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Lotus Evora. Instruction - part 50

Lotus Service Notes

Section JL

Pressure Reduction

Once the LH front wheel brake circuit has been isolated from the master cylinder, the pressure must be

reduced in order to allow wheel speed to be restored. This pressure reduction is achieved by the ECM energis-

ing the dump valve solenoid, which then opens against spring pressure and bleeds off some of the fluid into the

low pressure accumulator shared with the RH front circuit. Very short activation pulses are used to maintain

close control of the pressure reduction, and to limit the reduction to that required to restore wheel speed. Fluid

displaced from the wheel brake circuit is stored in the front brake accumulator against spring pressure, and is

also used to prime the hydraulic pump.

Isolation valve Dump valve

energised and energised and

closed open

Fluid

bleeds

off from

LHF circuit

Inlet from

master

cylinder

Pump is

primed

Low pressure

accumulator

charged

j149c

Lotus Service Notes

Section JL

Pressure Increase (Re-apply)

As soon as imminent wheel lock is detected by the ECM, and the ABS control system is activated, the

pump motor is energised. When the dump valve is opened, and fluid is allowed to bleed off from the wheel

brake circuit into the low pressure accumulator, this fluid is scavenged by the pump and returned back into the

input circuit through an attenuator orifice. This action is the origin of the ‘pedal pushing back’ sensation felt by

the driver, with the pressure pulsations from the pump damped and quietened by the restriction of the orifice.

When wheel speed has been restored and the brake pressure is required to increase, the isolation valve is

momentarily opened, to allow master cylinder/pump pressure to raise the pressure in the wheel brake circuit

in increments. If imminent locking is again sensed, the isolation valve closes, the dump valve opens and the

cycle repeats, with the whole process occuring several times a second.

Isolation valve

pulsed open

Increasing

pressure

to LHF

brake

Inlet from

master

cylinder

Attenuator

Pump orifice

operating

Accumulator

discharges into

pump

j149d

Lotus Service Notes

Section JL

Brake Release

When no further wheel locking is sensed by the ECM, the ABS becomes inactive with the isolation valve

open (solenoid de-energised) to allow direct communication between the master cylinder and wheel brake

circuit, and the dump valve closed (solenoid de-energised) to seal off the pressure relief circuit. The pump will

remain running for a short time to help drain any fluid from the accumulator, whose piston is returned to its start

position under the action of the spring, and return the fluid to the master cylinder reservoir.

Isolation valve

de-energised

and open

Output

to LHF

brake

Inlet from

master

cylinder

Pump runs

for short

period

Fluid scavenged from

low pressure accumulator

j149e

Lotus Service Notes

Section JL

JL.12 - ELECTRO-HYDRAULIC UNIT

The electro-hydraulic unit is located on the front side of the driver's toebox, and is accessible from below

after removal of the front undertray. The protective cover may be removed after slackening the two retaining

nuts. The unit is secured to the mounting bracket via two studs and a bottom spigot, all supported in flexible

grommets. The mounting bracket is fixed to the chassis by four bolts. A single 38 pin connector plug with a

cam lever is provided to connect the vehicle harness to the control module.

CAUTION: Do not disconnect or connect the main connector plug with the ignition switched on. Switch

off the ignition and disconnect the harness before carrying out any electrical welding operations on

the car.

Hydraulic pipe connections to the unit comprise two input pipes from the master cylinder (one for the front

circuit, one for the rear) and four output pipes, one for each of the wheel brakes. Note that all hydraulic con-

nections are identified by engraved markings on the unit:

Input:

MC1 From master cylinder rear port (front brake circuit)

MC2 From master cylinder front port (rear brake circuit)

Output:

FL Front left

FR Front right

RR Rear right

RL Rear left

To Remove Electro-Hydraulic Unit

When removing the unit, beware of dripping brake fluid and take appropriate precautions to prevent dam-

age to paintwork.

1. Raise the vehicle and remove the front undertray. Remove the module protective cover.

2. Switch off the ignition before pressing the release tab and folding back the cam lever to disconnect the

harness plug.

3. Label each of the hydraulic pipes before disconnecting from the unit and immediately capping the pipes

and plugging the ports to reduce the spillage of brake fluid, and to prevent the ingress of dirt.

4. Release the four bolts securing the mounting bracket to the chassis and withdraw the bracket with ABS

unit.

5. To remove the unit from the bracket, release the two retaining nuts from the studs and slide the unit from

its three grommets.

6. To refit, reverse the removal procedure, taking care to connect the brake pipes correctly:

Mounting bracket to chassis; 24 Nm

Modulator inlet pipes; 18 Nm

Modulator outlet pipes; 16 Nm

7. Bleed the unit of air (see Sub-section JL.3).

8. Verify correct connection by using the ‘Lotus Techcentre’ tool in actuator tests with the car on a wheel free

lift. Check that operation of each solenoid valve affects the appropriate wheel.

Note that the ABS controller is calibrated specifically for the Evora. Do not use parts from other

sources.

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