Battery charging control device

The present invention relates to a battery charging control device that controls a voltage across a battery so as not to exceed a target value while charging the battery with a rectification output of an AC generator.

When a battery is mounted in a vehicle or the like driven by an engine, the battery is charged by a rectification output of an AC generator driven by the engine. When the battery is thus charged by the output of the AC generator, a battery charging control device that controls charging of the battery needs to be provided.

The battery charging control device comprises: a rectification and output adjustment circuit that can switch between a state where an output of an AC generator is rectified to supply a charging current to a battery, and a state where the supply of the charging current from the AC generator to the battery is stopped; and a battery voltage adjustment control circuit that controls the rectification and output adjustment circuit so as to supply the charging current from the AC generator to the battery when a voltage across the battery is equal to or lower than a target value, and stop the supply of the charging current to the battery when the voltage across the battery exceeds the target value.

In two-wheel vehicles, outboard motors, agricultural machinery, or the like, a magneto generator is used as an AC generator driven by an engine. When the magneto generator is used, a rectification and output adjustment circuit of generator output short-circuit type is frequently used. The rectification and output adjustment circuit comprises a diode bridge full-wave rectifier circuit that rectifies the output of the AC generator, and a generator output short-circuit switch element which is connected in anti-parallel with each of diodes that form a lower side of a bridge of the diode full-wave rectifier circuit, and a short circuit for short-circuiting the output of the AC generator is constituted by the generator output short-circuit switch element and some of diodes that form the lower side of the diode full-wave rectifier circuit when the generator output short-circuit switch element is turned on.

The generator output short-circuit switch element may be connected in anti-parallel with each of diodes that form an upper side of a bridge of said diode full-wave rectifier circuit. In this case, the short circuit for short-circuiting the output of the AC generator is constituted by the generator output short-circuit switch element and some of diodes that form the upper side of the diode full-wave rectifier circuit when the generator output short-circuit switch element is turned on.

FIG. 2 shows a construction of a conventional battery charging control device using a rectification and output adjustment circuit of generator output short-circuit type. In FIG. 2 , a reference numeral 1 denotes a magneto generator driven by a prime motor such as an engine, and 2 denotes a rectification and output adjustment circuit. The rectification and output adjustment circuit 2 is comprised of a diode bridge full-wave rectifier circuit constituted by diodes D 1 to D 6 , and thyristors S 1 to S 3 as generator output short-circuit switches connected in anti-parallel with the diode D 4 to D 6 on a lower side of a bridge of the rectifier circuit.

An output of the generator 1 is input into AC input terminals 2 u , 2 v and 2 w of the rectification and output adjustment circuit 2 , and a battery 4 is connected between DC output terminals 2 a and 2 b of the rectification and output adjustment circuit 2 through a fuse 3 . An appropriate load (a motor in the shown example) 6 is connected between the output terminals 2 a and 2 b of the rectification and output adjustment circuit 2 through a load switch 5 .

A battery voltage adjustment control circuit 7 comprised of a transistor TR 1 , a Zener diode ZD 1 , and resistances R 1 to R 8 is connected between the DC output terminals 2 a and 2 b of the rectification and output adjustment circuit 2 .

In the battery charging control device in FIG. 2 , the Zener diode ZD 1 is in off state when a voltage across the battery 4 is equal to or lower than a target value. At this time, no base current passes through the transistor TR 1 , and thus the transistor TR 1 is in off state. When the transistor TR 1 is in off state, no trigger signal is provided to the thyristor S 1 to S 3 , thus the output of the AC generator 1 is not short-circuited, and a charging current is supplied from the generator 1 to the battery 4 through the rectification and output adjustment circuit 2 . When the load switch 5 is closed, a drive current is supplied from the generator 1 and the battery 4 to the load 6 .

When the voltage across the battery 4 exceeds the target value, the Zener diode ZD 1 is turned on, thus the base current passes through the transistor TR 1 to turn on the transistor, and trigger signals are simultaneously provided from an output terminal side of the rectification and output adjustment circuit 2 to the thyristors S 1 to S 3 through the transistor TR 1 and the resistances R 1 to R 3 . At this time, the output of the generator 1 is short-circuited through any of the thyristors S 1 to S 3 and any of the diodes D 4 to D 6 to stop the supply of the charging current to the battery 4 . This reduces the voltage across the battery 4 . When the voltage across the battery 4 is reduced, the Zener diode ZD 1 is turned off to stop the supply of the base current to the transistor TR 1 , thus the transistor TR 1 is turned off to stop the provision of the trigger signals to the thyristors S 1 to S 3 . When the provision of the trigger signals to the thyristors S 1 to S 3 is stopped, the thyristors S 1 to S 3 are turned off when an anode current of each thereof becomes equal to or lower than a holding current, and thus the charging current is supplied from the generator 1 to the battery 4 through the rectification and output adjustment circuit 2 . Repeating these operations can keep the voltage across the battery 4 around the target value. Such a battery charging control device is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2003-111299.

Conventionally, a large load has been rarely connected to a battery, and most currents output from a battery charging control device have been charging currents of the battery, but in recent years, a relatively large load (an electric load, hereinafter the same) such as a fuel pump used in a fuel injection device or a radiator fan motor has been connected to the battery. For agricultural machinery, a fertilization blower motor or the like is also a large load of a battery.

In order to drive the electric load and charge the battery without a hitch by using the conventional battery charging control device when the large load is connected to the battery, a generator having a large output suitable for the load needs to be used, but actually, the generator having a large output cannot be used in many cases because of a limited mounting position of the generator or limited costs. An insufficient output of the generator prevents sufficient charging of the battery, which may cause the battery to run out.

An object of the present invention is to provide a battery charging control device that can drive a load connected to a battery and charge the battery without a hitch even without using a generator having a large output.

The present invention is applied to a battery charging control device comprising: a rectification and output adjustment circuit that can switch between a state where an output of an AC generator is rectified to supply a charging current to a battery, and a state where the supply of the charging current from the AC generator to the battery is stopped; and a battery voltage adjustment control circuit that controls the rectification and output adjustment circuit so as to supply the charging current from the AC generator to the battery when a voltage across the battery is equal to or lower than a target value, and stop the supply of the charging current to the battery when the voltage across the battery exceeds the target value.

In the present invention, the device further comprises: a load driving switch that is inserted between the battery and a load of the battery and kept turned on while receiving a drive signal; and a load driving switch control circuit that performs control to provide a drive signal to the load driving switch and turn on the load driving switch when the AC generator generates the output and a voltage across the load is equal to or lower than a set value, and stop the provision of the drive signal to the load driving switch and turn off the load driving switch when the voltage across the load exceeds the set value. The set value of the voltage across the load is set to be lower than the target value of the voltage across the battery.

With the above described construction, when the value of a current passing through the load that uses the battery as power supply increases, the voltage applied to the load can be limited to as low a value as possible to generate surplus power, and the surplus power is used for charging the battery to reduce the risk of the battery running out.

The load driving switch control circuit may comprise: a drive signal supply switch that conducts when receiving a control signal from the output of the AC generator and provides the drive signal to the load driving switch; a control signal bypass switch provided to bypass the control signal from the drive signal supply switch and interrupt the drive signal supply switch when turned on; and a control signal bypass switch control circuit that keeps the control signal bypass switch turned off when the voltage across the load is equal to or lower than the set value, and turns on the control signal bypass switch when the voltage across the load exceeds the set value.

When the AC generator is a magneto generator, the rectification and output adjustment circuit may comprise a diode full-wave rectifier circuit that rectifies the output of the AC generator, and a generator output short-circuit switch element which is connected in anti-parallel with each of diodes that form a lower side of a bridge of the diode full-wave rectifier circuit, and a short circuit for short-circuiting the output of the AC generator is constituted by the generator output short-circuit switch element and some of diodes that form the lower side of the diode full-wave rectifier circuit when the generator output short-circuit switch element is turned on.

The generator output short-circuit switch element may be connected in anti-parallel with each of diodes that form an upper side of a bridge of the diode full-wave rectifier circuit. In this case, a short circuit for short-circuiting the output of the AC generator is constituted by the generator output short-circuit switch element and some of diodes that form the upper side of the diode full-wave rectifier circuit when the generator output short-circuit switch element is turned on.

The rectification and output adjustment circuit may comprise a control rectifier circuit that has a bridge in which one of lower and upper sides is formed by diodes, and the other is formed by thyristors, supplies a charging current to the battery when the thyristors are turned on, and stops the supply of the charging current to the battery when the thyristors are turned off.

The load driving switch preferably comprises an MOSFET.

The above and other objects and features of the invention will be apparent from the detailed description of the preferred embodiment of the invention, which is described and illustrated with reference to the accompanying drawings, in which;

FIG. 1 is a schematic circuit diagram of a construction of a preferred embodiment of the present invention; and

FIG. 2 is a schematic circuit diagram of an exemplary construction of a conventional battery charging control device.

Now, a preferred embodiment of the present invention will be described in detail with reference to FIG. 1 .

In FIG. 1 , a reference numeral 1 denotes a magneto generator driven by a prime motor such as an engine. The magneto generator is comprised of an unshown magnet rotor rotatably driven by the prime motor, and a stator having three-phase armature coils Lu to Lw star connected, and induces a three-phase AC voltage in the armature coils Lu to Lw.

A reference numeral 2 denotes a rectification and output adjustment circuit, which is comprised of a diode bridge full-wave rectifier circuit constituted by diodes D 1 to D 6 , and generator output short-circuit switches connected in anti-parallel with the diodes D 4 to D 6 on a lower side of a bride of the rectifier circuit. In the shown example, thyristors S 1 to S 3 are used as the generator output short-circuit switches. Three-phase AC input terminals 2 u , 2 v and 2 w of the rectification and output adjustment circuit 2 are connected to three-phase output terminals of the generator 1 , and a battery 4 is connected between DC output terminals 2 a and 2 b of the rectification and output adjustment circuit 2 through a fuse 3 .

A source of a p-channel type MOSFET F1 that constitutes a load driving switch 8 is connected to a plus side output terminal 2 a of the rectification and output adjustment circuit 2 , and an appropriate load (a motor in the shown example) 6 is connected between a drain of the MOSFET and a minus side output terminal 2 b of the rectification and output adjustment circuit. A flywheel diode D 8 having an anode directed to the minus side output terminal 2 b is also connected between the drain of the MOSFET and the minus side output terminal 2 b of the rectification and output adjustment circuit.

A battery voltage adjustment control circuit 7 is also connected between the output terminals 2 a and 2 b of the rectification and output adjustment circuit 2 . The control circuit is comprised of a PNP transistor TR 1 having an emitter connected to the output terminal 2 a , resistors R 1 , R 2 and R 3 having one ends commonly connected to a collector of the transistor TR 1 , and the other ends connected to gates of the thyristors S 1 to S 3 , resistors R 4 to R 6 having one ends connected to the gates of the thyristors S 1 to S 3 , and the other ends commonly connected to the minus side output terminal 2 b of the rectification and output adjustment circuit, a resistor R 7 connected between the emitter and a base of the transistor TR 1 , and a Zener diode ZD 1 having a cathode connected to the base of the transistor TR 1 , and an anode connected to the minus side output terminal 2 b through a resistor R 8 . The resistor R 7 is resistance for adjusting sensitivity of the transistor TR 1 .

In the above described battery voltage adjustment control circuit 7 , a target value (for example, 14 V) of a battery voltage is set by the Zener diode ZD 1 and the resistor R 8 . When the voltage across the battery 4 is equal to or lower than the target value, the Zener diode ZD 1 does not conduct, thus no base current passes through the transistor TR 1 , and the transistor TR 1 is in off state. At this time, no trigger signal is provided to the thyristors S 1 to S 3 , thus an output of the generator 1 is rectified through the full-wave rectifier circuit constituted by the diodes D 1 to D 6 and supplied to the battery 4 to charge the battery 4 .

When the charging of the battery 4 continues, and the voltage across the battery 4 becomes equal to or higher than the target value, the Zener diode ZD 1 conducts and the base current passes through the transistor TR 1 , thus the transistor TR 1 is turned on, and trigger signals are simultaneously provided to the thyristors S 1 to S 3 through the transistor TR 1 and the resistors R 1 to R 3 . When the trigger signals are provided to the thyristors S 1 to S 3 , any of the thyristors S 1 to S 3 that receives a forward voltage between an anode and a cathode conducts, and the output of the generator 1 is short-circuited through the conducting thyristor and any of the diodes D 1 to S 3 to stop the supply of the charging current to the battery 4 .

When the voltage across the battery 4 becomes equal to or lower than the target value, the Zener diode ZD 1 is turned off, thus the transistor TR 1 is turned off to stop the provision of the trigger signals to the thyristors S 1 to S 3 . In this case, the thyristors S 1 to S 3 are interrupted when an anode current of each thereof becomes lower than a holding current to release the short circuit of the output of the generator. This causes the charging of the battery to restart. Repeating these operations can keep the voltage across the battery 4 around the target value.

A collector of an NPN transistor TR 2 is also connected to the plus side output terminal 2 a of the rectification and output adjustment circuit 2 through a series circuit of a resistor R 9 and a resistor R 10 , and an emitter of the transistor TR 2 is connected to the minus side output terminal 2 b . A base of the transistor TR 2 is connected to the minus side output terminal 2 b of the rectification and output adjustment circuit 2 through a resistor R 11 , and connected to a common connection point of cathodes of diodes D 11 to D 13 through a resistor R 12 , and anodes of the diode D 11 to D 13 are connected to the three-phase output terminals 1 u to 1 w of the magneto generator 1 . A capacitor C 1 is connected between the common connection point of the cathodes of the diodes D 11 to D 13 and the minus side output terminal 2 b.

In the control device shown in FIG. 1 , a series circuit of resistors R 13 and R 14 is connected in parallel with both ends of the diode D 8 with the resistor R 14 positioned on the anode side of the diode D 8 , and a capacitor C 2 is connected in parallel with both ends of the resistor R 14 . A cathode of a Zener diode ZD 2 is connected to a terminal of the capacitor C 2 on the side of the resistor R 13 , and an anode of the Zener diode ZD 2 is connected to the minus side output terminal 2 b of the rectification and output adjustment circuit 2 through a resistor R 15 . The anode of the Zener diode ZD 2 is also connected to a base of an NPN transistor TR 3 having an emitter connected to the minus side output terminal 2 b , and a collector of the transistor TR 3 is connected to the base of the transistor TR 2 . The gate of the MOSFET F1 is connected to a connection point of the resistors R 9 and R 10 . The transistors TR 2 and TR 3 , the diode D 8 , the Zener diode ZD 2 , the capacitors C 1 and C 2 , and the resistors R 9 to R 15 constitute a load driving switch control circuit 9 . The control circuit 9 performs control to provide a drive signal to a load driving switch 8 and turn on the load driving switch when the AC generator 1 generates the output and a voltage across the load 6 is equal to or lower than a set value, and stop the provision of the drive signal to the load driving switch 8 and turn off the load driving switch when the voltage across the load 6 exceeds the set value.

The set value of the voltage across the load 6 is lower than the target value (for example, 14 V) of the voltage across the battery 4 . The set value of the voltage across the load 6 is set by the resistors R 13 and R 14 and the Zener diode ZD 2 . The set value of the voltage across the load is preferably as low as possible (for example, 12 V) within a range that allows driving of the load.

In the load driving switch control circuit 9 , the transistor TR 2 constitutes a drive signal supply switch 9 A that receives a control signal (a base current in this example) through the diodes D 11 to D 13 by the output of the AC generator 1 and thus conducts, and provides a drive signal to the load driving switch 8 .

The transistor TR 3 constitutes a control signal bypass switch 9 B that bypasses the control signal from the drive signal supply switch (the transistor TR 2 ) to interrupt the drive signal supply switch when turned on.

Further, the resistors R 13 to R 15 , the capacitor C 2 , and the Zener diode ZD 2 constitute a control signal bypass switch control circuit 9 C that keeps the control signal bypass switch 9 B turned off when the voltage across the load 6 is equal to or lower than the set value, and turns on the control signal bypass switch 9 B when the voltage across the load 6 exceeds the set value.

In the battery charging control device shown in FIG. 2 , when the generator 1 starts generation of power, the output of the generator 1 is rectified by the full-wave rectifier circuit constituted by the diodes D 1 to D 6 and supplied to the battery 4 to start charging of the battery 4 . The voltage across the battery is kept around the target value by the above described operation.

When the generator generates the output, the base current (the control signal) is provided to the transistor TR 2 through the diodes D 11 to D 13 , and thus the transistor TR 2 conducts. When the transistor TR 2 conducts, an output voltage of the rectification and output adjustment circuit 2 and the voltage across the battery 4 cause a current to pass through the resistors R 9 and R 10 and the transistor TR 2 , and a voltage drop occurs at both ends of the resistor R 9 . Thus, a potential of the gate of the MOSFET F1 becomes lower than a potential of the source, and a drive signal is provided to the MOSFET F1. Thus, the MOSFET F1 is turned on, thus when the load driving switch 5 is in on state, the output voltage of the rectification and output adjustment circuit 2 and the terminal voltage of the battery 4 cause a current to pass through the MOSFET F1, the load driving switch 5 , and the load 6 to drive the load 6 .

When the voltage across the load 6 exceeds the set value lower than the target value of the battery voltage, the Zener diode ZD 2 conducts, thus a base current passes through the transistor TR 3 , and the transistor TR 3 conducts. When the transistor TR 3 conducts, the base current of the transistor TR 2 is bypassed from the transistor TR 2 , and thus the transistor TR 2 is turned off to stop the provision of the drive signal to the MOSFET F1 (the load driving switch 8 ). Thus, the MOSFET F1 is turned off to stop energization to the load 6 . When the voltage across the load 6 becomes equal to or lower than the set value, the Zener diode ZD 2 is turned off and the transistor TR 3 is turned off to restart the supply of the base current to the transistor TR 2 , and the transistor TR 2 is turned on. This causes the provision of the drive signal to the MOSFET F1 to restart, and thus the MOSFET F1 is turned on to restart the energization to the load 6 . Repeating these operations can keep the voltage across the load 6 around the set value lower than the target value of the voltage across the battery.

As described above, the load driving switch 8 that can perform on/off control is inserted between the battery 4 and the load 6 of the battery, and the load driving switch control circuit 9 is provided that performs control to turn on the load driving switch 8 when the AC generator 1 generates the output, and the voltage across the load 6 is equal to or lower than the set value sufficiently lower than the target value of the voltage across the battery 4 , and turn off the load driving switch 8 when the voltage across the load 6 exceeds the set value. Thus, when the current passing through the load 6 increases, the voltage applied to the load 6 can be limited to as low a value as possible to generate surplus power, and thus the surplus power can be used for charging the battery 4 to reduce the risk of the battery running out.

In the above described embodiment, the rectification and output adjustment circuit 2 of generator output short-circuit type is used, but the present invention may be applied to the case where a control rectifier circuit that has a bridge in which one of lower and upper sides is formed by diodes, and the other is formed by thyristors, full-wave rectifies an output of a generator and supplies a charging current to a battery when the thyristors are turned on, and stops the supply of the charging current to the battery when the thyristors are turned off is used as a rectification and output adjustment circuit.

In the above described embodiment, the magneto generator is used as the generator 1 , but the present invention may be applied to the case of using an excitation type AC generator. When the excitation type AC generator is used, a control rectifier circuit is used as a rectification and output adjustment circuit.

In the above described embodiment, the three-phase AC generator is used, but the present invention may be, of course, applied to the case of using a single-phase AC generator.

In the above described embodiment, the load driving switch 8 is constituted by the MOSFET, but the load driving switch 8 may be constituted by a switch element that can be controlled on/off, and the load driving switch 8 may be constituted by other switch elements such as a bipolar transistor. Although a preferred embodiment of the invention has been described and illustrated with reference to the accompanying drawings, it will be understood by those skilled in the art that it is by way of examples, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined only to the appended claims.