Active tensioner

1. A tensioner comprising:

an electric actuator;

a force imparting member engaged with a lever arm;

a pulley journalled to the lever arm, the pulley engagable with a belt;

the force imparting member engaged with the electric actuator whereby the force imparting member is axially moveable by the electric actuator;

a load sensor coaxially engaged with the force imparting member, the load sensor detecting and transmitting a load signal to a controller; and

the controller using the load signal to control a force imparting member position.

2. The tensioner as in claim 1 , wherein:

the force imparting member comprises a lead screw;

the lead screw rotatably engaged with a threaded collar.

3. The tensioner as in claim 1 , wherein the electric actuator comprises an electric motor.

4. The tensioner as in claim 1 , wherein the force imparting member is engaged with the electric actuator through a gear transmission.

5. The tensioner as in claim 1 , wherein:

the load sensor further comprises a bore, the load sensor coaxially engaged with the force imparting member through the bore.

6. The tensioner as in claim 1 , wherein the lever arm is pivotally engaged with a mounting surface.

7. A system for adjusting a tension of an endless belt comprising:

a tensioner having a toroid load sensor and a pulley journalled to a lever arm, the pulley in contact with an endless belt for applying a belt load to the endless belt;

the toroid load sensor detecting a belt load and transmitting a belt load signal to a controller; and

the controller using the belt load signal to select a pulley position for a belt load.

8. The system as in claim 7 , wherein the tensioner further comprises:

an axially moveable member moveable by an electric actuator;

the lever arm engaged with the axially moveable member; and

the toroid load sensor coaxially engaged with the axially removeable member.

9. The system as in claim 8 , wherein:

the electric actuator further comprises an electric motor, the electric motor engaged with the axially moveable member through a gear reduction transmission.

10. A method of controlling a belt load comprising the steps of:

engaging a belt with a pulley, the pulley journalled to a pivoting lever arm;

positioning the lever arm for a belt load;

using a toroid load cell to detect a belt load;

selecting a belt load value corresponding to a desired belt load;

comparing the belt load to the belt load value;

determining a new lever arm position based upon said belt load value; and

moving the lever arm to the new lever arm position to set the belt load to the belt load value.

11. The method as in claim 10 comprising:

detecting an engine parameter; and

selecting a belt load value with respect to the engine parameter.

12. A method of tensioning a belt comprising the steps of:

engaging a tensioner having a toroid load sensor with a belt;

adjusting the tensioner position to impart a belt load to the belt;

detecting the belt load with the toroid load sensor;

comparing the detected belt load with a desired belt load; and

adjusting the tensioner position with a controller until the detected belt load is substantially equal to the desired belt load.

13. The method as in claim 12 comprising the steps of:

selecting the desired belt load with respect to an engine operating parameter.

14. The method as in claim 13 comprising the step of:

selecting the desired belt load with respect to an engine operating speed.

15. The method as in claim 13 comprising the step of:

detecting an engine operating temperature;

selecting the desired belt load with respect to the engine operating temperature.

16. The method as in claim 15 comprising the step of storing an engine temperature history in a controller memory.

17. The method as in claim 12 comprising the step of selecting the desired belt load from a look up table.

18. The method as in claim 12 comprising the steps of:

using a reference tooth on the belt;

detecting each passage of the reference tooth with a sensor to determine cumulative belt cycles;

storing the cumulative belt cycles in a memory for analysis of a belt fatigue condition; and

informing a user.

19. A method of computing a belt modulus comprising the steps of:

engaging a tensioner having a load sensor with a belt;

adjusting the tensioner to a first position (P 1 ) to impart a first belt load (L 1 ) to the belt;

detecting the first belt load (L 2 ) with the load sensor;

adjusting the tensioner to a second position (P 2 ) to impart a second belt load (L 2 ) to the belt;

detecting the second belt load (L 2 ) with the load sensor; and

computing a belt modulus using (L 1 ), (L 2 ), (P 1 ), (P 2 ).

20. The method as in claim 19 further comprising the steps of:

storing the calculated belt modulus values in a controller memory;

comparing the calculated belt modulus values to identify a belt modulus trend; and

informing a user.

21. The method as in claim 19 comprising the steps of:

using a first limit switch to detect the first position (P 1 ); and

using a second limit switch to detect the second position (P 2 ).

22. The method as in claim 19 comprising the steps of:

adjusting the tensioner by driving the tensioner with a fixed duty cycle for a first duration to position (P 1 ); and

adjusting the tensioner by driving the tensioner with a fixed duty cycle for a second duration to position (P 2 ).

23. A method of computing a belt modulus comprising the steps of:

engaging a tensioner having a load sensor with a belt;

adjusting the tensioner to impart a first belt load (L 1 );

detecting the first belt position (P 1 ) with a limit switch;

adjusting the tensioner to impart a second belt load (L 2 );

detecting the second belt position (P 2 ) with a limit switch; and

computing a belt modulus using (L 1 ), (L 2 ), (P 1 ), (P 2 ).

24. The method as in claim 23 further comprising the steps of:

storing the calculated belt modulus values in a controller memory;

comparing the calculated belt modulus values to identity a belt modulus trend; and

informing a user.

25. A tensioner comprising:

an electric actuator;

a lead screw engaged with a lever arm;

a pulley engagable with a belt, the pulley journalled to the lever arm;

the lead screw engaged with the electric actuator whereby the lead screw is inoveable by the electric actuator;

a load sensor coaxially engaged with the lead screw, the load sensor transmitting a load signal to a controller; and

the controller using the load signal to control a lead screw position.

26. The tensioner as in claim 25 , wherein the electric actuator comprises an electric motor.

27. The tensioner as in claim 25 , wherein the lead screw is engaged with the electric actuator by a gear transmission.

28. The tensioner as in claim 25 , wherein:

the load sensor comprises a toroid load cell having a bore;

the toroid load cell coaxially engaged with the lead screw though the bore.

29. The tensioner as in claim 25 , wherein the lever arm is pivotally engaged with a mounting surface.

30. The tensioner as in claim 25 , wherein the lead screw is rotatably engaged with a collar.