Exactly 40 years ago, Audi revolutionized the automotive world. In 1980, with its permanent all-wheel drive called quattro, the company introduced a new approach to chassis technology which still expresses the motto "Vorsprung durch Technik" to this day. Today, thanks to the intelligent interconnection of the Electronic Chassis Platform (ECP), innovative chassis systems are able to unfold their full potential, such as the electromechanical active roll stabilization (eAWS), suspension Active predictive and dynamic four-wheel steering (DAS). In the Audi e-tron, the Integrated Brake Control System (iBRS) is an example of how efficiency will become the third variable in chassis development, alongside ride comfort and sportiness. As a high-tech control unit, the future vehicle dynamics computer can simultaneously manage up to 90 components.
Towards an integrated vehicle dynamics calculator
Audi is advancing the concept of integrating chassis and powertrain technology. In the future, an integrated vehicle dynamics processor will control longitudinal and transverse dynamics, as well as energy management and the driveline: energy recovery during braking, determination of the driving force in milliseconds, compression shock absorber and keeping the vehicle on the correct path, all at practically the same time. The development objective for future chassis generations is clear: in addition to a greater margin between sportiness and comfort, the integration of efficiency technologies will play a key role.
The future vehicle dynamics processor will be significantly more powerful than the current electronic chassis (ECP) and will control almost all longitudinal, transverse and vertical dynamics functions; for example, the chassis, powertrain and recovery functions. It will run about ten times faster than current systems and will be able to control up to 90 functions, compared to 20 that the current ECP can handle. Another novelty will be its modular ability to work with different types of propulsion systems: electric, hybrid or thermal engine vehicles, as well as front-wheel drive, all-wheel drive or propulsion for electric models. As a result, the central vehicle dynamics computer, in addition to the car-to-x functions, will also allow specific functions. Its precise data calculation will also perform the operations of the advanced driver assistance functions.
Through intelligent electronic control, the development of chassis technology at Audi results in the interconnection of individual mechatronic components and vehicle functions. The electronic chassis platform debuted on the Audi Q7 in 2015. Today, it interconnects the individual components of the chassis systems of Audi midrange, premium and luxury models. Thanks to this intelligent interconnection of constantly evolving chassis technologies, such as quattro permanent all-wheel drive, adaptive air suspension or dynamic all-wheel steering, Audi has forged a successful link between superior ride comfort and driving dynamics. of the first order.
Interconnection as a trigger: unprecedented flexibility, from the comfortable to the athletic
An example that perfectly illustrates the enormous effort that Audi invests in the technical design of the chassis is the electronic roll stabilization system of the Audi SQ7 and SQ8, which can unlock its full potential thanks to the intelligent interconnection. In these large SUVs, body movement in curves and load changes are minimized. In addition, the system offers surprisingly high transverse dynamics capabilities and therefore an exceptional driving experience.
In fast corners, thanks to the electronic adjustment of the anti-roll bar, the roll is reduced because, in a few milliseconds, it gently lifts the side of the body opposite the curve, applying a torque of up to 1200 Nm which opposes centrifugal force. This allows for higher cornering speeds and also drastically reduces load change reactions. On a straight path, for example on an uneven road, a gear system disconnects the two halves of the stabilizer, which improves ride comfort. As a central computer, the electronic chassis platform also combines information from other chassis technologies of the SQ7 and SQ8, such as the four-wheel steering system, air suspension and quattro sport differential. The driver experiences this tight interconnection with high precision and driving agility.
In the Audi A8 there is another important chassis function that improves comfort. It is based on a fully active electromechanically controlled suspension system. In each wheel there is an electric motor powered by the main 48 volt system. Every five milliseconds, the EPC sends control signals to the active suspension. A belt drive and compact wave gear convert the torque of the electric motor to 1,100 Nm and transfer it to a steel bar. From its end, the force reaches the frame through a lever and a connecting rod. On the front axle, it acts on the air suspension column of the adaptive suspension; on the rear axle, it does so in the transverse suspension control triangle.
In this way, each wheel of the Audi A8 can be subjected or unloaded independently of an additional load and adapted to the road conditions. As a result, it actively controls the position of the body in any situation. Thanks to the flexibility of the active suspension, the driving characteristics are extended to a whole new range.
When the driver selects dynamic mode with Audi drive select, the car becomes sportier: it becomes firmer, cutting body roll in half with normal suspension and with less pitch when braking. In comfort mode, however, it floats smoothly through irregularities on surfaces of any kind. To stabilize the body, active suspension continuously supplies or removes power from the structure. In this way, drivers and passengers are virtually "disconnected" from the mechanical powertrain and the effects of driving.
In addition, in the event of an impending side impact at over 25 km / h, the A8's active suspension instantly lifts the bodywork up to 80 millimeters, causing the involved vehicle to collide with an even more difficult area. In this way, the deformation of the passenger space and the impact on the occupants, in particular on the thorax and abdomen, can be up to 50% less than that of a side impact without lifting the suspension. . Again, the ECP is responsible for activating the active suspension and interconnecting it with other chassis components, such as air springs. The result: excellent suspension comfort and maximum safety.
Superior braking: the brake control system integrated in the Audi e-tron
The Integrated Brake Control System (iBRS) in Audi's e-tron models illustrates the growing interconnection between chassis and powertrain technology. Thanks to this, efficiency becomes the third objective of the development of the chassis, along with comfort and sportiness.
The recovery system, for example, contributes up to 30% of the range of the electric SUV. The iBRS includes in this process the two electric motors, as well as the integrated hydraulic brake system. It is the first to combine three different types of recovery: manual in retention thanks to the paddle shifters; automatic retention thanks to the predictive efficiency assistant; and regenerative braking with a smooth transition between electric and hydraulic deceleration. Up to 0.3 g, the Audi e-tron decelerates exclusively with electric motors, without using the conventional brake, which happens more than 90% of the time. As a result, virtually all normal braking maneuvers provide battery power.
Using the gearshift paddles, the driver of the Audi e-tron can select the level of recovery on hold. At the lowest level, when the driver takes his foot off the accelerator, the car drives without a grip. At the highest level, it significantly reduces speed; so much so that the driver can only decelerate and accelerate with the accelerator pedal. Under these conditions, the brake pedal is not used. The wheel brakes only act below the 10 km / h threshold, if the deceleration is greater than 0.3 g or if the battery is fully charged and therefore cannot be recovered. 'energy.
Thanks to this new concept of electro-hydraulic brake actuation, of which Audi is a world pioneer in an electric production car, the driver does not perceive the passage from the recovery phase with electric braking via the motors to conventional friction braking of the hydraulic system. This combination results in a variable pedal feel, with a clearly defined and constant pressure point, as in a vehicle equipped with a conventional internal combustion engine and hydraulic brakes. Since the brake pedal is not connected to the hydraulic system, the transition from electric retention to conventional brake is smooth and cannot be felt by the driver on the foot.
This is made possible by a complex electro-hydraulic system: a hydraulic piston in the compact brake module generates additional brake pressure and force to supplement the holding torque. In automated emergency braking, it only takes 150 milliseconds from the time deceleration begins until maximum brake pressure is applied between the pads and rotors. Depending on the driving situation, the integrated electro-hydraulic brake control system decides whether the Audi e-tron will decelerate by means of the electric motors, using the hydraulic brakes or a combination of both, individually on each axle. With this system, the electric SUV takes advantage of its maximum recovery potential.
The interconnection also stands out in the integrated brake control system, with the iBRS supplemented by the Efficiency Assistant, which is part of the standard equipment. The system recognizes the environment and the path of traffic using radar sensors, camera images, navigation data and car-to-x system information. As soon as it is convenient for the driver to take his foot off the accelerator pedal, this information will appear in the Audi virtual cockpit. In interaction with the optional adaptive cruise control, the Efficiency Assistant can also predictably slow and accelerate the electric SUV.