Jia Ma Delphi Powertrain Systems, Auburn Hill, MI 48326 e-mail: jia.ma@delphi.com Guoming G. Zhu e-mail: zhug@egr.msu.edu Harold Schock e-mail: schock@egr.msu.edu Michigan State University, East Lansing, MI 48824 A Dynamic Model of an Electropneumatic Valve Actuator for Internal Combustion Engines This paper presents a detailed model of a novel electropneumatic valve actuator for both engine intake and exhaust valves. The valve actuator’s main function is to provide vari- able valve timing and variable lift capabilities in an internal combustion engine. The pneumatic actuation is used to open the valve and the hydraulic latch mechanism is used to hold the valve open and to reduce valve seating velocity. This combination of pneu- matic and hydraulic mechanisms allows the system to operate under low pressure with an energy saving mode. It extracts the full pneumatic energy to open the valve and use the hydraulic latch that consumes almost no energy to hold the valve open. A system dynam- ics analysis is provided and followed by mathematical modeling. This dynamic model is based on Newton’s law, mass conservation, and thermodynamic principles. The air com- pressibility and liquid compressibility in the hydraulic latch are modeled, and the dis- continuous nonlinearity of the compressible flow due to choking is carefully considered. Provision is made for the nonlinear motion of the mechanical components due to the physical constraints. Validation experiments were performed on a Ford 4.6 l four-valve V8 engine head with different air supply pressures and different solenoid pulse inputs. The simulation responses agreed with the experimental results at different engine speeds and supply air pressures. DOI: 10.1115/1.4000816 Keywords: automotive systems, powertrain systems, camless valve actuation, hydraulic and pneumatic system model 1 Introduction In a camless valvetrain, the motion of each valve is controlled by an independent actuator. There is no camshaft or other mecha- nisms coupling the valve to the crankshaft as in a conventional valvetrain. This provides the possibility to control the valve events, i.e., timing, lift, and duration, independent of crankshaft rotational angle. Various studies have shown that an engine with variable valve actuation reduces pumping losses, adjusts the cycle-to-cycle internal residual gas recirculation RGR, and re- duces nitrogen oxide NO x emissions with improved perfor- mance over a wide operating range. A significant amount of research has been contributed to dem- onstrate the advantage of variable valve actuation VVAover the traditional cam-based valvetrain for both gasoline and diesel en- gines. The investigation of intake valve timing control of a spark ignited SIengine was conducted in Ref. 1. It was found that at low and partial load conditions, engine pumping loss was reduced by 20–80% due to throttless operation. Fuel consumption was improved up to 10% at idle. Through simulation and experiments, Negurescu et al. 2showed that SI engine efficiency can be im- proved up to 29% due to variable valve timing VVT, compared with a classic throttled engine. The engine torque output was also improved by up to 8% at low speed with wide open throttle. Research carried out in Ref. 3demonstrated how VVT and variable valve lift VVLaffect the partial load fuel economy of a light-duty diesel engine. In this study, the indicated and brake- specific fuel consumptions were improved up to 6% and 19%, respectively. The operation of an Otto–Atkinson cycle engine by late intake valve closing to have a larger expansion ratio than compression ratio was studied in Ref. 4. A significant reduction of carbon monoxide COand NO x emissions was obtained. Urata et al. 5also showed that the operational range of a homoge- neously charged compression ignition HCCIengine can be ex- panded to both high and low load ranges through the adoption of VVT and VVL. The advantages of VVT and VVL engines lead to combustion optimization over a broad engine operational range. For example, Trask et al. 6developed the VVT and VVL opti- mization methodologies for an I4 2.0 l camless ZETEC engine at various operational conditions including cold starts, cylinder de- activation, full load, idle, and transient operations. Three primary types of camless valve actuators are electromag- netic, hydraulic, and pneumatic actuators. Sugimoto et al. 7, Theobald et al. 8, and Pischinger and Kreuter 9presented the results of electromagnetic actuators. A hydraulic actuator was dis- cussed in Ref. 10. A pneumatic actuator incorporated with a permanent magnet control latch was presented in Ref. 11. The advantages and disadvantages of a pneumatic actuator over a hy- draulic actuator were addressed in Ref. 12, where a pneumatic valve actuator with a physical motion stopper was presented and the simulations of the valve actuation system were shown. Imple- mentation of various camless valve actuators was studied in 13. In order to provide an insight to the pneumatic actuator design and its control requirements, mathematical modeling was per- formed to the engine and its various actuation systems. A variable valve timing engine was modeled in Ref. 14, along with its engine control strategy. Tessler et al. 15analyzed and modeled the dynamics of a pneumatic system consisting of a double-acting or single-acting cylinder and servo valve. A mathematical model of a pneumatic force actuator was presented in Ref. 16. In this article, an electropneumatic valve actuator EPVAis employed to replace the traditional camshaft in an internal com- bustion engine. The EPVA is capable of varying valve lift, timing, and opening duration as desired in a variable valve timing engine. Different from the pneumatic valve discussed in Ref. 12, the EPVA is designed to extract the maximum work from the air flow by incorporating a hydraulic latch mechanism to hold valve open Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS,MEASUREMENT, AND CONTROL. Manuscript received November 15, 2008; final manuscript received November 20, 2009; published online February 3, 2010. Assoc. Editor: Bin Yao. Journal of Dynamic Systems, Measurement, and Control MARCH 2010, Vol. 132 / 021007-1 Copyright © 2010 by ASME Downloaded From: http://dynamicsystems.asmedigitalcollection.asme.org/ on 04/02/2015 Terms of Use: http://asme.org/terms