Tapered roller drive for electric vct phaser

Abstract

An electric phaser for dynamically adjusting a rotational relationship of a camshaft with respect to an engine crankshaft of an internal combustion engine includes an electric motor and a tapered roller drive. The tapered roller drive includes a sun, rollers, a carrier, at least one ring, and at least one load generator providing an axial load. The rollers are maintained in rolling engagement with the sun and the ring without the use of teeth. In some embodiments, the tapered roller drive is based on a fixed-sun design. In other embodiments, the tapered roller drive is based on a split ring design.

1 . An electric phaser for dynamically adjusting a rotational relationship of a camshaft with respect to a crankshaft of an internal combustion engine, the electric phaser comprising:
 an electric motor; and   a fixed sun tapered roller drive comprising:
 a sun driven to rotate around a sun axis by the electric motor, the sun having a sun contact surface having a circular cross section without teeth and tapering with respect to the sun axis; 
 a carrier rotatable around the sun axis and coupled to rotate with the camshaft; 
 a plurality of rollers arranged around the sun, each roller rotatable on a roller axis at a roller angle with respect to the sun axis, each roller having a roller contact surface without teeth in rolling engagement with the sun contact surface, wherein the rollers are rotatably mounted on the carrier to rotate on the roller axes; 
 at least one ring coupled to rotate with the camshaft having a ring contact surface without teeth in rolling engagement with the roller contact surfaces and defining a circular cross sectional interior space; and 
 a load generator applying an axial load to maintain the plurality of rollers in rolling engagement with the sun and the ring; 
   wherein the electric motor is driven at a motor speed to dynamically maintain or adjust the rotational relationship of the camshaft with respect to the crankshaft.   
     
     
         2 . The electric phaser of  claim 1 , wherein the plurality of rollers comprises three rollers. 
     
     
         3 . The electric phaser of  claim 1 , wherein the load generator is a plurality of disc springs. 
     
     
         4 . (canceled) 
     
     
         5 . The electric phaser of  claim 1 , further comprising a friction oil on the roller contact surfaces reducing slip between the roller contact surfaces and the sun contact surface and between the roller contact surfaces and the ring contact surface. 
     
     
         6 . The electric phaser of  claim 1 , wherein the roller angle is selected such that transfer of torque between the sun and the rollers and between the rollers and the ring is optimized. 
     
     
         7 . The electric phaser of  claim 1 , wherein:
 rotation of the sun by the electric motor at a nominal speed to compensate only for slippage between the rollers and the ring maintains a current phasing between the camshaft and the crankshaft;   rotation of the sun by the electric motor at an advancing speed greater than the nominal speed adjusts the phaser in an advancing direction; and   rotation of the sun by the electric motor at a retarding speed less than or in the opposite direction to the nominal speed adjusts the phaser in a retarding direction.   
     
     
         8 . (canceled) 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . A method of dynamically adjusting a rotational relationship of a camshaft with respect to a crankshaft of an internal combustion engine using an electric phaser comprising an electric motor; and a fixed sun tapered roller drive comprising a sun driven to rotate around a sun axis by the electric motor, the sun having a sun contact surface having a circular cross section without teeth and tapering with respect to the sun axis; a carrier coupled to rotate with the camshaft and rotatable around the sun axis; a plurality of rollers arranged around the sun, each roller rotatable on a roller axis at a roller angle with respect to the sun axis, each roller having a roller contact surface without teeth in rolling engagement with the sun contact surface, wherein the rollers are rotatably mounted on the carrier to rotate on the roller axes; and at least one ring driven by the engine crankshaft, the ring having a ring contact surface without teeth in rolling engagement with the roller contact surfaces and defining a circular cross sectional interior space, the method comprising:
 applying an axial load to maintain the sun, the plurality of rollers, and the ring in rolling engagement; and 
 dynamically selecting a motor speed of the electric motor and adjusting the electric motor to the motor speed to dynamically adjust the rotational relationship of the camshaft with respect to the crankshaft. 
 
     
     
         14 . The method of  claim 13 , wherein:
 rotation of the sun by the electric motor at a nominal speed to compensate only for slippage between the rollers and the ring maintains a current phasing between the camshaft and the crankshaft;   rotation of the sun by the electric motor at an advancing speed greater than the nominal speed adjusts the phaser in an advancing direction; and   rotation of the sun by the electric motor at a retarding speed less than or in the opposite direction to the nominal speed adjusts the phaser in a retarding direction.   
     
     
         15 . (canceled)