Electromechanical Valve Actuator Research Articles

Modelling and cycle‐by‐cycle control of an electromechanical engine valve actuator with impact speed limiter based on hydraulic damper

AbstractVariable valve actuation (VVA) systems based on electromechanical valve actuators (EMVAs) enable a flexible operation and management of internal combustion engines that results in a reduction of pollutant emission and fuel consumption while improving engine power and efficiency. However, to achieve the benefits promised by EMVAs, it is of utmost importance to guarantee the catch of the valve by the system magnets with an acceptable impact speed of the valve at the end‐strokes. Valve catching failures can severely damage engine valves while high impact speeds induce mechanical wear and unacceptable noise. The soft landing control of the valve at the end‐strokes is challenging because of system nonlinearities, parameter uncertainties, and external disturbances. The complexity of the control design increases further when industrial cost‐effective solutions are sought. This paper presents a novel solution for reducing the impact speed of the valve without the use of costly position valve sensors. The proposed solution leverages on a small hydraulic damper (HD) embedded into the EMVA and a feedback cycle‐by‐cycle controller. The passive element reduces the impact speed while the controller adjusts at every engine cycle the EMVA coil currents based on pressure peaks detected in the HD to guarantee valve catching while steering the impact speed toward its minimum. The design of the controller exploits a physics‐based model that maps the pressure peak in the HD onto the impact speed and a gradient descent algorithm is adopted searching the minimum. The closed‐loop permanence is assessed in simulation by using an experimentally validated EMVA model and considering detailed dynamics of the HD. Numerical results show the ability of the proposed control architecture to reduce the impact speed and its robustness to parameters variations (oil temperature) and external disturbances (gas pressure forces).

Direct Actuation of Large Sized Valves by a Hydraulically Relieved Electromechanical Actuation System

Extensive actuation forces and strokes are required for the actuation of large sized valves normally implemented in high power hydraulic systems. A hydraulically piloted operation is, for now, the most suitable solution and state of the art. However, there are some applications where electromechanical valve actuation systems are at advantage against common pilot operation systems. In this contribution it is analyzed in which cases the application of electro-mechanical actuators can be of advantage and why displacement-controlled systems may be one of these applications. A novel electromechanical valve actuation system for large sized 4/3-way directional control valves for the use in displacement-controlled systems is presented. This new actuation system is characterized by a hydraulic relief of the centering springs. Therefore, the springs are only active in safety-critical conditions, such as a power outage. Since the actuator is not working against the spring force during every displacement, the necessary actuation force is reduced drastically. Thus, common electromechanical actuators can be used. In case of a power outage, the spring relief is deactivated causing the stored energy to center the spool in its neutral position. The performance of the novel actuation system is examined through measurements conducted on a manufactured demonstrator for valves of nominal size 25 with a flow rate of up to 600 l/min.

Conceptual Design of Electromechanical Actuation Systems for Large-Sized Directional Control Valves

Increasing performance in modern hydraulics is achieved by a close investigation of possible enhancements of its components. Prior research has pointed out that electromechanical actuators can form suitable alternatives to hydraulically piloted control systems. Since the requirements at these actuation systems depend on the operating conditions of the system, each actuator can be optimized to the respective hydraulic system. Considering that many different conceptual designs are suitable, the phase of conceptual design plays a decisive role during the design process. Therefore, this paper focuses on the process of developing new conceptual designs for electromechanical valve actuation systems using the method of function structures. Aiming to identify special design features, which need to be considered during the design process of electromechanical actuation systems, an exemplary actuator was designed based on the derived function structure. To highlight the potential of function structures for the development of new electromechanical valve actuation systems, two principal concepts, which allow the reduction of the necessary forces, have been developed by extending the function structure. These concepts have been experimentally investigated to identify their advantages and disadvantages.

Stability analysis, routes to chaos, and quenching chaos in electromechanical valve actuators

The goal of this paper is to investigate the complex nonlinear dynamics and its control chaotic behavior in electromechanical valve actuator (EVA). The nonlinear phenomena can be expressed using numerical techniques, such as time responses, phase portraits, Poincaré maps, and frequency spectra. Lyapunov exponents and Lyapunov dimensions can be used to confirm chaotic behavior. Finally, state feedback control and dither signal control are applied to suppress chaotic motions effectively.

Modelling and analysis of spring return electromagnetic valve actuator for SI engine

In internal combustion engines, variable valve timing is one of the most important parameters that affects engine performance, fuel consumption and exhaust emission. In all engine speed values, electromechanical valve actuators (EVA) are needed for variable valve timing. EVAs allow the intake and the exhaust valves to be opened and closed at the right time by the camshaft. The valves can be opened and closed by the magnet circuits and the opening and closing time can be controlled without depending on the camshaft present in all engines. The most critical part for EVA design is the solenoid in terms of the limited space on the cylinder head, the magnetic force required to open and close the valve, the coil temperature and the valve speed. This study proposes a comprehensive design of piston-type EVA and an analysis of its performance. The simulation results of the analysis with finite element method have been verified with the experimental test results. In addition, the conventional valve profile has been compared with the EVA valve profile.

Optimal trajectory operation of a cogging torque assisted motor driven valve actuator for internal combustion engines

Cogging torque assisted motor drives (CTAMD) are a novel electromechanical valve actuation (EVA) technology for internal combustion engines that have a compact size and do not require conventional valve springs. Despite using an unoptimized position trajectory, the CTAMD was shown to produce the smallest ohmic loss at 6000 RPM when compared with other EVA systems found in literature. This paper presents a minimum-energy trajectory for a CTAMD and validates its improvements. First, an ohmic loss model for the CTAMD is formulated. Next, the optimized trajectory is generated through the use of the Nelder–Mead direct search algorithm. The optimized trajectory is then tested on a previously studied experimental CTAMD setup. Finally, the results of the experiments are analyzed to determine the performance improvements and practical advantages of the optimized trajectory. The optimized trajectory enables a further reduction of ohmic loss and reduces the number of MOSFETs required to drive the CTAMD by 75%.

Design of a hybrid magnetomotive force electromechanical valve actuator

We propose a novel axis-symmetric modified hybrid permanent magnet (PM)/electromagnet (EM) magnetomotive force actuator for a variable valve timing camless engine. The design provides a large magnetic force with low energy consump-tion, low coil inductance, PM demagnetization isolation, and improved transient response. Simulation and experimental results confirm forces of about 200 N (in the presence of coil current) at the equilibrium position and 500 N (in the absence of coil current) at the armature seat. We compared our proposed design with a double solenoid valve actuator (DSVA). The finite element method (FEM) designs of the DSVA and our proposed valve actuator were validated by experiments performed on manufactured prototypes.

Modeling and Control of an Electromagnetic Variable Valve Actuation System

A novel electromechanical valve actuation system comprised of a linear actuator, valve, and energy storing cam/spring mechanism is presented. The system dynamics are modeled using Lagrangian mechanics, and a minimum-energy point-to-point optimal control problem is solved to find an optimal trajectory and input. The optimal input is used as a feedforward component in a transition controller to move the valve between the open and closed positions. Between transitions, a simple linear controller stabilizes the valve in the open and closed positions. A high-order model capturing the distributed nature of valve springs is used to validate state constraints related to positive cam/follower forces and a nonslip condition on the cam/follower. Finally, a prototype system is fabricated and tested with promising results.

Experimental Validation of a Cogging Torque Assisted Valve Actuation System for Internal Combustion Engines

Electromechanical valve actuation (EVA) is an emerging technology that aims to optimize valve trains, allowing for significant improvements to engine performance, efficiency, and emissions. Recently, a simulation study introduced a novel cogging-torque-assisted motor-driven (CTAMD) valve actuation system. The actuator design emphasized a large output cogging torque that removed the need for conventional valve springs. The cogging torque developed by this actuator allows for highly efficient energy recovery that is superior to comparable systems that make use of mechanical springs. This paper experimentally validates the simulation study with a prototype actuator constructed using the specifications suggested in the previous simulation. The characterization procedure of the prototype is discussed and close agreement is found between the simulated and experimental motor parameters. Furthermore, this paper details a control system that minimizes Ohmic loss while providing fast transition times and low seating velocities. Finally, experimental results are displayed and compared to the simulated results as well as other EVA systems to validate the conjectured speed and efficiency of the CTAMD system.

Experimental Validation of a Hybrid Analytical-FEM Model of an Electromagnetic Engine Valve Actuator and Its Control Application

In this paper, a detailed mathematical model of an electromechanical valve actuator based on double electromagnets to actuate engine valves for camless engines is experimentally validated. The model was derived from an hybrid analytical finite element method approach and is here used as an effective tool to reproduce with high accuracy the behavior of such a variable valve timing actuator for different maneuvers of interest for camless engine applications. Experimental results of a model-based control strategy are also shown to give a first insight of its use for control purposes.

Energy-Based Key-On Control of a Double Magnet Electromechanical Valve Actuator

The aim of this paper is to design, analyze, and validate via experiments the control of a double magnet electromechanical valve actuator (EMVA). Such actuators have shown to be a promising solution to actuate engine valves during normal engine cycle. Their use can increase engine power, reduce fuel consumption and pollutant emissions, and improve significantly engine efficiency. To this aim, this actuator needs to be properly controlled at the engine startup for the first valve lift (key-on control). Mathematically, the EMVA system can be described as a highly nonlinear piecewise-smooth mechanical oscillator. The proposed control law is based on an energy control approach. Bifurcation analysis of the closed-loop system is carried out to characterize the nonlinear dynamics of the valve and to tune the controller. The numerical and theoretical analysis is in good agreement with the experimental results.

Design, Modeling, and Control of a Camless Valve Actuation System With Internal Feedback

This paper presents the modeling and control design of a new fully flexible engine valve actuation system, which is an enabler for camless engines. Unlike existing electromechanical or servo-actuated electrohydraulic valve actuation systems, precise valve motion control is achieved using a very stiff hydromechanical internal-feedback mechanism. The entire feedback mechanism is built into the physical design of the system. The external control only activates or deactivates the feedback mechanism in real time using simple two-state valves. This helps reduce the system cost, and thus enables mass production. The trajectory of the closed-loop system is purely dependent on the design parameters of the internal-feedback system. A mathematical model of the system has been developed and validated with experimental results from a prototype system. The “area-schedule” is identified as the most critical design feature, which affects the trajectory of the closed-loop system and, therefore, needs to be designed systematically to optimize the performance of the system as well as improve its robustness. By treating this feature as the feedback-control variable, the design problem is transformed into a nonlinear optimal control problem and solved numerically using dynamic programming. The effectiveness of the proposed design procedure is verified with case studies.

Modeling of an Electromechanical Engine Valve Actuator Based on a Hybrid Analytical--FEM Approach

The use of an electromechanical valve actuator (EMVA) formed by two magnets and two balanced springs is a promising tool to implement innovative engine management strategies. This actuator needs to be properly controlled to reduce impact velocities during engine valve operations, but the use of a position sensor for each valve is not possible for cost reasons. It is therefore essential to find sensorless solutions based on increasingly predictive models of such a mechatronic actuator. To address this task, in this paper, we present an in-depth lumped parameter model of an EMVA based on a hybrid analytical-finite-element method (FEM) approach. The idea is to develop a model of EMVA embedding the well-known predictive behavior of FEM models. All FEM data are then fitted to a smooth curve that renders unknown magnetic quantities in analytical form. In this regard, we select a single-wise function that is able to describe global magnetic quantities as the flux linkage and force both for linear and saturation working regions of the materials. The model intrinsically describes all mutual effects between two magnets. The goodness of the dynamic behavior of the model is finally tested on a series of transient FEM simulations of the actuator in different working conditions.

Electromechanical Valve Actuator with Hybrid MMF for Camless Engine

As one of variable valve timing (VVT) approaches, the electromechanical valve actuator (EMVA) uses solenoid to actuate valve movement independently for the application of internal combustion engine. This paper proposed an EMVA structure by incorporating the hybrid magneto-motive force (MMF) implementation in which the magnetic flux is combined by the coil excitation and permanent magnets. Making use of the dedicated flux arrangement, the proposed device can be used to fulfill the VVT features with reduced power source requirement and less electric device components. A dual flux channels EMVA is detailed and the design procedures are presented. Comparing with the conventional EMV, the proposed prototype shows a lot of advantages such as compactness, high temperature tolerance, fast response, relieve of starting current, and variable current actuating timing.

Output Feedback $H_{\infty}$ Preview Control of an Electromechanical Valve Actuator

In an electromechanical valve actuated engine, solenoid actuators drive the valves that control airflow into the cylinders, allowing elimination of the camshaft and flexible control of the valve timing. Individual control of the valves provides flexibility in valve timing over all engine operating conditions and fully enables the benefits of variable valve timing. This paper describes a closed-loop preview control of an electro-mechanical valve actuator that achieves quiet, robust, and reliable operation in the presence of significant delays in an electromagnetic system associated with eddy current losses. In this case, the desired trajectory of the armature position is known a priori. It is well known that preview control can greatly enhance disturbance rejection and tracking performance, when future information about the desired output is available. A detailed model is developed for the mechanical actuator system, the power electronics, and electromagnetic system. Illustrative experimental results are also presented

Enhancing the force capability of permanent magnet latching actuators for electromechanical valve actuation systems

This article introduces a topology of parallel-polarized permanent magnet latching actuator for use in electromagnetic valve actuation systems for internal combustion engines. The actuator has a number of advantages over reluctance actuators, commonly employed in such systems, in terms of reduced starting currents and fail-safe capability. The influence of a number of design features on actuator performance, such as tooth tapering, additional magnets to improve the main magnet flux path and prevent the onset of saturation, and mechanical clearances required to protect the permanent magnet from shock loads are investigated. The design study findings are verified by measurements on a prototype actuator.

Nonlinear Control of an Electromechanical Valve Actuator

Camless internal combustion engines offer major improvements over traditional engines in terms of efficiency, pollutant emissions, maximum torque and power. Electromechanical valve actuators are very promising in this context, but still present significant control problems. Low valve seating velocity, small transition time for valve opening and closing are conflicting objectives that need to be jointly considered when designing the valve control system. The paper presents a hybrid control system architecture capable to deal with all these issues. The design of the valve position controller is addressed in detail, in the framework of backstepping approach. Simulation results show the effectiveness of the proposed solution.

Control of a Camless Engine Electromechanical Actuator: Position Reconstruction and Dynamic Performance Analysis

Camless internal combustion engines offer major improvements over traditional engines in terms of efficiency, maximum torque and power, and pollutant emissions. Electromechanical valve actuators are very promising in this context, but they present significant control problems. Further, to keep system cost at an acceptable level, a control system without a valve position sensor needs to be adopted. Low valve seating velocity, small transition time for valve opening and closing, and unavailability of position sensor are conflicting objectives that need to be jointly considered. In this paper, a control system architecture is presented, capable of dealing with all these issues. It is shown that a position tracking controller is needed: a key point is the design of the reference trajectory to be tracked. Actuator physical limitations strongly influence the feasible trajectory when low valve seating velocity is required, thus affecting valve transition time. Owing to the same limitations, valve electromagnets have to be energized for a significant part of the trajectory, thus allowing valve position reconstruction starting from electrical measurements only. A method for position reconstruction is presented, which makes use of auxiliary coils to reconstruct electromagnets fluxes; it is shown via sensitivity analysis that the functional characteristics of position reconstruction and its accuracy are compatible with the required applications. The trajectory design is then addressed as an optimization problem that explicitly considers the tradeoff between fast dynamic performance and system robustness. The solution of this optimization problem enlightens the limitations on achievable dynamic performance, which are presented and discussed.

Extremum seeking control for soft landing of an electromechanical valve actuator

Many electromagnetic actuators suffer from high velocity impacts. One such actuator is the electromechanical valve actuator, recently receiving attention for enabling variable valve timing in internal combustion engines. Impacts experienced by the actuator are excessively loud and create unnecessary wear. This paper presents an extremum seeking controller designed to reduce the magnitude of these impacts. Based on a measure of the sound intensity at impact, the controller tunes a nonlinear feedback to achieve impact velocities of less than 0.1 m/s while maintaining transition times of less than 4.0 ms . The control strategy is implemented with an eddy current sensor, to measure the valve position, and a microphone.

Iterative learning control for soft landing of electromechanical valve actuator in camless engines

Variable valve timing allows improvements of internal combustion engines and can be achieved by camless actuation technology. In this paper we consider an electromechanical valve (EMV) actuator. One of the main problems in the EMV actuator is the noise and wear associated with high contact velocities during the closing and opening of the valve. The contact velocity of the actuator parts can be reduced by designing a tracking controller that consists of a linear feedback and a nonsquare iterative learning controller (ILC). With the ILC methodology we update the feedforward signal of the feedback controller every cycle based on the error between the actual valve position and the desired position. The methodology is reviewed and both simulation and experimental results are presented. We explore the disturbance rejection capability of the control scheme by simulating conditions with an unknown force acting on the valve similar to the ones present during varying engine load.