Abstract:
A starter control system is comprised of a starter motor, a control circuit for controlling the starter motor to rotate at a preliminary rotation speed that is high enough to engage a pinion with an engine for a predetermined time and low enough to suppress a harsh noise caused when the pinion engages the engine and, thereafter, at a normal rotation speed that is high enough to start the engine, and a control circuit for changing the preliminary rotation speed according to an engine temperature. The starter control system is effective to reduce noises that are caused when the engine is started by an economy-run system.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from Japanese Patent Applications: 2000-261110 filed Aug. 30, 2000; and 2001-131377, filed Apr. 27, 2001; the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system for controlling an engine-starting starter. 
     2. Description of the Related Art 
     Recently, an economy-run system has been employed in an automotive vehicle in order to improve fuel consumption of the vehicle and to reduce engine exhaust gases of vehicle engine. Such an economy-run system stops an engine whenever the vehicle makes a stop. In such a economy-run system, the engine is stopped according to a condition such as vehicle speed, open angle of accelerator, brake condition, etc. As soon as the brake pedal is eased up and the accelerator pedal is depressed, the starter is operated to start the engine, thereby starting the vehicle. 
     However, if a pinion gear of the starter abruptly engages a ring gear of the engine while the starter is rotating an engine at a normal speed, the starter may not start up the engine quickly due to a shock caused by the engagement. Such a conventional economy-run system takes a considerable time to fully start up the engine after making a stop. According to a report of the National Police Agency, traffic jam may be expected in a city where many vehicles are running if such a starting time becomes longer than a certain time. Therefore, it is necessary to shorten the engine starting time. 
     In such an economy-run system, the engine is stopped and started so frequently that the starting noise becomes harsh to an ordinary user of a vehicle. However, it is not sufficient to suppress such the starting noise by a noise absorption material or noise insulating material. A large amount of such materials may increase the vehicle weight and fuel consumption rate of the vehicle. Therefore, it is also necessary to decrease the starting noise. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-stated problem and has an object of providing a starter control system that can shorten the engine starting time and reduce the starting noises caused while the engine is being started. 
     According to a main feature of the invention, when an engine is driven or rotated by a starter, a starter motor rotates at a preliminary speed that is lower than a normal rotation speed. 
     If the engine is rotated at a suitable rotation speed that is lower than the normal speed for a predetermined period before it is rotated at a normal operation speed, the engine can fully start up more quickly. When the key switch is turned on, the starter rotates at the preliminary speed and the pinion of the starter engages the ring gear of the engine at a suitable low speed. Therefore, the rattling gear noise caused during the engagement is small. Because the engine is preliminary rotated at a suitable low speed for a predetermined period, noise caused during tottering cranking operation of the engine due to a large inertia thereof or fluctuation of pistons reciprocating between a bottom dead point and the top dead point of the engine can be reduced. Thus, the harsh noise during the engine cranking can be reduced. As a result, the engine starting time can be shorten and the noises can be reduced. 
     According to another feature of the invention, the preliminary rotation speed is changeable according to an engine condition. 
     According to another feature of the invention, the preliminary rotation period is changeable according to an engine condition. 
     According to another feature of the invention, the rotation speed is changed by a variable resistor or an electronic conduction element. 
     According to another feature of the invention, the engine condition is detected by an engine temperature sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is an electric circuit diagram of a starter control circuit according to a first embodiment of the invention; 
     FIG. 2 is a flow diagram of a process of controlling supply of starter current; and 
     FIGS. 3A,  3 B and  3 C are graphs showing starter current change while the engine is being started. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A starter control circuit according to a first embodiment of the invention is described with reference to FIG. 1. A starter  1  is comprised of a magnet switch  2  and a starter motor  3 . The starter motor  3  has a well-known ordinary structure that is comprised of a field coil  4  for generating magneto-motive force at a stator and an armature  5  that has an armature coil. 
     A coil  2   a  of the magnet switch  2  is comprised of a pull-in coil and a holding coil, which are connected to a vehicle battery  8  via a key switch  6  and starter relay  7 . When the key switch  6  is turned on, a coil  7   a  of the starter relay  7  is energized to close a normally-open movable contact of the starter relay  7  to energize the coil  2   a  of the magnet switch  2 . If the coil  2   a  is energized, the magnet switch  2 , which is a normally-open switch, is turned on. 
     A current control circuit  10  controls preliminary rotation speed of the starter motor  3  for a preliminary rotating period according to a condition of the engine. The preliminary rotating speed is high enough to engage a pinion of the starter  1  with a ring gear of the engine in the predetermined preliminary period. The preliminary rotating speed is lower than a normal operation speed that can fully start up the engine. The current control circuit  10  is comprised of a current change circuit  11  and an ECU  12 . The current change circuit  11  is comprised of a resistor  13  and a current switching relay  14 , which is a normally-open switch. If the current switching relay  14  turns off and the magnet switch  2  turns on, the starter motor  3  is energized via the resistor  13  to rotate at a preliminary speed that is lower than a normal operation speed. On the other hand, if the current switching relay  15  turns on and the magnet switch  2  turns on, the resistor  13  is short-circuited so that the starter motor  3  is energized directly to rotate at the normal operation speed. 
     The coil  14   a  of the current switching relay  14  is controlled by the ECU  12 . When the starter motor  3  is started, it rotates at the preliminary rotation speed first and at the normal operation speed thereafter. 
     Thus the ECU  12  controls the current switching relay  14  to change the preliminary rotation period according to an engine condition, such as engine temperature. For example, the engine temperature is represented by engine coolant temperature or temperature of the engine, which is detected by a temperature sensor  15 . 
     The ECU  12  has a map for determining the preliminary rotation period according to the engine temperature. The preliminary rotation period is set longer if the engine temperature is lower. On the other hand, the preliminary rotation period is set shorter if the engine temperature is higher. 
     The current control of the starter  1  is described with reference to a flow diagram shown in FIG.  2 . 
     At step  101 , if the key switch  6  is turned on (to start the starter  1 ), an engine start signal is inputted to the ECU  12 . The ECU  12  determines the preliminary rotation period, in which the starter  3  is rotated at a preliminary speed suitable for the engine temperature. 
     At step  102 , the starter motor  3  is energized via the resistor  13 . Consequently, the starter motor  3  rotates at the preliminary rotation speed that is lower than the normal operation speed. Accordingly, a pinion  3   a  of the starter  1  engages a ring gear (not shown) of the engine gradually to rotate the engine. 
     When the preliminary rotation period has passed, the current switching relay  14 , which is a normally-open switch, turns on, so that the resistor  13  is short-circuited and the starter motor  3  is energized directly. Therefore, the starter motor  3  rotates at the normal operation speed. 
     If the engine fully starts up and the key switch  6  is turned off, the starter motor  3  is de-energized at a step  104 . 
     In summary, when the key switch  6  is turned on, the magnet switch  2  are turned on. At this moment, the current switching relay  14  is turned off for a predetermined preliminary period, and the starter motor  3  is energized by the battery via the resistor  13  to rotate at a suitable low speed or a preliminary rotation speed. When the preliminary rotation period has passed, the current switching relay  14  is turned on by the ECU  12 . Consequently, the starter motor  3  is supplied with much more current by the battery  8  to rotate at the normal operation speed. 
     Thus, the engine rotation speed increases more quickly as soon as the engine is rotated by the starter. This shortens the starting period of the starter system during which the engine is rotated by the starter until the engine starts up full operation. 
     When the starter  1  starts rotation, the pinion  3   a  of the starter  1  engages the ring gear of the engine at the preliminary speed that is lower than the normal operation speed. Therefore, rattling noise of the gears is not very loud. Since the engine is preliminary rotated at the low preliminary speed before it is rotated at the normal operation speed, noise generated while the rotation speed of engine is changing can be suppressed. 
     Test results show that the engine can be started more quickly by a starter control system in which the engine is preliminary rotated at a suitable low speed before it is rotated at the normal speed than a conventional starter control system in which the engine is immediately rotated at the normal operation speed. The test results are data obtained when the engine is started at a cold temperature. 
     FIG. 3A is a graph showing current flowing through the starter motor  3  rotated by a conventional starter control system. FIG. 3B is a graph showing current flowing through the starter motor  3  rotated by the starter control system according to the first embodiment of the invention, in which resistance of the resistor  13  is a suitable value, such as 25-50 mΩ. FIG. 3C is a graph showing current flowing through the starter motor  3  in case resistance of the resistor  13  is a large value, such as 100-∞mΩ. 
     In the meantime, {circle around (1)} indicates the number of peaks of the starter current while the starter is cranking the engine, and {circle around (2)} indicates a period during which the engine is fully started. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 LOW 
                   
                   
                 {circle around (2)} 
               
               
                 ROTATION 
                   
                 {circle around (1)} 
                 STARTING 
               
               
                 PERIOD 
                 RESISTANCE 
                 NO. OF PEAKS 
                 TIME (msec) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  50 msec 
                 25 mΩ 
                 3.5 
                 685 
               
               
                  50 msec 
                 33 mΩ 
                 3 
                 551 
               
               
                  50 msec 
                 50 mΩ 
                 3 
                 565 
               
               
                  50 msec 
                 100 mΩ  
                 4 
                 825 
               
               
                  50 msec 
                 ∞ Ω 
                 4 
                 895 
               
               
                 100 msec 
                 25 mΩ 
                 3.5 
                 818 
               
               
                 100 msec 
                 33 mΩ 
                 3.5 
                 724 
               
               
                 100 msec 
                 50 mΩ 
                 3 
                 620 
               
               
                 100 msec 
                 ∞ Ω 
                 4 
                 910 
               
               
                 200 msec 
                 25 mΩ 
                 3.5 
                 886 
               
               
                 200 msec 
                 33 mΩ 
                 3 
                 746 
               
               
                 200 msec 
                 50 mΩ 
                 3 
                 767 
               
               
                 200 msec 
                 100 mΩ  
                 4 
                 858 
               
               
                 200 msec 
                 ∞ Ω 
                 4 
                 978 
               
               
                  0 msec 
                 ∞ Ω 
                 4 
                 783 
               
               
                 no current is 
               
               
                 supplied 
               
               
                   
               
             
          
         
       
     
     Table 1 shows relationship among preliminary rotation period, various resistances of the resistor  13 , the number of peaks {circle around (1)} of waves of the current supplied for cranking and engine starting time {circle around (2)}. 
     If the preliminary rotation is omitted (a conventional starter system) as shown in the bottom of the Table 1, the number of peaks {circle around (1)} is four (4) and the starting time {circle around (2)} is 783 msec. 
     On the other hand, if the low rotation period is 50 msec and the resistance of the resistor  13  is a value between 25 and 50 msec, the number of peaks {circle around (1)} is less than 4, and the starting time {circle around (2)} is less than 783 msec. If the resistance of the resistor  13  is 33 mΩ or 50 mΩ, the number of peaks {circle around (1)} is 3 and the starting time {circle around (2)} is 551 msec or 565 msec, which are shorter than the starting time of the conventional starter system. 
     If the preliminary rotation period is 100 msec and the resistance of the resistor  13  is 33 mΩ or 50 mΩ, the number of peaks {circle around (1)} is less than 4, and the starting time {circle around (2)} shorter than 783 msec. If the resistance of the resistor  13  is 50 mΩ, the number of peaks {circle around (1)} is less than 3, and the starting time is 620 msec, which is much shorter than the conventional starter system. 
     If the preliminary rotation period is 200 msec and the resistance of the resistor  13  is 33 mΩ or 50 mΩ, the number of peaks {circle around (1)} is less than 4, and the starting time {circle around (2)} is shorter than 783 msec. 
     In summary, it is preferable that the preliminary rotation period is 50 msec and the resistance of the resistor  13  is 33 or 50 mΩ, or that the preliminary rotation period is set 100 msec and the resistance of the resistor  13  is 50 mΩ, so that the engine starting time can be reduced much shorter than the starting time of the conventional starter system. The above data are only an example, and the optimum preliminary rotation period and the resistance of the resistor  13  may vary with type or size of the engine and the starter to be mounted on a vehicle. 
     When the starter  1  is started, the pinion  3   a  of the starter  1  engages the ring gear (not shown) of the engine at the preliminary rotation speed. Therefore, the rattling gear noise becomes small. Moreover, since the engine having a large inertia is preliminary rotated at a the preliminary rotation speed before it is rotated at a normal rotation speed, the noise caused by tottering cranking of the engine can be reduced. Thus, as compared with the conventional starter system, the rattling noise and the noise due to the cranking operation of the engine become lower. In other words, the engine starting noise can be reduced. 
     A starter control system according to a second embodiment is described hereafter. Instead of a mechanical switch having a normally-open movable contact of the starter control system according to the first embodiment, MOSFET or another electronic switching element (not shown) is used as the current switching relay  14 . 
     A starter control system according to a third embodiment is described hereafter. 
     In the above first embodiment, the preliminary rotation period is changed according to the engine condition. In the starter control system according to the third embodiment, the rotation speed of the starter motor  3  at the preliminary stage of the rotation is changed according to the engine condition. 
     The combination of the first embodiment and the second embodiment is also possible. That is, both the preliminary rotation speed and the rotation speed of the starter can be changed according to the engine condition. 
     A map that determines the preliminary rotation speed according to the engine temperature is installed in the ECU  12 . Therefore, the preliminary rotation speed of the starter  1  when the temperature of the engine is lower is set to be lower than the preliminary rotation speed when the engine temperature is higher. 
     It is possible to use a mechanical resistance changing element or an electronic conduction changing element (IGBT) to change the rotation speed of the starter motor  3 . 
     As a variation, the engine condition can be detected by a timer that counts time after the engine is stopped. 
     Instead of the key switch  6 , a switch controlled by the ECU  12  can be used to control the operation of the starter  1 . 
     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.