Patent Publication Number: US-11649750-B2

Title: Methods and systems for an exhaust muffler system

Description:
FIELD 
     The present description relates generally to methods and systems for an exhaust muffler system with multiple inlets of different diameters. 
     BACKGROUND/SUMMARY 
     Vehicle mufflers receive exhaust gases from an engine, such as an internal combustion engine or a diesel engine, for the purpose of attenuating the noise associated with the moving exhaust gas stream. Mufflers may include a plurality of tubes and sound attenuating chambers formed by baffles and/or chambers within a shell. The walls of the tubes may include small openings to attenuate sound waves and reduce noise levels surrounding the vehicle. Due to regulations, a higher level of noise attenuation may be desired in certain regions. 
     Various approaches are provided for mufflers attenuating and regulating exhaust noise. In one example, as shown in U.S. Patent Application No. 2009/0229913, Tonietto et al. teaches a dual mode exhaust muffler for the engine of a vehicle that may be operated in a quiet mode and a loud mode. The muffler may include three tubes with two tubes including structures such as openings for noise attenuation. A valve may control exhaust flow entering the tubes with attenuating structures. In a desired quiet mode, the valve opening may be adjusted to flow exhaust through each of the three tubes to attain the desirable exhaust sound attenuation. Whereas, in the loud mode, the valve may be actuated to a position to block exhaust gas from flowing through the attenuating tubes, thereby maintaining the higher noise levels of exhaust gas exiting the vehicle via the tailpipe. 
     However, the inventors herein have recognized potential issues with such systems. As one example, inclusion of a plurality of attenuating structures in a muffler may cause an increase in exhaust backpressure which may adversely affect engine power. In a smaller vehicle, the size of the muffler and the positioning options for muffler inlets and outlets may be limited, thereby making noise attenuation along with exhaust backpressure reduction challenging. Exhaust tuning valves may be used for adjusting noise level of exhaust exiting the vehicle; however, due to packaging constraints, the tuning valve at the inlet of the muffler reduces the tuning flexibility. The proximity of the muffler to the exhaust manifold, turbine, and catalysts may cause the temperature of the muffler to increase which may adversely affect the attenuation efficiency of the muffler. 
     In one example, the issues described above may be addressed by a method for an engine, comprising: a muffler system including two or more sets of inlet pipes to a muffler, each set of inlet pipes in the two or more sets including pipes of different diameters, two or more valves controlling exhaust flow through the pipes of different diameters, and each set of inlet pipes leading to one of two or more outlet pipes of the muffler system. In this way, by adjusting exhaust flow path through tubes of different diameters, attenuation of exhaust noise may be improved without a significant increase in exhaust backpressure. 
     As one example, a muffler system may include two sets of inlet pipes with the smaller diameter pipe opening to a baffled chamber within the muffler and the larger diameter pipe directly coupling to an outlet pipe via outlet perforations. Each set of inlet pipes may fluidically couple to the exhaust manifold of an engine bank. A valve may be positioned in the larger diameter pipe downstream of the smaller diameter pipe to adjust exhaust gas flow through the smaller diameter pipe and the larger diameter pipe. If a quiet mode is elected, the valve may be closed and the exhaust may be routed via the smaller diameter pipe, a center chamber of the muffler, baffle perforations, an outer chamber of the muffler, outlet perforations, and the outlet pipe. Whereas, if the quiet mode is not selected, the valve may be maintained in an open position and exhaust may flow through the larger diameter pipe, the outlet perforations, and the outlet pipe. 
     In this way, by flowing exhaust through pipes of different diameters, attenuation of exhaust noise may be increased while reducing exhaust backpressure. In the quiet mode, by flowing exhaust through the smaller diameter pipe and then expanding the gas in the center chamber, higher attenuation may be attained. Exhaust flow through the baffle perforations and outlet perforations may add acoustical impedance which may further attenuate the noise. The technical effect of operating the muffler system with the valve open during conditions when the quiet mode is not desired is that the smaller diameter pipe may function as a low frequency Helmholtz tuner which may improve the acoustics of the system without significantly affecting backpressure. By flowing the exhaust through the outlet perforations, exhaust sound attenuation may be achieved without sacrificing engine power. By distributing exhaust flow over multiple inlet pipes and muffler chambers, muffler durability may be improved due to reduced stress on each pipe and muffler end cap. Overall, a balance may be attained between sound attenuation and exhaust back pressure reduction, thereby improving operator satisfaction and fuel efficiency. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically shows an engine with a muffler system. 
         FIG.  2    schematically shows a V-engine with a dual bank exhaust system leading to the muffler system. 
         FIG.  3 A  schematically shows the muffler system with multiple inlet pipes operating in a first mode. 
         FIG.  3 B  schematically shows the muffler system with multiple inlet pipes operating in a second mode. 
         FIG.  4    shows a flow chart of an example method for operating the muffler system. 
         FIG.  5    shows an example operation of the muffler system. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for an exhaust muffler system with multiple inlet pipes of different diameters.  FIGS.  1  and  2    show an engine system with two cylinder banks with each bank leading to a muffler system. The muffler system with multiple inlet pipes is shown in  FIGS.  3 A-B . An engine controller may be configured to perform control routines, such as the example routine of  FIG.  4   , to adjust operation of the muffler system based on a desired exhaust noise level. An example operation of the muffler system is shown in  FIG.  5   . 
     Turning to  FIG.  1   , a schematic diagram of one cylinder of multi-cylinder engine  10 , which may be included in a propulsion system of a vehicle  5 , is shown. Vehicle  5  may be configured for on-road propulsion. Engine  10  may be controlled at least partially by a control system including controller  12  and by input from a vehicle operator  132  via an input device  130 . In this example, input device  130  includes an accelerator pedal and a pedal position sensor  134  for generating a proportional pedal position signal PP. Combustion chamber  30  (also termed, cylinder  30 ) of engine  10  may include combustion chamber walls  32  with piston  36  positioned therein. Piston  36  may be coupled to crankshaft  40  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  40  may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system (not shown). Further, a starter motor may be coupled to crankshaft  40  via a flywheel (not shown) to enable a starting operation of engine  10 . 
     Combustion chamber  30  may receive intake air from intake manifold  44  via intake passage  42  and may exhaust combustion gases via exhaust manifold  48 . Exhaust manifold  48  may include a temperature sensor  72 . Intake manifold  44  and exhaust manifold  48  can selectively communicate with combustion chamber  30  via respective intake valve  52  and exhaust valve  54 . In some embodiments, combustion chamber  30  may include two or more intake valves and/or two or more exhaust valves. 
     Fuel injector  66  is shown arranged in intake manifold  44  in a configuration that provides what is known as port injection of fuel into the intake port upstream of combustion chamber  30 . Fuel injector  66  may inject fuel in proportion to the pulse width of signal FPW received from controller  12  via electronic driver  68 . Fuel may be delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber  30  may alternatively or additionally include a fuel injector coupled directly to combustion chamber  30  for injecting fuel directly therein, in a manner known as direct injection. 
     Intake passage  42  may include a throttle  62  having a throttle plate  64 . In this particular example, the position of throttle plate  64  may be varied by controller  12  via a signal provided to an electric motor or actuator included with throttle  62 , a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle  62  may be operated to vary the intake air provided to combustion chamber  30  among other engine cylinders. The position of throttle plate  64  may be provided to controller  12  by throttle position signal TP. Intake passage  42  may include a mass air flow sensor  120  coupled upstream of throttle  62  for measuring the flow rate of aircharge entering into the cylinder through throttle  62 . Intake passage  42  may also include a manifold air pressure sensor  122  coupled downstream of throttle  62  for measuring manifold air pressure MAP. 
     In some embodiments, a compression device, such as a turbocharger or supercharger, including at least a compressor (not shown), may be arranged along intake manifold  44 . For a turbocharger, the compressor may be at least partially driven by a turbine (not shown), for example via a shaft, the turbine arranged along exhaust manifold  48 . For a supercharger, the compressor may be at least partially driven by the engine and/or an electric machine, and may not include a turbine. 
     Ignition system  88  can provide an ignition spark to combustion chamber  30  via spark plug  92  in response to spark advance signal SA from controller  12 , under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber  30  or one or more other combustion chambers of engine  10  may be operated in a compression ignition mode, with or without an ignition spark. 
     Exhaust gas sensor  126  is shown coupled to exhaust passage  58  upstream of emission control device  70 . Sensor  126  may be any suitable sensor for providing an indication of exhaust gas air-fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a narrow band (older systems treat as a two-state device) oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Emission control device  70  is shown arranged along exhaust passage  58  downstream of exhaust gas sensor  126 . The emission control device  70  may be a three-way catalyst (TWC), SCR catalyst, NOx trap, a gasoline particulate filter (GPF), a combination of two or more of these devices, or one of various other emission control devices. 
     Further, engine  10  may include an exhaust gas recirculation (EGR) system (not shown) to help lower NOx and other emissions. The EGR system may be configured to recirculate a portion of exhaust gas from the engine exhaust to the engine intake. In one example, the EGR system may be a low pressure EGR system wherein exhaust gas is recirculated from downstream of gasoline emission control device  70  to the engine intake. 
     The exhaust passage  58  may also include a muffler  71 . The muffler  71  may attenuate exhaust noise. A lower level of exhaust noise may sometimes be desired by the operation such as based on neighborhood of travel (proximal to school) or time of day (early morning). In one example, an operator may select a quiet mode of operation of the muffler  71  via an input to a dashboard console (such as touchscreen on a human machine interface) or a smart device (such as smart phone, tablet) communicatively connected to the engine control system. Based on the exhaust sound level selected, the controller may adjust a valve of the muffler  71  to route exhaust through a desired flow path corresponding to the selected sound level. 
     An exhaust passage receiving exhaust gas from an engine bank may lead to one of two or more sets of inlet pipes. Each set of inlet pipes in the two or more sets include a first inlet pipe and a second inlet pipe, a diameter of the first inlet pipe different from a diameter of the second inlet pipe. In one example, the diameter of the first inlet pipe may be smaller than the diameter of the second inlet pipe. In another example, the diameter of the first inlet pipe may be larger than the diameter of the second inlet pipe. The exhaust passage from the engine bank may bifurcate to form the first inlet pipe and the second inlet pipe. The first inlet pipe may lead to a center chamber of the muffler  71 , the muffler  71  including a center chamber positioned between a first outer chamber and a second outer chamber. The second inlet pipe may directly lead to an outlet pipe of the muffler  71 . The center chamber of the muffler  71  may be separated from the first outer chamber by a first baffle and the center chamber may be separated from the second outer chamber by a second baffle, each of the first baffle and the second baffle including baffle perforations. The second inlet pipe may be fluidically coupled to one of the first outer chamber and the second outer chamber via outlet perforations. A valve may be positioned downstream of a junction of the first inlet pipe and the second inlet pipe and upstream of the outlet perforations to regulate exhaust gas flow through each of the first inlet pipe and the second inlet pipe. When the valve is actuated to an open position, in the open position of each valve, exhaust gas from the exhaust passage may be routed via each of the second inlet pipe, the outlet perforations, and the outlet pipe. When the valve is actuated to a closed position, exhaust gas from the exhaust passage may be routed via each of the first inlet pipe, the center chamber, the baffle perforations, one of the first outer chamber and the second outer chamber, outlet perforations, the second inlet pipe, and the outlet pipe. Each of the baffle perforations and outlet perforations may include a plurality of individual holes. The muffler  71  is further discussed in relation to  FIGS.  2  and  3   . 
     Vehicle  5  may be a hybrid vehicle with multiple sources of torque available to one or more vehicle wheels  55 . In other examples, vehicle  5  is a conventional vehicle with only an engine, or an electric vehicle with only electric machine(s). In the example shown, vehicle  5  includes engine  10  and an electric machine  53 . Electric machine  53  may be a motor or a motor/generator. Crankshaft  40  of engine  10  and electric machine  53  are connected via a transmission  57  to vehicle wheels  55  when one or more clutches  56  are engaged. In the depicted example, a first clutch  56  is provided between crankshaft  40  and electric machine  53 , and a second clutch  56  is provided between electric machine  53  and transmission  57 . Controller  12  may send a signal to an actuator of each clutch  56  to engage or disengage the clutch, so as to connect or disconnect crankshaft  40  from electric machine  53  and the components connected thereto, and/or connect or disconnect electric machine  53  from transmission  57  and the components connected thereto. Transmission  57  may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various manners including as a parallel, a series, or a series-parallel hybrid vehicle. 
     Electric machine  53  receives electrical power from a traction battery  59  to provide torque to vehicle wheels  55 . Electric machine  53  may also be operated as a generator to provide electrical power to charge battery  59 , for example during a braking operation. 
     Controller  12  is shown in  FIG.  1    as a microcomputer, including microprocessor unit  102 , input/output ports  104 , an electronic storage medium for executable programs and calibration values shown as read only memory  106  in this particular example, random access memory  108 , keep alive memory  110 , and a data bus. Controller  12  may receive various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor  120 ; engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a profile ignition pickup signal (PIP) from Hall effect sensor  118  (or other type) coupled to crankshaft  40 ; throttle position (TP) from a throttle position sensor; position of the active exhaust valve  75  from position sensor  76 ; exhaust temperature in the exhaust manifold from sensor  72 , and absolute manifold pressure signal, MAP, from sensor  122 . Engine speed signal, RPM, may be generated by controller  12  from signal PIP. 
     Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor can give an indication of engine torque. Further, this sensor, along with the detected engine speed, can provide an estimate of charge (including air) inducted into the cylinder. In one example, sensor  118 , which is also used as an engine speed sensor, may produce a predetermined number of equally spaced pulses for each revolution of the crankshaft. Further, the controller  12  may receive one or more of a crankshaft acceleration signal from a crankshaft acceleration sensor, a vehicle wheel speed signal from a wheel speed sensor, steering movements from a steering sensor, and angular velocity and slip-angle of a yaw sensor. Additionally, controller  12  may communicate with a cluster display device, for example to alert the driver of faults in the engine or exhaust system. Storage medium read-only memory  106  can be programmed with computer readable data representing instructions executable by processor  102  for performing the methods described below as well as other variants that are anticipated but not specifically listed. 
     The controller  12  receives signals from the various sensors of  FIG.  1    and employs the various actuators of  FIG.  1    to adjust engine operation based on the received signals and instructions stored on a memory of the controller. For example, adjusting engine sound level may include actuating the active exhaust valve  75  to adjust the amount of exhaust gas flowing through the active exhaust valve  75 . 
     A navigation system  54  may be coupled to the controller  12  to determine a real-time location of the vehicle  5  at any given time (such as during vehicle travel) via a global positioning satellite (GPS) system. The navigation system may be connected to an external server and/or network cloud via wireless communication. The controller  12  may be coupled to a wireless communication device for direct communication of the vehicle  5  with a network cloud. Using the wireless communication device and the navigation system  54 , the controller  14  may retrieve road conditions, traffic conditions, elevation, and other travel conditions. 
     Turning to  FIG.  2   , an example version of engine  10  that includes multiple cylinders arranged in a V configuration (e.g., V-Engine) is shown as V-engine  202 . Engine  202  includes a plurality of combustion chambers or cylinders. The plurality of cylinders of engine  202  are arranged as groups of cylinders on distinct engine banks. In the depicted example, engine  202  includes two engine cylinder banks  30 A,  30 B. Thus, the cylinders are arranged as a first group of cylinders (four cylinders in the depicted example) arranged on first engine bank  30 A and label A 1 -A 4 , and a second group of cylinders (four cylinders in the depicted example) arranged on second engine bank  30 B labeled B 1 -B 4 . It will be appreciated that while the example depicted in  FIG.  1    shows a V-engine with cylinders arranged on different banks, this is not meant to be limiting, and in alternate examples, the engine may be an in-line engine with all engine cylinders on a common engine bank. 
     Engine  202  can receive intake air via an intake passage  42  communicating with branched intake manifold  44 A,  44 B. Specifically, first engine bank  30 A receives intake air from intake passage  42  via a first intake manifold  44 A while second engine bank  30 B receives intake air from intake passage  142  via second intake manifold  44 B. While engine banks  30 A,  30 B are shown with a common intake manifold, it will be appreciated that in alternate examples, the engine may include two separate intake manifolds. The amount of air supplied to the cylinders of the engine can be controlled by adjusting a position of throttle  62  on throttle plate  64 . Additionally, an amount of air supplied to each group of cylinders on the specific banks can be adjusted by varying an intake valve timing of one or more intake valves coupled to the cylinders. 
     Combustion products generated at the cylinders of first engine bank  30 A are directed to one or more emission control devices in first exhaust manifold  48 A where the combustion products are treated before being vented to the atmosphere. A first emission control device  70 A is coupled to first exhaust manifold  48 A. First emission control device  70 A may include one or more exhaust catalysts. Exhaust gas generated at first engine bank  30 A is treated at emission control device  70 A. 
     Combustion products generated at the cylinders of second engine bank  30 B are exhausted to the atmosphere via second exhaust manifold  48 B. A second emission control device  70 B is coupled to second exhaust manifold  48 B. Second emission control device  70 B may include one or more exhaust catalysts. Exhaust gas generated at second engine bank  30 B is treated at emission control device  70 B. 
     While  FIG.  2    shows each engine bank coupled to respective underbody emission control devices, in alternate examples, each engine bank may not be coupled to respective emission control devices  70 A,  70 B but to a common underbody emission control device positioned downstream in a common exhaust passageway. 
     Various sensors may be coupled to engine  202 . For example, a first exhaust gas sensor  126 A may be coupled to the first exhaust manifold  48 A of first engine bank  30 A, upstream of first emission control device  70 A while a second exhaust gas sensor  126 B is coupled to the second exhaust manifold  48 B of second engine bank  30 B, upstream of second emission control device  70 B. In further examples, additional exhaust gas sensors may be coupled downstream of the emission control devices. Still other sensors, such as temperature sensors, may be included, for example, coupled to the underbody emission control device(s). As elaborated in  FIG.  2   , the exhaust gas sensors  126 A and  126 B may include exhaust gas oxygen sensors, such as EGO, HEGO, or UEGO sensors. Various temperature sensors may be included in the exhaust system of engine  202 , including exhaust manifold temperature sensors  72 A and  72 B (adapted to measure temperature of exhaust gas within the exhaust manifold to which they are coupled). In alternate embodiments, the exhaust system may not include some or all of these temperature sensors, and instead, temperatures may be modeled based on other engine operating conditions, as explained further herein. 
     The first exhaust manifold  48 A may lead to a first exhaust passage  58 A via the first emission control device  70 A, and the second exhaust manifold  48 B may lead to a second exhaust passage  58 B via the second emission control device  70 B. The first exhaust passage  58 A may bifurcate into a first inlet pipe  208  and a second inlet pipe  212  leading to the muffler  71 . The second exhaust passage  58 B may bifurcate into a third inlet pipe  206  and a fourth inlet pipe  210  leading to the muffler  71 . The diameter of the first inlet pipe  208  and the second inlet pipe  206  may be smaller relative to the diameter of the second inlet pipe  212  and the fourth inlet pipe  210 . A first outlet pipe  216  and a second inlet pipe  214  may be coupled to the muffler  71  to flow exhaust from the muffler  71  out to the tailpipe and the atmosphere. A method of operation of the muffler  71  is elaborated with reference to  FIG.  4   . 
     In one example, the engine may include a single engine bank and exhaust from the single engine bank may be routed to the muffler via two inlet pipes (such as the first inlet pipe  208  and the second inlet pipe  212 ). Exhaust may flow out of the muffler  71  via a single outlet pipe  216  (such as single outlet pipe  216 ). 
       FIGS.  3 A-B  show a muffler system  301  including a muffler  302 . In one example, muffler  302  may be the muffler  71  in  FIGS.  1 - 2   . On one side, a first exhaust passage  324  (originating from a first engine bank) may bifurcate into a first inlet pipe  326  and a second inlet pipe  327  leading to the muffler  302 . On another side, a second exhaust passage  304  (originating from a second engine bank) may bifurcate into a third inlet pipe  306  and a fourth inlet pipe  307  leading to the muffler  302 . Each of the first inlet pipe  326  and the second inlet pipe  327  may enter the muffler from the one side, and each of the third inlet pipe  306  and the fourth inlet pipe  307  may enter the muffler  302  from the other side. The first and second inlet pipes may extend parallel to each other while the third and fourth inlet pipes extend parallel to each other. In one example, each of the inlet pipes may have a circular cross-section. Each of the first inlet pipe  326  and the third inlet pipe  306  may have a smaller diameter relative to the diameter of the second inlet pipe  327  and the fourth inlet pipe  307 . In one example, the diameter of the first inlet pipe  326  (as shown by D 1  in  FIG.  3 A ) and the third inlet pipe  306  (as shown by D 1  in  FIG.  3 A ) may be 2 inches (e.g., 5 cm) while the diameter of each of the second inlet pipe  327  (as shown by D 2  in  FIG.  3 A ) and the fourth inlet pipe  307  (as shown by D 2  in  FIG.  3 A ) may be 2.75 inches (e.g., 7 cm). In another example, the cross-section of each of the inlet pipes may be oval, square, rectangular, and any other shape. As an example, the area of cross-section of the second inlet pipe  327  and the fourth inlet pipe  307  may be 25-50% larger than that of the first inlet pipe  326  and the third inlet pipe  306 . 
     The muffler  302  may include a center chamber  316 , a first outer chamber  314 , and a second outer chamber  312 . The center chamber  316  may be separated from the first outer chamber  314  via a first baffle  320  while the center chamber  316  may be separated from the second outer chamber  312  via a second baffle  318 . The first baffle  320  may include first baffle perforations  311  to allow fluidic communication between the center chamber  316  and the first outer chamber  314 . The second baffle  318  may include second baffle perforations  309  to allow fluidic communication between the center chamber  316  and the second outer chamber  312 . In one example, each of the first baffle perforations and the second baffle perforations may include 36 individual perforations with each perforation having a diameter of 5 mm. 
     Each of the first inlet pipe  326  and the third inlet pipe  306  may open to the center chamber  316 . A first valve  334  may be coupled to the second inlet pipe  327  to regulate exhaust flow through the second inlet pipe  307 . A second valve  336  may be coupled to the fourth inlet pipe  307  to regulate exhaust flow through the fourth inlet pipe  307 . 
     First outlet perforations  329  may allow fluidic communication between the first outer chamber  314  and the second inlet pipe  327 . Second outlet perforations  310  may allow fluidic communication between the second outer chamber  312  and the fourth inlet pipe  307 . The first outlet perforations  329  and the second outlet perforations  310  may be positioned downstream of the first valve  334  and the second valve  336  respectively. In one example, each of the first outlet perforations  329  and the second outlet perforations  310  may include 194 individual perforations (holes) with each perforation having a diameter of 5 mm. Downstream of the first outlet perforations  329 , the second inlet pipe  327  may lead to a first outlet pipe  328 , and downstream of the second outlet perforations  310 , the fourth inlet pipe  327  may lead to a second outlet pipe  308 . Each of the first outlet pipe  328  and the second outlet pipe  308  may exit the muffler from the top of the muffler  302 . 
       FIG.  3 A  shows an example  300  operation of the muffler system  301  in a first mode. The first mode may also be termed as the engine power priority mode as during operation in this mode, exhaust back pressure is reduced thereby improving engine power output. In the first mode, each of the first valve  334  and the second valve  336  may be in their respective open positions. Exhaust gas from a first engine bank may flow into the muffler system via the first exhaust passage  324  while exhaust gas from a second engine bank may flow into the muffler system via the second exhaust passage  304 . Due to the open position of the first valve  334 , the exhaust gas entering through the first exhaust passage  324  may flow through the second inlet pipe  327  unobstructed. Likewise, due to the open position of the second valve  336 , the exhaust gas entering through the second exhaust passage  304  may flow through the fourth inlet pipe  307  unobstructed. The exhaust gas entering the second inlet pipe  327  may then flow through the first outlet perforations  329  while the exhaust gas entering the fourth inlet pipe  307  may then flow through the second outlet perforations  310 . The outlet perforations may add a controlled level of higher frequency broadband attenuation to the sound of the exhaust gas passing through the muffler system. The frequency and range of sound attenuation at the outlet perforations may be a function of the size of each perforation as well as the location of the perforations along the pipes  327  and  307 . After passing through the outlet perforations, the exhaust gas flowing through the second inlet pipe  327  (and through the fourth outlet pipe  307 ) may be routed to the tailpipe (and then the atmosphere). 
     A smaller portion of the exhaust gas from each of the first exhaust passage  324  and the second exhaust passage  304  may enter the center chamber  316  via the first inlet pipe  326  and the third inlet pipe  306 , respectively. The mixing of the exhaust gas from the engine banks may improve sound quality and character. After mixing in the center chamber, the exhaust may enter the first outer chamber  314  and the second outer chamber  312  via first baffle perforations  311  and the second baffle perforations  309  respectively. Communication of a small portion of the exhaust gas through the lower diameter pipes (first inlet pipe  326  and third inlet pipe  306 ) may improve quality and character of exhaust sound. From the first outer chamber  314 , the exhaust gas is routed to the second inlet pipe  327  via the first outlet perforations  329  and from the second outer chamber  312 , the exhaust gas is routed to the fourth inlet pipe  307  via the second outlet perforations  310 . The smaller portion of the exhaust gas routed through the center chamber may recombine with the primary exhaust gas flow through the second inlet pipe  327  and the fourth inlet pipe  307 . 
     Since during operation in the first mode, the primary exhaust flow is confined within the inlet pipes and a larger volume of the exhaust gas may not flow through the muffler  302  and is not expanded or impeded, exhaust backpressure may be reduced. Reduction of exhaust backpressure may result in increased engine performance and fuel efficiency. While operating in the first mode, the lower diameter pipes (first inlet pipe  326  and third inlet pipe  306 ) and the muffler  302  volume may act as low frequency Helmholtz tuner. The tuning improves quality of exhaust sound while having minimal effect on exhaust backpressure. The level of tuning attained may be adjusted based on size and shape (such as length, diameter, number of baffle perforations) of the lower diameter tubes and the muffler  302 . In this way, exhaust backpressure may be reduced while exhaust sound is attenuated and the exhaust sound quality is improved. Since the entire exhaust gas flow is not routed through the muffler, durability of the muffler may be improved. 
       FIG.  3 B  shows an example  350  operation of the muffler system  301  in a second mode. The second mode may also be termed as the quiet mode as during operation in this mode, a lower level of exhaust sound (sound audible to the vehicle passengers or outside the vehicle due to exhaust gas flow from engine to the atmosphere via the exhaust system and the tailpipe) is desired. In the second mode, each of the first valve  334  and the second valve  336  may be in their respective closed positions. Exhaust gas from the first engine bank may flow into the muffler system via the first exhaust passage  324  while exhaust gas from the second engine bank may flow into the muffler system via the second exhaust passage  304 . 
     Due to the first valve  334  and the second valve  336  being closed, exhaust gas from first exhaust passage  324  may enter the first inlet pipe  326  and the exhaust gas from second exhaust passage  304  may enter the third inlet pipe  306 . Due to the flow of exhaust through the smaller diameter tubes (first inlet pipe  326  and third inlet pipe  306 ) first, the exhaust sound may be attenuated. Exhaust from each of the first inlet pipe  326  and the third inlet pipe  306  may then enter the center chamber  316  wherein the exhaust flow is expanded. Expansion of the gas creates broadband attenuation of sound. Further, exhaust gas flow in the center chamber  316  may smooth out pulses of exhaust flow by mixing exhaust flow from two engine banks which may further attenuate the sound. 
     From the center chamber  316 , the exhaust may enter the first outer chamber  314  and the second outer chamber  312  via first baffle perforations  311  and the second baffle perforations  309  respectively. Exhaust flow through the baffle perforations may add acoustical impedance, thereby increasing sound attenuation. The level of attenuation attained and the associated change in backpressure may be adjusted based on the number of individual openings in the baffle perforations. The exhaust flow upon entering the outer chamber may further expand and cause sound level attenuation. 
     From the first outer chamber  314 , the exhaust gas is routed to the second inlet pipe  327  via the first outlet perforations  329  and from the second outer chamber  312 , the exhaust gas is routed to the fourth inlet pipe  307  via the second outlet perforations  310 . Exhaust gas flow through the outlet perforations may add impedance, thereby further attenuating the exhaust sound. The level of attenuation attained and the corresponding change in exhaust backpressure may be adjusted based on the number of individual openings in the outlet perforations. The location of the outlet perforations (with each of the second inlet pipe  327  and the fourth inlet pipe  307 ) may be adjusted to affect a standing wave in the larger diameter pipes (the second inlet pipe  327  and the fourth inlet pipe  307 ) and facilitate in tuning the sound. In this way, in the quiet mode, by flowing exhaust through the smaller diameter pipes and expanding exhaust within the muffler chambers, a higher level of attenuation of exhaust sound may be attained. By limiting the number of baffles within the muffler  302 , exhaust backpressure may be reduced. 
     In this way, the components of  FIGS.  1  and  2    enable an on-board controller including computer-readable instructions stored on non-transitory memory to: upon indication of operation of the muffler system in a quite mode, actuate a valve coupled downstream of a junction of a smaller diameter inlet pipe and a larger diameter inlet pipe originating from an exhaust passage coupled to an engine bank to a closed position, route exhaust through the smaller diameter inlet pipe, a center chamber of a muffler, baffle perforations in a baffle separating the center chamber form an outer chamber, outlet perforations fluidically coupling the larger diameter inlet pipe and the outer chamber, the larger diameter inlet pipe, and an outlet pipe to attenuate exhaust sound. When quite mode is not indicated, the valve is actuated to an open position to route exhaust directly from the exhaust passage to the larger diameter inlet pipe, then route the exhaust to the outlet pipe via the outlet perforations to reduce exhaust backpressure. 
       FIG.  4    shows a flow chart of a method  400  for operating a muffler system (such as muffler system  301  in  FIGS.  3 A-B ). As explained above, an exhaust system of a vehicle may include a muffler system adapted to control exhaust sound to a desired level. Exhaust sound is defined as a sound audible to the vehicle passengers or outside the vehicle due to exhaust gas flow from engine to the atmosphere via the exhaust system and the tailpipe. Instructions for carrying out method  400  and the rest of the methods included herein may be executed by a controller (e.g., controller  12  of  FIG.  1   ) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference to  FIGS.  1 - 3 A ,B. The controller may employ engine actuators of the engine system to adjust engine operation, according to the methods described below. 
     The method begins at  402  and includes estimating and/or measuring engine operating conditions. Engine operating conditions may include engine speed and/or load, engine temperature, ambient temperature, exhaust manifold temperature, exhaust temperatures in the exhaust pipes, gas pressures, mass air flow, etc. The vehicle location may be determined based on inputs from an onboard navigation system and/or from an external server. Further, permissible sound levels at the location of the vehicle may be retrieved from an onboard and/or off-board database. 
     At  404 , the method includes determining if a quiet mode of operation is desired for the muffler system. In a quiet mode of operation, the exhaust sound is attenuated to a higher level relative to muffler system operation outside the quiet mode. A lower exhaust sound may be desirable by the operator during vehicle travel through certain neighborhoods (such as proximal to schools and/or hospitals). Also, the operator may desire a lower exhaust sound during certain time periods of the day such as early morning. The operator may select a quiet mode of operation of the muffler via an input to a dashboard console (such as touchscreen on a human machine interface) or a smart device (such as a smart phone or tablet) communicatively connected to the engine control system. Further, the controller may operate the muffler system in the quiet mode if it is determined that the permissible sound levels at the location of the vehicle is lower than a threshold level (such as lower than lower than 74 dBA). 
     If it is determined that quiet mode is desired/selected, the muffler system may be operated in a second mode as elaborated with reference to  FIG.  3 B . At  406 , the muffler system valves (such as first valve  334  and second valve  336  in  FIGS.  3 A-B ) allowing exhaust gas flow into the larger diameter inlet pipes (such as second inlet pipe  327  and fourth inlet pipe  307  in  FIGS.  3 A-B ) may be closed. The controller may send a signal to the actuators of the corresponding valves to actuate the valves to respective to their respective fully closed positions. Due to the closing of the muffler system valves, the exhaust may be routed to flow from the exhaust passages corresponding to each engine bank to enter the smaller diameter inlet pipes (first inlet pipe  326  and third inlet pipe  306  in  FIGS.  3 A-B ). 
     At  410 , the exhaust gas may flow through the smaller diameter inlet pipes and enter the center chamber (such as center chamber  316  in  FIGS.  3 A-B ) of the muffler (such as muffler  302  in  FIGS.  3 A-B ). At  412 , at the center chamber, the exhaust gas coming from two engine banks via the two smaller diameter inlet pipes may be mixed and expanded. Flow of exhaust through the smaller diameter pipes and subsequent expansion at the center chamber may cause attenuation of exhaust sound. 
     At  414 , exhaust gas from the center chamber may be routed to flow to two outer chambers (such as first outer chamber  314  and second outer chamber  312  in  FIGS.  3 A-B ) located on each side of the center chamber via baffle perforations (such as first baffle perforations  311  and second baffle perforations  309  in  FIGS.  3 A-B ) on baffles (such as baffles  320  and  318  in  FIGS.  3 A-B ) separating the center chamber from the outer chambers. The exhaust may be further expanded at the outer chambers. Flow through the baffle perforations and further expansion may add acoustic impedance and further attenuate the exhaust sound. 
     At  416 , exhaust gas may be routed from the outer chambers to the larger diameter pipes via outlet perforations (such as first outlet perforations  329  and second outlet perforations  310  in  FIGS.  3 A-B ) fluidically coupling the outer chambers to the larger diameter pipes. Flowing exhaust through the plurality of openings in the outlet perforations adds more impedance and may further facilitate sound attenuation. From the larger diameter pipes, at  418 , the exhaust gas may flow to the tailpipe via the outlet pipes (such as outlet pipes  328  and  308  in  FIGS.  3 A-B ). In this way, the exhaust gas may be routed through pipes of different diameters and muffler chambers for effective sound attenuation without a significant increase in exhaust back pressure. 
     If at  404  it is determined that quiet mode of operation is not desired, the muffler system may be operated in a first mode as elaborated with reference to  FIG.  3 A . At  420 , the muffler system valves allowing exhaust gas flow into the larger diameter inlet pipes may be opened. The controller may send a signal to the actuators of the corresponding valves to actuate the valves to respective open positions. Due to the opening of the muffler system valves, at  422 , the exhaust may be routed to flow from the exhaust passages corresponding to each engine bank to enter the larger diameter inlet pipes and flow through the open valves. 
     At  422 , exhaust from the larger diameter pipes may be routed to the outlet pipe via the outlet perforations. The outlet perforations may add a higher frequency broadband attenuation to the sound of the exhaust gas passing through the muffler system. At  426 , the exhaust gas may flow to the tailpipe via the outlet pipes. When the quiet mode is not desired, by confining the exhaust flow to the larger diameter pipes and the outlet pipes, backpressure may be reduced. Reduction of exhaust backpressure may result in increased engine performance and fuel efficiency. While operating in the first mode, the lower diameter pipes and the muffler volume may act as low frequency Helmholtz tuner and improve quality of exhaust sound. 
     In one example, the muffler system valves may be eliminated and exhaust flow in the first mode may be carried out during all engine operating conditions. Without the muffler system valves, the exhaust sound attenuation as attained by exhaust flow through the outlet perforations and operation of the smaller diameter inlet tubes as tuners may be sufficient for all conditions and further attenuation may not be desired. By confining flow of a larger portion of the exhaust gas within inlet and outlet pipes without being expanded inside the muffler body, exhaust back pressure may be reduced. 
     As an example, the muffler valves may be controlled based on the exhaust sound level regulations of the region where the vehicle is being operated. In one example, if the vehicle is being operated in a region (such as a state or country) with a higher exhaust sound limit, the muffler valves may not be actuated to closed position and may be maintained in the open position (first mode of operation of the muffler system) for exhaust backpressure reduction. If the vehicle is being operated in a region with stricter such as lower exhaust sound limit, the muffler valves may be selectively actuated to a closed position to attain the desired noise attenuation. In this way, a single muffler design may be used in different geographical regions to attain exhaust backpressure reduction and engine sound attenuation based on engine sound regulations of the region. 
     In this way, during a first condition, a muffler system may be operated in a first mode to route exhaust gas from an exhaust passage through a larger diameter inlet tube of a muffler, bypassing a smaller diameter inlet tube and a muffler chamber before exiting the muffler system via an outlet pipe; and during a second condition, a muffler system may be operated in a second mode to route exhaust gas from the exhaust passage first through the smaller diameter inlet tube, the muffler chamber, and then the larger diameter inlet tube before exiting the muffler system via the outlet pipe. During the first condition, exhaust sound level is lowered and during the second condition, exhaust backpressure is lowered. In the first mode, a valve regulating flow into each of the smaller diameter inlet pipe and the larger diameter inlet pipe is actuated to an open position and in the second mode, the valve is actuated to a closed position. 
       FIG.  5    shows an example timeline  500  illustrating operation of a muffler system (such as muffler system  301  in  FIGS.  3 A-B ) to reduce exhaust sound and exhaust backpressure based on a selected mode of operation. The horizontal (x-axis) denotes time and the vertical markers t 1 -t 3  identify significant times in the routine for muffler system operation. 
     The first plot, line  502 , shows a change in engine speed over time as estimated via a crankshaft position sensor. The second plot, line  504 , shows a mode of operation of the muffler system. The muffler may be operated in a first mode (also referred herein as engine power priority mode) or a second mode (also referred herein as a quiet mode). In the first mode, exhaust backpressure reduction is prioritized with exhaust sound attenuation and in the second mode, exhaust sound attenuation is prioritized while maintaining lower exhaust backpressure levels. The muffler system may be operated in the first mode by default while the operator may select a quiet mode of operation (second mode) of the muffler via an input to a dashboard console (such as touchscreen on a human machine interface) or a smart device (such as a smart phone or a tablet) communicatively connected to the engine control system. The third plot, line  506 , shows a position of a first muffler valve (such as valve  334  in  FIGS.  3 A-B ) regulating exhaust gas flow into a first set of smaller diameter inlet pipes or larger diameter inlet pipes of the muffler system. The fourth plot, line  507 , shows a position of a second muffler valve (such as valve  336  in  FIGS.  3 A-B ) regulating exhaust gas flow into a second set of smaller diameter inlet pipes or larger diameter inlet pipes of the muffler system. The fifth plot, line  508 , shows a level of exhaust sound audible to the vehicle passengers or outside the vehicle due to exhaust gas flow from engine to the atmosphere via the exhaust system and the tailpipe. The sixth plot, line  510 , shows a level of exhaust backpressure. 
     Prior to time t 1 , the engine is not operated and the vehicle is not propelled via engine torque. At time t 1 , the engine is started from rest by combusting fuel and air in the engine cylinders and the engine speed gradually increases. Since the quiet mode is not indicated by the operator, the muffler system may be operated in the default, first mode with the muffler valves in the open position. In the first mode, the exhaust gas is primarily routed to the outlet pipes of the muffler system via the larger diameter inlet pipes without entering one or more muffler chambers. Due to the operation of the muffler system in the first mode, a lower exhaust backpressure may be maintained with the exhaust sound remaining within regulated limits (such as below 74 dBA). 
     At time t 2 , in response to an indication from an operator (e.g., requesting to operate in the second mode), the muffler system operation is shifted from the first mode to the quieter, second mode. To operate the muffler system in the second mode, the controller sends a signal to the actuators of the muffler valves to actuate the valves to their respective closed positions. In the closed position, the exhaust gas entering the muffler system is routed through the smaller diameter inlet pipes, center chamber of the muffler, baffle perforations, outer chambers of the muffler, outlet perforations, larger diameter inlet pipes, and finally the outlet pipe. Due to the exhaust flow through the smaller diameter inlet pipes followed by expansion of exhaust gas in the muffler chambers, as seen from the change in exhaust sound levels, attenuation of exhaust sound is improved. With the decrease in exhaust sound levels during operation of the muffler system in the second mode, there is an increase in exhaust backpressure. However, the magnitude of change in backpressure does not significantly affect engine performance. 
     At time t 3 , in response to an indication by the operator that the quiet mode of operation of the muffler system is no longer desired, the controller may send a signal to the actuator(s) of the muffler valves to actuate the valves to respective open positions. In the first mode, the exhaust gas is primarily routed to the outlet pipes of the muffler system via the larger diameter inlet pipes without entering one or more muffler chambers in order to prioritize exhaust back pressure reduction and engine performance. 
     In this way, by adjusting a muffler system valve position and flowing exhaust through inlet pipes of different diameters, the muffler system may be operated in one of a quiet priority mode and an engine power priority mode. In the quiet mode, by flowing exhaust through the smaller diameter pipe, expanding the gas in the center chamber, and flowing through baffle perforations and outlet perforations, higher sound attenuation may be attained. In the engine power priority mode, by confining exhaust flow with larger diameter pipes and not expanding the exhaust gas in the muffler chambers, exhaust backpressure may be reduced. Overall, by operating a muffler system with different inlet pipe diameters, attenuation of exhaust sound and exhaust backpressure reaction may be attained, thereby improving engine performance and operator satisfaction. 
     In one example, a system for an engine, comprises: a muffler system including two or more sets of inlet pipes to a muffler, each set of inlet pipes in the two or more sets including pipes of different diameters, two or more valves controlling exhaust flow through the pipes of different diameters, and each set of inlet pipes leading to one of two or more outlet pipes of the muffler system. In the preceding example, the system further comprising, additionally or optionally, an exhaust passage configured to receive exhaust gas from an engine bank, wherein the exhaust passage leads to one set of inlet pipes of the two or more sets of inlet pipes, the engine including two or more engine banks. In any or all of the preceding examples, additionally or optionally, the set of inlet pipes of the two or more sets include a first inlet pipe and a second inlet pipe, a diameter of the first inlet pipe different from a diameter of the second inlet pipe. In any or all of the preceding examples, additionally or optionally, the diameter of the first inlet pipe is smaller than the diameter of the second inlet pipe. In any or all of the preceding examples, additionally or optionally, the exhaust passage from the engine bank bifurcates into the first inlet pipe and the second inlet pipe. In any or all of the preceding examples, additionally or optionally, the first inlet pipe leads to a center chamber of the muffler, the center chamber positioned between a first outer chamber and a second outer chamber of the muffler. In any or all of the preceding examples, additionally or optionally, the second inlet pipe directly leads to an outlet pipe. In any or all of the preceding examples, additionally or optionally, the center chamber is separated from the first outer chamber by a first baffle and wherein the center chamber is separated from the second outer chamber by a second baffle, each of the first baffle and the second baffle including baffle perforations. In any or all of the preceding examples, additionally or optionally, the second inlet pipe is fluidically coupled to one of the first outer chamber and the second outer chamber via outlet perforations. In any or all of the preceding examples, additionally or optionally, one valve of the two or more valves is located downstream of a junction of the first inlet pipe and the second inlet pipe and upstream of the outlet perforations. In any or all of the preceding examples, additionally or optionally, in an open position of each valve, exhaust gas from the exhaust passage is routed via each of the second inlet pipe, the outlet perforations, and the outlet pipe, and wherein in the closed position of each valve, exhaust gas from the exhaust passage is routed via each of the first inlet pipe, the center chamber, the baffle perforations, one of the first outer chamber and the second outer chamber, outlet perforations, the second inlet pipe, and the outlet pipe. In any or all of the preceding examples, additionally or optionally, each of the baffle perforations and outlet perforations include a plurality of individual holes. 
     Another example method for an engine comprises: during a first condition, operating a muffler system in a first mode to route exhaust gas from an exhaust passage through a larger diameter inlet tube of a muffler; and during a second condition, operating a muffler system in a second mode to route exhaust gas from the exhaust passage first through a smaller diameter inlet tube, a muffler chamber, and then the larger diameter inlet tube before exiting the muffler system via the outlet pipe. In the preceding example, additionally or optionally, the second condition includes an indication by an operator to operate the muffler system in the first mode, and wherein the muffler system is operated in the second mode in an absence of the indication by the operator. In any or all of the preceding examples, additionally or optionally, in the first mode, a valve regulating flow into each of the smaller diameter inlet pipe and the larger diameter inlet pipe is actuated to an open position allowing exhaust gas to flow directly from the exhaust passage to the larger diameter inlet pipe, and wherein in the second mode, the valve is actuated to a closed position to route exhaust gas to the larger diameter inlet pipe via the smaller diameter inlet pipe and the muffler chamber. In any or all of the preceding examples, additionally or optionally, in the second mode, the exhaust gas flows from the smaller diameter inlet pipe to a center muffler chamber, then from the center muffler chamber, the exhaust gas flows to an outer muffler chamber via baffle perforations on a baffle separating the center muffler chamber from the outer muffler chamber, and then the exhaust gas flows to the larger diameter inlet pipe through outlet perforations housed in the larger diameter inlet pipe. In any or all of the preceding examples, additionally or optionally, the exhaust passage routes exhaust from one bank of the engine to the muffler system, the engine including two or more banks with each bank coupled to a distinct exhaust passage bifurcating into a distinct smaller diameter inlet pipe and a distinct larger diameter inlet pipe. 
     In yet another example, a muffler system for an engine, comprises: a controller including executable instructions stored in non-transitory memory to: upon indication of operation of the muffler system in a quite mode, actuate a valve coupled downstream of a junction of a smaller diameter inlet pipe and a larger diameter inlet pipe to a closed position, each of the smaller diameter inlet pipe and the larger diameter inlet pipe originating from an exhaust passage coupled to an engine bank; route exhaust through the smaller diameter inlet pipe, a center chamber of a muffler, baffle perforations in a baffle separating the center chamber form an outer chamber, outlet perforations fluidically coupling the larger diameter inlet pipe and the outer chamber, the larger diameter inlet pipe, and an outlet pipe to attenuate exhaust sound. In the preceding example, additionally or optionally, the controller includes further instructions to: when the quiet mode is not indicated, actuate the valve to an open position; and route exhaust directly from the exhaust passage to the larger diameter inlet pipe, then route the exhaust to the outlet pipe via the outlet perforations to reduce exhaust backpressure. In any or all of the preceding examples, additionally or optionally, the quiet mode is indicated by an operator via an input to a dashboard console or a smart device communicatively connected to the controller. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations, and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations, and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     As used herein, the term “approximately” is construed to mean plus or minus five percent of the range unless otherwise specified. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.