valvetrain feature etm107 mechadyne technologies

7/29/2019 Valvetrain Feature ETM107 Mechadyne Technologies

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New emissions legislation is one of the reasons for an

increase in the development of advanced valvetrains.

Elsewhere, time, cost and weight needs to be saved

valvetrains by Brian Cowan

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March 2007 | Engine Technology International

nThough not quite as mucho an ever-receding mirage asuel-cell vehicles, which havebeen ‘10 years rom production’or the past 15 years, advancedvalve systems too have stayedtantalizingly out o reach.However, with legislation ontougher CO

2standards looming,

and with researchers closing inon the Holy Grail o HCCI, therehas been a recent resurgence o interest in a eld that has beenrelatively quiescent ater a furryo activity in the late 1990s. Fullcamless variable valve actuation(VVA) is still some time away,but at least three suppliers arermly committed to developingproduction versions; also at anadvanced stage o developmentare several systems that retain thecamshat but oer a high levelo variability in both lit andduration. In the meantime, aclutch o ingenious phase-shiting

and prole-switching designs has just entered service or are closeto debut.

Schaefer KG is condent o being at the oreront o the newwave with its UniAir system,based on the core research –carried out originally by andlicensed rom Fi at’s CRF. UniAiris a lost motion design that usesthe camshat and engine oil tooperate a high-pressure pistonpump, and a ast-acting solenoidvalve to control the oil volumetrapped in the high-pressurearea, thereby generating variablelit and timing proles orindividual valves. The valvelanding velocity is adjusted usinga separate hydraulic braking

Engine Technology International | March 2007

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piston. John Taylor, director andgeneral manager o SchaeferUK’s automotive division,conrms that UniAir will soonreach production with anunnamed OEM. “Job one,”he says, “is set or 2009”.

Electro-hydraulic camlesssystems provider, SturmanIndustries, has had a recentsetback with the replacement o the HEUI (hydraulic electronicunit injector) uel system in thecompany’s 6.4-liter V8 dieselwith a more conventional piezo-triggered common rail design.The HEUI was based aroundSturman’s quick-acting digitalvalve, which seems to havesuered rom leakages in thepartial-stroke mode.

The change to the V8’s uel

system means that a proposeduture introduction o camlessoperation using the same oilsupply and similar stepped-piston actuators is now unlikely.Sturman, however, continues todevelop its amily o hydraulic

valve actuation systems,including a single stage, openloop, variable lit design anda research module.

While BMW’s Valvetroniccontinues as the only truevariable lit and duration designon the market, several othersimilar mechanically variabledesigns have been developed andare ready or production when

engine makers consider thatconditions warrant it, believesPhil Carden, rom Ricardo’sdesign analysis group. “Myopinion is that the suppliersin Europe have their own designsor this sort o system, either on

the shel or in development.Nobody else has so ar ollowedBMW, because though there arebenets to be gained with suchdesigns they are also veryexpensive and don’t suiteverybody at the moment.”

Tim Lake, rom Ricardo’sgasoline engineering group,concurs: “As CO

2legislation in

Europe and the US kicks in, youwill start to see more and more o these applications being put intoproduction – probably lteringrom the top down. There willalways be some manuacturersat the top end who will producewhat you might call haloproducts, but the likes o camlessengines are still a good way inthe uture in terms o mass-market applications.”

In the eld o advancedmechanical valve trains, oneo the more intriguing hasbeen developed by MechadyneInternational. At the heart o what can become a graduatedupdate path or an engine amily

is the company’s SCP orconcentric camshat design,which is to reach production inthe 2008 Dodge Viper. A hollowouter camshat tube carries oneset o lobes, with the second setbeing pinned to a solid innercamshat. The pins projectthrough slots cut in the surace o the hollow unit. The approach isespecially suited or cam in blockdesigns such as the Viper engine,and allows the use o phasers oneach o the inlet and exhaustcamshat elements.

In Mechadyne’s VLD (valve litand duration) design, the sametype o concentric camshatcarries two sets o lobes per inletor exhaust valve set, operatingthem through a compound rollerrocker that sums the proles.

Retaining the camshat in thesame position as a conventionalengine was one o the primaryreasons Mechadyne went orthe concentric approach, saystechnology director Dr TimLanceeld. “It means that i you

design an engine incorporatingour system, you can begin withconventional xed camshats,then stage through the twin-phaser approach and then on tothe ull VLD, giving you degreeso modularity in the system.

“Engine speed limits aredictated mainly by the extra masso the valve train componentsand (in EGR applications) theproportion o the main event littaken up by secondary events. We have designed systems thatwill run up to 6,500-7,000rpmin valve-head throttled SIapplications. In any event, thesetypes o systems are targetedmore at improved eciency andemissions than ultimate power,so high speed is not an issue.

“Duration control range o

the compound-rocker VLD isabout 100º o crankshatrotation, the turn-down ratioo lit is about 10:1, secondaryvalve lits can be generated witha range o 50-70º, with lits upto about 60% o the main valve

The concept o electromagnetically operated valve systems hasbeen studied or years by various companies, but without anygreat commercial success. This could be about to change as Valeois making great strides with a camless system it has been studyingsince 1998.

Loosely based on an idea originally rom FEV, Valeo believes thatthe time is nigh or electromagnetics. A Valeo spokesman told ETi :“The reason this technology has not been a commercial successin the past is that the electronics relating to the actuator havenot been good enough. Also both engine design and electronicengineering need to be married in the right way.” Valeo is condentthat the design currently under development will be in theshowrooms early in the next decade. Initially, high-CO

2emission

gasoline engines will benet, as the uel economy changesor diesel are less pronounced. However, as the Valeo spokesmancontinues, compression ignition is also o interest: “There are

denite benets or diesels as ar as closed loop control andmixture management goes.”

Increased uel economy, up by 15-20% on the petrol testengines, is not the only benet o the system, as torque improvesby a similar margin, depending on the state o tune. Valeo claimsthe system oers “the economy o a diesel with the perormanceo a petrol.”

The intake system is camless, while the exhaust side eaturesa hydraulic cylinder deactivation system. In act, to be strictlyaccurate, Valeo reers to the design as “hal camless.” The reasonor this is that the orces required to operate the exhaust side areso high, the perormance benets are o set by the increasedparasitic losses. The spokesman adds: “The main benets are onthe inlet side as pumping losses can be reduced. We concludedthat i 80% o the benet is on the inlet side, then this is thebest balance.”

To get round the low voltage problem that plagued the actuatorsin the past, Valeo uses an intelligent way o stepping up the 14Vvehicle architecture to 42 volts by me ans o a DC/DC converter.

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March 2007 | Engine Technology InternationalEngine Technology International | March 2007

Although there is a small weight penalty, the gain is well worth it.The spokesman continues: “This was one o the mistakes madeyears ago. When it was clear that 12 volts would not be enough,some tried to make the whole vehicle 42 volts which would haveworked out prohibitively expensive.” Power consumption hastraditionally been the system’s Achilles Heel, but Valeo has nowreduced the demand by 50% to an acceptable level. On the our-cylinder test car, power consumption at 5,500 rpm is 450 watts.Initially the system consumed 2 kW.

The secret o the system’s success is the balance o the valveverses the spring. This is complemented by a highly optimized

actuator, all governed by the most modern electronics. Thespokesman notes: “The electronics just wasn’t available ten yearsago.” Hall eect position sensors are completely embedded in thedesign, while two microprocessors do the thinking. Valeo is currently ne tuning the sotware and simulating system

reliability. It looks like with the current design, it would be good orat least 120 million actuator cycles which is equivalent to 90,000miles at ull load. “We will meet any durability targets that an OEMsets” adds the spokesman. No maintenance would be required orthis design.

The project has been combined with a mild hybrid based onStARS+X technology. In addition to the start-stop unction whichcuts o the engine when the vehicle is at a standstill, this systemeatures a regenerative braking unction, where energy generatedduring braking is recovered. Dubbed LOwCO2MOTION™, the twoconcepts together have been given a dramatic boost by the awardo US$108 million rom the French Industrial Innovation Agency(Agence de l’Innovation Industrielle).

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by Jonathan Lawson



rotary bridgeWhile looking at the technology o valve trains, it is easy to assumethat the poppet valve will continue as the dominant technology othe uture. Not i a dedicated group o believers in the merits osleeve, piston-port and rotary valves have their way. Though all o

them suer rom an inherent diculty with variable timing, the manypatents led each year relating to valve systems have includedenough rotary ideas to keep the fames o hope burning.

One o the more promising o the rotary brigade is the Coatesspherical valve. The basic idea was patented by ounder George JCoates in 1990 and has been quietly worked on since by the CoatesInternational company which he ounded.

The Achilles Heel o every rotary valve system yet developed hasbeen combustion product blow-by or leakage o the intake mixture.The Coates design claims to have answered this with foatingceramic seals carrying two piston-type rings that are momentarilypressurised against the valve shat by combustion pressure ventedbehind them. In other words, the seal is at its most eective whenmost needed. At other parts o the cycle the pressure is relieved,reducing wear between seals and shat.

The Coates technology has yet to be applied to a productionautomobile, though the company has developed an on-site electricalpower generator based around a six-cylinder in-line natural gas-powered CSRV engine o 855 cubic inches displacement and anoutput range o 174 to 280bhp.

event. In general terms, we ndthat there is no problem in usingthe standard valve springs.”

The latest prole-switchingsystem to hit the market is Audi’s

Valvelit, tted to the company’sFSI V-engines, beginning withthe 2.8-liter V6. The roller rockerdesign switches betweenadjoining ull-load and part-loadcam proles by shiting the

whole camshat longitudinally byaround 7mm, the motion beingtriggered by a ast-acting actuatorpin or each inlet shat thatmomentarily engages a shallow,spiral groove cut in the shatcircumerence. A second grooveand pin combination reverses the

motion, with the shatbeing retained in eitherposition by a sprung balland indent system.

The ull-load prole givesa lit o 11mm, the part-load anasymmetric 5.7mm and 2mmor the two valves, promotinga swirl and tumble motion tothe intake fow.

Suzuki has also ollowed an

axial-movement path with itsconcept Miller-cycle valve-throttled engine, but here the3D-ground cam lobes slide backand orward along their shatsunder electronic control andmechanical actuation. Because itscamshat drive and phaser layout

valvetrains

is conventional, the 3D head canbe virtually a direct replacement.

In the realm o vane-typehydraulic phasers, BorgWarnerMorse TEC has developed whatit calls its cam torque activated(CTA) and torsional assist(TA) units, which make use o

camshat torque reaction andtimed opening and closing o valves in the inter-chamber oilpassages to promote a asterphase shit. Actuation rates o 150/sec are claimed at low oilpressure and idle engine speeds,while the phasers have less thanhal the oil fow o conventionalvane designs. They are also lesssensitive to oil pressure andtemperature variations, saysthe company.

Meanwhile, Denso has taken

an entirely dierent route in itselectric motor driven phasers,introduced by Toyota as VVT-iEin the 2007 Lexus LS460. Inplace o hydraulic phase shitmechanisms, the Denso systemuses an electric motor in theactuator mounted axially withthe inlet camshat that spinsaster than the shat to advancethe timing, and slower to retardit. Benets claimed include betterresponse at low engine speedsand temperatures, positive

camshat positioning or starting,and a greater adjustment range.Lotus has plumped or the

electro-hydraulic route to ull VVA, primarily because o thecompany’s expertise in advancedhydraulic switching, gained romits active suspension Formula 1

March 2007 | Engine Technology International

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project o the early 1990s. As Jamie Turner, the company’schie engineer, powertrainresearch, explains, its whole AVT(active valve train) project sprungrom one o those ‘what i?’conversations, ollowing thedevelopment o the active

suspension system: “Somebodyspeculated that similar electro-hydraulic technology could beused in opening valves. We builta prototype, but then we madethe mistake o showing a clientwho said, ‘We’d like one’.”

Then ollowed developmento a research VVA system thathas gone on to be widely usedin combustion research, with 25in service at the present time.One o Lotus’ clients or the unitwas a European heavy-diesel

manuacturer who expressedinterest in a production version. A three-way collaborationbetween the client, Lotus andEaton Corporation is currentlyworking towards that goal.

The production system oersless fexibility in lit and timingthan the research design, butcompensates by being simplerand considerably less expensiveto produce. It uses conventionalclosing springs or valves, plussolenoid switching and actuator

valves in place o the wildly

expensive our-way electro-hydraulic servo valves that arethe heart o the AVT research.

Perormance parameters orthe system included individualvalve operation with continuouslyvariable lit between zero and15mm, unrestricted valve timing

and phasing, lit repeatability o 1%, timing repeatability o 1º o crankshat angle, and a maximumengine speed o 7,000rpm or SI/ HSDI and 2,400rpm or heavy-duty diesel. Because o the natureo the servo valves it uses, theresearch AVT has a speed limito around 4,500rpm.

In the production designbeing developed, a valve event istriggered by solenoid switchingvalves that introduce hydraulicpressure to the bigger actuator

valves. The latter are set to allowsome controlled leakage that litsthe valve o its seat, replicatingthe heel ramp o a conventionalcam lobe. The actuator valvethen opens ully or a asteropening rate, then closes nearull lit, with the built-in leakageallowing the valve to slow.

Approximately halwaythrough the valve event, theswitching valve will move toreturn (closed) mode, theactuator valve leakage now

allows the valve to begin closing

to send blow-down pulses toturbines at points in the cycle, ora more sophisticated control o two-stage charging systems.

“You can rid yoursel o the

requirement to run a our-strokecycle, ull stop. In some o thework we’ve done, we’ve shownthe ability o light-duty autovalves to be used on a two-strokecycle. Going the other way, youcan just as easily have six or eightcycles. That’s not just skippedcycles; there will be dedicatedevents on every stroke”

Turner continues: “Beyondthat, again there are such thingsas pneumatic hybridization.Imagine an engine in which adedicated valve is connected toa receiver. When you lit o theaccelerator, the engine switchesrom a our-stroke combustionmode to a two-stroke compressor,still unthrottled because it’s aully variable valvetrain. Thischarges the pressure receiver sothat when the vehicle moveso rom rest, the engine acts asa two-stroke air motor. Youhave an opportunity to provideparallel hybridization withinthe engine itsel, as a very cost-eective alternative to batteries

and electric motors. Ourcurrent estimates or production

AVT are that it could, in suitablevolumes, be cheaper thanelectric hybridization.” ETi

valvetrains

Engine Technology International | March 2007

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slowly under spring pressure.Open ully, the actuator providesa aster closing rate, nallyclosing once more near the endo the event, the leakage rate andthe reduced spring strainpromoting a sot landing.

Valve position is controlled viaa closed loop, with the positionsensor being in the actuator body:it is wrapped round the hydraulicchamber, the target or the sensorbeing the hydraulic piston.

The debut o the production AVT design is expected to be atleast three or our years away,says Turner. “But beyond that,once engineers have startedthinking about the wacky

possibilities that open up oncethe camshat has been tossed inthe waste bin, there are plentymore things you can do. Theyinclude separate exhaust ports

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