Kubota RTV 900 Workshop Manual page 12

RTV900, WSM
2. OIL FLOW
(1) HST Assembly
(2) Control Lever (Pedal)
(3) Servo Regulator Assembly
(4) Regulator Valve
(5) Oil Filter Cartridge
A charge pump (10) is used to feed oil to the hydrostatic transmission (HST). The oil coming from the charge pump
(10) flows through the oil cooler (6) and oil filter cartridge (5) into the HST main circuit and regulator valve (4). At this
time, the servo regulator valve and HST main circuit (that is closed with the control lever at neutral position) are kept
at the charge relief valve's (7) set pressure. Step on the pedal, and the regulator valve (4) switches its oil passage to
allow the oil into the service port. Being interlocked with the servo piston (12), the swashplate now tilts to activate the
variable pump (11). Pressurized oil is then forced into the stationary motor (16), which then rotates to circulate oil
between the pump and motor.
The heavier the load on the output shaft (15), the higher the pressure of the oil coming from the pump (11). Now
the assist motor (17) is activated to increase the output torque. When the load on the output shaft (15) decreases, the
oil pressure in the main circuit also drops and the assist motor (17) returns to its neutral position and just the stationary
motor (16) maintains torque to the output shaft (15). Now a closed circuit is formed by the pump (11) and stationary
motor (16).
When the bypass valve is opened, a loop circuit is created between the bypass valve (14) and the motor releasing
drive to the output shaft (15).
The bypass valve (14) is composed of the manual operation spool and the spool that operates in synchronization
with the brake.
(Reference)
• Valve Setting Pressure [Oil temperature : 40 to 60 °C (104 to 140 °F)]
Charge Relief Valve : 0.52 to 0.72 MPa (5.3 to 7.3 kgf/cm
Check and High Pressure Relief Valve : 25.5 to 26.5 MPa (260 to 270 kgf/cm
(6) Oil Cooler
(7) Check and High Pressure
Relief Valve
(8) Input Shaft (Pump Shaft)
(9) Strainer
(10) Charge Pump
(11) Cylinder Block (HST Pump)
(12) Servo Piston
(13) Charge Relief Valve
(14) Bypass Valve
2
, 75 to 104 psi)
2
9-M3
NEW TRANSMISSION
(15) Output Shaft (Motor Shaft)
(16) Cylinder Block (Stationary
Motor)
(17) Cylinder Block (Assist Motor)
(18) Control Piston
, 3698 to 3840 psi)
KiSC issued 04, 2006 A