Patent Publication Number: US-2019186329-A1

Title: Variable Exhaust Control System

Description:
TECHNICAL FIELD 
     The systems and methods disclosed and described in this document are directed generally toward the field of combustion engines and more specifically at high power/low noise combustion engines for aerial vehicles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view of an internal combustion engine. 
         FIG. 1B  is a front view of an internal combustion engine. 
         FIG. 2A  is a side cutaway view of a combustion chamber of an internal combustion engine. 
         FIG. 2B  is a side cutaway view of a combustion chamber of an internal combustion engine. 
         FIG. 3  is a perspective cutaway view of a combustion chamber of an internal combustion engine. 
         FIG. 4A  is a perspective interior view of an engine exhaust manifold. 
         FIG. 4B  is a perspective view of an engine exhaust manifold. 
         FIG. 5  is a perspective view of an unmanned aerial vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The apparatuses and methods disclosed and described below provide examples of how to make and use these apparatuses and methods. For ease of reading, not every possible combination or components or steps has been described together. Those having an ordinary level of skill in this art area will recognize from reading this disclosure that the components can be arranged in different combinations or that steps can be performed in parallel or in different orders in many circumstances. Additionally or alternatively, components not described below can be added to the apparatuses described and steps not described can be added to the methods without changing the core apparatuses or methods that significantly alters their structure or function. Any failure to disclose a specific combination of component parts already described or a specific ordering of steps in a method should not be taken as an indication that such combination or ordering is not possible or was not contemplated. 
       FIG. 1A  is a side view of an internal combustion engine  100 .  FIG. 1B  is a front view of the same internal combustion engine  100 . In this example, a two-stroke internal combustion engine is shown. The engine  100  can include a cylinder  102  with cooling fins  104 . A spark plug  106  can be used as an ignition source. The cylinder  102  can be mounted on a crankcase  108 . Each of the spark plug wires  110  can carry electrical energy to sparkplug  106 . A compression relief valve assembly  112  can be affixed within the cylinder  102 . Rotational power from the engine  100  can be transferred by driving components  114 , such as a transmission assembly. For ease of description, not every part of a complete internal combustion engine is shown and described. Those of ordinary skill in this art area will readily recognize from reading this disclosure that other components either can or must be present, depending upon the component and a particular implementation. 
     A typical two-stroke internal combustion engine that can use its piston to determine timing at which ports open and close exhibits symmetric port timing. Crank angle degrees for which a port is closed on upstroke are the same crank angle degrees for which the port is open on downstroke. When using a variable exhaust mechanism to change port height, timing of both port closing and opening are affected equally. 
     Timing of closing and opening events can have various effects on engine operation. On the port closing side, when a piston is rising and closing a port, an exhaust port that is located lower in a cylinder can trap contents of the cylinder earlier. Depending on scavenging characteristics of the cylinder, tuning of inlet and exhaust systems, and both speed and load of engine operation, timing of trapping of cylinder contents can bias charge purity (the ratio of fresh charge to left-over exhaust gasses from a previous power cycle) in either direction. Additionally or alternatively, earlier trapping of cylinder contents can increase a trapped compression ratio and yield higher thermal efficiency. 
     On the exhaust port opening side, combusting gasses inside the cylinder can exert force on the piston for a larger number of crank degrees, thereby performing more work and increasing thermal efficiency. Additionally, cylinder pressure is less at the time of port opening which can result in lower sound output. 
       FIG. 2A  is a side cutaway view of a combustion chamber of an internal combustion engine. The combustion chamber can include a piston head  114  and a push rod  116 . An exhaust passage  118  is shown with the compression relief valve assembly  112 . The exhaust bypass valve assembly is shown in  FIG. 2A  with valve  120  in a closed position. The piston head  114  is shown at the end of its travel with an exhaust port  122  exposed. In  FIG. 2B  the compression relief valve  120  is shown in an open position. In both  FIGS. 2A and 2B , the compression relief valve  120  can be actuated through the use of a vacuum line (not shown) that can be attached to a vacuum port  124 . It should be noted that although the compression relief valve  120  is shown only in a wholly open position in  FIGS. 2A and 2B , it can also be fully closed and partially closed to adjust adjust flow capacity through the compression relief passage. 
       FIG. 3  is a perspective cutaway view of a combustion chamber of an internal combustion engine. In this figure, a compression relief valve  126  can be actuated by an electromechanical actuator  128 , such as a solenoid switch or other suitable actuator. A compression relief passage can extend from an inlet port  130  located within a combustion chamber  129 , through a wall of the cylinder  112 , and terminate at an outlet port  134 . When the compression relief valve  126  is in an open position as shown here, exhaust fluid can travel through the compression relief passage along path  132  from the combustion chamber  129  into the exhaust passage  118  when the exhaust port  122  is closed by travel of the piston head  114 . Closing the compression relief valve  126  can restrict or wholly prevent the flow of exhaust fluid from the combustion chamber  129  into the exhaust passage  118  by at least partially blocking the outlet port  134 . It should be noted that although the compression relief valve  126  is shown only in a wholly open position in  FIG. 3 , it can also be fully closed and partially closed to adjust the size of the outlet port  134  and thereby adjust flow capacity through the compression relief passage. 
     Application of an exhaust port bypass valve can reduce noise at its source by waiting until cylinder pressure is relatively low before opening the exhaust port. This technique can reduce the pressure gradient at the time of exhaust port opening, reducing sound pressure levels and perceived noise. Energy that could have been consumer creating noise can be captured to increase efficiency of the engine. 
     The chart reproduced below as Table 1 shows sound pressure level charted against throttle position. Throttle position and engine speed at each point were held (as further described below) so that the engine was operating along a 16-14 propeller characteristic. Results are shown though 60% throttle. Above that level, the engine would be operating with both valves open and no noise benefit would be available. 
     Across the propeller curve, a consistent reduction of approximately 3.5 to 4 decibels (3.55-4 db) can be realized. If all else is constant, the overall system can be made quieter or the exhaust system can be made less restrictive to increase power. 

 
       FIG. 4A  is a perspective interior view of an engine exhaust manifold  200 . The manifold  200  can include an exhaust inlet  210 . A bypass valve  220  can control flow of exhaust fluid (depicted by flow lines  230 ). In  FIG. 4A , the bypass valve  220  is shown in a closed position. In the closed position, flow of the exhaust fluid can be directed toward a noise suppressor  240 . In  FIG. 4B , the bypass valve  220  can permit flow of the exhaust fluid to a vent  250 . The vent  250  can lead directly to outside atmosphere or to an exhaust system that bypasses the noise suppressor  240 . Those of ordinary skill in this art area will readily recognize from reading this disclosure that the noise suppressor  240  can have a different configuration or construction. Additionally, although the bypass valve  220  is shown only in fully open and fully closed positions, partially open and partially closed positions are possible. The bypass valve  220  can be operated by an electromechanical actuator, a solenoid, a vacuum system, or other suitable system. 
     A simplified method to visualize and estimate effects of variable exhaust port timing is through use of an idealized pressure versus volume (P-V) diagram of a combustion cycle shown in Table 2 below. Thermodynamic assumptions for an ideal cycle include adiabatic processes for both compression and expansion, constant pressure combustion, and scavenging at constant volume. 

 
     The shaded section of the chart represents the theoretical difference between an engine running with an exhaust port valve in a low position (the piston closes the port at V1*) versus running with the valve in the in the up position (the piston closes the port at V1). It should be noted that this is an idealized characterization that does not take into account differences in tuning or differences in scavenging between open and closed modes of operation. 
     Energy input during a combustion process and energy lost during scavenging can be calculated from temperatures and specific heats: 
         Q   c   =C   p ( T   c   −T   b ) 
         Q   s   =C   v ( T   a   −T   d )   (1)
 
     Thermal efficiency can then be defined as: 
     
       
         
           
             
               
                 
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     Using the Ideal Gas Law (PV =nRT) and defining the ratio of specific heats as 
       λ= Cp/Cv    (3)
 
     this can be written as 
     
       
         
           
             
               
                 
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                   4 
                 
               
             
           
         
       
     
     An increase in thermal efficiency with the engine running with the exhaust valve in the down position as opposed to the up position can be defined as: 
     
       
         
           
             
               
                 
                   
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                   5 
                 
               
             
           
         
       
     
     With increased compression and expansion ratios, more energy can be extracted from combustion and higher overall thermal efficiency can be achieved. A lower exhaust port can restrict the engine at higher engine speeds and can decrease the peak amount of power the engine can produce. When an engine such as this one is used in an aerial vehicle, lack of peak power can be noticed during takeoff and sprint conditions, especially when payload capacity is reached. 
     At wide-open throttle, the engine should produce more power in the lower portion of the speed range with both the bypass valve of the cylinder and the bypass valve of the exhaust with the valves shut. The engine should also produce more power in the higher portion of the speed range with both the bypass valve of the cylinder and the bypass valve of the exhaust with the valves open. This is illustrated in the chart at Table 3. 

 
     Up to approximately 6,000 revolutions per minute (rpm), valves in the closed position are shown as producing more shaft power. Above 6,000 rpm, valves in the open position are shown producing more power. Engine ports can be tuned to produce more overall peak power and variable exhaust mechanisms can be used to improve low speed torque, mitigating compromise between high and low speed power outputs. This can improve operation in conditions involving wind gusts, takeoff, and climbing over obstacles, among others. 
     The engine should run more efficiently with the exhaust bypass valve in the closed position. Test data gathered by running an engine on a propeller stand across its full speed range were used to create the graph at Table 4. Several distinct mini-map points were recorded along the propeller curve. The propeller was then removed and the engine placed on a dynamometer. Each mini-map point was recreated under controlled fuel-air ration conditions. Power and fuel flow were measured. Fuel flow was recorded using a temperature compensated, positive displacement flow measuring instrument that is accurate under low-flow conditions. Power was calculated from engine RPM and load cell-based torque measurements. 
     Output is Brake Specific Fuel Consumption (BSFC) as a function of engine speed. Along each efficiency curve, engine load varies at each RPM as required to spin the propeller. This measure of fuel consumption is normalized by engine power so engines of different displacement and type can be compared. With a 16-14 propeller, a 10% improvement in fuel consumption reduces fuel flow by approximately one gram per minute (1 g/min). 

 
       FIG. 5  is a perspective view of an unmanned aerial vehicle (UAV)  500 . For ease of discussion, a simplified diagram and discussion is provided. Those of ordinary skill in this art area will readily recognize from reading this disclosure that other components either can or must be present, depending upon the component and a particular implementation. 
     The UAV  500  can include a fuselage  510  with an airframe that has wings  520  affixed. Each of the wings  530  can include a control surface  530 . Stabilizers  540  can be affixed at the rear of the fuselage  510 . A propeller  550  can be used to provide forward thrust for the UAV  500 . The propeller  550  can be driven by the engine  100  shown and described in conjunction with earlier figures. 
     This written description sets for the best mode of carrying out the invention, and describes the invention so as to enable a person skilled in the art to make and use the invention, by presenting examples of elements recited in the claims. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples, which may be available either before or after the application filing date, are intended to be within the scope of the claims if they have elements that do not differ from the literal language of the claims, or if they have equivalent elements with insubstantial differences from the literal language of the claims.