CS258809B1 - Contactless electromagnetic rotating tachogenerator - Google Patents

Abstract

The tachometer is an application in contactless electrical motor drives with an electronic switch-over. At the output of the electronic switch a constant voltage value is obtained at a constant rotation speed of the tachometer's rotor. The voltage generator includes a stator, with m-phase winding longitudinal channels, connected to the input of the switch and rotor with poles of alternating polarity, excited by permanent magnets. The winding is symmetrical, two-layer, with one parallel branch for each phase and with the same coils, one side of which forms the under-layer and the other the upper-layer to the winding. The winding pitch is equal to the channel pitch and its relation to polarity division is different than the unity. This value is determined by the ratio between the number of poles and the total number of coil windings. Given a constant rotation speed of the tachometer, the voltage shall be inducted at each winding phase, to which the inverse value is added by the switch, so that its voltage has a constant value.

Description

The present invention relates to a contactless electromagnetic rotary tachogenerator whose magnetic circuit consists of a stator provided with a longitudinal groove with a m-phase winding connected in a star connected to the input of an electronic commutator and a rotor arranged in a stator bore having regularly spaced circumferentially poles of alternating polarity excited by permanent magnets, the radial distance of the peripheral surface of the poles from the axis of rotation of the rotor is constant and the pole width on the outer periphery of the rotor satisfies the condition ^b _P ² i ^{+ b} o ^{+ 28 +} | -7 ^T p I wherein denote

- width of the outside of the rotor,

- pole pitch related to stator bore,

- number of stages of stator winding, b _Q - width of stator slot opening,

- radial air gap between stator and rotor, v - stator winding step related to stator bore.

For precise speed control over a wide range of modern brushless electric drives, it is necessary to use a contactless electromagnetic tachogenerator coupled to an electronic commutator, which outputs a direct voltage, proportional to the rotational speed of the tachogenerator coupled mechanically to the controlled electric drive. These tachogenerators tend to have a stator provided with an m-phase winding connected to the input of the electronic commutator. In the stator bore there is a rotor having regularly distributed circumferentially polarity poles excited by permanent magnets, the radial distance of the circumferential pole surface from pole on the outer periphery of the rotor fulfills the condition

where ^T P m

- the pole width at the outer periphery of the rotor,

- pole pitch related to stator bore,

- number of phases of stator winding, b _Q - width of stator slot opening, δ - radial air gap between stator and rotor,

- stator winding step related to stator bore.

From an electromagnetic and manufacturing point of view, it is advantageous to arrange the stator windings in grooves. In this case, only one groove in which a single-layer winding consisting of a coil or a coil group of the same phase of the stator winding is placed on one stator bipole formed by two adjacent pole pitches. The coils or coil groups of the other phases of the stator windings are arranged on other two-poles, the coil or coil axis axes forming an electric angle of ₃₆₀ oim

Accordingly, when the stator windings are arranged in the grooves, the number of m-phases of the stator winding must be less than or equal to the number of pole pairs. This has the effect of limiting the feasibility of the tachogenerator. A further disadvantage of the present embodiments is the relatively high requirements for manufacturing accuracy and material properties, since the variations in the magnitude of the magnetic flux in the individual poles of the generator cause variations in the voltages induced in the individual phases of the stator windings and thereby ripple voltage at the electronic commutator output.

The above-mentioned drawbacks of the present embodiments are overcome by the solution according to the invention, characterized in that the m-phase winding of the stator is formed as a symmetrical two-layer winding with one parallel branch in each phase and with the same coils. the stator winding layer, where the winding step is equal to the groove pitch and its relative to the pole pitch is different from one and is given by ^τ Ρ

2B. m.N where denotes ε - the relative step size of the stator winding with respect to the pole pitch, 2p - the number of poles,

N - number of coils of one phase of stator winding.

The solution according to the invention achieves the feasibility of the windings in the stator grooves even if the number of m-phases of the stator windings is greater than the number of p pairs of poles. This arrangement is advantageous from the electromagnetic and manufacturing point of view, since a smaller air gap can be made and the required induced voltage can be achieved with less excitation magnetomotor force of the permanent magnets or fewer coil windings of the stator windings. This leads to savings in materials, installation dimensions and labor. This embodiment is also less demanding on manufacturing accuracy and material properties when the number of coils per phase is greater than 1.

In the accompanying drawing, an exemplary embodiment of a tachogenerator according to the invention is shown, in FIG. 1 in cross-section, in FIG. 2 in longitudinal section and in FIG. 3, the waveforms of induced voltages in the individual winding phases of the tachogenerator stator.

The contactless electromagnetic rotary tachogenerator of Figs. 1 and 2 has a magnetic circuit consisting of a stator 2 * provided at its bore Six longitudinal grooves 2 ^{with a} three-phase star-wound winding connected to an electronic commutator input and a rotor 2 arranged in the stator bore 4 poles 2 of alternating polarity excited by permanent magnets 4. Poles 2 1 permanent magnets 2 are arranged on the circumference of the hub 2 · The front walls of the permanent magnets 2 and the poles 2 are pulled over rivets 2 over the sides 2. 8 against movement relative to the poles 2 · The hub 5, the side plates 2 ^{and the} wedges 2 are made of a non-ferromagnetic material. The radial distance of the peripheral surface of the poles 2 ^{from the} axis of rotation of the motor 2 is constant and the pole width on the outer periphery of the rotor 2 satisfies the condition

where it indicates

pole width on the outer periphery of the rotor, pole pitch related to stator bore, number of phases of stator winding, b _Q - width of stator slot opening, δ - radial air gap between stator and rotor, у - stator winding step related to stator bore.

The three-phase stator winding is formed as a symmetrical two-layer winding with one parallel branch in each phase and with the same coils 10, one side of which forms the lower layer and the other side the upper layer of the stator winding. the pole pitch is different from one and is given by the relation

^r ₽

m.N where denotes ε - the relative size of the stator winding step with respect to the pole pitch,

2p - number of poles,

N - number of coils of one phase of stator winding.

the time courses of the voltages induced in the individual phases of the stator windings are shown in FIG. The electronic commutator generates an inverted voltage 12, i.e. a counter-phase voltage, to the induced voltage 11 of each stator winding phase. the constant voltage periods 13 of the individual phases and counter-phases overlap at time points 14, i.e. the respective stresses are equal to each other at these time points.

The electronic commutator provides successive switching of the induced voltages 11 and inverted voltages 12 to its output at the time points 14 of their overlap, so that a DC voltage is obtained at the output of the electronic commutator, almost without ripple. The electronic commutator receives the impulses to switch the voltage of the individual phases and counter-phases from the rotor position sensor. Methods of making and wiring an electronic commutator and rotor position sensor are known from existing solutions.

Claims (2)

SUBJECT OF THE INVENTION Contactless electromagnetic rotary tachogenerator, the magnetic circuit of which consists of a stator provided with longitudinal slots with a m-phase winding, connected in a star connected to the input of an electronic commutator, and a rotor arranged in a stator bore having regularly spaced poles of alternating polarity , driven by permanent magnets, the radial distance of the peripheral surface of the poles from the axis of rotation of the rotor is constant and the pole width on the outer periphery of the rotor satisfies the condition k IE m ⁺ b _o + 2 δ where bp - pole width on rotor outer circumference, tp - pole pitch # related to stator bore, m - number of stator winding phases, b _Q - width of stator slot opening, δ - radial air gap between stator and rotor, у - a stator winding step related to the stator bore, characterized in that the m-phase stator winding is formed as a symmetrical two-layer winding with one parallel branch in each phase and with the same coils (10), one side of which forms the bottom layer; on the other side, the upper layer of the stator winding, where the winding step is equal to the groove pitch and its relative size to the pole pitch is different from one and is given by the relation ^Γ Ρ 2 £ m.N where denotes ε - the relative step size of the stator winding relative to the pole pitch, 2p - the number of poles (3), N - number of coils (Ί0) of one stator winding phase.