TECHNICAL FIELD

[0001] The present disclosure is directed to jet engine actuators, and more particularly to jet engine hydraulic actuator assemblies.

BACKGROUND

[0002] Jet engines, such as gas turbine engines, often contain actuators configured to actuate moving parts of the engine. Such parts may include control flaps, guide vanes, doors, and the like.

BRIEF SUMMARY

[0003] With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, a hydraulic actuator assembly (15) operatively configured to hydraulically connect to a tank (20) of an aircraft is provided comprising: a hydraulic cylinder (30) orientated about a center axis (31) and having a first hydraulic port (32) for hydraulic fluid, a second hydraulic port (33) for the hydraulic fluid, a first end wall (35), and an inner cylinder surface (36) defining a cylinder bore (38); a piston (40) disposed in the cylinder bore of the hydraulic cylinder and separating a first chamber (42) of the hydraulic cylinder from a second chamber (43) of the hydraulic cylinder; the piston operatively configured for sliding linearly movement on the center axis relative to the hydraulic cylinder within a linear range of motion (41); the first chamber of the hydraulic cylinder in fluid communication with the first hydraulic port and the second chamber of the hydraulic cylinder in fluid communication with the second hydraulic port; the piston having an outer piston surface (44) orientated about the center axis; a tubular sleeve (60) disposed radially between the inner cylinder surface of the hydraulic cylinder and the outer piston surface of the piston; the sleeve having an outer sleeve surface (61) orientated about the center axis and a cylindrical inner sleeve surface (62) orientated about the center axis; the inner cylinder surface of the hydraulic cylinder having a first Rockwell C scale hardness; and the inner sleeve surface of the sleeve having a second Rockwell C scale hardness that is greater than the first Rockwell C scale hardness of the inner cylinder surface of the hydraulic cylinder by HRc 10 or greater.

[0004] The hydraulic cylinder may comprise titanium or a titanium alloy and the second Rockwell C scale hardness of the inner sleeve surface of the sleeve may be between about HRc 45 and HRc 75. The second Rockwell C scale hardness of the inner sleeve surface of the sleeve may be between about HRc 52 and HRc 55.

[0005] The sleeve may comprise carbon steel or stainless steel. The sleeve may comprise a welded belt. The sleeve may have a first radial thickness (65) between the inner sleeve surface and the outer sleeve surface and the first radial thickness may be between about 0.001 inches and 0.2 inches. The sleeve may comprise a first portion (64) having a first radial thickness (65) between the inner sleeve surface and the outer sleeve surface, and a second portion (66) having a second radial thickness (67) between the inner sleeve surface and the outer sleeve surface that is greater than the first radial thickness of the first portion. The sleeve may be axially restrained relative to the cylinder.

[0006] The hydraulic actuator assembly may comprise an annular bearing (80) disposed radially between the inner sleeve surface of the sleeve and the outer piston surface of the piston. The hydraulic actuator assembly may comprise an annular seal (82a) between the inner cylinder surface of the hydraulic cylinder and the outer sleeve surface of the sleeve.

[0007] The sleeve may extend longitudinally about the center axis for the full linear range of motion (41) between the inner cylinder surface of the hydraulic cylinder and the outer piston surface of the piston. The sleeve may be press fit in the cylinder bore of the cylinder. The hydraulic actuator assembly may comprise a position sensor (24) configured to sense position of the piston.

[0008] The hydraulic actuator assembly may comprise a cylindrical radial fluid relief gap (176) between the inner cylinder surface of the hydraulic cylinder and the outer sleeve surface of the sleeve and a fluid relief port (48) for hydraulic fluid, and the cylindrical radial fluid relief gap may be in fluid communication with the fluid relief port. The hydraulic actuator assembly may comprise an aircraft fuel tank (20) in fluid communication with the fluid relief port.

[0009] The hydraulic actuator assembly may comprise: an aircraft fuel tank (20); a hydraulic pump (22) connected with the fuel tank, the first hydraulic port of the hydraulic cylinder, and the second hydraulic port of the hydraulic cylinder; and the hydraulic fluid may comprise aircraft fuel. The piston may comprise a piston rod (45) having a portion sealingly penetrating the first end wall of the hydraulic cylinder. The piston rod may be configured to actuate a first object (91) of an aircraft. The hydraulic actuator assembly may comprise a linkage (90) between the piston rod and the first object. The hydraulic actuator assembly may comprise a motor (21) and the hydraulic pump may be operatively driven by the motor. The hydraulic actuator assembly may comprise a valve (23) connected with the hydraulic pump, the first hydraulic port of the hydraulic cylinder, and the second hydraulic port of the hydraulic cylinder. The valve may comprise an electrohydraulic servovalve.

[0010] The motor may comprise an electric brushless DC servo-motor. The motor may comprise an aircraft turbine engine. The hydraulic pump may be selected from a group consisting of a fixed displacement pump, a variable displacement pump, a two-port pump, and a three-port pump. The hydraulic actuator assembly may comprise a controller (52) that receives input signals and outputs command signals. The hydraulic actuator assembly may comprise a position sensor (24) configured to sense a position of the piston and to provide an input signal to the controller.

[0011] In another aspect, a method of assembling the hydraulic actuator assembly may be provided comprising the steps of providing a steel material; forming the material into the sleeve; and inserting the sleeve into the cylinder bore of the cylinder. The steel material may comprise carbon steel or stainless steel. The step of forming the material into the sleeve may comprise the steps of rolling a steel sheet material and welding longitudinally extending opposed edges of the rolled sheet material together. The steel sheet material may comprise stainless steel. The method may further comprise the steps of temporarily distorting at least one of the hydraulic cylinder and sleeve so as to permit the sleeve to be inserted axially into the cylinder bore of the hydraulic cylinder and allowing each of the hydraulic cylinder and sleeve that had been temporarily distorted to move back toward its original undistorted shape so as to form a tight interference fit between the hydraulic cylinder and the sleeve. The step of temporarily distorting at least one of the hydraulic cylinder and the sleeve may include the step of temporarily cooling the sleeve to temporarily reduce a sleeve outer diameter (68) of the outer sleeve surface. The step of temporarily distorting at least one of the hydraulic cylinder and the sleeve may include the step of temporarily heating the hydraulic cylinder to temporarily increase an inner bore diameter (39) of the inner cylinder surface. The step of allowing each of the hydraulic cylinder and sleeve that had been temporarily distorted to move back toward its original undistorted shape may include the step of operating the hydraulic actuator assembly in a heated environment and allowing the heated environment to heat the sleeve to increase the outer sleeve diameter of the outer sleeve surface. The step of allowing each of the hydraulic cylinder and sleeve that had been temporarily distorted to move back toward its original undistorted shape may include the steps of allowing the temporarily-heated hydraulic cylinder to cool to ambient temperature and allowing the temporarily-cooled sleeve to warm to ambient temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate embodiments of the presently disclosed subject matter and are illustrative of selected principles and teachings of the present disclosure. However, the drawings do not illustrate all possible implementations of the presently disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0013] FIG. 1 is perspective schematic view of an embodiment of the improved hydraulic actuator assembly mounted in a jet engine of an aircraft.

[0014] FIG. 2 is a longitudinal cross-sectional view of the hydraulic actuator assembly of FIG. 1.

[0015] FIG. 3 is a schematic cross-section view of an embodiment of the cylinder and sleeve shown in FIG. 2.

[0016] FIG. 4 is a schematic diagram view of the hydraulic system of the hydraulic actuator assembly of FIG. 1.

[0017] FIG. 5 is a partial enlarged cross-sectional view of the hydraulic actuator assembly of FIG. 2.

[0018] FIG. 6 is a longitudinal cross-sectional view of an alternative embodiment of the hydraulic actuator assembly of FIG. 2.

[0019] FIG. 7 is an off-center partial longitudinal cross-sectional view of the hydraulic actuator assembly of FIG. 6.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., crosshatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof (e.g., "horizontally", "rightwardly", "upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

[0021] It is to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application. It is to be appreciated that the present teaching is by way of example only, not by limitation. Where they are used herein, the terms “first,” “second,” and so on, do not necessarily denote any ordinal, sequential, or priority relation, but are simply used to distinguish one element or set of elements more clearly from another, unless specified otherwise.

[0022] The term “shaft" or “rod” includes, but is not limited to, cylindrical shafts or rods, shafts or rods of polygonal cross-section and shafts or rods without a uniform cross-section. It is further noted that a shaft or rods does not need to be cylindrical in order to define a radial direction or a lengthwise direction.

[0023] To the extent that the definitions provided above are consistent with ordinary, plain, and accustomed meanings (as generally evidenced, in alia, by dictionaries and/or technical lexicons), the above definitions shall be considered supplemental in nature. To the extent that the definitions provided above are inconsistent with ordinary, plain, and accustomed meanings (as generally evidenced, inter alia, by dictionaries and/or technical lexicons), the above definitions shall control. If the definitions provided above are broader than the ordinary, plain, and accustomed meanings in some aspect, than the above definitions will control at least in relation to their broadening aspects.

[0024] Referring now to the drawings, an improved hydraulic actuator assembly is provided, an embodiment of which is generally indicated at 15. As shown in FIG. 5, hydraulic actuator assembly 15 is a hydraulic piston assembly and is operatively configured to hydraulically connect to tank 20 of aircraft 16 via hydraulic pump 22 driven by motor 21 and electrohydraulic servovalve 23. Thus, in this embodiment, pump 22 pressurizes aircraft fuel from fuel tank 20 to raise the pressure in a hydraulic gap on one side or the other of hydraulic piston 40 of assembly 15.

[0025] Motor 21 may be a variable speed single or bidirectional electric servomotor and pump 22 may be a single or bidirectional pump driven by motor 21. In this embodiment, motor 21 is a brushless D.C. variable-speed servo-motor that is supplied with a current. Motor 21 has an inner rotor with permanent magnets and a fixed non-rotating stator with coil windings. When current is appropriately applied through the coils of the stator, a magnetic field is induced. The magnetic field interaction between the stator and rotor generates torque which may rotate an output shaft connected to pump 22. Other motors may be used as alternatives. For example, a variable speed stepper motor, brush motor or induction motor may be used.

[0026] Pump 22 may be a fixed displacement single directional gear pump or a bidirectional internal two-port gear pump. The pumping elements, namely gears, are capable of rotating in one or both directions and allows for fluid to be added into and out of the system as the system controller closes the control loop of position or pressure. The shaft of at least one gear of pump 22 is connected to the output shaft of motor 21 with the other pump gear following. Other pumps may be used as alternatives. For example, a variable displacement pump may be used. Also, in an alternative embodiment, pump 22 is driven by a gear box connected to the turbine shaft of the engine of the aircraft. In this embodiment, the shaft of at least one gear of pump 22 is connected to the output shaft of the gear box with the other pump gear following.

[0027] Servovalve 23 is an electrohydraulic servovalve that controls the pressurized fluid from pump 22 that is sent to actuator 15 and the hydraulic pressure differential on piston 40 of assembly 15. In this embodiment, servovalve 23 is a single stage servovalve having a torque motor that positions a spool valve in response to an input signal. Servovalve 23 receives pressurized hydraulic fluid from pump 22 and transfers the fluid to the ports 32 and 33 of hydraulic cylinder 30 in a controlled manner and based on feedback from position sensor 24.

[0028] In this embodiment, hydraulic piston assembly 15 includes piston 40 slidably disposed within cylindrical housing 30 such that piston 40 may be driven in both directions relative to housing 30. Piston 40 is slidably disposed within cylinder 30, and sealingly separates left chamber 42 from right chamber 43. In this embodiment, the leftwardly-facing annular vertical end surface of piston 40 faces into left chamber 42 and the rightwardly- facing annular vertical end surface of piston 40 faces into right chamber 43, creating an equal piston area configuration. Left chamber 42 has fluid port 32 and right chamber 43 has fluid port 33. Thus, hydraulic actuator 15 comprises chamber 42, chamber 43 and piston 40 separating the first and second chambers 42 and 43. Position sensor 24 is configured to sense the position of piston 40 in cylinder 30. As shown servovalve 23 communicates with left chamber 42 via cylinder port 32 and fluid line 33a and communicates with right chamber 43 via cylinder port 33 and fluid line 33a, respectively. Rod 45 is mounted to piston 40 for movement with piston 40 and extends to the right and sealably penetrates right end wall 35 of cylinder 30. Motor 21 turns pump 22 and pump 22 is hydraulically connected to equal area piston 40 via servovalve 23. Tank 20, pump 22, servovalve 23 and hydraulic cylinder assembly 15 provide a hydrostatic transmission, so as pump spins and valve 23 is actuated to a first position, piston 40 and rod 45 move in a first direction and as pump 22 spins and valve 23 is actuated to a second position, piston 40 and rod 45 move in the other direction. Thus, piston 40 will extend or move rod 45 to the right when valve 23 is in a first position and motor 21 rotates pump 22 to move fuel from fuel tank 20 into chamber 42 through port 32. Piston 40 will retract rod 45 or move to the left when valve 23 is in a second position and motor 21 rotates pump 22 to move fuel into chamber 43 through port 33. Port 48 in cylinder 30 provides a cylinder leakage relief conduit back to fuel tank 20.

[0029] The position of rod 45 is monitored via position sensor 24 and the position signals are then fed back to controller 52. In this embodiment, position sensor 24 is a linear variable differential transformers (LVDT) having an electromechanical transducer that provides a variable alternating current output voltage that is generally linearly proportional to the linear displacement of piston 40 and rod 45. Servovalve 23, motor 21 and pump 22 control the speed and force of piston 40 and in turn rod 45 by changing the flow and differential pressure acting on piston 40 in cylinder 30. This is accomplished by looking at the feedback of position sensor 24 and then closing the control loop by adjusting servovalve 23 and motor 21 accordingly. While in this embodiment position sensor 24 is a LVDT, other position sensor may be used such as without limitation encoders, hall position sensors, potentiometers, and resolvers.

[0030] As shown in FIG. 1, in this embodiment the left end of cylinder housing 30 is pivotally connected at pivot connection 46 to linkage 95, which is in turn connected to structure 17 of aircraft 16. The outer right end of rod 45 of assembly 15 is pivotally connected at pivot connection 89 to linkage 90, which is in turn connected to an object 91 to be actuated relative to structure 17 of aircraft 16. Thus, in this embodiment assembly 15 translates linearly to provide rotational motion. However, other types of connections and other types of linkages may be employed as alternatives.

[0031] As shown in FIGS. 2, 3 and 5, cylinder 30 is orientated about center axis 31 and has inner cylinder surface 36 defining cylinder bore 38. Piston 40 is disposed in bore 38, separating chamber 42 of the hydraulic cylinder from chamber 43 of the hydraulic cylinder. Piston 40 is operatively configured for sliding linearly movement on center axis 31 relative to cylinder 30 within linear range of motion 41. Piston 40 has outer piston surface 44 orientated about center axis 31.

[0032] Tubular sleeve 60 is disposed radially between inner cylinder surface 36 of cylinder 30 and outer piston surface 44 of piston 40. As shown, sleeve 60 has cylindrical outer sleeve surface 61 orientated about center axis 31 and cylindrical inner sleeve surface 62 orientated about center axis 31. In this embodiment, sleeve 60 is press fit into bore 38 of cylinder 30 such that outer surface 61 of sleeve 60 bears against inner surface 36 of cylinder 30 to form an interference fit. Sleeve 60 has an axial length at least as great as stroke region 43. Sleeve 60 thereby provides a bearing surface to cylinder 30 for piston 40 along all of stroke region 43 of piston 40.

[0033] Inner sleeve surface 62 of sleeve 60 has a Rockwell C scale hardness that is greater than the Rockwell C scale hardness of inner cylinder surface 36 of cylinder 30 and preferably has a Rockwell C scale hardness that is HRc 10 or greater than the Rockwell C scale hardness of inner surface 36 of cylinder 30.

[0034] In this embodiment, cylinder 30 is titanium or a titanium alloy and inner surface 36 of bore 38 has a Rockwell C scale hardness of about HRc 32. In this embodiment, sleeve 60 may be carbon steel or stainless steel and may be machined or formed from a welded belt. In this embodiment, the Rockwell C scale hardness of inner sleeve surface 62 of sleeve 60 is between about HRc 45 and HRc 75. Preferably, the Rockwell C scale hardness of inner sleeve surface 62 of sleeve 60 is greater than about HRc 48. For example, sleeve 60 may be formed from 4340 steel having a Rockwell C scale hardness of between about HRc 52 and HRc 55. Alternatively, sleeve 60 may be formed of heat treated hardened stainless steel, such as for example 420 stainless steel (716SS), with a Rockwell C scale hardness of about HRc 54. Sleeve 60 has a radial thickness 65 between inner sleeve surface 62 and outer sleeve surface 61 between about 0.001 inches and 0.4 inches. In a machined thin wall tube embodiment, sleeve 60 may have a radial thickness 65 of between about .013 inches and 0.2 inches. In a laser welded metal belt cylinder embodiment, sleeve 60 may have a radial thickness 65 of between about .002 inches and 0.06 inches. Other materials may be used for sleeve 60 to achieve the desired hardness and thickness.

[0035] In the embodiment shown in FIGS. 2 and 5, sleeve 60 has a dual outer diameter configuration and cylinder 30 is turned with a stepped dual inner diameter for constraining sleeve 60 axially. In particular, right portion 64 of sleeve 60 has radial thickness 65 between inner sleeve surface 62 and the outer sleeve surface 61 which is less than radial thickness 67 between inner sleeve surface 62 and outer sleeve surface 61 of left portion 66. Thickened left portion 66 extends to the left marginal end of sleeve 60 and is thicker due to having a greater outer diameter than the outer diameter of right portion 65. Rightwardly-facing annular surface 71 at the radial step between thinner portion 64 and thicker portion 65 of sleeve 60 abuts against leftwardly-facing annular surface 49 in inner surface 36 of cylinder 30. The radially overlapping and abutting annular faces of annular shoulder 71 of sleeve 60 and annular seat 49 of cylinder 30 thereby restrains axial movement of sleeve 60 to the right relative to cylinder 30 to maintain axial alignment of sleeve 30 in bore 38 of cylinder 30. In this embodiment, annular step 49 in cylinder 30 has a radial thickness that is about one half to three quarters of thickness 67 of thickened portion 66 of sleeve 60.

[0036] Annular bearing 80 is located in piston head 40 radially between inner sleeve surface 62 of sleeve 60 and outer piston surface 44 of piston head 40. In addition, annular seal 83 is located in a seal gland in piston head 40 radially to the right of bearing 80 between inner sleeve surface 62 of sleeve 60 and outer piston surface 44 of piston head 40.

[0037] In the embodiment shown in FIGS. 2, 3 and 5, annular seal 82a is located in a seal gland in cylinder 30 between outer sleeve surface 61 of thickened portion 66 of sleeve 60 and inner cylinder surface 36 of cylinder 30 to reduce leakage of fluid between sleeve 60 and cylinder 30. As shown in FIG. 3, additional annular seal 82b may be located in a second seal gland in cylinder 30 between outer sleeve surface 61 of thinner portion 64 of sleeve 60 and inner cylinder surface 36 of cylinder 30 to reduce leakage of fluid between sleeve 60 and cylinder 30. Seal 82a and 82b are thereby spaced axially from each other at the left and right marginal end portions of sleeve 60.

[0038] The hydraulic actuator assembly may be formed in a process that includes the steps of providing a steel material, forming the material into sleeve 60, and inserting sleeve 60 into cylinder bore 38 of cylinder 3. In embodiments, the steel material is a carbon steel material or a stainless steel material. The step of forming the material into sleeve 60 may comprise the steps of rolling a steel sheet material and laser welding longitudinally extending opposed edges of the rolled sheet material together. In an embodiment, the steel sheet material is stainless steel.

[0039] The method may further comprise the steps of temporarily distorting at least one of hydraulic cylinder 30 and sleeve 60 so as to permit sleeve 60 to be inserted axially into cylinder bore 38 of hydraulic cylinder 30 and allowing each of hydraulic cylinder 30 and sleeve 60 that had been temporarily distorted to move back toward its original undistorted shape so as to form a tight interference fit between hydraulic cylinder 30 and sleeve 60. [0040] The step of temporarily distorting cylinder 30 and sleeve 60 may include the step of temporarily cooling sleeve 60 to temporarily reduce outer diameter 68 of sleeve 60 due to the thermal treatment and temporarily heating hydraulic cylinder 30 to temporarily increase inner bore diameter 39 of cylinder 30 due to the thermal treatment. For example, for a machined tubular embodiment, sleeve 60 may be cooled to about -70 degrees Fahrenheit or lower, such as for example -150 degrees Fahrenheit, and cylinder 30 may be heated to between about 300 to 350 degrees Fahrenheit. When sleeve 60 is cooled and cylinder 30 is heated, sleeve 60 is inserted into the inner bore 38 of cylinder 30 because of the respective thermal contraction and expansion. This process should occur very quickly as the dissimilar temperature of the two subassemblies will quickly equalize such that the clearance gained by the temperature differential will evaporate and such assembly will no longer be possible.

[0041] The step of allowing each of hydraulic cylinder 30 and sleeve 60 to move back toward its original undistorted shape may include the step of operating the hydraulic actuator assembly 15 in a heated environment and allowing the heated environment to heat sleeve 60 to increase outer sleeve diameter 68 of surface 60. The step of allowing each of hydraulic cylinder 30 and sleeve 60 that had been temporarily distorted to move back toward its original undistorted shape may include the steps of allowing temporarily-heated hydraulic cylinder 30 to cool to room or ambient temperature and allowing temporarily-cooled sleeve 60 to warm to ambient temperature.

[0042] This thermal treatment allows sleeve 60 to be inserted in cylinder 30. As an alternative method, only sleeve 60 may be thermally treated (that is, cooled), or only cylinder 30 may be thermally treated (that is, heated). However, the thermal treatments must effect sufficient, temporary geometrical adjustment so that sleeve 60 will fit within cylinder 30. After the thermal treatment is over, the cylinder and sleeve assembly will shrink and expand toward their respective pre-thermal treatment sizes until the clearance between them is zero. At that time the pressure at the surfaces between the cylinder and the sleeve will begin to increase and continue to do so until their temperatures are fully equalized. However, care must be taken to assure an interface pressure not too great to crack the sleeve or split any welded seam.

[0043] In the welded belt sleeve embodiment, photo etching a thin micron depth and width track at one or more locations and at a desired spatial frequency may be employed to aid in flexure while allow minor leakage. In this embodiment, seals 82a and 82b may be added at the ends of sleeve 60 and may be located outside of stroke range 41, as shown in FIG. 3. Also, circumferential photoetching may be employed to act as balancing grooves if the temperature conditions are presented where the metal belt embodiment of sleeve 30 can slightly float on center with minor leakage.

[0044] This assembly process described, and the materials used in such process provide higher performance. Using this process, a precision thin-walled tubular sleeve having uniform wall thickness and straightness can be formed. After forming to precision tube dimensions, the described processing and heat-treatment provides a sleeve that is light, thin and has a high hardness suitable for a bearing surface. In addition, the assembly process provides a number of significant cost advantages. Thus, sleeve 60 is formed from a steel hardened to Rockwell C scale hardness of between about HRc 45 and HRc 75, and preferably greater than about HRc 48. The steel of sleeve 60 is strong, wear-resistant and can be made thinner. Sleeve 60 is thereby harder than the titanium alloy of cylinder 30 and may be employed in a jet fuel hydraulic cylinder assembly operating at high temperatures such as 300 degrees Fahrenheit. Sleeve 60 has a higher density than titanium alloy cylinder 30 and has a coefficient of thermal expansion (CTE) greater than titanium alloy cylinder 30 so that when press fit and in operating thermal conditions they behave with a contact pressure as one composite body.

[0045] An alternative embodiment hydraulic actuator assembly 115 is shown in FIGS. 6 and 7. Hydraulic actuator assembly 115 is similar to hydraulic actuator assembly 15 in that hydraulic actuator assembly 115 is operatively configured to hydraulically connect to tank 20 of aircraft 16 via hydraulic pump 22 driven by motor 21 and electrohydraulic servovalve 23 and that pump 22 pressurizes aircraft fuel from fuel tank 20 to raise the pressure in a hydraulic gap on one side or the other of hydraulic piston 40 of assembly 115. Hydraulic actuator assembly 115 is also similar to hydraulic actuator assembly 15 in that hydraulic actuator assembly 115 includes piston 40 slidably disposed within cylindrical housing 130 such that piston 40 may be driven in both directions relative to housing 130 and piston 40 sealingly separates left chamber 42 from right chamber 43, with the leftwardly-facing annular vertical end surface of piston 40 facing into left chamber 42 and the rightwardly-facing annular vertical end surface of piston 40 facing into right chamber 43, creating an equal piston area configuration. As with hydraulic actuator assembly 15, left chamber 42 of hydraulic actuator assembly 115 has fluid port 32 and right chamber 43 of hydraulic actuator assembly 115 has fluid port 33 and position sensor 24 of hydraulic actuator assembly 115 is configured to sense the position of piston 40 in cylinder 130, with servovalve 23 communicating with left chamber 42 via cylinder port 32 and fluid line 33a communicating with right chamber 43 via cylinder port 33 and fluid line 33a, respectively, and with the position of rod 45 being monitored via position sensor 24 and the position signals then fed back to controller 52. Also as with hydraulic actuator assembly 15, hydraulic actuator assembly 115 includes port 48 in cylinder 130 that provides a cylinder leakage relief conduit back to fuel tank 20.

[0046] However, in this embodiment, cylinder 130 and sleeve 160 are specially configured to provide fluid leakage gap 176 therebetween and cylinder 130 includes leakage relief passage 177 extending between cylindrical fluid leakage gap 176 and port 48 in cylinder 130 that provides a cylinder leakage relief conduit back to fuel tank 20.

[0047] As shown in FIGS. 6 and 7, cylinder 130 is orientated about center axis 31 and has inner cylinder surface 136 defining cylinder bore 38 and piston 40 is disposed in bore 38, separating chamber 42 of the hydraulic cylinder from chamber 43 of the hydraulic cylinder. Tubular sleeve 160 is disposed radially between inner cylinder surface 136 of cylinder 130 and outer piston surface 44 of piston 40. As shown, sleeve 160 has cylindrical outer sleeve surface 161 orientated about center axis 31 and uniform cylindrical inner sleeve surface 162 orientated about center axis 31 and have a uniform inner diameter along its axial length. Sleeve 160 is press fit into bore 38 of cylinder 130 such that outer surface 161 of sleeve 160 bears against inner surface 136 of cylinder 130 to form an interference fit and sleeve 160 has an axial length at least as great as stroke region 43 to thereby provide a bearing surface to cylinder 130 for piston 40 along all of stroke region 43 of piston 40.

[0048] In the embodiment shown in FIGS. 6 and 7, outer surface 161 of sleeve 160 has a stepped triple outer diameter configuration and inner surface 136 of cylinder 130 is turned with a stepped dual inner diameter such that opposed they constrain sleeve 160 axially and providing fluid leakage gap 176 therebetween. In particular, cylindrical intermediate portion 164 of sleeve 160, which is axially between left cylindrical portion 163a and right cylindrical end portion 163b of sleeve 160, has radial thickness 165 between inner sleeve surface 162 and outer sleeve surface 161. Left cylindrical portion 163a and right cylindrical portion 163b of sleeve 160 each have the same radial thickness 166 between inner sleeve surface 162 and outer sleeve surface 161. Radial thickness 165 of cylindrical intermediate portion 164 of sleeve 160 is less than radial thickness 166 of each of left cylindrical portion 163a and right cylindrical portion 163b of sleeve 160. End portions 163a and 163b are thicker than intermediate portion 164 of sleeve 160 due to having a greater outer diameter than the outer diameter of intermediate portion 164, and such difference in diameter against opposed cylindrical surface 136 of cylinder 130 forms cylindrical radial gap 176. As shown in FIG. 7, radial gap 176 is in fluid communication with fluid passage 177 via port 178 in cylinder 130. From outlet port 178 of radial gap 176, fluid passage 177 extends to inlet 179 of port 48 in cylinder 30, which in turn provides a cylinder leakage relief conduit back to fuel tank 20.

[0049] Radial thickness 166 of each of left cylindrical portion 163a and right cylindrical portion 163b of sleeve 160 is less than radial thickness 167 between inner sleeve surface 162 and outer sleeve surface 161 of left end portion 169 of sleeve 160. Thickened left end portion 169 extends to the left marginal end of sleeve 160 and is thicker due to having a greater outer diameter than the outer diameter of portions 163a and 163b of sleeve 160, with the outer diameter of portions 163a and 163b of sleeve 160 being greater than the outer diameter of intermediate portion 164 of sleeve 160. Rightwardly-facing annular surface 171 at the radial step between thinner portion 163a and thicker portion 169 of sleeve 160 abuts against leftwardly-facing annular surface 149 in inner surface 136 of cylinder 130. The radially overlapping and abutting annular faces of annular shoulder 171 of sleeve 160 and annular seat 149 of cylinder 130 thereby restrains axial movement of sleeve 160 to the right relative to cylinder 130 to maintain axial alignment of sleeve 130 in bore 38 of cylinder 130.

[0050] Annular bearing 80 is located in piston head 40 radially between inner sleeve surface 162 of sleeve 160 and outer piston surface 44 of piston head 40. In addition, annular seal 83 is located in a seal gland in piston head 40 radially to the right of bearing 80 between inner sleeve surface 162 of sleeve 160 and outer piston surface 44 of piston head 40.

[0051] In the embodiment shown in FIGS. 6 and 7, annular seal 82a is located in a seal gland in cylinder 130 between outer sleeve surface 161 of left portion 163a of sleeve 160 and inner cylinder surface 136 of cylinder 130 to reduce leakage of fluid between sleeve 160 and cylinder 130. Annular seal 82b is located in a second seal gland in cylinder 130 between outer sleeve surface 161 of right end portion 163b of sleeve 160 and inner cylinder surface 136 of cylinder 130 to reduce leakage of fluid between sleeve 160 and cylinder 130. Seal 82a and 82b are thereby spaced axially from each other at the left and right marginal end portions of sleeve 160 and on either side of intermediate portion 164 and leakage gap 176.

[0052] In the event that fluid leaks by annular seals 82a and 82b between opposed surfaces 161 and 136 of sleeve 160 and cylinder 130, respectively, under high pressure, such fluid is directed to flow into radial gap 176 and then from radial gap 176 into passage 177 via passage opening 178 and then from passage 177 into cylinder relief port 48 via outlet 179 from passage 177, and then from relief port 48 of cylinder 130 back to fuel tank 20.

[0053] In an alternative embodiment, hydraulic actuator assembly 115 may be configured without seals 82a and 82b and/or with tolerances such that a desired level of leakage between opposed surfaces 161 and 136 of sleeve 160 and cylinder 130 is permitted to flow into radial gap 176 and then from radial gap 176 into passage 177 via passage opening 178 and then from passage 177 into cylinder relief port 48 via outlet 179 from passage 177, and then from relief port 48 of cylinder 130 back to fuel tank 20.

[0054] It should be appreciated that certain features of the system, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination. While various embodiments have been described in detail above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.