Toro 07511AA, Руководство по обслуживанию

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traction pedal is pushed, solenoid AB-C2 on the front pump and solenoid CD-C2
on the rear pump are energized.
Front and rear drive axle motors are positive displacement, 2 position axial piston
motors. The 2 position drive motors can operate in either a low speed range or
high speed range. The motors are spring biased to maximum displacement
for low speed and are hydraulically shifted to minimum displacement for high
speed. Solenoid valve (SV1) in the main manifold is energized by the TEC when
the mode selector is set to the H
IGH
S
PEED
A
UTO
position. In high speed auto,
hydraulic flow from solenoid valve (SV1) moves the swash plate in the drive
motor to reduce the motor displacement and increase its potential rpm. The drive
axle motors include a flushing valve that bleeds off a small amount of hydraulic
fluid for cooling the closed-loop traction circuit. The charge circuit replenishes
fluid that is bled from the traction circuit by the flushing valve, and the fluid that
moves through the traction pump case to the tank during normal operation.
Operating pressure on the high pressure side of the closed-loop traction circuit is
determined by the amount of load developed at the drive axle motors. As the
load increases, circuit pressure can increase to the relief valve setting of 33,100
kPa (4800 psi) in either forward or reverse. Traction pressure to each axle can
be viewed while the machine is moving in the forward direction by using the
InfoCenter SERVICE–TRACTION–TRACTION INPUTS FRONT TRACTION and
REAR TRACTION readings. If pressure exceeds the relief setting, fluid flows
through the unseated relief valve to the low pressure side of the closed-loop
traction circuit.
Note: The tandem piston (traction) pump includes a set of 4 bypass valves. The
bypass valves are necessary to allow the machine to be towed a limited distance
if necessary;
Towing the Traction Unit (page 5–4) .
Traction Charge Circuit
The traction pumps and drive axle motors use a small amount of hydraulic fluid
for internal lubrication. Fluid is designed to leak across the pump and motor parts
and into the component case drain. The tandem piston (traction) pump drains
from its L3 port back to the hydraulic tank. The drive motors drain from their L1
ports back to the hydraulic tank. Each drive motor also includes a shuttle valve
to increase the amount for fluid change-out in the closed-loop traction circuit for
cooling purposes. The traction charge circuit is designed to replace the hydraulic
fluid that leaves the closed-loop traction circuit.
The gear pump section furthest from the piston pump, gear pump section
(P4), supplies fluid to a variety of circuits including the traction charge circuit.
Hydraulic fluid from gear pump (P4) enters the main manifold port P and flows
through the steering priority valve (EC1); refer to
Steering Circuit (page 5–18)
for a full explanation of the steering priority valve (EC1) operation. Fluid flow
continues through the flow regulator valve (EC2) until it reaches solenoid valve
(SP1). Solenoid valve (SP1) is responsible for raising the 3-point hitch cylinders
and is closed as long as the cylinders are not raising. Fluid is also sent to one
end of the flow regulator valve (EC2) spool. As long as circuit flow is blocked at
solenoid valve (SP1), the flow regulator valve (EC2) spool is shifted to direct flow
to the traction charge, 2 speed drive motor control, brake release, differential
lock and PTO clutch circuits.
Once the steering circuit needs have been satisfied, and since the 2 speed drive
motor control, brake release, differential lock and PTO clutch circuits place very
small demands on the fluid flow delivered by gear pump (P3), the remainder of
the flow is directed to the traction charge circuit. Charge circuit flow passes
through the charge filter before entering the tandem piston (traction) pump to
prevent contaminants from entering the closed-loop traction circuit. The charge
filter is located on the right side of the machine behind the front axle. Traction
Hydraulic System: Hydraulic Flow Diagrams Page 5–16 Outcross 9060
18234SL Rev B