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This invention relates to a cowl for small electric motor driven centrifugal air pumps

Small centrifugal air pumps are typically driven by a series wound AC motor in the power range of between 350 watts to 1500 watts and include an integral fan fitted at the brush end of the commutator which cooperate with brushes supported in protruding brush boxes. Product utilisation of such air pumps may not result in efficient use of cooling airflow from the fan. Such will be hereinafter referred to as motors of the type described Such air pumps are used in numerous applications from vacuum cleaners, where the suction created by the pump is utilised, hand dryers, spa air blowers and inflators where the air flow from the pump is utilised. In many applications they perform adequately but inefficiently due to high temperatures created in the electric motor as the cooling airflow is restricted in a normal operating condition by the configuration of the products in which they are utilised
Many manufacturers fit housings to their motors which only partially confine the cooling airflow because the housing covers less than half of the motor fields, core laminations and/or fan housing
Motors of the type described vary considerably in layout and dimensions
and include variations in:
• field winding size;
• overall core stack height and width;

• brush box dimensions and position;
• operational temperature;
• insulation rating;
• air flow requirements to meet manufacturers operational
• motor noise suppression;
• radio frequency transfer characteristics;
• housing composition, and
• fire retardation aspects.
Manufacturers of motors in Europe, North America & Asia, utilise varying fan blade angles, size and shape in the series wound electric motors they produce for vacuum cleaners and air pumps and the like. Furthermore such motors may include variations of the height of the fan over the brush box, depending on the system involved in the manufacturing process. Often the products to which these electric motors are fitted cause the motor to operate at an elevated temperature, which may cause problems for users and manufactures alike. Additionally manufacturers of products utilising such motors may swap and change electric motors in their products due to pricing or availability or such like and it is not practical for such downstream manufacturers to consider the motor design and in particular its cooling detail. Furthermore the present applicant believes that airflow characteristics are relevant not only to cooling but also service life of the brushes and commutator.
The present invention aims to alleviate one or more of the above mentioned disadvantages.


This invention in one aspect resides broadly in
a cowl suitable for a majority of the commercially available electric motors of the type described, and including:- a base which may be located sealably against a driven article to which such motors are mounted;
a confining housing formed for the motor of dielectric material and extending from the base and having inside dimensions which closely accommodates such motors;
a pair of opposed internal channels extending axially along said housing for accommodating the protruding brush boxes of such motors, the channels opening to the base and extending the full length of the housing;
air outflow apertures from said housing adjacent the base;
an integral cap terminating the other end of the housing able to accommodate the fan assembly of said motors, and
said cap having a transverse end wall provided with an air inlet disposed
substantially coaxially of said housing , whereby in use the cooling air flow is contained for flow across significant heat source components of the motor, such as the field windings, commutators and brush boxes, to assist in the dissipation of heat.
Suitably the cooling airflow is positively directed past the commutator and brush boxes and across the field windings before being discharged through said outflow apertures.

The air outflow apertures may be associated with exhaust manifolds extending from the housing.
The cowl may be made of glass filled nylon or any such like material, but may be of any dielectric material (complying with world electrical authority standards).
In use, the cowl is slid over the motor with the brush boxes accommodated in the opposed internal channels until substantially the entire brush box area and the field windings and laminations are covered to enable the base to be sealably secured to the driven article.

in order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a typical embodiment of this invention suitably for many of the series wound motors manufactured and commercially available throughout the world, and wherein:- FIG. 1 is a perspective view of the cowl, and
FIG. 2 is an inverted plan view of the cowl shown about one-half size and
FIG. 3 diagrammatically illustrates typical fan placements.
The cowl 10 has a cylindrical housing 11 of 105mm diameter, 8Omm long provided with opposed internal channels 12 of rectangular section and having a base opening of 3Omm wide and 15mm deep. The housing tapers from its base 14 to permit injection moulding from a plastics material and suitably glass filled nylon. A cap including an annular flange 15 extends about the outer end of the housing 1 1 and into a cap extension 16 which may accommodate a motor cooling fan. The cap extension has a base diameter of 75mm and the end wall 18 has a central aperture 19 therein. Typically the aperture 19 is 4Omm diameter for 1500 watt motors and 3Omm diameter for 500 watt motors.
A base mounting flange 20 extends about the part circular base and the channels 12. This flange may be readily adapted to suit the applicable driven article to which the motor is connected, such as by drilling or shaping as required. Other forms of base mounting may be provided to suit different mountings.
Air flow apertures 21 are formed in the housing 11 adjacent the base flange and opposed manifolds 22 extend from these apertures. The manifolds 22 expand toward outlet ports 23 which in this embodiment are coplanar but which may be otherwise configured as desired.
In a application a series-wound motor has a medially disposed laminated core about which the field coils are wound internally with the upper and lower portions exposed beyond the core. A brush box supports opposed brushes in engagement with the commutator of the rotor which extends beyond the commutator for support and to drive a cooling fan which drives air into the motor across the brush box and stator. The base supports a lower bearing and attaches to a mounting end wall of a centrifugal pump housing. The air inlet for the pump is in the opposite end wall of the pump housing. The base flange 20 mounts to the mounting end wall or to an adaptor therefore as required.
The housing 11 accommodates the core such that air flow from the fan must pass across the field windings before it can exit through the manifolds 22. However prior to reaching the field windings the air flow passes through the inlet aperture 19 whereby it is directed as a column of relatively fast moving air onto the commutator and brush box. This air flow impinges on the contact surfaces of the commutator and cleanses it of some of the brush dust. This maintains a cleaner commutator and minimises wear in the brushes.

This invention retains substantially all of the cooling air flow produced by the fan for passage through the motor as the resistance offered to the air flow between the cowl and the fan has the effect of blocking any of the cooling air flow from returning through the air inlet 19. As a result the cooling air finds a path of less resistance to ambient conditions across components as in a conventional arrangement. Thus, forced air flow across the surface of the laminations, field winding and commutator will reduce such hot spots which are common in series motors. Such hot spots reduce the efficiency of the operation of the motor.
The majority of fan cooled motors fall roughly into three catagories, namely:- (1 ) low flow velocity fan, usually 12 blades and up to 75mm diameter which are
more suited to higher ambient operational temperatures, as in the case of
motors available in Australia and North America. High performance models may be up to 1500 watts.
(2) High flow velocity fan, usually 50-65mm in diameter with very high air
displacement and typically very high speed (vicinity 21 ,000 rpm). These motors may be up to 1500 watts and typically these motors have a thicker and higher brush box and are usually fitted with additional core laminations and alloy
bearing support means. These motors may be as much as 25mm taller than
other classes of such motors.
(3) Small medium speed fan up to 65mm in diameter, a motor speed in the vicinity of 17,000 - 20,000 rpm, and a short core lamination stack.
Referring to Fig. 3 there is shown diagrammatically typical placements for the three categories of motors discussed above, namely large fans 54 which are confined in the cap extension 16 and small medium speed fans 50 which are supported in the aperture 19, which can be readily varied to suit the fan size.
As the operational temperature of motors fitted with the cowl of this invention should be reduced, the need for either factory fitted or after market application of a thermal cut-out should be reduced. Reduction in peak operating temperatures also prevents overheating which can cause performance reductions in the brush springs.
The cowl 10 will also provide a marked reduction of motor noise and will assist in the reduction of Electro magnetic emissions. The air flow created in the region of and through the commutator, fields and about the motor laminations will be a relatively high velocity due to the small available open cross-sectional areas in these zones within the cowl. This will assist in cooling and the flushing of brush dust from the motor.
It is believed that motors fitted with the present invention will demonstrate a reduction in brush wear, temperature rise under load conditions, and these reductions should provide enhanced performance or a significantly longer motor life.
It will of course be realised that the above has been given by way of illustrative example of the invention and that all such and other variations as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is defined in the appended claims