As the intelligence of vehicle electronic systems increases, wireless connectivity is becoming an important feature, enabling passenger communications and cloud connectivity for advanced features.
For example, Mercedes’ ‘me connect’ system includes three connectivity services: bCall, iCall and eCall. bCall is short for breakdown call, which will allow drivers to call for 24-hour roadside assistance in the event that the car breaks down. iCall, short for information call, will provide artificial intelligence based support, such as driving routes and restaurant locations. And eCall, short for emergency call, will automatically call the emergency services in the event of an accident or crash.
In fact, legislation on eCall functionality is one of the major factors driving advanced vehicle connectivity. This system will be mandatory for all cars and vans sold in the EU from April 2018.
eCall is intended to save lives on the roads. If an accident happens in a rural or remote area, or at night, valuable time can be lost while victims are not able to call the emergency services and there is no-one else around to do so. In this situation, getting to the hospital quickly can mean the difference between life and death. It is estimated that eCall can speed up emergency response times by 40% in urban areas and 50% in the countryside and can reduce the number of fatalities by at least 4% and the number of severe injuries by 6%.
eCall can be triggered by impact sensors in the car that are continuously monitored to detect an accident or crash. Airbag accelerometers may form part of this system. Alternatively, eCall systems may be triggered manually by the driver using a dedicated ‘SOS’ button in the car.
Once the call is placed, an operator will attempt to speak to the driver to find out what has happened and whether paramedics are required. If voice contact cannot be made, the paramedics are sent immediately. The eCall system also transmits data known as the ‘Minimum Set of Data’ (MSD) to the emergency services, which includes a timestamp for the incident, GPS location data and information about the direction the vehicle was travelling to allow the accident site to be found as quickly as possible. This data is actually sent by an in-band modem over the GSM voice channel, in a similar way to how fax machines work.
Vehicles, being mobile by nature, are of course not plugged in to power cables or data cables, so the major design challenges relate to battery power, RF connectivity, and the reliability of these systems under accident and crash conditions.
Battery power is particularly important, since in the event of a crash, the car’s main battery or its supply lines may no longer be functional. The eCall system therefore needs to be flexible enough to allow its power source to change from the car’s main battery to a backup battery when required. This backup battery should obviously be as robust as possible as it may have to endure many years before finally being used, and then it still needs to be powerful enough for a loud and clear call. The requirements are power delivery for ten minutes, from a very small battery, in temperatures as low as -40°C. The power supply required by communication modules is typically 350mA with peaks of 2A for data transmission, plus 500mA for audio operation, at 3.2-3.4V.
Tadiran has developed a special lithium metal-oxide battery technology especially to meet these demanding conditions, which can supply pulse currents up to 15A (permanent current capacity of 5A) at a rated voltage of 4V. Tadiran’s TLM-1550/HP, based on this specialised technology, is the size of an AA battery, showing good properties down to -40°C without additional heating. The rechargeable version can be used for standby times of eight to ten years.
As an alternative, Varta recommends using multiple coin cells in this application, suggesting three to five of its V500HT parts, depending on the power demand. The V500HT is part of its Powerful85 family of Ni-MH batteries, designed for high discharge currents (3A peak at 4.8V) and extended temperatures (-20 to 85°C). These batteries are rechargeable with a long lifetime of up to ten years.
The second biggest design challenge that eCall systems face is reliable GPS/GSM RF operation in low signal areas. Smart antenna designs, located in the car’s ‘shark fin’, will allow GPS and eCall communication alongside a host of other services such as radio, TV and vehicle-to-X communication. RF reliability can be improved using the right SAW filter to eliminate the effects of interference – RF360 is the leader in automotive SAW filters with a wide range of parts for all applicable frequencies and bands, including eCall.
Overall robustness of the in-vehicle communications system is probably the third biggest design challenge, as the system has to be robust enough to survive a crash. All components should obviously be able to withstand automotive temperature ranges and be AEC-Q100 certified, where applicable. For example, connectors should be the most robust possible, such as the HS Autolink family from Molex, which is designed for automotive data transfer. These rugged connectors feature fully protected perimeter seals and wire seals for IP67 and IP69K rating in wet locations.
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