US3848148A

US3848148A - Starter motors

Info

Publication number: US3848148A
Application number: US00413455A
Authority: US
Inventors: R Wilson
Original assignee: Lucas Electrical Co Ltd
Current assignee: Lucas Electrical Co Ltd
Priority date: 1972-11-10
Filing date: 1973-11-07
Publication date: 1974-11-12
Anticipated expiration: 1991-11-12
Also published as: FR2215093A5; AU6176773A; JPS5233734B2; JPS49133728A; ES420407A1; DE2355494B2; IT996406B; ZA738257B; DE2355494C3; DE2355494A1; GB1442601A; AR199595A1

Abstract

A starter motor for an internal combustion engine comprising an electric motor capable of rotating a shaft. A pinion gear wheel carried by the shaft, and rotatable therewith, the gear wheel also being movable axially relative to the shaft. An electromagnet including an armature which is coupled to the pinion gear wheel so that the two can move axially relative to the shaft. The electromagnet also includes a plurality of electromagnet poles which are equi-angularly spaced around the shaft in a plane at right angles to the axis of the shaft, and which are spaced apart by an amount such that the armature can enter between the poles. In the rest position of the armature there is a clearance between the poles and the armature in the direction of movement of the armature. The shaping of each pole is such that the surface of the pole presented to the armature includes regions which are spaced from the armature by different distances in the direction of movement of the armature, and which are equally spaced from the shaft in a radial direction. The electromagnet further includes a member which magnetically interconnects the poles and a winding associated with the poles so that when energised there is a flow of magnetic flux between the poles and the armature, within the armature at right angles to the direction of movement thereof, and between the poles by way of said member, such that the armature is attracted to the poles. The arrangement of said regions of the pole surfaces is chosen to achieve a predetermined attraction between the poles and the armature during the movement of the armature towards the poles.

Description

United States Patent [1 1 .Wilson 1 Nov. 12, 1974 STARTER MOTORS [75] Inventor: Ronald Wilson, Birmingham,

England [73] Assignee: The Lucas Electrical Company Limited, Birmingham, England [22] Filed: Nov. 7, 1973 [21] Appl. No.2 413,455

[30] Foreign Application Priority Data Nov. 10, 1972 Great Britain 51994/72 [52] U.S. Cl. 310/209, 123/179 M, 290/38 A, 310/216 [51] Int. Cl H02k 1/06, F02n 1l/02 [58] Field of Search 310/79, 17, 80, 216, 179, 310/193, 258, 209, 191; 290/38 A, 48;

Primary Examiner-J. D. Miller Assistant Examiner-Robert .l. Hickey Attorney, Agent, or Firm-Holman & Stern [57] ABSTRACT A starter motor for an internal combustion engine comprising an electric motor capable of rotating a shaft. A pinion gear wheel carried by the shaft, and rotatable therewith, the gear wheel also being movable axially relative to the shaft. An electromagnet including an armature which is coupled to the pinion gear wheel so that the two can move axially relative to the shaftLThe electromagnct also includes a plurality of electromagnet poles which are equi-angularly spaced around the shaft in a plane at right angles to the axis of the shaft, and which are spaced apart by an amount such that the armaturecan enter between the poles. in the rest position of the armature there is a clearance between the poles and the armature in the direction of movement of the armature. The shaping of each pole is such that the surface of the pole presented to the armature includes regions which are spaced from the armature by different distances in the direction of movement of the armature, and which are equally spaced from the shaft in a radial direction. The electromagnet further includes a member which magnetically interconnects the poles and a winding associated with the poles so that when energised there is a flow of magnetic flux between the poles and the armature, within the armature at right angles to the direction of movement thereof, and between the poles by way of said member, such that the armature is attracted to the poles. The arrangement of said regions of the pole surfaces is chosen to achieve a predetermined attraction between the poles and the armature during the movement of the armature towards the poles.

4 Claims, 12 Drawing Figures 25b 23a 25b PATENT L HUV 1 21974 SHEET 10F 3 FIG. i.

PATENTELNSV 1 21974 3,848,148

SHEET 20F 3 FIG] HG}.

25b 23a 25b 2 24 F\G.4. H65

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F169- F\G.10.

PATENTEL M 1 21914 3,848,148

SHEET 3 OF 3 FULL -05 '10 45 2O 25 3O '55 INCHES ARMATURE. & PINION MOVEMENT STARTER MOTORS This invention relates to starter motors for internal combustion engines.

A starter motor according to the invention comprises, an electric motor, a shaft rotatable by said motor and carrying a pinion gear wheel, the pinion gear wheel being rotatable with said shaft and being movable axially relative to the shaft between a rest position and an operative position, and an electromagnet including an armature coupled to the pinion gear wheel said armature and said pinion gear wheel being movable axially relative to said shaft, a plurality of electromagnet poles equi-angularly spaced around the axis of said shaft in a plane at right angles to said axis and spaced apart by an amount such that the armature can enter between the poles, the poles being spaced from the armature, in the rest position thereof, in the direction of movement of the armature relative to the shaft, each pole being shaped so that the surface of each pole presented to the armature in the rest position of the armature includes regions spaced from the armature by different distances in the direction of movement of the armature, and equally spaced from said shaft in a radial direction a member magnetically interconnecting the poles, and an electromagnet winding associated with the poles so that when energised the winding induces a flow of magnetic flux between the poles and the armature, within the armature at right angles to its direction of movement, and between the poles, by way of said member, so that the armature is attracted to the poles, the arrangement of said regions of the pole surfaces being chosen to achieve a predetermined attraction between the poles and the armature during the movement of the armature towards the poles.

One example of the invention is illustrated in the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of a starter motor,

FIG. 2 is a front elevational view of one of the electromagnet poles shown diagrammatically in FIG. 1,

FIG. 3 is a sectional view on the line 3-3 in FIG. 2,

FIG. 4 is a plan view of the pole shoe of the pole shown in FIGS. 2 and 3,

FIGS. 5 to 11 are plan views respectively of alternative forms of pole shoe for use with the pole body of the pole shown in FIG. 2 and,

FIG. 12 is a graph illustrating the effect of the pole shape shown in FIG. 5.

Referring to the drawings, the starter motor includes an electric motor indicated diagrammatically at 11 which rotates a shaft 12 supported in bearings (not shown) carried by the casing 13 of the starter motor. Carried by the shaft 12 is a pinion assembly 14 including a pinion gear wheel 15 and a roller clutch 16. The pinion assembly 14 is movable axially relative to the shaft 12 between a rest position, and an operative position in which the pinion gear wheel 15 engages, in use, a ring gear of an engine to be started. The pinion assembly rotates with the shaft 12, although in certain circumstances the pinion gear wheel 15 can rotate relative to the shaft 12 as permitted by the roller clutch 16. Normally however the pinion gear wheel 15 rotates with the shaft 12. Associated with the pinion assembly 14 is an electromagnet armature 17 which is generally in the form of a thick steel disc slidably mounted on a sleeve 14a of the pinion assembly. A spring 18 urges the armature 17 against an abutment 19 secured to the sleeve 14a.

The portion of the casing 13 encircling the shaft 12 adjacent the pinion assembly 14 is cylindrical, and is concentric with the shaft 12. This portion of the casing 13 is formed from mild steel, and asecured to the inner surface thereof are a pair of diametrically opposed electromagnet poles 21, the poles 21 are magnetically interconnected by the casing 13 and each pole includes a pole body 22 which extends radially inwardly from the casing 13 towards the shaft 12 at its innermost end each pole body 22 is shaped to receive a pole shoe which defines part of the surface of the pole which is presented to the armature 17, and also defines the radially innermost surface of the pole. The pole bodies 22 and pole shoes are shaped so that their radially innermost surfaces, presented to the shaft 12, are cylindrical, the radially innermost surfaces of the two poles defining parts of a common, imaginary cylinder having its axis coincident with the axis of the shaft 12 and of diameter such that the armature can enter between the poles with a minimal air gap. The two pole bodies 22 are substantially identical, and in use each will receive a substantially identical pole shoe. Several forms of pole shoe are possible, and eight different pole shoe forms are shown in FIGS. 4 to 11, respectively. The pole shoe 23 shown in FIG. 4 is symmetrical and the surface of the pole shoe 23 which is presented to the armature 17 in use is stepped at its opposite ends, in the direction of movement of the armature. Thus, in use the central land 23a of the front surface of the pole shoe 23 will be closer to the armature than the remainder of the pole shoe 23 by virtue of the steps 23b. The pole shoe 24 shown in FIG. 5 is again symmetrical, and differs from the pole shoe 23 in that the single step 23b of the shoe 23 is replaced by double steps 24b, 24c. Thus the central land 24a will be closer to the armature than the stepped region 24b and the stepped region 24b will be closer than the region 24a. The pole shoe 25 shown in FIG. 6 is not symmetrical, since the steps provided in one end of the front surface are dimensioned differently to the steps provided in the other end of the front surface. FIGS. 7 and 8 show further

asymmetric pole shoes

26, 27 wherein only one end of the front surface is stepped. FIGS. 9 and 10

show shoes

28 and 29 wherein the right angle steps are replaced by

linear tapering regions

28a, 29a and FIG. 11 shows a shoe 31, where the right angle steps are replaced by curved regions 31a. The regions of the poles spaced by different distances from the armature are, as is clear from the drawings, equally spaced from the shaft 12 in the radial direction.

Each of the pole shoes 23 to 31 is capable of being secured to the pole body 22, the pole body 22 having therein a pair of threaded bores which receive countersunk screws passing through countersunk holes in the pole shoes to retain the pole shoes on the pole body.

Encircling each of the poles 21 between the casing 13 and its respective pole shoe is an electromagnet winding 20. The windings 20 can be electrically interconnected in parallel or in series, and are so arranged that when current flows in the windings 20 the poles assume opposite magnetic polarities. Thus magnetic flux will flow from one of the poles to the armature 17, will flow in the armature 17 at right angles to the shaft 12, from the armature 17 back to the other of the poles, and

from said other pole back to said one pole by way of the casing 13, thereby attracting the armature 17 towards the poles and moving the pinion assembly 14 axially relative to the shaft 12 from its rest position towards its operative position. The winding 20 will normally be energised by way of a manually controlled switch which simultaneously, or after a short delay, also energises the motor 11. Alternatively, the motor 11 can be energised by closure of a further switch dependent upon movement of the armature to a position corresponding to the operative position of the pinion 15.

The imaginary cylinder defined in part by the radially innermost surfaces of the poles 21 is of slightly larger diameter than the external diameter of the disc-like armature 17. Thus the armature 17 can enter between the poles 21, and in the operative position of the pinion assembly 14 the armature 17 lies between the poles 21. The stepped nature of the surfaces of the poles presented to the armature 17, with the steps or curved surfaces running in the direction of movement of the armature 17, modifies the electromagnetic force acting on the armature 17 at various points in its movement between the rest position and the operative position. Thus the different pole shoes will provide different characteristics, and all of the pole shoes shown in the drawings are designed to modify in various ways the characteristics of the attraction which occurs between the armature and a pair of plain poles as the pinion assembly of the starter motor approaches its operative position. FIG. 12 shows in graph form a comparison between plain poles and poles of the form shown in FIG. 5. It can be seen that the plain pole arrangement (curve 1) shows a substantial drop in pull between 0.15 and 0.275 inches of pinion and armature movement. 0.00 represents the rest position and 0.35 represents the position wherein the pinion would be in full engagement with the toothed wheel of an engine to be started. The pole form shown in FIG. 5, as can be seen from curve 2 of FIG. 12 overcomes the drop in pull exhibited by the plain poles. The characteristics produced by the other pole forms shown will differ from the characteristics illustrated in curve 2 and the pole form which is chosen for a particular starter motor will of course depend upon the requirements of the starter motor. For example, in a starter motor where movement of the armature to a position equivalent to full pinion engagement controls energisation of the motor field then it is important that the attraction of poles can overcome the spring 18 in the event of tooth to tooth abutment between the pinion and the engine ring gear. In such a case the pole form of FIG. might be chosen to ensurehigh attraction at the point in the movement of the pinion assembly where the tooth to tooth condition would occur. Similarly the FIG. 5 pole form might be chosen for a starter motor where the spring 18 is dispensed with and there is no facility for relative movement between the armature and the pinion assembly, the motor field being energised a short predetermined time after the winding 20 is .energised. In this case it would be necessary'to have high attraction to move the pinion rapidly into full engagement before energisation of the motor field or immediately a tooth to tooth condition has been relieved by rotation of the pinion upon energisation of the motor field.

In order to ensure smooth axial movement of the armature a brass or other non-magnetic sleeve can be provided which is secured to and concentric with the armature and which slidingly engages the'inner surface of the poles. However, it will be appreciated that in theory since the two poles will carry substantially identical pole shoes, then even though asymmetric pole shoes may be used there will be no tendency for the armature to tilt relative to the' shaft 12 since equivalent steps in the two pole shoes will be diametrically opposite one another, and so the force acting at any point on the armature will be balanced by the same force at the diametrically opposite point on the armature.

In practice the armature, described above as being in the form ofa thick disc,will include a peripheral flange at its axial end remote from the poles, the flange engaging the poles in the full engagement position of the pinion assembly to limit the movement of the armature. A brass or other non-magnetic spacer can be secured to the flange to prevent the flange touching the poles and thereby facilitate return movement of the pinion and armature assembly upon de-energization of the winding 20. Moreover the poles described above as being formed in two separate parts can of course each be produced as a single part and furthermore in some starter motors more than two equi-angularly spaced poles can be utilized. It is to be appreciated that where the required radial depth of the shaping of the pole is greater than the radial thickness of the pole shoe then the shaping, be it stepping or tapering, can be continued on the pole body. Thus the shaping can be on part only of the radial thickness of the pole shoe, can be over the whole radial thickness of the pole shoe or can be over the whole radial thickness of the pole shoe and also on the pole body.

I claim:

l. A starter motor, for an internal combustion engine, comprising an electric motor, a shaft rotatable by said motorand carrying a pinion gear wheel, the pinion gear wheel being rotatable with said shaft and being movable axially relative to the shaft between a rest position and an operative position, and an electromagnet including an armature coupled to the pinion gear wheel said armature and said pinion gear wheel being movable axially relative to said shaft, a plurality of electro-' magnetic poles equi-angularly spaced around the axis of said shaft in a plane at right angles to said axis and spaced apart by an amount such that the armature can enter between the poles, the poles being spaced from the armature, in the rest position thereof, in the direction of movement of the armature relative to the shaft, each pole being shaped so that the surface of each pole presented to the armature in the rest position of the armature includes regions spaced from the armature by different distances in the direction of movement and the armature, and equally spaced from said shaft in a radial direction, a member magnetically interconnecting the poles, and an electromagnet winding associated with the poles so that when energised the winding induces a flow of magnetic flux between the poles and the armature, within the armature at right angles to its direction of movement, and between the poles, by way of said member, so that the armature is attracted to the poles, the arrrangement of said regions of the pole surfaces being chosen to achieve a predetermined attraction between the poles and the armature during the movement of the armature towards the poles.

2. A starter motor as claimed in claim 1 wherein said regions spaced from the armature by different distances in the direction of movement of the armature are defined by individual steps in said surface of the pole. I

3. A starter motor as claimed in claim 1 wherein said surface of each pole tapers linearly in a direction away 4. A starter motor as claimed in claim 1 wherein said surface of each pole is curved, and said regions spaced from the armature by different distances in the direction of movement of the armature are defined by areas from said armature, and said regions are constituted by 5 of said curved surface.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIUN PATENT NO. 1 3,848,148

DATED November 12, 1974 INVENTOR(S) 2 Ronald Wilson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Specification, column 3, line 33, cancel "0.15", insert 0.275 line 34, cancel "0.275", insert 0.15 Cancel 0.00, insert 0.35 line 35, cancel "0.35", insert 0.00

Bigncd and gcaled this Third Day Of July 1979 [SEAL] Arrest:

LUTRELLE F. PARKE};

Attesting Oflicer Acting Commissioui of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,848,148 DATED November 12, 1974 INVENTOR(S) Ronald Wilson It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Specification, column 3, line 33, cancel 0.15", insert 0.275 line 34, cancel "0.275", insert 0.15 Cancel 0.00", insert 0.35 line 35, cancel "0.35", insert 0.00

Signed and Scaled this Third Day of July 1979 [SEAL] Arrest.-

LUTRELLE F. PARKER Attestl'ng Oflicer Acting Commissioner ofPatents an; Trademarks

Claims

1. A starter motor, for an internal combustion engine, comprising an electric motor, a shaft rotatable by said motor and carrying a pinion gear wheel, the pinion gear wheel being rotatable with said shaft and being movable axially relative to the shaft between a rest position and an operative position, and an electromagnet including an armature coupled to the pinion gear wheel said armature and said pinion gear wheel being movable axially relative to said shaft, a plurality of electromagnetic poles equi-angularly spaced around the axis of said shaft in a plane at right angles to said axis and spaced apart by an amount such that the armature can enter between the poles, the poles being spaced from the armature, in the rest position thereof, in the direction of movement of the armature relative to the shaft, each pole being shaped so that the surface of each pole presented to the armature in the rest position of the armature includes regions spaced from the armature by different distances in the direction of movement and the armature, and equally spaced from said shaft in a radial direction, a member magnetically interconnecting the poles, and an electromagnet winding associated with the poles so that when energised the winding induces a flow of magnetic flux between the poles and the armature, within the armature at right angles to its direction of movement, and between the poles, by way of said member, so that the armature is attracted to the poles, the arrrangement of said regions of the pole surfaces being chosen to achievE a predetermined attraction between the poles and the armature during the movement of the armature towards the poles.

2. A starter motor as claimed in claim 1 wherein said regions spaced from the armature by different distances in the direction of movement of the armature are defined by individual steps in said surface of the pole.

3. A starter motor as claimed in claim 1 wherein said surface of each pole tapers linearly in a direction away from said armature, and said regions are constituted by areas of the tapering surface.

4. A starter motor as claimed in claim 1 wherein said surface of each pole is curved, and said regions spaced from the armature by different distances in the direction of movement of the armature are defined by areas of said curved surface.