Electric drive camshaft phaser with torque rate limit at travel stops

A camshaft phaser for controllably varying the phase relationship between a crankshaft and a camshaft in an internal combustion engine, said camshaft phaser comprising:

• a housing having a bore with a longitudinal axis;
• a harmonic gear drive unit disposed within said housing, said harmonic gear drive unit comprising a circular spline and an axially adjacent dynamic spline, a flexspline disposed within said circular spline and said dynamic spline, a wave generator disposed within said flexspline, and a rotational actuator connectable to said wave generator such that rotation of said wave generator causes relative rotation between said circular spline and said dynamic spline, wherein one of said circular spline and said dynamic spline is fixed to said housing in order to prevent relative rotation therebetween;
• a hub rotatably disposed within said housing axially adjacent to said harmonic gear drive unit and attachable to said camshaft and fixed to the other of said circular spline and said dynamic spline in order to prevent relative rotation therebetween;
• a first stop member rotatable with said circular spline in a one-to-one relationship;
• a second stop member rotatable with said dynamic spline in a one-to-one relationship for contacting said first stop member to limit relative angular travel between said circular spline and said dynamic spline when said camshaft phaser is phasing said camshaft in one of an advance direction and a retard direction;
• and
• a torque absorption means for limiting the rate at which torque is applied from said rotational actuator to said harmonic drive gear unit as said second stop member makes contact with said first stop member.