GB2309339A

GB2309339A - Eddy current brake cooling system

Info

Publication number: GB2309339A
Application number: GB9620715A
Authority: GB
Inventors: Neil Wells
Original assignee: TORSPEC INTERNATIONAL Inc
Current assignee: TORSPEC INTERNATIONAL Inc
Priority date: 1995-10-06
Filing date: 1996-10-04
Publication date: 1997-07-23
Also published as: GB9520480D0; GB9620715D0

Description

IMPROVED BRAKE FOR EDDY CURRENT DRIVE8 The present invention relates to eddy current drives and more particularly to a brake system for eddy current drives in which the heat generated within the brake system is better dissipated. The present invention also provides for improved means of protecting the torque tube on the brake system from deterioration due to excessive heat.

Eddy current drives are used extensively in all kinds of industries ranging from asphalt, beverages, pulp and paper, textiles to wastewater treatment. In many instances, it is desirable and even necessary to slow down the eddy current drive, and this is done by configuring the eddy current drive to operate as a brake. The brake system is operatively connected to the shaft of the equipment requiring braking and, through various means, provides resistance to the shaft, thereby slowing down the rotation of the shaft.

One embodiment of a presently used brake system consists of a rotor disposed on the shaft of the eddy current drive. A schematic of the rotor is shown in Fig. 1. The rotor 10 comprises a plate-shaped component 11 having a central opening 12 through which the shaft can be fitted. The plate of the rotor lies in a plane perpendicular to the axis of the shaft when mounted thereon. The rotor further includes a series of grilled openings 13 disposed circumferentially about the plate.

A cylindrical torque tube 14 is also provided on the rotor.

The brake system functions as follows. As the shaft of the equipment rotates, the rotor of the brake system also rotates.

The rotation of the grilled openings disposed circumferentially of the rotor plate causes air to be drawn into inlet grilles provided on the casing of the brake. This air therefore enters the casing, passes therethrough and is pushed out the grilled openings on the rotor. This suction and circulation of air creates resistance on the rotating rotor, which in turn also provides resistance to the shaft of the eddy current drive.

In other words, the rotor acts as a fan: drawing air into the brake system, circulating it therein, and forcing it out through the grilled openings of the rotor.

In addition to the above, the torque tube, which preferably has a inner laminate made of copper because of its electrical conductivity properties, creates resistance through an electrical charge generated thereon. These features of the brake system are well-known in the industry.

The major drawback to the brake system as currently known is the generation of excessive heat, and particularly within the rotor and on the torque tube. In current applications, it is desirable to place as much load as possible on the eddy current drives to get maximum productivity from them. Unfortunately, by doing so, the brake system is also asked to work harder, meaning that increased heat generation within the torque tube results. This generated heat has been found in certain applications to create temperatures on the casing of 2700F to 3000F, rather than the more typical 1500F to 2000F.

The increased temperature in the torque tube causes the copper tube to oxidize and deteriorate significantly, thereby resulting in a loss of the tube's electrical conductivity properties. This loss of conductivity in turn causes the coil voltage to rise, further increasing the temperature within the brake system. Thus, the deterioration of the copper tube, when it happens, is a significant problem which leads to even higher temperatures within the brake and the torque tube. The copper tube's deterioration also leads to a loss of power within the drive.

Accordingly, the present invention provides a means of reducing, and in fact eliminating, the deterioration of the copper on the torque tube, thereby retaining the tube's conductivity properties. The present invention provides that the temperature generated within the rotor is reduced by increasing the circulation of air within the brake system. The increased air circulation keeps the temperature of the torque tube within acceptable limits so as to prevent the copper on the torque tube from oxidation and deterioration. In addition, the present invention also prevents deterioration of the copper on the torque tube by preventing the copper from being exposed to atmospheric air, thereby also reducing oxidation of the copper.

According to a first aspect of the present invention, there is provided a brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, wherein there is also included means for increasing the circulation of air within the brake system such as to keep the temperature of the torque tube within acceptable limits.

Preferably, said means for increasing the circulation of air comprises one or more slots provided in the rotor (the primary rotor) and a secondary rotor disposed on and spaced from the primary rotor for rotation therewith and operable through said rotation to draw air through said slot(s) and out of the system through outlets provided on said secondary rotor.

Ideally, there would be provided a plurality of slots in the primary rotor, the size and shape of which, as well as their locations in the rotor plate, are determined to achieve maximum air circulation.

For additional protection, the torque tube, or more particularly the copper tube located within the torque tube, is sealed or plated with a protective layer to prevent deterioration of the tube and/or components thereof.

According to the first aspect of the present invention there is further provided, in a brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, a method of increasing the circulation of air within the brake system such as to keep the temperature of the torque tube within acceptable limits, comprising forming one or more slots provided in the rotor (the primary rotor) or replacing the primary rotor with another primary rotor having one or more slots provided therein, and fitting a secondary rotor disposed on and spaced from the primary rotor for rotation therewith and operable through said rotation to draw air through said slot(s) and out of the system through outlets provided on said secondary rotor.

According to a second aspect of the present invention there is provided, in a brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, a method of reducing or eliminating deterioration of the copper tube located within the torque tube by sealing or plating the copper with a protective layer to prevent deterioration of the tube and/or components thereof.

According to the second aspect of the present invention there is further provided a brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, said torque tube including a copper tube located therewithin, wherein the copper tube is sealed or plated with a protective layer, for example, nickel or chrome.

Embodiments of the present invention will now be described, by way of example only, with reference to Figure 2 of the attached drawings.

The first embodiment of the invention is illustrated in Figure 2, which is a cross-sectional view of the brake system 20. In order to increase the circulation of air within the brake system, a secondary rotor 22 is provided in addition to the primary rotor 23. The secondary system is similar in shape and configuration as the primary rotor. It is disposed on, and spaced from the primary rotor.

Primary rotor hub 38 is bolted to primary rotor plate 23 and the shaft 62 is mounted for rotation within stator body 52 by means of spacer 36, rear bearing 34 and circlip 40.

The whole system is enclosed with casings 48, 32 of which the former incorporates an eyebolt 42. Internally of casing 48 polewheel 44 is disposed around and bolted to stator body 52, and a coil 50 is disposed around stator body 52 and retained in position with a coil retaining ring 68.

At the point where the shaft 62 leaves the body of the brake system, there is a spacer 54, front bearing 56, tachogenerator 58, tachoarmature 66, output cover 60 and seal 64.

The secondary rotor 22 is bolted to the primary rotor 23 via bolts 31, and does not have the centrally located opening. The plate of the secondary rotor is parallel to the plate of the primary rotor. The secondary rotor further includes a series of grilled openings disposed circumferentially about the plate.

A cylindrical tube spacer 26 is provided on the secondary rotor 22. In the brake system of the present invention, the plate of the primary rotor is provided with one or more slots 23a that allow air to pass therethrough. The number, size and shape of the slots can vary to achieve maximum efficiency (that is, the greatest reduction in temperature). A backplate 30 is fixed to second outlet casing 32.

In operation the brake system of the present invention keeps the temperature within the brake system and of the rotors down by increasing the air circulation therein. In essence, the addition of the secondary rotor acts as a second fan as follows. The rotation of the shaft causes both rotors to also rotate. The grilled openings 24, 28 on each rotor draws air into the brake system via the inlet grills 46 on the brake's casing. The air passes through the clutch, with some of it being forced out the grilled openings 28 in the primary rotor.

The remainder of the air is forced by the secondary rotor 22 to pass through the slots 23a in the plate of the primary rotor, where it is then forced out the grilled openings 24 of the secondary rotor.

It has been found that the use of the dual-rotor brake system of the present invention can result in up to 37% more air being circulated within the brake system, leading to a temperature decrease of the torque tube of up to 320F. This is a significant decrease in the generated temperature, and in many cases is sufficient to prevent oxidation and deterioration of the copper.

In an alternate embodiment of the present invention, it has been found that the deterioration of the copper on the torque tube can be significantly decreased by sealing or plating the copper with electrolysis nickel or chrome. This sealing acts to insulate the copper surface of the torque tube from exposure to the atmospheric air circulating within the brake system.

Since it is the combination of the high temperature and the exposure to oxygen that causes the copper to deteriorate, the nickel or chrome plating prevents the tube from exposure to oxygen, thus reducing oxidation.

This second embodiment of the present invention can be used on single rotor brake systems as found in the prior art. That is, the copper on the torque tube of the single rotor is plated and protected from oxidation. In addition, the dual-rotor brake system of the present invention can be combined with the plating of the copper on the torque tubes so that maximum protection against deterioration is achieved. In such a case, not only is the temperature reduced by the use of the secondary rotor, but the copper on the torque tubes are further protected by a layer of plated nickel or chrome.

Modifications and alterations to the brake system of the present invention are contemplated and are within the scope of the invention. For example, the number, size and shape of the slots in the plate of the primary rotor can be varied to achieve maximum air circulation.

Claims

1. A brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, wherein there is also included means for increasing the circulation of air within the brake system such as to keep the temperature of the torque tube within acceptable limits.

2. A brake system according to Claim 1, wherein said means for increasing the circulation of air comprises one or more slots provided in the rotor (the primary rotor) and a secondary rotor disposed on and spaced from the primary rotor for rotation therewith and operable through said rotation to draw air through said slot(s) and out of the system through outlets provided on said secondary rotor.

3. A brake system according to Claim 1 or Claim 2, wherein there is provided a plurality of slots in the primary rotor, the size and shape of which, as well as their locations in the rotor plate, are determined to achieve maximum air circulation.

4. A brake system according to any of the preceding Claims, wherein the torque tube, or more particularly the copper tube located within the torque tube, is sealed or plated with a protective layer to prevent deterioration of the tube and/or components thereof.

5. A brake system according to Claim 4 wherein said protective layer is nickel or chrome.

6. In a brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, a method of increasing the circulation of air within the brake system such as to keep the temperature of the torque tube within acceptable limits, comprising forming one or more slots provided in the rotor (the primary rotor) or replacing the primary rotor with another primary rotor having one or more slots provided therein, and fitting a secondary rotor disposed on and spaced from the primary rotor for rotation therewith and operable through said rotation to draw air through said slot(s) and out of the system through outlets provided on said secondary rotor.

7. A brake system for an eddy current drive, substantially as herein described and illustrated in Figure 2 of the accompanying drawings.

8. A method of increasing the air circulation within the brake system, the method being substantially as herein described and illustrated in Figure 2 of the accompanying drawings.

9. In a brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, a method of reducing or eliminating deterioration of the copper tube located within the torque tube by sealing or plating the copper with a protective layer to prevent deterioration of the tube and/or components thereof.

10. A brake system for an eddy current drive, the system including a rotor disposed on the shaft of the eddy current drive and a torque tube provided on said rotor, said torque tube including a copper tube located therewithin, wherein the copper tube is sealed or plated with a protective layer, for example, nickel or chrome.

11. A method of reducing or eliminating deterioration of the copper tube located within the torque tube, in a brake system having either a single rotor, or primary and secondary rotors, the method being substantially as herein described.