GB2057589A

GB2057589A - A Distributor Type Fuel Injection Pump for an Internal Combustion Engine

Info

Publication number: GB2057589A
Application number: GB8028670A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-09-07
Filing date: 1980-09-05
Publication date: 1981-04-01
Also published as: JPS5644449A; GB2057589B; DE2936205A1; JPH0156267B2

Abstract

A distributor type fuel injection pump for internal combustion engines in which the pressure lines (29) leading to the injection nozzles of the engine are relieved of dynamic pressure in a throttled manner. The fuel injection pump incorporates a central relief pressure valve (13) which is disposed downstream of the pump working chamber (12) and which controls delivery by the pump into a blind chamber (20) from which the quantity of fuel fed for injection is distributed to the respective pump outlet (26) by way of a connection passage (24) and by way of a distributor point (25) on the pump piston (8). A return-flow throttle valve (32), preferably formed by a throttle plate is fitted in the connection passage (24) in the region of the sealing surfaces (17, 18) between a cylindrical sleeve (11) and a valve body (14). <IMAGE>

Description

SPECIFICATION A Distributor Type Fuel Injection Pump for an Internal Combustion Engine The invention relates to a fuel injection pump for an internal combustion engine.

A known fuel injection pump comprises a pump piston which reciprocates and simultaneously rotates in a cylindrical sleeve and thereby serves as a distributor for a plurality of pump outlets. A working chamber of the pump is connected by way of an interposed central pressure relief valve to a blind chamber.

A fuel injection pump of this kind, also called a distributor type fuel injection pump, is already known from German printed patent specification (Offenlegungsschrift) No. 24 50 521 which is equipped with a central relief pressure valve, the fuel delivered by the pump piston being distributed from the blind chamber, disposed downstream, of the relief pressure valve to the individual pump outlets by way of a connection passage and a distributor point on the pump piston. In order to avoid after-injection operations, a portion of the fuel located in the line leading to the injection nozzle is drawn back by the backsuction of the relief pressure valve after the termination of delivery for the purpose of relieving the pressure line.At specific engine speeds and quantities of fuel injected, the constant backsuction of the relief pressure valve causes socalled "overrelief" of the line which leads to cavitation and erosion of the components of the pump.

In order to avoid this disadvantage, relief pressure valves for in-line injection pumps are known (U.S.A. Patent Specification No. 2, 729, 169) in which a second valve provided with a return-flow throttle is provided coaxially downstream or upstream thereof. These known valves cannot be used in distributor type injection pumps without causing difficulties and without substantiai lengthening of the installation space.

According to the present invention there is provided a distributor type fuel injection pump for an internal combustion engine, having a pump piston which reciprocates and simultaneously rotates in a cylindrical sleeve and thereby serves as a distributor for a plurality of pump outlets and whose working chamber is connected by way of an interposed central pressure relief valve to a blind chamber which at least partially accommodates the pressure valve and which is in turn alternately connectible to the individual pump outlets by way of a connection passage, and by way of a distributor point disposed on the pump piston, and having a valve body for the relief pressure valve, a first portion of the connection passage extending through the valve body and a second portion of the connection passage extending through the cylindrical sleeve, a return-flow throttle valve which opens in the delivery direction and which, when in its closed state, throttles the return flow occurring during pressure relief being fitted in the connection passage.

In contrast to the prior art the fuel injection pump in accordance with the invention has the advantage that a single return-flow throttle valve can be used for all the pump outlets and, after the relief operation by the distributor point on the pump piston, is shut off from the pressure line leading to the injection nozzle, whereby no high demands are made on the tightness of this valve.

Since the return-flow throttle valve is disposed in the connection passage common to all the pump outlets, all the pump outlets are uniformly relieved, that is to say, without variations in the operating characteristics, and there is no need to increase the overall length of the injection pump in order to fit this valve.

Advantageously additional machining of a seat for the return-flow throttle valve, is avoided when the planar sealing surface of the valve body assumes this function, and, by virtue of the widened portion which is incorporated in the portion of the connection passage extending within the cylindrical sleeve, and which accommodates the movable valve mamber, no additional installation space is required for the return-flow throttle valve.

Further by providing an intermediate plate, between the cylindrical sleeve and the valve body, which accommodates the return flow throttle valve, such a valve can also be fitted in distributor type injection pumps in which there is no space for accommodating the return-flow throttle valve in the cylindrical sleeve owing to the relatively large diameter of the pump piston, and the components of fuel injection pumps not equipped with return-flow throttle valves can be substantially retained without modification.

Conveniently the movable valve member of the return-flow throttle valve is a throttle plate which is very simple to manufacture and which is of very small construction and, in particular, has a small diameter.

Improved sealing, particularly at the sealing surface of the pressure valve body which incorporates the valve seat for the return-flow throttle valve is made possible by the provision of a cap screw which clamps the valve body to the cylindrical sleeve. Advantageous venting for the blind chamber of the injection pump is achieved by the provision of a venting screw in the cap screw, and, advantageously the venting screw which is used can also fulfil additional functions as an abutment for the pressure relief valve spring and as a filler piece for the pressure relief valve.

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 cross section through those parts of a distributor type injection pump which are essential to the invention, Figure 1 a shows a portion, drawn to a larger scale, of Figure 1 in the region of the return-flow throttle valve, and Figure 2 is a fragmentary cross section through the second embodiment in the region of the relief and return-flow throttle valve.

A drive shaft 2 is journalled in a housing 1 of a distributor type fuel injection pump for multi cylinder internal combustion engines and is connected to a face cam plate 3. The face cam plate 3 is provided with cams 4 (equal in number to the number of cylinders of the internal combustion engine to be supplied with fuel) which, during rotation of the drive shaft 2, transmit, by way of fixed rollers 5, thd lifting movement required for pump delivery to a pump piston 8 which is driven by a coupling member 6 and which is loaded by at least one spring (not illustrated).

The pump piston 8 is axially movably and rotatably guided within a cylinder bore 9 in a cylindrical sleeve 11 fitted in a distributor head 10 of the pump housing 1. The end face of the piston 8 defines a pump working chamber 12 located in the cylinder bore 9. The pump working chamber 12 is closed in the feed direction by a relief pressure valve 13 whose valve body 14 has a planar sealing surface 17 which is clamped by a cap screw 1 6 and a thrust ring 1 5 against an end face 18, also in the form of a sealing surface, of the cylindrical sleeve 11.The pump working chamber 12 is connectible to, and separable from, a blind chamber 20, which at least partially accommodates the pressure valve 13, by means of a movable valve member 19 which is provided with a return collar and which is guided concentrically in the valve body 14. The blind chamber 20 is sealed by the cap screw 16 and, in the present case, also serves as a spring chamber accommodating a valve spring 21 of the pressure valve 13. A first portion 22 of a connection passage 24 leads from the blind chamber 20 and extends through the valve body 14 substantially parallel to the valve member 19, and a second portion 23 of the connection passage 24 leads from the end face 1 8 of the cylindrical sleeve 11 to a distributor point 25 on the pump piston 8.

This distributor point 25 comprises an annular groove and a longitudinal groove in the pump piston 8 and, according to the angle of rotation of the pump piston 8, connects the portion 24 of the connection passage to a feed passage 27 leading to one of the pump outlets 26.

Only one of the, for example, four outlets 26 of the illustrated distributor type injection pump is shown in Figure 1 and comprises a pressure line 29 which is provided with a conical connection nipple 28 and which leads to the injection nozzle (not illustrated) and is clamped in the distributor head 10 by a clamping nut 31.

A return-flow throttle valve 32 is fitted in the connection passage 24 in the region of the two sealing surfaces 1 7 and 18 which are clamped to one another. As will be seen more clearly in Figure 1 a drawn to a larger scale, the return-flow throttle valve 32 operating without a valve spring has a throttle plate 33 which serves as a movable valve member and which incorporates a concentric throttle bore 34, an annular flat seat 35 and, in its end face remote from the flat seat 35, a cylindrical counter-sunk portion 37 which is interrupted by at least one transverse groove 36.

The dynamic pressure remaining in the portion 23 of the connection passage after each injection operation presses the throttle plate 33 against the planar sealing surface 17 of the valve body 14, the planar sealing surface 1 7 thus serving as a valve seat at this location. Thus, additional machining of the seat for the return-flow throttle valve 32 is not required. A cylindrical widened portion 38 of the second portion 23 of the connection passage commences at the end face 1 8 of the cylindrical sleeve 11 and accommodates the throttle plate 33 with adequate clearance which does not obstruct the pump delivery, the stroke of the return-flow throttle valve 32 being determined by the depth of the widened portion 38.The described construction of the throttle plate 33 has the advantage that it is possible to substantially reduce the diameters of the valve plate 33 and the widened portion 38, so that the return-flow throttle valve 32 in accordance with the invention can also be used in confined installation conditions.

In order to regulate the quantity of fuel fed to the pump working chamber 12 from a suction chamber 41 by way of a line 42 and delivered to the individual pump outlets 26 by the pump piston 8, a control port 43 which is incorporated in the pump piston 8, and which is connected to the pump working chamber 12, is opened at an earlier or later instant by the axial position of an annular spool 45 determined by a governor lever 44 for the purpose of relieving the pump working chamber 12.

In order to ensure an adequate contact pressure between the planar sealing surface 1 7 of the valve body 14 and end face 18 of the cylindrical sleeve 11 for the purpose of sealing the pump working chamber 12 and to ensure the function of the return-flow throttle valve 32, that end of the valve body 14 which is remote from the planar sealing surface 1 7 is provided with a neck-line extension 46 serving as a clamping sleeve. The elastic deformation undergone by the neck-line extension 46 compensates for the changes in length of the cap screw 1 6 and its connection to the distributor head 10 occurring upon extremely large pressure changes in the blind chamber 20, so that the required contact pressure between the sealing surfaces 1 7 and 1 8 is maintained. The clamping force exerted on the pressure valve body 14 by the cap screw 16 is transmitted by the thrust ring 1 5 which is interposed between the extension 46 and a base 48 of the cap screw 16 and which is provided with cup points 47 on both end faces. The thrust ring 1 5 is made from heat-treated steel and is deformed to only an extremely slight extent when tightening the cap screw 1 6 for the purpose of improving the sealing effect, and, if required, is changed when repairing the pump and after loosening the cap screw 1 6. Thus, only a small, inexpensive part has to be changed compared with the expensive cap-shaped clamping sleeve described below with reference to Figure 2.

The base 48 of the cap screw 1 6 is provided with a through bore 52 which is closed by a venting screw 51. The venting screw 51 has a pin-like projection 54 which extends into the blind chamber 20 and which forms a shoulder 53, wherein the projection 54 serves as a filler piece for the pressure valve 13, and the shoulder 53 serves as an abutment for the valve spring 21.

The second embodiment of Figure 2, only a portion of which is illustrated, differs from the first embodiment of Figure 1 chiefly by virtue of an intermediate plate 57 which is interposed between the cylindrical sleeve 11 and a valve body 14' and which is provided with two planar end faces 55 and 56, and by virtue of a cupshaped clamping sleeve 58 which is clamped against the valve body 14' by a closed cap screw 16'. The intermediate plate 57 is secured in position relative to the cylindrical sleeve 11 and the valve 14' by a pin 59 and incorporates a passage 61 connecting the pump working chamber 12 to the pressure valve 13', and a third portion 62 of the connection passage, designated 24' in the present instance, which connects the first portion 22 of the connection passage to the second portion 23 thereof. In the present instance, the return-flow throttle valve 32 is fitted in a cylindrical widened portion 63 of the third portion 62 of the connection passage, and, in the same manner as in the first embodiment, the planar sealing surface 1 7 of the valve body 14' which rests on the planar end surfaces 55 of the intermediate plate 57 serves as a valve seat for the return-flow throttle valve 32. The return-flow throttle valve 32 is of the same construction as that described with reference to Figure 1 or 1 a.

It will be appreciated that, if necessary, the return-flow throttle valve 32 can be provided with a valve spring 65 supported in an additional widened portion 64 of the portion 23 of the connection passage, as is shown by dash-dot lines in Figure 1 a.

Claims

1. A distributor type fuel injection pump for an internal combustion engine, having a pump piston which reciprocates and simultaneously rotates in a cylindrical sleeve and thereby serves as a distributor for a plurality of pump outlets and whose working chamber is connected by way of an interposed central pressure relief valve to a blind chamber which at least partially accommodates the pressure valve and which is in turn alternately connectible to the individual pump outlets by way of a connection passage, and by way of a distributor point disposed on the pump piston, and having a valve body,for the relief pressure valve, a first portion of the connection passage extending through the valve body and a second portion of the connection passage extending through the cylindrical sleeve, a return-flow throttle valve which opens in the delivery direction and which, when in its closed state, throttles the return flow occuring during pressure relief being fitted in the connection passage.

2. A fuel injection pump as claimed in claim 1 in which the valve body has a planar sealing surface which is clamped against an end face of the cylindrical sleeve also in the form of a sealing surface.

3. A fuel injection pump as claimed in claim 2, in which the planar sealing surface of the valve body in the region of the mouth of the first portion of the connection passage at the same time serves as a valve seat for a moveable valve member, provided with a flat seat and a throttle bore, of the return-flow throttle valve and a widened portion accommodating the valve member and commencing from the end face of the cylindrical sleeve is incorporated in the second portion of the connection passage.

4. A fuel injection pump as claimed in claim 1, in which there is interposed between the valve body and the cylindrical sleeve an intermediate plate which is provided with two end faces and which is secured in position relative to the cylindrical sleeve and the valve body, the intermediate plate incorporating a central passage between the pump working chamber and the pressure valve and a third portion of the connection passage, which third portion accommodates the return-fiow throttle valve which cooperates with a planar sealing surface of the valve body and the planar sealing surface in the region of the mouth of the first portion of the connection passage serves as a valve seat for a moveable valve member of the return flow throttle valve.

5. A fuel injection pump as claimed in claim 3 or 4, in which the moveable valve member is formed by a throttle plate.

6. A fuel injection pump as claimed in claim 5, in which a cylindrical countersunk portion having an outer rim which is interrupted by at least one transverse groove is incorporated within that end face of the throttle plate which is remote from the preferably annular flat seat of the throttle plate.

7. A fuel injection pump as claimed in any of claims 2 to 6, having a cap screw which contains the blind chamber and which at least partially embraces the valve body and clamps the latter against the cylindrical sleeve by means of a clamping sleeve, in which that end of the valve body which is remote from the planar sealing surface serving as a valve seat has a neck-like extension which at least partially surrounds a valve spring and which serves as a clamping sleeve and abuts against the base of the cap screw surrounding the blind chamber.

8. A fuel injection pump as claimed in claim 7, in which the base of the cap screw is provided with a through bore which is closed by a venting screw.

9. A fuel injection pump as claimed in claim 8, in which the venting screw has an abutment for the valve spring.

10. A fuel injection pump as claimed in claim 9, in which the venting screw has a pin-like projection which serves as a filler piece for the pressure valve and which forms a shoulder for the abutment.

11. A fuel injection pump as claimed in any of claims 7 to 10 in which a thrust ring having cup points on both end faces is disposed between the base of the cap screw and the extension of the valve body.

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