Abstract:
A selectively operable vacuum source is disclosed. In one example, vacuum source supplies as much air to an engine as is drawn by the vacuum source from a vacuum reservoir. The approach may provide vacuum to a vehicle vacuum system efficiently and with less weight than other vacuum sources.

Description:
BACKGROUND/SUMMARY 
       [0001]    Vacuum has long been used in vehicles to operate actuators and other devices. Vacuum has been and continues to be an attractive power source because it may be less expensive and more readily available as compared to other power sources. For example, vacuum may be available from the intake manifold of an internal engine or from a vacuum pump powered by the engine or an electrical power source such as a battery. However, as manufacturers strive to increase engine efficiency, vacuum from the engine intake manifold may be less available from the engine intake manifold since engines are being operated more often at higher intake manifold pressures so as to improve engine operating efficiency. By operating an engine at a higher intake manifold pressure, it may be possible for a small engine to produce the same amount of power as a larger engine. For example, air entering a four cylinder engine can be pressurized so that the four cylinder engine has output power similar to a six cylinder engine. In this way, the smaller engine may be more efficient than the larger engine since it may have less friction and fewer pumping losses than the larger engine. However, when an engine is operated at higher intake manifold pressures, less vacuum may be available to power vacuum operated actuators and devices. 
         [0002]    Of course, vacuum may be also supplied to vacuum operated devices via a vacuum pump. However, vacuum pumps that have a capacity to source sufficient vacuum to operate a vehicle&#39;s brake system are often large and heavy. Further, some vacuum pumps require lubricating oil while some vacuum pumps expel oil mist when operated. Thus, vacuum pumps can have limitations that may be undesirable. 
         [0003]    The inventors herein have recognized the above-mentioned disadvantages and have developed a system for providing vacuum for a vehicle, comprising: an ejector; an ejector pump configured to pump only air drawn through a low pressure region of the ejector; and an air conduit, the air conduit housing the ejector and at least a portion of the ejector pump, the air conduit having a sole air inlet and a sole air outlet. 
         [0004]    By placing an ejector or a venturi within an air conduit that has a sole air inlet and a sole air outlet, it may be possible to generate vacuum for actuators and devices even during conditions of high intake manifold pressure. In particular, an ejector pump and/or a venturi pump can be configured to pump air without pump lubricating oil, excepting bearing lubrication which can be placed external to the air conduit so that oil may not enter the air conduit. Further still, since air can be directed from the pump outlet to the pump inlet, the pump may operate at a higher efficiency. 
         [0005]    In addition, by placing the ejector or venturi output at a low pressure, such as along an intake air system, conditions are favorable for producing vacuum. Further, placing the blower that is in communication with an ejector or venturi in a low pressure environment is favorable for reducing blower energy consumption. Ejectors and venturi are devices that are inherently volume flow devices, not mass flow devices, thus lowering the density of the air does not lower the vacuum making potential. 
         [0006]    The present description may provide several advantages. In particular, the approach can selectively provide vacuum based on vacuum consumption. Further, the approach may draw less air into the engine air intake system which bypasses the main air intake filter. Further still, approach may be realized with a light weight ejector or venturi pump. In addition, by using a blower instead of a vacuum pump the expense of sealing the pumping chambers of a vacuum pump are avoided. No conventional air seal is required in the blower configuration. 
         [0007]    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. 
         [0008]    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 
         [0009]      FIG. 1  shows a schematic depiction of an engine; 
           [0010]      FIGS. 2  show a schematic depiction of an air conduit; 
           [0011]      FIGS. 3-4  show simulated signals of interest during engine operation; 
           [0012]      FIG. 5  shows a high level flowchart of a method for providing vacuum to a vacuum system of a vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The present description is related to providing vacuum to assists in actuator operation.  FIG. 1  shows one example embodiment for providing vacuum to a vehicle vacuum system.  FIG. 2  provides one example of an air conduit and ejector for providing vacuum.  FIGS. 3 and 4  show simulated signals of interest when providing vacuum with an engine having a selectively operable ejector or venturi vacuum generating system.  FIG. 5  shows a method for providing the vacuum and control as illustrated in  FIGS. 3-4 . 
         [0014]    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 . 
         [0015]    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 optional electronic throttle  62  which adjusts a position of throttle plate  64  to control air flow from intake boost chamber  46 . 
         [0016]    Compressor  162  draws air from air intake  42  to supply boost chamber  46 . Exhaust gases spin turbine  164  which is coupled to compressor  162  via shaft  161 . Compressor bypass valve  158  may be electrically operated via a signal from controller  12 . Compressor bypass valve  158  allows pressurized air to be circulated back to the compressor inlet to limit boost pressure. Similarly, vacuum operated waste gate actuator  72  allows exhaust gases to bypass turbine  164  so that boost pressure can be controlled under varying operating conditions. Vacuum is supplied to waste gate actuator  72  via vacuum system reservoir  138 . In some examples, vacuum system reservoir  138  may be referred to as a vacuum system reservoir since it can supply vacuum throughout the vacuum system and since brake booster  140  may contain a vacuum reservoir too. Vacuum system reservoir  138  may be supplied vacuum from intake manifold  44  via check valve  63 . Check valve  63  allows air to flow from vacuum system reservoir  138  to intake manifold  44  and substantially prevents air flow from intake manifold  44  to vacuum system reservoir  138 . Vacuum system reservoir  138  may also be supplied vacuum via air conduit  24 . A low pressure region is created via connection through check valve  20  connecting to atmospheric pressure or check valve  21  connecting to intake manifold pressure. Air conduit  24  includes an ejector or a venturi. Ejector check valve  60  allows air to flow from vacuum system reservoir  138  to air conduit  24  and substantially prevents air flow from air conduit  24  to vacuum system reservoir  138 . Ejector or venturi pump  22  is selectively operable and may be comprised of an electrically driven motor. Ejector or venturi pump  22  compresses air within an air conduit  24  supplying air to a converging ejector or venturi nozzle within air conduit  24 . A low pressure region is created in air conduit  24  allowing air to flow from vacuum system reservoir  138  into air conduit  24 . Air exits air conduit  24  and enters the engine air intake system at a location upstream of compressor  162  via check valve  20 . Alternatively, air exits air conduit  24  and enters the engine air intake system at a location downstream of throttle  62 . Check valves  20  and  21  allow air to flow from air conduit  24  to the engine air intake system and substantially prevent air flow from the engine intake system to air conduit  24 . Vacuum system reservoir  138  provides vacuum to brake booster  140  via check valve  65 . Check valve  65  allows air to enter vacuum system reservoir  138  from brake booster  140  and substantially prevents air from entering brake booster  140  from vacuum system reservoir  138 . Vacuum system reservoir  138  may also provide vacuum to other vacuum consumers such as turbocharger waste gate actuators, heating and ventilation actuators, driveline actuators (e.g., four wheel drive actuators), fuel vapor purging systems, engine crankcase ventilation, and fuel system leak testing systems. Check valve  61  limits air flow from vacuum system reservoir  138  to secondary vacuum consumers (e.g., vacuum consumers other than the vehicle braking system). Brake booster  140  may include an internal vacuum reservoir, and it may amplify force provided by foot  152  via brake pedal  150  to master cylinder  148  for applying vehicle brakes (not shown). 
         [0017]    Check valve  63  provides that the reservoir  138  pressure does not exceed the intake manifold pressure. In other words, check valve  63  provides fast pull down of reservoir pressure when a low intake manifold pressure is available. Check valve  60  allows flow when the pressure produced via the ejector within air conduit  24  is lower than the pressure within reservoir  138 . 
         [0018]    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 . 
         [0019]    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. 
         [0020]    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 position sensor  154  coupled to brake pedal  150  for sensing brake pedal position; 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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    Referring now to  FIG. 2 , a schematic depiction of an air conduit is shown. In the illustrated example, air may enter air conduit assembly  200  via a sole air inlet  204 . In some examples, a check valve may be placed between air conduit assembly  200  and vacuum system reservoir  138  to substantially prevent air from flowing from air conduit assembly  200  to vacuum system reservoir  138 . In the example of  FIG. 2 , an ejector is mechanically coupled to air conduit assembly  200 . Thus, in some examples, the ejector may be included as part of air conduit assembly  200 . The ejector is comprised of suction inlet or sole conduit air inlet  204 , converging nozzle  206 , and diffuser outlet  210 . Alternatively, the ejector may be replaced by a venturi that operates in a similar manner as the ejector. Air is supplied to the converging nozzle  206  via conduits  220 . Air is directed from diffuser outlet  210  by ejector or venturi pump  208 . Ejector or venturi pump  208  is shown being driven via motor  22 . Motor  22  may be electrically, mechanically, or hydraulically driven. In one example, motor  22  has a shaft that enters air conduit assembly  200  via a seal that limits leakage of air from conduit  200  to atmosphere. Of course, if motor  22  is within air conduit assembly  200 , no dynamic seal is necessary. Air may exit air conduit assembly  200  via sole air outlet  212 . Check valve  20  allows air to flow from air conduit to engine  10  when a relief pressure of check valve  20  is overcome via pressure from ejector or venturi pump  208 . In other examples, a plurality of check valves may be positioned at the sole outlet of air conduit assembly  200  so that air may be directed to one or more locations. For example, one check valve may direct air to a location along the air intake of the engine while another check valve directs air to a location in the engine crankcase. 
         [0024]    Thus, ejector or venturi pump circulates air through air conduit assembly  200  by drawing air from the diffuser outlet  210  and directing the air back to the ejector inlet at converging nozzle  206 . The pressurized air accelerates through the nozzle and decreases in pressure. Further, the accelerated air exits the converging nozzle and creates a low pressure region  214  allowing air to flow into air conduit assembly  200  via suction inlet  204 . By circulating air around air conduit  220 , the efficiency of ejector or venturi pump  208  can be increased via recovered energy. As air enters air conduit assembly  200  via suction inlet  204 , the outlet pressure of ejector or venturi pump can increase causing check valve  20  to open and allowing a substantially same amount of air to exit air conduit assembly  200  as is drawn into air conduit assembly  200  via suction inlet  204 . In this way, vacuum is generated via air conduit assembly  200  and does not include inducting additional air beyond air displaced to create vacuum. Further, when sole air outlet  212  is coupled to the engine at a low pressure region (e.g., at the inlet of a turbocharger compressor), the efficiency of ejector or venturi pump  208  can be further increased. This is due to two reasons. First, ejectors produce better vacuum as the discharge pressure is lowered. Second, fans/compressors/blowers consume less energy as the air density decreases. As long as the same volumetric flow is maintained, the vacuum produced is unchanged at this lower density. 
         [0025]    Thus, the systems of  FIGS. 1 and 2 , provide for a system for providing vacuum for a vehicle, comprising: an ejector; an ejector pump configured to pump only air drawn through a low pressure region of the ejector; and an air conduit, the air conduit housing the ejector and at least a portion of the ejector pump, the air conduit having a sole air inlet and a sole air outlet. The system includes where the sole air inlet is a suction inlet of the ejector and where the sole air outlet includes at least one check valve positioned to allow air to exit the air conduit and substantially prevent air flow entering into the air conduit. The system also includes where the ejector pump is configured to pump an amount of air out of the sole air outlet that is substantially equivalent to an amount of air drawn through the sole air inlet. In this way, the amount of air drawn from the vacuum system reservoir via the ejector or venturi can reduce the amount of air filtered by the engine as compared to a blower-ejector system that does not circulate the motive fluid (air). In some examples, the system includes where the ejector pump is an electrically motivated pump. The system further includes where the sole air outlet is configured to exhaust air from the air conduit when a relief pressure of the at least one check valve is overcome via a pressure from the ejector pump. The relief valve can substantially limit air flow from the engine intake manifold to the vacuum system reservoir. The system also includes where an inlet to the ejector pump and an outlet of the ejector pump are sealed within the air conduit. The system includes where the air conduit is configured to route air exiting an outlet of the ejector pump to an inlet of the ejector and to route air exiting an outlet of the ejector to an inlet of the ejector pump. 
         [0026]    The systems of  FIGS. 1 and 2  also provide for vacuum system for a vehicle, comprising: an ejector or a venturi; an ejector pump or a venturi pump; an air conduit, the air conduit housing the ejector or the venturi and at least a portion of the ejector pump, the air conduit having a sole air inlet and a sole air outlet; and an engine configured to accept air output from the sole air outlet in an intake air passage. The system also includes where the engine is configured to accept air output from the air conduit to a first location in an air intake of the engine downstream of an air inlet throttle. In one example, the system includes where the engine is further configured to accept air from the air conduit at a second location upstream of a compressor input, and where the air inlet throttle is located downstream of a compressor output. By outputting air from the air conduit to the engine, the efficiency of the ejector pump may be increased. In one example, the system further comprises a first check valve and a second check valve, the first check valve configured to limit air flow from an intake manifold of the engine, the second check valve configured to limit air flow from upstream of the compressor input. In this way, the device always exhausts to the lowest available air pressure. 
         [0027]    The system further comprises a vacuum reservoir, the vacuum reservoir configured to supply air to the air conduit. In some examples, the system further comprises a controller, the controller including instructions for selectively operating the ejector pump or the venturi pump in response to a condition of the vacuum reservoir. Thus, operation of the ejector pump may be limited to conditions where operation of the ejector pump is more efficient. The system further comprises instructions for selectively operating the ejector pump or venturi pump responsive to a condition of an intake manifold of the engine. The system further comprises instructions for adjusting the condition of the vacuum reservoir in response to barometric pressure. The system further comprises a controller, the controller including instructions for selectively operating the ejector pump or venturi pump in response to a condition of a brake pedal. 
         [0028]    It should also be noted that the system of  FIG. 2  can be applied to fuel vapor purge systems. In particular, the suction inlet  204  of air conduit assembly  200  can be coupled to and in fluidic communication with a fuel vapor storage canister via a conduit and valves. The sole air outlet  212  can be coupled to the engine as shown in  FIG. 2 . The ejector pump  208  is operated when an amount of fuel vapors stored in the fuel vapor storage canister exceed a threshold amount. In one example, the air conduit may include a fuel vapor storage medium (e.g., activated charcoal) such that the air conduit acts as a fuel vapor storage device and a vacuum generator. With such a system, the amount of air entering the engine is substantially equivalent to the amount of air entering the air conduit via the fuel vapor storage system. Thus, lower flow rates of higher concentration fuel vapors may be directed to the engine. Consequently, engine air-fuel control may be improved along with fuel economy since the engine may operate with fewer lean or rich air-fuel excursions. 
         [0029]    Referring now to  FIGS. 3 and 4 , simulated signals of interest during engine operation are shown. Similar signals may be produced according to the method of  FIG. 5  with the system of  FIG. 1 .  FIG. 3  includes five plots and  FIG. 4  includes a single plot. The signals are referenced to vertical markers T 0 -T 11  that represent same times in each plot, and the sequences of  FIGS. 3 and 4  occur at the same time and are related. Accordingly,  FIG. 4  is explained with  FIG. 3  below. It should also be noted that the units between plots may be different. For example, a pressure in the intake manifold may appear at a same level as a vacuum reservoir pressure, however, the two pressures may be substantially different. Thus, the signals in  FIGS. 3 and 4  provide directional information rather than absolute data. 
         [0030]    The first plot from the top of  FIG. 3  shows an engine torque command versus time. Engine torque increases in the direction of the Y axis arrow. The X axis represents time, and time increases from the left to the right of the plot. 
         [0031]    The second plot from the top of  FIG. 3  shows engine speed versus time. Engine speed increases in the direction of the Y axis arrow. The X axis represents time, and time increases from the left to the right of the plot. 
         [0032]    The third plot from the top of  FIG. 3  shows engine intake manifold pressure versus time. Engine intake manifold pressure increases in the direction of the Y axis arrow. The X axis represents time, and time increases from the left to the right of the plot. Thus, the intake manifold is at a higher vacuum level when the engine intake manifold pressure is low.  FIG. 3  also includes horizontal line  500  that represents atmospheric pressure. Thus, the engine intake manifold holds a positive pressure when engine intake manifold pressure is above line  500 . On the other hand, the engine intake manifold holds a negative pressure or vacuum when the engine intake manifold pressure is below line  500 . 
         [0033]    The fourth plot from the top of  FIG. 3  shows secondary vacuum reservoir pressure versus time. Vacuum system reservoir pressure increases in the direction of the Y axis arrow. The X axis represents time, and time increases from the left to the right side of the plot.  FIG. 4  also includes two horizontal lines  502  and  504  that represent two threshold vacuum reservoir pressures. Line  504  represents a low pressure or high vacuum threshold whereby it may be desirable to deactivate the ejector or venturi pump. Line  502  represents a vacuum threshold whereby it may be desirable to activate the ejector or venturi pump. Thus, the ejector or venturi pump can be activated at a first pressure and deactivated at a second pressure. 
         [0034]    The fifth plot from the top of  FIG. 3  shows brake booster vacuum reservoir pressure versus time. Brake booster vacuum reservoir pressure increases in the direction of the Y axis arrow. The X axis represents time, and time increases from the left to the right side of the plot. 
         [0035]    Referring now to  FIG. 4 , the first plot from the top of  FIG. 4  shows an ejection or venturi pump command. The pump is commanded on when the signal is near the top of the plot. The pump is commanded off when the signal is near the bottom of the plot. Further, it should be mentioned that the pump may be operated at different speeds to provide different rates and amount of vacuum if desired. 
         [0036]    At time T 0 , the engine torque command is at a middle level as is the engine speed. The engine and vehicle may be cruising during similar conditions. Engine intake manifold pressure is also elevated to a positive pressure. Consequently, the engine intake manifold cannot supply vacuum to the vacuum system reservoir at time T 0 . However, pressure in the vacuum system reservoir is low at time T 0 . Therefore, additional vacuum is not needed at the secondary vacuum reservoir at time T 0 . Further, pressure in the brake booster vacuum reservoir is low at time T 0  so additional vacuum is not needed at time T 0 . Consequently, since there is a desirable level of vacuum in the consumer vacuum reservoir, the ejector or venturi pump is commanded off as indicated by the low level signal at T 0  of  FIG. 4 . 
         [0037]    At time T 1 , the engine torque command decreases and engine speed also starts to decrease as less torque is available to keep the engine at an elevated speed. Engine intake manifold pressure also decreases since the engine torque can be provided with less air to meet the engine torque command. Pressure in the brake booster also increases when the brake is applied to slow the vehicle, for example. Since the brake booster pressure increases above the vacuum system reservoir pressure, a pressure difference is created between the brake booster and the vacuum system reservoir that allows air to flow from the vacuum reservoir to the vacuum system reservoir. The pressure in the vacuum system reservoir may lag the pressure in the brake booster vacuum reservoir and the two pressures may during transient conditions since the reservoirs are linked via a conduit. The ejector pump remains off at time T 1  since pressure in the vacuum system reservoir is less than pressure threshold  502 . 
         [0038]    At time T 2 , the engine torque command remains low and the engine speed continues to fall. The intake manifold pressure also has decreased but remains above atmospheric pressure. Pressure in the vacuum system reservoir has reached pressure threshold  502  which causes the controller to activate the ejector or venturi pump as indicated in  FIG. 4 . Pressure also continues to increase in the brake booster vacuum reservoir in response to a release of the brakes, for example. Air can enter the brake booster vacuum reservoir during application and release of vehicle brakes. A larger quantity of air may enter the brake booster vacuum reservoir when the brake pedal is released as compared to when the brake pedal is applied since air at atmospheric pressure may be used to assist in the application of vehicle brakes. 
         [0039]    Between time T 2  and T 3 , the engine torque command stays low and the engine speed begins to approach idle speed. In addition, intake manifold pressure continues to decrease and goes from a positive pressure to a negative pressure near time T 3 . Pressure in the vacuum system reservoir peaks in response to air drawn into the vacuum system reservoir from the brake booster vacuum reservoir, and then, pressure starts to decrease in the vacuum system reservoir as air is drawn from the vacuum system reservoir into the ejector or venturi. Consequently, pressure in the brake booster also starts to decrease after peaking when air is drawn from the brake booster vacuum reservoir into the vacuum system reservoir. The ejector or venturi pump remains on between time T 2  and T 3 . 
         [0040]    At time T 3 , the engine torque command is low and the engine speed reaches idle speed. The intake manifold pressure also falls to a pressure less than atmospheric pressure so that air can be drawn into the engine intake manifold when pressure in the engine intake manifold is less than pressure in the vacuum system reservoir. A check valve (e.g., check valves  20  and  21 ) between the engine intake manifold and the vacuum system reservoir substantially prevents air flow from the engine intake manifold to the vacuum system reservoir and the check valve allows air flow from the vacuum system reservoir to the engine intake manifold. Pressure in the vacuum system reservoir decreases quickly after time T 3  at a time when the engine intake manifold pressure is less than vacuum system reservoir pressure. Pressure in the brake booster vacuum reservoir also decreases as air is drawn from the brake booster vacuum reservoir to the vacuum system reservoir. The ejector or venturi pump is deactivated when pressure in the vacuum system reservoir reaches pressure threshold  504 . Thus, near time T 3 , the intake manifold assists the ejector or venturi to remove air from the vacuum system reservoir. 
         [0041]    Between time T 3  and T 4 , the engine torque command is low and the engine is at idle speed. The intake manifold pressure is also below atmospheric pressure. Brake booster vacuum reservoir pressure and vacuum system reservoir pressure briefly increase as the brake pedal is depressed. Air that is released into the brake booster vacuum reservoir is quickly removed as the air flows into the engine intake manifold via the vacuum system reservoir. Shortly before time T 4 , the brake pedal is released and pressure in the brake booster vacuum reservoir and in the vacuum system reservoir increase. However, the pressure rise in the vacuum system reservoir lags the pressure rise in the brake booster vacuum reservoir. 
         [0042]    At time T 4 , the engine torque command increases followed shortly thereafter by an increase in engine speed. Intake manifold pressure is also increased so that the engine air amount can be increased to provide the commanded engine torque. Pressure in the vacuum system reservoir increases to a level above pressure threshold  502  causing the controller to reactivate the ejector or venturi pump as indicated by the high level ejector pump command signal in  FIG. 4 . The ejector or venturi begins to draw air from the vacuum system reservoir and pumps it into the engine at a location upstream of a turbocharger so that air enters the engine where pressure in the engine air intake system at a pressure tap is lowest. Pressure in the vacuum system reservoir decreases until it is less than pressure threshold  504 . The ejector or venturi pump is deactivated in response to pressure in the vacuum system less than pressure threshold  504  at time T 5 . 
         [0043]    At time T 6 , the engine torque demand is reduced and the engine speed is also reduced since less engine torque is available to rotate the engine. Intake manifold pressure is also reduced; however, intake manifold pressure remains above atmospheric pressure. The decrease in engine torque and speed may be representative of a vehicle coasting condition. In addition, the brake pedal is applied, but pressure in the vacuum system reservoir remains below pressure threshold  502 . Therefore, the controller does not reactivate the ejector or venturi pump as indicated by the low level pump command at time T 6  of  FIG. 4 . 
         [0044]    Just before time T 7 , the brake pedal is released and the engine torque command is increased shortly thereafter. Pressure in the brake booster vacuum reservoir increases above pressure threshold  502  in response to releasing the brake pedal. Consequently, the controller reactivates the ejector or venturi pump. Engine torque and engine speed are also increased after time T 7  to accelerate the vehicle, for example. Intake manifold pressure also increases as engine cylinder air charge is increased to meet the increased engine torque command. 
         [0045]    Pressure in the vacuum system reservoir and the brake booster vacuum reservoir are gradually pumped down by the ejector or venturi until time T 8  where the brake pedal is reapplied and pressure in the brake booster vacuum reservoir increases. As a result, the ejector or venturi pump remains activated. Shortly after time T 8 , engine intake manifold pressure decreases below atmospheric pressure and consequently air is drawn from the vacuum system reservoir into the engine intake manifold. The intake manifold and the ejector or venturi pump combine to draw air from the brake booster vacuum reservoir and the vacuum system reservoir until pressure in the vacuum system reservoir reaches pressure threshold  504  shortly after time T 8 . The ejector or venturi pump is deactivated when pressure in the vacuum system reservoir reaches pressure threshold  504 . 
         [0046]    Shortly before time T 9 , the brake pedal is released and the engine torque demand is increased to accelerate the vehicle, for example. Releasing the brake causes pressure to rise in the brake booster reservoir and in the vacuum system reservoir. Pressure in the vacuum system reservoir increases to a level greater than pressure level threshold  502 . Consequently, the ejector or venturi pump is reactivated and pressure in the vacuum system reservoir and the brake booster vacuum reservoir is lowered as air is drawn into the ejector or venturi. 
         [0047]    At time T 10 , pressure in the vacuum system reservoir reaches pressure threshold  504  and the controller deactivates the ejector or venturi pump in response to the pressure in the vacuum system reservoir. The engine torque and engine speed are at an elevated level as is the intake manifold pressure. As a result, the ejector or venturi pump is the sole device that reduces pressure in the vacuum system reservoir and the brake booster vacuum reservoir. 
         [0048]    Thus, it can be seen from  FIGS. 3 and 4  that the ejector or venturi pump can be selectively activated and deactivated in response to a pressure in the vacuum system. Further, in some examples, a timer can be activated and incremented when the ejector or vacuum pump is activated. The control strategy may require that the vacuum pump be activated for a minimum time period to reduce cycling of the vacuum pump. In addition, when the ejector or venturi is configured as is shown in  FIG. 2 , the engine inducts only the amount of air removed from the vacuum reservoirs. And, the ejector or venturi pump efficiency may be improved since the ejector or venturi pump is in communication with a lower pressure region of the engine intake system. 
         [0049]    Referring now to  FIG. 5 , method  500  is executable as instructions of a controller such as illustrated in  FIG. 1  with an ejector illustrated in  FIG. 2 . Further, method  500  may provide signals similar to those illustrated in  FIGS. 2 and 3 . 
         [0050]    At  502 , method  500  determines engine operating conditions. Engine operating conditions may include but are not limited to engine temperature, brake booster vacuum reservoir pressure, vacuum system reservoir pressure, ambient pressure and temperature, engine speed, engine intake manifold pressure, and engine torque. Method  500  proceeds to  504  after engine operating conditions are determined. 
         [0051]    At  504 , method  500  judges whether or not vacuum system reservoir pressure is greater than a threshold pressure. In some examples, the threshold pressure may be adjusted to account for barometric pressure. For example, if barometric pressure decreases the threshold pressure may be decreased so that a desired pressure differential exists between atmospheric pressure and pressure in the vacuum system reservoir. Consequently, the pressure at which the ejector pump is activated may be adjusted for changes in barometric pressure. 
         [0052]    If vacuum system reservoir pressure is greater than a threshold pressure, method  500  activates a timer, begins to accumulate time, and proceeds to  506 . Otherwise, method  500  moves to  514 . In other examples, method  500  may also require that intake manifold pressure be greater than atmospheric pressure to activate the ejector or venturi pump so that pump operation may be reduced an so that vacuum in the intake manifold provides vacuum to the vacuum system. Thus, method  500  allows pressure to be drawn from the vacuum system reservoir via the intake manifold without activating the ejector or venturi pump when engine intake manifold pressure is low. In addition, method  500  may activate the ejector or venturi pump at a first threshold pressure and deactivate the ejector of venturi pump at a second threshold pressure. As such, the ejector or venturi pump may cycle on and off less often. 
         [0053]    At  506 , method  500  activates the ejector or venturi pump. In one example, the ejector or venturi pump may be electrically motivated. In other examples, the ejector or venturi pump may be mechanically driven and engaged and disengaged via a clutch. Method  500  proceeds to  508  after activating the ejector or venturi pump. 
         [0054]    At  508 , method  500  pumps air from the vacuum system reservoir. In one example, air is pumped from a vacuum system reservoir  138  as shown in  FIG. 1  via an air conduit and ejector pump as illustrated in  FIG. 2 . Method  500  proceeds to  510  when air is pumped from the vacuum system reservoir. 
         [0055]    At  510 , method  500  re-circulates air through an ejector via a pump as described in  FIG. 2 . In particular, air is drawn into an air conduit via a sole air inlet of the ejector. A low pressure region is created in the ejector by compressing and accelerating air through a converging nozzle of the ejector. The air that is drawn into the ejector is expanded as it passes from a suction input to a diffuser outlet. An ejector pump re-circulates at least a portion of the air drawn into the suction inlet to the converging nozzle. Further, the ejector pump re-circulates air that has already passed through the converging inlet nozzle. Method  500  proceeds to  512  after re-circulating at least a portion of air in the ejector. 
         [0056]    At  512 , method  500  pushes air from the vacuum system reservoir to the engine. Since the air conduit of  FIG. 2  has only a sole air inlet and a sole air outlet, substantially the same amount of air that is drawn into the air conduit via the air inlet exits the air conduit via a sole air outlet. Air proceeds to the engine air intake system or the engine crankcase and check valves substantially prevent air from flowing from the engine intake system or crankcase to the vacuum system reservoir. Method  500  proceeds to  514  after air begins flowing to the engine. 
         [0057]    At  514 , method  500  judges whether or not vacuum system reservoir pressure is less than a threshold pressure. Further, in some examples, method  500  judges whether or not engine intake manifold pressure is less than atmospheric pressure minus a pressure offset and that the ejector pump has been operating for a predetermined amount of time. If vacuum reservoir pressure is less than a threshold pressure, method  500  proceeds to  516 . Otherwise, method  500  proceeds to exit. It should be noted that in some examples, the threshold pressure may be adjusted to account for barometric pressure. Consequently, the pressure at which the ejector pump is deactivated may be adjusted for changes in barometric pressure. For example, if barometric pressure decreases the pressure at which the ejector pump is deactivated may be increased. 
         [0058]    At  516 , method  500  deactivates the ejector pump. The ejector pump may be deactivated by decoupling mechanical or electrical power sources from the ejector pump. Method  500  proceeds to exit after deactivating the ejector pump. 
         [0059]    Thus, the method of  FIG. 5  provides for producing vacuum for a vehicle, comprising: drawing an amount of air from a vacuum reservoir via a low pressure region of an ejector or venturi into an air conduit having a sole air inlet and a sole air outlet; providing at least a portion of the amount of air from the vacuum reservoir to a converting nozzle of the ejector or venturi; and providing an amount of air to an engine via the sole air outlet, the amount of air provided to the engine substantially equivalent to the amount of air drawn from the vacuum reservoir. In one example, the method includes where an ejector pump or venturi pump is selectively operated in response to an operating condition of a vacuum system. The method also includes where operating condition is a pressure of a vacuum reservoir, and where at least a portion of the ejector pump is sealed within the air conduit. Further, the method includes where the amount of air provided to the engine is provided to a first or a second location along an air intake system of the engine depending on a pressure at the first location and a pressure at the second location. 
         [0060]    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. In addition, the terms aspirator or venturi may be substituted for ejector since the devices may perform in a similar manner. 
         [0061]    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.