Function Theory; Behavior Of Proportional Valve - Kubota KX91-3a Workshop Manual

WSM Minor Change

3. Function theory

Behavior of proportional valve

Balance of proportional valve forces
sp1
Proportional solenoid
magnetic force
Behavior of solenoid proportional valve
Definitions of values
F : Solenoid magnetic force generated according to current
sol
F
sol
F : Solenoid's spring load
sp1
F : Valve's spring load (constant during pressure control)
sp2
F : Pressure applied by setup area difference
p
F = A x Pa (A and Pa are setup area difference and pressure at port A, respectively.)
p
P: Primary pilot pressure from the pilot pump controlled by the unload relief valve
P : Secondary pilot pressure to control the main control valve spool
a
Balance of forces
The balance of forces for the valve spool (see above) is expressed like this.
F
sol
When the left term is greater, the spool moves rightward and ports P and A open one after the
other.
When the right term is greater, the spool moves leftward and ports A and P open one after the
other.
The above expression is rearranged as follows.
F
sol
P =
a
Transfer
spring
= C1 x I (C1 and I are solenoid's intrinsic constant and current, respectively.)
+ F = P A + F
sp1 a sp2
+ F - F = P A
sp1 sp2 a
F + F - F
sol sp1 sp2
A
P A
sp2
P
a
Reducing valve spool
hydraulic pressure force
II - 53
II Service Engineering Section
T
A
Pressure receiving
area difference