Electromagnetic Fully Flexible Valve Actuator

8/12/2019 Electromagnetic Fully Flexible Valve Actuator

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2006-01-0044

Electromagnetic Fully Flexible Valve Actuator

David Cope and Andrew WrightEngineering Matters, Inc

Copyright 2006 SAE International

ABSTRACT

An electromagnetic fully flexible valve actuator(FFVA) for internal combustion engines is describedwhich offers the potential for significant improvements infuel economy, emissions, and performance, especially atlow end torque, in internal combustion engines. TheFFVA offers variable lift and timing combined withcontrollable seating velocity. It operates on a design

principle distinct from existing actuators: theelectromagnetic actuator exerts appreciable bi-directional force throughout the device stroke mitigatingthe need for mechanical spring-derived resonance. TheFFVA is a direct drive device with a unique magneticstructure that combines high bandwidth and strongforces to meet the engine performance requirements.

This paper presents the innovative electromagneticdesign, simulation, and bench testing of the actuator ona single cylinder engine.

INTRODUCTION

Variable valve actuator (VVA) strategies have beenproposed for decades as a means for improvingperformance and efficiency while controlling emissions[1,2]. The benefits to engine performance of variousvalve actuation strategies, such as Early Intake ValveClosing (EIVC), Late Intake Valve Closing (LIVC), LateIntake Valve Opening (LIVO), and Variable Max ValveLift (VMVL), have been thoroughly investigated andexperimentally verified. These strategies range fromcylinder deactivation to discrete step and continuouslyvariable cam profiling, and, ultimately, to camlesstechnologies such as electrohydraulic andelectromagnetic actuation [3,4,5,6]. However, despitethe performance benefits most current internalcombustion engines do not take advantage of VVA.Those that do are extensions of standard camtechnologies [1,3,7,8].

Camless technologies have the capability to fulfillthe promise of FFVA. Specifically, the ability to fullydefine the motion of the engine valves combined withintelligent control enables the adoption of any valveactuation strategy achieving the above mentionedbenefits. Electrohydraulic valve actuation has a longhistory as a research tool for quickly varying cam profilesto study valve lift vs. timing and is technically capable of

achieving all the requirements of FFVA. Recent effortsto apply electrohydraulic valve actuation to productionengines have focused on reducing power consumptionas well as redesigning prohibitively expensivecomponents such as the high pressure pump [6]Electromagnetic valve actuation potentially achieves therequirements of FFVA while avoiding the complexity oan additional hydraulic system. The potential barriers tothe FFVA adoption are increased electrical powe

consumption, too great a valve seating velocityunacceptable actuator failure modes, cost, and actuatopackaging difficulties. Additionally, current cam valvetrain technology has evolved to an extremely well-developed and thoroughly tested system setting a highstandard for replacement technologies [3].

The objective of the current research is to developan actuator capable of satisfying the FFVA concept. Anew, innovative, patented, and patent pendingelectromagnetic valve actuator for internal combustionengines is discussed. Fully flexible valve actuation isachieved through concurrent design of electromagneticelectrical, mechanical, and thermal aspects. Thisactuator achieves fully flexible valve actuation throughvariable valve timing as well as variable lift. Among thenumerous advantages of FFVA are increased engineefficiency over the engine speed and load range, andthe elimination of the cam and throttle subsystems.

Demanding power, force, speed, and controrequirements have prevented standard actuators fromfulfilling FFVA principles, prompting the development ohighly complex mechanical and electromechanicasystems. The innovative actuator discussed hereinconsists of stationary permanent magnets, a stationarycoil, and moving iron stem that transmits bi-directionaforces to the valve. Under contract to the NationaScience Foundation, an experimental proof-of-principle

actuator was developed and mounted on a singlecylinder engine. Experimental data confirm basicoperational capabilities, with both variable timing and liftThe projected system power requirements for a 16 valvesystem are low enough to be operable from a standard12V automotive electrical system with alternatoaugmentation [9,10,11].

Magnetic finite element analysis and simulation othe actuator demonstrated the achievement of thedesired performance objectives (power, force, andcontrol) for a FFVA.


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A traditional cam drive train, shown in Figure 1, actson the valve stems to open and close the valves. As thecrankshaft drives the camshaft through gears or a belt,the timing of the opening and closing of a valve iscontrolled by the cam design and is fixed relative to thepiston position. This means that the engineperformance is optimized only over a narrow range ofengine speed and load. Most existing electromagneticvalve actuators focus on variable timing (the ability toopen and close the valves at will) however, they do notallow for variable lift. The FFVA approach, shown inFigure 2, allows for fully flexible valve control (i.e. bothvariable timing and variable lift, low valve seatingvelocity, fast transition times (up to 6000 rpm), and fullstroke force authority).

Electromagnetically-controlled valves can operateoptimally at all engine speeds, torque levels, andtemperatures thereby greatly improving the engineperformance, including emissions. For example,improvement in fuel economy in excess of 15% isexpected for FFVAs [12, 13].

Figure 1. Traditional Mechanical Cam Drive Train

Figure 2. First Generation Fully Flexible Valve Actuator

VALVE ACTUATOR STRATEGIES

With the additional degrees of freedom offered byFFVA (lift, timing, and seating velocity) severastrategies for manipulating the intake flow exist. Themost attractive strategies are those which eliminate theneed for intake throttling and in the process, reducepumping losses. Specifically, EIVC, LIVO, LIVC, andVMVL are the general intake valve actuator strategies

which achieve this [3]. A qualitative comparison bySellnau of the performance of these four strategiesreveals EIVC to be the most favorable strategy forreducing pumping loss and LIVO to provide the besmixture motion at ignition. The other two strategiesLIVC and VMVL, employ only one of the alloweddegrees of freedom and are shown to be generally lesseffective by comparison. LIVC changes only theduration of the intake opening process, while VMVLvaries only the lift. The other two strategies, EIVC andLIVO may be accomplished with variable timing alonebut are preferentially combined with lower lift.

Two complementary methods for electromagneticvalve actuation exist: commanded holding and

commanded acceleration. The holding style actuatorelies on stored mechanical potential energy to bereleased into kinetic energy for transition, then storingonce again the kinetic energy into mechanical potentiaenergy to be held until the next desired transition. Theacceleration style actuator electrically supplies thekinetic energy, and then reclaims the kinetic energythrough regeneration. In theory, both methods requireonly the initial energy input for operation. In detailhowever, the power requirements and achievabledynamics of each method differ based upon the specificactuator properties such as force per current ovestroke.

In a practical embodiment, most actuators are ahybrid of these two methods. An example of the holdingstyle actuator, the Pischinger design, uses solenoids tohold the valve either in the fully open or fully closedposition while mechanical springs are in full compression[14]. When the solenoid releases the armature, the valvetravels through the spring equilibrium point thendecelerates to the end of the travel at which timeanother solenoid holds the armature in place. In thisway, electromagnetic force is used only to hold thesolenoid and spring force is used to acceleratedecelerate the valve. In order to achieve the fastransition times required at high RPM, the spring

constant is tuned to a resonance of the combined massof the armature and valve. The selection of solenoidactuation is well suited to this method because of theone-way actuation (holding) and the limited stroke rangeof appreciable force. The disadvantage of this method isthe dependence on resonant transition allows onlyvariations in the timing, but not the lift or speed otransition. While holding force alone is adequate foactuation, the inability to push the armature requirescomplex control for soft valve seating [15].

In contrast, the commanded acceleration methodwith force authority over the entire stroke, is capable of


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controlling the valve lift directly. A bidirectional forceapproach is also better suited to controllable valveseating. Potential difficulties with this method areobtaining enough force for high speed valve accelerationand maintaining reasonable power requirements. Thebenefits of the commanded acceleration method includethe capability of achieving the valve actuation strategiesmentioned above utilizing variable valve lift, variabletiming, and seating velocity control.

FFVA DESIGN

The primary thrust of the actuator design is to usethe best combination of methods discussed above,holding and accelerating, which will achieve the optimalvalve strategies with reasonable power requirementsand robust construction. The continuing development forfully flexible valve actuation is an iterative designprocess with the following stages: magnetic finiteelement analysis combined with parameter optimizationroutines, power minimization through a tailored currentprofile, thermal analysis, dynamic simulation, and failuremode effects and analysis.

ACTUATOR CONFIGURATIONS

A common issue for actuator design is whichcomponents move relative to an external body andwhich other components are stationary. Typically thereare two possibilities: (1) moving magnets (MM) andstationary coil, or (2) moving coils (MC) and stationarymagnets. As discussed in the following sections, wehave developed another option, (3) moving plunger (MP)with stationary coil and magnets.

Typical operation of an engine might average 2000-3000 rpm for 15,000 miles/year, which equates to

approximately 30-45 million actuation cycles/year. A MCconfiguration has potential issues with flexing ofelectrical leads, and a MM configuration has potentialissues with magnet mechanical damage (fatigue orcracking) due to the constantly reversing accelerationprofile. Therefore, a configuration without either of thesecomponents moving is indeed attractive. A MPconfiguration can be made extremely rugged and able towithstand the high acceleration cycles. Furthermore, thestationary magnets and stationary coil can beelectrically, thermally and mechanically buffered to someextent within their environment. As will be seen, this isthe approach used for the FFVA.

MAGNETIC FINITE ELEMENT ANALYSES (MFEA)

As mentioned above, the central concept of theactuator permits several quite different configurations[20,21]. Commercial magnetic finite element analysissoftware (Maxwell

3-D from Ansoft Corp. [16]) was

utilized to input the various configurations and analyzethe performance of each configuration. In addition,using the Optimetrics component, we performedoptimization of each configuration. The central idea ofOptimetrics is an automated way to numerically

determine the sensitivity of a design configuration to adefined goodness parameter and then to continue torefine the design in the direction of increasinggoodness. When the design space is large (manyindependent parameters), there are simply too manypossible permutations of design variables to computeeach one individually. For example, there are more thanfifteen individual dimensional characteristics whichcollectively, with materials choices and boundaryconditions, define a single design. If 6 values of eachdimension were to be analyzed, over 11 million designcombinations would result for each major configurationThis is too many to seriously evaluate and wouldrepresent analyst overload. Instead, Optimetricsessentially calculates the greatest slope towardincreasing goodness and marches along that pathLocalized extremes were encountered and dealt with byutilizing multiple starting designs to verify convergenceto an optimized specific design combination.

Nine design configurations were examined. Theeight unselected designs are shown in Figure 4 throughFigure 11 in Table 1 and the selected design is shown inFigure 12. (Figure 3 provides a key for interpretation o

the symbols in Table 1.) The configurations arecompared based upon the metric of the ratio of valveacceleration and square root of dissipated inpu

power, PA / . The best performing configurationFigure 12, has the greatest value of this metric. Thevalve acceleration is computed by computing theelectromagnetic force and dividing it by the sum omoving masses of the valve, the valve stem, andconnecting hardware. [Note: other bases focomparison could, of course, be used. In that case, theoptimized actuator design details would differ.] TheMFEA simulation takes current density in the coil as aninput and calculates the coil resistance and electricapower consumed. When configurations can beemployed as either MM or MC, the reported figure is forthe underlined configuration. There are, of course

many parameters upon which the value of PA /depends, and the utility of the actuator is not describedsolely by this metric. Therefore, although we considered

heavily the value of PA / in determining whichconfiguration to build for the feasibility demonstrationwe also considered aspects such as expected actuatorreliability and longevity. Based upon this analysis, thefinal FFVA design is markedly superior to the othedesigns. Fundamentally this is because the moving

portion is simply a steel plunger of relatively small radiusand relatively high magnetic saturation value. Thisdesign, once properly engineered for the environment, isexpected to have an excellent reliability record becauseof its simple, robust nature. In addition, by use of thereluctance forces, the actuator can be designed to havethe valve closed during power off. This will greatlyreduce potential valve-piston interference events.


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Figure 3. Key for Table 1.

Table 1. FFVA Configurations Analyzed and Optimized with Magnetic Finite Element Software; Axis of Symmetry is shown

dot-dashed on the left of each figure.

Coil

Coil

CL

Figure 4. Either MMor MC configuration.

PA =39.1sec

1

kg

Figure 5. Preferred MC,but could be MM

(magnets-plus-iron

move); the iron mass is a

significant penalty.

PA =45.6sec

1

kg

Figure 6. EitherMM or MC

configuration.

PA =28.5sec

1

kg

Coil

Coil

Coil

Figure 7. Either MM or MCconfiguration. Three coils

consume significant electrical

power but add substantial force

capability.

PA =29.1sec

1

kg

Figure 8. MC

configuration: iron

moves with the coil

and focuses the field.

PA =50.7sec

1

kg

Figure 9. MC

configuration: iron

moves with the coil and

focuses the field.

PA =59.4sec

1

kg

Figure 10. MC

configuration.

Connecting to valve

would be a

challenge.

PA =40.8sec

1

kg

Figure 11. MC configuration:

iron moves with the coil.

PA =60.0sec

1

kg


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Figure 12. Selected FFVA Design for the

demonstration engine. =PA / 75sec

1

kg

0 20 40 60 80

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Acceleration/Sqrt(Power) [1/sqrt(kg*sec)]

Figure 13. Comparison of FFVA Configurations:

Valve acceleration per square root of dissipated

power.

The preferred FFVA configuration is shown in Figure12. Figure 13 shows a chart comparing the predicted

values of PA . The selected design has a

substantially greater figure of merit than the otherdesigns. Figure 14 shows the FFVA selected design inRZ symmetry. Figure 15 shows the magnetic fieldvectors of the design to accelerate the valve in adownward direction. Figure 16 shows the magnetic fluxlines for this scenario.

Figure 17 shows the electromagnetic force on theplunger (connected to the valve via the stem). It is seenthat there is a force present even when there is nocurrent (middle curve). This is due to the magneticreluctance force of the ferromagnetic plunger in thepermanent magnet structure. Essentially, the plungetends to move upward if it is above the centerline ortends to move downward if it is below the centerline; itwould remain in either of the extreme upper or lowerpositions. Since this curve of force over stroke with nocurrent is approximately linear with distance, it can benearly cancelled by appropriate choice of mechanicaspring. The other two curves in the figure represent the

electromagnetic forces associated with applying positiveor negative current, respectively, to the actuator. Figure18 shows the results of using a linear mechanical springto cancel the reluctance force. Note the force is noquite constant over stroke and there is a slightly greateforce available at the beginning and end of a valvetransition to accelerate and decelerate the valverespectively.

Fe FeCoil

Axis of

Symmetry

Figure 14. Electromagnetic FFVA Geometry in R-Z

Symmetry


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Figure 15. FFVA Magnetic Field Vectors in R-ZSymmetry

Figure 16. FFVA Magnetic Flux lines in R-Z Symmetry

-200

-100

0

100

200

-4 -2 0 2 4

Positive CurrentZero CurrentNegative Current

Stroke, mm

Force,

N

Figure 17. Hysteretic FFVA Forces vs. Stroke and

Current, uncompensated (raw) electromagnetic forces.

-200

-100

0

100

200

-4 -2 0 2 4

Positive CurrentZero Current, reluctance forceNegative Current

Decreasing Stroke

Increasing Stroke

Stroke, mm

Force,

N

Figure 18. Hysteretic FFVA Forces vs. Stroke and

Current, compensated by a linear spring.

OPTIMUM DYNAMIC ACCELERATION PROFILE

In order to accomplish the rapid valve transitionsnecessary for high speed valve actuation (closed toopen, and open to close), various valve accelerationprofiles were investigated. Increasing the applied

current provides a greater acceleration force, but alsoincreases the dissipated electrical power. It was desiredto discover the acceleration profile which achieved thespecified dynamic performance (essentially moving afixed distance, d, in a time, t) at minimum electricadissipated energy. High speed transition dynamicsrequire valve motion of 8 mm in 3.3 ms. A symmetricacceleration/ deceleration profile requires a motion ofd0=4 mm in t0=1.65 ms. An actuator force linearlyproportional to the current was assumed. Figure 18shows the force is not constant over the stroke but isgreatest when accelerating the valve; for presen

purpose we assume a constantI

Fk= (force pe

current) is approximately achieved by a reluctance-compensated FFVA actuator. This assumption yields

acceleration,m

tIkxa

)(== && , so

=

0

0

0

)(t

dtm

tIkdtd

The dissipated energy to be minimized is 0

0

2 )(

t

dtRtI

and we desire to find the waveform ).(tI This

minimization problem is subject to the constraint that thevalve moves the specified distance in the specified time

It can be solved by calculus of variations and Lagrangianmultipliers or by trial and error. In either event, it can bereadily verified that a current waveform of

=

0

1 1)(t

tItI with an acceleration profile o

=

0

1 1)(t

tata , where


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===

=

2

0

002

0

011

2

2

3

2

33

t

da

t

d

m

Ika , meets the

constraints while minimizing the energy. 0a is the

constant value of acceleration required to move a

distance d0 in time t0. In fact, )(ta provides an energy

savings of 25% compared to a constant accelerationprofile (for a constant ratio of force and current).

Therefore, this is the desired acceleration waveform forthe FFVA. Note, however, that this optimized waveformrequires an increase in instantaneous force of 50%compared to a constant acceleration profile.

0

150

300

450

0 0.5 1.0 1.5 2.01.65

Optimized Linear ProfileConstant Acceleration Profile

Time, ms

Acceleration,gee

Figure 19. Ramped and constant acceleration profiles for

the first half of the opening transition.

0

1

2

3

4

0 0.5 1.0 1.5 2.01.65

Optimized Linear AccelerationConstant Acceleration Profile

Time, ms

ValveDisplacem

ent,mm

Figure 20. Valve displacement vs. time for the two

acceleration profiles for the first half of the opening

transition.

0

0.1

0.2

0.3

0 0.5 1.0 1.5 1.65

Difference in Valve Displacement

Time, ms

Displacement,mm

Figure 21. Difference in valve displacement for the two

profiles. The ramped acceleration profile opens the valve

more quickly than the constant acceleration profile.

THERMAL ANALYSIS

Most high performance electrical machines areultimately thermally limited. This is because electricamachines, especially permanent magnet machines

improve in performance with increases in excitationcurrent. Therefore, the common practice is to increasethe current until either portions of the designmagnetically saturate, or the local temperature increaserequired to transport the electrically dissipated power isunacceptably high. Since the neodymium-iron-boronmagnets themselves have a maximum operating

temperature of 150C, they frequently provide the lowesupper limit to allowable energy dissipation. Figure 22shows the geometry analyzed. A steady statetemperature plot is shown in Figure 23 for an excitationof 80W continuous and boundary conditions of forced

convection to 100C.

Note the annular heat pipes between magnetsappear to increase the magnet temperature locally, butthey transport heat from the coil and ultimately reduce

the magnet temperature by 5-10C. Heat flux vectorsare shown in Figure 24. As indicated in the figureroughly one-quarter of the heat leaves the actuatorthrough the top, one-quarter through the bottom, andone-half of the heat exits through the outer diameter ofthe device.

Fe FeCoil

Annularheat pipes

Annularheat pipes

Figure 22. Electromagnetic FFVA Geometry in R-Z

Symmetry. The 4 annular heat pipes help cool the coil.


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Figure 23. FFVA Steady State Temperature Plot showing

the magnets do not exceed 135

C.

Figure 24. FFVA Heat Flux Q. The annular heat pipes

between magnets transport significant thermal power.

DYNAMIC SIMULATION

The block diagram for the FFVA simulation is shownin Figure 25. Briefly it can be described as follows: Initialvalve position is determined and based upon an enginemap and a current command is issued to move the valveto a position. The coil current is converted to force bythe number of coil turns and look-up tables created from

MFEA output, which account for hysteresis of valveposition (i.e., reluctance forces) and desired direction ofmotion. The dynamic equations (F=ma, F = sum ofexternal spring forces, etc.) are then computed to obtainvalve acceleration, velocity and position. Force-per-current data derived from Figure 18 is compiled into alook-up table to provide accurate force and powercharacteristics over the full stroke. The simulation hasbeen utilized to simulate different acceleration profilesand failure modes and effects. Friction work of 100 mJper transition was taken into account.

Figure 25. Simplified FFVA Simulation Block Diagram

The most stressing dynamic scenario for theactuator is for high speed valve transitions. Thereforesimulations for 6000 rpm are provided below.

Figure 26 shows the forces required for threesimulated acceleration profiles: Constant accelerationRamped acceleration; and Ramped acceleration withspring-back. Constant acceleration is the simplest caseand allows for the minimum force to provide the required

dynamics. Ramped acceleration is the linear decreasein acceleration with time for minimum dissipated powerRamped acceleration with spring-back is the lineardecrease in acceleration for the first half of the openingtransition, followed by valve free-flight for the secondhalf of the transition, followed by a stiff spring encountewhich compresses and expands to reverse the valvevelocity, finally, the valve is gradually decelerated to alow velocity seating. The rebound spring significantlyreduces dissipated power for high speed operation andallows low lift operation at lower speeds since it does nocontact the valve below approximately 8 mm strokeNote that the constant acceleration profile swings

between equal and opposite acceleration valuesRamped acceleration is the linear decrease inacceleration with time, followed by a linear increase inacceleration with time. Ramped acceleration withspring-back is the linear decrease in acceleration incombination with a stiff spring at the extent of the valveopening. This utilizes a slightly-reduced peak force.

Computed valve motion resulting from these threeacceleration profiles is shown in Figure 27. It is seenthat the constant acceleration profile provides theslowest opening characteristic while the Rampedacceleration with spring-back may involve valve over-


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travel beyond the nominal 8 mm stroke. Alternatively,the spring-back can be designed to occur at 7.5mm-8mm and so not increase total valve displacement. Thiswould actually reduce the dynamic requirements on theactuator (reduced force, current, and power).

Based upon the simulation, the total dissipatedelectrical and mechanical energy can be calculated forthe different acceleration profiles. The results are shownin Table 2. In addition to the electrical energydissipation, 0.200 J work per cycle (100 mJ pertransition) has been included to account for friction andother energy loss mechanisms. Note that the Rampedacceleration profile reduces power consumption by 30%compared to the Constant acceleration profile, which isgreater than the 25% predicted earlier for a constantvalue of k=F/I. This is because, as shown in Figure 18,the force (and hence force per unit current) is greater forvalve acceleration and hence even more energy issaved. Basically, the actuator is more efficient at initialacceleration than at late acceleration. The Rampedacceleration with spring-back reduces the averagepower approximately 50% more since it essentiallyeliminates the energy for valve motion reversal.

-300

-200

-100

0

100

200

300

0 1 2 3 4 5 6 7 8 9 101.65

Constant accelerationRamped accelerationRamped acceleration with spring-back

ClosingOpening

Time, ms

Force,

N

Figure 26. Simulated Required Forces vs. Time for three

possible acceleration profiles (6000 rpm, 3.3 ms

transition).

-1

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9 101.65

Constant accelerationRamped accelerationRamped acceleration with spring-back

ClosingOpening

Time, ms

Strok

e,mm

Figure 27. Simulated Valve Stroke vs Time resulting from

the three acceleration profiles.

Table 2. Cycle energetics (6000 rpm, 3.3 ms transition

time, 20 ms period)

Profile CycleEnergy

AveragePower(1 valve)

AveragePower*(16 valves

Constant acceleration 3.75 J 188 W 3008 W

Ramped acceleration 2.65 J 133 W 2128 W

Ramped accelerationwith spring-back

1.36 J 68 W 1088 W

*Intake valves only.

FAILURE MODES

A common complaint against camless valveactuation technologies is the position of the valve after afailure in the valve actuation system. If the failure issudden, then mechanical inertia will continue to drive thepistons through their trajectory making valve-pistoninterference a possibility. In many systems the positionof the valve is indeterminate; while in others the valvereverts to a position midway between fully open and fullyclosed. In either event valve-piston collision is highlylikely, especially in todays high-compression-ratioengines.

Two features of the FFVA design presented heredictate the position of the valve in the event of a failure

As shown in Figure 18, the actuator will preferentiallyreside in the closed position due to magnetic reluctanceWithin limits, the reluctance force can be controlled byinitial design, recognizing that there is a trade-off withacceleration performance. A second feature of theactuator results from its full stroke force authority. Thecoil can be wound two-in-hand meaning thatelectrically isolated coils excite the actuator. Henceeven if an electrical short or open occurs in one of thesubcoils, then the other subcoil still has substantial force

over the valve. Shown in Figure 28 and Figure 29, aretwo simulations of sub coil failures at different timesThey show that upon failure of one subcoil, theremaining working subcoil can be excited to recall thevalve home (closed position) within a cycle before thepiston rises to top dead center (TDC), thereby avertingan interference condition. The working subcoil can holdthe valve in place, aided by the reluctance force. InFigure 28, the failure occurs at 1.0 ms and the valveopens 6 mm. In Figure 29, the failure occurs at 1.6 msand the valve opens the full 8 mm. A key feature of theRamped acceleration (and so ramped force) profile isevident here: due to the decreasing force profile, most o

the energy has already been imparted to the valve forthe transition by the time the failure has occurred.

Other failure modes are certainly possible and theseare presently being investigated.


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-50

0

50

100

150

200

250

0 2 4 6 8 10 12 14 16 18 20-2

0

2

4

6

8

10

ForceValve Displacement

Piston arrives at TDC

Valve parked home and held ClosedValve attracted home

with Subcoil #2

UsualClosedtime

Failure occursin Subcoil #1

Time, ms

Force,

N

Stroke,mm

Figure 28. Simulated failure of Subcoil #1 at t=1.0 ms.

Subcoil #2 has sufficient attractive force to retrieve and

park the valve Closed, thereby eliminating valve-piston

interference.

-50

0

50

100

150

200

250

0 2 4 6 8 10 12 14 16 18 20-2

-1

0

1

2

3

4

5

6

7

8

9

10

ForceValve Displacement

Piston arrives at TDCFailure occursin Subcoil #1

UsualClosedtime

Valve attracted homewith Subcoil #2

Valve parked home and held closed

Time, ms

Forc

e,

N

Stroke

,mm

Figure 29. Simulated failure of Subcoil #1 at t=1.6 ms.

Similar to the above figure, but the failure occurs very late

in the transition. Subcoil #2 has sufficient attractive force

to retrieve and park the valve Closed, thereby eliminating

valve-piston interference.

SINGLE CYLINDER ENGINE DEMONSTRATION

ACTUATOR CONSTRUCTION AND ENGINEPREPARATION

After optimizing the configuration and geometry ofthe actuator and running dynamic simulations, an intakevalve actuator was fabricated and installed on a single-cylinder engine. (The exhaust valve cam was retained.)

A drawing of the single-cylinder engine selected for thisdemonstration project is shown in Figure 30. Selectioncriteria for the engine were: relatively low power (4-hp),

light weight, and ease of access to the valves. Thisengine was particularly easy to modify the valve since ithas both overhead cams and overhead valves.

EXPERIMENTAL RESULTS

Feasibility of operating an internal combustionengine based upon the designed electromagnetic valveactuator was demonstrated. An increasingly difficultseries of actuator tests consisted of operating theactuator under the following conditions: on a bench top,

in the unassembled cylinder head, statically on theengine (assembled), slow motion on the engine (handcrank), fast motion on the engine (pull-cord operated)and during combustion.

SINGLE CYLINDER ENGINE OPERATION

Operation of an engine with the actuator controllingthe intake valve was the major goal of this feasibilitydemonstration project. Figure 31 shows the valvedisplacement during the cycle as a function of crankangle from a throttled no-load run at 1500 rpm. Twindesirable attributes of high opening speed (~890mm/sec) and low landing speed (~30 mm/sec) areevident in the figure. It should be remarked that theactuator operated the first time the engine was startedand the engine runs reliably, although changing enginespeeds requires a manual adjustment in valvecommands. Figure 32 and

Figure 33show the actuator mounted on the engineNote details of the setup and diagnostics are evident inthe figures.

Figure 30. Honda GC135QHA Engine [22]

0

1

2

3

4

0 90 180 270 360 450 540 630 720

Test #4

Opening speed~ 890 mm/sec

Landing speed~ 30 mm/sec

Crank Angle, deg

Lift,mm

Figure 31. Experimental Valve Displacement vs Crank

Shaft Angle


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Figure 32. Phantom Views of Cam Magnet Path

Figure 33. FFVA mounted on Engine

FUTURE WORK

The FFVA development effort is on-going under aNational Science Foundation grant. Continuingimprovements in magnetic configuration will influencethe other aspects of the design cycle: thermal, electrical,and mechanical. In addition to refining the concurrentdesign parameters, an in depth study of valve control willbe pursued. The current state of knowledge in variable

valve control strategies is well developed and largelyapplicable to the developing actuator [17, 18, 19].Further development in control is vital to realize the fullcapabilities of the actuator system. A position estimatorof some kind is certainly necessary. We presently use aposition sensor, but since the device is fundamentally apermanent magnet machine, sensorless control isentirely possible, eliminating a component of cost andfailure modes. Detailed simulations will be performed toinvestigate integrated valve actuation strategies andcontrol, as well as testing potential failure modes and

effects. The NSF grant will culminate with fabricationand installation of the FFVA system on an automotiveengine. The valve and engine performance will be testedwith dynamometer and gas analyzer to measure theFFVA-equipped engine performance and emissions.

Commercial feasibility of the actuator has not beendemonstrated. With the decreasing cost of permanenmagnets and the low cost of the remaining iron andcopper components, the high-volume cost estimate othe actuator may approach the value of the eliminatedand removed mechanical components.

SUMMARY & CONCLUSIONS

The major objectives of this research were todesign, build, and test an electromagnetic fully flexiblevalve actuator. These objectives were achieved. Thedesign process involved many configurations withmoving magnets, moving coils, and/or a moving plungerThe selected design performed significantly better thanother designs based on dynamic performance(acceleration per square root of dissipated power) andhad desirable characteristics such as stationary magnets

and stationary coil.A dynamic simulation was created to predic

performance of the valve under a variety of conditionsespecially various acceleration profiles. Valve-pistoninterference is avoidable during failure modes.

Detailed manufacturing drawings were made and anactuator was fabricated and assembled. A singlecylinder engine was chosen and modifications weremade to the cylinder head to mount the actuator andvarious sensors. A series of run-up tests was performedculminating in the feasibility demonstration of engineoperation under electromagnetic intake valve actuatocontrol. In conclusion, the results show the actuato

exhibits the inherent advantages of the fully flexiblevalve actuator such as variable timing, variable lift, andlow valve-landing speed.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Jim Cowart ofMIT and the U.S. Naval Academy, Dr. ChristopheCorcoran of Corcoran Engineering, and Mr. DavidFischer of DMF Associates for their input, support, andprofessional advice. The authors would also like tothank MIT graduate student Mr. Bernard Yen for his helpwith the experimental work. The authors acknowledge

the support of the National Science Foundation throughits SBIR program.


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CONTACT

The authors may be contacted at:

Engineering Matters, Inc.375 Elliot St., Suite 130K

Newton, MA 02464617-965-8974

Dr. David Cope: [email protected] Wright: [email protected].

NOMENCLATURE

PA / Ratio of Acceleration to the square root ofPower; used as a metric of valveperformance

EIVC Early Intake Valve Closing (valve actuationstrategy)

EVA Electromagnetic Valve ActuatorFFVA Fully Flexible Valve Actuator

LIVC Late Intake Valve Closing (valve actuationstrategy)

LIVO Late Intake Valve Opening (valve actuationstrategy)

MC Moving Coil

MFEA Magnetic Finite Element Analysis

MM Moving Magnet

MP Moving Plunger

R-ZSymmetry

Axisymmetric cross-section

VMVL Variable Max Valve Lift (valve actuation

strategy)VVA Variable Valve Actuator

Electromagnetic Fully Flexible Valve Actuator

Documents