DE1063412B - Magnet arrangement for eddy current tachometer - Google Patents

Description

For the measuring mechanisms of eddy current tachometers or speed meters, disk-shaped ones are usually used Sintered magnets based on Alnico are used, which are radially magnetized and a Have a series of pole pairs with alternating polarity. In such measuring works account for about 50% of the Material costs on the magnet, which is by far the most expensive part of the eddy current tachometer.

The invention relates to the task of the expensive Alnico magnet by a so-called ceramic To replace a magnet, the cost of which is only a fraction with the same magnetic effect. The use of cheap ceramic magnets has so far failed due to a number of disadvantages this magnetic material. Its strength is low, it is brittle and fragile. In magnetic Regarding the energy content is relatively low and a normal radial magnetization would be too result in weak torque. The flat demagnetization curve of these magnetic materials results in a field line course with only a relatively small field strength gradient in the vortex current bell of the Measuring mechanism. The main disadvantage hitherto opposed to the application, however, is the great dependence on temperature these magnetic materials.

The invention overcomes the difficulties encountered with the use of ceramic magnets in that it is for the preferably disk-shaped or ring-shaped magnet that for eddy current tachometers Axial magnetization, which is not common, but is known per se from other applications, is used and at the end faces two likewise known, butting pole shoes made of soft iron with radial extensions arranged, the ends of which are bent by 90 ° and the pole pieces on the cylindrical circumference of the magnet with alternating polarity.

With this arrangement, the brittle permanent magnet is held in a reinforcement made of soft iron pole pieces. For temperature compensation of the magnet arrangement, according to the invention, a cylindrical ring made of temperature-compensating material is arranged between the ceramic permanent magnet and the soft iron pole pieces, which rests on both pole pieces and thus a practically perfect magnetic shunt with respect to the for optimal temperature compensation in a temperature range of about - 20 to + 60 ° C necessary energy flow of the shunt forms about ¹ Jn to V _{s of} the total magnetic flux) with simultaneous production of complete saturation of the shunt body.

Due to the known reinforcement of the magnet with soft iron pole pieces, the magnet arrangement can be
for eddy current tachometers

Applicant:

VDO speedometer works

Adolf Schindling G.m.b.H.,

Frankfurt / M. W13, Graefstrasse. 103

Dr. Adam Wesp, Messenhausen near Ober Roden

(Hess.),
has been named as the inventor

table energy as an effective field 'completely on the Concentrate eddy current bell with a large field gradient. Despite the low energy content of the ceramic magnet material, a torque is achieved that is similar to that of high-quality sintered magnets Alnico base equals. The high temperature drift of the ceramic magnet is made possible by the perfect Shunt of the lines of force balanced over the compensation ring and the required high levels of relaxation achieved.

The magnet arrangement according to the invention has the advantage that its cost is only a fraction of the previous one usual sintered magnets. Another advantage is the reinforcement with the pole pieces and the compensation ring a high magnetic stability and an almost complete insensitivity against even the greatest demagnetizing influences.

An exemplary embodiment of the invention is shown in the drawing.

Fig. 1 shows the magnet partially in section and its arrangement in the measuring plant;

⁺ 5 Fig. 2 shows a plan view of the magnet.

The magnet 1 is held between two pole pieces 2 by a sleeve 3, which is on the in the housing 4 of the Device mounted magnetic shaft 5 is attached. The extensions 2a of the pole shoes 2 are bent by 90 ° and form on the cylindrical periphery of the magnet assembly the pole pieces. The compensation ring is located between the pole pieces 2 α and the magnet 1 6, which rests against the two pole pieces 2. The compensation ring could also be between

909 607/107

Claims (1)

be arranged the magnet 1 and the sleeve 3, but the drawn version is because of the magnetic Shielding cheaper. In Fig. 1, the arrangement of the magnet in the measuring mechanism is indicated. The rotating magnet 1 acts on S the eddy current bell 7, which is attached to the axis 8 carrying the pointer, not shown, and is twisted against the force of the spring 9. The axis 8 is mounted in a circuit board 10 in the housing. With the yoke ring for the magnetic flux of the system is designated. Claim: Magnet arrangement for eddy current tachometers, consisting of an axially magnetized permanent magnet, preferably in the form of a disk or ring, with two resting against the end faces of the magnet Pole pieces made of soft iron with radial extensions, the ends of which are bent by 90 ° and on the cylindrical periphery of the arrangement the pole pieces with alternately different ones Form polarity, characterized in that between the permanent magnet made of ceramic magnetic material and the soft iron pole pieces a cylindrical ring of temperature compensating Material is arranged on both PoI shoes is present. Considered publications:
German patent specification No. 922 445. 1 sheet of drawings 309 607/107 8.59