GB2251341A

GB2251341A - Pole polarity and eddy current member material for a dynamometer

Info

Publication number: GB2251341A
Application number: GB9025184A
Authority: GB
Inventors: Jack Humphrey Rolph
Original assignee: JACK ROLPH
Current assignee: JACK ROLPH
Priority date: 1990-11-20
Filing date: 1990-11-20
Publication date: 1992-07-01
Anticipated expiration: 2010-11-20
Also published as: GB2251341B; GB9025184D0

Abstract

The invention provides a dynamometer comprising pairs of magnets disposed such like pole pairs face each other with an induced field member between. This induced field member is of nonferrous material of low density having a long chain molecular structure. The invention can be either a rotary device where the induced field member rotates between fixed magnets, or a linear device where the induced field member rotates between fixed magnets, or a linear device where the induced field member is a fixed platelike object. A suitable induced field member material is high-tensile aluminium which has the required open molecular structure with a highly linear formation. <IMAGE>

Description

This invention relates to dynamometers, and concerns in particular dynamometers using relatively moving disks and magnetic fields There are many occasions when it is necessary to measure the power output of a motor or similar device. One conventional way of doing this is to connect the motor up to a load, and attempt to drive the load against some measurable retaining force, such as a load cell. The combination of load and measuring apparatus is known as a dynamometer, because it measures the dynamic output of the motor.

A particularly useful variety of dynamometer is one wherein the motor drives a ring of magnets against the attractive forces provided by a second adjacent ring of magnets orientated unlike poles together. Unfortunately, even the best of this type of equipment is inherently inaccurate, and unstable, and suffers seriously from heat effects. The invention proposes a novel form of magnetic dynamometer in which the required load-forming "braking" effect is achieved by generating strong eddy fields within a very powerful but uniform magnetic flux caused by two like poles close together. Such a device accurate, and gives repeatable results over a long period.

In one aspect, therefore, this invention provides a magnetic dynamometer comprising two aligned magnets positioned like pole to like pole a short distance apart, there being disposed between the two adjacent poles an induced-field member, relative movement between the pole pair and the member when one of these is driven inducing in the latter fields opposing the movement and causing there to be applied to whichever of the pair and member is not being driven a corresponding force measurable by force-measuring means operatively linked thereto, and wherein the member is a low density, high tensile non-ferrous electrically-conductive metal having a long chain molecular structure, and the field produced by the pole pair is a high density uniform field.

The dynamometer of the invention may be a rotary device that is to say, a device wherein the two main components, the pole pair and the induced-field member, rotate about a common axis - or a linear device - that is, one wherein one of the two moves linearly relative to the other.

The magnets may be permanent or, and preferably, electromagnets, and may be disposed North-North or South-South.

The distance they are apart depends upon their strength and field density, and on the thickness of the induced-field member therebetween, but a convenient distance is about 5 to 8 mm (roughly 1 mm spacing either side of a 3 or 6 mm member (see below). A suitable electromagnet is one having a 20 mm diameter mild steel core and carrying a current of around 3 amps.

The physical structure of the induced-field member may take any form appropriate to the particular variety of device. Thus, where the device is a linear one, the member may be an elongate plate-like object, similar to a length of railway line. On the other hand, where the device is a rotary one, the member is more conveniently a disc.

It is relative movement between the pole pair and the member that causes fields to be induced in the member resulting in an opposing force. Either can be driven - thus, the pole pair can be driven, the member remaining stationary, or the member can be driven, the pole pair remaining stationary (as is usually more convenient in a dynamometer).

Whichever of the pole pair and member is driven, the member experiences a force opposing the movement. Moreover, the other (which is held stationary) experiences a force that tries to "drag" it along with the driven item. This other item is held via some force-measuring means, and this means measures the "dragging" force. The movement-opposing force is proportional to the driving force, and the dragging force is proportional to the movement-opposing force. Thus, the output of the force-measuring means is indicative of the driving force - and hence the arrangement is useful as a dynamometer. A typical load-measuring means is a load cell.

The disc is, as stated, a low density, high tensile non-ferrous electrically-conductive metal having a long chain molecular structure. It is not entirely clear why such a structure is required. A suitable metal is that high-tensile aluminium known as HS30TF (or higher specification aluminium).

The thickness of the member may be any convenient, provided always that the magnetic field is appropriate thereto and that the distance apart of the poles matches the member thickness (as noted above, the pole separation is preferably about 2 mm more than the member thickness).

The magnetic field must be strong and uniform. A suitable field is that produced by an electromagnet of the type specified above.

The eddy-field dynamometer of the invention operates on the influence of basic particles by the high energy effect of an opposed magnetic field. The field effect is presented by two opposing electromagnets set up like pole to like pole. The field thus generated presents highly compressed lines of force.

A disc of non-ferrous metal is introduced into the centre of this force.

The non-ferrous metal has to be of open molecular structure with a highly linear formation, i.e. high-tensile strength aluminium of the highest grade.

As the disc is rotated between the two magnets there is a brief re-orientation of molecular polarisation presenting the opposite molecular pole to the magnetic polar force. This presents a high strength magnetic bond with the electromagnets.

By adjustment of disc thickness and magnetic force, it is essential to obtain as regular as possible lines of magnetic field.

If regular lines are not achieved, an effect similar to a microwave oven will occur, resulting in distortion an /or burning.

An example of a dynamometer of the invention is shown in the accompanying Drawings.

Claims

1. An electrical machine in which a disc of nonferrous material is rotated between fixed pairs of magnets axially aligned with poles of like polarity each side of the disc so that the machine acts in braking mode with little heat generation.

2. An electrical machine as claimed in Claim 1 in which the rotor disc is cooled with a cryogenic system where high power is involved.

3. An electrical machine in which pairs of magnets axially aligned with poles of like polarity are rotated alongside a fixed linear member so that the machine acts as a drive.

4. An electrical machine in which pairs of magnets axially aligned with poles of like polarity are rotated around a disc so that the machine acts as a drive or constant torque device.

5. An electrical machine as claimed in Claim 4 in which the machine acts as a constant torque brake device.