Patent Application
20130319377
The operation of a fuel injection system is well known in the art. Air enters the engine through the air induction system where it is measured by an air flow meter. As the air flows into the cylinder, fuel is mixed into the air by the fuel injector. Fuel injectors are arranged in the intake manifold behind each intake valve. The injectors are typically electrical solenoids that are operated by the engine control unit, or “ECU.” The ECU pulse the injectors by switching the injector ground circuit on and off to release fuel into the cylinders.
When the injector is turned on, the valve opens to spray atomized fuel at the back side of the intake valve. As fuel is sprayed into the intake airstream, it mixes with the incoming air and vaporizes. The ECU preferably causes the injector to deliver fuel to achieve an ideal air/fuel ratio for the given engine, e.g. 14.7:1 for many engines, often referred to as the stoichiometry. The precise amount of fuel delivered to the engine is a governed by ECU control. That is, the ECU determines the basic injection quantity based upon the measured intake air volume and engine speed. Depending on other engine operating conditions, injection quantity will vary. The ECU can monitor variables such as coolant temperature, engine speed, throttle angle, and exhaust oxygen content to make injection corrections that determine final injection quantity.
In order to achieve the precise balance of fuel and air, the most important characteristic in the determination is the cylinder air mass. There are a number of methods to calculate cylinder air volume in order to correctly meter injected fuel. The most common method is to measure air mass flow using an air flow meter (AFM), also known as a mass air flow (MAF) sensor, which measures the air flow into the engine. With the air flow (in mass units per time) and the engine speed, the air mass in each cylinder can be calculated by dividing the air mass flow over the engine speed, number of cylinders, and number of engine rotations per induction strokes.
Once the cylinder air mass is known, calculating the fuel injector open time to achieve a desired air-fuel ratio requires calculating the mass of fuel required (from the cylinder air mass and desired air-fuel ratio) and then looking up a reference table for the fuel injectors to determine the injector opening time to deliver the fuel mass. A common expression for the actual air-fuel ratio over the stoichiometric optimal ratio is referred to as “lambda.” The preceding two steps may be combined into one lookup table (from cylinder air mass to injector duration), or may be separated into tables indexed by fuel pressure, fuel temperature, battery voltage and other variables.
Air flow meters use a variety of methods to measure air flow, including hot wire and Karmen Vortex. These AFMs require a turbulence free air flow past the sensor in order to correctly meter the air flow. However, engine induction air flow consists of pulsations from each cylinder induction event. After-market engine modifications typically including larger duration camshafts, forced induction, high flow exhaust headers, etc., that can increase the pulsation effect in the intake system of the engine to such an extent that the AFM can no longer correctly meter the incoming air (see
The present invention utilizes a speed density method for determining the cylinder air mass using volumetric efficiency (VE) based on engine speed and manifold pressure. The VE data contain the cylinder filling efficiency for various engine speed and manifold pressure values. The manifold pressure is then measured by a manifold absolution pressure (MAP) sensor. Using the speed density has the advantage that it is much less affected by pulsation in the intake system of the vehicle, and does not require a linear air flow past a sensor in the engine intake system. For these reasons it is yields superior results to the prior injection systems that rely on AFMs for engine performance tuning (see
The present invention can be used to modify an existing ECU from a mass flow to a speed density system. Speed density is less effected by pulsations in the air flow, which lead to more accurate fuel injection determination and better performance. In order to change the operation of the ECU from mass flow to speed density, the ECU logic must be altered. First, volumetric efficiency tables with manifold pressure and engine speed indexes are added to the ECU program data. Intake air temperature compensation tables are also added to the ECU program data. During the operation of the ECU, the existing cylinder air mass to injector duration ECU code execution process is interrupted so that a new alternate program code routine is called rather than the cylinder air mass to injector duration subroutine. In one preferred embodiment, the alternate routine determines if the mass flow or speed density lookup should be performed. If using the customary mass flow, the program execution resumes with the normal cylinder air mass to injector duration subroutine. However, if the routine determines that the speed density is called for, a new subroutine is called that performs the VE table lookup and air temperature compensation, then resumes program execution at the point where the mass flow injector duration subroutine would normally return.
An overview of the system will now be examined.
Once the air flow and cylinder air mass are determined, the next step 120 is to determine if the speed density is to be used. This switch can be based on a predefined condition or on selected engine parameters such as load, engine speed, temperatures, and the like. The next step 130 is the injector duration (mass flow), which can be obtained from a lookup table 70 (
The next step 150 in the process is the injector duration. MAP and engine speed are used as indexes to lookup table 50 (
If the program code cannot be altered without requiring the program source code to be re-compiled, the program code must be patched to add the new functionality in such a way that its operation is not affected.
Existing Program Code
Modified Program Code
The altered routine changes the mass flow to injector duration original subroutine call so that it calls the replacement subroutine ‘speed_density_sub’. This subroutine then determines if speed density should be used to calculate the injector duration (step 120 above). If so, the speed density subroutine is called (steps 140, 150, and 160 above). After the speed density subroutine is executed, the register which holds the address of the mass flow subroutine is restored (lookup_table_sub above), otherwise subsequent calls using the register subroutine address will fail. If the speed density subroutine is not called, the original mass flow lookup subroutine is called, the register is restored, and the subroutine returns.
AFM=air flow meter. Also known as a MAF sensor.
IAT=intake air temperature.
ECU=engine control unit.
Lambda=the air/fuel ratio as a fraction of the stoichiometric ratio.
MAP=manifold absolute pressure. The air pressure in the intake manifold referenced to vacuum.
MAF=mass air flow.
Mass flow=one method of calculating engine fuel requirements be measuring the air mass entering the engine.
Speed density=one method of calculating engine fuel requirements by measuring manifold pressure (MAP) and engine speed, then referring to a VE (volumetric efficiency) lookup table.
