Abstract:
An automotive alternator comprises: a stator provided with a stator coil; a rotor supported for rotation in the stator to apply an alternative magnetic field to the stator; a regulator for regulating output; a rectifier for rectifying generated current; a plurality of housings holding the stator and the rotor; and a coolant path through which a coolant flows through at least one of the plurality of housings to transfer heat generated in the stator coil outside the automotive alternator. Fastening devices formed of a material having good heat conductance fasten the regulator and a heatsink for the regulator together to the housing at a position apart from the housing to transfer heat generated by the regulator to the housing. Thus, the automotive alternator can maintain a stable cooling ability in a hot atmosphere for a long time.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an alternator for a vehicle and more particularly, to a liquid-cooled alternator for a vehicle. 
   Most conventional automotive alternators are of an air-cooled type that dissipates heat generated therein into the atmosphere. Recently, the temperatures of parts arranged in an engine room have increased, and the temperature of air in the engine room has increased. Consequently, when the ambient air temperature rises, air-cooling cannot efficiently dissipate the heat generated by the alternator in some automobiles. 
   Although the heat generating ability of a regulator for regulating an automotive alternator is not high, it is important to cool the regulator efficiently because the absolute heat resistance of the regulator, as compared with that of stator coils, is not high. 
   Recently, automobiles are required to arrange parts in the engine room in a high density, to improve the efficiency of the engine and to reduce emissions for low noise and improvement of output and efficiency. Consequently, there is a tendency that the temperature in the engine room increases and radiant heat increases due to temperature rises in the parts disposed in the engine room. Therefore, an automotive alternator disposed in the engine room is exposed to a high-temperature atmosphere for a long time, which causes the deterioration of the performance and the shortening of the life of the automotive alternator. 
   A method of protecting the automotive alternator from heat damage disposes a heat shield plate formed of a material having low heat conductance between the automotive alternator and hot parts arranged in the engine room. However, the effect of this method in protecting the automotive alternator from heat damage is not satisfactory because air temperature in the engine room rises inevitably when the engine is operated continuously for a long time. 
   Liquid-cooled automotive alternators disclosed in JP 7-194060A and JP 2000-245111A are intended for use in a hot atmosphere. 
   Alternators disclosed in JP 7-194060A, EP 1041699A2 and EP 1096647A2 dissipate heat generated by a voltage regulator and a rectifier through a heatsink and a rear housing to cool the alternators. The alternator disclosed in JP 2000-245111A dissipates heat generated by a voltage regulator and rectifier through a heat-radiating plate, a rear bracket on a side opposite to the side of a pulley, a member having good heat conductance and a liquid-cooled housing to cool the alternator. 
   In the alternator disclosed in JP 7-194060A and JP 2000-245111A, the heatsink of the regulator must be in close contact with the rear housing and the rear bracket to water-cool the regulator. Consequently, the alternators are subject to restrictions on the arrangement of the regulator, the brushes and the rectifier, which causes structural inconvenience and problems with assembling work. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a liquid-cooled alternator for vehicle intended to be installed in a high-temperature engine room, providing high degree of freedom of disposition of a regulator, and having a sufficiently high cooling ability. 
   According to one aspect of the present invention, an alternator for a vehicle comprises: a stator provided with a stator coil; a rotor supported for rotation in the stator to apply an alternative magnetic field to the stator; a regulator for regulating output; a rectifier for rectifying generated current; a plurality of housings holding the stator and the rotor; a coolant path for allowing a coolant to flow through at least one of the plurality of housings to transfer heat generated in the stator coil outside; and fastening devices formed of a material having good heat conductance fasten the regulator and a heatsink for the regulator together to the housing at a position apart from the housing to transfer heat generated by the regulator to the housing. 
   According to another aspect of the present invention, an alternator for a vehicle comprises: a stator provided with a stator coil, a rotor supported for rotation in the stator to apply an alternative magnetic field to the stator, a regulator for regulating output, a rectifier for rectifying generated current, a plurality of housings holding the stator and the rotor; a cover covering the regulator and the rectifier, and a coolant path for allowing a coolant to flow through at least one of the plurality of housings to transfer heat generated in the stator coil outside; wherein the plurality of housings and the cover are formed of metals each having good heat conductance, the rectifier is held on one of the housings, the cover and one of the housings are in metal contact, fastening devices formed of a material having good heat conductance fasten the regulator and a heatsink for the regulator together to the housing at a position between said housing and the cover to transfer heat generated by the regulator to said housing. 
   According to the present invention, the fastening devices formed of a material having good heat conductance fixedly fasten the regulator and the heatsink of the regulator, or the rectifier at a position spaced from the housing and the cover. Most part of heat generated by the regulator and the rectifier is transferred to the coolant flowing through the housing. Therefore, the respective temperatures of the regulator substantially entirely covered with the cover and the housing, and the rectifier are dependent mainly on the temperature of the coolant, and are not dominated by the high temperature of the ambient air and the radiant heat radiated by high-temperature parts even when the automotive alternator is exposed to a high-temperature atmosphere. 
   Since the regulator does not need to be set in close contact with the housing, the freedom of selecting a place for placing the regulator is increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which: 
       FIG. 1  is a longitudinal sectional view of a liquid-cooled automotive alternator in a first embodiment according to the present invention; 
       FIG. 2  is a longitudinal sectional view of the alternator shown in  FIG. 1 ; 
       FIG. 3  is a perspective view of a part around a regulator of the alternator shown in  FIG. 1 , in which the rear cover is removed; 
       FIG. 4  is a side elevation of the alternator shown in  FIG. 1 , in which a rear cover is removed; 
       FIG. 5  is a circuit diagram of a regulator shown in  FIG. 1 ; 
       FIG. 6  is a graph showing results of experiments conducted to examine cooling ability; 
       FIG. 7  is a longitudinal sectional view of a liquid-cooled automotive alternator in a second embodiment according to the present invention; 
       FIG. 8  is a longitudinal sectional view of a liquid-cooled automotive alternator in a third embodiment according to the present invention; 
       FIG. 9  is a perspective view of a part around a regulator of the alternator shown in  FIG. 8 , in which a rear cover is removed; 
       FIG. 10  is a longitudinal sectional view of a liquid-cooled automotive alternator in a fourth embodiment according to the present invention; 
       FIG. 11  is a perspective view of a part around a regulator of the alternator shown in  FIG. 10 , in which a rear cover is removed; and 
       FIG. 12  is a longitudinal sectional view of a liquid-cooled automotive alternator in a fifth embodiment according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A liquid-cooled alternator for a vehicle in a first embodiment according to the present invention will be described with reference to  FIGS. 1  to  5 .  FIG. 1  is a longitudinal sectional view of the liquid-cooled automotive alternator in the first embodiment,  FIG. 2  is a longitudinal sectional view of the alternator shown in  FIG. 1 ,  FIG. 3  is a perspective view of a part around a regulator in a state where the rear cover is removed,  FIG. 4  is a side elevation of the alternator shown in  FIG. 1 , in a state where a rear cover is removed, and  FIG. 5  is a circuit diagram of the regulator. 
   An alternator  100  for a vehicle, which is also referred to as the automotive alternator, includes a center housing  102 , a front housing  103  behind a pulley, a rear housing  104  on a side opposite to the side of the pulley, and a rear cover  110 . The front housing  103  is formed by aluminum die cast. The front housing  103  holds a front bearing  132 , and a rotor shaft  101  is supported in the front bearing  132 . Similarly, the center housing  102  is formed by aluminum die cast. The center housing  102  holds a rear bearing  134 , and the rotor shaft  101  is supported in the rear bearing  134 . A stator  105  is held on the inner circumference of the center housing  102 . A coolant path  150  through which a coolant flows is formed inside the center housing  102  and inside the rear housing  104 . A pulley  130  is mounted on a front end part of the rotor shaft  101 , and slip rings  128  are mounted on a rear end part of the rotor shaft  101 . The pulley  130  is connected to a pulley mounted on the crankshaft of an engine by a belt. A rotor  107  is mounted on a middle part of the rotor shaft  101 . A pair of wedge-shaped claw poles  108  is formed in the circumference of the rotor  107 . The center housing  102  is provided with a built-in stator core  170 . A small gap is defined between the inner circumference of the stator core  170  and the surfaces of the claw poles  108  of the rotor  107 . Teeth and slots are arranged on the stator core  170 , and stator coils  106  for three phases are embedded in the slots of the stator core  105 . A field coil  109  is formed in a central part of the rotor  107 . Supplying a dc current to the field coil  109  through brushes  121  and the slip rings  128  magnetizes the claw poles  108 . Three-phase induced voltage is generated in the stator coils  106  when the rotor  107  is driven for rotation by the engine. 
   A regulator  120  for regulating the voltage of output, a brush holder  122  and a rectifier  124  for rectifying generated current are fastened to the rear housing  104  and are covered with the rear cover  110 . The regulator  120  includes a chip and the like formed on a thin substrate. A heatsink  127  having the shape of a flat plate is disposed so as to be in surface contact with the back surface of the substrate. 
   Referring to  FIGS. 3 and 4 , the regulator  120  and the heatsink  127  are held by a holder  122  formed integrally with the brushes  121  and a connector  126  for connection with the vehicle side. The regulator  120  and the heatsink  127  are fastened to the rear housing or the center housing with fastening devices  136 . The rear housing  104  is provided with mounting projections  138  provided with an internal thread. Mounting bosses formed on the heatsink  127  are set on the mounting projections  138  and the heatsink  127  is fastened t the rear housing  104  with long bolts  136  serving as the fastening devices. Thus, the heatsink  127  of the regulator  120  is spaced from the rear housing  104  by a distance corresponding to the sum of the respective heights of the mounting projections  138  and the bosses of the heatsink  127 . Also, the heatsink  127  is spaced from the rear cover  110 . Heat is transferred from the heatsink  127  of the regulator  120  through the fastening devices  136  to the rear housing  104 . 
   Desirably, the fastening devices  136  are formed of iron or brass having a heat conductivity λ of 30 W/m·K or above. The rear housing  104  and the rear cover  110  are formed of aluminum, i.e., a material having good heat conductance, by die cast. 
   The rear housing  104  and the rear cover  110  may be formed of aluminum plates by press molding instead of by aluminum die cast. 
   The regulator  120  and the heatsink  127  may be fixedly held in place by any suitable holding means instead of by the combination of the long bolts and the mounting projections, provided that the holding means is capable of holding the regulator  120  and the heatsink  127  apart from the rear housing  104  and the rear cover  110  and of efficiently transmitting heat generated by the regulator  120  to the rear housing. 
   The regulator  120 , the rectifier  124  for rectifying generated current, and the brushes  121  for supplying a field current to the rotor are arranged substantially in the same plane. 
   The center housing  102  holds the rear bearing  134 , on a side opposite to the pulley, on the inner side of the rear cover  110  covering the regulator  120 , the rectifier  124  and the brushes  121 . 
   In the first embodiment, heat generated by the regulator  120  flows to the heatsink  127  and is dissipated through the fastening devices  136  into the coolant flowing through the coolant path  150 . Since heat is dissipated through the fastening devices  136 , heat can be efficiently transferred from the regulator  120  to the rear housing  104  even if the holder  122  formed of a resin is held between the heatsink  127  and the rear housing  104 . 
   In this liquid-cooled alternator, the coolant path  150  formed in the alternator to allow the coolant to flow through the alternator has a cyclic channel  151  (see  FIG. 2 ) axially extending in the center housing. One of the opposite ends or both the opposite ends of the cyclic channel  151  are open, and the open end or the open ends are covered with the rear housing  104  to form a closed water path. In the first embodiment, only the rear end of the coolant path is open. The coolant path  150  communicates with an outlet and inlet coolant pipe  152  formed in the side wall of the center housing  102 . 
   The heatsink of the regulator  120  for controlling the voltage of output is fastened to the rear housing  104  forming part of the coolant path  150  by the fastening devices  136 , heat generated by the regulator  120  is transferred through the fastening devices  137  to the rear housing  104  and is dissipated into the coolant. The coolant path  150  communicates with an engine coolant circulation system by means of the outlet and inlet coolant pipe  152  formed in the side wall of the center housing  102 . A radiator, a thermostat and a pump are connected to the engine coolant circulation system. Heat generated by the alternator is absorbed by the coolant flowing through the engine coolant circulation system and is dissipated through the radiator by heat exchange. 
   Referring to  FIGS. 3 and 4 , the regulator  120  is held by a regulator holder  122  formed integrally with the brushes  121  and the connector  126  for connection with the vehicle side. The regulator  120 , the rectifier  124  for rectifying generated current and the brushes  121  for supplying current to the rotor are disposed substantially at the same axial position, i.e., substantially in the same plane. A rectification circuit includes diodes  125 . The brush holder is held fixedly between the heatsink  127  of the regulator  120 , and the rear housing  104 . 
   Referring to  FIG. 5 , the regulator  120  regulates the field current to maintain the voltage of the dc current produced by rectifying an alternating current by the rectifier  124  at a fixed voltage on the order of 14.3 V to charge a battery. The positive diode fins are connected to the positive terminal of the battery. The potential of negative diode fins are equal to that of the alternator  100 . The negative diode fins are connected electrically to the negative terminal of the battery. The rectifier including the diodes is a full-wave rectifier capable of rectifying the voltage of an alternate current induced in the stator coils  106  into a dc voltage. 
   In this embodiment, when the rotor  107  creating a magnetic field rotates, a current produced in the stator coils  106  flows in the stator  105  of the alternator and the thus produced current is rectified by the rectifier  124  to provide a direct current. The regulator  120  regulates the field current supplied to the rotor  107  to create a magnetic field. 
   The outer circumference of the stator  105  is in contact with the center housing  102 . The center housing  102  is formed of a material having good heat conductance, a heat conductivity of 80 W/m·K or above, such as aluminum, by die cast. The coolant flows through the coolant path  150  formed in the wall of the center housing  102 . Accordingly, most part of heat generated by the stator coil  106  can be dissipated into the coolant. 
   Although the regulator  120  generates heat at a comparatively low rate and hence the amount of heat to be dissipated is small, the regulator  120  has a comparatively low heat resistance and hence the temperature of the atmosphere affects the regulator  120  significantly. The present invention covers the regulator  120  and the rectifier  124  with the cover  110  formed of a material having good heat conductance of 80 W/m·K or above, such as aluminum, by die cast. The cover  110  has a peripheral part attached to the rear housing  104  formed of a material having good heat conductance, a heat conductivity of 80 W/m·K or above, such as aluminum, by die casting and fixed to the center housing  102 . The regulator  120  is in thermal contact with the heatsink  127  fixed to the rear housing  104  and formed of a material having good heat conductance, a heat conductivity of 80 W/m·K or above. Thus, heat generated by the regulator  120  can be transferred to the center housing  102  and can be dissipated into the coolant. 
   According to the present invention, the housings  102 ,  103  and  104  holding the stator  105  and the rotor  107  are formed of metals having good neat conductance, a hat conductivity of 80 W/m·K or above. Most part of heat generated by the stator coils  106  is transferred to the coolant flowing through the housings. 
   The rear cover  110  covering the regulator  120 , the regulator holder  122  and the rectifier  124  is formed of a metal having good heat conductance, a heat conductivity of 80 W/m·K or above. Most part of the peripheral part of the rear cover  110  is in metal contact with the housing. 
   Most part of heat generated by the regulator  120  is transferred through the fastening devices  136  to the coolant flowing through the housings ( 102 ,  103 ,  104 ). Therefore, the respective temperatures of the regulator  120  substantially entirely covered with the rear cover  110  and the housings ( 102 ,  103 ,  104 ), and the rectifier  124  are dependent mainly on the temperature of the coolant. 
   Thus, the respective temperatures of the regulator  120  and the rectifier  124  are not dominated by the high temperature of the ambient air and the radiant heat radiated by high-temperature parts even when the automotive alternator is exposed to a high-temperature atmosphere. 
   As mentioned above, the alternator, in which the heatsink of the regulator is in close contact with the housing provided with the coolant path, is subject to restrictions on the arrangement of the regulator, the brushes and the rectifier, which sometimes causes structural inconvenience and problems with assembling work. According to the present invention, the heat generated by the regulator is transferred through the fastening devices  136 . Therefore, the regulator  120  does not need to be held in close contact with the housing and hence the freedom of placing the regulator, the brushes and the rectifier is improved. 
     FIG. 6  is a graph showing the results of experiments performed to examine the respective cooling abilities of an air-cooled system that cools the regulator by air and a water-cooled system that cools the regulator through the fastening devices by water. Temperature difference between a heatsink cooled by the air-cooled system and a heatsink cooled by the water-cooled system is known from FIG.  6 . Experiments for the air-cooled system used a holder that can be used also in an air-cooled alternator of a regulator. The temperature difference known from the graph represents the effect of cooling using the fastening devices  136 . The regulator case cooled by the water-cooled system using the fastening devices of the present invention was kept at temperatures not higher than 70° C. The regulator case cooled by the air-cooled system was heated at high temperatures in the range of 90 to 120° C. As obvious from  FIG. 6 , the regulator can be cooled with reliability by the water-cooled system using the fastening devices, and the water-cooled system improves the freedom of placement. 
   The automotive alternator  100  may be provided with only the front housing  103 , the rear housing  104  and the rear cover  110 , and the center housing may be omitted. The regulator  120  is held on the rear housing  104 . In this case, the coolant path through which the coolant flows is provided in the walls of the front housing  103  and the rear housing  104 . Omission of the center housing reduces the number of parts. 
     FIG. 7  is a longitudinal sectional view of a liquid-cooled automotive alternator in a second embodiment according to the present invention. A holder formed integrally with brushes  121  and a connector  126  for connection with the vehicle side holds a regulator  120 . A heatsink  127  included in the regulator  120  is fastened to a rear housing  104  by fastening devices  136 . The regulator  120 , a rectifier  124  and the brushes  121  are disposed substantially in the same plane. 
   Although the heatsink  127  is fastened directly to the rear housing  104  by the fastening devices  136  without holding the holder between the heatsink  127  and the rear housing  104  in the second embodiment, the effect of the second embodiment is similar to that of the first embodiment. 
     FIG. 8  is a longitudinal sectional view of a liquid-cooled automotive alternator in a third embodiment according to the present invention, and  FIG. 9  is a perspective view of a part around a regulator of the automotive alternator shown in  FIG. 8 , in which a rear cover is removed. In the third embodiment, a regulator  120  is disposed between a holder  122  and a rear housing  104 , and a heatsink  127  included in the regulator  120  is fastened to a rear housing  104  by fastening devices  136 . The effect of the third embodiment is similar to those of the foregoing embodiments. 
     FIG. 10  is a longitudinal sectional view of a liquid-cooled automotive alternator in a fourth embodiment according to the present invention, and  FIG. 11  is a perspective view of a part around a regulator of the automotive alternator shown in  FIG. 10 , in which a rear cover is removed. An automotive alternator  100  in the fourth embodiment has a front housing  103 , a rear housing  104  and a rear cover  110 . A regulator holder  122  formed integrally with brushes  121  and a connector  126  for connection with the vehicle side holds a regulator  120 . The regulator  120  and the brushes  121  are arranged in the axial direction of the alternator with the regulator  120  disposed at the outermost axial end. A heatsink  127  and fastening devices  136  are formed of materials respectively having good heat conductance. Heat generated by the regulator  120  is efficiently transferred to the center housing  102  and is dissipated by a coolant. 
   The axial arrangement of the brushes  121  and the regulator  120  reduces the circumferential area of the holder  122  holding the regulator  120  to improve the freedom of placement of other parts in the rear cover  110 . 
     FIG. 12  is a longitudinal sectional view of a liquid-cooled automotive alternator in a fifth embodiment according to the present invention. The fifth embodiment differs from the foregoing embodiments in that slip rings  128  of a rotor are disposed on the inner side of a rear bearing  135  on a side opposite to the side of a pulley. In other words, this arrangement of the slip rings  128  enables disposing a regulator  120  and a rectifier closer to a center housing  102 , so that heat generated by the regulator  120  and the rectifier  124  can be effectively transferred to the center housing  102  for cooling. 
   According to the present invention, the regulator and the heatsink for the regulator are fixed at a position apart from the housing and the cover by the fastening devices formed of a material having good heat conductance. Most part of the heat generated by the regulator is transferred to the coolant flowing through the housing. Therefore, the temperature of the regulator entirely covered with the cover and the housing is dependent mainly on the temperature of the coolant. Therefore, even when the automotive alternator is exposed to a high-temperature atmosphere for a long time, the temperatures of the regulator is not dominated by the ambient temperature and radiant heat radiated by the adjacent high-temperature parts. Thus, the automotive alternator has a stable cooling effect. 
   Since the regulator does not need to be set in close contact with the housing, the freedom of placement of the regulator is improved. 
   While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.