11-10
• When the Powertard system is activated, the piston pressing
force works as a braking force during the compression stroke as
when the Powertard system is not activated. During the expan-
sion period, the exhaust valve is opened by the working of the
system to let some of the compressed air out through the ex-
haust po
rt.
• Thi
s causes the piston pressing force to be no longer generated.
As a result, the braking force obtained during the compression
period is maintained for effective use.
• After letting out more compressed air, the exhaust valve is
closed, which causes the combustion chamber to be closed up.
As a result, during the expansion period, a new force is generat-
ed which hinders the movement of piston when it goes down.
This force, following the braking force obtained during the previ-
ous compression period, also acts as a braking force, enhancing
greatly the vehicle’s engine brake capacity
.
The
operation of the system which causes the valve to be
opened and closed in agreement with the successive piston
strokes is called synchronized operation.
• As shown above, when the Powertard system is activated, the
engine brake provides more power than the ordinary engine
brake.
(2) Hydraulic pressure control
• When the solenoid valve is activated,
engine oil (oil pressure produced by
ordinary engine oil pump) is let in from
A to flow through the oil passage and
forces open the check valve in the
control valve.
• Oil pressure proceeds through the oil
passage to move the master piston
into contact with the dedicated Power-
tard cam.
• This allows the rotation of the dedicat-
ed Powertard cam to be transmitted to
the master piston. As the cam lobe top
is reached, oil pressure in the oil pas-
sage further builds up, forcing the
check valve in the control valve to
close and working on the slave piston
at the same time.
• The slave piston pushes the pin, which
in turn forces the exhaust valve to
open. As a result, the pressure in the
combustion chamber is released to
maintain effective braking force.
STRUCTURE AND OPERATION