Discovery 2. Manual - part 607

FRONT SUSPENSION

DESCRIPTION AND OPERATION

60-25

Operation

Hydraulic circuit diagram

1 Pressure transducer
2 Directional control valve 2
3 Front torsion bar assembly
4 Actuator
5 Actuator
6 Rear torsion bar assembly
7 Directional control valve 1

8 Valve block
9 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.

FRONT SUSPENSION

60-26

DESCRIPTION AND OPERATION

Vehicle moving and turning left
When the vehicle is turning left, the accelerometers detect the cornering forces applied and transmit signals to the
ECU. The ECU determines that an opposing force must be applied to the torsion bars to counter the cornering forces.
The ECU supplies a current to the solenoid of the DCV2. Simultaneously, a current is sent from the ECU to the
pressure control valve which operates to restrict the flow of fluid returning to the reservoir.

The restriction causes the hydraulic pressure in the system to rise and the pressure is sensed by the pressure
transducer which sends a signal to the ECU. The ECU determines from the inputs it receives what pressure is required
and adjusts the pressure control valve accordingly.

The pressure in the system is applied to the annulus of each actuator, applying an opposing force to the torsion bar
and minimising the cornering effect on the vehicle and maintaining the vehicle attitude. The fluid displaced from the
full area of the actuator is returned to the reservoir via the valve block.

As the cornering force is removed when the vehicle straightens up, the ECU opens the pressure control valve to
reduce the pressure in the system. The fluid bleeds from the actuator back into the system as the cornering force is
reduced, removing the force from the torsion bar. When the vehicle is moving in a straight line DCV 2 closes.

Vehicle moving and turning right
When the vehicle is turning right, the accelerometers detect the cornering forces applied and transmit signals to the
ECU. The ECU determines that an opposing force must be applied to the torsion bars to counter the cornering forces.
The ECU supplies a current to the solenoid of the DCV1. Simultaneously, a current is sent from the ECU to the
pressure control valve which operates to restrict the flow of fluid through the by-pass gallery.

The restriction causes the hydraulic pressure in the system to rise and the pressure is sensed by the pressure
transducer which sends a signal corresponding to the pressure to the ECU. The ECU determines from the inputs it
receives what pressure is required and adjusts the pressure control valve accordingly.

The pressure in the system is applied to the full area of each actuator, applying an opposing force to the torsion bar
and minimising the cornering effect on the vehicle and maintaining the vehicle attitude. The fluid displaced from the
annulus of the actuator is returned to the reservoir via the valve block.

Vehicle moving in a straight line
The ECU is constantly monitoring the signals received from the accelerometers and operates the DCV's and pressure
control valve to maintain the vehicle attitude when the vehicle is moving.

Off-road driving
Off-road detection is achieved by the ECU by monitoring the signals from the upper and lower accelerometers for
varying degrees of body movement. Off-road driving generates differing signals to the accelerometers which in turn
produce differing outputs due to their vertical separation and the location of the roll centre of the vehicle. The two
signals are passed through a filter to remove any offset caused by the vehicle leaning or the terrain. The ECU then
uses this signal to calculate the percentage of road roughness.

Below 25 mph (40 km/h) the percentage of road roughness calculated is used by the ECU to limit the operation of the
ACE system. The system is completely inoperative at speeds below 2 mph (3 km/h). At speeds above 25 mph (40
km/h) the system disables the percentage road roughness signal and full ACE system assistance is restored.

Side slope detection
The ECU uses side slope detection when the upper and lower accelerometers detect an average acceleration of more
than

0.2 g and a road speed of less than 25 mph (40 km/h).

When side slope is detected both DCV's close to provide a 'locked bars' condition. This condition increases stability
and gives a consistent vehicle response. As the road speed increases up to 25 mph (40 km/h), the level of average
lateral acceleration must also increase and be maintained for the system to recognise that the vehicle is on a side
slope. If the side slope angle is steep and the road speed is low, the ECU will detect the side slope in a short time.

FRONT SUSPENSION

ADJUSTMENTS

60-27

ADJUSTMENTS

ACE hydraulic system bleeding

$% 60.60.13

Introduction

CAUTION: The ACE hydraulic system is
extremely sensitive to the ingress of dirt or
debris. The smallest amount could render the
system unserviceable. It is imperative that the
following precautions are taken.

ACE components are thoroughly cleaned
externally before work commences;

all opened pipe and module ports are
capped immediately;

all fluid is stored in and administered
through clean containers.

Check

1. Check the ACE system fluid level.

FRONT SUSPENSION,

ADJUSTMENTS, Fluid level check - ACE
system.

Bleed

1. With vehicle on ramp, connect TestBook and

follow bleed procedure as described.

Fluid level check - ACE system

$% 60.60.14