|October 2, 2007
The Audi A4: Assistance Systems
Be more relaxed at the wheel, and reach your destination safely – the innovative assistance systems in the new Audi A4’s specification keep you in control of every situation that can occur during your journey. Audi, motor of progress in this area too, can supply various convenient high-tech systems derived from luxury cars for its new saloon model. They keep the A4 at a safe distance from the vehicle in front, for example, warn the driver if the car tends to stray from its lane and make parking much easier.
Passive and active systems have significantly reduced the number of road accidents and their severity in recent decades. Audi remains at the forefront of this development. New types of assistance system can be realised with the aid of sensor technologies developed a few years ago for luxury saloon models such as the A8, and with today’s high-speed control units. Their capabilities are almost human: they can for instance scan certain areas around the car and identify the decisions and actions that the driver should take.
A study conducted by German insurers indicates that 25 percent of all road accidents are due to lack of attention on the driver’s part – fatigue, distraction or poor concentration. This is the problem area that Audi’s systems are designed to defuse by making driving safer and more relaxed.
Although this rapid progress is fascinating in its way, Audi never forgets that technology is not an end in itself, but has to be developed to serve those who buy and use it. The aim must always be to relieve the driver’s workload, without absolving him or her from ultimate responsibility, and certainly without insisting on a certain course of action.
From 30 to 200 km/h: ACC keeps the car at a safe distance
Another assistance system that originally appeared on luxury-class cars is radar-aided control of the distance from the vehicle in front. The system used on the new Audi A4 is known as ‘adaptive cruise control’ (ACC). The driver preselects a suitable road speed between 30 and 200 km/h, and ACC keeps it constant for as long as the distance from the preceding vehicle permits; this can be up to 180 metres. The radar sensor detects when the car is approaching the vehicle ahead too closely.
If the driver decides to overtake, ACC is temporarily overridden by pressing the accelerator pedal down, but remains active and later restores the preselected road speed and the corresponding distance that the system maintains from the preceding vehicle. The system is de-activated whenever the brake pedal is pressed, however, and then has to be reset at the control lever. This restores the previously chosen settings.
Doppler effect and signal transmission time: how ACC takes its measurements
The radar sensor is located at the right, next to the single-frame grille, in an exposed housing with a plastic lens. The scanning angle is about eight degrees, the range approximately 180 metres. The radar sensor’s four transmitting/receiving units operate in the 76.5 GHz frequency range, which is licensed for radio signals. The transmitted signal is of the FMCW (frequency modulated continuous wave) type. The directly measured values are the differences in frequency between the transmitted and received radar signals. With the aid of the Doppler effect and the signal transmission/reception time, the speed of the vehicle in front and its distance from the car can be determined.
Comparison of the signals received at the four individual aerials also established the angle of the vehicle ahead in relation to the sensor’s central axis. However, before the relevant preceding vehicle can be identified from the various objects that the sensor has registered, the lane on which the car is travelling must be known. This is computed from the ESP yaw-rate and steering angle sensor signals and from radar information on road and lane limits (e.g. crash barriers) and movements of other road users.
The system is integrated into the CAN network, which extends through the entire car; it can therefore communicate within a few thousandths of a second with other control units, such as those for engine management, the automatic transmission and the brakes.
Controls and displays
The driver selects his or her preferred speed according to the speedometer calibrations: between 30 and 80 km/h in five km/h steps, above this in ten km/h steps. The preselected speed is shown by LEDs on the speedometer dial. The system’s status (on/off - vehicle identified) is also visible on the central display. The time interval between the car and the vehicle in front can be varied in four stages, from 1.0 to 2.3 seconds: the driver information system displays this graphically. There are also three settings for the dynamic character of the system: dynamic/standard/comfort. By accelerating or braking, the system adjusts the car’s speed until it matches the programme selected by the driver. The ‘comfort’ setting has a maximum retardation rate of 3 m/s2.
Lane monitoring as a collision warning – Audi braking guard
The ACC sensor also has an additional safety function. If there is a risk of colliding with the vehicle ahead, the system warns the driver in two successive steps. In the first, a gong signal is heard and a signal is displayed on the instrument panel. As a precaution, the ESP builds up a degree of pressure in the hydraulic system during this step, so that full braking performance is available if the driver reacts by applying the brakes.
If the driver does not react, a clearly noticeable warning follows: the system applies the brakes for a brief period. This only slows the car down slightly, but is sensed by the driver as a sudden jolt and is of course intended as a ‘wake-up’ reminder. By means of extensive testing, Audi has confirmed that this is a highly effective warning signal. If the driver now applies the brakes, full stopping power is available without delay, and even hesitant pressure on the pedal will cause the hydraulic brake assist to make a full brake application.
The braking guard remains on duty even if ACC is de-activated. However, either the early warning or the complete braking guard function can be switched off separately at the MMI.
A sidelong glance to the rear: Audi side assist
Audi side assist also makes use of intelligent radar technology. Designed specifically for lane changes, it warns the driver if a potentially hazardous situation is likely to arise. Two radar sensors in the rear bumper, operating at a frequency of 24 Gigahertz, scan the area next to and behind the new Audi A4, up to a distance of 50 metres from the car. A high-performance computer unit evaluates and interprets the signal data.
If another vehicle is moving at approximately the same speed in the critical zone, or is approaching rapidly from behind, a yellow LED display comes on in the left or right outside mirror housing. It is ‘subliminal’ in character: the driver only sees it when looking directly into the mirror, whereas it is not registered by the driver when looking forwards.
If the driver of the new A4 operates the flashing turn indicator in preparation for changing lanes, despite the illuminated warning signal, the intensity of the LEDs is increased and they flash for about a second at a higher frequency. This signal is very difficult to overlook, since the human eye is extremely sensitive to changes in contrast in the peripheral viewing area. Audi has analysed the viewing behaviour and the effect of the display in full detail in an extensive series of tests with drivers of various statures and ages.
The optics of the display on the inner face of the mirror housing has been carefully aligned so that it can be seen by the driver but only with difficulty by other occupants of the car. Vehicle licensing regulations call for the display to be invisible to drivers of following vehicles, and for psychological reasons it is not desirable for the car’s front passenger to be aware of it. The brightness of the display varies according to ambient light conditions, from a dark moonless night to the midday sun in southern climes; it can also be adjusted via the MMI control terminal. The system becomes active at a speed of 60 km/h and is therefore out of action in built-up areas; it can be switched off at a button near the exterior mirror.
Audi lane assist: lane changes without risk
Also available for the new Audi A4 is a third high-tech assistance system previously only found in luxury cars – Audi lane assist. Above a road speed of about 65 km/h, it warns the driver if the car is wandering to one side, out of the chosen lane. A small black-and-white camera mounted on the windscreen above the inside mirror observes the road ahead of the car. Its optics has a range of 60 metres and a viewing angle of about 40 degrees. A high-speed computer in the same housing identifies lane lines marked on the road surface and determines the car’s position in relation to them.
If the driver allows the car to wander in the direction of a lane marking but has not indicated that he or she intends to make a turn, Audi lane assist issues a warning in the form of a vibration through the steering wheel. Its intensity can be selected in three stages at the MMI. There are also three settings for the moment at which the warning is initiated: before a wheel reaches the line, when the line is crossed or according to the system’s own variable assessment of the situation.
Audi lane assist can be switched off if not required. A display on the instrument panel tells the driver when it is active but not capable of issuing a warning, possibly because the lane lines are not clearly marked or the car’s speed is too low.
Parking made easy: the APS systems
To make parking easier, Audi has made three different parking assistance systems available for the new A4. The best known of these is the successful Audi parking system (APS), which supplies an audible signal as the rear of the car approaches an obstruction while reversing. The second version, APS plus, has additional visual displays for the front and rear, with a total of eight ultrasonic sensors in the bumpers.
The high-tech solution is the Audi parking system advanced, which has an integral rear-view camera. This is built into the boot lid and is extremely sensitive. Its ‘fish-eye’ lens has a very short focal length and can therefore provide a 130-degree wide-angle view behind the car. Its images are processed to eliminate distortion before being displayed on the monitor of the MMI operating system.
The display includes various guide lines and zones to help the driver position the car correctly when reversing. When reversing into a parking bay at a right angle to the direction of travel – the standard mode – orange lines indicate the path that the car should follow. To park the car by reversing into a bay parallel with the road, an area shaded in blue indicates the space that the Audi A4 will occupy, so that the driver can see whether the parking manoeuvre will be successful. Blue lines indicate when to turn the steering one way and then the other.
The camera also shows the trailer tow hitch that can be installed as an optional extra. With the aid of this image, the Audi A4 can be reversed accurately up to the trailer towbar. In addition to this real-image mode, APS advanced also provides the classic visual and audible parking aids using signals from ultrasonic sensors. The driver can use the MMI controls to switch between the video-camera image, a graphic display or automatic changeover between the two.
The equipment, data and prices stated here refer to the model range offered for sale in Germany. Subject to amendment; errors and omissions excepted.