Bomag BW 156 D-3, Service Manual

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Service Training
BW 156/177 D-3/PD-3 - D 3 -
BW 178/179 D-3/PD-3
The travel system of the single drum roller product range BW 156/177/178/179 D/PD-3 and DH/PDH-3
is a closed hydrostatic circuit. The circuit consists mainly of
• the travel pump with control and safety elements,
• the drum drive motor with integrated multi-disc brake,
• the axle drive motor
• the charge pump (steering pump)
• the hydraulic oil filter in the charge circuit
• the hydraulic oil filter in the return flow to the tank
• and the pressure resistant connecting hoses
Travel pump and vibration pump are joined together to a tandem pump unit. The travel pump is the first
pump section, flanged directly to the flywheel side of the diesel engine.
The pump delivers the hydraulic oil to the parallel arranged motors on drum and rear axle. The pressure
in the closed travel circuit generated by the resistance of drum and drive wheels is limited by the high
pressure limitation in the pump to maximum 435 bar.
A flushing valve in the axle drive motor flushes a certain quantity of oil out of the closed circuit when the
machine is driving. This prevents the travel circuit from overheating.
Leakage in the individual components and flushing quantities are replaced by the charge circuit through
the boost check valves in the travel pump.
The charge pump draws the hydraulic oil out of the hydraulic oil tank and delivers it through the hydraulic
oil filter to the boost check valves in the travel pump, to the vibration pump and to the control valves for
the brakes (drum drive motor and wheel drives) as well as to the travel speed range selector valve (BW
156/177 D-3 only axle drive motor; all other machines drum drive motor and axle drive motor).
Apart from supplying the closed travel and vibration circuits with cool and filtered oil as compensation
for leaks and flushing quantities, the charge circuit is also used to operate (release) the brakes and to
change the speed ranges in the travel motors.
The axle drive motor of the BW 156/177 D-3 and both travel motors on all other machine types the
displacement can be reduced to half. This allows to drive the machine in different speed ranges without
having to change the pump displacement (BW 156/177D-3, BW 177 AD-3 two speed ranges; BW 178/
179 D-3 four speed ranges; DH/PDH-versions (machines with ASC) three speed ranges). However, the
higher speed ranges works with a reduced torque.
With this control the machine can be optimally adapted to the actual operating conditions.
On machines with ASC the torque in the individual travel speed ranges is adapted automatically (see
chapter ASC).