Abstract:
A turbocharger compressor bypass valve is disclosed. In one example, the compressor bypass valve operates inversely proportional to engine throttle operation. The approach may simplify compressor bypass valve control and reduced engine system complexity.

Description:
BACKGROUND/SUMMARY 
       [0001]    Turbo charging an engine allows the engine to provide power similar to that of a larger displacement engine while engine pumping work is maintained near the pumping work of a normally aspirated engine of similar displacement. Thus, turbo charging can extend the operating region of an engine. However, during conditions where there is low flow through a compressor of the turbocharger and a high pressure ratio across the compressor, the compressor speed may surge and cause noise or other undesirable responses. Compressor surge may be mitigated via an electrically operated compressor bypass valve (CBV). In particular, the CBV may be opened to allow air to flow from the compressor outlet to the compressor inlet so as to reduce the pressure ratio across the compressor. The electrically operated CBV may be commanded open when compressor surge conditions are approached. For example, the CBV may be opened when an operator releases a torque command actuator (e.g., an accelerator pedal) and the engine throttle is closed to reduce engine torque. The electrically operated CBV may reduce the possibility of compressor surge; however, the electrically operated CBV requires a controller with executable code to open the electrically operated CBV at proper timing. Further, additional electronics may be needed to operate the CBV. Further still, the CBV can add cost to the turbocharged engine. 
         [0002]    The inventors herein have recognized the above-mentioned disadvantages and have developed a system for reducing the possibility of turbocharger compressor surge, comprising: an engine throttle valve responsive to an engine torque command; and a compressor bypass valve in mechanical communication with the engine throttle. 
         [0003]    In this way, the possibility of turbocharger compressor surge may be reduced without incurring additional system cost for electronics and code to operate a compressor bypass valve. In one example, a compressor bypass valve may be configured as a butterfly valve operated via a shaft that operates the engine throttle which controls air flow to the engine. In another example, the compressor bypass valve may be configured as a poppet valve operated via a cam that is rotated via a shaft that adjusts a position of a throttle valve. Thus, the compressor bypass valve may be operated via the same electronics that operate the engine throttle. 
         [0004]    The present description may provide several advantages. In particular, the present description may simplify operation of the compressor bypass valve as it may be operated via the engine throttle actuator. Further, the present description may reduce system cost since the compressor bypass valve may be operated via the same electronics as the engine throttle. Further still, additional computer code for operating the compressor bypass valve may not be necessary. Consequently, additional time may be available for the engine controller to operate other actuators and monitor other system inputs. 
         [0005]    The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
         [0006]    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 FIGURES 
         [0007]      FIG. 1  shows a schematic depiction of an engine and turbocharger; 
           [0008]      FIGS. 2A-2B  and  3 A- 3 B show two example compressor bypass valves; 
           [0009]      FIG. 4  shows a simulated example engine operating sequence; and 
           [0010]      FIG. 5  shows a high level flowchart of a method for operating a turbocharger compressor bypass valve. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The present description is related to operating a turbocharger coupled to an engine.  FIG. 1  shows an example engine that includes a turbocharger and compressor bypass valve.  FIGS. 2A-2B  and  3 A- 3 B show example turbocharger compressor bypass valves.  FIG. 4  shows simulated signals of interest when operating a compressor bypass valve that is mechanically coupled to an engine throttle.  FIG. 5  shows a high level flowchart for controlling an engine having a compressor bypass valve that is in mechanical communication with an engine throttle valve that controls air flowing to engine cylinders. 
         [0012]    Referring to  FIG. 1 , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , is controlled by electronic engine controller  12 . Engine  10  includes combustion chamber  30  and cylinder walls  32  with piston  36  positioned therein and connected to crankshaft  40 . Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake cam  51  and an exhaust cam  53 . Alternatively, one or more of the intake and exhaust valves may be operated by an electromechanically controlled valve coil and armature assembly. The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . 
         [0013]    Fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct injection. Alternatively, fuel may be injected to an intake port, which is known to those skilled in the art as port injection. Fuel injector  66  delivers liquid fuel in proportion to the pulse width of signal FPW from controller  12 . Fuel is delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Fuel injector  66  is supplied operating current from driver  68  which responds to controller  12 . In addition, intake manifold  44  is shown communicating with throttle body  78  including electronic throttle  62  which adjusts a position of throttle plate  64  to control air flow from intake boost chamber  46 . In other examples, the throttle may be mechanically operated by a vehicle driver. Shaft  74  mechanically couples engine throttle plate  64  to compressor bypass valve  77 . 
         [0014]    Compressor  162  draws air through air filter  82  and air intake  42  to supply boost chamber  46 . Exhaust gases spin turbine  164  which is coupled to compressor  162  via shaft  161 . Waste gate actuator  165  may be electrically or vacuum operated and it allows exhaust gases to bypass turbine  164  so that boost pressure can be controlled under varying operating conditions. Compressor bypass valve  77  is operated via electronic throttle  62  and directs air from the outlet of compressor  162  to the compressor inlet of compressor  162  via conduit  76 . Boost pressure in boost chamber  46  may be reduced when compressor bypass valve  77  is opened since output of compressor  162  is fed back to the input of compressor  162 . 
         [0015]    Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . 
         [0016]    Engine exhaust gases are directed to converter  70 . Converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Converter  70  can be a three-way type catalyst in one example. 
         [0017]    Controller  12  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106 , random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  for sensing accelerator position adjusted by foot  132 ; a knock sensor for determining ignition of end gases (not shown); a measurement of engine manifold pressure (MAP) from pressure sensor  121  coupled to intake manifold  44 ; a measurement of boost pressure from pressure sensor  122  coupled to boost chamber  46 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120  (e.g., a hot wire air flow meter); and a measurement of throttle position from sensor  58 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. 
         [0018]    In some embodiments, the engine may be coupled to an electric motor/battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, series configuration, or variation or combinations thereof. Further, in some embodiments, other engine configurations may be employed, for example a diesel engine. 
         [0019]    During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g. when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head (e.g. when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 , resulting in combustion. During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is described merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
         [0020]    Referring now to  FIGS. 2A and 2B , one example of a compressor bypass valve mechanically coupled to an engine throttle is shown in two different positions.  FIGS. 2A and 2B  show plan view cross sections of throttle body  78 .  FIG. 2A  shows the throttle plate  64  of the engine throttle in a substantially fully closed position while  FIG. 2B  shows the throttle plate  64  in a substantially fully open position. The engine throttle and compressor bypass valves shown in  FIGS. 2A and 2B  may be coupled to an engine as shown in  FIG. 1 . Air flows through the throttle passage  204  and the compressor bypass passage  206  in the direction of the arrows. 
         [0021]    Throttle body  78  includes a first engine air passage  204  directing air to engine cylinders. Air flow through passage  204  may be restricted via throttle plate  64 . Throttle plate  64  may be rotated via shaft  74 . Shaft  74  is in communication with compressor bypass valve plate  208  and electric device  202 . In one example, electric device  202  may be a motor electrically coupled to controller  12  of  FIG. 1 . Throttle plate  64  and bypass valve plate  208  rotate together as shaft  74  is rotated via electric device  202 . Bypass valve plate  208  may restrict air flow through passage  206 . In one example, passage  206  provides a portion of a pneumatic coupling between a turbocharger compressor inlet and a turbocharger compressor outlet. 
         [0022]      FIG. 2A  shows that when throttle plate  64  is substantially fully closed, bypass valve plate  208  is substantially fully open. Bypass valve plate  208  moves inversely proportionately to throttle plate  64  when electric device  202  rotates shaft  74 . Air flowing through passage  206  is pneumatically isolated within throttle body  78  from air passing through passage  204 . In one example, bypass valve plate  208  and passage  206  are sized to provide an engine air amount to support combustion at stoichiometric conditions during warm engine idle. Thus, throttle plate  64  may be substantially fully closed during warm engine idle conditions while the engine idles. As throttle plate  64  opens in response to an increasing engine torque demand, the bypass valve plate  208  closes. Throttle plate  64  is shown perpendicular to air flow direction in passage  204  when throttle plate  64  is substantially fully closed. Bypass valve plate  208  is shown parallel to the air flow direction in passage  206 . 
         [0023]      FIG. 2B  shows throttle plate  64  in a substantially fully open position where air flow direction in passage  204  is in parallel with throttle plate  64 . At the same time, bypass valve plate  208  is perpendicular to the direction of air flow in passage  206 .  FIG. 2B  may represent throttle plate position during aggressive vehicle acceleration while  FIG. 2A  may represent throttle plate position after aggressive vehicle acceleration. Since throttle plate  64  is mechanically coupled to bypass valve plate  208 , bypass valve plate  208  may be operated without electronics additional to the electronics operating throttle plate  64 . 
         [0024]    Referring now to  FIGS. 3A and 3B , a second example of a throttle body  78  having a throttle plate  64  mechanically coupled to a bypass valve  314  is shown.  FIGS. 3A and 3B  are cross sections of a throttle body looking into the throttle body in a direction of air flow. In the present example, bypass valve  314  is shown as a poppet valve.  FIG. 3A  shows throttle plate  64  in a substantially fully open position while  FIG. 3B  shows throttle plate  64  in a substantially fully closed position. 
         [0025]      FIG. 3A  shows that electric device  302  is coupled to shaft  308  which in turn is mechanically coupled to throttle plate  64  and bypass valve  314  via cam  310 . A portion of cam  310  is a base circle that provides no lift to raise bypass valve  314  off of valve seat  325 .  FIG. 3A  shows the base circle of cam  310  interfacing with bypass valve  314 . Another portion of cam  310  is elevated from the base circle such that when shaft  308  is rotated, bypass valve  314  is lifted from valve seat  325  so as to allow air to flow through the compressor bypass valve inlet  320  to the compressor bypass valve outlet  318 . Bypass valve  314  is in a closed position as shown when throttle plate  64  is in an open position as shown. Engine throttle passage  304  is shown in a low flow restriction position when throttle plate  64  is parallel to the direction of air flow as shown. Spring  316  provides a force to close bypass valve  314  against valve seat  325 . Air can pass through throttle passage  304  when throttle plate  64  is positioned parallel to the air flow direction. 
         [0026]      FIG. 3B  shows that electric device  302  causes bypass valve  314  to open from valve seat  325  allowing flow from bypass valve inlet  320  to the compressor bypass valve outlet  318  when electric device  302  rotates. Cam  314  is shown in a high lift portion elevated from the base circle. The high lift portion of cam  314  compresses spring  316  and opens bypass valve  314  when throttle plate  64  is in a closed position. Engine throttle passage  304  is shown in a higher flow restriction position when throttle plate  64  is positioned perpendicular to the direction of air flow as shown. 
         [0027]    Thus, the systems as shown in  FIGS. 1-3B  provide for controlling turbocharger compressor surge, comprising: an engine throttle valve responsive to an engine torque command; and a compressor bypass valve in mechanical communication with the engine throttle. The system includes where the compressor bypass valve is a poppet valve. In another example, the system includes where the compressor bypass valve is a butterfly valve. The system also includes where the compressor bypass valve and the engine throttle valve are integral to an engine throttle body. The system also includes where the compressor bypass valve is adjusted proportionally to adjustment of the engine throttle valve. In one example, the system includes where the compressor bypass valve is substantially fully open when the engine throttle valve is substantially fully closed. The system also includes where the compressor bypass valve and the engine throttle valve are operated by a single common shaft, and where a plate of the bypass valve and a plate of the engine throttle valve are coupled to the single common shaft. 
         [0028]    In addition, the systems as shown in  FIGS. 1-3B  provide for controlling turbocharger compressor surge, comprising: a turbocharger coupled to an engine; an engine throttle valve responsive to an engine torque command; and a compressor bypass valve mechanically coupled to the engine throttle valve, the compressor bypass valve positioned along an air flow path between an inlet and an outlet of a compressor of the turbocharger. The system further comprises a controller, the controller including instructions to adjust exhaust gas flow through a turbine of the turbocharger. In yet another example, the system further comprises additional instructions for reducing exhaust flow through the turbine in response to a reduction in an engine torque request. The system also includes where the compressor bypass valve is a poppet valve. The system further includes where the poppet valve is opened via a cam and returned via a spring. In one example, the system includes where the engine throttle valve is an electrically actuated throttle valve. Therefore, the bypass valve and the throttle may be controlled via a single group of electronics directed to controlling the throttle. The system also includes where the engine throttle valve is positioned along an engine air intake path downstream of the compressor. 
         [0029]    Referring now to  FIG. 4 , prophetic signals of interest during an engine operating sequence are shown. The signals of  FIG. 4  may be provided by the system of  FIG. 1  executing the method of  FIG. 5  via instructions of controller  12 . Vertical markers T 0 -T 6  are provided to indicate conditions of interest during the sequence. 
         [0030]    The first plot from the top of  FIG. 4  represents engine throttle plate position (e.g.,  64  of  FIG. 1 ). The X axis represents time and time increases from the left to right side of the plot. The Y axis represents throttle plate position and increasing throttle plate position increases throttle opening allowing greater air flow. The throttle opening area increases in the direction of the Y axis arrow. The throttle position may be adjusted in response to an engine torque command. 
         [0031]    The second plot from the top of  FIG. 4  represents CBV plate position. The CBV plate is mechanically coupled to the engine throttle plate an responds inversely proportionate to engine throttle plate. The X axis represents time and time increases from the left to right side of the plot. The Y axis represents CBV plate position and compressor bypass plate position increases in the direction of the Y axis arrow. Air flow through the CBV can increase when the position of the bypass plate increases so as to increase the CBV opening area. 
         [0032]    The third plot from the top of  FIG. 4  represents compressor pressure ratio versus time. The X axis represents time and time increases from the left to right side of the plot. The Y axis compressor pressure ratio and compressor pressure ratio increases in the direction of the Y axis arrow. 
         [0033]    The fourth plot from the top of  FIG. 4  represents compressor flow (e.g., compressor  162  of  FIG. 1 ) versus time. The X axis represents time and time increases from the left to right side of the plot. The Y axis represents compressor flow rate and compressor flow rate increases in the direction of the Y axis arrow. 
         [0034]    The fifth plot from the top of  FIG. 4  represents compressor bypass flow rate versus time. The X axis represents time and time increases from the left to right side of the plot. The Y axis represents compressor bypass flow rate and compressor bypass flow rate increases in the direction of the Y axis arrow. 
         [0035]    At time T 0 , the throttle plate position is substantially closed and the compressor bypass plate position is substantially open. During such conditions the engine may be at warm idle conditions combusting a substantially stoichiometric air-fuel mixture. The compressor pressure ratio is also shown at a low level as is the compressor flow. Consequently, the turbocharger compressor is not at surge conditions. The compressor bypass flow is at a relatively high flow rate for a compressor bypass passage. 
         [0036]    At time T 1 , engine throttle plate position begins to increase to allow additional air to enter the engine. Since the CBV responds inversely proportional to the engine throttle, air flow through the compressor bypass passage (e.g.,  76  of  FIG. 1 ) is reduced. The increasing throttle position is indicative of an increasing engine torque request, a request to accelerate the vehicle for example. The compressor pressure ratio also increases as the engine throttle opening increases. The compressor pressure ratio increases as air flowing through the compressor increases. The fourth plot from the top of  FIG. 4  indicates an increasing compressor air flow rate. Air flow through the CBV decreases as the throttle opening is increased via moving the throttle plate. 
         [0037]    At time T 2 , engine throttle opening is reduced at a relatively low rate via changing the position of the throttle plate. Since the throttle opening is changing at a relatively low rate, the engine can consume air from the compressor at a rate that reduces the possibility of compressor surge. In particular, the engine consumes air at a rate that limits the pressure ratio across the compressor and allows a middle level of air to flow through the compressor even though the throttle opening is reduced. The CBV position also changes so as to increase air to flow from the compressor outlet to the compressor inlet. 
         [0038]    At time T 3 , engine throttle opening increases to allow additional air to flow to the engine. The compressor bypass valve position decreases to reduce the amount of air flowing from the compressor outlet to the compressor inlet, thereby increasing the turbocharger compressor efficiency. The pressure ratio across the turbocharger compressor also increases as the compressor air flow rate increases so that additional air may be provided to the engine so that the engine torque demand may be met. 
         [0039]    At time T 4 , engine throttle position changes at a higher rate of speed so as to reduce engine torque in response to an engine torque command reduction. During a similar transition where no CBV is present, closing the throttle at a higher rate of speed can reduce air flow through the turbocharger compressor and increase the compressor pressure ratio. However, when the CBV is mechanically coupled to the throttle and the throttle closes, air flow from the outlet of the turbocharger compressor increases to the inlet of the compressor. Consequently, the compressor flow rate and compressor pressure ratio are maintained at levels that limit the possibility of turbocharger compressor surge. Further, compressor efficiency may be reduced. Thus, it can be seen after time T 4 , the compressor pressure ratio decays over time as does the compressor flow rate even though the engine throttle is closed. Air continues to flow through the compressor via the CBV as shown in the fifth plot from the top of  FIG. 4 . 
         [0040]    At time T 5 , the engine throttle position is increased again and the bypass valve is closed in proportion to the opening of the engine throttle. The compressor flow rate and the compressor pressure ratio also increase so as to supply additional air to meet the engine torque request. The compressor bypass flow rate decreases as the engine throttle opening is increased. 
         [0041]    At time T 6 , the engine throttle is reduced at a rate slower than at time T 4  and faster than at time T 2 . The compressor pressure ratio and the compressor flow rate decrease as the throttle opening is decreased. In particular, the compressor flow rate and compressor pressure ratio are at levels that limit the possibility of compressor surge. Thus, a portion of air flowing through the turbocharger compressor flows into the engine while the remaining amount of air flowing through the turbocharger compressor is directed through the CBV. 
         [0042]    In this way, it may be possible to reduce the possibility of compressor surge without having to control a CBV via electronics separate from engine throttle electronics. Thus, control of the CBV occurs by controlling the position of the engine throttle. Consequently, control of the CBV may be simplified. 
         [0043]    Referring now to  FIG. 5 , a method for operating a turbocharger compressor bypass valve is shown. The method  FIG. 5  may be executed via instructions of controller  12  in the system as shown in  FIG. 1 . Further, the method of  FIG. 5  may provide the operating sequence illustrated in  FIG. 5 . 
         [0044]    At  502 , method  500  determines engine operating conditions. Engine operating conditions may include but are not limited to engine speed, engine air amount, engine temperature, engine torque demand, ambient temperature, and ambient pressure. Method  500  proceeds to  504  after engine operating conditions are determined. At  504 , method  500  judges whether or not engine torque demand is increasing. 
         [0045]    The engine torque demand may be made via an operator request or a request of a controller (e.g., a hybrid engine controller). If it is judged that the torque demand is increasing, method  500  proceeds to  506 . Otherwise, method  500  proceeds to  512 . 
         [0046]    At  506 , method  500  adjusts air flow through the turbocharger compressor to provide a desired engine torque. The compressor air flow rate can be increased by adjusting a position of a turbocharger wastegate or of a turbocharger turbine vane. The compressor air flow rate may be increased as the engine torque demand increases. Method  500  proceeds to  508  after the compressor flow rate is adjusted. 
         [0047]    At  508 , method  500  increases engine throttle opening to provide the desired torque level. In one example, a position of a throttle plate is adjusted based on a pressure ratio across the throttle and the desired engine air flow rate. The desired engine air flow rate may be empirically determined and related to the desired engine torque amount. Method  500  proceeds to  510  after the engine throttle plate is adjusted. 
         [0048]    At  510 , method  500  decreases the CBV opening amount inversely proportional to the engine throttle opening amount. In an example where the CBV is mechanically coupled to the engine throttle, the bypass valve opening amount may be reduced by simply opening the engine throttle as shown in  FIGS. 2A-2B  and  3 A- 3 B. In other examples, a position of the CBV may be electrically adjusted in response to engine throttle position. Method  500  proceeds to exit after the bypass valve opening is at least partially closed in response to partially closing an engine throttle in response to an engine torque demand. 
         [0049]    At  512 , method  500  adjusts the turbocharger compressor air flow to provide a desired amount of engine torque. The air flow rate through the turbocharger compressor may be decreased in response to a decrease in engine torque request. In one example, flow rate through a turbocharger compressor may be decreased by opening a normally closed turbocharger wastegate. Method  500  proceeds to  514  after the air flow rate through the compressor is adjusted. 
         [0050]    At  514 , method  500  adjusts an engine throttle opening amount to provide a desired level of engine torque. In one example, the throttle opening amount can be adjusted by closing a throttle plate. Further, the throttle opening amount can be decreased in response to a decreasing engine torque request. Method  500  proceeds to  516  after adjusting the engine throttle opening amount. 
         [0051]    At  516 , method  500  adjusts a position of a CBV to provide a desired compressor flow rate. In one example, the CBV and bypass passage are mechanically sized to provide a threshold level of compressor bypass air flow so as to reduce the possibility of the turbocharger compressor entering surge conditions. In particular, the CBV is sized to maintain compressor flow above a threshold level that limits the possibility of compressor surge. The compressor bypass valve may be configured as illustrated in  FIGS. 2A-2B ,  3 A- 3 B, or in an alternative configuration, if desired. Method  500  proceeds to exit after the position of the CBV is adjusted to provide a desired compressor flow rate. 
         [0052]    Thus, the method of  FIG. 5  provides for a method for controlling surge of a turbocharger compressor, comprising: adjusting a position of an engine throttle valve in response to an engine torque request; and adjusting a position of a compressor bypass valve via the engine throttle. The method also includes where a position of the compressor bypass valve is adjusted proportionately with a position of the engine throttle valve. The method further comprises adjusting a position of a turbocharger wastegate in response to the engine torque request. The method also includes where the compressor bypass valve is mechanically coupled to the engine throttle valve. The method further includes where air is directed from an outlet of a compressor to an inlet of the compressor via the compressor bypass valve when flow through the compressor is less than a threshold level and when a pressure ratio across the compressor is greater than a threshold level. The method further comprises directing air flow from the outlet of the compressor to the inlet of the compressor via the compressor bypass valve during engine idle conditions when the engine throttle valve is substantially closed. 
         [0053]    As will be appreciated by one of ordinary skill in the art, the methods described in  FIG. 5  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 steps 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 objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. 
         [0054]    This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.