Automatic start-stop systems are common in cars today, so here’s a quick look into how they work their magic
When you turn your vehicle’s key or press the start button, what gets everything going is the starter. It’s an electric motor with the sole purpose of spinning the crankshaft to start the engine, but on many newer vehicles it plays that role even more often. Several auto manufacturers are adding start-stop technology, which shuts off the engine at idle and then starts it up again when you’re ready to go.
The heart of an engine is its central crankshaft, which spins to produce the motion that eventually turns the wheels. It’s turned by the pistons, which move up and down to spin it the same way your legs power a bicycle. In order for the engine to start and run, most of its associated functions also have to start at the same time. Some are launched by the crankshaft’s first turns; the electrical system also comes on to power the fuel pump and the ignition system for the spark plugs.
Attached to the rear of the crankshaft is a disc, called the flywheel, which spins whenever the crankshaft does. One of its functions is to even out the crankshaft’s motion to reduce vibration, but it’s also essential to starting the engine thanks to the ring gear, a set of teeth around its rim. A solenoid on the starter creates a contact that sends the battery’s power through to the starter motor. A drive mechanism on the starter, called the Bendix gear, meshes its small pinion gear with the teeth on the ring gear. As the pinion gear turns, the ring gear does also, which causes the crankshaft to spin.
That spinning gets everything going. The crankshaft pulls down some of the pistons, forming a vacuum in each cylinder that sucks in fuel and air. The spark plug ignites the mixture, creating the combustion that powers each piston and taking over to spin the crankshaft. The starter is no longer needed. A spring disengages it from the ring gear, and the solenoid contact opens and cuts off the power to it.
On a conventional vehicle, starting the engine is the battery’s primary job. Once the engine is running, it spins an alternator/generator that provides power for the vehicle’s electrical needs, from igniting the spark plugs to running the lights. It also feeds electricity back into the battery, where it’s stored for the next engine start. The battery’s only other tasks are to run accessories when the engine’s off — such as when you’re sitting with your stereo on — or to take over if the alternator fails, in which case the car will run until the battery is drained.
You’ve probably seen vintage pictures of motorists cranking a handle on the front of their cars. On these early vehicles, spinning the crankshaft to start the engine was done solely with muscle power. Cadillac introduced the first car with a self-starter in 1912, and that basic design is still the one used.
Hybrid vehicles also need to start their gasoline engines, but in addition to the engine, they have an electric motor-generator. This either works by itself when the vehicle runs on electricity alone, or in conjunction with the gas engine for extra acceleration. Instead of a conventional starter, it also spins the crankshaft to start the engine as needed — not just when the car first starts, but any time that the system needs to go from electric-only to gas-and-electric. The motor spins the crankshaft very fast and the engine start is generally smoother. In some hybrids, it can be difficult to tell when the gasoline engine kicks in during driving.
Hybrids turn off the gasoline engine at idle, such as when you’re sitting at a stop light, and now many non-hybrids do as well in order to save fuel and reduce emissions. Everything else continues to operate, including the climate control, lights and stereo, and the engine restarts as soon as you take your foot off the brake.
These non-hybrid vehicles use a starter, of course, but because the engine stops and starts so many times, the starter and its system are optimized to reduce wear-and-tear. This can include specific materials and bearings for longer life, enhanced pinion gear ratio so the starter doesn’t have to turn as fast, and control modules that stop the engine’s cylinders at a point where it’s easiest to start everything up again. The start-stop system also doesn’t engage unless all conditions are right for it, including ambient temperature and if the engine has sufficiently warmed up. Most vehicles give the driver the option of temporarily disabling the system if start-stop isn’t desired, and also automatically shut it off if the car is put into “Sport” mode.
A few vehicles have mild hybrid systems, such as the eTorque system available on the 2019 Ram 1500. These pair a motor-generator with a 48-volt battery, and while they don’t drive the vehicle on electricity alone as a full hybrid can, they start the gasoline engine and smooth out acceleration. Expect to see this even more, as automakers work to meet efficiency standards — and get you started as well.
