Abstract:
A permanent magnet rotor having a shaft, a hollow cylindrical permanent magnet and an elastic connecting medium between the shaft and the permanent magnet. The permanent magnet is arranged co-axially around the shaft to ensure that the permanent magnet is mounted securely, that it is not damaged during large temperature fluctuations, and that it is not deflected impermissibly from the axis of rotation in case of heavy radial load. A simple installation process uses a mechanical connection between the shaft and the permanent magnet. This task is performed by virtue of the fact that an elastic connecting medium is arranged along the periphery of the shaft at several first areas in which the distance between the shaft and the permanent magnet is enlarged. These first areas are separated from the second areas in which the distance between the shaft and the permanent magnet is minimized but not zero.

Description:
BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The invention is related to a permanent magnet rotor with a shaft, a hollow cylindrical permanent magnet and an elastic connecting medium between the shaft and the permanent magnet, with the permanent magnet arranged coaxially around the shaft. 
   (2) Description of Related Art 
   A generic permanent magnet rotor is known from DE 23 28 886. In this design, a hollow cylindrical permanent magnet is mounted with the help of an elastic intermediate layer. The radial thickness of the elastic intermediate layer is measured in such a way that in case of sudden braking of the motor shaft, the permanent magnet can swing in the direction of the periphery, and thus prevent damage to the gear pinion. Other applications in which there are large temperature fluctuations, elastic intermediate layers help prevent mechanical tensions between materials subject to different degrees of heat expansion. However, it is this elastic intermediate layer that prevents a reliable permanent mechanical connection between the shaft and the permanent magnet. Another disadvantage is that the precision of the circular motion cannot be adequate in case of radial load, because the elastic material is of a yielding variety. Moreover, the material should not swell under the influence of humidity. Swelling could lead to the bursting of the permanent magnet. 
   BRIEF SUMMARY OF THE INVENTION 
   The task of the invention is to ensure that the permanent magnet is mounted securely, that it is not damaged under large temperature fluctuations, and that it is not deflected to an impermissible extent from the rotary axis. A simple and cost-effective assembly method is used in which a secure mechanical connection between the shaft and the permanent magnet is guaranteed over the entire life of the device. 
   According to the invention, this problem is solved by arranging the elastic connecting medium on the periphery of the shaft in several first areas in which the distance between the shaft and the permanent magnet is enlarged, and they are separated from the second areas in which the distance between the shaft and the permanent magnet is minimum, but not zero. The areas having larger distance provide secure support to the elastic connecting medium, and the areas with less distance allow only a limited deflection of the permanent magnet with reference to the shaft or a component surrounding the permanent magnet. This increases the precision of the circular motion even under conditions of heavy radial load. The areas with less distance can absorb the volume changes occurring in the elastic connecting medium to a certain extent during assembly or on account of temperature of pressure loads, and thus avoid tensions in the magnet material. Here and in the following pages, shaft also means a rotor body that is integrated with the pump impeller into one single unit, which carries the permanent magnet. The elastic connecting medium is preferably an elastic adhesive. The adhesive creates a compact connection between the shaft and the permanent magnet, which guarantees a stable inner connection between the two components. Silicon was found to be an ideal adhesive with adequate elastic properties. RTV-1 Silicon rubber variants of the ELASTOSIL® series are also suitable, which react to the humidity in the air as an elastic Silicon rubber (RTV-1=Room Temperature Wetting, 1-Component). 
   To implement a preferred embodiment of the invention, it is recommended that the elastic connecting medium be arranged in several grooves parallel to the axle. It is also recommended that the number of grooves should not be equal to half the number of poles or the total number of poles of the permanent magnet. Further, the number of grooves should not be equal to the number of wings of the impeller. These measures minimize the noise buildup. To establish a stable connection, the number of grooves should be equal to or more than three, the preferred number being three. The grooves should be distributed at uniform distances on the periphery of the shaft, so that an exact centering of the shaft can be achieved with reference to the permanent magnet. “Wings” have the same meaning as “vanes.” 
   Instead of using straight grooves, the elastic connecting medium can be arranged in meander-shaped or spiral-shaped grooves around the shaft. There can be one or several grooves. What is crucial is that the elastic connecting medium is not applied on the full surface, and that no air cushions are formed. 
   To be able to establish a maximum possible robust and mechanically stable connection, the elastic connecting medium should be distributed across the entire length of the permanent magnet. In principle, the recommended magnet mounting can be used in all permanent magnet materials. Ferrite magnets are particularly ideal for this type of connection, because Ferrites are very brittle and prone to ruptures, particularly under thermal and other mechanical tensions. 
   For a large number of applications, it is cost-effective to produce the shaft from plastic material that can be processed through injection molding. The suggested geometry of the shaft is suitable for this production process, especially on account of the missing undercuts that would have been unavoidable if the grooves were arranged in cross-section. It is recommended that the shaft be designed as hollow, and that it be mounted on an axle so that it can rotate. 
   The dimensioning of the two different areas is selected in such a way that an undesirably large deflection of the permanent magnet with reference to the shaft or a component surrounding the permanent magnet at a very small distance can be ruled out. Electric engines/motors constitute the most frequent application of the invention in question. In this case, an undesirably large deflection with respect to a stator is ruled out. The ratio (L/A) of the air gap length (L) between the permanent magnet rotor and the stator, and the minimum distance (A) of the second area between the shaft and the permanent magnet is to be selected as more than 1. This way the permanent magnet can be deflected only within the allowed limits. The permanent magnet rotor has a locating bearing that is fixed permanently to the axle or rotor. Normally, the locating bearing is fixed to the rotor so that the bearing surface may have a low friction radius. 
   In a preferred embodiment, the locating bearing is made of a plastic material that can be processed through injection molding and is joined to the permanent magnet rotor through original forms. The bearing material in this case is connected to the permanent magnet rotor through injection molding, insertion molding or tagged molding. If it is necessary to use a special bearing material that should not be used for the permanent magnet rotor for technical or economic reasons, one can use different plastic materials adapted to the concerned objective. 
   If these aspects are only of subordinate importance, one can also use the same plastic material for permanent magnet rotor as well as locating bearing, and manufacture both in a single operation. It may be necessary to produce the locating bearing from a friction-proof plastic material or from a material having better sliding properties than the shaft material. Filling material such as graphite is ideal for improving sliding properties. Graphite is well-known as a solid lubricating agent. 
   While using different materials for locating the bearing and the shaft, one can use a two-component injection molding process in which the locating bearing and the shaft are manufactured one after the other in a single injection molding tool. 
   A special design of an electric motor contains a permanent magnet that has a second magnetization coordinating axially with a stator-proof magnet sensor in addition to a first magnetization with a radial magnetization cooperating with a stator magnetic field. The permanent magnet is designed as a one-piece unit. 
   Electric motors having a permanent magnet rotor according to the invention are ideal especially for use as pump drives, where the shaft works in tandem with a pump impeller. The shaft and the impeller should preferably be integrated in a single unit. Of course, it is known that the entire pump rotor, i.e., permanent magnet and pump impeller are manufactured from the same material and in one operation, but more permanent material is consumed in this way than is actually necessary. This also has an effect on the weight and the moment of inertia of the pump rotor. Further, it has been established that such one-piece pump rotors can burst under extreme temperature fluctuations, although the permanent material is plastic bound. 
   The mentioned temperature fluctuations occur frequently in wet running centrifugal pumps for cooling water pumps in the motor vehicles sector. Depending on the application in question, the cooling medium is also ideal for cooling the pump itself. The components to be cooled are the stator, particularly a stator coil or in case of electronically commutated DC motors—the integrated control circuit (IC) for switching the stator coil. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A design example of the invention is explained in greater detail in the following pages with the help of the drawing. The following are available for viewing: 
       FIG. 1A  perspective view of a rotor, 
       FIG. 2  A front view of the rotor, 
       FIG. 3  A side view of the rotor, 
       FIG. 4  A front view of a pump impeller, and 
       FIG. 5  An assembly drawing of a centrifugal pump. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     FIG. 1  illustrates a spatial representation of a rotor  50 , which is mounted on an axle  49  through a locating bearing  54 . The bearing is connected permanently to a shaft  51  designed as a hollow shaft. The outer periphery of the shaft  51  has four grooves  511  running parallel to the axle. An elastic connecting medium  53  is arranged in the grooves in such a way that it establishes a connection between the shaft  51  and a hollow cylindrical permanent magnet  52 . The connecting medium here is an elastic adhesive, e.g., Silicon. The inner diameter of the permanent magnet  52  is slightly more than the maximum outer diameter of the shaft  51  in the area within the permanent magnet  52 . The diameter difference is calculated in such a way that on the one hand excess adhesive can go into the gap between the shaft  51  and the permanent magnet  52  so that in case of external load, a small deviation of the permanent magnet  52  from the center is possible. However, this deviation is very limited. The adhesive medium is filled in the grooves with the help of hollow needles. The shaft  51  and the pump impeller  59  are integrated into one piece that has wings  591 . The wings  591  spring out of a disk  512 . The opposite side of the disk  512  serves as the supporting surface for the permanent magnet  52 . A longitudinal groove  58  that is open to the bearing and axle  49  is provided on the inner side of the shaft. This groove serves as a secondary cooling channel. 
     FIG. 2  shows a front view of the permanent magnet rotor  50  according to the invention, with an axle  49  that is fixed in a pump housing. The locating bearing  54  and the shaft  51  are integrated with the pump impeller  59  into one piece. The pump impeller is integrated with the disk  512  that supports the permanent magnet  52 . 
     FIG. 3  shows a side view of the permanent magnet rotor  50  according to the invention, along with the pump impeller  59 , the wings  591 , the disk  512  and the permanent magnet  52 , where the permanent magnet has an axial sensor trace magnetization  522  with alternating poles in a front side area. The permanent magnet is preferably magnetized radially at the time of production. The axial sensor trace magnetization  522  takes place only after the magnetization of the permanent magnet  52 . 
     FIG. 4  shows a front view of the pump impeller  59  with disk  512 , the wings  591 , the locating bearing  54  and the longitudinal groove  58 . 
     FIG. 5  shows a sectional view of a centrifugal pump  100  according to the invention, with a pump housing  102  consisting of a first housing part  103  and a second housing part  104  attached to it. A motor housing part  44  limits a dry chamber which is occupied by a stator  40  of an electronically commutated DC motor and its activation electronics. The motor housing part  44  is connected to the second housing part  102 . The first and the second housing parts  103 ,  104  limit a wet chamber  101  of the centrifugal pump. The second housing part  104  is integrated into one piece with a split case  116 , which separates the wet chamber  101  from the dry chamber  99 . 
   The wet chamber  101  contains an axle  49  which is installed permanently between a split case side axle support  48  and a suction nozzle side axle support  47 . A bordering at the axle end prevents unintentional rotation of axle  49  when the pump is in operation. A locating bearing  54  (not shown here) is mounted on Axle  49  in such a way that it can rotate. It is pressed into a hollow shaft  51  of the rotor  50 . The shaft  51  forms a single piece with a pump impeller  59  that contains several approximately spiral-shaped wings  591  for pumping the liquid. The front surfaces of the locating bearing  54  can be supported axially by an intermediate layer of start disks against the split case side axle support  48  and against the suction nozzle side axle support  47 . A hollow cylindrical Ferrite magnet  52  is pasted on the hollow shaft  51 . An elastic adhesive is used, which is guided into four or five grooves  511  (not shown here) formed in the hollow shaft parallel to the axle. 
   The dry chamber  99  contains the stator  40  of the electronically commutated DC motor  10  which is designed as a hollow cylindrical stator coil  41 . Under operation, its magnetic field is guided alternately to the periphery of the split case  116  through the claw poles  42  and it interacts with the hollow cylindrical permanent magnet  52  in the wet chamber  101 . The magnetic circuit is closed with the help of a return ring  43  that is connected to the claw poles  42 . The claw poles  42  are provided with an insulating body  46  which connects the claw poles  42  to each other mechanically but not magnetically. In the current example, the stator  40  has four pole pairs. 
   The insulating body  46  is shaped geometrically in such a way that the coil wires of the stator coil  41  can be connected through contact pins  62  having clamping blade contacts. These clamping blade contacts can be mounted mechanically in the insulating body  46 . The contact pins  62  are designed as combo-contacts and they are pressed into the circuit board  61  at the end opposite the clamping blade contact  63 , and contacted with it in this way. The contact pins  62  contain one or two deformable pressing zones for this. The circuit board  61  contains a hall sensor  71 , an integrated control  70  for switching the stator coil, a PTC for coil protection and male connector pins for the voltage supply. The motor housing part  44  contains a male connector housing (not shown here) in which the male connector pins  64  are arranged. Electronic components with large heat losses are heated with the help of heat conduction foils  67  from the wet chamber  101 . Conductors that serve the purpose of contacting the elements to be cooled are dimensioned in such a way that maximum possible wide conductors  66  are provided for easier heat emission on the circuit board  61 . To exploit the circuit board  61  well and to achieve optimal heat emission, the different conductors  66  have different widths, depending on how much heat is generated in the component connections to be contacted. A longitudinal groove is formed in the shaft  51  as cooling channel between a bottom  117  of the split case  116  and the pump impeller  59 , which also forces a continuous circulation of the pumped medium even in the inner areas of the split case  116 . The circuit board is arranged between the front side  45  of the motor housing  44  and the bottom  117  of the split case  116 , and maintained in heat conducting contact with the bottom  117  over the heat conducting foil  67 . 
   The first housing part  103  has a first flange  130  and a first ring  131  connected to it. The second housing part  104  has a second flange  140  and a second ring  141  connected to it. The motor housing part has a third ring  441 . The second flange  140  and the second ring  141  together form a cross-sectional T shape. Four sealing areas are provided. The first sealing area is located in the first housing part  103  on the radial outer side of the first ring  131 . The second sealing area  144  is located opposite, on the radial inner side of the second ring  141  and the second housing part  104 . Similarly, there is a third sealing area located radially on the inner side of second ring  141  and the second housing part  104 . The fourth sealing area is located opposite, on the radial outer side of the third ring  441  and the motor housing part  44 . The second housing part  104  consists of a material that allows a laser beam of a certain wavelength or a wavelength range to pass through it. The first housing part  103  and the motor housing part  44  are made of a material that absorbs the same laser beam. This way a laser beam is guided to a seam without heating the transparent material. There the beam encounters material that absorbs the light and converts it into heat, which melts the plastic and establishes an inner connection with the neighboring material. 
   As the two sealing areas to be welded are close to each other, it is not difficult to undertake the two sealing actions with one device and in one operation. The welding device can have two individual lasers so that each laser beam can create one seam, or it can have just one laser, the output beam of which is divided into two sections with the help of a splitter, each of which then creates one welded seam. In the example cited here, the laser rays are guided radially to the pump housing. 
   Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.