Internal-combustion engines – Charge forming device – Auxiliary control of carburetor fuel metering
Reexamination Certificate
1997-10-09
2001-02-13
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Auxiliary control of carburetor fuel metering
C123S0740AP, C261SDIG006
Reexamination Certificate
active
06186117
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates to a new or improved fuel supply system for an internal combustion engine, to a manifold specifically designed for use in such system, to a kit of parts to enable retrofitting of such system in an existing engine and to a method of controlling the fuel supply to achieve the improved response to a number of environmental conditions.
B. Description of the Prior Art
In internal combustion engines having carburetor controlled fuel supplies, as is typical of engines used in vehicles such as snowmobiles and personal watercraft, it is well known that the rate of fuel flow in a fixed or variable venturi carburetor is dependent upon the pressure differential existing in the fuel system between the venturi and e.g. a fuel bowl (otherwise called a float bowl or a float chamber). In a conventional float bowl carburetor the pressure differential is measured between the pressure in the fluid float chamber (which is normally atmospheric pressure) and the pressure at the discharge orifice of the fuel metering system which is normally located in or adjacent the venturi in the induction passage.
For optimum combustion, the relationship between the mass air flow and the mass fuel flow delivered to the engine by the carburetor should be kept constant, and to achieve this the carburetor employs either a fixed or a variable venturi (or some equivalent structure) such that when air velocity in the induction passage is increased a pressure reduction (often called a vacuum) is created in the venturi zone. This pressure reduction creates a pressure differential between the induction passage and the fuel in the float chamber, causing fuel to be drawn into the induction passage at a flow rate that is proportional to the pressure differential.
The amount or level of the venturi underpressure or vacuum is mainly a function of air velocity through the induction passage, but as is well understood, at a given velocity, the mass air flow rate is affected by air density which in turn is mainly a function of barometric pressure and air temperature.
For example for a snowmobile operating at an altitude of 2000 meters, a given air velocity in the carburetor induction passage will deliver a very much reduced mass air flow to the engine as compared to the same air velocity when the snowmobile in operating at seal level, this being due to the reduced barometric pressure and air density at altitude. However since fuel flow is mostly a function of the venturi underpressure or vacuum, the engine when operating at altitude would tend to be supplied with a mixture that is over rich in fuel. This phenomenon is well understood. For example U.S. Pat. No. 5,021,198 Bostelmann discloses a carburetor system that is designed to adjust the fuel flow to maintain the mass air fuel mixture ratio constant despite changes in altitude.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a fuel supply control system and method which without the use of a choke or the like is adapted to adjust the air fuel mass flow ratio to provide a fuel enriched mixture in certain situations, e.g. for starting a cold engine.
The invention provides a method for modifying the air/fuel mixture ratio supplied to an internal combustion engine of a vehicle to achieve a constant mass flow ratio in spite of changes in atmospheric temperature conditions, said fuel being drawn from a float chamber into a venturi in a carburetor, wherein it is mixed with air before being delivered into the engine, said method comprising: (a) sensing the atmospheric temperature in the vicinity of said vehicle and generating a signal indicative of said sensed temperature; (b) supplying said signal to a control unit; (c) operating said control unit to modify pressure within said float chamber thus varying the pressure differential between the venturi and said float chamber so that the mass flow ratio of said mixture remains substantially constant.
The engine preferably also includes an air pressure sensor and an engine temperature sensor both of which feed signals to the electronic control unit which signals are also used in modifying the fuel/air ratio of the mixture.
From another aspect the invention provides a method for reducing the air/fuel mixture ratio supplied to an internal combustion engine in cold start situations, said fuel being drawn from a float chamber into a venturi in a carburetor where it is mixed with air and delivered into the engine, said method comprising: (a) sensing the temperature of the engine and generating a signal when said temperature is below a normal operating temperature range; (b) supplying said signal to a control unit; (c) operating said control unit to elevate the pressure within said float chamber to increase fuel flow into the venturi and thus increase the fuel content of said mixture during periods when said signal is received.
The engine crankcase chamber is subject to pressure fluctuations during operation of the engine, and this chamber can be utilized as the pressure generator by including a line communicating the crankcase chamber to the control unit. At low speeds of rotation of the engine corresponding to cranking thereof this line will provide a sufficient flow of pressurized air. However at higher engine speeds and throttle openings the pressure will be insufficient so that an external pump may be required. Preferably such pump is a mechanical pump constructed to be driven by pressure pulse in the crankcase chamber. The pump is provided for delivering the flow of pressurized air at higher speeds of operation of the engine, i.e. at speeds of idling and above. Alternatively, the pressure generator may be a separate pump, for example electrically driven from a vehicle battery.
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patent: 4216174 (1980-08-01), Szott
patent: 4556081 (1985-12-01), Sugiura
patent: 4813391 (1989-03-01), Geyer
patent: 5021198 (1991-06-01), Bostelmann
patent: 5879595 (1999-03-01), Holtzman
Bombardier Inc.
Miller Carl S.
Pillsbury Madison & Sutro LLP
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