JPS61147704A - Chopper circuit protecting device of electric automobile - Google Patents

Abstract

PURPOSE:To prevent a chopper circuit form overheating by restricting an input voltage of the circuit when the temperature of the circuit becomes the prescribed value or higher. CONSTITUTION:Since a bimetal switch 29 is closed when a power transistor 17 for forming a chopper circuit is the prescribed temperature or lower, a control transistor 25 is interrupted. Accordingly, a pulse signal in response to an input voltage Vin from an accelerator circuit 18 is applied to the transistor 17. When the temperature of the transistor 17 becomes the prescribed value, the switch 29 is opened to conduct the transistor 25. Therefore, an input voltage Vin of an operational amplifier 23 reduced to lengthen the OFF time of a pulse signal output from a PWM modulator 35. Thus, the heat of the transistor 17 is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a chopper circuit protection device for an electric vehicle, and more particularly to a chopper circuit protection device for an electric vehicle that prevents overheating of a chopper circuit for speed control.

(Prior art) Conventionally, in electric vehicles, the conductivity of the motor current is changed using a chopper circuit according to the output of the accelerator output circuit.
Some devices are designed to control the speed of an electric motor.

This chopper circuit is equipped with a switching element such as a transistor or a thyristor as disclosed in Japanese Patent Application Laid-Open No. 53-114113, and the conductivity of the motor current is changed by the switching operation of this switching element.

Since motor current flows through this switching element, it generates heat when driving uphill for a long time.

Therefore, when the temperature of the chopper circuit exceeds a predetermined value,
Measures are taken to prevent overheating by stopping the electric motor.

(Problem to be Solved by the Invention) By the way, stopping the electric motor while driving is undesirable as it causes discomfort to the passengers, so it is possible to prevent overheating of the chopper circuit without stopping the electric motor and with a simple structure. There is a need for a means to do so.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a chopper circuit protection device for an electric vehicle that prevents the chopper circuit from overheating without stopping the electric motor.

(Function) In this invention, the temperature of the chopper circuit that controls the speed of the electric motor is detected by the temperature detection means, and when the temperature exceeds a predetermined value, the protection circuit is driven to adjust the input voltage of the chopper circuit to the accelerator opening. are regulated regardless. This reduces the conductivity of motor radio waves in the chopper circuit, thereby reducing the motor current flowing through the chopper circuit and preventing overheating.

At this time, since the motor radio waves are reduced to prevent overheating, the drive of the electric motor is not stopped, so the first rider does not feel uncomfortable.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a perspective view of an electric golf car showing an example of an electric vehicle to which the present invention is applied, FIG. 2 is a side view thereof, and FIG. 3 is a plan view thereof.

In the figure, reference numeral 1 denotes an electric golf car as an example of a one-seater electric vehicle used on a golf course, and this electric golf car l is provided with one front wheel 2 and two rear wheels 3. ing. * Mounted in the center of the body are an electric motor 4 that drives the rear wheels 3, two batteries 5 that are the power source for the electric motor 4, and a control device 6 that controls the electric motor 4 and the like. and,
A riding platform 7 is provided between the rear wheels 3, and loading platforms 8 for loading golf trucks are provided on both sides of the vehicle body.

The front wheels 2 are turned by a steering shaft 9, and this steering shaft 9 is supported by a support IO supported by the rear wheels 3. A handle 11 is located above the steering shaft 9.
is fixed, and on the right side there is an accelerator 12 that drives the electric motor 4.
is provided. A support frame 13 for supporting the northern part of the golf pack is provided on both upper sides of the support lO.

Further, a main switch 14 is provided at the center of the handle 11 to enable the electric motor 4 to be driven.

FIG. 4 is a schematic circuit diagram of the drive device of this electric golf car, and FIG. 5 is a circuit diagram showing an embodiment of the present invention.

A relay 15 is connected to a drive circuit composed of a battery 5 and an electric motor 4 that utilizes the magnetic flux of a permanent magnet. This relay 15 consists of an a contact 15a and a coil part 15b, the coil part 15b is connected to the main switch 14, and the a contact 15a is connected in conjunction with the opening and closing of the main switch 14.
It is designed to open and close.

Further, a chopper circuit 16 that changes the conductivity of the motor current is connected to the drive circuit. This chopper circuit 1
6 is built in the control device 6, and by switching a power transistor 17 forming a part thereof,
The speed of the electric motor 4 is controlled by changing the conductivity of the motor current supplied from the battery 5. This chopper circuit 16 switches the power transistor 17 according to the output of the accelerator output circuit 18.

The accelerator output circuit 18 is composed of a potentiometer,
It is connected to the accelerator 12 by a wire, and its output is controlled according to the opening degree of the accelerator 12.

A flywheel diode 19 is connected in parallel to the electric motor 4, so that when the chopper circuit 16 cuts off the motor current, the energy of the electric motor 4 is released.

The chopper circuit 16 and the accelerator output circuit 18 are the fifth
It is configured as shown in the figure. That is, the potentiometer 20 constituting the accelerator output circuit 18 is connected to the resistor 21. It is connected to a non-inverting input terminal of an operational amplifier 23 via a variable resistor 22. A resistor 24 and a control transistor 25 are inserted between the resistor 21 and the resistor 22 with their emitters grounded. A divided voltage of a resistor 26 and a resistor 27 is input to the base of the control transistor 25, and the resistor 26 is connected between a resistor 28 inserted between the power supply voltage Vcc and ground and a bimetal switch 29 serving as a temperature detection means. ing. The bimetal switch 29 is provided near the power transistor 17 that generates heat, and this bimetal switch 17
is normally open to maintain the base voltage of control transistor 25 at ground potential and to cut off control transistor 25.

The input voltage V i n at this time is V i n = (RO/Z) * Given error at Vcc.

Z indicates the total resistance value of the potentiometer 20.

RO is a resistance between A and B, and when the accelerator is fully open, the input voltage Vin=Vcc.

When the temperature of the power transistor 17 rises and reaches the set value, the bimetal system 2 opens and the power supply voltage VCC
is applied to the base of the control transistor 25 to make it conductive;
The input voltage Win is designed to decrease.

At this time, even when the accelerator is fully open, the input voltage Win=[resistance 24/(resistance 21 + resistance 24)]·Vcc, and the input voltage Vin does not rise.

The input voltage Vin output from the potentiometer 20 is further divided by a variable resistor 22 and a resistor 30, and is input to a non-inverting input terminal of an operational amplifier 23. The variable resistor 22 is grounded via a capacitor 31, and the capacitor 31 is charged with the input voltage Win at a predetermined time constant.

A diode 32 and a resistor 33 are connected between the variable resistor 22 and the capacitor 31 and between the variable resistor 22 and the resistor 21, and when the input voltage Tin decreases, the capacitor 31 is connected to the non-inverting input terminal of the operational amplifier 23. In order to prevent voltage from being applied, the charge in the capacitor 31 is transferred to a diode 32,
It is designed to escape to the potentiometer 20 side via the resistor 33. Therefore, the resistance value of the resistor 33 is the variable resistor 2
The resistance value is set smaller than the resistance value of 2.

A power supply voltage vCC is applied to the inverting input terminal of the operational amplifier 23 via a resistor 34, and a part of the output voltage is returned to the inverting input terminal via a resistor 35. By applying this negative feedback to the operational amplifier 23, accurate amplification can be obtained. The output of the operational amplifier 23 is input to a pulse width modulation circuit (PWM modulation circuit) 36, and a pulse signal of a predetermined width is obtained from the analog input signal of this PWM transformation circuit 36. Pulse signal is power transistor 1
7, and performs a switching action at time intervals according to the pulse signal.

Next, the operation of this embodiment will be explained.

When the temperature of the power transistor 17 is below a predetermined value, the bimetal switch 17 is closed, so that the power supply voltage Vcc is not applied to the base of the control transistor 25 and is cut off.

Therefore, a predetermined input voltage Vin is applied from the accelerator circuit 18 to the non-inverting input terminal of the operational amplifier 23.

By the way, when the accelerator is operated and the potentiometer 20 is moved to the power supply side at the time of starting, an output voltage corresponding to the accelerator opening is outputted and inputted to the non-inverting input terminal of the arithmetic wm unit 23. At this time, the input voltage Win is charged to the capacitor 31 at a predetermined time constant, and the input voltage Win increases in accordance with this charging. Since the output of the operational amplifier 23 increases in accordance with this rise in the input voltage Win, the off interval of the pulse signal from the PWM modulation circuit 36 becomes narrower. The power transistor 17 performs a switching operation in response to this pulse signal, gradually increases the motor current supplied to the electric motor 4, and the drive of the electric motor 41!4 does not correspond to the speed of the accelerator opening, but is controlled by the capacitor 31. It depends on the input voltage V in of the operational amplifier 23.

After the vehicle starts, the speed of the electric motor 4 is controlled in accordance with a predetermined input voltage V in obtained by operating the accelerator.

When the temperature of the power transistor 17 rises to a predetermined value, the bimetal switch 29 opens and the power supply voltage Vcc is applied to the base of the control transistor 25.
Control transistor 25 becomes conductive. Therefore, the input voltage Win of the potentiometer 20 does not increase even when the accelerator is fully opened, and the input voltage V in of the operational amplifier 23 decreases, and its output signal also decreases.
6. The off time of the output pulse signal becomes longer. The power transistor 17 performs a switching operation in accordance with the on/off state of this pulse signal to reduce the conductivity of the motor current, so that heat generation of the power transistor 17 is suppressed.

At this time, the conductivity of the motor current is reduced, but since a constant motor current is supplied, even if the speed of the electric motor 4ta decreases, it will not stop, and the power transistor 1
7. Drive in a state that suppresses heat generation.

In the above embodiment, a chopper circuit using a power transistor 17 was explained, but it may also be a chopper circuit using a thyristor, etc. The temperature detecting means may be a thermoelectric element that converts heat into electricity, or a resistivity that changes depending on the temperature. The switch function may be performed using a temperature sensing element that changes the temperature.

Further, in the above embodiment, the input voltage of the chopper circuit is controlled, but the output of the operational amplifier may be controlled. When the sensor circuit reaches a predetermined temperature or higher, the protection circuit is activated to reduce the conductivity of the motor current. The speed is reduced without stopping the motor. Therefore 1
Overheating of the chopper circuit can be prevented with a simple structure without causing discomfort to passengers.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an electric golf car showing an example of an electric vehicle to which the present invention is applied, Fig. 2 is a side view thereof, Fig. 3 is a plan view thereof, and Fig. 4 is a drive system of this electric golf car. FIG. 5 is a schematic circuit diagram showing an embodiment of the present invention. 4...Electric motor 5...Puffteri 16...
Chopper circuit 1B... Accelerator circuit 25... Control capacitor 29... Pimetals inch

Claims (1)

[Claims] An electric vehicle equipped with a chopper circuit that controls the speed of the motor by changing the conductivity of a motor current according to the output of an accelerator output circuit, further comprising a temperature detection means for detecting the temperature of the chopper circuit, the temperature detection means A chopper circuit protection device for an electric vehicle that drives a protection circuit to reduce the conductivity of motor current when the chopper circuit reaches a predetermined temperature or higher.