Abstract:
A manual transmission is provided having a plurality of planar gear sets for achieving multiple forward gear ratios. The transmission also has an idler gear, a first planar gear set, a first shift linkage member, and an intermediate linkage member. The first shift linkage member has a synchronizer portion and a fork portion. The intermediate linkage member has a partial engagement cam portion that contacts and urges the fork portion of the shift linkage member to partially engage the synchronizer and the output member with the third gear prior to shifting the idler gear to mesh the input shaft with the output shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Provisional U.S. Application No. 62/066,032 filed Oct. 20, 2014. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to transmissions and more specifically to manual transmissions having an idler gear brake employed to reduce gear clash when shifting into a reverse gear ratio. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0004]    A typical manual transmission includes a plurality of shafts, gears, shift mechanisms, synchronizers or other torque-transmitting mechanisms that cooperate to provide a plurality of forward and reverse gear or speed ratios. The transmission input shaft is selectively connected to an engine output shaft and includes a number of gears that are selectively connectable to the input shaft using, for example, synchronizers. The gears of the input shaft mesh with corresponding gears that are selectively connectable to an output shaft. To achieve a particular forward gear ratio between the transmission input and output shafts, the driver operates a shift mechanism, such as a manual shifter, that controls the engagement of the synchronizers with the desired gears. To achieve a reverse gear ratio, an idler gear is used to slide between an input shaft gear and an output shaft gear to reverse the rotational direction of the output shaft, and thus the drive wheels. 
         [0005]    The idler gear is free to rotate on an idler gear shaft and the idler gear is not necessarily rotating when the idler gear is engaged to the input shaft reverse gear. However, the input shaft is often rotating at a high speed having only recently been disengaged from the engine output shaft. Once the idler gear is meshing with the input shaft reverse gear they will both be rotating at the same high speed. The idler gear must then engage the output shaft gear to complete the torque transfer to the output shaft. However, as often is the case, the output shaft is not rotating and may even be rotating in the opposite direction as the driver may be shifting into reverse before the vehicle has stopped moving forward. The meshing of the fast rotating idler gear with a stationary output gear causes an impact or gear clash that creates noise and grinding that is very objectionable to the driver. Furthermore, gear clash is detrimental to the long term durability of the transmission and is the source of costly customer repair bills. 
         [0006]    Accordingly, there is room in the art for a transmission that includes a mechanism to reduce or eliminate gear clash and premature component wear by reducing the input shaft and idler gear rotational speed when the driver is shifting into a reverse gear ratio. 
       SUMMARY 
       [0007]    A transmission having a plurality of forward gear ratios and at least one reverse gear ratio is provided. The transmission includes an input and output member, an idler gear, a planar gear set, a first shift linkage member, and an intermediate linkage member. The input member is selectively connected to an engine output. The output member is connected to a vehicle drive shaft. The idler gear rotatably is supported by an idler member. The idler gear is selectively translated axially to mesh with each of a first gear and a second gear. The first gear is fixed for common rotation with the input member. The second gear is fixed for common rotation with the output member to achieve the reverse gear ratio between the input and output members. 
         [0008]    The planar gear set has a third gear in mesh with a fourth gear. The third gear is rotatably supported by the output member and the fourth gear coupled for common rotation with the input member. The third gear is selectively coupled to the output member through axial movement of a synchronizer to achieve one of the plurality of forward gear ratios between the input and output members. 
         [0009]    The first shift linkage member has a synchronizer portion and a fork portion. The synchronizer portion is engaged for common axial movement with the synchronizer. 
         [0010]    The intermediate linkage member has a shift linkage portion, a reverse idler gear portion, and a partial engagement cam portion. The intermediate linkage member is selectively translated in an axial direction and a rotational direction. 
         [0011]    The partial engagement cam portion of the intermediate linkage member contacts and urges the fork portion of the shift linkage member to partially engage the synchronizer and the output member with the third gear. 
         [0012]    In another example of the present invention, the cam portion of the intermediate linkage member contacts the fork portion of the shift linkage member prior to the reverse idler gear portion of the intermediate linkage member rotates and engages the idler member to mesh the reverse idler gear with the first and second gears. 
         [0013]    In yet another example of the present invention, the planar gear set achieves an intermediate gear ratio when the third gear is engaged for common rotation with the input member. 
         [0014]    In yet another example of the present invention, the planar gear set achieves one of a third and fourth gear ratio when the third gear is engaged for common rotation with the input member. 
         [0015]    In yet another example of the present invention, the shift linkage includes a cam contact portion that extends from the fork portion to contact the cam portion of the intermediate linkage member. 
         [0016]    In yet another example of the present invention, the cam contact portion includes a resilient ball mechanism to contact the cam portion of the intermediate linkage member. 
         [0017]    In yet another example of the present invention, the cam portion of the intermediate linkage member includes a partial engagement profile that prevents synchronizer clash with the third gear. 
         [0018]    In yet another example of the present invention, the transmission includes a second shift linkage member having an idler gear fork and an elongated member. The idler gear fork is engaged for common axial movement with the idler gear. The elongated member is fixed to the idler gear fork. The elongated member includes a notch that is selectively engaged by the reverse idler gear portion of the intermediate linkage member. 
         [0019]    Further objects, aspects and advantages of the present disclosure will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
     
    
     
       DRAWINGS 
         [0020]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0021]      FIG. 1  is a perspective view of a transmission according to the present disclosure; 
           [0022]      FIG. 2  is plan view of a shift fork and intermediate shaft assembly according to the present disclosure; 
           [0023]      FIG. 3  is a detailed plan view of a shift fork and intermediate lever assembly according to the present disclosure; 
           [0024]      FIG. 4  is a perspective view of a shift fork and intermediate shaft assembly according to the present disclosure; 
           [0025]      FIG. 5  is a close-up perspective view of a shift fork assembly according to the present disclosure; 
           [0026]      FIG. 6A  is a plan view of a shift fork and intermediate lever assembly in a first position according to the present disclosure; 
           [0027]      FIG. 6B  is a plan view of a shift fork and intermediate lever assembly in a second position according to the present disclosure; 
           [0028]      FIG. 6C  is a plan view of a shift fork and intermediate lever assembly in a third position according to the present disclosure; and 
           [0029]      FIG. 6D  is a plan view of a shift fork and intermediate lever assembly in a fourth position according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0031]    Referring to the drawings, wherein like reference numbers refer to like components, in  FIG. 1  a perspective view of a partial transmission  10  of the present invention is illustrated. The transmission  10  includes an input shaft  12 , a main shaft or output shaft  14  and an idler shaft  16  each supported by a housing  18 . The input shaft  12  is connected to, for example, an engine output shaft (not shown) and the main shaft  14  is connected to, for example, a vehicle drive shaft (not shown) that provides torque to a drive wheel of the vehicle. The input and main shafts  12 ,  14  rotatably support a plurality of gears that intermesh to form a plurality of gear sets  15 . A plurality of sleeves and synchronizers  17  is selectively manipulated to achieve a desired forward gear ratio between the input shaft  12  and the main shaft  14 . For example, to achieve a forward gear ratio, one of the plurality of sleeves and synchronizers  17  is engaged to couple a gear from one of the gear sets  15  to one of the input shaft  12  and the main shaft  14  in order to transfer torque from the input shaft  12  to the main shaft  14 . 
         [0032]    The idler shaft  16  is fixed securely with the housing  18  and supports an idler gear assembly  20 . The idler gear assembly  20  is capable of selective movement along the idler shaft  16  to engage a reverse gear or member  22  of the input shaft  12  and a sleeve gear or member  24  on the main shaft  14 . When a reverse gear ratio is desired, the idler gear assembly  20  meshes independently with the reverse gear  22  that is engaged with the input shaft  12  and the sleeve gear  24  that is engaged with the main shaft  14 . The engaged idler gear assembly  20  reverses the direction of the sleeve gear  24  of the main shaft  14  and therefore reverses the direction of rotation of the drive shaft of the vehicle. For example, the idler gear assembly  20  is manipulated by a shift fork linkage  26  that includes a first end  26 A secured to a reverse shaft or member  28  and a second end  26 B that engages and moves the idler gear assembly  20  axially along the idler shaft  16 . However, other methods or mechanisms of manipulating the idler gear assembly  20  may be employed without departing from the scope of the present invention. 
         [0033]    Referring now to  FIGS. 2 and 5  with continuing reference to  FIG. 1 , an example of a shift fork and intermediate lever assembly is illustrated and will now be described. For example, the shift fork and intermediate lever assembly  30  is shown fully in  FIG. 2  and partially in  FIG. 1 . The assembly  30  includes a first and second gear shift fork  32 , a third and fourth gear shift fork  34 , a fifth and sixth gear shift fork  36 , and an intermediate lever  38  (shown in  FIG. 2 ). The intermediate lever  38  includes a shift fork actuator portion  40 , a reverse idler gear actuator portion  42 , and a partial engagement cam  44  and is capable of axial movement in a first and second direction D 1 , D 2  and rotational movement in a first and second rotational direction R 1 , R 2 . The partial engagement cam  44  has a profile shape including ramping portions  44 A and an engagement portion  44 B. Each of the shift forks  32 ,  34 ,  36  include a fork portion  32 A,  34 A,  36 A having a first and second finger or prong  32 B,  32 C,  34 B,  34 C,  36 B,  36 C extending from the fork portion. Each first finger  32 B,  34 B,  36 B has a gear surface  32 D,  34 D,  36 D for individually engaging the shift fork actuator portion  40  of the intermediate lever  38  when the intermediate lever is rotated in the first rotational direction R 1 . Each second finger  32 C,  34 C,  36 C has a gear surface  32 E,  34 E,  36 E opposite the gear surface  32 D,  34 D,  36 D of the first finger  32 B,  34 B,  36 B, respectively, for individually engaging the shift fork actuator portion  40  of the intermediate lever  38  when the intermediate lever is rotated in the second rotational direction R 2 . For example, the fork portion  32 A of the first and second shift fork  32  includes a first finger  32 B having a first gear surface  32 C and a second finger  32 D having a second gear surface  32 E opposing the first gear surface  32 C. The fork portion  34 A of the third and fourth shift fork  34  includes a first finger  34 B having a third gear surface  34 C and a second finger  34 D having a fourth gear surface  32 E opposing the third gear surface  34 C. The fork portion  36 A of the fifth and sixth shift fork  36  includes a first finger  36 B having a fifth gear surface  36 C and a second finger  36 D having a sixth gear surface  36 E opposing the fifth gear surface  34 C. As the intermediate lever is manipulated in the first and second directions D 1 , D 2  the shift fork actuator portion  40  passes between the gear surfaces  32 D,  3 E,  34 D,  34 E,  36 D,  36 E until the shift fork actuator portion  40  arrives at the desired gear shift fork  32 ,  34 ,  36 . The lever is then manipulated in the first or second rotational direction R 1 , R 2  depending on the desired gear ratio and the shift fork actuator portion  40  is subsequently rotated into the desired gear surface  32 D,  3 E,  34 D,  34 E,  36 D,  36 E engaging the desired shift fork  32 ,  34 ,  36  and thus synchronizing the desired gear with the output shaft  14 . 
         [0034]    Referring now to  FIGS. 3 and 4  with continued reference to  FIG. 2 , the third and fourth gear shift fork  34  also includes a partial engagement lever  46  extending from the first finger  34 B of the fork portion  34 A. The partial engagement lever  46  has a first end  46 A fixedly attached to the first finger  34 B and a cam follower portion  48  disposed on a second end  46 B. The cam follower portion  48  opposes the partial engagement cam  44  when the partial engagement cam is in a neutral position or not rotated in either the first or second rotational directions R 1 , R 2 . The cam follower portion  48  includes a spring loaded ball  48 A that follows the profile of the partial engagement cam  44  when the intermediate lever  38  translates in the first and second directions D 1 , D 2 . 
         [0035]    Referring now to  FIGS. 6A-6D  with continuing reference to  FIGS. 2-4 , the intermediate lever  38  and third and fourth gear shift fork  34  is illustrated and will now be described. The intermediate lever  38  is capable of being moved to each of four positions. In a first position P 1 , the intermediate lever  38  is manipulated so that the shift fork actuator portion  40  is disposed between the fifth gear and sixth gear surfaces  36 D,  36 E of the fifth and sixth gear fork  36 . In a second position P 2 , the intermediate lever  38  is manipulated so that the shift fork actuator portion  40  is disposed between the third gear and fourth gear surfaces  34 D,  34 E of the third and fourth gear fork  34 . In a third position P 3 , the intermediate lever  38  is manipulated so that the shift fork actuator portion  40  is disposed between the first gear and second gear surfaces  32 D,  32 E of the first and second gear fork  34 . In a fourth position P 4 , the cam follower portion  48  of the third and fourth gear shift for  34  is positioned in contact with the an engagement portion  44 B of the partial engagement cam  44  and the shift fork actuator portion  40  is disposed below the first and second gear fork  34 . In a fifth position P 5 , the intermediate lever  38  is manipulated so that the reverse idler gear actuator portion  42  is engaged with the a reverse shaft or member  28 . As the intermediate lever  38  translates from the fourth position P 4  to the fifth position P 5 , the cam follower portion  48  engages the partial engagement cam  44 , the third and fourth gear shift fork  34  translates laterally to engage the third and fourth gear synchronizer with the third gear, and thus the output shaft  14  to reduce the speed of the input shaft  12  prior to the meshing of the reverse idler gear with the output shaft  14  which is approximately a first gear ratio thus making the synchronization of the reverse idler gear with the output shaft  14  smoother by avoiding gear clash from high speed synchronization. 
         [0036]    The description of the disclosure is merely exemplary in nature and variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.