This paper describes a theory and experiments for the conversion of electric current to mechanical torque by a torque motor in servo valves. The feature of the torque motor treated in this paper is the use of a permanent magnet. These kinds of torque motors are most commonly used in modern servo valves. For this type of torque motor, the theory developed by Merritt is most notable among fluid power engineers and scientists. However, his theory does not agree very well with experiments because he ignored the magnetic reluctance and leakage flux of permanent magnets. This paper corrects these points and offers some formulae that agree well with experiments.
MaskreyR. H.ThayerW. J.A brief history of electrohydraulic servomechanisms. Moog Tech. Bull., 1978, 141.
2.
SunY.ParkerG. A.Steady-state theoretical model of an electro-hydraulic single-disk pilot valve. Trans. ASME, J. DSMC, 1992, 114, 293–298.
3.
BangY.-B.LeeK.-Y.JooC.-S.HurJ.-W.Two-stage electrohydraulic servovalve using stach-type piezoelectric elements. Proc. Instn Mech. Engrs, Part C: J. Mechanical Engineering Science, 2004, 218, 53–65.
4.
MerrittH. E.Hydraulic control systems, 1967 (John Wiley and Sons, Inc.).
5.
BurrowsC. R.Fluid power servomechanisms, 1972 (Van Nostrand Reinhold Co.).
6.
McCloyD.MartinH. R.Control of fluid power: Analysis and design, 2nd edition, 1980 (Ellis Horwood Limited).
7.
WattonJ.Fluid power systems, 1989 (Prentice Hall).
UrataE.Influence of fringing on servovalve torquemotor characteristic. In Proceedings of the 5th JFPS International Symposium on Fluid Power, Nara, Japan, 2002, pp. 769–774.
11.
GierasJ. F.WingM.Permanent magnet motor technology, 1997 (Marcel Dekker).
12.
CampbellP.Permanent magnet materials and their application, 1994 (Cambridge University Press).
13.
ParkerR. J.StuddersR. J.Permanent magnets and their application, 1962 (John Wiley and Sons, Inc.).
14.
HadfieldD. (Ed.) Permanent magnets and magnetism, 1962 (Iliffe Books Ltd.).
15.
McCaigM.Permanent magnets in theory and practice, 1977 (Pentech Press).
IdaN.Engineering electromagnetics, 2000 (Springer-Verlag, New York, Inc.).
18.
JIS (Japan Industrial Standard) C 2503. Soft magnetic iron bars, 1990.
19.
JIS C 2504Soft magnetic iron plates, 1990.
20.
BozorthR. M.Ferromagnetism, 1951 (Van Nostrand).
21.
JIS C 2502Materials for permanent magnet, 1989.
22.
UrataE.Study of magnetic circuits for servovalve torque motors. Bath Workshop on Power transmission and motion control 2000 (PTMC 2000), Bath, 2000, pp. 269–291 (Professional Engineering Publishing, Bury St Edmunds and London).
