Jaguar XJ (X350). Manual — part 1044

Transmission Shift selection

Shift Map Selection

The transmission control system utilizes a number of driver selectable operating modes and also a

number of adaptive/automatically selectable modes. Sport, Normal and Cruise Control mode are all

driver selectable. Hot mode, traction control mode and trailer towing mode are all adaptive modes

i.e. the transmission will automatically select this mode dependent upon the current driving

conditions.

Normal Mode

Normal mode can be selected by activation of the transmission mode switch located on the J-Gate.

Once activated this mode will remain engaged until the driver deselects the mode or engages the

cruise control system. If the driver engages cruise control when Normal mode is active upon

deactivation of the cruise system the transmission will automatically re-engage Normal mode. This

mode can be over-ridden by a number of adaptive modes.

The mode switch is of the momentary type.

Cruise Mode

When the driver engages the cruise control system the TCM receives a CAN message transmitted by

the Adaptive Cruise Control (ACC) or engine electronic controls which informs the TCM that cruise

control is currently active. Upon receipt of this message the TCM selects a new transmission shift

map. This map has been developed to reduce busy gearshift during cruise mode. It has also been

developed to increase fuel economy.

Hot Mode

This is one of the adaptive modes the transmission can enter when conditions are correct. When the

transmission fluid temperature, chip temp, engine oil temp or coolant temperature becomes hot

enough to reach threshold values, the TCM will cause the transmission to enter Hot mode. This mode

will automatically engage new shift and lock-up maps to reduce heat generated within the

transmission. The shift map will enable the transmission to change to higher gears at lower vehicle

speeds and the lock-up map will engage the lock-up clutch at lower vehicle speeds and in lower

gears. The effect of this is that less heat will be generated within the transmission due to the effects

of lock-up clutch slip and churning effects. There will be forced upshift strategy used in hot mode. To

exit hot mode the selector lever must be moved or the brake pedal applied or the accelerator pedal

applied 100%, during all of these methods of exiting from hot mode the fluid temperature must be

lower than the threshold values.

Traction Control Mode

Traction Control Mode is an adaptive mode, which is automatically engaged when a traction event

occurs. When driving on slippery surfaces (i.e.sand, ice) it is possible for the driven wheels to begin to

spin. The TCM believes the vehicle speed is increasing and therefore it may begin to upshift. These

upshifts reduce the torque at the wheel and so tend to reduce wheel slip. The downshift lines are

forced downwards to prevent unwanted shifts. To reduce the effects of this, if a traction event

occurs a signal is transmitted by the ABS module to the TCM over the CAN network, the TCM uses

this signal to change the currently selected shift map. The new shift map will have gearshift lines

further apart, thus inhibiting the transmission shifting to a lower gear.

Hill/Trailer Towing Mode

This is an adaptive mode. When the TCM detects reduced vehicle acceleration for a certain

percentage of throttle opening then this mode is automatically engaged by the TCM. When this

mode is engaged a new shift map and torque converter lock-up map is selected. This new shift map is

designed to reduce the number of gearshifts when towing a trailer or with the car climbing a steep

hill. The shift map will cause the transmission to hold on to gears for longer this increases

acceleration and reduces the number of gearshifts. This mode can also give an advantage when

driving at high altitudes, where the torque produced by an engine is greatly reduced by the effects of

reduced ambient pressure and airflow.

Driving Mode Priority

Each of the above modes has an associated priority i.e. Normal mode cannot over-ride cruise mode

etc.

Adaptive Shift Strategies

The TCM of the six speed ZF automatic transmission incorporates adaptive strategies which improve

the accessibility of the vehicle`s performance in driving conditions while maintaining a relaxed driving

experience when cruising.

In "Sport" mode, accelerator pedal usage and cornering behaviour are monitored to assess driving

style and road conditions. When an enthusiastic driving style or a demanding road is detected, 6th

gear is inhibited and the lower gears are made slightly more accesssible in order to prevent

unwanted "hunting" between gears. Conversely, when cruising conditions are detected, 6th gear is

once again made available to maximise driving refinement and economy.

Under conditions of heavy braking, the transmission will perform one or more downshifts to improve

response to a subsequent accelerator pedal application. Similarly if the accelerator pedal is released

rapidly following hard acceleration, one or more upshifts are inhibited to increase engine braking and

also improve subsequent response.

To complement these features, when a corner is detected transmission upshifts are inhibited. This

inhibition is also maintained for a short distance after the corner allowing the driver to achieve a

smooth balance through the bend without unwanted shifting mid-corner.

Safety features

The safety functions are designed to safeguard against mis-operation by the driver as well as against

system malfunctions. The mis-operation system prevents reverse gear from being engaged at high

forward speeds (Above 5 kph) and prevents manual downshifting at excessive engine speeds.

Great attention has been paid to safeguarding against, and detecting, malfunctions in the electronic

control system. The design of the electrical and diagnostic system is such that system integrity is

protected at all times.

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The hydraulic system has "fail-safe" characteristics regarding its electrical energisation, i.e. as a result

of the power supply being lost to the electro-hydraulic actuators the transmission engages a reliable

emergency gear ratio to facilitate a basic limp-home mode.

Recognition of critical shift operation by monitoring the last element in the signal path, i.e. the

solenoid valve, and checking by means of redundant measured variables, i.e. engine speed, input

speed and output speed.

Measures are in place which guarantee a high degree of availability of safeguard functions, i.e.

monitoring of safety circuits. For this purpose each time the vehicle is started there is a check on the

entire safety hardware, this is during TCM initialization and the associated program parts and signal

paths used during the TCM operation status. A malfunction in this part of the system, or triggering of

the safety circuit, will be communicated to the driver by the instrument cluster message centre.

Diagnosis and testing

Diagnostic Strategy

No Data Available

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