Patent Publication Number: US-8991299-B2

Title: Reinforced thermoplastic actuator with wear resistant plastic liner

Description:
BACKGROUND 
     This disclosure relates to a fluid actuator, for example, for an aircraft. More particularly, the disclosure relates to a thermoplastic fluid actuator. 
     Typically, aluminum actuators have been used in the aerospace industry for a variety of fluid actuator applications, such as fueldraulic variable stator vane actuators. Aluminum actuators are rather costly. Composite actuators for non-aerospace hydraulic applications have been proposed. 
     One such actuator is provided by high strength reinforced composite liner forming the cylinder. The liner is wound with a resin impregnated fiber about its circumference to minimize diametrical expansion of the cylinder. However, many of the structural components of the actuator are still constructed from aluminum to provide the desired strength. 
     Similarly, composite piston rods have also been proposed for hydraulic actuators. The piston rod is constructed out of a metallic jacket with a polymer core. Again, a metallic structure still comprises a significant portion of the actuator. 
     SUMMARY 
     A fluid actuator includes a housing having a fluid chamber providing a first friction surface. An actuating member is arranged in the fluid chamber and has a second friction surface slideably engaging the first friction surface. The actuating member is configured to slide within the chamber between first and second positions. An insert is constructed from a first thermoplastic material and provides one of the first and second friction surfaces. A body structurally supports the insert and provides one of the housing and actuating member. The body is constructed from a second thermoplastic material molded about the insert and including short reinforcing fibers. 
     A method of manufacturing an actuator includes positioning an insert into a mold. The insert provides a friction surface and is constructed from a first thermoplastic material. A second thermoplastic material is injection molded about the insert to provide a body. A unitary actuator component is formed that includes the insert and the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a highly schematic view of a hydraulic system. 
         FIG. 2  is a cross-sectional view of an example fluid actuator. 
         FIG. 3  is a flowchart depicting an example method of manufacturing an actuator. 
     
    
    
     DETAILED DESCRIPTION 
     A hydraulic control system  10  is schematically depicted in  FIG. 1 . The system  10  includes a component  12  having a subcomponent  16  controlled by an actuator  14 . In one example, the component  12  is a gas turbine engine, and the subcomponent  16  is a variable stator vane system. The actuator  14  is connected to the subcomponent  16  by an actuating member  18 , such as a rod, that is manipulated between multiple positions to control the subcomponent  16 . 
     Regulated fluid is provided from a fluid source  20  through a control valve  22  to a first fluid port  24  of the actuator  14 . Fluid exits the actuator  14  through a second fluid port  26 . In the example, the actuator  14  is a fueldraulic actuator, and the fluid source  20  is a fuel tank. The fuel from the second fluid port  26  may be routed to a combustor, for example. It should be understood, however, that the system  10  illustrated in  FIG. 1  is exemplary and the actuator  14  may be configured in a manner suitable for any given application. 
     Referring to  FIG. 2 , the actuator  14  includes a housing  28  having a cylinder  30 . The cylinder  30  provides a chamber  32  within which the actuating member  18  is arranged. In the example, the actuating member  18  is provided by a rod  34  having an end  36  extending through a hole  35  in the cylinder  30  and a piston  38  arranged opposite the end  36 . The piston  38  is moveable between first and second position P 1 , P 2  along an axis A. Although a linear fluid actuator is illustrated, it should be understood that this disclosure may apply to other actuator configurations. 
     The example actuator  14  is constructed from a thermoplastic material. To ensure sufficient structural rigidity and to avoid component fatigue, the body of the cylinder  30  and rod  34 /piston  38  in the example is constructed from a fiber reinforced thermoplastic, such as a polyamide imide, for example, TORLON 5030. The fiber reinforced thermoplastic is constructed from short reinforcing fibers, such as fiberglass or graphite to enable the body to be injection molded, which enables complex features of the actuator to be constructed from thermoplastic material thereby avoiding the use of many metallic structural components. “Short fibers” means fibers of a length less than the circumference of the diameter of the respective rod or piston. In one example, the fibers are chopped. 
     To avoid exposure to the fibers of the cylinder and/or rod body at the sliding surfaces of the actuator components, a cylinder insert  42  and a rod insert  46  are used to respectively provide cylinder and rod friction surfaces  40 ,  44 . A seal  39  is carried by the piston  38  and engages the cylinder insert  42 . Seals  39  are arranged in the hole  35  and engage the rod insert  46 . The cylinder and rod inserts  42 ,  46  are constructed from a thermoplastic material that is different than the thermoplastic material of the body, for example non-abrasive, a non-fiber reinforced thermoplastic. However, non-abrasive fibers may be used to improve structural integrity, such as graphite fibers. In one example, the inserts are constructed from a polyamide imide, such as TORLON 4301. The insert thermoplastic material contains a lubricant, such as a polytetrafluoroethylene (PTFE) material, molybdenum disulfide, tungsten disulfide and/or graphite. One example of a suitable PTFE is TEFLON. 
     A method  48  of constructing the actuator  14  is illustrated in  FIG. 3 . The method  48  includes the step of providing a friction surface insert, as indicated at block  50 . In one example, the friction surface insert is constructed from a non-reinforced, lubricant-impregnated thermoplastic material. An actuator component body, such as a cylinder, rod and/or piston, is molded about the insert, as indicated at block  52 . The body structurally supports and is adhered to the insert during molding providing a unitary actuator component. It may be desirable to machine the insert friction surface to provide a machined surface having more precise dimensional characteristics, as indicated at block  54 . 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.