Since the Obama Administration finalized standards in 2012, to encourage the automotive industry to reach a 54.5 miles per gallon corporate fuel economy average by 2025, manufacturers have been employing every means possible to squeeze another mile out of a gallon of gasoline. A combination of aerodynamics, weight savings, electrification, hybrid technologies and advanced engine management software has gone a long way, but it doesn’t take a rocket scientist to understand that you save a lot of fuel when the car isn’t running.
Auto-Stop/Start technology automatically shuts the engine off when the vehicle comes to a full stop, and then starts it again when the driver wants to get moving. If your commute consists of a single stoplight and a long stretch of highway, Auto-Stop/Start isn’t going to save a lot of fuel, but if you drive in a lot of stop-and-go traffic, it can make a big difference in your fuel economy- typically between 3-5%.
How Does It Work?
There are a few different suppliers of such technology, but one of the biggest is Denso. It supplies the technology to all three American manufacturers, as well as the Land Rover, Audi, Fiat, Hyundai, Toyota and Volvo brands.
In general, auto-stop/start senses that the vehicle has come to a stop, that the engine RPM has fallen either to a full stop or close to it, and that the brake is depressed.
At that point, the system shuts the engine down, and disengages the transmission. When the system senses that the driver is taking her foot off the brake, it restarts the engine while the transmission is still in gear.
This technology is more than just a starter that spins the engine to a start more frequently, but the starter is the single most important component.
How Is the Starter Different?
Since its very introduction, the electric starter on your car has had two jobs: Primarily, to spin the flywheel to start the engine. But they also need to get the pinion gear (see diagram, below) out of the way so that it’s not engaged with the ring gear on the flywheel once the engine is running.
For a vehicle that only needs to start a few times a day, it’s an ingenious little device that has existed almost unmodified since Charles Kettering received a patent for it in 1917.
But vehicles with auto-stop/start systems have to fire up dozens, and perhaps hundreds of times in a single commute. A traditional starter like Boss Kettering’s simply won’t do the job.
Denso has three different types of Auto-Stop Start starters, depending on the application the manufacturer’s need:
· The first is a pretty traditional starter, but it’s engineered to be more durable, with dual layer, long-life electrical brushes and a unique pinion spring mechanism that reduces ring gear and flywheel wear caused by a typical starter by about 90%.
· The second is a “Tandem Solenoid” starter that allows the engine to re-engage with the starter motor anywhere between idle (about 600 RPM) and zero RPM. That means shaving a second and a half off a restart when compared with a traditional starter.
· The most advanced Denso starter was developed in partnership with Toyota. It’s called a “Permanently Engaged” starter, and as its name suggests, the pinion gear is permanently meshed with the ring gear on the flywheel, which completely eliminates any lag time when the vehicle needs to be restarted.
When you’re out shopping for a new car, sample a few different vehicles to see how they accomplish the auto-stop/start system. There are some that do it more or less seamlessly, like BMW. Others, restart with a significant shudder.
Starter manufacturers also use rubber shock absorbers and a clutches to isolate engine oscillations that help reduce engine-restart noise and engine-stop vibrations.
But the big difference between a smooth start and a rougher one is down to whether they’re using a Permanently Engaged starter or not.
What About the Transmission?
The transmission represents a huge challenge in restarting an engine. In fact, the only vehicles that had auto-stop/start technology prior to 2007 were those with a manual transmission.
When you start your car in the morning, whether you drive a car with a manual or an automatic transmission, the car is either in Park, Neutral, or in gear, but with your foot to the floor on the clutch.
But when you’re in traffic, you’re not shifting the car to park every time you come to a stop. So how does the transmission not stay engaged using an auto-stop/start system? They automatically shift into neutral when the vehicle is stopped. Some incorporate an “Auto Hold” feature like BMW does, that allows the driver to release brake pressure while the engine is still turned off. It reengages when the driver hits the accelerator.
How About Engine Wear?
As is commonly known, cold engine startup is recognized as the most vulnerable time for internal engine components. Lubricant is cold, and it hasn’t had time to pressurize and lubricate all of the moving components on the top of the engine.
Stop/Start systems aren’t as potentially damaging as cold starts, though, simply because the engine isn’t cold. Not only are the engines at operating temperature before the stop/start system begins to work, the vehicles also use electric water pumps to maintain optimal engine temperature when they’re stopped. If the engine is off long enough to reduce engine temperature significantly, the engine will automatically restart.
Secondly, while the engine’s oiling system isn’t completely pressurized as it when it’s running, the oil in the passages hasn’t been allowed to completely run down into the oil pan.
Finally, suppliers are addressing wear with dry lubricants on components like main engine bearings. Engine bearings are typically designed to withstand 100,000 start cycles. New bearings are now in use that are designed to withstand 250,000 to 300,000 start cycles. Federal Mogul, for example, has been incorporating polymers on the connecting rod bearings for cars with auto-stop/start systems to reduce friction when oil isn’t pumping.
What if I Don’t Want It?
To date, every vehicle with this technology allows you to manually override it at the push of a button (see photo of the “A" button, below).
The downside of disabling this feature is that your fuel economy will be reduced by 3-5% and ( you’ll have to turn it off every time you get into the car. No manufacturer allows you to permanently disable the function.
Owners of sporty cars with “Dynamic” or “Sport” modes will notice that selecting those modes will automatically disable the system, too.
None of this technology is completely settled, and manufacturers and suppliers are working to develop new methods of accomplishing the same goals without the technical hurdles.
For example, Mazda has a technology called i-Stop that doesn’t use a starter for re-starts at all. It uses engine combustion. As a driver releases the brake pedal, the fuel injector in one cylinder fires, and the spark plug ignites, allowing the engine to start with combustion, rather than an electric starter motor.
In the short term, though, you don’t have to worry too much about whether your engine or its various components are being damaged by frequent starts. They’ve been engineered for it, and they’re different than the components in a vehicle without this technology.