Abstract:
An electrical machine formed as a generator for a motor vehicle, comprising a stator provided with a stator winding; a cooling casing which surrounds said stator and through which a heat transmitting medium can pass; a circuit in which the heat transmitting medium circulates; at least one heat exchanger for heating purposes arranged in said circuit, said stator being provided with a selectively activatable medium for increasing a stator stray power.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an electrical machine, in particular a generator for a motor vehicle.  
           [0002]    A known electrical machine is disclosed in the European patent document EP 0 841 735 A1 and used as a water-cooled alternating or rotary current generator in motor vehicles. Its cooling casing is integrated in the cooling water circuit of the combustion engine. In the cooling water circuit also a motor cooler and air-water heat exchanger for a heating device, a circulating pump as well as regulating valve for a throughflow control of the cooling water are arranged. The unavoidable stray power of the generator can be efficiently withdrawn through the water-through flowed cooling casing. Moreover, there is the advantage that this stray power, differently from air-cooled generator, is not lost, but instead is taken by the cooling water which flows through the heat exchanger and is used in the heat exchanger for improving its feed power. This is especially advantageous for diesel motors with direct injection of multi-purpose motor vehicles, having high efficiency, since in this motor type the heating of the cooling water is moderate and allows only a little efficient inner space heating.  
         SUMMARY OF THE INVENTION  
         [0003]    Accordingly, it is an object of the present invention to provide an electrical machine of the above mentioned general type, which avoids the disadvantages of the prior art.  
           [0004]    In keeping with these objects and with others which will become apparent herein after, one feature of present invention resides, briefly stated in an electrical machine which has a stator provided with a stator winding; a cooling casing which surrounds said stator and through which a heat transmitting medium can pass; means forming a circuit in which the heat transmitting medium circulates; at least one heat exchanger for heating purposes arranged in said circuit, said stator being provided with a selectively activatable medium for increasing a stator stray power.  
           [0005]    The inventive electrical machine has the advantage that when a desired inner space temperature is not reached through the heating heat exchanger the stator stray power of the machine can be purposely increased when and then supplied through the heat transmitting means of the heating heat exchanger and there is used to a greater part for the inner space heating.  
           [0006]    In accordance with a preferable embodiment of the invention, the stator stray power can be easily manipulated in that, a multi-phase or a multi-strand stator winding has at least two parallel branches per phase or strand, and switching means are provided which in each phase or in each strand selectively switch at least one branch parallel or separate from the other branch.  
           [0007]    Thereby, for example for a three-phase stator winding with two parallel branches per phase, by switching off of one branch per phase the stator stray power in idle running of the combustion engine is increased from approximately 600 W to approximately 1100 W, 5% of current losses of the generator taken into consideration in this operational condition. This stray power which increases with increasing rotary speed of the combustion engine and thereby increasing rotary speed of the generator, provides an additional heating power for heating the interior space between 500W and 750W which is supplied to the heat transmitting means. These numbers are applicable for example for a rotary current generator with a stator winding switched in a triangle with an applied nominal current of 150 A.  
           [0008]    The desired additional heating power can be realized with relatively low additional expenses, when in accordance with a preferable embodiment of the present invention for the use in a motor vehicle, the stator winding is connected to a full-wave rectifier bridge. The first ends of the switchable branches connected to the rectifier bridge are separated from the non-switchable branches in the phases or strands and are connected through each rectifier formed for example as a diode to a common tap point, and the switching means include a controllable switch which on the one hand is connected to the tap point and on the other hand is connected to one of the both bridge outlet terminals of the rectifier bridge. The additional expenses amount then to three diodes, a power-MOSFET as a switch, and a simple control electronic circuit for the MOSFET. 
       
    
    
       [0009]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a longitudinal section of a generator for a motor vehicle;  
         [0011]    [0011]FIG. 2 is a switching diagram of a generator which is coupled with a board electrical system of the vehicle of FIG. 1; and  
         [0012]    [0012]FIG. 3 is a block switching diagram of a cooling water circuit of the motor vehicle with the generator of FIGS. 1 and 2.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    As an example of a general electrical machine, a water-cooled generator  10  for a motor vehicle is shown in a longitudinal section in FIG. 1. It has in a known manner a so-called claw pole rotor  11  which is arranged non-rotatably on a rotor shaft  12 . The rotor shaft  12  is rotatably supported by roller bearings  13 ,  14  in coaxial bearing shields  15 ,  16 . The rotor is composed of two claw shells  111 ,  112  which engage one another with their claw poles formed as teeth. An excitation winding  17  is received between the claw shells  111 ,  112 . A field excitation voltage is applied to the excitation winding  17  by two not shown grinding rings which are arranged on the rotor shaft  12 .  
         [0014]    A stator  21  surrounds in a known manner the rotor  11  with a gap therebetween. It has a stator plate pack  22  or a so-called iron plate pack, as well as a stator winding  23 . The stator winding is inserted in axial grooves provided in a known manner in the stator plate pack  22 . The winding head  20  of the stator winding  23  which extend from the stator plate pack  22  at both end sides are shown in a section of FIG. 1. The stator plate pack  22  is pressed into a cup-shaped stator housing  24  which is surrounded by a cooling casing  25 . The cooling casing  25  is also cup-shaped, and its cup bottom forms a bearing shield  15 . The other bearing shield  16  is placed on the cup edge and closes the cooling jacket  25  at the end side. A fluid-tight closed ring chamber  26  is provided between the cooling casing  25  and the stator housing  24 . It communicates with a supply pipe  27  and a not shown discharge pipe.  
         [0015]    The ring chamber  26  in the cooling casing  25  is incorporated in the cooling water circuit  28  of the internal combustion of the vehicle through both connections, mainly the supply pipe  27  and the discharge pipe. The cooling water circuit  28 , as schematically shown in FIG. 3 in addition to the combustion engine  29  and the generator  30 , also incorporates a motor cooler  30 , an air-throughflow heating heat exchanger  31  for a heating or a climate device of the vehicle, a circulating pump  32 , as well as a thermostat valve  33 . The thermostat valvel is formed so that under a predetermined operational temperature of the combustion engine, the cooling water which is heated by the combustion engine flows only through the heating heat exchanger  31 , and when the operational temperature is exceeded the motor cooler  30  is introduced into the circulation of the cooling water.  
         [0016]    In order to improve the efficiency of the combustion engine  29  which is formed as direct injection diesel motor for multi-purpose motor vehicle and provides a little efficient inner space heating, the generator  10  which is connected with its cooling medium  25  to the cooling water circuit  28  is formed so that, via internal, selectively activatable medium its efficiency can be worsened and thereby the high stray power produced in the generator is withdrawn directly to the cooling water, so that the heating heat exchanger  31  makes available a greater heating potential of the cooling water. These means are realized by a circuit change in the stator  21 .  
         [0017]    [0017]FIG. 2 shows a block diagram of the generator  10  which is connected through a rectifier bridge  34  to the 12 V board electrical system. The stator winding  23  is formed as a three-phase winding and connected in a triangle. The stator winding  23  is associated with the rotor  11  of the excitation winding  17 . A controller  41  controls the field excitation. The three-phase stator winding  23  is provided with two parallel branches  231 ,  231 ′,  231 ″ and  232 ,  232 ′,  232 ″. The triangle points are connected at the central taps  341 ,  342 ,  343  with the three-phase full-wave rectifier bridge  34 . The both output terminals  344 ,  345  of the rectifier bridge  34  are connected to a positive pole  35  and a negative pole  36  of the vehicle battery. In order to purposely provide worsening of the efficiency for increasing the stray power of the stator  21 , in each phase or each strand of the stator winding  23  the strand ends of the branches  232 ,  232 ′,  232 ″ which are connected with the central tap of the rectifier bridge  34  are separated from the strand ends of the branches  231 ,  231 ′ and  231 ″ and are placed each through a diode  37 , which is formed here is a Zener diode, on a common tap point  38 . A field effect transistor  39 , for example a power MOSFET is connected on the one hand to the tap point  38  and on the other hand to the output terminal  344  of the rectifier bridge  34  connected to the positive pole  35 . The field effect transistor  39  is controlled by a simple control electronic unit  40 . When the field effect transistor  39  is controlled, the branches  232 ,  232 ′,  232 ″ are connected in parallel to the branches  231 ,  231 ′,  231 ″. The stator winding  23  is then a conventional three-phase winding with two parallel connected branches per each strand or phase. When the field effect transistor  39  is blocked, the parallel branches  232 ,  232 ′,  232 ″ are switched off. Thereby the stator stray power is increased to a relatively high degree. This increased stray power of the generator  10  is given away to the cooling water in the cooling water circuit  28  and makes available in the heating heat exchanger  31  a very high portion for the inner space heating of the vehicle.  
         [0018]    The present invention is not limited to the above described embodiment. For example three phrase stator winding  23  in FIG. 2 can be also connected in a star. In this case the star point for the parallel branches  232 ,  232 ′,  232 ″ is released and the stand ends of this parallel branches  232 ,  232 ′,  232 ″ are applied in the same way on the tap point  38  through a diode  37 .  
         [0019]    It is also not necessary to connect the field effect transistor  39  of the tap point  38  with the output terminal  344  located at the positive pole  35  of the vehicle battery. Alternatively, the tap point  38  can be applied through the field effect transistor  39  also to the output terminal  345  connected to the negative pole  36 . In this case the polarity of the diodes  37  is to be inverted.  
         [0020]    The invention is also not limited to a three-phrase or a three-strand stator winding  23 . Any phase number can be selected for the stator winding  23 .  
         [0021]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.  
         [0022]    While the invention has been illustrated and described as embodied in electrical machine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0023]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.  
         [0024]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.