TRANSMISSION
L3301, L3901, L4701, WSM
3-M20
L4701
Oil flows in HST case from b-port and is sent to c-port with the charge pump (9). Oil from c-port is sent to HST
circuit and the PTO clutch valve.
The oil in the regulator valve (14) is used for the movement of the servo piston (8) which is operated by the
regulator valve (14) and the HST pedal (15). And the oil in the HST main circuit gets circulated between the variable
displacement pump cylinder block (4) and the fixed displacement motor cylinder block (12), which forms a closed
circuit.
The case relief valve (7) controls pressure in the HST case.
The PTO pressure priority valve (16) switches the pressurized oil from the charge pump (9) to the PTO clutch and
HST regulator valve (HST servo valve) (14). When the oil pressure at the PTO pressure priority valve (16) is below
the setting pressure, approx. 14.0 to 15.0 kgf/cm
2
(1.38 to 1.47 MPa, 199 to 213 psi) at engine idling speeds, the PTO
pressure priority valve (16) delivers preferentially the oil from the charge pump (9) to the PTO clutch valve to operate
the PTO clutch.
(Reference)
• Valve Setting Pressure [Oil temperature: 40 to 60 °C (104 to 140 °F)]
– Charge Relief Valve: 2.3 to 2.6 MPa (23.5 to 27.0 kgf/cm
2
, 334 to 384 psi)
– Check and High Pressure Relief Valve: 33.3 to 36.3 MPa (340 to 370 kgf/cm
2
, 4836 to 5262 psi)
– Case Relief Valve: 0.29 MPa (3.0 kgf/cm
2
, 42.7 psi)
9Y1211012TRM0021US0
(1) Transmission Case
(2) Hydraulic Filter
(3) Hydraulic Pump
(4) Pump Cylinder Block
(5) Oil Cooler
(6) HST Assembly
(7) Case Relief Valve
(8) Servo Piston
(9) Charge Pump
(10) Check and High Pressure
Relief Valve
(11) Charge Relief Valve
(12) Motor Cylinder Block
(13) Filter
(14) Regulator Valve
(15) HST Pedal
(16) PTO Clutch Pressure Priority
Valve
A: To Hydraulic Block and
3- point Hitch
B: From Power Steering
Controller
C: To Power Steering
Controller
D: To PTO Clutch Valve
a: a port
b: b port
c: c port
d: d port
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