A NEW ELECTROMAGNETIC VALVE TRAIN WITH PM/EM ACTUATOR IN SI ENGINES
Yaojung Shiao and Ly Vinh Dat
National Taipei University of Technology, Taipei, Taiwan
E-mail: [email protected]; [email protected]
ICETI 2012-J1105_SCI
No. 13-CSME-64, E.I.C. Accession 3522
ABSTRACT
This paper proposes a new electromagnetic valve train (EMV), which uses hybrid permanent magnet and
electromagnetic coil (PM/EM). The new EMV is characterized by a special structure, simple actuator as well
as optimal parameter designs. This EMV brings many benefits, such as valve dynamic, actuator control,
and low operation energy consumption, etc. The simulation results show that this EMV achieves a 15%
volume reduction and a 20% enhancement in holding force by special armature design. Additionally, the
estimated energy consumption of EMV operation for the proposed EMV indicates that this EMV has the
lowest operating energy compared with other EMVs.
Keywords: electromagnetic valve train; variable valve timing; engine efficiency; camless engine.
UNE SOUPAPE D’ÉCHAPPEMENT ÉLECTROMAGNÉTIQUE INNOVATRICE AVEC
ACTIONNEUR PM/EM POUR MOTEUR À ÉTINCELLES
RÉSUMÉ
Une soupape d’échappement électromagnétique innovatrice (EMV), qui utilise un aimant permanent hybride
et une bobine électromagnétique (PM/EM), est l’objet de cette étude. La nouvelle soupape d’échappement se
caractérise par une structure spéciale, un actionneur simple ainsi que des paramètres de conception optimale.
Cette soupape comporte plusieurs avantages au niveau de la dynamique de la soupape, de la commande de
l’actionneur, de mème qu’une faible consommation d’énergie etc. Les résultats de la simulation démontre
que la soupape a un volume réduit de 15% et une augmentation de 20% de sa force de détention par une
conception spéciale de l’armature. En outre, l’estimation de la consommation d’énergie pour la soupape
proposée indique que cette dernière démontre une diminution de la consommation d’énergie opérationnelle
comparée à d’autres.
Mots-clés : soupape d’énergie électromagnétique ; réglage de la distribution ; efficacité du moteur ; moteur
sans arbre à cames.
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
787
1. INTRODUCTION
The use of EMV, which replaces the traditional cam valve train, has brought many benefits in executing
variable valve timing (VVT) for SI engines [1, 2]. EMV becomes a potential technique for high efficiency
engines and is interested by researches. Many mechanisms have developed to achieve VVT in SI engines by
different techniques such as: mechanical, hydraulic, motor driven or electromagnetic actuation. Camshaftbased mechanism is commonly used for valve train. However, to control valve timings and duration events
in wide operation ranges, this mechanism requires a complex structure and its valve timings are totally
limited by cam profile. Meanwhile, the use of electric motor to control valve motion is studied by some
researchers [3, 4]. It has advantages about flexibility of valve timing and effective energy. However, this
technology is being at first stage of development. Compared with other mechanisms, electromagnetic valve
train can control the valve events fully and flexibly. A solenoid-type electromagnetic valve, which features
simple structure and easy control [5], can control coil current to hold or release valve to achieve VVT [6].
However, this solenoid-type EMV consumes large amounts of energy for operating.
There are several critical designs in an EMV such as actuation energy, soft landing, valve wear and valve
speed, etc. The proposed EMV in this paper equips a set of permanent magnets (PM) to generate a magnetic
force for holding a valve at top or bottom position. Hence, no extra energy is needed to make the engine
valve fully open or close. This novel PM EMV overcomes the drawbacks of solenoid EMV. The PM EMV
has some advantages such as:
1. Low actuation energy: valve is held at top/bottom position by the holding force generated by PMs.
Coil are only electrified to release valves from top or bottom position. The valve can be kept at top
opening or bottom closing position without consumed energy.
2. Zero starting current: solenoid EMV needs large power to create a large magnetic force to catch
armature to closed position from its middle neutral position at engine start. But the armature in new
PM EMV is attracted by PM forces to closed position. Thus a PM EMV needs no starting current.
3. Low valve wear and noise: the armature in this study was designed to cylindrical shape to reduce wear
and noise between the armature and its seat. Armature also slowly rotates to keep even wear.
4. Special armature structure: the armature has protruding cylinder and groove as shown in Fig. 1 to
allow producing larger holding force to keep valve open. The simulation results show that the holding
force increases from 823 N in conventional armature to 977 N in the special armature (about 20% increment). The magnetic flux through the armature increases due to increasing of contact area between
the armature and housing seat.
Furthermore, the effects of factors on proposed EMV dynamics have been examined and analyzed [7].
The study showed that this EMV could satisfy the requirements about valve velocity and acceleration for
application in internal combustion engines.
2. DESIGN OF NEW EMV SYSTEM
2.1. Configuration of a New EMV
In this PM EMV, a permanent magnet producesa magnetic force to hold the armature. The magnitude of
the magnetic force depends on the PM dimension, armature contact area and distance between PM and
armature. To effectively hold the armature, the magnetic force from PM must exceed the inversed valve
spring force. The electromagnet (EM) is used to reduce the magnetic flux through armature for releasing
armature by the inversed spring force. Therefore, actuating energy is only needed for the electromagnet to
release the armature. No energy is needed for armature holding.
788
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
Fig. 1. The special armature structure.
Fig. 2. Proposal EMV structure.
The proposed EMV, which is a PM/EM hybrid device, includes two PMs, one electromagnetic coil,
armature, valve, and springs. A type of PM EMV has earlier been proposed by Kim [8] and Liu [9], but
our type of EMV has a more compact design and lower actuation energy. The PM EMV has a PM and EM
coil in the upper part, and armature in the lower part. This structure is helpful in reducing the EMV size.
Besides, this structure allows a much easier control of valve catching, holding and releasing compared to
traditional solenoid EMV. Benefits of this new PM EMV are as follows:
• The structure of the novel EMV was designed as a cylindrical shape so that the EMV has a larger ratio
of holding force to its volume. Our simulated results indicate that the holding force increases from
375 N in conventional squared structures to 977 N in cylindrical shaped structures. It means that more
than 15% volume reduction can be earned for the new cylindrical EMV.
• Similarly, the armature was also designed with a cylindrical shape to effectively decrease armature
wear and noise in operation.
• When the current is supplied to the coil, the coil generates a magnetic flux to neutralize the magnetic
flux produced by PM. Therefore, the magnetic force on the armature will reduce significantly. The
coil has a special inversed U-shape, shown in Fig. 2, to shorten the travelling distance of the magnetic
flux. In this way, the PM magnetic flux is weakened and the actuation energy for EMV is effectively
reduced.
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
789
Fig. 3. Operation principle for the PM EMV. (a) hold armature at top position; (b) supply current to coil; (c) release
armature; (d) hold armature at bottom position; (e) supply current to coil; (f) release armature.
2.2. Operation Principle of EMV
Figure 3 describes the operation principle of proposed PM EMV. The solid line shows the magnetic flux that
generated by PMs, while the dashed line represents the electromagnetic flux by coil. At starting state, PMs
create the magnetic force exceeding the inversed spring force to hold the armature at the top position, and the
valve moves to the closing position as in Fig. 3a. When the coil is charged by some controlled current, the
magnetic flux (dashed line in Fig. 3b) is generated to weaken the PM magnetic flux. This results in reducing
the magnetic force on the armature. Therefore, the armature is released, runs to the bottom position, and the
valve opens. At this position, no charging current is needed, and the PM magnetic flux crosses the armature
to hold it at bottom position firmly as in Fig. 3d. Subsequently, the armature moves from bottom to top in
the same way, and the process is illustrated in Figs. 3e to 3a.
Conventional solenoid EMV always requires actuation current to catch and hold the valve at closing or
opening position, whereas this PM EMV only needs actuation current at the moment of the valve releasing
at opening or closing position. So the actuating strategy for current to EMV is quite simple. Besides, the
PM EMV is a low power EMV since there is no need for an extremely large starting current to catch the
armature at start state.
3. SYSTEM OPTIMIZATION AND ACTUATION
3.1. Optimal EMV Parameters
The holding force is analyzed with different parameter values to find the optimal parameters. The critical
holding-force related parameters in EMV design are dimensions of EMV structure, armature, permanent
magnet and air gaps. These parameters are illustrated in Fig. 4.
790
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
Fig. 4. Critical parameters of EMV.
Fig. 5. Sensitivity of holding force to yoke radius.
3.1.1. Dimension of EMV structure
The yoke in EMV is made of ferromagnetic material. Its radius is a major factor of holding force in the EMV
system. The effects of yoke radius on the holding force are described in Fig. 5. The holding force increases
as the yoke radius increases. The optimization yoke radius met about the holding force and minimum size.
The holding force must overcome the maximum spring force at engine speed of 6000 rpm. Additionally,
the EMV structure size has to be minimized because of the limited space over the engine head. Therefore, a
21 mm yoke radius is selected, and the holding forces at valve closing and opening positions are 1511.8 N
and 977.8 N, respectively.
3.1.2. Dimension of armature
The armature dimensions in EMV system include armature radius and thickness. The armature radius is
smaller than 15 mm due to the size limit of the EMV structure. The sensitivity of the holding force to
armature dimensions is shown in Figs. 6 and 7. The results show that holding forces of 11 mm armature
radius and 7 mm armature thickness satisfy the minimum holding force requirement at opening and closing
positions. Hence, the optimal armature dimensions are 11 mm and 7 mm for the radius and thickness of
armature, respectively.
3.1.3. Thickness of permanent magnet
The PM thickness affects the magnitude of holding force. Effects of PM thickness on holding force are
described in Fig. 8. If the PM thickness increases, the holding force also increases. However, the magnetic
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
791
Fig. 6. Sensitivity of holding force to armature radius.
Fig. 7. Sensitivity of holding force to armature thickness.
Fig. 8. Sensitivity of the holding force to the yoke thickness at various PM thicknesses.
792
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
Fig. 9. The relationship between air gaps and holding force.
Fig. 10. The effects of first and second gaps on holding force.
flux in armature will be saturated when the PM flux density is too large. Thus the holding force keeps
decreasing for thick PM. The yoke thickness also affects the holding force. The effects of yoke thickness on
the holding force at various PM thicknesses are shown in Fig. 8. The results show that the optimal holding
forces occurred at 7 mm for a yoke thickness with 1.5 mm PM thickness for valve closing and opening
positions.
3.1.4. Air gaps
Air gaps between the armature and housing seat are descbried by Wy1 and Wy2 , respectively. These airgaps
block unnecessary magnetic fields which produce lateral forces (x- and y-directions) to damage the armature
and structure. Effects of air gaps on the holding force are shown in Fig. 9. The peak forces are achieved at
0.6 mmm for closing and opening positions.
The first gap Wy3 affects the contact area between the structure and armature, while the second gap Wy5
affects the flux leakage. Both of them influence the EMV holding force. According to Fig. 10, only a 1.2 mm
first gap satisfies the force requirement. And the optimal second gap was 1 mm to have a peak force.
Based on the above analyzed results, the EMV parameters have been optimized and their values are
listed in Table 1. With the setting of these parameter values, the EMV holding force for different armature
displacement is shown in Fig. 11.
3.2. Actuation Current
When the coil is charged by actuating current, magnetic flux is created to weaken the magnetic flux generated
by PM. This process releases armature and makes valve open or close. Initial value for spring force was set
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
793
Table 1. Values of the optimal EMV parameters.
Description of variables
Symbol of variables
Yoke dimension (mm)
rsystem × Htop
Armature dimension (mm)
rsystem × Harm
Thickness of PM (mm)
Hpm
First gap (mm)
Wy3
Second gap( mm)
Wy5
Air gaps between armature and housing seating (mm)
Wy1 ,Wy2
Value of variables
21 × 7
11 × 7
1.5
1.2
1
0.6
Fig. 11. EMV holding force for different valve positions.
to 1% of total spring force (about 8N). In this study, the NI is examined from 0 to 400 ampere turns (At) due
to limit of actuation current and space. Figure 12 shows the holding forces at different currents. As a result,
if the current is optimized at 320 At, the holding forces then reduces to 5.87 N. This maintained holding
force is smaller than the initial spring force, so the armature is released and runs in the opposite position.
An appropriate timing of charging current occurs at 0.2 mm away from the top or bottom position.
The valve releasing profile is shown in Fig. 13. The rectangular bar is the applied pulsed current of 320 At
with 50 turns and 6.4 ampere. The valve displacement in the figure shows that valve lifting time is about
2.5 ms. This value satisfies the requirement of lifting time at 6000 rpm engine speed for SI engines.
3.3. Energy Consumption for Actuating New EMV
Energy consumption for the EMV operation is an important factor to evaluate the EMV design. The releasing current for proposed EMV is a pulsed current with a duration of 0.28 milliseconds for releasing the
valve at 8000 rpm as shown in Fig. 13. A voltage of about 42 V is supplied to coil to control the releasing
and catching of valve at opening and closing positions. The pulsed current with peak 6.4 amperes will be
activated to the coil for opening and closing valves at 8000 rpm (Fig. 13). Therefore, the power consumption
is 268.8 W and the energy consumption for controlling the valve opening or closing is about 0.015 J. The
energy consumption for EMV actuation compared with other EMVs is described in Table 2. The proposed
EMV with the optimal current for controlling valve has the lowest energy consumption. This shows that our
new EMV has good performance in energy consumption for EMV operations.
794
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
Fig. 12. The holding force at different currents.
Fig. 13. Valve lifting profile with actuation current.
Table 2. Energy consumption in new EMV compared with other EMVs.
EMV types
Energy consumption
Conventional EMV [10]
0.5 J
1.625 J
0.5 J
2.275 J
4.9 J
Conventional EMV [11]
0.164 J 0.34 J 0.164 J 0.34 J
1.008 J
EMV type 1 [8]
4.32 J
0J
1.305 J
0J
5.625 J
EMV type 2 [8]
1.52 J
0J
0.616 J
0J
2.1365 J
EMV with hybrid NMF [9] 0.455 J
0J
0.455 J
0J
0.91 J
Proposal EMV
0.075 J
0J
0.075 J
0J
0.15 J
4. CONCLUSIONS
A novel PM EMV, which differs from conventional solenoid EMV, has been designed in this paper. With
the unique structure and operating method, this PM EMV has several benefits in easy controllability and low
actuation energy. After parametric optimization, the EMV volume is reduced by about 15%. The special
armature design also increases the holding force by about 20% and prevents damage to the armature and
EMV structure. The special electromagnetic coil shortens the travelling of the magnetic flux to effectively
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013
795
weaken PM flux density for armature releasing. Therefore, this EMV equips compact valve actuation and
low actuation energy.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
796
Hong, H., Parvate-Patil, G.B. and Gordon, B., “Review and analysis of variable valve timing strategies-eight
ways to approach”, Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile
Engineering, Vol. 218, pp. 1179–1200, 2004.
Gray, C., “A review of variable engine valve timing”, SAE Technical Paper 880386, 1988.
Chang, W.S. et al., “A new electromagnetic valve actuator”, IEEE Transactions on Power Electronic in Transportation, Vol. 17, pp. 109–118, 2002.
Chang, W.S., Parlikar, T., Kassakian, J.G. and Keim, T.A., “An electromagnetic valve drive incorporating a
nonlinear mechanical transformer”, SAE Technical Paper Series 2003-01-0036, 2003.
Giglio, V., Iorio, B. and Police, G., “Analysis of advantages and of problems of electromagnetic valve actuators”,
SAE Technical Paper 2002 01-1105, 2002.
Wang, Y., Megli, Haghgooie, M., Peterson, K.S. and Stefanopoulou, A.G., “Modeling and control of electromechanical valve actuator”, SAE Technical Paper 2002-01-1106, 2002.
Shiao, Y. and Dat, L.V., “Dynamics of hybrid PM/EM electromagnetic valve in SI engines”, Journal of Vibroengineering, Vol. 14, No. 3, pp. 1122–1131, 2012.
Kim, J. and Lieu, D.K., “Design for a new, quick-response, latching electromagnetic valve”, in 2005 IEEE
International Conference on Electric Machines and Drives, Texas, USA, pp. 1773–1779, May 15, 2005.
Liu, J.J., Yang, Y.P. and Xu, J.H., “Electromechanical valve actuator with hybrid NMF for camless engine”,
in Proceedings of the 17th World Congress, the International Federation of Automatic Control, Seoul, Korea,
pp. 10698–10703, July 6–11, 2008.
Boccaletti C., Felice, P.D. and Santini, E., “Dynamic analysis of electromechanical valve actuators by means
of FEM techniques”, in Proceedings International Conference on Electrical Machine, Queensland, Australia,
p. 628, 2004.
Sugimoto C., Sakai H., Umemoto, A. and Shimizu Y., “Study on variable valve timing system using electromagnetic mechanism”, SAE Technical Paper Series 2004-01-1869, 2004.
Transactions of the Canadian Society for Mechanical Engineering, Vol. 37, No. 3, 2013