Mitsubishi 6M70 Workshop Manual page 20

STRUCTURE AND OPERATION
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 port.
• This 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.