Power Transfer Units Having Torque Limiting Clutches

Abstract

A power transfer unit is provided with a torque limiting assembly that limits the torque transferred to driveline components when torque peaks occur. The power transfer unit can include, a first shaft, a second output shaft receiving drive torque, a second output shaft, and a torque transfer mechanism. The torque transfer mechanism includes a coupling member and a biasing member. The coupling member is located between a driving member and a driven member and provides selective engagement therebetween when in an engaged position. The driving member and/or the driven member includes a recess therein receiving a portion of the coupling member when in the engaged position. The biasing member urges the coupling member and the driving member and/or driven member into the engaged position.

1 . A power transfer unit, comprising:
 a first rotary member;   a second rotary member;   a drive assembly driven by said first rotary member; and   a torque limiting mechanism drivingly disposed between said drive assembly and said second rotary member, said torque limiting mechanism including a first engagement member driven by said drive assembly, a second engagement member driving said second rotary member, a coupling member and a biasing member, at least one of said first and second engagement members has a plurality of recesses configured to engage said coupling member, said biasing member urging said coupling member into an engaged position relative to said recesses, and wherein said coupling member is removed from one of said recesses when a torque value applied by said first rotary member and said drive assembly to said first engagement member exceeds a torque limit so as to permit said first engagement member to rotate relative to said second engagement member.   
   
   
       2 . The power transfer unit of  claim 1  wherein said drive assembly includes a first sprocket fixed for rotation with said first rotary member, a second sprocket fixed for rotation with said first engagement member, and a chain encircling said first and second sprockets. 
   
   
       3 . The power transfer unit of  claim 1  wherein said first engagement member is rotatably supported on said second rotary member, wherein said second engagement member is fixed for rotation with said second rotary member, and when said first and second engagement members have a common axis of rotation. 
   
   
       4 . The power transfer unit of  claim 3  wherein said biasing member is arranged to exert a biasing force on said coupling member in a radial direction relative to said axis of rotation. 
   
   
       5 . The power transfer unit of  claim 4  wherein said second engagement member has an outer surface having a series of radial protrusions which alternate with said recesses to define a ratchet surface, and wherein said coupling member is a poppet partially disposed within a bore formed in said first engagement member and having an end portion urged by said biasing member into continuous engagement with said ratchet surface. 
   
   
       6 . The power transfer unit of  claim 4  wherein said first engagement member has an inner surface having a series of radial protrusions which alternate with said recesses to define a ratchet surface, and wherein said coupling is a poppet partially disposed within a bore formed in said second engagement member and having an end portion urged by said biasing member into continuous engagement with said ratchet surface. 
   
   
       7 . The power transfer unit of  claim 3  wherein said biasing member is arranged to exert a biasing force on said coupling member in a direction generally parallel to said axis of rotation. 
   
   
       8 . The power transfer unit of  claim 7  wherein said first engagement member has a radially-extending flange ring defining a plurality of circumferentially aligned and axially extending first ratchet lugs which alternate with a plurality of first recesses to define a first ratchet surface, wherein said second engagement member has a radially-extending ring segment defining a plurality of circumferentially aligned and axially extending second ratchet lugs which alternate with a plurality of second recesses to define a second ratchet surface, wherein said coupling member is a plurality of rollers disposed in aligned pairs of said first and second recesses, and wherein said biasing member urges said second engagement member toward said first engagement member. 
   
   
       9 . The power transfer unit of  claim 8  wherein said torque limiting mechanism further includes a third engagement member fixed for rotation with said second rotary member and located adjacent to said second engagement member, and wherein said biasing member includes a spring disposed between said second and third engagement members. 
   
   
       10 . The power transfer unit of  claim 9  wherein said torque limiting mechanism further includes an adjustment member operable for adjusting the position of said third engagement member relative to said second engagement member so as to vary the biasing force exerted by said spring on second engagement member relative to said first engagement member. 
   
   
       11 . The power transfer unit of  claim 7  wherein said second engagement member has a series of radial protrusions which alternate with said recesses to define a ratchet surface, and wherein said coupling member is a poppet partially disposed within a bore formed in said first engagement member and having an end portion urged by said biasing member into continuous engagement with said ratchet surface. 
   
   
       12 . The power transfer unit of  claim 7  wherein said first engagement member has a series of radial protrusions which alternate with said recesses to define a ratchet surface, and wherein said coupling is a poppet partially disposed within a bore formed in said second engagement member and having an end portion urged by said biasing member into continuous engagement with said ratchet surface. 
   
   
       13 . The power transfer unit of  claim 1  wherein said torque limiting mechanism includes an adjustment member operable for adjusting a biasing force exerted by said biasing member on said coupling member. 
   
   
       14 . The power transfer unit of  claim 1  wherein said first rotary member is coupled to a first driveline of a motor vehicle and said second rotary member is coupled to a second driveline of the motor vehicle. 
   
   
       15 . The power transfer unit of  claim 14  wherein said first driveline is a rear driveline and said second driveline is a first driveline. 
   
   
       16 . A transfer case comprising:
 a first shaft;   a second shaft; and   a torque limiting mechanism including a driving member supported for rotation on said second shaft and driven by said first shaft, a driven member driven by said second shaft, a coupling member and a biasing member, at least one of said driving member and said driven member having a ratchet surface engaged by said coupling member, said biasing member urging said coupling member in engagement with said ratchet surface, such that said coupling member is permitted to ratchet over said ratchet surface when a torque level applied by said first shaft to said torque limiting mechanism exceeds a torque limit.   
   
   
       17 . A transfer case comprising:
 an input shaft;   a first output shaft driven by said input shaft;   a second output shaft driven by one of said input shaft and said first output shaft; and   a torque limiting mechanism drivingly disposed between said first output shaft and said second output shaft and including a coupling member and a biasing member, at least one of a driving member and a driven member having a ratchet surface engaged by said coupling member, said biasing member urging said coupling member into engagement with said ratchet surface such that said coupling member is permitted to ratchet over said ratchet surface when a torque level applied by said first output shaft to said torque limiting mechanism exceeds a torque limit.   
   
   
       18 . The transfer case of  claim 17  wherein said coupling member is fixed for rotation with the other of said driving member and said driven member. 
   
   
       19 . A power transfer unit comprising:
 a first shaft;   a second shaft; and   a torque limiting mechanism drivingly disposed between said first shaft and said second shaft and including a coupling member and a biasing member, at least one of a driving member and a driven member having a ratchet surface defined by a plurality of alternating recesses and protrusions, said biasing member operable to urge said coupling member into engagement with one of said recesses, and wherein said coupling member is removed from said recess when a torque level applied by said first shaft to said torque limiting mechanism exceeds a torque limit.   
   
   
       20 . The power transfer unit of  claim 19  wherein said coupling member is fixed for rotation with one of said driving member and said driven member, the other of said driving member and said driven member having said ratchet surface.