GB2185540A

GB2185540A - Distributor-type fuel injection pump for internal combustion engines

Info

Publication number: GB2185540A
Application number: GB08700934A
Authority: GB
Inventors: Franz Eheim
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1986-01-17
Filing date: 1987-01-16
Publication date: 1987-07-22
Also published as: FR2593240B1; JPS62117263U; FR2593240A1; GB8700934D0; GB2185540B; DE8601064U1

Abstract

In a distributor-type fuel injection pump for an internal combustion engine, comprising a piston (12) for generating delivery pressure in a working chamber (13), a delivery chamber (24) connected by way of a distributor (16, 17, 18) to a respective injection nozzle, and a pressure valve (41) which is disposed between the chambers (13, 24), and which opens once a predetermined delivery pressure has been reached; a pressure-equalising valve (34) is integrated into the pressure valve (41) for the purposes of preventing after-injection, cavitation and erosion of the pump components. To do this, the valve element (26) of the pressure valve (41) is provided with a longitudinal passage (31) connected at one end to the delivery chamber (24) by a throttle bore (38), and having its other end closable by the non-return element (33) of the equalizing valve. <IMAGE>

Description

SPECIFICATION Distributor-type fuel injection pump for internal combustion engines The invention relates to distributor-type fuel injection pumps for internal combustion engines, and more particularlyto a fuel injection pump ofthetype having a pressure valve between the pump working chamber and a delivery chamber connected by a delivery passage to an annular groove in the periphery ofthe rotatable and axially displaceable piston of the pump, the piston having an axial distributor groove which leads from the annular groove and which communicates in turn with each of a number of radial distributor bores in the cylinder bush in which the piston is received.

In the case of such distributor-type fuel injection pumps, it is necessary, in order to avoid so-called after-injection on closing of the injection nozzle, to relieve the pressure lines leading from the distributor bores to the injection nozzles.

To do this, the valve element of the pressure valve in a known distributor-type fuel injection pump (German Offenlegungsschrift No. 29 36 205) carries are lief or back-suction collar by means of which the pressure valve is opened by the pressure waves occurring when the injection nozzle is closed and a partofthefuel in the pressure line is "sucked back".

In order to prevent the occurrence of so-called "overrelief" atparticularspeedsandfuel injectionquantitles, which is determined by the constant back- suction volume and which is in turn the cause of cavitation and erosion in the pump components, a return-flowthrottle valve is disposed in the delivery passage between the delivery chamber and the annular groove. The return-flow throttle valve opens in the direction of delivery and, when closed, throttles the return fuel flow occurring on pressure relief in the delivery passage in the opposite direction. The return-flowthrottle valve is inserted in the pump housing and is covered bythevalve body of the pressure valve.

The present invention resides in a distributor-type fuel injection pump for an internal combustion engine, comprising a pump housing, a cylinder bush disposed in the housing, a simultaneously reciprocable and rotatable pump piston in the cylinder bush, the piston, together with the cylinder bush defining a pump working chamber, the piston having in its per ipheryan annular groove and an axial distributor groove opening into said annular groove and the cylinder bush having radial distributor bores distributed about the periphery ofthe pump piston such that the distributor groove co-operates successively with the distributor bores, a delivery chamber connected to the annular groove bywayofa delivery passage in the cylinder bush, a pressure valve between the pump working chamber and the delivery chamber, the pressure valve having a valve element which is urged against a valve seat surrounding a valve opening leading from the pump working chamber by a valve closure spring supported in the delivery chamber, and a retu rn-flow throttle from the delivery chamber the pump working chamber, the retu rn-flow th rottle being integrated in the valve element of the pressure valve in that the valve element has a longitudinal passage which is connected buy a throttle boreto the delivery chamber and which opens atthe end face ofthevalve elementfacing the pump working chamber and in thatthe longitudinal passage is closable by a closure element of anon- return valve, such element being urged by a spring againstavalveseatsurroundingthe longitudinal passage, whereby the pressure in the delivery passage is relieved upon relief of pressure in the working chamber.

This has the advantage that it provides a central valve combination comprising a pressure valve, non-return valve and return-flowthrottlewhich is inexpensive to manufacture and easy to assemble, and which maintains the above-described functions for pressure relief and prevention of cavitation and erosion. The valve element of the pressure valve can be simply and cost-effectively manufactured without a relief or back-suction collar. The pressure maintained by the non-return valve, also called a pressure-equalizing valve, can easily be adjusted byway ofthe initial stress of the spring and independently of the opening pressure of the pressure valve. Only one single valve combination is necessary for all the pressure lines, connected by way of the delivery bores, to the injection nozzles.

The invention is further described, byway of example, with referenceto the accompanying drawing, which is a fragmentary longitudinal section through a distributor-type fuel injection pump in accordance with the invention.

A cylinder bush 11 is held in a pump housing 10of a distributor-type injection pump. A pump piston 12 is axially and rotata bly guided by the cylinder bush 11 and is driven in a known way with a rotating and reciprocating motion by a cam drive coupled to a drive shaft. Together with the cylinder bush 11, the pump piston 12 defines a pumpworking chamber 13 which is connected by way of a supply passage 14to a fuel-filled suction chamber (not shown) of the dis- tributor-type injection pump.The end region of the pump piston 12 is provided with longitudinal grooves 1 5which open in the end face ofthe pump piston 12 and by way ofwhichaconnection can be made during each suction stroke ofthe pump piston 12 between the supply passage 14 and the pump working chamber 13. At a distance from its end face defining the pump working chamber 13, the pump piston 12 has in its periphery an annular groove 16 and an axial distributor groovel7opening intothe annular groove 16. Radial distributor bores 18 in the cylinder bush 11 are uniformly distributed aboutthe periphery of the pump piston 12 and are each connected by way of a respective distributor passage 19 to a connecting nipple (notshown)forconnecting a pressure line leading to a corresponding fuel injection nozzle. The distributor groove 17 co-operates with these distributor bores 18 in such a waythat, during rotation ofthe pump piston 12, the distributor groove l7connectstheannulargroovel6toeach one of the distributor bores 18 in succession.

The pump working chamber 13 is connected to a central bore 21 in a valve body 20 which is seated on the end face ofthecylinder bush 11. The valve body 20 is secured to the end face ofthe cylinder bush 11 by means of a housing cap 22 which engages over thevalve body 20 like a hat and is screwed into an internalthread 23 ofthe pump housing 10. The housing cap 22 has a blind-ended delivery chamber 24 whose longitudinal axis is in alignment with the axes of the central bore 21 andthepumpworking chamber 13. The delivery chamber 24 is connected byway of a lateral delivery passage 25tothe annular groove 16 ofthe pump piston 12, one section ofthe delivery passage being in the valve body 20 and an othersection being in the cylinder bush 11.

An axially displaceable valve member 26 of a pressurevalve 41 is disposed in the central bore 21 ofthe valve body 20, which separates the pump working chamber 13 in the cylinder bush 11 from the delivery chamber 24 in the housing cap 22. The valve member 26 has a conical closure body 27 which projects into the delivery chamber 24 and whose conical surface rests on a valve seat 28 surrounding the opening of the central bore 21 on the delivery-chamber side. The closure body 27 is pressed onto the valve seat 28 by a valve closure spring 29, which rests byway of a hatshaped spring abutmentwasher 30 on the base of the blind-ended delivery chamber 24.The valve seat 28, closure body 27 and valve closure spring 29 form the pressurevalve41. Upon a delivery pressure in the pump working chamber 13 being reached, which pressure is adjustable by means ofthevalveclosure spring 29, the pressure valve 41 opens and allows fuel to flowfrom the pump working chamber 13 by way of the delivery chamber 24 and the delivery passage 25 into the annular groove 16 of the pump piston 12. The fuel is then fed from the annular groove 16 byway of the distributor 9 roove 17 to one of the distributor bores 18.

The valve element 26 has a central longitudinal passage31 which opens in the end faceofthevalve element 26 facing the pump working chamber 13.

The opening is encircled buy a valve seat 32 onto which a conical closure element 33 of a non-return valve 24 is pressed by a compression spring 35, which in turn acts by way of a pressure body 36 on the closure element 33 and rests against an abut mentshoulder37 projecting radially into the central bore 21. The longitudinal passage 31 ,which is in the form of a blind bore in thevalve element 26, is con nected byway of a throttle bore 38 to the delivery chamber24.

In a first embodiment (right-hand half in valve body 20), the abutment shoulder 37 is formed by making the central bore 21 a stepped bore, in thatthe valve body 20 has, on the end face closing offthe pump working chamber 13, an integral annular flange 39 which projects into the central bore 21. In a second embodiment (left-hand half of valve body 20),thevalve body20 is made oftwo parts and its end face facing the pump working chamber carries a disc-shaped section 201. An annular disc40 is held between this disc-shaped section 201 andthe re- maining stepped cylindrical section 202 and projects into the central bore 21 to serve as an abutment shoulder 37 for the compression spring 35.

The distributor-type fuel injection pump described above operates as follows: The fuel injection quantity displaced by the pump piston 12 passes, following raising of the valve el ement 26 from the valve seat 28, by way of the delivery chamber 24 and the delivery passage 25 into the annular groove 16, and from there by way ofthe distributor groove 27 into the individual distributor bores 18 in succession, from where it passes byway of the pressure lines to the associated injection nozzles in turn. During this pressure stroke, the non- return valve 34, also called a pressure-equalizing valve, is closed.

Following termination of fuel delivery, the pres- sure line is relieved in the opposite direction. With the valve element 26 seated on the valve seat 28, the relief quantity flowing back passes through the throttle bore 38 and enters the longitudinal passage 31. The non-return valve 34, which is set to an opening passage of approximately 50 to 60 bar, is opened and the reliefquantityflows into the pump working chamber 13. Thus the line connection to the injection nozzle is relieved and after-injection is prevented.

Claims

1. Adistributor-typefuel injection pump for an internal combustion engine, comprising a pump housing, a cylinder bush disposed in the housing, a simultaneously reciprocable and rotatable pump piston in the cylinder bush, the piston, together with the cylinder bush defining a pump working chamber, the piston having in its periphery an annulargroove and an axial distributor groove opening into said annular groove and the cylinder bush having radial distributor bores distributed aboutthe periphery of the pump piston such that the distributor groove cooperates successively with the distributor bores, a delivery chamberconnected to the annular groove byway of a delivery passage in the cylinder bush, a pressure valve between the pump working chamber and the delivery chamber, the pressure valve having a valve element which is urged against a valve seat surrounding a valve opening leading from the pump working chamber by a valve closure spring supported in the delivery chamber, and a return-flow throttle from the delivery chambertothe pump working chamber, the return-flow throttle being in tegrated in the valve element ofthe pressure valve in that the valve element has a longitudinal passage which is connected by a throttle bore to the delivery chamber and which opens at the end face ofthe valve elementfacing the pump working chamber and in thatthe longitudinal passage is closable by a closure element of a non-return valve, such element being urged by a spring against a valve seatsurrounding the longitudinal passage, wherebythe pressure in the delivery passage is relieved upon re liefofpressureintheworkingchamber.

2. A distributor-type injection pump as claimed in claim 1, in which the valve element ofthe pressure valve is axially guided in a central bore of a valve body secured to the pump housing and has a conical closure body which projects into the delivery chamber and its conical surface co-operates with the valve seat which surrounds the central bore, and the delivery chamber informed by a pocket-like recess in a housing cap engaging in a hat-like manneroverthe valve body, and in which the valve closure spring of the pressure valve is a compression spring and is supported between said conical closure body and the base of the delivery chamber.

3. A distributor-type injection pump as claimed in claim 2, in which an abutment shoulder is provided in said central bore, and projects radially from the bore wall close to its opening on the pump working chamber side, and the compression spring, which acts at least indirectly on the closure element ofthe non-return valve is supported on this abutment shoulder.

4. A distributor-type injection pump as claimed in claim 3, in which the abutmentshoulder isformed by making the central bore a stepped bore.

5. A distributor-type injection pump as claimed in claim 3 in which the valve body is made oftwo pieces and comprises a cylinder-shaped section and a disc-shaped section, and an annular disc projecting into the central bore is held between the two body sections and formsthe abutment shoulder.

6. A distributor-type fuel injection pump constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.