GB2231097A

GB2231097A - Hand-operated pump for a feed pump of a fuel injection system for an internal combustion engine

Info

Publication number: GB2231097A
Application number: GB9000714A
Authority: GB
Inventors: Klaus Stieninger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1989-01-13
Filing date: 1990-01-12
Publication date: 1990-11-07
Anticipated expiration: 2010-01-12
Also published as: IT9019029A1; JPH02227554A; IT9019029A0; GB9000714D0; DE3900875A1; GB2231097B; IT1238144B

Description

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DESCRIPTION HAND-OPERATED PUMP FOR A FEED PUMP OF A FUEL INJECTION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE

This invention relates to a hand-operated pump for a feed pump of a fuel injection system for an internal combustion engine.

-In a known manually operated pump (EP-OS 02 19 635), the hand-operated pump serves to fill the injection system when it is put into operation or to refill it and ventilate it following an operation which resulted in a reduction in pressure which deviated from the operating behaviour, such as, for example, changing a filter insert. To do this, a piston is actuated in the hand-operated pump, and is guided with clearance of motion in a cylinder which partially surrounds it. Since the piston, which is made of a plastics material, swells up somewhat during operation with alternative fuels, piston clearance must be allowed for accordingly. By increasing the piston clearance, the radial prestress on the piston underneath the guide element, which is formed in one piece, may be reduced to such an extent that the seal may become inadequate under more difficult operating conditions, for example at low temperatures, in which the elasticity of the seal also deteriorates, and hence there is insufficient pressure build-up.

-2Sealing is additionally impaired if, as in practice, force is applied to the actuating element at an angle with respect to the axis of the piston, and hence the prestress of the piston seal is further reduced at one side.

In accordance with the present invention there is provided a handoperated pump for a feed pump of a fuel injection system for an internal combustion engine, having a cylinder which can be fastened to the housing of the feed pump, and having a piston which is longitudinally displaceable in the cylinder, which is provided with a piston seal in the form of a double-lip seal and a guide collar, wherein the piston forms a working chamber within the cylinder and starting from the position of rest of the piston, fuel or a fuellair mixture is forced during the working stroke of the piston from the working chamber into the system (pressure system) of the feed pump and, during the return stroke of the piston, fuel is sucked out of the system (intake system) of the feed pump into the working chamber, the pump also having a return spring for the piston, which spring is disposed between an actuating element fixed on the upper end of the piston remote from the working chamber and a shoulder of the cylinder, a shut-off member, which is disposed between the working chamber and the system of the feed pump 11 4,.

t 1 i L i i and which is indirectly pushed up by the piston during its inward stroke and, shortly before the end of its return stroke, closes-independently, and wherein the lower end of the piston facing the working chamber has an additional guide bushing which is disposed between the working chamber and the piston seal.

This has the advantage that the problem expounded with respect to the above-mentioned prior art can be solved in a reliable manner. Thus, according to the invention, the piston has an additional guide element, which defines a working chamber and is in the form of a guide bushing which is mounted on the lower end of the piston, hence increasing the guide length of the piston in such a way that the angular deflection of the piston remains small upon an inclined application of force to the actuating element. The piston seal is mounted remote from the working chamber beyond the guide bushing. As a result, it is both relieved in terms of pressure and, in the event of deflection of the piston up inclined application of force, it is located substantially at the fulcrum between a guide collar on the upper part of the piston and the additional guide bushing mounted on the lower end of the piston, where the influence of the deflection is at a minimum. Minimum possible deflection of the piston seal out of its centre position means minimum loss of prestress of the sealing lips of the piston seal, so that the piston remains sealed even in the event of a loss in prestress following extended stress caused by high temperatures and even a deterioration in elasticity at low temperatures of the pump.

As a result of the proposed improvements, the pump can still be operated without loss of function even under unfavourable operating conditions, even when installed in such a way as to be not easily accessible.

One embodiment of the invention is further described hereinafter, by way of example, with reference to the accompanying drawing which illustrates an axial sectional view through the hand-operated pump for a feed pump of a fuel injection system for an internal combustion engine.

A hand-operated pump, for a feed pump of a fuel injection system for an internal combustion engine, has a cylinder 1 with a base part in the form of a part-threaded piece 2 on one end face thereof, and a piston 3.

The part-threaded piece 2 has a bore 4 which enlarges to form a valve seat 5, and then becomes a second bore 6 which has a pressed-in spring support sleeve 7. A valve ball 8 is pressed by a valve spring 9, which abuts against the support sleeve 7, against the valve seat 5. The valve seat 5, together with the 1 1 I i i : 1 -5valve ball 8, forms a shut-off element. The cylinder 1 is sealed and secured to the part-threaded piece 2 by way of an 0-ring 10 and/or by a plurality of caulked locations 11 distributed about its periphery. The part-threaded piece 2 has a threaded spigot 12 which is screwed with the interposition of a sealing ring 13 into an internal thread 14 of a passage leading to the pressure chamber of a feed pump 15.

The piston 3 has a stepped, concentric longitudinal bore 16 with an annular inner shoulder 17 formed by the transition area between the smaller and larger diameter sections thereof. A valve tappet 18 in the form of a hollow cylinder has an outer collar 19 at one end.abutting against the inner shoulder 17 and, at its other end, it has a plurality of radialslots 20 and a central pin 21. One end face of the valve tappet 18 forms a stop 22, which co-operates with an end face 23 of the partthreaded piece 2 in a manner described below.

Underneath the outer collar 19, a guide bushing 25 abuts with a sleeveshaped neck part 24 against the valve tappet 18. The outer face 51 of the neck part 24 remote from the valve tappet 18 is defined by the part of the longitudinal bore 16 of the piston 3 which is smaller in diameter, and an inner bore 50 of the neck part 24 of the guide bushing 25 serves to hold -6and fix the valve tappet 18. A guide collar 26 of the guide bushing 25 lies displaceably against the inside 27 of the cylinder 1, whose basic form is that of a hollow cylinder. The guide bushing 25 is secured by ultrasonic welding to the lower end of the piston 3 (the smaller diameter end) in a front annular groove 52 which is disposed in the transition between the neck part 24 and the guide collar 26. The hollow chamber between the side of the guide bushing 25 facing the feed pump 15 and the end face 23 forms a substantial part of a working chamber 28, which is defined radially by the inside 27 of the cylinder 1. A piston seal 29, which is in the form of a double-lip seal, acts on the inside 27, and is disposed with respect to the working chamber 28 in the axial direction beyond the guide bushing 25 and is pressed onto the outside of the part of the piston 3 having the smaller diameter.

A cap-shaped actuating element 30, which is made of plastics material, comprises a base plate 31, from whose outer edge a sleeve 32 extends. A ridge 34 of a stop ring 35 engages in an inner groove 33 on the end face of the sleeve 32. The ridge 34 is secured by ultrasonic welding to the sleeve 32. A projection 36 is connected to the periphery of the cylinder 1, the stop ring 35 being supported on one shoulder thereof GC R 1 1 and a return spring 38, in the form of a compression spring, for the piston 3 being supported on its opposite shoulder 37. At the other end, the return spring 38 presses against an annular shoulder 39 of the actuating element 30.

The piston 3 is fastened by ultrasonic welding by its upper end in an annular groove 40 in the actuating element 30. The upper part of the piston 3, which has the larger diameter, has an offset guide collar 41 above the transition to the inner shoulder 17, which guide collar 41 is displaceable with clearance of motion against the inside 27 of the cylinder 1 in the event of deflection of the piston 3. A prestressed holding spring 42, in the form of a compression spring, is supported on a second annular shoulder 43 of the actuating element 30 and holds the outer collar 19 of the valve tappet 18 pressed against the inner shoulder 17 of the piston 3.

The above-described device operates as follows: as shown in Fig.1, the actuating element 30 and the parts which are frictionally coupled to it in the system, such as, for example, the piston and the valve tappet 18, are in the uppermost position of movement,. so that, on the one hand, the working chamber 28, which is filled with a fuel/air mixture has maximum volume and. on the other hand, the working chamber 28 1 is not yet connected to the pressure chamber of the feed pump 15. Pressure in the direction of the arrow 44 on the actuating element 30 causes the piston 3 to perform its inward stroke against the force of the return spring 38, wherein the pin 21 moves the valve ball 8 against the force of the valve spring 9 away from the valve seat 5 and hence medium is pressed out of the working chamber 28 into the pressure system of the feed pump 15. The continuing inward stroke of the valve tappet 18 is limited by the abutment of the stop 2 against the end face 23, so that the pressure force 44, in addition to the force of the return spring 38, acts against the force of the holding spring 42. Nevertheless, the shut- off element 8, 9, 5 remains open and the piston 3 can displace the volume of the working chamber 28 into the pressure chamber of the feed pump 15 by means of the seal of the working chamber 28 through the guide bushing 25, aided by the piston seal 29 following in the direction of movement of the piston 3, until the pressure force in the direction of the arrow 44 ceases or the movement of the actuating element 30 is effectively stopped by the projection 36 of the cylinder 1 as a result of closing up of the return spring 38.

k j 1 i 1 If the pressure force according to the arrow 44 is less than the return force of the holding spring 42 and the return spring 38, the return stroke of the piston 3 is effected in reverse order. Medium is sucked out of the intake system of the feed pump 15 into the working chamber 28 until the valve tappet 18, which is moving back, allows the valve ball 8 to reach the valve seat 5 and to interrupt the connection between the feed pump 15 and the working chamber 28. one operating cycle is thus completed. The injection system is filled and simultaneously ventilated by alternately sucking in medium from the intake system of the feed pump 15 and pressing medium into the pressure system of the feed pump 15.

The arrangement of the guide bushing 25, which is separate from the guide collar 41 of the piston 3, and the increased guide length of the piston 3 obtained as a result, enable the piston seal 29, which is then pressurerelieved, and disposed in the centre between the guide collar 41 and the guide bushing 25, to maintain the operation of the hand pump even under difficult operating conditions.

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Claims

-10CLAIMS

1. A hand-operated pump for a feed pump of a fuel injection system for an internal combustion engine, having a cylinder which can be fastened to the housing of the feed pump, and having a piston which is longitudinally displaceable in the cylinder, which is provided with a piston seal in the form of a double-lip seal and a guide collar, wherein the piston forms a working chamber within the cylinder and starting from the position of rest of the piston, fuel or a fuel/air mixture is forced during the working stroke of the piston from the working chamber into the system (pressure system) of the feed pump and, during the return stroke of the piston, fuel is sucked out of the system (intake system) of the feed pump into the working chamber, the pump also having a return spring for the piston, which spring is disposed between an actuating element fixed on the upper end of the piston remote from the working chamber and a shoulder of the cylinder, a shut-off member, which is disposed between the working chamber and the system of the feed pump and which is indirectly pushed up by the piston during its inward stroke and. shortly before the end of its return stroke, closes independently, and wherein the lower end of the piston facing the working chamber has an additional guide bushing which is disposed between the working chamber and the piston seal.

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2. A pump as claimed in claim 1, wherein the guide bushing, which is contiguous with the working chamber. comprises a guide collar and a sleeve-shaped neck part, whose inner bore serves to hold and fix the valve tappet and which is fitted into a longitudinal bore in the piston and secured therein by means of a cylindrical outer face on the neck part. ,

3. A pump as claimed in claim 2, wherein the lower end of the piston facing the working chamber is fixedly attached to the transition between the guide collar and the neck part remote from the working chamber.

4. A pump as claimed in claim 3, wherein the lower end of the piston facing the working chamber is in the form of a sleeve and is fitted into an annular end groove on the transition between the guide collar and the neck part of the guide bushing remote from the working chamber and is secured therein by means of ultrasonic welding.

5. A hand-operated pump constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.

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l,.ibll-hed 1990 asThe Patent Office, State House. 66.171 High Holborn. LondonWC1R4TP.Further copies maybe obtainedfrom The PatentOffice. GE1es Bi,anc,, St Mary Cray, Orpington. Kent BR5 3RJ). Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187