Patent Publication Number: US-7216617-B2

Title: Engine starting assist system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2004-297594 filed on Oct. 12, 2004, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an engine starting assist system having an engine starter. 
     BACKGROUND OF THE INVENTION 
     An engine starting system having an engine starter has been known (for example, US 2004-0168664A1 corresponding to JP-A-2004-257369). In the system, an electric current is supplied to a starter motor of the engine starter to start an engine. 
       FIG. 4  is a schematic circuit diagram of an engine starting system  40  experimentally built to improve a conventional engine starting system. The system  40  includes two switches  101 ,  102 , a starter relay  103  having a coil  103   a  and a relay switch  103   b,  a starter  104  having a starter motor  104   a  and a electromagnetic switch coil  104   b  for engaging the starter motor  104   a  to an engine, and an engine electronic control unit (ECU)  105 . The switch  101  is turned on, when a key cylinder is turned to a start position. In an automatic transmission vehicle, the switch  102  is turned on when a gear is in a neutral position or a parking position. In a manual transmission vehicle, the switch  102  is turned on when a clutch pedal is pressed. When a driver turns the key cylinder to the start position as long as the switch  102  is ON, a current I  107  is supplied from a terminal  107  to the starter relay  103  and the engine ECU  105  receives a signal indicating that the key cylinder is turned on. Then, the engine ECU  105  provides a fuel injection signal to the engine and supplies a current I  105  to the starter relay  103 . In this case, not only the current I  107  but also the current I  105  flow through the starter relay  103 . Therefore, the starter relay  103  is surely activated during starting of the engine. 
     When the current I  105 , or I  107  flows through the coil  103   a  of the starter relay  103  through the switch  102 , an electromagnetic force is generated around the coil  103   a.  The starter switch  103   b  is attracted by the force and turned on. Consequently, a power source (battery)  106  supplies a current I  106  to the electromagnetic switch coil  104   b  and the starter motor  104 . Thus, the engine is started. 
     The engine ECU  105  is supplied with electric power from the power source  106  through a terminal  108  and supplies the current I  105  to turn the starter switch  103   b  on. Likewise, the terminal  107  is supplied with electric power from the power source  106  and supplies the current I  106  to drive the starter motor  104   a.  The current I  106  becomes relatively large so that the power source voltage drops rapidly during starting of the engine. 
     Referring to a timing diagram of  FIG. 5 , the power source voltage drops below a predetermined reset level L 2  at a time T 1 . The engine ECU  105  resets a supply of the current I  105  at the time T 1 , because the power source voltage is not high enough to operate the engine ECU  105  properly. 
     In this case, the current I  107  is continuously supplied from the terminal  107  to the coil  103   a,  as long as the key cylinder is in the start position, i.e., the switch  101  is ON. Therefore, the starter switch  103   b  stays ON and the starter motor  104   a  runs. As the starter motor  104   a  runs, a current load required to crank the engine decreases. The power source voltage increases accordingly between the time T 1  and a time T 2 . Then, when the power source voltage reaches a predetermined return level L 1  at the time T 2 , the reset state of the engine ECU  105  is released. Then, the engine ECU  5  restarts the supply of the current I  105  at a time T 3  to start the engine. The engine can be thus started, even if the power source voltage drops rapidly during starting of the engine. 
     However, in a latest-type engine starting system in which an engine is started by pressing a push switch, there is no current path to supply the current I  107  when the engine ECU  105  falls into the reset state. Therefore, the engine cannot be started, if the engine ECU  105  resets the supply of the current I  105 . 
     Specifically, the power source voltage returns to an initial level before starting of the engine, after the engine ECU  105  resets the supply of the current I  105  and the engine start-up sequence stops. Even when the engine start-up sequence is restarted and the engine ECU  105  restarts the supply of the current I  105 , the power source voltage drops below the reset level L 2  again. That is because the current load required to crank the engine has not been reduced. Therefore, no matter how many times the push switch is pressed for starting the engine, the engine cannot be started. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an engine starting assist system, in which an engine can be started even if a voltage of a power source drops below a reset level during starting of the engine. 
     An engine starting assist system includes an auxiliary ECU having a voltage booster, an engine ECU, a power source, a starter relay, and a starter. The auxiliary ECU and the engine ECU are supplied with electric power from a power source of a vehicle and supply a current to the starter relay. When the current flows through the starter relay, the power source supplies a current to the starter to crank the engine. Even when the engine ECU resets the supply of the current to the starter relay because of a voltage drop of the power source during starting of the engine, the auxiliary ECU increases a voltage supplied from the power source using the booster, thereby supplying the current to the starter relay. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a block circuit diagram of an engine starting assist system according to a first embodiment of the present invention; 
         FIG. 2A  is a timing diagram illustrating a starter relay activation time without an auxiliary ECU, and  FIG. 2B  is a timing diagram illustrating the starter relay activation time with the auxiliary ECU; 
         FIG. 3  is a block circuit diagram of an engine starting assist system according to a second embodiment of the present invention; 
         FIG. 4  is a block circuit diagram of an engine starting system according to a related art; and 
         FIG. 5  is a timing diagram illustrating a voltage level of a power source during starting of an engine in the engine starting system of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Reference is made to  FIG. 1 , which shows a block circuit diagram of an engine starting assist system  20 . The system  20  includes an auxiliary ECU  1  having a booster  1   a,  an engine ECU  2 , a switch  3 , a starter relay  4 , and a starter  5 . 
     The auxiliary ECU  1  is supplied with electric power from a power source (storage battery)  9  through a terminal (power supply device)  6  and included in a power supply ECU, for example. The booster  1   a  of the auxiliary ECU  1  increases a voltage supplied from the terminal  6 , when the voltage of the terminal  6  becomes lower than a predetermined level. Thus, the auxiliary ECU  1  keeps the voltage supplied from the terminal  6  above a voltage level required for the auxiliary ECU  1  to perform an engine starting assist control, i.e., to supply a current I 3  to the starter relay  4 . 
     As shown in  FIG. 5 , a reset level L 3  of the auxiliary ECU  1  is lower than a reset level L 2  of the engine ECU  2  by performing the engine starting assist control. Therefore, the auxiliary ECU  1  can supply the current I 3  to the starter relay  4  even when the engine ECU  2  falls into the reset state at the reset level L 2 . As an example, the reset level L 2  is set to 4 volts and the reset revel L 3  is set to 3.5 volts. 
     The push switch  7  provides a first signal to the auxiliary ECU  1 , when the push switch  7  is pressed. The brake switch provides a second signal to the auxiliary ECU  1 , when a brake pedal is pressed and the brake switch  8  is turned on. When the auxiliary ECU  1  receives the first signal from the push switch  7  while receiving the second signal from the brake switch  8 , the auxiliary ECU  1  provides an engine start signal for starting the engine to the engine ECU  2  through a signal line (not shown) between the auxiliary ECU  1  and the engine ECU  2 . Then, the auxiliary ECU  1  and the engine ECU  2  start to supply the current I 3  and a current I 2  to the starter relay  4  through an output terminal  1   b  and an output terminal  2   a,  respectively. The auxiliary ECU  1  continues to supply the current I 3  for a predetermined time period, even after the engine ECU  2  falls into the reset state, i.e., resets the supply of the current I 2 . 
     Here, a first time period is defined as a time period when the engine ECU  2  falls into the reset state to when the engine ECU  2  restarts the supply of the current I 2  to start the engine. A second time period is defined as a time period from when the engine ECU  2  falls into the reset state to when the engine is started by the restarted supply of the current I 2 . 
     The predetermined time period is set longer than the first time period and set shorter than the second time period to make sure the engine is started. For example, if the first time period is 150 milliseconds and the second time period is 500 milliseconds, the predetermined time period can be set to about 300 milliseconds. 
     Alternatively, the auxiliary ECU  1  can continuously supply the current I 3  not only for the predetermined time period as long as the push switch  7  is ON. Further alternatively, the auxiliary ECU  1  can continuously supply the current I 3  not only for the predetermined time period as long as the push switch  7  is ON, in case that the first attempt to start the engine ends in failure. 
     However, a time period during which the auxiliary ECU  1  continuously supplies the current I 3  to the starter relay  4  is partly limited because of preventing breakdown of the starter  5 . 
     Here, a third time period is defined as a time period within which the engine ECU  2  can continuously supplies I 2  to the starter relay  4 . A fourth time period is defied as a time period beyond which a current I 1  cannot be continuously supplied to the starter  5  from the power source  9  without the breakdown of the starter  5 . A fifth time period is defined as the limited time period of the current I 3 . 
     When the third time period is set to 30 seconds and the fourth time period is set to 60 seconds, the fifth time period is set to 15 seconds, for example. Specifically, the fifth time period is set shorter than a time period determined by subtracting the third time period from the fourth time period. In this case, the current I 1  does not flow through the starter  5  beyond the fourth time period, even if the engine ECU  2  continuously supplies the current I 2  to the starter relay  4  during the third time period. Therefore, the breakdown of the starter  5  is prevented. 
     The engine ECU  2  is also supplied with the electric power from the terminal  6  and performs functions such as outputting a fuel injection signal to the engine in accordance with the pressure on an accelerator (not shown). 
     Further, the engine ECU  2  determines whether a condition for starting up the engine is met, when the engine ECU  2  receives an engine start signal from the auxiliary ECU  1 . If the condition is met, the engine ECU  2  supplies the current I 2  to the starter relay  4  through the output terminal  2   a.    
     Furthermore, the engine ECU  2  determines whether the voltage of the terminal  6  is higher than the reset level L 2 . If the voltage of the terminal  6  becomes lower than the reset level L 2 , the engine ECU  2  resets the supply of the current I 2  to the starter relay  4 . Then, the engine ECU  2  stops the supply of the current I 2  until the voltage of the terminal  6  returns to a return level L 1 . The return level L 1  is set higher than the reset level L 2 . 
     The switch  3  is turned on in accordance with a gear position. In an automatic transmission vehicle, the switch  3  is turned on, when the gear is in the neutral position or the parking position. In a manual transmission vehicle, the switch  3  is turned on, when the clutch pedal is pressed. 
     The starter relay  4  includes a coil  4   a  and a relay switch  4   b.  When the current I 2  or the current I 3  flows through the coil  4   a,  an electromagnetic force is generated around the coil  4   a.  The relay switch  4   b  is attracted by the force and turned on. 
     The starter  5  includes a starter motor  5   a  and an electromagnetic switch coil  5   b.  The starter  5  is powered by a power source  9 , which is supplied with the electric power from the terminal  6  and supplies the current I 1  to the starter  5 . As an example, the power source  9  has a voltage of 12 volts under normal operation. The current I 1  is controlled by turning the relay switch  4   b  on and off. 
     Operations of the engine starting assist system  20  will be described below. 
     The auxiliary ECU  1  provides the engine start signal to the engine ECU  2 , when the auxiliary ECU  1  receives the first signal indicating that the push switch  7  is ON while receiving the second signal indicating that the brake switch  8  is ON. Then, the engine ECU  2  determines whether the condition for starting of the engine is met. For example, the engine ECU  2  determines whether water temperature is higher than a predetermined level, or whether an immobilizer code is authorized. If the condition is met, the engine ECU  2  supplies the current I 2  to the starter relay  4  in order to drive the starter  5 . Likewise, the auxiliary ECU  1  supplies the current I 3  to the starter relay  4  in order to drive the starter  5 . 
     When the current I 2  or the current I 3  flows through the coil  4   a  of the starter relay  4 , an electromagnetic force is generated around the coil  4   a.  The starter switch  4   b  is attracted by the force and turned on. Then, the power source  9  supplies the current I 1  to the electromagnetic switch coil  5   b  and the starter motor  5   a  of the starter  5 . Thus, the starter motor  5   b  runs and the engine is started. 
     The engine ECU  2  is supplied with the electric power from the terminal  6  and supplies the current I 2  to the starter relay  4 . If the voltage of the terminal  6  drops below the reset level L 2 , the engine ECU  2  falls into the reset state and stops the supply of the current I 2 . 
     In this case, however, the booster  1   a  of the auxiliary ECU  1  increases the voltage supplied from the terminal  6 , thereby keeping the voltage supplied from the terminal  6  above the voltage level required for the auxiliary ECU  1  to perform the engine start assist control. Therefore, the auxiliary ECU  1  can supplies the current I 3  to the starter relay  4 , even when the engine ECU  2  falls into the reset state. 
     Thus, the starter switch  4   b  is turned on and the power source  9  supplies the current I 1  to the electromagnetic switch coil  5   b  and the starter motor  5   a  of the starter  5 . Consequently, the starter motor  5   a  runs. 
     Then, the engine may be started. Even if the engine cannot be started, the current load required to crank the engine is reduced as the starter motor  5   a  runs. Therefore, the voltage of the terminal  6  increases accordingly. When the voltage of the terminal  6  returns to the return level L 1 , the reset state of the engine ECU  2  is released. Then, the engine ECU  2  restarts the supply of the current I 2  to the starter relay  4 , thereby starting the engine. 
     As shown in a timing diagram of  FIG. 2A , if the assistance (i.e., the current I 3 ) of the auxiliary ECU  1  is not provided, no current flows through the starter relay  4  during the reset state of the engine ECU  2 , and therefore, the starter relay  4  is not activated. As a result, the current I 1  is not supplied from the power source  9  and the starter  5  is not energized. 
     In contrast, as shown in a timing diagram of  FIG. 2B , if the assistance of the auxiliary ECU  1  is provided, the current I 3  flows through the starter relay  4  during the reset state of the engine ECU  2 , and therefore, the starter relay  4  is activated. As a result, the current I 1  is supplied from the power source  9  and the starter  5  is energized to start the engine. 
     The assistance of the auxiliary ECU  1  is provided in the system  20 . Therefore, the engine can be started in the system  20 , even if the engine ECU  2  falls into the reset state during starting of the engine. 
     Second Embodiment 
     Reference is made to  FIG. 3 , which shows a block circuit diagram of an engine starting system  30 . 
     The system  30  has the similar basic configuration as the system  20  and has a relay  10  besides. The relay  10  includes a coil  10   a  and a relay switch  10   b.  A voltage of an ignition switch (IG) is applied to the coil  10   a,  only when the ignition IG is ON. In other words, the voltage of the ignition switch is not applied to the coil  10   a,  when the ignition IG is OFF. When an electric current flows through the coil  10   a,  the relay switch  10   b  is turned on by magnetic attractive force generated around the coil  10   a.  The relay switch  10   b  controls a current path through which the auxiliary ECU  1  or the engine ECU  2  supplies the current I 3  or the current I 2  to the starter relay  4 , respectively. 
     In short, the relay switch  10   b  is turned on and off in accordance with the ON and OFF state of the ignition switch, and accordingly the current path is turned on and off. Thus, the auxiliary ECU  1  or the engine ECU  2  supplies the current I 3  or the current I 2  to the starter relay  4 , only when the ignition switch is ON. 
     If the auxiliary ECU  1  or the engine ECU  2  breaks down, the current I 3  or the current I 2  may be continuously supplied to the starter relay  4  at the time when the current I 2 , I 3  are not required. However, the relay switch  10   b  interrupts the current I 2 , I 3 , when the ignition switch is turned off. Therefore, safety of the system  30  can be improved. 
     (Modifications) 
     The embodiments described above may be modified in various ways. 
     For example, the terminal  6  may be connected to another power source (not shown) different from the power source  9 . In such a case, the voltage of the terminal  6  will no fall during staring of the engine, because the terminal  6  may not be affected by the starter motor  5   b.  The voltage of the terminal  6 , however, may drop below the reset level L 2  because of electrical loads other than the starter motor  5   b,  deterioration of the terminal  6 , noise, temperature, for example. Even in this instance, the booster  1   a  enables the auxiliary ECU  1  to supply the current I 3  to the starter relay  4 . Therefore, the starter motor  5   b  runs and the engine may be started, even when the engine ECU  2  resets the supply of the current I 2 . 
     The booster  1   a  of the auxiliary ECU  1  is optional as long as the auxiliary ECU  1  can supply the current I 3  to the starter  4  during the reset state of the engine ECU  2 . 
     The above embodiments may be modified to an engine starting system in which an engine is started by turning a key cylinder instead of pressing the push switch  7 . 
     Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.