Patent Application
20170058818
The present invention relates to an air/fuel mixture control system for internal combustion engines. More particularly, the present invention relates to a system which provides automatic mixture control for internal combustion engines having fixed orifice fuel injectors. The system is particularly well suited as a modification to an existing carbureted or mechanically fuel injected aircraft engine to provide automatic air/fuel mixture control for the engine.
Internal combustion engines are used to power many different kinds of vehicles including aircraft but engines in aircraft present some unique design challenges. For example, aircraft often fly at different altitudes and hence aircraft engines encounter substantially different induction air pressures which requires means for adjusting the ratio of air to fuel in the engine's cylinders. Although there have been many improvements relating to the adjustment of the air/fuel ratio in aircraft, such as the development of precise engine monitoring systems, there remains room for further improvements, particularly with respect to setting a precise air/fuel mixture for the conditions being encountered by the engine.
Of course, it is important that aircraft engines be reliable, hence, aircraft engines are designed with fail-safe features such as dual ignition systems, electric fuel pumps to back up mechanical fuel pumps, alternate air sources, and “fail safe” systems. Fuel injection systems have replace carbureted fuel systems and carbureted engines can be modified to have fuel injected systems such as is disclosed in my earlier U.S. Pat. No. 7,290,531 Nov. 6, 2007 for “Integrated Fuel Supply System for Internal Combustion Engine” which is specifically incorporated by reference herein. However, although many piston engines for aircraft have fuel injection systems, most use mechanical fuel injectors rather than electronic fuel injectors because of cost and reliability concerns. Mechanical fuel injectors are fixed orifice designs which are reliable but provide constant flow for a given fuel pressure and do not offer automatic control of the air/fuel mixture. Electronic fuel injectors offer a means for automating air/fuel mixture control but are more expensive and require circuitry which can fail or be subject to interference leading to engine failure.
There are many existing aircraft engines which would benefit if they could be modified to have precise automatic air/fuel mixture control at a reasonable cost. Most aircraft engines operate over a wide range of atmospheric conditions which affect air density which in turn affects the ration of air to fuel going into the cylinders . During a typical flight using a typical aircraft engine, the air/fuel mixture control must be manually adjusted by the pilot several times to compensate for different air densities as well as for different operating conditions such as different altitudes or power settings. For example, take-off might be carried out using a high power throttle setting and a full rich mixture to provide power and cooling, then the power is reduced and the mixture is “leaned” slightly for climbing to a desired altitude and then the power is further reduced and the mixture is further “leaned” for cruising. Subsequent changes in altitude, power settings, etc. will require further adjustments to the mixture, either enriching or leaning the mixture. Some aircraft have engine monitoring systems to assist the pilot but the pilot must manually adjust the mixture which imposes an additional workload on the pilot and can be a distraction. Often mixture adjustments are made late and are not very precise.
A few modern aircraft have FADEC systems which accomplish the leaning procedure automatically. A FADEC system is a full authority digital electronics control consisting of a digital computer and related accessories for controlling air/fuel mixture and other aircraft engine parameters. However, FADEC systems are generally too expensive for use to retrofit existing engines and involve the use of electronic fuel injectors. It would be highly desirable to have an automatic system which would provide full authority digital electronics control of the air fuel mixture of a conventional aircraft engine which has mechanical fuel injectors.
Furthermore, there remains a need for an improved system for modification of existing aircraft engines so that they can enjoy the advantages of precise automatic adjustment of air/fuel mixture and the associated improved performance, efficiency and reliability. There also remains a need for an automatic air/fuel control system which has a “fail safe” mode and goes to an enriched mixture using the preexisting mechanical fuel system with fixed orifice fuel injector nozzles if there is a system failure so that the engine can continue to operate.
Accordingly, the present invention is directed to a system which can be adapted to a conventional certified or experimental aircraft engine designs to improve their performance and efficiency. The system of this invention provides precise automatic mixture control which reduces pilot work load, making “real time” instantly proper mixture in response to changing conditions such as changing air density and/or power settings. By ensuring that the engine runs at the proper mixture, the present system improves the durability of engines which leads to longer times between overhauls and reduced costs. The system avoids problems caused by the pilot forgetting to adjust the mixture which can lead to spark plug fouling, fuel exhaustion or engine damage due to detonation or overheating. An engine employing the system of this invention will run more smoothly, have improved efficiency and provide real time precise mixture adjustment automatically. And if the automatic air/fuel mixture control fails for some reason, the system will go to an enriched mixture allowing the pilot to manually lean the mixture if necessary.
Further understanding of the present invention will be had from the following description and claims taken in conjunction with the accompanying drawings.
A system of the present invention automatically adjusts the air/fuel mixture in the combustion chamber or chambers of an internal combustion engine having a fixed orifice fuel injector system. The system has an electronic control unit (ECU) which is programmed to automatically adjust the air/fuel mixture in each combustion chamber by controlling the amount of fuel provided to each fixed orifice fuel injector in response to sensor input in accordance with desired parameters. The system adjusts the mixture from a fuel mixture system which is set to default to run relatively rich so that if there is a failure of the automatic electronic system, there is a virtually seamless ability to revert back to the pre-existing mechanical system. The system is particularly well-suited to be retrofit onto existing aircraft engines which have mechanical fuel injectors or have carburetors but can be modified to have mechanical fuel injectors.
Broadly speaking, the present invention relates to a method and system for controlling the air/fuel mixture provided to an internal combustion engine having fixed orifice fuel injectors, commonly referred to as mechanical fuel injectors. The system is also useful for engines which have carburetors but can be modified to have mechanical fuel injectors for use in accordance with the present invention. The method and system of the present invention uses an electronic fuel control unit to automatically and precisely lean the air/fuel mixture in response to inputs from various sensors and in accordance with desired parameters by reducing the quantity of fuel fed into mechanical type fuel injectors in the cylinders of an internal combustion engine.
The system of the present invention is particularly well adapted to retrofit aircraft engines which have mechanical fuel injectors or can be modified to have mechanical fuel injectors. Mechanical fuel injectors have constant flow nozzles with fixed orifices and are usually located in the intake manifold near the intake valve of each cylinder. The air/fuel ratio of aircraft engines using mechanical fuel injectors is traditionally accomplished by the pilot manually adjusting a “mixture” control to reduce fuel pressure at the input side of each fixed orifice injector to thereby reduce the amount of fuel supplied to each cylinder at a given throttle setting. Traditional mixture adjustments are often not very timely or precise. Some aircraft engines also have a mechanical arrangement in the throttle body which makes approximate adjustments to the mixture to compensate for altitude changes. However, further manual adjustment of the mixture is required for precise mixture adjustment.
In accordance with the present invention, an electronic, automatic mixture adjustment system is provided for fuel injected engines having mechanical fuel injectors. The air/fuel mixture in each cylinder is adjusted by an electronic control unit which reduces the quantity of fuel supplied to each cylinder in response to sensor input. The present invention uses an electronic control unit or ECU to provide the advantages of a FADEC system to aircraft engines with fixed orifice fuel injectors. Furthermore, the present invention provides a system which is a “fail safe” in that it reverts back to the original mechanical fuel supply system if the electronic control system should fail.
The electronic control unit or ECU of the present system is operatively connected to function to reduce the fuel supply to each cylinder by reducing the fuel pressure to each constant orifice injector. The ECU includes a microprocessor which is programmed to compute the desired air/fuel mixture for the particular operating conditions of the engine. The operating conditions are signaled to the ECU by inputs from various sensors. If the electronic fuel control unit fails then the fuel pressure is not reduced and the engine is set to run rich under the existing mechanic al fuel supply system. The ECU reduces fuel supply by either:
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Fuel pump 26 is in fluid communication with fuel tank 28 and pumps fuel through fuel line 30 to throttle body 32. Throttle 34 is connected to throttle body 32 having throttle plate 33 and which meters fuel in a conventional manner in response to throttle position to provide metered fuel through metered fuel line 36 to fuel pressure bleed valve 14. As is conventional in the art, throttle body 32 also controls the amount of intake air, indicated by arrow 38, provided to intake manifold 40 which provides air/fuel mixture to cylinder 42 of engine 44. . It will be appreciated by those skilled in the art that, while only one cylinder 42 is shown in the Figure, it is contemplated that multiple cylinders 42 of engine 44 will be connected to intake manifold 40 as is conventional in the art.
Throttle body 32 controls manifold pressure in intake manifold 40 and provides metered fuel through fuel line 36 at a pressure to provide metered fuel at a “full rich” mixture. ECU 12 controls fuel bleed valve 14 to reduce the pressure and thereby the quantity of fuel flowing through fuel line 46 to flow divider 48 and hence to adjust the amount of fuel flowing through a plurality of injector lines 50, each of which is in fluid communication with a fuel injector 52 which injects fuel into each cylinder 42 in a conventional manner. Fuel injectors 52 are generally located near an intake valve of an associated cylinder 42. System 10 is shown as having six injectors for six cylinders but the exact number of injectors and cylinders may vary within the scope of the present invention.
It is intended that throttle body 32 be set to provide metered fuel at a pressure that would provide a “rich” mixture into cylinders 42 through injectors 52 if fuel pressure bleed valve 14 did not reduce the quantity of fuel going to the fuel injectors 52 to provide a leaner air/fuel mixture to cylinder 42. Fuel bleed valve 14 functions to either not to reduce or to reduce the fuel pressure going to flow divider 48 and hence to injectors 52. Thus, injectors 52 run at full rich or are leaned from full rich mixtures as controlled by ECU 12 controlling fuel bleed valve 14. While operating in automatic mode, throttle body 32 is always run or set to a relatively rich configuration. System 10 adjusts fuel by only reducing the amount of fuel so that if system 10 fails, fuel supplied to cylinders 42 provides a “rich” mixture.
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The fuel pressure in fuel line 346 is controlled by ECU 312 which is operatively connected to electric pulse width fuel pump 326. ECU 312 controls pulse width modulated fuel pump 326 to control the fuel pressure in fuel line 336 to thereby control the amount of fuel flowing into flow divider 348 and hence to adjust the amount of fuel flowing through each fuel injector line 350 and through each fuel injector 352 into intake manifold 340 and associated cylinder 242 of the engine (not shown but analogous to engines 44 and 144). Only one injector 352 is shown in the figure but it will be appreciated by those skilled in the art that each fuel line 350 feeds an associated injector 352. The exact number of injector fuel lines and injectors is dependent upon the number of cylinders and design of the engine. The fuel line pressure is determined by ECU 212 based on rpm and manifold pressure taking into consideration outside air pressure and temperature as well as EGTs and other desired parameters. Throttle body 332 controls the amount of air 338 provided to intake manifold 340.
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It will be appreciated by those skilled in the art that the present invention is subject to modification and variation. It is intended that such modifications and variations are considered to be within the broad scope of the invention which is intended to be limited only by the following claims. Such modifications are intended to be included herein so long as they operate in accordance with the principles of this invention.
