Patent ID: 8033273

Claim:
A plasma ignition system for an internal combustion engine, said system comprising: an ignition plug attached to the engine and having a center electrode, a ground electrode, and a discharge space, which is formed between the center electrode and the ground electrode; a discharge power source circuit configured to apply a high voltage to the ignition plug; a plasma generation power source circuit configured to supply a high current to the ignition plug, wherein the ignition plug is configured to put gas in the discharge space into a plasma state having high temperature and pressure thereby to ignite a fuel/air mixture in the engine, as a result of the application of the high voltage to the ignition plug by the discharge power source circuit and the supply of the high current to the ignition plug by the plasma generation power source circuit; a resistance element disposed and electrically connected along a first line between the discharge power source circuit and the center electrode; a rectifying device disposed and electrically connected along a second line between the plasma generation power source circuit and the center electrode, the first and second lines being arranged parallel to each other and with respect to the center electrode; and an element receiving portion disposed about a periphery of the center electrode, wherein the resistance element and the rectifying device are disposed in the element receiving portion; wherein at least part of the element receiving portion is placed in a plug hole formed in an engine block of the engine; the resistance element and the rectifying device are located in the plug hole of the engine block; the gas, which is put into the plasma state, is injected downward in a vertical direction from the ignition plug into a combustion chamber of the engine; a first distance from a lower end portion of the resistance element to an upper end portion of the center electrode in the vertical direction is equal to or smaller than 30 mm; and a resistance value of the resistance element is one of: (a) equal to or larger than 3 kΩ, and smaller than 15 kΩ; and (b) equal to or larger than 5 kΩ, and smaller than 15 kΩ.