CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and all the benefits of U.S. Provisional Application No. 61/953,202, filed on March 14, 2014, and entitled "Pneumatic Actuator With Multiple Diaphragms," which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

This invention relates to a pneumatic actuator that uses multiple diaphragms to provide redundancy and to reduce the negative effects on actuator durability of contaminants that enter the pneumatic actuator, thereby extending pneumatic actuator life.

2. Description of Related Art

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'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

In some aspects, a pneumatic actuator includes a housing having a first end, a second end, a sidewall that extends between the first end and the second end, and a fluid inlet. The first end, the second end and the sidewall together define a single chamber. The pneumatic actuator includes a separating member disposed in the housing and extending between opposed faces of the sidewall so as to subdivide the chamber into a first compartment and a second compartment, a piston disposed in the housing, the piston connected to the separating member, and a spring disposed in the housing and extending between the piston and one of the first end and the second end. The separating member comprises a primary diaphragm and a secondary diaphragm. The pneumatic actuator may include one or more of the following features: The primary diaphragm and the secondary diaphragm are nested. The primary diaphragm and the secondary diaphragm are formed of the same material. The primary diaphragm is formed of a first material and the secondary diaphragm is formed of a second material, and the first material is different than the second material. The outer diameter of the primary diaphragm is less than the outer diameter of the secondary diaphragm. The pneumatic actuator is a single-acting pneumatic actuator. The primary diaphragm and the secondary diaphragm each comprise a peripheral edge that is secured to the sidewall, a central portion of the secondary diaphragm is secured to a central portion of the piston, and a central portion of the primary diaphragm is secured to the central portion of the secondary diaphragm. The primary diaphragm and the secondary diaphragm each comprise a peripheral edge that is secured to the sidewall, and a central portion of the secondary diaphragm and a central portion of the primary diaphragm are secured to the piston. The peripheral edge of the primary diaphragm and the peripheral edge of the secondary diaphragm are secured together via a crimped portion of the sidewall. The peripheral edge of the primary diaphragm is secured to the sidewall at a first location, and the peripheral edge of the secondary diaphragm is secured to the sidewall at a second location that is different than the first location. The primary diaphragm and the secondary diaphragm each comprise a peripheral edge that is secured to the sidewall, a central portion of the primary diaphragm is secured to a central portion of the piston, and a central portion of the secondary diaphragm is secured to the rod via a plate. The secondary diaphragm is supernumerary. The secondary diaphragm is configured to suppress a resonant vibration response of a spring-mass system of the pneumatic actuator that includes the spring, the piston and a rod that extends from the piston. In some aspects, a pneumatic actuator includes a housing including a first end, a second end, a sidewall that extends between the first end and the second end, and a fluid inlet. The first end, the second end and the sidewall together define a single chamber. The pneumatic actuator includes a separating member disposed in the housing and extending between opposed faces of the sidewall so as to subdivide the chamber into a first compartment and a second compartment, a piston disposed in the housing, the piston connected to the separating member, and a spring disposed in the housing and extending between the piston and one of the first end and the second end. The separating member comprises a primary diaphragm and a supernumerary diaphragm. In some aspects, a pneumatic actuator includes a housing including a first end, a second end, a sidewall that extends between the first end and the second end, and a fluid inlet. The first end, the second end and the sidewall together define a single chamber. The pneumatic actuator includes a diaphragm disposed in the housing and extending between opposed faces of the sidewall so as to subdivide the chamber into a first compartment and a second compartment, a piston disposed in the housing, the piston connected to a second compartment-side of the diaphragm, a rod extending from the piston through an opening in the second end, and a shield that includes a peripheral edge that is secured to an exterior surface of the pneumatic actuator, and a central portion that is secured to the rod.

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. 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 end, a second end, a sidewall that extends between the first end and the second end, and a fluid inlet. The first end, the second end and the sidewall together define a single chamber. The pneumatic actuator includes a separating member disposed in the housing and extending between opposed faces of the sidewall so as to subdivide the chamber into a first compartment and a second compartment, a piston disposed in the housing, the piston connected to the separating member, a spring disposed in the housing and extending between the piston and one of the first end and the second end. The separating member comprises a primary diaphragm and a secondary diaphragm.

A single-acting pneumatic actuator includes a housing separated into a first compartment and a second compartment by a main diaphragm that is movable within the housing 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 at least one secondary diaphragm arranged in series with the primary diaphragm. The secondary diaphragm is redundant to the primary diaphragm, and is included, in part, as a precaution against failure of the primary diaphragm. For example, if any of the diaphragms ceases to be gas tight, the remaining diaphragm takes over. Moreover, since only the primary diaphragm is loaded during actuator operation, employing multiple diaphragms may also double the operating life of the pneumatic actuator, even in the absence of contamination or corrosion. This is because the remaining diaphragm(s) (e.g. one or more secondary diaphragms) are unloaded until failure of the primary diaphragm, and the operating life of the secondary diaphragm(s) begins at the time of failure of the primary diaphragm.

The single-acting pneumatic actuator that includes multiple diaphragms can be compared to some conventional single-acting pneumatic actuators that include only a single diaphragm. In such single-diaphragm pneumatic actuators, air from the atmosphere is drawn into the second compartment when the piston is retracted into the actuator. In these conventional devices, as the air enters the second compartment, water and debris also enter into the second compartment. The water, oil and debris contact the diaphragm, and can lead to premature failure of the diaphragm. Advantageously, by providing the pneumatic actuator with a secondary diaphragm, air flow drawn into the second compartment is prevented from contacting the primary diaphragm whereby the operating life of the primary diaphragm, and thus the pneumatic actuator, is improved. Moreover, oil contaminants from a closed crankcase ventilation system (CCV) or leaked from the compressor housing entering the first compartment are prevented from fouling the secondary diaphragm by the primary diaphragm. Where CCV or compressor housing oil contaminants may foul and lead to premature failure of the primary diaphragm, the secondary diaphragm can take over, extending the operating life of the pneumatic actuator.

In some embodiments, the single-acting pneumatic actuator that includes multiple diaphragms can reduce pneumatic actuator noise associated with vibration response compared to some conventional single-acting, single-diaphragm pneumatic actuators. For example, a secondary diaphragm can be configured to suppress the resonant vibration response of the actuator spring-mass system (e.g., the spring, rod and piston subassembly) that can occur in single-diaphragm pneumatic actuators at certain vibration frequencies and result in actuator ringing. In some cases, the spring mass system has distinct resonant frequencies that are particularly damaging to the primary diaphragm, since the side -to-side movement of the piston generates wear as it rubs on the primary diaphragm. The secondary diaphragm can be strategically arranged within the actuator housing and include material properties such as specific elastic modulus and damping coefficient to suppress the resonant vibration response of the spring-mass system and increase the life of the primary diaphragm. BRIEF DESCRIPTION OF THE DRAWINGS

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: Fig. 1 is a partially-sectioned perspective view of an exhaust gas turbocharger including a wastegate valve connected to a pneumatic actuator.

Fig. 2 is a cross-sectional view of the pneumatic actuator of Figure 1, illustrating a primary diaphragm arranged in series with a secondary diaphragm.

Fig. 3 is a cross-sectional view of an alternative crimp configuration used to secure the diaphragms to the housing sidewall.

Fig. 4 is a cross-sectional view of another alternative crimp configuration used to secure the diaphragms to the housing sidewall.

Fig. 5 is a cross-sectional view of another pneumatic actuator, illustrating an alternative arrangement of the primary and secondary diaphragms. Fig. 6 is a cross-sectional view of another pneumatic actuator, illustrating another alternative arrangement of the primary and secondary diaphragms.

Fig. 7 is a cross-sectional view of another pneumatic actuator, illustrating still another alternative arrangement of the primary and secondary diaphragms.

Fig. 8 is a cross-sectional view of portion of another pneumatic actuator, illustrating an external contaminant shield with the rod in a retracted configuration.

Fig. 9 is a cross-sectional view of the pneumatic actuator of Fig. 8, illustrating the external contaminant shield with the rod in an advanced configuration.

Fig. 10 is a cross-sectional view of another pneumatic actuator, illustrating the external contaminant shield welded to the pneumatic actuator via a weld ring. Fig. 11 is a top perspective view of the external contaminant shield of Fig. 10 including the weld ring. Fig. 12 is a cross-sectional view of still another pneumatic actuator, illustrating the external contaminant shield secured to the pneumatic actuator via studs.

Fig. 13 is a top perspective view of the external contaminant shield of Fig. 12 including a ring having apertures configured to receive studs. DETAILED DESCRIPTION

Referring to Figure 1, an exhaust gas turbocharger 1 includes a turbine section 2, a compressor section 4, and a bearing housing 6 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.

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's cylinders via an outflow from the compressor air outlet 24, which is connected to the engine's air intake manifold.

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.

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 a fluid inlet 126 of the pneumatic actuator 100 via a line 32. When the compressor output pressure is high, the pneumatic actuator 100 opens the wastegate valve 30.

Referring to Fig. 2, the pneumatic actuator 100 has housing 101 that includes a first portion 102 at a first end 104 thereof, and a second portion 103 at a second end 106 thereof. The first portion 102 includes the housing first end 104 and a first sidewall portion 105 that extends generally normal to the housing first end 104 and toward the housing second end 106. Similarly, the second portion 103 includes the housing second end 106 and a second sidewall portion 107 that extends generally normal to the housing second end 106 and toward the housing first end 104. The respective free ends 105a, 107a of the first sidewall portion 105 and the second sidewall portion 107 are joined together by a crimp 111, whereby the first end 104, the second end 106 and the sidewall portions 105, 107 together define a single chamber 108.

The pneumatic actuator 100 includes a flexible, gas-impermeable primary diaphragm 114 disposed in the housing 101 in a manner such that a peripheral edge 114a of the primary diaphragm 114 is held by the crimp 111 so as to form a seal between the primary diaphragm 114 and the housing 101. A first compartment 109 is defined between the housing first portion 102 and the primary diaphragm 114, and a second compartment 110 is defined between the housing second portion 103 and the primary diaphragm 114.

The pneumatic actuator 100 includes a flexible, gas-impermeable secondary diaphragm 117 disposed in the housing 101 in series with the primary diaphragm 114. In particular, a peripheral edge 117a of the secondary diaphragm 117 is held by the crimp 111 so as to form a seal between the secondary diaphragm 117 and the housing 101. The secondary diaphragm 117 is disposed in the second compartment 110.

A piston 112 resides in the second compartment 110. The piston 112 is generally cup shaped (e.g., is U-shaped in cross-section), and includes a closed end 112a, an open end 112b, and a piston sidewall 112c that extends between the open and closed ends 112a, 112b. The piston 112 also includes an outwardly protruding flange 112d formed along the circumference of the open end 112b. The piston open end 112b faces the housing second end 106. The piston 112 is urged toward the housing first end 104 via a spring 120 that extends between the piston closed end 112a and the housing second end 106. The piston 112 is connected to the wastegate valve 30 by a rod 34 that extends out of the second portion 103 of the housing 101 through a bushing 122. The bushing 122 is secured to the housing second end 106 via a baseplate 121.

The housing first portion 102 includes the pressurized fluid inlet 126, through which the first compartment 109 receives pressurized air from the compressor section 4 via the line 32. Thus, the first compartment 109 includes air at a positive pressure, which is defined as being at a pressure greater than atmospheric pressure. The second compartment 110 is substantially at atmospheric pressure. The pressurized air in the first compartment 109 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 34, 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 109 is not at the sufficient pressure, the piston 112 is retracted toward the housing first end 104 due to the resilient properties of the spring 120. As the piston 112 moves toward the housing first end 104, the wastegate valve 30 moves from the open position to a closed position.

The pneumatic actuator 100 is single-acting, e.g., the piston 112 is advanced using pressurized fluid applied to one side of the piston via the primary diaphragm 114, and the piston 112 is returned to a retracted position by the spring 120 which acts on the opposed side of the piston 112. 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).

The primary diaphragm 114 and the secondary diaphragm 117 each comprise a peripheral edge 114a, 117a that is secured to the sidewall portions 105, 107 via the crimp 111. In addition, a central portion 117b of the secondary diaphragm 117 is secured to a centrally- located closed end 112a of the piston, and a central portion 114b of the primary diaphragm 114 is secured to the central portion 117b of the secondary diaphragm 117. While the respective central portions 114b, 117b of the diaphragms 114, 117 are joined, and the peripheral edges 114a, 117a of the diaphragms 114, 117 are joined, intermediate portions 114c, 117c of the diaphragms 114, 117 are not joined, and are freely movable with respect to each other. By this arrangement, the primary diaphragm 114 and the secondary diaphragm 117 are layered in a nested configuration, e.g., they fit together with one within the other. In addition, the outer diameter of the secondary diaphragm 117 is slightly larger than the outer diameter of the primary diaphragm 114 such that some spacing exists between the primary diaphragm intermediate portion 114c and the secondary diaphragm intermediate portion 117c. As a result, the primary diaphragm 114 is loaded during normal operation of the pneumatic actuator 100, while the secondary diaphragm 117 remains unloaded.

In these embodiments, the secondary diaphragm 117 is supernumerary. As used herein, the term "supernumerary" refers to the secondary diaphragm 117 as "being in excess of the usual number, a duplicate as a precaution against failure." Since the pneumatic actuator 100 includes multiple diaphragms 114, 117, the actuator B10 life (e.g., the lifetime total number of inches traveled under a rated load) may be extended by a factor of two or more. In cases where dirt contamination is an issue, the secondary, unloaded diaphragm 117 prevents dirt from coming into contact with the primary, loaded diaphragm 114. In cases where CCV exhaust or oil contamination from the compressor housing causes a premature failure of the primary diaphragm 114, the secondary diaphragm 117 becomes loaded, and the primary diaphragm, which remains in place, serves to limit fouling of the secondary diaphragm 1 17 by CCV exhaust and/or oil contamination. Although two diaphragms 114, 117 are shown in Fig. 1, the pneumatic actuator 100 is not limited to having two diaphragms.

In some embodiments, the primary diaphragm 114 and the secondary diaphragm 117 are formed of the same material. However, the diaphragm 114, 117 is typically one of the most expensive components of the pneumatic actuator 100. For this reason, using multiple, full- specification diaphragms may not be justified. Thus, in other embodiments, the primary diaphragm 114 is formed of a first material and the secondary diaphragm 117 is formed of a second material, and the first material is different than the second material. For example, one of the diaphragms (e.g., the primary diaphragm 114) is formed of a material that fully complies with the specifications of the application, and the other of the diaphragms (e.g., the secondary diaphragm 117) is made from a material that is inexpensive relative to the material used to form the primary diaphragm, and thus serves as a contamination shield. In this example, since the secondary diaphragm 117 serves as a contamination shield, the second diaphragm 117 need not be gas-impermeable, and the second material can be selected accordingly. Provided that the two different diaphragms are similar in geometry, then the two may be assembled and crimped together, thereby incurring no additional assembly time and/or cost for this improvement.

In the illustrated embodiments, the crimp 111 is formed by layering the primary diaphragm peripheral edge 114a and the secondary diaphragm peripheral edge 117a over the free end 105 a of the first sidewall portion 105, which is turned outward. The second sidewall portion 107a is wrapped around the layers formed by the primary diaphragm peripheral edge 114a, the secondary diaphragm peripheral edge 117a, and the first sidewall portion free end 105a. The second sidewall portion 107a is then crimped onto these layers to form the crimp 111 (see, for example, Fig. 2). Retention of the diaphragms 114, 117 within the crimp 111 may be improved by providing a bead along the peripheral edge of one or both of the primary diaphragm 114 and the secondary diaphragm 117. For example, with reference to Fig. 3, one of the diaphragms, i.e., the primary diaphragm 114, includes a bead 115 formed along the peripheral edge 114a that protrudes toward the other of the diaphragms, i.e., the secondary diaphragm 117. The secondary diaphragm 117 is bead-free, and conforms to the shape of the bead within the crimp 111 '. The second sidewall portion 107a is wrapped around the layers formed by the primary diaphragm peripheral edge 114a, the secondary diaphragm peripheral edge 117a, and the first sidewall portion free end 105a. The second sidewall portion 107a is then crimped onto these layers to form the crimp 111 ', whereby both diaphragms 114, 117 are surely secured within the crimp 111 '.

Referring to Fig. 4, in another example, the primary diaphragm 114 includes a bead 115 formed along the peripheral edge 114a that protrudes away from the secondary diaphragm 117. In addition, the secondary diaphragm 117 includes a bead 118 formed along the peripheral edge 117a that protrudes away from the primary diaphragm 114. In addition the respective free ends 105 a, 107a of the housing sidewall portions 105, 107 are curved to accommodate the shape of the beads 115, 118. The second sidewall portion 107a is wrapped around the layers formed by the primary diaphragm peripheral edge 114a, the secondary diaphragm peripheral edge 117a, and the first sidewall portion free end 105a. The second sidewall portion 107a is then crimped onto these layers to form the crimp 111 ", whereby both diaphragms 114, 117 are surely secured within the crimp 111 ". Referring to Fig. 5, an alternative embodiment pneumatic actuator 200 is substantially similar to the pneumatic actuator 100 described above, whereby common components will be referred to with common reference numbers, and the description thereof will be omitted. Like the pneumatic actuator 100, the pneumatic actuator 200 includes multiple diaphragms. In particular, the pneumatic actuator 200 includes a flexible, gas-impermeable primary diaphragm 214 disposed in the housing 101 in a manner such that a peripheral edge 214a of the primary diaphragm 214 is held by the crimp 11 1 so as to form a seal between the primary diaphragm 214 and the housing 101. In addition, a central portion 214b of the primary diaphragm 214 is secured to the central portion 112a of the piston 112. The pneumatic actuator 200 also includes a flexible, gas-impermeable secondary diaphragm 217 disposed in the housing 101 in a manner such that a peripheral edge 217a of the secondary diaphragm 217 is held by the crimp 111 so as to form a seal between the secondary diaphragm 217 and the housing 101. The secondary diaphragm 217 is disposed in the second compartment 110. In addition, a central portion 217b of the secondary diaphragm 217 is secured to a second end-facing surface of the piston flange 112d. In addition, the outer diameter of the secondary diaphragm 217 is much larger than the outer diameter of the primary diaphragm 214 such that spacing exists between the primary diaphragm intermediate portion 214c and the secondary diaphragm intermediate portion 217c. In particular, the secondary diaphragm intermediate portion 217c drapes away from the primary diaphragm intermediate portion 214c to a sufficient extent that the primary diaphragm 214 and the secondary diaphragm 217 are in contact only at the crimp 111, regardless of the position of the piston 112.

As in the previous embodiment, the primary diaphragm 214 is loaded during normal operation of the pneumatic actuator 200, while the secondary diaphragm 217 remains unloaded. In addition, since the primary diaphragm 214 and the secondary diaphragm 217 only contact each other at their respective peripheral edges 214a, 217a, the diaphragm configuration used in the pneumatic actuator 200 avoids a circumstance in which the performance or durability of the primary diaphragm 214 is adversely affected by contact with the secondary diaphragm 217 during actuator operation.

Referring to Fig. 6, another alternative embodiment pneumatic actuator 300 is a variation of the embodiment illustrated in Fig. 5. The pneumatic actuator 300 is substantially similar to the pneumatic actuator 100 described above, whereby common components will be referred to with common reference numbers, and the description thereof will be omitted. Like the pneumatic actuator 100, the pneumatic actuator 300 includes multiple diaphragms. In particular, the pneumatic actuator 300 includes a flexible, gas-impermeable primary diaphragm 314 disposed in the housing 101 in a manner such that a peripheral edge 314a of the primary diaphragm 314 is held by the crimp 111 so as to form a seal between the primary diaphragm 314 and the housing 101. In addition, a central portion 314b of the primary diaphragm 314 is secured to the central portion 112a of the piston 112.

The pneumatic actuator 300 also includes a flexible, gas-impermeable secondary diaphragm 317 disposed in the housing 101 in a manner such that no contact exists between the primary diaphragm 314 and the secondary diaphragm 317. In particular, a peripheral edge 317a of the secondary diaphragm 317 secured to an inner surface of the piston sidewall 112c, and a central portion 317b of the secondary diaphragm 317 is secured to the housing second end 106, for example by clamping the secondary diaphragm central portion 317b between the base plate 121 and the housing second end 106. As in the previous embodiments, the secondary diaphragm 317 is disposed in the second compartment 110. As a result, the secondary diaphragm 317 is configured to prevent fouling of the primary diaphragm 314 via contaminant entry into the chamber 108 via the housing second end 106, while avoiding contact with the primary diaphragm 314, regardless of the position of the piston 1 12. In some embodiments, the secondary diaphragm 317 may include features that suppress the resonant vibration response of the actuator spring-mass system that includes the spring 120, the rod 34 and the piston 1 12. For example, the secondary diaphragm 317 is connected to the pistion 112 and houisng 101 indendently of the primary diaphragm 314 and can be formed having material properties such as specific elastic modulus and damping coefficient that are designed to supress the resonant vibration response of the spring-mass system. Suppression of the resonant vibration respons reduces actuator noise and reduces wear due to piston motion relative to the primary diaphragam, thus increasing the life of the primary diaphragm. Although the secondary diaphragm 317 is arrranged such that a peripheral edge 317a of the secondary diaphragm 317 secured to an inner surface of the piston sidewall 112c, and a central portion 317b of the secondary diaphragm 317 is secured to the housing second end 106, it is contemplated that other arrangments can be employed that will likewise reduce lateral motion of the piston 112 with respect to the housing 101. Referring to Fig. 7, another alternative embodiment pneumatic actuator 400 is a further variation of the embodiment illustrated in Fig. 5. The pneumatic actuator 400 is substantially similar to the pneumatic actuator 100 described above, whereby common components will be referred to with common reference numbers, and the description thereof will be omitted. Like the pneumatic actuator 100, the pneumatic actuator 400 includes multiple diaphragms. In particular, the pneumatic actuator 400 includes a flexible, gas-impermeable primary diaphragm 414 disposed in the housing 101 in a manner such that a peripheral edge 414a of the primary diaphragm 414 is held by the crimp 11 1 so as to form a seal between the primary diaphragm 414 and the housing 101. In addition, a central portion 414b of the primary diaphragm 414 is secured to the central portion 112a of the piston 112.

The pneumatic actuator 400 includes a flexible, gas-impermeable secondary diaphragm 417 disposed in the housing 101 in series with the primary diaphragm 414. In particular, a peripheral edge 417a of the secondary diaphragm 417 is held by the crimp 111 so as to form a seal between the secondary diaphragm 417 and the housing 101. The secondary diaphragm 417 is disposed in the second compartment 110.

The pneumatic actuator 400 includes a secondary base plate 424 that is fixed to the rod 34. The secondary base plate 424 is annular, and the rod 34 passes through an opening 425 formed in a central portion 424a of the secondary base plate 424. The secondary base plate 424 includes a lip 424c formed along the circumference of the peripheral edge 424b. The lip 424c extends in parallel to a longitudinal axis of the rod 34. The secondary base plate 424 is disposed within the inner space defined by the piston 112 so that the central portion 424a is closely spaced from the piston closed end 112a, and the lip 424c confronts the piston sidewall 112c. A central portion 417b of the secondary diaphragm 417 is secured to the secondary base plate 424, for example by clamping the secondary diaphragm central portion 417b between the secondary base plate 424 and an inner surface of the piston closed end 112a. Thus the central portions 414b, 417b of the respective diaphragms 414, 417 are separated by the piston 112. Although the peripheral edges 414a, 417a of the diaphragms 414, 417 are joined, intermediate portions 414c, 417c of the diaphragms 414, 417 are not joined, and are freely movable with respect to each other. By this arrangement, the primary diaphragm 414 and the secondary diaphragm 417 are layered in a nested configuration, e.g., they fit together with one within the other. In addition, the outer diameter of the secondary diaphragm 417 is larger than the outer diameter of the primary diaphragm 414 such that some spacing exists between the primary diaphragm intermediate portion 414c and the secondary diaphragm intermediate portion 417c. As a result, the primary diaphragm 414 is loaded during normal operation of the pneumatic actuator 400, while the secondary diaphragm 417 remains unloaded. As in the previous embodiments, the secondary diaphragm 417 is disposed in the second compartment 110, whereby the secondary diaphragm 417 is configured to prevent fouling of the primary diaphragm 414 via contaminant entry into the chamber 108 via the housing second end 106, while contacting the primary diaphragm 414 at only the peripheral edge 414a, 417a, regardless of the position of the piston 112. In this configuration, contact between the diaphragms 414, 417 is minimized during operation of the pneumatic actuator 400, whereby diaphragm durability is increased.

Referring to Figs. 8-9, in cases where an additional internal diaphragm or contaminant shield is unfavorable or unfeasible, an external contaminant shield 550 can be used. In one example, a pneumatic actuator 500 includes the external contaminant shield 550. The pneumatic actuator 500 is substantially similar to the pneumatic actuator 100 described above, whereby common components will be referred to with common reference numbers, and the description thereof will be omitted. In the pneumatic actuator 500, the secondary diaphragm 117 may be omitted since its shielding function will be performed by the external contaminant shield 500. The external contaminant shield 550 is a flexible, gas-impermeable sheet that includes a peripheral edge 550a that is connected to the housing second end 106 adjacent to housing second sidewall portion 107, as discussed further below. The external contaminant shield 550 includes a central opening 552 through which the rod 34 extends. A seal 554 (i.e., an O-ring seal) is secured to the opening 552 and provides a sealed connection between rod 34 and the external contaminant shield 550. The rod 34 may include a groove 36 that maintains the seal 554 in a desired axial position.

The external contaminant shield 550 is sufficiently elastic to change between a first configuration corresponding to a retracted position of the piston 112, in which the shield generally conforms to the shape and size of the housing second end 106 (Fig. 8), and a second configuration corresponding to an advanced position of the piston 112, in which the central portion 550b of the external contaminant shield 550 is pulled away from the housing second end 106 and is thus enlarged (Fig. 9). In the second configuration, the space between the external contaminant shield 550 and the housing second end 106 defines an external air storage compartment 560 that receives, and causes displacement of, air from the second compartment 110 as the pneumatic actuator 500 operates. By providing the external air storage compartment 560, air exchange between the second compartment 110 and the environment is significantly reduced, thus contaminant ingress into the second compartment 110 is reduced. In some embodiments, the seal 554 is configured to provide a hermetic seal.

In some embodiments, the peripheral edge 550a of the external contaminant shield 550 may be connected to the actuator housing 101 using conventional techniques that may include welding, use of adhesives, interference fit, etc. In other embodiments, the peripheral edge 550a of the external contaminant shield 550 may be connected to the actuator housing 101 via a crimp in the actuator housing 101.

Referring to Figs. 10 and 11, in still other embodiments, the external contaminant shield 550' includes a weldable ring 570 secured to the shield peripheral edge 550a, for example via rivets 572. The pneumatic actuator 500' may be provided with a bracket 578 that is fixed to the housing second end 106. The external contaminant shield 550' is secured to the housing second end 106 by welding the ring 570 to the bracket 578.

Referring to Figs. 12 and 13, in still other embodiments, the external contaminant shield 550" includes a molded plastic ring 580 secured to the shield peripheral edge 550a, for example via adhesive. The ring 580 includes apertures 582 that are shaped and dimensioned to receive studs 584 in an interference fit. The pneumatic actuator 500" includes a stud plate 590 having studs 584. The stud plate 590 is secured to the housing second end 106 via a bracket 588. The external contaminant shield 550 is secured to the housing second end 106 by mounting the ring 580 to the studs 584.

The external contaminant shield 550 is not limited to one particular material. Instead, the selection of the material used to form the external contaminant shield 550 is based on the concerns (e.g., dirt ingress, dust ingress, water ingress, oil ingress, etc.) of the specific application.

In the illustrated embodiment, the external contaminant shield 550 is included as part of the pneumatic actuator 500 at the time of manufacture. It is contemplated, however, that the external contaminant shield 550 can be provided as a separate component that is used to retrofit pre-existing, non-shielded actuators.

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.