GB1598295A

GB1598295A - Fuel injection systems for internal combustion engines

Info

Publication number: GB1598295A
Application number: GB1687378A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-12-13
Filing date: 1978-04-28
Publication date: 1981-09-16
Also published as: DE2755400A1

Description

(54) IMPROVEMENTS IN OR RELATING TO FUEL INJECTION SYSTEMS FOR INTERNAL COMBUSTION ENGINES (71) We, ROBERT BOSCH GMBH, a Germany company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to fuel injection systems for internal combustion engines. The present invention is particularly applicable to fuel injection systems for stratified charge internal combustion engines.

One known form of fuel injection system comprises a fuel pump and a pressure regulating valve for creating a substantially constant system pressure, and at least one electromagnetic injection valve which has a valve closure member cooperating with a valve seat and injection ports at which a substantial part of the system pressure is dropped. The valve closure member of the valve is influenced by the armature of the electromagnet and by a closure spring by way of a push rod which is closely guided in a valve housing bore and on one end of which the system pressure exerts a force which at least approximately compensates for the resulting force exerted by the system pressure on the valve closure member. In this case one end of the push rod of the injection valve, both when the valve is closed as well as when the valve is opened, is subjected to the system pressure of the fuel.

This has the disadvantage that when the valve is closed complete pressure equalisation can in fact be achieved, but that no account is taken of the alterations in force on the valve closure member which occur when the valve is opened, and additional steps have to be taken to obtain pressure equalisation when the valve is open. For this purpose, the fuel is fed throttled through the valve closure member in such a manner that the pressure difference created thereby upstream and downstream of the valve closure member exerts on the push rod coupled to the valve closure member a force which compensates for the force exerted on the one end of the push rod by the system pressure.In the case of another known embodiment, the pressure equalisation when the valve is open is achieved by a special construction of the valve closure member which in addition to its surface which engages the valve seat is provided with a pin which engages tightly in a valve seat bore. Fuel passes through the inside of this pin which carries the injection ports at its free end. The deliberate throttling of the fuel at the valve closure member necessitates a correspondingly higher system pressure for a predetermined stream quality and the special construction of the valve closure member having a pin which fits into the valve seat bore and has the injection ports involves an increased manufacturing cost as compared to conventional designs in which the valve closure member is simply supported on the valve seat and the further path of the fuel leads through passages in a valve housing.

According to the present invention, a fuel injection system for an internal combustion engine comprises a pump and a pressure regulating valve for supplying fuel under a substantially constant system pressure, and at least one electromagnetic injection valve which has at least one injection port, a valve seat, a valve closure member disposed in a dead space between the injection port or ports and the valve seat and cooperating with the latter so that the closure member opens in the direction of fuel flow through the valve seat, a closure spring acting on the valve closure member though a push rod which is closely guided in a bore in the valve housing, and an electromagnet having an armature which acts on the push rod in the opening direction against the force of the closure spring, the system pressure in operation exerting on one end of the push rod in a direction to close the valve a force which at least approximately compensates for the resulting force exerted by the system pressure on the valve closure member, the system pressure, when the valve is open, being dropped substantially across the injection port or ports so that substantially system pressure prevails in the dead space and acts on the other end of the push rod, which has an effective cross-section substantially equal to the cross-section of the valve seat.

A fuel injection system embodying the present invention can have the advantage that both when the valve is closed and when the valve is open complete or almost complete pressure equalisation can be achieved without additional steps which would make production more expensive or reduce the stream quality. A further advantage is that a leakage conduit, which is necessary in some prior art systems can be dispensed with and the system for this reason can also be produced more simply and cheaply than some prior art systems.

The volume of the dead space can be kept small if preferably the other end of the push rod projects directly into the dead space.

A further advantage is that the fuel supply as in the case of conventional valves can take place through a central bore in the electromagnet which accommodates the armature so that the valves to this extent do not require alteration.

The valve closure member of the injection valve can be simply a ball or a spherical segment which is pressed against the valve seat by the push rod.

The dead space can be kept particularly small if the end of the rod facing the valve closure member is provided with a head whose diameter is at least as great as the diameter of the valve closure member. The dead space can in this manner be kept so small that the injection valve under certain circumstances is also suitable for direct injection into a combustion chamber.

The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a flow diagram of a fuel injection system according to one embodiment of the invention showing an injection valve in section. and Figure 2 is a detail section of part of a modified form of Figure 1.

Referring first to Figure 1, a fuel injection system embodying the present invention has a plurality of electromagnetic fuel injection valves of which each one has a valve housing 10. The housing 10 is secured to an iron flange 12 with a washer 11 in between, and the flange has an annular shoulder 13 onto which is welded a sleeve 14 of a nonmagnetic material. A magnetic coil 16 is seated on the shoulder 13 and the sleeve 14 and is enclosed by a bell-shaped iron casing 17. A soft iron core 18 projects into the sleeve 14 and has a central bore 19 forming a fuel feed line 20. The iron casing 17 provides a flux return path between the flange 12 and the soft iron core 18.

An armature 22 is substantially coaxial with the soft iron core 18 and is guided with clearance in bore 28 of the flange 12 and in the sleeve 14. A push rod 23 is firmly connected at one end to the armature 22 and is closely guided in a bore 24 of a bush 25 which is screwed into the valve housing 10.

The other end of the push rod 23 projects through the bush 25 into a dead space 26 which is connected by way of a passage 27 to the bore 28 of the flange 12 and thence through passages 29, 30 and 31 in the armature 22 to the bore 19 forming the fuel feed line 20. At the opening of the passage 27 into the dead space 26 there is formed a valve seat 32 for which a ball 33 serves as a valve closure member, The section of the passage 27 directly upstream of the valve seat 32 is formed by a stepped bore 34 which is sealed from outside by a plug 35. A plurality of injection ports 36 through which ports fuel is injected into the inlet manifold of an internal combustion engine. particularly a stratified charge engine, lead obliquely outwards from the dead space 26.The geometrical dimensions of the parts are selected so that the total pressure drop occurs substantially at the injection ports 36, which have the required direction and spacing.

The region of the push rod 23 which is closely guided in the bush 25 has a diameter D1 which is substantially equal to the diameter D2 of the valve seat 32. The other end of the push rod 23 which projects into the dead space 26 has a head 38 whose diameter is somewhat larger than the diameter of the ball 33. The head 38 is connected by a reduced diameter section 40 to the remainder of the push rod 23. The bush 25 forms a narrow end face 41 which serves as a stroke limitation for the push rod 23. A valve closure spring 42 abuts an end of a sleeve 43 inserted in the fuel feed line 20 and acts on the armature 22 to press the ball 33 against the valve seat 32 by way of the armature 22 and the push rod 23.

The injection valves are fed by a pump 50 which by means of a pressure regulating valve 51 produces and maintains a substantially constant system pressure in a line network 52 which supplies all the valves.

The quantity and timing of fuel injection are determined by electrical operation of the valve.

When the valve is closed, the system pressure prevailing in the network 52 acts on the ball 33 over the cross-section of the valve seat 32. At the same time the system pressure also exerts on the push rod 23 a force, which due to the substantially equal diameters Dl and D2, substantially compensates for the force exerted on the ball 33.

The pressure in the dead space 26 likewise acts in a substantially compensating manner (due to the substantially equal diameter D1 and D2) on the push rod 23 and on the ball 33 so that in order to open the valve the electromagnet has actually substantially only to overcome the force of the closure spring 42.

When the electromagnet 16 is energised, the armature 22 draws the push rod 23 upwards away from the ball 33 so that the ball 33 is lifted away from the valve seat 32 by the action of the system pressure of the fuel and fuel is delivered through the injection ports 36. At the end of the opening stroke, the head 38 of the push rod 23 abuts the end face 41 of the bush 25. When the valve is open, pressure equalisation obtains on the ball 33 and approximately also on the push rod 23 because, as a result of design, the pressure of fuel flowing through the valve seat 32 is not substantially reduced before the fuel reaches the injection ports 36, so that fuel in the dead space 26 is under a pressure which corresponds to the pressure in the bore 19, which forms the fuel feed line 20, and in the bore 28 of the flange 12.

The valve is thus effectively pressureequalised when it is open so that the injection timings preset by the electrical operation of the valve can be maintained with considerable accuracy.

Figure 2 is a detail view showing a modification of part of the injection valve of Figure 1 whereby the dead space 26 can be kept particularly small. The valve closure member 33' is constructed as a segment of a sphere and the push rod 23 is provided with an appropriately thickened head 38', special steps to prevent tilting of the member 33' not being necessary because the push rod 23 only required a relatively short stroke.

The number of the injection ports 36, their direction, lengths and diameters can be adapted to the requirements of the engine or the injection method desired.

WHAT WE CLAIM IS: 1. A fuel injection system for an internal combustion engine, comprising a pump and a pressure regulating valve for supplying fuel under a substantially constant system pressure, and at least one electromagnetic injection valve which has at least one injection port, a valve seat, a valve closure member disposed in a dead space between the injection port and ports and the valve seat and co-operating with the latter so that the closure member opens in the direction of fuel flow through the valve seat, a closure spring acting on the valve closure member through a push rod which is closely guided in a bore in the valve housing, and an electromagnet having an armature which acts on the push rod in the opening direction against the force of the closure spring, the system pressure in operation exerting in one end of the push rod in a direction to close the valve a force which at least approximately compensates for the resulting force exerted by the system pressure on the valve closure member, the system pressure, when the valve is open, being dropped substantially across-the injection port or ports so that substantially the system pressure prevails in the dead space and acts on the other end of the push rod, which has an effective cross-section substantially equal to the cross-section of the valve seat.

2. A system as claimed in claim 1, in which the fuel supply to the valve seat of the injection valve takes place centrally from the electromagnet side of the injection valve through a passage which runs substantially parallel to and spaced from the push rod and passes by the dead space.

3. A system as claimed in claim 1 or 2, in which said other end of the push rod projects directly into the dead space.

4. A system as claimed in claim 3, in which the valve closure member of the injection valve is a ball which is urged against the valve seat by said other end of the push rod.

5. A system as claimed in claim 3, in which the valve closure member of the injection valve is a segment of a sphere which is urged against the valve seat by said other end of the push rod and has a flat surface facing such push rod end.

6. A system as claimed in claim 4 or 5, in which said other end of the push rod which faces the valve closure member has a head whose diameter is at least as large as the diameter of the valve closure member.

7. A system as claimed in claim 6, in which the head of the push rod is connected by a reduced diameter portion to a main part of the push rod which has a diameter corresponding substantially to the diameter of the valve seat.

8. A fuel injection system for an internal combustion engine, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figure 1 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pressure prevailing in the network 52 acts on the ball 33 over the cross-section of the valve seat 32. At the same time the system pressure also exerts on the push rod 23 a force, which due to the substantially equal diameters Dl and D2, substantially compensates for the force exerted on the ball 33. The pressure in the dead space 26 likewise acts in a substantially compensating manner (due to the substantially equal diameter D1 and D2) on the push rod 23 and on the ball 33 so that in order to open the valve the electromagnet has actually substantially only to overcome the force of the closure spring 42. When the electromagnet 16 is energised, the armature 22 draws the push rod 23 upwards away from the ball 33 so that the ball 33 is lifted away from the valve seat 32 by the action of the system pressure of the fuel and fuel is delivered through the injection ports 36. At the end of the opening stroke, the head 38 of the push rod 23 abuts the end face 41 of the bush 25. When the valve is open, pressure equalisation obtains on the ball 33 and approximately also on the push rod 23 because, as a result of design, the pressure of fuel flowing through the valve seat 32 is not substantially reduced before the fuel reaches the injection ports 36, so that fuel in the dead space 26 is under a pressure which corresponds to the pressure in the bore 19, which forms the fuel feed line 20, and in the bore 28 of the flange 12. The valve is thus effectively pressureequalised when it is open so that the injection timings preset by the electrical operation of the valve can be maintained with considerable accuracy. Figure 2 is a detail view showing a modification of part of the injection valve of Figure 1 whereby the dead space 26 can be kept particularly small. The valve closure member 33' is constructed as a segment of a sphere and the push rod 23 is provided with an appropriately thickened head 38', special steps to prevent tilting of the member 33' not being necessary because the push rod 23 only required a relatively short stroke. The number of the injection ports 36, their direction, lengths and diameters can be adapted to the requirements of the engine or the injection method desired. WHAT WE CLAIM IS:

1. A fuel injection system for an internal combustion engine, comprising a pump and a pressure regulating valve for supplying fuel under a substantially constant system pressure, and at least one electromagnetic injection valve which has at least one injection port, a valve seat, a valve closure member disposed in a dead space between the injection port and ports and the valve seat and co-operating with the latter so that the closure member opens in the direction of fuel flow through the valve seat, a closure spring acting on the valve closure member through a push rod which is closely guided in a bore in the valve housing, and an electromagnet having an armature which acts on the push rod in the opening direction against the force of the closure spring, the system pressure in operation exerting in one end of the push rod in a direction to close the valve a force which at least approximately compensates for the resulting force exerted by the system pressure on the valve closure member, the system pressure, when the valve is open, being dropped substantially across-the injection port or ports so that substantially the system pressure prevails in the dead space and acts on the other end of the push rod, which has an effective cross-section substantially equal to the cross-section of the valve seat.

9. A fuel injection system as claimed in

claim 8, including the modification constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illus trated in Figure 2 of the accompanying drawings.