Range Rover P38
44
AUTOMATIC GEARBOX
NEW RANGE ROVER
20
DESCRIPTION AND OPERATION
When the EAT ECU receives confirmation of the
torque reduction from the ECM, it then signals the
shift solenoid valves in the gearbox to produce the
shift. To further improve shift quality, the EAT ECU
also signals the pressure regulating solenoid valve to
modulate the hydraulic pressure and so control the
rate of engagement and disengagement of the brake
clutches.
With time, the components in a gearbox wear and the
duration of the gear shifts tends to increase, which
has an adverse affect on the brake clutches. To
counteract this, the EAT ECU applies a pressure
adaptation to each shift. To calculate the adaptations,
the EAT ECU monitors the pressure modulation used,
and time taken, for each shift. If a subsequent shift of
the same type, in terms of throttle position and engine
speed, has a longer duration, the EAT ECU stores an
adaptation for that type of shift in a volatile memory.
The adaptation is then included in future pressure
calculations for that type of shift, to restore shift
duration to the nominal.
Kickdown
The EAT ECU monitors the input of the throttle
position sensor to determine when kickdown is
required and select a gear to give the best available
acceleration. When it detects a kickdown situation, the
EAT ECU immediately initiates a down shift of one or
two gears or will maintain the current gear to avoid
engine overspeed.
Torque Converter Lock-Up
The EAT ECU energises the lock-up solenoid valve to
engage the lock-up clutch. Lock-up clutch operation is
dependent on throttle position, engine speed,
operating mode and the range selected on the
transfer box.
High Range
Unique lock-up maps, similar to the shift maps, are
incorporated in the economy and sport modes for all
forward gears. Engagement and disengagement of
the lock-up clutch is dependent on throttle position
and engine speed.
Low Range
To enhance off road control, particularly when
manoeuvring at low speeds, torque converter lock-up
does not occur when there is any degree of throttle
opening. When the throttle is closed above a preset
engine speed, the lock-up clutch engages to provide
maximum engine braking.
Increased Load/Reduced Torque Compensation
To aid performance and driveability in the high range
economy mode, the EAT ECU has three adaptive shift
and lock-up maps. These maps delay upshifts and
torque converter lock-up similar to the sport mode if
the inputs from the engine indicate:
•
A sustained high load on the engine, such as
occurs when the vehicle is ascending a steep
gradient or towing a trailer.
•
The EAT ECU monitors the engine inputs and
selects the most appropriate adaptive map for
the prevailing conditions.
•
On vehicles from 99MY, a lower than normal
engine torque, such as occurs at altitude or high
ambient temperatures.
Diagnostics
While the ignition is on, the EAT ECU diagnoses the
system for faults. The extent of the diagnostic
capability at any particular time depends on the
prevailing operating conditions, e.g. it is not possible
to check torque converter lock-up while the vehicle is
stationary, or to check for a short circuit to earth if the
circuit concerned is already at a low potential.
If a fault is detected, the EAT ECU immediately stores
a fault code and the values of three operating
parameters associated with the fault. Depending on
the fault, there are four possible effects:
•
The fault has little effect on gearbox operation or
vehicle emissions. The driver will probably not
notice any change and the warning lamps
remain extinguished.
•
All gears are available but kickdown does not
function. ’GEARBOX FAULT’ will be displayed
on the instrument pack message centre. The
MIL remains extinguished.
•
Limp home mode is selected and vehicle
performance is greatly reduced. ’GEARBOX
FAULT’ will be displayed on the instrument pack
message centre. If the fault is detected on a
second consecutive drive cycle, the MIL
illuminates.