GB2073502A - Improvements in or relating to alternating current generators - Google Patents

Abstract

An alternating current generator, particularly a three-phase generator for motor vehicles and the like, is proposed in which, after a recess in the slip ring casing (bearing frame) for installation of the stator assembly including the end turns of its winding, the diameter of the slip-ring casing is reduced, thereby resulting in a slip-ring casing having a triple stepped configuration; the printed circuit board and diode heat sinks are located in the mid region of intermediate diameter of the casing. The rotor shaft bearing is located in the central inner region of the smallest diameter part. The casing has ventilation openings disposed in the region interconnecting the central inner region and the annular wall of the region of intermediate diameter. <IMAGE>

Description

SPECIFICATION Improvements in or relating to alternating current generators The present invention relates to alternating current generators, especially three-phase generators for mobile unitssuch as motor vehicles.

Alternating current generators, that is to say, in particular, three-phase generators of a wide variety of constructions for the power supply of, for example, motor vehicles, ships, railways, aircraft, are known. The generally comprise an external, stationary stator part having a three-phase stator winding as a fixed conductor part, and a rotor which is rotated to induce in the stator winding a voltage which is rectified for d.c. electrical systems, for which purpose power diodes disposed in a rectifier bridge circuit are provided.

In a self-supporting three-phase generator, the rotor shaft is held in bearings at each end of the housing which is normally formed by an A- or drive end bearing frame at the drive end and a B-bearing frame at the slip-ring housing end. The rotor in a slip-ring three-phase generator is normally in the form of a claw pole rotor between the two halves of which is located an excitation winding which rotates with the rotor and to which excitation current is fed by two carbon brushes which are pressed against slip-rings secured to the rotor shaft. Connection terminals may be provided on the generator for electrically connecting the generator to a regulator and to the electrical system.Diodes which rectify the three-phase current induced in the stationary stator winding are connected to a printed circuit board and are held in heat sinks which are located in the flow of air for cooling the generator. The printed circuit board having the heat sinks for the diodes is located at the slip-ring casing end, where the regulator determining the excitation current is normally secured directly to the generator (built-in regulator). The size and the dimensions of the slip-ring casing can give rise to disadvantages in a three-phase generatorofthis kind.

According to the present invention there is provided an alternating current generator, particularly a three-phase generator, having an A- or drive end bearing frame and a B-bearing frame, a stator assembly and a rotor for the power supply of a moble unit such as a motor vehicle, in which after a recess to receive the stator assembly including end turns of its windings, the diameter of the B-bearing frame is reduced to produce a stepped B-bearing frame which has three annular wall regions of differing diameters and which are integrally interconnected, and of which the central inner region of smallest diameter receives a slip-ring end bearing forthe rotor shaft, and of which its mid region of intermediate diameter accommodates a printed circuit board together with diodes and their heat sinks.

An electrical a.c. generator embodying the present invention has the advantage that the diameter of the slip-ring casing is reduced to a considerable extend immediately after space for installing the stator and the end turns of the stator winding, so that the overall dimensions of the electrical parts of the generator, that is to say, the stator, the rotor and the slip-rings, can be substantially reduced virtually without changing the efficiency of the basic three phase generator.Thepowerto be produced by the generator can be virtually undiminished, or only very slightly reduced, by reducing the size ofonly the printed circuit board having the diode heat sinks, with the retention of the other dimensions of known three-phase generators, since the dimensions of the fan wheel and consequently the airflow produced thereby when in operation can remain unchanged, thereby resulting in virtuallythesame cooling effect on the rectifier diodes, which can then be disposed close together, as a result of a stronger flow of cooling air.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Fig. lisa plan view of the slip-ring side bearing of a three-phase generator in accordance with one embodiment of the invention, and Fig. 2 is a section through the three-phase generator of Fig. 1, taken along the line ll-ll.

A self-supporting swivel-arm generator 1 is illustrated in Figures 1 and 2. In a conventional manner, an A- or drive end bearing frame 2 incorporates a first bore 3 and a second bore 4 (see Figure 1) for securing the swivel arm of the generator 1, a fan wheel 6 and a drive belt pulley 7 for driving the rotor being arranged externally adjacent to a first rotor shaft bearing 5 in the A- or drive end bearing frame 2. A stator assembly 8, comprising a stator core 9 and a stator winding 10, has axially opposite faces of its core 9 seated in stepped recesses 11 and 12 in the Bearing frame 2 and in a B-bearing frame 13, respectively.The rotor is generally designated 14 and comprises two claw pole halves 15a and 1 5b and an excitation winding 16 mounted on the rotor shaft 17 whose end remote from the drive end bearing 5 is held in a further slip-ring end bearing 18 in the B-bearing frame.

The B-bearing frame 13 (which can also be described simply as a "slip-ring casing") is constructed such that, after the stator assembly has been installed in a recess, the diameter of the B-bearing frame is immediately reduced to a considerable extent after allowing space for the end turns of the stator winding 10, that is to say from a diameter A determined by the dimension of the A- or drive end bearing frame and the stator assembly to a reduced diameter B.The slip-ring casing 13 is thus of triple cup-shaped construction and comprises a first cup- or dish-shaped central depression 13a for receiving the slip-ring end bearing 18 of the rotor shaft 17, a second dish- or cup-shaped depression 13b which is integrally formed at the edge of the first dish-shaped depression and which receives the entire assembly of the slip-rings, printed circuit board and diode heat sinks, and a third dish-shaped depression 1 3c whose diameter then corresponds to the dimensions of the three-phase generator as determined by the A- or drive end bearing frame.

Reduction of the diameter in the mid part 13b of the portion of the housing formed by the slip-ring casing 13 results in a considerable increase in external free space, and this can overcome installation difficulties which can arise in the case of only a limited space being available for the generator, although the performance of the basic generator system can remain substantially unchanged, since the other structural components such as the drive end bearing frame, the rotor, the stator, the rectifier and the regulator can remain unchanged. A printed circuit board which carries heat sinks 19 for diodes 19a is desig nated 20 in Fig. 2. The dimensions of the printed circuit board and of the diode heat sinks can be reduced relative to those of a conventional generator of similar power rating. A carbon brush holder assembly is designated 21 and is secured externally to the regulator 22 fitted to the slip ring casing.

As is shown in Fig 1, the slip-ring casing is provided with large ventilation openings 23 which are disposed in a generally radially extending region interconnecting the central inner region 13a and the annular wall 13b ofthe region of intermediate diameter and which serve effectively to conduct the flow of cooling air, created by the fan wheel 6, to the heat sinks of the diodes. The A-bearing frame 2 and the B-bearing frame 13 serving as a slip-ring casing are clamped to one another and to the stator assembly 9 by means of bolts 24.

Claims (4)

1. An alternating current generator, particularly a three-phase generator, having an A- or drive end bearing frame and a B-bearing frame, a stator assembly and a rotor for the electrical power supply of a mobile unit such as a motor vehicle, in which, after a recess to receive the stator assembly including end turns of the windings, the diameter of the B-bearing frame is reduced to produce a stepped B-bearing frame which hasthree annular wall regions of differing diameters and which are integrally interconnected and of which the central inner region of smallest diameter receives a slip-ring end bearing forthe rotor shaft, and of which its mid region of intermediate diameter accommodates a printed circuit board together with diodes and their heat sinks.

2. An alternating current generator as claimed in claim 1, in which the dimensions of the printed circuit board and of the diode heat sinks are reduced relative to those of a conventional generator of similar power rating.

3. An alternating current generator as claimed in claim 1 or 2, in which the B-bearing frame has ventilation openings disposed in a generally radially extending region interconnecting the central inner region and the annular wall of the region of intermediate diameter.

4. An alternating current generator, having a B-bearing frame constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.