FR2864369A1 - Electromagnetic retarder for heavy vehicle e.g. bus, has rotating ventilator driven by shaft for creating air currents flowing towards rotor coils and including disengaging unit to prevent ventilator from being driven by shaft - Google Patents

Abstract

The retarder has a rotor (101) comprising coils (107) mounted on a shaft (102). A stator is mounted opposite to the rotor. A generator (106) is mounted on an end of the shaft for supplying the coils of the rotor. A rotating ventilator (108) is driven by the shaft for creating air currents flowing towards the coils. The ventilator has a disengaging unit (111) for preventing the ventilator from being driven by the shaft.

Description

Electromagnetic retarder comprising means for creating a

air flow.

  Field of the Invention The present invention relates to an electromagnetic retarder having means for creating an air stream. One of the aims of the invention is to facilitate a cooling of the coils of such a retarder, while limiting a torque consumption due to the presence of at least one fan. By facilitating the cooling of the coils, the invention makes it possible to increase the performance of the retarder and / or to reduce its size. The invention finds an advantageous, but not exclusive, application in the field of heavy-duty motor vehicles, such as buses or trucks.

  STATE OF THE ART In general, an electromagnetic retarder makes it possible to slow down a motor vehicle in order to make the braking thereof more safe and more enduring.

  Such an electromagnetic retarder comprises at least one stator and at least one rotor for slowing down the motion transmission shaft to at least one wheel of the vehicle. The stator is connected for example to a gearbox housing or to a housing of a transmission bridge of a vehicle. In this case, it does not cut the drive shaft, also called motor shaft, to mount the retarder. When the drive shaft is not cut, it is called Focal retarder (registered trademark). In a variant, the stator is fixed on the chassis of the vehicle and this transmission shaft is cut.

  The rotor is connected to a plate coupled to a flange of a universal joint of the drive shaft. This plate is coupled to an input shaft of the vehicle deck or to an output shaft of the gearbox or to a linkage shaft. This connecting shaft can be connected to another plate when the transmission shaft is cut. In one example, the rotor is in two parts and is located on either side of a stator and rotates about the axis of the stator.

  In one embodiment described in the document FR-A-2577357, the stator of the electromagnetic retarder carries a ring of coils axially oriented and generates a magnetic field. More specifically, each coil is mounted on a core of magnetic material integral with the stator. When it carries the coils, the stator is inductive and the rotor is induced. This rotor is made of a magnetic material and is shaped to present fins that provide ventilation of the retarder.

  In another embodiment described in EP-A-0 331 559, the rotor carries the coil crown and the cores. In this embodiment, the rotor is an inductor and the stator is induced. This stator also carries a chamber inside which circulates a fluid for cooling. Such a retarder is said water-cooled retarder or Hydral retarder (registered trademark).

  The birth of a braking torque generated by an electromagnetic retarder is based on a principle of eddy currents. Indeed, for example in the case of a Hydral retarder, the induced stator, inside which an inductor rotor rotates, is subjected to an electromagnetic field. This field is generated by the coils mounted on the rotor which preferably operate in pairs, each coil being wound around a radially projecting core belonging to the rotor. Each of the pairs of coils forms a magnetic field which closes from one coil core to the other passing through the stator and the rotor.

  Thus, when the rotor returns to rotation, currents called eddy currents arise inside the induced stator. These currents generate a couple that tends to oppose the movement of the rotor. As the rotor rotates with a motor shaft, this braking torque also opposes the movement of the motor shaft of the vehicle. This couple is involved in a slowdown or a stop of the vehicle.

  For a retarder comprising an inductor rotor, the eddy currents cause a heating of the stator and the rotor. Indeed, the currents flowing through the stator and the coils made of conductive materials tend to heat the walls of the stator and the entire rotor. This heating phenomenon is called Joule effect and is generally observable when an electric current passes through an electrical conductor. The power of such a retarder is limited by its ability to release heat from the stator and coils.

  In the retarder described in EP A 0331 559, the outer peripheral wall of the induced stator carries a cooling chamber inside which circulates a cooling fluid, such as the cooling fluid of the engine of the motor vehicle.

  This chamber is used to cool the heating elements of the retarder and in particular the stator. However, this chamber is remote from the coils of the inductor rotor so that these coils are not cooled as efficiently as desired.

  This document EP A 0 331 559 also describes an arrangement comprising a fan for cooling heating elements such as coils or electronic circuits. This fan is integral in rotation with the retarder rotor and also slows the movement of the drive shaft. Thus, when the retarder comes into operation (is active), this fan creates a stream of air that cools the coils of the inductor rotor. This cooling makes it possible to avoid a fall in performance of the hot retarder. Overall a fan helps to create up to ten percent of the total deceleration torque generated by the retarder.

  However, the use of this fan has limitations.

  Indeed, as the rotor is connected in the aforementioned manner for example to the output shaft of the gearbox or to the input shaft of the rear axle, this shaft rotates constantly. A drive of the fans therefore generates a consumption of a significant mechanical power, even when the retarder is not in operation. In other words, when the retarder is not in operation, the fan consumes unnecessary mechanical torque.

  Thus, when the retarder does not work, aeraulic losses due to the fan drive, also called no-load losses, are observable and help to reduce the speed of the vehicle. These losses increase with a power of three of the rotational speed of the rotor shaft.

  It is desirable to reduce these empty losses.

  OBJECT OF THE INVENTION The object of the invention is to solve this problem of excessively high losses.

  For this purpose, the invention uses a fan which can be disengaged from its drive by a retarder shaft. This fan comprises means for being disengaged from its drive by the retarder shaft.

  This means belongs to coupling means intervening between the retarder shaft and the fan. These coupling means are controlled in particular electrically or mechanically This fan is for example a rotary fan mounted on the rotor shaft of the retarder by means of a disengaging device, such as a device comprising a rotary electric machine of the type. asynchronous. In one embodiment, the electric machine uses at least one excitation coil and a squirrel cage, which are in mutual influence.

  The spool is carried by the rotor shaft of the retarder and the squirrel cage is secured to the fan or vice versa.

  A bearing, such as a ball bearing, is interposed radially between the fan and the rotor shaft of the retarder.

  When the retarder is in operation, a pair of at least its coils then being electrically powered, the disengaging device provides a rotational coupling between the fan and the rotor shaft. The fan is then in the active position and rotates with the shaft.

  When the retarder is not in operation, the disengaging device no longer ensures the coupling between the rotating shaft and the fan, which is then rotatably mounted on the bearing.

  More specifically, in the case of a disengaging device comprising at least one coil adapted to be electrically powered, when the retarder does not operate, the disengaging device is not powered electrically. The fan is then not driven, that is to say is inactive, and is then mounted on the rotor shaft via the bearing.

  On the other hand, when the retarder operates, the disengaging device is electrically powered and then creates an electromagnetic force. This force causes a coupling between the fan and the shaft. The fan can then provide cooling primarily of the coils of the retarder.

  In such a configuration, it is only when the retarder is in operation, that the fan cools the machine, consumes torque and contributes to slowing the rotor shaft of the retarder. This couple contributes to the slowdown of the vehicle.

  The fan used in the invention may be axial, centrifugal or helico-centrifugal type. Such a fan is made according to a given application for which a given air flow is required to cool the coils of the retarder placed in a particular configuration.

  The declutching device can be controlled via wire connections connected to the generator, more specifically to the induced rotor thereof adapted to electrically supply the coils of the retarder rotor. The current supplying the coils of this retarder rotor can then partly serve to excite one or more coils located inside the disengaging device, these coils then being advantageously secured to the rotor shaft of the retarder.

  In a variant, the coil or coils of the disengaging device are carried by the fan so that they are adapted to be powered electrically by means of brushes mounted in a fixed brush holder and cooperating with slip rings integral with the fan and connected by wire links to this or these coils.

  A microcontroller comprising a microprocessor, memories and an input input buffer or an input input register may further participate in a command of this or these coils in this case.

  In a particular embodiment, a fan comprises a support, for example in the form of a sleeve carrying a squirrel cage.

  The rotor shaft of the retarder carries the coil or coils of the disengagement device. When the coils of the shaft are excited, a magnetic field is created and a magnetic connection is established between the cage, carried by the fan via its support, and the shaft. This magnetic connection allows the rotor shaft to rotate the fan.

  The fan can then provide cooling of the coils of the retarder rotor. The excitation of the coils of the disengaging device corresponds to an operation of the retarder. When the retarder does not work, the coils are not excited and the cage 5 is not rotated.

  In one embodiment additional magnets carried by the fan are additionally provided. These magnets are located opposite the rotor cores of the retarder.

  When the retarder operates, as is known, it is creates magnetic poles at the rotor cores and a mutual influence between these poles and the permanent magnets of the fan so that a synchronism of movement is achieved between the fan and the rotor shaft.

  Coupling between the retarder shaft and the rotary fan may also be controlled mechanically or by means of electromagnetic coupling means.

  These coupling means of the electromagnetic type comprise for example a coil (or a group of coils) of generally annular shape mounted. on a support, for example of transverse orientation integral with the rotor shaft of the retarder or this rotor, and an annular plate, advantageously made of ferromagnetic material, rotatably connected to the fan while being axially movable relative thereto , for example using tongues elastically deformable axially. These tongues are for example of tangential orientation as the connecting tabs between the pressure plate and the cover of a motor vehicle clutch.

  When the coil is not energized, that is to say is not electrically powered, the tongues provide a return action of the plate towards the fan, which is then uncoupled from the rotor shaft.

  When the coil is energized, that is to say electrically powered, an axial magnetic field is created and the annular plate is drawn axially in the direction of the support to come into contact therewith, more specifically to come to stick against a face carried by the support, and perform a coupling between the fan and the shaft. The face of the support is then magnetized and constitutes a fixed core, while the plate then constitutes a movable core which moves in the direction of the fixed core. The support comprises a housing cavity of the closed coil for example by a yoke of ferromagnetic material adapted to form the fixed core.

  Advantageously a friction lining is fixed on the plate and / or on the face of the support.

  The coil is advantageously electrically powered from the induced rotor of the generator.

  Alternatively the plate is rotatably connected to the fan by a spline system and elastic means axial action, such as a Belleville washer, rest on a shoulder integral with the fan and on the plate to urge the plate towards an axial stop integral with the fan and exert a return action. When the coil is electrically powered, the plate moves axially against the force exerted by the axially acting resilient means.

  As a variant, the configuration is annular and concentric, the coil and its support, integral for example with the rotor shaft, being surrounded by a plurality of ring-shaped segments that are rotatably connected and can move radially relative to the fan. When the coil is activated, a radial magnetic field is created which attracts the segments towards the face of the support to form a coupling between the retarder shaft and the fan.

  Alternatively the coupling between the fan and the rotor shaft is achieved using an electromagnetic powder clutch. A radial air gap exists between a first annular element integral with the fan and a second annular element integral with the rotor shaft of the retarder. This gap is filled with magnetic powder, which is magnetized when the coil is electrically powered. A coupling is then performed.

  The coil is advantageously carried by the second annular element. The invention therefore relates to an electromagnetic retarder for a motor vehicle comprising: - a shaft, at least one rotor mounted on the shaft, this rotor carrying coils - at least one stator mounted opposite this rotor and intended for to be mounted on a fixed part of the motor vehicle, - a generator mounted on one end of the rotor shaft, the generator supplying the rotor coils, and - at least one rotary fan driven by the rotor shaft to create air currents flowing to the coils, characterized in that - the rotary fan comprises means, said means for disengaging, to be disengaged from its drive by the rotor shaft.

  Thanks to the invention reduces the no-load losses, also due to mechanical losses, which come in particular from ball bearings, knowing that these vacuum losses come mainly from the fan or fans.

  In one embodiment these losses are decreased by ten.

  Thanks to the disengageable fan or fans can reduce the size and weight of the retarder and / or increase its performance, while having low no-load losses.

  The retarder can rotate at a higher speed via, for example, a speed multiplier, and can be mounted in place of a hydrodynamic-type retarder engaged for example with a secondary output shaft of the gearbox.

  When several fans are used these can occur one after the other depending on the number of activated coil pairs of the retarder rotor and therefore the need for slowing down.

  One of these fans can be permanently connected in rotation to the retarder shaft and in this case advantageously has a small size.

  The fans may be provided with disengaging devices that is to say coupling means of a different nature. For example one of the devices uses coils and a squirrel cage, while the other has an electromagnetic or magnetizable powder clutch. These fans can be disengaged and engaged with different laws and at different speeds of the retarder shaft. One of the fans is in an embodiment independent of the retarder shaft and comprises means for being disengaged, this means being controlled for example electrically. Thus, in one embodiment, this independent fan is controlled by an independent electric motor. This independent fan is associated with a fan according to the invention; these fans can be disengaged and engaged with different laws and speeds of the different retarder shaft. All combinations are possible.

Brief description of the drawings

  The invention will be better understood on reading the description which follows and on seeing the figures that accompany it. These figures are given by way of illustration and are not limiting of the invention. These figures show: - Figure 1: a retarder according to the invention in axial section with a disengageable fan mounted on a shaft driven by an output shaft of a gearbox.

  - Figure 2: a partial view on a larger scale of the disengaging device between the fan and the shaft of the figurel.

  - Figure 3: a retarder according to the invention, seen in partial axial section, having two centrifugal fans disengageable mounted on either side of a rotor of a generator.

  DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 shows an electromagnetic retarder 100 comprising a rotor 101 mounted on a shaft 102. This shaft 102 is intended to be hooked, that is to say linked in rotation, to a shaft 103 for example a gearbox output shaft 104 through a speed multiplier device 105, such as a speed multiplier having at least two gears as schematically shown in Figure 1. The shaft 103 is here parallel to the shaft 102, having an axis referenced XX in Figures 2 and 3. The axis XX is the axis of rotation of the retarder, including the rotors thereof described below.

  In a variant, the shaft 102 is perpendicular to the shaft 103. In this case the speed multiplier comprises at least two conical gears. With this configuration it is possible to implement the retarder 100 in the available space.

  The shaft 103 is for example a secondary output shaft on which is connected a retarder of the hydrodynamic type impeller wheel and turbine wheel. The retarder 100 is then mounted in place of this hydrodynamic retarder. In a variant, the shaft 103 is the main output shaft of the gearbox designed to drive the motion transmission shaft to at least one wheel of the motor vehicle, also called motor shaft, intervening between the output shaft. main gearbox and the input shaft of the rear axle of the vehicle.

  The speed multiplier reduces the size of the retarder and acts on the motion transmission shaft, directly or indirectly (via the secondary output shaft of the gearbox), to slow down the speed. this.

  Of course the presence of the speed multiplier is not mandatory. Thus the shaft 102 is alternatively an intermediate shaft interposed between two parts of said motion transmission shaft.

  In all cases the retarder is equipped with at least one disengageable fan 108, described below.

  In this Figure 1 the retarder comprises, as in the EP A 0 331 559 cited above, an induced stator 110 traversed by eddy currents, which surrounds the rotor 101, here inductor. A generator 106 having a generator rotor 106a and a generator stator 106b is mounted on the end of the shaft 102. The retarder also has a housing 41, which is shaped to be mounted on a fixed part of the vehicle. The fan 108 and the rotors 101 and 106a are housed inside the casing 41 through which the shaft 102 passes.

  This housing 41 here has an annular peripheral wall 42 of axial orientation closed at each of its ends by a cover 43, 44 of transverse orientation relative to the shaft 102.

  One of these covers is in one embodiment with the wall 42, while the other of these covers is attached to this wall. In a variant, the two covers are attached to the wall 42.

  Advantageously ball bearings, shown diagrammatically by crosses in FIG. 1, intervene between the shaft 102 and the edge of the central openings of the covers 43, 44.

  Of course the presence of the cover adjacent to the speed multiplier is not mandatory when the housing 41 is fixed for example directly on the housing of the gearbox.

  For more details on the generator, reference is made to this document EP A 0 331 559, in particular to FIGS. 1 and 2 thereof.

  For the record, it will be recalled that the generator 106 comprises an inductor stator 106b having a body secured here to the wall 42. This body has radially inwardly projecting arms towards the shaft 102. Around these arms, presenting advantageously retaining heads are mounted coils whose ends are connected to an electrical control circuit comprising for example a manual adjustment member.

  The generator rotor 106a of the generator comprises a body provided with grooves, for example of the semi-closed type, for mounting coils whose ends are connected to a rectifying bridge, integral with this body, for rectifying the alternating current produced by this rotor. 106a DC to electrically power the coils 107 that has the inductor rotor 101 of the retarder. The rotor 106a has for example a ring in which are made the mounting grooves of the coils of the rotor 106a.

  This ring is secured to a transverse web intended to be fixed to the shaft 102.

  The rotor 101 also has a body having at its outer periphery radially projecting cores and oblong. The body of the rotor is fixed on the shaft 102 for example by means of a transverse web or directly on the shaft 102. The coils 107 are wound around the cores and generate a radial magnetic flux when they are electrically powered. from the induced rotor 106a. These coils work in pairs, one or more pairs involved according to the slowing needs of the vehicle. This type of rotor is said to have salient poles and magnetic north-south poles are created at the cores of the rotor 101, when the retarder operates. Retention heads of the coils 107 are attached to these cores, for example by screwing as visible in FIG. Figure 2 of EP A 0 331 559 showing in section one of these radial cores axially oblong. Of course, insulators are interposed between the cores or the edges of the grooves and the coils respectively of the stator 106b, the rotor 106a and the induction rotor 101, whose bodies are made of magnetic material just like the induced stator 110.

  The stator 110 is in Figure 1 attached to the wall 42 of the casing 41. In a variant, the casing 41 coincides with the induced stator 110, as can be seen in FIG. 3, in which the casing carries the reference 515.

  The stator 110 is implanted vis-à-vis the rotor 101 of the retarder with the presence of a small gap, called the gap, between the stator 110 and the rotor 101. Here the stator 110, intended to be mounted on a fixed part of the motor vehicle, surrounds the rotor 101 with the presence of a gap, radial in Figures 1 and 3, maintained constant through the presence of at least the fan 108 so that the performance of the retarder is increased.

  This fan 108 internal to the housing 41 is intended to create air currents 109 which flow to the coils 107 of the rotor 101.

  The fan blades are configured so that the fan is axially acting, the covers 43, 44 having for this purpose respectively openings 45, 46 for air circulation, more precisely drafts 109.

  More specifically, the fan 108 is mounted on the shaft 102 via a disengaging device 111 and also a bearing, here a ball bearing 300, intervening between the outer periphery of the shaft 102 and the internal periphery of the fan 108.

  Here the blades of the fan 108 are integral at their inner periphery with a sleeve 400 in contact with its inner periphery with the bearing 300, here with the outer ring of the ball bearing, whose inner ring is fitted on the shaft 102.

  This bearing is alternatively two rows of balls.

  This device 111 allows to disengage, that is to say uncoupling, the fan 108 from its drive by the motor shaft 102. Indeed, when the retarder is in operation, the device 111 makes it possible to make the fan 108 of the shaft 102. When the retarder is not in operation, the device 111 disengages the fan 108 from the axis of the rotor 102. In other words, when the retarder 100 does not work, the device 111 releases the fan from its drive by the shaft 102.

  To disengage the fan from its drive the electrical device 111 comprises in the embodiment of Figures 1 and 2 at least one excitation coil 60 and a squirrel cage 70. This means therefore comprises an asynchronous rotating electrical machine. More precisely when this or these coils are electrically powered, they create a field that gives rise to an electromagnetic force. This force influences the squirrel cage 70 so as to create a magnetic coupling between the fan 108 and the shaft 102.

  The squirrel cage comprises for example a magnetic ring crossed by bars, for example aluminum, connected to each of their axial ends to a ring for example aluminum. The rings are arranged on both sides of the ring.

  In this embodiment the squirrel cage 70 is integral with the sleeve 400, while the coil or coils 60 are integral with the shaft 102.

  In one embodiment, there are several coils mounted on a rotor body integral with the shaft 102. This body comprises projecting arms, or cores, projecting radially around which the coils are wound in the same manner as that which is achieved. for the rotor 101. The coils 60 then belong to a rotor with salient poles. The fan 108 is mounted rotatably around these current-controlled coils.

  Alternatively there is provided a single coil 60 controlled by current and intervening between two pole wheels of a claw rotor. More precisely each wheel has a flange carrying at its outer periphery trapezoidal shaped teeth and axial orientation. The teeth of one wheel are directed towards the teeth of the other wheel with interlocking teeth from one wheel to another. The coil is mounted on a core interposed between the flanges of the pole wheels with formation of magnetic poles at the teeth when the coil is activated.

  The cage 70, integral with the rotary fan 108, surrounds or the coils 60, which are adapted to be electrically powered from the induced rotor 106a by wire links intervening between the rotor 106a, more specifically the rectifier bridge, for example with associated diodes. at the outputs of the coils thereof, and this or these coils. No broom and slip ring device is expected.

  The coil or coils 60 of the device 111 are therefore electrically powered (current-controlled) by a current I coming from the generator 106. The generator 106 and the device 111 are thus directly connected to one another.

  Quantities are therefore related to the current I created by the generatrix coils for supplying the coils of the rotor 101 and generating a braking torque for the rotation of the shaft 102. Indeed, the greater this current I, the larger the field. electromagnetic generated by the coil or coils 60 of the device 111 is large. Thus, the larger the current I, the more magnetic coupling between the fan 108 and the shaft 102 is intense. And the more intense this coupling, the more the fan 108 rotates at a high speed making it possible to optimally cool the coils 107 of the rotor 101. A control lever could be used so as to vary an intensity of the current I. Of course, can reverse the structures, the coils being carried by the sleeve 400 and the cage 70 by the shaft 102.

  In this case it is necessary to provide slip rings on the sleeve 400 and brushes to cooperate with these rings connected to the coils 60. The brushes are slidably mounted inside cages of a brush holder mounted on a fixed part.

  The brushes are electrically powered from, for example, an electrical circuit connected to the battery and having a switch.

  In one embodiment, this switch is controlled by an order coming from an input input register of a microcontroller comprising memories M. This microcontroller can make it possible to control the device 111 by closing an excitation circuit coils disposed within this device 111 in the form of rotating electrical machine of the asynchronous type. This microcontroller can also provide regulation and / or synchronization of the rotation of the fan 108 with respect to a rotational speed of the shaft 102.

  Of course, the present invention is not limited to the described embodiments.

  In particular, as described in document EP A 0 331 559, the wall 42 of the casing 41 can carry a cooling chamber inside which a cooling fluid circulates, such as the cooling fluid of the engine of the motor vehicle.

  The covers 43, 44 may also carry cooling chambers.

  Several fans can be provided.

  FIG. 3 shows an exemplary embodiment of the invention in which two centrifugal fans 501 disengageable are mounted on either side of a rotor 502 induced generator type of that of Figure 1. It is the same for inductor stator 503 of the generator which thus has coils.

  The fans 501 comprise blades integral with a flange. For example the flange is metallic and the blades are obtained by cutting and folding from the flange. Alternatively the blades are overmolded on the metal flange. In a variant, the blades are molded with the flange. In one embodiment this flange has at its inner periphery a sleeve for intervention of a disengaging device 111. More precisely in this FIG. 3, the fans are mounted on the shaft 102 of the rotor by means of electrical disengaging devices 111. . A retarder rotor 505 rotates inside a housing 515. This housing 515 has a peripheral wall 512, similar to the wall 42 of Figure 1 and at least one cover 510 of transverse orientation. Inlet louvers 511 and exit louvers 513, 541 are made in this casing, respectively in cover 510 and in the annular peripheral wall 512 and axially oriented of casing 515. These openings provide an entrance and exit of an air stream 521, 522.

  A stator 515, coinciding with the casing 515 is dug to form a cooling chamber 530 aforesaid, which is therefore carried by the housing 515. This chamber 530 is opposite the rotor 505 similar to that of Figure 1, and which therefore has coils 514. Inside this chamber 530 circulates a cooling liquid, such as the engine engine coolant of the motor vehicle as disclosed in Figure 1 of EP A 0 331 559. The chamber 530 of cooling ensures cooling of the stator walls.

  The fans 501 disengageable are in this example of the centrifugal type. Indeed, these fans 501 ensure the creation of a suction air stream 521 parallel to the shaft 102 and a creation of output air currents 522 in a direction generally perpendicular to the shaft 102.

  The currents 522 of air come into contact with the heads of the coils of the stator 503 and the rotor 505 and thus provide cooling of these coils. These coil heads are located at the right of the openings 541, 513 and extend on either side of the bodies respectively of the stator 503 and the rotor 505. These air currents 521 and 522 also make it possible to cool the casing and / or the stator of the retarder.

  The coils 514 are oriented radially with respect to the shaft 102 and create an electromagnetic field of generally radial orientation. The eddy currents generated by this magnetic field thus circulate in the axial wall of the stator.

  Alternatively, the coils 514 are oriented axially and the associated cores. For example the cores are integral at each of their axial ends with a transverse flange fixed on the shaft 102 for example by welding or press fitting, the shaft 102 being knurled for this purpose. This method of attachment is also conceivable for fixing the rotors of FIGS. 1 to 3.

  Preferably, in this case, the cooling chambers 530 are oriented transversely relative to the shaft 102 of the rotor.

  In this case the stator is in two stator parts of transverse orientation mounted axially on either side of the rotor. Each stator part constitutes an elementary stator. These stator parts are each arranged vis-à-vis the rotor flange concerned with the presence of a small clearance, here axial, called air gap between each stator portion and the roto. The transverse portions of the stator are interconnected by an axially oriented portion surrounding the rotor. This part is full or split for example in tie rods.

  In all cases the stator, in one or more stator parts, is implanted opposite the rotor with the presence of a radial or axial air gap.

  The stator parts advantageously carry at least one cooling chamber, in particular of transverse orientation.

  Of course, other types of fans 501 disengageable can be used in a retarder according to the invention. For example, helical centrifugal fans can be used which provide the creation of an air current parallel to the shaft 102 and a discharge air stream inclined relative to a direction perpendicular to the shaft 102. also use axial fans to create a flow of suction and discharge air that propagates both parallel to the shaft 102.

  The rotor 502 of the generator advantageously has openings 621 passing through axially and allowing passage of the air flow towards the rotor 505 and its coils 514.

  Similarly, the fan 501 adjacent to the cover 510 has openings 624 corresponding to the openings 621. In a variant, the rotor 505 has axially through openings in its base and two disengageable fans are mounted on either side of this rotor. .

  Of course we can increase the number of stator and rotor. Thus in Figure 1 an additional rotor can be provided.

  Two rotors are alternatively provided with the presence of three transverse cooling chambers belonging to the housing; one of the chambers being located between the two rotors. Each room belongs to an elementary stator. Of course, in this case, in at least one embodiment, at least three fans are provided in other embodiments of the invention for disengaging the fan.

  108, use is made of a device 111 using a magnetizable powder, the viscosity of which varies as a function of an intensity of an electric current flowing through it. This magnetizable powder is disposed in an air gap existing between a first annular element integral with the fan and a second annular element integral with the shaft 102.

  The first element, in one embodiment, surrounds the second element. Of course the opposite is possible.

  By varying the viscosity of this powder by means of an excitation coil carried for example by the annular element of the shaft 102, a mechanical coupling is controlled between the fan and the shaft.

  In a variant, a disengaging device comprising an electromagnetic clutch is used.

  In a variant, a mechanical disengaging device, for example a friction device, is used.

  This device may comprise a part mounted axially with respect to the shaft being integral in rotation with this shaft. This part comprises a first conical bearing intended to cooperate with a second conical bearing surface secured to the fan when this part is in the engagement position.

  For example, a joystick actuated by a user or a controlled cylinder ensures movement of the workpiece and controls the disengaging device 111 disposed between the rotary fan 108 and the shaft 102.

  When the retarder is in operation, a translation of the workpiece along an axis of the shaft 102 makes it possible to penetrate the first conical bearing surface inside the second conical bearing surface to engage therewith. The fan 108 is then rotated.

  Of course the bearings of the friction clutch have alternatively another form, for example these spans are portions of the sphere. When the control uses a jack, for example of the hydraulic type associated with a transmitter or an electric jack, this jack can be controlled from a microcontroller comprising memories to ensure regulation and / or synchronization of the rotation of the cylinder. fan according to a rotation speed of the shaft, the contact force between the complementary scopes of varying friction. Input and output registers can also be provided.

  In a variant, use is made of interconnection means.

  Of course, the present invention is not limited to the described embodiments.

  Thus alternatively the generator comprises brushes mounted in cages of a brush holder secured to the housing and / or the stator of the retarder. These brushes are subjected to the action of resilient means mounted in cages for biasing these brushes in contact with collector rings integral with the shaft and connected by wire links to the coils of the rotor of the retarder.

  In a variant, the disengaging device comprises an electric machine of the asynchronous reluctance type.

  The invention therefore provides for the presence of at least one rotary fan 108. which comprises a means, said means for disengaging, to be disengaged 5 of its drive by the shaft.

  Advantageously, this means for disengaging is controlled.

Claims (17)

  1 - Electromagnetic motor vehicle retarder (100) comprising: - a retarder shaft (102), - at least one rotor (101) mounted on the retarder shaft, this rotor carrying coils (107), at least one stator (110) mounted opposite this rotor and intended to be mounted on a fixed part of the motor vehicle, - a generator (106) mounted on one end of the retarder shaft, the generator supplying the rotor coils (101), and - at least one rotatable fan (108) driven by the retarder shaft (102) to create air currents flowing to the coils (107), characterized in that - the fan (108) ) rotative comprises means (111), said means for disengaging, to be disengaged from its drive by the shaft (102).   2 - retarder according to claim 1 characterized in that the means (111) for disengaging is controlled.   3 - retarder according to claim 2 characterized in that it comprises means for electrically controlling the means (111) for disengaging.   4 - retarder according to claim 3 characterized in that the means for electrically controlling the means (111) for disengaging comprise at least one coil.   5 - retarder according to any one of claims 2 to 4, characterized in that the means for controlling the means for disengaging comprise a microcontroller which comprises in particular a memory and an input and output register.   6 - retarder according to one of claims 1 to 5, characterized in that the fan (108) rotatable is rotatably mounted around current-controlled coils.   7 - retarder according to one of claims 1 to 5, characterized in that the fan (108) rotatable is secured to a squirrel cage mounted around current-controlled coils and integral with the retarder shaft.   8 - retarder according to one of claims 1 to 7, characterized in that the means (111) for disengaging is a rotating electrical machine of the asynchronous type comprising at least one coil integral with the rotor shaft and electrically powered by the generator .   9 - retarder according to one of claims 1 to 5, characterized in that the means (111) for disengaging comprises an electromagnetic clutch.   10. Retarder according to one of claims 1 to 5, characterized in that the means (111) for disengaging comprises a magnetizable powder whose viscosity varies as a function of an intensity of an electric current flowing through it and in that this magnetizable powder is disposed in an air gap existing between an annular element integral with the fan (108) and an annular element integral with the shaft (102).   11. Retarder according to one of claims 1 to 3, characterized in that the means (111) for disengaging comprises a mechanical disengaging device, such as a mechanical friction device.   12. Retarder according to one of claims 1 to 11, characterized in that a bearing (300), such as a ball bearing, is interposed radially between the fan and the rotor shaft of the retarder.   13. Retarder according to one of claims 1 to 12, characterized in that it comprises at least two fans.   14. Retarder according to claim 13, characterized in that one of the fans is integral in rotation with the shaft (102) of the retarder, while the other fan comprises means (111) to be disengaged from its drive by the retarder shaft (102).   15. Retarder according to claim 13, characterized in that one of the fans is independent of the shaft (102) of the retarder and has a control to be disengaged, while the other fan comprises means (111) to be disengaged from its drive by the shaft (102) retarder.   16. Retarder according to claim 13, characterized in that each fan comprises means (111) for being disengaged from its drive by the shaft (102) retarder.   17. Retarder according to claim 15 or 16 taken in combination with claim 2, characterized in that the control for disengaging the fan is different from one fan to another.