Patent Publication Number: US-8535007-B2

Title: Hydraulic actuator locking device

Description:
BACKGROUND 
     The present disclosure relates to a hydraulic system, and more particularly to a hydraulic actuator lock. 
     Linear hydraulic actuators include a piston and cylinder arrangement where differential pressure across the piston is operable to support an external load. A lock is often utilized to support the external load in the event of a hydraulic pressure loss. 
     SUMMARY 
     A hydraulic lock system according to an exemplary aspect of the present disclosure includes a cylinder which defines an axis and an actuator rod movable along the axis. A spring pack is defined between a female spring support and a male spring support. The spring pack includes a multiple of serrated washers, each of which defines an inner diameter which is greater than a diameter of the actuator rod and an outer diameter greater than an inner diameter of the cylinder. 
     A hydraulic lock system according to an exemplary aspect of the present disclosure includes a cylinder which defines an axis and an actuator rod movable along the axis. A female spring support is defined about the actuator rod, the female spring support defines a female frustroconical surface and a male spring support defined about the actuator rod, the male spring support defines a male frustroconical surface. A spring pack is defined between the female spring support and the male spring support. 
     A method of locking a hydraulic actuator according to an exemplary aspect of the present disclosure includes jamming a spring pack of a multiple of serrated washers which forms a frustroconical shape between an actuator rod outer diameter and a cylinder inner diameter, each of the multiple of serrated washers defines an inner diameter which is greater than a diameter of the actuator rod and an outer diameter greater than the cylinder inner diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a general perspective view an exemplary gas turbine turboprop engine embodiment for use with the present application; 
         FIG. 2  is a schematic sectional view of the turboprop system illustrating an example hydraulic actuator system with a lock system; 
         FIG. 3  is an expanded schematic sectional view of the hydraulic actuator system with a uni-directionally activatable lock system. 
         FIG. 4  is a face view of a spring, forming an element of a spring pack; 
         FIG. 5A  is a sectional view of a spring in the spring pack in a free state condition; 
         FIG. 5B  is a sectional view of a spring in the spring pack in an installed condition; 
         FIG. 5C  is a sectional view of a spring in the spring pack in an inactivated condition; 
         FIG. 5D  is a sectional view of a spring in the spring pack in a lock condition; and 
         FIG. 6  is an expanded schematic sectional view of a hydraulic actuator system with a bi-directionally activatable lock system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a propeller system  20  such as that for an aircraft. It should be understood that although a propeller system  20  typical of a turboprop aircraft is illustrated in the disclosed embodiment, various aircraft configurations and/or machines which utilize linear hydraulic actuators will benefit herefrom. 
     The propeller system  20  in one non-limiting embodiment is powered by a gas turbine engine  22  which rotates a turbine output shaft  24  at a high speed. The turbine output shaft  24  drives a gearbox  26  which in general decreases shaft rotation speed and increase output torque. The gearbox  26  drives a propeller shaft  28  which rotates a propeller hub  30  and a plurality of propeller blades  32  which extend therefrom. It should be understood that propeller blades  32  as utilized herein include various aerodynamic surfaces such as blades, rotors, prop-rotors and others. In the disclosed non-limiting embodiment, the turbine output shaft  24  and the propeller shaft  28  rotate about a common axis X. Axis X is substantially perpendicular to a plane P which is defined by the propeller blades  32 . 
     The gearbox  26  is within a stationary reference frame while the propeller system  20  is within a rotating reference frame. That is, the gearbox  26  is fixed structure typically attached, for example to an airframe  34  while the propeller system  20  rotates relative thereto in a rotational reference frame. 
     With reference to  FIG. 2 , a hydraulic system  36  operable to actuate various mechanisms such as an actuator system  38 . The actuator system  38  may be mounted along the hub axis X to drive a yoke assembly  40  through translation of a pitch change actuator  42  along axis X. The yoke assembly  40  is attached to a pitch trunnion pin  44  which extends from each propeller blade  32  to control the pitch thereof (illustrated schematically). That is, the yoke assembly  40  interfaces with the trunnion pin  44  at a pivot axis P which is offset from a blade axis B to convert axial motion of the yoke assembly  40  into pitch motion of each propeller blade  32 . It should be understood that various linear hydraulic actuator arrangements may alternatively or additionally benefit herefrom. 
     It should be understood that under normal operational conditions, the actuator system  38  drives the actuator rod  42  within a cylinder  43  to move the yoke assembly  40  and pitch the propeller blade pitch propeller system  20 . The cylinder  43  defines chambers PC, PF which are respectively supplied with coarse pitch pressure PCp and fine pitch pressure PFp from a coarse pitch pressure communication circuit  36 C and a fine pitch pressure communication circuit  36 F from the hydraulic system  36 . Selective communication of coarse pitch pressure PCp and fine pitch pressure PFp to the actuator system  38  provides, for example, speed governing, synchrophasing, beta control, feathering, unfeathering as well as other control of the propeller blades  32 . It should be understood that the hydraulic system  36  disclosed herein is illustrated schematically as various pressure communication circuits may be alternatively or additionally utilized herewith. 
     With reference to  FIG. 3 , the actuator system  38  includes a lock system  50 . Although illustrated in the disclosed non-limiting embodiment as a pitch lock for the propeller system  20 , it should be understood that the lock system  50  disclosed herein may be utilized in various linear hydraulic actuator systems in which a lock is required to support a load in the event of a hydraulic pressure loss. 
     The lock system  50  generally includes the actuator rod  42 , the cylinder  43 , a spring pack  56 , which may include one or more springs, a piston  58 , a female spring support  60  and a male spring support  62 . The male spring support  62  may or may not be an integral part of the piston  58  as may be dictated by material selection, manufacturing and or assembly preferences. The lock system  50  operates in a unidirectional manner. That is, the load is only applied in one direction typical of a hydraulic linear actuator. 
     The actuator rod  42  defines a fine pitch abutment  64  and a coarse pitch abutment  66  which selectively interact with the female spring support  60  and the piston  58 . The fine pitch abutment  64  and the coarse pitch abutment  66  may be lock rings axially fixed to the actuator rod  42  at an axial distance slightly greater than that provided by the spring pack  56 , the piston  58 , the female spring support  60  and the male spring support  62  axial length to define a gap  68 . Gap  68  is sufficient to permit some axial free motion of the lock system  50  relative to the actuator rod  42  when, the lock system  50  locks. 
     The spring pack  56  generally includes a series of springs  56 A. Each spring  56 A is a compact cylindrical spring which is generally in the shape of a serrated frustroconical washer ( FIG. 4 ). That is, each spring  56 A may have a slight conic in a free state ( FIG. 5A ). Each spring  56 A of the spring pack  56  may be manufactured of a resilient material such as nylon or other material to include metallic material which minimizes scoring within a bore  70  of the cylinder  43 . Each spring  56 A is essentially a compression disc which provides an outer diameter  72  which defines an interference fit within the bore  70  and an inner diameter  74  which provides a slight clearance fit with the actuator rod  42 . 
     The female spring support  60  and the male spring support  62  each define a respective frustroconical surface  60 C,  62 C to support the spring pack  56  therebetween. In one non-limiting embodiment, the frustroconical surface  60 C of the female spring support  60  defines an angle just less than an installed obtuse angle (f) of the spring pack  56  and the frustroconical surface  62 C of the male spring support  62  defines an angle just greater than the installed acute angle (m) of the spring pack  56  ( FIG. 5B ). The angle arrangement assures that force is applied generally adjacent the inner diameter of the spring pack  56  by the female spring support  60  and the male spring support  62  dependent upon the axial direction of the actuator rod  42 . 
     In operation, the hydraulic system  36  provides differential pressure to the coarse pitch actuator chamber PC and the fine pitch actuator chamber PF to drive the piston  58 , female spring support  60  and the male spring support  62  such that the lock system  50  is maintained in an inactivated condition ( FIG. 5C ). The spring pack  56  is maintained in an inactive deflected condition between the female spring support  60  and the male spring support  62  which are squeezed together to maintain the deflected position ( FIG. 5C ). That is, a distance A between the respective frustroconical surface  60 C,  62 C which contact the spring pack  56  to maintain the deflection. 
     In response to a release or loss of hydraulic pressure, the load on the actuator rod  42  will drive the actuator rod  42  to the right in the Figure. That is, gap  68  is sufficient to permit free motion of the actuator rod  42  when, for example, PC p -PF p  is equal to 50% of a minimum load to lock the lock system  50 . This value being determined by design of the stiffness of the spring pack  56 . The axial distance between the abutments  64 ,  66  permits the squeeze on the spring pack  56  to relax. The fine pitch abutment  64  will drive the female spring support  60  into the spring pack  56  which will jamb the spring pack  56  between the actuator rod  42  and the bore  70  to support the load in the absence of hydraulic pressure. The spring pack  56  is jammed because the squeeze force otherwise provided between the female spring support  60  and the male spring support  62  is relaxed due to loss of the hydraulic pressure. A distance B between the bore  70  and a point of contact  60 A between the female spring support  60  and the spring pack  56  drives the spring pack  56  to the jamb position ( FIG. 5D ) which locks the lock system  50 . The lock system  50  thereby advantageously supports the load in close proximity to the load position prior to loss of hydraulic pressure. 
     In response to return of hydraulic pressure the spring pack  56  is again squeezed between the female spring support  60  and the male spring support  62  to again place the spring pack  56  in the deflected inactivated position ( FIG. 5C ). 
     With reference to  FIG. 6 , another non-limiting embodiment of a lock system  80  provides for a bi-direction lock. The lock system  80  generally duplicates the unidirectional lock described above and operates in each direction generally as discussed above. A selector valve  82  located within an actuator rod  42 ′ selectively maintains the lock system  80  in an inactivated state when adequate pressure is maintained in the coarse pitch actuator chamber PC and the fine pitch actuator chamber PF. The selector valve  82  supplies the lowest of the pressure within either the coarse pitch actuator chamber PC or the fine pitch actuator chamber PF to the center section of the piston assembly  84 . In  FIG. 6 , the lock system  80  is shown with the fine pressure PF p  greater than course pressure PC p . 
     The present disclosure provide a linear hydraulic lock which is of a compact size and light weight that readily fits within an actuator system for operation without additional stroke length. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
     The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.