Optimize start-stop systems for efficiency

Start-stop systems automatically switch off the engine every time the vehicle is stood still (e.g. at a light or in a queue) and restart it instantly when needed. It is particularly efficient in urban traffic where this type of cycle is repetitive and systems using an Integrated Starter Alternator (ISA) can cut fuel consumption dramatically in heavy traffic conditions.

Instant communication between various systems and having them operate seamlessly is key for Start-Stop systems. Before switching the engine off, the Engine Control Unit needs to confirm that vehicle is halted and the gear has been disengaged. When the gear or the clutch is inserted and accelerator pedal pressed, the engine should immediately re-start.

NXP's automotive portfolio, from our sensors and networking products to audio amplifiers and immobilizers, has a significant role to play in start-stop systems. Amongst the more obvious requirements our portfolio ensures all communications are managed efficiently while accurately measuring speed and pedal position. Our low RDS(on) MOSFETs in KGD (Known Good Die) can handle the very high currents of the ISA inverter at the same time reducing energy waste.

But start-stop systems also have an impact on other systems, including car radio / infotainment and immobilization systems. As the engine restarts, board voltages can momentarily drop to 6 V. Audio amplifiers such as NXP's TDF853x / TDF859x Class D families and TDF854x Class AB series ensure audio quality is maintained during voltage drops, while with our keyless go ICs the car only starts when an active key is in the car.

With NXP's MOSFETs in KGD for active excitation, brake blending can easily be introduced further improving overall efficiency. This also enables the evolution from start-stop to micro and mild-hybrids and helps pave the way to full electric vehicles.