Abstract:
An electric power generating system for a vehicle includes a generator having a field coil, a voltage regulator, a temperature sensor for sensing temperature of the voltage regulator, a field current restricting circuit that directly restricts field current if temperature of the voltage regulator becomes higher than a maximum level and a device that prevents temperature of the voltage regulator from further rising without directly restricting field current if temperature of the voltage regulator becomes a warning level that is lower than the maximum level.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is based on and claims priority from Japanese Patent Application 2004-147095, filed May 18, 2004, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an electric power generating system to supply electric power to a battery or various electric loads that is or are mounted in a vehicle.  
         [0004]     2. Description of the Related Art  
         [0005]     When temperature of a voltage generator that is built in a vehicle&#39;s electric power generator rises up, field current supplied by the voltage regulator to the field coil of the generator is controlled to prevent the temperature from further rising up, as disclosed in JP-A-8-9567 or in JP-B2-3159976.  
         [0006]     If the temperature around the voltage regulator rises up, the output power of the generator decreases in case the above temperature control is carried out. This may cause insufficient performance or operation of the electric loads such as head lamps.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is to provide an improved electric power generating system. That is, the improved electric power generating system does not significantly decrease the output power even if the ambient temperature of a built-in voltage regulator rises up.  
         [0008]     According to an embodiment of the invention, an electric power generating system for a vehicle includes a generator having a field coil, a voltage regulator that includes an overheat control circuit for controlling field current if temperature of the voltage regulator becomes higher than a first threshold value, a temperature sensor that senses temperature of the voltage regulator, cooling means for cooling the voltage regulator and control means for operating the cooling means if temperature of the voltage regulator becomes higher than a second threshold value that is lower than the first threshold value. Therefore, the output power of the generator will not decrease as long as the control means effectively operates the cooling means. In the electric power generating system as described above the cooling means preferably includes a motor-driven cooling fan. The motor-driven cooling fan is preferably disposed near an engine to also cool engine coolant.  
         [0009]     According to another embodiment of the invention, an electric power generating system for a vehicle includes a generator having a field coil, a voltage regulator that includes an overheat control circuit that controls field current supplied to the field coil if temperature of the voltage regulator becomes higher than a first threshold value, a temperature sensor that senses temperature of said voltage regulator, and control means that turns off such electric loads that do not affect vehicle driving conditions if temperature of the voltage regulator becomes higher than a second threshold value that is lower than the first threshold value. Therefore, the output power of the generator will not decrease as long as the control means effectively turns off such electric loads. In the above-described embodiment, the electric loads to be turned off may be an audio device or a seat heater. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:  
         [0011]      FIG. 1  is a block diagram of an electric power generating system according to the first embodiment of the invention;  
         [0012]      FIG. 2  is a flow diagram of operation of the electric power generating system according to the first embodiment of the invention;  
         [0013]      FIG. 3  is a block diagram of an electric power generating system according to the second embodiment of the invention; and  
         [0014]      FIG. 4  is a flow diagram of operation of the electric power generating system according to the second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Two kinds of electric power generating systems according to preferred embodiments of the present invention will be described with reference to the appended drawings.  
         [0016]     An electric power generating system for a vehicle according to the first embodiment of the invention will be described with reference to  FIGS. 1 and 2 .  
         [0017]     As shown in  FIG. 1 , the power generating system according to the first embodiment includes a vehicle&#39;s electric power generator (hereinafter referred to the generator)  1 , a voltage regulator  2 , an on-vehicle battery  3 , an engine control unit (hereinafter referred to as the ECU)  4 , an electric load  5 , a head lamp  7 , etc. The ECU  4  connects to an engine  80  and a motor-driven cooling fan  82  that cools the engine  80 .  
         [0018]     The generator  1  has a stator core on which three-phase stator winding  11  is mounted, a three-phase full-wave rectifying unit  12  and a rotor on which a field coil  13  is mounted. The output voltage of the generator  1  is controlled by the voltage regulator  2  that switches on or off field current supplied to the field coil  13  in a controlled manner. The generator  1  is connected to the battery  3  at its output terminals to charge the battery  3 . The battery  3  connects to the ECU  4 , the electric load  5  and the head lamp  7 .  
         [0019]     The voltage regulator  2  controls the field current supplied to the generator so that the output voltage of the generator  1  becomes a predetermined voltage. The voltage regulator  2  includes a control circuit  21 , power transistor  22 , a flywheel diode  23 , a temperature sensor  24 , etc. The control circuit  21  turns on or off the power transistor  22  so that the output voltage of the generator  1  can be the same voltage level as the predetermined voltage. The control circuit  21  includes a temperature detecting circuit  211 , an overheat protecting circuit  212  and a data transmission circuit  213 . The control circuit  21  detects temperature of the voltage regulator  2 , sends temperature data to the ECU  4  and controls the field current according to the temperature. The temperature detecting circuit  211  detects the temperature of the voltage regulator  2  with the temperature sensor  24 , which is disposed inside the voltage regulator  2 . The temperature detecting circuit  211  has two output terminals S 1 , S 2  respectively connected to the overheat protecting circuit  212  and the data transmission circuit  213 . If the detected temperature T becomes higher than a first threshold value T 1 , the output terminal S 1  provides a high level signal. If the detected temperature T becomes higher than a second threshold value T 2  that is lower than the first threshold value, the output terminal S 2  of the temperature detecting circuit  211  provides a high level signal. In other words, if the temperature of the voltage regulator  2  continuously rises up after the generator  1  starts generating electric power, the signal of the output terminal S 2  changes from a low level signal to a high level signal. Then, the signal of the other output terminal S 1  changes from a low level signal to a high level signal while the output terminal S 2  maintains the high level signal.  
         [0020]     If the output terminal S 1  of the temperature detecting circuit  211  provides a high level signal, the overheat protection circuit  212  controls or reduces the field current supplied to the field coil  13 . If the output terminal S 2  of the temperature detecting circuit  211  provides a high level signal, the data transmission circuit  213  sends a temperature rise signal to the ECU  4  via a terminal X. These signals are maintained continuously or cyclically until the temperature T detected by the temperature detecting circuit  211  becomes lower than the second threshold value T 2 , and the signal of the output terminal S 2  of the temperature detecting circuit  211  comes back to a low level signal.  
         [0021]     The power transistor  22  is connected in series with the field coil  13  of the generator  1 . The field current is supplied to the field coil  13  when the control circuit  21  turns on the power transistor  22 . When the field current is to be reduced, the overheat protection circuit  212  reduces the duty ratio of the field current control signal applied to the power transistor. The flywheel diode  23  is connected in parallel with the field coil  13  to pass the field current when the power transistor  22  is turned off.  
         [0022]     The ECU  4  is an outside unit that controls the operation of the engine  80  according to a depressing amount of an accelerator pedal (not shown here) and operates the motor-driven cooling fan  82  to cool engine coolant if the temperature of the engine coolant becomes higher than a predetermined value. The ECU  4  also turns on the motor-driven cooling fan  82  when a temperature rise signal is sent from the terminal X of the voltage regulator  2 . The ECU  4  is empowered by the battery  3  like the electric load  4  and the head lamp  7 .  
         [0023]     The generator  1  and the voltage regulator  2  are directly fixed to the engine via fixing members. When the motor-driven fan  82  is operated in order to cool the coolant flowing into the radiator  81 , a portion of air that is introduced to spaces around the engine is further supplied to spaces around the generator  1  and the voltage regulator  2 . Thus, the motor-driven fan  82  functions to cool the voltage regulator  2 .  
         [0024]     The control operation of the electric power generating system according to the first embodiment will be described with reference to a flow diagram shown in  FIG. 2 .  
         [0025]     When the engine  80  starts and the generator  1  and the voltage regulator  2  start their operation, the temperature detecting circuit  211  of the control circuit  21 , whether the temperature T indicated by the temperature sensor  24  is higher than the second threshold value T 2  or not is examined at step  100 . If the result is NO, the above step is repeated. If the result is YES, the output terminal S 2  of the temperature detecting circuit  211  provides a high level signal, so that the data transmission circuit  213  sends a temperature rise signal to the ECU  4  via the terminal X at step  101 . When the ECU  4  receives the temperature rise signal, it operates the motor-driven cooling fan  82  at step  102 . Therefore, outside air is introduced into the spaces around the engine  80  through the radiator  82 .  
         [0026]     Then, the temperature detecting circuit  211  examines whether the temperature T returns to a temperature lower than the second threshold value T 2  or not at step  103 . If the temperature T is still higher than the second threshold value T 2 , NO is provided. Next, the temperature detecting circuit  211  further examines whether the temperature T becomes higher than the first threshold value T 1  or not at step  104 . If the temperature T is higher than the second threshold value T 2  and lower than the first threshold value T 1 , No is provided and the control operation goes to step  103 .  
         [0027]     After the motor-driven cooling fan  82  is operated, the temperature T may gradually drop and become lower than the second threshold value T 2 . In that case, YES is provided at step  103 . Then, the data signal that has been sent from the data transmission circuit  213  to the ECU  4  is stopped at step  105 . Accordingly, the ECU  4  stops operation of the motor-driven cooling fan  82  at step  106 , and the control operation returns to step  100 .  
         [0028]     If the temperature T rises up to a temperature higher than the first threshold value T 1  even though the motor-driven cooling fan  82  is operated, YES is provided at step  104 . In that case, the output terminal S 1  of the temperature detecting circuit  211  provides a high level signal, so that the overheat protection circuit  212  limits the field current at step  107 . Thereafter, the control operation returns to step  104 .  
         [0029]     Thus, the motor-driven cooling fan  82  is operated before the temperature becomes higher than the first threshold value T 1  at which the overheat protection circuit  212  starts to limit the field current. Therefore, the output power of the generator does not decrease even if the temperature gradually rises.  
         [0030]     Usually, the generator  1  and the voltage regulator  2  are disposed near the engine  80 . Therefore, the voltage regulator  2  is effectively cooled when the motor-driven cooling  82  takes air into spaces around the engine  80  to cool the radiator  81  and the engine  80 , thereby reducing radiant heat thereof.  
         [0031]     An electric power generating system for a vehicle according to the second embodiment of the invention will be described with reference to  FIGS. 3 and 4 .  
         [0032]     As shown in  FIG. 3 , the power generating system according to the second embodiment includes a vehicle&#39;s electric power generator (hereinafter referred to the generator)  1 , a voltage regulator  2 , an on-vehicle battery  3 , an engine control unit (hereinafter referred to as the ECU)  4 , a first electric load  5 , such as an audio device or a seat heater, which does not relate to or affect vehicle driving conditions, a second electric load  6 , such as a head lamp  7  or the ECU  4 , which may affect vehicle driving conditions, etc. Incidentally, the same reference numeral represents the same or substantially the same part, component or step as presented in the above description and drawings.  
         [0033]     The ECU  4  is different in function from that of the first embodiment. The ECU  4  turns off the second electric load  5  when it receives a temperature rise signal from the voltage regulator  2  and turns on the second electric load when it does not receive the temperature rise signal.  
         [0034]     A portion of the control operation of the electric power generating system according to the second embodiment that is different from the operation of the first embodiment will be described with reference to a flow diagram shown in  FIG. 4 .  
         [0035]     When the ECU  4  receives the temperature rise signal from the voltage regulator  2 , it sends a stop signal to the first electric load  5  to turn off at step  102 A. The ECU  4  may turn off a switch connected between the electric load  5  and a power source. When the voltage regulator  2  stops the temperature rise signal at step  105 , the ECU  4  turns on the electric load  5  at step  106 A.  
         [0036]     Thus, the field current is reduced without affecting vehicle driving conditions before the temperature becomes higher than the first threshold value T 1  at which the overheat protection circuit  212  starts to limit the field current. Therefore, the output power of the generator does not decrease even if the ambient temperature gradually rises.  
         [0037]     It is possible to employ an additional cooling fan to exclusively cool the voltage regulator  2  in substantially the same manner as the above-described motor driven cooling fan  82  for the radiator  81 . The temperature sensor  24  that is disposed in the voltage regulator  2  can be disposed outside the voltage regulator  1 .  
         [0038]     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.