Chun Tai

Using Camless Valvetrain for Air Hybrid Optimization

The air-hybrid engine absorbs the vehicle kinetic energy during braking, puts it into storage in the form of compressed air, and reuses it to assist in subsequent vehicle acceleration. In contrast to electric hybrid, the air hybrid does not require a second propulsion system. This approach provides a significant improvement in fuel economy without the electric hybrid complexity. The paper explores the fuel economy potential of an air hybrid engine by presenting the modeling results of a 2.5L V6 spark-ignition engine equipped with an electrohydraulic camless valvetrain and used in a 4531 kg passenger car. It describes the engine modifications, thermodynamics of various operating modes and vehicle driving cycle simulation. The air hybrid modeling projected a 64% and 12% of fuel economy improvement over the baseline vehicle in city and highway driving respectively. This is possible without reducing the vehicle weight to compensate for additional hardware and without reducing engine displacement.

Modeling and controller design of an electromagnetic engine valve

A control-oriented linear model was constructed for an electromagnetic camless valvetrain (EMCV) based on a gray-box approach that combines mathematical modeling and system identification. An inner-loop feedback stabilizing controller and a cycle-to-cycle repetitive learning feedforward controller were designed for the EMCV to meet the quiet-seating requirement. The performance of this control system is demonstrated by experimental results.

Control of an electromechanical camless valve actuator

This paper addresses the modeling analysis and soft seating control of an electromagnetic actuator used in electromechanical camless valve-trains. Our mathematical modeling analysis reveals the instability of the actuator dynamics linearized around the seating position and zero velocity. This implies that an open loop pulse shaping alone cannot render repeatable valve closing and seating motions. Closed loop feedback control is necessary to generate repeatable motions that is insensitive to disturbances. A linear model is constructed based on a gray-box approach that combines mathematical modeling and system identification. Notch filtering and linear quadratic optimal control are designed and experimentally tested. The control performance is evaluated in terms of the closing time, valve seating velocity and seating tail-length, armature crossing velocity and armature seating velocity.

Control of an electromechanical actuator for camless engines

This paper presents a gray box approach for identifying physical parameters of an electromechanical actuator based on frequency response data. A feedforward and linear-quadratic regulator feedback controller was developed to control the EMCV actuator for soft seating. A repetitive learning controller was designed to enhance the control performance through cycle-to-cycle iterations. Experimental results achieved 0.61 m/s valve seating speed with 0.02 m/s standard deviation.

Demonstration of Air-Power-Assist Engine Technology for Clean Combustion and Direct Energy Recovery in Heavy Duty Application

The first phase of the project consists of four months of applied research, starting from September 1, 2005 and was completed by December 31, 2005. During this time, the project team heavily relied on highly detailed numerical modeling techniques to evaluate the feasibility of the APA technology. Specifically, (i) A GT-Power{sup TM}engine simulation model was constructed to predict engine efficiency at various operating conditions. Efficiency was defined based on the second-law thermodynamic availability. (ii) The engine efficiency map generated by the engine simulation was then fed into a simplified vehicle model, which was constructed in the Matlab/Simulink environment, to predict fuel consumption of a refuse truck on a simple collection cycle. (iii) Design and analysis work supporting the concept of retrofitting an existing Sturman Industries Hydraulic Valve Actuation (HVA) system with the modifications that are required to run the HVA system with Air Power Assist functionality. A Matlab/Simulink model was used to calculate the dynamic response of the HVA system. Computer aided design (CAD) was done in Solidworks for mechanical design and hydraulic layout. At the end of Phase I, 11% fuel economy improvement was predicted. During Phase II, the engine simulation group completed the engine mapping work. The air handling group made substantial progress in identifying suppliers and conducting 3D modelling design. Sturman Industries completed design modification of the HVA system, which was reviewed and accepted by Volvo Powertrain. In Phase II, the possibility of 15% fuel economy improvement was shown with new EGR cooler design by reducing EGR cooler outlet temperature with APA engine technology from Air Handling Group. In addition, Vehicle Simulation with APA technology estimated 4 -21% fuel economy improvement over a wide range of driving cycles. During Phase III, the engine experimental setup was initiated at VPTNA, Hagerstown, MD. Air Handling system and HVA system were delivered to VPTNA and then assembly of APA engine was completed by June 2007. Functional testing of APA engine was performed and AC and AM modes testing were completed by October 2007. After completing testing, data analysis and post processing were performed. Especially, the models were instrumental in identifying some of the key issues with the experimental HVA system. Based upon the available engine test results during AC and AM modes, the projected fuel economy improvement over the NY composite cycle is 14.7%. This is close to but slightly lower than the originally estimated 18% from ADVISOR simulation. The APA project group demonstrated the concept of APA technology by using simulation and experimental testing. However, there are still exists of technical challenges to meet the original expectation of APA technology. The enabling technology of this concept, i.e. a fully flexible valve actuation system that can handle high back pressure from the exhaust manifold is identified as one of the major technical challenges for realizing the APA concept.

Adaptive nonlinear feedforward control of an electrohydraulic camless valvetrain

Camless engine operation offers potential benefits for making a high-performance engine. Control of the peak value of engine valve lift is a critical step in achieving these benefits. Nonlinearities and parameter variations in the valvetrain dynamics restrict the performance that can be achieved by the traditional PID feedback control approach. An adaptive control algorithm is presented with judicious selection of the model structure, adaptation parameters, and controller configuration. The experimental results demonstrate superior transient and steady state performance.

Modeling of Compressed Air Hybrid Operation for a Heavy Duty Diesel Engine

Internal combustion engines can be modified to operate regenerative braking cycles by using compressed air power. This paper presents a particular air hybridization design from among many possible configurations. The engine cycles are enabled by a highly flexible engine valvetrain, which actuates engine valves to generate desired torque with optimal efficiency. A lumped parameter model is developed first to investigate the cylinder-tank mass and energy interaction based on thermodynamic relationships and engine piston kinematics. Special consideration is given to the engine valve timing and air flow. A high fidelity, detailed model using the commercially available GT-Power software is developed for a commercial 10.8 liter heavy-duty diesel engine with a 280 liter air tank in order to capture the effects of engine friction, heat transfer, gas dynamics, etc. The model is used to develop optimal valve timing for engine control. The established engine maps are incorporated into the ADVISOR vehicle simulation package to evaluate the potential fuel economy improvement for a refuse truck under a variety of driving cycles. Depending on the particular driving cycle, the simulation has shown a potential 4% – 18% fuel economy improvement over the truck equipped with the conventional baseline diesel engine.Copyright