Patent Publication Number: US-2021180654-A1

Title: Transmission

Description:
RELATED APPLICATION DATA 
     This application is a continuation of International Patent Application No. PCT/CN2019/103375, filed Aug. 29, 2019, which claims the benefit of European Patent Application No. 18192795.5, filed Sep. 5, 2018, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The invention relates to a transmission comprising a first component and a second component, which are journaled for rotation relative to each other, and a locking mechanism for rotationally locking the first component and the second component relative to each other in a predetermined mutual rotation position. 
     BACKGROUND 
     In some technical fields, a shaft with a propeller may have to be locked against rotation during certain operation conditions. It may be a propeller driven by a motor or a propeller driven by the wind for generating electrical power, for instance. 
     For example, for a roadable aircraft, such as an aircraft that can be converted into an automotive vehicle capable of driving on a road, the propeller has to be disconnected from the driveline during road driving when the motor drives the wheels. When the propeller is disconnected for road driving, the propeller has to be kept stationary to prevent spinning of the propeller by the wind. Further, for other reasons, such as for reducing the air resistance and achieving balance, the angular position of the propeller will be predetermined, and the propeller will be kept in this specific position in the automotive mode. For a three-bladed propeller where the angular distance between each pair of two adjacent propeller blades is 120°, one propeller blade will usually be kept vertically in an upper position. 
     A drawback of known locking devices used for locking the propeller during the automotive mode is the addition of components to the transmission making the design more complicated, space-consuming and costly. 
     SUMMARY 
     An objective of the invention is to provide a transmission having a lock that can be used for locking a component, such as a propeller, while enabling at least some problem with known locking devices to be reduced or eliminated. 
     The objective is achieved by a transmission comprising a first component and a second component which are journaled for rotation relative to each other, and a locking mechanism for rotationally locking the first component and the second component relative to each other in a predetermined mutual rotation position, wherein the locking mechanism comprises a sleeve and a dog clutch, and the sleeve is rotationally locked relative to the first component and the dog clutch is rotationally locked relative to the second component, the sleeve and the dog clutch are axially displaceable relative to each other for engagement of the sleeve and the dog clutch such that the first component and the second component are rotationally locked relative to each other, and wherein the sleeve and the dog clutch are engageable only in a mutual rotation position corresponding to the predetermined mutual rotation position of the first component and the second component. 
     The invention is based on the insight that by such a transmission, the lock for a propeller can be integrated in the transmission with a minimum of additional components in a way making the design less complicated while saving space. 
     For example, the transmission may have at least two modes selectable by displacement of the sleeve, a first stationary mode where the first component and the second component are locked relative to each other in the predetermined mutual rotation position and a second driving mode where the first component is connected to a drive motor for rotating the first component relative to the second component. Hereby, the lock is integrated in the transmission in a rational way providing a safe lock, since disconnection of the driving mode can be automatically performed when the stationary mode is activated, and vice versa. 
     It should be stressed that by the expression “predetermined mutual rotation position” is meant a certain position selected for rotationally locking the first component and the second component relative to each other with respect to their respective angular position, as opposed to any random position of a finite number of possible mutual rotation positions provided by a conventional spline joint for instance. 
     The number of predetermined mutual rotation positions in which the first component and the second component can be locked relative each other by the locking mechanism can be varied. For some applications there is only one such predetermined mutual rotation position. In other applications a few predetermined mutual rotation positions are possible, and often the number of predetermined mutual rotation positions is in the interval 1-5. For example, for a three-bladed propeller, three predetermined mutual rotation positions can be used since it will be possible to lock the propeller in three equivalent positions giving the same symmetry provided that the angular distance between two adjacent propeller blades is 120°. 
     According to one embodiment, the transmission has a first locking part and a second locking part, where the first locking part and the second locking part are arranged for preventing the sleeve and the dog clutch to be engaged in any other mutual rotation position than a mutual rotation position corresponding to the predetermined mutual rotation position of the first component and the second component. Hereby, the first component and the second component can be locked relative to each other in the predetermined mutual rotation position in a non-complicated way. 
     The dog clutch can be provided with one of the first locking part and the second locking part and the sleeve can be provided with the other of the first locking part and the second locking part, and preferably the sleeve and the dog clutch are engageable when the rotation position of the first locking part and the rotation position of the second locking part are matching each other. 
     For example, the dog clutch can have external teeth and the sleeve can have internal teeth for engagement of the sleeve and the dog clutch, and the first locking part can comprise a tooth of the dog clutch which tooth is different from the other teeth of the dog clutch and the second locking part can comprise a gap between two teeth of the sleeve which gap is different from the other gaps of the sleeve, wherein the sleeve and the dog clutch are engageable when the rotation position of said tooth and the rotation position of said gap are matching each other. The tooth and the gap have a size and/or shape different from the other teeth and gaps. The tooth has suitably a width exceeding the width of the remaining teeth, and the gap has a corresponding width exceeding the width of the remaining gaps, making an engagement of the sleeve and the dog clutch possible only when the tooth and the gap are at the same rotation position. 
     According to a further embodiment, the first locking part is a set of axial protrusions and the second locking part is a set of corresponding recesses for receiving the protrusions, and preferably a play in the rotation direction is arranged such that when the set of protrusions is engaged with the set of corresponding recesses, the first component and the second component can be somewhat rotated relative to each other before engagement of the sleeve and the dog clutch by an engagement means, such as a spline joint for instance. Hereby, it can be ensured that the locking parts are used only for achieving the desired rotation position while the engagement means is used for transferring any torque required. 
     For example, the play can be arranged by having the size of the recesses exceeding the size of the protrusions, and the size of the play is adapted to the engagement means ensuring that any torque is transferred by the engagement means when the sleeve and the dog clutch are engaged by the engagement means. 
     According to a further embodiment, an additional ring is rotationally locked to the sleeve, where the ring is provided with the set of protrusions or the set of recesses, and preferably the play in the rotation direction is arranged between the additional ring and the sleeve. Hereby, it can be ensured that any torque is transferred by the engagement means. Further, the sleeve can be designed with minor amendments from a conventional sleeve, such as a synchronizer sleeve, since the current locking part is provided by the additional ring. 
     According to a further embodiment, the transmission comprises a spring arranged for moving the sleeve and the dog clutch axially relative to each other such that the sleeve and the dog clutch are brought into engagement, and preferably the dog clutch is axially displaceable relative to the second component and the spring is arranged between the dog clutch and the second component for counteracting displacement of the dog clutch relative to the second component. Hereby, engagement between the sleeve and the dog clutch can be secured by the spring force after some relative rotation between the sleeve and the dog clutch in case the sleeve and the dog clutch do not match each other initially when being brought together. 
     According to a further embodiment, the sleeve is part of a synchronizer device for synchronizing the rotation speed of the first component relative to the second component when the sleeve and the dog clutch are to be engaged. Hereby, a fast and smooth engagement of the sleeve and the dog clutch can be achieved. 
     According to another aspect of the invention, a further objective is to provide a roadable aircraft comprising a transmission having a lock that can be used for locking a propeller of the aircraft. 
     The advantages of the roadable aircraft are substantially the same as the advantages already discussed hereinabove with reference to the different embodiments of the transmission. Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. 
       In the drawings: 
         FIG. 1A  is a perspective view of a roadable aircraft, 
         FIG. 1B  is a rear view of the roadable aircraft shown in  FIG. 1A , 
         FIG. 2A  is a partly cut side view of a transmission in a neutral mode, 
         FIG. 2B  is the transmission shown in  FIG. 2A  in an intermediate mode, 
         FIG. 2C  is the transmission shown in  FIG. 2A  in a locked mode, 
         FIG. 2D  is the transmission shown in  FIG. 2A  in a driving mode, 
         FIG. 3  is an end view of the transmission shown in  FIG. 2A  in a locked mode, 
         FIG. 4A  shows a dog clutch of a locking mechanism, 
         FIG. 4B  shows a sleeve of a locking mechanism, 
         FIG. 5  shows a variant of the transmission in  FIG. 2A , 
         FIG. 6  shows an alternative design of a sleeve and a dog clutch of a locking mechanism, 
         FIGS. 7A and 7B  show alternative designs of locking parts, and 
         FIGS. 8A and 8B  show a further design of the locking parts. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  show a roadable aircraft  1 .  FIG. 1A  shows the aircraft  1  in a perspective view and  FIG. 1B  shows the aircraft  1  in a rear view. The aircraft  1  can be converted into an automotive vehicle capable of driving on a road and interacting with a land-based traffic system. The aircraft  1  is shown when used as an automotive vehicle during road driving. In the automotive mode, the propeller  2  is disconnected from the driveline since the motor is used for driving the wheels  3 . When the propeller  2  is disconnected for road driving, the propeller  2  is preferably kept stationary to prevent spinning of the propeller by the wind. For reducing the air resistance and achieving balance, for instance, the propeller  2  will be kept in a specific position in the automotive mode. For a three-bladed propeller  2  as illustrated in  FIGS. 1A and 1B , where the angular distance  4  between each pair of propeller blades  5   a ,  5   b ;  5   b ,  5   c ;  5   c ,  5   a  is 120°, one propeller blade  5   a  will usually be kept vertically in an upper position. Thus, the upper propeller blade  5   a  is directed in a vertical direction  6 , at least as long as the aircraft  1  is standing on a substantially even ground  7 , and each of the other propeller blades  5   b ,  5   c  is directed obliquely downwards. 
     The propeller  2  is arranged on a propeller shaft of a transmission of the roadable aircraft  1 . The transmission will be described hereinafter with reference to the remaining figures. 
       FIG. 2A  shows the transmission  8  in a partly cut side view. The transmission  8  comprises a first component  9  and a second component  10  which are journaled for rotation relative to each other by a bearing  11 . In the example embodiment illustrated in  FIG. 2A , the first component is a propeller shaft  9  on which the propeller  2  is arranged and the second component is a housing  10  of the transmission  8 . The housing  10  constitutes a fixed point on the aircraft  1 . 
     The transmission  8  further comprises a locking mechanism  12  for rotationally locking the first component  9  and the second component  10  relative to each other in a predetermined mutual rotation position. The locking mechanism  12  comprises a sleeve  13  and a dog clutch  14 . By “dog clutch” is meant any equal component that also can be named dog ring, dog teeth or clutch teeth or clutch cone. The sleeve  13  is rotationally locked relative to the first component  9  and the dog clutch  14  is rotationally locked relative to the second component  10 . Further, the sleeve  13  and the dog clutch  14  are axially displaceable relative to each other for engagement of the sleeve  13  and the dog clutch  14  such that the first component  9  and the second component  10  are rotationally locked relative to each other. The sleeve  13  and the dog clutch  14  are engageable only in a mutual rotation position corresponding to the predetermined mutual rotation position of the first component  9  and the second component  10 . In the example embodiment illustrated in  FIG. 2A  (and  FIGS. 1A and 1B ) the predetermined mutual rotation position of the first component  9  and the second component  10  corresponds to a predetermined rotation position of the propeller  2  arranged on the propeller shaft  9 . Thus, the propeller  2  is locked relative to the air craft  1  in the way as described hereinabove with reference to  FIGS. 1A and 1B . 
     As examples, the number of predetermined mutual rotation positions of the first component  9  and the second component  10  can be 1 or 3 when using a propeller with three propeller blades. In the first case, it is always the same propeller blade  5   a  that is directed in the vertical direction  6  when the propeller is locked. However, in the other case, due to the symmetry, the propeller  2  can be locked such that any of the propeller blades  5   a ,  5   b ,  5   c  is directed in the vertical direction  6 , since there are three equivalent locking positions for the propeller  2 . 
     As illustrated in  FIG. 2A , the transmission  8  suitably comprises a hub  15  arranged on the propeller shaft  9  on which hub  15  the sleeve  13  is arranged. The hub  15  is fixed relative to the propeller shaft  9 . The sleeve  13  is rotationally locked to the hub  15  and thereby rotationally locked relative to the propeller shaft  9  but is displaceable in an axial direction  16  relative to the hub  15 . The dog clutch  14  is rotationally locked relative to the housing  10  and is suitably displaceable relative to the housing  10  in the axial direction  16 . The transmission may comprise a spring  17  arranged for moving the sleeve  13  and the dog clutch  14  in the axial direction  16  relative to each other such that the sleeve  13  and the dog clutch  14  are brought into engagement. 
     In the example embodiment illustrated in  FIG. 2A , the dog clutch  14  is displaceable relative to the second component  10  in the axial direction  16  and the spring  17  is arranged between the dog clutch  14  and the second component  10  for counteracting displacement of the dog clutch  14  relative to the second component  10 . The spring  17  can be for example a wave spring or coil spring. 
     The sleeve  13  can be displaceable in the axial direction  16  by means of a shift fork  50  of a gear actuator as schematically illustrated. 
     Although, in the example embodiments illustrated, the spring  17  is arranged on the “dog clutch side” between the dog clutch and the second component, in another solution the spring could be arranged on the “sleeve side”, for example between an actuator part of the gear actuator (moving the shift fork) and the shift fork, or between the shift fork and the sleeve. 
     The transmission  8  has preferably at least two modes selectable by displacement of the sleeve  13 . In the example embodiment illustrated in  FIGS. 2A, 2B, 2C and 2D , the transmission  8  has a first stationary mode where the first component  9  and the second component  10  are locked relative to each other in the predetermined mutual rotation position as previously described hereinabove. The transmission  8  has further a second driving mode where the first component being connected to a drive motor (not shown) for rotating the first component  9  relative to the second component  10 . Finally, the transmission  8  has also a neutral mode where the first component  9  and the second component  10  are not rotationally locked relative to each other and the first component  9  is disconnected from the drive motor. 
     In  FIG. 2A , the transmission  8  is in the neutral mode, since the sleeve  13  is positioned in a centre position not engaging the dog clutch  14  or any other connection component. 
     In  FIG. 2B , the sleeve  13  is displaced in the axial direction  16  towards the dog clutch  14 . In this case, initially, the sleeve  13  and the dog clutch  14  are not matching each other with respect to the mutual rotation position, and therefore due to the sleeve motion the dog clutch  14  is pressed by the sleeve  13 . Thus, the dog clutch  14  is somewhat displaced relative to the second component  10  in the axial direction  16 , to the right, while the displacement motion being counteracted by the spring load created by the spring  17  arranged between the dog clutch  14  and the second component  10 . This intermediate mode will end as soon as the first component  9  and the second component  10  have been further rotated relative to each other such that the sleeve  13  and the dog clutch  14  are matching. The spring  17  will then secure that the sleeve  13  and the dog clutch  14  will be brought into engagement with each other to reach the mode where the first component  9  and the second component  10  are locked relative to each other in the predetermined mutual rotation position. 
     In  FIG. 2C , the sleeve  13  and the dog clutch  14  are engaged, rotationally locking the first component  9  and the second component  10  relative to each other in the predetermined mutual rotation position. 
     In  FIG. 2D , the sleeve  13  is axially displaced in the opposite direction, i.e. to left, for engagement with a further connection component (not shown) connecting the first component  9  to the drive motor for rotating the first component  9  relative to the second component  10 . The driving mode can be used for driving the propeller  2  in the flight mode of the aircraft  1 . 
       FIG. 3  shows the transmission  8  in an end view where the transmission is in the locked mode corresponding to  FIG. 2C . The propeller shaft  9  and the propeller  2  is locked relative the housing  10  in the predetermined mutual rotation position. One blade  5   a  of the three-bladed propeller  2  is positioned in the vertical direction  6 . 
       FIG. 4A  shows the dog clutch  14  with external splines  20  in a side view.  FIG. 4B  shows the sleeve  13  with corresponding internal splines  21  in a side view. Although the engagement means for connection of the sleeve  13  and the dog clutch  14  is exemplified by a spline joint  22 , in another solution any other suitable engagement means enabling torque to be transferred between the sleeve and the dog clutch could be used. 
     The transmission has a first locking part  23  and a second locking part  24 , the first locking part  23  and the second locking part  24  are arranged for preventing the sleeve  13  and the dog clutch  14  to be engaged in any other mutual rotation position than a mutual rotation position corresponding to the predetermined mutual rotation position of the first component  9  and the second component  10 . The dog clutch  14  is preferably provided with one of the first locking part  23  and the second locking part and the sleeve  13  is provided with the other of the first locking part and the second locking part  24 . Here, the dog clutch  14  has the first locking part  23  and the sleeve  13  has the second locking part  24 . The first locking part  23  and the second locking part  24  are suitably arranged for preventing the sleeve  13  and the dog clutch  14  to be engaged in any other mutual rotation position than a mutual rotation position corresponding to the predetermined mutual rotation position of the first component  9  and the second component  10 . Thus, the sleeve  13  and the dog clutch  14  are engageable only when the rotation position of the first locking part  23  and the rotation position of the second locking part  24  are matching each other. As soon as the sleeve and the dog clutch are engaged, this mutual rotation position is preferably kept by the splines  20 ,  21 . 
     In the example embodiment illustrated in  FIGS. 4A and 4B , where the dog clutch  14  has external teeth  20  and the sleeve  13  has internal teeth  21  for engagement of the sleeve  13  and the dog clutch  14 , the first locking part  23  comprising a tooth  25  of the dog clutch  14  which tooth  25  is different from the other teeth  20  of the dog clutch  14  and the second locking part  24  comprising a gap  26  between two teeth  21  of the sleeve  13  which gap  26  is different from the other gaps  27  of the sleeve. The sleeve  13  and the dog clutch  14  are engageable when the rotation position of said tooth  25  and the rotation position of said gap  26  are matching each other. The number of such different teeth  25  and different gaps  26  can be varied. In this case there are three teeth  25  and three gaps  26  enabling engagement of the sleeve  13  and the dog clutch  14  in three mutual rotation positions where the angular distance  4  between two adjacent positions is 120°. 
     The tooth  25  and the gap  26  have a unique size and/or shape which is different from the other teeth  20  and gaps  27 . As illustrated, the tooth  25  has suitably a width  28  exceeding the width of the remaining teeth  20 , and the gap  26  has a corresponding width  29  exceeding the width of the remaining gaps  27 , making an engagement of the sleeve  13  and the dog clutch  14  possible only when the tooth  25  and the gap  26  are at the same rotation position. 
     Further, in  FIG. 4A  the dog clutch  14  has recesses  30  for connection to corresponding protruding portions of the second component  10  such that the dog clutch  14  can be rotationally locked relative to the second component  10 . The sleeve  13  in  FIG. 4B  is rotationally locked to the first component  9  by means of the splines  21  connecting to the hub  15  which in turn is rotationally locked to the first component  9 . In a way similar to the dog clutch, the hub  15  can have recesses for connection to corresponding protruding portions of the first component  9 . 
       FIG. 5  shows a variant of the transmission  8 ′ where the sleeve  13 ′ is part of a synchronizer device  40  for synchronizing the rotation speed of the first component  9  relative to the second component  10  when the sleeve  13 ′ and the dog clutch  14 ′ are to be engaged. Such a synchronizing device  40  can be designed with one or more synchronizing rings  41  in a way well known to the person skilled in the art. 
     Although the sleeve and the dog clutch can be engaged in a proper way by a spline joint and locking parts constituted by a radially protruding portion (such as a unique tooth) and a corresponding recess (such as a unique gap), other solutions are also possible. For example, the locking parts can be inverted such that the sleeve has a protruding portion and the dog clutch has a corresponding gap receiving the protruding portion. Further, the protruding portion could protrude in the axial direction instead of the radial direction. In another solution, the locking parts could be used both for allowing locking of the first component and the second component only in the predetermined mutual rotation position and for keeping them in this position without use of any other joint such as splines. In addition, in other example embodiments, the dog clutch is not provided with one of the locking parts but instead this locking part is arranged in another component rotationally locked to the second component. 
     In  FIG. 6  a sleeve  13 ″ and a dog clutch or dog ring  14 ″ with an alternative design are illustrated in a perspective view. The sleeve  13 ″ has protrusions  60  extending in the axial direction and the dog clutch  14 ″ has corresponding holes  61  for receiving the protrusions and enabling engagement of the sleeve and the dog clutch. 
     In  FIGS. 7A and 7B , further example embodiments are shown. The first locking part  23 ′ is a set of axial protrusions  70  and the second locking part  24 ′ is a set of corresponding recesses  71  for receiving the protrusions  70 . Such a set of protrusions may comprise one or more protrusions, preferably 1-5 protrusions, for interacting with a corresponding number of recesses. In  FIG. 7A  there are three protrusions and three recesses since the first component and the second component are rotationally lockable relative to each other in three equivalent rotation positions. The recesses  71  for receiving the protrusions  70  can be through holes forming openings or slots in a support portion  72  receiving the protrusions  70 . The support portion  72  is rotationally locked to the second component. In the example embodiment illustrated in  FIG. 7A , the support portion  72  is a plate which has through holes  73  for attachment to the housing. Although the protrusions  70  are arranged on the sleeve  13 ″′ and the recesses  71  in the support portion  72  in  FIG. 7A , it would be possible to instead arrange the recesses  71  in the sleeve  13 ″′ and the protrusions  70  on the support portion  72  as illustrated in  FIG. 7B .As can be seen from  FIG. 7A , the sleeve  13 ″′ has internal splines  75  for movement in the axial direction relative to the hub and the dog clutch  14 ″′ as previously described herein. The dog clutch  14 ″′ is provided with external splines  74  for engagement with the internal splines  75  of the sleeve  13 ″′. These splines constitute the engagement means for transferring any torque between the sleeve  13 ″′ and the dog ring  14 ″′ when engaged, while the first locking part  23 ′ and the second locking part  24 ′ are used only for initially achieving the predetermined mutual rotation position of the first component and the second component. 
     The dog clutch may have internal splines for allowing axial movement relative to the second component. In other example embodiments, the dog clutch is instead fixed to the housing also in the axial direction. In such a case, the dog clutch can be attached to the second component either directly or via a further component by welding, gluing, press fit or any other suitable means. 
     In the example embodiment shown in  FIG. 7A , a play is arranged in the rotation direction such that when the set of protrusions  70  is engaged with the set of corresponding recesses  71 , the first component and the second component can be somewhat rotated relative to each other before engagement of the sleeve  13 ″′ and the dog clutch  14 ″′ by the engagement means. Such play is relatively small, for example in the order of 0.5-3 mm, preferably 1-2 mm, ensuring that the desired rotation position is achieved. 
     The play can be obtained by making the size of the recesses  71  slightly exceeding the size of the protrusions  70  in the rotation direction. Further, the size of the play is adapted to the engagement means, which here is the spline joint, ensuring that any torque is transferred by the engagement means when the sleeve  13 ″′ and the dog clutch  14 ″′ are engaged by the engagement means. 
     In  FIGS. 8A and 8B  a further example embodiment comprising an additional ring  80  attached to the sleeve  130  is illustrated. In  FIG. 8A , the ring  80  and the sleeve  130  are separated for illustration purposes. When mounted to the sleeve, as illustrated in  FIG. 8B , the ring  80  is rotationally locked to the sleeve  130 . The ring  80  is also provided with the set of protrusions  70 ′ (or recesses) for engagement with the set of recesses  71  (or protrusions) of the support portion  72 . 
     The ring  80  can be clamped to the sleeve  130  and should be rotationally locked to the sleeve  130 . This can be arranged by a further protrusion  81  on the inside of the ring  80  interacting with a corresponding further recess  82  on the outside of the sleeve  130 . Further, the ring  80  will follow the movement of the sleeve  130  when being axially displaced towards the dog clutch. By the use of the additional ring  80 , a play in the rotation direction can be arranged between the additional ring  80  and the sleeve  130  by making the size of the further recess  82  slightly exceeding the size of the further protrusion  81  in the rotation direction. Such a play can be used instead of or in combination with a play between the protrusions of the ring and the recesses of the support portion. 
     It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.