JP2598664Y2 - DC motor protection device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor protection device for protecting a DC motor driven by a rectified output of a magnet type AC generator driven by an internal combustion engine from overvoltage.

[0002]

2. Description of the Related Art In recent years, in the field of agricultural machines such as agricultural chemical sprayers, self-propelled watering machines and tea-cutters, it has become necessary to drive complicated mechanisms. Instead, a magnetic AC generator driven by an internal combustion engine and a DC motor driven by the rectified output of the generator are provided, and the working machine is driven by the DC motor in many cases.

[0003] Magnet type AC power generation driven by an internal combustion engine
Output voltage varies almost in proportion to the engine speed.
You. The rotation speed of the DC voltage is almost proportional to the power supply voltage.
You change. Therefore, the magnet driven by the internal combustion engine
Work with DC voltage obtained by rectifying the output of the AC alternator
When a DC motor with a load as a load is driven,
The rotation of the DC motor is controlled by adjusting the rotation speed of the fuel engine.
Control the fuel supply to the internal combustion engine.
By adjusting the rotation speed of the working machine can be adjusted.
Wear.

FIG. 3 shows a structural example of an agricultural machine using a DC motor as a drive source. In the figure, 1 is a vehicle body having a driving wheel 2 and a driven wheel 3, 4 is a DC motor, 5
Is a gear box in which an output shaft is connected to the drive wheel 2. A pulley 6 attached to the output shaft of the DC motor 4 and a pulley 7 attached to the input shaft of the gear box 5 are connected by a belt 8. Reference numeral 9 denotes an engine generator including an internal combustion engine and a magnet type AC generator driven by the internal combustion engine. The output of the engine generator 9 is rectified and supplied to the DC motor 4. Reference numeral 10 denotes a working machine, and the output of the electric motor 4 is transmitted to the working machine 10 via the gear box 5. The work machine 10 is, for example, a pesticide spraying machine including a tank for storing the pesticide and a pump for feeding the pesticide in the tank.

FIG. 4 shows the configuration of a conventional DC motor drive circuit used in the field of agricultural machinery. In FIG. 4, reference numeral 11 denotes a generator coil of a magnet generator, and 12 denotes a bridge connection of diodes D1 to D4. Full-wave rectifier,
C1 is a smoothing capacitor connected to the output terminal of the rectifier 12, and a DC voltage obtained at both ends of the capacitor C1 is applied to both ends of the armature winding of the DC motor 4. Normally, a circuit is provided for adjusting the magnitude of the drive current given to the DC motor 4 to adjust the rotation speed of the motor.
Illustration of this circuit is omitted.

[0006]

Since the output voltage of a magnet type alternator increases as the number of revolutions increases, when a DC motor is driven by a drive circuit as shown in FIG. When the rotation speed increases and the rotation speed of the generator increases, the voltage applied to the DC motor increases, the input voltage of the motor becomes excessive, and the armature winding may burn out. The purpose of the present invention is to protect the motor by preventing the input voltage of the DC motor from becoming excessive when the rotation speed of the engine is increased and the rotation speed of the magnet AC generator is increased. An object of the present invention is to provide a protection device for an electric motor.

[0007]

SUMMARY OF THE INVENTION The present invention provides a DC motor protection device for protecting a DC motor driven by a DC voltage obtained by rectifying the output of a magnet type AC generator driven by an internal combustion engine from overvoltage. The protection device according to the present invention includes an energization control switch provided to turn on and off the drive current of the DC motor, a voltage detection circuit that detects an output voltage of the generator, The on / off duty ratio (the ratio of the on-period to the sum of the off-period and the on-period) of the energization control switch is set according to the output of the voltage detection circuit so as to prevent the input voltage of the motor from becoming excessively high with the rise. And a switch control circuit for changing.

[0008]

With the above construction, when the rotational speed of the magnet type alternator increases and its output voltage increases, the on / off duty ratio of the switch means becomes small and the drive current supplied to the motor decreases. Engine speed .
When the number of rotations of the generator is increased by raising the voltage, the input voltage of the motor is prevented from becoming excessively large, thereby preventing the armature winding from burning.

Therefore, according to the present invention, the armature winding
Without causing the risk of burnout of the internal combustion engine.
Adjust the number of rotations of the motor by adjusting the number of turns.
By simply adjusting the fuel supply to the internal combustion engine,
The rotation speed of the electric motor can be adjusted. I
Therefore, it is the same as when the load is driven directly by the internal combustion engine.
The load can be driven with the same driving feeling.

[0010]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a power generating coil of a magnet type AC generator driven by an internal combustion engine, 12 denotes a full-wave rectifier, and C1 denotes a smoothing capacitor. These are the same as those shown in FIG. Reference numeral 13 denotes a constant voltage power supply such as a three-terminal regulator to which the voltage between both ends of the capacitor C1 is input, and C2 denotes a power supply capacitor connected between the output terminals of the constant voltage power supply 13,
A DC constant voltage VD obtained between both ends of the power supply capacitor C2 is used as a power supply voltage of a switch control circuit described later.

In the present invention, an energization control switch 14 connected in series with the armature winding 4a of the DC motor 4 to turn on and off the drive current of the DC motor, and detects the output voltage of the magnet type AC generator. And a switch control circuit 16 for controlling an energization control switch.

The energization control switch 14 comprises a field-effect transistor FET whose source is grounded. When a voltage equal to or higher than a predetermined level is applied to the gate of the FET, the FET is turned on and the armature winding is turned on. A driving current is supplied to 4a. D5 is a flywheel diode connected to both ends of the armature winding 4.

The voltage detecting circuit 15 includes a smoothing capacitor C
1 comprises a series circuit of resistors R1 and R2 connected to both ends of the resistor 1, and outputs a voltage detection signal Vb having a magnitude corresponding to the output voltage of the magnet type alternator to both ends of the resistor R2.

The switch control circuit 16 comprises a triangular wave signal generation circuit 17, a voltage comparator CP1, and resistors R3 and R4. The input voltage of the non-inverting input terminal (+ terminal) of the comparator CP1 is inverted. During a period in which the input voltage of the terminal (− terminal) is higher than the input voltage of the terminal (− terminal) and the potential of the output terminal of the comparator CP1 is at a high level, the field effect transistor FET conducts and a current flows through the armature winding 4a. .

The triangular wave signal generation circuit 17 includes a voltage comparator C
P2, resistors R5 to R9, a diode D6 and a capacitor C3. A constant frequency that changes between voltages V _{+ H} and V _{+ L} as shown in FIG. Is obtained. In the triangular wave signal generation circuit 17, when the potential of the output terminal of the comparator CP2 is at a high level,
2, the voltage V _{+ at} the non-inverting input terminal changes the power supply voltage VD to
V _{+ H} [= R6VD / (R5
+ R6)], while the capacitor C3 is connected to the resistor R8
And R9, and the voltage Va across the terminals rises at a constant gradient. Voltage V across capacitor C3
When a becomes higher than V ₊ (Va> V ₊ ), the comparator CP
2 is low, the voltage V _{+ at} the non-inverting input terminal of the comparator causes VD to pass through resistor R5 and resistors R6 and R7.
V _{+ L} [= R7 · R6]
· VD / {R7 · R6 + R5 (R7 + R6)}], and the electric charge of the capacitor C3 is reduced by the resistor R9 and the comparator CP2.
Discharge through the output stage. This allows the capacitor C
The voltage Va at both ends of 3 decreases with a constant slope. The voltage Va across the capacitor C3 is lower than V _{+ L} (Va <
V _{+ L} ), the output of the comparator CP2 goes high again, and the charging of the capacitor C3 is restarted. Since these operations are repeated, the voltage Va across the capacitor C3 becomes a voltage having a triangular waveform as shown in FIG.

The voltage comparator CP1 outputs the triangular wave voltage Va.
Is compared with the output voltage Vb of the voltage detection circuit 15, and
> Vb, the high level state is maintained and Va
A rectangular wave signal Vq [FIG. 2 (B)] which maintains a low level state during a period of ≤Vb is output. Switch means 1
The field effect transistor FET constituting the transistor 4 conducts while the rectangular wave signal Vq is at a high level, and supplies a drive current to the motor 4.

When the output voltage of the magnet-type alternator is low and the voltage detection signal Vb is low, the period during which the rectangular wave signal Vq is at a high level is long, so the period t1 during which the FET is in the cut-off state is short. The conduction period t2 becomes longer. Therefore, the ON / OFF duty ratio τ [= t2 / (t1 + t2)] of the switch means 14 is increased. At this time, since the voltage applied to the armature winding 4a is low, the power applied to the armature winding 4a does not become excessive.
The armature winding does not burn out. When the rotation speed of the generator increases and its output voltage increases, the voltage detection signal V
Since b rises, the period during which the rectangular wave signal Vq is at a high level becomes shorter, and the on / off duty ratio of the switch means 14 becomes smaller.

As described above, in the present invention, the input to the electric motor is always kept in an appropriate range in order to control the on / off duty ratio of the switch means to be reduced as the output voltage of the generator increases. When the number of revolutions of the generator increases and its output voltage becomes excessive, it is possible to prevent the input of the electric motor from becoming excessive and prevent the armature winding from burning.

In the above embodiment, a field effect transistor is used as a switch element constituting the switch means 14. However, the switch element may be any element that can be controlled on and off, and a bipolar transistor or the like may be used. .

[0020]

As described above, according to the present invention, the switch means for turning on / off the energization of the motor is provided to prevent the input voltage of the motor from becoming excessive with the increase of the output voltage of the generator. As described above, since the on / off duty ratio of the switch means is changed according to the detected value of the output voltage of the generator, the input voltage of the motor is set to an appropriate range regardless of the rotation speed of the generator. Can keep
There is an advantage that it is possible to prevent the input voltage of the motor from becoming excessive when the output voltage of the generator rises due to an increase in the rotation speed of the engine and the armature winding thereof is burned.

Therefore, according to the present invention, the armature winding is
Rotation of the internal combustion engine without risk of burnout
Adjusting the number of rotations of the motor by adjusting the number
Just adjust the fuel supply to the internal combustion engine.
In, you can adjust the rotational speed of the electric motor, the internal combustion engine
Drive the load with the same driving feeling as driving the load more directly.
Can be turned over.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2A is a waveform diagram showing a triangular wave signal and a voltage detection signal used in the embodiment of FIG. FIG. 2B is a waveform diagram showing a waveform of a rectangular wave signal used in the embodiment of FIG.

FIG. 3 is a schematic configuration diagram showing an example of a configuration of an agricultural machine as an example of an application of the DC motor to which the protection device of the present invention is applied.

FIG. 4 is a circuit diagram showing a drive circuit of a conventional DC motor.

[Explanation of symbols]

 Reference Signs List 4 DC motor 4a Armature winding 14 Conduction control switch 15 Voltage detection circuit 16 Switch control circuit 17 Triangular wave signal generation circuit CP1 Voltage comparator

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02P 5/00-5/26 H02P 7/00-7/34 H02P 1/18 H02P 9/30 H02P 9/48

Claims (1)

(57) [Scope of request for utility model registration] 1. A DC motor protection device for protecting a DC motor driven by a DC voltage obtained by rectifying an output of a magnet type AC generator driven by an internal combustion engine from an overvoltage, the drive current of the DC motor An energization control switch provided to turn on and off, a voltage detection circuit for detecting an output voltage of the generator, and an input voltage of the motor becoming excessive with an increase in an output voltage of the generator. And a switch control circuit for changing an on / off duty ratio of the energization control switch in accordance with an output of the voltage detection circuit so as to suppress the current.