Discovery 2. Manual - part 184

 

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Discovery 2. Manual - part 184

 

 

FRONT SUSPENSION

DESCRIPTION AND OPERATION

60-19

When system faults are detected by the ECU, the ACE warning lamp in the instrument pack is illuminated by the ECU 
continuously in amber for minor faults or flashing red with an audible warning for faults which require the driver to stop 
the vehicle immediately.

The ACE ECU supplies a control current to the pressure control valve in the valve block. The current supplied by the 
ECU is determined by a number of input signals from the upper and lower accelerometers, road speed etc.. The 
pressure control valve controls the hydraulic pressure supplied to the actuators proportional to the current supplied 
by the ECU.

Power is supplied to the two solenoid operated directional control valves (DCV's) in the valve block by the ECU. 
Together, the DCV's control the direction of flow of hydraulic fluid to the actuators. When the ECU supplies power to 
the solenoids the valves open allowing hydraulic fluid to flow to the actuators. When power is removed the valves 
close.

The pressure transducer in the valve block receives a 5 V supply from the ECU. The pressure transducer measures 
hydraulic pressures in the range of 0 to 180 bar (0 to 2610 lbf.in

2

) and returns a linear output voltage to the ECU 

dependent on hydraulic pressure. 

The ECU supplies a 5 V current to each of the accelerometers. Each accelerometer is capable of measuring lateral 
acceleration in the range of 

±

 1.10 g. An analogue input to the ECU of between 0.5 and 4.5 V relative to the lateral 

acceleration sensed is returned by each accelerometer. The ECU processes the two signals received to produce a 
'pure' lateral acceleration signal which is then used as the main control signal for the ACE system.

ACE ECU connector pin details

Pin No.

Description

Input/Output

1

Not used

-

2

Not used

-

3

Spare

Input

4

Not used

-

5

Road speed

Input

6

ARC  relay

Output

7 to 9

Not used

-

10

K line (diagnostics)

-

11

Ignition switch

Input

12

Accelerometer - lower (supply)

Output

13

Pressure transducer (supply)

Output

14

Reverse switch

Input

15

Accelerometer - lower (signal)

Input

16

Pressure transducer (signal)

Input

17

Accelerometer - upper (signal)

Input

18

Accelerometer - upper (supply)

Output

19

Engine speed

Input

20

Main earth 1

-

FRONT SUSPENSION

60-20

DESCRIPTION AND OPERATION

Failure modes
Failures where the vehicle can still be driven safely are indicated by the ACE warning lamp illuminating continuously 
with an amber colour. The amber warning lamp will remain illuminated until the ignition is turned off. For all faults the 
warning lamp will only illuminate again if the fault is still present. Failures which require the driver to stop the vehicle 
immediately are indicated by the ACE warning lamp flashing with a red colour and an audible warning. All faults are 
recorded by the ACE ECU and can be retrieved with diagnostic equipment.

The following tables show the type of system failures and their effects on the system operation. Torsion bar 'floppy' 
means that fluid is allowed to circulate freely through the system. With no pressure in the actuators the torsion bar will 
have no effect on vehicle roll. 'Locked bars' means that all pump flow is directed through the valve block and returns 
to the reservoir. Both DCV's close and fluid is trapped in the actuators but can flow from one actuator to the other via 
the valve block. In this condition the torsion bar will perform similar to a conventional anti-roll bar, resisting roll but still 
allowing the axles to articulate.

Acceleration sensors

Pressure transducer

Road speed signal

21

Pressure transducer (earth)

Input

22

DCV 2 (earth)

Input

23

DCV 1 (earth)

Input

24

DCV 1 & 2 (supply)

Output

25

Pressure control valve (earth)

Input

26

Not used

-

27

Pressure control valve (supply)

Output

28

Main supply (+ V Batt)

Input

29 to 31

Not used

-

32

Main earth 2

-

33

Accelerometer - lower (signal)

Input

34

Accelerometer - upper (signal)

Input

35

Not used

-

36

Warning lamp

Output

Failure

Effect

Valve stuck closed

No ACE control

Short circuit - Ground

No ACE control

Short circuit - VBatt

No ACE control

Loose sensor

Erractic ACE activity when driving in straight line

Failure

Effect

Short circuit - VBatt

Large sensor dead band - possible random 
movements

Failure

Effect

Open circuit

No ACE control - 'Locked bars' condition

Short circuit - Ground

No ACE control - 'Locked bars' condition

Short circuit - VBatt

No ACE control - 'Locked bars' condition

Pin No.

Description

Input/Output

FRONT SUSPENSION

DESCRIPTION AND OPERATION

60-21

Engine speed signal

Reverse gear signal

Ignition ON signal

Pressure control valve failure

Directional control valves

Failure

Effect

Open circuit

No ACE control - 'Locked bars' condition

Short circuit - Ground

No ACE control - 'Locked bars' condition

Short circuit - VBatt

No ACE control - 'Locked bars' condition

Failure

Effect

Open circuit

No reverse signal to ECU. ACE active in reverse, 
may give abnormal handling when reversing

Short circuit - Ground

No reverse signal to ECU. ACE active in reverse, 
may give abnormal handling when reversing

Short circuit - VBatt

Permanent reverse signal to ECU. Permanent 
'Locked bars' condition

Failure

Effect

Open circuit

ECU does not receive ignition ON signal. No ARC 
control, 'Locked bars' condition

Short circuit - Ground

ECU does not receive ignition ON signal. No ARC 
control, 'Locked bars' condition

Short circuit - VBatt

Permanent ignition ON signal to ECU. Possibility of 
flat battery

Failure

Effect

Open circuit

No ACE control

Short circuit - Ground

No ACE control

Short circuit - VBatt

No ACE control

Valve stuck open

No ACE control

Valve stuck closed

Maximum system pressure - no proportional control. 
Pressure relief valve operating at 185 bar (2683 
lbf.in

2

)

Failure

Effect

DCV 1

DCV 2

Valve open or stuck open Valve open or stuck open No ACE control - Anti-roll bars floppy

Valve closed or stuck 
closed

Valve closed stuck 
closed

No ACE control - 'Locked bars' condition (default)

Valve open or stuck open Valve closed or stuck 

closed

Vehicle leans to left when pressure is applied to 
actuators

Valve closed or stuck 
closed

Valve open or stuck open Vehicle leans to right when pressure is applied to 

actuators

FRONT SUSPENSION

60-22

DESCRIPTION AND OPERATION

Operation

Hydraulic circuit diagram

Pressure transducer
Directional control valve 2
Front torsion bar assembly
Actuator
Actuator
Rear torsion bar assembly
Directional control valve 1

Valve block
Pressure control valve

10 Reservoir
11 Filter
12 High pressure filter
13 Hydraulic pump
14 Attenuator hose

Vehicle not moving
When the engine is running and the vehicle is not moving, both DCV's are closed, locking fluid in each side of the 
actuator pistons. The hydraulic pump draws fluid from the reservoir and passes it at very low pressure to the valve 
block. Because both DCV's are closed, after the fluid passes through the high pressure filter, it is directed through the 
pressure control valve to the reservoir. The pressure control valve is open fully to allow the full flow to pass to the 
reservoir. The DCV's will remain closed until the ECU detects a need to operate.

 

 

 

 

 

 

 

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