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Automotive Innovative Sensor Technology for Autonomous Driving

created by Tamara Drexler, Product Manager Sensor Systems – Automotive Business Unit; Tobias Maier, Field Application Engineer – Automotive Business Unit |   Rutronik

Autonomous cars are driven by sensor and camera based computers that are intended to make road traffic safer - that's the idea. According to the market research institute Emnid, 41% of Germans believe driverless cars can achieve this goal. Accordingly, the demand for advanced driver assistance systems is increasing sharply in most automotive classes.

Autonomous driving is set to be marketable by 2025. Drivers can then relax and leave the tasks of monitoring the roadway and controlling the vehicle to the system, as complete vehicle control will be achieved by highly innovative and precise sensors and efficient microcontrollers. Drivers will be able to watch a video, write e-mails, use their smartphone or enjoy a meal or drink. This not only enhances driving comfort but also offers considerable time-saving benefits.

Completely new services also arise in the commercial sector: A rental car can, for instance, drive autonomously and directly to the user at a specific time and not the other way around, i.e. the user to the vehicle. Or a moving van returns unmanned to the rental company after completing its task.

More safety

Besides increased comfort, driverless cars also offer decisive advantages with regard to two essential areas: Safety and environmental protection.

According to the German Federal Statistical Office, there were more than 2.5 million road traffic accidents, 300,000 of which resulted in personal injuries, in Germany in 2015. Advanced driver assistance systems (ADAS) will help to minimize this huge figure, as they increasingly exclude human errors, e.g. due to fatigue, strong emotions or other distractions.

More economy

If assistance systems are complemented with car-to-car and car-to-x communication, it is possible to reduce CO2emissions drastically. Route-related details, e.g. the latest traffic light status, traffic jam and road work information, guarantee proactive and efficient driving behavior. Unnecessary acceleration before a red light or the inefficient bypassing of a traffic jam will then be a thing of the past. The limit values for CO2 emissions of 95 g/km by 2020, as stipulated by the EU, will then be within reach.

From ADAS to autonomous driving

Current models are already equipped with a multitude of assistance systems. However, drivers still have full control over their vehicles. According to the classification of the Society of Automotive Engineers (SAE) for autonomous driving, this corresponds to SAE level 3 - "partial automation". Depending on the driving mode, electronic systems assume all aspects of the dynamic driving task, the driver only needs to respond appropriately to the requirements, e.g. conditional deceleration or acceleration. An example of this is the automatic park pilot system, which maneuvers the car into an appropriately-sized parking spot. This system has been integrated in almost all luxury class cars.

Autonomous driving involves replicating the human senses of seeing and hearing as well as the way the brain processes data. These tasks are assumed by highly innovative and extremely precise sensors and electronic control units (ECUs). Both the systems and the individual components must fulfill the highest demands regarding functional safety (ISO 26262). Some examples of current assistance systems illustrate the function:

Lane departure warning system or steering pilot

A steering pilot supports the driver with lateral control and helps to keep the vehicle in the middle of the lane when the road is straight and the bends moderate. This type of steering pilot has, for instance, been integrated in the new Mercedes Benz E-Class (model 213).

One of the basic prerequisites for this technology is a camera system that records the environment and an angle sensor that reads the current steering angle. Using the lane markings detected by the camera, the ECU determines a target course based on the middle of the lane and sends this data to the steering system. This system can then actively respond to this by intervening in the steering process or passively through an acoustic or haptic warning signal.

State-of-the-art camera systems use stereo cameras, consisting of two high resolution CMOS mono-cameras installed in a casing approx. 20 cm behind the windshield. While a mono-camera simply estimates distances, the stereo version can measure the distance to an object and its height above the road surface. At a mean distance of between 20 and 30 m, it can determine the distance to an object down to 20 to 30 cm.

Distance assistant

The distance assistant uses a radar system to measure the distance and the relative speed to vehicles on the road ahead. Such radar systems with a small range of up to 250 m are also used for parking, braking, and distance warning systems at approx. 75 GHz to 76 GHz (wideband). Images of the stereo camera ensure enhanced object and distance detection through object fusion.

The AEC-Q100 certified STRADA431 from STMicroelectronics is, for instance, recommended as a 24 GHz radar sensor due to its compact design in a QFN package with a footprint of 6x6mm². The 3.3V supply voltage, the on-chip power sensor, and the additional temperature sensor enable the setup of an ASIL B compatible system.

Cruise control

Cruise control is of key importance for autonomous driving. Since the driver is no longer actively involved in the driving process, acceleration and deceleration must take place automatically. To achieve this goal, sensors measure the current speed, and the opening time of the throttle valve is controlled accordingly. The rotational speed sensor TLE4941plusC from Infineon has been developed as an ABS and ESP sensor. A sensor has to be installed on all four wheels for this purpose. In this respect, the TLE4941plusC, designed as a differential Hall Effect sensor, not only delivers accurate values but also exhibits high robustness.

The Infineon sensor offers ESD protection up to 12kV and has been qualified for automotive applications in line with AEC-Q. It can be applied with a maximum voltage of 20V which is converted internally into a 3V supply via a voltage regulator.

Current challenges

A number of challenges still have to be overcome in order to realize more advanced ADAS and finally autonomous driving. One arises from the trend away from local toward central processing of sensor data. This has the advantage that data from all the sensors of the various subsystems are available to the processing ECU and that the relevant data can be used for a variety of functions. The sensor modules then perform purely sensory and data transmission functions without any processing and decision-making functions, thus eliminating data losses due to pre-processing or compression in the sensor module. As a result, the sensor modules can become smaller, more cost effective, and energy saving.

This does, however, require a "super ECU". Taking all the required sensors into account, tier 1 supplier Continental AG believes roughly 1 Gb of data will be generated each minute. The data must be processed in real time for safety-relevant systems. At the moment, there is no computing unit that can achieve this safely.

Ensuring safety and security is another challenge. As both functional safety and data security must be guaranteed. The problem of data security must be solved at the latest when a car-to-x communication system is implemented in a vehicle. Since security gaps offer hackers the opportunity to log into the car in order to read out data, to stop the car via remote control or to take control of the car.

Component manufacturers, distributors as well as suppliers and vehicle manufacturers are working hand in hand to solve these issues so that nothing prevents you from reading messages, chatting or working while out and about in your car.