Measuring and testing – Dynamometers – Responsive to torque
Patent
1994-05-23
1996-04-16
Chilcot, Richard
Measuring and testing
Dynamometers
Responsive to torque
G01L 0800
Patent
active
055071910
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to dynamometers of the class known as absorption dynamometers. The invention has particular though by no means exclusive application to drum dynamometers, especially magnetic eddy current drum dynamometers, and it is this application which is primarily discussed in this specification.
BACKGROUND ART
Magnetic eddy current drum dynamometers generally include a longitudinally ribbed rotor and a surrounding stator which is restrained against rotation by means able to measure the torque developed in the stator. The stator typically includes a central field coil and the dynamometer operates as a brake or absorption dynamometer by absorbing energy dissipated into the stator by way of eddy currents induced in the stator as the revolving ribs cyclically modify the magnetic flux. Means is provided to extract the heat from the stator, and in one known arrangement, coolant fluid is continuously supplied to a central annular chamber housing the coil and then extracted through multiple spiral galleries in a pair of stator rings to either side of the chamber. This arrangement has the disadvantages that it is critically dependent for its continued safe operation on the integrity of the seals which prevent the coolant fluid leaking into the coil and that any blockage or significant flow restriction in any one of the spiral galleries can easily lead to a thermal runaway condition before the blockage is realised. The latter occurs because a localised blockage in one gallery (while the dynamometer is under load) immediately causes a localised increase in temperature which can easily and very rapidly cause severe damage to or destruction of key internal components of the dynamometer before performance loss is noticeable.
It is accordinly one objective of the present invention, in one of its aspects, to provide an improved cooling arrangement for absorption dynamometers of the general type under discussion.
An important potential new application for a dynamometer is in the field of testing power tools such as chainsaws. The traditional practice when servicing or repairing chainsaws is to conclude with a direct on-site test on a waste log or the like but there is growing dissatisfaction with the noise and materials waste that this practice entails, and also with the relative inaccuracy inherent in such practice.
The present applicant has constructed an eddy current dynamometer test unit to which a chainsaw drive head may be rigidly mounted but it has been found that the results do no accurately reflect the subsequent working performance of the chainsaw. The applicant has appreciated, in accordance with the second aspect of the invention, that this discrepancy arises because the rigidly fixed disposition of the chainsaw on the dynamometer test unit does not properly reflect the normal hand held condition in which the chainsaw and its drive components are free to vibrate. It is to the resolution of this disconformity that the second aspect of the invention is directed.
DISCLOSURE OF THE INVENTION
The invention accordingly provides, in its first aspect, an absorption dynamometer which includes a rotor and restrained stator means, and in use of which the rotor energy is substantially dissipated as heat in the stator means, a cooling arrangement for the stator means comprising passage means for coolant fluid, said passage means extending, at least in part spirally, from a fluid intake port at or adjacent a first end of the stator means to an outlet port at or adjacent a second end of the stator means.
The invention also provides, in its first aspect, an absorption dynamometer which includes a rotor and restrained stator means, and in use of which the rotor energy is substantially dissipated as heat in the stator means, a cooling arrangement for the stator means comprising passage means for coolant fluid, said passage means including one or more spiral duct segments arranged so that, at least for a major part of the length of the stator means, the flow in the or each spiral duct seg
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Chilcot Richard
Dombroske George M.
Galbraith Engineering Pty. Ltd.
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