Patent Publication Number: US-11643193-B2

Title: Aircraft landing gear assembly

Description:
This application is a divisional application of U.S. application Ser. No. 15/955,910, filed on Apr. 18, 2018, which claims the benefit of and priority to European Application No. 17167354.4, filed on Apr. 20, 2017, the contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     An aircraft landing gear for medium to large aircraft typically includes a pair of wheel assemblies mounted on a common axle. For larger aircraft, a landing gear may include an elongate bogie beam which supports two or more axles, each of which carries a pair of wheel assemblies. 
     A landing gear is designed to withstand operation loads when one of the tyres on an axle is deflated. In the case of a multi axle landing gear, the gear must be designed to withstand operation loads arising from a worst case combination of deflated tyres. 
     The present inventor has identified that the weight of known landing gear can be reduced. 
     SUMMARY 
     In accordance with a first aspect of the invention there is provided an aircraft landing gear assembly comprising:
         an elongate bogie beam including a mounting formation via which the bogie beam is arranged to be movably mounted to an aircraft landing gear main strut, first and second end regions, a first longitudinal axis extending between the mounting formation and the first end region and a second longitudinal axis extending between the mounting formation and the second end region;   a first axle mounted at a first end region of the bogie beam, the first axle defining a first wheel mounting portion on a first side of the bogie beam for supporting a first wheel assembly and a second wheel mounting portion on a second side of the bogie beam for supporting a second wheel assembly; and   a second axle mounted at a second end region of the bogie beam, with the mounting formation between the first and second end regions, the second axle defining a third wheel mounting portion on the first side of the bogie beam for supporting a third wheel assembly and a fourth wheel mounting portion on the second side of the bogie beam for supporting a fourth wheel assembly,   wherein the bogie beam is arranged to enable the first and second axles to each pivot relative to the mounting formation about the longitudinal axis of the bogie beam by an amount which is sufficient to place a wheel rim of a wheel assembly in contact with the ground in the event of a tyre of the wheel assembly deflating.       

     Thus, the bogie beam provides sufficient degrees of freedom to ensure that the wheel loads are equal for various degrees of tyre inflation and/or runway camber. 
     The bogie beam may be arranged to enable the first and second axles to each pivot relative to the mounting formation about the longitudinal axis of the bogie beam by at least 8°. 
     The mounting formation of the bogie beam can be a circular cross section profiled bearing arranged to pivotally couple the bogie beam to the main strut via a pivot pin. 
     The first longitudinal axis can be coaxial with respect to the second longitudinal axis. 
     The bogie beam can be arranged to enable the first and second axles to each pivot relative to the mounting formation about the longitudinal axis of the bogie beam by virtue of first and second flexure zones of the bogie beam, the first flexure zone being located between the mounting formation and the first axle and the second flexure zone being located between the mounting formation and the second axle. Flexure zones advantageously require no maintenance and do not suffer from operational contact wear. 
     The flexure zones can each comprise a portion of the bogie beam which has a box section, C section or I section profile. 
     The flexure zones can each occupy a majority of the length of the bogie beam between the mounting formation and the respective axle. 
     The bogie beam can comprise a central body portion which includes the mounting formation and a pair of rotatable mounted end bosses which support the axles, the bogie beam being arranged to enable the first and second axles to each pivot relative to the mounting formation about the longitudinal axis of the bogie beam by virtue of the end bosses. Such an arrangement can be simpler to design and can be tailored to specific load requirements based on the configurations of the joints and bearings employed. 
     In accordance with a second aspect of the present invention, there is provided an aircraft landing gear assembly comprising:
         a first elongate bogie beam including a first mounting formation via which the first bogie beam is arranged to be pivotally mounted to an aircraft landing gear main strut and defining a first bogie pivot axis;   a second elongate bogie beam including a second mounting formation, defining a second bogie pivot axis, via which the second bogie beam is arranged to be pivotally mounted to the aircraft landing gear main strut in a side by side adjacent relationship with the first bogie pivot axis being coaxial with respect to the second bogie pivot axis;   a first axle mounted at a first end region of the first bogie beam, the first axle defining a first wheel mounting portion on a first side of the first bogie beam for supporting a first wheel assembly;   a second axle mounted at a second end region of the first bogie beam, the second axle defining a second wheel mounting portion on the first side of the first bogie beam for supporting a second wheel assembly;   a third axle mounted at a first end region of the second bogie beam, the third axle defining a third wheel mounting portion on a second side of the second bogie beam for supporting a first wheel assembly, the second side facing away from the first bogie beam; and   a fourth axle mounted at a second end region of the second bogie beam, the fourth axle defining a fourth wheel mounting portion on the second side of the bogie beam for supporting a fourth wheel assembly,   such that the first and second bogie beams can independently pivot about the respective bogie pivot axes in order to place a wheel rim of a wheel assembly in contact with the ground in the event of a tyre of the wheel assembly deflating.       

     Thus, two parallel bogie beams are provided in a ‘dual bicycle’ arrangement in which the bogie beams can pivot about their mounting axes independently to account for any difference in rolling radius between the front and back tyres. Such an arrangement can limit the number of joints requiring maintenance. The splitting of the bogie beams can also permit a segregation of the systems supporting braking and, if necessary, brake torque compensation, which can be advantageous from a safety perspective. 
     The aircraft landing gear assembly can further comprise the aircraft landing gear main strut, the main strut comprising:
         a body portion including a main aircraft coupling via which the main strut is arranged to be movably coupled to an aircraft;   a bogie mounting portion including a first axle portion arranged to pivotally mount the first bogie beam via the first mounting formation and a second axle portion arranged to pivotally mount the second bogie beam via the second mounting formation; and   a flexible or dynamic bearing region connecting the body portion to the bogie mounting portion for pivotal movement between them.       

     The flexible or dynamic bearing region can comprise a spherical bearing. This enables the landing gear assembly to place the wheel rims on one side of the landing gear in contact with the ground in the event of their tyres deflating when the wheels on the other side are inflated. 
     In accordance with a further aspect of the invention, there is provided an aircraft including one or more aircraft landing gear assemblies according to the first aspect or the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG.  1   a    is a schematic side view of a known aircraft landing gear assembly including a bogie beam; 
         FIG.  1   b    illustrates the landing gear assembly of  FIG.  1   a    with a deflated tyre; 
         FIG.  2   a    is a schematic front view of a known landing gear assembly in which two wheels are mounted on a common axle; 
         FIG.  2   b    illustrates the landing gear assembly of  FIG.  2   a    with a deflated tyre; 
         FIG.  3    is a longitudinal cross section diagram of an aircraft landing gear assembly according to an embodiment of the present invention; 
         FIG.  4    is a longitudinal cross section diagram of an aircraft landing gear assembly according to an embodiment of the present invention; 
         FIG.  5    is a longitudinal cross section diagram of an aircraft landing gear assembly according to an embodiment of the present invention; and 
         FIG.  6    is a schematic diagram illustrating a bottom end of a strut which can carry the landing gear assembly of  FIG.  5   . 
         FIGS.  7   a - 7   c    schematically illustrate a cross section view of a bogie beam flexure zone, as viewed along a longitudinal axis of the bogie beam, in which the cross section comprises a box section, a C section, and an I section, respectively. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1   a    illustrates a known aircraft landing gear assembly generally at  100 . 
     The landing gear assembly  100  includes a main strut  102  which is movably coupled to an aircraft (not shown). A bogie beam  104  is pivotally mounted at a lower end of the main strut  102  via a pivot pin  106 . At one end, or front, of the bogie beam  104  there is mounted a wheel assembly  112  on axle  108 . At the other end, or back, of the bogie beam  104  there is mounted a second wheel assembly  114  via a second axle  110 . Each wheel assembly can incorporate a brake assembly. 
       FIG.  1   b    shows the landing gear assembly of  FIG.  1   a    with a deflated rear tyre  114 . As can be seen, the bogie beam  104  has rotated relative to the strut  102  to account for the difference in rolling radius due to the deflated tyre  114 . 
     However, as illustrated in  FIGS.  2   a  and  2   b   , in the case of landing gear assemblies in which a pair of wheel assemblies  112   a ,  112   b  are mounted on a common axle  108 , and one wheel  112   b  deflates, the bogie beam  104  cannot pivot to account for the deflated tyre  112   b  because the end region of the bogie beam  104  adjacent the axle  108  is supported by the inflated tyre  112   a . This results in flexure of the landing gear components including the axle  108 , bogie beam  104  and strut  102 . Consequently, these components must be of sufficient size and/or strength to withstand such loading. Other components of the landing gear also need to be sized to deal with the increased load on them i.e. the full load taken on three tyres, or the full load taken on two tyres. 
     The present inventor has identified that the weight of known landing gear can be reduced by designing a landing gear assembly in which the bogie beam is arranged to place a wheel rim of a wheel assembly in contact with the ground in the event of a tyre of the wheel assembly deflating. As such, the landing gear can be designed for the full load distributed evenly across four loading points (tyre or wheel rim). 
       FIG.  3    is a diagram of part of an aircraft; more specifically, an aircraft landing gear assembly  10  according to an embodiment of the invention. The landing gear assembly  10  is shown in cross section through the longitudinal axis of the bogie beam  12 . 
     The bogie beam  12  is generally of conventional construction in that it includes a central pivot bearing  14  by which it can be pivotally connected to an aircraft landing gear main strut (not shown), such as a rigid strut or a shock absorbing strut, so as to pivot about a bogie pivot axis M. 
     At a first end region  22 , the bogie  12  includes axle mounting bushes  16  in which a first axle  18  is mounted. A second end region  24  of the bogie  12  also includes axle mounting bushes  16  via which a second axle  20  is mounted. The longitudinal axis B of the first axle  18  is parallel with respect to the longitudinal axis B of the second axle  20 . 
     The aircraft landing gear assembly  10  of the illustrated embodiment differs from a conventional aircraft landing gear assembly in that it includes flexure zones FZ 1 , FZ 2 . 
     The first flexure zone FZ 1  is located between the bogie pivot bearing  14  and the first axle  18 . It encompasses a majority of the length of the bogie beam  12  between these two items. However, in other embodiments the flexure zone can be defined by the entirety of the distance between the bogie pivot bearing  14  and the first axle  18 , or the flexure zone FZ 1  can be defined by less than half the distance between these two items. 
     Similarly, the second flexure zone FZ 2  is located on the other side of the bogie beam  12  between the bogie pivot bearing  14  and the second axle  20 . Otherwise, the second flexure zone FZ 2  can be identical to the first flexure zone FZ 1 . 
     The flexure zones FZ 1 , FZ 2  are arranged to permit the axles  18 ,  20  to rotate relative to bogie pivot bearing  14  about the longitudinal axis L of the bogie beam. As such, in the event of a tyre deflating, the bogie beam  12  can flex to allow the axle to rotate sufficiently to place the deflated wheel assembly in contact with the ground, meaning that each wheel is equally loaded despite the deflated tyre(s). For a wheel assembly with a deflated tyre, the load can be supported by the wheel rim. 
     The present inventor found a bogie beam  12  with flexure zones FZ 1 , FZ 2  of box section, or open section, such as C or I section, can provide the required degree of flexure in the event of a tyre deflation. Suitable geometries can be determined using routine testing. 
       FIG.  4    shows an aircraft landing gear assembly according to a further embodiment of the invention generally at  30 . The aircraft landing gear assembly  30  is similar to the aircraft landing gear  10  according to the previous embodiment and like parts have been given like reference numerals. For brevity, the following description will focus on the differences. 
     The aircraft landing gear assembly  30  of the present embodiment is configured to enable the axles  18 ,  20  to rotate or pivot relative to the bogie pivot axis M about the longitudinal axis L of the bogie beam by virtue of rotatable end sections  34 ,  36 . 
     More specifically, the bogie beam  32  comprises a main body portion  32  which has cylindrical end bearings  32   a ,  32   b  at its ends. The end bearings  32   a ,  32   b  are arranged to rotatably support first and second end bosses  34 ,  36  such that the end bosses  34 ,  36  can rotate relative to the bogie body  32  about the longitudinal axis L. The bosses  32 ,  36  each include axle mounting bushes  16  arranged to mount the first and second axles,  18 ,  20  in the conventional manner. 
     In the event of a tyre on an axle deflating, the boss and axle can rotate together relative to the bogie beam in order to place the rim of the deflated wheel assembly in contact with the ground, thereby equalizing loading on the wheel. 
     Means can be provided to maintain the orientation of the axles  18 ,  20  relative to the bogie pivot axis M during ‘weight off wheels’ operations such as pre-touchdown landing descent and immediately following take off. For example, biasing means such as springs may be provided to bias the axles to parallel planes with respect to the longitudinal axis and bogie pivot axis M, the spring forces being such that it can be overcome in the event of a tyre deflating. 
     Thus, both of the above-identified embodiments of the invention include a bogie beam which is arranged to permit the axles to rotate relative to the central portion of the encompassing the bogie pivot axis in the event of tyre deflation. 
       FIG.  5    shows an aircraft landing gear assembly  40  according to a further embodiment of the invention. The landing gear assembly  40  includes first and second bogie beams  42   a ,  42   b  arranged to be mounted in a parallel side by side relationship. The bogie beams  42   a ,  42   b  each include identical pivot bearings  44   a ,  44   b  arranged to receive a common bogie pivot pin, or coaxial bogie pivot pins, (not shown) so that the bogie beams  42   a ,  42   b  pivot about a common bogie pivot axis M. 
     At a first end, the first bogie beam  42   a  includes a conventional mounting bushing  46   a  by which a first axle half  50   a  is mounted. The second bogie beam  42   b  includes a corresponding mounting bushing  46   b  which carries a second axle half  50   b . The first and second axle halves  50   a ,  50   b  are aligned with a common axis B when the bogie beams  42   a ,  42   b  are aligned in registration with one another i.e. in the same plane. 
     Similarly, a second end of the first bogie beam  42   a  includes a conventional mounting bushing  46   a  which mounts a third axle half  48   a  and the second  42   b  includes a conventional mounting bushing  26   b  which mounts a fourth axle half  48   b.    
     Each axle half  50   a ,  50   b ,  48   a ,  48   b , is arranged to mount a single wheel assembly. 
     Therefore, in the event of the tyre of a wheel assembly mounted on the first axle half  50   a  deflating, the first bogie  42   a  can rotate about the bogie pivot axis M independently of the second bogie  42   b  so as to place the rim of the deflated wheel assembly in contact with the ground. Likewise for any of the other wheel assemblies. 
     While the arrangement of the landing gear assembly  40  reduces the amount of flexure required by components of the aircraft landing gear in order to account for the deflated tyre, it does not substantially eliminate such flexure. 
     Therefore, and referring additionally to  FIG.  6   , the strut  52  can comprise an upper strut portion  54  that extends along a longitudinal axis  64  and is arranged to be movably coupled by a main aircraft coupling  62  (illustrated schematically) to an aircraft (not shown), and a bogie mounting formation  58  connected to the upper portion  54  via a multi-axis joint  56 , such as a spherical joint. The bogie mounting formation  58  can include a first axle portion  60   a  arranged to mount the first bogie beam  42   a , and a second, coaxial, axle  60   b  arranged to mount the second bogie beam  42   b . Thus, the bogie mounting formation  58  can move relative to the upper strut portion  54  in a lateral direction to substantially isolate the remaining components of the landing gear assembly from loads that would otherwise be imparted due to tyre deflation. 
     In any embodiment, it is preferred that the bogie beam is arranged to enable the first and second axles to each pivot relative to the mounting formation about the longitudinal axis of the bogie beam by at least 8° and in some embodiments at least 10° or 12°. The degree of pivoting required depends on the ratio of tyre rolling radius to wheel rim radius and the spacing between the two wheel assemblies on the axle. In one example, a wheel assembly may have a rolling radius of approximately 0.65 m, a wheel rim radius of approximately 0.36 m and a spacing of approximately 1.4 m centre to centre between wheel assemblies on an axle, meaning that one flat tyre would require an angle of approximately 12° to place the wheel rim in contact with the ground in the event of the tyre fully deflating. In another example, a wheel assembly may have a rolling radius of approximately 0.65 m, a wheel rim radius of approximately 0.36 m and a spacing of approximately 1.74 m centre to centre between wheel assemblies on an axle, meaning that one flat tyre would require an angle of approximately 9.6° to place the wheel rim in contact with the ground in the event of the tyre fully deflating. 
     Landing gear assemblies according to embodiments of the invention can be formed of conventional aerospace materials, such as stainless steel, aluminum or titanium. Certain components such as the bogie beam can be formed from fibre reinforced composite material. 
     Landing gear assemblies according to embodiments of the invention can be main landing gear assemblies for medium to large aircrafts. 
     Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications can be made without departing from the scope of the invention as defined in the appended claims. The word “comprising” can mean “including” or “consisting of” and therefore does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.