This invention relates to laminated commutators for electrical machines. A conventional commutator may be described as several bars oF copper Fitted together like segments oF an orange, each copper bar has to be machined or extruded to shape with precision to enable the several bars to Form a cylindrical shape. The advantages offered by the invention are that it enables symmetrical wedge-shaped sections, suitable For a commutator to be manufactured using Flat copper plates. The plates may be shaped on a simple press tool producing several plates in the time it takes to make one conventionally machined bar. According to the invention there is provided a plurality oF shaped Flat plates, in which each plate has at least two edges which are preferably parallel but not essentially so, shaped by removing at substantially right angles to one selected preferably parallel edge, one or more substantially rectangular or quadrilateral portion or portions, or a mixture of substantially rec¬ tangular or quadrilateral portion or portions of depth CD) where the number of portions removed of depth (D) is preferably but not essentially, numerically equal to the number of portions remaining, substantially of depth (D),

such that when two shaped plates are laid one upon the other in coincident superposition and where subsequently one plate is rotated 180 degrees relative to the other plate about a centreline between the plates at right angles to both preferably parallel edges, then if such plates are tilted relative to one another, on or about a longitudinal axis that is located at depth (D) and parallel to the selected preferably parallel edge then both plates may share a common axis without overlap, coincident with this selected edge, enabling a symmetrical wedge shaped section to be formed from two shaped flat plates. Two such plates may be called a congruent set. One or more congruent sets may form a segment, several segments together with intersegment electrically insulating material may form a cylindrical assemblage.

The terms cylindrical assemblage and commutator are freely interchangable .

One type of congruent set may be adjacent to another similar or different set, either axially or radially or both within a cylindrical assemblage. Individual shaped metallic plates used singly may interlay between congruent sets, particularly on very large commutators to minimise depth (D). Individual plates may be of any thickness commensurate with intelligent design, except that all plates in a congruent set should preferably be of the same thickness .

Plate material may follow conventional practice for commutators .

Risers may be included, either integral with the plates or as attachments to the plates. One or more locating and/or restraining means may be provided, by circular means of round, square, or any other suitable cross section, located within the cylindrical assemblage or external at either or both ends or on the outside diameter at any position. Such locating and/or restraining means may be loose insertions or integral with the machine shaft on which the commutator is mounted. Plates may be located and/or restrained by means of projections integral with the plates with corresponding iπdeπta- tions on other plates in place of or in addition to, other locating and/or restraining means.

The cylindrical assemblage may be coated in part or in whole substantially with tin, lead, silver or antimony either singly or in combination to fill the interstices on the circumference and provide a degree of cohesion. Intersegment electrically insulating material may be shaped in a similar manner to plates either as individual plates used singly or in the form of congruent sets as previously described. Individual plates may be coated with an electrically insulating material in whole or part in addition to or in place of intersegment electrically insulating material .

Provision may be made For electrically conducting paths between two or more plates in a cylindrical assemblage that are by design electrically insulated one from the other within a cylindrical assemblage, by means of integral extensions of the plates for equalisers or integral windings.

Preferred embodiments will now be described by way of example only and in no way restrictive of the scope of the invention with reference to drawings Figure 1 to Figure 10 inclusive, in which firstly, referring to a cylindrical assemblage of plates, 0D refers to the outside diameter. PCD refers to a reference diameter for design purposes. ID refers to the inside diameter. Referring to the individual plates, A may be described as part of, or all of, the length of the inside edge or edges of a plate located on the ID. Variations of length A are design functions and are denoted by numerals 1, 2, 3 etc. (eg: A1, A2) . L may be described as the length of the outside edge of a plate located on the 0D and may also be the length of the commutator face.

F refers to optional indentations for accepting, locating and restraining means. C is the wearing depth of a plate D is a design function, the depth of the rectangular or quadrilateral shape or shapes. E is C plus D the total depth of a plate.

B is the length of a bridging arm or side arm. Variations in length of B are design functions and are denoted by numerals 1, 2, 3 etc. , (eg: B1 B2).

Examples of congruent sets are, two plates as in Figure 1 as depicted assembled in Figure 5. The first Figure 1 may be placed first, the second Figure 1 facing the opposite way is placed on top of the first Figure 1 with their centrelines (1) coincident.

A second example of a congruent set would be two of . Figure 2 as depicted assembled in Figure B. The first Figure 2 may be placed first, with the second Figure 2 facing the opposite way placed on top of the first Figure 2 with centreline (2) of the first Figure 2 coincident with centreline (3) of the second Figure 2. A third example of a congruent set would be two of Figure 3 as depicted assembled in Figure 7. The first Figure 3 may be placed first, the second Figure 3 facing the opposite way placed on top of the first Figure 3 with centreline (4) of the first Figure 3 coincident with centreline (6) of the second Figure 3. A fourth example of a congruent set is two of Figure 4 as depicted assembled in Figure 8. The first Figure 4 may be placed first, with the second Figure 4 facing the opposite way, placed on top of the first Figure 4 with centreline (7) of the first Figure 4 coincident with centreline (10) of the second Figure 4. Figures 1 to B inclusive, are given as a guide only, as many variations are possible, for example, if Figure 1 is regarded in essence as a basic shape then all other shapes in Figures 2 to 8 are derivatives. Figure 2 is two of Figure 1. Figure 3 is three of Figure 1 ,

- ε -

Figure 4 is four of Figure 1 , and so forth. It is clear that multiples of Figure 1 Bre infinite, with four, five, six or more basic shapes in a row. As an example of a commutator according to the inven- tion consider a commutator with 150 segments, 5mm pitch, 0.8 mica, 240mm long. Using Figure 3 plates as appropriate to a short commutator, one of the first considerations is to keep length B1 short to minimise deflection under centrifugal force, to a lesser extent this also applies to B2. In this example using simple beam calculations as applicable to a cantilever with a uniformly distributed load stressed by centri¬ fugal force, a length of 30mm is appropriate for B1. To make up the balance of length L the following design details are appropriate :-

(a) Length B1 = Length A1 - self evident.

(b) Length B2 = Length A2 - plus clearance.

(c) Length B3 = Length A3 - plus clearance. Clearance, if required, is a vertical gap adjacent to a reinforcing means to enable plates to be inserted radially and then slid right or left into final position. In (a) when two plates are in coincident superposition eg: two of Figure 1 as depicted in Figure 5 , it is self evident B1 and A1 should be substantially equal in length.

Using simple beam calculations as applicable to a beam simply supported at each end with a uniformly dis¬ tributed load stressed by centrifugal force, then

a length of BOm is acceptable for B2 and B3.

With B2 and B3 at twice the length of B1 as in this example, clearance is academic.

The dimensions so far are, A1 = B1 therefore : A1 = 30 A2 = 30 A3 = 30 B1 = 30 B2 = BO B3 = 60 which complies with the design details. All add up to 240mm, the overall length of the commutator face. All A lengths may be the same. L will be 240 long with a 10mm wide riser on the top edge as an integral extension to each plate. The risers extending from alternate ends, eg: one riser on the A1 end then one riser on the B1 end coming together at one end when assembled. Due con¬ sideration should be given to the additional ceπtri- fugal stress generated by the additional mass of risers. Returning to the example : First step number of plates to a segment, if the segment is made up exclusively of congruent sets then it has to be a multiple of two, the number of plates in a congruent set, we will use 4x1mm plates. The total number of plates will be 150x4 = BOO. The relevant formulae are approximately :-

PCD = (Pt) + (Mt) ID = (ht) + (Mt)

7T

G = 0D x TT - (Mt + Pt) h

Where PCD is the reference diameter

P - The total number of plates. t - The thickness of one plate or one mica.

M - The total number of mica segments. m - Half the number of mica segments. h - Half the number of plates.

G - The width of one gap between plates on the 'OD '

We will make C = 11 and proceed as follows :-

PCD = (BOOxp + (150x0.8) = 229.2 Seg 150

TT 4x1 Pitch 5.27

ID = (300x1) + (150x0.8) = 133.7 mica 0.8

~rr PCD 230

ID 134

G = 252x7V - ( 120+500) = 0.24 D 48

300 C 11

0D 252

E 5B

G 0.24 Obviously : (PCD-ID) = D, PCD+2C = 0D , C+D = E

2

The pitch on the 0D will be : 252x7r = 5.27

150

An alternative design using electrically insulating material in the form of congruent sets would be as above but using 2x0.4 thick micas in place of 1x0.8

ID = (ht) + (mt) G = ( t x OD-ID) - _t) χ2 TV (PCD-ID 2 ) 2) otherwise as above.

PCD = (600x1) + (300x0.4) = 223.2 Seg 150

Pitch 5.27 ID = (300x1) + (150x0.4) = 114.6 mica 2x0.4

⁷ T PCD 230

ID 116

^G = ( "1 x252-116)-1) x 2 = 0.193 D 57

(230-116 2 ) 2). C 11

0D 252

E 68

G 0.19

The result of using shaped electrically insulating material in the form of congruent sets is a smaller gap between plates on the circumference. All designs should maximise C for strength and conductivity while keeping G to 0.25 or less.

Indentations F will be provided for three electrically insulated reinforcing means.

Plates may be assembled on a cylindrical mandril inserting the three reinforcing means on the first plate resting on the mandril. Subsequent plates are inserted radially then slid sideways onto the means, alternately inserting a left facing plate with a right facing plate . The whole assemblage may then be solder dipped to fill the interstices on the outside diameter and to provide coherence, then finally turned to size.

An alternative method particularly, but not exclusivel suitable for large commutators may be to assemble a proportion of shaped plates as previously described, no as congruent sets .

Instead of plates being assembled as congruent sets eg: a left facing plate inserted radially then slid left into position onto the reinforcing means followed by a similarly shaped plate right facing, inserted radially then slid right into position. One or more plates may be assembled not as congruent sets eg: a left facing plate inserted radially then slid left into

position followed by a similarly shaped plate also left facing inserted radially then BIBO Blid loft Into position on the reinforcing means.

The numerical portion of plates assembled as non- congruent sets to the portion of plates assembled as congruent sets is a design function.

The relevant formulae are approximately :-

PCD = (Pt) + (Ptn) + (Mt)

TV

ID = (ht) + (Ptn) + (Mt) 7X

G = 7T x 0D - (Pt + Ptn + Mt) h

Where (Pt) indicates plates assembled as congruent sets and (Ptn) indicates plates not assembled as congruent sets. Note: h is half of P, in the expression Pt . Another alternative particularly, but not exclusively, suitable for very large commutators may be to assemble shaped plates as previously described not as congruent sets. With intersegment electrically insulating material as congruent sets. The relevant formulae are approximately :-

PCD = (Pt) + (Mt) ID = (Pt) + (mt)

7T 7T

G = 0D x 7T - (Pt + Mt) Gm = n x t + G

Where n is a multiple of 2 and is the number of pieces of material comprising the intersegment electrically insulating material per segment. t is the thickness of one piece of intersegment insulating material .

G is the gap on the OD between the two pieces of inter¬ segment insulating material in consequence of being in the form of a congruent set. Gm is the total length of gap on the 00 between any two commutator segments .

Provision may be made for electrically conducting paths between two or more plates in a cylindrical assemblage that are by design electrically insulated one from the other within a cylindrical assemblage, by means of integral extensions of the plates for equalisers or integral windings.

An example is given in Figure 9 in which two plates are conductably connected by integral extensions to the plates . Extensions may be from either end of the plates, not necessarily the same ends, one plate may be inverted relative to the other the accommodate an involute. The extended portion between plates may be folded to the required slot pitch in the conventional manner, one plate end forming part of one segment the other integral plate may form part of another segment. Extensions may be wholely integral with the plates as in Figure 9 , or releasably connected as shown in the upper detai1. IF an integral winding is oF laminated construction, as is most likely, being derived From a laminated segment, then the Following design criteria are relevant, ref e r¬ r i ng to Figure 10 showing a laminated coil in plan vie

The non-commutator end oF the laminated coil should be Folded at the end, as shown, Forming an involute. IF you trace out one side oF the coil starting at X, the outward excursion is on the leFt oF the coil but the return path, because oF the involute is still on the leFt, terminating at Y. Consequently the outgoing and incoming paths are substantially the same length, an obvious advantage. A second point, with an involute, one plate will be inverted relative to the opposite end, trace the top edge From point X, it becomes the bottom edge at Y. Figure 10 refers of course to a lap winding, similar consideration may not be applicable to a wave winding as it is largely self correcting regarding unequal length due to wide coils.

Note: In one segment up to half of the plates may form part of the outgoing end of a coil and up to half of the plates the incoming end of another coil, in common with conventional practice. Such plate extensions could replace windings or equalisers, or both, in a rotating electrical machine to confer greater reliability and integrity .

This invention is particularly, but not exclusively, suitable for commutators for use in rotating electrical machines.