Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1995-08-17
1997-02-04
Argenbright, Tony M.
Internal-combustion engines
Charge forming device
Fuel injection system
123416, 123527, F02D 1902, F02D 2302
Patent
active
055988253
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an Engine Control Unit (ECU) for a gas fuelled internal combustion engine, and relates particularly, though not exclusively, to an ECU for a spark ignition gas fuelled engine converted from a turbocharged diesel engine.
BACKGROUND TO THE INVENTION
In the prior art, naturally aspirated diesel engines have been converted to operate on a gaseous fuel, for example natural gas, using carburetted technology. However, problems have risen with the use of gas carburettors, particularly when using compressed natural gas (CNG) as a fuel. Furthermore, the advent of turbocharged diesel engines has created further difficulties for most engine converters as the engines are more highly stressed.
The temperature of natural gas after passing through the pressure regulators has been measured to be as low as -40.degree. C. when operating with fully charged CNG cylinders. Gas carburettors deliver fuel on a volume basis rather than a mass (or heat value) basis, and therefore there is a tendency for the carburettors to overfuel the engine. This characteristic affects both naturally aspirated and turbocharged engines with gas carburettors.
Problems also arise due to the design of the intake manifold and carburettor location which can result in some cylinders receiving more or less gas than other cylinders. This causes a tendency for some cylinders to detonate under certain load conditions. Attempts to control this by the use of detonation sensors have not been entirely successful.
A further problem with turbocharged engines is the inability to control the performance of the turbocharger since it is essentially a "free agent" which is not controlled directly by the throttle. Therefore it is also difficult to measure its performance and adjust the fuel flow and boost pressure accordingly.
The Engine Control Unit of the present invention was developed with a view to overcoming one or more of the above-noted problems in the prior art.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a method of controlling the operation of a gas fuelled internal combustion engine, the engine having a gas injector for injecting gaseous fuel into each cylinder, the method comprising the steps of: throttle position; and, full load value whereby, in use, the correct amount of gaseous fuel can be injected into each cylinder responsive to the current throttle position to achieve optimal engine performance.
Typically the method also comprises detecting the current speed of the engine and employing the current engine speed in said step of calculating the percent full load value. Preferably the percent full load value is employed, together with the current engine speed, to calculate a required manifold pressure value. The calculated value of required manifold pressure may then be employed, together with the percent full load value, in calculating a percent allowable load value.
Advantageously the position of a manifold valve in the engine intake manifold is calculated for controlling manifold pressure based on said calculated percent full load value and detected engine speed. Advantageously a pressure detector is provided for detecting the actual manifold pressure. If the engine is a turbocharged engine the position of a boost pressure control valve is preferably controlled based on a comparison of said calculated value of the required manifold pressure with the detected actual manifold pressure. Typically both said required and actual manifold pressure are absolute pressure values.
According to another aspect of the present invention there is provided an engine control unit for controlling the operation of a gas fuelled internal combustion engine, the engine having a gas injector for injecting gaseous fuel into each cylinder, the system comprising: position of the engine; based On said current throttle position, and for calculating an injector ON time for each cylinder based on said percent full load value whereby, in use, the correct amount of gaseous f
REFERENCES:
patent: 4379332 (1983-04-01), Busser et al.
patent: 5268842 (1993-12-01), Marston et al.
patent: 5351656 (1994-10-01), Teramoto et al.
Argenbright Tony M.
Transcom Gas Technologies Pty Ltd.
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