Subaru 2002 Impreza Service Manual page 147

AUTOMATIC BELT TENSION ADJUSTER
Mechanical
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Timing belt tensioning action
When the belt becomes slack, the adjuster rod is pushed upward by the return spring. The oil in
the reservoir chamber, which is pressurized by the plunger spring to a certain level, pushes open
the check ball and flows into the oil pressure chamber to keep the pressure constant.
The thrust force F resulting from extension of the adjuster rod applies a counterclockwise torque
to the tensioner bracket, which causes the belt tension pulley at its end to turn in the same direc-
tion. This applies tensioning pressure Pb to the timing belt.
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Timing belt tension balancing action
When the belt tension pulley is pushed against the timing belt with pressure Pb, reaction force Tb
of the timing belt generates the reaction force P at the point on which the adjustor rod force is act-
ing.
This force P pushes the adjuster rod until it balances with the sum of the thrust force F and the
pressure of the oil in the oil pressure chamber. Therefore, the timing belt tension is kept constant.
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Overtension correction action
If the tension of the timing belt increases excessively, the force P becomes larger than the thrust
force F and silicone oil is returned from the oil pressure chamber to the reservoir chamber little by
little until the force P balances again with the thrust force F. Thus the timing belt tension is main-
tained at the specified level at all times.
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