Patent Publication Number: US-2021162450-A1

Title: Impregnation plant and method for components of electric motors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a § 371 National Stage Application of International Application No. PCT/IB2018/060010 filed on Dec. 13, 2018, claiming the priority of Italian Patent Application No. 102017000149039 filed on Dec. 22, 2017. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to an impregnation plant and an impregnation method for components of electric motors and, in particular but not exclusively, to an impregnation plant and an impregnation method for electric windings and stators manufactured according to the so-called “hair pin” technology. 
     BACKGROUND OF THE INVENTION 
     As is known, an electric motor is formed of a stator and a rotor. These two components, when properly combined together, generate a magnetic field as necessary for the operation of the electric motor. 
     In electric motors using a wire wound stator, the stator is in fact provided with windings traditionally formed of a coil of copper wires. The coil of copper wires shall be impregnated with specific resins in order to increase its mechanical strength. 
     Unlike electric motors using wound wire stators, in an electric motor using a “hair pin” stator such stator is provided with a plurality of metal bars, typically made from copper, instead of a coil of copper wires. Electric motors using hair pin stators are widely used in the automotive sector. Because of the heavy-duty use which they are intended for, the metal bars of the electric motors using “hair pin” stators also require an impregnation with specific resins in order to increase their mechanical strength and to prevent wires from rubbing with each other, which might result in jeopardizing their insulation. 
     Irrespective of the manufacturing technology, a stator for electric motors generally consists of an internally hollow cylinder. The copper wires or bars are incorporated in the wall of the cylinder and run all along the length of such wall, in the direction of their respective generatrixes, and consequently they project at the two circumferential ends, or heads, of the cylinder itself. 
     An impregnation process for stators of electric motors can traditionally be implemented by using the so-called “trickling” technology. The traditional process comprises a first step wherein the stator is pre-heated to a predefined temperature, which is variable according to the type of resin that will be used. 
     Following the pre-heating step, a specific amount of resin is trickled onto well determined zones of the copper wires or bars, for a determined period of time and according to a determined sequence of positioning of the dispensers of the impregnation plant. The parameters relevant to amount of resin, dispensing time and dispenser positionings vary according to the type of stator. 
     During impregnation, the stator shall be held in rotation in order to prevent resin from trickling (trickle losses). The resin, which is only deposited onto the heads of the cylinder which forms the stator, flows by capillarity along the wires or bars, up to penetrating and filling the cavities placed inside the wall of such cylinder. The main aim of an impregnation process is to saturate all of these cavities, with a consequent compacting of the wires aiming at prevent them from rubbing. 
     After the trickling step, the stator, still held in rotation, undergoes a high temperature baking step. This step first causes a gelation (the resin thickens or, in other words, its viscosity rises up to glass transition which determines its transition from the liquid state to the solid state) and subsequently the baking of the resin, which polymerizes and definitively hardens. During this step the stator is held in rotation, because the rotation movement is an essential condition during gelation, whereas it is just a recommended condition during the baking step. 
     After the baking step, the stator might be cooled down before being unloaded from the impregnation plant. These cooling down step is usually performed, however it is not decisive for a good success of the impregnation process. 
     The evolution of electric motors, used in particular in the automotive sector, gave rise to stators wherein the wires (in the case of wound wire stators) or the bars (in the case of “hair pin” stators) are much compressed. In other words, the interstices or cavities between the individual wires or bars are very narrow and/or winding. 
     Consequently, whereas it was sufficient to trickle the resin onto the heads of the stator in the case of traditional electric motors, such stator being arranged horizontally and held in rotation about its own axis, in the case of the present electric motors such process is not effective any longer. As a matter of fact, such process does not make it possible to guarantee that the resin effectively fills all cavities/interstices between the individual wires and, most of all, between the individual bars, which are typically arranged according to an extremely compact configuration. Besides providing penetration of the resin, a good impregnation process is such as to prevent the surfaces from being dirtied, or at least to limit such dirtying. 
     Impregnation plants for components of electric motors are known, such as, for instance, those described in documents DE 1538918 A1, IT 1177448 B, U.S. Pat. No. 5,685,910 A, and AU 4207768 A respectively. Document DE 1538918 A1 discloses an impregnation plant for components of electric motors, in particular rotors of electric motors, wherein the rotor is held in a vertical position for being induction heated. Then the rotor, still being in a vertical position, undergoes an impregnation step. Then the rotor is arranged horizontally and goes through the plant with the possibility for it of rotating about its own axis, and enters a baking oven. However, in a plant according to document DE 1538918 A1 apparently no possibility is provided for a rotor of tilting and rotating in the impregnation station. 
     Document AU 4207768 A discloses an impregnation plant for rotors of electric motors wherein each rotor can be tilted during the impregnation step and can be made rotate at an adjustable speed. However, the plant according to document AU 4207768 A is a “static” one, i.e. it comprises one workstation only which performs the pre-heating, impregnation, and baking steps. 
     In general, the impregnation methods for rotors of electric motors substantially differ from those used for stators of electric motors, in particular from those used for “hair pin” stators. As a matter of fact, in order to perform a correct impregnation in such type of stators, it is necessary to have the following tools at disposal:
         specific collets, designed to make it possible a geometric positioning of the tricklers inside the stator;   specific tilting modules, capable of controlling all tilting movements of the axes and the different rotations as a function of the points where the impregnating resin is to be applied;   calibrated centering pins, configured for accommodating a device that transports the collet-stator assemblies;   specific clutches which, once the impregnation step is completed, are movable to guarantee a continuous rotation of the stator from a workstation to another one, thus preventing resin losses from the stator itself;   specific thermal recovery sources and inductive movable assemblies in the trickling stations.       

     In an impregnation plant, a complete availability of all of these tools makes a corresponding impregnation method for “hair pin” stators effective. 
     Document IT 1177448 B discloses a traditional impregnation plant wherein each stator is put on a cantilevered collet. In this plant there are no provisions for induction heating, nor there is any possibility of tilting the stators, and the collets are constrained to the transport chain in a rigid architecture. Finally, document U.S. Pat. No. 5,685,910 A discloses a laboratory machine configured to process individual components, put in a vertical position but with tilting capabilities. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is thus to provide an impregnation plant and an impregnation method for components of electric motors that are capable of solving the above-mentioned drawbacks of the prior art in a particularly functional manner. 
     In details, an object of the present invention is to provide an impregnation plant and an impregnation method for components of electric motors that allow to coat the wires or bars of the windings of each individual component with resins or other similar fluids in a complete and effective manner. 
     Another object of the present invention is to provide an impregnation plant and an impregnation method for components of electric motors that allow to precisely control each step of the method itself. 
     These objects according to the present invention are achieved by way of an impregnation plant and an impregnation method for components of electric motors as disclosed in the independent claims. 
     Further characteristics of the invention are highlighted in the dependent claims, which are an integral part of the present disclosure. 
     In particular, as already mentioned before, the parameters that are traditionally controllable in an impregnation plant according to the prior art are the speed of rotation of the component (stator), the positioning of the nozzles used to dispense the resin, and the flow rate of the dispensed resin. The impregnation plant according to the present invention also controls the parameters related to the sense of rotation, either clockwise or counterclockwise, of the component (stator) and the tilt of such component (stator) with respect to a predefined axis of rotation, as well as the possibility of varying the speed of rotation independently in the individual impregnation stations. 
     Controlling sense of rotation and controlling tilt are indispensable for controlling the behavior of the resin dispensed onto the metal material which the windings are made from. Otherwise, the resin would not be able to penetrate the cavities of the windings and would finally follow other paths, different from those which contribute to achieve the result of a total coating of the windings themselves, and would possibly dirty the surface of the laminated core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The characteristics and advantages of an impregnation plant and an impregnation method for components of electric motors according to the present invention will be more apparent from the following description, which is provided for explanatory non-limitative purposes only, which makes reference to the attached schematic drawings, wherein: 
         FIG. 1  is a side elevation view of an embodiment of the impregnation plant for components of electric motors according to the present invention; 
         FIG. 2  is a perspective view of a workstation of the impregnation plant depicted in  FIG. 1 ; 
         FIG. 3  is another side elevation view of the workstation depicted in  FIG. 2 , wherein an impregnation device is also highlighted; 
         FIG. 4  is a perspective view of a typical component part to be impregnated, specifically formed of a “hair pin” stator; and 
         FIG. 5  is a perspective view of the metal bars that form the winding of the stator depicted in  FIG. 4 . 
     
    
    
     With a specific reference to  FIG. 1 , an embodiment of the impregnation plant for components of electric motors according to the present invention, identified by the reference numeral  10  as a whole, is here shown. The plant  10  comprises a plurality of working stations arranged linearly and sequentially one after another, wherein each component  100  is first prepared for impregnation, then at least partially coated with an impregnating substance (resin), and subsequently finished in a fully automated manner. As a matter of fact, all working stations that form the plant  10  are managed and controlled by a central processing unit (CPU) the function of which is to program, control, manage, and optimize all steps of the impregnation method. 
     Specifically, as shown in  FIGS. 4 and 5 , each component  100  to be impregnated is typically a stator for electric motors comprising an internally hollow cylindrical body  110 . The cylindrical body  110  is provided with windings formed of metal wires or bars  120  incorporated in the wall of the cylindrical body  110 , which run all along the length of such wall, in the direction of their respective generatrixes, thus projecting at the two circumferential ends, or heads, of the cylindrical body  110  itself. The surface of the windings, in particular that incorporated in the wall of the cylindrical body  110 , shall be fully coated with an impregnating substance (resin) in order to increase the mechanical strength of the windings themselves. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The plant  10  comprises first of all a plurality of support devices  12  for supporting the individual components  100 . Each support device  12  rotatably supports the respective component  100  and is configured to be inserted into the individual working stations that form the plant  10 . 
     Each support device  12  is provided with a spring collet  14 , which is in turn provided with blocks which are used to clamp the component  100  onto the inner diameter of the respective cylindrical body  110 . The spring collet  14  entirely crosses the cylindrical body  110  of the component  100 , so as to possibly rest on both the respective circumferential ends. This feature makes it possible for the component  100  both to rotate, in the two directions of rotation, and to tilt, in both directions with respect to a predefined plane, during the impregnating substance trickling process, as better described below. 
     Each support device  12  preferably comprises a pallet configured to make the rotation of the spring collet  14  possible. In details, each of the two ends of the spring collet  14  rests on one or more rollers  16  placed on respective opposing ends of the support device  12 . 
     The plant  10  comprises a plurality of motor-driven means  18  configured to impart both a rotatory motion, in both directions of rotation, and a tilting motion, in both directions with respect to a predefined plane, on each component  100  mounted on its respective support device  12 , when such support device  12  is inserted into the working stations of such plant  10 . In particular, the motor-driven means  18  impart a rotatory motion to the rollers  16  placed on one single side of the support device  12 , via a chain transmission device  20  which acts onto two pinions integral with such rollers  16 . On the other side of the support device  12 , the rollers  16  are idle and free to follow the rotatory motion of the spring collet  14 . 
     The plant  10  also comprises one or more heating stations  22 , configured to heat each individual component  100  to a predefined temperature, which is variable as a function of the type of impregnating substance that will be used in the subsequent working stations. Each component  100  is introduced into the heating station  22  after being mounted onto a respective support device  12 . Each component  100 , once introduced into the heating station  22 , is driven into rotation on its respective support device  12 , as better specified below. 
     The plant  10  also comprises, downstream of the heating stations  22 , one or more impregnation stations  24 , configured to cover at least a portion of each component  100  with an impregnating substance. The motor-driven means  18  which operate at each impregnation station  24  are configured to impart to each component  100  both a rotatory motion about the axis of the spring collet  14 , in both directions, and a tilting motion of such axis of the spring collet  14  with respect to a predefined plane of the support device  12 . 
     Each impregnation station  24  is provided, preferably at its upper part, with one or more impregnating substance dispenser means  30 , moved by controlled axles. The dispenser means  30  are positioned in their exact positions where the impregnating substance is to be dispensed, via their respective axles, according to a predefined amount and period of time. The dispenser means  30  are fed via one or more metering pumps, configured to accurately meter the impregnating substance. 
     The plant  10  might comprise at least one temperature recovery station  26  between adjacent pairs of impregnation stations  24 . Each temperature recovery station  26  is configured to set a predefined temperature value on each component  100 , coming from the impregnation station  24  arranged upstream of such temperature recovery station  26 , before entering the subsequent impregnation station  24 . 
     The plant  10  also comprises, downstream of the impregnation stations  24 , at least one gelling station  28  and at least one baking station, arranged sequentially to each other, configured to fix the impregnating substance on each component  100 , via subsequent steps described in more details below. At least the gelling station  28  might be provided with an induction heating system, configured to rapidly rise the temperature of the component  100 . 
     The number of impregnation stations  24  that a plant  10  is provided with is variable and depends on the cadence requested to the plant  10  itself, as well as on the time requested by each component  100  to absorb the resin. In one preferred but non-limitative embodiment, the plant  10  can sequentially comprise five heating stations  22 , two sets each comprising three impregnation stations  24 , separated by two temperature recovery stations  26 , and three gelling and baking stations  28 . 
     The impregnation method for components of electric motors according to the present invention consequently comprises the following operating steps. The first and last steps of such method possibly consist of respective weighing operations. 
     As a matter of fact, each component  100  is automatically weighed both before entering its respective support device  12 , i.e. before entering the plant  10 , and after being unloaded from its respective support device  12 , i.e. after leaving the plant  10 , in order to monitor the effectiveness of the impregnation method. The difference in weight between the component  100  before applying the impregnating substance and the same component  100  after applying the impregnating substance provides an indication on how much solid impregnating substance (resin) remained on such component  100 , thus determining a first qualitative assessment of the component  100  itself. 
     Then the method comprises a step whereby each component  100  is inserted onto the spring collet  14  of a respective support device  12 , so that the component  100  is rotatable in both directions about the axis of such spring collet  14 , as well as tiltable with respect to a predefined plane of the support device  12 . 
     A preliminary step of pre-heating such component  100  before entering the plant  10  is possibly specified before the step of inserting each individual component  100  onto its respective support device  12 . Not necessarily shall the component  100  be in rotation during this preliminary pre-heating step, which can be performed either rapidly by using an induction heating system, or slowly by using a hot air blowing system. 
     The method also comprises a step of loading each individual support device  12  complete with its respective component  100  in the plant  10 , so that the motor-driven means  18  can engage the spring collet  14  and make the component  100  rotate in both directions of rotation about the axis of such spring collet  14  and/or tilt such component  100  with respect to a predefined plane of the support device  12 . 
     At this point, the component  100  undergoes a heating step, during which the spring collet  14  and the component  100  supported by it are made rotate in one or both directions about the axis of such spring collet  14 . During the heating step, each component  100  moves forward inside the heating station  22 , step by step, up to reaching the optimum temperature for the subsequent impregnation or resin coating step. 
     During the impregnation or resin coating step, each component  100  is made rotate in both directions (as a function of the geometric requirement of the winding), at a variable speed, independent of the remaining working stations of the plant  10 , about the axis of the spring collet  14  and/or is tilted with respect to a predefined plane of the support device  12 , so as to be at least partially, but effectively, coated with the impregnating substance. In each impregnation station  24 , the speed of rotation, the sense of rotation, and the angle of tilt of the component  100  are controlled in a fully independent manner with respect to the remaining working stations of the plant  10 . 
     A gelling step is provided after the impregnation or resin coating step, during which the spring collet  14  and the component  100  supported by it are made rotate in one or both directions and are brought to a temperature that is suitable for baking the resin. Since the baking temperature is higher than the temperatures of the heating and pre-heating steps, the gelling step can be performed by way of an induction heating system, configured for rapidly raising the temperature of the component  100 . 
     After the gelling step, which results in a first thickening of the resin, a baking step is performed to obtain the final solidification of the resin. It is advisable, even if not indispensable, to drive the spring collet  14  and the component  100  supported by it into rotation also during the baking step. The times and temperatures used both in the gelling step and in the baking step depend on the type of resin used in the previous impregnation or resin coating step. 
     After the baking step, it is advisable to perform a cooling step, configured for bringing the component  100  down to a temperature that is compatible with the requirements of the manufacturing line downstream of the plant  10 , where such component  100  will continue its assembling path. 
     The impregnation plant and the impregnation method for components of electric motors described so far are particularly effective in processing “hair pin” stators, an embodiment of which is shown in  FIGS. 4 and 5 . As a matter of fact, in this type of stators the metal bars that form the windings are joined two by two, by welding, at either end or head of the cylinder. 
     Following this welding process, the metal bars lose, on these ends, the insulating surface layer with which they are coated upon being manufactured. It is therefore necessary to coat the welded ends of the bars again with appropriate insulating substances. One of these insulating substances comprises, for example, a so-called “gel coat” resin. 
     The here disclosed impregnation plant  10  is well suited for performing this coating process. As a matter of fact, it is sufficient to add, downstream of the gelling station  28  and upstream of the baking station, one or more further impregnation stations  24  configured to dispense a further insulating substance, such as for instance “gel coat”, aiming at coating welded or insulation-free metal areas. 
     It is thus proved that the impregnation plant and the impregnation method for components of electric motors according to the present invention achieve the previously highlighted objects. 
     The thus conceived impregnation plant and impregnation method for components of electric motors according to the present invention are in any case susceptible of numerous modifications and variants, all falling within the scope of the same inventive concept; also, all details are replaceable with technically equivalent elements. In practice, the materials used, as well as shapes and dimensions, can be materials, shapes, and dimensions whatsoever, depending on the technical requirements. 
     Therefore, the scope of protection of the invention is that defined by the attached claims.