I really have to give Bosch a big hand of applause. It seems to have a good instinct for where to use and promote its MEMS-based sensor technology. In this case the company has with its new SMA6xy/7xy MEMS sensor family zeroed in on vehicle airbags as well as driver assistance systems and vehicle dynamics applications.
The problem in vehicle air bags is this: The sensors that control the airbag systems are typically distributed across the vehicle. Some are in or near the airbag control system; others are located in the front or rear section or in the doors for early crash detection. So how do you make sure they release in a coordinated fashion and not only take into account normal x- and -y movements (left and right, forward and sideways) but vertical (z-axis)? And make sure they register as instantaneously as possible in the event of a crash.?
Figure 1: Bosch’s latest MEMS acceleration sensors make driving or riding in a vehicle safer, providing air bag electronics with critical measurements of acceleration and force that allow them to adjust instantaneously to protect the humans inside.
The company's new SMA6xy sensors take all of this into account, with versions that are designed for peripheral deployment and for the airbag control unit with variations available for the nature of the forces that must be dealt with, up to .120g or 480g, depending on the type. There are also versions that take into account the orientation needed to register the x-, -y and -z- directions, giving the designers of the airbag systems greater flexibilty.
The company's sensor designers have also taken into account the problem of microcuts, which are essentially exteremely brief microsecond interruptions in the power supply to the sensors that often occur in an impact. These devices able to tolerate interrupts of up to 10 microseconds.
They have clearly analyzed the G-forces involved and built in a lot of headroom: the SMA6xy series for the airbags senses forces up to 120 Gs in all three directions and have also made allowances for designer caution and preferences with sensors types available in either one or two axes.
The SMI7xy series devices are designed for use in a broad range of body and ADAS applications — not only in electronic stability control, but for use in hill-hold systems or rollover detection. There, they also reflect the same degree of thought on the part of the Bosch designers.
This series measures forces of up to 35g and are optimized for robust operation in environments with limited space conditions, something auto mechanics will appreciate if they ever have to get in to the frame and replace one of these components. The SMI720 and SMI740 are designed for basic applications, while the SMI700 and SMI710 meet higher requirements. Depending on the application, the devices meet safety levels up to ASIL D (the highest).
To achieve this degree of ASIL qualification, the SMI700 and SMI710 each contain a yaw rate sensor and a 2-axis acceleration sensor; with the the axis configuration varies by type. The SMI720 is designed for for rollover detection and contains a yaw rate and an acceleration sensor, each with one axis. The SMI740 features similar characteristics but is optimized for vehicle dynamics control.
As a newspaper reporter in the past, I learned by experience at auto crash sites, how dangerous it is to drive or be a passenger in a vehicle. No one seems to quite realize that driving a several thousand pound mass of metal at speeds even as low as 15 to 30 miles an hour does not give a human driving or riding much chance to prepare.
That is why I have been dead-against any form of electronics in the passenger/driver cabin especially in those with the auto infotainment systems that now seem standard in new cars. Auto entertainment subsystems are distracting enough, but the same drawback applies to the information side of the equation as well. Any time the driver's eyes are drawn away from the road – even to check to see how the engine is running, how the wheels are acting or where you are compared to where you want to be – is a danger period during which the unanticipated can happen.
The one exception to this rule of mine has to do with the seat belts and airbags and the electronics they use. Years ago at crash sites I saw first hand how the primitive electronics used then in seat belts and airbags saved countless lives and reduced injuries.
The kinds of improvements represented in Bosch's MEMS sensors will be a counterbalance to the distractions that I believe auto infotainment represent and reduce the number of injuries and deaths that may result.
I find it ironic that the aftermarket for adding advanced vehicle automotive infotainment is alive and well and thriving on-line and in my local auto retail stores. But kits for something like this are much harder to find. Given the much longer time to market for anything other than consumer electronics, it will be years – and a lot of deaths and injuries – before things like Bosch's new sensors are available to not only the new model automobiles, but also in the after market to sometime DIYers who want to see if they can make their existing vehicle safer.
Embedded.com Site Editor Bernard Cole is also editor of the twice-a-week Embedded.com newsletters as well as a partner in the TechRite Associates editorial services consultancy. He welcomes your feedback. Send an email to , or call 928-525-9087.