JPS6129201B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for an electric vehicle, and particularly to a protection circuit for a large-capacity electric vehicle.

For electric vehicles, for example, forklifts, 10
If the capacity is relatively large, such as the ton class, the traveling motor will be considerably large and its output will also be large. Based on this, a shaft for transmitting the rotational force of the motor,
The power transmission mechanism such as gears is also large-sized. However, even if the transmission mechanism is made large, there is a risk that the transmission mechanism will be damaged if a large current flows through the travel motor and a large torque is suddenly generated. The point in time when a large current flows occurs frequently when the short circuit contact of the chopper circuit is closed and the full voltage is applied to the motor.

In other words, Figure 1 shows the general main circuit of an electric car, where 1 is a DC power supply, 2 is a running motor, field winding F, and a flywheel diode.
It has DF ₁ , DF ₂ and switching contacts MR and MF. 3 is a chopper circuit, and this chopper circuit 3 includes a contact 4 of an electromagnet 4 that is excited when the depression angle of an accelerator (not shown) exceeds a certain angle.
a are connected in parallel. That is, 5 is a key switch, 6 is an accelerator switch that closes when the depression angle of the accelerator exceeds a certain value, and _S1 is a thyristor, which are connected to the electromagnet 4 in series.

Therefore, running control of an electric vehicle is performed by controlling the conductivity of the chopper circuit 3 using the output of an oscillator (not shown) that outputs according to the depression angle of the accelerator. is further depressed to close the contact 4a and short-circuit the chopper circuit 3. Therefore, full voltage will be applied to the electric motor 2, and the electric car will run at maximum speed, but if the load is reduced for some reason, such as when a wheel falls into a groove while running, the electric car will run at maximum speed. When the voltage increases, the chopper circuit 3 for voltage regulation is inactive since the contact 4a is closed, and the load current and torque increase rapidly, causing damage to the transmission mechanism. For this reason, in the past, the transmission mechanism was made larger to increase its strength, but there is a limit to increasing the size, and when using a large-capacity electric motor, damage accidents are inevitable depending on the operating conditions. There are problems.

In view of this, the present invention is designed to suppress the large current by immediately opening the contacts connected in parallel to the chopper circuit and shift to chopper operation when a large current flows, thereby eliminating the above-mentioned drawbacks. The purpose of this invention is to provide a control circuit that provides a controlled control circuit.

An embodiment of the present invention will be described in detail below with reference to FIG. In FIG. 2, the same symbols as in FIG. 1 indicate the same names or corresponding parts.

7 is a current detection circuit, and this current detection circuit 7 consists of a detection resistor R for detecting the load current, reference voltage resistors R ₂ and R ₃ , input resistors R ₄ and R ₅ , and a comparator 8. Reference numeral 9 denotes a constant voltage circuit, which is composed of a resistor R ₆ and a zener diode ZD ₁ , and the resistor R ₆ and the zener diode ZD ₁ are connected in series between the connection point of the key switch 5 and accelerator switch 6 and the negative pole side of the power supply 1. It is connected.

In the current detection circuit 7, the current detection resistor R ₁
are connected in series to the contact 4a, and resistors R ₂ and R ₃ are connected in parallel to the zener diode ZD ₁ . Also, one input terminal 8a of the comparator 8 is connected to the connection point between the resistors R2 and R8 via the resistor _R4 , and the other terminal 8a is connected to the connection point between the resistors _R2 and _R8 .
b is connected to the connection point between the contact 4a and the resistor _R1 via the resistor _R5 .

S ₁ is a first switching element, here a thyristor, and _{the accelerator switch 6, the electromagnet 4 and the thyristor S 1 constitute} a closing circuit 10 for the contact 4a. R ₇ , capacitor C ₁ , zener diode ZD ₁ and resistor R ₈ . 12 is a dropout circuit of the contact 4a, which connects the electromagnet 4 and the thyristor S ₁
resistor R ₉ and the second connected in series circuit with
The switching element here consists of a series circuit of thyristors S ₂ and a commutating capacitor C ₂ connected between the anodes of each thyristor S ₁ and S ₂ .
And D ₁ is a diode connected between the output terminal of zener diode ZD ² and the anode of thyristor S ₂ .

The operation of the circuit of the present invention configured as described above will be explained.

When moving the electric vehicle forward, by turning on the key switch 5 and depressing the accelerator, the electromagnet for contact MF (not shown) is energized, and the changeover switch is activated.
The MF is switched to the position shown by the dotted line, and at the same time, the oscillator (not shown) is also driven, the chopper circuit 3 is operated, and voltage is applied to the electric motor 2, thereby causing the electric vehicle to run. Gradually increase the depression angle of the accelerator, and by depressing the accelerator beyond a certain value, the accelerator switch 6 of the closing circuit 10 is closed, and the key switch 5 - accelerator switch 6 - electromagnet 4 resistor R ₇
Charging current flows into capacitor _C1 through.
The charging voltage from this charging is the Zener diode
When the zener voltage value exceeds the zener voltage value of ZD ₂ , it is applied to the gate of thyristor S ₁ via the zener diode ZD ₂ , thyristor S ₁ becomes conductive, and the electromagnet 4 is energized, so that its contact 4a is Injected.
As a result, the chopper circuit 3 is short-circuited, and the electric vehicle runs at maximum speed. Note that when the thyristor _S1 is conductive, the capacitor _C2 of the falling circuit 12 is charged with the illustrated polarity.

In such a state, if the load increases for some reason and the proportional value of the load current detected by the detection resistor _R1 exceeds the reference value previously set in the comparator 8, the comparison is performed. The device 8 generates an output, and the output signal fires the thyristor _S2 . Capacitor by conduction of thyristor S ₂
The charge stored in _C2 is discharged and the thyristor
_S1 is made non-conductive, contact 4a is forcibly separated, and the operation is shifted to chopper operation. Here, when the thyristor S ₂ is turned on and the thyristor S ₁ is turned off, even if the accelerator switch 6 remains on, the capacitor C is turned off unless the thyristor S ₂ is turned off by the action of the diode D ₁ . ₂
The electromagnet 4 is not charged and the electromagnet 4 is not turned on again.

In electric vehicles, a method is generally adopted in which an overcurrent limiting circuit is provided in order to limit the motor current under heavy load even during chopper operation, and the conductivity of the chopper circuit is limited. The contact 4a is forcibly separated to shift to chopper operation, and at the same time, the conductivity of the chopper circuit 3 is set to such a level that overcurrent is limited by the overcurrent limiting circuit.

Figure 3 shows an example of an overcurrent limiting circuit, where 7a is a current detection circuit, and this current detection circuit 7a is provided in the current path l ₁ through which the motor current flows when the contact 4a is closed. The current detector consists of a transformer CT, for example, and resistors R ₁₀ , R ₁₁ connected to the secondary winding W of the transformer CT. Current detection circuit 7
The anode of the diode D ₂ is connected to the connection point of the resistors R ₁₀ and R ₁₁ of a, and the resistor R ₁₁ is connected to the diode D ₂ .
Capacitor _C3 is connected in parallel through.
Further, diode D ₂ is connected to the base of transistor Q via diode D ₃ connected in the forward direction. Reference numeral 13 denotes an oscillation circuit, which normally emits a signal that defines the conductivity of the chopper circuit in response to an accelerator signal supplied to the base of the transistor through a diode _D4 .

In the overcurrent limiting circuit configured as described above, when the current flowing through the current path _l1 increases for some reason, the current detection signal is transmitted from the current detection circuit 7a through the diode _D3 to the transistor Q in accordance with this increased current. supplied to the base. This biases transistor Q and supplies its output signal to oscillator 13. Oscillator 13 supplies an overcurrent limit signal to the chopper circuit in response to a signal from transistor Q.

As explained above, in the present invention, when the contact point for applying full voltage to the traveling motor by short-circuiting the chopper circuit is short-circuited, the current of the traveling motor is detected and the current increases, causing the motor to When a torque that affects the strength of the shaft or gear is generated, the contact point is separated and a transition is made to a chopper operation. Therefore, according to the present invention, the power transmission mechanism can be made smaller and less expensive, and excellent effects such as prevention of damage and accidents and improved reliability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram of a general electric vehicle control circuit, FIG. 2 is an electrical wiring diagram of an electric vehicle protection circuit according to an embodiment of the present invention, and FIG. 3 is an electrical wiring diagram of an overcurrent control circuit used in the present invention. DESCRIPTION OF SYMBOLS 1...DC power supply, 2...Travel motor, 3...Chopper circuit, 4...Electromagnet, 4a...Contact, 6...
...Accelerator switch, 7...Current detection circuit, 10
...Contact closing circuit, 12...Contact falling circuit.

Claims (1)

[Scope of Claims] 1 Voltage from a DC power source is adjusted by a chopper circuit and applied to the traveling motor to control the traveling speed, and the chopper circuit is short-circuited by a contact to apply the full power supply voltage to the traveling motor. In the electric vehicle, the electric vehicle includes a contact closing circuit that closes the contact, a current detection circuit that detects an increase in the current flowing through the traveling motor when the contact is closed, and a detection signal of the current detection circuit. a contact drop-off circuit that causes the contact to fall off; a series circuit consisting of a first circuit of the series circuit;
a capacitor connected in parallel to the first switch element via a resistor, and an ignition circuit that conducts the first switch element when the charging voltage of the capacitor reaches a predetermined value; , a comparator that outputs an output when the input voltage exceeds a set value when the current flowing through the contact reaches a predetermined value, and the dropout circuit connects the first switch to the first switch via a commutating capacitor. a second switch element connected in parallel to the element and made conductive by the output of the comparator; and a second switch element connected between the connection point of the resistor and capacitor of the ignition circuit and the connection point of the commutating capacitor and the second switch element. A protection circuit for an electric vehicle, comprising a diode that prevents charging of the commutating capacitor when the second switch element is conductive.