Electronic Automatic Transmission - Operation

Operation

Driving Modes
There are a number of different driving modes of operation. Some can be selected by the driver and some are automatically initiated by the EAT ECU during driving:
^ Normal mode
^ Sport mode
^ Manual (Steptronic) mode
^ Engine warm up mode
^ Hill Descent Control 2 (HDC) mode
^ Cruise mode
^ Winter mode
^ Hill mode
^ Default (Limp home) mode
^ Reverse lock-out mode.

Normal Mode
Normal mode is automatically selected by the EAT ECU on power up. In this mode all automatic and adaptive modes are active. Normal mode uses gear shift and lock-up maps to allow vehicle operation which is a compromise between performance, fuel consumption and emissions. If the transmission is operated in sport or manual mode and the selector lever is moved to the "D" position, normal mode is automatically resumed.

Sport Mode
In sport mode the EAT ECU uses shift maps which allow the transmission to downshift more readily and hold gears for longer at higher engine speeds. This provides enhanced acceleration and responsiveness.

Sport mode is selected by moved the selector lever to the left into the "M/S" position. "SPORT" is displayed in the message center when sport is selected.

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

Shift maps are provided for manual mode to protect the engine at high engine speeds. The EAT ECU will automatically change up to a higher gear ratio to prevent engine overspeed and change down to a lower gear ratio to avoid engine laboring and stalling.

Engine Warm-Up Mode
The EAT ECU monitors the output from the transmission fluid temperature sensor in the transmission and also receives an ECT sensor signal from the ECM on the CAN. When the transmission fluid and/or the engine coolant temperature is less than 60°C (140°F), the EAT ECU initiates the shift maps used in sport mode, when driving after a cold start.

The sport mode shift points raise the engine speed. This, in turn, promotes faster transmission fluid warm-up and also decreases the warm-up time for the catalytic converter to reach optimum temperature.

The warm-up mode is terminated if the vehicle speed exceeds 37 mph (60 km/h), the transmission fluid or the engine coolant temperature exceeds 60°C (140°F) or a maximum time of 3 minutes is exceeded.

Hill Descent Control (HDC) Mode
The HDC mode assists the ABS ECU in controlling the downhill speed of the vehicle when HDC is selected on. HDC can be selected under any conditions where low range is selected and below the 35 kph speed threshold while high range is selected. The selected ratio is transmitted on the CAN to the ABS ECU which allows HDC only if fist gear or reverse gear selected message is present. For HDC to be active, the correct gear must be selected, the HDC switch must be pressed and the throttle pedal must be released. The HDC symbol in the instrument pack will be illuminated and the selected gear (1 or R) illuminated in the instrument pack display.

The EAT ECU will maintain the selected year ratio end apply engine braking to assist the ABS ECU in controlling the vehicles descent.

Cruise Mode
When cruise control is activated, the EAT ECU receives a cruise active message on the CAN. The EAT ECU activates a cruise control map which prevents locking and unlocking of the torque converter clutch and minimizes up and down shifts. If cruise control is operative and the vehicle speed increases due to coasting downhill, the EGM can request a down shift via a CAN message if the vehicle speed exceeds the set cruise limit.

Winter Mode
Winter mode is a modified shift map to improve traction in slippery conditions. Each wheel speed sensor transmits a pulsed signal to the ABS ECU which calculates the rotational speed of each individual wheel. This information is transmitted on the CAN for use by other systems.
The EAT ECU uses these signals to determine when slippery road conditions occur. When active, the EAT ECU will select 2nd gear when the vehicle starts in preference to fist gear, improving driveability. Additionally, shift points are lowered further improving traction.

Hill Mode
Hill mode is initiated by the EAT ECU when high engine torque, high throttle angle and low engine speed is detected via ECM signals on the CAN. The EAT ECU defines this combination of signals to determine when the vehicle is traveling on a steep gradient

In response to these signals, the EAT ECU modifies the transmission shift pattern to raise the shift points to prevent repetitive up and down shifts. This mode can also be initiated when the vehicle is at very high altitudes.

Default (Limp Home) Mode
If a transmission fault is detected by the EAT ECU, the ECU adopts a limp home mode strategy. "TRANS. FAIL-SAFE" is displayed in the message center and, if the fault has an effect on engine emissions, the MIL will also be illuminated.

In default mode, P, R and N functions operate normally (if the fault allows these selections) and the EAT ECU locks the transmission in 4th gear to allow the driver to take the vehicle to the nearest dealer. The torque converter lock-up clutch is disabled and reverse lock-out will not function.

If the vehicle is topped and subsequently restarted in the default mode condition, the EAT ECU operates normally until the fault which caused the condition is detected again.

Reverse Lock-Out Mode
When the vehicle is traveling forwards, selecting reverse could cause transmission damage. To protect against this, reverse gear is prohibited if the vehicle is traveling forwards at a road speed above 5 mph (8 km/h.

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

When in any gear other than 5th or when in 5th gear at a speed of 38 mph (61 km/h), if the transmission fluid temperature increases to 124°C (255°F) or higher, the EAT ECU employs the cooling strategy.

The strategy uses a specific shift and torque converter lock-up clutch map. This map allows torque converter clutch lock-up and gear shifts to operate outside of their normal operation. This will reduce the engine speed and/or slip in the torque converter, therefore reducing heat generated by the engine and the transmission.

The cooling strategy is canceled when the transmission fluid temperature decreases to 120°C (248°F) or below.

Transmission Fault Status
If the EAT ECU detects a fault with the transmission system, it will enter a default mode to prevent further damage to the transmission and allow the vehicle to be driven.

When a fault is detected a CAN message is sent from the EAT ECU and is received by the instrument pack. The instrument pack illuminates the MIL and displays "TRANS. FAIL-SAFE" in the message center.

Some transmission faults may not illuminate the MIL or display a fault message, 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. The EAT ECU uses this information to calculate the correct and appropriate timing of shift changes.

If the messages are not received by the ECM, the EAT ECU will implement a back-up strategy to protect the transmission from damage and allow 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 shift changes
^ No kickdown
^ Torque reduction request inhibited.