MX2008004979A - Spark plug for motor vehicle internal combustion engine - Google Patents

Abstract

The invention concerns a spark plug (1) for a motor vehicle internal combustion engine, substantially elongated in shape, comprising:two coaxial electrodes:an inner electrode (D) called central electrode (3) and an outer electrode called base (2) enclosing the central electrode (3);an electrically insulating annular block, called insulation (4) interposed between the central electrode (3) and the base (2) having an annular shoulder (5). The invention is characterized in that the insulation (4) comprises an annular groove (8) located at the shoulder (5).

Description

SPARK PLUG FOR MOTOR VEHICLE INTERNAL COMBUSTION ENGINE The invention relates to a spark plug for the internal combustion engine of a motor vehicle, essentially elongated in shape, comprising: - two coaxial electrodes: an inner electrode with an axis called a central electrode and an outer electrode called a body that surrounds the central electrode; and - an electrically insulating block called an insulator, placed between the central electrode of the body, of annular shape and having an annular shoulder. Spark plugs are multi-spark emission systems of high frequency, capable of providing the best quality ignition conditions in controlled emission engines, but at the same time reduce polluting emissions, particularly with a poor mixture. On the other hand they are subject to incrustation, particularly when they are cold. Like all spark plugs, they are classified in terms of a heat interval. This heat interval takes into account its thermal behavior at particular moments of the motor operation. Expresses in particular its ability to withstand temperatures that are sufficiently high to remove the scale by pyrolysis, without causing any "pre-ignition". The publications FR2,859,830, FR2,859,869 and FR2,859,831 mention a multi spark spark plug called a cold spark plug because its temperature does not rise fast enough to avoid scaling. In these spark plugs, in fact, accumulation of the carbon deposit in the insulator has been observed, which significantly reduces the required insulation between the tip of the central electrode and the body. With poor insulation, the spark plug's high-voltage supply may then be too low to cause the required spark-generating "discharges". To prevent the formation of carbon-containing deposits, in particular when they are cold or in the spark plug insulation exposed to the environment in the combustion chamber, an effort can be made to increase the temperature of the insulation, to promote the destruction of the deposits by the phenomenon of pyrolysis, of which the efficiency depends on the thermal resistance of the spark plug structure, including the insulator. The measures usually taken to Increasing the temperature of the insulator is limited by the occurrence of "pre-ignition" in the spark plugs, when they reach operating temperatures that are very high. To overcome these disadvantages, the invention is directed to adjusting the heat range of a multi spark spark plug, so that it behaves like a very hot spark plug when the engine is still cold and in such a way that it behaves like a warm spark plug when the engine is hot. The invention is directed to increasing the surface temperature of the insulator while at the same time retaining its electrically insulating properties. For this purpose, the invention provides a spark plug of the aforementioned type, characterized in that the insulator comprises an annular groove. According to other features of the invention, the slot is located on the shoulder.

According to other features of the invention, the slot has a rectangular cross section. According to other features of the invention, the groove has a triangular cross section. Other features and advantages of the invention will emerge when reading the description of modalities with reference to the appended figures. Figure 1 illustrates a middle section view of a multi spark spark plug known in the art. Figure 2 illustrates a middle section view of a multi spark spark plug according to a first embodiment of the invention. Figure 3 illustrates a middle section view of a multi-sparking spark plug according to a second embodiment of the invention. Elements that are the same or similar are designated by the same reference numbers. As illustrated in FIGS. 1, 2 and 3, a multi-sparked spark plug 1 comprises two coaxial plasma generating electrodes. An outer electrode called a body 2 is intended to be grounded. Circumde an electrode interior called a central electrode 3, which is essentially cylindrical, with a symmetry axis D, which acts as a high-voltage electrode. The materials of the electrodes 2, 3 are chosen from a conductive material such as a nickel alloy. An electrically insulating block, called an insulator 4, is placed between the body 2 and the central electrode 3. The body 2, on the outer face of its lower portion closest to the cylinder head of the internal combustion engine adapted with the spark plug 1, has appropriate means of positioning, support on site and tightening of the spark plug 1 in the head of the cylinder (for example, and not in a limiting manner, as illustrated in Figure 1: a thread). The insulating material can be selected from ceramics. The insulator 4 has an annular shoulder 5 that covers the entire circular outer surface 6 of the body 2. The shoulder 5 increases the distance, passing through the gas mixture, between the central electrode 3 and the body, avoiding the creation of an arch between the central electrode 3 and the body 2. Independently of the embodiment of the invention, the shoulder 5 comprises an annular groove 8. According to a first embodiment, as illustrated in Figure 2, the annular groove 8 has a rectangular cross section. According to a second embodiment, as illustrated in Figure 3, the annular groove 8 has a triangular cross section. In this way, a thermal resistance is created in the center of the insulator and this increases the surface temperature of the insulator. The dimensions of this slot 8 are calculated in such a way that the slot can not be closed, which will result in a non-elevation of the surface temperature. Slot 8 has two parameters: its height h and its depth p. Height h adds a heat source inside the insulator. The height h varies according to the area of heat collection that alters the distribution of the heat flows that enter the insulator. The depth p of the groove 8 makes it possible to adjust the thermal resistance of the system. In fact, changes in longitudinal thermal conductivity (on the D axis) make it possible to vary the temperature gradients in the axial direction and therefore the temperature distributions.

The shape of the groove 8 is illustrated in Figures 2 and 3 but the invention is not limited in this way and other ways to increase the temperature of the insulator surface can be selected. The groove 8 creates a restriction in the insulator 4 and this way reduces its longitudinal thermal conductivity. In addition, the slot 8 increases the exposed area of insulator 4 for a smaller volume. This area is totally exposed to the flame produced by the spark plug which leads to a greater flow of heat from the flame to the insulator 4 and therefore greater heating of the insulation. Slot 8 therefore does not prevent soot deposition but increases the temperature of the insulator and allows cleaning of the soot by pyrolysis.

Claims (3)

1. CLAIMS 1. A spark plug for the internal combustion engine of a motor vehicle, with an essentially elongated shape, comprising: - two coaxial electrodes: an inner electrode with an axis called a central electrode and an outer electrode called a body that surrounds the electrode central; and - an electrically insulating block called an insulator, placed between the central electrode and the ring-shaped body and having an annular shoulder, characterized in that the insulator comprises an annular groove located in the shoulder.
2. 2. The spark plug according to claim 1, characterized in that the groove is a thermal resistance in the insulator. The spark plug according to one of the preceding claims 1 to 2, characterized in that the groove has a rectangular cross-section. . The spark plug according to one of the preceding claims 1 to 2, characterized in that the groove has a triangular cross section.