GB1586509A

GB1586509A - Multi-coil field magnets for electric motors

Info

Publication number: GB1586509A
Application number: GB5078777A
Authority: GB
Original assignee: Societe de Paris et du Rhone SA
Current assignee: Societe de Paris et du Rhone SA
Priority date: 1976-12-07
Filing date: 1977-12-06
Publication date: 1981-03-18
Also published as: DE2754331A1; JPS5439802A; IN150118B; ES464783A1; FR2373907B1; FR2373907A1

Description

(54) IMPROVEMENTS IN OR RELATING TO MULTI-COIL FIELD MAGNETS FOR ELECTRIC MOTORS (71) We, SOCIETE DE PARIS ET DU RHONE, a French Societe Anonyme, of 36 Avenue Jean Mermoz, 69008 Lyon, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements made to multi-coil field magnets for electric motors, particularly, though not necessarily exclusively, in relation to starters for internal combustion engines. The invention is more particularly concerned with the positioning and retaining of the magnet coils in the yoke.

Field magnets of the kind in question are generally made with the aid of laminae which are stacked inside a yoke to form a structure comprising a certain number of slots with projections between the slots to form the poles of the field magnet. The coils are then placed individually in the slots so as to surround each pole, whereupon they are connected up electrically. This assembly is time consuming and expensive and constitutes a not negligible burden in then cost price of electric starters provided with field magnets made in this manner.

Furthermore, these field magnets have contact areas between the poles and the yoke which constitute parasitic air gaps.

Solid pole pieces may also be fixed direct on the yoke. Here again there are leakages of magnetic flux because of the parasitic air gaps.

According to the present invention we provide a field magnet for an electric motor of the type having an annular yoke with pole pieces extending radially inwardly from the inner periphery of the yoke and coils having central openings snugly fitting around the pole pieces, comprising multiple identical segments joined to form the magnet yoke, the number of segments being the same as the number of pole pieces, each segment comprising a part of the annular yoke having a portion of a pole piece at each end, one end of each segment having a first pole piece portion and the other end having a second pole piece portion with a beak thereon which extends - from the inner face of the second portion towards the attached first portion, each pole piece being formed by adjacent first and second portions which provide lateral faces of the pole which are spaced apart so that they fit the central opening of a coil, each pole piece being divided into first and second portions along a dividing line which extends through the pole piece at an oblique angle to the radial, and the distance from the end of the beak to the dividing line being less than the width of the opening through the coil, said dividing line being disposed such that said second portion of the pole piece is of greater annular extent near its inner surface and of lesser annular extent where it joins the yoke portion of the segment and being disposed such that said first portion of the pole piece is of lesser annular extent near its inner surface and of greater annular extent where it joins the yoke portion of the segment.

Other features which may form part of the present invention will be apparent from the accompanying drawing, given by way of example only, which is an end view of a multi-coil field magnet constructed in accordance with the invention.

In the illustrated embodiment the field magnet 1 is to have four pole pieces and a tubular yoke 2' made up from four segments of which three are shown in position and the fourth is being fitted in place. Each segment may be made from multiple stacked laminae.

Each of the four segments comprises a segment portion 2'b of the yoke having at each end a portion of a pole integral therewith. At one end of each segment is a first pole portion having a radially directed edge 12 followed by another edge 13 which diverges in the direction of the other end of the segment in question, the said edges being of complementary shape to edges 14, 15 at the other end of the segment. This other end has a second pole portion including a beak 4' extending parallel to the inner face 2'a and turned in the direction of the first end. Similar segments may be fitted together along with the corresponding coils, on account of the special shape of the lines of separation 12, 13 and 14, 15 of the segments. For this purpose a coil is first mounted by engaging its longitudinal portion 6a on the second pole portion in the channel behind the beak 4' of each segment. The first pole portion of each pole which is not provided with a beak is then engaged in the centre of the successive coils. It can be seen from the drawing that the first portion of each segment is of lesser annular extent near its inner surface and of greater annular extent where it joins the yoke portion of the segment, whereas the second portion of each segment is of greater annular extent near its inner surface and of lesser annular extent where it forms the yoke portion of the sequence. The drawing illustrates the mounting of the last segment, and of its coil in relation to the other three segments which are already in position. When in position the segments may by suitable means, for example by soldering or welding along the nicks shown between the segments, be retained in place. It will be appreciated that each pole piece portion is integral with that part of the yoke to which it is adjacent.

It will be noted that the pole arc a is equal to two-thirds of the pole pitch, while the distance 1 of the inner end of the portion 15 (i.e. the end nearer the centre of the device) from the end of the beak 4' is slightly less than the width of the opening of the coil. Thus each coil can be introduced radially and slipped into its channel behind the beak 4'.

It is thus possible to produce economically multi-coil electric starter field magnets having excellent electric efficiency.

WHAT WE CLAIM IS: 1. A field magnet for an electric motor of the type having an annular yoke with pole pieces extending radially inwardly from the inner periphery of the yoke and coils having central openings snugly fitting around the pole pieces, comprising multiple identical segments joined to form the magnet yoke, the number of segments being the same as the number of pole pieces, each segment comprising a part of the annular yoke having a portion of a pole piece at each end, one end of each segment having a first pole piece portion and the other end having a second pole piece portion with a beak thereon which extends from the inner face of the second portion towards the attached first portion, each pole piece being formed by adjacent first and second portions which provide lateral faces of the pole which are spaced apart so that they fit the central opening of a coil, each pole piece being divided into first and second portions along a dividing line which extends through the pole piece at an oblique angle to the radial, and the distance from the end of the beak to the dividing line being less than the width of the opening through the coil, said dividing line being disposed such that said second portion of the pole piece is of greater annular extent near its inner surface and of lesser annular extent where it joins the yoke portion of the segment and being disposed such that said first portion of the pole piece is of lesser annular extent near its inner surface and of greater annular extent where it joins the yoke portion of the segment.

2. A field magnet according to claim 1, wherein each segment comprises multiple stacked laminae.

3. A field magnet according to claim 1 substantially as herein described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of complementary shape to edges 14, 15 at the other end of the segment. This other end has a second pole portion including a beak 4' extending parallel to the inner face 2'a and turned in the direction of the first end. Similar segments may be fitted together along with the corresponding coils, on account of the special shape of the lines of separation 12, 13 and 14, 15 of the segments. For this purpose a coil is first mounted by engaging its longitudinal portion 6a on the second pole portion in the channel behind the beak 4' of each segment. The first pole portion of each pole which is not provided with a beak is then engaged in the centre of the successive coils. It can be seen from the drawing that the first portion of each segment is of lesser annular extent near its inner surface and of greater annular extent where it joins the yoke portion of the segment, whereas the second portion of each segment is of greater annular extent near its inner surface and of lesser annular extent where it forms the yoke portion of the sequence. The drawing illustrates the mounting of the last segment, and of its coil in relation to the other three segments which are already in position. When in position the segments may by suitable means, for example by soldering or welding along the nicks shown between the segments, be retained in place. It will be appreciated that each pole piece portion is integral with that part of the yoke to which it is adjacent. It will be noted that the pole arc a is equal to two-thirds of the pole pitch, while the distance 1 of the inner end of the portion 15 (i.e. the end nearer the centre of the device) from the end of the beak 4' is slightly less than the width of the opening of the coil. Thus each coil can be introduced radially and slipped into its channel behind the beak 4'. It is thus possible to produce economically multi-coil electric starter field magnets having excellent electric efficiency. WHAT WE CLAIM IS:

1. A field magnet for an electric motor of the type having an annular yoke with pole pieces extending radially inwardly from the inner periphery of the yoke and coils having central openings snugly fitting around the pole pieces, comprising multiple identical segments joined to form the magnet yoke, the number of segments being the same as the number of pole pieces, each segment comprising a part of the annular yoke having a portion of a pole piece at each end, one end of each segment having a first pole piece portion and the other end having a second pole piece portion with a beak thereon which extends from the inner face of the second portion towards the attached first portion, each pole piece being formed by adjacent first and second portions which provide lateral faces of the pole which are spaced apart so that they fit the central opening of a coil, each pole piece being divided into first and second portions along a dividing line which extends through the pole piece at an oblique angle to the radial, and the distance from the end of the beak to the dividing line being less than the width of the opening through the coil, said dividing line being disposed such that said second portion of the pole piece is of greater annular extent near its inner surface and of lesser annular extent where it joins the yoke portion of the segment and being disposed such that said first portion of the pole piece is of lesser annular extent near its inner surface and of greater annular extent where it joins the yoke portion of the segment.