IMPROVEMENTS IN AND RELATING TO SPARK PLUGS This invention relates to spark plugs All the current automobiles and motor cycles use spark plugs to ignite the fuel/gas mixture to yield driving power. Generally, spark plugs are classified as "cold plugs" and "hot plugs". Spark plugs conventionally comprise a central electrode, a ground electrode, a metallic (usually steel) thread portion and an insulating portion. Since ignition of internal combustion engines is well-known, no further description will be included in this specification. However, the gap between the said two electrodes bears a close relation to the ignition function in that gap dimensions are varied according to the compression ratio of engine as well as characteristics of the combustion chamber and the ignition system.
The ground electrode of a conventional spark plug is formed from a bar bent at an angle and attached to the bottom of the thread portion so as to form a suitable gap relative to the central electrode (i.e. the ignition gap). Since the angled ground electrode is fixed at one end, certain drawbacks arise in that at the temperatures generated in the cylinder the angled ground electrode bends away from the centre electrode and the gap therebetween increases. As soon as the said gap increases, a higher voltage is then necessary to generate spark across the electrode gap. Therefore, inspection and adjustment on the plug are necessary from time to time.
Further, when a higher voltage is applied across the electrode gap, wear and tear of the electrodes increases. Such phenomenon not only affects the normal ignition function of an engine but also shortens the serviceable life of the spark plug.
Where an engine is fitted with conventional plugs and is run continuously at relatively low speed, the electrodes of the conventional plug are liable to ,4 , .
fouling due to accumulation of carbon deposits. Under these conditions, the available voltage to be applied to the two electrodes is lower than the voltage required by the gap to generate spark and, as a result, misfiring is likely to occur. The engine will, therefore, be unable to run normally due to poor ignition. Again, since the fuel/air mixture is not burned completely, fouling of the electrodes occurs more rapidly than would otherwise be the case.
It is an object of the present invention to provide a spark plug which overcomes the drawbacks outlined above and, accordingly the angled ground electrode of a conventional spark plug, is replaced by at least one bridge electrode dispersed across the metallic thread portion of the plug relative to the central electrode and to form an electrode gap between the electrodes. Since the or each ground/bridge electrode is fixed at both ends, it possesses greater strength to withstand the high operational temperatures for longer periods without adjustment of the spark or electrode gap. In addition, the ground/bridge electrode spark plug of the present invention has larger spark generating area and, as a result, an improved spark is generated.
Further, the spark plug of the invention has the advantage of improved electrode gap condition thereby reducing a build-up of carbon deposit as the electrodes and consequent fouling of the plug. Thus, a lower electrical resistance exists between the bridge and central electrodes and the voltage required to produce a spark between the two electrodes is lower than the maximum available voltage provided by the ignition coil. By means of the single or dual bar bridge electrode, a cold or hot plug may also be designed so as to have the fuel mixture completely burned either at high or low engine speeds. Moreover, when the engine running for a long time under full load, the wear and tear of the plug electrodes' under overheat condition will be reduced thereby extending the serviceable life of the plug, increasing the horsepower of engine, and reducing fuel consumption.
A spark plug in accordance with the present inverr tion will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective of a dual bar bridgespark plug according to the present invention; Figure 1A is a front view of the dual bar bridge spark plug of Figure 1; Figure 2 is a perspective of a single bar bridge spark plug according to the present invention, and Figure 2A, is a front view of the single bar bridge spark plug of Figure 2.
As shown in Figures 1 and 2A, spark plug according to the present invention comprises a central electrode (1), a metallic (e.g. steel) threaded portion (2) and a bridge electrode generally indicated at (3). The bridge electrode (3) may be a dual bar bridge type as shown in Figures 1 and 1A, or may be a single bar bridge type as shown in Figures 2 and 2A.
The gap between said two electrodes, (central and bridge/ground) may be varied in accordance with the compression ratio of engine, the characteristics of the combustion chamber and the ignition system. The bridge electrode (3) is made by fixedly connecting both ends thereof to the bottom of the threaded portion (2) by, for example, welding (as shown in Figures 2 and 2A), or by welding the bridge bars to projections 2A extending longitudinally from the bottom of the threaded portion (2) (as shown in Figures 1 and lA). Since the both ends of the bridge electrode (3) are fixedly attached directly or indirectly to the bottom of the threaded portion (2),
the electrode arrangement possesses improved strength to maintain the required gap relative to the central electrode (1) without change under normal high temperature of the engine.
since the single bar and the dual bar type of bridge electrode (3) has a larger spark generating area tlian the conventional spark plug, it has better spark generating capacity. Further, since the bridge electrode is fixed to the bottom of the steel thread portion with two ends, it may be deemed as a low resistance circuit in terms of the current jumping between the centre electrode (1) and the bridge electrode (3) and, consequently, the voltage required to generate a spark is low, and the fouling would also be low.
Under these circumstances, the voltage provided by the ignition coil to the plug should always be higher than that actually required to generate a spark and the normal spark generating function can be maintained substantially constantly so as to have the fuel mixture in the engine completely burned irrespective of whether the engine is operated under high or low running speed. Consequently, fouling of the plug by carbon deposits will be reduced to a minimum so that the engine cannot only be run longer under full load condition but, also, wear and tear of the plug is minimized because the plug is not normally subjected to over-heat condition.
Finally, the intervals between servicing of plug is extended, and the horsepower of the engine is increased but the fuel consumption will be reduced.
Since the aforesaid bridge electrode (3) is classified as single bar bridge type and dual bar bridge type, the resistance and heat-resistance are also varied so as to adopt to the different type of temperature, i.e., the cold plug and hot plug.