GB2067024A - An electrical stepping drive motor - Google Patents

Abstract

An electrical stepping drive motor comprises a rotor (2) having an even number of areas (28, 29) of permanent magnetization, separated in an angular manner by one step. A stator (1) comprises the same number of poles (31, 32) also distributed along the inner periphery and along the outer periphery of the rotor (2) in identical radial positions. Means (36) are provided for establishing at will reverse polarities in the stator poles (31, 32) located respectively inside and outside the rotor (2) and for reversing these polarities at will. The motor has particular application to the construction of reduction gear units and mileage recorders. <IMAGE>

Description

SPECIFICATION An electrical stepping drive motor The present invention relates to an electrical stepping drive motor and a reduction gear unit making use of the latter.

In a known method of construction, stepping motors, used for example for driving mileage recorders on the dashboard of motor vehicles, comprise a stator and a rotor which is constructed in the form of a permanent magnet. The magnet comprises an outer periphery of revolution about its axis of rotation along which alternately positive and negative poles are distributed in a uniform manner, at a relative angular distance equal to one step.

The stator comprises the same number of poles around the outer periphery of the rotor which poles are distributed in the same manner. At each pole a winding located either as an axial extension of the rotor, or around the outer periphery of the latter, makes it possible to impart at will magnetization in the opposite direction to the direction of magnetization of two directly adjacent stator poles, the polarity of all the stator poles being able to be reversed at will in order to cause rotation of the rotor step by step.

This type of motor is quite satisfactory, apart from the fact that its demensions, either in the direction of the axis if the coil is placed beside the rotor in this direction, or as regards its diameter if the coil is placed around the rotor, sometimes cause difficulties as regards being incorporated in an arrangement such as the dash-board of a vehicle.

To the extent that the overall dimensions of the motor are closely linked with its number of poles and where this number cannot be considerably reduced, the desirable reduction in the overall dimensions of the motor seems difficult to achieve if one retains this known design of stepping motor.

The object of the invention is to reduce the overall dimensions of stepping motors, in order to facilitate their incorporation for example in the dash-boards of motor vehicles, generally in the form of reduction gear units and to this end to propose a new structure of electrical stepping drive motor.

According to a first aspect of the present invention there is provided an electrical stepping drive motor, comprising a rotor and a stator mounted for relative rotation about an axis, and characterised in that: - the rotor comprises an even number of areas uniformly distributed in an angular manner about an annulus of the axis, each of these areas being separated in an angular manner from its two adjacent similar areas by the angular length of one step and comprising permanent magnetization in a radial direction which is in a direction the reverse of that of said adjacent areas; the stator comprises the same number of poles or a number of poles which is an even sub-multiple of this number by an even number, the stator poles comprising two steps uniformly distributed respectively along the inner periphery and along the outer periphery of said annulus, one pole of one set being located radially opposite one pole of the other set; and means are provided for establishing the same polarity at will in the poles of one of the sets of the stator poles and the same polarity, which is the reverse of the former, in the poles of the other set of the stator poles, and in order to reverse the said respective polarities of the two sets at will and thus to bring about a rotation of the rotor with respect to the stator, by the value of one step.

According to a second aspect of the present invention there is provided a reduction gear unit according to the first aspect of the present invention the rotor having an output shaft on which a satellite-carrier is mounted to rotate freely, which satellite-carrier supports a planetgear wheel with an axis parallel to said axis of the motor and meshing with outer teeth of the output shaft of the rotor and with inner teeth of a ring with an axis coinciding with that of the rotor.

Means are provided for establishing the same polarity at will in stator poles located inside the rotor annulus and the same polarity, namely the reverse of the former, in the other stator poles. A stable position of the rotor with respect to the stator is a position in which the rotor comprises, opposite two respectively inner and outer poles of the stator occupying the same radial position, an area of its inner periphery which has reverse polarity to the instantaneous polarity of the inner stator pole in question and an area of its outer periphery having reverse polarity to that of the outer stator pole in question, i.e. identical to that of the inner stator pole.In view of the distribution of the various poles, the magnetized areas of the rotor directly adjacent areas arranged in this way are thus free, i.e. in an intermediate radial position between the respective radial positions of adjacent stator poles in a peripheral direction.

The reversal of the polarity of the stator poles, which leads to the location of each of the latter opposite an areas of the rotor respectively having the same polarity, brings about a rotation of the rotor, by the value of one step, in order to re-establish equilibrium, the direction of rotation being determined by an advantageous design of the stator poles.

One should note that in a structure of this type each magnetized area of the rotor is constituted by two radially adjacent poles, of permanent reverse polarity. If one makes a comparison between a motor according to the present invention and a motor of traditional design having the abovementioned known structure, then with regard to the number and configuration of the poles of the stator for the same number of poles of the rotor in the case of a motor according to the invention the stator poles are arranged respectively around the outer and the inner periphery of the rotor so that in the case of the motor according to the invention, half the number of poles are distributed along the outer periphery of the rotor as in the case of a motor of traditional design.

An arrangement of this type is advantageous in that for any give total volume of a motor, it is possible to increase the diameter of the permanent magnet constituting the rotor and thereby to increase the torque developed by this motor, since this torque is substantially proportional to the square of the radius of the magnet. In other words, with equal developed torque, it is possible to reduce the diameter of the magnet and therefore to reduce the dimensions of the motor in view of the fact that it is also possible to increase the angular development of the stator poles and to reduce their radial dimension.

Furthermore, the structure of the motor according to the invention makes it possible to utilize the permanent magnet constituting the rotor to the best effect, since this magnet is magnetized radially which closes the magnetic circuit to the maximum extent, in a manner which is quite favourable for magnets having a high coercive field such as plastoferrites generally chosen for this type of use.

For example, in the case of an application in a mileage recorder for a motor vehicle, the coupling of a motor having a structure according to the invention and of a planet gear train makes it possible to provide a particularly compact reduction gear unit providing an adequate reduction ratio with a low number of pinions.

Preferably, the inner and outer poles of the stator are magnetized at will by a common winding housed inside the inner stator poles, i.e. inside the rotor, about the axis, which makes it possible to use the inner space of the rotor advantageously and, whilst eliminating any outer winding, to considerably reduce the overall dimensions of the motor or of the reduction gear unit making use of the latter.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross-sectional view of a reduction gear unit according to the invention for driving a mileage recorder and trip recorder of a motor vehicle; Figure 2 is a cross-sectional view on the line ll-ll of Fig. 1; Figure 3 is a view of an outer pole of the stator, as it appears in a centripetal direction; and Figure 4 shows diagrammatically the supply of electric power to the winding of the stator.

The reference numeral 1 designates the stator of the motor, the numeral 2 its rotor, which is able to rotate about an axis 3 with respect to the stator and the numeral 4 a reduction planet gear train moved by the rotor 2 as it rotates. The function of this planet gear train 4 for example is to rotate two sets of graduated drums respectively 7 and 8 about their respective axes, 5 and 6 respectively, parallel to the axis 3, the first of which drums constitutes a mileage recorder and the second a trip recorder, both being of known type and not shown in detail (see in particular Fig. 1).

In the example illustrated, the rotor 2 is constituted by a disc 9 centred on the axis 3 and arranged transversely with respect to the latter and by an annular ring 10 constituting a peripheral rim of the disc. Respectively towards the axis 3 and in the direction moving away therefrom the annular ring 10 is defined by an inner periphery 11 and by an outer periphery 12, both being cylinders of revolution about the axis 3.

In a central area, the disc 9 is mounted to rotate freely about the axis 3 and to this end comprises, in an integral manner, a central sleeve 13, comprising a general shape of revolution about the axis 3 and in particular comprising a central bore 14 which is a cylinder of revolution about this axis 3. This bore 14 is engaged around the periphery 1 5, which is also a cylinder of revolution about the axis 3, of a shaft 1 6 integral with the stator 1 by one of its transverse ends bearing the reference numeral 1 7 in Fig. 1 and which is located inside the ring 1 0.

The sleeve 1 3 is flush with the side of the disc 9 from which the ring 10 projects and projects from the second side of this disc, in an area where it comprises externally straight gear teeth 1 8 with which mesh the peripheral teeth of a satellite pinion 19, which is mounted to rotate freely about an axis 20, parallel to the axis 3, on a satellite-carrier 21 itself mounted to rotate freely about this axis 3.At its transverse end 23 remote from the end 17, the shaft 1 6 comprises a fixed stopper 22 which prevents the satellite-carrier 21 from moving axially, against the sleeve 1 8 itself abutting against the fixed core 24 which, as will be seen hereafter, constitutes the central part of the stator 1 and receives the end 1 7 of the shaft 1 6 in an integral manner.

Meshing firstly with the teeth 1 8 of the sleeve 13, the satellite pinion 1 9 also meshes with a fixed toothed ring 25 on the axis 3, provided along the inner periphery, which is a cylinder of revolution about the axis 3, of a fixed housing 26 also receiving on its interior, the stator 1, in an integral manner.

Thus, the rotation of the rotor 2 about the axis 3, causes a rotation of the satellite-carrier 21 about this same axis 3, in the same direction but at a lower speed. The satellitecarrier 21 in turn comprises external teeth 27 which mesh, in manner known per se, with complementary outer teeth, respectively on the axis 5 and on the axis 6, comprised by the sets of drums, constituting the mileage recorder and trip recorder respectively 7 and 8.

According to the invention, as is shown particularly clearly in Fig. 2, the rotor 2 constructed from a material which is well suited to permanent magnetization, comprises in the vicinity of the ring 10, a uniform alternation of an even number of areas having permanent magnetization in a radial direction, respectively in one direction and the other.

In the example illustrated, the ring 10 thus comprises five areas such as 28 comprising a basic south pole, identified by the letter S, in the immediate vicinity of the outer periphery 1 2 and a basic north pole, identified by the letter N in the immediate vicinity of the inner periphery 11, these areas such as 28 alternating with areas such as 29 comprising a north pole, identified by the letter N, in the immediate vicinity of the outer periphery 1 2 and a south pole, identified by the letter S, in the immediate vicinity of the inner periphery 11, the two basic N and S poles defining each of these areas such as 28 and 29 being arranged respectively in the same radial direction with respect to the axis 3.The angular distance separating an area 28 from each of the directly adjacent areas 29, or each of the areas 29 from the directly adjacent areas 28, is equal to the angular length of the step of the motor, i.e. to the angular travel of the rotor, with respect to the stator, for each of its rotations about the axis 3 in a pre-determined direction shown diagrammatically in Figs. 2 and 3 by an arrow 30.

In the example illustrated, a rotation of the rotor through 360 about the axis 1 corresponds to 10 steps, the total number of intervals between an area 28 and an area 29 being equal to 10, but one could naturally construct stepping motors according to the invention whereof the rotor would comprise a different number of magnetized areas such as 28 and 29, provided that this number is even in order to take into account the alternation of magnetized areas in the reverse radial direction such as 28 and 29 respectively. The number of these magnetized areas corresponds to the number of steps for a rotation of the rotor through 360 about its axis, with respect to the stator.

In a complementary manner, the stator 1 comprises poles whereof the polarity is reversed in order to cause the rotation of the rotor step by step.

According to the invention, these poles of the rotor are distributed both along the inner periphery 11 and along the outer periphery 1 2 of the ring 10, their total number being equal to the total number of magnetized areas 28 and 29 of the ring 10, or possibly to an even sub-multiple of this number by an even number. Half of these poles of the stator are arranged along the outer periphery 1 2 of the ring 10 and the other half along the inner periphery 11 of the latter, in both cases in a uniform manner, there being associated with each pole located outside the ring a pole located inside the latter, in the same radial direction.

Thus, in the example illustrated in Fig. 2, five stator poles such as 31 are arranged along a virtual ring on the axis 3, opposite the inner periphery 11 of the rotor ring 10 and five other poles 32 are arranged along a virtual annular ring on the axis 3 opposite the outer periphery 1 2 of the ring 10, one pole 31 being associated with a pole 32 in the same mean radial direction. The mean orientations of two adjacent poles 31, or of two adjacent poles 32, are offset in an angular manner by the value of two steps.

In the example illustrated, each of the poles 31 is constituted by a finger-shaped member arranged substantially or approximately parallel to the axis 3, supported by the periphery of a pole-piece 33 in the form of a basic centred on the axis 3 and arranged perpendicular to this axis, in a fixed position, in the immediate vicinity of the side of the disc 9 from which the ring 10 projects.In the immediate vicinity of the axis 3, the disc 33 is integral with the above mentioned core 24, which is in the form of a sleeve extending in the direction moving away from the rotor disc 9 and in its area furthest from the latter comprising a fixed disc 34 centred on the axis 3 and arranged transversely with respect to the latter, which disc 34 overlaps the free edge 35 of the ring 10 and on its periphery, beyond this ring, comprises finger-shaped members located opposite the periphery 1 2 of the latter and each of which constitues a pole 32.

The finger-shaped members defining the poles 31 and 32, the pole-pieces in the form of discs 33 and 34 and the core 24 are made from a material which is sensitive to magnetic phenomena and give rise to hysteresis phenomena which are as unnoticeable as possible and housed in the annular space defined around the core 24 by the discs 33 and 34 and by the virtual ring along which the poles 31 are distributed is at least one winding 36 connected to an external supply circuit 39 (see Fig. 4) by leads 37 passing through the disc 34 via an orifice 38 in the latter.

The function of the winding 36 and of its supply circuit 39 is to establish at a given instant a magnetization of the same polarity in all the poles 31 and magnetization of the same polarity, which is the reverse of the former, in all the poles 32, in order to bring about rotation of the rotor 2 by one step in the direction of arrow 30 and then to reverse at will the respective polarities of the poles 31 and 32 when it is necessary to bring about a new rotation of the rotor 2 by the value of one step in the direction of arrow 30.

To this end, the winding 36 may be constituted by a single winding in which a circulation of electric current is established alternately in one direction and the other in order to bring about successive rotations by one step. Another embodiment is illustrated in which the winding 36 is split into two windings of reverse direction, respectively 36a and 36b, comprising a common terminal 0 and an individual terminal respectively A and B.

In addition, the supply circuit 39 comprises terminals 0', A', B', connected respectively to the terminals O,A,B.

The circuit 39, which can be easily constructed by a man skilled in the art, is chosen so that on receiving successive control pulses coming, in the case of the example illustrated, from a pick-up 40 counting the revolutions of the output shaft of the gear box (not shown), it emits alternately at its output terminal A', leading to the terminal A and the winding 36a and at its terminal B', leading to the terminal B and the winding 36B, an electrical current of the same polarity which, depending on whether it passes through the winding 36a or the winding 36b, causes a polarization of the finger-shaped members 31 and 32 in one direction or the other.

Fig. 4 shows diagrammatically, in two simultaneous diagrams respectively 41 and 42 the evolution in time of the electrical signal coming from the terminal A' and of the electrical signal coming from the terminal B' in consequence of the reception by the circuit 39 of successive pulses coming from the circuit 40.

This figure shows that a square-wave signal corresponding to the injection of a current into one of the terminals, respectively A or B, of the winding 36 in consequence of the reception by the circuit 39 of a control pulse coming from the circuit 40 follows and precedes a time during which no current is injected into this terminal and during part of which the other terminal receives a current consecutive to the reception by the circuit 39 of the immediately preceding or immediately following pulse coming from the pick-up 40.

The times for injection of a signal in one or other of the terminals A and B, bearing the references T, and T2 for example in Fig. 4, correspond respectively to a rotation of the rotor 2 in the direction of arrow 30, by the value of one step; owing to the fact that the supply of power to the winding 36 respectively causes the appearance at the poles 31 and 32 of polarities identical to those of the basic poles of the immediately adjacent rotor, which in the vicinity of each of the poles 31 and 32 causes the repulsion of the basic poles and the attraction of the directly adjacent basic poles, the rotation stopping when the latter are located opposite the poles of the stator. The intermediate times T3 and T4, when no signal is injected either at terminal A or at terminal B, correspond to a period of stoppage of the motor.

The motor has been illustrated in Fig. 2 at the beginning of a time of rotation such as T, or T2, where the poles 31 have a south polarity opposite the basic south poles of the inner periphery 11 of the ring 10 and where the poles 32 have a north polarity opposite the basic north poles of the outer periphery 12 of the ring 10.

In order that successive injections of current into the terminals A and B produce a rotation of the rotor 2 always in the same pre-determined direction illustrated by arrow 30 in Figs. 2 and 3, it is possible to adopt various known solutions and for example to split each stator pole 31 or 32 into two, namely into a main pole and an auxiliary pole, located directly upstream of the main pole, referring to the direction of rotation 30, the main pole having a greater mass than that of the auxiliary pole in order that, when the rotor is immobilized with respect to the stator, the mean radial position of the rotory poles is slightly off-set in the downstream direction, taking into account the pre-determined direction of rotation 30, with respect to the mean radial direction of the corresponding stator poles (as shown in Fig. 2, where the rotor at the very beginning of its rotation by one step still occupies this position).

Fig. 3 illustrates two methods of splitting a pole 32 into a main pole and an auxiliary pole, the splitting of each of the poles such as 31 taking place in the following manner.

A first method of splitting the poles, shown diagrammatically in broken line, consists of splitting the finger-shaped member constituting the pole 32, in the form of a downstream finger-shaped member 32a and a fingershaped member 32b located directly upstream, the finger-shaped member 32a having a mass greater than that of the finger-shaped member 32b in order to form the main pole, the auxiliary pole being constituted by the finger-shaped member 32b.

Another method of splitting the poles is illustrated in full line. According to this embodiment, the projection formed by the single finger-shaped member 32, with respect to the stator disc 34, increases progressively from an upstream point to a downstream point, in order to define from an upstream point to a downstream point, the auxiliary pole then the main pole, which may be accentuated by a sudden increase in the height of the fingershaped member 32 in its downstream region, as illustrated.

Other arrangements could naturally be adopted without diverging from the scope of the invention.

Generally, the present invention may have numerous variations with respect to the em bodiment described and illustrated. In particular, for each application, a man skilled in the art will chose the most suitable electrical control circuit such as 39 and the most suitable construction of the winding 36, as well as the number of poles chosen according to the torque and the number of desired steps per revolution of the rotor, as well as according to requirements relating to dimensions.

It will be noted that, in particular as has been described and illustrated as a non-limiting example, a stepping motor constructed according to the present invention is insensitive to possible external magnetic fields and itself does not emit a parasite magnetic field towards the exterior despite the fact that its winding is supplied with pulses, the surrounding stator acting as a type of screening.

Claims (10)

1. An electrical stepping drive motor, comprising a rotor and a stator mounted for relative rotation about an axis, and characterised in that: - the rotor comprises an even number of areas uniformly distributed in an angular manner about an annulus of the axis, each of these areas being separated in an angular manner from its two adjacent similar areas by the angular length of one step and comprising permanent magnetization in a radial direction which is in a direction the reverse of that of said adjacent areas; the stator comprises the same number of poles or a number of poles which is an even sub-multiple of this number by an even number, the stator poles comprising two steps uniformly distributed respectively along the inner periphery and along the outer periphery of said annulus, one pole of one set being located radially opposite one pole of the other set; and means are provided for establishing the same polarity at will in the poles of one of the sets of the stator poles and the same polarity, which is the reverse of the former, in the poles of the other set of the stator poles, and in order to reverse the said respective polarities of the two sets at will and thus to bring about a rotation of the rotor with respect to the stator, by the value of one step.

2. A motor as claimed in claim 1, in which said means comprise at least one winding common to all the poles of the stator within the annulus and a core arranged along the axis of and within the winding, the core comprising two pole-pieces arranged transversely with respect to the axis respectively on either side of the winding, and the said polepieces comprising, respectively along the inner periphery and along the outer periphery of the ring, finger-shaped members which are arranged substantially parallel to the axis and each of which defines a pole respectively of one and the other set of stator poles.

3. A motor as claimed in claim 2, in which the winding comprises a single winding and in that means are provided for establishing at will in this single winding, a circulation of electric current of pre-determined polarity alternately in one direction and the other.

4. A motor as claimed in claim 2, in which the winding comprises two windings of opposite directions and means are provided for making current of the same polarity circulate alternately in one winding and the other.

5. A motor as claimed in any one of the preceding claims, in which each pole of the stator comprises a main pole and an auxiliary pole, which is located immediately upstream of the main pole with regard to the direction of rotation of the rotor and which has a mass less than that of the main pole.

6. A motor as claimed in claim 5 when dependent on any one of claims 2 to 4 in which the main pole and the auxiliary pole are defined by respectively downstream and upstream areas of a single finger-shaped member, the mass of which increases progressively from the upstream end towards the downstream end.

7. A motor as claimed in claim 5 when dependent on any one of claims 2 to 4, in which the main pole and the auxiliary pole are defined by two adjacent separate fingershaped members, comprising one upstream finger-shaped member and one downstream finger-shaped member having a mass greater than that of the upstream finger-shaped member.

8. A reduction gear unit comprising a motor according to any one of the preceding claims, the rotor having an output shaft on which a satellite-carrier is mounted to rotate freely, which satellite-carrier supports a planetgear wheel with an axis parallel to said axis of the motor and meshing with outer teeth of the output shaft of the rotor and with inner teeth of a ring with an axis coinciding with that of the rotor.

9. A mileage recorder comprising a reduction gear unit as claimed in claim 8, the satellite-carrier comprising external teeth and having an axis coinciding with the axis of the rotor, these teeth meshing with complementary teeth of a mileage-recorder drum, and the means provided for establishing and reversing at will the polarity of the poles of the stator being controlled by pulses representative of the rotation of the output shaft of the gearbox.

10. An electrical stepping drive motor substantially as hereinbefore described with reference to the accompanying drawings.