GB2136504A

GB2136504A - Flame glow-in plug for preheating the intake air of internal combustion engine

Info

Publication number: GB2136504A
Application number: GB08406601A
Authority: GB
Inventors: Hannes Pflug; Leo Steinke
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1983-03-15
Filing date: 1984-03-14
Publication date: 1984-09-19
Also published as: JPS59173631A; GB2136504B; GB8406601D0; DE3309133A1

Abstract

The plug 10, particularly for diesel engines, comprises a metal housing (11) secured in the air intake of the engine and to which fuel is fed via a nipple (20) and which contains a glow pin (23) heatable by means of a coil (33). The metered fuel is heated and vapourized in a tube (40), mixed with air and subsequently ignited. The coil comprises three portions, firstly a combustion chamber end portion (33/1) whose resistance is temperature independent and which serves to ignite the fuel vapour/air mixture, secondly a central portion (33/2) which has a positive temperature coefficient of resistance and which ensures rapid heating of the glow pin and subsequent reduction of the heating current, and thirdly a portion (33/3) whose resistance is temperature independent and which is connected to a terminal stud (25) and prevents high thermal stress of the first portion upon the introduction of the relatively cold fuel into the plug. <IMAGE>

Description

SPECIFICATION Flame glow-pin plug for preheating the intake air of internal combustion engines The invention relates to a flange glow-pin plug for internal combustion engines, particularly for diesel engines.

A flame glow-pin plug is known (German Offenlegungsschrift No. 21 15 620) for preheating the intake air of an internal combustion engine, said plug having a fuel feed line which is located at the connection end of its housing, and a glow pin which, in use, extends into the air intake line of the internal combustion engine and which, by means of the heat generated thereby, heats and then vapourizes the fuel fed and finally ignites the fuel at its combustion chamber end portion together with air fed in the air intake pipe of the internal combustion engine, and which (glow pin) has a metal glow tube which provided with a bottom at the combustion chamber end thereof and in which an electrical resistance coil is embedded in an electrically insulated packing of good thermal conductivity and has at its combustion chamber end a coil portion which is secured to the bottom of the glow tube and which is made from a material having a substantially temperature-independent resistance behaviour, and contiguous thereto a second coil portion which is made from a material having a positive resistance temperature behaviour (PTC).

This has the advantage that its glow pin is heated very rapidly as a result of the regulating behaviour of a resistance coil portion having PTC resistance behaviour, although the current intensity is reduced during rapid heating. If the starter is then actuated, relatively cold fuel is fed to the flame glow-pin plug.

This fuel enters the flame glow-pin plug in the region of the resistance coil portion having PTC resistance behaviour, cools this portion of the heating coil, and consequently reduces its electrical resistance and hence again increases the current intensity in the portion of the resistance coil at the combustion chamber end thereof. With the generator voltage of, for example, 27.5 volts existing in the vehicle, the portion of the resistance coil at the combustion chamber end is thereupon subjected to considerable thermal stress and is consequently endangered. However, overcoming this problem by varying the resistance ratios of the two resistance coil portions involves undesirable prolongation of the heating-up time of the glow pin.In the described flame glow-pin plug, the fuel is heated and vapourized within a tube which extends spirally around the glow pin and emerges as fuel vapour from the combustion chamber end of this so-called vapourizer tube where it is then mixed with intake air and is subsequently ignited by the free end portion of the glow pin.

In another known flame glow-pin plug (German Patent Specification No. 1 301 631), a tube is disposed coaxially to, and spaced from, the glow pin, and the fuel to the connection end of the flame glow-pin plug is heated and vapourized in the annular gap formed between the glow pin and the tube and finally emerges from the combustion chamber end of the annular gap where it is then also mixed with intake air and subsequently ignited.

In accordance with the invention the glow pin has a third coil portion of the resistance coil and which is contiguous to the second portion and which is located between said second portion and the terminal stud of the flame glow-pin plug and made from a material having a substantially temperature independent resistance behaviour, said means in the flame glow-pin plug for feeding the fuel to be heated and vapourized being disposed substantially in the region of the third and second portions of the resistance coil.

This has the advantage that, although it is also heated very rapidly, the portion of the resistance coil at the combustion chamber end is not subjected to excessive thermal stress in the glow tube, even when the relatively cold fuel is fed to the flame glow-pin plug.

In a preferred embodiment it is particularly advantageous if a vapourizer tube disposed coaxially to, and at a distance from, the glow pin is used in the flame glow-pin plug as a means for feeding the fuel to be heated and to be vapourized.

The invention will be described further hereinafter by way of the example only, with reference to the accompanying drawing, which is a longitudinal section through a flame glow-pin plug in accordance with the invention.

The flame glow-pin plug 10 has a metal housing 11 whose outside is provided with a screw thread 1 2 and a hexagonal portion (not illustrated) for applying a spanner for fitting the flame glow-pin plug 10, usually radially, in an air intake pipe (not illustrated) of an internal combustion engine (such as a diesel engine). A lock nut 1 3 engaging the screw-in thread 1 2 serves to secure the flame glow-pin plug 10 against unintentional release from the air intake pipe. The end portion ofthe housing 11 at the connection end generally has a smaller diameter than the remaining portion of the housing 11 and is designated housing neck 14.The housing 11 incorporates a multi-stepped longitudinal bore 15, and the individual steps decrease in diameter from the end portion at the combustion chamber end to the end portion at the connection end. A metal screening sleeve 1 6 is secured coaxially to the end portion of the metal housing 11 at the combustion chamber end thereof and in corporates a number of openings 1 7 and 1 8 serving for ingress of the intake air required for the flame glow-pin plug 10. The number, arrangement, design and size of these openings 1 7 and 1 8 depend upon the conditions of the given internal combustion engine.In the present embodiment, the end portion of the screening sleeve 1 6 at the connection end is flanged into the combustion chamber end portion of the longitudinal bore 17, although alternatively, it can be secured to the metal housing 11 by equivalent means such as welding or the like. The end of the screening sleeve 1 6 facing the combustion chamber is left completely open, although there are also screening sleeves 1 6 whose opening at the combustion chamber end thereof contains a transverse perforated plate or the like. Screening sleeves 1 6 are also known whose interiors contain coaxial tubes or sieves in order to prevent rectilinear ingress of the intake air.

A transverse bore 1 9 is incorporated in the metal housing 11 adjacent to the neck 14 at the connection end thereof and communicates with the longitudinal bore 1 5 in the housing, and a metal fuel nipple 20 is secured in the bore 1 5 by, for example, hard soldering. The fuel nipple 20 has a drilled bore 21 by which it is connected to the longitudinal bore 1 5 in the metal housing. A known filter (not illustrated) and frequently a known fuel metering nozzle (also not illustrated) are generally disposed in the bore 21. The exterior of the free end portion of the fuel nipple 20 carries a screw-threaded portion 22 for connecting a fuel connection line (not illustrated).

A glow pin 23 is fixed in the longitudinal bore 1 5 in the housing in a known manner, such that the end portion of its metal, thinwalled glow tube 24, at the connection end thereof, is sealingly pressed-in in the region of the housing neck 14. The end face of the glow tube 24 at the combustion chamber end thereof is flush with the end face of the housing 11 at the combustion chamber end thereof. A terminal stud 25 electrically insulated from the glow tube 24 extends out of the glow tube 24 at the connection end thereof and is provided with a connection thread 26. An insulating washer 27, a round metal nut 28 incorporating an annular groove 29, and a metal locking disc 30 are slipped onto the said portion of the terminal stud 25 which is provided with the connection thread 26.The round nut 28 serves as a support for a cable shoe (not illustrated) for an electrical connection lead and, by the action of pressure in the region of its annular groove 29, is secured to the terminal stud 25. The cable shoe (not illustrated) is secured to the round nut 28 by means of the locking washer 30 and a connection nut 31. That portion of the terminal stud 25 which extends into the interior 32 of the glow tube 24 is connected to the electrical resistance coil 33 whose end facing the combustion chamber is connected to the bottom 34 of the glow tube 24.

Preferably, the resistance coil 33 is connected to the terminal stud 25 and to the bottom 34 of the glow tube by welding.

The resistance coil 33 is rigidly embedded in an electrically insulating packing 35 of good thermal conductivity which is made from, for example, magnesium oxide. The interior 32 of the glow tube is filled with a suitable, known seal 36 (for example, an insulating ring made from resilient material such as viton or fluoroelastomer) in order to seal the glow tube 24 at the connection end thereof and to insulate the terminal stud 25 electrically from the glow tube 24. The glow pin 23, which is terminated at the combustion chamber end by the bottom 34, extends approximately into the region of the screening sleeve 1 6 at the combustion chamber end thereof.

The electrical resistance coil 33 has three portions 33/1, 33/2 and 33/3. The first coil portion 33/1 is disposed approximately in that region of the screening sleeve 16 which incorporates the openings 1 7 and 18, and its portion at the combustion chamber end thereof is welded in the bottom 34 of the glow tube. The first coil portion 33/1 is made from a material having a substantially temperature-independent resistance behaviour (for example NiCr 80/20, Kanthal, Megapyr). The length of this first coil portion 33/1 is approximately 1 5 mm with an external diameter of approximately 5 mm.

A second coil portion 33/2 is contiguous to the first coil portion 33/1 and is wound preferably in the same direction as the first coil portion 33/1 and is connected to the latter by laser welding. The second coil portion 33/2 is made from a material having a positive resistance temperature behaviour (such as nickel, nickel/iron 701). The diameter of the second coil portion 33/2 is also approximately 5 mm, and its length is such that approximately 25 mm still remain for the third coil portion 33/3 between the second coil portion and the terminal stud 25. The third coil portion 33/3 is in turn made from a material having a substantially temperature independent resistance behaviour, such as is also used for the first coil portion 33/1. That end of the coil portion 33/3 which is pre sented to the combustion chamber is con nected to the second coil portion 33/2 by welding (preferably by laser welding) and, as already mentioned, its end portion at the connection end is secured to the terminal stud 25. The external diameter of this third coil portion 33/3 is also in the region of 5 mm.

While the diameters of the wires of the first and third coil portions 33/1 and 33/2 are approximately 0.6 mm, the wire used for the second coil portion 33/2 has a diameter of 0.4 mm. The glow tube 24 has a wall thick ness of 0.7 mm and an external diameter of 7.5 mm. The dimensions specified have to be adapted to the particular case of application.

A gap 38 is formed between the glow pin 23 and that end face 37 of the fuel nipple 20 which faces the glow pin 23 and continues as an annular gap 39 along the glow tube 24 towards the combustion chamber. While the annular gap 39 is defined by the glow tube 24 of the glow pin 23 on the one hand, it is defined towards the outside by a so-called vapourizer tube 40 which is disposed coaxially around the glow pin 23 at a distance of approximately 0.6 mm therefrom. The vapourizer tube 40 is made from a heat-resistance metal and has a wall thickness of 0.5 mm.

The connection end of the vapourizer tube 40 is fixed in a corresponding drilled-out portion 41 of the longitudinal bore 15 in the housing and its combustion chamber end terminates approximately at the combustion chamber end of the housing 11. The greater portion of the length of the vapourizer tube 40 is spaced from the surface of the longitudinal bore 1 5 in the housing in order to avoid unnecessary conduction of heat, produced by the glow pin 23, by way of the housing 11. In a known manner, a distributor 42, illustrated only by broken lines, for the fuel fed may be disposed in the annular gap 39 formed between the glow pin 23 and the vapourizer tube 40.A distributor 42 of this kind may be a sieve-like tube or, alternatively, protuberances and depressions can be provided on the inside of the vapourizer tube 40 and on the outside of the glow tube 24 respectively.

Fuel entering the flame glow-pin plug 10 through the bore 21 in the fuel nipple 20 flows into the gap 38 located between the end face 37 of the nipple and the glow pin 23 and consequently comes into contact with that region of the glow pin 23 in which the third portion 33/3 of the resistance coil 33 is located. Alternatively, according to the case of application of the flame glow-pin plug 10, the pitch between the individual turns of the third coil portion 33/3 may vary if it is advantageous to provide zones of differing energy emission on the glow tube 24. In principle, this also applies to the first coil portion 33/1 and also to the second coil portion 33/2.If the terminal stud 25 is to be connected to a voltage source by way of a switch (not illustrated) for the purpose of starting the internal combustion engine, the resistance coil 33, electrically connected to earth by way of the glow tube 24 and the housing 11, is heated.

A relatively high current flows through the resistance coil 33 as a result of the low electrical resistance of the second coil portion 33/2 at low temperatures, and ensures that the resistance coil 33 is heated very rapidly.

The electrical resistance of the first coil portion 33/1 and of the third coil portion 33/3 remains substantially constant as the temperature of the resistance coil 33 increases, although the second coil portion 33/2 very rapidly assumes a higher resistance value as a result of its PTC resistance behaviour and consequently reduces the value of the electric current in the resistance coil 33. The starter is actuated after the glow pin 23 has been heated up, and fuel is at the same time fed to the flame glow-pin plug 10 through the bore 21 in the fuel nipple 20. This relatively cold fuel is heated up and partially vapourized in that region of the glow pin 23 in which the third portion 33/3 of the resistance coil 33 is located, and is conducted as fuel or fuel vapour along the annular gap 39 between the glow tube 24 and the vapourizer tube 40.A distributor 42 in the form of a tubular sieve disposed in the annular gap 39 ensures that the fuel is satisfactorily distributed and is slightly retarded in this region. When the fuel or fuel vapour then enters that region of the glow pin 23 in which the second coil portion 33/2 having the PTC resistance behaviour is located, it does not cool this second coil portion 33/2 to such an extent that there is any considerable increase in the current flowing in the resistance coil 33. In the known flame glow-pin plugs in which the third portion 33/3 of the resistance coil 33 was not provided, the relatively cold fuel cooled the second coil portion 33/2 such that the current in the resistance coil 33 was again increased to an extent that the first coil portion 33/1, serving particularly to ignite the fuel vapour/air mixture, was subjected to the risk of excessive thermal stress.The fuel emerges as fuel vapour from the combustion chamber end of the annular gap 39, enters the interior of the screening sleeve 1 6 where it is mixed with intake air entering through the openings 1 7 and 1 8 in the screening sleeve 16, and is finally ignited by the heated end portion of the glow pin 23 at the combustion chamber end thereof.

While the flame glow-pin plug 10 described above has an annular gap 39 disposed around the glow pin 23, German Offenlegungsschrift No. 21 15 620 also describes a flame glowpin plug in which a tubular coil is coiled around the glow pin of the said glow pin plug and along which the fuel is guided, heated and vapourized. A glow pin 23 having a resistance coil 33 which comprises the three coil portions 33/1, 33/2 and 33/3 described in the above embodiment, is also suitable for these kinds of flame glow-pin plugs.

Claims

1. A flame glow-pin plug for preheating the intake air of an internal combustion engine, said plug having a fuel feed line which is located at the connection end of its housing, and a glow pin which, in use, extends into the air intake line of the internal combus tion engine and which, by means of the heat generated thereby, heats and then vapourizes the fuel fed and finally ignites the fuel at its combustion chamber end portion together with air fed in the air intake pipe of the internal combustion engine, and which (glow pin) has a metal glow tube which is provided with a bottom at the combustion chamber end thereof and in which an electrical resistance coil is embedded in an electrically insulated packing of good thermal conductivity and has at its combustion chamber end a coil portion which is secured to the bottom of the glow tube and which is made from a material having a substantially termperature-independent resistance behaviour, and contiguous thereto a second coil portion which is made from a material having a positive resistance temperature behaviour (PTC) and a third coil portion of the resistance coil and which is contiguous to the second portion and which is located between said second portion and the terminal stud of the flame glow-pin plug and made from a material having a substantially temperature- independent resistance behaviour, said means in the flame glow-pin plug for feeding the fuel to be heated and vapourized being disposed substantially in the region of the third and second portions of the resistance coil.

2. A flame glow-pin plug as claimed in claim 1 wherein said fuel feeding means is a tube which is disposed coaxially of the glow pin and which forms an annular gap and into the connection end region of which the fuel feed line opens and out of the open combustion chamber end of which the fuel vapour emerges.

3. A flame glow-pin plug as claimed in claim 1 or 2, wherein all three coil portions of the resistance coil are wound in the same direction.

4. A flame glow-pin plug constructed substantially as herein described with reference to and as illustrated in the accompanying drawing.