Lotus Evora. Manual - part 49

 

 

Lotus Service Notes   

 

 

    Section JL

6.  Remove the 4 remaining fixings securing the pedal shaft bracket to the pedal box, and manoeuvre the 

pedal assembly from the car.

7.  Release the three Torx head screws securing the pedal shaft and withdraw the shaft and pedals

8.  Refit the pedals in reverse order to removal, noting that the pivot bushes of the brake and clutch pedals 

should be lubricated with Syntheso GLK1 or equivalent.

 

Torque Settings                         Nm

 

Brake servo to alloy spacer                  25

 

Pedal shaft bracket to pedal box                16

 

Throttle pedal mounting bracket to pedal box  - M6    16

 

                              - M8    25          

JL.11 - ABS THEORY OF OPERATION

The Bosch antilock brake system is an ‘add on’ type used to supplement the dual circuit, tandem master 

cylinder, vacuum servo assisted brakes fitted to the Evora.  A single electro-hydraulic unit comprising a hydraulic 

modulator, hydraulic pump, microprocessor and solenoid valve bank, is flexibly mounted on the forward side of 

the driver's toebox, and plumbed into the front and rear brake circuit lines from the tandem master cylinder.

The microprocessor receives signals from magnetic wheel speed sensors integrated into each of the four 

road wheel hubs, and interprets the individual wheel acceleration, deceleration, and comparative wheel speeds.  

From this data, the processor is able to determine if any wheel is tending to lock up, and if imminent lock up 

is sensed, the unit commands the relevant solenoid valves firstly to reduce pressure in that particular brake 

circuit in order to restore wheel speed, and then to modulate pressure to that providing the maximum braking 

force consistent with continued wheel rotation.  The system is able to monitor and independently control each 

of the four wheel brakes, and is referred to a 4-channel system.

In order to achieve the required pressure modulation, three basic modes are used:

- 

Pressure hold;

- 

Pressure reduction;

- 

Pressure increase;

In order to maintain the safety provision of two entirely independent hydraulic circuits, one for the front 

brakes, and one for the rear, the hydraulic elements of the control unit are doubled up, with no part of the sys-

tem shared between the two circuits.  For the pressure hold function, four isolation solenoid valves are used, 

one in the hydraulic circuit for each wheel brake.  The pressure reduction function is achieved by a separate 

dump solenoid valve in each of the four wheel brake circuits, and the pressure increase provided for by a single 

electric motor operating two hydraulic pumps, one serving the front, and on the rear brake circuit.  Separate 

low pressure accumulators are used for the front and rear circuits.

Electro-Hydraulic Control Unit

The electro-hydaulic control unit comprises an alloy valve block containing the four isolation valves, four 

dump valves, two hydraulic pumps and two accumulators, with the single pump motor screwed to the housing, 

and with a solenoid block and ECM unit attached.  The complete assembly is flexibly mounted via a bottom 

spigot and two threaded studs, each of which engage with a rubber grommet in a mounting bracket secured by 

4 bolts to the front side of the driver's toebox.  A protective alloy shield is secured by two nuts.  

The isolation and dump valves share a similar construction, but the spring loaded isolation valves are 

normally open, and the dump valves normally closed.  

 

 

Lotus Service Notes   

 

 

    Section JL

Anti-Lock Braking 

Maximum braking force is provided from a tyre when there is around 15% slippage, dependent on road 

surface conditions and tyre characteristics.  The function of the ABS is to limit tyre slippage when braking to 

around this figure in order to provide optimum grip, and also, by preventing wheel lock, to ensure that steering 

control of the vehicle is retained. 

A high brake pedal pressure (or low road surface friction) may initiate the locking of one or more wheels.  

In the diagram below, a typical control strategy is shown:

1.  Normal braking occurs until, as the applied pressure increases, the wheel speed signals received by the 

ECM indicate that the left hand front wheel (for example) is tending to lock. i.e. its deceleration is too rapid, 

with too great a speed differential with the other wheels.

2.  The connection between the master cylinder and the LH front brake circuit is interrupted (by the isolation 

valve), and the rate of slip increase is reduced.

3.  If the wheel speed continues to depart significantly from vehicle speed, the dump valve is energised to 

reduce pressure in the LH front circuit until wheel speed begins to increase.  The dump valve is then 

closed, as is the isolation valve. 

4.  As wheel speed approaches that providing optimum grip, the isolation valve is pulsed open to allow a 

stepped pressure increase.

5.  As wheel speed begins to drop off and depart from vehicle speed again, a new cycle starts, repeating 

steps (1) to (4).

6.  When wheel speed increases sufficiently to meet vehicle speed, ABS intervention ceases, although moni-

toring is continued throughout each braking event.

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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

                            

                   

 

 

 

         

 

 

 

 

 

 

 

 

 

 

 

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Lotus Service Notes   

 

 

    Section JL

Pressure Isolation (Pressure Maintain)

If signals received from the wheel speed sensors indicate imminent lock up of the LH front wheel, the first 

step in the anti-lock sequence is to isolate that wheel brake circuit from the master cylinder.  The ECM energises 

the isolator valve solenoid, which closes the valve against spring pressure and maintains existing pressure in 

the left hand front brake circuit regardless of any increase in pedal pressure.

        Isolation valve

        energised and 

        closed

Pressure

trapped

in LHF

brake

line

                                                            Inlet from

                                                            master

                                                            cylinder

                                                       

                   

 

 

  

 

 

         

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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