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AUTO TWO SPEED CHANGE MECHANISM
Ps : Pilot pressure
PM1 :Motor pressure
Pin :Inlet pressure
PM2 :Motor pressure
Am :Motor inlet pressure
Ap : Pilot pressure area
High speed position
To chamber of
two speed piston
Automatic two speed (Motor pressure is low)
4)
R35Z72TM11
Auto two speed control mechanism consists of two spools and spring. This valve automatically
changes motor displacement in portion to motor pressure. This valve works while the pilot port Ps
is pressurized.
Motor pressure is low
The motor displacement is small (high speed displacement) as shown in the figure.
When the two speed spool is on the right position, motor pressure PM1 and PM2 are connected
to each side of chamber of two speed piston. So swash plate is moved to high speed position by
two speed piston and motor displacement is kept on high speed position.
Pilot pressure is applied on the area Ap when Ps port is pressurized. Then the pressure of Ps
pushes the spool to the right direction on the figure. At the same time, motor inlet pressure is
applied on the area Am. So, the spool is also applied to the left direction by Am pressure.
According to above, if the motor pressure is lower and keep the following condition, the spool stay
on the right position.
Ps
Ý
Dp > Am
Ý
Ý
Pin + Kx
Kx : the force of spring
Motor pressure is low : (Ap
Ý
Ps) > (Am
Ý
Pin+Kx)
((1)
