Abstract:
A gearbox comprises a plurality of gear pairs each having a specific gear ratio, and a plurality of selectors each mounted between two gear pairs for selecting one of the two gear pairs, wherein the gear ratio of the selected gear pair is cascaded through an output shaft to another two gear pairs having another selector, and so on. In this way, the effective or aggregate gear ratio of the gearbox is the product of the gear ratios of the selected gear pairs. Thus, the number of available output speeds excluding neutral is given by 2 n , where n=(number of gear pairs)/2.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to gearbox transmissions for converting an input rotational speed to a selectable output rotational speed. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known that internal combustion engines operate most efficiently within a limited range of engine revolutions-per-minute (rpm). An engine with limited rpm range will require the use of many gears to enable a vehicle powered by the engine to be used over its desired speed range, which may be from standstill to the national speed limit or some other upper limit. A conventionally operated gearbox requires the vehicle driver to continually shift gears to maintain engine rpm within the optimum range. There are also available transmissions which provide a continuously variable input/output rotational speed ratio, but these are expensive to manufacture and inefficient to operate. 
         [0003]    A conventional six-speed gearbox configuration is shown in  FIG. 1  as comprising an input shaft  110  for receiving input torque. A first input gear  112  and a second input gear  116  are mounted coaxially on input shaft  110  for rotation relative to the input shaft. First input gear  112  is meshed with a first output gear  114  to form a first gear pair having a first gear ratio determined by the respective diameters or numbers of teeth of the first input gear and the first output gear. Likewise, second input gear  116  is meshed with a second output gear  118  to form a second gear pair having a second gear ratio. The first and second output gears  114  and  118  are mounted coaxially on an output shaft  140  and are fixed to output shaft  140  to rotate together therewith. A third input gear  122  and a fourth input gear  126  are mounted coaxially on input shaft  110  for rotation relative to the input shaft. Third input gear  122  is meshed with a third output gear  124  to form a third gear pair having a third gear ratio. In similar fashion, fourth input gear  126  is meshed with a fourth output gear  128  to form a fourth gear pair having a fourth gear ratio. The third and fourth output gears  124  and  128  are mounted coaxially on output shaft  140  and are fixed to the output shaft to rotate together therewith. A fifth input gear  132  and a sixth input gear  136  are also mounted coaxially on input shaft  110  so as to permit rotation relative to the input shaft. Fifth input gear  132  is meshed with a fifth output gear  134  to form a fifth gear pair having a fifth gear ratio. Likewise, sixth input gear  136  is meshed with a sixth output gear  138  to form a sixth gear pair having a sixth gear ratio. Like the first through fourth output gears, the fifth and sixth output gears  134  and  138  are mounted coaxially on output shaft  140  and are fixed to the output shaft  140  to rotate together therewith. A first selector  152  rotating with input shaft  110  is arranged movably between first gear pair  112 ,  114  and second gear pair  116 ,  118  to select either of the first and second gear pairs, a second selector  154  rotating with input shaft  110  is arranged movably between third gear pair  122 ,  124  and fourth gear pair  126 ,  128  to select either of the third and fourth gear pairs, and a third selector  156  rotating with input shaft  110  is arranged movably between fifth gear pair  132 ,  134  and sixth gear pair  136 ,  138  to select either of the fifth and sixth gear pairs. 
         [0004]    The selector positions for the six available speeds (gears), not including neutral (already shown in  FIG. 1 ), are illustrated in  FIGS. 2A through 2F . First gear is selected by moving the first selector  152  to the left as shown in  FIG. 2A  to drivably engage first input gear  112 , whereby the first gear ratio associated with first gear pair  112 ,  114  is chosen and is outputted by output shaft  140 . Second gear is chosen by moving first selector  152  to the right as shown in  FIG. 2B  to drivably engage second input gear  116 , whereby the second gear ratio associated with second gear pair  116 ,  118  is chosen and transmitted through output shaft  140 . In similar fashion, second selector  154  is moved to the left to select third gear ( FIG. 2C ) and to the right to select fourth gear ( FIG. 2D ), and third selector  156  is moved to the left to select fifth gear ( FIG. 2E ) and to the right to select sixth gear ( FIG. 2F ). Thus, there are six gear pairs and six selectable speeds. Under a conventional configuration, two additional gear pairs and an additional selector are required to provide eight selectable speeds. 
         [0005]    Therefore, a need exists to provide more discreet selectable speeds without adding gears and selectors to the gearbox configuration, as these bring added weight to the gearbox that is of course undesirable from the standpoint of fuel efficiency. Stated differently, a need exists to maximize the number of discreet speeds available using a given number of gear pairs and selectors. 
       SUMMARY OF THE INVENTION 
       [0006]    Therefore, it is an object of the present invention to configure a gearbox such that it provides more discreet selectable speeds without adding gears and selectors to the gearbox configuration. 
         [0007]    It is another object of the present invention to configure a gearbox that is lighter than conventional gearboxes having the same number of output speeds. 
         [0008]    It is a further object of the present invention to configure a gearbox that is capable of providing a large range of selectable output speeds in response to input closely matching optimal engine rpm. 
         [0009]    In furtherance of these and other objects, a gearbox of the present invention comprises a plurality of gear pairs each having a specific gear ratio, and a plurality of selectors each mounted between two gear pairs for selecting one of the two gear pairs, wherein the gear ratio of the selected gear pair is cascaded through an output shaft to another two gear pairs having another selector, and so on. In this way, the effective or aggregate gear ratio of the gearbox is the product of the gear ratios of the selected gear pairs. 
         [0010]    A gearbox formed in accordance with an embodiment of the present invention generally comprises a plurality of gear pairs, an input shaft and a plurality of output shafts, and one selector for every two gear pairs. More particularly, an embodiment comprises six gear pairs each including a respective input gear and output gear defining a respective gear ratio. An input shaft drives a selected one of the first gear pair and the second gear pair, a first output shaft is driven by output of the selected one of the first and second gear pairs and transmits its motion to input gears of the third and fourth gear pairs, a second output shaft is driven by output of a selected one of the third and fourth gear pairs and transmits its motion to input gears of the fifth and sixth gear pairs, and a third output shaft is driven by output of a selected one of the fifth and sixth gear pairs. Three selectors are respectively arranged between the first and second gear pairs, the third and fourth gear pairs, and the fifth and sixth gear pairs, wherein each selector is movable to select one of the two gear pairs it is between by engagement with the selected gear pair. The total number of output speeds (excluding neutral) available to the third output shaft is given by 2 n  where n=(number of gear pairs)/2. Thus, with six gear pairs, there are 2 3 =8 available speeds. 
         [0011]    The cascading gearbox configuration may be extended to include additional gear pairs. With eight gear pairs, the total number of available output speeds increase exponentially to 16. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The nature and mode of operation of the present invention will now be more fully described in the following detailed description of various embodiments taken with the accompanying drawing figures, in which: 
           [0013]      FIG. 1  shows a conventional six-speed gearbox of the prior art, in neutral; 
           [0014]      FIG. 2A  shows the conventional six-speed gearbox of the prior art, in first gear; 
           [0015]      FIG. 2B  shows the conventional six-speed gearbox of the prior art, in second gear; 
           [0016]      FIG. 2C  shows the conventional six-speed gearbox of the prior art, in third gear; 
           [0017]      FIG. 2D  shows the conventional six-speed gearbox of the prior art, in fourth gear; 
           [0018]      FIG. 2E  shows the conventional six-speed gearbox of the prior art, in fifth gear; 
           [0019]      FIG. 2F  shows the conventional six-speed gearbox of the prior art, in sixth gear; 
           [0020]      FIG. 3  shows a binary gearbox formed in accordance with a first embodiment of the present invention, in neutral; 
           [0021]      FIG. 4A  shows the binary gearbox of  FIG. 3 , in first gear; 
           [0022]      FIG. 4B  shows the binary gearbox of  FIG. 3 , in second gear; 
           [0023]      FIG. 4C  shows the binary gearbox of  FIG. 3 , in third gear; 
           [0024]      FIG. 4D  shows the binary gearbox of  FIG. 3 , in fourth gear; 
           [0025]      FIG. 4E  shows the binary gearbox of  FIG. 3 , in fifth gear; 
           [0026]      FIG. 4F  shows the binary gearbox of  FIG. 3 , in sixth gear; 
           [0027]      FIG. 4G  shows the binary gearbox of  FIG. 3 , in seventh gear; 
           [0028]      FIG. 4H  shows the binary gearbox of  FIG. 3 , in eighth gear; 
           [0029]      FIG. 5  shows a binary gearbox configuration formed in accordance with a second embodiment of the present invention, wherein three selectors of the gearbox configuration are aligned along a common axis; 
           [0030]      FIG. 6  shows a binary gearbox configuration formed in accordance with a third embodiment of the present invention, wherein three selectors of the gearbox configuration are aligned along a common axis, and the input and final output shaft of the gearbox configuration are on the same end of the configuration; 
           [0031]      FIG. 7  shows a binary gearbox configuration formed in accordance with a fourth embodiment of the present invention, wherein a selector of the gearbox configuration is aligned on an axis of a final output shaft of the configuration; 
           [0032]      FIG. 8  shows a binary gearbox configuration formed in accordance with a fifth embodiment of the present invention, wherein eight gear pairs are provided. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      FIG. 3  schematically illustrates a binary gearbox  4  formed in accordance with a first embodiment of the present invention. Gearbox  4  includes a housing  6  having bearings  8  for rotatably supporting elements of a variable speed drive mechanism of the gearbox. 
         [0034]    Gearbox  4  comprises an input shaft  10  for receiving input torque, such as torque from a motor drive. A first input gear  12  and a second input gear  16  are mounted coaxially on input shaft  10  for rotation relative to the input shaft. First input gear  12  is meshed with a first output gear  14  to form a first gear pair having a first gear ratio determined by the respective diameters (or respective numbers of teeth) of the first input gear and the first output gear. Likewise, second input gear  16  is meshed with a second output gear  18  to form a second gear pair having a second gear ratio. The first and second output gears  14  and  18  are mounted coaxially on a first output shaft  20  and are fixed to first output shaft  20  to rotate together therewith. 
         [0035]    A third input gear  22  and a fourth input gear  26  are mounted coaxially on first output shaft  20  for rotation relative to first output shaft  20 . Third input gear  22  is meshed with a third output gear  24  to form a third gear pair having a third gear ratio. In similar fashion, fourth input gear  26  is meshed with a fourth output gear  28  to form a fourth gear pair having a fourth gear ratio. The third and fourth output gears  24  and  28  are mounted coaxially on a second output shaft  30  and are fixed to second output shaft  30  to rotate together therewith. Second output shaft  30  is coaxially aligned with input shaft  10  but rotates relative to the input shaft. 
         [0036]    Also mounted coaxially on second output shaft  30  are a fifth input gear  32  and a sixth input gear  36 . Fifth and sixth input gears  32  and  36  are mounted so as to permit rotation relative to second output shaft  30 . Fifth input gear  32  is meshed with a fifth output gear  34  to form a fifth gear pair having a fifth gear ratio. Likewise, sixth input gear  36  is meshed with a sixth output gear  38  to form a sixth gear pair having a sixth gear ratio. The fifth and sixth output gears  34  and  38  are mounted coaxially on a third output shaft  40  and are fixed to third output shaft  40  to rotate together therewith. Third output shaft  40  is coaxially aligned with first output shaft  20  but rotates relative to the first output shaft. 
         [0037]    Gearbox  4  further comprises a first selector  52  arranged movably between first gear pair  12 ,  14  and second gear pair  16 ,  18  to select either of the first and second gear pairs, a second selector  54  arranged movably between third gear pair  22 ,  24  and fourth gear pair  26 ,  28  to select either of the third and fourth gear pairs, and a third selector  56  arranged movably between fifth gear pair  32 ,  34  and sixth gear pair  36 ,  38  to select either of the fifth and sixth gear pairs. Selectors  52 ,  54 , and  56  may be moved by any of a variety of actuation mechanisms known in the art, including without limitation mechanical drum actuators, pneumatic actuators, hydraulic actuators, and electromechanical actuators. The type of actuation mechanism used will depend upon the particular application of gearbox  4 , and is not considered part of the present invention. 
         [0038]    In the embodiment shown in  FIG. 3 , first selector  52  is mounted on input shaft  10  for axial movement therealong to select either first gear pair  12 ,  14  by engagement with a coupling  13  fixed to first input gear  12 , or second gear pair  16 ,  18  by engagement with a coupling  17  fixed to second input gear  16 . A travel slot  11  is indicated schematically along input shaft  10  for first selector  52 , it being understood that first selector  52  is mounted on input shaft  10  to rotate together with the input shaft and move axially along the input shaft. Accordingly, when first selector  52  is engaged with coupling  13 , the first input gear  12  is coupled to input shaft  10  to rotate together with the input shaft such that torque is transmitted from the input shaft to first gear pair  12 ,  14 . Alternatively, when first selector  52  is engaged with coupling  17 , the second input gear  16  is coupled to input shaft  10  to rotate together with the input shaft such that torque is transmitted from the input shaft to second gear pair  16 ,  18 . First selector  52  may also occupy a neutral position in which it is between and disengaged from couplings  13  and  17  as depicted in  FIG. 3 , such that torque from input shaft  10  is not transmitted to either first gear pair  12 ,  14  or second gear pair  16 ,  18 . 
         [0039]      FIG. 3  shows second selector  54  mounted on first output shaft  20  for axial movement therealong to select either third gear pair  22 ,  24  by engagement with a coupling  23  fixed to third input gear  22 , or fourth gear pair  26 ,  28  by engagement with a coupling  27  fixed to fourth input gear  26 . A travel slot  21  is indicated schematically along first output shaft  20  for second selector  54 , which is mounted on first output shaft  20  to rotate together with the first output shaft and move axially along the first output shaft. Thus, when second selector  54  is engaged with coupling  23 , the third input gear  22  is coupled to first output shaft  20  to rotate together with the first output shaft such that torque is transmitted from the first output shaft to third gear pair  22 ,  24 . Alternatively, when second selector  54  is engaged with coupling  27  as depicted in  FIG. 3 , the fourth input gear  26  is coupled to first output shaft  20  to rotate together with the first output shaft such that torque (if any) is transmitted from the first output shaft to fourth gear pair  26 ,  28 . Second selector  54  may also occupy a neutral position in which it is between and disengaged from couplings  23  and  27  to prevent torque transmission from first output shaft  20  to either third gear pair  22 ,  24  or fourth gear pair  26 ,  28 . 
         [0040]    With continued reference to  FIG. 3 , it can be seen that third selector  56  is mounted on second output shaft  30  for axial movement therealong to select either fifth gear pair  32 ,  34  by engagement with a coupling  33  fixed to fifth input gear  32 , or sixth gear pair  36 ,  38  by engagement with a coupling  37  fixed to sixth input gear  36 . A travel slot  31  is schematically drawn along second output shaft  30  for third selector  56 , which is mounted on second output shaft  30  to rotate together therewith and move axially therealong. Thus, when third selector  56  is engaged with coupling  33 , the fifth input gear  32  is coupled to second output shaft  30  to rotate together with the second output shaft to transmit torque from the second output shaft to fifth gear pair  32 ,  34 . When third selector  56  is engaged with coupling  37  as depicted in  FIG. 3 , the sixth input gear  36  is coupled to second output shaft  30  to rotate together with the second output shaft to transmit torque (if any) from the second output shaft to sixth gear pair  36 ,  38 . Third selector  56  may also occupy a neutral position in which it is between and disengaged from couplings  33  and  37  to prevent torque transmission from second output shaft  30  to either fifth gear pair  32 ,  34  or sixth gear pair  36 ,  38 . The gearbox configuration shown in  FIG. 3  provides eight selectable speeds or “gears,” as well as a neutral setting. The eight gears are shown in  FIGS. 4A through 4H , respectively. First gear, shown in  FIG. 4A , corresponds to a condition wherein first selector  52  engages first gear pair  12 ,  14 , second selector  54  engages third gear pair  22 ,  24 , and third selector  56  engages fifth gear pair  32 ,  34 . In this condition, rotational motion is transmitted from input shaft  10  to first input gear  12 , from first input gear  12  to first output gear  14 , from first output gear  14  to first output shaft  20 , from first output shaft  20  to third input gear  22 , from third input gear  22  to third output gear  24 , from third output gear  24  to second output shaft  30 , from second output shaft  30  to fifth input gear  32 , from fifth input gear  32  to fifth output gear  34 , and from fifth output gear  34  to third output shaft  40 . As will be understood, the ratio of rotational speed of input shaft  10  to that of third output shaft  40  is given by: 
         [0000]    
       
         
           
             
               
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         [0000]    which is the product of the gear ratios of the selected gear pairs. In this regard, the first, second, and third selectors  52 ,  54 , and  56  can be thought of as having binary engagement settings. First selector  52  can engage first gear pair  12 ,  14  (binary “0” setting) or second gear pair  16 ,  18  (binary “1” setting). Likewise, second selector  54  has a “0” setting in engagement with third gear pair  22 ,  24  and a “1” setting in engagement with fourth gear pair  26 ,  28 . Finally, third selector  56  has a “0” setting in engagement with fifth gear pair  32 ,  34  and a “1” setting in engagement with sixth gear pair  36 ,  38 . Accordingly, the first gear condition shown in  FIG. 4A  may be referred to as a “000” setting of the gearbox. Thus, the total number of available speeds or gears is given by 2 n  where n=(number of gear pairs)/2. 
         [0041]      FIG. 4B  illustrates gearbox in second gear, or “001”. In this condition, the overall rotational speed ratio of input shaft  10  to third output shaft  40  the first gear ratio, the third gear ratio, and the sixth gear ratio.  FIGS. 4C through 4H  show the selector positions when gearbox  4  is in third gear through eighth gear. Merely by way of example, and not by limitation, the following gear ratios may be assumed for sake of illustration: 
         [0000]                                                    DECIMAL       GEAR PAIR   GEAR RATIO   DESIGNATION   VALUE                   First (12, 14)   33:21   R1   1.57143       Second (16, 18)   21:33   R2   0.63636       Third (22, 24)   30:24   R3   1.25000       Fourth (26, 28)   24:30   R4   0.80000       Fifth (32, 34)   28:25   R5   1.12000       Sixth (36, 38)   25:28   R6   0.89286                    
The table below shows computation of the ratio of input shaft rotational speed to third output shaft rotational speed for each of the eight gear speeds available in the depicted embodiment, assuming the example gear ratios listed above.
 
         [0000]                                            GEAR (SPEED)   FIG.   BINARY   PRODUCT   I/O RATIO                   1   4A   000   R1 × R3 × R5     2.2:1       2   4B   001   R1 × R3 × R6    1.75:1       3   4C   010   R1 × R4 × R5    1.408:1       4   4D   011   R1 × R4 × R6    1.122:1       5   4E   100   R2 × R3 × R5   0.8909:1       6   4F   101   R2 × R3 × R6   0.71023:1        7   4G   110   R2 × R4 × R5   0.5702:1       8   4H   111   R2 × R4 × R6   0.4545:1                    
wherein R1 through R6 are the gear ratios of the respective first through sixth gear pairs.
 
         [0042]      FIG. 5  shows a gearbox configuration according to a second embodiment of the present invention. In this embodiment, third input gear  22  and fourth input gear  26  are fixed to first output shaft  20  to rotate together therewith, while third output gear  24  and fourth output gear  28  are mounted on second output shaft  30  in a manner permitting relative rotation between the mounted output gears  24 ,  28  and the second output shaft  30 . Second selector  54  is mounted on second output shaft  30  for axial movement therealong to select either third gear pair  22 ,  24  by engagement with coupling  23  now fixed to third output gear  24  or fourth gear pair  26 ,  28  by engagement with coupling  27  now fixed to fourth output gear  26 . Travel slot  21  is now indicated schematically along second output shaft  30 . Second selector  54  rotates together with second output shaft  30 . In other respects, the second embodiment is generally similar to the first embodiment of  FIG. 3 . As is readily apparent from  FIG. 5 , all three selectors  52 ,  54 , and  56  are aligned along a common axis in this embodiment. 
         [0043]      FIG. 6  shows a gearbox configuration according to a third embodiment of the present invention that is substantially similar to the embodiment shown in  FIG. 5 , except that third output shaft  40  is arranged to extend through a central bore in first output shaft  20 , whereby an output end of third output shaft  40  is located on the same side of the gearbox as an input end of input shaft  10 . 
         [0044]    A gearbox configuration formed in accordance with a fourth embodiment of the present invention is shown in  FIG. 7 . The fourth embodiment is generally similar to the embodiment shown in  FIG. 5 , except that fifth input gear  32  and sixth input gear  36  are fixed to second output shaft  30 , and third selector  56  is mounted on third output shaft  40  so as to rotate together therewith. In this configurations travel slot  31  is now indicated schematically along third output shaft  40  to allow third selector  56  to move axially to select either fifth gear pair  32 ,  34  by engagement with coupling  33  now fixed to fifth output gear  34  or sixth gear pair  36 ,  38  by engagement with coupling  37  now fixed to sixth output gear  36 . 
         [0045]    As will be appreciated, the embodiments of  FIGS. 5 through 7  offer eight speeds or gears in a manner similar to the embodiment of  FIG. 3  by utilizing a cascading arrangement of gears and shafts. This principle may be extended by adding additional gear pairs and an associated selector, as illustrated by a fifth embodiment shown in  FIG. 8 . The fifth embodiment is similar to the first embodiment of  FIG. 3 , except that it includes two additional gear pairs and one additional selector. In particular, a seventh gear pair defining a seventh gear ratio includes a seventh input gear  42  and a seventh output gear  44 , and an eighth gear pair defining an eighth gear ratio includes an eighth input gear  46  and an eighth output gear  48 . The seventh and eighth input gears  42  and  46  are mounted on third output shaft  40  to allow relative rotation between the mounted input gears  42 ,  46  and the third output shaft  40 . A fourth selector  58  is mounted on third output shaft  40  to be movable along a travel slot  41  in the third output shaft and to rotate with the third output shaft. Fourth selector  58  can be moved to select seventh gear pair  42 ,  44  by engagement with a coupling  43  fixed to seventh input gear  42  or eighth gear pair  46 ,  48  by engagement with a coupling  47  fixed to eighth input gear  46 . Seventh and eighth output gears  44  and  48  are fixed to a fourth output shaft  50 , which provides the final output motion in the present configuration. The configuration of  FIG. 8  provides a total of 2 4 =16 different speeds or gears. 
         [0046]    From the foregoing description, it will be understood that a cascading binary gearbox of the present invention uses multiple fixed gear ratios in a novel way that provides more discreet input/output speed ratios than conventional gearboxes. The novel gearbox is applicable to internal combustion engines, and allows an engine to operate within its optimum rpm range to increase fuel efficiency. As a result, the invention is expected to aid in the development of light-weight, fuel-efficient motor vehicles. 
       PARTS LIST 
       [0000]    
       
         
           
               4  Gearbox 
               6  Housing 
               8  Bearing 
               10  Input shaft 
               11  Travel slot for first selector 
               12  First input gear 
               13  Coupling 
               14  First output gear 
               16  Second input gear 
               17  Coupling 
               18  Second output gear 
               20  First output shaft 
               21  Travel slot for second selector 
               22  Third input gear 
               23  Coupling 
               24  Third output gear 
               26  Fourth input gear 
               27  Coupling 
               28  Fourth output gear 
               30  Second output shaft 
               31  Travel slot for third selector 
               32  Fifth input gear 
               33  Coupling 
               34  Fifth output gear 
               36  Sixth input gear 
               37  Coupling 
               38  Sixth output gear 
               40  Third output shaft 
               41  Travel slot for fourth selector 
               42  Seventh input gear 
               43  Coupling 
               44  Seventh output gear 
               46  Eighth input gear 
               47  Coupling 
               48  Eighth output gear 
               50  Fourth output shaft 
               52  First selector 
               54  Second selector 
               56  Third selector 
               58  Fourth selector