1. Field of the Invention
The present invention relates to an engine starter for starting an engine with a starter motor and to a resistor short-circuiting device used for the engine starter.
2. Description of the Related Art
For starting an engine, a coil of a starter switch is energized to close an internal contact of the starter switch. In this manner, electric power is supplied from a vehicle power source to the starter motor to cause the starter motor to generate a rotary torque. A rotating force of the starter motor is transmitted to a crank shaft of the engine through an intermediation of a pinion gear and a ring gear which mesh with each other, thereby starting the engine. In this case, when the starter switch is closed, the starter motor is still in a static condition and a counter electromotive voltage is not generated. Therefore, a rush current of several hundreds to one thousand and several hundreds of amperes flows due to an extremely small internal resistance of the starter. At this time, a voltage drop, which is a reduction in terminal voltage due to an internal specific resistance of the vehicle power source, occurs in the vehicle power source.
Therefore, in starting the engine, there is a problem of instantaneous interruption occurring due to the voltage drop of the vehicle power source, which is caused by the current at the time of starting of the starter motor, when another electrical device provided in the vehicle, for example, a stereo, a navigation system, an air conditioner, or the like is used. The instantaneous interruption is not a particular problem in starting a normal engine. In a vehicle having an idle-stop function or the like, however, the instantaneous interruption occurs when the engine is restarted after the vehicle makes an idle-stop, bringing about a situation where a driver or a passenger in the same vehicle is made uncomfortable. Thus, in order to avoid the instantaneous interruption, measures of providing a standby power source, mounting a booster DC-DC converter, or mounting an electromagnetic switch for short-circuiting voltage drop suppression means are taken to prevent the voltage of the vehicle power source from dropping.
A conventional engine starter described in JP 2004-308645 A includes a motor, a starting resistance, a control element, and the like. The motor includes a series coil and a shunt coil. The starting resistance is connected in series to an armature of the motor. The control element controls a field current of the shunt coil. At the time of engine start, the motor is energized through an intermediation of the starting resistance. As a result, a starting current (rush current) flowing to the motor is reduced to suppress the voltage drop of a battery to 2 V or less. Moreover, a high-torque motor is employed, and hence a torque required for a piston to pass a first TDC position can be ensured even if the starting current of the motor is small. Further, after the piston passes the first TDC position, the field current of the shunt coil is controlled to obtain high rotation characteristics. As a result, the number of revolutions during cranking, which is required to start the engine, can be ensured. In this manner, the voltage drop exceeding 2 V is not brought about at the time of engine start, thereby enabling the engine start without the instantaneous interruption.
A conventional internal combustion engine starter disclosed in JP 2005-105861 A includes a DC motor, a capacitor, and an H-type controller. The DC motor is a compound-wound motor. The capacitor is connected in series to a shunt coil. The H-type controller performs switching between a first energization direction for charging the capacitor and a second energization direction for causing the capacitor to discharge charged power to the shunt coil. Then, at starting the DC motor, the energization is performed in the first energization direction. Then, at the time of starting of the DC motor, the energization direction is switched by the H-type controller from the first energization direction to the second energization direction. As a result, the voltage drop of a main power source which occurs with the start of the DC motor is compensated for, thereby ensuring a required torque of the starter. In this manner, the voltage drop of a main power source which occurs with the start of the DC motor is compensated for without increasing a capacity of the main power source nor boosting a voltage of the main power source with booster means. As a result, the starter without the instantaneous interruption is realized.
Further, a conventional starter described in JP 2009-167967 A includes an electromagnetic switch having voltage drop suppression means. The electromagnetic switch short-circuits the voltage drop suppression means. With this structure, after a current suppressed by the voltage drop suppression means is caused to flow through the motor, the voltage drop suppression means is short-circuited to apply a full voltage of the main power source to the motor. As a result, the voltage drop of the main power source which occurs with the start of the DC motor is suppressed without increasing the capacity of the main power source nor boosting the voltage of the main power source with the booster means, thereby realizing the starter without the instantaneous interruption.
In the engine starter disclosed in JP 2004-308645 A cited above, however, the starting resistance is connected to suppress the voltage drop at the time of engine start. Therefore, the controller for the switch which short-circuits the starting resistance is required. Moreover, the voltage drop at the time of engine start is monitored and controlled so as to be suppressed to 2 V or less, and hence the controller and the creation of a program are required for the control. As a result, an engine starter circuit disadvantageously becomes complex.
Moreover, in the internal combustion engine starter disclosed in JP 2005-105861 A cited above, in order to prevent the voltage drop at the time of starting of the DC motor, a method of compensating for the voltage drop of the main power source by charging the capacitor in advance and then causing the charged power to be discharged at the time of starting of the DC motor is used. Therefore, the capacitor having a large capacity, which is capable of accumulating necessary electric power as an auxiliary power source, and the H-type controller corresponding to means for switching the energization direction to allow the control element to perform switching between the charging and the discharging for the capacitor are additionally required. Thus, the starter circuit and the control become disadvantageously complex. Moreover, in an operating environment where starts and stops are required to be frequently repeated, the discharging is forced to be performed before the capacitor is sufficiently charged. As a result, there is a fear in that performance cannot be satisfactorily demonstrated.
Further, the voltage drop suppression means is included in the electromagnetic switch in the starter disclosed in JP 2009-167967 A cited above, and hence there is a fear in that cost is undesirably increased if the electromagnetic switches cannot be mass-produced by using conventional electromagnetic switches.