1999 LAND ROVER DISCOVERY ECU

FRONT SUSPENSION
DESCRIPTION AND OPERATION 60-7
DESCRIPTION AND OPERAT ION
ACE system component layout
1Anti-roll bar link
2Suction hose
3ACE/PAS reservoir
4Return pipe
5ACE pump
6Pressure pipe
7Torsion bar - front
8Actuator hose
9Actuator hose
10Actuator
11Short arm
12Long arm
13Anti-roll bar link14Isolator and bracket (2 and 4 way) 7 off
15Pressure transducer
16Valve block
17Directional control valve 2 off
18Pressure control valve
19Long arm
20Actuator
21Anti-roll bar link
22Torsion bar - rear
23Short arm
24ACE ECU
25Accelerometer - lower
26Accelerometer - upper

FRONT SUSPENSION
60-8 DESCRIPTION AND OPERATION
ACE system control diagram
1Upper accelerometer
2Lower accelerometer
3Pressure transducer
4Directional control valve
5Directional control valve
6Pressure control valve
7Instrument pack warning lamp
8Diagnostic socket9Reverse lamp switch
10SLABS ECU
11Engine Control Module (ECM)
12Ignition feed
13ACE relay
14Battery supply
15ACE ECU
M60 0589B
12
5
4
3
6
7
8
9
10
11
12
13
14
15

FRONT SUSPENSION
60-10 DESCRIPTION AND OPERATION
ACE system
aDirection of travel - Right hand bend
bBody roll
cAxle roll
dTyre squash
eTorsion/Anti-roll barfDirection of torsion/anti-roll bar twist
gCoil springs
hBody roll angle
iAxle roll angle
jReduced body roll angle with ACE system
The system is electrically and hydraulically operated with all operations controlled by an ACE ECU located behind the
glovebox in the passenger side footwell. The ACE system comprises front and rear torsion bars and actuators, two
accelerometers, ECU, hydraulic pump, valve block and a fluid reservoir.
The ACE system gives improved vehicle handling and suspension characteristics and is active for both on and off-
road driving. This is achieved by hydraulic actuators applying torque to the front and rear torsion bars in response to
lateral forces sensed by accelerometers. The ACE system prevents body roll with cornering forces of up to 0.4 g. From
0.4 g there is a progressive increase in body roll but significantly lower than a passive system. A passive system will
have a progressive increase in roll angle as soon as cornering forces are applied and will have a higher roll angle than
the ACE system for the same cornering force.
The ACE system can also detect if the vehicle is driven off-road. If off-road conditions are detected the ACE system
operation will be reduced or completely disabled at a speed of 25 mph (40 km/h) or less.
Lateral acceleration of the body is sensed by two accelerometers and signals are transmitted to the ECU. The engine
driven hydraulic pump supplies a constant hydraulic flow to the valve block. Two directional control valves are
solenoid operated by the ECU and these supply fluid to the applicable side of each actuator to apply an equal and
opposite force to the torsion bar. In operation the ACE system maintains the attitude of the vehicle body when
cornering.

FRONT SUSPENSION
DESCRIPTION AND OPERATION 60-11
The ACE system uses a semi-synthetic hydraulic fluid which is the same as the fluid used for the PAS system. The
total capacity of the ACE system is 1.62 litres (0.42 US Gallons).
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.
lACE components are thoroughly cleaned externally before work commences;
lall opened pipe and module ports are capped immediately;
lall fluid is stored in and administered through clean containers.
In the event of an ECU or hydraulic failure the system will fail safe to a 'locked bars' condition. The 'locked bars'
condition will allow the torsion bars to operate in a similar manner as conventional 'passive' anti-roll bars. Prolonged
cornering forces will allow a progressive increase in roll angle due to hydraulic leakage through the actuators and
valve block. Failures will be relayed to the driver by the illumination of the ACE warning lamp in the instrument pack.
Faults are recorded by the ECU and can be retrieved using TestBook.
When the ignition switch is moved to position II, the warning lamp will illuminate for two seconds to check functionality.
The warning lamp functionality can also be checked using TestBook.
TestBook must also be used to perform a bleeding procedure after maintenance operations have been performed to
ensure that complete system bleeding is performed. Trapped air in the system can seriously reduce the system
performance.
Fluid reservoir
The moulded plastic fluid reservoir is mounted on the left hand side of the engine compartment on a bracket which is
attached to the inner wing. The reservoir is dual purpose, being divided into two separate chambers; one for the ACE
system and one for the PAS system. Each chamber has its own filler neck and cap and is identified by moulded
lettering on the reservoir adjacent to each filler.
A non-serviceable filter assembly is fitted in the base of each chamber. The filter is made from fine stainless steel
mesh which is moulded into the body of the reservoir. The filter removes particulate matter from the fluid before it is
drawn into the hydraulic pump.
Upper and lower fluid level marks are moulded onto the reservoir body. The capacity of the ACE reservoir chamber
to the upper level mark is 0.5 litre (0.13 US Gallon).

FRONT SUSPENSION
60-14 DESCRIPTION AND OPERATION
Valve block
1Cap
2'O' ring
3Coil
4'O' ring
5Directional control valve 1 (extend)
6Pressure transducer
7Mounting bush 3 off
8Valve block
9'O' ring
10High pressure filter
11'O' ring
12Cap13Stud 4 off
14Pipe connections
15Cap
16'O' ring
17Coil
18'O' ring
19Pressure control valve
20Directional control valve 2 (retract)
21'O' ring
22Coil
23'O' ring
24Cap
The valve block directs hydraulic pressure to the actuators via solenoid operated directional control valves. A solenoid
operated pressure control valve regulates the required pressure to the actuators. The three valve solenoids are
controlled by signals received from the ACE ECU. A pressure transducer monitors the pressure delivered by the
pump. A replacable high pressure filter is installed into the lower face of the valve block and filters fluid before it
reaches the valves.
The valve block is located on the outside of the right hand chassis longitudinal. The valve block is secured to the
chassis with three bolts and rubber bushes. The rubber bushes isolate the valve block from the chassis, preventing
hydraulic noise from the valve block transmitting through the chassis and body.

FRONT SUSPENSION
DESCRIPTION AND OPERATION 60-15
The two solenoid operated directional control valves (DCV's) are fitted to ports in the top face of the valve block. The
DCV's are screwed into the valve block and sealed with O ring seals. Each DCV has a solenoid for electrical operation
of the valve. The solenoid is sealed to the DCV with two O ring and secured with a cap. The cap, coil and O rings are
serviceable items. The DCV's are non-serviceable and failure of a DCV requires the replacement of the valve block
assembly.
The pressure control valve is fitted to a port in the rear face of the valve block. The pressure control valve is screwed
into the valve block and sealed with O rings. The pressure control valve has a coil for electrical operation. The coil is
sealed to the pressure control valve with two O rings and secured with a cap. The cap, coil and O rings are serviceable
items. The pressure control valve is non-serviceable and failure requires replacement of the valve block assembly.
The pressure transducer is fitted to a port in the forward face of the valve block. The pressure transducer is screwed
into the valve block and sealed with an O ring seal. The pressure transducer is a serviceable item.
The high pressure filter locates in a port on the lower face of the valve block. The gauze and fibre filter is sealed in
the port with O ring seals. A threaded cap secures the filter in the valve block and is also sealed with an O ring seal.
A threaded hole on the lower face of the filter allows a bolt to be fitted to remove the filter from the port. If a system
component is replaced, the filter must be changed.
Four ports are located on the forward face of the valve block and two ports on the rear. Each port is fitted with a seal
pack which contains two O ring seals and backing rings. The ACE pipes locate and seal in the seal packs and are
secured to the valve block with the studs and nuts located on the forward and rear faces.
Actuators
Two actuators are used for the ACE system and are attached to the front and rear torsion bars. The actuators apply
hydraulically generated force to the torsion bar to oppose lateral forces caused by the vehicle cornering.
Each actuator is a conventional double-acting cylinder. A piston is attached to a rod and moves within the cylinder
when hydraulic pressure is applied. The rod is sealed at the point where it exits the cylinder. The outer end of the rod
is threaded and locates in a bush in the ACE long arm and secured with a nut. A rubber gaiter covers the rod and
prevents dirt and moisture from damaging the rod surface and cylinder seals. The cylinder has a forked attachment
which locates on the short arm bush and secured with a bolt and nut.
Two banjo connections provide for the attachment of the hydraulic hoses from the ACE valve block. The connections
provide hydraulic flow to each side of the piston to extend or retract the rod.

FRONT SUSPENSION
60-16 DESCRIPTION AND OPERATION
Torsion bar
Front torsion bar shown, rear torsion bar similar
1Locknut
2Actuator
3Locknut
4Locknut 2 off
5Washer
6Anti-roll bar link
7Locknut
8Bush
9Clamp plate
10Bolt 2 off11Torsion bar
12Short arm
13Bush
14Bolt
15Outer slipper bush 2 off
16Inner slipper bush 2 off
17Washer
18Bolt
19Long arm
20Bush
The front and rear torsion bar assemblies are similar in their construction, the rear torsion bar being narrower than the
front. Each torsion bar is made from 35 mm (1.38 in.) diameter spring steel bar.
The right hand end of the torsion bar has a machined spigot which provides for the attachment of the forged steel
short and long arms. The spigot for the short arm is splined and mates with splines in the short arm. The short arm is
located in a specific position on the splines and clamped to the spigot with a Torx bolt and locknut. The short arm is
not a serviceable item other than the actuator attachment bush. The smaller spigot diameter locates the long arm.
The long arm is fitted with a slipper bush which is located on the spigot and secured with a large washer and a special
bolt. The slipper bush comprises two inner and two outer bushes which are installed from each side of the long arm.
The outer bushes have three lugs which locate in the long arm to prevent the bush from rotating. The long arm also
provides the attachment point for the actuator piston rod and the anti-roll bar link.

FRONT SUSPENSION
DESCRIPTION AND OPERATION 60-17
The actuator has a forked end which locates on the bush in the short arm and is secured with a bolt and nut. The
piston rod of the actuator locates through a hole in a cast boss on the long arm which is fitted with a special bush. A
shoulder on the piston rod seats in a hole in the bush and a locknut on the end of the piston rod secures the rod to
the long arm and bush.
The front torsion bar is attached to the front chassis cross member. Two rubber bushes are fitted to the torsion bar
and are located in clamp plates. The clamp plates are located in slots in the cross member and secured with bolts.
The rear torsion bar is attached to the tubular cross member at the rear section of the chassis. Two rubber bushes
are fitted to the torsion bar and are located in clamp plates. The clamp plates are located in fabricated brackets
attached to the tubular cross-member and secured with bolts.
Two anti-roll bar links are mounted on brackets on the front and rear axles. Each anti-roll bar link is fitted with a
spherical bearing at each end. One bearing is attached to the link at a 90° angle. The threaded shank of the bearing
is located through a hole in a bracket on the axle and secured with a locknut; a washer is installed on the threaded
shank between the bearing and the bracket. The second spherical bearing is attached in-line with the link and locates
in the torsion bar on the left hand side and the long arm on the right hand side. The front anti-roll bar links are longer
than the rear links and are not interchangeable.
Accelerometers
Two accelerometers are used for the ACE system. The upper accelerometer is mounted on a bracket, behind the
headlining adjacent to the rear view mirror and the sunroof ECU. The lower accelerometer is located on a bracket on
the inner sill panel under the RH front floor.
The lower accelerometer is the primary sensor used to measure lateral acceleration of the vehicle for roll control. The
upper accelerometer is used by the ECU for roll correction and fault detection in conjunction with the lower
accelerometer.
Each accelerometer is a solid state capacitive acceleration sensor and operates on a 5 V supply from the ECU. The
upper and lower sensors can measure acceleration in the range of ± 1.10 g and return an output to the ECU of
between 0.5 and 4.5 V.
Failures of an accelerometer are recorded by the ECU and can be retrieved using TestBook. A special tool is required
to remove and replace a sensor in the bracket.