Dynamic Skip Fire Research Articles

Application of Dynamic Skip Fire for NO <sub>x</sub> and CO2 Emissions Reduction of Diesel Powertrains

<div class="section abstract"><div class="htmlview paragraph">Dynamic Skip Fire (DSF®) has been shown to significantly reduce CO2 on gasoline engines and has been in mass production since 2018. Diesel Dynamic Skip Fire (dDSF™) builds upon the technology and extends it to diesel engine applications. dDSF is an advanced cylinder deactivation technology that allows the deactivation of any number of cylinders dynamically to deliver the requested torque while maintaining acceptable noise, vibration, and harshness (NVH) performance. NO<sub>x</sub> regulations are becoming progressively more stringent on light, medium and heavy-duty (HD) diesel engines. Meeting low NO<sub>x</sub> standards is becoming increasingly challenging, especially in lightly loaded operating conditions where maintaining ideal aftertreatment system efficiency is difficult. Most existing techniques to increase aftertreatment temperatures at low loads incur a fuel consumption penalty, which increases greenhouse gas emissions. In this study, dDSF is shown to combine benefits by reducing both NO<sub>x</sub> and CO<sub>2</sub> simultaneously. Detailed studies were conducted on a Cummins X15 HD diesel engine. Engine testing and vehicle level simulation studies were followed by transient testing conducted on an engine dynamometer as well as on-road vehicle tests. NVH testing and evaluation was performed at the vehicle level to characterize vehicle response and ensure acceptability. dDSF calibrations were optimized to provide best thermal benefits at low loads. System level considerations such as coordination of air handling and fueling during transitions between firing densities, detection of valve actuation errors and mitigation of oil consumption concerns were studied. Results from system simulations using engine test data show 74% reduction of NO<sub>x</sub> and 5.0% reduction in CO2 on the Low Load Cycle (LLC) compared to the baseline engine with conventional thermal management. This simultaneous reduction helps compliance of NO<sub>x</sub> regulations while also reducing overall greenhouse gas emissions.</div></div>

Electrified Deceleration Cylinder Cutoff Engine Control Benefits and Strategies

<div class="section abstract"><div class="htmlview paragraph">Cylinder deactivation is a fuel consumption and CO<sub>2</sub> reduction technology for internal combustion engines that deactivates cylinders at light to moderate loads, allowing the remaining firing cylinders to operate near optimum efficiency. Dynamic Skip Fire (DSF) uses full-authority cylinder deactivation that allows any cylinder of the engine to be deactivated in sequence. In previous SAE papers, both DSF technology and the synergies between DSF and electrification (eDSF) have been described.</div><div class="htmlview paragraph">Recent engine technology includes deactivation mechanisms that do not effectively incorporate individual cylinder control. Nevertheless, it is still quite possible to improve the efficiency of engines equipped with these ganged-deactivation mechanisms. By grouping all cylinders into a deactivation mode, no air is pumped through the cylinders as it would be during the corresponding conventional operation that deactivates fuel alone. The engine equipped with deactivating cylinders can eliminate pumping work and provide more opportunity to recuperate electrical energy from the vehicle, as well as prevent oxygen saturation of the exhaust aftertreatment system.</div><div class="htmlview paragraph">This paper presents the substantial benefits of this approach, showing both simulated and experimental fuel economy improvements for a C-segment vehicle exceeding 5% in the WLTC class 3 drive cycle. It discusses control strategies for managing transitions in and out of deactivation to achieve customer-pleasing NVH and drivability. Finally, the value proposition is presented for this electrified deceleration cylinder cutoff (eDCCO) system, also known as Hybrid++.</div></div>

Controls and Hardware Development of Multi-Level Miller Cycle Dynamic Skip Fire (mDSF) Technology

<div class="section abstract"><div class="htmlview paragraph">mDSF is a novel cylinder deactivation technology developed at Tula Technology, which combines the torque control of Dynamic Skip Fire (DSF) with Miller cycle engines to optimize fuel efficiency at minimal cost. mDSF employs a valvetrain with variable valve lift plus deactivation and novel control algorithms founded on Tula’s proven DSF technology. This allows cylinders to dynamically alternate among 3 potential states designated as: High Fire, Low Fire, and Skip (deactivation). The Low Fire state is achieved through an aggressive Miller cycle with Early Intake Valve Closing (EIVC). The three operating states in mDSF can be used to simultaneously optimize engine efficiency and driveline vibrations. Acceleration performance is retained using the all-cylinder, High Fire mode. mDSF can be implemented cost-effectively using an asymmetric intake valve lift strategy, with one high-flow power charging port and one high-efficiency Miller port.</div><div class="htmlview paragraph">Prototype mDSF cylinder heads were based on the EA888 Gen 3B engine by retrofitting the valvetrain with asymmetric intake cams, deactivatable roller finger followers and two oil control valves per cylinder. Event-based engine controls were developed to enable for each cylinder dynamic selection of the three mDSF operating modes: High Fire, Low Fire and Skip. Appropriate air estimation, fuel control and ignition control techniques were employed to ensure acceptable torque delivery and tailpipe emissions.</div><div class="htmlview paragraph">Engine dynamometer tests showed a 23% reduction in engine fuel consumption at 1500 rpm, 2 bar NMEP. Maximum torque and power from the baseline production engine up to 5000 rpm were also achieved. mDSF vehicle tests on the WLTC demonstrated a 6% reduction in CO<sub>2</sub> from Miller 2-step. Euro 6d compliant emissions were also reported. Further improvements in fuel economy, drivability and NVH may be possible by leveraging mixed firing densities more extensively.</div></div>

Research on the fuel consumption conservation potential of ADAS on passenger cars

Under the trend of automobile electrification, network connection, and intelligence, EU and USA have carried out fuel-saving research and initiatives on ADAS and CAV. The eCoMove project has aimed at economically optimal driving control and traffic management; MAVEN discusses the technical path of GLOSA (Green Light Optimal Speed Advisory) and ecological auto-driving EAD (Eco-Autonomous Driving) by smoothing the vehicle speed. The American NEXTCAR project contains multiple projects. When supplemented with DSF (Dynamic Skip Fire) and 48V technology, the road test led by Ohio State University resulted in a 15% fuel saving rate. Platoon and optimizing intersection signal lights can offer vehicles a more fuel-efficient condition; slope energy utilization, HEV SOC active management, cold storage evaporator, coasting, 48V and mDSF (miller cycle Dynamic Skip Fire) fuel-saving potential has been fully utilized.

Fast Catalyst Light-Off with Dynamic Skip Fire

<div class="section abstract"><div class="htmlview paragraph">Catalytic aftertreatment is commonly used to reduce regulated gas emissions from Internal Combustion (IC) engines. Achieving fast catalyst light-off has always been a challenge for automobile IC engine applications. This paper experimentally studied the thermal management and regulated gas emissions from a Spark Ignition (SI) engine with Dynamic Skip Fire (DSF®) technology during cold start period.</div><div class="htmlview paragraph">The study has found that DSF can increase exhaust gas temperature at the catalyst inlet by up to 100°C, and the exhaust enthalpy by up to 20%. Cold start tailpipe carbon monoxide (CO) and hydrocarbon (HC) emissions can be reduced by 10% to 20% largely due to the increased exhaust gas temperature and enthalpy. Dynamic air pumping can further increase exhaust gas temperature by 30 °C, and can nearly double enthalpy delivered to the catalyst, which reduces cold start HC emissions by more than 50%.</div></div>

Vibration Rating Prediction Using Machine Learning in a Dynamic Skip Fire Engine

<div class="section abstract"><div class="htmlview paragraph">Engines equipped with Dynamic Skip Fire (DSF) technology generate low frequency and high amplitude excitations that could reduce vehicles drive quality if not properly calibrated. The excitation frequency of each firing pattern depends on its length and on the rotational speed of the engine. Excitation amplitude mainly depends on the requested engine torque by the driver. During the calibration process, the torque characteristics that results in production level of noise, vibration, and harshness (NVH), must be identified, for each firing pattern and engine speed. This process is quite time consuming but necessary.</div><div class="htmlview paragraph">To improve our process, a novel machine learning technique is utilized to accelerate the calibration effort. The idea is to automate the vibration rating procedure such that given the relevant power-train parameters, a vibration rating associated with that driving condition can be predicted. This process is divided into two <span class="xref">(2)</span> prediction models. The first model is a multiple additive regression trees that predicts the seat accelerometer data based on the various engine and vehicle parameters. The predicted seat accelerometer data is used as an input to the second machine learning model which correlates, along with other relevant engine and vehicle parameters, to a final vibration rating score. The results indicate that using this machine learning approach can significantly improve capability of automating the DSF calibration process delivering commercial NVH performance.</div></div>

Method to Compensate Fueling for Individual Firing Events in a Four-Cylinder Engine Operated with Dynamic Skip Fire

Method to Compensate Fueling for Individual Firing Events in a Four-Cylinder Engine Operated with Dynamic Skip Fire

Machine Learning for Misfire Detection in a Dynamic Skip Fire Engine

Machine Learning for Misfire Detection in a Dynamic Skip Fire Engine

Low Load Extension and Improved Fuel Economy of Homogeneous Lean Burn Using Dynamic Skip Fire

Low Load Extension and Improved Fuel Economy of Homogeneous Lean Burn Using Dynamic Skip Fire

Methods of Evaluating and Mitigating NVH when Operating an Engine in Dynamic Skip Fire

Methods of Evaluating and Mitigating NVH when Operating an Engine in Dynamic Skip Fire

Design and Benefits of Dynamic Skip Fire Strategies for Cylinder Deactivated Engines

Cylinder deactivation is a fuel consumption reduction technology for throttled internal combustion engines and other engines with thermal efficiency loss at part cylinder load. Recent production implementations, deactivating fixed sets of cylinders under part-load operating conditions, have had limited “fly zones” due to issues with drivability and noise, vibration and harshness (NVH). Dynamic skip firing, which in its ultimate form incorporates anytime, any-cylinder deactivation, continuously varies the number of firing cylinders, along with cylinder load, obtaining flexible control of acoustic and vibrational excitations from the engine, and allowing an expanded operational envelope with fewer drive ability/NVH issues. This paper outlines design considerations of dynamic skip fire operational strategies, discusses implementation of the system on a vehicle, and presents benefits to fuel economy and NVH.