Abstract:
A turbocharger ( 1 ) includes a wastegate valve ( 30 ) supported on the turbine housing ( 8 ), and a pneumatic actuator ( 100 ) configured to actuate the wastegate valve ( 30 ). The pneumatic actuator ( 100 ) includes a housing ( 101 ) separated into compartments ( 104, 108 ) by a separating member ( 110, 112 ). The actuator ( 100 ) includes a piston ( 112 ) disposed in the housing ( 101 ) that defines at least a portion of the separating member ( 110, 112 ), a piston-biasing spring ( 120 ) disposed in the housing ( 101 ), a first in let ( 126 ) that is in fluid communication with the first compartment ( 104 ), the first inlet configured to be connected to a non-zero-pressure fluid source ( 8 ), and a second inlet ( 116 ) that is in fluid communication with the second compartment ( 108 ), the second inlet ( 116 ) configured to be connected to a non-zero-pressure fluid source ( 104 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and all the benefits of U.S. Provisional Application No. 61/938,284, filed on Feb. 11, 2014, and entitled “Corrosion Resistant Pneumatic Actuator,” which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a pneumatic actuator that uses a flow of air to prevent air and water from entering the pneumatic actuator and to drive water and debris out of the actuator, whereby actuator corrosion and abrasion are reduced. 
         [0004]    2. Description of Related Art 
         [0005]    A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine&#39;s horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, naturally aspirated engines. Using a smaller engine in a vehicle has the desirable effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment. 
       SUMMARY 
       [0006]    In some aspects, a single-acting pneumatic actuator includes a housing having a first portion, a first compartment that is defined in part by the first portion, a second portion, and a second compartment that is defined in part by the second portion and is separated from the first compartment by a separating member. The pneumatic actuator includes a piston disposed in the housing, the piston defining at least a portion of the separating member. The pneumatic actuator includes a spring disposed in the housing and extending between the piston and one of the first portion and the second portion. In addition, the pneumatic actuator includes a first inlet that is in fluid communication with the first compartment, the first inlet configured to be connected to a non-zero-pressure fluid source, and a second inlet that is in fluid communication with the second compartment, the second inlet configured to be connected to a non-zero-pressure fluid source. 
         [0007]    The pneumatic actuator may include one or more of the following features: The second inlet comprises an orifice in the separating member. The second inlet comprises an opening in the second portion of the housing. The second inlet is connected to the first inlet via a fluid line. The second inlet includes a flow restrictor. A valve is disposed in a fluid path between the first inlet and the housing, and the valve controls fluid flow through the second inlet. The valve is a solenoid-operated valve that is configured to control flow of non-zero-pressure fluid from the non-zero-pressure fluid source to the first compartment. The pneumatic actuator further includes the non-zero-pressure fluid source connected to the first inlet, wherein the non-zero-pressure fluid source is configured to provide fluid at a pressure greater than atmospheric pressure. The pneumatic actuator further includes the non-zero-pressure fluid source connected to the first inlet, wherein the non-zero-pressure fluid source is configured to provide fluid at a pressure less than atmospheric pressure. The separating member includes a diaphragm that is connected to the piston, and the second inlet comprises a first opening in the diaphragm and a second opening in the piston. The separating member includes a diaphragm that is connected to the piston, and the second inlet is an opening in the second portion of the housing at a location spaced apart from the diaphragm. The separating member includes an O-ring disposed about a circumference of the piston and providing a seal between the outer surface of the piston and an inner surface of the housing, and the second inlet comprises an orifice in the piston. The separating member includes a diaphragm that is connected to the piston, and the second inlet comprises a single orifice in the diaphragm having a diameter between 0.25 mm and 2.0 mm and a single orifice in the piston having a diameter between 0.25 mm and 2.0 mm. The separating member includes a diaphragm that is connected to the piston, and the second inlet comprises diaphragm orifices and piston orifices, and the total opening area of the orifices is in a range of 0.049 mm 2  to 3.154 mm 2 . The spring is disposed in the second compartment, and the pressure of the fluid supplied to the first compartment is greater than the pressure of the fluid supplied to the second compartment. 
         [0008]    In some aspects, a turbocharger includes a compressor section including a compressor wheel, and a turbine section including a turbine housing that surrounds a turbine wheel, where the turbine wheel is connected to the compressor wheel via a shaft. The turbocharger includes a wastegate valve supported on the turbine housing, and a single-acting pneumatic actuator configured to actuate the wastegate valve. The pneumatic actuator includes a housing having a first portion, a first compartment that is defined in part by the first portion, a second portion, and a second compartment that is defined in part by the second portion and is separated from the first compartment by a separating member. The pneumatic actuator includes a piston disposed in the housing and connected to the wastegate, the piston defining at least a portion of the separating member. The pneumatic actuator includes a spring disposed in the housing and extending between the piston and one of the first portion and the second portion. The pneumatic actuator also includes a first inlet that is in fluid communication with the first compartment, the first inlet configured to be connected to a non-zero-pressure fluid source, and a second inlet that is in fluid communication with the second compartment, the second inlet configured to be connected to a non-zero-pressure fluid source. 
         [0009]    A single-acting pneumatic actuator includes a housing separated into a first compartment and a second compartment by a piston. A biasing spring is disposed in the housing and extends between the piston and an inner surface of the housing. The first compartment includes a first inlet that is configured to be connected to a source of non-zero pressure fluid, and the second compartment includes a second inlet that is configured to be connected to a source of non-zero pressure fluid. The pressurized fluid in the first compartment has a pressure sufficient to overcome the biasing force of the spring and move the piston relative to the housing. The fluid in the second compartment is at a relatively low pressure relative to the absolute pressure of the fluid in the first compartment, and serves to lessen the amount of water and debris which enter the second compartment from the environment. 
         [0010]    The single-acting pneumatic actuator can be compared to some conventional single-acting pneumatic actuators that provide a non-zero pressure to only the first compartment of the actuator. In such conventional pneumatic actuators, air from the atmosphere is drawn into the second compartment when the piston is refracted into the actuator. In these conventional devices, as air enters the second compartment, water and debris may also enter into the second compartment. The water and debris can interfere with the operation of the piston, and can lead to corrosion and abrasion. Advantageously, by providing the pneumatic actuator with a positive pressure in the second compartment, air flow into the second compartment is reduced or eliminated, whereby corrosion and abrasion are reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Advantages of the pneumatic actuator will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0012]      FIG. 1  is a partially-sectioned perspective view of an exhaust gas turbocharger including a wastegate valve connected to a pneumatic actuator. 
           [0013]      FIG. 2  is a cross-sectional view of the pneumatic actuator of  FIG. 1 , illustrating a single small orifice formed in each of the piston and the diaphragm. 
           [0014]      FIG. 3  is a cross-sectional view of another embodiment pneumatic actuator in which the air inlet tube from the first compartment is connected to the second compartment by a fluid line. 
           [0015]      FIG. 4  is a cross-sectional view of another embodiment pneumatic actuator including a separate air inlet tube for each of the first compartment and the second compartment. 
           [0016]      FIG. 5  is a cross-sectional view of another embodiment pneumatic actuator in which a solenoid operated valve connects the first compartment and the second compartment. 
           [0017]      FIG. 6  is a cross-sectional view of another embodiment pneumatic actuator including a vacuum-actuated piston. 
           [0018]      FIG. 7  is a cross-sectional view of another embodiment pneumatic actuator including an O-ring-sealed piston. 
           [0019]      FIG. 8  is a cross-sectional view of another embodiment pneumatic actuator in which the piston and diaphragm each have two small orifices. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring to  FIG. 1 , an exhaust gas turbocharger  1  includes a turbine section  2 , a compressor section  4 , and a bearing housing  4  disposed between and connecting the compressor section  4  to the turbine section  2 . The turbine section  2  includes a turbine housing  8  that defines an exhaust gas inlet  10 , an exhaust gas outlet  12 , and a turbine volute  14  disposed in the fluid path between the exhaust gas inlet  10  and the exhaust gas outlet  12 . A turbine wheel  16  is disposed in the turbine housing  8  between the turbine volute  14  and the exhaust gas outlet  12 . A shaft  18  is connected to the turbine wheel  16 , is rotatably supported within in the bearing housing  6 , and extends into the compressor section  4 . The compressor section  4  includes a compressor housing  20  that defines an air inlet  22 , an air outlet  24 , and a compressor volute  26 . A compressor wheel  28  is disposed in the compressor housing  20  between the air inlet  22  and the compressor volute  26 . The compressor wheel  28  is connected to, and driven by, the shaft  18 . 
         [0021]    In use, the turbine wheel  16  is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold of an engine (not shown). Since the shaft  18  connects the turbine wheel  16  to the compressor wheel  28 , the rotation of the turbine wheel  16  causes rotation of the compressor wheel  28 . As the compressor wheel  28  rotates, it provides a pressure boost to the engine by increasing the air mass flow rate, airflow density and air pressure delivered to the engine&#39;s cylinders via an outflow from the compressor air outlet  24 , which is connected to the engine&#39;s air intake manifold. 
         [0022]    When the pressure of the exhaust gas is high, there may be more exhaust pressure than is required to provide the desired pressure boost. One solution for this problem is to divert exhaust gas away from the turbine wheel  16  during high exhaust gas pressure conditions, so that the amount of exhaust gas reaching the turbine wheel  16  is the quantity needed to provide optimum pressure boost. A wastegate valve  30  is used to divert exhaust gases away from the turbine wheel  16 . Diversion of exhaust gases controls the turbine wheel rotational speed, which in turn controls the rotational speed of the compressor wheel  28 . By controlling the rotational speed of the compressor wheel  28 , the wastegate valve  30  is able to regulate the maximum boost pressure provided to the engine by the turbocharger  1 . 
         [0023]    The wastegate valve  30  is disposed on the turbine housing  8  upstream of the turbine wheel  16 , and is actuated by a pneumatic actuator  100  that uses the turbocharger  1  as a source of pressurized fluid. For example, a portion of the pressurized air from the compressor section  4  is conducted to an air inlet  126  of the pneumatic actuator  100  via a line  109 . When the compressor output pressure is high, the pneumatic actuator  100  opens the wastegate valve  30 . 
         [0024]    Referring to  FIG. 2 , the pneumatic actuator  100  has housing  101  that includes a first portion  103  at a first end  102  thereof, and a second portion  107  at a second end  106  thereof. The first portion  103  and the second portion  107  are held together by a crimp  114  in the housing  101 . The pneumatic actuator  100  includes a flexible, gas-impermeable diaphragm  110  disposed in the housing in a manner such that the peripheral edge of the diaphragm  110  is also held by the crimp  114 . A first compartment  104  is defined between the housing first portion  103  and the diaphragm  110 , and a second compartment  108  is defined between the housing second portion  107  and the diaphragm  110 . 
         [0025]    The diaphragm  110  is connected to a piston  112  that resides in the second compartment  108 . The piston  112  is urged toward the housing first end  102  via a spring  120  that extends between the piston  112  and the housing second end  106 . The piston  112  is connected to the wastegate valve  30  by a rod  124  that extends out of the second portion  107  of the housing  101  through a bushing  122 . 
         [0026]    The pneumatic actuator  100  is single-acting, e.g., the piston  112  is advanced using pressurized fluid applied to one side  112   a  of the piston (e.g., via the diaphragm  110 ), and the piston  112  is returned to a retracted position by the spring  120  which acts on the opposed side  112   b  of the piston. This can be compared to a double-acting pneumatic actuator (not shown) in which a piston is advanced using pressurized fluid applied to one side of the piston, and is retracted using pressurized fluid applied to the opposed side of the piston (e.g., the spring is omitted). 
         [0027]    The first portion  103  includes the pressurized air inlet  126 , through which the first compartment  104  receives pressurized air from the compressor via the line  109 . Thus, the first compartment  104  includes air at a positive pressure, which is defined as being at a pressure greater than atmospheric pressure. The second compartment  108  is nominally pressurized, as discussed in detail below, and thus is substantially at atmospheric pressure. The pressurized air in the first compartment  104  acts on the piston  112 , and when it has sufficient pressure, the air pushes the piston  112  against the force of the spring  120  toward the housing second end  106 . Due to its connection to the wastegate valve  30  via the rod  124 , movement of the piston  112  toward the housing second end  106  results in movement of the wastegate valve  30  from a closed position to an open position. When the first compartment  104  is not at the sufficient pressure, the piston  112  is retracted toward the first end  102  due to the resilient properties of the spring  120 . As the piston  112  moves toward the housing first end  102 , the wastegate valve  30  moves from the open position to a closed position. 
         [0028]    The pneumatic actuator  100  is configured to minimize or eliminate entry of water and debris into the housing  101 . In particular, the diaphragm  110  includes a diaphragm orifice  116 , and the piston  112  includes a piston orifice  118 . The diaphragm orifice  116  and the piston orifice  118  cooperate to permit fluid communication between the first compartment  104  and the second compartment  108 . For example, pressurized air flows from the first compartment  104  into the second compartment  108  through the diaphragm orifice  116  and the piston orifice  118  to provide nominal pressurization of the second compartment  108 . The diaphragm orifice  116  and the piston orifice  118  are relatively small openings, such that the amount of air admitted is sufficient to allow for air to flow through of the second compartment  108 , and prevent the inflow of air into of the second compartment  108  through the clearance space  125  between the bushing  122  surrounding the shaft  124  and an outer surface of the shaft  124 . However, the amount of air admitted through the orifices  116 ,  118  is not large enough to raise the air pressure in of the second compartment  108  to a level that prevents the air in the first compartment  104  from moving the piston  112  in response to the admission of pressurized air through the air inlet  126 . 
         [0029]    The second compartment  108  is vented to the atmosphere through the clearance space  125 . The clearance is small, and in practice a slight (e.g., nominal) positive pressure builds up in the second compartment  108 . By admitting the small amount of pressurized air into the second compartment  108  via the orifices  116 ,  118 , the amount of water and debris entering the second compartment  108  is reduced or eliminated. 
         [0030]    In normal flow, the air flow through an orifice is proportional to the area of the orifice and thus it is proportional to the square of the diameter of the orifice. In general, the flow through an orifice is proportional to the square root of the pressure difference across the orifice. However, in order to avoid over-pressurizing the second compartment  108 , it is preferred that the orifices  116 ,  118  are small and operate in a choked flow mode. In choked flow, at low pressure differences across the orifice, the gas flow is roughly proportional to the area of the orifice, or the square of the diameter of the orifice. This is shown in Table 1. However, in choked flow, the flow through an orifice is not proportional to the square root of the pressure difference. Instead, as the pressure difference across the orifice increases, the increase in flow is smaller than would be expected. 
         [0031]    In order to keep the air flow from the pressurized first compartment  104  to the second compartment  108  in the correct range, the diaphragm orifice  116  and the piston orifice  118  are rather small. Circular orifices between 0.25 mm to 2.0 mm in diameter have been found to be appropriate. Such orifices have an opening area of 0.049 mm 2  to 3.154 mm 2 . At pressure differences, across the orifice, of at least 5 PSIG, that is the pressure relative to atmospheric pressure, the volume of air flowing through an orifice 0.25 mm to 2.0 mm in diameter is choked. At pressure differences less than 20 PSIG, the flow through the orifice increases as the pressure difference gets larger, although not as much as expected. However, when the pressure difference across the orifice is greater than 20 PSIG, there is little increase in the volume of gas flowing through the orifice. In a pneumatic actuator having such an orifice, the air flow the from the first compartment  104  to the second compartment  108  does not increase as the pressure difference between first compartment  104  and the second compartment  108  goes above 20 PSIG. Table 1 shows the calculated flow volumes in mm 3  (cubic millimeters) flowing through a circular orifices of different sizes and various pressure differences in PSIG. These flows are at room temperature, which is maintained constant. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Orifice 
                 Pressurized Portion 
               
               
                 Diameter 
                 Pressure in PSIG 
               
             
          
           
               
                 in mm 
                 5 
                 10 
                 20 
                 30 
                 40 
                 50 
               
               
                   
               
             
          
           
               
                 0.25 
                 10,582 
                 13,867 
                 15,248 
                 15,248 
                 15,248 
                 15,248 
               
               
                 0.5 
                 42,327 
                 55,467 
                 60,994 
                 60,994 
                 60,994 
                 60,994 
               
               
                 1.0 
                 169,309 
                 221,868 
                 243,974 
                 243,974 
                 243,974 
                 243,974 
               
               
                 1.5 
                 380,946 
                 499,202 
                 548,942 
                 548,942 
                 548,942 
                 548,942 
               
               
                 2.0 
                 677,237 
                 887,471 
                 975,897 
                 975,897 
                 975,897 
                 975,897 
               
             
          
           
               
                   
                 Flow Volume in mm 3   
               
               
                   
                   
               
             
          
         
       
     
         [0032]    The single-acting pneumatic actuator  100  can be compared to some conventional single-acting pneumatic actuators that do not include diaphragm openings  116  and piston openings  118 . In such conventional pneumatic actuators, air from the atmosphere is drawn into the first compartment when the piston is retracted toward the second end. In these conventional devices, as air enters the first compartment, water and debris may also enter into the first compartment. 
         [0033]    The water and debris can interfere with the operation of the piston, and can lead to corrosion and abrasion. Advantageously, by providing the pneumatic actuator  100  that includes the diaphragm openings  116  and piston openings  118 , air flow into the second compartment  108  through the clearance space  125  is reduced or eliminated, whereby ingress of foreign matter such as water and debris into the housing  101  is reduced or eliminated. 
         [0034]    Referring to  FIG. 3 , another embodiment single-acting pneumatic actuator  200  includes a housing  201  having a first portion  203  at a first end  202  thereof, and a second portion  207  at a second end  206  thereof. The first portion  203  and the second portion  207  are held together by a crimp  214  in the housing  201 . The pneumatic actuator  200  includes a flexible, gas-impermeable diaphragm  210  disposed in the housing in a manner such that the peripheral edge of the diaphragm  210  is also held by the crimp  214 . A first compartment  204  is defined between the housing first portion  203  and the diaphragm  210 , and a second compartment  208  is defined 
         [0035]    The diaphragm  210  is connected to a piston  212  that resides in the second compartment  208 . The piston  212  is urged toward the housing first end  202  via a spring  120  that extends between the piston  212  and the housing second end  206 . The piston  212  is connected to the wastegate valve  30  by a rod  224  that extends out of the second portion  207  of the housing  201  through a bushing  222 . 
         [0036]    Pressurized air is admitted to the first compartment  204  through a first air inlet tube  226 . In addition, pressurized air is admitted to the second compartment  208  through a second inlet tube  228 . The second inlet tube  228  connects to an opening  205  in the second portion  207  of the housing  201  at a location spaced apart from the diaphragm  210 . A fluid line  227  connects the first inlet tube  226  to the second inlet tube  228 . The fluid line  227  has a relatively small internal diameter, for example in a range of 0.25 mm to 2.0 mm. However, in some applications, it may be more convenient to use an ordinary diameter pipe or hose and include a flow restrictor  236  such as an orifice plate with an orifice 0.25 mm to 2.0 mm in diameter within the pipe or hose. 
         [0037]    The air flowing through the fluid line  227  is choked, and accordingly, beyond a certain point, increases in the air pressure difference between the first compartment  204  and the second compartment  208  do not lead to increases in air flow through the fluid line  227 , as previously discussed. The second compartment  208  is vented to the atmosphere through the clearance space between the bushing  222  surrounding the shaft  224  and an outer surface of the shaft  224 . 
         [0038]    The clearance is small, and in practice a slight (e.g., nominal) positive pressure builds up in the second compartment  208 . As discussed with respect to the previous embodiment, by admitting the small amount of pressurized air into the second compartment  208  via the second inlet tube  228 , the amount of water and debris entering the second compartment  208  is reduced or eliminated. 
         [0039]    Referring to  FIG. 4 , another embodiment single-acting pneumatic actuator  300  includes a housing  301  having a first portion  303  at a first end  302  thereof, and a second portion  307  at a second end  306  thereof. The first portion  303  and the second portion  307  are held together by a crimp  314  in the housing  301 . The pneumatic actuator  300  includes a flexible, gas-impermeable diaphragm  310  disposed in the housing in a manner such that the peripheral edge of the diaphragm  310  is also held by the crimp  314 . A first compartment  304  is defined between the housing first portion  303  and the diaphragm  310 , and a second compartment  308  is defined between the housing second portion  307  and the diaphragm  310 . 
         [0040]    The diaphragm  310  is connected to a piston  312  that resides in the second compartment  308 . The piston  312  is urged toward the housing first end  302  via a spring  320  that extends between the piston  312  and the housing second end  306 . The piston  312  is connected to the wastegate valve  30  by a rod  324  that extends out of the second portion  307  of the housing  301  through a bushing  322 . 
         [0041]    Pressurized air is admitted to the first compartment  304  through a first air inlet tube  326 . In addition, pressurized air is admitted to the second compartment  308  through a second inlet tube  328 . The second inlet tube  328  connects to an opening  305  in the second portion  307  of the housing  301  at a location spaced apart from the diaphragm  310 . Unlike the pneumatic actuator  200  shown in  FIG. 3 , the first air inlet tube  326  and second air inlet tube  328  are not connected, and instead are independent of each other. The amount of air admitted to the second compartment  308  is controlled by the size of the second inlet tube  328 , or alternatively, by placing the flow restrictor  336  in the second inlet tube  328  ( FIG. 4 ). The flow restrictor  336  may be an orifice plate having an orifice with a diameter that is between 0.25 mm to 2.0 mm. The source of pressurized air admitted to the second compartment  308  may be the same source that provides pressurized air to the first compartment  304 . The second compartment  308  is vented to the atmosphere through the clearance space between the bushing  322  surrounding the shaft  324  and an outer surface of the shaft  324 . The clearance is small, and in practice a slight (e.g., nominal) positive pressure builds up in the first portion  308 . As discussed with respect to the previous embodiments, by admitting the small amount of pressurized air into the second compartment  308  via the second inlet tube  328 , the amount of water and debris entering the second compartment  308  is reduced or eliminated. 
         [0042]    Referring to  FIG. 5 , another embodiment single-acting pneumatic actuator  400  includes a housing  401  having a first portion  403  at a first end  402  thereof, and a second portion  407  at a second end  406  thereof. The first portion  403  and the second portion  407  are held together by a crimp  414  in the housing  401 . The pneumatic actuator  400  includes a flexible, gas-impermeable diaphragm  410  disposed in the housing in a manner such that the peripheral edge of the diaphragm  410  is also held by the crimp  414 . A first compartment  404  is defined between the housing first portion  403  and the diaphragm  410 , and a second compartment  408  is defined between the housing second portion  407  and the diaphragm  410 . 
         [0043]    The diaphragm  410  is connected to a piston  412  that resides in the second compartment  408 . The piston  412  is urged toward the housing first end  402  via a spring  420  that extends between the piston  412  and the housing second end  406 . The piston  412  is connected to the wastegate valve  30  by a rod  424  that extends out of the second portion  407  of the housing  401  through a bushing  422 . 
         [0044]    The pneumatic actuator  400  includes a solenoid operated valve  434  disposed in a housing  432  that is supported on the pneumatic actuator housing  401 . Pressurized air is admitted to solenoid operated valve  434  through a first air inlet tube  430 . A second air inlet tube  426  conducts air from the solenoid operated valve  434  to the first compartment  404 . The solenoid operated valve  434  can admit air to an air inlet  428  of the second compartment  408 . The air inlet  428  is opening in the second portion  407  of the housing  401  at a location spaced apart from the diaphragm  410 . When activated, the solenoid operated valve  434  directs air from the first compartment  404  to the second compartment  408 . 
         [0045]    Thus, the first compartment  404  and the second compartment  408  are connected to each other by the solenoid operated valve  434 . At times where less activation of the pneumatic actuator  400  is required, the solenoid operated valve  434  opens and bleeds air to the second compartment  408 . This provides occasional bursts of air to the second compartment  408  to drive out debris and moisture. In the illustrated embodiment, pressurized air is admitted to the solenoid operated valve  434  through the first inlet tube  430 , and the second air inlet tube  426  conducts pressurized air from the solenoid operated valve  434  the first compartment  404 . Alternatively, pressurized air could be directly admitted to the first compartment  404  and the solenoid operated valve  434  would simply conduct pressurized air from the first compartment  404  to the second compartment  408 . The electrical signal to operate the solenoid operated valve  434  can come from a turbocharger controller or from the engine electronic control unit. 
         [0046]    Referring to  FIG. 6 , another embodiment single-acting pneumatic actuator  500  includes a housing  501  that is divided into a first portion  503  at a first end  502  thereof, and a second portion  507  at a second end  506  thereof. The first portion  503  and the second portion  507  are held together by a crimp  514  in the housing  501 . The pneumatic actuator  500  includes a flexible, gas-impermeable diaphragm  510  disposed in the housing in a manner such that the peripheral edge of the diaphragm  510  is also held by the crimp  514 . A first compartment  504  is defined between the housing first portion  503  and the diaphragm  510 , and a second compartment  508  is defined between the housing second portion  507  and the diaphragm  510 . 
         [0047]    The diaphragm  510  is connected to a piston  512  that resides in the first compartment  504 . The piston  512  is urged toward the housing second end  506  via a spring  520  that extends between the piston  512  and the housing first end  502 . The piston  512  is connected to the wastegate valve  30  by a rod  524  that extends out of the second portion  507  of the housing  501  through a bushing  522 . 
         [0048]    A vacuum is applied to the first compartment  504  via a first tube  526 , and is used to control the position of the piston  512  relative to the housing  501 , and thus the position of the wastegate valve  30 . Thus, the first compartment  504  includes air at a negative pressure, which is defined as being at a pressure less than atmospheric pressure. The second compartment  508  is nominally pressurized, and thus is substantially at atmospheric pressure. For example, a small (e.g. nominal) amount of pressurized (e.g., positive pressure) air is admitted to the second compartment  508  through a second tube  528 . The second inlet tube  528  connects to an opening  505  in the second portion  507  of the housing  501  at a location spaced apart from the diaphragm  510 . 
         [0049]    The amount of positively-pressured air admitted to the second compartment  508  is controlled by the size of the second tube  528  or, alternatively, by placing a flow restrictor  536  in the second tube  528  ( FIG. 5 ). The flow restrictor  536  may be an orifice plate having an orifice that has a diameter of 0.25 mm to 2 mm. The turbocharger  1  or other convenient source of pressurized air may be the source providing pressurized air to the second tube  528 . The second compartment  508  is vented to the atmosphere through the clearance space between the bushing  522  surrounding the shaft  524  and an outer surface of the shaft  524 . The clearance is small, and in practice a slight (e.g., nominal) positive pressure builds up in the second compartment  508 . 
         [0050]    As discussed with respect to the previous embodiments, by admitting the small (e.g., nominal) amount of pressurized air into the second compartment  508  via the second tube  528 , the amount of water and debris entering the second compartment  508  is reduced or eliminated. 
         [0051]    Referring to  FIG. 7 , another embodiment single-acting pneumatic actuator  600  includes a housing  601  that is divided into a first portion  603  at a first end  602  thereof, and a second portion  607  at a second end  606  thereof. The first portion  603  and the second portion  607  are held together along a flange  609  by fasteners. A piston  612  is disposed in the housing  601  so as to slide between the first end  602  and the second end  606 . A first compartment  604  is defined between the housing first portion  603  and the piston  612 , and a second compartment  608  is defined between the housing second portion  607  and the piston  612 . 
         [0052]    The piston  612  includes two O-rings  650  that extend around the circumference of the piston  612 . The O-rings  650  provide a fluid-impermeable seal between an outer periphery of the piston  612  and an inner surface of the housing  601 . The piston  612  is urged toward the housing first end  602  by a spring  620  that extends between the piston  612  and the housing second end  606 . The piston  612  is connected to the wastegate valve  30  by a rod  624  that extends out of the second portion  607  of the housing  601  through a bushing  622 . The housing first portion  603  includes an air inlet  626 , and pressurized air (e.g., air at a positive pressure) enters the first compartment  604  through the air inlet  626 . 
         [0053]    The piston  612  includes a piston orifice  618 . In particular, the piston orifice  618  is positioned at a location spaced from the piston outer periphery, and thus does negatively affect the seal provided by the O-rings  650 . The piston orifice  618  provides fluid communication between the first compartment  604  and the second compartment  608 . For example, pressurized air flows from the first compartment  604  into the second compartment  608  through the piston orifice  618 . The piston orifice  618  is dimensioned to provide a relatively small opening, such that the amount of air admitted is sufficient to allow for air to flow through the second compartment  608 , but not large enough to raise the air pressure in the second compartment  608  to a level that prevents the air in the first compartment  604  from moving the piston  612  in response to the admission of pressurized air to the first compartment  604 . For example, the piston orifice  618  has a diameter in a range between 0.25 mm to 2 mm. The quantity of air which bleeds from the first compartment  604  to the second compartment  608  through the orifice  618  is small and thus the high pressure in the first compartment  604  of the pneumatic actuator  600  is not substantially decreased. The second compartment  608  is vented to the atmosphere through the clearance space between the bushing  622  surrounding the shaft  624  and an outer surface of the shaft  624 . A slight (e.g., nominal) positive pressure may build up in the second compartment  608 , but by controlling the orifice size the nominal positive pressure will not interfere with the operation of the pneumatic actuator  600 . Accordingly, the pneumatic actuator  600  will operate normally in the presence of the piston orifice  618 . As discussed with respect to the previous embodiments, by admitting the small amount of pressurized air into the second compartment  608  via the piston orifice  618 , the amount of water and debris entering the second compartment  608  is reduced or eliminated. 
         [0054]    Although the pneumatic actuator  600  is described as having two O-rings  650 , it is understood that one O-ring  650 , or more than two O-rings  650 , can be employed to seal the piston  612  relative to the housing  601 . 
         [0055]    Referring to  FIG. 8 , although the pneumatic actuators  100 ,  600  are described herein as including a single orifice (e.g., a single diaphragm orifice  116  and a single piston orifice  118  for the pneumatic actuator  100 , and a single piston orifice  618  for the pneumatic actuator  600 ), the pneumatic actuators  100 ,  600  are not limited to having a single orifice. For example, another single-acting pneumatic actuator  700  includes a diaphragm  110 ′ having two diaphragm orifices  116 , and a piston  112 ′ having two piston orifices  118 . The pneumatic actuator  700  is otherwise similar in form and function to the pneumatic actuator  100 , and like reference numbers are used to refer to like parts. 
         [0056]    The diaphragm orifices  116  and the piston orifices  118  have a total opening area of 0.049 mm 2  to 3.154 mm 2 . However, the diaphragm  110  and/or the piston  112 ,  612  may include more than two orifices  116 ,  118 ,  618 , and the orifice shapes are not limited to a circular shape, provided that the total opening area of the orifices  116 ,  118 ,  618  is between 0.049 mm 2  to 3.154 mm 2 . 
         [0057]    Pressurized air enters the first compartment  104  through the air inlet  126 . The pressurized air flows into the second compartment  108  through the diaphragm orifices  116  and the piston orifices  118 . The quantity of air which bleeds from the first compartment  104  to the second compartment  108  through the diaphragm orifices  116  and the piston orifices  118  is small and thus the high pressure in the first compartment  104  of the pneumatic actuator  700  is not substantially decreased. A slight positive pressure may build up in the second compartment  108 , but by controlling the size of the diaphragm orifices  116  and the piston orifices  118 , the air admitted to the second compartment  108  will not interfere with the operation of the pneumatic actuator  700 . Accordingly, the pneumatic actuator  700  will operate normally in the presence of the diaphragm orifices  116  and the piston orifices  118 . As discussed with respect to the previous embodiments, by admitting the small amount of pressurized air into the second compartment via diaphragm orifices  116  and the piston orifices  118 , the amount of water and debris entering the second compartment  108  is reduced or eliminated. 
         [0058]    The embodiments described herein include orifices  116 ,  118 ,  618  and or second inlet tubes  228 ,  328 ,  428 ,  528  having a suggested dimension and/or a range of dimensions. It is understood that the dimensions of these orifices and inlets may be decreased to improve actuator reaction timing, or increased to provide additional corrosion resistance. 
         [0059]    A selected illustrative embodiment of the invention is described above in some detail. It should be understood that only structures considered necessary for clarifying the present invention have been described herein. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art. Moreover, while a working example of the present invention has been described above, the present invention is not limited to the working example described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims.