Electrical Variable Valve Timing Systems Research Articles

Review of Advancement in Variable Valve Actuation of Internal Combustion Engines

The increasing concerns of air pollution and energy usage led to the electrification of the vehicle powertrain system in recent years. On the other hand, internal combustion engines were the dominant vehicle power source for more than a century, and they will continue to be used in most vehicles for decades to come; thus, it is necessary to employ advanced technologies to replace traditional mechanical systems with mechatronic systems to meet the ever-increasing demand of continuously improving engine efficiency with reduced emissions, where engine intake and the exhaust valve system represent key subsystems that affect the engine combustion efficiency and emissions. This paper reviews variable engine valve systems, including hydraulic and electrical variable valve timing systems, hydraulic multistep lift systems, continuously variable lift and timing valve systems, lost-motion systems, and electro-magnetic, electro-hydraulic, and electro-pneumatic variable valve actuation systems.

Optimum shape design of a BLDC motor for electric continuous variable valve timing system considering efficiency and torque characteristics

Recently, environmental problems caused by global warming and exhaust gas have been increasing, leading governments all over the world to implement strict environmental regulations. For this reason, the automotive industry has begun working to increase fuel efficiency and reduce emissions. In addition, in order to improve the performance of engines implemented in internal combustion engines (ICEs) and hybrid electric vehicles (HEVs), electronic control actuators are becoming increasingly preferred over conventional mechanical parts. In particular, engine intake and exhaust valve timing techniques are critical to improving fuel economy and reducing vehicle emissions. Previously, a hydraulic continuous variable valve timing (CVVT) system was used for valve timing control. However, a disadvantage of this type of system is that the response speed is slow at low and high engine temperatures; these conditions limit the extent of automobile fuel efficiency improvement. Therefore, an electric variable valve timing system (E-CVVT) is being studied to overcome this disadvantage. In this paper, we propose a shape optimum design method for brushless DC (BLDC) motors used in an electric continuous variable valve timing (E-CVVT) system, which is employed in ICEs and HEVs. The proposed design aims to maximize the maximum torque and rated efficiency of BLDC motors, and minimize cogging torque. To select the optimal design variables, we chose to implement Latin hypercube sampling (LHS) to avoid duplication of sampling points. The characteristics of the sampling points obtained via the LHS method were calculated by using finite element (FE) analysis. In order to consider the nonlinearity of properties, we have created an approximate modeling technique that uses a radial basis function. Finally, genetic algorithms were used to determine the design parameters of the optimum model. The effectiveness of the proposed BLDC motor design process is verified by comparing the FE analysis and experimental results. Simulation and experimental results confirmed that the proposed optimized design procedure yields improved operating characteristics. Specifically, testing the proposed optimized design yielded a 16.7% increase in the maximum torque, and a 66.2% reduction in the cogging torque. In addition, the vehicle test confirmed that the proposed design was suitable for an E-CVVT system equipped with a BLDC motor. In addition, the optimum model of the BLDC motor was applied to the E-CVVT system. The response characteristics of the conventional hydraulic CVVT system and E-CVVT were compared via vehicle testing. The response speed of the E-CVVT system was 0.65 s faster than that of the CVVT system during the retard angle phase. Therefore, it was a 39.4% improvement in the response performance.

Modeling and Control of an Electric Variable Valve Timing System

This paper presents a model of an electric variable valve timing (EVVT) system and its closed-loop control design with experimental validation. The studied EVVT uses a planetary gear system to control the engine cam timing. The main motivation of utilizing the EVVT system is its fast response time and the accurate timing control capability. This is critical for the combustion mode transition control between the spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustion, where the engine cam timing needs to follow a desired trajectory to accurately control the engine charge and recompression process. A physics-based model was developed to study the characteristics of the EVVT system, and a control oriented EVVT model, with the same structure as the physics-based one, was obtained using closed-loop system identification. The closed-loop control strategies were developed to control the EVVT to follow a desired trajectory. Both simulation and bench test results are included.

SI and HCCI Combustion Mode Transition Control of an HCCI Capable SI Engine

The combustion mode transition between spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustion of an internal combustion (IC) engine is challenging due to the distinct engine operating parameters over the two combustion modes and the cycle-to-cycle residue gas dynamics during the mode transition. The control problem becomes even more complicated for a multicylinder engine without camless variable valve actuators. This paper studies the combustion mode transition problem of a multicylinder IC engine equipped with dual-stage valve lift and electrical variable valve timing (VVT) systems. Hardware-in-the-loop (HIL) simulations were used as a tool to develop and validate the proposed control strategies. Based on the HIL simulation results, this paper shows that smooth combustion mode transition can be realized in a few engine cycles. During the mode transition, a model-based linear quadratic tracking strategy was used to track the desired engine manifold pressure through the engine throttle control to maintain the engine AFR in a desired range; the fuel quantity of individual cylinder was controlled via the iterative learning; and engine spark was maintained for the SI-HCCI (or spark assistant) hybrid combustions during the combustion mode transition. The HIL simulations demonstrated the effectiveness of the developed control strategies under both steady state and transient engine operating conditions. As a result, it is feasible to have a smooth combustion mode transition for an HCCI capable SI engine equipped with dual-stage valve lift and electrical VVT systems.