reception chamber and which can be brought into register with the mouth of the reception line leading from the pump working chamber to the cylinder, the displaceable piston being provided with a turning device which enables the displaceable piston, acting as the rotary valve to be turned but permits axial displacement of the displaceable piston.

The fuel injection pump in accordance with he invention has the advantage that the displaceable piston at the same time serves as a valve closure member with only slight modifications to the piston and with a device of simple construction for rotating the piston. In an advantageous development, the end face of the displaceable piston remote from the reception chamber has a guide portion which is positively connected in a rotary sleeve to a correspondingly adapted part of the turning device which adjoins the displaceable piston axially.

This has the advantage that the rotating device, or the valve for shutting off the reception line, can be disposed coaxially of the axis of the pump piston together with the displaceable piston, hence resulting in advantageous possibilities of fitting a fuel injection pump designed in accordance with the other features. This applies particularly to distributor-type fuel injection pumps of the lifting piston type in which good possibilities of fitting additional devices of this kind are provided on the end face of the pump working chamber.

Advantageously, the turning device has a rotatable stem which is disposed coaxially of the displaceable piston and which is surrounded by the return spring which loads the displaceable piston. This results in a very compact construction.

Preferably at least a longitudinal groove is provided in the displaceable piston. This advantageously ensures that the connection to the pump working chamber can be controlled irrespective of the axial position of the displaceable piston.

Preferably a drainage line branches from the cylinder in the region of overlap of the longitudinal extension of the longitudinal groove. In this way, after the connection to the pump working chamber has been shut off, the reception chamber upstream of the displaceable piston can be relieved of pressure, hence preventing the displaceable piston from being brought into a disengaged position by quantities of leakage fuel when the connection to the pump working chamber is shut off.

Upon switching on the drain again, which, as is common knowledge, occurs regularly during idling, this would lead to instantaneous, gross faulty adaptation as a result of the stored quantity of fuel which then has to be displaced.

Advantageously, a second longitudinal groove is provided in the displaceable piston and is permanently connected to the reception chamber, the second longitudinal groove being connected to the drainage line when the displaceable piston is in an angular position in which the reception line is closed. In this way, it is possible to keep the rotary travel of the displaceable piston very small, since the drainage line of the reception chamber upstream of the displaceable piston can be opened thereby immediately after the connection to the pump working chamber has been closed.

The invention will now be described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of a first embodiment with a fragmentary section through the top of a fuel injection pump; Figure 2 is a section taken at right angles through the control portion of the displaceable piston of Fig. 1; Figure 3 shows a second embodiment of the invention; and Figure 4 is a section through the control portion of the displaceable piston at right angles to the sectional plane shown in Fig. 3.

Fig. 1 is a diagrammatic section through a portion of a distributor-type injection pump. A pump piston 1 defines a pump working chamber 3 in a cylinder 2, and means (not illustrated) impart to the pump piston 1 a reciprocating, pumping and simultaneously rotating movement during which the pump piston acts as a distributor. Fuel is delivered by way of a distributor groove 4 in the outer surface of the pump piston from the pump working chamber into one of a pluraity of injection lines 5 which are equal in number to the number of the cylinders of the associated internal combustion engine to be supplied with fuel and are distributed around the cylinder 2 and lead to individual injection valves 6.In order to terminate the injection operation, the pump working chamber can be relieved by way of a spill passage 7 which extends in the pump piston 1 and branches from the pump working chamber 3, so that, from the instant at which the spill passage is opened by a spill port (not shown), the fuel displaced during a further stroke of the pump piston is no longer displaced into the injection line, but is displaced or relieved by way of the spill port.

Furthermore, a fuel reception line 9 leads from the pump working chamber 3 in the longitudinal direction of the pump piston. The reception line 9 leads into a cylinder 1 5 of a quiet-idle device 14 by way of a hollow screw 10 which is screwed into the top of the housing 12 of the fuel injection pump coaxially of the axis of the pump piston and which serves to secure the quiet-idle device to the housing 1 2 of the injection pump. A displaceable piston 1 6 is sealingly guided in the cylinder 1 5 and its end face defines a fuel reception chamber 1 7 in the cylider.A portion of the reception line 9 extends through the displaceable piston whose outer surface incorporates a longitudinal groove 1 9 which acts as a control port and which is connected by way of a throttle 20 to an axial blind bore 21 which in turn commences from that end face of the displaceable piston which defines the reception chamber 1 7. When the displaceable piston 1 6 is in a predetermined angular position, the longitudinal groove 19, -irrespective of the stroke position of the damping piston, is connected to the point at which the reception line 9 opens into the cylinder 1 5.

In addition to acting as a movable wall of a fuel accumulator, the displaceable piston 1 6 equipped with the longitudinal groove 1 9 also acts as a rotary valve. That end face of the displaceable piston 1 6 which is remote from the reception chamber 1 7 extends into a spring chamber 23 where it has a shaped part 24 which engages a complementary recess in a spring abutment plate 25. A return spring 26 abuts against the spring abutment plate 25 and its other end abuts against the oppositely located end face of the spring chamber 23.A stem 29 extends coaxially of the axis of the displaceable piston and of the spring chamber 23 and through a cover 27 which closes the spring chamber 23, the stem 29 being guided in a guide bore 28 in the cover 27 and being povided with a pin 30 which engages a complementary opening 31 in the spring abutment plate 25. The pin 30 is mounted in the end face 32 of a flange 33 of the stem 29, the stem 29 being axially fixed by the collar and a portion of the cover 27.

Furthermore, the stem 29 has a blind bore 34 which commences from the end face 32 of the stem and permits the shaped part 24 to enter the blind bore until the spring abutment plate 25 abuts against the end face 32. The pin 30 is sufficiently long to enable it to be positively connected to the spring-abutment plate 25 when the latter is in any position, such that the displaceable piston can be rotated by means of a lever 39 which is connected to the stem 29 outside the housing of the quiet-idle device 14. The other extreme position of the spring abutment plate 25 is determined by the bottom of the spring chamber 23, or by a portion, extending into the spring chamber 23, of a sleeve 35 which is.

provided for guiding the displaceable piston 1 6 and which incorporates the cylinder 1 5.

The sleeve 35 can also be adjustable for the purpose of adjusting or limiting the stroke of the displaceable piston 16, and has corresponding openings for connecting the reception line 9 to the groove 1 9.

A drainage line 36 leads from the spring chamber, and a drainage line 37 also leads out of the cylinder 1 5 and, when the displa ceable piston is in a second angular position, the mouth of the drainage line 37 is connecti ble to the reception chamber 1 7 by way of a recess in the form of a second longidutinal groove 38 connected to the axial blind bore 21. When the displaceable piston 1 6 is in this second angular position, the other recess in the piston 16, that is to say, the longitudinal groove 19, is no longer in register with the mouth of the reception line 9. This correlation is shown.in Fig. 2.

The quiet-idle device operates in the follow ing manner: When the quiet-idle device is switched on to produce softer combustion during, for example, idling of the internal combustion engine, a portion of the quantity of fuel delivered by the pump piston 1 is fed to the cylinder 1 5 by way of the reception line 9 during the delivery stroke of the pump piston. When in the switched-on state, the displaceable piston 1 6 is in an angular position in which the longitudinal groove 1 9 is in register with the mouth of the reception line 9, so that fuel can flow from the pump working chamber 3 into the reception chamber 1 7 by way of the throttle 20 and the blind bore 21.The pressure building up in the reception chamber results in an axial movement of the displaceable piston 16, whereby the piston 1 6 stores or accumulates the fuel extracted. The quantity of fuel accumulated is determined by the throttle, chiefly together with the absolute duration of the delivery stroke, determined by the stroke H of the displaceable piston 1 6.

The quiet-idle device can be switched off in a simple manner by turning the lever 39, and the reception chamber 1 7 can at the same time be connected to the drainage line 37.

Hence, leakage fuel cannot accumulate in the reception chamber 1 7 when the quiet-idle device is switched off, and cannot bring the displaceable piston 1 6 into an undesired position.

There are other possibilities of constructing the turning device for the displaceable piston illustrated in Fig. 1..Fig. 3 shows a modified embodiment in which the length of the reception line 9 has been considerably reduced, so that the dead space between the pump working chamber and the reception chamber 1 7 can be kept as small as possible. In the present instance, the quiet-idle device 14' comprises a closure member 40 which is screwed into the top of the housing 1 2 of the fuel injection pump coaxially of the axis of the pump piston and which sealingly closes the end face of the pump working chamber 3. A sleeve 41 is sealingly inserted into the closure member and incorporates the cylinder 1 5 in which the displaceable piston 16' is guided.

The end face 42 of the displaceable piston defines the reception chamber 17' in the cylinder 1 5. The sleeve 41 is fixed in position by a cup-shaped insert 43 which is screwed in coaxially of the axis of the displaceable piston 16', the interior of the insert 43 contains the spring chamber 23, and the stem 29' extends through the base of the insert 43 into the spring chamber 23. The stem 29' is provided externally with an adjusting lever 39' by means of which the stem 29 can be turned.

That end face of the stem which is located opposite the displaceable piston 16' has a transverse rib 44 which engages a complementary groove 45 in the end face of a head 46 of the displaceable piston 16' which extends into the spring chamber 23, and permits the axial travel of the displaceable piston 16' but remains permanently angularly connected thereto in a positive manner. The stem 29' is embraced by the return spring 26 which is supported between the inside of the base of the insert 43 and the end face of the head 46.

A fuel reception line 9' leads from the pump working chambr 3 to the sleeve 41 at a point at which the wall of the latter incorporates a throttle 47 which establishes a radial connection to the cylinder 15'. The displaceable piston 16' has a longitudinal groove 48 which commences from its end face 42 and which comes into register with the throttle 47 upon appropriate angular displacement effected by way of the stem 29'. When in this position, the quiet-idle device is "on" and operates in the manner descried with reference to the embodiment of Figs. 1 and 2. The stem 29' is turned in order to shut off the quiet-idling device, so that the longitudinal groove 48 comes into register with a radial bore 49 in the wall of the sleeve 41, and the throttle 47 is closed.

The drainage line 37' is permanently connected to the radial bore 49 and is also connected to the spring chamber 23 by way of a drainage line 36. When in this angular position, and as already described with reference to Fig. 1, the reception chamber 17' is relieved of pressure in order that the function of the quiet-idle device is not impaired by accumulating leakage fuel at the instant of switching-on. The co-axial arrangement has the considerable advantage that the fuel reception line 9' can be very short.

Claims

1. A fuel injection pump for an internal combustion engine, having a pump piston which reciprocates in a pump cylinder and which defines a pump working chamber, the latter being connectible to a fuel injection line during at least a portion of the delivery stroke of the pump piston and also connectible by way of a throttle and a fuel reception line to a fuel reception chamber upstream of a springloaded displaceable piston which is guided in a cylinder and which is in the form of a rotary valve in the said fuel reception line; for which purpose the outer surface of the displaceable piston incorporates a control port which is permanently connected to the reception chamber and which can be brought into register with the mouth of the reception line leading from the pump working chamber to the cylinder, the displaceable piston being provided with a turning device which enables the displaceable piston, acting as the rotary valve to be turned but permits axial displacement of the displaceable piston.

2. A fuel injection pump as claimed in claim 1, in which the end face of the displaceable piston remote from the reception chamber has a guide portion which is positively connected in a rotary sleeve to a correspondingly adapted part of the turning device which adjoins the displaceable piston axially.

3. A fuel injection pump as claimed in claim 1 or 2, in which the turning device has a rotatable stem which is disposed coaxially of the displaceable piston and which is surrounded by the return spring which loads the displaceable piston.

4. A fuel injection pump as claimed in claim 2, in which said guide portion is of prismatic shape.

5. A fuel injection pump as claimed in any of claims 1 to 4, in which the control port comprises at least a longitudinal groove provided in the displaceable piston.

6. A fuel injection pump as claimed in claim 5, in which a drainage line branches from the cylinder in the region of the longitudinal extent of the longitudinal groove.

7. A fuel injection pump as claimed in claim 6, in which a second longitudinal groove is provided in the displaceable piston and is permanently connected to the reception chamber, the second longitudinal groove being connected to the drainage line when the displaceable piston is in an angular position in which the reception line is closed.

8. A fuel injection pump as claimed in any of claims 1 to 7, in which the displaceable piston is axially parallel to the axis of the pump piston.

9. A fuel injection pump as claimed in any of claims 1 to 7, in which the displaceable piston is axially aligned with the pump piston.

10. A fuel injection pump as claimed in claim 9, in which the housing accommodating the displaceable piston and the turning device for the piston, comprises a closure portion of the pump working chamber which is fitted into the housing of the fuel injection pump.

11. A fuel injection pump as claimed in any of claims 1 to 10, which is a distributortype injection pump of the lifting-piston type of construction.

12. A fuel injection pump for an internal combustion engine, constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.