Lotus 2004 ELISE Service Notes page 232

Lotus Service Notes
Maximum Assistance
If the pedal is pressed hard, the atmospheric port will be held open, so that the left hand chamber will be
subject to full atmospheric pressure. This is full servo assistance which will, with 0.8 bar of vacuum available
from the engine, increase the force applied to the master cylinder pushrod by approximately four times.
Input from
brake pedal
When pedal pressure is relaxed, the vacuum port in the driving piston will open and bleed the higher
pressure from the left side of the diaphragm into the right hand chamber and thence into the engine plenum,
collapsing the pressure differential across the diaphragm. The driving piston is moved fully to the left by the
main spring.
The pliant reaction disc fitted between the input and output rods ensures a graduated application of servo
assistance and provides pedal feedback and 'feel' to the driver.
Atmospheric
pressure
Atmospheric
port open
Section JJ
Intake manifold
depression
Output to
master
cylinder
Contact between
input and output rods
via reaction disc
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