GB1560614A

GB1560614A - Fuel injection nozzle

Info

Publication number: GB1560614A
Application number: GB911878A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-03-09
Filing date: 1978-03-08
Publication date: 1980-02-06
Also published as: JPS612782B2; JPS53110720A; FR2383324A1; DE2710217A1; FR2383324B1

Description

(54) IMPROVED FUEL INJECTION NOZZLE (71) We, ROBERT BOSCH GMBH, a German 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 invention relates to fuel injection nozzles, for internal combustion engines, of the type having a displaceable needle, which allows the flow of fuel into a blind bore of the nozzle and through injection orifices to the combustion chambers of the engines.

In known fuel injection nozzles of this type, fuel is displaced from the blind bore, between the needle and its seat, to the pressure chamber when the valve needle closes, so that the residual quantity, remaining in the blind bore after the valve needle has come into abutment against the valve seat, forms a type of resilient cushion.

Although it is desirable to keep the residual volume of the blind bore as small as possible, it is, from the view-point of manufacturing technology, virtually impossible to produce a nozzle which does not have a blind bore. This is connected with the fact that sealing cones of the valve needle and the valve seat surface have to be precision machined and, for this purpose, it is necessary to limit the conical or tapered surface.

In other known fuel injection nozzles, the injection orifices commence in the blind bore, although this has the disadvantage that the volume of the blind bore acts directly as a dead space which results in a deterioration in the composition of the exhaust gas in respect of hydrocarbons. In order to obtain complete closure of the valve needle in the known fuel injection nozzles first mentioned, in which the injection orifice commences in the seating surface, a certain residual connection must exist from the blind bore towards the injection orifice. Although the injurious HC content of exhaust gas is reduced compared with the known fuel injection nozzles mentioned in the second instance, it is not reduced to the required or desired extent.

Thus it is an object of this invention to provide a fuel injection nozzle in which the dead space is kept to a minimum and in which the residual volume is not connected to combustion chambers of the engine when the valve is closed.

In accordance with this invention there is provided a fuel injection nozzle for an internal combustion engine comprising a nozzle body which is provided with a pressure chamber, a valve seat with injection orifices extending therefrom and a blind bore, and a valve needle, which is displaceably received within the nozzle body and has a valve nose co-operating with the body valve seat to form a seal therewith when the valve needle is in its closed position, the injection orifices being sealed, on the one hand, with respect to the pressure chamber and, on the other hand, with respect to the blind bore, when the valve needle is in said closed position but being open with respect to both on displacement of the valve needle into an open position, and a relief passage through the valve needle being provided to relieve any residual fuel pressure in the blind bore and communicate it to the pressure chamber on displacement of the valve needle from the open to the closed position.

In contrast to the aforementioned constructions, therefore the fuel injection nozzle in accordance with the invention, has the advantage that no residual quantities of fuel can flow into the combustion chamber after the valve needle has closed, so that the injurious hydrocarbons in the exhaust gas can be reduced to a considerable extent.

The invention will be further described hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure I is a partial longitudinal section through a first embodiment of this invention; Figure 2 is a partial longitudinal section through a second embodiment of this invention; and Figure 3 is a partial longitudinal section through a third embodiment of this invention.

In all three embodiments illustrated, the valve sealing nose 3 of a valve needle 4 rests on a valve seat 2 arranged in a nozzle body 1. Fuel flows under pressure from a fuel injection pump (not illustrated) into a pressure chamber 5 (only partially illustrated) which is disposed between the nozzle body 1 and the valve needle 4 and in which the fuel acts in the opening direction upon pressure shoulders 6 (only partially illustrated) arranged on the valve needle 4. When an adequate pressure prevails in the pressure chamber 5, the nose 3 of the valve needle 4 is lifted off seat 2 against a force tending to hold the needle 4 down on seat 2, generally that of a closure spring, so that the fuel can flow from the pressure chamber 5 into the combustion chamber (not illustrated) of the internal-combustion engine by way of injection orifices 7.The injection orifices 7 lead outwardly from the valve seat 2 and are sealed from chamber 5 by the valve nose 3 when the valve needle is closed. The conical valve seat 2 merges into a blind bore 8 which is interconnected with the pressure chamber 5 by way of a relief passage 9, extending through the valve needle 4 and being in the form of a throttle passage having a narrow flow-through cross section.Thus, fuel, trapped in the blind bore 8, can flow into the pressure chamber 5 by way of the passage 9 when the valve needle is closing so that leakage of fuel through the injection orifices 7, previously possible in earlier constructions by virtue of the cushion of trapped fuel in the blind bore, and by the fact that the blind bore remained in communication with the orifices or was isolated to form a resilient cushion after the injection operation has terminated and the valve had closed, is avoided.

However, communication between the pressure chamber 5 and the blind bore 8 requires satisfactory sealing between the valve nose and the valve seat around the edges of the blind bore 8 beyond the injection orifices 7, so that no fuel can flow from the pressure chamber 5 into the combustion chamber by way of the passage 9 and the blind bore 8 when the valve is closed. As already set forth above, this would result in a substantial deterioration in the composition of the exhaust gas.

In the embodiment illustrated in Figure 1, the valve seat 2 is in the form of a conical surface having rectilinear surface lines. On the other hand, the valve nose 3 is of rounded profile in the region of its transition into the main cylindrical stem of the valve needle 4. The rounded or part-spherical portion 10 which does not come into abutment with seat 2 when the nozzle is closed acts as part of the pressure shoulder 6 of the valve needle 4. The linearity of the contiguous valve cone has been chosen, for technical reasons, in order to ensure satisfactory sealing between the valve nose 3 and the valve seat 2 in the region of the injection orifices 7. It is common knowledge that, with conical seats of this type, the degree of difficulty when lapping-in the mutually oppositely located faces increases as the diameter of the nose decreases.As is shown in the embodiment of Figure 1, the injection orifices 7 generally commence in the conical seat in a region thereof which has a relatively small diameter. This is structurally connected with the fact that the injection orifices are disposed as near the bottom of the nozzle body 1 as possible, in order to ensure that the fuel injection nozzle extends to a minimum extent into the combustion chamber. By virtue of the rounded or spherical construction 10, the actual sealing region of the nose 3 is disposed in a region of smaller diameter, namely opposite the injection orifices 7. This also results in the advantage of a construction which is favourable to flow.

In the second embodiment illustrated in Figure 2, it is the region 12 of the valve nose 3 which is located opposite the injection orifices 7 that is of rounded, profiled or part-spherical configuration. Correspondingly, the valve seat 2 is also provided with a matching profile in the region 13 of the injection orifices 7, so that the profiled portions 12 and 13 abut sealingly against one another when the valve is closed. Advantageously (as shown in Figure 2), the central point M of this spherical zone is formed by the point of intersection of the axes of the injection orifices 7 and the axis of the valve needle. Thus, the sealing region is advantageously limited to a relatively narrow frustum having a spherical outer surface.

In the third embodiment illustrated in Figure 3, an annular groove 14 is incorporated in the valve nose 3 in order to further reduce the size of the cone performing a sealing action in the region of the injection orifices 7 when the valve is closed. The conical regions 15 and 16 at each side of the annular groove 14 undertake the sealing action between cone 3 and the valve seat 2.

Although the dead volume for exhaust gases increases within narrow limits as a result of the annular groove 14, the contact surface serving for sealing is reduced, and it becom es a simpler matter to lap-in the sealing surfaces.

WHAT WE CLAIM IS: 1. A fuel injection nozzle for an internal-combustion engine comprising a nozzle body which is provided with a pressure chamber, a valve seat with injection orifices extending therefrom and a blind bore, and a valve needle, which is displaceably received within the nozzle body and has a valve nose co-operating with the body valve seat to form a seal therewith when the valve needle is in its closed position, the injection orifices being sealed, on the one hand, with respect to the pressure chamber and, on the other hand, with respect to the blind bore, when the valve needle is in said closed position but being open with respect to both on displacement of the valve needle into an open position, and a relief passage through the valve needle being provided to relieve any residual fuel pressure in the blind bore and communicate it to the pressure chamber on displacement of the valve needle from the open to the closed position.

2. A fuel injection nozzle as claimed in claim 1, in which the relief passage is in the form of a throttle passage having a narrow flow-through cross section.

3. A fuel injection nozzle as claimed in claim 1 or 2, in which the slopes of the valve nose and of the valve seat are identical.

4. A fuel injection nozzle, as claimed in claim 1 or 2, in which the valve nose is slightly convex in the region of the injection orifices.

5. A fuel injection nozzle as claimed in claim 4, in which, in any plane which incorporates the axis of the valve needle the convex region of the nose forms an arc of a circle the centre of which lies at the point of intersection between the axes of the injection orifices and the axis of the valve needle.

6. A fuel injection nozzle as claimed in claims 4 or 5, in which the valve seat has a curved recess corresponding to the convexity of the valve nose.

7. A fuel injection nozzle as claimed in any of the claims 1 to 3, in which the transition region between the valve nose and the main stem of the valve needle is part-spherical and the injection orifices commence opposite the substantially rectilinear portion of the nose.

8. A fuel injection nozzle, as claimed in any preceding claim, in a groove disposed in the valve nose and is located directy opposite the injection orifices.

9. A fuel injection nozzle as claimed in claim 8, in which the groove is an annular one.

10. A fuel injection nozzle substantially as hereinbefore particularly described with reference to, and as illustrated in, Figure 1 of the accompanying drawings.

11. A fuel injection nozzle substantially as hereinbefore particularly described with reference to, and as illustrated in Figure 2 of the accompanying drawings.

12. A fuel injection nozzle substantially as hereinbefore particularly described with reference to, and as illustrated in Figure 3 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 **. es a simpler matter to lap-in the sealing surfaces. WHAT WE CLAIM IS:

1. A fuel injection nozzle for an internal-combustion engine comprising a nozzle body which is provided with a pressure chamber, a valve seat with injection orifices extending therefrom and a blind bore, and a valve needle, which is displaceably received within the nozzle body and has a valve nose co-operating with the body valve seat to form a seal therewith when the valve needle is in its closed position, the injection orifices being sealed, on the one hand, with respect to the pressure chamber and, on the other hand, with respect to the blind bore, when the valve needle is in said closed position but being open with respect to both on displacement of the valve needle into an open position, and a relief passage through the valve needle being provided to relieve any residual fuel pressure in the blind bore and communicate it to the pressure chamber on displacement of the valve needle from the open to the closed position.