CAN-based in-vehicle networks - continued
Accident avoidance systems
Accident-free driving may be a long-term dream, but automotive engineers have already started to develop accident avoidance systems. Several suppliers have presented promising driver-assistance technologies. Besides the above-mentioned ESC, Bosch has introduced two forward-looking driver-assistance systems: The parking assistance and the adaptive cruise control (ACC).
ACC is already in production. Bosch has introduced the ACCplus, an adaptive cruise control system for slow-moving traffic. In the future driver assistance systems will integrate video (in addition to ultrasonic and radar) sensors. For this application, the bandwidth of CAN networks maybe not sufficient.
Simple ACC systems are enabled if the vehicle speed is higher than 30 km/h. Stop-and-go ACC systems are active also at lower speeds. All these systems are semi-autonomous. This means the driver has always the possibility to interact and to take control and of course responsibility. BMW called its ACC program “ConnectedDrive”. This program includes lane-departure-warning and lane-changing-assistance. The system that is in development, detects fast moving cars in the mirror and will warn the driver. It also warns the driver, if the car departs the lane accidentally.
Continental has launched its Full Range ACC systems in 2005. It went into the latest Mercedes-Benz s-class. The system aids the driver in keeping distance from the vehicle in front. In previous systems, the driver had to take over as soon as the speed dropped below 30 km/h. The included Active Distance Support (ACDIS) is the first system to network the distance sensors at the front of the vehicle with a force feedback gas pedal that was developed together with AB Elektronik.
Siemens VDO has released an ACC system that warns the driver, if the car driving ahead is too close. This works also in foggy situations. The system based on radar sensors is planned for middle-class and compact cars by 2008. The system automatically reduces the vehicle speed in order to keep the distance depending on the velocity. The automatic speed reduction is only performed when the driver has enabled the automatic speed control.
ACC does not just reduce accidents, but also saves energy. According to VDO research studies, it is possible to reduce fuel consumption by using ACC systems due to the fact that they prevent traffic jams. ACC systems will prevent traffic from slowing down and keep it smoother.
The combination of ACC and ESC would increase the ACC performance. ESC provides an increased deceleration capability through active braking without endangering the vehicle stability. Additionally, in the event of an emergency brake situation, ESC allows the vehicle to maximize braking, which in the future will assist collision-mitigation technologies in avoiding an accident or at least in minimizing the effects of a collision. All the necessary data exchange will be done via CAN networks.
Bosch aims to prevent rear-end collisions by further developing driver-assistance systems. The first step was the development of the Predictive Brake Assist (PBA), which debuted in 2005 on the Audi A6. If the ACC radar identifies a critical situation, the brake pads move closer to the brake discs in preparation for possible emergency braking to gain precious fractions of a second for quicker response. A second development will extend the functional range of PBA to a predictive collision warning to quickly alert a driver of a critical situation, allowing for a faster reaction and, hopefully, avoid accidents.
For instance, the system could warn a driver by a brief pull on the brakes and activate reversible protection systems such as electric seatbelt tensioners. The third step will be predictive emergency brakes (PED): They will make use of video sensors in addition to long-distance radar by triggering automatic emergency braking in extreme circumstances. This function would only be activated if the driver had not adequately reacted to prior warning and a collision is unavoidable. This allows the force of the collision to be significantly reduced. Bosch is planning to offer such a system by the end of this decade. The company - just as their competitors do - is working on combined passive and active safety systems (Caps).
First presentations of brake assistance systems by Mercedes-Benz and Honda have not been successful. The collision mitigation brake systems introduced this spring and demonstrated to journalists failed: They did not brake the cars as expected and promised. The CAN communication was not the reason, but the application software should be corrected and might even be redesigned.
Parking assistance
The next generation of semi-autonomous parking assistance systems, which will be introduced in the next years to mid-range cars, uses ultrasonic sensors mounted on the sides of the vehicle to measure parking space length and depth as a vehicle passes it. The system calculates the required steering and informs the driver visually or acoustically. In more advanced systems such as park steering control, the steering will be handled by the electronically controlled power steering. Of course, parking assistance systems need communication to other sub-systems, and CAN would be a natural choice.
Body electronics
Historically, the second CAN application in in-vehicle networking was connecting comfort electronics such as power-mirrors, power-windows, lightning units, seat controllers, etc. First introduced in premium cars, those functions are nowadays provided even in compact cars. Typically, these CAN networks run at lower bit-rates than the power-train communication systems. Some carmakers have chosen the fault-tolerant CAN physical layer (ISO 11898-3). However, there is a trend to move to the high-speed low-power CAN physical layer (ISO 11898-5). Some pessimists expect that the ISO 11898-3 low-speed transceiver may be discontinued some day.
The innovations in this body electronics will rely on CAN connectivity. Hella has developed adaptive headlamps. The first car that has made use of this technology is the E-class from Mercedes-Benz. Adaptive headlamps adjust to different driving and weather situations and thereby offer significant improvements to driving safety. The system from Hella provides five lighting functions: country, motorway, active bend lighting, fog and cornering. The country light illuminates the left-hand edge of the road brighter and over a grater range than the previous low beam. The motorway light switches on automatically from speed of 90 km/h. The cornering light function is used when driving slowly through bends. Some of these intelligent light functions require information from other ECUs. Those are made available through the CAN in-vehicle networks.
ESC reduces fatal accidents
The electronic stability control, first introduced by the ESP system from Bosch, reduces the fatal accidents by 43%, reports a study from the Insurance Institute for Highway Safety (IIHS) in North America. In consequence, the institute is calling for ESC to be fitted as standard in all vehicles. High-end and middle-class cars are already equipped with ESC; however only one in twelve cars below the compact class is fitted with this life-saving technology. “Too few, given that it is precisely this kind of car that is driven by inexperienced, young people,” says Herbert Hemming from Bosch. “It is precisely these drivers who need the guardian angel of ESP.” Bosch’s ESP system comprises a hydraulic modulator with add-on ECU, wheel-speed sensors, steering-angle sensor, yaw-rate and lateral acceleration sensors, and last but not least the CAN-connected engine-management ECU.
