FR2756660A1 - Electromagnetic actuator for limited movement rotation mechanism - Google Patents

Abstract

The electromagnetic actuator has a principal magnetic circuit (4) made up of a number of magnetic poles and an electric coil. The section is circular, and there is a magnetic gap, inside which is placed a thin magnet (2,2'). There is an outer ring section (1) which is coaxial and through which the magnetic flux from the second magnet passes.

Description

Electromagnetic actuator for the rotational movement of a movable member on a limited stroke
The present invention relates to an electromagnetic actuator for the rotational displacement of a movable member on a limited stroke, formed by a main magnetic circuit having 2N magnetic poles and at least one electric coil, and a second magnetic circuit defining with the main magnetic circuit an annular air gap inside which is placed a thin magnet magnetized radially.

Such actuators are known in the prior art from the patents FR2670629, WO90 / 16107 and
FR2688105. The object of the invention is to improve the performance of such actuators, in particular by increasing the torque for a given size and a given type of permanent magnet.

 For this purpose, the invention consists in that the second magnetic circuit is constituted by a coaxial cylindrical stream return yoke with the tubular permanent magnet, the main magnetic circuit being disposed inside said second magnetic circuit.

 Placing the main magnetic circuit carrying the coil inside the permanent magnet makes it possible to optimize the size of the actuator and to increase the average radius of the magnet, with identical dimensions to that of the magnet. an actuator of the prior art.

 Advantageously, the main magnetic circuit comprises a single coil.

 According to an alternative embodiment, the main magnetic circuit comprises a plurality of coils each surrounding at least one magnetic pole.

 According to another variant, the permanent magnet is integral with the external magnetic circuit.

The invention will be better understood on reading the description which follows, with reference to the accompanying drawings in which
- Figure 1 shows a cross-sectional view of a first variant of the actuator according to the invention;
FIG. 2 represents a sectional view
AA of the actuator shown in Figure 1
FIG. 3 represents a cross-sectional view of an actuator for the positioning of a rotating member
FIG. 4 represents a cross-sectional view of a second variant of the actuator according to the invention;
FIG. 5 represents a sectional view
AA of the actuator shown in FIG.

 FIG. 1 represents a cross-sectional view of a first variant of the actuator according to the invention. The actuator comprises a cylindrical cylindrical stream return outer cylinder head (1) made of a soft magnetic material. The outer yoke (1) is rotatable in the example described. Inside this yoke (1) is arranged a main magnetic circuit (4) fixed having two magnetic poles (14, 15) diametrically opposed. The main magnetic circuit (4) is surrounded by an electric coil (5). The annular space formed between the main magnetic circuit (4) and the flux closing yoke (1) constitutes an air gap. Inside this gap is placed a permanent magnet (2) formed of two magnets (2, 2 '> half-cylindrical radially magnetized, in alternating directions, separated by transitions (3, 6). , 2 ') are thin magnets with a mean radius Rm.

The stator action torque on the magnets is
C = 2NBr L / EZ nI. rm
or
N is the number of pairs of magnet poles
Br denotes the remanent induction of the permanent magnet
L is the radial thickness of the magnet
E denotes the radial thickness of the air gap, including the thickness L of the magnet, between the inner stator (4) and the flux return yoke (1)
Rm is the average radius of the magnet
nI is the number of ampere-turns applied to the coil (5).

 The increase in the average radius Rm of the permanent magnet, for a constant external bulk, results in an increase in the torque. In addition, the use of a single coil, in the case where N = 1, results in a lower average coil length than in the structures of the state of the art, since the single coil is wound on the core (4). At equal power available, it is therefore possible to put a greater number of ampere-turns nI in the magnetic circuit.

This characteristic is also reflected in an increase in torque.

The magnetic poles (14, 15) have a developed width Y defined by the following relation
Y = C + 2E
or
C denotes the useful travel of the rotor with a substantially constant torque, measured on the mean radius Rm;
E denotes the radial thickness of the gap, including the thickness L of the magnet, between the inner stator (4) and the flux return yoke (1).

Moreover, the actuator structure according to the invention verifies the following relationship
N <s.2.Rm / 8E
so that the flow variation without current in the core (4) is a linear function of the rotation angle of the rotor, and that the torque with current is substantially constant as long as the transitions (3, 6) remain substantially in the race useful defined by the width Y of the poles (14, 15).

 In the example shown in FIG. 1, the useful travel is of the order of 920.

FIG. 2 represents a view according to a section
AA of the actuator shown in Figure 1. The coil (5) surrounds the inner stator pole (4). The height Z of the magnet (2) may be smaller than the height H of the yoke (1) so as to increase the flow return section of the yoke (1). When the dimensions of the actuator lead to a permanent magnet of large dimensions, it may be appropriate to use flexible magnets sold in the form of thick rollers
In such flexible magnets, a strip of width Z and of length 7tRm is cut out, and a flat magnetization is carried out through the thickness L. The flexible magnet is then rolled to form a half-pole of magnet. radially magnetized.

 Figure 3 shows a cross sectional view of an actuator for the positioning of a rotating member. An application of such an actuator is the coupling of the structure to a valve shaft (17) guided in rotation by two bearings (18, 19) and coupled to the cylinder head (1). The stator portion (4) is fixed on a support (16).

Such an actuator is in particular adapted to the actuation of an air intake butterfly valve.

 FIG. 4 represents a cross-sectional view of a second variant of the actuator according to the invention. It relates to an embodiment using two coils (5, 7) and 2 pairs of magnetic poles (10 to 13). It is possible to make a structure having a higher number of pole pairs. With two pairs of poles, the maximum stroke C constant torque will be close to 820, since an air space must remain air must exist between two adjacent stator poles.

 In the case shown in FIG. 4, only the poles 11 and 13 are surrounded by a coil. It is also possible to surround each pole (10 to 13) by a coil. The actuator is represented in the middle of the race, the NORTH / SOUTH transitions (3, 9, 6, 8) are represented in the middle of the poles (10, 13, 12, 11).

FIG. 5 represents a sectional view
AA of the actuator shown in FIG.

 The invention is described in the foregoing by way of non-limiting example.

Claims (5)

R E SELL T C AT T TONS  1 - Electromagnetic actuator for the rotational displacement of a movable member on a limited stroke, formed by a main magnetic circuit (4) having 2N magnetic poles and at least one electric coil, and a second magnetic circuit (1) defining with the main magnetic circuit an annular air gap inside which is placed a thin magnet (2, 2 ') magnetized radially characterized in that the second magnetic circuit (1) is constituted by a cylindrical stream return yoke coaxial with tubular permanent magnet, the main magnetic circuit being disposed inside said second magnetic circuit.  2 Ac - Electromagnetic actuator for moving in rotation of a movable member according to claim 1 characterized in that the main magnetic circuit comprises a single coil.  3 Ac - Electromagnetic actuator for moving in rotation of a movable member according to claim 1 characterized in that the main magnetic circuit comprises two coils.  4 - electromagnetic actuator according to any one of the preceding claims characterized in that the permanent magnet (2) is integral with the external magnetic circuit (1).  5 - Electromagnetic actuator according to any one of the preceding claims, characterized in that the magnetic poles (14, 15) have a developed width Y defined by the following relation  Y = C + E  or  C denotes the useful travel of the rotor with a substantially constant torque, measured on the mean radius Rm;  E denotes the radial thickness of the gap, including the thickness L of the magnet, between the inner stator (4) and the flux return yoke (1).  6 - electromagnetic actuator according to any one of the preceding claims characterized in that the actuator structure verifies the following relationship  N <w.2.Rm / 8E 7 - Electromagnetic actuator for moving in rotation of a movable member according to claim 2 characterized in that the useful stroke at substantially constant torque is of the order of 920.  8 - Electromagnetic actuator for moving in rotation of a movable member according to claim 3 characterized in that the useful stroke at substantially constant torque is of the order of 820.  9 - electromagnetic actuator according to any one of the preceding claims characterized in that the permanent magnet is a thin flexible magnet.