DE2854587A1 - CONTROL CIRCUIT FOR A CONTACT - Google Patents

Description

Munich, the ~. \ - 'C i ^s · "78-S-3114

TOWMOTOR CORPORATION

Control circuit for a contactor

The invention relates to a control circuit for an electromagnetically operated contactor, having one or more pairs of contacts and an electromagnet is energized which ι by direct current so as to cause the closing of the contacts.

Such contactors are designed in such a way that they provide a nominal operating voltage for the solenoid coil but will attract at a slightly lower applied voltage. When the voltage applied to the coil after tightening the contactor is reduced, the contacts remain closed until the voltage applied Drop-out voltage reached, which is noticeably lower than the pull-in voltage.

Such a contactor can be used to supply the supply from a battery to an electric motor turn on, such as a motor that drives a hydraulic pump in a battery-operated vehicle, such as a forklift.

Many electrically operated forklifts have hydraulic systems for raising and lowering the forks and for tilting the mask with respect to the support frame. The hydraulic one Fluid pressure is thereby generated by such a hydraulic

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pump generated. The drive motor is started and stopped by closing and opening microswitches, whereby the Microswitches can be controlled by opening and closing a hydraulic control valve. These switches energize the contactor. The hydraulic control valve normally has a spring centering assembly to return the valve spool to its neutral position when the Control lever is released in an operating position.

One of the problems with this arrangement is that the control valves have a tendency to bend sufficiently beyond running to cause the switch contacts and thus the power contactor to settle for a Close for a fraction of a second and then open again. Typically DC motors draw a high peak current during initial start-up, and reopening of the contactor occurs during a time where the peak current flows through the contactor contacts. This causes intense arcing, which is a results in rapid burning of the contacts. A quick opening and closing of the switch contacts is also common caused by the driver, who actuates the control valve with quick short lever movements to open the fork or move the mast in small increments or sections for precise positioning.

Another problem is that when the battery discharges during normal vehicle use the battery terminal voltage will decrease, if a high current stress occurs on the battery, for example When starting the engine under high load conditions, the terminal voltage to a very low value can fall off.

Since the contactor coil supply is also taken from the battery, this, low terminal voltage can

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not be sufficient to hold the contactor under heavy loads. Thus, when the load is applied, so the contactor begins to drop out, but when the contacts open the load is removed from the battery and the terminal voltage increases instantaneously. This in turn causes the contactor to be attracted, whereby in turn, the load is applied to the battery. This effect is repeated over and over again. When the contacts open and Continuing to close in this manner during heavy DC loads can create two extremely serious situations enter. The contacts can weld together, making the motor no longer controllable. If on the other hand the contacts continue to open and close cyclically, so they burn as a result of the arcing that occurs, and the contactor can be destroyed.

It is therefore desirable to prevent the undesired opening and closing the contacts of a direct current operated electromagnetic To avoid contactor.

Summary of the invention. The invention aims to address one or more of the above problems to solve.

According to the invention a control circuit for a contactor is provided which has at least one pair of contacts and an actuating device which can be excited by direct current under the control of a switch, to cause the contacts to close. The control circuit has a switching device to the actuator coil to be connected in series with the switching device and in parallel with the contacts. A first timing device actuates the switching device to energize the actuating device at a predetermined time after Closing the switch. A second timing device prevents a second operation of the switching device to at a point in time after the lapse of another predetermined period of time.

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Further advantages, goals and details of the invention emerge in particular from the claims and the description of an exemplary embodiment with reference to the drawing, which schematically shows the control circuit according to the invention .

As shown in the drawing, a contactor has an electromagnetic coil 1 and contacts 2 and 3, the can be closed by energizing the coil 1. A pump motor 4 is connected between a positive battery lead 5 and a End of a fuse 6. The other end of fuse 6 is Connected to contact 2 via contacts 7 and 8 of a switch 9. A shunt resistor is parallel to contacts 7 and 8 10 switched. Finally, the contact 3 is connected to the negative battery line 11.

The voltage between lines 5 and 11 is normal any voltage suitable for the motor 4, for example a selected nominal or nominal voltage between 36 and 80 volts.

A line 12 is preferably with a tap on the Battery or connected to line 5, so that line 12 is at a voltage of, for example, +36 volts opposite line 11 is located. The line 12 is connected to a contact 13 of a switch 14 which is a microswitch can be and simultaneously with the opening and closing of a hydraulic control valve, not shown, can be actuated. The other contact 15 of the switch 14 is with a clamp 16 of the electromagnetic coil 1 connected.

A control circuit designed according to the invention is shown within the dashed rectangle 17. The circuit has switching means, such as a thyristor 18, the anode of the same via a diode 19 with the other terminal 20 of the coil 1 is connected. The cathode of the thyristor 18 is connected to a line 21 which has a Diode 22 is connected to line 11. The ver

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connection point between the anode of the diode 19 and the terminal 20 of coil 1 is connected to contact 2 via a diode 23. A polarity reversal circuit (freewheeling circuit) from a series circuit from a diode 24 and a resistor 25 is connected to the coil 1 to the controllable breakdown of each to allow electromagnetic field.

The gate driver circuit for the thyristor 18 includes one Capacitor 26, one end of which is connected to the thyristor via a diode 27, while the other end is connected Line 21 is, the connection point between the capacitor 26 and the anode of the diode 27 is via a resistor 28 and a diode 29 on contact 15 of switch 14.

The collector-emitter circuit of a transistor 30 is connected to the capacitor 26. A network of a resistor 31 connected in series with a parallel circuit of a capacitor 32 and a resistor 33 has one end at the junction of diode 29 and resistor 28, and the other end to line 21. The base of the transistor 30 is at the connection point of resistor 31 and the parallel connection of capacitance 32 and resistor 33.

A power-up suppression circuit from one Capacitor 34 with resistor 35 connected in parallel lies between the gate and the cathode of thyristor 18.

In operation, the switch 14 is initially open, so that no current flows through the coil 1 and the switching of the transistor 30 is also not aroused. When a valve lever (not shown) coupled to switch 14 is operated, so that the switch 14 closes, the capacitor 26 charges from the direct current line 12 via the diode 29 and the resistor 28 is charged, and the capacitor 32 is charged via the diode 29 and the resistor 31.

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After a predetermined time of for example 10 milliseconds - determined by the values of capacitor 26 and resistor 28 - the voltage on the capacitor 26, which is applied to the thyristor gate, becomes the ignition potential of the thyristor Reach 18. The thyristor will thus conduct, which causes the electromagnet 1 to close the contacts 2 and 3 conclude. The time required to reach the ignition potential can be increased by having the The size of the capacitor 26 or the resistor 28 is increased, and downsizing can be achieved by reducing it the value of capacitor 26 or resistor 28.

The delay before triggering the thyristor is provided in such a way that that any inherent bouncing (bouncing) of the switch 14 is terminated before the solenoid current his Flow through contacts 13 and 15 begins. Through this it eliminates the harmful arcing that would occur at the contacts if they were to move quickly with flowing Electromagnetic current could open and close. This also eliminates voltage switch-on processes that are described in the coil 1 would then be induced if repeated interruptions of the coil current occur due to contact bouncing could.

The closing of contacts 2 and 3 requires a considerable time, for example 50 milliseconds after the thyristor 18 has ignited. Closing these contacts lowers the voltage across the thyristor 18 to a level that is through the forward voltage of the diode 23 and the voltage drop is determined on the closed contacts. The thyristor therefore switches itself off because this low voltage does not sufficient to keep the thyristor switched on.

The values of the resistors 31 and 33 and of the capacitor are selected in such a way that the capacitor 32 moves more slowly charges than capacitor 26. By this construction, capacitor 26 charges and ignites the thyristor before the capacitor 32 charges and turns the transistor on

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switches, and switches off the thyristor. Reached after a predetermined time of, for example, 25 milliseconds the voltage on capacitor 32 has a level sufficient to cause transistor 30 to conduct. The values of resistors 28 and 31 are chosen so that the potential of the collector of transistor 30 to, for example 0.2 volts then drops when the transistor is fully conductive. This sets the gate of the thyristor 18, so that then, if contacts 2 and 3 reopen immediately after closing, thyristor 18 cannot conduct to them again to cause it to close. This definition (clamping) remains on the thyristor gate or gate until the switch 14 is open and for a sufficient period of time 50 milliseconds, for example, has passed thereafter, so that the capacitor 32 via the resistor 33 on can discharge a voltage level at which transistor 30 turns off.

Let us now consider the operation of the circuit in the event of a severely discharged battery. Closing the contacts 2 and 3, thereby connecting the motor 4 to the battery, causes the battery voltage to drop to a low one Level. If this level is so low that the voltage on line 12 is less than the dropout voltage of the contactor, so the contacts 2 and 3 open and interrupt the circuit of the contactor coil 1. The determination is made already at the gate of the transistor 18, so that even if the line 12 is at zero volts when the contacts 2 and 3 drops, the thyristor cannot conduct again when the contacts are opened again.

In summary, the control circuit described above has a number of advantages over known contactor control circuits on. Arcing of the contactor contact is prevented, a condition that will then occur would if the contacts were to close and open quickly under a heavy DC load. The time constant the capacitor 26 and associated components

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prevents the thyristor from firing up to a predetermined time after the switch is closed, and thus the electromagnet current is prevented from flowing flows through contacts 13 and 15 until any bouncing of these contacts has ceased during closing. The arcing of the contacts during the closing of the switch 14 is therefore limited and the repeated opening and closing of contacts 2 and 3 is prevented.

In summary, the invention thus provides a control circuit for a contactor that has a pair of contacts 2 and and an actuator coil 1, which is below the control of a switch 14 is operable to cause the contacts to close. The control circuit sees a temporary path for energizing the coil 1 and a permanent path through the contacts 2, 3. The control circuit delays the excitation of the coil for a preselected time to stop the switch contact bouncing 13, 15 to allow. The control circuit prevents re-establishment of the temporary path for a preselected one Time span after closing contacts 2, 3.

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Claims (11)

PATENT CLAIMS Control circuit for a contactor with at least one pair of contacts (2,3) and an actuating coil (1), which by direct current under the control of a Switch (14) can be excited to cause the contacts (2,3) to close, characterized by Switching means (18) for coupling the actuating coil (1) in Series with the switching means (18) in parallel with the contacts (2,3), first time control means (26) for actuating the switching means and energizing the actuating coil (1) a predetermined one Time span after closing the switch (14) and for the controllable coupling of the actuating coil (1) in series with the contacts (2,3) and second time control means (3O) for preventing a second actuation of the switching means (18) until another actuation has elapsed predetermined time period. 2. Circuit according to claim 1, characterized in that the switching means has a thyristor (18) with a gate exhibit. 3. A circuit according to claim 1 and / or 2, characterized gekt eichnet that the first timing means (26) means to apply a trigger signal to the gate of the thyristor (18), and wherein the second timing means (30) Have means to remove the trigger signal after a time sufficient to trigger the thyristor (18) to have caused. 4. Circuit according to one or more of the preceding claims, in particular claim 2, characterized in that that the first time control means (26) have a first capacitor (26) which is subsequently to the Closing the switch (14) charges, with the voltage on first capacitor (26) acts as the trigger signal for the gate of the thyristor (18). 909826/0813 ORIGINAL INSPECTED 5. Circuit according to one or more of the preceding Claims, in particular claim 4, characterized in that the second time control means (30) is a semiconductor switching device (30) which can be actuated to short-circuit the first capacitor (26) and to remove the trigger signal. 6. Circuit according to one or more of the preceding claims, in particular claim 5, characterized in that that the semiconductor switching device is a transistor (30) with a base and a collector-emitter circuit, which latter is connected to the first capacitor (26), and wherein the second timing means comprise a second capacitor (32), which is subsequently charged when the switch (14) is closed and controls the base voltage of the transistor (30). 7. In a control circuit with a power supply with first and second terminals (5,11), a switch (14) with first and second terminals (13,1 ^r >, the first terminal (13) with the first terminal {■ - ■} the power supply is connected, and with a contactor with an actuating coil (1) and first and second contacts (2,3), wherein a first end (16) of the coil (1) of the second terminal (15) of the switch (14 ) and a second end (20) of the coil is coupled to the first contact (2), and finally the second contact (3) is connected to the second terminal (11) of the power supply, characterized by a thyristor (18 ) with an anode, cathode and a gate, in series with the coil and parallel to the contacts (2,3), first means (26) connected to the gate for the automatic controllable ignition of the thyristor (18) and for the excitation of the Coil (1) and to close the contact (2,3) at a preselected time after closing the switch (14), second means (23) for switching off the thyristor (18) as a result of the closing of the contacts (2,3) and third means (30) 'for fixing the gate and for preventing a second ignition of the thyristor (18) for one 98982S / 0813 3 285A587 preselected time after initial ignition. 8. Control circuit according to claim 7, characterized in that that the first means comprises a capacitor (26) coupled to the switch (14) and gate, the Charging of the capacitor (26) when the switch is closed (14) follows and a voltage signal is developed across it, and the thyristor (18) then ignites when the gate does Receives voltage signal and this reaches a selected size. 9. Circuit according to claim 7, characterized in that that the second means comprise a diode (23) with an anode and a cathode, the anode with the second End of the coil (1) and the cathode with the first contact (2) is connected. 10. A circuit according to claim 7, characterized in that the third means is a transistor (30) with an emitter, Have base and collector, the emitter or collector being coupled to the gate and the transistor (30) being coupled to the gate Thyristor gate potential sets or clamps at a voltage level below the ignition voltage level of the Thyristor (18) when the transistor (30) is switched on. 11. Circuit according to claim 9, characterized by a capacitor (32) coupled at one end to the base of the transistor and the second terminal (15) of the switch (14) and further coupled at the other end to the second terminal (11) the power supply, the capacitor (32) being when the switch (14) is closed and a voltage signal arises thereon, the transistor (30) as a result this voltage signal is then switched on when it reaches a preselected value. 9 0 9 8 2 6/0813