Alternator for vehicle

In a stator of an alternator for a vehicle, a stator winding has a plurality of conductor segments having ends extending in opposite directions and a plurality of ball-shaped connected portion between the conductor segments forming continuously connected coils. Each of the ball-shaped connected portions is composed of one end of one conductor segment and the other end of another conductor segment.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a stator of a vehicle alternator.
 2. Description of the Related Art
 An alternator disclosed in JP-A-3-235644 has a pair of cooling fans fixed
 to opposite sides of a rotor. The pair of inner cooling fans take cooling
 air into frames and discharge the cooling air from windows formed in the
 circumferential surface of the frames, thereby cooling the stator winding.
 U.S. Pat. No. 1,822,261 and WO92/06527 disclose a plurality of U-shaped
 conductor segments welded to form a stator winding. However, sharp edges
 may be formed on the welded portions. Such edges may cause concentration
 of mechanical stress and electrochemical stress, thereby resulting in
 mechanical breakdown or electrochemical corrosion. Moreover, dust or
 foreign particles introduced with the cooling air may accumulate on the
 edges if such a stator winding is cooled by such a inner cooling fans. If
 salt water is introduced by the inner cooling fans, insulation members
 disposed in the stator may be deteriorated.
 SUMMARY OF THE INVENTION
 The present invention is to prevent such mechanical and electrochemical
 troubles on the connected portion of conductor segments forming a stator
 winding.
 In a stator of an alternator for a vehicle according to a main aspect of
 the invention, the stator winding is composed of a plurality of conductor
 segments having end portions extending in opposite direction to each other
 and a plurality of ball-shaped connected portions between the conductor
 segments to form continuously connected coils. Each of the ball-shaped
 connected portions includes one end of one conductor segment and the other
 end of another conductor segment.
 Preferably, the ball-shaped connected portions are disposed at the same end
 of said stator core. Each of the conductor segments can have a U-shaped
 portion.
 The conductor segments are preferably welded by a non-contact type welder,
 such as a tungsten inert gas (TIG) welder, to form the connected portions
 into a ball shape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 First Embodiment
 A stator of a vehicle alternator according to a first embodiment of the
 invention is described with reference to FIGS. 1-6.
 In FIG. 1, vehicle alternator 1 is composed of stator 2, rotor 3, a pair of
 frames 4, rectifier 5 and others.
 Stator 2 is composed of stator core 32, a plurality of conductor segments
 33 forming a stator winding and insulator 34 disposed between stator core
 32 and the conductor segments 33. Stator core 32 is a laminate of
 cylindrical thin steel sheets which has a plurality of slots in the inner
 periphery thereof. Conductor segments 33 extend from stator core 32 to
 form coil ends 31.
 Rotor 3 is composed of cylindrical field coil 8, a pair of pole cores 7
 respectively having six claw poles which enclose field coil therebetween
 and shaft 6 press-fitted to the pair of cores 7. Rotor 3 has a mixed flow
 type cooling fan 11 at the front end thereof to supply cooling air from
 front portions of the rotor in the axial and radial directions and a
 centrifugal type cooling fan 12 at the rear end thereof to supply cooling
 air from rear portions of the rotor in the radial direction.
 The pair of frames 4 accommodates and supports stator 2 and rotor 3 so that
 rotor 3 can rotate about shaft 6 and stator core 2 can be disposed around
 circumference of rotor 3 at a certain air gap. The pair of frames 4 has
 air-discharge windows 42 at the portions thereof opposite to coil ends 31
 of stator 2 and air-intake windows 41 at the axially opposite surfaces
 thereof.
 Vehicle alternator 1 is driven to rotate by an engine (not shown) via
 pulley 20 and a belt. When field coil 8 is supplied with exciting current,
 the claw poles of the pair of pole cores 7 are excited to generate
 three-phase ac voltage in the stator winding, and dc power is supplied
 from output terminals of rectifier 5.
 As shown in FIG. 2, each of the U-shaped copper conductor segments 33 has
 U-turn portion 33c, inner-portion 33a to be disposed in one of slots 35 at
 a circumference inside U-turn portion 33c and outer-portion 33b to be
 disposed in another of slots 35 at a circumference outside U-turn portion
 33c. Each of inner-portion 33a and outer-portion 33b has a straight
 portion to be disposed in one of slots 35 and a portion to extend outward
 from the one of slots 35.
 When the stator winding is formed, two conductor segments 33 are inserted
 in every one of slots 35 and each end portion 33d is connected with a
 different end portion 33d extending from a different one of slots 35. As
 shown in FIG. 3, both inner-portion 33a and outer-portion 33b have a
 rectangular cross-section with the radial sides being longer than the
 circumferential sides. Because conductor segments 33 are not coated with
 insulating material, a S-shaped insulator 34 is disposed in each of slots
 35 to insulate two conductor segments from each other.
 As shown in FIG. 4, U-turn portions 33c are disposed at the same end of
 stator core 32. Inclined portions 33e extending left are formed from
 outer-portion 33b , and inclined portions 33e extending right are formed
 from inner-portion 33a to form uniform coil ends 31. Each of connected
 portions 33f is formed to join another as shown in FIG. 5A.
 Joining end portions 33d are welded together by a contactless type welder
 such as a tungsten inert-gas welder (hereinafter referred to as the TIG
 welder) so that only limited area of end portions can be melted to form
 ball-shaped or raindrop-shaped connected portions 33f. The TIG welder
 discharges arc current between a tungsten electrode and a base metal
 member in an inert gas to melt the base metal member and a filler metal
 member for welding. The TIG welder can control quantity of heat and
 quantity of filler material separately.
 End portions 33d of neighboring conductor segments 33 are put side by side,
 and a nozzle having a tungsten electrode is brought near the end portions
 33d to be welded by the TIG welder.
 Because conductor segments 33 made of copper are highly heat conductive,
 each of connected portions 33f is melted wide enough to form a
 raindrop-shaped ball without any edge due to surface tension as shown in
 FIG. 5B. Each of connected portions 33f becomes larger than conductor
 segment 33 both in thickness (T&gt;t) and in width (W&gt;2w). Thus, sufficient
 mechanical strength and electrical connection can be provided at the
 connected portions 33f. The edge-less ball-shaped portions are free from
 concentration of stresses and corrosion. The ball-shaped surface of the
 connected portion 33f is coated evenly with resinous film 33g for
 protection and insulation as shown in FIG. 5C.
 The stator winding is formed as follows. U-shaped conductor segments 33 are
 inserted into respective slots 35 of stator 2 so that U-turn portions 33c
 are disposed on the same axial end of stator core 32, so that
 outer-portions 33b are disposed at the inner portion of slots 35 (or an
 outer circumference of stator core 32), and inner-portion 33a are disposed
 in the outlet portion of slots 35 (or an inner circumference of stator
 core 32) as shown in FIG. 3.
 Each of conductor segments 33 is manufactured as follows. A copper plate is
 bent and press-formed into a U-shape so that opposite sides of
 outer-portion 33b and inner-portion 33a are inserted in one of slots 35 to
 be in contact with the parallel side walls of one of slots 33 via
 insulator 34.
 As shown in FIG. 6, each of two end portions 33d of one of conductor
 segments 33 is bent in the circumferential direction opposite to each
 other so that outer-portion 33b of the one of conductor segments 33 can be
 connected to inner-portion 33a of another of conductor segments extending
 from different one of slots 35 and inner-portion 33a of the former can be
 connected to outer-portion 33b of another of conductor segments 33
 extending from different one of slots 35 at end portions 33d , thereby
 forming a ring of connected portions 33f, at a certain height from stator
 core 32. Then, connected portions 33f is dipped in a tank of liquid
 insulation material, and taken out from the tank to form uniform
 insulation film on connected portions 33f.
 Because all end portions 33d are disposed on the same end of stator core
 32, the connection can be carried out by a TIG welder without turning the
 stator core 32. Because all conductor segments 33 are almost the same in
 shape and connected portions 33f are located at the same height, the
 dipping process for the insulation of all connected portions 33f can be
 carried out at the same time. Thus, the insulation process can be made
 simple, and production cost can be reduced.
 Second Embodiment
 The number of conductor members per slot can be increased to more than two.
 As shown in FIG. 7, a stator according to a second embodiment of the
 invention has four conductor segments 133 aligned in the radial direction
 in one of slot 135. Conductor segments 133 have insulation coating
 thereon, and a insulator 134 is disposed between conductor segments 133
 and inner wall of slot 135. The connected portions are shown in FIG. 8.
 Four conductor segments 133 in one of slots 135 extends alternately in the
 opposite circumferential directions. That is, the outermost segments
 extend clockwise, and the innermost segments extend counter-clockwise, as
 shown in FIG. 8. End portions 133d of conductor segments 133 extending
 from one of slots 135 are respectively connected to end portions 133d
 extending from different one of slots 135 spaced apart at a certain pitch
 therefrom. In other words, the innermost conductor segments 133 are
 connected respectively to the second inner conductor segments 133, and
 third inner conductor segments 133 are connected respectively to the
 outermost conductor segments 133. Accordingly, a plurality of connected
 portions 133f are formed into two rings so that each of connected portions
 133f is spaced apart from another in both radial and circumferential
 directions. All the connected portions 133f are welded by a TIG welder to
 have edgeless raindrop shape in the manner substantially the same as the
 stator according to the first embodiment.
 The above structure is effective to provide a smaller-sized vehicle
 alternator having the same number of slots 35, the distance between the
 connected portions is closer.
 Third Embodiment
 Conductor segments 33 illustrated in FIG. 2 can be separated at the middle
 of U-turn portion, as shown in FIG. 9. Such conductor segments 233 can be
 used to a stator according to a third embodiment of the invention. In FIG.
 9, conductor segment 233 is composed of straight inner portion 233h and
 outer portions 233i extending axially outward from opposite ends of inner
 portion 233h. Outer portions 233i incline at a certain angle to the axial
 direction so that end portions 233d extending from one of slots can be
 welded to end portions 233d extending from another slot to form a stator
 winding. Connected portions 233f are formed at both ends of the stator
 core and cooled by the pair of cooling fans 11, 12 (FIG. 1). The connected
 portions 233f are also formed into an edgeless raindrop shape as described
 before.
 Fourth Embodiment
 Each connected portion 33f shown in FIG. 5B can be substituted by connected
 portion 333f shown in FIG. 11. Connected portion 333f is shaped like a
 slender pillow or a rugby ball, which is smaller than that shown in FIG.
 5B. Connected portion 333f has a shape solidified from a liquid drop and
 has a smooth roundish surface.
 End portion 333d before TIG welding is shown in FIG. 12. End portion 333d
 is made of copper and has edge 333g and sloped surfaces 333h. Accordingly,
 end portion 333d has a decreasing cross-section, as shown in FIG. 12.
 Adjacent two end portions 333d are put together to form a trapezoid.
 Because of a reduced volume to be welded by TIG welder, connected portion
 333f becomes smaller than connected portion 33f shown in FIG. 5B.
 Connected portion 33f has width W which is equal to or smaller than double
 the width w of the conductor member. The thickness T of connected portion
 333f is a little larger than the thickness t of the conductor member.
 These sizes varies a little between connected portions 333f, and the
 sloped surface may remain after the welding. However, the surfaces around
 the remaining sloped surface are not so sharp to be eliminated.
 Edge 333g is entirely melted and sharp edges shown in FIG. 12 are
 eliminated.
 Connected portion 333f is disposed so that the thickness W can be aligned
 with the radial direction of the stator. Because all connected portions
 333f are disposed in the circumferential direction, compact connected
 portion as shown in FIG. 11 provides more spaces between connected
 portions 333f.
 Fifth Embodiment
 Each of connected portion 33f shown in FIG. 5B can be also substituted by
 connected portion 433f shown in FIG. 13. Connected portion 433f is shaped
 like a liquid ball hanging down, a raindrop, or a flat ball. As shown in
 FIGS. 14 and 15, connected portion 433f covers the edge and side surfaces
 of end portion 433d, thereby covering all sharp corner edges. Connected
 portion 433f has a shape solidified from a liquid drop and has a smooth
 roundish surface.
 Connected portion 433f shown in FIG. 13 is formed according to the
 following steps. As shown in FIG. 16, melted solder 430 is put in tank
 440, and end portion 433d is dipped therein by a suitable length. Then,
 end portion 433d is taken out to coat melted solder 430 on end portion
 433d. Melted solder 430 forms into the shape shown in FIG. 13 by its
 capillary attraction. The same shape is maintained when the solder cools
 and becomes solid. Solder 430 can be a soft solder, a copper solder, or
 the like.
 Variations
 As shown in FIGS. 17 and 18, end portion 533d or end portion 633d can be
 substituted for end portion 433d.
 End portion 533d has sloped surfaces 533h to form a V-shaped convex edge.
 End portion 633d has inverted sloped surfaces 633h to form a V-shaped
 convex edge. These edges provide a wide surface to be covered by solder.
 Each of end portions 533d and 633d is dipped into melted solder 430 to the
 level indicated by a one-dot chain line. As a result, all sharp corner
 edges of end portions 533d and 633d are covered with the solder.
 As shown in FIGS. 19-21, end portion 733d can be substituted for end
 portion 433d. End portion 733d is dipped into melted solder having lower
 viscosity than melted solder 430 of the precedent embodiments so that
 connected portion 733f can be formed more rectangular than connected
 portion 433f. This reduces the size of connected portion 733f, providing
 longer distance between adjoining connected portions 733d.
 It is also possible to provide a single centrifugal cooling fan to cool
 connected portions 33f instead of a pair of cooling fans. The cooling fan
 can be axial flow fan also. The ball-shaped connected portions can be
 applied to an any kind of electric machine having water cooling structure.
 The cross-section of conductor segments 33 can be circular, elliptic or
 polygonal. A contactless arc welder other than TIG welder can be
 applicable to connect end portions 33d of conductor segments 33.
 In the foregoing description of the present invention, the invention has
 been disclosed with reference to specific embodiments thereof. It will,
 however, be evident that various modifications and changes may be made to
 the specific embodiments of the present invention without departing from
 the broader spirit and scope of the invention as set forth in the appended
 claims. Accordingly, the description of the present invention in this
 document is to be regarded in an illustrative, rather than restrictive,
 sense.