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  Compression ratio mode selection logic for an internal combustion engine having discrete variable compression ratio control mechanismUSPTO Application #: 20050273245Title: Compression ratio mode selection logic for an internal combustion engine having discrete variable compression ratio control mechanism Abstract: A method and system for operating an internal combustion engine. The internal combustion engine is operable in a plurality of compression ratio operating modes. The method includes determining a relationship between a base engine threshold load where the high compression and low compression provide substantially the same engine fuel consumption and engine speed. The determined nominal relationship is modified by a factor, such factor being a function of a condition under which such engine is operating, to obtain a modified relationship. The modified relationship is a function of engine speed and the condition has an effect on knock generation in such engine. The modified relationship and engine speed are used in selecting one of the plurality of compression ratio operating modes for the engine. A hysteresis load as a function of engine speed is determined and applied to the determined hysteresis load to the modified relationship to inhibit switching oscillations between a pair of the plurality of compression ratio operating modes. (end of abstract)
Agent: Ford Global Technologies, LLC. - Dearborn, MI, US Inventors: Yin Chen, Woong-chul Yang, William R. Dutcher, David K. Trumpy, In Kwang Yoo, Chris P. Glugla, Diana Brehob USPTO Applicaton #: 20050273245 - Class: 701111000 (USPTO) Related Patent Categories: Data Processing: Vehicles, Navigation, And Relative Location, Vehicle Control, Guidance, Operation, Or Indication, With Indicator Or Control Of Power Plant (e.g., Performance), Internal-combustion Engine, Digital Or Programmed Data Processor, Vibration, Roughness, Knock The Patent Description & Claims data below is from USPTO Patent Application 20050273245. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This invention relates generally to variable compression internal combustion engines. BACKGROUND [0002] As is known in the art, the "compression ratio" of an internal combustion engine is defined as the ratio of the cylinder volume when the piston is at bottom-dead-center (BDC) to the cylinder volume when the piston is at top-dead-center (TDC)--generally, the higher the compression ratio, the higher the thermal efficiency and fuel economy of the internal combustion engine. Unfortunately, compression ratios are limited by the availability of high-octane fuels needed to prevent combustion detonation or knock at high engine loads, and therefore a compression ratio is selected to operate on available fuels, and avoid knock. So-called "variable compression ratio" internal combustion engines have been developed, for example, having higher compression ratios during low load conditions and lower compression ratios during high load conditions. [0003] In an engine with a variable compression ratio mechanism, the engine compression ratio can be selected to achieve the best fuel economy of a vehicle. However, drivability and engine knock issues may occur by changing engine compression ratio while driving a vehicle in different environmental conditions. To ensure the switching of compression ratio happens with minimum knock and as smooth as possible at every possible real-world driving condition, not only must the engine operating conditions be taken into consideration but also environmental conditions have to be taken into considered in the compression ratio selection. The problem is how to take into account those factors so as to select appropriate engine compression ratio to obtain optimum fuel economy without sacrificing drivability. SUMMARY [0004] In accordance with the present invention, a method and system are provided for operating an internal combustion engine. The internal combustion engine is operable in a selected one of a plurality of compression ratio operating modes. The method includes determining a relationship between: (1) a base engine threshold load providing substantially equal engine fuel consumption for a pair of the plurality of compression ratio operating modes; and (2) engine speed. The determined relationship is modified by a factor, such factor being a function of a condition under which such engine is operating to obtain a modified relationship. The modified relationship is a function of engine speed and the condition is one having an effect on knock generation in such engine. The modified relationship and engine speed are used in selecting the one of the pair of the plurality of compression ratio operating modes for the engine. [0005] In one embodiment, the method and system include determining a hysteresis load as a function of engine speed and applying such determined hysteresis load to the modified relationship to inhibit switching oscillations between a pair of the plurality of compression ratio operating modes. [0006] In one embodiment, the factor is a function of at least one of engine coolant temperature, engine air charge temperature and barometric pressure. [0007] In one embodiment, the factor is a function of at least two of engine coolant temperature, engine air charge temperature and barometric pressure. [0008] In one embodiment, the factor is a function of coolant temperature, engine air charge temperature and barometric pressure. [0009] In one embodiment, the factor is a function of the product of correction factors for at least two of engine coolant temperature, engine air charge temperature and barometric pressure. [0010] In one embodiment, the factor is a function of the product of correction factors for coolant temperature, engine air charge temperature and barometric pressure. [0011] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. DESCRIPTION OF DRAWINGS [0012] FIG. 1 is a diagram of an internal combustion engine having variable compression ratio and a controller for selecting such ratio in accordance with the invention; [0013] FIG. 2A is a curve showing the relationship between a base cylinder air charge (load) and engine speed at a nominal air charge temperature (act), nominal engine cooling temperature (ect) and nominal barometric pressure (bp), such curve showing that for a given engine speed and cylinder air charge below the curve, the engine has minimal fuel consumption using a high compression ratio and that for a given engine speed and cylinder air charge above the curve, the engine has minimal fuel consumption using a high compression ratio. [0014] FIG. 2B is a curve showing a correction factor corr_act, to be applied to the curve of FIG. 2A as a function of deviation of the air charge temperature from the nominal air charge temperature (act) used in generating the curve in FIG. 2A; [0015] FIG. 2C is a curve showing a correction factor corr_ect, to be applied to the curve of FIG. 2A as a function of deviation of the engine cooling temperature from the nominal engine cooling temperature (ect) used in generating the curve in FIG. 2A; [0016] FIG. 2D is a curve showing a correction factor corr_bp, to be applied to the curve of FIG. 2A as a function of deviation of the barometric pressure from the nominal barometric pressure (bp) used in generating the curve in FIG. 2A; [0017] FIG. 2E is a curve showing a bias as a function of engine speed, such curve being used in the generation of a pair of curves shown in FIG. 2F and applied to prevent oscillations between the engine operating in the high and low compression ratio modes; [0018] FIG. 2F show a pair of curves used in the selection of the high or low combustion ratio operating modes for the engine of FIG. 1; [0019] FIG. 3 is a flow diagram of a process used to control the engine of FIG. 1 in accordance with the invention; [0020] FIG. 4A shows the relationship between Brake Specific Fuel Consumption (BSFC) and spark advance (SA) for an engine operating at a constant speed, barometric pressure (bp), engine air charge temperature (act) engine coolant temperature (ect), one curve therein being generated with the engine operating in the low compression mode and a second curve therein being generated with the engine operating in the high compression mode; and Continue reading... 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