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In one aspect, the invention is directed to a belt tensioner for tensioning a belt, comprising a pivot shaft that is fixedly mountable with respect to an engine block of an engine, a tensioner arm rotatably mounted to the pivot shaft for pivoting about a tensioner arm axis in a first direction and i

In one aspect, the invention is directed to a belt tensioner for tensioning a belt, comprising a pivot shaft that is fixedly mountable with respect to an engine block of an engine, a tensioner arm rotatably mounted to the pivot shaft for pivoting about a tensioner arm axis in a first direction and in an opposing second direction, a pulley rotatably mounted to the tensioner arm for rotation about a pulley axis, and a tensioner spring positioned to bias the tensioner arm in the first direction, wherein the tensioner spring has a first end and a second end, wherein the first end is engaged with the tensioner arm, and a micro adjustment mechanism that is operatively connected to control the position of the second end of the tensioner spring so as to control the tension in the tensioner spring.

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1. A belt tensioner for tensioning a belt, comprising: a pivot shaft that is adapted to be fixedly mountable with respect to an engine block of an engine;a tensioner arm rotatably mounted to the pivot shaft for pivoting about a tensioner arm axis between a free arm stop position and a load stop posi

1. A belt tensioner for tensioning a belt, comprising: a pivot shaft that is adapted to be fixedly mountable with respect to an engine block of an engine;a tensioner arm rotatably mounted to the pivot shaft for pivoting about a tensioner arm axis between a free arm stop position and a load stop position;a pulley rotatably mounted to the tensioner arm for rotation about a pulley axis; anda tensioner spring biasing the tensioner arm towards the free arm stop position, wherein the tensioner spring has a first end and a second end, wherein the first end is engaged with the tensioner arm; anda micro adjustment mechanism that is operable for directly controlling the position of the second end of the tensioner spring relative to the first end of the tensioner spring to thereby control the tension in the tensioner spring, the micro adjustment mechanism having an output member that is directly mounted to the second end of the tensioner spring such that movement of the output member causes corresponding movement of the second end of the tensioner spring relative to the pivot shaft. 2. The belt tensioner of claim 1, further comprising a free arm stop and a load stop, wherein the free arm stop and the load stop control the free arm stop position and the load stop position respectively of the tensioner arm, wherein the micro adjustment mechanism controls the amount of angular range available between the tensioner arm and the free arm stop position and between the tensioner arm and the load stop position. 3. The belt tensioner of claim 1, wherein the micro adjustment mechanism includes a linear actuator that includes an actuation member that engages the second end of the tensioner spring. 4. The belt tensioner of claim 3, wherein the actuation member is a piston that is positioned in a fluid chamber that has a first end and a first fluid port at the first end for receiving fluid at a first selectable pressure for urging the piston in a first direction and wherein the micro adjustment mechanism further includes a piston biasing member positioned for biasing the actuation member in a second direction that is opposed to the first direction. 5. The belt tensioner of claim 3, wherein the actuation member is a piston that is positioned in a fluid chamber that has a first end and a first fluid port at the first end for receiving fluid at a first selectable pressure, and wherein the fluid chamber has a second end and has a second fluid port at the second end for receiving fluid at a second selectable pressure, wherein the piston is movable as a result of the pressures of the fluid at the first and second ends between a first position and a second position, the first and second positions corresponding to first and second positions of the second end of the tensioner spring. 6. The belt tensioner of claim 5, wherein the fluid chamber further includes a biasing structure for biasing the piston towards a third position that is between the first and second positions, and which corresponds to a third position of the second end of the tensioner spring. 7. The belt tensioner of claim 3, wherein the linear actuator is a solenoid that is connectable to an electrical source. 8. The belt tensioner of claim 3, wherein the rotary actuator is a solenoid that is connectable to an electrical source. 9. The belt tensioner of claim 1, further comprising a controller, wherein the controller is operatively connected to the micro adjustment mechanism and is configured to adjust the position of the second end of the spring based on at least one parameter. 10. The belt tensioner of claim 1, wherein the at least one parameter includes the temperature of the engine block. 11. The belt tensioner of claim 1, wherein the at least one parameter includes the tension in the belt. 12. The belt tensioner of claim 1, further comprising a base plate that is connected to the pivot shaft, wherein the base plate is engageable with a base plate locking structure on the engine block to fix the rotational position of the base plate relative to the engine block. 13. The belt tensioner of claim 1, further comprising a fail-safe spring limit structure that is connectable to the engine block at a selected position to prevent the movement of the second end of the tensioner spring therepast in the event of a failure of the micro adjustment mechanism. 14. The belt tensioner of claim 1, further comprising a macro-adjustment mechanism operatively connected to control the position of the tensioner arm axis. 15. The belt tensioner of claim 14, wherein the pivot shaft has a fastener aperture that extends along a pivot shaft rotation axis, and that is configured for the pass-through of a pivot shaft fastener, and wherein the pivot shaft has a tensioner arm mounting surface about which the tensioner arm is rotatably mounted for rotation along a tensioner arm pivot axis, wherein the tensioner arm pivot axis and the pivot shaft rotation axis are spaced from each other, and wherein the position of the fastener aperture and the position of the tensioner arm mounting surface are included in the macro-adjustment mechanism. 16. The belt tensioner of claim 1, wherein the micro adjustment mechanism includes an actuation member and a motor, wherein the motor is stoppable in at least three positions of the actuation member. 17. The belt tensioner of claim 16 wherein the motor is operatively connected to a worm, and the worm has a selected flight profile to prevent backdriving of the motor, and wherein the worm is operatively connected to the actuation member. 18. A method of tensioning a belt on an engine, comprising: a) providing a tensioner that includes a pivot shaft, a tensioner arm rotatably mounted to the pivot shaft for pivoting about a tensioner arm axis between a free arm stop position and a load stop position, a pulley rotatably mounted to the tensioner arm for rotation about a pulley axis, a tensioner spring positioned to bias the tensioner arm towards the free arm stop position, wherein the tensioner spring has a first end and a second end, wherein the first end is engaged with the tensioner arm;b) mounting the tensioner to an engine block of the engine in such a way that the tensioner arm axis is fixed and such that the pulley is engaged with the belt; andc) moving the second end of the tensioner spring relative to the first end of the tensioner spring while keeping the tensioner arm axis fixed, to adjust the biasing force with which the tensioner arm engages the belt;wherein step c) includes determining the temperature of the engine block, and moving the second end of the tensioner spring based on the temperature of the engine block; and wherein the tensioner further includes a micro adjustment mechanism that is operatively connected to control the position of the second end of the tensioner spring, wherein the micro adjustment mechanism includes an actuator that includes an actuation member that engages the second end of the tensioner spring. 19. A method as claimed in claim 18, further comprising a controller that is operatively connected to the micro adjustment mechanism through which the controller is configured to adjust the position of the second end of the spring. 20. A method as claimed in claim 19, further comprising adding fuel to the engine, starting the engine and operating the engine by combusting the fuel, and carrying out step c) during operation of the engine.