Patent Publication Number: US-11639684-B2

Title: Exhaust gas bypass valve control for a turbocharger for a two-stroke engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/776,635, filed on Dec. 7, 2018. The above-mentioned patent application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to a vehicle engine and, more particularly, to controlling the opening of an exhaust gas bypass valve in response to sensed conditions. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     A vehicle, such as a snowmobile, generally includes an engine assembly. The engine assembly is operated with the use of fuel to generate power to drive the vehicle. The power to drive a snowmobile is generally generated by a combustion engine that drives pistons and a connected crank shaft. Two-stroke snowmobile engines are highly tuned, and high specific power output engines that operate under a wide variety of conditions. 
     Vehicle manufacturers are continually seeking ways to improve the power output for engines. Turbochargers have been used together with two-stroke engines to provide increased power output. However, improving performance of a turbocharged two-stroke engine is desirable. Back pressure in a two stroke engine has an effect on engine performance. 
     SUMMARY 
     This section provides a general summary of the disclosures, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one aspect of the disclosure, a method of operating an exhaust gas bypass valve includes determining an engine speed. When the engine speed is at idle, partially opening the exhaust gas bypass valve with a first predetermined effective area greater than fully closed. The method further includes determining an acceleration event and holding the exhaust gas bypass valve open at least a second predetermined effective area greater than fully closed in response to the acceleration event. 
     In another aspect of the disclosure, a system for operating an engine includes an engine speed sensor determining an engine speed, an exhaust gas bypass valve, an exhaust gas bypass valve actuator coupled to the exhaust gas bypass valve and a controller. The controller partially opens the exhaust gas bypass valve with a first predetermined effective area greater than fully closed when the engine speed is at idle. The controller determines an acceleration event, holding the exhaust gas bypass valve open at least a second predetermined effective area greater than fully closed in response to the acceleration event. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
         FIG.  1    is a perspective view of a snowmobile. 
         FIG.  2    is an exploded view of the snowmobile of  FIG.  1   . 
         FIGS.  2 A and  2 B  are enlarged exploded views of  FIG.  2   . 
         FIG.  3    is a block diagram of the engine of  FIG.  2   . 
         FIG.  4    is an exploded view of the engine of  FIG.  3   . 
         FIG.  5 A  is a perspective view of a turbocharger according to the present disclosure. 
         FIG.  5 B  is a side view of the turbocharger  FIG.  5 A . 
         FIG.  5 C  is a cutaway view of the turbine housing of the turbocharger of  FIG.  5 A . 
         FIG.  5 D  is a partial cross-sectional view of the turbine housing of the turbocharger of  FIG.  5 A . 
         FIG.  5 E  is a cutaway view of the turbocharger having the diverter valve in a position closing off the first scroll. 
         FIG.  5 F  is a partial cutaway view of the turbocharger having the diverter valve in a neutral position. 
         FIG.  5 G  is a partial cutaway view of the turbocharger having the diverter valve in a position closing off the second scroll. 
         FIG.  5 H  is a partial cutaway view of an alternate valve for controlling flow to the scrolls in a partially open position. 
         FIG.  5 I  is a partial cutaway view of the valve in  FIG.  5 H  in a closed position. 
         FIG.  5 J  is a partial cutaway view of another alternate valve for controlling flow to one of the scrolls in a closed position. 
         FIG.  5 K  is a partial cutaway view of the valve in  FIG.  5 J  in a partially open position. 
         FIG.  6 A  is a cross-sectional view of an exhaust gas bypass valve. 
         FIG.  6 B  is the exhaust bypass valve of  FIG.  6 A  in a first open position. 
         FIG.  6 C  is the exhaust bypass valve of  FIG.  6 A  in a second open position. 
         FIG.  6 D  is the exhaust bypass valve of  FIG.  6 A  in a third open position. 
         FIG.  6 E  is the exhaust bypass valve of  FIG.  6 A  in a fully open position. 
         FIG.  6 F  is a perspective view of the exhaust bypass valve with an actuator arm. 
         FIG.  6 G  is an end view of the exhaust bypass valve in the position illustrated in  FIG.  6 E . 
         FIG.  6 H  is a block diagrammatic view of a system for operating the exhaust bypass valve of  FIG.  6 A . 
         FIG.  6 I  is a perspective view of an exhaust bypass valve and diverter valve controlled by a common actuator. 
         FIG.  7 A  is a schematic view of a system for bypassing exhaust gas. 
         FIG.  7 B  is a schematic view of a second example for bypassing exhaust gas. 
         FIG.  7 C  is a schematic view of a third example of bypassing exhaust gas. 
         FIG.  7 D  is a schematic view of a fourth example of bypassing exhaust gas. 
         FIG.  7 E  is a diagrammatic representation of an engine system including exhaust bypass for increasing the stability of a two-stroke engine. 
         FIG.  7 F  is a diagrammatic representation of an engine assembly comprising a second example of increasing the stability of a two stoke engine. 
         FIG.  7 G  is a diagrammatic representation of an engine assembly having a third example of an exhaust bypass valve for increasing the stability of a two-stroke engine alternate positions of the exhaust bypass valve are illuminated. 
         FIG.  7 H  is a diagrammatic representation of a control valve within a stinger of the exhaust system of a normally aspirated two-stroke engine assembly. 
         FIG.  7 I  is a diagrammatic representation of a control valve within a silencer. 
         FIG.  7 J  is a diagrammatic representation of a control valve within a sub-chamber of a silencer. 
         FIG.  7 K  is a schematic view of another example of bypassing exhaust gas using a silencer and supplemental silencer with a common wall. 
         FIG.  8 A  is a schematic view of a system for bypassing the compressor of a turbocharged engine to provide airflow to the engine. 
         FIG.  8 B  is a rear side of the boost box of  FIG.  8 A . 
         FIG.  8 C  is a left side view of the boost box of  FIG.  8 A . 
         FIG.  8 D  is a front side view of the boost box of  FIG.  8 A . 
         FIG.  8 E  is a right side view of the boost box of  FIG.  8 A . 
         FIG.  8 F  is an enlarged view of the one way valve of  FIG.  8 A . 
         FIG.  8 G  is a side view of an engine compartment having the boost box oriented so that the one way valve is located rearwardly. 
         FIG.  8 H  is a side view of a boost box coupled to a duct. 
         FIG.  8 I  is a side view of the boost box coupled to a channel integrally formed with a fuel tank. 
         FIG.  9 A  is a block diagrammatic view of a system for controlling an exhaust bypass valve. 
         FIG.  9 B  is a flowchart of a method for controlling the exhaust gas bypass valve. 
         FIG.  9 C  is a plot of boost error versus time for a plurality of signals used for updating the exhaust gas bypass valve position. 
         FIG.  9 D  is a plot of the calculation multiplier versus boost error. 
         FIG.  9 E  is a graph illustrating the absolute pressure and changes over various altitudes. 
         FIG.  9 F  is a flowchart of a method for controlling an exhaust gas bypass valve to increase power or stability of a two-stroke engine. 
         FIG.  9 G  is a block diagrammatic view of a first example of the exhaust gas bypass valve position control module. 
         FIG.  9 H  is a flowchart of a method for operating the exhaust gas bypass valve in response to an idle and acceleration event. 
         FIG.  10 A  is a side view of a rotor of a turbocharger. 
         FIG.  10 B  is an end view of the rotor of  FIG.  10 A . 
         FIG.  10 C  is a diagrammatic representation of the exducer area. 
         FIG.  10 D  is a plot of the ratio of exhaust gas bypass valve or bypass valve area to exducer area for known four stroke engines, two stroke engines and the present example. 
     
    
    
     DETAILED DESCRIPTION 
     Examples will now be described more fully with reference to the accompanying drawings. Although the following description includes several examples of a snowmobile application, it is understood that the features herein may be applied to any appropriate vehicle, such as motorcycles, all-terrain vehicles, utility vehicles, moped, scooters, etc. The examples disclosed below are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed in the following detailed description. Rather, the examples are chosen and described so that others skilled in the art may utilize their teachings. The signals set forth below refer to electromagnetic signals that communicate data. 
     Referring now to  FIGS.  1  and  2   , one example of an exemplary snowmobile  10  is shown. Snowmobile  10  includes a chassis  12 , an endless belt assembly  14 , and a pair of front skis  20 . Snowmobile  10  also includes a front-end  16  and a rear-end  18 . 
     The snowmobile  10  also includes a seat assembly  22  that is coupled to the chassis assembly  12 . A front suspension assembly  24  is also coupled to the chassis assembly  12 . The front suspension assembly  24  may include handlebars  26  for steering, shock absorbers  28  and the skis  20 . A rear suspension assembly  30  is also coupled to the chassis assembly  12 . The rear suspension assembly  30  may be used to support the endless belt  14  for propelling the vehicle. An electrical console assembly  34  is also coupled to the chassis assembly  12 . The electrical console assembly  34  may include various components for displaying engine conditions (i.e., gauges) and for electrically controlling the snowmobile  10 . 
     The snowmobile  10  also includes an engine assembly  40 . The engine assembly  40  is coupled to an intake assembly  42  and an exhaust assembly  44 . The intake assembly  42  is used for providing fuel and air into the engine assembly  40  for the combustion process. Exhaust gas leaves the engine assembly  40  through the exhaust assembly  44 . The exhaust assembly  44  includes the exhaust manifold  45  and tuned pipe  47 . An oil tank assembly  46  is used for providing oil to the engine for lubrication where it is mixed directly with fuel. In other systems oil and fuel may be mixed in the intake assembly. A drivetrain assembly  48  is used for converting the rotating crankshaft assembly from the engine assembly  40  into a potential force to use the endless belt  14  and thus the snowmobile  10 . The engine assembly  40  is also coupled to a cooling assembly  50 . 
     The chassis assembly  12  may also include a bumper assembly  60 , a hood assembly  62  and a nose pan assembly  64 . The hood assembly  62  is movable to allow access to the engine assembly  40  and its associated components. 
     Referring now to  FIGS.  3  and  4   , the engine assembly  40  is illustrated in further detail. The engine assembly  40  is a two-stroke engine that includes the exhaust assembly  44  that includes an exhaust manifold  45 , tuned pipe  47  and exhaust silencer  710 . 
     The engine assembly  40  may include spark plugs  70  which are coupled to a one-piece cylinder head cover  72 . The cylinder head cover  72  is coupled to the cylinder  74  with twelve bolts which is used for housing the pistons  76  to form a combustion chamber  78  therein. The cylinder  74  is mounted to the engine upper crankcase  80 . 
     The fuel system  82  that forms part of the engine assembly  40 , includes fuel lines  84  and fuel injectors  86 . The fuel lines  84  provide fuel to the fuel injectors  86  which inject fuel, in this case, into a port in the cylinder adjacent to the pistons  76 . In other cases, an injection may take place adjacent to the piston, into a boost box (detailed below) or into the throttle body. An intake manifold  88  is coupled to the engine upper crankcase  80 . The intake manifold  88  is in fluidic communication with the throttle body  90 . Air for the combustion processes is admitted into the engine through the throttle body  90  which may be controlled directly through the use of an accelerator pedal or hand operated lever or switch. A throttle position sensor  92  is coupled to the throttle to provide a throttle position signal corresponding to the position of the throttle plate  94  to an engine controller discussed further herein. 
     The engine upper crankcase  80  is coupled to lower crankcase  100  and forms a cavity for housing the crankshaft  102 . The crankshaft  102  has connecting rods  104  which are ultimately coupled to the pistons  76 . The movement of the pistons  76  within the combustion chamber  78  causes a rotational movement at the crankshaft  102  by way of the connecting rods  104 . The crankcase may have openings or vents  106  therethrough. 
     The system is lubricated using oil lines  108  which are coupled to the oil injectors  110  and an oil pump  112 . 
     The crankshaft  102  is coupled to a generator flywheel  118  and having a stator  120  therein. The flywheel  118  has crankshaft position sensors  122  that aid in determining the positioning of the crankshaft  102 . The crankshaft position sensors  122  are aligned with the teeth  124  and are used when starting the engine, as well as being used to time the operation of the injection of fuel during the combustion process. A stator cover  126  covers the stator  120  and flywheel  118 . 
     Discussed below are various features of the engine assembly  40  used in the snowmobile  10 . Each of the features relate to the noted section headings set forth below. It should be noted that each of these features can be employed either individually or in any combination with the engine assembly  40 . Moreover, the features discussed below will utilize the reference numerals identified above, when appropriate, or other corresponding reference numerals as needed. Again, as noted above, while the engine assembly  40  is a two-stroke engine that can be used with the snowmobile  10 , the engine assembly  40  can be used with any appropriate vehicles and the features discussed below may be applied to four-stroke engine assemblies as well. 
     The engine assembly  40  also includes an exhaust manifold  45  that directs the exhaust gases from the engine. The exhaust manifold  45  is in fluid communication with a tuned pipe  47 . The tuned pipe  47  is specifically shaped to improve the performance and provide the desired feedback to the engine assembly  40 . The tuned pipe  47  is in communication with a stinger  134 . The tuned pipe  47  has a bypass pipe  136  coupled thereto. The bypass pipe  136  has an exhaust gas bypass valve  138  used for bypassing some or all of the exhaust gases from being directed to a turbocharger  140 . Details of the turbocharger  140  are set forth in the following figures. 
     Referring now to  FIGS.  5 A- 5 G , the turbocharger  140  includes a turbine portion  510  and a pump or compressor portion  512 . The turbine portion  510  and the compressor portion  512  have a common shaft  521  that extends there between. That is, the rotational movement within the turbine portion  510  caused from the exhaust gases rotate a turbine wheel  520  which in turn rotates the shaft  521  which, in turn, rotates a compressor wheel  519 . The compressor portion  512  includes an inlet  514  and an outlet  516 . Movement of the compressor wheel  519  causes inlet air from the inlet  514  to be pressurized and output through the outlet  516  of the housing  518 . 
     The turbine portion  510  includes a turbine wheel  520  with housing  522 . The housing  522  includes a turbine inlet  524  and a turbine outlet  526 . The inlet  524  receives exhaust gas through the tuned pipe  47  and the stinger  134  as illustrated above. The exhaust gases enter the inlet  524  and are divided between a first scroll  528  and a second scroll  530 . Of course, more than two scrolls may be implemented in a system. The scrolls  528 ,  530  may also be referred to as a volute. Essentially the first scroll  528  and the second scroll  530  start off with a wide cross-sectional area and taper to a smaller cross-sectional area near the turbine wheel. The reduction in cross-sectional area increases the velocity of the exhaust gases which in turn increases the speed of the turbine wheel  520 . Ultimately, the rotation of the turbine wheel  520  turns the compressor wheel  519  within the compressor portion  512  by way of a common shaft  521 . The size of the first scroll  528  and the second scroll  530  may be different. The overall area to radius (A/R) ratio of the scrolls may be different. The first scroll  528  has a first end  528 A and a second end  528 B and the second scroll has a second first end  530 A and a second end  530 B. The first ends  528 A,  530 A are adjacent to the turbine inlet  524 . The second ends  528 B,  530 B are adjacent to the turbine wheel  520  within the housing  522 . The volume of the first scroll  528  and second scroll  530  may be different. The cross-sectional opening adjacent to the turbine wheel  520  may be different between the scrolls. 
     The first scroll  528  and the second scroll  530  are separated by a separation wall  532 . The separation wall  532  separates the first scroll  528  from the second scroll  530 . The separation wall  532  may extend from the first end  528 A of the first scroll  528  and the first end  530 A of the second scroll  530  to the second end  528 B,  530 B of the respective scrolls. 
     The turbine portion  510  includes an exhaust gas diverter valve  540  mounted adjacent to the separation wall  532 . The exhaust gas diverter valve  540  is used to selectively partially or fully close off either the first scroll  528  or the second scroll  530 . A valve seat  542 A is located adjacent to the first scroll  528 . A second valve seat  542 B is located adjacent to the second scroll  530 . Either one of the valve seats  542 A,  542 B receive the exhaust gas diverter valve  540  when the exhaust gas diverter valve  540  is in a completely closed position. The valve seats  542 A,  542 B may be recesses or grooves that are formed within the housing  522 . The valve seats  542 A,  542 B form a surface that receives an edge  541  of the exhaust gas diverter valve  540  so that when exhaust gases push the exhaust gas diverter valve  540  into the scroll outer wall, the valve seats  542 A,  542 B provide a counter force. The edge  541  is the end of the valve  540  opposite a pivot pin  544 . The valve seats  542 A,  542 B may be circumferentially formed within each of the first scroll  528  and the second scroll  530 . The seal between the valve  540  may be on the edge  541  or on the surface of the valve  540  on each side of the edges  541 . 
     The pivot pin  544  which extends across the turbine inlet  524  to selectively separate or close off the first scroll  528  or the second scroll  530 . A partial closing of either the first scroll  528  or the second scroll  530  may also be performed by the exhaust gas diverter valve  540 . The exhaust gas diverter valve  540  pivots about the pivot pin  544 . As is best shown in  FIG.  5 B , an actuator  548  such as a motor or a hydraulic actuator may be coupled to the exhaust gas diverter valve  540 . Other types of actuators include pneumatic actuator. The actuator  548  moves the exhaust gas diverter valve to the desired position in response to various inputs as will be described in more detail below. That is, there may be conditions where both scrolls may be fully opened, or one or the other scroll may be opened, at least partially. The opening and closing of the valve may be used to control the pressure in the tuned pipe. Further, one scroll may be partially closed using the exhaust gas diverter valve  540  while one scroll may be fully open as indicated by the dotted lines. That is, in  FIG.  5 E  the scroll  530  is completely closed by the edge  541  of the exhaust gas diverter valve  540  being received within the valve seat  542 B. In  FIG.  5 F  the exhaust gas diverter valve  540  is in a middle or neutral position in which the first scroll  528  and the second scroll  530  are fully opened. That is, the valve is in a fully opened position and is coincident to or parallel with the separation wall  532 . In  FIG.  5 G  the edge  541  of the exhaust gas diverter valve  540  is received within and rests against the valve seat  542 A to fully close the first scroll  528 . 
     Referring now to  FIGS.  5 H and  5 I , a butterfly type valve  550  may be used in place of the diverter valve  540 . The butterfly valve  550  pivots about pivot pin  544 . The edge  552  of the valve  550  rests against the valve seat  556  in a closed position ( FIG.  5 I ). The closure may result in a seal or a near closure if a protrusion  553 A is on the edge  552  of valve or bump  553 B on the seat  556 . A dotted protrusion  553 B is shown on the edges  552  and valve seat  556 . The valve  550  may be in communication with an actuator and motor (or hydraulic actuator or a pneumatic actuator) to move the valve  550  into the desired position. In this manner the valve  550  is more balanced with respect to exhaust gas acting on the valve blade than the diverter valve  540 . 
     Referring now to  FIGS.  5 J and  5 K , alternate configuration for a butterfly type valve  560  may be used in place of the diverter valves  540  and  550 . The butterfly valve  560  is disposed within one of the scrolls. In this example scroll  530  has the first butterfly type valve  560 . The butterfly valve  560  pivots about pivot pin  564 . The edge  562  of the valve  560  rests against the valve seat  566  in a closed position ( FIG.  5 J ). The valve  560  may be in communication with an actuator and motor (or hydraulic actuator or a pneumatic actuator) to move the valve  560  into the desired position. In this manner, the valve  560  is more balanced with respect to exhaust gas acting on the valve blade than the diverter valve  540 . 
     In any of the examples in  FIGS.  5 A- 5 K , the valve  550  may also be made oval. The closed position may be less than 90 degrees. The closure may not be air tight intentionally. In addition, any of  FIGS.  5 A- 5 K  may have the protrusions  553 A and/or  553 B. 
     Referring now to  FIGS.  6 A- 6 F , an exhaust gas bypass valve  138  is set forth. By way of example, for a turbocharged engine the exhaust gas bypass valve  138  may be implemented in a wastegate. The exhaust gas bypass valve  138  may be configured in the bypass pipe  136  that connects the exhaust gas from the exhaust manifold  45  and the tuned pipe  47  to an exhaust pipe  142  coupled to the outlet of the turbine portion of the turbocharger. Of course, as detailed below, the exhaust gas bypass valve  138  may be used in various positions within the exhaust assembly  44 . 
     The exhaust gas bypass valve  138  has an exhaust gas bypass valve housing  610 . The exhaust gas bypass valve housing  610  may have a first flange  612 A and a second flange  612 B. The flanges  612 A,  612 B are used for coupling the exhaust gas bypass valve to the respective portions of the bypass pipe  136 A,  136 B. Of course, direct welding to the tuned pipe or bypass piping may be performed. The housing  610  has an outer wall  611  that is generally cylindrical in shape and has a longitudinal axis  613  which also corresponds to the general direction of flow through the exhaust gas bypass valve housing  610 . The outer wall  611  has a thickness T 1 . 
     The housing  610  includes a valve member  614  that rotates about a rotation axis  616 . The rotation axis  616  coincides with an axle  618  that is coupled to the housing  610  so that the valve member  614  rotates thereabout in a direction illustrated by the arrow  620 . The valve member  614  is balanced to minimize the operating torque required to open/close the valve member  614 . The butterfly arrangement has exhaust gas working on both sides of the valve member  614 , which effectively causes the forces to counteract and ‘cancel’ each other that results in a significantly reduced operating torque. Consequently, the valve member  614  may be sized as wastegate as big as necessary without significantly increasing the operating torque to actuate it. Advantageously a smaller (and likely less expensive) actuator may be utilized. 
     The housing  610  may include a first valve seat  622  and a second valve seat  624 . The seats  622  and  624  are integrally formed with the housing. As is illustrated, the valve seats  622  and  624  are thicker portions of the housing. The valve seats  622 ,  624  may have a thickness T 2  greater than T 1 . Of course, casting thicknesses may change such as by providing pockets of reduced thickness for weight saving purposes. The valves seats  622 ,  624  are circumferential about or within the housing  610 . However, each of the valve seats  622  and  624  extends about half way around the interior of the housing to accommodate the axle  618 . 
     The valve seats  622 ,  624  have opposing surfaces  626 ,  628  that have a planar surface that are parallel to each other. The surfaces  626 ,  628  contact opposite sides of the valve member  614  in the closed position. This allows the valve member  614  to rest against each valve seat  622 ,  624  to provide a seal in the closed position. The exhaust gas bypass valve  138  and the valve member  614  therein move in response to movement of an actuator  630 . The actuator  630  rotates the valve member  614  about the axis  616  to provide the valve member  614  in an open and a closed position. Of course, various positions between open and closed are available by positioning the actuator  630 . As will be further described below, the actuator  630  may actuate the valve member  614 , exhaust gas diverter valve  540  and valves  550 ,  560  as described above. As mention above the surface area of the valve member  614  is the same above and below the axis  616  so that the operating toque is minimized due to the exhaust gas load being distributed evenly on both sides of the axis  616 . 
     The effective cross-sectional area of opening, passage or port P 1  available to the exhaust gasses flowing through the interior of the exhaust gas bypass valve is limited by the distance T 2  and the valve member  616  and axle  616 . After experimentation, it was found that the effective cross-sectional area of the exhaust gas bypass valve  138  may be formed as a function of an exducer of the turbine wheel  520  as is described in greater detail below. 
     To vary the effective area, the valve member  614  of the exhaust gas bypass valve  138  has different angles α 1 -α 4  illustrated in  FIGS.  6 B to  6 E  respectively. The angles α 1 -α 4  progressively increase. The angular opening corresponds directly with the effective area of the exhaust gas bypass valve  138 . The angular opening of the exhaust gas bypass valve  138  may be controlled in various ways or in response to various conditions. Although specific angles are illustrated, the exhaust gas bypass valve  138  is infinitely variable between the fully closed position of  FIG.  6 A  and the fully open position of  FIG.  6 E . 
     Referring now to  FIG.  6 G , and end view of the exhaust gas bypass valve  138  is illustrated in the open position corresponding to  FIG.  6 E . 
     Referring now to  FIG.  6 H , the exhaust gas bypass valve  138  may be in communication with an electrical motor  640 . The electrical motor  640  has a position sensor  642  that provides feedback to a controller  644 . The controller  644  is coupled to a plurality of sensors  646 . The sensors provide feedback to the controller  644  to control the position of the valve  614  of the exhaust gas bypass valve  138 . The sensors  646  may include a boost pressure sensor, tuned pipe pressure sensor, exhaust manifold pressure sensor and a barometric pressure sensor. Other types of sensors that may be used for controlling the motor may include various types of temperature and pressure sensors for different locations within the vehicle. 
     Referring now to  FIG.  6 I , the turbine portion  510  is shown in relation to an exhaust gas bypass valve  138 . In this example, a dual actuation system  650  is used to simultaneously move the diverter valves  540 ,  550  and  560  illustrated above. The diverter valve  540  moves about the pivot pin  544 . The exhaust gas bypass valve  138  opens and closes as described above. In this example, a rotating member  652  is coupled to a first actuator arm  654  and a second actuator arm  656 . As the rotating member  652  moves under the control of a motor  658 , the first actuator arm  654  and the second actuator arm  656  move. According to that described below. Each actuator arm  654  and  656  may have a respective compensator  660 ,  662 . Although the type of movement described by the rotating member is rotating, other types of movement for the actuator arms may be implemented. A compensator  660 ,  662  may thus be implemented in a plurality of different ways. The compensator  660 ,  662  may be used to compensate for the type of movement as described below. 
     In this example, when the rotating member  652  is in a starting or home position, the exhaust gas bypass valve is closed and one scroll in the turbine is closed. As the dual actuation system  650  progresses the turbocharger scroll is opened and the diverter valve is positioned in a center position so that both scrolls are open. As the dual actuation system  650  progresses to the end of travel the exhaust gas bypass valve starts to open until it is fully open at the end of the actuator&#39;s travel. The exhaust gas bypass valve  138  does not start to open until the diverter valve is in the neutral position and both scrolls are open. Once both scrolls are opened further actuator movement results in no movement of the diverter valve in the turbo. The compensator  660 ,  662  may be slots or springs that allow the exhaust gas bypass valve to continue to move. The compensators may also be a stop on the diverter valve so that when a diverter valve hits the center position the stop may prevent the adjacent scroll from being closed. A compression spring or other type of compensator may be used so that when the stop is hit, the actuator rod allows the compensator  662  to compress, thus still allowing the actuator to turn the exhaust gas bypass valve  138 . Of course, various types of mechanisms for the dual actuation system  650  may be implemented. 
     Referring now to  FIGS.  7 A- 7 C , the position of the exhaust gas bypass valve  138  relative to the turbocharger and the silencer of the vehicle may be changed. Although the turbocharger  140  is illustrated, the following descriptions may be applied to normally aspirated (non-turbocharged) engines. 
     Referring now specifically to  FIG.  7 A , the engine assembly  40  has the exhaust manifold  45  as illustrated above. The tuned pipe  47  communicates exhaust gases from the exhaust manifold  45  to the stinger  134 . The stinger  134  is in communication with the turbocharger  140 , and in particular the turbine inlet  524  of the turbine portion  510 . In a non-turbocharged engine the stinger  134  may be communicated to the silencer  710 . Exhaust gases pass through the turbine portion  510  and exit through outlet  526  at a lower total energy. In this example the bypass pipe  136 A extends from the tuned pipe  47  to the exhaust pipe  142 . In particular, the bypass pipe is illustrated in communication with the center portion  47 B of the tuned pipe  47 . The exhaust gas bypass valve  138  is positioned within the bypass pipe  136 A. The outlet of the bypass pipe  136  communicates with the exhaust pipe  142  before a silencer  710 . The silencer  710  has an exhaust outlet  143 . 
     An inlet source  712  communicates air to be compressed to the compressor portion  512  of the turbocharger  140 . The compressed air is ultimately provided to the engine assembly  40 . 
     As shown is dotted lines, the bypass pipe  136 A may also be coupled to the exhaust manifold  45 , the diverging portion  47 A of the tuned pipe  47 , the converging portion  47 C of the tuned pipe or the stinger  134 . 
     Should the turbocharger  524  be removed, the exhaust pipe  142  is connected directly to the stinger  134 . The inlet source  712  is not required. 
     Referring now to  FIG.  7 B , the silencer  710  may include a plurality of chambers  720 A- 720 C. In the example set forth in  FIG.  7 B , all of the same reference numerals are used. However, in this example, the bypass pipe  136 B communicates exhaust gases around the turbocharger by communicating exhaust gases from the center portion  47 B of the tuned pipe  47  through the exhaust gas bypass valve  138  to a first chamber  720 A of the silencer  710 . It should be noted that the outlet of the bypass pipe  136 B is in the same chamber as the exhaust gases entering from the exhaust pipe  142 . 
     As shown in dotted lines, the bypass pipe  136 B may also be coupled to the exhaust manifold  45 , the diverging portion  47 A of the tuned pipe  47 , the converging portion  47 C of the tuned pipe or the stinger  134 . 
     As in  FIG.  7 A , should the turbocharger  524  be removed, the exhaust pipe  142  is connected directly to the stinger  134 . The inlet source  712  is not required. 
     Referring now to  FIG.  7 C , the bypass pipe  136 C communicates fluidically from the tuned pipe  47  to a chamber  720 A of the silencer  710 . In this example, the chamber  720 A is different than the chamber that the exhaust pipe  142  from the turbocharger entering the silencer  710 . That is, the exhaust pipe  142  communicates with a third chamber  720 C of the silencer while the bypass pipe  136 C communicates with a first chamber  720 A of the silencer  710 . Of course, multiple chambers may be provided within the silencer  710 . The example set forth in  FIG.  7 C  illustrates that a bypass pipe  136 C may communicate exhaust gases to a different chamber than the exhaust pipe  142 . 
     As in the above, should the turbocharger  524  be removed, the exhaust pipe  142  is connected directly to the stinger  134 . The inlet source  712  is not required. 
     Referring now to  FIG.  7 D , engine assembly  40  is illustrated having a fourth example of an exhaust gas configuration. In this case, bypass pipe  136 D does not connect to the exhaust pipe  142 . The outlet of the exhaust gas bypass valve  138  connects to the atmosphere directly or through a supplemental silencer  730  then to the atmosphere. The configuration of  FIG.  7 D  is suitable if packaging becomes an issue. 
     As shown is dotted lines, the bypass pipes  136 C,  136 D in  FIGS.  7 C and  7 D  may also be coupled to the exhaust manifold  45 , the diverging portion  47 A of the tuned pipe  47 , the converging portion  47 C of the tuned pipe or the stinger  134 . 
     As in the above, should the turbocharger  524  be removed, the exhaust pipe  142  is connected directly to the stinger  134 . The inlet source  712  is not required. 
     Referring now to  FIG.  7 E , a two-stroke engine system is set forth. In the present system an engine assembly  40  is coupled to an exhaust manifold  45 . The exhaust manifold  45  is in communication with the tuned pipe  47 . The tuned pipe  47  has a divergent portion  47 A, a center portion  47 B and a convergent portion  47 C. The divergent portion  47 A widens the tuned pipe  47  to the center portion  47 B. The center portion  47 B may be a relatively straight portion or a portion that has a generally constant cross-sectional area. The convergent portion  47 C reduces the diameter of the center portion  47 B to a diameter that is in communication with the stinger  134 . Exhaust gases from the exhaust manifold  45  travel through the divergent portion  47 A and the center portion  47 B and the convergent portion  47 C in a “tuned” manner. That is, the portions  47 A- 47 C are tuned for the particular design of the engine to provide a certain amount of back pressure. Thus, a certain amount of power and stability is designed into the engine assembly. The exhaust gases travel from the stinger  134  to a silencer  710 . As described above a turbocharger  140  may be used to recover some of the energy in the exhaust gases. The tuned pipe  47  has a tuned pipe pressure sensor  734  that is coupled to the tuned pipe  47  to sense the amount of exhaust gas pressure within the tuned pipe  47 . The tuned pipe pressure sensor  734  generates a signal corresponding to the exhaust gas pressure within the tuned pipe  47 . 
     An exhaust gas bypass valve  740  in this example is coupled directly to the exhaust manifold  45 . The exhaust gas bypass valve  740  provides a bypass path through the bypass pipe  136  which may enter either the silencer  710  or communicate directly to atmosphere through a supplemental silencer  730 . Of course, the bypass pipe  136  may be configured as set forth above in the pipe between the turbocharger  140  and the silencer  710 . The exhaust gas bypass valve  740  may be electrically coupled to a controller as will be described further below. Based upon various engine system sensor signals, exhaust gas bypass valve  740  may be selectively opened to provide an increase in power and or stability for the engine assembly  40 . The exhaust gas bypass valve  740  changes the pressure within the tuned pipe  47  so the airflow through the engine is increased or decreased, by changing the differential pressure across the engine. A change in the airflow may be perceived as an increase in power, engine stability or improved combustion stability or a combination thereof. 
     Referring now to  FIG.  7 F , the exhaust gas bypass valve  740 ′ may be disposed on the center portion  47 B of the tuned pipe  47 . However, the exhaust gas bypass valve  740 ′ may also be located on the divergent portion  47 A or the convergent portion  47 C as illustrated in dotted lines. In the example set forth in  FIG.  7 F  the exhaust gas bypass valve  740 ′ is mounted directly to the outer wall  741  of the center portion  47 B of the tuned pipe  47 . The exhaust gas bypass valve  740 ′ may also be coupled to the stinger  134  also as illustrated in dotted lines. 
     Referring now to  FIG.  7 G , the exhaust gas bypass valve  740 ″ may be positioned away from the outer wall  741  of the tuned pipe  47  by a standoff pipe  742 . The standoff pipe  742  may be very short such as a few inches. That is, the standoff pipe  742  may be less than six inches. Thus, the exhaust gas bypass valve  740 ″ may be positioned in a desirable location by the standoff pipe  742  due to various considerations such as packaging. 
     In this example standoff pipe  742  and hence the exhaust gas bypass valve  740 ″ is coupled to the center portion  47 B of the tuned pipe  47 . However, as illustrated in dotted lines, the standoff pipe  742  may be may be coupled to the exhaust manifold  45 , the diverging portion  47 A, the converging portion  47 C or the stinger  134 . 
     The valve  740 ′″ may also be located within the center portion  47 B of the tuned pipe  47 . The control valve  740 ′″ may also be located within the divergent portion  47 A or the convergent portion  47 C or in the exhaust manifold  740 ′″ as illustrated in dotted lines. 
     Referring now to  FIG.  7 H , a control valve  740 ′″ may be disposed within the stinger  134 . The control valve  740 ″ may not communicated bypass exhaust gasses out of the exhaust stream but the valve  740 ′″ may be configured in a similar manner as the exhaust gas bypass valves described above with controlled closed flow through. Valve  740 ″ may be partially opened in the most closed position to allow some exhaust gasses to flow there through. Although the valve  740 ′″ may be used in a turbocharged application, a normally aspirated application may be suitable as well. The valve  740 ′″ may open in response to various conditions so that the power output of the engine may be adjusted depending on such inputs as throttle, load engine speed, tuned pipe pressure and temperature, exhaust pressure and temperature. 
     The exhaust gas bypass valves  740 ,  740 ′,  740 ″ and  740 ′″ may have various types of configurations. In one example the exhaust gas bypass valve  740 - 740 ′″ may be configured as an exhaust gas bypass valve similar to that set forth above and used to bypass the turbocharger  140 . The structural configuration of the valves  740 - 740 ′″ may include but are not limited to a butterfly valve, a slide valve, a poppet valve, a ball valve or another type of valve. 
     Referring now to  FIG.  7 I , the exhaust bypass valve  740  illustrated above may be implemented within a chamber  720 A of the silencer  710 . In this example, the tune pipe  47  communicates exhaust gasses to the silencer  710 . The tune pipe  47  may communicate exhaust gasses from a first portion  747 A, a center portion  747 B, or a third portion  747 C. These are illustrated in the above examples. The exhaust bypass valve  740 ′″ is disposed within one of the chambers  720 A- 720 C. In this example, the exhaust bypass valve  740 ′″ is disposed within the first chamber  720 A. In this example, the turbocharger  140  communicates exhaust gasses to the silencer through the pipe  142 . In this example, the turbocharger  140  is coupled to the pipe  142  which is in communication with the first chamber  720 A. However, any one of the chambers  720 A- 720 C may receive exhaust gasses from the turbocharger  140  through the pipe  142 . 
     Referring now to  FIG.  7 J , the chamber  720 A illustrated in  FIG.  1    is divided into a first chamber portion  720 A′ and a second portion  720 A″ which are separated by a wall  746 . Exhaust gasses are communicated between the first chamber portion  720 A′ and the second portion  720 A″ through the exhaust bypass valve  740   IV . 
     The valve  740 ′″ and  740   IV  are provided to control the amount of pressure in various tuning characteristics of the tune pipe  47 . In  FIG.  7 J , the turbocharger  140  may be in communication with any one of the chambers  720 A″, chamber  720 B, and chamber  720 C. 
     Any of the chambers  720 A-C may be divided into two chambers. 
     Referring now to  FIG.  7 K , the supplemental silencer  730  and the silencer  710  may be disposed as a single unit. The supplemental silencer  710  may be disposed in a common housing but maintain separate flow paths from the valve  138  and the turbo  524 . The silencer  710  and the supplemental silencer  730  may have a common wall  730  therebetween. The common wall reduces manufacturing costs and vehicle weight by reducing the amount of wall material. 
     Referring now to  FIG.  8 A , schematic view of an engine air system that a boost box  810  is illustrated. The boost box  810  has a one way valve  812  coupled therein. The valve  812  may be an active valve such as a motor controlled valve or a passive valve such as a reed valve. When a lower pressure is present in the boost box  810  than the ambient pressure outside the boost box  810 , the valve  812  opens and allows air to bypass the compressor portion  512  of the turbocharger  140 . That is, a bypass path is established through the boost box from the valve  812  through boost box  810  to the engine. That is, the air through the valve  812  bypasses the compressor portion  512  of the turbocharger  140  and the air in boost box  810  is directed to the air intake or throttle body of the engine assembly  40 . 
     The one-way valve  812  may be a reed valve as illustrated in further detail in  FIG.  8 F . By using a one way valve  812 , engine response is improved to activate turbocharger  140  sooner. When the engine response is improved the turbo lag is reduced by allowing the engine to generate exhaust mass flow quicker, in turn forcing the turbine wheel speed to accelerate quicker. When the compressor portion  512  of the turbocharger  140  builds positive pressure the one way valve  812  closes. When implemented, a decrease in the amplitude and duration of the vacuum present in the boost box  810  was achieved. In response, the engine speed increased sooner, and the compressor built positive pressure sooner. 
     Referring now to  FIGS.  8 A- 8 F , the boost box  810  has the one way valve  812  as described above. The one way valve  812  allows air into the boost box  810  while preventing air from leaving the boost box  810 . The boost box  810  also includes a compressor outlet  814 . The compressor outlet  814  receives pressurized air from the compressor portion  512  of the turbocharger  140 . However, due to turbo lag the compressor takes some time to accelerate and provide positive pressure to the boost box  810  particularly when wide open throttle is demanded suddenly from a closed or highly throttled position. 
     The boost box  810  also includes a pair of intake manifold pipes  816  that couple to the throttle body  90  of the engine assembly  40 . 
     A portion of a fuel rail  820  is also illustrated. The fuel rail  820  may be coupled to fuel injectors  822  that inject fuel into the boost box  810  or throttle body  90 . The fuel rail  820  and fuel injectors  822  may also be coupled directly to the throttle body  90 . 
     A boost pressure sensor  824  may also be coupled to the boost box  810  to generate an electrical signal corresponding to the amount of pressure in the boost box  810 , which also corresponds to the boost provided from the compressor portion  512  of the turbocharger  140 . 
     Referring now to  FIG.  8 F , the one way valve  812  is illustrated in further detail. The one way valve  812  may include a plurality of ports  830  that receive air from outside of the boost box  810  and allow air to flow into the boost box  810 . That is, when a lower pressure is developed within the boost box  810  such as under high acceleration or load, the turbocharger  140  is not able to provide instantaneous boost and thus air to the engine is provided through the one way valve  812  to reduce or eliminate any negative pressure, relative to ambient pressure outside the boost box, within the boost box  810 . When compressor portion  512  of the turbocharger  140  has reached operating speed and is pressurizing the boost box  810 , the pressure in the boost box  810  increases and the one way valve  812  closed. That is, the ports  830  all close when pressure within the boost box  810  is higher than the ambient pressure outside the boost box. 
     Referring now to  FIG.  8 G , the boost box  810  is illustrated within an engine compartment  832 . The engine compartment  832  roughly illustrates the engine assembly  40  and the turbocharger  140 . In this example the one way valve  812  is illustrated rearward relative to the front of the vehicle. The position of the one way valve  812  allows cooler air to be drawn into the boost box  810 . 
     Referring now to  FIG.  8 H , the one way valve  812  may be coupled to a duct  840 . The duct  840  allows cooler air to be drawn into the boost box  810  from a remote location. In this example, an upper plenum  842  is coupled to the duct  840 . The upper plenum may pass the air through a filter  862 , such as a screen or fine mesh, prior to being drawn into the boost box  810 . The filter  862  may filter large particles and prevent damage to the boost box  810  and the one way valve  812 . The upper plenum receives air from a vent  846 . A filter  862 ′ may be located at the vent  846  or between the vent  846  and upper plenum  842 . Of course, in one system one filter  862  or the other filter  862 ′ may be provided. 
     The vent  846  may be located in various places on the vehicle. For example, the vent  846  may draw air externally though the hood of the vehicle, the console of the vehicle or from a location under the hood that has clean and cool air. 
     Referring now to  FIG.  8 I , a channel  850  may be formed in the fuel tank  852 . That is, the channel  850  may act as the duct  840  illustrated above in  FIG.  8 H . The channel  850  may be integrally formed into the outer walls  854  of the fuel tank. The boost box  810  may be attached to the fuel tank  852  so that the air drawn into the boost box  810  is received through the channel  850 . A seal  856  may be used between the boost box and the fuel tank  852  so that the air is completely drawn through the channel  850 . Various types of seals may be used. Rubber, foam, thermoplastics are some examples. The seal  856  may be a gasket. A duct  860  may be coupled between the fuel tank  852  and the boost box  810  to receive air from a remote location such as the vent  846  illustrated in  FIG.  8 H  or another location within the engine compartment  832  of the vehicle. Of course, the duct  860  may draw air from other portions of the vehicle or outside the vehicle. A filter or screen  862  may be used to prevent debris from entering the channel  850 . 
     Referring now to  FIG.  9 A , a block diagrammatic view of a control system for a two-stroke turbocharged engine is set forth. In this example a controller  910  is in communication with a plurality of sensors. The sensors include but are not limited to a boost pressure sensor  912 , an engine speed sensor  914 , an atmospheric (altitude or barometric) pressure sensor  916 , a throttle position sensor, tuned pipe pressure sensor  734 , an exhaust valve position sensor  937  and an exhaust manifold pressure sensor. Each sensor generates an electrical signal that corresponds to the sensed condition. By way of example, the boost pressure sensor  912  generates a boost pressure sensor signal corresponding to an amount of boost pressure. The engine speed sensor  914  generates an engine speed signal corresponding to a rotational speed of the crankshaft of the engine and the atmospheric pressure sensor  916  generates a barometric pressure signal corresponding to the atmospheric ambient pressure. 
     The tuned pipe pressure sensor  734  may also be in communication with the controller  910 . The tuned pipe pressure sensor  734  generates a tuned pipe pressure signal corresponding to the exhaust pressure within the tuned pipe  47  as described above. The exhaust valve position sensor  937  and the exhaust manifold pressure sensor  939  generates a respective exhaust valve position signal corresponding to the position of the exhaust valve and the pressure in the exhaust manifold. 
     The controller  910  is used to control an actuator  920  which may be comprised of an exhaust gas bypass valve actuator  922  and exhaust gas diverter valve actuator  924 . An example of the actuator is illustrated in  FIG.  6 I  above. Of course, as mentioned above, the actuators may be one single actuator. The actuator  922  is in communication with the exhaust gas bypass valve  138 . The actuator  924  is in communication with the exhaust gas diverter valve  540 . The controller  910  ultimately may be used to determine an absolute pressure or a desired boost pressure. 
     A boost error determination module  930  is used to determine a boost error. The boost error is determined from the boost pressure sensor  912  in comparison with the desired boost pressure from the boost pressure determination module  932 . The boost pressure error in the boost pressure determination module  930  is used to change an update rate for determining the boost pressure for the system. That is, the boost error determination is determined at a first predetermined interval and may be changed as the boost error changes. That is, the system may ultimately be used to determine an update rate at a faster rate and, as the boost pressure error is lower, the boost pressure determination may determine the desired boost pressures at a lower or slower rate. This will be described in further detail below. This is in contrast to typical systems which operate a PID control system at a constant update rate. Ultimately, the determined update rate is used to control the exhaust gas bypass valve using an exhaust gas bypass valve position module  934  which ultimately controls the actuator  920  or actuator  922  depending if there is a dedicated actuator for the exhaust gas bypass valve  138 . By determining the boost target in the boost pressure determination module  932 , the update rate may be changed depending on the amount of boost error. By slowing the calculations, and subsequent system response, during the approach of the target boost value, overshoot is controlled and may be reduced. Also, the update rate may be increased to improve system response when large boost errors are observed. 
     The controller  910  may be coupled to a detonation sensor  935 . The detonation sensor  935  detects detonation in the engine. Detonation may be referred to as knock. The detonation sensor  935  may detect an audible signal. 
     The controller  910  may also include an absolute pressure module  936  that keeps the engine output constant at varying elevations. That is, by comparing the altitude or barometric pressure from the atmospheric pressure sensor  916 , the boost pressure may be increased as the elevation of the vehicle increases, as well as to compensate for increased intake air charge temperature due to increased boost pressure to maintain constant engine power output. This is due to the barometric pressure reducing as the altitude increases. Details of this will be set forth below. 
     The controller  910  may also include a second exhaust gas bypass valve position control module  938 . The exhaust gas bypass valve position control module  938  is used to control the exhaust gas bypass valve and position the actuator  926  which may include a motor or one of the other types of valve described above. The exhaust gas bypass valve position control module  938  may be in communication with the sensors  912 - 918 ,  935  and  734 . The amount of pressure within the tuned pipe may affect the stability and power of the engine. Various combinations of the signals may be used to control the opening of the exhaust gas bypass valve  740 - 740 ″. The exhaust gas bypass valves  740 - 740 ″ may, for example, be controlled by feedback from the tuned pipe pressure sensor  734 . The tuned pipe pressure sensor signal may be windowed or averaged to obtain the pressure in the tuned pipe as a result of the opening or closing of the exhaust gas bypass valve  740 - 740 ″. The tuned pipe pressure sensor  734  may be used in combination with one or more of the other sensors  912 - 918 ,  734  and others to control the opening and closing of the exhaust gas bypass valve  740 - 740 ″. The boost pressure or average boost pressure from the boost pressure sensor  912  may also be used to control the exhaust gas bypass valves  740 - 740 ″. The boost pressure determination module  932  may provide input to the exhaust gas bypass valve position control module  938  to control the exhaust gas bypass valve based upon the boost pressure from the boost pressure determination module  932  as described above. 
     A map may also be used to control the specific position of the exhaust gas bypass valve  740 - 740 ″. For example, the engine speed signal, the throttle position signal and/or the barometric pressure signal may all be used together or alone to open or close the exhaust gas bypass valve  740 - 740 ″ based on specific values stored within a pre-populated map. 
     Referring now to  FIG.  9 B , in step  940  the actual boost pressure is measured by the boost pressure sensor  912  as mentioned above. In step  942  a boost pressure error is determined. Because this is an iterative process, the boost error is determined by the difference between the target boost and the actual boost pressure. Once the process is cycled through once, a boost error will be provided to step  942 . 
     Referring to step  944 , the update interval is changed based upon the boost error determination in step  942 . That is, the boost error is used to determine the update rate of the exhaust gas bypass valve control method. That is, the update rate corresponds to how fast the method of determining error, then moving the exhaust gas bypass valve actuator, and determine timing of the next cycle is performed. As mentioned above, as the actual boost or measured boost pressure becomes closer to the target boost pressure the update rate is reduced in response to the observed boost error. 
     In step  946  a desired absolute pressure is established. Step  946  may be established by the manufacturer during the vehicle development. The desired absolute pressure may be a design parameter. In step  948  the barometric pressure of the vehicle is determined. The barometric pressure corresponds to the altitude of the vehicle. In step  950  a required boost pressure to obtain the absolute pressure and overcome additional system losses due to elevation is determined. That is, the barometric pressure is subtracted from the required absolute pressure to determine the desired boost pressure. In step  952  the exhaust gas bypass valve and/or the exhaust gas diverter valve for the twin scroll turbocharger is controlled to obtain the desired boost pressure. Because of the mechanical system the desired boost pressure is not obtained instantaneously and thus the process is an iterative process. That is, the required boost pressure from step  950  is fed back to step  942  in which the boost error is determined. Further, the after step  952  step  940  is repeated. This process may be continually repeated during the operation of the vehicle. 
     Referring now to  FIG.  9 C , a throttle position sensor  918  may provide input to the controller  910 . The throttle position sensor signal  954  is illustrated in  FIG.  9 C . The engine speed signal  960  is also illustrated. The signal  958  illustrates the position of the exhaust gas bypass valve. The signal  956  illustrates the amount of boost error. 
     Referring now to  FIG.  9 D , a plot of a calculation multiplier delay versus the absolute boost error pressure is set forth. As can be seen as the boost error decreases the frequency of calculations decreases. That is, as the boost error increases the frequency of calculations increases. 
     Referring now to  FIG.  9 E , a plot of absolute manifold pressure versus elevation is set forth. The barometric pressure and the boost pressure change to obtain the total engine power or target absolute pressure. That is, the absolute pressure is a design factor that is kept relatively constant during the operation of the vehicle. As the elevation increases the amount of boost pressure also increases to compensate for the lower barometric pressure at higher elevations as well as increased intake air temperature. 
     Referring now to  FIG.  9 F , a method for operating the exhaust gas bypass valve  740 - 740 ″ is set forth. In this example the various engine system sensors are monitored in step  964 . The engine sensors include but are not limited to the boost sensor  912 , the engine speed sensor  914 , the altitude/barometric pressure sensor  916 , the throttle position sensor  918  and the tuned pipe pressure sensor  734 . 
     In step  966  the exhaust gas bypass valve  740 - 740 ″ is adjusted based upon the sensed signals from the sensors. The adjustment of the opening in step  966  may be calibrated based upon the engine system sensors during development of the engine. Depending upon the desired use, the load and other types of conditions, various engine system sensors change and thus the amount of stability and power may also be changed by adjusting the opening of the exhaust gas bypass valve. 
     In step  968 , the pressure within the tuned pipe is changed in response to adjusting the opening of the exhaust gas bypass valve  740 - 740 ″. In response to changing the pressure within the tuned pipe, the airflow through the engine is changed. When the airflow through the engine is changed the stability of the engine, the power output of the engine or the combustion stability or combinations thereof may also be improved. It should be noted that the opening of the exhaust gas bypass valve  740 - 740 ″ refers to the airflow though the exhaust gas bypass valve  740 - 740 ″. Thus, the opening may be opened and closed in response to the engine system sensors. 
     Referring now to  FIG.  9 G , the exhaust gas bypass valve position control module  934  is illustrated in further detail. As mentioned above, the exhaust gas bypass valve effective area may be varied depending on various operating conditions. The addition of a turbocharger to a two-stroke engine adds the restriction of the turbine which causes the engine to respond slower than a naturally aspirated engine of similar displacement. The loss of response caused from the turbine may be viewed by a vehicle operator as turbo lag. 
     The exhaust gas bypass valve position module  934  is illustrated having various components used for controlling the exhaust gas bypass valve. An idle determination module  970  is used to receive the engine speed signal. The idle determination module may determine that the engine speed is below a predetermined speed. A range of speeds may be used to determine whether or not the engine is at idle. For example, a range between about 1000 and 2000 rpms may allow the idle determination module  970  to determine the engine is within or at an idle speed. Idle speeds vary depending on the engine configuration and various other design parameters. Once the engine is determined to be at idle the exhaust gas bypass valve effective area module  972  determines the desired effective exhaust gas bypass valve area for the exhaust gas bypass valve. The exhaust gas bypass valve effective area module  972  determines the opening or effective area of the exhaust gas bypass valve for the desired control parameter. For idle speed, a first effective exhaust gas bypass valve area may be controlled. That is, one effective exhaust gas bypass valve area may be used for idle speed determination. Once the exhaust gas bypass valve area is determined the exhaust gas bypass valve actuator  922  may be controlled to open the exhaust gas bypass valve a first predetermined amount. The exhaust gas bypass valve for idle may be opened a small effective area. That is, the exhaust gas bypass valve may be opened further than a fully closed position but less than a fully opened position. For exhaust gas bypass valve such as those illustrated in  FIG.  6    above about twenty degrees of opening may be commanded during the idling of the two-stroke engine. By opening the exhaust gas bypass valve a predetermined amount some of the exhaust gases are bypassed around both the turbine portion  510  of the turbocharger  140  and the stinger  134  at the end of the tuned pipe. The effective predetermined area may change depending on various sensors including but limited to in response to one or more of the engine speed from the engine speed sensor, throttle position from the throttle position sensor or a detonation from the detonation sensor. 
     The exhaust gas bypass valve position control module  934  may also control the exhaust gas bypass valve position during acceleration or to improve engine stability. Acceleration of the engine may be determined in various ways including monitoring the change in engine speed, monitoring the throttle position or monitoring the load on the engine. Of course, combinations of all three may be used to determine the engine is accelerating. When the engine is accelerating as determined in the acceleration determination module  974  the exhaust gas bypass valve effective area module  972  may hold the exhaust gas bypass valve open a predetermined amount. The predetermined amount may be the same or different than the predetermined amount used for the engine idle. Again, some of the exhaust gases are bypassed around the stinger  134  and the turbine portion  510  of the turbocharger  140 . The determined exhaust gas bypass valve effective area is then commanded by the exhaust gas bypass valve effective area module  972  to control the exhaust gas bypass valve actuator module  922 . In a similar manner, the engine sensor may be used to monitor engine stability. In response, the wastegate may open for various amounts of time to increase engine stability. 
     Referring now to  FIG.  9 H , a method for operating the exhaust gas bypass valve in response to acceleration and idle is set forth. In step  980  the engine speed is determined. As mentioned above, the crankshaft speed may be used to determine the speed of the engine. In step  982  is to determine whether the engine is at idle. Determining the engine is at idle may be performed by comparing the engine speed to a threshold or thresholds. The engine speed below a threshold or between two different thresholds may signal the engine is at idle. When the engine is at idle, step  984  determines an effective area for the exhaust gas bypass valve and opens the exhaust gas bypass valve accordingly. In step  986  some of the exhaust gases are bypassed around the stinger  134  and the turbine portion  510  as described above. 
     When the engine is not at idle in step  982  and after step  986 , step  988  determines whether the engine is in an acceleration event. As mentioned above, the acceleration event may be determined by engine speed alone, load alone or the throttle position or combinations of one or more of the three. When the engine is in an acceleration event step  990  holds the exhaust gas bypass valve to a predetermined amount to reduce the backpressure. The predetermined amount may be the same predetermined amount determined in step  984 . The effective area may be controlled by the valve in the exhaust gas bypass valve or another type of opening control in a different type of exhaust gas bypass valve. In step  992  some of the exhaust gases are bypassed around the stinger  134  and turbine portion  510 . 
     Referring back to step  988 , if the engine is not in an acceleration event the engine operates in a normal manner. That is, in step  994  the boost pressure or exhaust backpressure is determined. In step  996  the exhaust gas bypass valve opening is adjusted based upon the boost pressure, the exhaust backpressure or both. After step  996  and step  992  the process repeats itself in step  980 . 
     Referring now to  FIGS.  10 A,  10 B,  10 C and  10 D , the compressor wheel  519 , the turbine wheel  520  and the shaft  521  are illustrated in further detail. The compressor wheel  519  is used to compress fresh air into pressurized fresh air. The compressor wheel  519  includes an inducer diameter  1010  and an exducer diameter  1012 . The inducer diameter  1010  is the narrow diameter of the compressor wheel. The exducer diameter  1012  is the widest diameter of the compressor wheel  519 . 
     The turbine wheel  520  includes an exducer diameter  1020  and an inducer diameter  1022 . The exducer diameter  1020  is the small diameter of the turbine wheel  520 . The inducer diameter  1022  is the widest diameter of the turbine wheel  520 . That is, the top of the blades  1024  have the exducer diameter  1020  and the lower portion of the blades  1024  have the inducer diameter  1022 . The exducer diameter  1020  is smaller than the inducer diameter  1022 . The area swept by the blades  1024  is best illustrated in  FIG.  10 C  which shows the exducer area  1030  and the inducer area  1032 . The area of the port of the exhaust gas bypass valve was described above relative to  FIG.  6 G . The port area is the amount of area available when the valve member  614  is fully open. By sizing the area of the exhaust gas bypass valve port in a desirable way the operation of the two-stroke engine performance is increased. As has been experimentally found, relating the exhaust gas bypass valve effective area (port area) to the area of the turbine wheel exducer is advantageous. The exducer area  1030  may be determined by the geometric relation π times half of the exducer diameter squared. By way of a first example, the port area for a two-stroke engine may be greater than about thirty-five percent of the exducer area. The port area of the exhaust gas bypass valve may be greater than about fifty percent of the exducer area. In other examples the port area of the exhaust gas bypass valve may be greater than about sixty percent of the exducer area. In another example the port area of the exhaust gas bypass valve may be greater than about sixty-five percent of the exducer area. In yet another example the port area of the exhaust gas bypass valve may be greater than about sixty-five percent and less than about ninety percent of the exducer area. In another example the port area of the exhaust gas bypass valve may be greater than about sixty-five percent and less than about eighty percent of the exducer area. In yet another example the port area of the exhaust gas bypass valve may be greater than about seventy percent and less than about eighty percent of the exducer area. In yet another example the port area of the exhaust gas bypass valve may be greater than about seventy-five percent and less than about eighty percent of the exducer area. 
     As is mentioned above, the exhaust gas bypass valve may be incorporated into a two-stroke engine. The exhaust gas bypass valve may be in communication with the tuned pipe  47  and bypassing the turbocharger through a bypass pipe  136 . The exhaust gas bypass valve  138  may be coupled to the center portion of the tuned pipe  47  The effective area of the port is determined using the diameter P 1  shown in  FIG.  6 G  and subtracting the area of the valve member  614  and the axle  618 . 
     Referring now to  FIG.  10 D , a plot of the ratio/percentage of exhaust gas bypass valve or bypass valve area to exducer area for known four stroke engines, two stroke engines and the present example are illustrated. As was observed, providing a higher ratio improved engine performance. The ratios or percentages may be used is four stroke and two stroke engines. From the data set forth is  FIG.  10 D , four stoke engines have a maximum ratio of the port area to the exducer area of 0.5274 or 52.74 percent and for two stroke engines a 35.54 percentage port area to exducer area was found. 
     The foregoing description has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.