JPS62233194A - Radio wave operation type electromotive model car with eddy current preventing apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention provides a radio-controlled electric model car equipped with an overcurrent prevention device using a positive temperature coefficient thermistor that prevents the motor and fixed resistor for speed control from overheating during abnormal use. It is related to.

2. Description of the Related Art Conventionally, this type of radio-controlled electric model vehicle has had a configuration as shown in FIG. In FIG. 7, 1 is a rechargeable battery such as a nickel-cadmium battery. 2 is a motor for running, and 3 is a fixed resistor for speed control.

4 is a speed selector switch, and each contact point is a.

By setting it to positions b, c, and d, high speed, medium speed, low speed, and stopping are possible. Further, the changeover switch 4 is operated by a signal from a transmitter (not shown), and can be controlled remotely by the driver. 5 is the main switch, which is attached to the body of the model car and is operated directly by hand.

Problems to be Solved by the Invention In such conventional radio-controlled electric model cars, if the user accidentally leaves the main switch 5 closed,
The receiver may be activated by various noises or radio waves, and the selector switch 4 may remain in one of the positions a, b, and c. At this time, the car could not move because it was in a stored state, and a large current flowed through the vehicle with the driving motor 2 locked, which could cause the fixed resistor 3 and motor 2 to heat up and burn out.

The present invention solves these problems, and even if current flows while the motor is accidentally locked during abnormal use,
The purpose of this invention is to provide a safe radio-controlled electric model car in which the motor and fixed resistor for speed control will not burn out.

Means for Solving the Problem In order to solve this problem, the present invention provides an overcurrent prevention device constituted by a positive temperature coefficient thermistor and a metal heat sink thermally coupled to the positive temperature coefficient thermistor, and a driving motor. and one or more fixed resistors for speed control, and the power supply, the overcurrent prevention device, and the motor are connected in series by a changeover switch, or the power supply, the overcurrent prevention device, and the motor are connected in series. The fixed resistor for speed control is connected in series.

Effect With this configuration, the current does not necessarily pass through the overcurrent prevention device consisting of a positive temperature coefficient thermistor, regardless of the position of the changeover switch, so when the motor locks and a large current flows, the A large current also flows through the PTC thermistor, and the PTC thermistor itself generates heat due to the current, increasing its own resistance value and reducing the current to prevent burnout of the fixed resistor and motor. In addition, the room temperature resistance value of the positive temperature coefficient thermistor is 1 of the sum of the resistance values of the fixed resistor for speed control.
By setting it to 1/0 or less, the voltage drop due to the overcurrent prevention device is small in normal running conditions, and the influence on running can be reduced.

Embodiment FIG. 1 is a circuit diagram of a radio-controlled electric model car equipped with an overcurrent prevention device according to an embodiment of the present invention, and FIG. 2 is a front view of the overcurrent prevention device used therein.

In FIG. 1, numeral 6 is a nickel-cadmium battery, for example, a battery having a voltage of 7.2 V and constructed by connecting six 1.2 V batteries in series. 7 is a DC motor for running. Two fixed resistors 8 are used for speed control, each having a resistance of 0.3Ω, for example. Reference numeral 9 denotes an overcurrent prevention device consisting of a positive characteristic thermistor, through which the current necessarily passes. 10
is a changeover switch whose position is changed to e, f, g, h by a signal from a transmitter (not shown), and the current flowing to the motor 7 depends on the presence or absence and number of fixed resistors 8 inserted in the circuit. Yes, the speed of the car will be high, medium, slow, or stopped accordingly. Reference numeral 11 is a main switch that is attached to the vehicle body and can be opened and closed directly manually.

In FIG. 2, numeral 12 is a positive temperature coefficient thermistor made of barium titanate semiconductor ceramic, for example, and has resistance-temperature characteristics as shown in FIG. That is, the resistance value is almost constant up to a certain predetermined temperature (switching temperature Ts), and the resistance value increases rapidly when the temperature exceeds that temperature. Reference numeral 13 denotes electrodes provided on both sides of the PTC thermistor 12, which are provided by aluminum spraying, silver paste, or the like. 14 is a heat sink made of aluminum or the like, and is connected to the electrode 1 of the positive temperature coefficient thermistor 12.
It is fixed on three sides with conductive adhesive (not shown) or the like. Therefore, the heat sink 14 also serves as a conductive terminal. Also,
The normal temperature resistance value of the positive temperature coefficient thermistor 12 is set to 0.06Ω, which is less than 1/10 of 0.8Ω (o, 3Ω×2), which is the sum of the resistance values of the fixed resistor 8 for speed control.

In a radio-controlled electric model car with an overcurrent prevention device configured as described above, the main switch 11 is closed and the selector switch 1o is operated using the transmitter to set high speed or medium speed.

When running at low speed and under normal driving conditions, each
0m, 6 people, 6m current is flowing. At that time, the power consumption of the positive temperature coefficient thermistor 12 is 10X10X0.
05,6X6X0.05,5X5xo,ostonashi,6
W, 1.8W, and 1.25W.

Even if the power consumption is, for example, 6W under such normal running conditions, since the heat sink 14 is fixed to the positive temperature coefficient thermistor 12, its temperature will not rise above the switching temperature Ts, and the resistance value will remain low. Since it is maintained, you can continue driving without any problems.

Further, its room temperature resistance value is 0.05Ω, which is very small. If this value is too large, power consumption during normal running will increase, and a large heat sink 14 will be required to keep the temperature below the switching temperature Ts, increasing cost and weight. Therefore, it is better that this value is as small as possible. Furthermore, if this value is large, the voltage applied to the motor 7 will drop even when the vehicle is running at high speed, and the real thrill of driving will be lost. Therefore, the normal temperature resistance value is preferably smaller than the resistance value of the speed control fixed resistor 8, and preferably one-tenth or less.

-Next, with the motor 7 locked, turn the main switch 11
Close the selector switch 10 and set it to high speed or medium speed.

When the speed is low, that is, at positions e, f, and g, currents of 25A, 12μ, and 7μ flow, respectively, and the positive temperature coefficient thermistor 12 self-heats and its temperature rises above the switching temperature Ts, reducing the current. , burnout of the motor 7 and fixed resistor 8 can be prevented.

FIG. 4 is a diagram showing one example of mounting the overcurrent prevention device according to the present invention. In Fig. 4, reference numeral 15 denotes an overcurrent prevention device.If this is installed exposed outside the car body so that it receives wind pressure while driving, even if the shape of the heat sink is small, the positive temperature coefficient thermistor will be affected by the wind pressure while driving. is cooled and its temperature is kept below the switching temperature TS. In addition, when the power is turned on while stopped, there is no wind pressure, and since the shape is small, the temperature quickly rises to the switching temperature Ts or higher, and the current can be reduced. Therefore, the operation of the overcurrent prevention device 16 becomes more sensitive and safer.

FIG. 5 is a configuration diagram showing another example of mounting the overcurrent prevention device according to the present invention. In FIG. 5, reference numeral 16 denotes a positive temperature coefficient thermistor, and metal heat sinks 17 are fixed to electrode surfaces on both sides of the thermistor, constituting an overcurrent prevention device 18. 192L,
19b is a fixed resistor for speed control, which is a prismatic cement resistor. And the above-mentioned overcurrent prevention device 1
8 is closely attached to two fixed resistors 19&, 19b so as to be thermally coupled, and fixed with a metal fixing band 2o. 21 is a film made of insulating resin or the like. In this way, the overcurrent prevention device 18 and the fixed resistor 198
If L and 19b are thermally coupled and fixed, the changeover switch will be set to medium speed and low speed, and the fixed resistor 191L.

When the motor is locked and a large current flows with current flowing through 19b, the heat generated by fixed resistors 19λ and 19b is transferred to overcurrent prevention device 18, and the positive temperature coefficient thermistor 1 is quickly
6 temperature can be increased, the current can be reduced, the operation will be more sensitive and safer.

As mentioned above, FIG. 3 shows the resistance temperature characteristics of the positive temperature coefficient thermistor used in the overcurrent prevention device of the present invention. Some commonly known positive temperature coefficient thermistors made of barium titanate-based semiconductor ceramics have a minimum resistance value TL between the switching temperature 'rs and room temperature. If the overcurrent prevention device is constructed using a device in which the minimum resistance value TL is higher than room temperature, that is, 40'C or higher, the electric model car can start quickly. To start an electric model car, the selector switch is normally set to the high speed position, but at this time the motor rotates rapidly, causing the wheels to spin and delaying the car's actual movement. However, as mentioned above, if an overcurrent protection device is used in which the minimum resistance value TL is higher than room temperature, the moment the switch is turned on, the positive characteristic resistor is at room temperature, so the resistance is high and then it gradually heats up. Therefore, under normal running conditions, the resistance is stabilized at the minimum resistance value TL. Therefore, the current is small at the moment of start, and reaches the maximum current immediately thereafter. As a result, it takes a short amount of time for the motor to reach its maximum rotation speed, resulting in fewer wheels spinning and a faster start.

FIG. 6 is a front view showing another embodiment of the overcurrent prevention device used in the present invention. 22a, 22b.

22.0 and 22d are positive temperature coefficient thermistors, and 23 are electrodes provided on both sides thereof. 24&.

24b is a heat radiator made of aluminum with many holes, and four of the positive temperature coefficient thermistors 222L to 22d are arranged side by side.
The heat sinks 24 and 24b serve as a common electrode, and the positive temperature coefficient thermistors 22a to 22d are fixed with a conductive adhesive (not shown) or the like so as to be connected in parallel. By connecting a plurality of positive temperature coefficient thermistors in parallel in this way, the resistance value of the overcurrent prevention device can be easily lowered. Furthermore, since the size of one positive temperature coefficient thermistor can be made small, it can be thin and have less warpage, which can also lower the resistance value and can have a highly accurate shape.

Effects of the Invention As described above, according to the present invention, the resistance is low during normal running and there is no problem with running, and when an abnormality occurs such as when the motor locks, the resistance increases and the current is attenuated, and the fixed resistor or It can prevent motor overheating and burnout.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a radio-controlled electric model car equipped with an overcurrent prevention device according to an embodiment of the present invention, FIG. 2 is a front view of the overcurrent prevention device used therein, and FIG. A diagram showing the resistance-temperature characteristics of a characteristic thermistor, FIG. 4 is an explanatory diagram showing an example of the mounting position of the overcurrent prevention device according to the present invention, and FIG. 5 is another example of mounting the overcurrent prevention device according to the present invention. FIG. 6 is a front view showing another embodiment of the overcurrent prevention device according to the present invention, and FIG. 7 is a circuit diagram showing a conventional radio-controlled electric model car. 6... Power supply, 7... Travel motor (DC motor for traveling), 8, 19a, 19b...
・Fixed resistor for speed control, 9, 18...
...Overcurrent prevention device, 12, 18, 22a, 22b,
22c. 22d...Positive characteristic thermistor, 14, 17, 2
4a. 24b...Metal heat sink. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure Figure 3 □”υ Break Figure 4 Figure 5 Figure 6 Figure 7

Claims (5)

[Claims] (1) It has an overcurrent prevention device constituted by a positive temperature coefficient thermistor and a metal heat sink thermally coupled to the positive coefficient thermistor, a running motor, and one or more fixed resistors for speed control, A changeover switch connects the power supply, the overcurrent prevention device, and the motor in series, or the power supply, the overcurrent prevention device, the motor, and the speed control fixed resistor are connected in series. A radio-controlled electric model car with an overcurrent prevention device. (2) The radio-controlled electric model car with an overcurrent prevention device according to claim 1, wherein the overcurrent prevention device is installed at a position that receives wind pressure while driving. (3) A radio-controlled electric model car with an overcurrent prevention device according to claim 1 or 2, wherein the overcurrent prevention device is thermally coupled to and attached to a fixed resistor for speed control. (4) A radio-controlled electric model car with an overcurrent prevention device according to claim 1 or 2, wherein the temperature at which the minimum resistance value of the positive temperature coefficient thermistor used in the overcurrent prevention device is 40° C. or higher. . (5) A radio-controlled electric model car with an overcurrent prevention device according to claim 1 or 2, wherein the overcurrent prevention device is configured by connecting a plurality of positive temperature coefficient thermistors in parallel.