Internal-combustion engines – Means to whirl fluid before – upon – or after entry into... – Having multiple oxidant inlet means
Reexamination Certificate
2001-10-24
2003-09-02
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Means to whirl fluid before, upon, or after entry into...
Having multiple oxidant inlet means
C123S432000
Reexamination Certificate
active
06612285
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to four-stroke spark-ignition engines in which internal combustion of a barrel stratified charge improves fuel efficiency.
Prior to about 1985, most passenger car engines employed one or another combustion chamber configuration with only one intake valve per cylinder. Pentroof chamber configurations with two poppet valves for inducting the engine combustion air (and most often the fuel also) into each engine cylinder have now largely superseded the combustion chamber designs with only a single intake valve. Although the classic four-valve pentroof chamber was incorporated in car racing engines as early as 1912, the unusual placement of the valves in Bristol radial aircraft engines suggests that early designers may not have been very cognizant of the motion of the bulk of the air-fuel charge filling the cylinder at the end of the intake stroke. The combustion chamber configuration of these radial engines (in separate models named Jupiter, Mercury and Pegasus) placed the two intake valves directly opposite each other on facing sides of the pentroof.
In more detail of bulk charge motion, the usual placement of both intake valves on the same side of the pentroof can be combined with appropriate design of the intake passages leading up to these two valves to thus generate a strong swirling motion about an axis perpendicular to the geometric axis of the cylinder. In a longitudinally mounted aircraft engine like the vee-twelve engines widely used in the second World War, this swirl axis parallels the axis about which the aircraft would execute a barrel roll. Barrel swirl is in fact one of the names used to describe the swirl inherent to the classic four-valve pentroof combustion chamber, but tumble is the more commonly used name (unless the engine in question is a barrel stratified charge engine). Even though it is relatively uncommon design practice, barrel swirl can be induced in single intake valve combustion chambers, as demonstrated by Laszlo Hideg in some of the combustion systems disclosed in his U.S. Pat. No. 3,318,292.
This Hideg '292 patent does include perhaps the earliest disclosure of one type of charge stratification that can easily be induced in a reciprocating engine characterized by barrel swirl. Nevertheless, distinctly segregated barrel swirl layers of fueled and unfueled mixture can more conveniently be generated simply by utilizing two intake valves per engine cylinder so that fuel can be metered into the combustion air inducted through only one of the two intake valves. Just such an arrangement for generating two-layer barrel stratification is disclosed by Mitsubishi engineers Ishida et al. in U.S. Pat. No. 5,050,557. In their U.S. Pat. No. 4,494,504, Honda engineers Yagi et al. also disclose the two-layer type of barrel stratification, including a three-valve combustion chamber of the basic type later employed by Mitsubishi in their first mass produced barrel stratified charge engine as described in SAE paper 920670. Since this particular approach positions the single spark plug in a location generally opposite the one of the intake valves which inducts fueled intake mixture, the single exhaust valve is at least moderately offset from a diametral line of symmetry and thus is doubly compromised in comparison to the flow capacity afforded by the twin exhaust valves of the classic four-valve configuration.
In FIGS. 11B and 12A of Ishida '557, the Mitsubishi inventors implicitly acknowledge that the original, centrally located spark plug is by itself insufficient when the classic pentroof combustion chamber, with its twin exhaust as well as twin intake valves, functions in a barrel stratified charge operating mode via restriction of fuel delivery to an intake passage serving just one of the two intake valves. This conclusion seems obvious in view of the fact that the central spark plug will lie on the original plane of symmetry, which now theoretically separates the fueled and unfueled barrel swirl layers. As a result, these FIGS. 11B and 12A of Ishida '557 show an additional spark plug offset nearly all the way to the cylinder wall on the side of the combustion chamber which is fueled during barrel stratified engine operation.
FIG. 12A of Ishida '557 additionally shows a separate fuel injector located in each of the two intake passages serving the four-valve combustion chamber. This configuration with independent fueling of the two intake passages, augmented by central plus offset ignition, in reality composes the basic structural arrangement for a combustion system according to the present invention. However, FIGS. 12B and 12C of Ishida '557 proceed with the Mitsubishi inventors' control strategy and thus verify that their disclosure teaches away from the present invention with its staggered spark timing schedules.
More specifically, FIG. 128 of Ishida '557 clearly reveals the central spark plug as being inoperative whenever just the one of the two barrel swirl layers enveloping the electrodes of the offset spark plug is fueled. The offset spark plug will provide consistent and reliable ignition at this time, but the much faster burning rate for the ten to ninety percent mass fraction as achieved with central ignition is of course sacrificed. FIG. 12C confirms that only the central spark plug is to be fired when both fuel injectors are activated for nominally homogeneous charge engine operation, to thereby effectively duplicate performance long available from the classic four-valve combustion chamber.
Nevertheless, the full extent to which Ishida '557 teaches away from the present invention does not become apparent until its drawing FIGS. 13A, 13B, 13C and 14 are considered. These drawing Figures show, first, that engine operation in the barrel stratified charge mode is not altered when the central spark plug is moved to an offset location symmetric to that of the original offset plug. This is true because the second spark plug, now being completely within the unfueled barrel swirl layer, still is not fired during stratified charge engine operation. Therefore, this change in spark plug location does nothing to remedy the slow burn rate experienced in the stratified charge mode. During high BMEP (brake mean effective pressure) engine operation, however, both spark plugs simultaneously ignite the the air-fuel charge which is nominally a homogeneous charge due to the activation of the individual fuel injectors in both intake passages serving the combustion chamber. In discussion specifically of their drawing FIG. 14, Ishida et al. argue that the two offset spark plug locations provide better engine performance in homogeneous charge mode than does the central-plus-offset placement of the two plug locations. This discussion includes neither the possibility of utilizing earlier ignition at the offset location in order to create more favorable conditions for ignition at the central location during stratified charge engine operation, nor the possibility of using the offset spark plug to also improve engine performance during higher BMEP engine operating conditions bordering on homogeneous charge operation.
In U.S. Pat. No. 5,379,743, Ricardo engineers Stokes et al. disclose their own version of what is in effect a barrel stratified combustion system derived from the classic four-valve pentroof combustion chamber by (1) restricting fuel delivery to the combustion air inducted through only one of the two intake valves and (2) augmenting the original centrally located spark plug with another spark plug offset nearly to the cylinder wall on the fueled side of the combustion chamber. Here again, the engineers specify that one or the other, but not both, of the two spark plugs in each combustion chamber be activated in order to accommodate various engine operating conditions. This stipulation may have added significance in the case of the Ricardo engineers because rather extensive development work was based on the Stokes '743 combustion system, as described in SAE papers 940482 and
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