Patent Document

TECHNICAL FIELD 
     This invention is related to actuation systems, and more particularly to a compact asymmetry brake for use in aircraft flight control actuation systems. 
     BACKGROUND 
     Modern aircraft wings often include a series of movable flight control surfaces, known as flaps or slats, that can be selectively extended or retracted to modify the lift producing characteristics of the wings. Extension and retraction of such flaps or slats is accomplished by a flight control actuation system mounted in the wing. 
     A typical actuation system includes a series of actuators spaced along the span of each wing, and operably connected to move one or more individual flight control surfaces. Adjacent actuators are connected to each other by drive shafts, to in essence form a chain of actuators and shafts extending along the span of the wing. A power drive unit (PDU) connected to the inboard end of the chain provides motive power for driving the actuators to selectively extend or retract the flight control surfaces. 
     Because control surfaces such as flaps or slats significantly alter the lift producing characteristics of the wings, it is critical for safe operation of the aircraft that the actuation system also include safety features for detecting and reacting to problems such as jamming, or failure of one of the actuators or drive shafts in the aircraft flight control system. Of particular concern are problems which cause the position of the flaps or slats on one wing to lose synchronization with the flaps and slats on the other wing of the aircraft. Such a condition is referred to as asymmetry. To prevent asymmetry, actuation systems for flaps and slats often include a device known as an asymmetry brake which engages to hold the chain of actuators and shafts in a known position, should a problem occur in the actuation system that cannot be corrected through use of the power drive unit alone. For example, should one of the shafts connecting adjacent actuators break, the PDU would not be able to control the position of flaps or slats outboard of the broken shaft. Without some means, such as an asymmetry brake at the outboard end of the chain of actuators and shafts, for holding the flaps or slats downstream from the broken shaft against further movement, aerodynamic loads acting upon the flaps or slats could move them to an uncommanded position which would create serious flight control problems for the aircraft. 
     U.S. Pat. No. 3,662,550 to Lichtfuss, U.S. Pat. No. 4,779,822 to Burandt et al., and U.S. Pat. No. 5,484,043 to Quick et al., describe flight control actuation systems and asymmetry brake devices such as those described above. As will be readily apparent from these patents, actuation systems for critical aircraft flight control surfaces, such as flaps and slats, are designed to have a high degree of redundancy for monitoring and reacting to problems which could lead to asymmetry. 
     On one recently designed aircraft, very narrow, supercritical, wings were utilized to minimize fuel consumption. The wings were so narrow at their tips, that there was not enough space within the wing for mounting an asymmetry brake at the outboard end of the chain or actuators and interconnecting shafts, as in prior flight control systems. 
     As a result, a novel approach was developed in which the asymmetry brake was positioned between the two outermost actuators, and the outermost actuator was provided with an integral no-back device to maintain position of the outermost actuator, in the event that the driving connection fail between the asymmetry brake and the outermost actuator. This actuation system is described in detail in co-pending patent application Ser. No. 08/602,190, which is assigned to the assignee of the present invention and incorporated herein by reference. 
     Even with the asymmetry brake repositioned between the two outermost actuators, however, there was still insufficient space within the wing to house an asymmetry brake of any known prior construction at the new location. It was, therefore, necessary to develop a new, more compact asymmetry brake. 
     In addition to making the brake physically smaller, a number of other design constraints made designing a new asymmetry brake for the new aircraft described above a significant challenge. The overall design of the flight control system required that the brake be applied and released several times during each flight of the aircraft. This requirement ruled out the use of many prior brake designs which could only be reset manually on the ground once they had been triggered in flight. 
     The actuators used on the new aircraft were of a type having little inherent friction and are thus readily backdrivable by aerodynamic loads. This created high backdriving loads which had to be reacted by the brake. Braking devices using friction plates, of the type utilized in some prior asymmetry brakes, having enough braking capacity to react the backdriving loads were physically too large to fit within the available space. 
     The large backdriving loads created an additional problem in that the actuator for engaging and disengaging the brake had to be capable of overcoming the large backdriving loads to apply or release the brake. The overall design of the flight control system required that the brake actuator be electrically operated. The small available space did not allow for the use of an electrical motor and geartrain. Existing electrical solenoid designs were physically too large, or required too much current. To make matters worse yet, the overall system design required that the electrical actuation means utilized in the brake incorporate redundant features which would allow the actuator to apply full rated engagement force when supplied with current from either of two sources of electrical current which were electrically isolated from one another. This meant that the solenoid had to have two separate windings, each capable of generating full rated force of the solenoid. 
     In its new location, the asymmetry brake had to include a thru-shaft, making attempts to diametrically shrink the size of the brake more difficult. 
     In addition to providing a design meeting the requirements listed above, it was also desired to provide an improved asymmetry brake which would significantly reduce the incidence of nuisance trips and irregular operation experienced with prior asymmetry brakes. 
     Accordingly, it is an object of our invention to provide an improved braking apparatus, suitable for use in an application such as the flight control actuation system for the new aircraft described above. It is also an object of our invention to provide such a braking apparatus that is physically compact, powerful, and highly reliable in a form that includes a minimal number of parts of straightforward design which can be produced at reasonable cost. 
     SUMMARY OF THE INVENTION 
     Our invention provides a braking device meeting the above requirements and objects through the use of a jaw type clutch coupled to an electrical solenoid through a ball spline mechanism. 
     The jaw type clutch provides significantly greater braking capacity in a given volume that other types of braking devices, such as those relying on friction. The particular jaw clutch utilized has negatively raked teeth which lock together upon engagement to positively prevent rotation of the shaft or the braking device. The locking and positive anti-rotation features of the jaw clutch in our braking device thus preclude the need for more complex mechanisms, such as ratchets or ball ramps, used in some prior braking devices to provide positive locking and anti-rotation. The jaw clutch in our invention thus allows a braking apparatus fabricated per our invention to be smaller, more reliable, and producible at lower cost than prior braking devices. 
     The ball spline mechanism of our invention significantly reduces the internal frictional load which the actuator means, such as the solenoid, must overcome to apply or release the brake. As a result, the physical size and current draw of the solenoid are reduced. 
     The jaw clutch and ball spline of our invention are also configured to reduce or absorb shock loads on the various internal components of the braking apparatus when the brake is engaged. Specifically, a rotating element of the jaw clutch is configured to minimize the rotational inertia which must be reacted when the brake is engaged. The rotating jaw is further configured to have its teeth mounted on torsionally flexible arms which twist to help absorb shock loads during engagement. The ball spline is configured to have flexible inner and outer races which bend elastically during engagement of the brake to absorb shock loads. 
     The shaft of the braking apparatus is also configured to have a long span with a narrow cross-section to work in concert with the shafts in the driveline in which the brake is installed to absorb torsional shock loads when the brake is engaged. By configuring the shaft, the ball spline and jaw clutch to function as shock absorbers while performing their primary functions, our invention eliminates the need for the separate elastomeric shock absorbers, etc., that are required in prior braking devices. 
     This internal shock absorber is one piece of the system&#39;s total shock absorber which also includes the narrow cross-section through shaft and the driveline shafts. 
     The solenoid of our invention provides more actuation force in a smaller package with less current draw than prior solenoid designs through the use of strategically placed conically shaped surfaces of the plunger and electromagnetic core of the solenoid. The conical surfaces also provide a longer stroke with less current draw than prior solenoids. The specific placement and cone angle of our solenoid strikes an optimal balance between actuation force, stroke, and current draw by placing the conical surfaces strategically in such a manner that both the primary magnetic flux and the leakage flux generated by the electromagnetic coil combine and contribute to generating the actuation force. 
     Some embodiments of solenoids according to our invention also utilize two conical surfaces strategically placed and configured to work in unison to provide increased actuation force. Similar designs commonly use one working air gap and one air gap parallel to the plunger to complete the magnetic flux circuit. The two cone arrangement shown turns the second air gap into a working air gap which eliminates the frictional forces at this gap common to the usual construction. 
     Also, in some embodiments of our invention, the solenoid coil includes a pair of electrically isolated electrical windings that are wound in a bifilar manner to provide a solenoid that can produce a substantially identical amount of actuation force, for a given stroke and current draw, from either of two independent sources of electrical current. 
     The solenoid of our invention also includes drain passages for removal of condensation from the conical airgaps defined by the conical surfaces of the plunger and the electromagnetic coil. The conical surfaces themselves are coated with a material resistant to retention of a condensate thereupon. The coating causes condensation on the surfaces to run off and be conducted through the passages out of the airgap. 
     These features for removing condensate from the air gaps are particularly important in a device, such as an aircraft asymmetry brake, that may develop condensation on surfaces located outside of the pressurized cabin spaces when the aircraft lands in a humid environment after a period of operation at high altitude where the temperature may be −40 to −65° F. When the aircraft lands after a prolonged cruise at such temperatures, surfaces external to the pressurized cabin, such as the conical surfaces of our solenoid may still be very cold. Water vapor from the air will condense on such cold surfaces. As long as the aircraft is on the ground, such condensation normally does not interfere with operation. But if the aircraft should then take-off and climb to high altitude, the condensate will freeze, and potentially inhibit operation of the solenoid. Temperature-altitude testing of the solenoid of our invention has indicated that the drain passages and coating of our invention can prevent such a problem with essentially no weight or negative operational impact on the solenoid. 
     In fact, where a thick enough coating is applied, the coating actually enhances operation of the solenoid by acting like an air gap to more rapidly dissipate magnetic flux generated by the coil, when the solenoid is de-energized. By more rapidly dissipating the magnetic flux, the coating allows the plunger of the solenoid to begin moving away from the electromagnetic coil more quickly than it could if the conical surfaces made metal-to-metal contact with one another. The coating thus reducing the time it takes to re-engage the jaw clutch and providing a significant operational advantage in a braking apparatus, such as an aircraft asymmetry brake, which must engage virtually instantaneously to stop further rotation of the drive shaft stationary after a failure in a flight control system. 
     These and other aspects and advantages of our invention will be apparent to those having skill in the art upon consideration of the following drawing figures and detailed descriptions of exemplary embodiments of our invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-section of an exemplary embodiment of a braking apparatus according to our invention, illustrating the brake in a locked, or engaged, position with the solenoid de-energized; 
     FIG. 2 is a partial sectional view of the braking apparatus illustrated in FIG. 1 showing the brake apparatus in an unlocked, or disengaged, position with the solenoid energized; 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG. 4 illustrating construction details of jaw teeth on a rotating and a translating element of a jaw clutch according to our invention; 
     FIG. 4 is a view taken along line  4 — 4  of FIG. 2 illustrating a rotating element of the jaw type clutch of FIGS. 1 and 2; 
     FIG. 5 is a transverse view taken along line  5 — 5  of FIG. 1 illustrating features of the rotating and translating elements of the jaw clutch of the exemplary embodiment depicted in FIGS. 1 and 2; 
     FIG. 6 is a transverse view of a ball spline of the braking assembly depicted in FIGS. 1 and 2 taken along line  6 — 6  of FIG. 2; 
     FIG. 7 is an enlarged view of a portion of the ball spline depicted in FIG. 6; and 
     FIG. 8 is a schematic representation of an alternate embodiment of a bifilar winding for use in a braking assembly according to our invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 1 depicts an exemplary embodiment of our invention in the form of an asymmetry brake  10  including a housing  12  having a rotating member in the form of a shaft  14  mounted therein by bearings  16 ,  18  for rotation relative to the housing  12  about an axis of rotation  20 . 
     A jaw type clutch, generally indicated as referenced numeral  26 , is disposed about the axis  20 . The jaw clutch  26  includes a rotating element  28  thereof operably connected to the shaft  14  by means of a spline  30  or similar type of connection which constrains the rotating element  28  to rotate with the shaft  14 , but allows the rotating element  28  to move axially to the right with respect to the shaft  14 . 
     The inner race of the bearing  16  is journaled over a hub portion  36  of the rotating element  28 . The outer race of the bearing  16  is guided within a bearing liner  32  pressed into the housing  12  in a manner allowing the bearing  16  to move freely in an axial direction with the rotating element  28 . A stack of belleville washers  34  disposed between the liner  32  and the outer race of the bearing  16  pre-load the rotating element  28  against a shoulder  24  formed integrally with the shaft  14 . This pre-load is transformed through the rotating element into the shaft  14 , and subsequently transferred from the shaft  14  to the housing  12 , via a second shoulder  22  formed integral with the shaft  14  and the bearing  18 , to constrain the shaft  14  against unlimited movement along the axis  20 . 
     As best seen in FIG. 2, the liner  32  includes an axially extending stop  38  which defines a gap  40  between the stop  38  and a web portion  42  of the rotating element  28 , when the belleville springs  34  are biasing the bearing  16  and rotating element  28  against the shoulder  24  of the shaft  14 . The shoulder  24  of the shaft  14  and the stop portion  38  of the liner  32  in combination thus provide a means for limiting the rotating element  28  against unlimited axially movement with respect to the shaft  14  after the solenoid is de-energized. 
     Returning to FIG. 1, the jaw clutch  26  also includes a translating element  44  operatively connected to the housing  12  in a manner, to be described in greater detail below, which allows the translating element  44  to move axially with respect to the housing  12  from a locked position as depicted in FIG. 1 to an unlocked axial position as depicted in FIG. 2, and in a manner constraining the translating element  44  against unlimited rotation about the axis  20  with respect to the housing  12 . The rotating and translating elements  28 , and  44  respectively, each include complimentary jaw tooth means  46 ,  48  respectively extending axially therefrom in a juxtaposed relationship, as best seen in FIGS. 3-5, for engagement of the rotating and translating elements  28 ,  44  in an interlocking relationship with one another when the translating element  44  is disposed in the locked position as depicted in FIG.  1 . 
     As shown in FIG. 1, actuator means in the form of an electrical solenoid  50 , and a helical spring  51 , are provided for moving the translating element  44  between the locked and unlocked axial positions. The helical spring  51  is operably disposed between the housing  12  and the translating element  44  in a manner urging the translating element to move toward the right from the unlocked position depicted in FIG. 2 to the locked position depicted in FIG.  1 . 
     The solenoid  50  includes a plunger  52  disposed about the axis  20  and attached to the translating element  44  by a shoulder  58  and a snap ring  56  extending from the plunger  52 , in a manner constraining the translating element  44  to move axially with the plunger  52 . The solenoid  50  also includes an electromagnetic coil assembly  54  disposed about the plunger  52  and fixedly attached to the housing  12  by bolts  60 . The electromagnetic coil  54  is configured to produce a magnetic field intersecting the plunger  52 , when the coil  54  is supplied with electrical current via connector  62  from a source of electrical current, (not shown) for inducing an electromotive force on the plunger  52  acting in a direction urging the plunger  52  to move the translating element  44  from the locked position illustrated in FIG. 1 to the unlocked axial position illustrated in FIG.  2 . 
     As shown in FIGS. 1 and 6, the asymmetry brake  10  also includes ball spline means  64  operably disposed between the translating element  44  and the housing  12 , for operably connecting the translating element  44  to the housing  12  in a manner allowing the translating element  44  to move axially, with respect to the housing  12 , between the locked and unlocked positions of the translating element  44 , and constraining the translating element  44  against unlimited rotation about the axis  20  with respect to the housing  12 . As best seen in FIG. 6, the ball spline means  64  includes an outer race  66  operably connected to the housing  12  by torque reacting pins  68  for constraining the outer race  66  against rotation relative to the housing  12 . The outer race  66  also defines a plurality of circumferentially spaced axially oriented ball tracks  70 , in a radially inner surface  72  of the outer race  66 , for receipt of ball bearings  74 . The ball spline means  64  also includes an inner race  76  integrally attached to the translating element  44  for movement therewith. The inner race  76  also defines a plurality of circumferentially spaced axially oriented ball tracks  78  in a radially outer surface  80  of the inner race  76 . The ball tracks  78  in the radially outer surface  80  of the inner race  76  are juxtaposed and generally circumferentially aligned with the ball tracks  70  of the outer race  66  for receipt of the ball bearings  74 . The ball bearings  74  disposed within the ball tracks  70 ,  80  of the outer and inner races  66 ,  76  operably connect the inner and outer races  66 ,  76  in such a manner that the inner race  76  is constrained against unlimited relative rotation with respect to the outer race  66  about the axis  20 , and such that the inner race  76  may translate axially with respect to the outer race  66 , through substantially rolling motion of the ball bearings  74  traveling in an axial direction within the ball tracks  70 ,  78 . The rolling motion of the ball bearings in the axial direction within the ball tracks  70 ,  78  significantly reduces the internal frictional load of the brake apparatus  10  that the solenoid  50  must overcome to apply or release the brake  10 . 
     As shown in FIG. 5, the complimentary jaw teeth  46 ,  48  of the rotating and translating elements  28 ,  44  respectively of the jaw clutch  26  are configured to provide a backlash clearance ‘C’ between mating adjacent pairs of mating jaw teeth  46 ,  48  when the translating element  44  is disposed in the locked position. The backlash clearance ‘C’ allows a limited amount of relative rotation of the translating and rotating elements  44 ,  28  between a first locked position, as illustrated by FIG.  5  and at reference numeral  82  of FIG. 3 whereat the translating element  44  constrains the rotating element  28  against rotation in a counterclockwise direction about the axis  20 , and a second locked position as illustrated at  84  in FIG. 3 whereat the translating element  44  constrains the rotating element  28  against rotation in an opposite clockwise direction about the axis  20 . 
     The jaw teeth  46 ,  48  of the exemplary embodiment depicted in FIGS. 3-5 are configured to include mating faces  46   a,    48   a  having negative rake angles  47  for locking the teeth  46 ,  48  together, in a manner resisting axial movement of the translating element  44  relative to the rotating element  28 , when the teeth  48  of the translating element are engaged with the teeth  46  of the rotating element  44  in either the first or second locked positions  82 ,  84 . 
     The jaw clutch  26  and ball spline means  64  of the exemplary braking apparatus  10  of our invention are also configured to reduce or absorb shock loads imposed on the various internal components of the braking apparatus  10  when the jaw clutch  26  is engaged. As shown in FIG. 4, the web portion  42  of the rotating element is configured to form a plurality of arm-like web portions  84  extending generally radially outward from the hub portion  36  for operably connecting the jaw teeth  46  of the rotating element  28  to the hub  36 . Each arm-like web portions  84  of the rotating element  28  extends along a generally radially directed twisting axis  86  passing through the axis  20  of the shaft  14 . Configuring the web  42  of the rotating element  28  in this fashion provides two advantages with respect to reducing and absorbing shock loads imposed on the internal components when the jaw clutch  26  is engaged. First, by cutting away a portion of the web between adjacent teeth  46 , the rotational inertia generated by the rotating element  28  which must be reacted when the jaw clutch  26  engages is reduced. Second, the arm-like web portions  84  allow a limited twisting motion of each of the arm-like web portions  84  and the tooth  46  attached thereto about its respective twisting axis  86 , for absorbing circumferentially directed shock forces generated by engagement of the teeth  46  of the rotating element  44  with the teeth  48  of the translating element  44  of the jaw tooth clutch  26 . 
     The ball spline means  64  are also configured to provide means for absorbing circumferentially directed shock loads generated by engagement or disengagement of the translating element  44  with the rotating element  28 . As shown in FIG. 6, the inner race  76  includes relief cuts  88 , in the outer surface  80 , disposed between circumferentially adjacent ball tracks  78  for providing a pre-determined radial and circumferential flexibility of the inner race  76 , allowing the inner race  76  to absorb circumferentially directed shock loads through bending of the inner race  76  between the ball tracks  78 . 
     The outer race  66  also includes relief cuts  90 ,  91  in the radially inner wall  72  thereof disposed in portions of the outer race  66  extending between circumferentially adjacent ball tracks  70 . In similar fashion to the relief cuts  88  in the inner race, the relief cuts  90 ,  91  in the outer race  66  provide a pre-determined radial flexibility of the outer race  66  for absorbing circumferentially directed shock loads through bending of the outer race  66  in the portions of the outer race  66  extending between adjacent ball tracks  70 . 
     The housing  12  also includes relief cuts  92  disposed adjacent the portion of the outer race  66  extending between the ball tracks  70  for providing clearance for the bending of the outer race  66  in the portion thereof extending between adjacent ball tracks  70 . 
     As shown in FIG. 7, the ball bearings  74  in the exemplary embodiment of the brake  10  have a diameter ‘d’ defining a radially outer surface  94  thereof. The ball tracks  70 ,  78  in the inner and outer races  76 ,  66  and the ball bearings  74  are mutually configured and radially disposed to provide a closely toleranced fit of the outer surfaces  94  of the ball bearing  74  in the ball tracks  70 ,  78  in a radial direction with respect to the axis  20  when the ball tracks  78  in the inner race  76  are circumferentially aligned in a radially juxtaposed relationship with the ball tracks  70  in the outer race  66 . The ball tracks  78 ,  70  in the inner and outer races  76 ,  66  are further configured to define ball ramps  96  for applying bending forces to the inner and outer races  76 ,  66  when the races are urged to rotate relative to one another about the axis  20  from the relative position illustrated in FIG. 6 whereat the ball tracks  78  and the inner race  76  are circumferentially aligned in a radially juxtaposed position with the ball tracks  70  in the outer race  66 . 
     As shown in FIG. 6, the ball tracks  70  and the outer race  66  are circumferentially disposed relative to the torque reacting pins  68  about the axis  20  of the shaft  14  in an angular relationship pre-determined to provide a desired circumferential stiffness of the ball race means  66 . Specifically, as shown in FIG. 6, the three ball bearings  74  of the exemplary embodiment are angularly displaced from the three torque reacting pins  68  in a manner respectively creating one short and one long relief cut  90 ,  91  between adjacent torque reacting pins  68 , rather than being positioned an equal angular distance from adjacent torque reacting pins  68 . Those having skill in the art will readily recognize that as the ball bearings  74  are moved closer to an equal distance angular relationship between adjacent torque reacting pins  68 , the circumferential and radial stiffness of the ball spline means  64  will be reduced. Those skilled in the art will further recognize that by adjusting the angular relationship between the balls  74  and the torque reacting pins  68 , the shape of the relief cuts in the inner and outer races  76 ,  66 , and by adjusting the number and mutual configuration of the ball bearings  74  and the ball ramps  96  utilized in the ball spline device  64 , a desired circumferential stiffness of a ball spline mechanism  64  according to our invention can be readily provided to meet the needs of a particular embodiment of a device incorporating the ball spline  64  of our invention. 
     The shock absorbing features of the ball spline  64  and jaw clutch  26  of our invention described above allow an asymmetry brake  10  as shown in FIGS. 1-7 to engage and stop a shaft rotating at about 1500 rpm in a total time of less than about 0.05 seconds, without any of the additional shock absorbing devices, made from an elastomer, etc., that are required to protect the internal components of prior asymmetry brakes. 
     The plunger  52  and electromagnetic coil  54  of the solenoid  50  of the exemplary embodiment of the braking apparatus  10  respectively include a portion of a radially outer and inner surface thereof configured to define first generally conically shaped surfaces  98 ,  100 . Each of the respective first conical surfaces  98 ,  100  converge toward a respective apex  99 ,  101  of a cone defined by that conical surface, with the apex of each of the defined cones coinciding with the axis  20  in such a manner that the first conical surfaces  98 ,  100  converge toward their respective apexes  99 ,  101  in a direction consistent with axial motion of the plunger  52  when the translating element  44  moves from the locked position shown in FIG. 1 to the unlocked axial position as shown in FIG.  2 . The first conical surfaces  98 ,  100  define a generally annular conical first air gap  102  therebetween when the translating elements  44  is in the locked axial position as depicted in FIG.  1 . As shown in FIG. 1, the plunger  52  and electromagnetic coil  54  are configured such that the first conical surfaces  98 ,  100  and air gap  102  are equally disposed axially about a plane  104  extending perpendicularly through the axis  20  at a point on the axis  20  substantially bisecting an axial length ‘L’ of the electromagnetic coil  54 . 
     The electromagnetic coil  54  also includes a drain passage  106  for conducting a flow of fluid away from the first air gap  102 , as indicated by arrows  108 . The first conical surfaces  98 ,  100  are also coated with a thickness of about 0.002 inches of a material which is resistant to retention of a condensate thereupon, in order to cause any fluid condensing on the first conical surfaces  98 ,  100  to run down through the first air gap  102  and be conducted away from the air gap  102  by the drain means  106 . A material such as a product sold under the trade name Wear Cote plus CF x  by Wear Cote International, Co. of Rock Island, Ill. has been found to provide not only the desired resistance to retention of condensate, but also provides a measure of anti-corrosion protection for the first conical surfaces  98 ,  100 . The Wear Cote material is a combination of a fluorinated carbon and nickel which is applied by a procedure similar to that used for applying electroess nickel plating. 
     In addition to providing resistance to moisture retention and corrosion, the coating on the conical surfaces of the plunger and electromagnetic coil  52 , 54  enhances operation of the solenoid  50  by acting like an air gap to more rapidly dissipate magnetic flux generated by the coil  54 , when the solenoid  50  is de-energized. By more rapidly dissipating the magnetic flux, the coating allows the plunger  52  of the solenoid  50  to begin moving away from the electromagnetic coil  54  more quickly than it could if the conical surfaces  98 ,  100  made metal-to-metal contact with one another. The coating, thus reducing the time it takes to re-engage the jaw clutch  26  and providing a significant operational advantage in a braking apparatus, such as an aircraft asymmetry brake, which must virtually instantaneously to stop further rotation of the drive shaft stationary after a failure in a flight control system. 
     Conical air gaps such as the first air gap  102  of the solenoid of our invention are known to produce a solenoid with a reduced current draw for a given stroke length by virtue of the angular relationship between the stroke and an effective air-gap distance measured perpendicular to the conical surfaces. Although theoretical calculations would indicate that a cone angle  110  as small as possible between the conical surfaces  98 ,  100  and the axis  20 , as shown in FIG. 1, would create the longest stroke with the smallest current draw, our experience has shown that a cone angle  110  of about 30° with respect to the axis  20  provides an optimum stroke length for a given current draw. 
     As shown in FIG. 1, the electromagnetic coil  54  includes a core  112  defining a generally annular shaped cavity  116  therein disposed about the axis  20  for receipt of an electrical winding  114 . The core  112  defines radially inner and outer walls  118 ,  120  of the annular shaped cavity  116 , connected by radially extending end walls  122 ,  124  at both axial ends of the annular cavity  116 . The end walls  122 ,  124  have a radial width ‘W’ centered about a mean radius  126  of the annular cavity  116  extending radially outward from the axis  20  to define a cylindrical plane  128  generally radially bisecting the annular shaped cavity  116 . 
     The electrical winding  114  is configured to produce a magnetic field intersecting the plunger  52  when the winding is supplied with electrical current via connector  62  from a source of electrical current, for inducing an electromotive force on the plunger  52  in a direction urging the plunger to move the translating element  44  from the locked position illustrated in FIG. 1 to the unlocked axial position illustrated in FIG.  2 . The winding  114  includes a plurality of layers of turns helically wound in a continuous manner about the radially inner wall  118  of the core  112 , with each turn of the winding  114  substantially abutting a previous turn, and each layer overlaying a previous layer, such that the winding  114  extends radially completely across the radial width ‘W’ of the end walls  124 ,  122  and substantially fills the annular shaped cavity  116 , as shown in FIGS. 1 and 2. 
     As shown in FIG. 1, the plunger  52  and electromagnetic coil  54  of the exemplary embodiment also each include a second portion of the radially outer and inner surfaces thereof respectively configured to define complimentary second generally conically shaped surfaces  130 ,  132  thereof. Each of the respective conical surfaces  130 ,  132  converge toward a respective apex  131 ,  133  of a cone defined by that second conical surface coinciding with the axis  20  in such a manner that the second conical surface  130  of the plunger  52  converges toward its respective apex  131  in a direction consistent with axial motion of the plunger  52  when the solenoid  50  is urging the translating element  44  to move from the locked to the unlocked positions, or to the left as depicted in FIG.  1  and FIG. 2, in similar fashion to the first conical surface  98  of the plunger as described above. The second conical surfaces  130 ,  132  define a second generally annular conical air gap  134  therebetween, having an axial length S 2  substantially equal to an axial length S 1  of the first air gap  102  when the translating element  44  is in the locked axial position as depicted in FIG.  1 . 
     The second conical surfaces  130 ,  132  of the plunger  52  and electromagnetic coil  54  are radially and axially disposed such that the second conical surfaces  130 ,  132  and second air gap  134  are equally disposed radially about the cylindrical planes  128  defined by the mean radius  126  of the annular cavity  116 . The second conical surfaces and second air gaps  130 ,  132 ,  134  are further disposed axially adjacent to the second radially extending end wall  124  of the annular cavity  116 . 
     The second conical surfaces  130 ,  132  of the plunger and electromagnetic coil  52 ,  54  are coated with a material resistant to retention of a condensate thereupon in similar fashion to that described above with respect to the first conical surfaces  98 ,  100 . The braking apparatus  10  also defines a second drain means, generally indicated at  136 , for conducting a flow of fluid away from the second air gap  134  and out of the braking apparatus  10 , as indicated by arrow  138  in FIG.  1 . 
     Those skilled in the art will readily recognize that by positioning the second conical surfaces  130 ,  132  and second air gap  134  as described above, both the primary flux and leakage flux generated by the winding  114  and core  112  pass through the second air gap  134 , and combine to create more actuation force on the plunger for a given current draw supplied to the winding  114  than would be achievable if the second conical surfaces and air gap  130 ,  132 ,  134  were located at another position whereat the leakage flux could not be utilized. Our experience has also shown that by adding the second conical surfaces  130 ,  132  and air gap  134  configured in the manner described above, the plunger  52  tends to center itself better within the electromagnetic coil  54 , than in other possible arrangements where the second surface and air gap  130 ,  132 ,  134  are angled in a direction opposite to the angle of first conical surface, or where the second conical surfaces and air gap are located at the radially outer edge of the electromagnetic coil  54 . The improved centering of the plunger provided by the second surfaces  130 ,  132  and air gap  134  serves to keep the plunger from dragging against the electromagnetic coil  54 , thereby reducing inherent friction between the plunger  52  and coil  54  in such a manner that a larger proportion of the electromotive force imparted to the plunger  52  by the coil  54  is usable as actuation force for moving the plunger  52 . 
     For the specific embodiment of our invention depicted in the braking apparatus  10  illustrated in FIGS. 1-7, therefore, the spring  51  will urge the jaw teeth  46  of the rotating elements  28  of the jaw clutch  26  to engage the teeth  48  of the translating element  44  when the winding  114  is not being supplied with electrical current. 
     To release the brake  10 , electrical current is supplied to the winding  114  for energizing the solenoid  50  to produce an electromotive force urging the plunger  52  to move to the left as depicted in FIGS. 1 and 2, from the locked position depicted in FIG. 1 to the unlocked position depicted in FIG.  2 . The backlash clearance ‘C’ allows the rotating element  26  to rotate a small angular distance about the axis  20  to release the negatively raked teeth  46 ,  48  from one another so that the plunger  52  can pull the translating element  44  away from the rotating element  28  to release the brake  10 . 
     To apply the brake, electrical current to the winding  114  is cut off, causing the spring  51  to drive the translating element  44  to the right as depicted in FIG. 1, so that the teeth  48  of the translating element may engage and lock with the teeth  46  of the rotating element  28  to stop the shaft  14  from rotating. 
     When the teeth  48  of the translating element  44  contact the teeth  46  of the rotating element  28  during engagement of the brake  10 , the arm like web  84  of the rotating element  28 , in combination with the flexible inner and outer races  76 ,  66  and ball ramp means  96  of the ball spline  64 , absorb the circumferentially directed shock generated by contact between the translating and rotating elements  44 ,  28 . As the teeth  48  of the translating element  44  contact the teeth  46  of the rotating element  28 , axially directed impact forces cause the rotating element  28  to move axially to the right as depicted in FIG. 2 such that the web portion  42  of the rotating element  28  is driven into contact with the stop  38  of the liner  32 , against the force of the belleville spring  34 , in such a manner that the axially directed impact forces are not applied across the bearing  16 , but are transferred into the housing  12  through the liner  32 . 
     FIG. 8 illustrates an alternate embodiment of our invention in which the electromagnetic coil includes a pair of first and second electrical windings  140 ,  142  wound about the core  112  to form a bifilar winding  144 , having axially alternating turns  140   a,b;    142   a,b;  etc., of the first and second windings  140 ,  142  wound in a paired, helical, axially side-by-side manner about the core  112 , with each subsequent pair of turns substantially abutting a previous pair of turns. Each of the first and second windings  140 ,  142  of the bifilar winding  144  are electrically isolated from one another and independently adapted for connection to a separate source (not shown) of electrical current. Through utilization of such a bifilar winding  144 , each of the first and second windings  140 ,  142  will independently generate sufficient electromotive force for moving the translating element from the locked to the unlocked axial position. Unlike other arrangements for forming two windings on the same core, such as stacking them axially, or winding the second winding  142  radially over the top of the first winding  140 , the bifilar winding  144  as described above generates a substantially identical electromotive force on the plunger for a given value of current supplied to either the first or second winding  140 ,  142 . 
     From the foregoing description, those having skill in the art will readily recognize that our invention overcomes problems encountered in prior braking devices and provides an improved braking apparatus suitable for use in applications for requiring a physically compact, powerful and highly reliable braking device, that includes a minimal number of parts of straightforward design that can be produced at reasonable cost. Those having skill in the art will also recognize that the braking apparatus of our invention can readily be incorporated into aircraft actuation system hardware, and provides a unique solution to the problems of fitting an asymmetry brake into the limited envelope available in the supercritical wing of the new aircraft described above in the Background section of this application. 
     Those having skill in the art will further recognize that although we have described our invention herein with respect to specific embodiments and applications thereof, many other embodiments and applications of our invention are possible within the scope of our invention as described in the appended claims. For example, our invention is not limited to asymmetry brakes for use in aircraft actuation systems, but may be used with equal utility anywhere a compact powerful braking device of a highly reliable robust construction is required. 
     We also wish to specifically point out that the individual novel elements of our invention as described herein, such as the solenoid with dual conical surfaces, the shock absorbing ball spline device  64 , and the self-locking shock absorbing jaw clutch, of our invention can be used individually or in other combinations than those specifically described herein within the scope of the appended claims. 
     It is understood, therefore, that the spirit and scope of the appended claims should not be limited to the specific embodiment described and depicted herein.

Technology Category: b