Automatic gearbox - Jatco (Hill Mode): Description and operation

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 recognised by EAT ECU as an increase in vehicle speed with the decrease in throttle angle.

When a downhill slope is recognised 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' and '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: l Decrease in fuel economy l Increase in engine emissions.