US 3204155 A
Description (OCR text may contain errors)
1965 CHARPENTIER 3,204,155
MAGNET STRUCTURE HAVING A FIXED AND VARIABLE AIR GAP Filed July 31. 1961 4 Sheets-Sheet l Fig.5 L
Aug. 31, 1965 R. CHARPENTIER MAGNETIC STRUCTURE HAVING A FIXED AND VARIABLE AIR GAP 4 Sheets-Sheet 2 Filed July 31. 1961 Allg- 1965 R. CHARPENTIE 3,204,155
MAGNETIC S HAVI TRUCTURE N FIXED AND VARIABLE AIR GAP Filed July 31. 1961 4 Sheets-Sheet s IE6 6 4" R\\\ 1 4 z- 2 2/\ 11 A 4 m 6 4 Fig [5 F79. 76
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MAGNETIC STRUCTURE HAVING A FIXED AND VARIABLE AIR GAP Filed July 51, 1961 4 Sheets-Sheet 4 E Q Q g-pa suag H p ay uo/ p2l au5owaa' 003 005 005 .nDLL /r Q m Lu .A in 0a 1 Q: Q B I: a m I: G Inauc/z'oo -B- ki/ogauss United States Patent 3,204,155 MAGNETIC STRUCTURE HAVING A FIXED AND VARIAllLE AIR GAP Roger Charpentier, 27 bis Ave. des Lilas, Pau, Basses-Pyrenees, France Filed July 31, 1961, Ser. No. 128,098 Claims priority, application France, July 29, 1960, 834,372, Patent 1,272,074; Dec. 22, 1960, 847,671 Claims. (CL 317-201) For a magnet to be economically useful it is necessary for it to work in a zone of the demagnetization curve in which the product of its induction B and the demagnetizing field H has its maximum value or is close to this value; this result is obtained by giving predetermined dimensional characteristics to the magnet and to the gap existing between the poles or the pole pieces.
In practice, in particular for magnetic catches, one generally uses the magnet, not by itself, but in combination with two pole pieces such as is seen in FIGURE 1 in which the references 1 and 2 indicate respectively the magnet and the pole pieces. To obtain the maximum value for the product BH, the length L of the magnet is made relatively great with respect to the cross section S, particularly for Ticonal magnets or magnets having a similar demagnetization curve. Ticonal is a magnet made of an iron base alloy containing, in addition, cobalt, nickel and aluminum. The content of cobalt is between 16 and 30%; that of nickel is between 12 and 20%; and that of aluminum is between 6 and 11%.
. There exist in practice several varieties of Ticonal. That which is most common has the following composition:
Percent Cobalt 24 Nickel 14 Aluminum 8 Copper 3 The remainder being iron.
Variations contain, in addition to the above proportions of nickel, cobalt, aluminum and copper, a titanium content of between 0.5 and 1.5%.
The above compositions of Ticonal, together with their characteristics, are listed and identified as Ticonal in a published table which lists the different varieties (and their characteristics) of permanent magnets that were on the market in 1957. The table was published in issue No. 4 of the Revue de Cobalt (pages 36-39) published in September 1959, and is a reproduction of a table which appeared in the February 1957 issue of the Electrical Energy Revue (Electrical Energie). Just below the middle of the table on page 38 there appear several listings of Ticonal with the compositions indicated above, together with the residual magnetism Br in gauss, the maximum value of the product (BH) expressed in 10 gauss-oersteds, the magnetomotive force H in oersteds, and the density.
The applicant has sought to reduce the length of the magnet and has realized that it was possible, in spite of this reduction, to make the magnet function in the best conditions it two non-magnetic gaps are provided, one fixed, the other variable according to the distance of the armature cooperating with the pole pieces, and by giving the magnet and the pole pieces dimensions and shapes according to precise conditions, these dimensions and shapes permitting the obtaining of a product of permanence which is favorable to a good distribution of the flux, whatever the distance of the armature from the pole pieces.
Consequently the present invention has for an object a practical arrangement, particularly for magnetic catches, comprising a magnet and two pole pieces arranged in a manner to give a double gap of which one gap is fixed and the other variable. For a Ticonal type magnet or one having a similar curve and of which the dimensions have the following proportions that is to say working at an unfavorable point on the demagnetisation curve, its point on the curve will be caused to ascend, thus augmenting the product BH, if one adopts, for the pole pieces, the shapes and proportions which give a fixed gap of which the proportions will be between:
and a surface s" in this fixed gap:
It is also preferred that for s If these conditions are observed, experience shows that the total of the fixed permanences, variable and leakage, is such, in open circuit, that the magnet operates in optimum conditions, that is to say the value of the product B H approaches its maximum.
When the armature is at a considerable distance from the pole pieces, the total flux of the magnet is distributed between the circuit of the fixed air gap and leakages-the magnet operating in the neighborhood of the maximum of the product BH-the dimensions of the fixed gap are such that the length and the cross-section of this gap may be great, similar to the cross-section of the surrounding iron. In this way, one part of the iron is close to saturation, on the other hand, the leakage away from the large surfaces are great.
When the armature is relatively close to the pole pieces, a new field is offered for the passage of flux, and the total permanence of the circuits increased; the magnetomotive force of the magnet diminishes (the magnet moves up its curve). The leakage diminishes proportionally to the reduction of the magnetomotive force of the magnet and just as the leakage was important when the armature was distant, the reduction is equally important.
On the other hand, thanks to the big cross-section of iron of the circuit of the fixed gap, the flux which passes through this circuit diminishes equally and proportionally to the reduction of the magnetomotive force of the magnet, while if the iron section were to be small, the flux would diminish less quickly than the magnetomotive force (with a small cross section of iron, when the armature is remote, the magnetomotive force becomes such as to force the flux to pass through the iron and this represents a waste of the flux).
The choice of the dimensions of the fixed air gap thus creates two conditions: a rapid reduction of the leakage, a slow reduction of the flux passing through the fixed air gap, which ensure that the part of the flux which passes through the armature is a maximum, thus the attraction is a maximum even when the armature has not yet contacted the pole pieces.
There is described hereafter, by way of example only, various constructions of magnet according to the invention, reference being made to the accompanying drawings in which:
FIGURE 2 is a view in longitudinal section of a first construction of magnet according to the invention;
FIGURE 3 is a view similar to FIGURE 2 of a second construction;
FIGURE 4 is a section along the line IVIV of FIGURE 3;
FIGURE 5 is a plan view of a third construction;
FIGURE 6 is a View in sectional elevation of FIG- URE 5;
FIGURE 7 is a sectional view of a fourth construction;
FIGURE 8 is a plan view of FIGURE 7;
FIGURES 9 and 11 are views similar to FIGURE 7 of two modifications;
FIGURES and 12 are plan views corresponding respectively to FIGURES 9 and 11;
FIGURE 13 is a sectional view of another construction;
FIGURE 14 is a plan view of the construction of FIG- URE 13;
FIGURE 15 is a sectional view of a further construction;
FIGURE 16 is a sectional view along the line XVIXVI of FIGURE 15;
FIGURE 17 is a section of another construction;
FIGURE 18 is a plan view of the construction shown in FIGURE 17;
FIGURE 19 is a view in elevation of another construction;
FIGURE 20 is a section along the line XXXX of FIGURE 19;
FIGURE 21 is a modification of the construction shown in FIGURE 19;
FIGURE 22 is a view along the line XXII-XXII of FIGURE 21; and
FIGURE 23 is a graph showing the demagnetization curves of several materials which may be used for the construction of the magnet of the present invention.
FIGURE 1 shows the known construction in which references 1 and 2 indicate respectively the magnet and the pole pieces. To obtain the maximum value for the product BH, the length L of the magnet 1 must be relatively large by comparison with the cross-section S.
In FIGURE 2, each of the pole pieces has a contact surface s for an armature 3 and has in its rear part a transverse portion 2a; these two portions 2a are so located that there exists at the rear of the magnet a fixed nonmagnetic gap 4 of length 0, the cross-section of the portions 2a of the pole pieces constituting this gap having a value s".
The magnet 1 being in Ticonal or in a material having a demagnetization curve analogous to that of Ticonal, its length being between /S and /S/2, one chooses according to the present invention a length e for the gap between L/ 15 and L/3 and preferably equal to L/8, at the same time the surface s", at this gap is chosen to be between 58/12 and 38.
The contact surface s of each of the pole pieces with the armature is, preferably, between S/ 3 and S.
In the construction of FIGURES 3 and 4 there is also a double non-magnetic gap, but the pole pieces 2 are planar and the fixed gap, which in this case is double, is obtained by locating a piece of soft iron 5 behind the magnet 1 at a distance e/2 from each of the pole pieces, this soft iron piece being held in place, for example, by members of non-magnetic material in the spaces between the soft iron piece and the pole pieces and between the soft iron piece and the magnet. In a modification, the soft iron member is arranged to be in contact with one of the pole pieces and at a distance e from the other.
In the arrangement of FIGURES 5 and 6, the magnet '1 and the pole pieces 2 are arranged in the form of a cylinder. The external shape of the two pole pieces 2 is substantially semi-cylindrical, their axes being perpendicular to the magnetic axis of the magnet 1. Their edges are separated one from the other to form two fixed gaps of length e, which are located on opposite sides of the magnet. The armature 3 is movable along the axis of the cylinder parallel to the longitudinal direction of the fixed gaps.
As may be seen from these figures, each of said pole pieces is so shaped that magnetic flux traveling in a circular manner in a direction perpendicular to the cylindrical axis of the magnet assembly finds its path substantially narrowed at two points on each pole piece (at each edge of the area of contact between the magnet and the pole piece) in such a way that the pole pieces become easily saturated in the vicinities of these constrictions. This saturation tends to urge a large proportion of the flux to act on armature 3 as it approaches the pole pieces and thus tends to substantially increase the magnetic attraction exerted on the former.
The construction of FIGURES 7 and 8 is generally similar to that of FIGURES 3 and 4 but the pole pieces 2 have a substantially cylindrical external shape so as to form part of a cylinder. Their inner face is planar and abuts the magnet 11, the latter being surmounted by a soft iron member 5 located at a distance 6/ 2 from each of the pole pieces.
The construction of FIGURES 9 and 10 is different from that of FIGURES 7 and 8 in that the fixed gap is obtained by means of a soft iron piece 6 located at a distance e/ 2 from the end of the pole pieces 2 opposite to the movable armature.
The arrangement of FIGURES 11 and 12 is a combination of the two preceding constructions. The fixed gap is provided by a soft iron piece 7 providing a circular part surmounting the pole pieces 2 and a substantially parallelepiped portion which is arranged between the pole pieces above the magnet 1.
In the construction of FIGURES 13 and 14, the fixed gap is obtained by means of a soft iron sleeve 8 the interior radius of which is greater than the external radius of the pole pieces 2 by an amount equal to e/2.
The construction of FIGURES 15 and 16 is a modification of that of FIGURES 9 and 10 in which the pole pieces 2 are planar.
In the construction of FIGURES 17 and 18, the magnet 1 is surrounded by a soft iron piece 9 of U-section and is located at a distance e/2 from each of the pole pieces 2.
In the construction of FIGURES 19 and 20, the fixed gap is obtained by means of a soft iron sleeve 10 which surrounds the magnet I and whose axis is coaxial with the magnetic axis of the magnet 1, the latter being of circular cross-section in this construction. The length of this soft iron sleeve is less than the distance between the pole pieces, which are planar, by an amount equal to e. Each edge of this soft iron sleeve is at a distance e/ 2 from the respective pole piece.
In the modifications of FIGURES 21 and 22, one of the edges of the soft iron sleeve 10 is in contact with one of the pole pieces and is located at a distance e from the other pole piece.
In the various constructions, the gap or gaps can be filled by a non-magnetic material and the dimensions of the pole pieces and of the magnet are determined in accordance with the above indicated conditions.
FIG. 23 is a graph showing the demagnetization curves of several materials, from which the magnet 1 of the various embodiments described above may be made. These materials have been selected only by way of example and it should be understood that other varieties having similar curves may be used. These curves are plotted in terms of the induction (B) in kilogauss vs. the demagnetization field (H) in oersteds and show that the mater als represented, i.e., Ticonal G D (Ugimax) and Ticonal 600, 700, 750 and 800, all of which are the designations under which these materials are sold, have in common that the flux density (B) is high for low values of the demagnetization field and decreases rapidly with increases in the field after this field increases beyond a certain value.
It will be understood that the invention is not limited to the constructions described and illustrated, but to the contrary covers all modifications.
1. A magnet composed of an aluminum-nickel-cobaltcopper-iron base composition, and having a length L between /S/ 2 and /S, the magnet being combined with pole pieces arranged to provide a double non-magnetic gap of which one is fixed and theother variable, the dimensions of the fixed gap satisfying the following conditions:
S is the area of contact of the magnet with the pole pieces,
L is the length of the magnet between the surfaces of con tact with the pole pieces,
e is the length of the fixed gap,
s the surface area of each of those parts of the pole pieces which form the fixed air gap.
2. A magnet according to claim 1, wherein the fixed gap further satisfies the following condition where S has the above signification and s represents the area of contact of each of the pole pieces with the armature. 3. A magnet according to claim 1, wherein the pole pieces provide two fixed non-magnetic gaps located on opposite sides of the magnet.
4. A magnet according to claim 1 wherein the fixed gap is formed by a piece of soft iron located behind the magnet between the pole pieces, the latter having planar or substantially planar inner faces.
5. A magnet according to claim 1 wherein the magnet and the pole pieces form a cylinder.
6. A magnet according to claim 1 wherein the direction of the fixed gap is perpendicular to the direction of movement of the armature.
7. A magnet according to claim 1 wherein the direction of the fixed gap is parallel to the direction of movement of the armature.
8. A magnet according to claim 1, wherein the fixed gap is formed by a soft iron member located above the end of the pole pieces opposite to the armature.
9. A structure comprising a magnet, the poles of which are situated laterally, and two pole pieces arranged on the poles of the magnet and protruding beyond the end faces of the magnet, each of the longitudinal edges of one of the pole pieces being adjacent to one of the longitudinal edges of the other pole piece, so as to form two air gaps arranged substantially symmetrically with respect to the longitudinal axis of the magnet so that the longitudinal axes of said air gaps are perpendicular to those surfaces of said pole pieces which contact an armature.
10. A structure as recited in claim 9 wherein said pole pieces present at least one constriction to the flux flowing perpendicularly to said longitudinal edges of said pole pieces.
References Cited by the Examiner UNITED STATES PATENTS 2,812,203 11/57 Scholten 317159 3,095,525 6/63 Hansen 317201 BERNARD A. GILHEANY, Primary Examiner.
SAMUEL BERNSTEIN, JOHN F. BURNS, LARAMIE E. ASKINS, Examiners.