Citroën: New Electronic Transmission for Diesel C4

The French are boosting fuel economy to 52 mpg.

Citroën is introducing a new six-speed electronic transmission system on its 1.6 HDi 110 hp diesel models of the C4 in Europe.

The automated gear changes and clutch control of the new system reduce fuel consumption by up to 6% compared to current models, resulting in a promised 4.5 liters/100 km (52 mpg US) and CO2 emissions of just 120g/km. These new 1.6 HDi 110hp models are now also fitted with a Diesel Particulate Filter System (DPFS).

The new transmission eliminates the clutch pedal, and gives the driver the flexibility to choose between a manual mode, with paddleshift or gear lever (which has no mechanical link with the gearbox), or an automatic mode. A Sport function is also available, while a hill-start assist feature contributes to improved safety and ease-of-use.

Using new electro-hydraulic actuators to ensure gentle and smooth gear shifts, the system can also recognize and automatically adapt to individual driving styles. In manual mode, the driver maintains full control of the gear change by using either the paddles that are set behind the steering wheel, or the sequential gear lever, which can be flicked forwards or backwards to change up or down.

The Sport function is available in both manual and automatic modes. Engaged by pressing the S button next to the gear lever, the Sport function speeds up the gear changes, from 0.8 to 0.4 seconds in manual mode and from 1.2 to 0.5 seconds in automatic mode.

The hill-start assist makes it easier to start on slopes by preventing the car from rolling and giving the driver time to accelerate away safely and confidently. Activated on both uphill and downhill slopes with a gradient of 3% or higher, the control holds the car steady for two seconds when the brake is released.

A control unit controls the two actuators of the gearbox system. The first-the gearbox actuator-ensures the selection and engagement of the gears, and the second-the clutch actuator-controls the clutch.

When a gear change is requested, either by the driver directly issuing a gear change command or indirectly by the driver depressing the accelerator or the brake or as a function of the gradient of the road, engine speed, vehicle speed and grip conditions, the gearbox control takes control of the engine controller and the clutch actuator.

Engine torque is reduced and the clutch is opened progressively to avoid jolting. Once the clutch is open, the gearbox control unit activates the gearbox actuator. The selector fork is disengaged, the new gear is selected and synchronized, the selector fork is reengaged.

The gearbox control unit then progressively closes the clutch and controls torque increase to complete the gear change without jolts or rebounds. When upshifting, the entire process takes between 0.4 and 1.2 seconds.

A 1.6 HDi C4 was also one of the platforms for PSA Peugeot Citroën's introduction of two diesel-electric parallel hybrid applications earlier this year. The C4 Hybride HDi prototype delivers average combined city and highway fuel consumption of 3.4 liters per 100 kilometers (69 mpg US), with 90 grams of CO2 emitted per kilometer.

Related news: Foursprung, P4MR, Citroën

Source: Green Car Congress

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