Internal-combustion engines – Igniters – Sparkers
Reexamination Certificate
2000-10-13
2002-05-07
Kwon, John (Department: 3754)
Internal-combustion engines
Igniters
Sparkers
C123S1690EB, C313S120000
Reexamination Certificate
active
06382159
ABSTRACT:
BACKGROUND OF THE INVENTION
Automatically actuated pressure relieving spark plugs have been described by Philips (U.S. Pat. No. 4,699,096) and Shifflette (U.S. Pat. No. 5,799,634). The Philips device consists of an unconventionally designed spark plug which incorporates one or more axial passages. These axial passages are outfitted with a tapered shoulder, which acts as a ball seat. A ball is forced against this seat by a helical spring which is oriented axially. Opposite the ball, the helical spring has a spring seat, which is often shown to be adjustable, via an adjusting screw. Excessive cylinder pressure, acting against the ball and its biasing spring, will unseat the ball such that pressure may be relieved upon reaching a predetermined (and adjustable) pressure. As the over-pressure is relieved, or otherwise abated (as at the end of the engine cycle stroke), the ball returns to the seated position by the biasing spring.
Manually induced keyseat style cylinder venting is also disclosed in U.S. Pat. No. 4,326,145 to Foster et. al. (Compression Relief Adapter). One design involves cutting a keyseat-style channel across the spark plug threads. This design develops a robust, pressure holding channel that terminates at a pressure transducer. This design communicates cylinder pressure upward, past the seal, but has no component that is engineered to automatically relieve cylinder pressure upon experiencing excessive temperature or pressure. As such, these designs cannot protect an engine against the deleterious effects of excessive pressure or temperature (or a combination of both) that may be encountered in a running engine.
Detonation will result in an engine at excessive values or combinations of the following: (1) static compression ratio, (2) inlet pressure or boost, (3) advanced ignition timing, (4) lean mixture, (5) low grade fuel. These will be referred to as engine parameters and causes of detonation. Detonation causes cylinder gas temperatures and pressures to greatly exceed normal levels. These are deleterious to engine components, hence unabated detonation will result in engine damage.
The Philips sparkplug reacts to excessive cylinder pressure, characteristic and indicative of detonation. But once the detonating cycle is completed, the vent port in the spark plug is reset, such that the detonating cycle can be repeated. This is, at best, a reactive strategy. Detonation is detected (by pressure which un-scats the ball from its seat) and perhaps abated to some degree by a release of cylinder pressure through the vent port. If the operator is audibly alerted to the venting event, he must then find the cause and correct it without much information available to assist him. One or more of the spark plugs were venting, but the number and location of the detonating cylinders has not been elucidated by the Philips design spark plug.
The design taught in U.S. Pat. No. 5,799,634 to Shifflette also vents in response to excessive cylinder pressure. This design, however, employs permanent deformation of a pressure containing structural member to initiate venting. Once venting is initiated, the spark plug continues to vent cylinder contents until it is repaired or replaced. This device includes multiple stages for the venting of gasses (a small passage, responsive to detonation) or for the venting of liquids (a large passage, responsive to hydrolock). As a detonating condition is developed within the engine from one of the five (5) causes, stated above, this device will respond by forming a small, permanent passage from the combustion chamber to the atmosphere.
The first of the five (5) stated causes of detonation is excessive static compression ratio. In an internal combustion engine, this ratio determines the final compressed pressure (and temperature) of the fuel air mixture. Near the end of the compression stroke, the charge is ignited by the spark. Cylinder pressures and temperatures then increase to effectively drive the piston downward, applying torque to the crankshaft. The proper combustion event is characterized by a flame front progressing through the unburned charge to oxidize the fuel at a finite rate. If the charge is ignited by the spark at excessively high pressures and temperatures the oxidation of the fuel air mixture will occur at an infinite rate. This is descriptive of an instantaneous combustion event and is termed detonation. Detonation in an internal combustion engine can produce instantaneous pressures in excess of 3000 psi, in contrast to the normal operating peak pressure of about 800 psi. Shock waves are generated and gas temperatures increase at a nearly infinite rate. The combustion chamber, valve faces, piston face and cylinder walls arc considerably cooler than the cylinder gas temperature; hence the gas transfers heat to these members at a high rate. This heat transfer to the surrounding surfaces cools the gas, which causes it to contract and decrease in pressure. The thermal energy of the gas is irreversibly lost through heat transfer to the surrounding surfaces. Shock waves, impinging on the surrounding surfaces, lose much of the kinetic energy of the gas to those surfaces. The thermal and kinetic energy of the gas is lost to irreversibilities including heat transfer and sound generation. Engine performance will suffer from detonation. The fuel's chemical potential energy is released to the cylinder gas, which in turn, irreversibly loses the energy to the surroundings. There is little of the potential energy left over to drive the piston down. The detonation, shock wave generation and abatement and heat transfer occur over only a few degrees of crankshaft revolution; the depleted cylinder gas has no more energy to convert to work.
Detonation is detrimental to engine performance, but it is disastrous to engine components. High pressures can severely overload the structural members of the engine, including the piston, connecting rod, crankshaft, bearings, cylinder head and fasteners. High heat transfer rates will cause localized component temperatures which exceed the melting temperature. Mild detonation is often evidenced by aluminum specks on the insulator of the spark plug. This is caused by the aluminum piston having undergone surface vaporization at the face, and the vaporized aluminum having condensed and solidified on all internal engine surfaces. Since the spark plug insulator is white, the gray aluminum may be easily recognized. Severe detonation will erode a hole in the piston, beat the bearings out of the crankshaft and connecting rods, and break components from structural overload.
In newer engines, detonation has been controlled quite successfully with oxygen sensors and knock sensors. Recently manufactured, well-tuned passenger cars and light trucks seldom suffer from detonation. But a large market segment is not presently served: high performance and racing applications.
Many drag racing applications do not employ oxygen and knock sensors because the technology was not built into the selected powerplant. Aftermarket high-performance accessories can expose a critical weakness of another system which is not capable of preventing detonation. An example is the installation of an aftermarket turbo- or super-charger. The increased air mass entering the cylinder during the intake stroke must be accompanied by proportionally more fuel. If the fuel system is incapable of providing adequate additional fuel, the engine will detonate. During high performance engine tuning, the engine variables are adjusted to produce maximum power. This performance maximum occurs just at the verge of detonation. Maximizing all of the first four (4) of the five (5) engine parameters, listed above, will result in maximum power. Exceeding the limit of any one of the above, or excessive combinations thereof, will result in detonation.
The high performance engine tuner must juggle the engine parameters to produce acceptable power, with a margin of error to the onset of detonation. Such sources of error could include: a drop in ambient temperature, a drop in amb
Akerman Senterfitt & Eidson, P.A.
Cesarano Michael C.
Kwon John
Vo Hieu T.
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