DE2600181A1 - PALLET TRUCK - Google Patents

Description

Coventry, Warwickshire, UK

¹¹ pallet trucks "

Priority: 7 January 1975, Great Britain, No. 565/75

The invention relates to a lift truck such as a forklift truck. In particular, it deals with the control of a hydraulic System that is used for functions such as fork lift, (horizontal) laying out or tilting.

The invention makes a lift truck with one of a pulse controlled Motor driven hydraulic pump available, which is characterized in that for pulse control a thyristor is provided, which can be bridged by means of a switch, and that the switch is operated by a solenoid (cylinder coil) is operable, which is coupled to the control electrode of the thyristor such that the thyristor conducts when the solenoid "is excited or de-excited.

In a further development of the pallet truck according to the invention that is

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Solenoid designed so that a counter electromotive force induced when the solenoid is de-energized to Maintaining the conductive state of the thyristor can be used is. This prevents the switch contact tips from opening or closing under load.

Another embodiment of the invention provides a lift truck with a hydraulic pump that is driven by a motor, which is pulse-controlled over part of its speed range, which is characterized in that for pulse control a thyristor is provided which can be bridged by means of a switch, and that a delay circuit is provided is such that the motor is accelerated under the pulse control up to about half full speed before the Switch is closed in order to connect the motor to a power supply battery independently of the thyristor.

The invention and its advantages are described below with reference to an embodiment. In the accompanying drawing show:

1 is a circuit diagram of a control circuit for a lift truck;

2 shows a schematic view of a lifting control; and

3 is a schematic view of an extension or tilt control.

Fig. 1 shows a hydraulic pump motor 11, which is provided with a pulse generation network including a main thyristor 12 is coupled. A switch 13 that can be actuated via a button enables a battery B to be operated under the control of the pallet truck

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or forklift driver to connect to the circuit or from to separate this .; . ^

An oscillator module card 14 and a control module card 15 are used for regulating the lifting, spreading and tilting functions »

Fig. 2 shows a lift control lever 16 attached to a pivot pin 17 is attached to pivot a plate 18 and thereby operate microswitches LS1 and LS2, which are shown in FIG are.

Fig. 3 shows a deployment or extension control lever 19 which is attached in the same way as the lever 16 in Fig. 2 and is used to actuate microswitches LS3 and LS4, which also are shown in FIG.

The pump motor, which is connected in parallel to a flywheel diode 20, is connected to battery B via a short-circuiting switch S1 tied together. With this switch, the main thyristor 12 (which is connected in series with a blocking diode 22) can be bridged. A commutation or polarity reversal thyristor 23 and an auxiliary diode 24 are connected in parallel with the main thyristor 12.

The oscillator card 14 is connected to the in connection with FIGS. and 3 mentioned switches LSI to LS4 connected ..

The hydraulic control circuitry is designed to allow a choice of three motor speeds, two of which by setting potentiometers R37.1 and W2 to either

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desired value can be preset. The third and highest speed is obtained by closing the short-circuiting one Switch S1, which briefly bridges the main thyristor 12 and the blocking diode 22. The motor can now run at full battery voltage run without any diode voltage drops in the circuit. The main feature of the shorting switch S1 is in that it is opened and closed under no-load conditions so that wear on the contact tips is minimal is held. The control wiring for the microswitch LS1 to LS4 is connected in such a way that it is ensured that the motor 11 during horizontal extension or tilting operations cannot run at high speed. If a polarity reversal error occurs, a safety circuit switches a supply line switch L1 off when either a (horizontal) laying out or a tilting is carried out. The lifting process (lifting or Lowering) is not influenced.

The pulse train speed of the hydraulic motor 11 becomes controlled by the oscillator module 14. A resistor of 47KiI is connected between a terminal 10 and a terminal 7, to allow about 1 second for the acceleration deceleration up to full speed. The pulse train speed of the oscillator changes with the voltage value at a terminal 2, and this voltage is preset by RV1 and RV2. The microswitches LS1 to LS4 are shown in Fig. 1 in the rest position, which means that terminal 2 has a resistance of 22 -ft is kept at a low potential of O V. In this condition the pulses are prevented from a terminal 9 to the main thyristor control electrode 25 and consequently the engine is at a standstill. The commutation or reversing thyristor 2 3

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continuously receives pulses at a predetermined interval set by the oscillator module 14.

To start the system and set the required pulse values, the button switch is turned to position 3 and then released to return to position 2 under spring tension. This causes the power line switch coil 26 to be energized at 36V and then kept energized at 15V when the key switch is in position 2. A low hold voltage is used to ensure that switch L1 can be de-energized quickly when a thyristor TH1 set in module 15 and thus the coil is bridged by a short-circuit connection. When the contacts of switch L1 are closed, voltage is applied to the main hydraulic power circuit. If the main thyristor is switched off, the motor stops. If the key switch is in position 2, a supply line is established that supplies the oscillator module 14 and the hydraulic i-iodule 15 with 10 V in a stabilized form. The oscillator begins to operate and pulses are supplied to the commutation thyristor 23, which is switched on and remains switched on until the commutation capacitor is fully charged to battery voltage. The '! Otcr power circuit is now ready for operation. On actuation of the switch LS1 (this means the position for slow, centimeter-precise stroke) with a setting of RV1 and RV2 as above , terminal 2 of the oscillator is kept at a low potential of 0 V via the resistor of 22 S1 and the input Pulses from the oscillator are blocked. If the resistor RV2 is now turned clockwise, the voltage at the connection increases

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on until, when the voltage is above 0.5 V, the one-pulse blocking canceled and the main thyristor is switched on. The motor now begins a pulsating step movement, whereby the Pulse transmission time varies between 1 msec ON / 80 msec OFF and 80 msec ON / 1 msec OFF. The resistance RV2 is now set in such a way that that a predetermined time is reached for an unloaded stroke. When the lifting lever 16 is released, the microswitch closes LSI and the resistor RV2 is bridged by a short circuit, which means that the terminal 2 of the oscillator 0 V drops' and the motor with its impulsive step movements stops. When either the unloading lever or the rocker arm is operated, the microswitches LS3 and LS4 work simultaneously. counter LS3 allows the original voltage drop across the resistor To feed RV2 to the oscillator connection 2 and therefore the motor runs at a slow lifting speed. If now the resistance When RV1 is turned counterclockwise, the voltage at terminal 2 and the motor pulse train speed decrease is humiliated. The final position of RV1 is determined by the desired movement time of either the extend or tilt function of a special vehicle. When the lever is released, the resistor RV2 is short-circuited again bridged and the motor sets its pulse-like step movement a. Low lift, extend and tilt speeds are now set and no further setting is required.

Actuation of the short-circuiting switch

In order to maintain the quick lift state, in which the short-circuiting Switch S1 closes, the following procedure is selected. Of the Lift lever 16 is pulled to the full extent. The microswitch LS1

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(to which the position of the pulse-like slow stroke is assigned) closes first and the motor runs up to the previously described state. When the lever is withdrawn quickly, microswitch LS2 closes almost simultaneously with switch LS1. Provided that LS4 is closed (when tilting or extending are not used), a terminal 7 of the hydraulic card 15 is supplied with 48 volts. This initiates a timing period of 600 msec before the short-circuiting switch S1 closes. This period of time allows the motor to accelerate under pulsed conditions up to about half full speed before the shorting switch S1 closes, so that the motor starting currents are kept at a reasonably low value. A timing network in the hydraulic module 15 operates as follows. The thyristor TH2 prevents the 48 V at terminal 7 from reaching the short-circuit switch coil 28. Thyristor TH2 is switched on when the capacitor C5 is charged to about 5.5 V via R19 in the period of 600 msec. Thereafter, a 5, 1-V Zener diode D9 conducts and supplies current to the control electrode of the thyristor TH2, so that this thyristor is turned on. The charge in the capacitor C5 can then discharge via a resistor R20, a diode D10 and the thyristor TH2. When the thyristor TH2 is switched on, current flows through the coil 23 and the resistor 29 to the hydraulic module connection 6 and via a diode D7 and a transistor T7 to 0 V. This causes a series of processes:

Ca) A diode D5 in the hydraulic module causes a setting Level detector reference point of 3.9 V. In the normal state there is a Transistor T5 biased via a resistor R16, a diode D6, the terminal 5 and through the resistor 29, the terminal 6, the

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Diode D7 and transistor T7 connected to O V. The on-state of the transistor T5 allows a transistor T6 and the transistor T7 to be switched on. Transistors T3 and T4 are in the off state held because the voltage at terminal 5 is low. When the timing circuit is actuated, the voltage starts to rise across coil 28 and resistor 29. The transistor T4 is turned on and then the transistor T3 becomes strong controlled conductive state, the terminal 4 drops to 0.5 V and is held there. Any "off" pulse from the oscillator connector 6 cannot reach the commutation thyristor control electrode 30 and instead the pulses are passed through transistor T3 delivered on the hydraulic card 15. When the voltage across the resistor 29 has reached about 3 V, the transistor T5 biased in blocking and the transistors T6 and T7 v / ground switched off, i.e. they lock. All of the current through resistor 29 is now fed into the main thyristor control electrode discharged and the thyristor becomes highly conductive and remains conductive. S1 takes about 80 msec to close after the coil has been excited. Since the main thyristor 12 for about 90% was fully conductive at this time, the ilotor / could run at almost full speed run up before the contacts of S1 close. In this way the contacts close in a practically no-load condition. The order has been chosen so that the control electrode lock of the commutation thyristor 23 and the activation of the main thyristor cause the plate A of the Konunutationskondensators 27 with respect to the plate B is negative, so that the polarity reversal or commutation of the main thyristor 12 takes place when the original order is reversed. If the switch LS1 is released, the thyristor TH2

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switched off in the hydraulic card, i.e. this thyristor blocks, and the energy supply to the coil 28 is interrupted. The inductance of the coil 28 causes a voltage reversal at its terminals and drives current through resistor 29. The voltage across this resistor retains its original polarity, namely via the main thyristor control electrode 25 and back to the coil 28 via the diode D8 in the hydraulic module. All of this leads to one Decrease in the voltage observed across resistor 29. After 80 msec of this voltage drop, the contact tips open of switch S1. However, there is still current in the main thyristor control electrode 25 driven so that this thyristor conducts when its anode voltage begins to positive v / ground, and zv / ar with an amount equal to its own voltage drop plus the voltage drop of the blocking diode 22 is. The motor current v / ird is diverted from flowing into the short-circuiting switch Ξ1 Main thyristor 12. In this way, the flashover or arcing on the short-circuiting switch is kept to a minimum. If the If the voltage across the resistor 29 falls further, the transistor T5 is switched on again, i.e. it becomes conductive when the connection reached about 3V. The transistors T6 and T7 v / ground again and bring the terminal 6 to a low voltage, so that the permanent By controlling the Ilaunt thyristor 12 is ended and this is again subjected to the oscillator control. The voltage across resistor 29 drops further, and at about 1.5 V the transistors T4 and T3 are switched off, i.e. they block, so that clamping or fixing the "off" pulses from the oscillator card 14 is repealed. The next time an "off" pulse is supplied by the oscillator card, the commutation thyristor will ignite 23 and switches the main thyristor 12 in a normal manner

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the end. When the lever 1G is completely released, you will hear "On" pulses open completely and the motor 12 stops. When the slow stroke position is selected with the switch LS1 remains open, the system performs impulsive step movements at the preset value.

Safety circuit

The safety circuit on the hydraulic card 15 contains a 150 msec unijunction timing circuit that is fed by the anode of the main thyristor 12 is controlled via the terminal 2. Whenever the main thyristor 12 blocks, its anode voltage is 48 V, so that diodes D1 and D2 conduct through a resistor R1 and keep a transistor T1 conductive. In this state, a capacitor C1 cannot charge through a resistor R4, to switch a unijunction or unipolar transistor T2. When transistor T2 conducts, a pulse is sent to thyristor TH1 which brings terminal 3 to 0.5 V. If a switching error occurs, the main transistor 12 is fully conductive and its r.node voltage is only 1 V. The transistor T1 vräre biased into the off state, which allows charging of the capacitor C1, which leads to the firing of the thyristor TH1. if the tilting or spreading or feed function is used, if a fault occurs, terminal 3 is connected to line switch coil 26 through switch LS4 and it would short it, so that the coil L1 is de-energized and the power circuit is disconnected. If no safety circuit were provided and the motor 11 would run at high speed, the movement time would the advancing or "tilting" functions of the cart or vehicle excessively fast, and when the vehicle is fully loaded,

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a dangerous condition could develop, especially when the load is at full height. If an error occurs, if a hub is performed, it does not mean a dangerous one State and the lifting process continues to put the load in be able to raise or lower a safe position before the fault has to be corrected. When the short-circuit switch S1 closes, Terminal 2 sees that the main thyristor 12 is in error state and could turn it off. However, a blocking circuit composed of diodes D4, D3 and a resistor R7 is at connection 5 led out to the point at which the resistor 29 is monitored, so that the safety circuit closes can distinguish between a real mistake and a real mistake State in which the main thyristor 12 is intentionally by the Short circuit switch SI is bridged by a short circuit. The switching timing of 150 msec has been chosen to cover approximately two full cycles of the oscillator module (i.e. 2 χ 80 msec). The locking speed is not important because the oil flow through the even when the engine is running fast Operator who controls the particular rocker arm or feed lever in question can be moved, controlled. . .

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Claims (3)

Claims 1 J pallet truck rait one driven by a pulse-controlled ilotor hydraulic pump, characterized / that a thyristor (12) is provided for the pulse control, which can be bridged by means of a switch (S1), and that the switch (S1) is actuatable by a solenoid (26) which is coupled to the control electrode (25) of the thyristor (12) in this way is that the thyristor (12) conducts when the solenoid (26) is energized or de-energized. 2. Lift truck according to claim 1, characterized in that the solenoid (26) is such that a counter-electromotive Force induced when the solenoid (26) is de-energized to maintain the conduction of the thyristor (12) can be used. 3. Pallet truck with a hydraulic pump that is driven by a motor that has a part of its speed range is impulsgssteuert, characterized in that a thyristor (12) is provided for the pulse control, which by means of a switch (S1) can be bridged, and that a delay circuit (15) is provided in such a way that the motor (11) accelerates under the pulse control up to about half full speed before the switch (S1) is closed in order to connect the motor (11) to a power supply battery (B) independently of the thyristor (12). 4 _9-lift truck according to claim 3, characterized in that 609328/0286 the delay circuit has a thyristor (TH2) with a control electrode which is coupled to an input electrode of the thyristor via a capacitor (C5), the capacitor (C5) is provided for switching over the control electrode of the thyristor or its ignition after a delay time that depends on the charging speed of the capacitor (C5) depends. 609828/028 6 4H Blank page