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SYSTEMS OPERATION
3. Modulation action
Upon prefihling the forward clutch piston cham
ber, differential valve 7 is returned to its pressur~
regulating position for maintaining the difference
between the 1 st-speed clutch pressure and forward
clutch pressure at constantlevel (2kgf/cm2(28 psi)
[0.2 MPaJ) and, at the same time, accumulator
valve 1 starts moving to the left to cover main
port 2.
Then, only the oil metered by main oii~Ice 5
flows into the 1st-speed clutch circuit to move
accumulator valve 1 slowly and to increase both
forward and 1st-speed clutch pressures gradu
ally. This is called "modulation action."
Since the speed clutch pressure is always higher
than the directional clutch pressure, the 1st-
speed clutch and forward clutch are engaged in
that sequence. This means that shock produced
during shifting is arrested by the forward clutch.
Both forward and 1st-speed clutches are en
gaged during this modulation action to insure
smooth shifting.
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