June 25, 2005 Citroen has revealed a fly-by-wire prototype C5 that has done away with all mechanical links between the driver and the car, along with the conventional pedals, to save weight, boost safety and cut costs. Already used in a variety of Citroen Show cars, such as the C-Crosser and the C-Airdream, the 'C5 by Wire' replaces the mechanical connections between controls (steering wheel, pedal assembly, etc.) and sub-systems (steering, brakes, etc.) with electronic computer-controlled connections in a production car for the first time. Not only have the pedals disappeared in the 'C5 by Wire', a special steering wheel now contains all the controls required by the driver for the steering, braking and acceleration.
The Citroën"X-by-Wire" technology also opens new possibilities in interior design by replacing mechanical components such as the pedal assembly and the steering column. Grouping all the driving controls on the wheel is an ergonomic solution that also promotes easy use. As a result, controls can be activated more quickly for enhanced safety.
Operating principle of the driver interface Essential driving functions are managed by the driver, who holds the steering wheel in the "quarter-to-three" position in order to activate the controls.
The lower and upper parts of the steering wheel hoop have been removed, allowing full use of the all-electric variable-ratio steering, which is particularly quick at low speeds.
The driver uses the right or left thumb to reach the forward-facing acceleration paddles on either side of the wheel. It was necessary to provide two paddles in order to allow the driver to accelerate and, at the same time, to activate the lighting on the left, and the windscreen wipers, headlamp washers and horn on the right.
Automatic cruise control is also available to regulate speed and enhance driving comfort, avoiding the need for the driver to keep pressing the paddles. Cruise control is disconnected when the driver brakes or accelerates.
The brakes are controlled by "triggers" located at either end of the steering wheel. The driver uses the right or left index finger to reach these controls. Brake force is applied intuitively.
These controls are all highly ergonomic. They feel completely natural to use, after just a short time behind the wheel.
The "X-by-Wire" system: technology serving safety The multifunctional steering wheel plays an essential role. Easy to use, it allows the driver to concentrate on the road, thus clearly contributing to safety. Safety was an essential factor in the development of "X-by-Wire" systems for the automotive industry.
The absence of the pedal assembly and steering column considerably enhances safety, since the risk of injury in the event of impact is significantly reduced. In addition, the space freed up for the legs improves ergonomics and postural comfort.
Also, having the controls on the steering wheel increases the speed of execution, particularly when braking. Precious time is gained, since the driver no longer has to reach for the brake pedal.
Variable-ratio electric steering
The all-electric steering system provides a variable steering wheel angle/wheel angle ratio, adjusted automatically to suit the driver's requirements and the speed of the vehicle. In particular, this function makes parking much easier, thanks to the more direct steering ratio (between one and two turns of the wheel compared with three turns in normal cars). This feature also ensures pin-sharp steering at high speeds.
Ò Considerable latitude in adapting and defining steering parameters in terms of torque (controlling wheel vibration, for example), angle (small turns of the wheels) and vehicle behaviour (overall chassis control).
" Electro-hydraulic braking system
The braking system is electro-hydraulic. There is no pedal assembly, but the electric button on the steering wheel plays exactly the same role as a conventional system. Brake force is applied progressively, in an intuitive and natural way. To brake, the driver simply applies pressure to one or both of the steering wheel handles.
With the "C5 by Wire", Citroën is exploring new technological options. By eliminating mechanical limits and constraints, it aims to pioneer more attractive and ergonomic cockpit design that adapts to the needs of each driver and brings significant progress in active safety.