Special Functions

Special Functions

- Launch Control (racing start function)
This function is available both in selector-lever position "D" and "M" in Sport Plus mode. Preconditions are as follows: Vehicle is stationary, brake is applied, kick-down is active. The function is triggered by releasing the brake. The Doppel-kupplung in the transmission now enables optimum wheel slip at maximum acceleration.

Stress on components increases significantly when driving off at maximum acceleration in comparison with driving off "normally". In addition, there is a high temperature burden on the components in the clutches. To protect the components in this case, this function is disabled for a distance of 1.5 miles (2,5 km) after a racing start. During the 1.5 miles (2,5 km) drive, the clutches are cooled with the maximum cooling volume flow.

- Prevention of downshifts in overrun state, e.g. approaching a corner (Fast Off)
If the driver decelerates, i.e. releases the accelerator pedal quickly, when approaching a corner, the currently engaged gear is retained. If the driver also actuates the brake now, downshifts adapted to the vehicle speed are performed so that engine braking support is available when approaching a corner and the vehicle can be accelerated out of the corner in the optimum gear. If the accelerator pedal is now moved towards throttle valve "open" again, gearshifts are performed once again according to the driver request.

This function responds differently, depending on which mode was selected. If "Normal" mode is selected, the function is only activated for a high negative accelerator pedal gradient. In "Sport" mode, the function is activated for a medium negative accelerator pedal gradient, while it is activated for a low negative accelerator pedal gradient in "Sport Plus" mode.

- Downshifts while braking (Fast Back)
A downshift is initiated immediately if the driver switches quickly (within approx. 1 second) from accelerating to braking. However, the sportiness characteristic and the selected mode dictate how early a downshift is initiated.

- Gear retention while cornering
The lateral-acceleration sensor (single component with rotation-rate sensor), which is located under the centre console and works for the PSM system, is used to detect lateral acceleration and retain the engaged gear and lateral acceleration in the relevant gear, depending on the shift map.

- Active switching to a sporty gear-changing map
For increased spontaneity, the system switches to a sporty and dynamic shift map when the driver uses fast, positive accelerator pedal movements. The previous map is then activated again afterwards. This function is intended, for example, for situations in which a driver is driving at an extremely comfortable speed on a country road, but now decides to overtake and wants the vehicle to drive dynamically for a short time.

- Manual momentary intervention in selector-lever position "D"
To enable manual downshifts even in the automatic gear-selection gate, e.g.:
- when approaching a corner
- when entering villages/small towns
- when driving downhill

the upshift and downshift buttons (both on the steering wheel and on the selector lever) are active in the automatic gear-selection gate. In other words: PDK transmission switches to the manual programme when the corresponding button is pressed. "M" appears in the instrument cluster and the requested gearshift is performed. At the same time, an 8-second timer is started in the control unit. If the upshift or downshift button is pressed again within this 8 seconds, the timer is restarted. The PDK transmission automatically switches back to Automatic mode ("D" appears in the instrument cluster) if:

- the timer runs out, no cornering is performed and the vehicle is not in overrun state
- the selector lever is moved from "D" to "M" and back to "D"
Automatic upshifts and downshifts at the engine speed limits remian active.
The deceleration downshift function is also active.

Warm-up program

The warm-up map is a shift program with raised gear-changing points, which has the effect of heating the catalytic converters to their operating temperature as quickly as possible. Even the engine and transmission reach their operating temperature more quickly with this map. The coolant temperature of the engine is checked when the engine is started. If this is less than approx. 68° F. (20° C), the warm-up programme is activated and is deactivated again when the coolant temperature is 86° F. (30° C).

Overheating protection

Various measures are implemented on the transmission in order to protect the transmission and Doppelkupplung from overheating. The temperature sensor, which is fitted above the hydraulic control unit and measures the oil sump temperature, is used for this purpose. A calculation model, which calculates the clutch temperature from the engine torque and the slip at the clutch, is also used.

Overheating protection is activated in several stages and actively prompts the driver to adapt his driving style. Clearly perceptible jerking occurs in the first stage due to continuous opening and closing at drive-off and crawling speed, thereby prompting the driver to change the driving situation. Engine torque and kickdown rpm are also reduced. This is not displayed in the instrument cluster. A fault is stored in the control unit.

If the temperature continues to rise, stage two is activated. This means that jerking continues. The engine torque and kickdown revs are reduced more drastically in this case. The white warning "Transmission temperature too high" appears in the instrument cluster and another fault is stored in the fault memory.

If the temperature rises even further, the red warning "Transmission emergency run" appears in the instrument cluster. A short time later, the Doppelkupplung is opened completely and power transmission is no longer available. Another fault is stored in the fault memory. If the driver now presses the accelerator, the vehicle will drive off, but not with the usual level of comfort. After implementing these measures, the transmission activates a special shift program in which gear changes are performed very slowly, with a high level of discomfort. Once the temperature falls below a certain temperature threshold, the transmission reverts to its normal program.

Upshift suppression for 7th gear

7th gear is designed as an overdrive on PDK transmissions. This means that in various driving situations, e.g. high road resistance, the vehicle would decelerate when 7th gear is engaged. As a result, 7th gear is not engaged in such situations.

Upshift interruption

In automatic transmissions, the time that elapses between triggering a change in speed and starting to change speed is called the response time. Naturally, this response time depends on the shift program and the gearshift characteristic. During this time, the driver does not yet notice that the gearshift operation has already started. If the driver request changes, e.g. the driver quickly eases off the accelerator, the upshift that has started is interrupted provided the engine speed remains unchanged.

One-touch Hold function

The one-touch button on the steering wheel or the selector lever must be held in a downshift ("-") or upshift direction ("+") in order to engage the lowest or highest possible gear. Tipping the button back initially triggers the first gear change in accordance with the touch command. The next lower or next higher gear is then always engaged by holding the button. This saves the driver from having to touch the button repeatedly. This function is switched off after 25 seconds to prevent malfunctions.

Crawling

To ensure that the PDK transmission behaves in the same way as a Tiptronic transmission when driving off, clutch 1 is already slightly engaged so that the transmission becomes positively engaged and must be held by the brake. Another advantage of this measure is that the vehicle drives off very comfortably and generally smoothly when only a light load is applied. Driving off at a higher load results in higher drive-off power.

Stationary decoupling

When the vehicle comes to a stop, the clutch is generally opened as long as the brake is applied. However, the clutch remains slightly engaged in order to take full advantage of crawling. The reason for this measure is reduced fuel consumption.

Drive-Off Assistant

If the vehicle is stopped on an incline, the driver will apply the brake and set a certain brake pressure. When the driver now switches from the brake pedal to the accelerator pedal in order to drive off, the set brake pressure is maintained for as long as it takes for the vehicle to drive off. This prevents the vehicle from rolling back while the driver is switching pedals. Rollback prevention is enabled for max. 2 seconds.

Tow-starting/towing

NOTE: Never lift the vehicle at just one axle when towing all-wheel-drive vehicles

The vehicle cannot be tow-started, nor should this be attempted due to the risk of serious transmission damage.

When the engine is not running, adequate lubrication of the transmission is not guaranteed. Therefore the following points must be observed:

1. Engage selector-lever position "N"

2. Top speed = 30 mph (50 km/h)

3. Maximum towing distance = 30 miles (50 km)

4. In the case of long towing distances, the all-wheel-drive vehicle must be transported on a trailer.