Pre-Chamber Spark Plug

• US 20090309475A1
• Filed: 08/25/2009
• Published: 12/17/2009
• Est. Priority Date: 06/07/2005
• Status: Active Grant

• Current Assignee: Woodward Incorporated
• Original Assignee: Woodward Governor Company
• Inventors: Tozzi, Luigi P.
• Granted Patent: US 7,922,551 B2
• Time in Patent Office: Days
• US Class Current: 313/143
• CPC Class Codes: F02B 19/08 the chamber being of air-swirl type
• CPC Class Codes: F02B 19/12 with positive ignition engines with non-timed positive ignition, and with incandescent chambers F02B9/08
• CPC Class Codes: H01T 13/32 characterised by features of the earthed electrode
• CPC Class Codes: H01T 13/467 in parallel connection
• CPC Class Codes: H01T 13/54 having electrodes arranged in a partly-enclosed ignition chamber
• CPC Class Codes: H01T 21/02 of sparking plugs
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A method and apparatus to maximize spark plug life in pre-chamber spark plugs operating with ultra-lean mixtures and/or elevated engine BMEP is presented. Electrode erosion is reduced by spreading discharge energy over a wider surface area, maintaining fuel concentration in the spark gap, controlling gas static pressure during discharge, and maintaining safe electrode temperature. Energy is spread via a swirling effect created by periphery holes in an end cap, resulting in a lower specific energy discharge at the electrodes. Divergently configured electrodes reduce the spark voltage at high operating pressures and the energy required for ignition. The flow field generated at the electrodes prevents electrical shorts due to water condensation and avoids misfire. The center electrode insulation provides an effective heat transfer path to prevent electrode overheating and pre-ignition. The volume behind the electrodes provides a volume for burnt products from previous combustion cycles and leads to more reliable ignition.

Claims

1. A method to extend the life of a pre-chamber spark plug comprising the steps of:

providing a metal shell;

arranging electrodes within the metal shell in a divergent configuration;

providing a volume behind a gap of the electrodes for burnt products from a previous ignition cycle; and

configuring an endcap with a plurality of induction holes to generate non-magnetic flow field forces that act upon an electrical arc within a pre-combustion chamber with sufficient force to cause the electrical arc to move, thereby distributing electrical energy over an area of the electrode surface greater than the area over which energy would be distributed in the absence of the non-magnetic flow field;

wherein the endcap is mounted to the metal shell such that the endcap and metal shell substantially define the pre-combustion chamber; and

wherein each of the induction holes has a hole axis that is substantially perpendicular to a longitudinal axis of the pre-chamber spark plug.

2. The method of claim 1, wherein the endcap includes four induction holes.

3. The method of claim 2, further comprising configuring the plurality of induction holes such that no hole axis of the four induction holes intersects the longitudinal axis of the pre-chamber spark plug.

4. The method of claim 2, wherein the four hole axes lie in a plane substantially perpendicular to the longitudinal axis of the pre-chamber spark plug.

5. The method of claim 4, wherein any one hole axis is parallel to another hole axis and perpendicular to two other hole axes.

6. The method of claim 1, wherein the endcap further includes an induction hole having a hole axis that is parallel to the longitudinal axis of the center electrode.

7. The method of claim 1, wherein the metal shell and endcap are sized such that the endcap can be located within a combustion chamber of an engine when the pre-chamber spark plug is installed in the engine.

8. The method of claim 1, wherein the plurality of induction holes is configured to create a flow field velocity of 5 to 30 meters per second in the pre-combustion chamber.

9. The method of claim 1, wherein the step of providing a volume behind a gap of the electrodes further comprises providing a heat transfer path to prevent overheating of at least one of the electrodes.

10. The method of claim 1, wherein the step of arranging the electrodes within the metal shell in a divergent configuration comprises arranging the electrodes to have a minimum spark gap of 0.005 to 0.010 inches.

11. The method of claim 10, wherein the step of arranging the electrodes within the metal shell in a divergent configuration further comprises arranging the electrodes to have a maximum spark gap of 0.03 to 0.05 inches.

12. The method of claim 1, wherein the step of arranging the electrodes within the metal shell in a divergent configuration comprises arranging at least one lobe-shaped electrode within the metal shell in a divergent configuration.

13. The method of claim 1, further comprising providing ceramic insulation between a center electrode and the metal shell, and wherein the step of providing a volume behind a gap of the electrodes for burnt products comprises configuring the ceramic insulation to thermally insulate an electrode.

14. The method of claim 1, wherein the step of providing a volume behind a gap of the electrodes comprises providing a volume according to the equation: