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9.1 Operation of Powertard brake system
• The Powertard brake system is a device to enhance the engine brake performance. It opens and closes the ex-
haust valve (one side only) to control the volume of compressed air in the combustion chamber in accordance
with the movement of the piston, thereby providing a boosted braking force. Powertard components are located in
the cylinder head.
• The valve bridge is provided with an adjusting screw and a pin that allow the exhaust valve to be opened and
closed under the control of the Powertard, in addition to ordinary valve control.
• The pin is free to move in the adjusting screw. Its movement is controlled by the control valve.
• The adjusting screw is used to adjust the timing (Powertard clearance) for the control valve to press the pin.
(1) Operating principle
• In the ordinary engine brake, the piston is forced up during its
compression stroke when compressed air A develops a counter
force B to press the piston. This force works as a braking force.
However, the piston is forced down during its expansion stroke
to let compressed air expand. This causes an accelerating force
C to work on the piston downward, resulting in the braking force
obtained during the compression period being lost largely.
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