Komatsu 114E-3 Series Shop Manual page 75

10 Structure, function and maintenance standard
Wastegated turbochargers are used to optimize
performance. The wastegated design allows maxi-
mum boost to be developed quickly while making
sure that the turbocharger does not overspeed at
higher engine rpm's.
Wastegate operation is controlled by an actuator
that senses compressor pressure and balances it
against a preset spring load. The wastegate valve
is located in the turbine inlet passage. When open,
it diverts a portion of the exhaust gas away from the
turbine wheel, thereby controlling the shaft speed
and boost.
The variable geometry turbocharger functions as a
standard turbocharger with the addition of the fol-
lowing:
A speed sensor (1) in the bearing housing to
q
monitor turbocharger operation
Water-cooled bearing housings (in addition to
q
oil lubrication)
The sliding nozzle (2) is actuated by a pneu-
q
matic actuator attached to the vehicle (brake)
air supply system
The pneumatic actuator (3) operated by an air
q
control valve (4) and receives air from the air
supply tank (5)
When the variable geometry turbocharger
q
mechanism opens, a noise can be heard as air
is released from the actuator (3) through the
control valve (4).
The wastegated turbocharger is a Holset Model
HX40. It is comprised of a turbocharger, wastegate
actuator, and wastegate valve in the turbine hous-
ing. A wastegated turbocharger provides improved
response at low engine speeds without sacrificing
turbocharger durability at high speeds. This is
accomplished by allowing the exhaust gases to
bypass the turbine wheel during certain modes of
engine operation.
During low rpm operation, the turbocharger oper-
ates as a closed-system turbocharger where the
gases' energy is transferred to the compressor
wheel and used to compress intake air.
During high rpm operation however, the turbo-
charger becomes an open-system turbocharger
and allows exhaust gas to bypass the turbine.
Since the exhaust gas is gated around the turbine
wheel, less energy is absorbed through the turbine
and transferred to the compressor, reducing the
intake manifold pressures and turbine speeds.
114E-3 Series
SEN00176-02
5