Electrified Cars – Part 2: Stop-Start

Posted on April 16th, 2020 by Rob Marshall

Electrified Cars - Part 2: Stop-Start

Many modern hybrid vehicles, the half-way house between a conventional combustion-engined vehicle and an electrified one, have their technical roots in Stop-Start technology. As its name describes, the system stops the engine from idling under certain running conditions. Once the engine ceases running, the car’s electrical system is put into ‘standby’ mode, ready for a swift restart, typically when the brake pedal is released, or when the clutch pedal is depressed.


Stop-Start was popularised a little over a decade ago. Some systems are clunky, dim-witted and annoying but others are very unobtrusive. Yet, the system demands not only more expensive batteries, (https://blog.motoringassist.com/car-maintenance/start-stop-battery-advice/) either EFB or AGM types, but also smart alternators and more complicated starter systems.


Stop-Start technical details

While conventional starter motors have a typical design life of 50,000 starts, a Stop-Start equivalent may have to tolerate as many as 300,000. Therefore, they need internal reinforcement. Typical examples of this include longer internal brushes, dual solenoids and strengthened bearings. Some exceptions exist. Toyota, for example, tends to have starter motors that are engaged permanently with the ring gear and the flywheel boasts a one-way clutch.


Early Stop-Start systems were not very good at reacting to sudden changes of mind, where a need for engine power arises just as the ‘stop’ aspect of the system has been engaged and the engine crankshaft has not yet come to a halt. Some modifications were made to the belt drive to incorporate a combined starter-alternator – more about which will follow next time.


Coming in Part 3: Rob details how Stop-Start evolved into Micro Hybrids.