FR2863787A1 - Electromagnetic retarder`s annular rotor for terrestrial vehicle`s transmission, has undercut formed between lateral edge of axial end of fin and lateral side of induced disc for forming heat barrier - Google Patents

Abstract

The rotor has a flange (38) parallel to an induced disc (36) and ring gear cooling fins (40), where each fin extends between a lateral side (48) of the disc and internal lateral side (50) of the flange. Some fins radially extend inside the rotor to form a series of fixation arms (62). An undercut (74) is formed between a lateral edge (58) of an axial end of the fin and the side (48) for forming a heat barrier.

Description

"Advanced ring rotor

  The present invention relates to an annular electromagnetic retarder rotor, in particular for a land motor vehicle transmission.

  The invention more particularly relates to a rotor of the type comprising: a flat annular armature disk intended to extend facing a series of pole assemblies of a stator of the retarder - a flat annular cheek parallel to the disk; and a ring of cooling fins forming axial spacers each of which extends axially between the lateral faces facing the disk and the cheek and some of which extend radially inwards, beyond the edge inner peripheral of the disc, to form a series of rotor attachment arms.

STATE OF THE ART

  It is known that to slow down vehicles having a high inertia related to the weight and speed of the vehicle, it is necessary to use so-called endurance braking. Indeed, a conventional braking service called involving brake pads that rub against a disk hub of a wheel, is not always sufficient to ensure the safe braking of heavy vehicles, especially following a long descent. Endurance braking thus makes it possible to maintain a determined and desired speed of the vehicle.

  In addition, even if conventional braking with pads seems suitable and does not require the introduction of endurance braking, premature wear of the pads is unavoidable. Without endurance braking, a driver must constantly change the brake pads. Endurance braking thus also makes it possible to limit platelet changes and thus to save money.

  In order to achieve this endurance braking, an electromagnetic retarder is often used.

  There are three types of electromagnetic retarders. There are electromagnetic "Axial" type retarders (trademark), electromagnetic "Focal" type retarders (trademark io filed), and "Hydral" type electromagnetic retarders (registered trademark).

  The three types of electromagnetic retarders cited are characterized by their location on a motor shaft or motion drive shaft to at least one wheel of the vehicle.

  Axial type retarders are located on the drive shaft. They "cut" this drive shaft into two sections or parts. Two cardan joints are used for axial retarders. These universal joints connect the axial retarders to both ends of the drive shaft. These cardan joints are intended to prevent the axial retarder from becoming mechanically hyperstatic by giving it sufficient degrees of freedom. In the case where the system would be hyperstatic, the retarder would not have enough degrees of freedom allowing its proper rotation, and the slightest shock it would yield and separate the vehicle. Conventionally an axial electromagnetic retarder is in the transmission line of motion between a bridge and a gearbox of the vehicle and has a connecting shaft between the two universal joints.

  In an axial-type electromagnetic retarder, the stator carries at its radially inner periphery a sleeve equipped with bearings. These bearings can be conical type. These bearings act radially between the connecting shaft and the sleeve and they ensure the maintenance of the shaft by preventing it from being offset. These bearings wedge the shaft so that the degrees of freedom of the shaft allow it a continuous rotation. The axial retarder is thus "connected" to the drive shaft.

  As regards Focal-type electromagnetic retarders, they are located at the entrance of the bridge or at the output of the gearbox of the engine of the vehicle. In one example, the Focal type retarders are attached to or connected to a deck of a bridge input shaft via a universal joint. For these electromagnetic retarders, the motion transmission shaft is in one piece. The bridge of a vehicle is the part that drives a wheel shaft. This wheel shaft drives at least one wheel of the same vehicle. Such a retarder is described in document FR-A-2,577,357 and is connected to the output shaft of the gearbox or the input shaft of the bridge.

  The electromagnetic retarder Hydral type is described for example in the document FR-A-2,627,913. This retarder is usually mounted in focus. The cooling of a Hydral retarder is performed by a cooling water circuit of the vehicle engine, while a Focal or axial retarder uses a fan to achieve this cooling. Compared with a conventional Focal or axial electromagnetic retarder, the water circuit of the Hydral electromagnetic retarder makes it more efficient.

  In general, the basic structure of an electromagnetic retarder, of whatever type, comprises at least one stator and at least one rotor. A very small axial gap corresponding to a space exists between the rotor and the stator. The stator, if it is inductive, carries near and along a periphery, at least one coil. The induced rotor is placed in a plane parallel to a plane of the inducing stator. The rotor rotates around an axis of the stator. A rotational movement is imparted to the rotor via a drive shaft of the vehicle.

  The rotor, if it is induced, does not carry a coil (s). The induced rotor is provided to close the magnetic field produced by the coils integral with the stator.

  In some cases, for example in document FR-A-2,627,913, the stator may be induced and the rotor inductor. In these cases, the inductor rotor carries the coils and the induced stator carries no coil.

  Generally, the electromagnetic retarders comprise an even number of alternating polarity coils. Electromagnetic retarders often have at least six coils. A coil has a hollow annular cylindrical shape. However, the section of the coil may be other than circular annular. A coil may be for example square, elliptical or any other geometric form.

  The coils are formed by the winding of an electrical wire around the chosen form of revolution. In one example, the coils are made from a copper wire covered with an insulating citric layer. The winding of the copper wire makes it possible to define an axis of the coil orthogonal to the direction of winding of the electric wire.

  Axial type electromagnetic retarders generally comprise two rotors and two stators. The two stators comprise flanges contiguous on a face opposite an insertion face of the coils and thus form a single stator connected to the chassis of the vehicle. The connection between the two stators and the frame is preferably made by means of elastic blocks.

  The electromagnetic Focal type retarders generally comprise two rotors and a stator. The stator is connected to the case of the gearbox or the deck. The two rotors are assembled together. In one example, the rotors are fixed on the axial ends of an axial axial piece in the form of a sleeve, or rings, passing through the central orifice of the stator. This intermediate piece carries a disc on which are mounted a drive shaft and a drive shaft of the gearbox or led deck.

  A physical phenomenon called eddy current phenomenon allows the electromagnetic retarders to achieve the actual slowdown of the vehicle and thus the endurance braking. These eddy currents are also called magnetic currents. These currents appear in a metal mass placed in a variable magnetic field.

  In one application, the magnetic field of the three types of retarder is provided by coils whose polarities are alternated. The three types of retarders have preferably soft iron poles mounted in the coils and spurs which are intended to prolong and guide the magnetic effect of the coil.

  Polar expansion is a polar piece that guides the magnetic field of the coils. In some cases, the development has a particular shape that makes it protrude axially from the coil to optimize the passage of a magnetic flux. The magnetic flux is related to the intensity of the magnetic field, as well as to the surface of the pole piece that the field crosses.

  The blossoming and the poles form a metallic mass. In the presence of this metallic mass, and the magnetic field created by the coils, and when a rotor of the retarder rotates, the value, the direction and the direction of the magnetic field become variable. The eddy currents then appear so that a pair associated with them opposes the rotation of the rotor. This torque related to the appearance of current and allows the electromagnetic retarders to oppose the movement of the motor shaft of the vehicle and slow the movement of the vehicle.

  This slowdown is performed as a function of the intensity of the current flowing through the coils and as a function of the speed of rotation of the rotor. The currents and the rotational speed of the rotor are at the origin of a braking torque and a braking energy. The braking energy is converted into heat. To dissipate this heat, electromagnetic retarders use cooling systems.

  The power of a retarder depends on that of the eddy currents. However, the field or the magnetic flux produced by the coils forms a magnetic circuit between the coil, the expansion and the rotor. More particularly, the power of a retarder also depends on the magnetic flux that the retarder is able to transmit between the rotor and the bloom.

  The development and the rotor each have flat and smooth surfaces and they are separated by the air gap.

  More precisely, the planar surface of the rotor belongs to a ring or annular disc that it comprises.

  The rotor, also called armature rotor, comprises for example a flat "thick" annular disc made of ferromagnetic material which, in operation, rotates in rotation with respect to a succession of alternating magnetic pole, positive and negative, which are also arranged circumferentially in a ring.

  The side face of the disk adjacent to the pole assemblies is separated from them by an air gap or axial clearance.

  The thick disk, and therefore the rotor, is braked by the formation of eddy currents in the mass of the disk.

  The radially inner ends of the rotor attachment arms are for example connected to an inner ring or drum.

  Document FR-A-2,577,357 describes and illustrates the general design of an exemplary embodiment of such a retarder comprising two identical armature rotors arranged axially on either side of the stator and whose arms are connected to adjacent central rings to which a transmission universal joint flange is fixed and rotatably connected.

  The evacuation of the calories resulting from the heating of the rotor disk by the eddy currents, during the operation of the retarder comprising such a rotor, is done by thermal conduction through the fins towards the cheek and by radiation and convection from the disc, fins, arms and cheek. There is also a phenomenon of ventilation, or self-ventilation, because the design of the rotor with its crowns of fins makes the rotor a fan wheel which sweeps a cooling air which, while circulating through the rotor , cools the hot surfaces.

  The power of a retarder, that is to say its braking capacity for a given supply current of the coils is electromagnetic pole assemblies, depends on that of the eddy currents formed in the disk and therefore the temperature of the coil. latest.

  Indeed, more specifically, the available effective deceleration torque decreases significantly depending on the heating of the disk resulting from the formation of eddy currents.

  The "hot" value of the deceleration torque, for example after a few minutes of continuous and prolonged operation, can be reduced for example by about one-third compared to its instantaneous "cold" value, for given values of the operating speed. rotation and the electrical power consumed, when the temperature of the disk rises from the ambient temperature to an operating temperature of the order of 700 C to 750 C.

  The ability of the rotor to cool is therefore an important factor in the effectiveness or efficiency of the electromagnetic retarder.

  In the context of this cooling, the calories removed by thermal conduction in the fins propagate, on the one hand, in the outer lateral cheek and, on the other hand, in the rotor attachment arms in the case of the fins which are extend by such attachment arms.

  Thus, for a maximum temperature of about 750 ° C of the disc, the temperature of the cheek is 450 ° C., and the temperature of the arms is 350 ° C.

  The choice of the constituent material of the fins and the arms, which is the same as that of the disc and the rotor when the assembly is made in one piece by molding, is therefore usually a compromise.

  Indeed, the material must have good "magnetic" performance and a very good endurance "thermomechanical".

  When a steel (SM 101) having very good magnetic performance is chosen, these thermomechanical performances can prove to be insufficient because of the very high temperature reached by the fixing arms.

  In order to improve the thermomechanical behavior, it is necessary to use more alloyed steels (SM 125 or SM 130).

  However, improved thermomechanical performance is detrimental to magnetic performance.

  Thus, there is a 5% drop in magnetic performance, with an overall cost increase of 10% (SM 125) for a 5% improvement in thermomechanical performance, or even a 15% decrease in magnetic performance, with an increase of cost of 25% (SM 130) for a gain of 10% in thermomechanical performance.

  Thus, the simple choice of a material, or of several materials when the rotor is made by assembling components of different materials, for example by welding, does not make it possible to obtain a satisfactory compromise.

Claims (1)

SUMMARY OF THE INVENTION In order to overcome these disadvantages, the invention proposes a rotor of the type mentioned above, characterized in that thermal barrier means are interposed between the axial end lateral edge of at least one fin adjacent to the disc and said side face of the disc. Thus, the transfer of heat loads towards the arms is significantly reduced. Advantageously and at a very low cost, the means forming a thermal barrier are constituted by axial clearance (j) between at least one portion of said axial end lateral edge of the fin and said lateral face of the disc. The thermal barrier is thus constituted by air. According to other features of the invention: the axial end lateral edge of the fin has a recess whose axial end lateral edge constitutes said portion which extends with axial clearance opposite said lateral face of the fin; disk; the axial clearance is substantially constant along said section; the axial clearance varies along said section; the recess opens out radially inwards; - The extension radially inwardly of the fin to form a rotor attachment arm extends with play opposite the inner peripheral edge of the disc; - Thermal barrier means are interposed between the axial end side edge of each of the fins which extends radially inwardly to form a rotor attachment arm, and the disk. DESCRIPTION OF THE FIGURES Other features and advantages of the invention will become apparent on reading the following detailed description for the understanding of which reference will be made to the appended drawings, in which: FIG. 1 is a perspective view with cutaways an embodiment of an electromagnetic retarder 5 according to the state of the art; - Figure 2 is a detail view on a larger scale and in section through the median axial plane of a pole assembly; FIG. 3A is a diagrammatic cutaway perspective view illustrating an exemplary embodiment of an armature rotor according to the state of the art with a single ring of vanes; FIG. 3B is a diagrammatic cut-away perspective view which illustrates another exemplary embodiment of an armature rotor according to the state of the art with several concentric crowns of fins and of which some fins of the crown radially more interior extend globally radially to constitute arms; - Figure 4 is a view similar to that of Figure 2 which illustrates an embodiment of the invention of rotor 20 armature. DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS In the following description, like, like or like elements and components will be referred to by the same reference numerals. The retarder has, for most of its components and in particular for its two rotors, a design symmetry with respect to the median radial plane PRM indicated in FIG. 2. The retarder 10 is generally annular in shape with a central axis XX and comprises a central stator 12 and two lateral rotors 14.   The stator 12 comprises eight pole assemblies 16 angularly distributed regularly around the axis X-X.   Each pole assembly 16 comprises a central pole of axial orientation 18 which passes, at its two opposite ends, a right annular radial plate 20 and a thicker left annular radial flange 22 and whose peripheral edge 24 is axially folded down to give it great rigidity.   Each pole 18 is surrounded by an electric wire winding 26 so as to constitute an electromagnetic coil.   Each end radial transverse face 28 of the pole 18 is provided with an insert plate 30 called polar expansion which is fixed by means of a central axial screw 32.   Each expansion 30 is delimited axially by an external end lateral face 34 and all the external lateral faces 34 of the openings 30 located on the same side of the stator are coplanar.   Each armature rotor 14 is a radially oriented generally annular overall assembly which consists essentially of an internal annular armature annular disk 36, an outer annular lateral cheek 38 parallel to the disk 36, and fins 40 forming axial spacers between the disk 36 and the cheek 38. As a variant not shown, the cheek 38 may be frustoconical and thus inclined relative to the disk 36.   The annular disk 36 is delimited radially by an outer annular peripheral edge 42 and by an inner annular peripheral edge 44.   The disk 36 is delimited axially by an upright lateral lateral face 46 which is adjacent to the external lateral faces 34 of the openings 30 with an axial gap or gap "e".   The disk 36 is also delimited axially by an external lateral face 48 which is parallel to the face 46 and which extends in a radial plane vis-à-vis an inner radial side face of the cheek 38. variant not shown, the outer side face 48 may be frustoconical and thus inclined relative to the face 46.   The flange 38 is also delimited axially by an outer lateral face 52, and radially by an outer annular peripheral edge 54 and by an inner annular peripheral edge 56.   As can be seen in FIGS. 1 and 2, the height or radial width of the armature disc 36 is greater than that of the shoes 30 so as to ensure a "covering" thereof.   The height or radial width of the outer cheek 38 is smaller than that of the disk 36 and is generally "centered" radially with respect to the disk 36.   In known manner, the fins 40 are generally distributed circumferentially in a regular manner and they constitute axial spacers between the disc 36 and the cheek 38.   Each fin 40 extends generally in a radial orientation, whether in a known manner, in the form of a plate with flat and parallel external faces or in the form of curved tiles with concave and convex parallel external faces.   Each fin 40 is delimited axially on the one hand by an internal lateral edge 58 of axial end through which it is connected to the outer lateral face 48 of the disk 36 and, on the other hand, by an external lateral edge 60 of the end axial through which it is connected to the inner lateral face 50 of the cheek 38.   In known manner, some of the fins 40, such as those visible in Figures 1 to 3, extend generally radially inwardly by an arm 62 for fixing the armature rotor.   The attachment arms 62 are angularly distributed regularly and are for example four or eight in number.   In the embodiment illustrated in the figures, each attachment arm 62 is "inclined" and also extends axially in the direction of the median radial plane PRM.   Each inclined arm 62 terminates in an end axial portion 64 which is connected to a radially inner central ring 66.   The two central fastening rings 66 face each other by their internal lateral faces 68 situated on either side of the plane PRM and they are fixed and braced by a series of lo-studs 70 and nuts 72.   A central plate or plate belonging to a rotating motor vehicle transmission member, not shown in the figures, is mounted tightly axially between the faces 68 of the central rings 66 and is connected in rotation to the latter by the studs 70.   In order to allow rotation of the integral rotors 14 with respect to the stator 12, there is naturally a space radially between the inner annular periphery of the stator 12 and the subassemblies constituted by the arms 64, the rings 66 and the studs 70.   As can also be seen in FIG. 3A, each fixing arm is also inclined with respect to a radial plane passing through the axis, that is to say that its radially inner axial section is offset angularly towards the front relative to at its radially outer end by which it is connected to the fin 40, considering the direction "R" of rotation of the rotors 14 with respect to the stator 12.   According to the state of the art which has just been described with reference to FIGS. 1 to 3A, it can be seen that the entire length of the internal axial end edge 58 of each of the fins 40 is connected to the external lateral face 48. of the disc 36 and in particular the edges 58 of the fins 40 which extend by arms 62.   This results in a large area, corresponding to the area of the axial end edge 58, of the heat exchange surface between the disk and the fins, and therefore the arms 62.   As illustrated in FIG. 3B, the fins forming spacers between the disc 36 and the flange 38 can also be distributed in three concentric rings of cooling fins.   A first set of fins 40A constitutes the radially innermost ring and some of the fins 40A extend to constitute the arms 62 for fixing the rotor 14.   A second series of fins 40B constitutes the radially outermost ring.   Finally, the rotor comprises a third series of fins 40C which constitutes a third ring of fins which is radially intermediate between the first and second rings.   In other words, a cooling fin consists of three sections 40A, 40C and 40B which are consecutive radially from the inside to the outside.   Again, the entire length of the inner axial end edge of each of the fins 40A is connected to the outer lateral face of the disc 36 and in particular the edges of the fins 40A which extend by arms 62.   This results in a large area, corresponding to the area of the axial end edge, of the heat exchange surface between the disc and the fins 40A, and thus the arms 62.   According to the teachings of the invention, it is proposed to reduce this heat exchange surface by providing thermal barrier means which are interposed between the axial end lateral edge 58 and the outer lateral face 48 of the disk.   According to the preferred embodiment of the invention illustrated in FIG. 4, the thermal barrier means are advantageously constituted by a clearance 74 formed in the axial end internal lateral edge 58 of the fin 40.   By way of example, the clearance here is of substantially rectangular contour and it opens radially towards the inside in the direction of the X-X axis and facing the inclined arm 62.   The clearance 74 is delimited radially outwards by an edge 76 of axial orientation and axially by a radially oriented edge 78 which, for example, is here parallel to the edge 58.   Thus, the length of the inner axial end edge 58 of the fin in contact with the outer face 48 of the disc is reduced compared to the state of the art (see Figure 2).   The section, in axial recess, 78 of the axial end of the fin 40 extends parallel to the outer lateral face 48 of the disc 36, with an axial play "j" which constitutes a thermal barrier insofar as the air received in the recess 74 is very poor thermal conductor.   In the example illustrated in FIG. 4, the radial length or height "H2" of the recess 74 is substantially equal to the length or radial height "H1" of the axial end edge 58 in contact with the lateral face 48, and therefore substantially equal to about half the length or total radial height "H" of the axial end edge 58 of the fin which, according to the state of the art illustrated in Figure 2, was in full contact with the external lateral face 48 of the disk 36.   The invention is not limited to the embodiment which has just been described.   For example, according to a variant not shown, it is possible to provide several clearances or recesses 74 in the edge 58 which then has a profile "castellated".   Similarly, the value of the set "j" is not necessarily constant along a clearance 74, ie the edge 78 is not necessarily straight or parallel to the lateral face 48.   Similarly, the thermal barrier is not necessarily air, that is to say that the recess can be "filled" by a thermal insulating material.   The "reduction" in the length of the axial end lateral edge 58 of the fin 40 which connects the latter, and therefore the attachment arm 62, to the disc 36 is negligible from the mechanical point of view with respect to the very important reduction. the temperature obtained for each arm 62.   The invention is applicable to any type of retarder, and particularly to the "Hydral", "Axial" or Focal "models marketed by TELMA.   As variants not shown, the outline of the clearance 74 may be of any shape and therefore not only rectangular, its edges may not be more rectilinear.   A retarder rotor according to the invention is arranged, according to one embodiment, so that between at least two fins 40 extended by arms 62 is at least one cooling fin 40 without attachment arm 62.   According to another embodiment, all the fins 40 of the rotor, or all the fins of the inner ring are extended by fixing arms 62.   An annular rotor (10) for electromagnetic retarder, in particular for a land motor vehicle transmission, of the type comprising: a flat annular armature disk (36) intended to extend opposite a series of assemblies pole (16) of a stator (12) of the retarder; - a flat annular cheek (38) parallel to the disc (36); and a ring of cooling vanes (40) forming axial spacers each of which extends axially between the lateral faces facing each other (48) of the disc (36) and (50) of the cheek (38). and some of which extend radially inwardly beyond the inner peripheral edge (44) of the disc (36) to form a series of arms (62) for securing the rotor (14), characterized in that means (74) are interposed between the axial end side edge (58) of at least one fin (40) adjacent the disc and said side face (48) of the disc (36).   2. annular rotor of electromagnetic retarder according to the preceding claim, characterized in that said thermal barrier means are formed by axial play (j) between at least one portion (78) of said lateral end edge (58) axial end of the fin (40) and said side face (58) of the disc (36).   3. Ring annular electromagnetic retarder according to the preceding claim, characterized in that said axial end lateral edge of the fin has a recess whose axial end lateral edge (78) constitutes said stretch which extends with play. axial (j) facing said lateral face (48) of the disc (36).   4. annular rotor electromagnetic retarder according to the preceding claim, characterized in that said axial play (j) is substantially constant along said section (78).   An annular electromagnetic retarder rotor according to claim 3, characterized in that said axial clearance (j) varies along said length (78).   6. annular rotor electromagnetic retarder according to any one of claims 3 to 5, characterized in that said recess (74) opens radially inwardly.   7. Ring annular electromagnetic retarder according to the preceding claim, characterized in that said extension radially inwardly of the fin (40) to form an arm (62) for fixing the rotor (14) extends with play facing the inner peripheral edge (44) of the disc (36).   8. annular electromagnetic retarder ring according to any one of the preceding claims, characterized in that means (74) forming a thermal barrier are interposed between the axial end side edge (58) of each of the fins (40) which is extends radially inward to form an arm (62) for fixing the rotor (14), and the disk.