Illustration 9
g02269817
Turbocharger with the wastegate (if equipped)
(12) Actuating lever
(13) Wastegate actuator
(14) Line (boost pressure)
When the load on the engine increases, more fuel is
injected into the cylinders. The combustion of this
additional fuel produces more exhaust gases. The
additional exhaust gases cause the turbine and the
compressor wheels of the turbocharger to turn faster.
As the compressor wheel turns faster, air is
compressed to a higher pressure and more air is
forced into the cylinders. The increased flow of air into
the cylinders allows the fuel to be burnt with greater
efficiency. This produces more power.
A wastegate may be installed on the turbine housing
of the turbocharger. The wastegate is a valve that
allows exhaust gas to bypass the turbine wheel of the
turbocharger. The operation of the wastegate is
dependent on the pressurized air (boost pressure)
from the turbocharger compressor. The boost
pressure acts on a diaphragm that is spring loaded in
the wastegate actuator which varies the amount of
exhaust gas that flows into the turbine.
The shaft that connects the turbine to the compressor
wheel rotates in bearings (4) and (6). The bearings
require oil under pressure for lubrication and cooling.
The oil that flows to the lubricating oil inlet port (5)
passes through the center of the turbocharger which
retains the bearings. The oil exits the turbocharger
from the lubricating oil outlet port (10) and returns to
the oil pan.
Valve System Components
Illustration 10
g02263874
Valve system components
(1) Rocker arm
(2) Spring
(3) Valve
(4) Pushrod
(5) Lifter
The valve system components control the flow of inlet
air into the cylinders during engine operation. The
valve system components also control the flow of
exhaust gases out of the cylinders during engine
operation.
The crankshaft gear drives the camshaft gear through
an idler gear. The camshaft must be timed to the
crankshaft in order to get the correct relation between
the piston movement and the valve movement.
The camshaft has two camshaft lobes for each
cylinder. The lobes operate the inlet and exhaust
valves. As the camshaft turns, lobes on the camshaft
cause the lifter (5) to move the pushrod (4) up and
down. Upward movement of the pushrod against
rocker arm (1) results in downward movement
(opening) of valve (3). The opening of valve (3)
compresses the valve spring (2). When the camshaft
has rotated to the peak of the lobe, the valve is fully
open. When the camshaft rotates further, the valve
spring (2) under compression start to expand. The
valve stems are under tension of the spring. The
continued rotation of the camshaft causes the rocker
arm (1), the pushrods (4) and the lifters (5) to move
downward until the lifter reaches the bottom of the
lobe. The valve (3) is now closed. The cycle is
repeated for all the valves on each cylinder.
UENR0617
15
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