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Review of Advancement in Variable Valve Actuation of Internal Combustion Engines

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Review of Advancement in Variable Valve Actuation of Internal Combustion Engines applied sciences Review Review of Advancement in Variable Valve Actuation of Internal Combustion Engines Zheng Lou 1,* and Guoming Zhu 2 1 LGD Technology, LLC, 11200 Fellows Creek Drive, Plymouth, MI 48170, USA 2 Mechanical Engineering, Michigan State University, East Lansing, MI 48824, USA; [email protected] * Correspondence: [email protected] Received: 16 December 2019; Accepted: 22 January 2020; Published: 11 February 2020 Abstract: 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. Keywords: engine valve systems; continuously variable valve systems; engine valve system control; combustion optimization 1. Introduction With growing concerns on energy security and global warming, there are global efforts to develop more efficient vehicles with lower regulated emissions, including hybrid electrical vehicles, electrical vehicles, and fuel cell vehicles. Hybrid electrical vehicles became a significant part of vehicle production because of their overall efficiency, and they still pose a significant cost penalty, resulting in a stagnant market penetration of 3.2% and 2.7% in 2013 and 2018, respectively, in the United States (US), for example [1]. Electrical vehicles reached a market penetration of 1.3% in the US in 2018 [1], still limited by high cost and concerns on well-to-wheel CO2 emissions, charging speed, driving range, battery safety, and battery recycling issues. Fuel cell vehicles offer truly low overall emissions with driving range and fueling time comparable to vehicles powered by internal combustion engines. Hydrogen [2], the favorable fuel for fuel cells, can be generated from diverse sources, including natural gas, nuclear, coal, and renewable sources such as solar, wind, biomass, hydro, and geothermal sources. The development of fuel cell vehicles [3] is still in its infancy because of issues in technology maturity, cost, and performance, with only a few thousands of pilot vehicles on the road worldwide. Internal combustion engines are believed to remain as a major part of vehicle powertrains in the foreseeable future, either standing alone or being part of highly electrified powertrains such as hybrid electrical vehicles, plug-in hybrid vehicles, and range extender vehicles, unless there is a major technology breakthrough in battery and/or fuel cell technology. For these reasons, it is imperative to continue advancement in more efficient and less polluting internal combustion engines. Appl. Sci. 2020, 10, 1216; doi:10.3390/app10041216 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 19 The combustion in an internal combustion engine involves three key components: in-cylinder fuel, air, and ignition. In gasoline engines, the fuel injection process evolved from a pure mechanical process such as via a carburetor to an electronically controlled process such as via port fuel injection Appl.or the Sci. recently2020, 10, 1216adopted direction injection (see Figure 1). Spark ignition via a spark plug is completely2 of 20 electronically controlled for spark energy and timing. With its gaseous state, low density, and, thus, large volume, the electronic control of air exchange was a slow evolution process, from variable valve 1.1. Combustion and Need for Electronic Control of Gas Exchange time (VVT) to more sophisticated systems such as discrete variable valve lift (DVVL), continuous variableThe valve combustion lift (CVVL), in an internalcam-based combustion variable va enginelve actuation involves (VVA), three keyandcomponents: camless VVA, in-cylinder which are fuel,reviewed air, and later ignition. in this In article. gasoline There engines, were the also fuel efforts injection to develop process evolvedcamless fromVVA ato pure have mechanical complete processelectronic such control as via of a the carburetor air exchange to an electronicallyprocess, whic controlledh is a major process enabler such for advanced as via port combustion fuel injection such or theas homogeneous recently adopted charge direction compression injection ignition (see Figure (HCCI1).) Spark to improve ignition engine via a fuel spark economy plug is completelyand reduce electronicallyemissions [4–7]. controlled To improve for spark engine energy fuel economy, and timing. engine With downsi its gaseouszing state,techniques low density, are widely and, thus,used largewith volume,the help theof turbochargers. electronic control In this of air case, exchange the VVT, was VVL, a slow or VVA evolution system process, is able from to improve variable engine valve timesystem (VVT) transient to more responses. sophisticated systems such as discrete variable valve lift (DVVL), continuous variableIn diesel valve engines, lift (CVVL), fuel cam-basedinjection evolved variable from valve pure actuation mechanical (VVA), pumping and camless and injection VVA, which systems are reviewedto common-rail later in fuel this injection article. Therevia electronically were also e ffcontrolledorts to develop fuel pressure camless and VVA injectors. to have Note complete that electronicinjection timing control ofdirectly the air controls exchange the process, ignition which because is a major of the enabler compression for advanced ignition. combustion There is such less asdemand homogeneous or development charge compression on controlling ignition gas exchange (HCCI) to in improve traditional engine diesel fuel engines economy because and reduce of its emissionscompression [4–7 ignition]. To improve and lean engine combustion fuel economy, process. engine More downsizing sophisticate techniques air charge are widely management used with is theneeded help for of turbochargers.more advanced In combustions this case, the such VVT, as VVL, the orMiller VVA cycle system and is PCCI. able to However, improve engine this review system is transientlimited to responses. valve systems for gasoline engines. FigureFigure 1.1. More electronic controlcontrol ofof inputsinputs intointo gasolinegasoline engineengine combustion.combustion. In diesel engines, fuel injection evolved from pure mechanical pumping and injection systems to 1.2. Valve Lift, Valve Timing, and Valve Duration common-rail fuel injection via electronically controlled fuel pressure and injectors. Note that injection timingThe directly main function controls of the an ignition engine becausevalve actuation of the compression system is to ignition.control the There gas exchange is less demand into and or developmentout of a combustion on controlling chamber gas via exchangeintake and in exhaust traditional valves, diesel respectively. engines because The associated of its compression valve lift or ignitiontravel is andtypically lean combustion illustrated in process. a valve More timing sophisticate diagram (see air charge Figure management 2 for an example), is needed where for morevalve advancedtiming, valve combustions lift, and valve such asduration the Miller are cycledefined. and A PCCI. valve However, lift profile this describes review isthe limited valve tolift valve as a systemsfunction for of gasolinecamshaft engines. angle between its opening and closing. The opening and closing points define the valve timing in the crank angle domain and, thus, the relationship between the lift profile and the 1.2.rest Valveof the Lift, engine Valve components Timing, and Valveand events Duration such as the piston movement and ignition. Valve lift is oftenThe optimized main function for minimal of an enginepumping valve loss. actuation Often, intake system and is toexhaust control valve the gas lifts exchange are the same, into and but outthe ofdiameter a combustion of the chamberintake valve via intake is larger and exhaustthan the valves, exhaust respectively. one to ensure The associatedthat fresh valveair can lift be or traveleasily ischarged typically into illustrated the cylinder. in a Note valve that timing variable diagram valve (see lift Figure has the2 forpotential an example), of throttling where the valve cylinder timing, by valvereducing lift, the and intake valve valve duration lift to are reduce defined. the Apumpin valve liftg losses profile associated describes with the valvethe conventional lift as a function throttle. of camshaftHowever, angle this requires between very its openingclose control and of closing. lift to match The opening changes andin engine closing speed points and define load conditions, the valve timingwhich inis yet the to crank be fully angle proven. domain The and, overlap thus, the betw relationshipeen the intake between valve the opening lift profile and andthe theexhaust rest ofvalve the engineclosing components is an important and eventssecondary
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