Internal-combustion engines – Charge forming device – Supercharger
Reexamination Certificate
1997-05-23
2001-08-28
Koczo, Michael (Department: 3746)
Internal-combustion engines
Charge forming device
Supercharger
C060S609000, C123S562000, C123S316000, C123S432000
Reexamination Certificate
active
06279550
ABSTRACT:
BACKGROUND OF INVENTION
It is well known that as the expansion ratio of an internal combustion engine is increased, more energy is extracted from the combustion gases and converted to kinetic energy and the thermodynamic efficiency of the engine increases. It is further understood that increasing air charge density increases both power and fuel economy due to further thermodynamic improvements. The objectives for an efficient engine are to provide a high-density charge, begin combustion at maximum density and then expand the gases as far as possible against a piston.
Conventional engines have the same compression and expansion ratios, the former being limited in spark-ignited engines by the octane rating of the fuel used. Furthermore, since in these engines the exploded gases can be expanded only to the extent of the compression ratio of the engine, there is generally substantial heat and pressure in the exploding cylinder which is dumped into the atmosphere at the time the exhaust valve opens resulting in a waste of energy and producing unnecessarily high polluting emissions.
Many attempts have been made to reduce the compression ratio and to extend the expansion process in internal combustion engines to increase their thermodynamic efficiency, the most notable one being the “Miller” Cycle engine, developed in 1947.
Unlike a conventional 4-stroke cycle engine, where the compression ratio equals the expansion ratio in any given combustion cycle, the Miller Cycle engine is a variant, in that the parity is altered intentionally. The Miller Cycle uses an ancillary compressor to supply an air charge, introducing the charge on the intake stroke of the piston and then closing the intake valve before the piston reaches the end of the inlet stroke. From this point the gases in the cylinder are expanded to the maximum cylinder volume and then compressed from that point as in the normal cycle. The compression ratio is then established by the volume of the cylinder at the point that the inlet valve closed, being divided by the volume of the combustion chamber. On the compression stroke, no actual compression starts until the piston reaches the point the intake valve closed during the intake stroke, thus producing a lower-than-normal compression ratio. The expansion ratio is calculated by dividing the swept volume of the cylinder by the volume of the combustion chamber, resulting in a more-complete-expansion, since the expansion ratio is greater than the compression ratio of the engine.
In the 2-stroke engine the Miller Cycle holds the exhaust valve open through the first 20% or so of the compression stroke in order to reduce the compression ratio of the engine. In this case the expansion ratio is probably still lower than the compression ratio since the expansion ratio is never as large as the compression ratio in conventional 2-stroke engines.
The advantage of this cycle is the possibility of obtaining an efficiency higher than could be obtained with an expansion ratio equal to the compression ratio. The disadvantage is that the Miller Cycle has a mean effective pressure lower than the conventional arrangement with the same maximum pressure, but with no appreciable improvements in emissions characteristics.
The Miller Cycle is practical for engines that are not frequently operated at light-loads, because at light-load operation the mean cylinder pressure during the expansion stroke tends to be near to, or even lower than, the friction mean pressure. Under such circumstances the more-complete-expansion portion of the cycle may involve a net loss rather than a gain in efficiency.
This type of engine may be used to advantage where maximum cylinder pressure is limited by detonation or stress considerations and where a sacrifice of specific output is permissible in order to achieve the best possible fuel economy. The cycle is suitable only for engines that operate most of the time under conditions of high mechanical efficiency, that is, at relatively low piston speeds and near full load.
SUMMARY OF THE INVENTION
Briefly described, the present invention comprises an internal combustion engine system (including methods and apparatuses) for managing combustion charge densities, temperatures, pressures and turbulence in order to produce a true mastery within the power cylinder in order to increase fuel economy, power, and torque while minimizing polluting emissions. In its preferred embodiments, the method includes the steps of (i) producing an air charge, (ii) controlling the temperature, density and pressure of the air charge, (iii) transferring the air charge to a power cylinder of the engine such that an air charge having a weight and density selected from a range of weight and density levels ranging from atmospheric weight and density to a heavier-than-atmospheric weight and density is introduced into the power cylinder, and (iv) then compressing the air charge at a lower-than-normal compression ratio, (v) causing a pre-determined quantity of charge-air and fuel to produce a combustible mixture, (vi) causing the mixture to be ignited within the power cylinder, and (vii) allowing the combustion gas to expand against a piston operable in the power cylinder with the expansion ratio of the power cylinder being substantially greater than the compression ratio of the power cylinders of the engine. In addition to other advantages, the invented method is capable of producing mean effective [cylinder] pressures (“mep”) in a range ranging from lower-than-normal to higher-than-normal. In the preferred embodiments, the mean effective cylinder pressure is selectively variable (and selectively varied) throughout the mentioned range during the operation of the engine. In an alternate embodiment related to constant speed-constant load operation, the mean effective cylinder pressure is selected from the range and the engine is configured, in accordance with the present invention, such that the mean effective cylinder pressure range is limited, being varied only in the amount required for producing the power, torque and speed of the duty cycle for which the engine is designed.
In its preferred embodiments, the apparatus of the present invention provides a reciprocating internal combustion engine with at least one ancillary compressor for compressing an air charge, an intercooler through which the compressed air can be directed for cooling, power cylinders in which the combustion gas is ignited and expanded, a piston operable in each power cylinder and connected to a crankshaft by a connecting link for rotating the crankshaft in response to reciprocation of each piston, a transfer conduit communicating the compressor outlet to a control valve and to the intercooler, a transfer manifold communicating the intercooler with the power cylinders through which manifold the compressed charge is transferred to enter the power cylinders, an intake valve controlling admission of the compressed charge from the transfer manifold to said power cylinders, and an exhaust valve controlling discharge of the exhaust gases from said power cylinders. For the 4-stroke engine of this invention, the intake valves of the power cylinders are timed to operate such that charge air which is equal to or heavier than normal can be maintained within the transfer manifold when required and introduced into the power cylinder during the intake stroke with the intake valve closing at a point substantially before piston bottom dead center position or, alternatively, with the intake valve closing at some point during the compression stroke, to provide a low compression ratio. In some designs another intake valve can open and close quickly after the piston has reached the point the first intake valve closed in order to inject a temperature adjusted high pressure secondary air charge still at such a time that the compression ratio of the engine will be less than the expansion ratio, and so that ignition can commence at substantially maximum charge density. The 2-stroke engine of this invention differs in that the intake valves of the pow
Koczo Michael
Womble Carlyle Sandridge & Rice
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