GB2385715A

GB2385715A - Double Bladed Fan

Info

Publication number: GB2385715A
Application number: GB0202842A
Authority: GB
Inventors: Lap Keung Chan
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2002-02-07
Filing date: 2002-02-07
Publication date: 2003-08-27
Also published as: GB0202842D0

Abstract

A fan 23 for a miniature electric motor, particularly a PMDC motor, has two sets of fan blades 27, 28 mounted on opposite sides of a divider 26 to form two centrifugal type fans joined back to back, to generate two separate air flows. One air flow is drawn from the commutator area and the other air flow is drawn over the rotor windings. Projections 31 engage the winding slots.

Description

Electric Motor This invention relates to electric motors and in particular, to a cooling fan for a permanent magnet DC micromotor.

DC micromotors or subfractional horsepower motors are very common and often are used without any assisted cooling. Certain applications require motors to run in adverse conditions requiring assisted cooling as shown, for example, in British patent GB 2189944.

Current demands require more power from smaller packages resulting in assisted cooling becoming mandatory. However, the current design of the small fans attached to the rotor core do have a drawback. The fan is arranged to draw air over the commutator as well as over the windings. However, as the air flow resistance is low over the commutator and high through the winding tunnels of the rotor, especially when the winding tunnels are relatively full of winding turns, the air flow generated is predominantly over the commutator. In the past, this has been an acceptable trade off as the commutator was the greatest source of heat. However, with the larger demands made of the motors, cooling of the windings is an important issue.

The present invention addresses this issue by providing a single fan with a divided air flow which can control the amount of air or percentage of air flow drawn over the commutator and over the windings.

This is achieved by the use of a centrifugal fan having a divider plate creating two separate air flow paths through the fan.

Accordingly, the present invention provides a fan for an electric motor comprising: an annular planar disc having a first face and a second face; a first set of fan blades formed on the first face of the disc; a second set of fan blades formed on the second face of the disc; and mounting means for fixing the fan to a rotor core of the motor.

Preferred and/or optional features are described in the dependent claims.

The invention also relates to a miniature electric motor especially a permanent magnet direct current micromotor incorporating such a fan.

A preferred embodiment of the invention will be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a PMDC motor with a wound rotor incorporating a fan according to the present invention, and Figure 2 is a perspective view of the fan of Figure 1.

Referring firstly to Figure 1 where a PMDC micromotor is shown in section. The motor comprises a deep drawn rear housing 10 with an open end closed by a resin moulded end cap 11. The end cap 11 supports motor terminals 12 connected to brush gear designated generally 13. The rear housing accommodates a permanent magnet stator 14 and a rotor joumalled in bearings 16,17 held by the rear housing 10 and the end cap 11. The rotor comprises a shaft 18, a laminated rotor core 19 fitted to the shaft 18 and a commutator 20 fitted to the shaft 18 adjacent one end of the rotor core 19. Rotor windings 21 are wound about poles of the rotor core 19 and terminated on tangs or terminals 22 of the commutator 20 A fan 23 is fitted to the commutator end of the rotor core 19.

The fan 23 is of the centrifugal type having an open eye into which air is drawn in use and expelled radially. The fan 23 is attached to an axial end face of the rotor core 19 adjacent the radially outer periphery by fingers projecting into the winding slots in the rotor core. Blades of the fan 23 extend generally radially in the space generally radially outward of and about the terminals 22 of the commutator to draw cooling air over the commutator 20 and over or through the rotor windings 21. Holes (not shown) are provided in the end cap to provide ventilation for the commutator. Holes 24 in the closed end of the rear housing provide ventilation for the rotor. Holes 25 are provided in the rear housing, aligned with the fan 23, to allow cooling air to be expelled from the motor by the fan 23. If the rotor winding tunnels are not full, cooling air flow through the winding tunnels and over the winding heads can be achieved. For rotors with relatively full winding tunnels, winding cooling air flow may be limited to cooling of the winding heads and/or cooling air flow over the outer surface of the rotor core.

The fan 23 is more clearly shown in Fig. 2. The fan 23 comprises an annular plate 26. On both sides of the plate 26 are located radially extending fan blades. A first set of blades 27 on one side of the plate 26 align with a second set of blades 28 on the opposite side of the plate 26 so that the plate 26 appears to divide each fan blade into two axial parts. However, there is no need for the blades 27,28 to be aligned or for the number or size of blades of each set 27,28 to be equal.

Axial projections 29 extend from the first set of blades 27 on the rotor core side to space the fan blades a distance from the rotor core 19. A ring 30 is formed at the end

of the axial projections 29 which supports the projections 29 and abuts the rotor core 19 to set the distance. Mounting fingers 31 extend from the ring 30 and engage the rotor core 19 to align the fan 23 radially with respect to the rotor core 19 and thus, the shaft 18. The fingers 31 may be used to secure the fan 23 to the rotor core by being dimensioned to fit within the winding tunnels of the rotor core or preferably, as shown, a press fit within the slot in the rotor core forming the winding gap or otherwise engage the rotor core on either side of the winding gap. The mounting fingers 31 alone may hold the fan to the rotor core or glue or other suitable fastening methods can be used to secure the fan to the rotor core.

The plate 26 divides the fan blades into two separate sets of fan blades 27,28, each set generating its own air flow path, By changing the size or number of blades of each set, the relative percentage of air flow or other characteristics of the fan can be changed. For example, a fan with low air pressure differential but high volume can be formed on the axially outer face of the plate to draw air from the relatively open space about the commutator while a fan with a high air pressure differential can be formed on the axially inner face of the plate to draw air through the relatively restricted space of the winding tunnels and over the winding heads.

By varying the size and/or number of blades, the air flows of the two sections of the fan can be adjusted or optimized for a particular motor construction and application.

As can be seen, both sets of fan blades, 27,28, form a centrifugal type of fan with an open eye. This means that the radially inner edge of the fan blades are open or freeot- otherwise substantially unobstructed to draw air into the fan from the radially inner edge of the blades. This has the effect of drawing air from closer to the motor axis, either trom closer to the commutator surface or from closer to the inner, portion of the rotor core and windings, where greater cooling effect can be achieved. Alternatively, the blades can be shorter for a similar cooling effect.

The embodiment described above is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

Claims 1. A fan for use in a miniature electric motor comprising: an annular planar disc having a first face and a second face; a first set of fan blades formed on the first face of the disc; a second set of fan blades formed on the second face of the disc; and mounting means for fixing the fan to a rotor core of the motor.
2. A fan according to claim 1 wherein the mounting means includes a ring for abutting an axial end face of the rotor core and is axially spaced from the disc on the first side thereof by projections extending from the first set of fan blades.
3. A fan according to claim 1 wherein the mounting means further includes fingers extending from the ring for engagement with the rotor core.
4. A fan according to any one of the preceding claims wherein the fan blades of at least one set of blades has the same radial extent as the disc.
5. A fan according to any one of the preceding claims wherein the fan blades of the first set have the same radial extent as the fan blades of the second set.
6. A fan according to any one of the preceding claims wherein the number of blades in the first set of fan blades is equal to the number of blades in the second set of fan blades.
7. A fan according to any one of the preceding claims wherein both sets nfh.) a have open eyes.
8. A fan substantially as hereinbefore described with reference to the accompanying drawings.
9. A small electric motor having a rotor incorporating a fan as defined in any one of the preceding claims.
10. A motor according to claim 9 wherein the rotor has n salient poles separated by n winding slots and the fan has n fingers which are pressed into respective winding slots to fix the fan to the rotor.
11. A motor according to claim 9 or claim 10 wherein the fan is fixed to the rotor by glue.