Operation

Operation
General
The EAT ECU controls the following functions:
^ Gear shift scheduling
^ Lock-up control
^ Line pressure control
^ Driving mode engagement
^ Sport mode engagement
^ Manual (Steptronic) mode engagement
^ Reverse inhibit
^ Hill mode strategy engagement
^ Downhill recognition
^ Cruise mode engagement
^ Cooling strategy engagement
^ Selector position display
^ Driving mode display
^ Fault status
^ Fault code storage
^ Emergency/Fail-safe program control.

Gear Shift Scheduling
The EAT ECU uses the relationship between the vehicle speed and the throttle position to carry out gear shift scheduling. Depending on these inputs, the EAT ECU controls gear selection using the three shift solenoid valves located in the valve block.

Lock-Up Control
The EAT ECU monitors the relationship between vehicle speed and throttle position to calculate when to lock-up the torque converter.

Lock-up control is possible in 4th and 5th gears. For example, lock-up is possible at high speed cruising with low throttle position. Torque converter lock-up is also provided in 2nd and 3rd gears when high fluid temperatures are detected by the ECU.

A refinement to the torque converter lock-up system is the reduction of harshness or shock during torque converter lock-up.

The EAT ECU controls the lock-up solenoid valve to provide a smooth lock-up function. The solenoid is operated slowly, and gradually varies the fluid pressure to the lock-up control valve. This causes the lock-up clutch to engage slowly, producing a smooth operation.

To promote engine warm-up at low temperatures, the EAT ECU will inhibit lock-up if the gearbox fluid temperature is below 40°C (104°F).

Line Pressure Control
Line pressure refers to the operating fluid pressure that is supplied to the multi-plate clutches, multi-plate brakes and brake band within the gearbox.

Line pressure control provides smooth vehicle operation and gear shift action. The line pressure control is continuously responding to current driving conditions to regulate and deliver the optimum operating pressure at all times. For example, line pressure is lower under normal operating conditions than it would be under hard acceleration.

The EAT ECU controls line pressure by actuating the line pressure solenoid valve in the valve block. The ECU calculates the line pressure required by using engine speed, vehicle speed and throttle position.

High line pressures will cause very harsh gearshifts and gear engagement. Low line pressure will cause gearshifts to take an excessive amount of time to change, which will quickly burn out the clutches, brakes and brake band within the gearbox.

Driving Modes
There are five different driving modes that the driver can select:
^ Normal mode
^ Sport mode
^ Manual (Steptronic) mode
^ Hill Descent Control (HDC) mode
^ Cruise mode.

Normal, sport, cruise and HDC modes are selected manually by the driver. Fast off and stop go modes are controlled by the EAT ECU responding to driving conditions.

The different modes are selected by the gear selector lever or, in the case of cruise mode and HDC, a separate switch. The gear change scheduling is altered to correspond with the mode selected.

Normal Mode
On power up the EAT ECU always initializes normal mode. In this mode all automatic/adaptive modes are active. Normal mode uses gear shift and lock-up maps which allows vehicle operation which is a compromise between performance, fuel consumption and emissions.

Sport Mode
In sport mode the EAT ECU controls the gearbox to downshift more readily and use gear change schedules that hold the lower gears for longer at high engine speeds. This enhances acceleration and vehicle responsiveness. Sport mode is selected by moving the gear selector lever to the 'S/M' position. 'Sport' is displayed in the instrument pack LCD when this mode is selected.

Manual (Steptronic) Mode
Manual mode allows the driver to operate the gearbox as a semi-automatic, Steptronic gearbox. The driver can change up and down the five gears with the freedom of a manual transmission.

Gearshift maps programmed in the EAT ECU protect the engine at high engine speeds by automatically changing up to prevent engine over speed and changing down to prevent stalling.

Manual mode is entered by moving the selector lever to the 'S/M' position and then moving the lever to either the + or - positions to move the gearbox up and down the five gear ratios. Manual mode is exited by moving the selector back to position 'D'.

HDC Mode
The HDC mode assists the ABS in controlling the descent of the vehicle in either 1st gear ratio or reverse gear ratio. HDC mode is initiated by selecting 1 or R on the selector lever, depressing the HDC button adjacent to the selector lever and throttle pedal released (low demand position). The instrument pack illuminates the HDC warning lamp and the LCD will display the selected gear (1 or R).

The EAT ECU will maintain the selected gear ratio and apply engine braking to assist the ABS in controlling the vehicle's descent.

Cruise Mode
Cruise control is activated by depressing the cruise control switch in the center console. When cruise control is active, the EAT ECU senses this as a hardwired input from the cruise control ECU (non NAS KV6 models) or interface unit (Td4 and NAS KV6 models). In cruise mode the EAT ECU uses a dedicated gearshift map to control the gearbox and assist in maintaining the set vehicle speed. The gearbox cruise mode is cancelled by applying the brake pedal or deselecting cruise control. Cruise mode is suspended when the throttle demand is increased and is reinstated when the pedal is released and the set speed resumed. Cruise mode is also suspended when the suspend switch on the steering wheel is pressed.

Reverse Inhibit
If the vehicle exceeds 6 mph (10 km/h) in the forward direction, and Reverse (R) gear is selected, the EAT ECU switches on the low clutch timing solenoid valve in the valve block, which drains the fluid from the reverse clutch.

This function prevents the gearbox from engaging reverse gear when the vehicle is moving in a forward direction, so preventing damage to the gearbox.

Hill Mode
Hill mode modifies the gearbox shift pattern to assist driveability on steep gradients. The EAT ECU detects the conditions to activate hill mode by monitoring the engine torque values, throttle angle and engine speed. This mode also assists driving at high altitudes and trailer towing.

Downhill Recognition
On downhill slopes there is a tendency for automatic gearboxes to upshift due to the increase in vehicle speed and the decrease in throttle angle.

The reduction in engine braking causes the driver to use the brakes. A downhill slope is recognized by EAT ECU as an increase in vehicle speed with the decrease in throttle angle.

When a downhill slope is recognized and the brakes are applied, the shift pattern is over-ruled and the gearbox shifts down a gear if engine speed allows. The downhill mode is cancelled upon application of the throttle.

Cooling Strategy
The purpose of the cooling strategy is to reduce engine and gearbox temperatures during high load conditions, for example when towing trailers. Under these conditions the engine and gearbox may generate excessive heat.

While in any gear other than 5th, or in 5th gear with the vehicle speed above 38 mph (61 km/h), if the gearbox fluid temperature increases to 127°C (260°F), the EAT ECU employs the cooling strategy.

This strategy consists of a separate shift and torque converter lock-up map that allows torque converter lock-up or gear changes to occur outside of their normal operating parameters.

This will reduce either the engine speed or the slip in the torque converter, therefore reducing the heat generated.
The EAT ECU cancels the cooling strategy when gearbox fluid temperature decreases to 120°C (248°F).

Engine Cooling Fan
If the gearbox fluid temperature increases to 110°C (230°F), the EAT ECU sends a cooling request message to the ECM on the CAN bus. The ECM then switches the engine cooling fan on, or if it is already on, keeps it on, to maintain the air flow through the fluid cooler.

The EAT ECU cancels the cooling request when the fluid temperature decreases to 100°C (212°F).

Diagnostics
If the EAT ECU detects a failure in an associated component, a fault code will be stored in the EAT ECU memory. TestBook/T4 is used to retrieve these fault codes to identify the cause of the failure.

Gearbox Fault Status
If the EAT ECU detects a fault with the gearbox system it will enter a fail safe mode. There are many fail safe modes the EAT ECU can adopt.

The EAT ECU will adopt the fail safe mode most acceptable for the driver and will ensure the least amount of damage to the gearbox.

When a fault is detected a CAN message is sent from the EAT ECU to the instrument pack and the MIL will be illuminated if the fault is related to OBD. If the ECU is able to implement a limp home mode, the instrument pack LCD will display '4' and 'F' alternately as the gearbox status display. Some faults may not display '4' end 'F' in the instrument pack, but the driver may notice a reduction in shift quality.

Engine Speed and Throttle Monitoring
The ECM constantly supplies the EAT ECU with information on engine speed and throttle angle through messages on the CAN bus. This information is used by the EAT ECU to calculate the correct timing of gear changes.

If the messages are not received from the ECM, the EAT ECU will implement a back-up strategy to protect the gearbox from damage, whilst allowing the vehicle to be driven.

In the event of an engine speed signal failure any of the following symptoms may be observed:
^ Decrease in fuel economy
^ Increase in engine emissions.

In the event of a throttle position signal failure, any of the following symptoms may be observed:
^ Harsh gear changes
^ No kickdown
^ Torque reduction request inhibited.