Service Manuals, User Guides, Schematic Diagrams or docs for : . Car Manuals Subaru Impreza 2001-2002.2004-2007 Approved Subaru Impreza 2004 WRX STi 08. MECHANISM AND FUNCTION 15. MECHANICAL 03. Automatic Belt Tension Adjuster
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W1860BE.book Page 4 Tuesday, January 28, 2003 11:01 PM
AUTOMATIC BELT TENSION ADJUSTER
MECHANICAL
3. Automatic Belt Tension Adjuster
The automatic belt tension adjuster consists of a tensioner unit and a bracket. It maintains the timing
belt tension automatically at a specified level to enable the belt to transmit power correctly, reduce
operating noise and increase the life of the belt.
The cylinder of the tensioner unit incorporates an adjuster rod, wear ring, plunger spring, return
spring, check ball and silicone oil.
The automatic belt tension adjuster gives tension to the belt by a levering action which is produced
by the push force of the tensioner unit's adjuster rod. It operates in the process detailed below.
P
(1)
(12)
(2)
(11)
(3)
F
(4)
(5)
(13)
(6)
(7)
Pb (8)
(10)
(9)
Tb
ME-00314
(1) Oil seal (8) Plunger spring
(2) Wear ring (9) Check ball
(3) Oil reservoir chamber (10) Timing belt
(4) Return spring (11) Belt tension pulley
(5) Adjuster rod (12) Tensioner bracket
(6) Plunger (13) Cylinder
(7) Oil pressure chamber
ME(H4DOTC)-4
W1860BE.book Page 5 Tuesday, January 28, 2003 11:01 PM
AUTOMATIC BELT TENSION ADJUSTER
MECHANICAL
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 direction.
This applies tensioning pressure Pb to the timing belt.
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 acting.
This force P pushes the adjuster rod until it balances with the sum of the thrust force F and the pres-
sure of the oil in the oil pressure chamber. Therefore, the timing belt tension is kept constant.
Over-tension 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.
ME(H4DOTC)-5
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