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Lotus Service Notes Section JL
Sequence of Operation
In the following diagrams, one half of the hydraulic modulator is shown schematically, representing the
front brake control circuit, with the sequence of operation described for the left hand front wheel brake. This
sequence would be similar for any of the other three wheel brakes. A typical emergency braking event is
described where, in this example, the left hand front wheel tends to lock. Note that the complete system is
duplicated for the rear brake circuit, which remains completely independent of the front circuit.
Normal Braking
During normal braking, when the wheel speed sensors indicate no imminent wheel locking, the ABS is
inactive. The solenoids are unenergised, so that the isolation valves are sprung open, and the dump valves
sprung closed.
Hydraulic fluid from the master cylinder enters the modulator via the inlet port, by-passes the attenuator
orifice, passes through the open isolation valve and out to the LH front wheel brake.
LHF LHF RHF RHF
Isolation Dump Dump Isolation
valve valve valve valve
To LHF To RHF
circuit circuit
Inlet from
master
cylinder
Pump
Low pressure
accumulator
Pump motor
j149a
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