A big V8 might make around 500 horsepower, but in most driving, the car only needs a tenth of that output. That power overhead, with all cylinders working, leads to a lot of waste. Recognizing this, Delphi has partnered with Silicon Valley startup Tula to deliver a new cylinder deactivation scheme it calls Dynamic Skip Fire.
Unlike current systems that simply shut down a set number of cylinders when power demands are low, Dynamic Skip Fire uses the engine’s processor to continually make decisions on the fly as to which cylinders should fire. Tula CEO Scott Bailey said the company figured out this technology when it began to “look for ways to use the increased compute capacity in cars to increase efficiency.”
Delphi will formally present this technology at, but I was given a demonstration drive in a Volkswagen Jetta modified with Dynamic Skip Fire on its four-cylinder engine, along with Delphi’s own 48-volt mild hybrid technology. With this combination, which Delphi calls eDSF, tests show an 8 percent fuel economy increase for four-cylinder engines, and 15 percent for eight cylinders.
Despite growing electric car sales, combustion engines will still be in play for many decades in passenger cars. A Bloomberg study predicts nonplugin cars will still make up two thirds of sales in 2040. The problem of climate change caused by burning fossil fuels, along with the economic and political costs of oil extraction, are causing governments and people to demand lower carbon dioxide output and better fuel economy from cars.
An 8 to 15 percent decrease in carbon dioxide, a reduction tied directly to increases in fuel economy, would make a big difference. For example, the Toyota Corolla already averages 34 mpg in EPA tests. An 8 percent increase would push that number to a not insignificant 37 mpg.
To demonstrate the technology, Delphi invited me to drive its modified Volkswagen Jetta, also equipped with displays showing which cylinders were firing. Over a short route that included a 65 mph freeway and 35 mph surface street, the engine ran smoothly, responding well when I mashed the accelerator. The activity of Dynamic Skip Fire was most apparent, however, when I feathered the throttle.
The display showed cylinders firing or deactivating too quickly for me to track. A Delphi spokesman said that Dynamic Skip Fire makes “6,000 decisions per minute for a four-cylinder engine running at 3,000 rpm.” When I lifted off the throttle, the system stopped firing all cylinders, as the engine didn’t need to produce any power.
One challenge Delphi and Tula needed to overcome was the potential for increased or uncomfortable engine vibration due to the cylinders not firing in an even pattern. Tula took that problem into account with its firing algorithm, but Delphi’s mild hybrid system also factors in. The 48-volt system gathers electricity from regenerative braking, but unlike a full hybrid, it can’t drive the car under electric power. It can, however, assist the engine, so Delphi’s system serves to smooth over what might otherwise be a rough point in Tula’s cylinder firing.
Beyond implementing the Tula software in an engine’s controller, the system also requires valvetrain modification, so it can control the cylinders individually.
The eDSF system has not been announced for any specific car models to date, but Delphi CTO Mary Gustanski said the company is working with automakers now, and 2021 or 2022 are likely production dates.