Abstract:
Disclosed is a dynamoelectric machine having improved heat dissipation capabilities. The dynamoelectric machine includes a three-phase stator winding with a rectifier assembly electrically connected to the stator winding. The rectifier assembly includes an end frame having at least one negative diode contained therein and a positive heat sink which has at least one positive diode disposed therein. Connecting the negative diodes and positive diodes is a terminal assembly. The terminal assembly includes one or more electrically conductive and heat dissipative straps. The straps electrically connect one or more negative diodes and one or more positive diodes. Also disclosed is a method for dissipating heat from a rectifier of a dynamoelectric machine.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to dynamoelectric machines. More specifically, this invention relates to the cooling of a rectifier and/or stator of dynamoelectric machines. 
     A common application of a dynamoelectric machine is to utilize it as an alternator in a motor vehicle. The alternator produces three-phase alternating current which is rectified into a direct current. This energy can be stored in a battery of the motor vehicle or used by the electrical circuitry of the vehicle which utilizes direct current (DC) voltage. The three-phase alternating current is rectified to direct current by means of a rectifier bridge having a plurality of diodes, commonly either 6 diodes for a normal three-phase alternator or 12 diodes for a parallel three-phase alternator. Half of the diodes (either 3 or 6) are positive diodes. Each positive diode is connected between a phase terminal of a stator winding of the alternator and a positive terminal of the alternator. The positive terminal is connected to the battery and the electrical circuitry of the vehicle. The remaining diodes are negative diodes and are each connected between a phase terminal of the stator winding and electrical ground of the vehicle. 
     The diodes can experience current in excess of 200 amps. This level of current creates a significant amount of heat that must be dissipated to preserve alternator function and reliability. Heat is typically dissipated via carrier plates that the diodes are embedded in. The carrier plates act as heat sinks and may include fins which are exposed to cooling air. With this configuration, heat from the diodes is transferred to the carrier plates and to the fins where the heat is radiated to the atmosphere. 
     Current rectifier and heat sink configurations do not provide sufficient cooling to maintain component temperatures at a safe, reliable level in alternators where an output current exceeds 200 amps. The art would well receive an improved rectifier and heat sink configuration to sufficiently dissipate heat from the components in high current alternators. 
     SUMMARY OF THE INVENTION 
     A rectifier for a dynamoelectric machine includes an end frame having at least one negative diode disposed therein which is electrically connectable to a stator winding of the dynamoelectric machine. Included is a positive heat sink having at least one positive diode disposed therein which is electrically connectable to the stator winding. A terminal assembly including one or more electrically conductive and heat dissipative straps electrically connects one or more negative diodes and one or more positive diodes. 
     A method for dissipating heat from a rectifier of a dynamoelectric machine includes conducting heat into the end frame from at least one negative diode disposed therein. The positive heat sink conducts heat from at least one positive diode disposed therein. The straps of the terminal assembly further conduct heat from the negative diodes and the positive diodes into the terminal assembly. Cooling air is urged through the rectifier to radiate heat from the end frame, the positive heat sink, and or the straps. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
         FIG. 1  is an embodiment of a rectifier for a dynamoelectric machine; 
         FIG. 2  is a view of an embodiment of an end frame of the rectifier of  FIG. 1 ; 
         FIG. 3  is a view of an embodiment of a positive heat sink of the rectifier of  FIG. 1 ; 
         FIG. 4  is a sectional view of the rectifier of  FIG. 1 , depicting cooling air flow through the rectifier; and 
         FIG. 5  is an enlarged view of a detail of a terminal assembly of the rectifier of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in  FIG. 1  is an embodiment of a bridge rectifier  10  of a three-phase alternator (not shown). The rectifier  10  includes an end frame  12  having at least one negative diode  14  disposed therein. In the embodiment shown in  FIG. 1 , six negative diodes  14  are disposed in the end frame  12 , but it is to be appreciated that other quantities of negative diodes  14  are contemplated within the scope of this invention. Each negative diode  14  is electrically connected to a phase of a three-phase stator winding (not shown). In the example shown in  FIG. 1  where rectifier  10  has six negative diodes  14 , two negative diodes  14  are connected to each phase of the three-phase stator winding. 
     Referring now to  FIG. 2 , the negative diodes  14  are disposed in apertures in frame face  16 . The end frame  12  in this example is cast aluminum, but other materials for end frame  12  are contemplated within the scope of this invention. The end frame  12  is configured as an electrically and thermally conductive element (a negative heat sink) of the rectifier  10 . The end frame  12  conducts heat from the negative diodes  14  which is then radiated to the atmosphere. To encourage airflow through the end frame  12  and thereby increase its heat transfer capacity, a plurality of inner vents  18  are disposed radially inward of the negative diodes  14 , and a plurality of outer vents  20  are disposed radially outward of the negative diodes  14 . The inner vents  18  and outer vents  20  shown in one embodiment are elongated slots, but other vent  18 ,  20  shapes are contemplated within the scope of this invention. The outer vents  20 , in particular, aid in radiating heat from an outer wall  22  which extends axially from the frame face  12 . The outer wall  22  adds a significant amount of surface area to the end frame  12 , thereby increasing a cooling capacity of the end frame  12 . An additional benefit of the outer wall  22  is that it provides mechanical protection for the rectifier  10  from physical damage due to handling or while in use in a vehicle. 
     Returning to  FIG. 1 , at least one positive diode  24  is located in a positive heat sink  26  which is located directly over the negative diodes  14  disposed in the end frame  12 . In the embodiment shown in  FIG. 1 , positive diodes  24  are disposed in the positive heat sink  24 , but it is to be appreciated that other quantities of positive diodes  24  are contemplated within the scope of this invention. Each positive diode  24  is electrically connected to a phase of a three-phase stator winding (not shown). In the example shown in  FIG. 1  where rectifier  10  has six positive diodes  24 , two positive diodes  24  are connected to each phase of the three-phase stator winding. 
     As shown in  FIG. 3 , the positive heat sink  26  is configured with at least one diode opening  28  in a positive heat sink face  30  for receiving the positive diodes  24  and at least one of lead hole  32  in the positive heat sink face  30  configured such that a negative diode lead  34  from each of the negative diodes  14  extends through each of the lead holes  32 . The positive heat sink  26  is formed from a thermally conductive material, and is configured to conduct heat from the positive diodes  24 . A plurality of inner fins  36  extend from the positive heat sink face  30  and are disposed radially inboard of the positive diodes  24 . The inner fins  36  increase the surface area of the positive heat sink  26  thereby increasing the efficiency of heat transfer from the positive diodes  24 . The positive heat sink  26  further includes a plurality of outer fins  38  extending from the positive heat sink face  30  at a perimeter  40  of the positive heat sink  26 . In one embodiment, the inner fins  36  and outer fins  38  extend radially and/or axially from the positive heat sink  26 , but it is to be appreciated that the invention is not limited to fins extending radially and/or axially. 
     Cooling air is provided to the rectifier  10  by a centrifugal fan (not shown) or other means, which directs air substantially axially through the alternator and, as shown in  FIG. 4 , through the inner vents  18  and outer vents  20  in the end frame  12 , and through slots  42  defined by adjacent fins  38  in the positive heat sink, thus increasing the cooling performance of the fan. Additionally, the location and configuration of vents  18  and  20  and slots  42  causes cooling air through the alternator to impinge directly on end turns of one or more stator windings (not shown). This aids in keeping the stator windings uniformly and efficiently cooled. 
     Referring again to  FIG. 1 , a terminal assembly  44  is attached to the positive heat sink  26 . The terminal assembly  44  comprises a plurality of bosses  46  connected to each other by electrically conductive and heat dissipative straps  48 . One or more of the bosses  46  each includes a terminal hole  50  which corresponds with one or more screw holes  52  in the positive heat sink  26  thus allowing connection of the terminal assembly  44  to the positive heat sink  26  via a screw (not shown) or other means. 
     As illustrated in  FIG. 5 , the straps  48  are arranged in a dual configuration, meaning that each negative diode lead  34  and each positive diode lead  54  is electrically connected to two straps  48 .The invention is not limited, however, to the utilization of two straps  48  to connect each negative diode lead  34  and each positive diode lead  54 . Other quantities of straps  48 , for example, three or four, may be utilized. Further, in one embodiment the straps  48  are electrically connected to each negative diode lead  34  and each positive diode lead  54  by welding, although it is appreciated that other means of connection are contemplated within the scope of the invention. In one embodiment, the straps  48  are further configured and arranged such that the two positive diodes  24  and the two negative diodes  14  electrically connected to a phase of the stator winding are electrically connected to one another in parallel. By having multiple positive diodes  24  and multiple negative diodes  14  a current capability of the rectifier  10  is increased, and thermal characteristics for a current are improved due to a spatial distribution of a heat load among the multiple diodes. Because of the heat dissipating characteristics of the straps  48 , the terminal assembly  44  itself becomes a source for cooling the negative diodes  14  and the positive diodes  24  by allowing heat to radiate from the straps  48 . In one embodiment, the straps  48  are substantially bare, thus adding to their heat dissipating capacity. Arranging the straps  48  in a dual configuration provides a larger cross-sectional area for electrical conduction, thereby reducing ohmic heating of the straps  48  and provides a larger surface area for removal of heat from the negative diodes  14  and the positive diodes  24 . 
     In an alternative embodiment, three negative diodes  14  are included in the rear frame  12 , and three positive diodes  24  are included in the positive heat sink  26 . The positive diodes  24  and negative diodes  14  are electrically connected to the phases of the three phase stator winding such that one negative diode  14  and one positive diode  24  are electrically connected to each phase of the stator winding. 
     While embodiments of the invention have been described above, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.