Abstract:
A control apparatus for controlling a starter used to start an engine mounted on a vehicle, the starter generating a torque and having a first gear mechanically engaged with a second gear of the engine to start the engine. The control apparatus includes a trigger circuit adapted to output a trigger signal in response to a start request; a detection circuit adapted to detect an electrical state and a mechanical state of the starter while the starter is powered on; and a controller adapted to control power on and off of the starter. The controller powers on the starter in response to the trigger signal outputted by the trigger circuit, and powers off the starter when the controller detects that a predetermined condition is satisfied based on the state of the starter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to Japanese Patent Application No. 2010-30400 filed on Feb. 15, 2010, the contents of which are hereby incorporated by reference. 
       TECHNICAL BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a control apparatus for starting an engine mounted on a vehicle, and more particularly to a control apparatus having power-off control function adapted to starters for starting engines. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, starters for starting engines are powered off when the starter completes starting of the engine. A control apparatus is used to control powering off of the starter when a predetermined power-off condition is detected. The power-off condition varies depending on types of starter operations. Conventionally, the starter operations include the following three types. 
         [0006]    (a) One of three types of starter operations implements a rotary-type switch (ignition key switch) for starting the engine: the driver triggers the starter operation such that the driver turns the ignition key switch from the ON position to the START position whereby the starter is powered to crank the engine, and therefore the engine starts. The driver turns the ignition key from the START position to the ON position to stop the starter operation (powering off the starter) when the driver determines the engine is started. 
         [0007]    (b) One of three types of starter operations implements a press-type start switch (ignition switch) for starting the engine: the driver triggers the starter operation such that the driver presses the start switch for powering the starter to start cranking the engine, thereby starting the engine. The starter operation is controlled to be stopped (powering off the starter) when a complete engine-start is detected depending on whether or not the engine rotational rate exceeds a predetermined threshold value. 
         [0008]    (c) One of three types of starters implements an idle stop system (automatic engine stop/restart system): The starter is controlled to start the operation when a predetermined automatic start condition is met during an idle stop condition such that the starter is powered and starts cranking the engine thereby starting the engine. The starter operation is controlled to be stopped (powering off the starter) when a complete engine-start is detected depending on whether or not the engine rotational rate exceeds a predetermined threshold value. Specifically, a Japanese Patent No. 4214401 discloses the above-described technique used for an automatic stop/restart control apparatus. 
         [0009]    Conventionally, in the above-described starter operations, the starter is supplied with power continuously until completion of the starter operation. Meanwhile, when the engine completely starts, the rotational rate of the engine is higher than the no-load rotational rate (i.e., rotational rate when no-load is applied) of the starter so that the pinion gear of the starter is rotatable by rotational force of the engine after rotational rate of the pinion gear exceeds the no-load rotational rate of the starter. However, the power is continuously supplied to the starter until the engine rotational rate reaches the predetermined threshold value. Therefore, while the starter is continuously powered, the battery power is consumed unnecessarily, which affects the battery to shorten its life-time of operation and also affects durability of the starter. 
         [0010]    Specifically, since the idle stop system requires frequent engine restart operations, load on the battery significantly increases and therefore, the durability of the starter decreases. To enhance the durability of the starter, it may cause an increase of manufacturing cost thereof. 
       SUMMARY 
       [0011]    An embodiment provides a control apparatus used for starting engine. Specifically, a control apparatus for starting the engine is provided in which operating period of supplying power to the starter is shortened whereby the load of the battery is reduced and the durability of the starter is enhanced. 
         [0012]    As a first aspect of the embodiment, a control apparatus for controlling a starter used to start an engine mounted on a vehicle, the starter generating a torque for starting the engine and having a first gear (i.e., pinion gear) outputting the generated torque, the engine having a second gear (i.e., ring gear) to receive the torque, the first gear mechanically engaging with the second gear to start the engine, and the control apparatus includes: a trigger circuit adapted to output a trigger signal in response to a start request; a detection circuit adapted to detect an overall state of the starter which comprises an electrical state and a mechanical state of the starter while the starter is powered on; and a controller including first means configured to power on the starter in response to the trigger signal outputted by the trigger circuit, and second means configured to power off the starter when the controller detects that a predetermined condition of the starter is satisfied based on the state of the starter. 
         [0013]    In the above-described control apparatus, the starter can be powered off when the predetermined condition (i.e., a condition where the starter cannot drive the engine to rotate) is detected even when the engine rotation rate does not reach the predetermined threshold value while the starter is powered on. As a result, operation period of the starter can be shortened and load of the battery used for the starter can be reduced, and also durability of the starter can be enhanced. 
         [0014]    Specifically, the detection circuit can be configured to detect a torque at the first gear as a mechanical state of the starter, the torque at the first gear being transmitted to the second gear, and the controller detects the predetermined condition when the torque is a predetermined value or less and stops supplying power to the starter. While the engine is starting, when the rotational rate of the engine increases, an operational state where the first of the starter drives the second gear changes to an inverted state where the second gear drives the first to rotate thereby. As a result, rotation of a motor of the starter becomes idle rotation so that the torque applied to the second gear by the first gear becomes an idle torque. Accordingly, the above-described predetermined value is set to be a torque value which is the idle torque or around the idle torque so that the inverted state can be detected correctly. 
         [0015]    Further, the detection circuit can be configured to detect a torque at the first gear as a mechanical state of the starter, the torque at the first gear being transmitted to the second gear, and the controller can be configured to detect the predetermined condition when a change rate of the torque is a predetermined value or more. When the first gear of the starter is driven by the second gear, the torque at the first gear becomes the idle torque. Hence, detecting the change rate of the torque whether or not the change rate of the torque rapidly changes, it is determined that the first gear of the starter is rotated (driven) by the second gear. 
         [0016]    Alternatively, the detection circuit can be configured to detect a rotational rate of the first gear as a mechanical state of the starter, and the controller can be configured to detect the predetermined condition when the rotational rate of the first gear is a no-load rotational rate or more. Since the first gear is rotated by the second gear, the rotational rate of the first gear exceeds the no-load rotational rate. 
         [0017]    Also, the detection circuit can be configured to detect a change rate of the rotational rate of the first gear as a mechanical state of the starter, and the controller can be detect the predetermined condition when the change rate of the rotational rate is a predetermined value or more. In a region where rotational rate at the first gear of the starter exceeds the no-load rotational rate, the engine rotational rate rapidly increases due to a combustion pressure whereby the rotational rate of the first gear rapidly increases as well. Therefore, by detecting the change rate of the rotational rate of the first gear, it is determined that the first gear of the starter is driven by the second gear. 
         [0018]    Further, the detection circuit can be configured to detect a drive current or a drive power as an electrical state of the starter. The controller can be configured to detect the predetermined condition when the drive current or the drive power is a predetermined value or is less. While the engine is starting, load (torque) of the starter decreases when the rotational rate of the engine rotation rate increases so that the drive current of the starter decreases. Accordingly, it is determined that the first gear of the starter has been driven by the second gear when the drive current of the starter reaches the predetermined value or less. 
         [0019]    Alternatively, the detection circuit can be configured to detect a drive voltage as an electrical state of the starter and the controller can be configured to detect the predetermined condition when the drive voltage is a predetermined value or more. While the engine is starting, the torque (load) of the starter decreases in response to an increase of the engine rotational rate whereby the drive voltage of the starter increases. Accordingly, it is determined whether or not the first gear has been driven by the second gear by detecting whether or not the drive voltage of the starter reaches the predetermined value or more. 
         [0020]    The detection circuit can be configured to detect any one of a drive current or a drive voltage or a drive power as an electrical state of the starter. The controller can be configured to detect the predetermined condition when a change rate of any one of a drive current or a drive voltage or a drive power is a predetermined value or more. When the rotational rate at the first gear of the starter exceeds the no-load rotational rate, the engine rotational rate rapidly increases due to a combustion pressure so that the load (torque) of the starter rapidly changes. Therefore, by detecting whether or not the change rate of any one of the drive voltage, the drive current or the drive power of the starter changes rapidly, it is determined that the first gear has been driven by the second gear. When the rotational rate of the first gear exceeds the no-load rotational rate, the rotational rate of the engine rapidly increases due to a combustion pressure whereby the load (torque) of the starter deceases. Accordingly, it is determined whether or not the first gear has been driven by the second gear by detecting whether or not the change rate of any one of a drive current or a drive voltage or a drive power as an electrical state of the starter rapidly changes. 
         [0021]    Also, the detection circuit can be configured to detect a drive current as an electrical state of the starter. The controller can be configured to detect the predetermined condition when the drive current is a no-load current value. When the rotational rate of the first gear reaches the no-load rotational rate, the drive current of the starter becomes the no-load current value. Accordingly, it is determined whether or not the first gear has been driven by the second gear by detecting whether or not the drive current of the starter becomes the no-load current value. 
         [0022]    Above-described techniques can be adapted to either a vehicle provided with a rotary-type switch or a vehicle provided with a push-type switch. However, the techniques can be adapted to an automatic stop/restart system in which an engine is controlled to be stopped when an automatic stop condition is met and restarts when a predetermined start condition is met. Since the idle stop system requires frequent engine restart operation, a load of the battery significantly increases. Therefore, load of the battery and enhanced durability of the starter can be achieved by the above-described techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    In the accompanying drawings: 
           [0024]      FIG. 1  is a diagram showing an overall configuration of a control system for starting an engine according to a first embodiment of the present invention; 
           [0025]      FIG. 2  is a timing diagram that exemplifies a drive current of the starter, a drive voltage of the starter, a pinion rotational rate and a behavior of an engine rotational rate while the engine is starting; 
           [0026]      FIG. 3  is a flowchart for explaining a technical feature of a power-off control of the starter; 
           [0027]      FIG. 4  is a flowchart showing a detail procedure of the power-off control of the starter according to a first embodiment; 
           [0028]      FIG. 5  is a diagram showing an overall configuration of a control system for starting the engine according to a second embodiment; 
           [0029]      FIG. 6  is a flowchart showing a detail procedure of the power-off control of the starter according to the second embodiment; 
           [0030]      FIG. 7  is a diagram showing an overall configuration of a control system for starting the engine according to a third embodiment; 
           [0031]      FIG. 8  is a flowchart showing a detail procedure of the power-off control of the starter according to the third embodiment; 
           [0032]      FIG. 9  is a diagram showing an overall configuration of a control system for starting the engine according to a fourth embodiment; 
           [0033]      FIG. 10  is a flowchart showing a detail procedure of the power-off control of the starter according to the fourth embodiment; and 
           [0034]      FIG. 11  is a flowchart showing a procedure of the power-on control of the starter. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    With reference to the drawings, hereinafter will be described embodiments of the present invention. 
       First Embodiment 
       [0036]    With reference to  FIGS. 1 to 4 , hereinafter will be described a first embodiment of the present invention. First, with reference to  FIG. 1 , a configuration of an automatic stop/restart system (idle stop system) is described as follows. The starter  11  is what is called pinion push out type starter including a motor section  12 , a pinion  13  driven by the motor section  12  to allow the pinion  13  to rotate and a pinion actuator  14  used for pushing out the pinion  13 . 
         [0037]    The pinion  13  is connected to a rotary shaft of a reduction mechanism (not shown) of the motor section  12  via a one-way clutch (not shown). The pinion  13  is configured to be movable in an axial direction of the rotary shaft. The pinion actuator  14  includes a plunger  15  and a plunger solenoid  16  and is configured to push out the pinion  13  when the engine starts. The plunger  15  is connected to the one-way clutch of the pinion  13  via the lever  17 . The plunger  15  is suctioned towards a direction A indicated by the arrow when the plunger solenoid  16  is powered whereby the lever  17  rotates about a shaft  18  so as to allow the pinion  13  to push out together with the one way clutch. Therefore, the pinion  13  meshes with a ring gear  21  that is connected to the crank shaft of the engine  20 . At this time, a movable contact  15   a  disposed at the end portion of the plunger  15  closes contacts of a power switch  22  of the motor section  12  so that the power switch  22  is turned on. As a result, power is supplied to the motor section  12  to allow the pinion  13  to rotate whereby the engine  20  starts cranking and therefore starts operation. 
         [0038]    The rotational rate of the engine  20  (i.e., rotational rate of the ring gear  21 ) when the engine-start operation completes is higher than the no-load rotational rate (i.e., rotational rate when no-load is applied) of the starter  11 . Hence, after the rotational rate of the pinion  13  of the starter  11  exceeds the no-load rotational rate, the pinion  13  of the starter  11  can be rotatable by the ring gear  21  of the engine  20 . However, since the one way clutch of the pinion  13  runs idle, the motor section  12  of the starter  11  is not rotated by the ring gear  21 . 
         [0039]    Meanwhile, a gear-shape signal rotor  24  is disposed at the crank shaft of the engine  20  to engage therewith and a crank angle sensor  25  is arranged at a position facing to periphery of the signal rotor  24 . A pulse signal outputted per predetermined crank angle from the crank angle sensor  25  is inputted to an engine control unit (hereinafter referred to ECU)  26 . The ECU  26  is configured to calculate the engine rotational rate based on intervals of the output pulse signal of the crank angle sensor  25 . Also, the ECU  26  counts output pulses from the crank angle sensor  25  referenced to a position where the pulse is outputted from a cam angle sensor (not shown) and detects the crank angle from the count value. 
         [0040]    A power relay circuit  28  which is normally open type is arranged between the power supply terminal of the plunger solenoid  16  and the battery  27 . The ECU  28  controls a coil  28   a  of the power relay circuit  28  to be ON and OFF. Note that the ECU  26  corresponds to a controller that includes power on-off control of the starter (the power on-off control function corresponds to first and second control means respectively). As shown  FIG. 11 , the ECU  26  powers on the starter to start the engine when a trigger signal is active. The trigger signal becomes active in response to a start request which is depends on types of vehicle. Specifically, the ECU  26  is configured such that the ECU  26  acquires an ON/OFF signal (i.e., trigger signal) from a press type start switch  30  and supplies the power to the coil  28   a  of the power relay circuit  28   b  so as to enable the power relay circuit  28   b  to be ON when the ON/OFF signal from the start switch is ON. As a result, the plunger solenoid  16  of the pinion actuator  14  in the starter  11  is powered to allow the pinion  13  to mesh with the ring gear  21  and then, the movable contact  15   a  disposed at the end portion of the plunger  15  closes the contacts of the power switch  22  thereby supplying power to the motor section  12  so that the pinion  13  starts to rotate whereby the engine  20  is cranked and started. 
         [0041]    Regarding the start switch, instead of the press-type start switch, the rotary-type ignition key switch can be used. When the rotary type ignition key switch is used, when the driver turns the ignition key to the START position from the ON position (i.e., start request), the coil  28   a  of the power relay circuit  28  is supplied with the power to turn the switch  28   b  of the power relay circuit  28   b  ON. 
         [0042]    The ECU  26  executes an engine automatic stop/restart control procedure (not shown) to perform an engine automatically stop/restart control (i.e., idle stop control). In the engine automatically stop/restart control, when the driver operates the vehicle to be slowdown (applying a braking operation during accelerator pedal being off, i.e., throttle valve is fully closed) while the vehicle is running so that a predetermined deceleration state where the vehicle may stop is detected, the ECU  26  determines that an automatic stop request (idle stop request) has been occurred and controls the combustion of the engine  20  (fuel injection and/or ignite operation) to be stopped whereby the engine  20  is automatically stopped (i.e., idle stop). Also, the ECU  26  determines occurring of the automatic stop request when the braking operation is continued while the vehicle is stopped and performs the idle stop by stopping the combustion of the engine  20 . 
         [0043]    Subsequently, when the driver operates necessary operation to run the vehicle such as releasing of the brake, shifting transmission gear to drive position or pressing down the accelerator pedal, the ECU  26  determines that the restart request has occurred (i.e., start request). Then, the ECU  26  supplies power to the coil  28   a  of the power relay circuit  28  to turn the switch  28   b  of the power relay circuit  28  to be ON. Therefore, the plunger solenoid  16  is powered and the plunger  15  is suctioned by the electromagnetic force whereby the pinion  13  moves towards the ring gear  21  and meshes thereto. At the same time, the movable terminal  15   a  disposed at the end portion of the plunger  15  closes the contacts of the power switch  22  of the motor section  12  to turn the power switch  22  ON. Accordingly, the power is supplied to the motor section  12  and the pinion  13  starts to rotate thereby cranking the engine  20  and the fuel injection starts to restart the engine  20 . 
         [0044]    Further, it is considered that the restart request occurs at an on-vehicle control system such as a battery charge control system or an air conditioner. The restart request occurs while the engine rotational rate is decreasing (hereinafter referred to engine rotational rate decrease period) or occurs after the engine rotation stops. 
         [0045]    Moreover, the ECU  26  monitors whether or not the pinion  13  of the starter  11  is rotatable by the ring gear  21  while the starter is powered (both switches  28   b  and  22  are ON). When the pinion  13  of the starter  11  is rotatable by the ring gear  21 , the ECU  21  stops supplying power to the coil  28   a  of the power relay circuit  28  to make the switch  28   b  of the power relay circuit  28  OFF whereby the plunger solenoid  16  of the pinion actuator  14  is powered OFF. Therefore, the plunger  15  returns to the OFF position by a return spring (not shown) of the pinion actuator  14  whereby the pinion  13  is detached from the ring gear  21  and the contacts of the power switch  22  becomes open. As a result, supplying power to the motor section  12  of the starter  11  is stopped. 
         [0046]      FIG. 2  is a timing diagram that exemplifies a drive current of the starter  11 , a drive voltage of the starter  11 , a pinion rotational rate and a behavior of an engine rotational rate while the engine is starting. When the rotational rate of the engine and the rotational rate of the pinion of the starter  11  increase while the engine is starting, the load (torque) of the starter  11  decreases. The drive current and power of the starter  11  decreases in response to decreasing of the load of the starter. However, the drive voltage of the starter  11  increases. 
         [0047]    According to the first embodiment, since a torque of the pinion  13  applied to the ring gear  21  is detected, it is determined whether or not the pinion  13  of the starter  11  is rotatable by the ring gear  21  (i.e., pinion  13  is driven by the ring gear  21 ). Therefore, a torque sensor  32  is arranged to detect the torque applied to the ring gear  21  (applied by the pinion  13 ) and the output signal of the torque sensor  32  is inputted to the ECU  26 . 
         [0048]    The ECU  26  is configured to monitor the torque detected by the torque sensor  32  while the starter  11  is powered. The ECU  26  determines that the pinion gear  13  of the starter  11  has been driven by the ring gear  21  when the detected torque is equal to or less than a predetermined value and then, the ECU  26  controls the switches  28   b  and  22  to be OFF to stop supplying power to the starter  11 . 
         [0049]    While the engine is starting, when the rotational rate of the engine increases, an operational state where the pinion  13  of the starter  11  drives the ring gear  21  changes to an inverted state where the ring gear  21  drives the pinion  13  to rotate thereby. As a result, rotation of a motor of the starter  11  becomes idle rotation so that the torque applied to the ring gear by the pinion  13  becomes an idle torque. Accordingly, the above-described predetermined value (predetermined threshold value) is set to be a torque value which is the idle torque or around the idle torque so that the inverted state can be detected correctly. 
         [0050]    Alternatively, the ECU  26  monitors a change rate of the torque which is applied to the ring gear  21  by the pinion  13  to detect whether or not the operational state changes to the inverted state. Specifically when the change rate of the torque reaches a predetermined value or more, the ECU  26  determines that the operational state changes to the inverted state where the ring gear  21  drives the pinion  13  to rotate thereby, and then the ECU  26  stops supplying power to the starter  11 . When the pinion  13  of the starter  11  is driven by the ring gear  21 , the torque applied to the ring gear  21  by the pinion  13  of the starter  11  becomes idle. Hence, by monitoring the change rate of the torque, the ECU  26  can determine whether or not the inverted state occurs. 
         [0051]      FIG. 3  is a flowchart for explaining a technical feature of a power-off control of the starter. The power-off control of the starter of the present invention is periodically executed while the ECU  26  is powered on. At step  101 , the ECU  26  determines whether or not the starter  11  is powered-on (engine is starting). The procedure is ended if the starter is not powered on. 
         [0052]    When the ECU  26  determines that the starter  11  is powered-on at step  101 , the ECU  26  proceeds to step  102 . At step  102 , the ECU  26  determines whether or not the pinion  13  has been driven by the ring gear  21 . This procedure is repeated until the pinion  13  is driven by the ring gear  21 . 
         [0053]    Subsequently, when the pinion  13  come to a state where the pinion  13  is driven by the ring gear  21 , the ECU  28  proceeds to step  103  and turns the switches  28   b  and  22  OFF in order to stop supplying power to the starter  11 . 
         [0054]      FIG. 4  is a flowchart showing a detail procedure of the power-off control of the starter according to the first embodiment. This procedure is periodically executed while the ECU  26  is powered ON. First, the ECU  26  determines whether or not the starter  11  is powered ON (engine is starting). The ECU  26  terminates the procedure if the starter is not operating (powered OFF). 
         [0055]    At step  201 , when the ECU  26  determines that the starter  11  is powered ON (engine is starting), the ECU  26  proceeds to step  202  and detects the torque of the pinion  13  applied to the ring gear  21  by using the torque sensor  32 . Subsequently, at step  203 , the ECU  26  determines whether or not the torque detected by the torque sensor  32  is a predetermined value or less (or change rate of the torque reaches the predetermined value or more). When the ECU  26  determines “NO”, then returns to step  202 . Accordingly, the ECU  26  continue to execute this procedure (steps  202  to  203 ) until the torque detected by the torque sensor  32  reaches predetermined value or less (or the change rate of the torque reaches the predetermined value or more). 
         [0056]    Subsequently, when the torque detected by the torque sensor  32  reaches the predetermined value or less (or the change rate of the torque reaches the predetermined value or more), the ECU  26  determines that the pinion  13  of the starter  11  has been driven by the ring gear  21  and proceeds to step  204 . At step  204 , the ECU  26  controls the switches  28   b  and  22  to be OFF in order to stop supplying power to the starter  11 . 
         [0057]    As described, according to the first embodiment, even when the engine rotational rate does not reach the predetermined threshold value while the starter  11  is powered, the starter  11  can be powered off at a time when the inverted state where the pinion  13  of the starter  11  is driven by the ring gear  21  disposed at the engine  20  side (at a time when the starter  11  cannot drive the engine to rotate) is detected. As a result, the operating period (period for powering ON) of the starter  11  can be shortened compared to a starter used in prior art. Also, load of the battery  27  can be reduced and durability of the starter  11  can be enhanced. 
       Second Embodiment 
       [0058]    With reference to  FIGS. 5 and 6 , hereinafter will be described a second embodiment of the present invention. According to the above-described first embodiment, to detect the state where the pinion  13  of the starter  11  has been driven by the ring gear  21  of the engine  20  side while the starter  11  is powered, the torque sensor  32  is arranged. However, according to a second embodiment of the present invention as shown in  FIGS. 5 and 6 , a pinion rotational rate sensor  33  to detect a rotational rate of the pinion of the starter  11  is provided (torque sensor  32  in the first embodiment is not provided). 
         [0059]    According to the second embodiment, while the starter  11  is powered ON, the ECU  26  determines whether or not the pinion rotational rate detected by the pinion rotational rate sensor reaches the no-load rotational rate or more. When the pinion rotational rate reaches the no-load rotational rate or more, the ECU  26  determines that the pinion  13  has been driven by the ring gear  21 . The ECU  26  is configured to stop supplying power to the starter  11  since the pinion rotational rate is larger than or equal to the no-load rotational rate when the pinion  13  of the starter  11  is driven by the ring gear  21 . Note that the no-load rotational rate is referred to a rotational rate when no load is applied. 
         [0060]    Alternatively, the ECU  26  may be configured to monitor whether or not the change rate of the pinion rotational rate reaches a predetermined value or more, and determines that the pinion  13  of the starter  11  has been driven by the ring gear  21  when the change rate of the pinion rotational rate reaches a predetermined value or more. Then, the ECU  26  stops supplying power to the starter  11 . In a region where the pinion rotational rate of the starter  11  exceeds the no-load rotational rate, the engine rotational rate rapidly increases due to a combustion pressure whereby the pinion rotational rate rapidly increases as well. Therefore, by detecting the change rate of the pinion rotational rate, the ECU  26  can determine that the pinion  13  of the starter  11  is driven by the ring gear  21 . 
         [0061]    According to the second embodiment, as shown in  FIG. 6 , the ECU  26  repeatedly executes the power-off control routine of the starter at a predetermined period while the ECU  26  is powered ON. When the power-off control routine is activated, the ECU  26  determines whether or not the starter  11  is powered ON (engine is starting) at step  301 . This routine is terminated when the starter  11  is not powered ON. 
         [0062]    The ECU  26  executes step  302  when it is determined that the starter  11  is powered ON (engine is starting) at step  301 . At step  302 , the pinion rotational rate of the starter  11  is detected by the pinion rotational rate sensor  33 . At step  303 , the ECU  26  determines whether or not the pinion rotational rate detected by the pinion rotational rate sensor  33  is no-load rotational rate or more (or whether or not the change rate of the pinion rotational rate reaches a predetermined value or more). When the determination result is NO, then the ECU  26  returns to step  302 . Accordingly, this procedure is repeated until the pinion rotational rate reaches the no-load rotational rate or more (or the change rate of the pinion rotational rate reaches a predetermined value or more). 
         [0063]    Subsequently, when the pinion rotational rate reaches the no-load rotational rate or more (or the change rate of the pinion rotational rate reaches a predetermined value or more), the ECU  26  determines that the pinion  13  of the starter  11  has been driven by the ring gear  21  and proceeds to the step  304 . Then, the ECU  26  turns the switches  28   b  and  22  OFF to stop supplying the power to the starter  11 . 
         [0064]    According to above-described second embodiment, the operating period (period for powering ON) of the starter  11  can be reduced as well as the first embodiment. Further, reducing the load of the battery  27  and enhancing the durability of the starter  11  can be achieved. 
       Third Embodiment 
       [0065]    With reference to  FIGS. 7 and 8 , hereinafter will be described a third embodiment of the present invention. As shown in  FIGS. 7 and 8 , a current sensor  34  is arranged to detect drive current of the starter  11  (drive current of the motor section  12 ). In this configuration, it is determined that the pinion  13  of the starter  11  has been driven by the ring gear  21  when the drive current of the starter  11  reaches a predetermined value or less whereby the ECU  26  stops supplying power to the starter  11 . 
         [0066]    As shown in  FIG. 2 , while the engine is starting, load (torque) of the starter  11  decreases when the rotational rate of the engine rotation rate increases so that the drive current of the starter  11  decreases. Accordingly, it is determined that the pinion  13  has been driven by the ring gear  21  when the drive current of the starter  11  reaches the predetermined value or less. 
         [0067]    Alternatively, it is determined that the pinion  13  has been driven by the ring gear  21  when the change rate of the drive current of the starter  11  reaches a predetermined value or more and then, the ECU  26  stops supplying power to the starter  11 . When the pinion rotational rate of the starter  11  exceeds the no-load rotational rate, the engine rotational rate rapidly increases due to the combustion pressure whereby the load (torque) of the starter  11  rapidly changes. Therefore, monitoring the change rate of the drive current of the starter  11 , it is determined that the pinion  13  has been driven by the ring gear  21  when the change rate of the drive current rapidly increases. 
         [0068]    According to the third embodiment, the ECU  26  periodically executes the power-off control of the starter as shown in  FIG. 8 . When the power-off control of the starter is activated, the ECU  26  checks whether or not the starter  11  is powered on (engine is starting). The ECU  26  terminates the procedure when the starter  11  is not powered ON. 
         [0069]    At step  401 , the ECU  26  determines whether or not the starter  11  is powered ON (engine is starting). When the starter  11  is powered ON, the ECU  26  proceeds to step  402  where the drive current of the starter  11  is detected by the current sensor  34 . Subsequently, at step  403 , it is determined whether or not the drive current of the starter  11  detected by the current sensor  34  is predetermined value or less (or the change rate of the drive current of the starter  11  reaches a predetermined value or more). When a judgment at step  403  is NO, then the ECU  26  returns to step  402 . Accordingly, this procedure is repeated until the drive current of the starter  11  reaches the predetermined value or less (or the change rate of the drive current of the starter reaches the predetermined value or more). 
         [0070]    Subsequently, when the drive current of the starter  11  decreases to reach the predetermined value or less (or the change rate of the drive current of the starter  11  reaches a predetermined value or more), it is determined that the pinion  13  has been driven by the ring gear  21  and proceeds to step  404 . At step  404 , the ECU  26  turns OFF switches  28   b  and  22  so as to stop supplying power to the starter  11 . As described, in the third embodiment, the operating period of the starter  11  can be shortened as similar to the one of the first embodiment. Therefore, the load of the battery  27  can be reduced and the durability of the starter  11  is enhanced as well. 
         [0071]    Alternatively, the ECU  26  monitors whether or not a drive current value of the starter  11  detected by the current sensor  34  while the starter  11  is powered ON (engine is starting) reaches a no-load current value. The ECU  26  determines that the pinion  13  has been driven by the ring gear  21  when the drive current reaches the no-load current value and controls the switches  28   b  and  22  to be OFF to stop supplying power to the starter  11 . Since the drive current of the starter  11  decreases to reach the no-load current value when the rotational rate of the pinion  13  reaches the no-load rotational rate, the ECU  26  can determine that the pinion  13  has been driven by the ring gear  21  by monitoring the drive current of the starter  11 . 
         [0072]    Further, a drive power of the starter  11  can be detected to determine whether or not the drive power of the starter  11  decreases to a predetermined value or less (or a change rate of the drive power of the starter  11  reaches a predetermined value or more). When the drive power of the starter  11  is predetermined value or less, it is determined that the pinion  13  has been driven by the ring gear  21  so that the switches  28   b  and  22  are controlled to be OFF to stop supplying power to the starter  11 . 
       Fourth Embodiment 
       [0073]    With reference to  FIGS. 9 and 10 , a fourth embodiment of the present invention is now described as follows. According to the fourth embodiment, a voltage sensor  35  is arranged to detect a drive voltage of the starter  11  (voltage applied to the motor section  12 ). The drive voltage is monitored to detect whether or not the drive voltage reaches the predetermined value or more. The ECU  26  determines that the pinion  13  has been driven by the ring gear  21  when the drive voltage reaches the predetermined value or more and then, the ECU  26  stops supplying power to the starter  11 . While the engine is starting, the torque (load) of the starter  11  decreases in response to an increase of the engine rotational rate whereby the drive voltage of the starter  11  increases. Accordingly, it is determined whether or not the pinion  13  has been driven by the ring gear  21  by detecting whether or not the drive voltage of the starter  11  reaches the predetermined value or more. 
         [0074]    Alternatively, a change rate of the drive voltage of the starter  11  can be used to determine that the pinion  13  has been driven by the ring gear  21 . Specifically, the ECU  26  detects whether or not the change rate of the drive voltage reaches predetermined value or more and determine that the pinion  13  has been driven by the ring gear  21  when the change rate of the drive voltage reaches the predetermined value or more. Then, the ECU  26  stops supplying power to the starter  11 . When the pinion rotational rate of the starter  11  exceeds the no-load rotational rate, the engine rotational rate rapidly increases due to a combustion pressure so that the load (torque) of the starter  11  rapidly changes. Therefore, by detecting whether or not the change rate of the drive voltage of the starter  11  changes rapidly, the ECU can detect that the pinion  13  has been driven by the ring gear  21 . 
         [0075]    According to the fourth embodiment, as shown in  FIG. 10 , the ECU  26  repeatedly executes a power-off control of the starter in a predetermined period. Once the procedure is activated, the ECU  26  determines whether or not the starter  11  is powered ON (engine is starting) at step  501 . The ECU  26  terminates the procedure when the starter  11  is not powered ON. 
         [0076]    When the ECU  26  determines the starter  11  is powered ON (engine is starting) at step  501 , then proceeds to step  502  where the voltage sensor  35  detects the drive voltage of the starter  11 . Subsequently, at step  503 , it is determined whether or not the drive voltage of the starter  11  is predetermined value or more (or the change rate of the drive voltage of the starter  11  reaches the predetermined value or more). When the judgment at step  503  is NO, then returns to step  502 . Accordingly, this procedure is repeated until the drive voltage of the starter  11  reaches the predetermined value or more (or the change rate of the drive voltage of the starter reaches the predetermined value or more). 
         [0077]    Subsequently, when the drive voltage of the starter  11  reaches the predetermined value or more (or the change rate of the drive voltage of the starter  11  reaches the predetermined value or more), the ECU  26  determines that the pinion  13  has been driven by the ring gear  21  and proceeds to step  504  where the switches  28   b  and  22  are turned OFF whereby the starter  11  is powered OFF. Similarly to the first embodiment, according to the above-described fourth embodiment, the operating period (period for powering ON) of the starter  11  can be shortened compared to a starter used in prior art. Also, load of the battery  27  can be reduced and durability of the starter  11  can be enhanced. 
         [0078]    The present invention can be applied to a vehicle without having an automatic stop/restart system (idle stop system). However, the present invention is preferably applied to a vehicle having an automatic stop/restart system. Since the automatic stop/restart system requires frequent engine restart operation, the present invention has significant advantages in view of reducing the load of the battery and durability of the starter  11  which should be enhanced in the automatic stop/restart system. 
         [0079]    In addition, the configuration of the starter  11  is not limited to those as shown in  FIG. 1  or the like, however, various modification can be made. For instance, the motor section  12  and pinion actuator  14  can be configured to be controlled separately (respective switches  22  and  28   b  can be configured to be controlled separately). 
         [0080]    Further, the configuration of the present invention can be adapted to a permanently engaged starter in which the pinion and the ring gear of the engine side are always engaged even after completion of the engine start. Moreover, the present invention is not limited to the above-described embodiments. However, various modifications can be made within a scope of the invention. For instance, any combination of the above-described embodiments can be adapted to the present invention.