GB2135833A - Brushless alternator - Google Patents

Abstract

A brushless alternator 10 comprises a stator assembly 12 retained between end frames 14, 16, a hollow rotor assembly 22 carried on a shaft 24 rotatable within the stator assembly 12, and a stationary cylindrical field core 32 fixed to the end frame 14 of the alternator 10 and extending within the hollow interior of the rotor assembly 22. The field core 32 houses adjacent the free end thereof a rear bearing 48 for the shaft 24, said shaft 24 being rotatably mounted in said rear bearing 46 and a drive-end bearing 52 housed in said drive-end frame 14. The shaft 24 of the alternator 10 does not carry a field core mounted thereon. In a preferred embodiment, said one end of the stationary field core 32 locates and retains said drive-end bearing 52 both radially and axially with respect to said rear bearing 48 and said drive end frame 14. <IMAGE>

Description

SPECIFICATION Brushless alternator This invention relates to brush less alternators, in particular brushless alternators of the Lundell type, as used in motor vehicles.

Alternators of the brushless Lundell type are distinguished by having a stator assembly retained between a drive end frame and a rear end frame, a segmented, hollow rotor assembly carried on a shaft rotatable within the stator assembly, and a stationary cylindrical field core fixed to one of the end frames and extending within the hollow interior of the segmented hollow rotor assembly, there being a rotating core located on the shaft inside the segmented hollow rotor assembly and concentric therewith, which rotating core co-operates with the fixed core in transmitting the magnetic field produced by an annular excitation coil mounted on said fixed field core, thus inducing and generating current within the stator assembly. Brush less Lundell type alternators are described in a S.A.E. article by W.S. Liston and L.J.Raver, entitled "A New Generation of Brushless Charging System for FCIM Equipment", dated 1977. The segmented hollow rotor assemblies used in such brushless alternators are commonly of the claw-pole design, in which the rotor assembly is in the form of a cup-shaped assembly in which the side walls are constituted by two claw-pole rings with the claw-poles thereon interdigitated with one another. An example of such a claw-pole rotor assembly is disclosed in British patent specification number 1 560 746.

Brush less alternators of the Lundell type were developed primarily for use in motor vehicles, and are often called upon to operate in harsh, confined environments, involving high temperatures and substantial vibration. Since the shaft and rotor assembly of such alternators commonly rotate at speeds in excess of 10000 r.p.m., the alternators are customarily constructed with substantial bearings at either end of the alternator shaft, each bearing being supported within a substantial end frame of the alternator. In order for the alternator to give a satisfactory output of current, it is necessary for the stator assembly, rotor assembly, stationary field core and the end frames to be accurately made and accurately assembled, which inevitably leads to a high manufacturing cost.There is a need, therefore, for a compact brushless alternator which can be manufactured more quickly at less cost.

A brushless alternator according to the present invention comprises a stator assembly retained between a drive end frame and a rear end frame, a segmented hollow rotor assembly carried on a shaft rotatable within the stator assembly, and a stationary cylindrical field core fixed to one of the end frames and extending within the hollow interior of the segmented hollow rotor assembly, characterised in that said stationary cylindrical field core is fixed at one end to the drive end frame of the alternator and, adjacent the free end thereof, houses a rear bearing for said shaft, said shaft is rotatably mounted in said rear bearing and a drive end bearing housed in said drive end frame, and said shaft does not carry a field core mounted thereon.

The rear bearing housed in the stationary cylindrical field core is preferably a needle bearing.

There are advantages in manufacturing assembly for the rear bearing to be a self-sealing shell bearing, since such a shell bearing can be obtained ready packed with a suitable high temperature lubricant, and can be readily and effectively pressed into place within the opening provided in the stationary cylindrical field core adjacent the free end thereof.

A preferred embodiment of the present invention is one in which said one end of the stationary field core locates and retains said drive end bearing both radially and axially with respect to said rear bearing and to said drive end frame. With such an arrangement, one can readily ensure that the rear bearing and drive end bearing are satisfactorily aligned with one another in order to accurately locate and support the shaft carrying the rotor assembly of the alternator.

A preferred embodiment of the present invention will now be particularly described with reference to the accompanying drawing, which shows an alternator according to the present invention in cross section.

Referring now to the accompanying drawing, this shows a brushless alternator 10 according to the present invention which comprises a stator assembly 12 retained between a drive end frame 14 and a rear end frame 16. The stator assembly 12 comprises a phase winding 18 wound upon a laminated annular frame 20. A segmented hollow rotor assembly 22 is carried on a shaft 24 rotatable within the stator assembly 12, said segmented, hollow rotor assembly 22 comprising a cup-shaped assembly formed from a base member 26 having an upturned, claw-like castellated edge 28, the claw-like castellations of which form part of the wall of the cup-shaped assembly. The remaining portion of the wall of the cup-shaped assembly is formed by a castellated ring 30, the castellations of which are a similar claw-like shape to the castellations of the castellated edge 28.The claw-like castellations on ring 30 are interdigitated with the claw-like castellations on the upturned edge of base member 26, and they are retained in position relative to the claw-like castellations of the base member 26 by means of an annular ring which is secured to the tips of the claw-like castellations of both members. The center of the base member 26 of the segmented hollow rotor assembly 22 is secured to one end of the shaft 24 so that the wall of the cup-shaped assembly is coaxial with the axis Of the shaft 24.

A stationary, cylindrical field bore 32 is fixed to the drive end frame 14 by means of bolts 34, and extends within the hollow interior of the segmented hollow rotor assembly 22 so as to substantially fill the annular space existing between the shaft 24 and the wall portion of the cup-shaped assembly of the rotor assembly 22. An annular radial air gap 36 extends between the cylindrical field core 32 and the wall portion of the cup-shaped assembly, and an axial air gap extends between the free end of the cylindrical field core 32 and the base of the cup-shaped rotor assembly 22. The cylindrical field core 32 carries wound thereon an annular field excitation coil 40 adjacent the wall portion of the cup-shaped rotor assembly 22. The cylindrical field core 32 has formed therein a cylindrical, concentric, stepped bore 42 which houses a shaft 24 of the alternator 10.The stepped bore 42 is divided into two sections 44 and 46, the diameter of bore section 44 being such that the shaft 24 is freely rotatable therein. The core section 46 is formed adjacent the free end of the cylindrical field core 32, and houses therein a needle bearing 48 which constitutes the rear bearing of the alternator 10. The needle bearing 48 is an interference fit within the bore section 46, and is packed with a suitable high temperature lubricant prior to the insertion of the shaft 24 within the stepped bore 42, there being a lubricant seal 50 provided to close the annular aperture between the shaft 24 and the end of the bore section 46.

The forward end of the shaft 24 is carried by a drive end ball bearing 52 which is housed in a stepped aperture within the drive end frame 14 that is concentric with the stepped bore 42 in the cylindrical field core 32. Drive end ball bearing 52 is a close sliding fit within the stepped aperture in the drive end frame 14, and is retained securely therein by a clamping force exerted thereon by the cylindrical field core 32 and a wave washer 54 retained with the stepped aperture ofthe drive end frame 14. Consequently, the drive end ball bearing 52 is both located and retained in its position in the drive end frame 14 by means of the cylindrical field core 32 so a to accurately locate this drive end ball bearing 52 with respect to both the needle bearing 48 and the drive end frame 14.This, in turn, ensures that the shaft 24 and the segmented rotor assembly 22 are accurately aligned with respect to the cylindrical field core 32.

The stepped aperture in the drive end frame 14 also accommodates an annular sleeve 56 which encircles the end of the shaft 24 protruding from the ball bearing 52, and serves as a spacer element against which a cooling fan 58 for the alternator 10 is clamped. Cooling fan 58 is clamped against the end ofthe annular sleeve 56 by means of a grooved pulley 60 which is retained upon the end of the shaft 24 by means of a retaining nut 62 and retaining washer 64 threaded on the end of a threaded end 66 of th shaft 24. when the alternator 10 is in operation, the cooling fan 58 forces airthrough apertures (not shown) in the drive end plate 14 and over and around the stator assembly 12, the rotor assembly 22 and the stationary cylindrical field core 32 in order to cool these items. The spent cooling air is discharged through slots (not shown) in the rear end frame 16.The drive end frame 14 also includes a mounting lug 68, having a threaded bore 70 formed therein, and a mounting spool 72 having formed therein a cylindrical mounting bore 74. It will be understood by those skilled in the art that these mounting arrangements on the drive end frame 14 allow the alternator 10 to be mounted upon a motor vehicle in such a manner that the tension in flexible drive bands linking the grooved pulley 60 of the alternator 10 to the drive unit of the motor vehicle can be readily adjusted.

Turining now to the rear end frame 16 of the alternator 10, this rear end frame is used to clamp the stator assembly 12 into position upon the drive end frame 14, and also it carries mounted thereon a voltage regulator 76 for the alternator 10, a field supply diode assembly 78, and a diode rectifier assembly 80. These items constitute the electronic equipment required for the operation of the alternator 10 and are exactly the same as those electronic components used in standard prior art Lundell type brushless alternators.

Accordingly, further description of these electronic components and their operation is not necessary for the purposes of understanding the present invention. As can be seen in the drawing, the voltage regulator 76, the field supply diode assembly 78 and the diode rectifier assembly 80 are all housed in a chamberformed in the rear end frame 16, the entrance to this chamber being closed by a removable cover lid 82, which is retained upon the rear end frame 16 by means of threaded bolts (not shown). The portions of the rear end frame 16 which constitute the side walls of this chamber are provided with cooling apertures (not shown) through which air passes in order to cool the electronic components retained therein.

As can be seen from the drawing, and as will be appreciated by a man skilled in the art, the brushless alternator disclosed therein utilises a segmented hollow rotor assembly which does not include a field core mounted on the shaft of the alternator. Instead, the stationary field core is enlarged and modified so as to support the rear shaft bearing of the alternator. Consequently, a substantial decrease in the weight and inertia of the shaft and segmented hollow rotor assembly becomes possible.

An example of a brush less alternator according to the present invention was built that was designed to produce 40 amps at 24 volts. The actual performance data available on this brush less alternator was as follows: Cut in speed - 1600 r.p.m.

Zero Charge Speed - 1300 r.p.m.

Current Generated at 1600 r.p.m. = 10 amps Current Generated at 2000 r.p.m. = 21 amps Current Developed at 3000 r.p.m. = 35 amps Current Developed at 6000 r.p.m. = 45 amps Maximum Current Output 47 amps at 7000 r.p.m.

It is believed that the advantages of the brushless alternator according to the present invention are as follows: 1. An increased output performance capability of the alternator by reason of the substantially increased field iron circuit.

2. Much tighter control of the radial air gaps within the alternator (i.e. between rotor and stator and rotor and field core). This is due to the fact that all three major components of the alternator are registered together as a single unit (i.e., rotor, stator and field core) and this registration is not dependent upon the alignment of two separate end frames. In effect the tolerance build up during assembly is very much reduced from the prior art design. This also improves the electrical performance of the alternator.

3. It is possible to produce an axial air gap between the rotor and field core and to control the dimensions of this axial air gap during manufacture due to the fact that only two dimensions are involved in establishing this axial air gap, which leads to a much reduced tendency for tolerance stack up. This fact aliows an axial air gap to be introdiced into the magnetic circuit without detriment to the electrical performance of the alternator.

4. The rear end frame of the alternator requires no machining as no registers are required on the rear end frame for the accurate location of rotating and non-rotating components of the alternator.

5. The rear end frame can be made very much lighter in construction than it can in prior art Lundell alternators, as the rear end frame is only subjected to vibration stresses when the alternator is in operation.

6. The rear end frame now acts simply as a retainer for the stator assembly and as a carrier for the sundry electronic components required for the alternator, and does not have the requirement of providing a rear end support for the shaft of the alternator.

7. The lack of a bearing support boss in the rear end frame means that the ventilation area available for cooling is substantially increased, thus increasing the performance potential of the alternator.

8. The shift in the center of gravity towards the drive end enables spool type mounting to be employed, thus simplifying mounting arrangements for the alternator.

9. An overall reduction in length of the alternator of approximately 25% appears to be possible.

Consequently, the aforesaid advantages of a brushless alternator according to the present invention means that, in practice, a brushless alternator can be produced that is capable of producing an electrical output suitable for use in a heavy commercial vehicle, yet the physical size of the brushless alternator approximates to the physical size of prior art brush less alternators as used in passenger cars.

Claims (5)

1. A brushless alternator comprising a stator assembly retained between a drive end frame and a rear end frame, a segmented, hollow rotor assembly carried on a shaft rotatable within the stator assembly, and a stationary cylindrical field core fixed to one of the end frames and extending within the hollow interior of the segmented hollow rotor assembly, characterised in that said stationary cylindrical field core is fixed at one end to the drive end frame of the alternator and, adjacent the free end thereof, houses a rear bearing for said shaft, said shaft is rotatably mounted in said rear bearing and a drive-end bearing housed in said drive end frame, and said shaft does not carry a field core mounted thereon.

2. A brushless alternator according to claim 1, characterisedin that said rear bearing is a needle bearing.

3. A brushless alternator according to claim 1 or 2, characterised in that said rear bearing is a self-sealing shell bearing.

4. A brushless alternator according to any one of the preceding claims, characterised in that said one end of the stationary field core locates and retains said drive end bearing both radially and axially with respect to said rear bearing and said drive end frame.

5. A brush less alternator substantially as hereinbefore particularly described and as shown in the accompanying drawing.