Abstract:
The present invention concerns an aircraft landing gear comprising a wheel rotatably mounted on an axle, a first gearing element that rotates with the wheel, a second gearing element configured to mesh with the first gearing element such that rotation of the first gearing element causes rotation of the second gearing element, wherein the second gearing element is connected to a generator, such that rotation of the second gearing element causes the generator to generate electrical energy, further comprising a heat dissipation device connected to the generator wherein the heat dissipation device comprises an electrical heating element connectable to the generator to receive generated electrical energy and convert it to heat energy, and a fluid receptacle adjacent the heating element, such that fluid in the receptacle can be heated. The present invention also concerns an aircraft landing gear comprising a cavitation braking device, an aircraft and a method of braking.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present disclosure relates to aircraft landing gear. 
         [0002]    The present invention concerns aircraft landing gear. More particularly, but not exclusively, this invention concerns an aircraft landing gear comprising an axle and a wheel rotatably mounted on the axle. 
         [0003]    The invention also concerns an aircraft and a method of braking. 
         [0004]    Many commercial passenger aircraft use carbon brakes, comprising a number of “carbon-carbon” composite disks that can be pushed together by hydraulic actuators, in order slow relative rotation of the disks. The carbon disks are subject to wear, both during high-speed braking and especially during low-speed braking due to “surface plucking” of the brake disk surfaces. 
         [0005]    Various e-taxi systems have been proposed, where a motor is used to drive rotation of the landing gear wheels whilst the aircraft is on the ground. One such system is proposed in WO 2015/025131 and describes the motor being connected to a toothed drive pinion that can mesh with a toothed ring gear on the wheel hub. An actuator is proposed to be used to move the toothed drive pinion and ring gear into and out of engagement with each other. When engaged, the motor can drive rotation of the wheel. There is also a proposal for the e-taxi system to include the ability to provide a reverse braking function (i.e. by using the motor as a generator to convert kinetic energy into electrical energy and slow forward movement of the wheel). 
         [0006]    However, such an arrangement would require a large (and heavy) resistor to be connected to the generator so that the electrical energy generated from the kinetic energy can be converted into heat energy and dissipated. Alternatively, large batteries or super conductors may be used. 
         [0007]    The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved aircraft landing gear. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides, according to a first aspect, an aircraft landing gear comprising an axle and a wheel rotatably mounted on the axle, a first gearing element connected to the wheel, such that it rotates with the wheel, a second gearing element, wherein the second gearing element is configured to mesh with the first gearing element such that rotation of the first gearing element causes rotation of the second gearing element, wherein the second gearing element is connected to a generator, such that rotation of the second gearing element causes the generator to generate electrical energy, the aircraft landing gear further comprising a heat dissipation device connected to the generator such that electrical energy generated by the generator is dissipated in the form of heat energy by the heat dissipation device, wherein the heat dissipation device comprises an electrical heating element connectable to the generator to receive generated electrical energy and convert it to heat energy, and a fluid receptacle adjacent the heating element, such that fluid in the receptacle can be heated by the heating element. 
         [0009]    In use, the second gearing element is rotated by the first gearing element. This rotation (kinetic energy) is converted into electrical energy by the generator. This electrical energy is converted into heat energy by the electrical heating element. This heat energy is then dissipated by the fluid in the fluid receptacle. Hence, the arrangement acts to slow rotation of the first gearing element (and therefore slow rotation of the wheel and the ground speed of the aircraft itself). 
         [0010]    Such an arrangement allows the heat energy to be dissipated quickly by the fluid in the fluid receptacle. 
         [0011]    The second gearing element may be directly or indirectly connected to the generator. 
         [0012]    The walls of the fluid receptacle may be relatively thin and/or conductive so that the heat energy is efficiently transferred from the electrical heating element to the fluid. 
         [0013]    The fluid receptacle may be provided with fluid. The fluid is preferably a liquid and may turn into a gas upon heating. That gas may then leave the fluid receptacle. 
         [0014]    The fluid receptacle may be connected to a fluid supply line. 
         [0015]    The fluid supply line may comprise a pump for urging fluid from a fluid reservoir to the fluid receptacle. 
         [0016]    The generator may be configured to act as a motor to rotate the second gearing element and thus drive rotation of the first gearing element and wheel, wherein the motor is controlled by motor control electronics. 
         [0017]    For example, when the generator acts as a motor to drive rotation of the first and second gearing elements and the wheel, the generator rotates either in a first direction to drive the wheel in a forwards direction or in a second, opposite direction to drive the wheel in a backwards direction, and wherein, when the generator acts as a generator to slow rotation of the wheel and first and second gearing elements, the generator is rotated in either the first direction when the wheel rotates in the forwards direction or in the second direction when the wheel rotates in the backwards direction. 
         [0018]    The first and second gearing elements may be moveable between a meshing configuration and a non-meshing configuration, the movement being effected by an actuator controlled by actuator control electronics. 
         [0019]    The fluid supply line may include a flow passage through or adjacent the motor control electronics or actuator control electronics, such that the fluid in the fluid passage is heated by the control electronics. 
         [0020]    The fluid may comprise water. Hence, the water may turn to gas (i.e. steam) during heating. The steam may evaporate or otherwise leave the fluid receptacle. 
         [0021]    The heat dissipation device may be a steam generator. 
         [0022]    The steam generator may be a mono tube steam generator. 
         [0023]    The first and second gearing elements may comprise a roller gear and corresponding sprocket. 
         [0024]    According to a second aspect of the invention there is also provided an aircraft comprising the aircraft landing gear as described above in relation to the first aspect of the invention. 
         [0025]    According to a third aspect of the invention there is also provided a method of braking an aircraft wherein the aircraft is the aircraft as described above in relation to the second aspect of the invention. 
         [0026]    According to a fourth aspect of the invention there is also provided a method of braking an aircraft, the aircraft comprising the aircraft landing gear as described above in relation to the first aspect of the invention, the method comprising the steps of rotating the wheel about the axle, meshing the first and second gearing elements, thereby causing the second gearing element to be rotated by the first gearing element and causing the generator to generate electrical energy, and connecting the generator to the heating element of the heat dissipation device and providing fluid to the fluid receptacle, thereby causing the generated electrical energy to heat the fluid. 
         [0027]    According to a fifth aspect of the invention there is also provided an aircraft landing gear comprising an axle and a wheel rotatably mounted on the axle, a cavitation braking device for slowing rotation of the wheel about the axle, wherein the braking device comprises a first part connected to the axle, the first part having a first cavitation surface, a second part connected to the wheel, the second part having a second cavitation surface, and a liquid channel between the first and second cavitation surfaces, wherein both of the first and second cavitation surfaces are provided with a number of indent portions such that, when the wheel is rotating on the axle and the second part is rotating with respect to the second part and when liquid is supplied to the liquid channel, the liquid is caused to cavitate when at least one indent portion on the first cavitation surface lines up with an indent portion on the second cavitation surface. 
         [0028]    Cavitation is the sudden formation and collapse of low-pressure bubbles. In the above arrangement, the lining up of the indents causes the liquid in the channel adjacent to the indents to suddenly expand to fill the suddenly increased volume available. This lower pressure causes gas bubbles to form. The bubbles then collapse as the indentations move away from each other. This rapid expansion and contraction generates heat in the liquid that can then be dissipated. 
         [0029]    In use, the second part is rotated by the wheel. This rotation (kinetic energy) is converted into heat energy by the cavitation braking device. This heat energy is then dissipated by the liquid. Hence, the arrangement acts to slow rotation of the wheel and the reduce the ground speed of the aircraft itself. 
         [0030]    At least one of the indent portions may be in the form of a blind hole in the cavitation surface. This provides a sudden increase in volume available to the liquid when the indent lines up with another similar indent. 
         [0031]    The braking device may further comprise a liquid supply line for supplying liquid to the liquid channel. 
         [0032]    The liquid supply line may comprise a pump for urging liquid into the liquid channel. 
         [0033]    The aircraft landing gear may further comprise a first gearing element connected to the wheel, such that it rotates with the wheel, a second gearing element, wherein the second gearing element is configured to mesh with the first gearing element such that rotation of the second gearing element causes rotation of the first gearing element, wherein the second gearing element is connected a motor, such that rotation of the second gearing element by the motor drives rotation of the first gearing element and the wheel. 
         [0034]    The motor may be configured to act as a generator to generate electrical energy upon rotation of the second gearing element by the first gearing element. 
         [0035]    The first and second cavitation surfaces may be substantially parallel to each other and at an angle to the wheel axle, such that the liquid channel forms a cone shape. 
         [0036]    Bearings may be provided between the first part or axle and the second part. This allows the first part and second part to be freely rotating when there is no liquid present in the channel. 
         [0037]    The second part may be mounted externally to the first part with respect to the axle. This allows the second part to be mounted effectively on the wheel. 
         [0038]    The first cavitation surface may be externally facing with respect to the axle and the second cavitation surface may be internally facing with respect to the axle. 
         [0039]    The aircraft landing gear may further comprise an additional braking device for slowing rotation of the wheel about the axle at lower rotational speeds than the cavitation braking device. 
         [0040]    According to a sixth aspect of the invention there is also provided an aircraft comprising the aircraft landing gear as described above in relation to the fifth aspect of the invention. 
         [0041]    According to a sixth aspect of the invention there is also provided a method of braking an aircraft wherein the aircraft is the aircraft described above in relation to the sixth aspect of the invention. 
         [0042]    According to a seventh aspect of the invention there is also provided a method of braking an aircraft, comprising the steps of providing the aircraft landing gear as described above in relation to the fifth aspect of the invention, rotating the wheel about the axle such that the second part rotates with respect to the first part, thereby causing the indent portions in the first and second cavitation surfaces to momentarily line up with each other, and supplying liquid to the liquid channel, such that the liquid cavitates when the indent portions momentarily line up. 
         [0043]    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 
         [0044]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 
           [0045]      FIG. 1  shows a diagrammatic view of an e-taxi system architecture, according to a first embodiment of the invention; 
           [0046]      FIG. 2  shows a diagrammatic view of an e-taxi system architecture, according to a second embodiment of the invention; 
           [0047]      FIG. 3  shows a side view of a cavitation braking device according to a third embodiment of the invention; 
           [0048]      FIG. 4  shows a partly diagrammatic view of an aircraft landing gear according to the present invention; and 
           [0049]      FIG. 5  shows an aircraft including an aircraft landing gear according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]      FIG. 1  shows a diagrammatic view of an e-taxi system architecture  100 , as part of an aircraft landing gear, according to a first embodiment of the invention. The e-taxi architecture  100  may be part of an otherwise known landing gear arrangement, such as described in WO 2015/025131. The e-taxi system  100  comprises a wheel actuator  101  connected by an electrical connection  102  to the e-taxi power electronics  103 , including a motor (not shown) that can also act as a generator. The power electronics  103  are connected by an electrical connection  104  to a mono tube steam generator  105 . 
         [0051]    Also shown is an aircraft water supply  110  connected by a water supply line  111   a  to a pump  112  and from the pump  112  by water supply line  111   b  to the mono tube steam generator  105 . Also shown is the exhaustion of steam from the mono tube steam generator at arrow  113 . Also shown is an electrical connection  106  between the e-taxi power electronics  103  and the pump  112  so that the power electronics  103  can provide power to the pump  112  to pump water from the aircraft water supply  110  to the mono tube steam generator  105 . 
         [0052]    In use, the e-taxi power electronics  103  are used to control the wheel actuator  101  in the normal way. In other words, the power electronics  103  can control the actuator  101  to move a second gearing element, not shown (connected to the motor/generator) to mesh with a first gearing element, not shown (connected to the landing gear wheel) to either drive or brake the wheel in the forwards or backwards direction. 
         [0053]    When braking the wheel, the motor acts as a generator and rotation of the wheel (and first gearing element) causes rotation of the second gearing element. This enables the generator to generate electrical energy from the kinetic energy of the second gearing element. This electrical energy is provided through electrical connection  104  to the mono tube steam generator  105 . The mono tube steam generator  105  includes a heating element (not shown) so that the electrical energy is converted to heat energy. 
         [0054]    In use, the pump  112  is powered to supply water (from the aircraft water supply  110 ) to the mono tube steam generator  105 . The water is contained within a fluid receptacle (not shown) in the mono tube steam generator  105  so that the water is heated by the heating element of the mono tube generator  105 . The water then turns to steam and can be exhausted at  113 . 
         [0055]    Hence, kinetic energy is taken out of the wheel and converted into heat energy in the water, which is then exhausted as steam. Hence, the rotation of the wheel and movement of the aircraft is slowed. 
         [0056]      FIG. 2  shows a diagrammatic view of an e-taxi system architecture  200 , according to a second embodiment of the invention. This second embodiment is similar to the first embodiment and the same numbering will be used (preceded by a “2” instead of a “1”) for like elements. 
         [0057]    The e-taxi architecture  200  may be part of an otherwise known landing gear arrangement, such as described in WO 2015/025131. The e-taxi system  200  comprises a wheel actuator  201  connected by an electrical connection  202  to the e-taxi power electronics  203 , including a motor (not shown) that can also act as a generator. The power electronics  203  are connected by an electrical connection  204  to a mono tube steam generator  205 . 
         [0058]    Also shown is an aircraft water supply  210  connected by a water supply line  211   a  to a pump  212  and from the pump  212  by water supply line  211   b  to a valve  213  and from the valve  213  to the mono tube steam generator  205  thorough water supply line  212   e . Also shown is the exhaustion of steam from the mono tube steam generator at arrow  213 . Also shown is an electrical connection  206  between the e-taxi power electronics  203  and the pump  212  so that the power electronics  203  can provide power to the pump  212  to pump water from the aircraft water supply  210  to the mono tube steam generator  205 . 
         [0059]    In addition, there is a water supply line  212   c  from the pump  212  to the e-taxi control electronics  203  and a return water line  212   d  from the e-taxi control electronics  2013  to the valve  213 . This allows water to be supplied adjacent the control electronics  203  so that they can cool the electronics  203 . The return water can then be provided to the mono tube steam generator  205  through valve  213  and water supply line  212   e.    
         [0060]    There is another flow line connected to the valve  213  in the form of a water return line  212   f  from the valve  213  back to the aircraft water supply  210 . Hence, valve  213  can be controlled to return water to the aircraft water supply  210 . 
         [0061]    The valve  213  can have various positions to allow/prevent the following flow paths: i) from the pump  212  to the water supply line  212   e  through supply line  212   b , ii) from the control electronics  203  to the water supply line  212   e , iii) from the pump  212  to the water return line  212   f  through supply line  212   b  and iv) from the control electronics  203  to the water return line  212   f.    
         [0062]    In use, the e-taxi power electronics  203  are used to control the wheel actuator  201  in the normal way. In other words, the power electronics  203  can control the actuator  201  to move a second gearing element, not shown (connected to the motor/generator) to mesh with a first gearing element, not shown (connected to the landing gear wheel) to either drive or brake the wheel in the forwards or backwards direction. 
         [0063]    When braking the wheel, the motor acts as a generator and rotation of the wheel (and first gearing element) causes rotation of the second gearing element. This enables the generator to generate electrical energy from the kinetic energy of the second gearing element. This electrical energy is provided through electrical connection  204  to the mono tube steam generator  205 . The mono tube steam generator  205  includes a heating element (not shown) so that the electrical energy is converted to heat energy. 
         [0064]    In use, the pump  212  is powered to supply water (from the aircraft water supply  210 ) to the mono tube steam generator  205  in two ways. The first way is through supply line  212   b , valve  213  and supply line  212   e . The second way is through supply line  212   c , past the control electronics  203  to cool them and then through supply line  212   d , valve  213  and supply line  212   e . The water from supply line  212   e  is contained within a fluid receptacle (not shown) in the mono tube steam generator  205  so that the water is heated by the heating element of the mono tube generator  205 . The water then turns to steam and can be exhausted at  213 . 
         [0065]    Hence, kinetic energy is taken out of the wheel and converted into heat energy in the water, which is then exhausted as steam. Hence, the rotation of the wheel and movement of the aircraft is slowed. 
         [0066]    It is also possible, during use, to return water from either of supply lines  212   d  or  212   b  back to the aircraft water supply  210  via valve  213  and return line  212   f.    
         [0067]      FIG. 3  shows a side view of a cavitation braking device  300  according to a third embodiment of the invention. The cavitation braking device  300  may be part of an otherwise known landing gear arrangement, such as described in WO 2015/025131. The cavitation device  300  comprises an inner first part  311  fixedly attached to a wheel axle  310 . Hence, the first part does not rotate. The cavitation braking device also comprises an outer second part  320  mounted inside a wheel hub (not shown). The second part therefore rotates (shown by arrow  321 ) with the wheel so that it rotates around the first part  311 . 
         [0068]    The first part  311  is in the form of a cone with the slanted surface  312  being at an angle of approximately 30 degrees to the axle. This slanted surface  312  is a first cavitation surface  312  and comprises a number of blind holes  313  extending from the surface. 
         [0069]    The second part  320  also has a cavitation surface, the second cavitation surface  322 . This surface is parallel to but slightly spaced from the first cavitation surface  312  and also has a number of blind holes extending from the surface. 
         [0070]    The second part  320  extends over the first part  311  and over part of the axle  310 . Bearings  340  are provided in between the second part and the axle  310  such that the second part  320  can rotate smoothly around the first part  311  and axle  310 . 
         [0071]    The spacing of the cavitation surfaces  312 ,  322  provides a fluid channel  330 . There is an inlet  331  to the fluid channel at the narrow end (i.e. top of the cone) of the cavitation device (left hand side of  FIG. 3 ) to allow fluid in and two outlets  332   a  and  332   b  at the wider end (i.e. bottom of the cone) of the cavitation device (right hand side of  FIG. 3 ) to allow fluid out. 
         [0072]    In use, the wheel (not shown) is rotated around the axle  310 , causing the second part  320  to rotate around the first part  311 . 
         [0073]    When it is wished to brake the wheel rotation, water is supplied through a fluid supply line to the fluid inlet  331  and enters the fluid channel  330 . As the second part  320  rotates, blind holes in the second part  320  momentarily line up with blind holes  313  in the first part  311 . As this occurs, the water located there rapidly expands into the suddenly larger volume available. This causes the water to suddenly form low pressure gaseous water bubbles. Then, when the blind holes no longer line up, the water rapidly contracts, re-forming liquid water. This sudden formation and collapse of the gaseous water is known as cavitation and generates heat in the water. 
         [0074]    Thus, when water is in the fluid channel, the kinetic energy of the wheel and first part is converted into heat energy in the water and the rotation of the wheel is slowed. 
         [0075]      FIG. 4  shows a partly diagrammatic view of an aircraft landing gear  500  according to the present invention. The landing gear  500  includes at least one wheel  550  rotatably mounted on an axle  520 . The axle  520  is mounted at a lower end of a main landing gear leg  510 . An e-taxi system is mounted on the landing gear and comprises a motor/generator  530 , a clutch  540 , a roller gear  571  (first gearing element) connected to the wheel rim and a corresponding sprocket  572  (second gearing element) connected to the motor/generator  530  via the clutch  540 . There is also an actuator  560  for moving the sprocket  572  into and out of meshing engagement with the roller gear  571 . 
         [0076]    The aircraft landing gear  500  includes either the e-taxi architecture of  FIG. 1  ( 100 ) or  FIG. 2  ( 200 ) and/or the cavitation braking device  300  of  FIG. 3  (shown diagrammatically). These are connected to the motor/generator  530  by electrical connection  104 / 204  and have a fluid inflow  401  (including pump  404 ) and fluid outflow  402  with a fluid path/receptacle  403  inside. Also shown is a heating element  440  inside. 
         [0077]      FIG. 5  shows an aircraft  1000  including the aircraft landing gear  500  of  FIG. 4 . 
         [0078]    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. 
         [0079]    The above example use water as the fluid being used. However, any other suitable fluid may be used. 
         [0080]    The mono tube steam generator of  FIGS. 1 and 2  may be replaced by a different type of steam generator or any other type of suitable heat dissipation device. 
         [0081]    Optionally, the steam (or gaseous form of the supplied fluid) may be exhausted or otherwise allowed to escape from the cavitation device or heat dissipation device. Alternatively, the gaseous fluid may be retained. For example, the gaseous fluid may be allowed to cool and be re-used in the heat dissipation device/cavitation device or the gaseous fluid might be re-used elsewhere on the aircraft. 
         [0082]    The aircraft landing gear may comprise any other number of other braking devices, in addition to those described here. 
         [0083]    The blind holes in the cavitation device may be replaced by any other suitable surface indentation. 
         [0084]    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.