Submitted for MAE 442 (sec 001)Dr. Klang

May 4, 2007

Chris DiritoTaylor HobgoodDawn GloverAdvanced Valve Control

Outline Valve BasicsAdvantages of Variable Valve ControlOperation CharacteristicsTypes of Variable Valve ControlLiftDurationPhaseManufacturers and ExamplesFuture Possibilities

Variable Valve Timeline VVT- Variable Valve Timing It can be seen that according to the trend VVT will reach ~ 90 percent of vehicles in 2010 (according to Prof. Dr. Peter Walzer)

Variable Valve IntroductionWhy Use Variable Valve Timing and Lift? Most basic form of a push rod valvetrain is shown in the adjacent picture.

This systems Valvetrain characteristics cannot be changed once the engine is started

Limitations: Fuel Economy and Power are only optimized at one particular RPM, Throttle PositionBroad torque curves are sacrificed

VVT AdvantageIt can be seen from the graph the increases in torque across the power range of the VVT engine

Chart1

112126

115128

115135

130143

125137

124142

131148

137147

137145

136142

133137

127134

118128

107119

98112

Convential Engine

Varable Valve Engine

Engine Speed (rpm)

Brake Torque (N*m)

Advantages of Variable Valve Engine

Sheet1

Engine SpeedBrake Torque ConventialBrake Torque Varable

rpmNm

1.21200112126

1.61600115128

22000115135

2.42400130143

2.82800125137

3.23200124142

3.63600131148

44000137147

4.44400137145

4.84800136142

5.25200133137

5.65600127134

66000118128

6.46400107119

6.8680098112

Sheet1

Convential Engine

Varable Valve Engine

Engine Speed (rpm)

Brake Torque (N*m)

Advantages of Variable Valve Engine

Sheet2

Sheet3

Variable Valve TypesValve LiftSpecified Amount the Valve Opens to Allow Air and/or Fuel Air Mixture Into Combustion ChamberControlled by Camshaft Lobe Height, Maximum at the Cam NoseTypically Specified as Height Valve Lifts Away From Valve Seat

Variable Valve TypesValve DurationSpecified Time the Valve is OpenControlled By Camshaft Profile Geometry, Length of LobeMeasured in Degrees of Rotation, Either from Camshaft or Crankshaft

Variable Valve TypesValve TimingChanges Point at which Valve Opening begins with respect to crankshaft position.Typically attained by controlling an interface between the timing belt or chain, and the camshaft itself.Allows for finer tuning of Combustion chamber cross flow, and coupled with variable ignition timing can be adjusted to increase Combustion Efficiency.

Operation Characteristics

Intake Opening Intake valves are opened before TDC (~10-25degrees)Higher engine speed have shorter time for air/fuel ingestionHigher Speeds decrease volumetric flow rateTime delay for valve to open fullyAt higher engine speeds intake valves must open earlier Intake Closingclosed after BDC (~40-50degrees)The intake flow momentum is greater than pressure created by upstroke of pistonThis momentum is greater at higher engine speedsthus at higher engine speeds intake valve will close later in cycle.

Operation Characteristics(cont)Valve OverlapDefinition: Valve overlap occurs when both intake and exhaust valves are opened

At higher engine speeds exhaust from other cylinders in exhaust manifold will pull more air into cylinder

Increased valve overlap is desired at higher engine speeds

Decreased valve overlap at lower engine speeds increases effective compression ratio which in turn increases torque.

Variable Valve Types and Common Manufacturers

ValvetronicOffers continuously variable valve timing and valve lift on the intake cam only. Relies on amount of valve lift to throttle engineBMW VANOSVaries the timing of the valves by moving the position of the camshafts in relation to the drive gear.BMWVTECUtilizes two camshaft profiles and electronically selects between the profilesHondaVarioCamVaries intake timing by adjusting the tension of a cam chainPorcheAVCS/AVLSAVCS - varies timing (phase) with hydraulic pressureAVLS - Varies duration, timing and lift by switching between two different sets of cam lobesSubaruMitsubishi MIVEC similar to AVLS

Variable Valve Types and Common ManufacturersToyota Schematic of VVTL-i

VVT-i / VVTL-iVVT-i varies timing of intake valves by adjusting the relationship between camshaft drive and intake camshaftVVTL-i alters valve lift and timingToyota - Avalon, RAV4, Camry, Corolla, CelicaPontiac - VibeVVCVaries timing with eccentric diskRover

http://en.wikipedia.org/wiki/Image:VVTLi.jpg

Valvetronic Variable Valve Control which uses variable valve Lift(lift can be altered in 300 milliseconds)

Under high loads valve lift will increasesDuring low load situations valve lift will decrease

Advantages:Fuel consumption reduced by 10 %No need for throttle butterfly (increased throttle response) (Due to no throttle butterfly pumping loss is reduced )No timing belt or chain required) (Belt/chain only required to spin cam shafts)

Disadvantages:Low valve spring rates are required (stepper motor needs to be able to compress valve springs), thus high engine speeds are not able to be achieved.

Valvetronic Simplified Explanation: Valvetronic varies valve lift by adjusting the fulcrum point of the rocker arm.

The eccentric shaft is turned by an electric stepper motor which is controlled by the engine control unit.This will influence how much the cam can push down on the valve

Valvetronic in Actionhttp://youtube.com/watch?vrEELtXVTymU

The Mystical Vtec Explained VtecVariable valve Timing and Electronic lift ControlVariable in that two or more camshaft profiles can be utilzedElectronic due to the fact that an electronic solenoid controls the oil flow used to activate and deactivate the systemStandard VtecVaries Valve lift and/or duration by utilizing multiple camshaft profiles.Two Camshaft Profiles can be used. Each cam lobe has its own rocker arm. Desired cam profile is then locked together with the rocker arm controlling the valve on which desired effect is to take place. Locking is accomplished with oil pressure and a sliding pin mechanism. A solenoid triggers at the specified kick-in speed and allows oil flow to the sliding pin mechanism.Advantages are better fuel economy and smoother engine operation at low speeds, while at higher speeds more aggressive camshaft profile allows more power to be utilized.System shown varies both valves the same. Both valves are either at low speed profile or high speed profile

Vtec in Action

Vtec-eVtec-eVtec system where a extremely low cam profile is used at low rpm for one valve. And a standard cam profile is used for the other valve at low rpm and the standard cam profile is used for both valves at higher rpm speeds.This effectively closes one valve on a 16 valve cylinder head. Allowing a lean mixture to be used through the one open valve.Lean mixture is swirled through the open valve creating a more efficient distribution of the fuel in the combustion chamber.Leads to increased fuel mileage, increased engine efficiency, and decreased emissions. Does not create more power, is purely for efficiency reasons.Interestingly the one closed valve is slightly opened to allow any residual fuel that may pool in the closed intake passage to be used, but this lift is miniscule.Example Head

3 Stage Vtec3 Stage VtecVtec system which combines the standard Vtec and Vtec-e concepts to create a high power, fuel efficient valvetrain.Utilizes 3 separate Camshaft Profiles. This system operates like Vtec-e closing one valve at low speeds and then opening both valves at a standard lift and duration at a midrange rpm. It then has a high rpm cam which opens both valves aggressively as in standard Vtec.Like standard Vtec one rocker arm, usually on the highest lift profile, is not attached to a valve so that the highest lift is only used when the system is in operational Vtec range.In the illustration below the three significant camshaft profiles can be seen. And the sliding pins for each stage are shown as well

Vanos Valve Timing ControlMethod of adjusting cam sprocket relation to camshaft position. Allows for advanced or retarded valve timing to be used.Typical SystemTypically phase angle is adjusted with oil pressure radially. Most Japanese and American Manufacturers use this method.Usually only intake camshaft is adjusted.VanosBMW utilizes Vanos which adjusts relation between camshaft and sprocket by using two concentric pitched gears. A oil fed cup pushes one sprocket through the other axially thereby adjusting their relative phase angle. This allows for more precise movement, and a more controllably linear motion as opposed to the radial motion of other systems.Oil Flow is Controlled by electronic solenoid.Double Vanos controls both intake and exhaust camshafts

Other Phase Changers i-VtecUtilizes Oil actuated cam sprocket and follower.Angle is adjusted using oil pressure as in Vanos but is actuated in a rotational method, as opposed to BMWs linear actuation.Oil pressure controlled with electronic solenoid TypicallyOther manufacturers use similar technology

Japanese Continuous Lift Modification A-VtecStands For Advanced VtecUtilises a Intermediate Rocker Arm between the Camshaft and the Valve Rocker.This is housed in a rotating housing, allowing for camshaft lift to be mechanically adjusted from no lift to maximum lift.

Aftermarket Adjustments Infinite AdjustabilityAlmost all systems controlled electronically. Either directly by solenoids or stators, or by electronically actuated oil flow.These electronic components can be tapped into and controlled by remappable software.This allows for updates to be implemented without major tear down and rebuild. In car capabilitiesA laptop with correct software can be used to continuously analyze engine performance.Ignition Timing and Phase Timing can be measured and changed to optimize performance.Multi-stage systems such as Vtec can be changed to engage at different RPM settings.BenefitsCan readily change engine tuning from a useful efficient street setting to an aggressive racing setting at the push of a button.Allows for changes to be made on site to experiment with the most useful settings without extensive R&D.Personalized Engine performance, Not just what the Pros think is right, whatever You think is right.

FuturePneumatic ValvesThe valve spring pocket is replaced with a chamber pressurized with a gas (usually nitrogen because it is less temperature-sensitive than O2)Still use traditional camshaftsThe system has been used in Formula 1 racing since 1980sAllows higher RPMs valve springs have to be very stiff to allow high RPMs which creates more engine drag and slower valve timing

FutureElectrical SolenoidsPresently only used in the most modern systemsOpen and close valves without using valve springs as the main mode of valve closer. Solenoids accomplish this either directly or through electromechanical or electro-hydraulic connections.Soft closings less destructive force can allow for use of ceramic valves which can withstand higher temperaturesCan potentially have infinite variability in controlling valve timing, duration, and liftDrawback large size of components may be impractical for some vehicles with standard 12-volt systemInstead can use 42-volt electrical system with smaller components which also eliminates camshafts and thus reduces engine friction and increases mechanical efficiency

FutureCamless Valve Actuation

FutureSolenoids Camless Valve Actuation1. Current flows through the coil and a magnetic field forms around the coil2. The magnetic field attracts the armature toward the center of the coil3. As the armature moves upward, the spring collapses and the valve opens4. When current stops flowing to the coil, the magnetic field collapses and the spring expands and shuts the valve

References:Delphi Variable Cam Phasers. 2006. 1 May 2007 http://www.delphi.com/manufacturers/auto/powertrain/gas/valvetrain/vcp/

VANOS. 2007. 1 May 2007. http://www.bmw.dk/teknisk/en_artikkel.asp?id=5

Different Types of VVT. 2005. 3 May 2007. http://www.autozine.org/technical_school/engine/vvt_2.htm

US Patent # 6,968,819. USPTO. 4 May 2007. http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,968,819.PN.&OS=PN/6,968,819&RS=PN/6,968,819

Honda Worldwide. 2003. 1 May 2007. http://world.honda.com/motorcycle-technology/vtec/img/p3_04.jpg

VTEC. 2004. 1 May 2007. http://www.luk-korbmacher.de/Autos/Technik/vtec.htm

BMW Valvetronic. 2007. 4 May 2007. http://youtube.com/watch?v=rEELtXVTymU

References:Hope A. Bolton and Jay M. Larson. Valvetrain System Design and Materials. Materials Park, OH, 1997

Willard W. Pulkrabek. Engineering Fundamentals of the Internal Combustion Engine, 2nd Edition. Pearson Education, Inc, NJ, 2004

BMW World. 2005. 2 May 2007.

Ford Muscle. 2004. 1 May 2007.

Honda Engines. 2007. 2 May 2007.

Prof. Dr. Peter Walzer. Technology Highlights and R and D Activities. 2002 http://www.fev.com/data/documents/spectrum20.pdf

ReferencesWikipedia: Variable Valve Timing. 2007. 1 May 2007.

RACER MAGAZINE: F1 Engine Power Secrets. 2000. 3 May 2007.

Motorcycle Daily. The Sportbike Engine of the Future: Other Valvetrain Options. 2006. 3 May 2007.

Smart Valve Actuation: The Camless Engine Becomes a Reality. 2005. 3 May 2007.

Engineers Edge. 2007. 3 May 2007.

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