Simplicity AGCO Allis 2000 Series, Service & Repair Manual

Page: 143 / 312

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Figure 2. U-Type Hydrostatic Unit
A. Fan Shaft
E. Oil Filter Base
B. Control Trunnion F. Motor Output Shaft
C. Input Shaft G. Implement Relief
D. Charge Pressure Relief Valve
Valve
10 U-Type Hydrostatic Unit Service
System Description
E
D
F
A
B
C
G
CASE DRAIN
RESERVOIR
FLOW
(BI-DIRECTIONAL)
OUTPUT SHAFT
BI-DIRECTIONAL
MANUAL
CONTROL
MF AXLE ENGINE
INPUT SHAFT
BI-DIRECTIONAL
PV
Figure 3. Pump/Motor
System Description
PUMP MOTOR
The 15 Series Hydrostatic Transmission consists of a
variable displacement axial piston pump connected in a
closed loop to a fixed displacement axial piston motor.
The variable displacement pump is driven by the engine.
The fixed motor, which is driven by the fluid from the
pump, drives the tractor. The direction of rotation and
speed of the fixed motor output shaft depends on the
flow from the pump, and the system pressure is deter-
mined by the machine load. See Figure 3.
ven directly by the engine through the variable displace-
ment pump shaft. This charge pump provides a predeter-
mined amount of fluid that is used by the pump/motor cir-
cuit as required to replenish leakage losses. See Figure
4.
Since the pump/motor circuit is a closed loop, and either
side can be pressurized, two directional control check
valves are needed to direct charge pump flow into the
low pressure side of the circuit.
The pressure in this charge pump circuit is limited by a
factory set, direct operating relief valve. Any fluid not
being used is discharged from the circuit over this valve
and passes through the pump, the motor housings, and
back to the system reservoir.
IMPLEMENT
RELIEF
CHARGE
RELIEF
RESERVOIR
TO
CASE
DRAIN
PV INPUT PF
MOTOR
CHARGE CHECK VALVE
CHARGE
PUMP
CHARGE
CHECK
VALVE
Figure 4. Charge Pump and Check Valves
CONTROL
The speed at which the output shaft turns depends on
the position of the control lever and is infinitely variable
between zero and maximum speed. The direction of
rotation of the output shaft depends on the position of the
control lever in relation to the neutral position.
The variable displacement pump has a manual control
lever connected directly to the tiltable swashplate, so that
as the operator moves the control, the swashplate tilts
resulting in fluid flow from the pump. The fluid enters the
fixed displacement motor, and pressure increases until
the motor (output) shaft begins to rotate. See Figure 5.
Figure 5. Forward
CHARGE PUMP AND CHECK VALVES
The axial piston pump and motor have a small amount of
internal leakage which is removed from the pump/motor
closed loop. This results in a fluid loss from that circuit
which must be replenished. To accomplish this task, a
fixed displacement pump (gerotor type) is used. It is dri-
Not
for
Reproduction