GB2182104A - Improvements in or relating to bearing assemblies - Google Patents

Description

SPECIFICATION Improvements in or relating to bearing assemblies This invention relates to bearing assembliesfor rotatable members and has particular but notexclu sive reference to bearing assemblies forthe armature shafts of electric motors.

The invention relates especiallyto bearing assemb lies including plain bearings. It isfoundthat, in use, the bearing may become overheated unless steps are taken to dissipate the heat generated and it is an object of the present invention to provide a bearing assembly with effective heat dissipation.

According to the present invention, a bearing assemblycomprises a bearing mounted in the bore of a mounting sleeve having a plurality of spaced, externat, radially-extending fins.

The fins may be of a reduced height over a part of theiraxial length ascomparedwiththefin heightover the remainderofthe axial length.

The junction betweenthe parts of reduced height and the remainder ofthefins is adapted to form a seating surfacefor an annular mounting member by which the mounting sleeve is mounted.

The mounting member is preferably of a resilient material.

The assembly mayfurthercomprise a member having an orifice, the member being contoured round the orifice in a manner such that there is provided a surfacefor locatingthe mounting member, the bearing assembly being located inthe orifice and being supported therein bythe mounting member.

The bearing may be a bearing sleeve which may be an interferencefit in the bore.

The invention also envisages an electric motor including an armature mounted upon an armature shaft, one end of which is rotatably supported in a bearing assembty embodying the invention as above stated.

The motor may be incorporated in a powertool which may be a hand-hetd power tool.

Byway of example only, embodiments of the invention and an electrictool including the embodi- mentswill now be described in greater detail with reference to the accompanying drawings of which :- Fig. I isasideviewofthetoolwith a housing half removed, Fig. 2 is a side view of a motor assembly, on a different scale, Fig. 3 is an explodedview, on a differentscale, ofthe motor assembly of Fig. 2, Fig. 4 is a plan view of a component of the motor assembly, Fig. 5isa sideviewofthecomponentof Fig. 4, Fig. 6 is a section on the line VI-VI of Fig. 4, Fig. 7 is a section on the line VH-V ! ! of Fig. 4, Fig. 8 is a plan view, on a different scate of part of the component of Fig. 4, Fig. 9 is a section on the line IX-tX of Fig. 8, Fig. 10 is an underneath view of the component of Fig. 4, Fig. 11 is a perspectiveviewfrom above and partly in exploded form of a brush ring and other components, Fig. 12 is a perspective view from below of the brush ring shown in Fig. 11, Fig. 13 is an explanatory diagram of an electrically conductive array, Fig. 14 is a plan view of a brush ring with some components removed, Fig. 16 is a vertical section of an endfitting and including some other components, Fig. 17 is a scrap view of a part of the end fitting, Fig. 18 is an end view of a bearing assembly, Fig. 19 is a vertical cross section of the bearing assembly mounted in a wall, Figs. 20, 21 and 22 are diagrammatic representations of various circuit configurations, Fig. 23 is an explanatory diagram of anotherform of brush ring and electrically-conductive array, Fig. 24 is a plan view of the otherform of brush ring with certain components mounted thereon, Fig. 25 is an underneath view of the brush ring of Fig.

24, Fig. 26 is a perspective viewfrom above of the brush ring of Fig. 24, Fig. 27 is a vertical section of a switch assembly, Fig. 28 is a perspectiveview ofthe switch assembly with a component removed, Fig. 29 is a plan view on an enlarged scale of part of the brush ring of Fig. 24, Fig. 30 isa plan view of the brush ring of Fig. 24 showing certain components only, Fig. 31 is an explanatory diagram of a switch operating member and switch assemblies, Figs. 32 and 33 are, respectively, plan view and circuit diagram of a first circuit configuration incorporating the brush ring of Fig. 24, Figs. 34 and 35 are, respectively, plan view and circuit diagram of a second circuit configuration incorporating the brush ring of Fig. 24, Figs. 36 and 37 are, respectively, plan view and circuit diagram of a third circuit configuration incorporating the brush ring of Fig. 24, Figs. 38 and 39 are, respectively, plan view and circuit diagram of a further circuit configuration incorporating the brush ring of Fig. 24, and, Figs. 40 and 41 are, respectively, plan view and circuit diagram of a fifth circuit configuration incorporating the brush ring of Fig. 24.

Theappliance shown in Fig. 1 isa hand-held power drill. The drill has a casing of two-part clam-shell form, the clam-shells being made of a suitable plastics material. The drawing shows one half only of the casing, the other half being removed to reveal some of the working parts ofthe drill. Inthe half 1 is shown a motor unit 2 whose output shaft drives, via reduction gearing 3, a chuck4 mounted upon the outputshaft 5 of the gearing 3.

The casing is of"pistol"form with a handle 6 which is shown as accommodating a switch mechanism indicated at7 andoperable by a trigger 8 for controlling the application of powerto the motor unit 2. The switch mechanism 7 is connected to a source of electric powervia a drop-lead 9 held in a conventional cable clamp or labyrinth indicated at 10. As will be made clearer below, the switch mechanism may, alternatively, be housed elsewhere.

The insidefaces ofthe clam-shell halves areformed with location surfaces to locate the motor unit 2 and the gearing 3 and hold them securely in position but those surfaces are not shown in Fig. 1.

The motor unit 2, shown by itself in Fig. 2 on a larger scale and in exploded form in Fig. 3 on a smaller scale, comprises a field stack 11 of the conventional lamin- atedform. Thefield stack 11 carriesfieldwindings, the projecting parts of which are shown at 12 in Fig. 3. The projecting parts of the field coils are supported by end fittings 13, 14ofan electrically-insulating material, for example a plastics material secured to the end faces of the field stack 11.

End fitting 13 is shown in more detail in Figs. 4-10. It comprises a base 15 of generally annularform from one face of which extend four pins 16 integral with the base 15 and arranged in two pairs in diametrically- opposed positions.

Between the pins of each pair are holes 17 by which the ring is secured tothe end ofthefield stack. From the otherface of the ring in positions corresponding approximatelywith those of the pins 16 are larger projectionsformed as sockets 18. The sockets are stepped internallyas at 19 as can be seen in Fig. 9.

Each socket also has an integral projecting tab 20.

When seen in plan as in Figs. 4 and 8, the sockets are of rectangularshape.

Located between the sockets 18 are supports 21 that extend inwardlyfrom the base 15 and have arcuately curved portions 22 spaced overtheir extremitiesfrom the base and that conform to the shape of the internal pole pieces on the field stack. Seen in side view as in Fig. 5, each supportis oftruncatedtriangularform and carries, at its upper end, afinger 23 that extends outwardlyfrom the support and is aligned with a partial gap 24 in the base 15.

The sockets 18 house metallicterminalsthatengage theterminal connectors referred to below and to which the ends ofthefield coils are joined.

The pins 16 are located in holes in the end face of the stackwhilstthe supports 21 retain the projecting ends 12ofthefield windings in the conventional manner.

The other end fitting 14 is identical with fitting 13 but does not havethe sockets 18.

Mountedforrotationinthefieldstaek11 isan armature 25 (Fig. 3) supported on an armature shaft 26 having a commutator 27 at one end and a motor cooling fan 28 atthe other. The cooling fan end of the shaft26isformedasa driving pinion 29 which meshes with input pinion 30 (Fig. 1) of the reduction gearing 3.

The ends of the armature shaft 26 are supported in bearings in housings mounted upon the ends of the field stack 11. The commutator end of the shaft 26 is mounted in a plain bearing 30forming part of a heat sink 31. The heat sink31 is located in an aperture 32 in the end wall of a commutator end housing 33 and held in that aperture by a mounting ring 34 of a resilient material, example rubber. Details ofthe end housing 33 andthe heatsink31 and its method of mounting will be given below.

The commutator end housing 33 is a body of electrically insulating material and of generallytubu- larform with an annular portion 35 sized internallyto fit overthe end fitting 13 and the adjacent end of the field stack as can be seen in Fig. 2. Parts of the sidewall of the housing 33 are cut away as at 36 to allow passage of cooling air. Two of the parts 36 in diametrically opposed positions have cut-away extensions 37 whose purpose will be described below. The housing 33 has an internal shoulder 38 against which seats a brush ring 39 when the motor unit is assembled.

The fan end of shaft 26 is supported in a plain bearing 40 supported in an end wall 41 of a fan end housing 42. The housing 42 has an annular portion 43 which seats orrthe other end of the field stack 11 over end fitting 14. Portion 43 has two axially extending limbs 44 of arcuate form seen in end view, to the end faces of which the end wall 41 is secured by means of sector-shaped bosses 45 which locate in slots 46 in the limbs 44 and screws 47 that pass through screw holes in the end wall and screw into the bosses 45. Afibre washer 48 is located between the fan 28 and the end face of the plain bearing 40.

The brush ring 39, further details of which are given below, supports carbon commutator brushes 49 and hasfourterminal connectors 50 extending at right anglesfrom one of its faces. Connectors 50 connect electricallywith the metallicterminals in the sockets 18 during assembly of the motor unit 2 as will be described below.

The brush ring 39 also has input connectors 51 extending at right anglesfrom its otherface. Connectors 51 projectthrough holes in the end wall ofthe housing 33 and enable electrical connection to be made to switch mechanism 7. The brush ring 39 also carries other components as will be made clear below.

The brush ring 39 is a composite structure of generally annularform as can be seen from Figs. 11 and 12. The ring 39 is ofan electrically-insulating material for example a plastics material incorporating an array of conductors that is encapsulated into the material during the moulding thereof.

The array 52 shown hatched in Fig. 13isformed from brass sheet, by stamping for example, and inclues an external'frame'53 which serves to supportthe array during the moulding of the plastics material. The array comprises the input connectors 51 that extend at rightanglestothe plane of the array but which are also shown, for convenience, in Fig. 13 as lying in that plane.

Plastics material is moulded round the array to encapsulatethegreaterpartthereof. Theterminal connectors 50 emerge from the edge of the ring 39 as shown in Figs. 11 and 12. Afterthe brush ring 39 has been moulded, theframe 53 is removed bytrimming off thereby leaving a basic circuit configuration that will be described below. Selected areas of the array are left exposed through the lower surfaces of the ring 39, such areas being indicated at 54. Further selected areas 55 of the array are also left exposed on both surfaces of the ring 39. Exposure of those surfaces is effected bythe use of appropriately positioned cores during the moulding ofthering 39.

Moulded integrallywith the ring 39 round the central, circular aperture 56 therein is an upstanding wali 57 gapped at diametricallyopposed positions 58.

The upper edge ofthe wall 57 has two fingers 59 with bevelled upper edges 60. The fingers 59 are also located at diametrically opposed positions.

As can be seen from Figs. 11 and 12, mou [ding material extends part-way up the input connectors 51 as indicated at 61 to form an electrically protective sheath round the connectors. That part of the sheath adjacentthe surface of the brush ring is shaped to form spaced seating surfaces 62.

Also moulded integrallywith the ring 39 are spaced walls 63 that are aligned in a radial direction with the edges of the gaps 58 in the wall 57, and protective tubular extensions 64.

Thewalls 63 extend, attheir outer edges, to the periphery of the ring 39 and border recessed portions 65 of the edge of the brush ring that allowthe connectors 50 to be turned from the plane of the array within the periphery of the ring. That edge also has other recesses 66 whose function is described below.

The edge of the ring 39 is also cored out as at 67 on its upper surface (as seen in Fig. 12) to expose other areas of the array.

The inner edge of the brush ring 39 is formed during moulding at areas 68 to expose other portions of the array and at other areas 69 intermediate areas 68.

The wall 57 forms a bearing surface for a switch body 70 that is employed in certain embodiments of the invention as will be described below and which is held in place bythe fingers 60. The switch body 70 shown in Fig. 11 has a central tubular portion 71 whose curved wall is cut-away as at72 over circum- ferential distances somewhat greaterthan that of the gaps 58. The upper (as seen in Fig. 11) edge of the curved wall is also cut away as indicated at73.

Extending radially from the portion 71 and at diametrically opposed positions are bosses 74 each with a transverse passage 75 closed at its inner end.

Each passage accommodates a metal ball 76 urged outwardlyfrom the passage by means of a helical spring 77 housed in the passage.

The metal balls 76 constitute moving switch contacts andthey co-operatewith exposed parts of the array, those exposed parts constituting the fixed contacts ofthe switch. Some ofthe fixed contacts are visible in Fig. 11 at 78. There are two sets of such fixed contacts disposed in diametrically opposed positions.

One set co-operates with one ofthe metal balls 76 and the otherset co-operates with the other ofthe metal balls.

Theswitch body70 is rotatable roundthewall 57 within limits imposed bythe brush boxesthat extend through the gaps 58 in thewall 57. However, the actual movement of the body 70 is less and is indicated in Fig.

14, the two extreme positions of the body 70 being shown.

Movement ofthe switch body70 is effected bythe uservia a linkage connecting the bodyto an actuator which may be a member accessible through an aperture in the casing ofthetool containing the motor, for examplethe drill shown in Fig. 1. Alternatively, the body 70 may be linked to the trigger 8 which, in this case, will be a multi-position trigger.

The brush ring 39 supportstwo brush boxes 79. The brush boxes 79 are open-ended sheet brass pressings with axial tongues 80 which are crimped over the internal and external edges of the brush ring so making electrical connection with the exposed portions of the array in areas 67 and 68. As can be seen from Fig. 11, the walls 63 lie between the brush boxes 79 and the connectors 50 to provide a degree of electrical insulation and alsoto increasethetracking distance between those components.

In addition to providing electrical connection forthe brush boxes 79 to the array, the tongues 80 also securethe boxes physicallytothe brush ring 39.

Each brush box 79 has a slot81 in its upper (as seen in Fig. 11) surface. The slots 81 permit engagement with the outer ends of brushes 49 of end portions 82 of brush springs. The brush springs include helical portions 83 mounted upon the sheathed parts of the connectors 51 and resting upon the seating surfaces 62. The other ends 84 of the brush springs are hooked to engage and be retained by lugs 85 pressed out of the side walls of the brush boxes. The sheaths 61 insulatethe brush springs electricallyfrom the connectors 51.

The slots 81 are of a length sufficientto allowthe spring end portions 82 to retain contact with the brushes and to keep the latter in engagementwith the commutator despite brush wear.

Figs. 14-17 show in more detail the way in which the brush ring 31 is accommodated within the commutator end housing 25, some components being omitted forthe sake of clarity.

Figs. 15 and 16 showthe contourofthe end wall 86 of the commutator end housing and the aperture 32 in which the heat sink 31 and bearing 30 are located. The aperture 32 isformed in an upstanding central boss 87 of the end wall 86, the inner side of the boss accommodating a part of the heat sink. Fig. 17 shows one of the holes through which extend the input connectors 51, the hole being indicated by reference numeral 88. The sheath 61 on the connector assists in the location of the connector centrally in the hole 88.

Figs. 15 and 16 also showthe encapsulation of the array in the plastics material of which the brush ring is formed, and the manner in which the tongues 80 of the brush boxes 79 make electrical contactwiththe array after having been crimped overthe respective exposed partsthereof.

Fig. 19 which is a scrap section through part of the end wall 86 shows form of and the manner in which the heat sink 31 is secured in the aperture 32.

The heatsink31 is a lightalloycasting of generally tubularform with an axial bore 31 a and spaced, radially extending fins 31 b along its external surface.

As can be seen from Fig. 19, the depth ofthefins 31 b is greater at one end of the heat sink, the junction betweenthepartsofgreaterandsmallerdepth being rounded as at 31 eto form part of a location for an'0' ring 31 c.

The internal contourof that part of the boss 87 surrounding aperture32 provides a rounded seat31 d which forms the other part of a location forthe'O'ring 31 c.

Located in the bore 31 a is the plain bearing 30 which is an interference fit in the bore.

The spaced fins allow the circulation of air between them, such circulation being assisted, when the motor is in use bythe action of the fan 28.

The array 53 provides a network of conductors that may be modified to provide different electrical circuits each suitable for a particular set of controls with which the motor unit isto be provided.

Fig. 20 shows, shaded, the basic circuit configuration ofthe conductor network, the field coils 89 being indicated diagrammatically as joined to the connec- tors 50. By removing part 90 of the array, a simple series connected motor circuit is provided from the upper inputterminal 51 then via the left-hand connec tor 50 to the left-hand field coil 89 andthen via the lower brush 49, commutator 27 to the upper brush 49 and thencethrough the right-hand field coil 89 to the lower inputterminal 51. Part 90 of the network is accessiblefor removal because it is one of the exposed parts 55 referred to above.

In the simple case just described, the switch body 70 is not present and the switch contacts 78 are not part of the operative circuit.

Ifthe motorcircuit justdescribed isto includetwo RF chokes, parts 91 and 92 of the network are removed, such parts being left exposed during the moulding of the brush ring and are designated 55 above. Part90 is also removed as before. Chokes 93 are connected in circuit by soldering them between the appropriate exposed parts 55 of the array. In Fig.

20, those parts are referenced 94, 95 for one choke and 96, 97 forthe other choke. The choke leads are protected, atleastpartially, bythetubularextensions 64 of the brush ring 39 through which those leads pass. One of the chokes 93 is shown in Fig. 11 in its final position.

A circuit including the chokes iscompletedfrom upper input 51 through left-handfield coil 89 to choke terminal 94, choke93, choketerminai 95to lower brush 49, commutator 27, upper brush 49, choke terminal 97, choke 93, other choke terminal 96, right-handfield coil 89 and backtothe lowerinput terminal 51. Again, in this case, the switch body 70 is not presentand the switch contacts 78 are not partof the operative circuit.

Fig. 21 is a view of the conductor array with speed control providing full speed and reduced speed.

Speed reduction is provided by including a half-wave rectifier W1 in the circuit and using the switch body 78 to switch the rectifierW1 in and out of circuit in accordance with the motor speed required.

As before, part 90 of the array is removed as are additional parts 88 and 105. This provides a circuit from upperinner51, through left-handfield coil 89to fixed contact 102 of the switch, moving ball contact 76, to second fixed contact 101, lower brush 49, commutator 27, upper brush 49, fixed contact 100, moving ball contact76, tosecondfixedcontact99, right-handfield winding 89 and lower input 51.

The circuit just traced givesfull speed. Reduced speed is obtained by rotating switch body 70 to switch intherectifierW1therebycompletingacircuitfrom upper input51, left-hand field coil 89, fixed contact 102, movable ball contact 76to fixed contact 101, lower brush 49, commutator 27, upper brush 49, fixed contact 100, rectifier W1, movable ball contact 76, fixed contact 103, fixed contact 99, right-hand field coil 89 and lower input 51.

Chokes can befittedtothedual speed circuit just described by removing parts 91 and 92 as before and fitting the chokes in the positions described above.

Reversal of the direction of rotation of the motor can also be obtained. The rectifier W1 is maintained to limitthe motor speed in the reverse direction. The conductor array is shown in Fig. 22.

As before, parts 88, 90 of the array are removed togetherwith part 105.

Theforward direction of the motor is achieved via a circuitfrom upperinput51, left-handfieldcoil 89, fixed contact 102, movable ball contact76, fixed contact 101, lower brush 49, commutator27, upper brush 49, fixed contact 100, fixed contact 99, right-hand field coil 89 to lower input 51.

To reverse the direction of rotation, switch body 70 is rotated to a position providing a reverse direction circuit as follows :- upper input 51, left-hand field coil 89, fixed contact 102, movable ball contact76, fixed contact 104, upper brush 49, commutator 27, lower brush 49, rectifier W1, contact 103, movable ball contact76, fixed contact 99, right-hand field coil 89 to lower input51.

Again, if required, chokes can be added, in the mannerdescribed above, to the speed reversal circuit just described.

Whilstthe motor unit 2 can be assembled manually, it is preferred to assemble the components on an automated assembly line. However, in both cases, the assembly process is basicallythe same.

Thefield stack 11 is made and assembled in a conventional manner as isthe armature 25.

A brush ring 39, complete exceptfor brushes, is then offered up to the end ring 13 and connectors 50 firmly engaged in sockets 18.

The commutator end bearing is puttogether by pressing the bearing 30 into the heat sink 31.

Thefan end bearing is puttogether in a generally similarfashion by pressing bearing 40 into the aperture in the end wall 41.

The resilient ring 34 is mounted in a recess (described below) in the end wall of housing 35 after which the heat sink assembly comprising heat sink 31 and bearing 30 is pressed into the aperture inthe end wall.

Housing 35 isthen located overthe brush ring 39, the end fitting 13 and the adjacent end ofthefieid stack 11. The periphery of the brush ring seats on the internal shoulder 38 referred to above. Housing 42 is next located overthe end fitting 14 and the adjacent end ofthefield stack.

Long field screws 104 are passed through axial holes in housing 43 and in thefield stack and screwed into blocks 105to hold the end housings33 and 43 on tothefired stack, the brush ring 39 being sandwiched between endfitting 13 and the internal shoulder 38.

The blocks 105 are located in the extensions 37 ofthe cut-aways 36 in end housing 33.

The next stage is to fitwashers 48 and 106 and a spring washer 107 to the respective ends of the shaft 26 as shown in Fig. 3 and enterthe armature 25 through the open end of housing 43 until the commutator end of the shaft engages in bearing 30.

Atthis stage, a measurement is taken of the distance from the outer end face of one ofthe limbs 44to the fan end housing location as identified by the adjacent end face of the stack 11. If the motor unit is being assembled manually, furtherwashers are addedto thefan end of the shaft 26 to bring the measured distance up to a specified value.

In the case of automated assembly, the location of the bearing sleeve 40 in the end plate 41 is adjusted to provides distance of the specified value and isthen locked in position.

In those ways, the degree of axial movement of the armature is confined to within an acceptable known value.

End wall 41 is nowsecured to the limbs 44 of housing 43 using thetwo screw bosses 45which locate in the recesses 46 in the limbs 44, th e wa 11 th en being secured in place by screws 47 which screw into the bosses 45.

Brushes 49 are now located in brush boxes 79 on the brush ring 39 and held in place bythe brush springs.

Atthis stage, the motor unit 2 can be tested both electrically and mechanically and iffound to be satisfactory isthen readyfor inclusion in an appliance, for example, the hand drill on Fig. 1.

Figs. 23-30 show anotherform of brush ring.

Fig. 23 shows an array 120 with its external supporting frame 121 that serves to supportthe array during the moulding of the brush ring 122 which is of a plastics material as before and is shown in Fig. 23 with the array 120 superimposed on it. The array 120 is generally similarto that described above having a terminal connectors 123that connecttofield windings via terminal connectors in the commutator end ring as before. ltwill beunderstoodthattheframeconnection shown in Fig. 23 to theterminal connectors 123 will be trimmed offafterthe ring has been moulded.

The position of the power inputterminals 124 is differentfrom those of inputterminals 51 described above. The positions of terminals 124 are spaced furtherfrom the terminal connectors 123 than is the case in the construction described above, the extra spacing accommodating further connectors 125 whose function will be described below.

To enablethe physical form of the input connectors 124 and the further connectors 125 to be seen clearly, these connectors are shown additionally in the plane of the array 120.

During moulding, the ring 122 isformed with "windows"that expose certain parts of the array. The windows which expose the parts shown cross hatched within the windowthrough both the upper and lower faces of the ring are indicated at 126 in Fig. 23.

Additional windows 127 areformed on the ring but these do not expose parts of the array and their functionwitl bedescribed below. In addition, further parts of the array indicated at 128 are left exposed on both faces of the ring 122. The upper surface of the ring 122isalsoformedtoexposethosepartsofthe array shown cross hatched in Fig. 23. The undersur faceofthe ring is also formed to expose other parts of the array also shown cross hatched as indicated at 129 in Fig. 25. Those parts include areas 130 atthe inner and outer peripheries of the ring 122forthe connection of brush boxes in a manner similar to that described above.

During the moulding of the ring 122, integral supports 131 (Fig. 26) are provided forthe brush spring 132, those supports having bases 133 on which the springs 132 rest. Sheathing 134 is alsoformed during moulding round the greater part of the terminals 124, 125 and the brush springs 132 could be mounted upon thatsheathing if desired, instead of on the supports 131 which could then be dispensed with.

Alsoformed integrallywith the ring 122 during the mouldingthereof isthe gappedwall 135, a seriesof partitions 136thatform pockets extending aroundthe windows 126 and 127, long tubularcolumns 137 and walls 138 between thefield connectors 123 and brush boxes 139, and shorttubular extensions 140.

The brush boxes 139 are secured physicallyto the brush ring 122 and electricallyto the exposed portions by crimping overthe exposed parts 130 of the array tongues 139a that are integ ral with the boxes.

Brushes, one of which is shown at 141, are urged into contact with the armature commutator by end 142 of the brush springs, the boxes 139 being slotted as at 143 to allow movement of the ends 142 along part of the length of the box as the brushes wear.

The pockets 144-149 formed by the partitions 136 each accommodate switch contact assemblies shown in section in Fig. 27 and in perspective in Fig. 28.

Each switch contact assembly comprises a cylin- drical body 150 of a plastics material with an internal bore 151 thatterminates at an internal transverse wall 152. The upperend ofthe body 150 has a peripheral wall 153 gapped at 90 intervals as indicated at 154.

Theupperfaceofthewall 152issemi-sphericalas indicated at 155 in Fig. 27, the curved contour extending upthe inside of the wall 153.

The side walls of the body 150 are slotted as at 156, 157 in diametrically opposed positions, the lower slots 157 lying on a diameterthat is at right anglestothat on which the upper slots 1561ie. As can be seen clearly in Fig. 27, thetop and bottom length of the right-hand (as seen in Fig. 27) slot 156 is somewhat greaterthan that of the left-hand slot.

Located in the upper slots 156 and guided for up and down movementthereby is a contact bar 158 whose ends projectfrom the body 150 and have downwardly extending rounded contacts 159. The contact bar is of copper or some other material of low electrical resistivity. The upperface ofthe bar 158 has a central protuberance 160 thatforms a lowerseating for a helical spring 161 that locates between the seat 160 and the transverse wall 152, thus biassing the bar 158 into the position shown in Figs. 27 and 28 in which the bar is in contact with the lower edges of the slots 156.

The spring 161 isenteredthroughthelargerright- hand slot ofthe slots 156 afterthe bar 158 has been positioned in the slots.

Located in the lower slots 157 is pin 162 of a plastics material that also projects at both ends from the body 150. A second helical spring 163 of frusto conical form is located between the bar 158 andthe pin 162 biassing the latter into the position shown in Figs. 27 and 28 in which the pin is in contactwith the lower edges of the slots 157.

The space bounded by the wall 153 accommodates partof a roller 164 supported upon stub axles 165that locate in diametrically opposed slots 154.

The switch assemblies are positioned in the pockets bythe lower ends of the bodies 150 that locate in the windows 126, 127 in the brush ring, the pins 162 resting upontheupperfacthereof. Inthecaseof windows 126, the exposed parts of the array that bridge thewindows are punched out leaving an unobstructedwindowwith exposed portions of the arrayin diametrical opposed positionswith respectto thewindow. Examples ofthe remaining exposed portions are referenced 166 (Fig. 26 and 27).

Fig. 29 shows three of the pockets 144, 145 and 146 with spring assemblies locatedtherein and itwill be observed that in the case ofthe spring assemblies in pockets 144 and 145, the axles 165 of the rollers 164 are in the vertical same plane as that of the contact bar 158 but in the other spring assembly in pocket 146, the axles 1651ie in a vertical plane that is at rightangles to that containing the associated contact bar 158. The provision of four slots 154 in the body 150 of the switch assembly enables the appropriate choice of two to be made in dependence upon the required orientation of the roller.

The contact bars 158 of the various switch assemblies in the pockets 144, 145, 147 and 148 co-operate with exposed parts 166 of the array to carry out various switching operations connected with the operation of the motor. The assemblies in pockets 146 and 149 provide power supplyswitching aswill be described below. A choice can be made during manufacture of the switching facilities that are to be provided and the array 122 will be modified accordingly and the necessary switch assemblies provided.

When fitted, the assemblies are actuated by a cam plate 167 (Fig. 30) of annularform that is rotatably mounted overthe wall 135 and rest upon the upper ends of the partitions 136. The plate 167 has a radially extending finger 168 bywhich the plate can be rotated into one or other of its various control positions. The fingerextends outwardly beyond the outer periphery ofthe brush ring 122. Thefinger 168 is linked to an actuating member accessible to a user. The member may be accessible through an aperture in the casing of thetoolforexamplethedrill shown in Fig. 1.

Alternatively, the finger 168 may be linked to the tool triggerwhich, in this case will be a multi-position trigger.

The underneath (as viewed in Fig. 30) face of the cam plate 167 isformed with a circular cam track a part of which is shown at 169 in Fig. 31 and which is configured to provide actuation of the switch assemblies as required bythe switching facilities to be provided. Thetrack 169 has recessed portions 170 and when one ofthem is alignedwith a switching assembly, the lowerspring 163 allowsthe assembly to rise, the left-hand assembly seen in Fig. 31 being in that raised position. The cam plate 167 also has raised portions 171 which when aligned with the switch assembly contactthe roller 164 and push down the assembly compressing both springs 161 and 163 and bring the rounded contacts 159 into electrical contact with the exposed parts 166 of the array. The use of the twosprings 161 and 163allowsformanufacturing tolerances and avoids overstressing any components of the switch assembly.

The array 120 provides a network of conductors that may be modified to provide different electrical circuits each suitable for a particular set of controls with which the motor unit is to be provided. Depending upon the particularset, a combination of switching assemblies isfitted although in a particularset no assembliesare fitted.

Byway of example, particular sets of controls will now be described with reference to Figs. 32-41.

Fig. 32 shows the configuration of the array 120 for a basic motor circuit with a triggercontrolled ON-OFF powerswitch inthe handleofthetool containingthe motor unit. There is no modification of the array and an electrical circuit is provided from the upper (Fig. 33) power inputterminals 124to connector 123 and thenceto the left-hand field coil 172 and via connector 123 and the appropriate part of the array 120 to the lower brush 141, through the commutatortothe upper brush 141. From the upper brush the appropriate parts of the array 122 connectwith a connector 123 to the right-hand field winding and thence backto the lower inputterminai 124. No switch assemblies are used and the motor unit has a single speed only.

Fig. 34 shows the configuration of the array 120 for a motor unit in which a single pole power supply switch is mounted upon the brush ring 122 and replaces the trigger operated handle switch referred to in the immediately preceding example. To permit connection of the switch, that part 173 of the array 120 lying acrossthe lower right-hand (Figs. 23 and 34) window 126 is removed and a switch assembly is located in the associated pocket 146. The contact bar 158 of the switch assembly is shown schematically in Fig. 35 and it controlsthe connection ofthe lower input connector 124to the adjacentterminal 123. A cam plate 167 is seated overthe wall 135 and secured in place against the upper surfaces of the partitions 136 by the end moulding within which the brush ring is located.

The circuit of the example shown in Figs. 34 and 35 is identical with that described above with reference to Figs. 32 and 33 exceptthatto energisethe motorthe user has to rotate the cam ring 167 using the finger 168 from position POS1 to position POS2 to depress the switch assemblyto bring the contact barthereof into electrical contactwith the related exposed parts 166 of the array. Rotation of the cam ring 167 in the opposite direction switchesthe motor unit off.

If desired, a double pole power switch may be provided by punching out part 174 of the array (Figs.

23 and 34) and fitting a switch assembly in the associated pocket.

The array 120 can be adapted to provide a degree of control of the speed of the motor by connecting a diode in circuit and by including a switch assemblyto short outthe diode to give full motor speed.

Fig. 36 shows an array 120 adapted to receive a diode 175that is connected across parts of the array connection of the latter being effected to parts 176 that are exposed on the underneath surface of the brush ring 122. The diode leads are protected by the short tubular extensions 140 referred to above.

Short circuiting of the diode 175, when required, is effected bythe inclusion of a switching assernblyin the pocket 177 (Fig. 36), the contact bar of the assembly being shown at 178 (Fig. 37).

The example shown in Figs. 36 and 37 also includes asinglepoleswitch controlling powerinputtothe motor unit. This is identical with the single pole switch described above with reference to Figs. 34 and 35.

Rotation of cam ring 167from position POS1 to position POS2 energises the motor unit at reduced speed, the diode 175then being in circuit. Movement of cam ring 67to posítiorrPOS3shortcircuitsthe diode and this aiiows the motor to run atfull speed Afurther setof controls isshown in Figs. 38 and 39.

Control of power supply is effected by a trigger controlled switch on the handle ofthetool containing the motor unit so that no power control switches are mounted upon the brush ring. The control includes a reversing ability and a speed control unit shown in Fig.

39 by block 179. The unit is connected in powersupply leads to terminals 124 and is housed in the casing of thetool. The unit is usercontrolled and enablesone or other of several different motor speeds to be selected.

The circuit of Fig. 39 also includes suppression chokes 180, 181 that are connected to the array 120 at points 182, 183 (Fig. 25) using parts 129 of the array exposed on the undersurface of the brush ring. To bring the chokes into circuit, it is also necessary to remove parts 184 (Fig. 25) of the array that are exposed through windows 128.

Reversa of the direction of rotation of the motor is provided by switching assemblies located in pockets 185, 186, 187 and 188 (Fig. 38) and by adding a connecting iink 189 across connecting points 190 (Figs. 23 and 24) of the array. Such connecting points are accessible through the upperface of the brush ring and shorttubular shields similarto shields 140 but not visible in Fig. 26.

As before, position POS2 of the cam ring 167 is the "OFF"position of the motor unit. Movement of the cam ring 167 to position POS1 applies powerto the unit and allows rotation of the motor in a forward direction via a circuitfrom the speed control unit 179 to left-hand upperconnector 123, left-hand field coil 172, lower left connector 123, choke 180, closed switch assembly in pocket 186, lower brush 141, commutator, upper brush 141, closed switch assembly in pocket 187, choke 181, upper right connector 123, right-hand field coil 172, backto the speed control unit 179.

Movement of the cam ring 167 to position POS3 reverses the direction of rotation of the motor by opening the switch assembly in pocket 186, closing that in pocket 185, opening that in pocket 187 and closing that in pocket 188.

Those changes provide a circuit from the speed control unittothe upper left connector 123, left-hand field coil 172, closed switch assembly in pocket 185, upper brush 141, commutator, lower brush 141, closed switch assembly in pocket 188, choke 181, right-hand field coil 172 and backto the speed control unit.

Afurthervariation on the possible motor unit control is shown in Figs. 40and41. Thevariation includes reversat of rotation, chokes 180, 181, diode 191 effective iMhe reverse direction of rotation of the motor ans a double pole power input switch. The rotational speed of the motor in the reverse direction of rotation is restricted by the diode which is connected across points 190 (Fig. 23).

In the forward direction of the motor, the control circuit is energised when the cam ring 167 is moved from its"OFF"position-POS2-to position 1. The circuit can be traced from upper inputterminal 124, closed input switch 158, upperleftconnector 123, left-hand field coil 172, lower left-hand connector 123, choke 180, closed switch assembly in pocket 186, lower brush 141, commutator, upper brush 141, closed switch assembly in pocket 187, choke 181, right-hand field coil 172 and via closed input switch 158to right-hand inputterminal 124.

Movement of the cam ring to position POS3, closes the switch assembly in pocket 185and opensthatin pocket 186, closes switch assembly in pocket 188 and opens that in pocket 187. That action brings diode 191 into circuit and reverses the direction of rotation of the motorunit.

The circuit can betraced from upper inputterminal 124, closed inputswitch 158, left-hand field coil 172, lower left-hand connector 123, choke 180, closed switch assembly in pocket 185, upper brush 141, commutator, lower brush 141, diode 191, closed switch assembly in pocket 187, choke 181, right-hand field coil 172, lower right-hand connector 123, closed input switch 158 and right-hand inputterminal 124.

Other combinations of the various circuit components are possible as will be evident to those skilled in the art.

Although it is assumed in the description of the brush ring shown in Fig. 26that power connections are made to inputterminal 24 by means of space terminals, the terminals have apertures 195to enable screw type terminations to be fixed to the connectors.

Claims (11)

1. A bearing assemblyfor a shaft comprising a bearing mounted in the bore of a mounting sleeve having a plurality of spaced, external, radially-extend- ing fins.

2. An assemblyasclaimed in claim 1 in which the fins are of a reduced heightover part oftheiraxial length as compared with the fin height over the remainder of the axial length.

3. An assembly as claimed in claim 2 in which the junction between the parts of reduced height and the remainder ofthefins is adapted to form a seating surface for an annular mounting member bywhich the mounting sleeve is mounted.

4. An assembly as claimed in claim 3 in which the mounting member is of a resilient material.

5. An assembly as claimed in claim 4 and further comprising a member having an orifice, the member being contoured round the orifice in a manner such thatthere is provided a surface for locating the mounting member, the bearing assembly being located in the orifice and being supported therein by the mounting member.

6. An assembly as claimed in any one of the preceding claims in which the bearing is a bearing sleeve.

7. An assembly as claimed in claim 6 in which the bearing sleeve is an interference fit in the bore.

8. An assembly as claimed in claim 1 substantially as herein described with reference to and as illustrated by Figs. 18 and 19 of the accompanying drawings.

9. An electric motor assembly including an armature mounted upon an armature shaft, one end of which is rotatablysupported ina bearing assembly as claimed in anyone of the preceding claims.

10. An electric motor assembly as claimed in claim 9 in which the bearing assembly is mounted in an end housing ofthe motorassembly.

11. An electric powertool including an electric motor assembly as claimed in claim 9 or 10.