Technological systems in vehicles are constantly improving and many cars are fitted with high-end safety components. A new European ruling makes it obligatory for cars to be equipped with new safety systems from the year 2022. Most of these are related with functional safety systems or they are dependent on an electric, electronic or programmable system.
In the last few years, there has been a considerable increase in the number of components in a car, due to the higher levels of comfort and driver assistance offered by vehicles. Furthermore, while the role played by electronics grows, driverless cars and advanced driver assistance systems (ADAS) are already a reality. In this context, functional safety is a requirement to ensure that the general automotive system is as reliable as possible and to guarantee the safety of the occupants of the vehicle.
Nevertheless, the electronic system can fail due to component ageing, defects in the manufacturing process, temperature, humidity, atmospheric pressure, power dissipation and voltage rails. Therefore, the design of a car must reduce any risk in or malfunction of the electronic systems, as established by the ISO 26262 international standard for road vehicles.
Both the microcontroller (MCU) suppliers and the original equipment manufacturers (OEM) must guarantee a system with fewer risks. This system requires continuous monitoring of critical elements, either through the software or in the hardware.
Moreover, the change in vehicles from a mechanical system to an electronically controlled system has led to an increase in the number of electronic control units, which in turn gives impetus to safety standards designed to reduce any situations of risk.
The importance of functional safety
Driver assistance, radar and vision systems in today’s vehicles mean that data from many sensors is continuously processed. But a failure in any of the sensors can lead to error in the data processing systems and cause serious accidents. This is the case of the sensors whose purpose is to acquire data related with vehicle dynamics, for example: lateral acceleration and yaw rate, steering wheel turn and revolution sensors in ESP systems on some models. Therefore, sensors and the correct flow of data are essential for safety.
New safety systems
In addition to the basic active and passive safety features for cars (ABS braking system, brake assist, safety belt, airbag and headrests), from 2022, cars that are sold in the EU will have to include new safety systems, which will largely depend on the correct operation of the electric system:
- Automatic emergency braking. Warns other road users by means of hazard warning lights. When an obstacle is detected and the driver does not react, the brake on the vehicle is automatically applied.
- Intelligent speed assist. Maintains the vehicle at a given speed without exceeding the established speed limit.
- Advanced driver distraction warning
- Electronic data recorders which will provide information about what occurred moments before a collision. A kind of ‘black box’ which will make it possible to analyse why the accident occurred.
- Lane departure warning
- Lane keeping These warn the driver when he/she changes lane.
- Rear seat safety belt At present, this is already applied to the front seats.
When functional safety faults occur
However, some typical problems in the system can lead to faults that affect the functional safety of the car. For example:
- Clock variations: a clock in continuous operation which shuts down or is defective can cause a fault in the system and affect the safety of the vehicle. To prevent this, continuous monitoring must be applied, measuring the frequency and indicating whether the clock is within the safe range (in the car industry, clocks with very low ppm ratings are used to avoid temperature fluctuations). To avoid clock failures, the two most common mechanisms are the WDT (watchdog) ASIL B and WWDT (windowed watchdog) for ASIL >=ASILB.
- Memory faults. Memory, especially static RAM, is an integral part of the vehicle’s digital system. During read and write operations, a digital one (1) may flip to a digital zero (0) or vice versa. This bit inversion is dangerous, and therefore safety-critical memory must support error correctable codes. Besides EDC and ECC, other mechanisms can be applied, such as safety-relevant variable redundancy and reverse order redundancy, which is even safer.
- Additionally, an MPU (Memory protection unit) is common for memories.
- Instruction faults. When the read core gets corrupted, a damaged instruction is executed and incorrect logic is exercised. To avoid this, on occasions it is recommended that there are several cores which execute the same instruction and their outputs are compared in parallel, so there is a lower probability of the same instruction fault occurring in all the cores.
In short, functional safety requires that both the vehicle’s hardware and its software function perfectly. For this purpose, Idneo offers a comprehensive service for the development of products designed to ensure the functional safety of cars, in compliance with the safety standard ISO-26262, including solutions such as FSC, TSC, FMEA, FTA, FMEDA, ASIL decomposition and ADF.
Contact us here and we will be delighted to help you.