Abstract:
The present invention provides an actuator comprising an actuator body, a piston relatively moveable within the actuator body, and a rod attached to the piston and extending out of the actuator body, the actuator body comprising a port for conveying actuator fluid, wherein the actuator also has a damping control portion provided with damping control fluid containing magnetic particles, wherein the piston or the rod is adjacent the damping control fluid, and a first electrical coil associated with the damping control portion, such that an electrical current supplied to the first electrical coil induces a magnetic field and causes the effective viscosity of the damping control fluid to increase, thus increasing the damping effect of the damping control fluid on the piston or rod. The invention also provides an aircraft assembly, such as a landing gear assembly, an aircraft and a method of operating an actuator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present disclosure relates to an actuator. 
         [0002]    The present invention concerns an actuator. More particularly, but not exclusively, this invention concerns an actuator comprising an actuator body, a piston moveable within the actuator body, and a rod attached to the piston and extending out of a first end of the actuator body, the actuator body comprising a port for conveying actuator fluid to or from the actuator body to effect movement of the piston and rod. 
         [0003]    The invention also concerns an aircraft assembly, such as a landing gear assembly, comprising the actuator, an aircraft comprising the actuator and a method of operating an actuator. 
         [0004]    Prior art actuators, for example actuators to effect movement of landing gear doors on an aircraft, often suffer from dynamic load peaks, such as when the piston of the actuator reaches the end of its travel in an actuator body or because of hydraulic peaks due to valve switching, dynamically generated loads or a hydraulically generated feature during actuator travel. The load peaks may occur when there is acceleration or deceleration of the piston. These load peaks can cause fatigue effects on both the actuator and surrounding attachment structure. This requires that the actuator and structure are designed to allow for these effects and may be bigger or heavier than otherwise required. 
         [0005]    To overcome these problems, many actuators are provided with snubbing rings to reduce the load peaks at the end of piston travel. These snubbing rings, or other snubbing devices, restrict the flow of fluid in or out of an actuator, which minimises piston acceleration/deceleration at the end of travel. However, the response of the actuator can be detrimentally affected by the use of snubbing devices. In addition, the snubbing devices offer limited flexibility for design alterations and are not readily able to “fade” in or out—in other words, there are essentially either “on” or “off” and have limited or no “ramping” up/down capability. They also have a fixed performance and cannot easily be altered for different operating conditions (e.g. aircraft speed, fluid temperature etc.). Furthermore, failure in a mechanical snubbing device can be difficult to detect, so that failure exposes the actuator and airframe structure to high loads. The actuator and structure have to be designed to allow for these high loads after snubbing device failure. 
         [0006]    The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved actuator. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides, according to a first aspect, an actuator comprising an actuator body, a piston relatively moveable within the actuator body, and a rod attached to the piston and extending out of a first end of the actuator body, the actuator body comprising a port for conveying actuator fluid to or from the actuator body to effect relative movement of the piston and rod with respect to the actuator body, wherein the actuator also has a damping control portion provided with damping control fluid containing magnetic particles, wherein the piston or the rod is adjacent the damping control fluid, and a first electrical coil associated with the damping control portion, such that an electrical current supplied to the first electrical coil induces a magnetic field over the damping control fluid and causes the effective viscosity of the damping control fluid to increase, thus increasing the damping effect of the damping control fluid on the piston or rod. 
         [0008]    The actuator may comprise a pump associated with the actuator body for conveying fluid to or from the actuator body. The pump may be associated with an inlet or outlet port passage of the actuator body for conveying fluid through the port passage(s). 
         [0009]    The damping control fluid may be a magnetorheological fluid. It may also be a ferrofluid (with smaller magnetic particles). 
         [0010]    Such an actuator with such a damping control fluid offers a simple, cheap and lightweight alternative to an actuator with a snubbing device. In addition, it enables greater speed control of the piston and greater design flexibility. There is also reduced risk of mechanical failure (compared to, for example, snubbing devices) and greater potential for damping failure modes of the system before they propagate. There is also greater potential for failure detection. In addition, the actuator itself and the surrounding attachment airframe structure can be lighter as less fatigue and lower loads may be experienced. In addition, there are no moving parts in the damping mechanism, making the actuator more reliable. Furthermore, the damping can be controlled so as to overcome any temperature effects that change the viscosity and pressure differences of the actuator fluid during use. For example, when it is cooler, the actuator fluid naturally damps movement of the piston more, hence, in cooler temperatures, less current than otherwise would have been, could be supplied to the first electrical coil, to reduce the damping effect. 
         [0011]    Previously, such damping control fluid has only been used in relation to dampers (closed volume systems) and not with actuators (open volume systems). 
         [0012]    Preferably, the damping control portion comprises a chamber located past the first end of the actuator body and wherein the rod extends through the first end of the actuator body and (is connected to a mechanism that extends) into a first end of the chamber, such that the damping control fluid in the chamber is adjacent to the rod (or mechanism) and wherein an increase in viscosity of the damping control fluid increases the damping effect of the damping control fluid on relative movement of the rod through the chamber. 
         [0013]    In this arrangement, the damping control fluid damps movement of the actuator piston by increasing the friction the actuator rod experiences as it moves relatively through the damping control fluid. 
         [0014]    The chamber may be fitted to an end of an existing actuator body for a retrofit option. 
         [0015]    More preferably, the rod extends out of a second opposite end of the chamber. 
         [0016]    Preferably, the first electrical coil extends around the chamber. Preferably, the first electrical coil extends around an extension of the rod axis. 
         [0017]    Alternatively, the damping control portion may be part of an inlet or outlet port passage of the actuator body and wherein the actuator fluid contains magnetic particles and thus provides the damping control fluid and wherein an increase in viscosity of the actuator fluid increases the damping effect of the actuator fluid on the relative movement of the piston in the actuator body. 
         [0018]    In this arrangement, the damping control fluid damps movement of the actuator piston by reducing the flow-rate of actuator fluid through the port passage (effectively reducing the orifice size of the port passage), increasing the pressure drop across the port passage and increasing the time it takes for actuator fluid to pass through the port passage, thus slowing movement of the piston through the actuator body. 
         [0019]    Preferably, the first electrical coil extends around the inlet or outlet port passage of the actuator body. 
         [0020]    The actuator body may have two (or more) ports and an electrical coil may extend around each of the port passages. 
         [0021]    Preferably, the actuator also has a controller unit for controlling the electrical current supplied to the first electrical coil. 
         [0022]    More preferably, the controller unit is provided with an input related to the relative position and/or speed of the piston within the actuator body. 
         [0023]    The controller unit can supply the required electrical current to the first electrical coil to damp relative movement of the piston, based on the relative position and/or speed of the piston within the actuator body. For example, a current may be supplied to the first electrical coil when the piston approaches either end of the actuator body. 
         [0024]    Alternatively, the piston or rod may be provided with a magnet and an inducer coil is provided around the actuator body, such that relative movement of the piston or rod within the actuator body induces an electrical current in the inducer coil. 
         [0025]    For example, the faster the piston or rod moves, the more electrical current induced. This is because current induced is proportional to the rate of “cutting” of magnetic flux lines. 
         [0026]    Alternatively, the actuator body may be provided with a magnet and the piston or rod provided with an inducer coil such that relative movement of the piston or rod within the actuator body induces an electrical current in the inducer coil. 
         [0027]    The magnet may be a permanent magnet or an electromagnet. 
         [0028]    Preferably, the electrical current supplied to the first electrical coil is dependent on the electrical current induced in the inducer coil. More preferably, the induced electrical current (in the inducer coil) is supplied to the first electrical coil. The two coils may be electrically connected by a resistor, for example. 
         [0029]    There may be provided more than one inducer coil. The inducer coils may have a different number of windings or a different density of windings. This allows the damping effect to be increased for relative piston movement in specific areas of the actuator body. For example, towards the end of piston travel in the actuator body, the windings may be provided more densely. This would induce more current for the same relative movement of the piston, compared to a more central position of the piston in the actuator body. 
         [0030]    Preferably, the actuator has a plurality of electrical coils associated with the damping control portion. The coils may have a different number of windings or density of windings. 
         [0031]    The actuator may have an actuator fluid pressure of approximately 3000 to 5000 psi. 
         [0032]    The present invention provides, according to a second aspect, an aircraft assembly, such as a landing gear assembly, comprising the actuator as described above. For example, the actuator may be an actuator for opening landing gear doors in a landing gear assembly. The actuator may actuate movement of the landing gear itself. The actuator may actuate movement of an aircraft control surface. The actuator may be used to damp oscillations of the control surface. 
         [0033]    The present invention provides, according to a third aspect, an aircraft comprising the actuator as described above. 
         [0034]    The present invention provides, according to a fourth aspect, a method of operating the actuator as described above, wherein the method comprises the steps of conveying actuator fluid to or from the actuator body to effect relative movement of the piston and rod, and damping such movement by supplying an electrical current to the first electrical coil. 
         [0035]    Preferably, the electrical current supplied to the first electrical coil is based on a current induced in an inducer coil, the current induced in the inducer coil being related to the position and/or speed of relative movement of the piston or rod. 
         [0036]    Preferably, the actuator is part of an aircraft or aircraft assembly. 
         [0037]    It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0038]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 
           [0039]      FIG. 1  shows a schematic side view of an actuator according to a first embodiment of the invention; 
           [0040]      FIG. 2  shows a schematic side view of an actuator according to a second embodiment of the invention; 
           [0041]      FIG. 3  shows a schematic side view of an actuator according to a third embodiment of the invention; 
           [0042]      FIG. 4  shows a schematic side view of an actuator according to a fourth embodiment of the invention; and 
           [0043]      FIG. 5  shows an aircraft provided with an actuator, according to any of the first to fourth embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]      FIG. 1  shows a schematic side view of an actuator  100  according to a first embodiment of the invention. 
         [0045]    The actuator  100  comprises an actuator body  110  with a left hand end  111  and a right hand end  112 . The actuator is provided with a first inlet/outlet port  114  and first port passage  115  towards the right hand end  112 , and a second inlet/outlet port  116  and second port passage  117  towards the left hand end  111 . Actuator fluid  113  is fed in and from the actuator body  110  via these ports  114 ,  116 . 
         [0046]    A piston  118  is located within the actuator body and is attached to a rod  119  extending out of the right hand end  112  of the actuator body. The rod  119  is able to move in and out of the actuator body  110 . Arrow  119   a,  for example, shows the rod  119  moving into the actuator body  110 , as a result of actuator fluid  113  being fed into port  114  and fed out of port  116 . The piston  118  (and rod  119 ) move relative to the actuator body  110  as a result of the actuator fluid  113  fed in and out of ports  114 ,  116 . 
         [0047]    A first electrical coil  120  is provided around the first port passage  115  and a similar second electrical coil  130  is provided around the second port passage  117 . The first coil  120  is supplied with electricity from a control unit  140  via a first electrical line  142 . The second coil  130  is supplied with electricity from the control unit  140  via a second electrical line  141 . 
         [0048]    The actuator fluid  113  contains magnetic particles. Hence, when electricity is supplied by the control unit  140  to either first coil  1120  or second coil  130 , a magnetic field is produced around the first or second port passage  115  or  117 . This increases the viscosity of the actuator fluid  113  in that vicinity and slows movement of the fluid through the port passage  115  or  117 . This damps movement of the piston  118  in the actuator body  110 , and therefore movement of the rod  119 . 
         [0049]    The control unit  140  is connected to the piston  118  such that a signal is sent through an electrical piston line  143  to the control unit  140  to indicate the position of the piston  118  within the actuator body  110 . The control unit  140  controls the electricity supplied to the first and/or second coil  120 / 130  based on this indication of the position of the piston  118 . For example, if the piston  118  is nearing the left hand end  111  of the actuator body  110 , the control unit  140  may supply electricity to second coil  130  to slow down the movement of the piston  118  in that direction. This is active control. 
         [0050]    In the embodiment of  FIG. 1 , the claimed “damping control portion(s)” comprise the areas of the port passages  115 ,  117  that are associated with the electrical coils  120 ,  130 . 
         [0051]      FIG. 2  shows a schematic side view of an actuator  200  according to a second embodiment of the invention. The actuator  200  is similar to the actuator  100  of  FIG. 1 , and the same reference numerals will be used for like elements, but prefixed by a “2” instead of a “1”. 
         [0052]    The actuator  200  comprises an actuator body  210  with a left hand end  211  and a right hand end  212 . The actuator is provided with a first inlet/outlet port  214  and first port passage  215  towards the right hand end  212 , and a. second inlet/outlet port  216  and second port passage  2117  towards the left hand end  211 . Actuator fluid  213  is fed in and from the actuator body  210  via these ports  214 ,  216 . 
         [0053]    A piston  218  is located within the actuator body and is attached to a rod  219  extending out of the right hand end  212  of the actuator body. The rod  219  is able to move in and out of the actuator body  210 . Arrow  219   a,  for example, shows the rod  219  moving into the actuator body  210 , as a result of actuator fluid  213  being fed into port  214  and fed out of port  216 . The piston  218  (and rod  219 ) move relative to the actuator body  210  as a result of the actuator fluid  213  fed in and out of ports  214 ,  216 . The piston  218  includes a magnet within it. 
         [0054]    A first electrical coil  220  is provided around the first port passage  215  and a similar second electrical coil  230  is provided around the second port passage  217 . The first electrical coil  220  is supplied with electricity via a first electrical line  251 . The second electrical coil  230  is supplied with electricity via a second electrical line  252 . 
         [0055]    The actuator fluid  213  contains magnetic particles. Hence, when electricity is supplied to either first electrical coil  220  or second electrical coil  230 , a magnetic field is produced around the first or second port passage  215  or  217 . This increases the viscosity of the actuator fluid  213  in that vicinity and slows movement of the fluid through the port passage  215  or  217 . This damps movement piston  218  in the actuator body  210  and therefore movement of the rod  219 . 
         [0056]    There is also provided an inducer coil  250  around the actuator body  210  towards the left hand end of the actuator body  210 . When the piston (and the magnet inside it) moves through the inducer coil  250 , electricity is induced in the inducer coil. The inducer coil  250  is connected to the first electrical line  251  and the second electrical line  252 . So, the induced electricity is supplied to the first electrical coil  220  and second electrical coil  230 . This allows the amount of electricity supplied to the first and second electrical coils  220 ,  230  to be passively controlled based on the position of the piston  218  in the actuator body  210  and/or the speed of movement of the piston  218  through the inducer coil  250 . 
         [0057]    In the embodiment of  FIG. 2 , the claimed “damping control portion(s)” comprise the areas of the port passages  215 ,  217  that are associated with the electrical coils  220 ,  230 . 
         [0058]      FIG. 3  shows a schematic side view of an actuator  300  according to a third embodiment of the invention. The actuator  300  is similar to the actuator  100  of  FIG. 1 , and the same reference numerals will be used for like elements, but prefixed by a “3” instead of a “1”. 
         [0059]    The actuator  300  comprises an actuator body  310  with a left hand end  311  and a right hand end  312 . The actuator is provided with an first inlet/outlet port  314  and first port passage  315  towards the right hand end  312 , and a second inlet/outlet port  316  and second port passage  317  towards the left hand end  311 . Actuator fluid  313  (not containing magnetic particles—i.e. a traditional actuator fluid) is fed in and from the actuator body  310  via these ports  314 ,  316 . 
         [0060]    A piston  318  is located within the actuator body and is attached to a rod  319  extending out of the right hand end  312  of the actuator body. The rod  319  is able to move in and out of the actuator body  310 . Arrow  319   a,  for example, shows the rod  319  moving into the actuator body  310 , as a result of actuator fluid  313  being fed into port  314  and fed out of port  316 . The piston  318  (and rod  319 ) move relative to the actuator body  310  as a result of the actuator fluid  313  fed in and out of ports  314 ,  316 . 
         [0061]    A chamber  350  is provided at the right hand end  312  of the actuator body  310  so that its left hand end  352  abuts against the right hand end  312  of the actuator body  310 . The chamber  350  comprises walls but is open ended to allow the rod  319  to extend through the left hand end  352  and out the right hand end  353 . Contained within the walls is a chamber fluid  354  containing magnetic particles. The rod  319  extends through the chamber fluid  354 . An electrical coil  351  extends around the body of the chamber  350 . 
         [0062]    The electrical coil  351  is supplied with electricity from a control unit  340  via an electrical line  344 . 
         [0063]    As the fluid  354  contains magnetic particles, when electricity is supplied by control unit  340  to the electrical coil  351 , a magnetic field is produced over the chamber fluid  354 . This increases the viscosity of the chamber fluid  354  and slows movement of the rod  319  through the chamber  350 . This slows movement of the piston  318  through the actuator body  310 . 
         [0064]    The control unit  340  is connected to the piston  318  such that a signal is sent through an electrical piston line  343  to the control unit  340  to indicate the position of the piston  318  within the actuator body  310 . The control unit  340  controls the electricity supplied to electrical coil  351  based on the position of the piston  318 . For example, if the piston  318  is nearing either end  311 ,  312  of the actuator body  310 , the unit  340  may supply electricity to the electrical coil  351  to slow down the movement of the rod  319  and piston  318 . This is active control. 
         [0065]    In the embodiment of  FIG. 3 , the claimed “damping control portion” comprises the chamber  350 . 
         [0066]      FIG. 4  shows a schematic side view of an actuator  400  according to a fourth embodiment of the invention. The actuator  400  is similar to the actuator  200  of  FIG. 2  and the actuator  300  of  FIG. 3 , and the same reference numerals will be used for like elements, but prefixed by a “4” instead of a “2” or “3”. 
         [0067]    The actuator  400  comprises an actuator body  410  with a left hand end  411  and a right hand end  412 . The actuator is provided with a first inlet/outlet port  414  and first port passage  415  towards the right hand end  412 , and a second inlet/outlet port  416  and second port passage  417  towards the left hand end  411 . Actuator fluid  413  (not containing magnetic particles—i.e. a traditional actuator fluid) is fed in and from the actuator body  410  via these ports  414 ,  416 . 
         [0068]    A piston  418  is located within the actuator body and is attached to a rod  419  extending out of the right hand end  412  of the actuator body. The rod  419  is able to move in and out of the actuator body  410 . Arrow  419   a,  for example, shows the rod  419  moving into the actuator body  410 , as a result of actuator fluid  413  being fed into port  414  and fed out of port  416 . The piston  418  (and rod  419 ) move relative to the actuator body  410  as a result of the actuator fluid  413  fed in and out of ports  414 ,  416 . The piston  418  includes a magnet within it. 
         [0069]    A chamber  450  is provided at the right hand end  412  of the actuator body  410  so that its left hand end  452  abuts against the right hand end  412  of the actuator body  410 . The chamber  450  comprises walls but is open ended to allow the rod  419  to extend through the left hand end  452  and out the right hand end  453 . Contained within the walls is a chamber fluid  454  containing magnetic particles. The rod  419  extends through the chamber fluid  454 . An electrical coil  451  extends around the body of the chamber  450 . 
         [0070]    The electrical coil  451  is supplied with electricity via an electrical line  453 . 
         [0071]    As the fluid  454  contains magnetic particles, when electricity is supplied to the electrical coil  451 , a magnetic field is produced over the chamber fluid  454 . This increases the viscosity of the chamber fluid  454  and slows movement of the rod  419  through the chamber  450 . This slows movement of the piston  418  through the actuator body  410 . 
         [0072]    There is also provided an inducer coil  450  around the actuator body  410  towards the left hand end of the actuator body  410 . When the piston (and the magnet inside it) moves through the inducer coil  450 , electricity is induced in the inducer coil. The inducer coil  450  is connected to the electrical line  453 . So, the induced electricity is supplied to the electrical coil  451 . This allows the amount of electricity supplied to the electrical coil  451  to be passively controlled based on the position of the piston  418  in the actuator body  410  and/or the speed of movement of the piston  418  through the inducer coil  450 . 
         [0073]    In the embodiment of  FIG. 4 , the claimed “damping control portion” comprises the chamber  450 . 
         [0074]      FIG. 5  shows an aircraft  1000  provided with an actuator  3000 . The actuator  3000  is provided on a landing gear assembly  2000  of the aircraft  1000 . The actuator may be any of the actuators  100 ,  200 ,  300  or  400 . The rod of the actuators  100 ,  200 ,  300 ,  400  may be attached to landing gear doors of the aircraft, for example, to effect movement of the doors to allow the landing gear to deploy from and be stowed within the doors. 
         [0075]    Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. 
         [0076]    As an alternative to a double acting actuator, the actuator may be a single acting actuator with only one port and port passage. Such a single acting actuator may be provided with a spring (or similar) to return the piston to a default position may use gravity to do so). 
         [0077]    The actuator may comprise a piston with a rod attached to either side of the piston, each rod extending out of opposite ends of the actuator body. 
         [0078]    The control unit  140 ,  340  may be connected to the rod  119 ,  3109 , instead of the piston  118 ,  318 . The control unit  140 ,  340  may be provided (through electrical piston line  143 ,  343  or electrical rod line) with a signal that indicates the speed of the piston  118 ,  318  additionally or as an alternative to the position indication. 
         [0079]    There may be more than one inducer coil  250 ,  450  provided around the actuator body  210 ,  410 . For example, there may be an inducer coil towards the left hand end  211 ,  411  and/or an inducer coil towards the right hand end  212 ,  412 . These inducer coils could be used to induce electricity and therefore damp movement of the piston  218 ,  418  as it approaches the relevant end of the actuator body  210 ,  410 . 
         [0080]    The coils mentioned above (e.g. first electrical coil, second electrical coil, inducer coil, other electrical coils) may have any suitable number of windings on them. There may be more than one coil in each coil location (or spread out) and those coils may have a different number of windings. 
         [0081]    The number or density of windings on inducer coil(s) may chosen to provide a different amount of induced electricity depending on where the piston is. For example, very near the ends of travel, the windings may be more dense to induce greater electricity to stop the piston quickly. 
         [0082]    There may be any number of electrical components (e.g. resistors) in the electrical lines. For example, a resistor on lines  251 ,  252  or  453  would enable a correct proportion of the electrical current induced to be supplied to the electrical coils  220 ,  230 ,  451  not shown. 
         [0083]    There may be more than one chamber  350 ,  450  adjacent to the rod  319 ,  419 . 
         [0084]    The chamber (or chambers) may be located at any position along the rod. As an alternative, the chamber may be located adjacent a mechanism to be moved by the rod/actuator. 
         [0085]    As an alternative to having a magnet on piston  218  or  418 , the piston may include the inducer coil  250 ,  450  and a magnet may be provided around the actuator body  210 ,  410 . 
         [0086]    The piston/rod may be stationary and the actuator body (and chamber) may move instead (or as well). What is important is that there is some relative movement of the piston/rod and the actuator body. 
         [0087]    The actuator may be used for landing gear doors but may also be applied to any other landing gear actuation or any other aircraft assembly or even in a non-aircraft application. 
         [0088]    Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.