GM develops cylinder deactivation technology to quickly reduce fuel consumption

    GM expects to launch a more advanced rapid cylinder deactivation system within five years that will revolutionize the engine and enable internal combustion engines to fire based on cylinder needs.

    With Dynamic Skip Firing (DSF) technology, a V-8 SUV like the GMC Yukon Denali can achieve smooth cruising at highway speeds with just two cylinders firing, which improves fuel economy by 21 percent and significantly reduces CO2 emissions.

    Tula Technology, a Silicon Valley software company in the United States, is responsible for developing the algorithms for designing DSF technology. GM and Delphi have invested in Tula Technology and are working with the company to jointly develop the technology and introduce it into the automotive market.

    Delphi CTO said that the first models using DSF technology are expected to hit the road in 2020.

working principle

    Traditional cylinder deactivation systems usually work in the following way: V-8 engines shut down four cylinders, and V-6 engines shut down two or three cylinders. DSF keeps all cylinders active and makes dynamic firing decisions for each cylinder continuously at any time. This also allows the engine to maintain a reasonable operating temperature and run smoothly.

    Another major difference is the way the engine's throttle system is managed: gasoline engines use a butterfly valve at the throttle body to regulate the amount of air entering the intake manifold. The butterfly valve is usually closed, which also requires the engine to do more work to complete the intake operation. DSF can keep the throttle fully open and control the engine's power by changing the number of cylinders.

    When the engine needs higher power output and greater torque, it means that the accelerator pedal needs to be stepped on more, and a higher proportion of cylinders need to be fired. DSF technology is similar to achieving variable displacement through software functions.

    A V-8 SUV only needs about 30 horsepower to cruise smoothly at highway speeds, and in this case, DSF technology shuts down six cylinders, improving fuel economy by 21% according to EPA testing standards.

    Engineers demonstrated DSF technology on a GMC Yukon Denali equipped with a 6.2-liter V-8 engine. When the car is at idle, once the acceleration operation is taken, the eight cylinders of the engine work normally and the vehicle operates normally; once the driver's foot is lifted from the accelerator pedal, the number of ignition cylinders begins to decrease. When the speed is maintained at 65 miles per hour, only two cylinders work, but it produces unnecessary noise or vibration. When the driver pursues power and needs to accelerate, the other six cylinders are activated without any hysteresis or other negative effects.

Improvements and upgrades

    The DSF is suitable for all types and sizes of petrol engines, overhead cam or pushrod, whether in horizontally opposed V or inline L layout, and is also compatible with engines with four or more cylinders.

    DSF also uses a variety of cylinder deactivation hardware that has been developed. For example, on GM's engines equipped with Active Fuel Management, cylinder deactivation is achieved by cutting off the flow of fuel to the valve lifters. On a traditional 16-valve V-8 engine, only eight valves have specific lifters to allow cylinder deactivation. With DSF technology, all 16 valves require specific valve lifters.

    Engineers have previously summarized two advantages of DSF technology: First, fuel economy is improved by eliminating pumping losses and optimizing combustion. Each engine speed corresponds to an optimal thermal efficiency value, and minimizing pumping losses can increase the power load of a throttled engine. During the combustion process, the engine combustion system may be optimized to adapt to the vehicle's operating conditions. Therefore, once the intake/exhaust valves are properly adjusted, inactive cylinders will not pump air into the engine, allowing the three-way catalyst technology to fully function.

    Second, effectively control vibration and noise. In conventional engine throttling operation, the excitation spectrum is closely related to the engine speed, and the vibration amplitude is also determined by the throttling. Using DSF technology, the torque of the vehicle powertrain can be changed, thereby solving noise, vibration and harshness (NVH) problems in a flexible and systematic way.