GB2147357A

GB2147357A - Fuel injectors for I.C. engines

Info

Publication number: GB2147357A
Application number: GB08419402A
Authority: GB
Inventors: Werner Grunwald; Gerhhard Auwarter; Ernst Imhof; Iwan Komaroff
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1983-09-29
Filing date: 1984-07-30
Publication date: 1985-05-09
Also published as: GB8419402D0; GB2147357B; JPS6073043A; DE3335298A1

Abstract

A fuel injector comprises an injection nozzle (10) and an incandescent coil (40) downstream thereof. The fuel jets from the nozzle suck in air from the engine combustion space through gaps (46), which air, in the interior of the incandescent coil (40), penetrates into the edge zones of the spray jets, where an easily ignitable mixture is obtained. The incandescent coil (40) is formed by the heating region (49) of a heater (50) which is provided with a dimensionally stable sheathing (68) and the unheated current-supply region (52) of which is fixed to the injection nozzle (10), preferably to its cap nut (28). <IMAGE>

Description

SPECIFICATION Device for injecting fuel into combustion spaces of internal-combustion engines Prior Art The invention starts from a device for fuel injection according to the pre-characterising clause of the main claim. The advantage of devices of this generic type is that braking of the spray jet as a result of the formation of a partial vacuum and jet deformation in the incandescent coil can be prevented practically at all the operating points of the internalcombustion engine, so that spray jets issue from the incandescent coil with the desired geometry and, not being braked, at a maximum outflow speed.The air sucked into the interior of the incandescent coil laterally heats up and penetrates into the edge zone of the spray jet, where finer fuel droplets are located, in contrast to the core zone, and also, because of a lower droplet density than in the core of the jet, a fuel/air ratio very favourable for ignition and combustion prevails. When the spray jet flows through the incandescent coil, heat is supplied to the edge zone of the spray jet, so that when the latter issues into the combustion space the cloud of droplets, vapour and air, surrounding the core of the jet, is ignited. Since this cloud represents only a small proportion of the total quantity in the spray jet, the heater device of the generic type requires only relatively little heating energy to initiate ignition.In addition, the energy of penetration of the spray jet is not reduced here, so that the spray jet, with a burning envelope, can spread unimpeded in the combustion space.

In the exemplary embodiments according to the main patent, the incandescent coil is formed by a heating wire which consists of a solid noble-metal profile and which is connected at one end to a current supply conductor and at the other end to a protective capsule surrounding the incandescent coil and which is earthed via this protective capsule.

This design is simple and stable per se, but is not yet the best possible in terms of a method of assembly which is convenient for production.

Advantages of the invention In contrast, the advantage of the arrangement according to the invention, having the characterising features of the main claim, is that the two junction points of the incandescent coil, together with the lines continuing further, are omitted and the appropriately preformed coaxial heating conductor can be fixed as a whole to the injection nozzle, with the result that it becomes substantially simpler to assemble the parts. Moreover, noble metal can be saved, and the incandescent coil made cheaper because of this. Coaxial heating conductors are known and have proved appropriate in various sectors of engineering. Both coaxial heating conductors with a current return conductor arranged within the sheath and coaxial heating conductors in which the sheath itself serves as a current return conductor can be used for the present practical purpose.The sheath forms, together with the mass of insulating material enclosed by it and consisting of MgO and with the inner heating conductor, an inherently rigid unit which is not deformed as a result of the thermal and mechanical forces arising during operation.

Advantageous developments of the arrangement according to the main patent are possible as a result of the measures listed in the sub-claims.

As regards devices, the injection-nozzle housing of which consists of two parts (the nozzle body and nozzle-holder) connected to one another by means of a cap nut, the coaxial heating conductor forming the incandescent coil can advantageously be fixed to the cap nut, so that no changes to a commercially available design have to be made on the nozzle body having the spray orifices.

The coaxial heating conductor is fixed precisely and securely to the cap nut when the heating conductor is fixed in a pressure-tight manner between a bearing surface matched to its cross-sectional profile and located on the cap nut and an appropriately matched counter-surface of an annular body fastened to the cap nut. Fixing can be carried out by clamping or glueing or by both measures.

Appropriately, the annular body can be designed so that it surrounds that heating region of the coaxial heating conductor forming the incandescent coil at a radial distance. This at the same time results in the formation of a flow channel for the combustion air which is sucked in from the combustion space through between the individual turns of the incandescent coil by the fuel spray jets.

A design which is conenvient in production terms is obtained when the cap nut has on the end face located on the same side as the combustion space a conically tapering shellsurface portion in which the bearing surface for the coaxial heating conductor is formed, and when the counter-surface is formed on a bore portion which widens with the same conicity and belongs to the annular body and which is appropriately welded to the cap nut.

Brief Description of the Drawing An exemplary embodiment according to the invention is illustrated in the drawing and explained in more detail in the following description. Fig. 1 shows, in section, that part of an injection nozzle located on the same side as the combustion space, with an incandescent coil located after it, and Fig. 2 shows, partially in section, the coaxial heating conductor forming the incandescent coil accord ing to Fig.

Detailed Description of the Exemplary Embodiment The injection nozzle 10 has a nozzle body 1 2 in which a valve seat 14 is formed and a valve needle 1 6 is mounted displaceably. This needle has a sealing cone 1 8 which interacts with the valve seat 14 and which has adjoining it a throttling pintle 20 penetrating into a spray orifice 22 in the nozzle body 1 2. The spray orifice 22 opens out on that end face 24 of the injection nozzle 10 which faces the combustion space and which merges via a conical wall portion 26 into the cylindrical shell surface of the nozzle body 1 2.

The nozzle body 1 2 is clamped, as is customary, by means of a cap nut 28, together with an intermediate washer 30, to a nozzleholder not shown in more detail in the drawing, which has a connection for a fuel line and which is provided in its interior with a chamber for receiving a closing spring which presses the valve needle 1 6 against the valve seat 14. The cap nut 28 matches the outer shape of the nozzle body 1 2 and is provided accordingly with a conical bore portion 31. A fuel channel leads from the nozzle-holder through the intermediate washer 30 into an annular groove 32 in the nozzle body 1 2 which is connected via an inflow line 34 to a pressure space 36.In the region of the pressure space 36, the valve needle 1 6 has a thrust shoulder 38 on which the fuel pressure gives rise to a force counteracting the closing spring and displacing the valve needle in the opening direction.

Located coaxially after the injection nozzle is an incandesent coil 40 which forms a channel for the contact-free passage of the fuel spray jets 42. The incandescent coil 40 is surrounded at a radial distance by an annular body 44 which is welded at 45 to the cap nut 28. When the internal-combustion engine is in operation, the spray jets 42 flowing through-the incandescent coil 40 suck in air through the gaps 46 between the individual turns of the incandescent coil 40 and the annular gap 48 formed between this and the annular body 44, from a region of the combustion space where there is a relatively high proportion of oxygen.The air sucked in is heated at the turns of the incandescent coil 40 to a higher temperature level than in the remaining combustion space and in the interior of the incandescent coil 40 penetrates into the edge zones of the spray jets 42, where a fuel/air mixture very favourable for ignition and combustion is obtained and is ignited reliably when it flows into the combustion space.

The incandescent coil 40 is formed by the heating region 49 (Fig. 2) of a so-called coaxial heating conductor 50 which has a dimensionally stable sheathing and the cold current-supply region 52 of which is integrally connected to the heating region 49 by means of a transitional region 54. In the heating region 49, the coaxial heating conductor 50 contains on the inside two heating wires 56, 58 which have a relatively high specific electrical resistance and which are welded to one another at their ends 60. The heating wires 56, 58 are connected in the transitional region 54 to connecting wires 62, 64 which have a substantially lower specific electrical resistance and also a larger cross-section than the heating wires 56, 58.The heating wires 56, 58 and the connecting wires 62, 64 are embedded in a ceramic insulating compound 66, preferably MgO, and are surrounded by a sheath 68 consisting of heat-resistant material with good thermal conductivity, for example Inconel. This construction gives the coaxial heating conductor 50 such a high inherent rigidity that the incandescent coil 40 formed by its heating region 49 is not deformed during operation as a result of thermal and mechanical stresses. Because of the different specific resistances and cross-sections, the temperature of the heating wires 62 and 64 increases only negligibly or only to the temperature of the injection nozzle 10.

The coaxial heating conductor 50 is retained against the cap nut 28 by means of the annular body 44. For this purpose, the cap nut 28 has a conically tapering shell-surface portion 70 against which rests a bore-wall portion 72 designed with the same conicity and belonging to the annular body 44. At one point, the cap nut 28 has a yroove-like depression 74 in the shell wall portion 70 which is located opposite a groove-like depression 76 in the bore-wall portion 72 of the annular body 44. A channel through which one region 78 of the coaxial conductor 50 is guided is formed as a result. The two groove-like depressions 74 and 76 are matched in their cross-section to the cross-sectional profile of the heating-conductor region 78, in such a way as to result in a slight gap which, to retain the coaxial heating conductor 50, is filled with an adhesive which at the same time ensures a pressure-resistant seal.

Claims

1. Device for injecting fuel in combustion spaces of internal-combustion engines, with at least one injection nozzle and an incandescent coil which is located after the latter and through which the fuel spray jets flow free of contact, and also with at least one aerating orifice which opens from the side into the path of the spray jets and via which air passes from the combustion space into the edge zone of the spray jets as a result of an injector effect, according to Patent (Patent Application P 3307109.8), characterised in that the incandescent coil (40) is formed by the appropriately shaped heating region (49) of a heat ing conductor (50) which is known as a "coaxial heating conductor" and has dimensionally stable sheathing and of which the cold current-supply region (52) connected integrally to the heating region (49) or the incandescent coil (40) is fixed to the injection nozzle (10).

2. Device according to Claim 1, the injection-nozzle housing of which consists of two parts (the nozzle body and nozzle-holder) which are connected to one another by means of a cap nut, characterised in that the heating conductor (50) is fixed to the cap nut (28).

3. Device according to Claim 2, characterised in that the heating conductor (50) is fixed in a pressure-tight manner between a bearing surface (74) matched to its cross-sectional profile and located on the cap nut (28) and an appropriately matched counter-surface (76) of an annular body (44) fastened to the cap nut (28).

4. Device according to Claim 3, characterised in that the annular body (44) surrounds at a radial distance (48) that heating region (49) of the heating conductor (50) forming the incandescent coil (40).

5. Device according to Claim 3 or 4, characterised in that the cap nut (28) has on the end face located on the same side as the combustion space a conically tapering shellsurface portion (70) in which the bearing surface (74) for the heating conductor (50) is formed, and in that the counter-surface (76) is formed on a bore-wall portion (72) widening with the same conicity and belonging to the annular body (44).

6. Device according to one of Claims 3 to 5, characterised in that the annular body (44) is connected to the cap nut (28) by means of welding.

7. A fuel injection device substantially as herein described with reference to the accompanying drawing.