GB2262345A

GB2262345A - Shaft horsepower measuring device

Info

Publication number: GB2262345A
Application number: GB9126517A
Authority: GB
Inventors: Richard Lunn
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-12-13
Filing date: 1991-12-13
Publication date: 1993-06-16
Also published as: GB9126517D0

Abstract

The power being transmitted by a shaft can be determined from measurements of its torsional deflection and angular velocity whilst in service. Electronic signals are induced in magnetic pick-ups located adjacent to the shaft a known distance apart by magnets or iron studs situated on the shaft itself. The frequency of, and the phase difference between, the signals allows for the determination of angular velocity and torsional deflection of the rotating shaft. From these two parameters and the section properties of the shaft, the horsepower being transmitted by the shaft is calculated, e.g. by a microprocessor. <IMAGE>

Description

SHAFT HORSEPOWER ItEASERING DEVICE This invention relates to a shaft horsepower measuring device.

Steel shafts are often used to transmit power from a prime mover, for example, a diesel engine, to driven ecuipment requiring power such as a generator or a ships propeller.

The power being transmitted by a shaft is often deduced by measuring the power generated by the prime mover itself, for example, from the indicated horsepower of a diesel engine.

The rotary deflection, or twist, in a shaft is directly proportional to the torque applied within the elastic limits of the material. Furthermore, the horsepower being transmitted by the shaft is a function of the torque applied to the shaft and its angular velocity According to the present invention, the power being transmitted by a shaft is calculated from the angular velocity of the shaft and from its mean deflection under load. The princisse components of the device are two collars each containone or more small magnetic, or iron, studs fitted to the fore and aft ends of the shaft, magnetic pick-ups which are situated off the shaft adjacent to the collars, and a microprocessor programed to analyse impulsive electronic signals from the magnetic pick-ups which are induced every time the shaft rotates.

Calculations on which the analysis is based are given overpage.

CALCULATIONS For uniform hollow circular shaft, the following equations relate angular deflection and velocity to the torquf applied and horsepower transmitted: Torque, T = GJ# L Horsepower, H = T# where; # = angle of deflection L = length of shaft G = elastic shear modulus of material # = angular velocity J = polar second moment of area of shaft =

a = Internal diameter external diameter A specific embodiment of the invention will now be described with reference to the accompanying drawing - Figure 1. Shows the arrangement of collars and magnetic pick-ups.Each time a magnet on the collar passes the pick-up as the shaft rotates, an electronic impulse is induced in the pick-up.

The phase difference between the occurrence of peaks in the two signals, A and 3, indicates the degree of twist in the shaft. The frequency at which the peaks occur indicates the angular velocity of the shaft. Processing of the signals could be done in either an analogue mode, or digital mode using a microprocessor.

The as-built dimensions for the internal and external diameters of the shaft, and the spacing between collars on this arrangement would be measured to provide input to the calculations described earlier.

The device is easy to calibrate and could be done at any time when the shaft is rotating and transmitting a known or zero load, such as when the driven equipment is disconnected or in a neutral gear.

The technique does not cause any operational constraints on the prime mover or driven equipment and does not cause any loss of power in the system. Should any component in the invention fail, there will be no effect on the performance of i:ho nlrnt. zsa R mauls.

Claims

1. A shaft horsepower measuring device comprising magnets within collars mounted on the fore and aft end of the shaft, and magnetic pick-ups located off the shaft by the collars to obtain impulsive electronic signals from the shaft as it rotates. The torsional deflection of the shaft is measured from the phase difference between the signals, and the angular velocity is deter mined from the frequency of the signals.

2. A shaft horsepower measuring device as claimed in Claim 1, wherein the magnets are set directly into the shaft rather than being on collars.

3. A shaft horsepower measuring device as claimed in Claim 1, wherein the magnets are replaced by iron studs and the collar is of a non-ferrous material, for example, aluminium.

4. A shaft horsepower measuring device as claimed in Claims 1, 2 and 3, wherein a number of magnets or iron studs are used at each fore and aft location on the shaft to provide more signals per rotation of the shaft. Post processors would be used to filter out signals resulting from torsional vibrations caused by, for example, the operation of the prime mover or the driven equip- ment.