EP2351173B1

EP2351173B1 - Sparkplug with integrated coil

Info

Publication number: EP2351173B1
Application number: EP09783863A
Authority: EP
Inventors: Volker Heise
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2008-10-13
Filing date: 2009-10-08
Publication date: 2012-11-07
Anticipated expiration: 2029-10-08
Also published as: EP2351173A1; WO2010043544A1

Description

TECHNICAL FIELD

The present invention relates generally to a spark plug for an internal combustion engine.

BACKGROUND OF THE INVENTION

The traditional ignition system consists of a spark plug acting as an electrical feed into a combustion chamber of a gasoline engine, providing concentrated thermal energy release, in the form of a spark, to initiate the combustion. A conventional transformer is used, incorporating electronics to condition and to feed energy from the electrical network in vehicles (Battery, Generator).
Future direct injection combustion systems are targeting stratified fuel injection, promising significant fuel reduction at low speed and partial load. These stratified gasoline mixtures tend to be difficult to ignite with existing ignition systems, mostly because of the limited energy and the very local distribution of the released heat of the spark itself.
Alternatives are intelligently controlled resonance structures which allow emitting heat over larger space, constant over time, and at extended time compared to existing ignition systems. These systems require at minimum, the resonance structure, and a driving generator.
As shown on figure 1, a resonance based ignition system comprises of a resonator (2), a generator (1) and heat release interface (3).
If one part of the resonator is realized by conventional high frequency coils, then a resonance ignition system requires an electrical feed through into the combustion chamber as conventional systems.
Conventional ignition systems do have at least two separate elements aside of the variety of harnesses topologies: Spark plug, Ignition-coil.
Whereas the shaft of the sparkplug is designed to withstand the voltages applied to the centre electrode of this removable interface: Sparkplug to Ignition-coil or Spark plug to harness-terminal. The purpose is to not let the spark finding its path to ground outside the combustion chamber. Such interface is adding mechanical length, which is adding electrical capacitance to the output or load of and ignition system.
In such resonance based ignition system this additional capacitance is limiting the voltage (amplification) increase of the resonance structure.
A sparkplug according to the preamble of claim 1 has been proposed in document US2004/0025854A1 .
It has been proposed in document EP1758219 A1 to design a spark plug with a serially connected resonator comprising a center electrode which is attached directly to the lower end of the resonator, the coil being connected directly to the upper end of the center electrode. However, this spark plug is not entirely satisfactory as for ignition efficiency and it requires some specific assembly steps which are not easy to implement.
It is an objective of the present invention to solve the above mentioned problems in a simple and economic way.

SUMMARY OF THE INVENTION

In order to solve the above mentioned problems, the present invention provides integration of the electrical feed-through with the resonance coil, while combining both into one element.
The result is that there is no removable interface between the spark plug and the ignition resonance coil. The benefit is a reduced capacitance of the electrical feed through side, which allows a higher amplification of the resonance structure. Furthermore it reduces the variability of resonance frequency compared to a separate design of two elements, because the resonance frequency is a function of the electrical features of both elements.
According to the present invention, it is proposed a spark plug for an internal combustion engine comprising a lower centre electrode and a ground electrode facing the combustion side of the engine, said ground electrode extending from an electrically conductive annular body connected to the ground, and comprising a hollow shaft made of insulating material, said shaft comprising a lower portion extending between the centre electrode and the body, said shaft comprising an upper portion around which an ignition coil is wound, characterized in that the upper end of the centre electrode is accessible through an open side of the shaft and designed/finished in form of a terminal suitable to connect the starting wire of the coil at the lower end of the coil.
According to other features of the present invention:

the shaft is made out of ceramic material and is cylindrical and hollow in geometry;
- -- the coil is made of a single layer coil;
it further comprises a nonmagnetic metal layered shield on top of the coil.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

figure 1 is a bloc-diagram showing a resonance based ignition system;
figure 2 is a perspective view showing a conventional sparkplug;
figure 3 is a cross sectional view showing a sparkplug according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown on figure 2, a conventional spark plug centre electrode 10 is made out of three major elements, which are the lower electrode 12 facing the combustion side, conductive cement 14 forming a current limiting resistor and an upper electrode 16 pointing towards the ignition-coil interface 18. The conductive cement 14 and the upper electrode 16 are built in the shaft 20 of the spark-plug 22 which is made of insulating material such as ceramic material.
The centre electrode 10 and the shaft 20 are arranged in a generally cylindrical tubular metal body 24 which acts as the ground for the sparks passing through the center electrode 10 to a ground electrode 26 extending from the lower tip of the body 24. The body 24 comprises a threaded outer portion 28 to be threadedly engaged in the cylinder head of the engine.
The ground electrode 26 can be made from high nickel steel and is welded to the side of the body lower end 30. Multiple side electrodes may also be used, so that they do not overlap the centre electrode 10.
According to the present invention, the spark-plug 22 is designed such that a single layer coil 32 can be wound on the shaft 20 like in figure 3. The possible implementation would extend the shaft 20. The lower end 34 (engine face) of the spark-plug 22 would remain unchanged compared to conventional spark-plug.
The shaft 20 is made out of the existing ceramic material and is cylindrical and hollow in geometry, forming a central bore 38 such that the centre electrode upper end 36 at the lower end of the central bore 38 is accessible through the open side 40 of the shaft end and designed/finished in form of a terminal 42 suitable to connect the starting wire 44 of the coil 32. This means that the conventional cement and upper centre electrode are removed.
The single layer coil wire 46 of diameter 0.5mm<d<2mm is contacted through a hole 48 at the low bottom side of the ceramic directly on the lower electrode surface or in case the electrode 10 requires an additional anchor, the anchor provides suitable terminal 42. The open side 40 of the shaft 20 allows inserting suitable means to contact this wire end on the terminal 42 inside the hollow shaft 20 with any suitable brazing and soldering method. Thereafter the wire 46 is wound on the shaft 20.
The wire 46 requires defined guidance for winding on either the shaft 20 itself, or through an additional sleeve 50 on the shaft 20. Both options require suitable grooves 52 in form of a screw to guide the wire 46 and to define the distance from turn to turn.
Such construction requires further an insulation layer 54 and a nonmagnetic metal layered shield 56 on top of the single layer coil 32.
The hollow shaft 20 comprises a lower portion 58 standing between the centre electrode 10 and the annular body 24, and an upper portion 60 forming the core member of the ignition coil 32, said ignition coil 32 being wound around said upper portion 60. The lower portion 58 and the upper portion 60 of the shaft 20 are made of one piece.
The centre electrode 10 extends essentially from the lower end 62 to the upper end 64 of the hollow shaft lower portion 58. The centre electrode 10 is inserted coaxially in the through bore portion extending axially in the shaft lower portion 58.

Claims

Spark plug (22) for an internal combustion engine comprising a lower centre electrode (10) and a ground electrode (26) facing the combustion side of the engine, said ground electrode (26) extending from an electrically conductive annular body (20) connected to the ground, and comprising a hollow shaft (20) made of insulating material, said shaft (20) comprising a lower portion (58) extending between the centre electrode (10) and the body (20), said shaft (20) comprising an upper portion (60) around which an ignition coil (32) is wound, characterized in that the upper end (36) of the centre electrode (10) is accessible through an open side (40) of the shaft (20) and designed/finished in form of a terminal (42) suitable to connect the starting wire (44) of the coil (32) at the lower end of the coil (32).
Spark plug (22) according to claim 1, characterized in that the shaft (20) is made out of ceramic material and is cylindrical and hollow in geometry.
Spark plug (22) according to any of the preceding claims, characterized in that the coil (32) is made of a single layer coil.
Spark plug (22) according to any of the preceding claims, characterized in that it further comprises a nonmagnetic metal layered shield (56) on top of the coil (32).