Engine crankshaft isolator assembly

1. A crankshaft isolator assembly comprising:

a hub adapted to be fixed for rotation with an engine crankshaft;

a crankshaft isolator pulley coupled to the hub and adapted to engage a belt engaged with an accessory drive system; and

a mechanical clutch engaged with the hub and the crankshaft isolator pulley and fixing the hub for rotation with the crankshaft isolator pulley during a first operating condition and allowing relative rotation between the hub and the crankshaft isolator pulley during a second operating condition, wherein the crankshaft isolator pulley is rotatable relative to the hub in a first rotational direction until the mechanical clutch fixes the hub for rotation with the crankshaft isolator pulley in first rotational direction, wherein the mechanical clutch allows for at least 5 degrees of rotation of the crankshaft isolator pulley in the first rotational direction relative to the hub before the mechanical clutch fixes the hub for rotation with the crankshaft isolator pulley in first rotational direction.

2. The crankshaft isolator assembly of claim 1 , further comprising a torsional spring engaged with the hub and the crankshaft isolator pulley, the torsional spring transmitting rotation of the hub to the crankshaft isolator pulley while allowing limited relative rotation between the hub and the crankshaft isolator pulley.

3. The crankshaft isolator assembly of claim 2 , wherein the crankshaft isolator pulley is rotatable relative to the hub by at least 10 degrees in first and second rotational directions opposite one another during the second operating condition.

4. The crankshaft isolator assembly of claim 1 , wherein the mechanical clutch includes a clutch actuator fixed for rotation with one of the hub and the crankshaft isolator pulley and a clutch stop defined on the other of the hub and the crankshaft isolator pulley, the hub being fixed for rotation with the crankshaft isolator pulley during the first operating condition when the clutch actuator abuts the clutch stop.

5. The crankshaft isolator assembly of claim 4 , further comprising a torsional spring engaged with the hub and the crankshaft isolator pulley, the torsional spring transmitting rotation of the hub to the crankshaft isolator pulley while allowing limited relative rotation between the hub and the crankshaft isolator pulley, the crankshaft isolator pulley defining a cavity forming an inner circumferential surface defining the clutch stop, the clutch actuator being fixed for rotation with the hub and having a biasing member forcing the clutch actuator in an outward radial direction and into engagement with the inner circumferential surface of the crankshaft isolator pulley.

6. An engine assembly comprising:

an engine structure;

a crankshaft rotationally supported on the engine structure;

a crankshaft isolator assembly including:

a hub fixed for rotation with the crankshaft;

a crankshaft isolator pulley coupled to the hub; and

a mechanical clutch engaged with the hub and the crankshaft isolator pulley and fixing the hub for rotation with the crankshaft isolator pulley during a first operating condition and allowing relative rotation between the hub and the crankshaft isolator pulley during a second operating condition;

a belt engaged with the crankshaft isolator pulley and an accessory drive system; and

a motor that forms a starter including a motor pulley engaged with the belt, wherein the first operating condition includes engine start-up with the motor powering rotation of the crankshaft via the belt, wherein the crankshaft isolator pulley is rotated relative to the hub in a first rotational direction until the mechanical clutch fixes the hub for rotation with the crankshaft isolator pulley, wherein the mechanical clutch allows for at least 5 degrees of rotation of the crankshaft isolator pulley in the first rotational direction relative to the hub before the mechanical clutch fixes the hub for rotation with the crankshaft isolator pulley in the first rotational direction.

7. The engine assembly of claim 6 , wherein the second operating condition includes the crankshaft powering rotation of the motor pulley via the belt.

8. The engine assembly of claim 7 , wherein the crankshaft isolator assembly includes a torsional spring engaged with the hub and the crankshaft isolator pulley, the torsional spring transmitting rotation of the hub to the crankshaft isolator pulley while allowing limited relative rotation between the hub and the crankshaft isolator pulley.

9. The engine assembly of claim 8 , wherein the crankshaft isolator pulley is rotatable relative to the hub by at least 10 degrees in first and second rotational directions opposite one another during the second operating condition.

10. The engine assembly of claim 6 , wherein the mechanical clutch includes a clutch actuator fixed for rotation with one of the hub and the crankshaft isolator pulley and a clutch stop defined on the other of the hub and the crankshaft isolator pulley, the hub being fixed for rotation with the crankshaft isolator pulley during the first operating condition when the clutch actuator abuts the clutch stop.

11. The engine assembly of claim 10 , wherein the mechanical clutch includes a torsional spring engaged with the hub and the crankshaft isolator pulley, the torsional spring transmitting rotation of the hub to the crankshaft isolator pulley while allowing limited relative rotation between the hub and the crankshaft isolator pulley, the crankshaft isolator pulley defining a cavity forming an inner circumferential surface defining the clutch stop, the clutch actuator being fixed for rotation with the hub and having a biasing member forcing the clutch actuator in an outward radial direction and into engagement with the inner circumferential surface of the crankshaft isolator pulley.

12. The engine assembly of claim 6 , further comprising a crankshaft damper coupled to the crankshaft and adapted to damp torsional vibrations of the crankshaft during the second operating condition.

13. An engine assembly comprising:

an engine structure;

a crankshaft rotationally supported on the engine structure;

a crankshaft isolator assembly including:

a hub fixed for rotation with the crankshaft and defining a plurality of first spring seats;

a crankshaft isolator pulley coupled to the hub and defining a plurality of second spring seats;

a plurality of torsion spring members each engaged with a corresponding one of the plurality of first spring seats of the hub and with a corresponding one of the plurality of second spring seats of the crankshaft isolator pulley and coupling the hub and the crankshaft isolator pulley for rotation with one another while allowing limited relative rotation between the hub and the crankshaft isolator pulley; and

a mechanical clutch engaged with the hub and the crankshaft isolator pulley and fixing the hub for rotation with the crankshaft isolator pulley during a first operating condition and allowing the limited relative rotation between the hub and the crankshaft isolator pulley during a second operating condition;

a motor that forms a starter including a motor pulley; and

a belt engaged with the crankshaft isolator pulley and the motor pulley.

14. The engine assembly of claim 13 , wherein the first operating condition includes engine start-up with the motor powering rotation of the crankshaft via the belt and the second operating condition includes the crankshaft powering rotation of the motor pulley via the belt.