Abstract:
When in a change speed mode, the transmission has an input shaft that provides driving power to an axially aligned but separately rotatable output shaft through a countershaft assembly situated alongside the input shaft and containing a series of change speed gears. A special slider assembly located on the input shaft and the output shaft between the input and output gears is in meshing engagement with the output gear at this time to operably connect the output gear with the output shaft. When the slider assembly is shifted to its fully forward direct drive mode, however, the countershaft assembly is decoupled from the input shaft and the slider assembly serves to directly couple the input shaft with the output shaft. The slider assembly is comprised of two relatively rotatably parts, one comprising a slider sleeve that meshes with the output gear when the slider assembly is in its changed speed position and the other comprising a slider collar circumscribing the sleeve that is telescopically received within a socket in the hollow input gear. When the slider assembly is in its direct drive position, the slider collar is fully received within the profile of the input gear and thereby adds no additional length to the transmission.

Description:
TECHNICAL FIELD 
     The present invention relates to automotive gearboxes and, more particularly, to a gearbox having an improved way of operably decoupling a countershaft assembly from the gearbox input shaft when the gearbox is placed in a direct drive mode. 
     BACKGROUND AND SUMMARY 
     My earlier U.S. Pat. No. 5,381,703 titled “Gearbox Countershaft Decoupler” discloses an energy and performance saving alternative to conventional manual gearboxes by providing a way of operatively decoupling a countershaft assembly provided with change speed gears from the input shaft of the gearbox when the gearbox is operating in a direct drive mode. Because the countershaft assembly with its change speed gears is typically immersed in relatively viscus lubricant within the gearbox, a substantial amount of energy is consumed just in turning the countershaft and gears of the countershaft assembly. In my prior patent, therefore, when the gearbox is in the direct drive mode in which the input shaft is coupled directly to the output shaft without transferring power through the decoupled countershaft assembly, a substantial energy savings is obtained because the countershaft assembly does not turn. In the interest of completeness, my prior U.S. Pat. No. 5,381,703 is hereby incorporated by reference into the present specification. 
     While the decoupling arrangement of the &#39;703 patent has proven to be highly effective and successful in producing energy and performance savings, my prior arrangement has certain drawbacks with respect to space requirements and the need for additional shifting mechanisms. In this respect, it was found that original equipment gearbox housings could not be retrofitted with my prior mechanism because of an increased overall length of the mechanism. Furthermore, an additional shifting mechanism such as a fork, hydraulic clutch, or the like needed to be added to the overall mechanism, adding complexity and cost. 
     In accordance with my present invention, a manual transmission or gearbox that provides decoupling of the countershaft assembly in the direct drive mode can be retrofitted to existing transmissions and uses no extra room within the transmission casing or housing and requires no additional shift mechanisms. Furthermore, a transmission in accordance with the present invention does not lose any surface area contact between gears of the transmission and thus will not suffer in terms of strength and reliability over conventional arrangements. Additionally, the principles of the present invention can be applied to transmissions having many different change speed gears, can be utilized in synchromesh transmissions, and can also be utilized in connection with an auxiliary gearbox at the rear end of the drive train of a vehicle in association with a high/low speed gearbox. 
     In a preferred embodiment of the invention, the gearbox includes a shaft assembly comprising an input shaft and an output shaft in axial alignment with the input shaft. An input gear on the input shaft transfers driving power to a countershaft assembly in all modes other than the direct drive mode, and the countershaft assembly in turn drives an output gear that becomes drivingly coupled with the output shaft when a special two-part slider assembly on the shaft assembly, comprising a slider sleeve and a slider collar rotatably encircling the sleeve, is in a change speed position. On the other hand, when the slider assembly is in a direct drive position, the input gear is effectively decoupled from the input shaft and the slider assembly serves as the means by which driving power is transferred directly from the input shaft to the output shaft, completely bypassing the countershaft assembly and the output gear. 
     The input gear is hollow, presenting a recess or socket that faces the slider assembly and serves to telescopically receive the collar of the slider assembly. Thus, in the direct drive mode the collar is fully housed within the input gear and takes up no more of the axial length of the shaft assembly than the input gear itself. External teeth on the slider collar are in constant meshing engagement with internal teeth on the socket of the input gear, but internal teeth on the slider collar are received within an annular void on the input shaft when the slider assembly is in the direct drive position so as to avoid operative engagement between the slider collar and the input shaft at that time. Although this decouples the input gear from the input shaft, teeth on the sleeve part of the slider assembly mesh with a set of strategically located teeth on the input shaft at this time so that the slider sleeve receives driving input from the input shaft. That input power is then transferred directly by the slider sleeve to the output shaft through intermeshing teeth on the slider sleeve and the output shaft. 
     The slider sleeve is retained within the outer slider collar by releasable detent structure that also permits relative rotation between those two parts. Thus, they are releasably held together for conjoint movement along the shaft assembly when a shifter fork attached to the slider sleeve shifts the slider assembly between the direct drive position and a neutral position. However, the detent structure releases the slider sleeve when the fork shifts the sleeve to a further, change speed position in driving engagement with an output gear, leaving the slider collar behind in the input gear. The detent structure readily recouples the two parts of the slider assembly back together when the sleeve is pushed back into the collar to re-establish the neutral position or the direct drive position. Special yieldable stop structure on the input gear and the slider collar keeps the collar from being pulled completely out of the input gear when the slider sleeve is shifted into its change speed position from the neutral position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary, rear perspective view of a gearbox transmission constructed in accordance with the principles of the present invention; 
     FIG. 2 is an enlarged, fragmentary exploded perspective view of portions of the transmission illustrating in particular components along the input and output shafts of the transmission; 
     FIG. 3 is a fragmentary cross-sectional view through the transmission showing the apparatus in a direct drive mode; 
     FIG. 4 is a fragmentary cross-sectional view similar to FIG. 3 but showing the apparatus in a neutral position; and 
     FIG. 5 is a fragmentary cross-sectional view similar to FIGS. 3 and 4 with the apparatus in a change speed mode. 
    
    
     DETAILED DESCRIPTION 
     The present invention is susceptible of embodiment in many different forms. While the drawings illustrate and the specification describes certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments. 
     In addition to U.S. Pat. No. 5,381,703, the inventor also incorporates by reference into the present specification page 214 through 219 of Volume II of  How Things Work  published by Edito-Service, S.A., and pages 2710 and 2711 from Volume 20 of  The New Illustrated Science and Invention Encyclopedia , published by H. S. Stuttman, Inc., copyright Marshall Cavendish Limited 1987, 1989. 
     FIG. 1 shows a three speed transmission constructed in accordance with the principles of the present invention, although it will be understood that the present invention is useful with gearboxes having as few as two speeds as well as gearboxes having five speeds or more, synchromesh and non-synchromesh. A shaft assembly  10  includes an input shaft  12  and an output shaft  14  supported in end-to-end axial alignment with one another and adapted for rotation relative to one another except when the gearbox is in a direct drive mode. As illustrated best in FIGS. 3,  4  and  5 , the rear end of input shaft  12  has an axially disposed, cylindrical stub  16  that is journaled within a receiving bore  18  in the forward end of output shaft  14  so that shafts  12  and  14  are adapted for rotation relative to one another. As understood by those skilled in the art, suitable means not shown are provided for lubricating the coupling provided between stub  16  and bore  18 . A case bearing  20  supported by a front wall  22  (FIGS. 3,  4  and  5 ) of the gearbox housing rotatably supports input shaft  12 , and similar bearing structure (not shown) rotatably supports output shaft  14 . 
     In the illustrated embodiment shaft assembly  10  carries an input gear  24  and three output gears  26 ,  28  and  30 . Generally speaking, input gear  24  and output gears  26 ,  28  and  30  are all rotatable relative to shaft assembly  10  except when selectively drivingly coupled therewith as hereinafter described. A countershaft assembly  32  is positioned alongside shaft assembly  10  in parallel relation thereto and includes a countershaft  34  that carries a driven or countershaft input gear  36  that is in constant mesh with input gear  24 . The driven countershaft gear  36  is fixed to countershaft  34 , as are change speed gears  38  and  40  that are in constant mesh with respective output gears  26  and  28 . A reverse gear  42  is also fixed to countershaft  34  at the rear end thereof and meshes with a small idler gear  44  that in turn meshes with output gear  30  to provide reverse drive of output shaft  14  when output gear  30  is engaged. 
     Selector mechanism well known by those skilled in the art includes a pair of shift rods  46  and  48  carrying respective shift forks  50  and  52  slidably thereon. Fork  50  is slidable along rod  46  for shifting between second and third gear (direct drive), while fork  52  is slidable along rod  48  for selecting between reverse gear and first gear. Shift fork  50  is operably coupled with a special slider assembly  54  in accordance with the present invention, while fork  52  is operably coupled with a conventional slider  56 . In accordance with known technology, when fork  52  shifts slider  56  forwardly into meshing engagement with output gear  28 , the gearbox is placed in first gear as gear  28  becomes operably coupled with output shaft  14  via slider  56  which is splined or otherwise adapted for rotation with output shaft  14 . On the other hand when slider  56  is shifted rearwardly into meshing engagement with output gear  30 , output gear  30  becomes operably coupled with output shaft  14  to rotate the latter in a direction opposite to the forward mode achieved in first, second and third gears. A neutral position for slider  56  is midway between the two output gears  28  and  30  wherein neither of such output gears is operably coupled with output shaft  14 . Likewise, when slider assembly  54  is shifted to its full rear position, output gear  26  becomes operably coupled with output shaft  14  to place the gearbox in second gear, while when slider  54  is shifted to its forwardmost position by fork  50 , the transmission is placed in its third gear which is a direct drive mode wherein input shaft  12  and output shaft  14  are directly drivingly interconnected with one another by slider assembly  54 . 
     FIGS. 2-5 focus primarily upon the special slider assembly  54  and its relationship with adjacent components of the gearbox. As illustrated in those figures, input shaft  12  has a set of external teeth  58  located a short distance inboard from the rear end of stub  16  on an enlarged portion of shaft  12  relative to stub  16 . Immediately inboard of external teeth  58  is an annular void  60  of reduced diameter relative to teeth  58 . Immediately inboard of void  60  is a circular flange  62  having a larger diameter than toothed portion  58 . The next inboard region of shaft  12  comprises another reduced diameter portion  63  of slightly larger diameter than void  60 , such portion  63  being received within the bearing  20 . 
     Input gear  24  is received on input shaft  12  in concentric relationship therewith. Input gear  24  is hollow, presenting an enlarged open area or socket  64  in the rear face thereof that has an annular sidewall  66  parallel to the longitudinal axis of input shaft  12  and an annular floor or ledge  68  at the innermost end of sidewall  66 . From ledge  68 , an inclined wall  70  tapers down to a bore  72  sized to fit on input shaft  12  immediately in front of flange  62  for bearing against such flange. The interface between wall  70  and flange  62  is such that input shaft  12  can rotate relative to input gear  24  when the gearbox transmission is in the direct drive mode. 
     The interior sidewall  66  of socket  64  is provided with a series of interior teeth  74  leading from ledge  68  rearwardly to the rear face of input gear  24 . Teeth  74  are spaced circumferentially around sidewall  66  and extend in the axial direction. At a number of spaced locations (preferably 6-8) on the socket sidewall  66 , the teeth  74  are interrupted generally adjacent the rear face of the input gear to present a notch  76  that in turn causes the rearmost portion  74   a  of the tooth  74  to serve as a limit stop as hereinafter described in more detail. Each notch  76  has beveled front and rear entry surfaces. 
     The slider assembly  54  has two primary parts, i.e, a slider sleeve  78  and a slider collar  80  that circumscribes the front end of sleeve  78 . Slider sleeve  78  has internal splines  88  that mate with the splined exterior of output shaft  14  so that sleeve  78  is fixed to output shaft  14  for rotation therewith but can move axially therealong. A set of beveled teeth  82  on the exterior of sleeve  78  at its rear end are adapted to mesh with an interior set of beveled teeth  84  on output gear  26  when slider assembly  54  is in its change speed position (FIG.  5 ). A circumferential groove  86  about the exterior of slider sleeve  78  forward of teeth  82  is adapted to receive shifter fork  50  to facilitate axial displacement of slider sleeve  78 . The internal splines  88  of slider sleeve  78  are adapted to matingly engage teeth  58  on input shaft  12  when slider assembly  54  is in the direct drive position of FIG.  3 . An annular groove or raceway  90  circumscribes slider sleeve  78  generally adjacent its forward end. 
     The slider collar  80  is adapted to be telescopically received within socket  64  of the hollow input gear  24 . The width of slider collar  80  in the axial direction is such that when collar  80  is fully received within socket  64  as illustrated in FIG. 3, no portion of collar  80  projects outwardly beyond the rear face of input gear  24 . Thus, when slider assembly  54  is in its direct drive position of FIG. 3, slider collar  80  takes up no more room along shaft assembly  10  than input gear  24 . On the other hand, slider collar  80  is adapted to be projected partially out of the rear face of input gear  24  such as when slider assembly  54  is in a neutral position of FIG. 4 or a change speed position of FIG.  5 . Slider collar  80  never completely leaves socket  64  in any of its operating modes. 
     A series of external teeth  92  on slider collar  80  are adapted to mesh with interior teeth  74  on input gear  24  at all times. Thus, slider collar  80  and input gear  24  are in constant driving relationship with one another, although the spline-like nature of teeth  92  and  74  permit axial displacement of slider collar  80  relative to input gear  24 . An interior set of teeth  94  on slider collar  80  are positioned to be non-drivingly received within void  60  when slider  54  is in the direct drive position of FIG. 3 so that, in such position, input shaft  12  can rotate relative to slider collar  80 , and thus also input gear  24 . Consequently, input gear  24  is effectively decoupled from input shaft  12  when slider assembly  54  is in the direct drive mode of FIG.  3 . 
     However, interior teeth  94  of slider collar  80  are adapted to matingly engage exterior teeth  58  of input shaft  12  when slider collar  80  telescopically is extended from input gear  24  as illustrated in FIGS. 4 and 5. To keep slider collar  80  from completely separating from input gear  24 , slider collar  80  is provided with a plurality of spring-loaded, radially projecting dog members  96  corresponding in number to the notches  76  in internal teeth  74  of input gear  24 . Dogs  96  are adapted to ride on and bear slidingly against the corresponding internal teeth  74  when collar  80  is in its retracted position of FIG. 3 but to snap out into notches  76  as illustrated in FIGS. 4 and 5 when collar  80  is in its extended position. With dogs  96  so received within notches  76 , the remaining portions  74   a  of the notched teeth  74  serve as limit stops bearing against dogs  96  to prevent further outward telescoping of slider collar  80  from socket  64 . 
     Slider collar  80  has an axially disposed recess  98  in its rear face having an inner diameter only slightly larger than the outer diameter of the forward end of slider sleeve  78 . The forward end of slider sleeve  78  thus can be received within recess  98  and, when so received, the forwardmost end edge  100  of slider sleeve  78  abuts against a recessed, annular floor  102  within collar  80 . Collar  80  is thus rotatable on sleeve  78 , and suitable detent structure broadly denoted by the numeral  104  releasably retains collar  80  and sleeve  78  in their intercoupled relationship. Such detent structure may take a variety of different forms, but in the illustrated embodiment it is in the nature of a plurality of generally cylindrical detents  106  received within and slightly longer than radial receiving holes  108  for the detents in the sidewall of recess  98  at three or more circumferentially spaced locations. 
     Opposite ends of each detent  106  are rounded, with the inner ends being adapted to matingly fit into raceway  90  of slider sleeve  78 . Each detent  106  has an elongated, radially extending slot  110  therein that is oversized with respect to a transverse retaining pin  112  so that the detent is free to move radially inwardly and outwardly to the extent permitted by retaining pin  112  working within slot  110 . Although detents  106  retain slider sleeve  78  intercoupled with slider collar  80  when slider  54  is in its direct drive mode of FIG.  3  and the neutral position of FIG. 4, detents  106  are also free to release sleeve  78  from collar  80  upon the application of sufficient rearward force to sleeve  78  by shift fork  50 . The radiused inner end of each detent  106  facilitates detents  106  being forced outwardly in a camming action as the forward edge of raceway  90  bears against such curved surfaces. Thus, slider sleeve  78  can assume a separated condition as illustrated in FIG. 5, the detents  106  being cleared by the interior sidewall of recess  98  at such time so as to pop out as shown in FIG.  5 . At all other times, detents  106  merely ride in raceway  90  and adapt sleeve  78  and collar  80  for rotation relative to one another. 
     Operation 
     When slider assembly  54  is in its direct drive position of FIG. 3, input gear  24  is effectively decoupled from input shaft  12 , and thus countershaft assembly  32  is likewise decoupled from input shaft  12 . In this condition, as input shaft  12  rotates, it has no driving connection with slider collar  80  which has its internal teeth  94  received within void  60  of input shaft  12  at this time. Thus, although slider collar  80  remains in meshing engagement with input gear  24  through exterior teeth  92  and interior teeth  74  at this time, no power is transferred to input gear  24 . 
     Instead, power from input shaft  12  is transferred to slider sleeve  78  via external teeth  58  on input shaft  12  and internal splines  88  on slider sleeve  78 . Thus, slider sleeve  78  rotates with input shaft  12 , and such rotation is relative to the stationary slider collar  80  as permitted by the detents  106  riding within raceway  90 . Since slider sleeve  78  is in constant driving engagement with output shaft  14  through external splines on shaft  14  and the internal splines  88  on sleeve  78 , the power from input shaft  12  is transferred directly to output shaft  14  via slider sleeve  78 . It will of course be noted that because output gear  26  is rotatable relative to output shaft  14  at all times unless operably coupled thereto by slider assembly  54 , there is no rotation of output gear  26  by output shaft  14  at this time. A bushing or bearing  114  between output gear  26  and output shaft  114  permits such relative rotation between those two components. 
     When the shifter fork  50  moves slider assembly  54  to the neutral position of FIG. 4, slider sleeve  78  and slider collar  80  move as a unit to such position. This is due to the connection afforded by the detents  106  within raceway  90 , which detents are kept from moving radially outwardly at this time by the sidewall  66  of socket  64 . When slider assembly  54  reaches the neutral position, dogs  96  snap out into notches  76  to retain slider collar  80  against further axial displacement. Interior teeth  94  on collar  80  come into meshing engagement with exterior teeth  58  on input shaft  12  such that driving power is transferred from input shaft  12  to input gear  24  via slider collar  80 . Thus, countershaft assembly  32  also receives input power, and output gear  26  is therefore caused to rotate. However, no power is delivered to output shaft  14  because output gear  26  merely rotates freely on output shaft  14  at this time. With slider assembly  54  in its neutral position, slider sleeve  78  is still out of engagement with output gear  26  such that the rotation of output gear  26  is not transferred to output shaft  14 . 
     When slider assembly  54  is shifted to its rearmost change speed position of FIG. 5, input power from input shaft  12  is directed to input gear  24 , then through countershaft assembly  32  to output gear  26 , and then to output shaft  14  via slider sleeve  78  which is drivingly coupled with output gear  26  at this time. Thus, output shaft  14  becomes driven at the ratio determined by the countershaft change speed gear  38  and output gear  26 , in this particular embodiment such ratio comprising second gear. To accomplish this condition, the slider sleeve  78  must separate from slider collar  80  in the axial direction, such separation being permitted by detents  106  which are snapped out to their outwardly projected positions as illustrated in FIG. 5 at this time to disengage from raceway  90 . Relative rotation between output shaft  14  and input shaft  12  is permitted by virtue of the fact that stub  16  of input shaft  12  is rotatably received within the bore  18  of output shaft  14 . It will be noted that it is easier for detents  106  to pop out radially than for dogs  96  to pull out of notches  76 . Thus, when slider assembly  54  moves to the change speed position of FIG. 5, it is the slider sleeve  78  that separates from collar  80  not, collar  80  from input gear  24 . 
     In order to place the gearbox transmission back into its neutral mode in which slider assembly  54  is in it neutral position of FIG. 4, fork  50  is shifted forwardly from its FIG. 5 position until the front end of slider sleeve  78  becomes received within recess  98  of slider collar  80  and edge  100  butts against floor  102  of collar  80 . Detents  106  may or may not reseat within raceway  90  at this time but, in any event, upon further forward shifting of fork  50  toward the direct drive position of FIG. 3, the proximal edges of the rear face of input gear  24  will come to bear against the rounded outer ends of detents  106  and cam them inwardly into raceway  90 . In that way, slider sleeve  78  and slider collar  80  will once again become operably coupled together for conjoint axial shifting movement along shaft assembly  10  while permitting relative rotational movement therebetween. 
     It will thus be seen that the special slider assembly  54  and its telescopic relationship with hollow gear  24  enables countershaft assembly  32  to be decoupled from input shaft  12  in the direct drive mode, but without increasing the overall length of the transmission. Consequently, the substantial energy savings made available by decoupling the countershaft assembly  32  in the direct drive mode can be achieved without requiring an entirely new gearbox housing, and additional actuators. Furthermore, when retro-fitting existing transmissions with the present invention, the original shift fork  50 , output gear  26  and output shaft  14  can be utilized, as well as the original countershaft assembly  32  of course, it being only necessary to substitute a new input shaft  12 , input gear  24  and slider assembly  54 . The total number of parts increases only by one, i.e., the slider collar  80 . 
     The inventor(s) hereby state(s) his/their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his/their invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.