DE3422485A1 - Method and device for limiting the current of an electric motor - Google Patents

Abstract

Method and device for limiting the current of an electric motor in a temperature-compensated manner, which electric motor is intended in particular for driving hand tools, chain saws and the like. Two actual-value sensors are provided, a first current sensor which is connected as a series shunt to the motor connections and a second temperature actual-value sensor which detects the temperature of the electric motor only indirectly and is thermally coupled to the current sensor. Both sensors are located in the cooling-air flow produced by the electric motor. On reaching a critical motor temperature, which is detected only indirectly on the basis of the behaviour of the current actual-value sensor, the current consumption of the electric motor is reduced (suddenly) to predetermined values via the temperature sensor and its influence on the electronic drive circuit for current regulation.

Description

BSG-Schalttechnik GmbH & Co. KG,
Wilhelmstrasse 8, 7460 Baiingen 1

Method and device for limiting the current in an electric motor

State of the art

The invention is based on a method and a device for limiting the current of an electric motor the genus of the main claim or the first device claim. Current limits in electric motors are Known in many ways - they are used, for example, for a soft start, especially with larger motors at the moment of switching on the circuit is not interrupted by external fuses, or they are generally used to protect the motor from excessively high currents, for example when it is heavily loaded is braked. In this context, it is known to design such current limiting means as bimetal switches, as was often the case in the past, or indirectly or directly those pulled by the engine To detect current in each case by means of sensors and to apply the actual value of the current to corresponding control circuits and to regulate the electricity as a whole.

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Bimetal switches are comparatively well suited for current limitation, because they detect the amount drawn by the motor Electricity direct as they can be connected in series with the motor and open the current path when they are by themselves are sufficiently heated by the current flowing through them, but the problem with bimetal switches is the need to having to install additional hardware with the overall system's otherwise ever smaller dimensions and the fact that bimetallic switches either switch off the current completely or switch it on completely can, in any case, can only be switched between two positions and the display of function progressions or exclude continuous regulations. There may be delays with bimetal switches, since these must be designed as over-center switches in order to avoid a creeping approach, which suddenly change to the other switching state.

Also known is the arrangement of a so-called series shunt with only a very low resistance value to the motor, with the current regulation in the sense of a phase control being carried out on this at the same time. The voltage recorded across the series shunt serves as a measure of the current flowing through the motor and is usually using prefabricated, integrated modules for controlling a thyristor or triac is used, which is also in the motor circuit. However, these known current controls have the disadvantage that they must be based on predetermined limit values, for example also a target current curve profile, and hence the full utilization of the engine power under special

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Exclude circumstances, even if this is for the engine in would not be harmful in any way. In other words, the motor current control or motor current limitation relates to their Control process does not adjust the temperature of the engine itself and therefore also regulates the engine output when a full load capacity of the engine is desired, can also be made available by the engine and this, since it is cold, for example, does no harm either.

On the other hand, it is known when controlling electric motors to take their heat balance into account, for example by being adjacent to the engine, but preferably immediately, preferably in the stationary Winding area of the motor corresponding sensors, for example NTC resistors, semiconductors or the like. arranges and its voltage related to the motor temperature used to control engine operation. As a result, the motor can, for example, if a predetermined value is exceeded Temperature value can be completely switched off or you can, if a corresponding motor current control or speed control including phase control is provided to low motor speeds go down to protect the engine.

However, there is the disadvantage of arranging such an NTC pill in the winding area of the motor, for example in that such a sensor reacts very slowly to the actual motor current and the corresponding regulation or the control is actually only switched off or influenced when the engine has become very hot; on the other hand but its control signal is maintained for a very long time because of the large heat capacity of the motor, so that

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the user is prevented for a very long time from to be able to use the engine again, possibly only with reduced power. Temperature controls with NTC pills in the winding area are therefore very sluggish and not acceptable for certain applications of electric motors, for example in chainsaws.

The following statements relate specifically to the use of a temperature compensated according to the invention Current limitation in an electric motor in application to a chainsaw - it goes without saying that the Invention is not limited to this area of application, but any electric motors, in particular those which are used to drive hand tools can be assigned. So, in summary, is the problem a temperature-compensated current limitation in electric motors can be seen in the fact that the motor temperature is basically can only be removed from the winding head, which is better ventilated than other engine parts when the engine is running so the temperature is lower. After switching off the loaded machine, however, the end winding temperature would then be as a result of the accumulated heat rise above the switching point of the associated electronics and that of the electric motor For example, a powered saw stops performing when it is switched on again until it has cooled down can.

It is therefore the task of the present invention to provide a temperature-compensated current limitation for To create an electric motor that reacts quickly on the one hand, but temperature measurements on the electric motor itself mowing unnecessary, but on the other hand ensures that with

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Reaching a specified related motor temperature, the current consumption of the motor to specified current values is withdrawn.

Advantages of the invention

This object is achieved by the method according to the invention with the characterizing features of the main claim and the method according to the invention Device with the characterizing features of the first device claim, wherein the The advantage is that, on the one hand, an intervention in the area of the electric motor to detect its temperature is then not required, but on the other hand a real temperature measurement is made, the the Series shunt effecting current limiting is taken as a model or simulation for the engine temperature response the additional advantages of a quick response both in the event of overuse and in terms of the cooling possibilities is ensured and the entire structure including electronics inexpensive and practical without additional hardware effort, possibly just additional Wiring, is possible. The invention ensures a particularly application-oriented use of electric motors, makes it fully ready for use even for extreme conditions and still guarantees a sufficient one Protection of the electric motor as soon as a certain temperature threshold in the sense of a critical motor temperature is reached is.

In doing so, the invention enables the motor to cool itself effectively, so preferably it will not completely switched off when the critical engine temperature

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achieved in the simulation model of the series shunt to the engine is, but has decreased to a lower threshold value of the current consumption.

From here, the desired, Usually current-limited output of the electric motor is possible because the series shunt cools down Current reduction from relatively quickly and is also in the cooling air flow of the motor. The invention can be compact built up separately on a small printed circuit board and assigned to any electric motors, whereby through appropriate dimensioning, for example, the wire length of the series shunt empirically the data and conditions of the assigned electric motor can be displayed.

A further advantage is that the invention enables the full engine use in any case as long as the Engine is cold; in other words, with appropriate dimensioning of the current and temperature sensor on the one hand and Dimensioning the electronics on the other hand, it is possible as long as full power, also rait maximum allowable Electricity to work as the motor is still sufficiently cool, with the temperature-compensated current limitation after The present invention only intervenes when necessary. This is particularly useful for the area of application of chainsaws, where the motors driving the saw often demand full power will. Finally, if the engine is subjected to a critical load, the invention can continuously, but preferably the performance should be limited so far that the user notices this and the chainsaw is unencumbered so that it quickly returns to idle

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can cool down for further full use. As mentioned, it is beneficial to limit the current when it is cold Machine to the highest possible values so that heavy loads are possible when cold - the machine will warmer, then the current limiting level can be achieved by the thermally active connection with the series shunt Temperature sensor can be shifted accordingly or abruptly to a correspondingly perceptible reduction Performance to be gone.

The invention therefore enables, for example

1. a start-up of an electric motor with (minor) Soft start, so that corresponding household safeguards do not respond;

2. can then for a predetermined period of time, for example 1 to 2 sec. a maximum load capacity can be made available, so that one may blocked chain can tear loose on a chainsaw.

3. This can then be done while the machine is still cold, which the temperature sensor can do reliably detected, with high current limiting values, i.e. with a high load capacity of the electric motor, whereby

4. when the motor has reached a certain temperature (optional) to that extent normal current limitation (for example can be used in numerical values between 16 and 20 A);

5. And finally, when a critical engine temperature is reached, the power consumption can drop to a lower Threshold value, for example 5.5 A, can be withdrawn, so that a safe motor protection starts at the same time fastest cooling of the device.

All of this is possible without a temperature measurement on the engine needs to be done by yourself.

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The measures listed in the subclaims are advantageous developments and improvements of the Invention possible. It is particularly advantageous to design the series shunt to the engine as a free length of wire, with the temperature sensor in the form of an NTC pill is surrounded by one or possibly two turns of the series shunt and is enclosed. Finally, a better thermal coupling can be achieved by adding a drop Achieve casting compound on both sensors, so that in the present invention two are electrically completely independent sensors that are switched from one another are used for combined temperature-compensated current limitation but are spatially in a thermal relationship, with the series shunt sensor being the engine module with respect to the Temperature response and its thermal characteristics simulated.

drawing

An embodiment of the invention is shown in the drawing and is described in the following description explained in more detail. Show it:

Fig. 1 in the form of a detailed circuit diagram, a possible embodiment of a circuit for temperature-compensated Current limitation in an electric motor using a known per se, integrated module and the

Figures 2a and 2b

a practical embodiment of the invention on a true-to-life scale, built on a corresponding PCB, whereby of the discrete components only the integrated module,

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the thyristor and the combination of current and

Temperature sensor are indicated, in plan view and side view.

Description of the exemplary embodiments

The basic idea of the present invention is to use a series shunt current sensor to form an electric motor to simulate a temperature image of the electric motor on the sensor and the current sensor in thermal operative connection to bring with a temperature sensor, which in turn also on the preferably with the help of known, integrated modules (phase control) reacts to the current regulation of the electric motor. There are so two actual value transmitters once for the current flowing through the electric motor and once for the temperature of the Electric motor available, whereby the temperature actual value transmitter is based on the temperature behavior of the current actual value transmitter. In the illustration of FIG. 1, this is indicated by a double-dashed line between the series shunt 11 for Electric motor 10 and the temperature sensor 12 indicated.

Since the current control of, for example, electric motors with the help of integrated modules is known per se is - the integrated module used in the present invention comes from Telefunken and is called U211B available - the circuit does not need to be discussed in detail; with the that The respective hand tool, preferably an electric motor 10 driving a chainsaw, is the triac 12 of the current control electronics connected in series, via a resistor 13 in the control line from the integrated electronic module 14 is applied. This gets it from him

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actual current value of the switching point required for current control P1 via a corresponding resistor 15 fed to one of its connections. An alternating supply voltage of, for example, 220 V passes through the input connections 16a, 16b and a double pole on-off switch 17 on the circuit and is behind a resistor 18 rectified via a diode 19 to supply direct current to the rest of the circuit.

The series shunt 11 is a particularly low resistance - for example with a resistance value between 10 to 20 mCl, preferably 14 mCl - which can be a resistance wire made of constantan. The voltage drop resulting from this series resistor at the circuit point P1 is used by the integrated module 14 to limit the current, whereby it can also cause the soft start to a certain extent. Despite the low resistance value, there is a certain heat loss in the current sensor series shunt 11 and the invention has recognized that this heat loss is an image of the heat characteristics or temperature response of the electric motor that also has additional advantageous properties, at least it can be evaluated as a representative of these, so that the heat loss of the series shunt 11 is used as a reference for the engine temperature.

This is done in detail as shown spatially in Fig. 2a; the soldered into the circuit board 20 or otherwise attached, the current sensor series shunt 11 forming Wire 11 'is wrapped around a wire shown at 21 Winding the pill or the cylindrical body of the temperature sensor 22, which is also, electrically seen separately, stored in the circuit board 20 and fastened accordingly, so also to achieve the electrical connection

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bindings is soldered. It can also be seen, best from the side view of FIG. 2b, that the circuit board 10 carries a heat sink 23 which is in operative connection with the triac 12, which is on this Diverting plate 23 is mounted and its connections via further discrete connecting elements (not shown) finally lead to the electronic control module 14. Since the representation of FIGS. 2a, 2b is viewed as true to scale v / can be grounded, one can also see how little effort is required for a temperature-compensated device according to the invention Current limitation is possible in particular in the sensor area for the actual value transmitter, it being understood that the entire circuit board 20 at a suitable location in the device and in the current generated by the motor by means of its cooling air fan Cooling air flow is arranged.

Not indicated in the illustration of FIG. 2a, but in advantageously carried out, a thermal, improved coupling between the two sensors 11 (11 ') and 21, which consists in putting a drop of potting compound on both of them. Of course it is possible, these two actual value sensors already in a suitable thermal relationship from their manufacture as a pair to be brought together and then coordinated with one another, each only in the corresponding circuit boards to solder.

This is how the thermistor, or the NTC pill, which form the temperature sensor 12, arranged so that there is a thermal information content for it, which corresponds to that which it would receive if it were directly in the area of the motor, for example in its winding head would be arranged.

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On the other hand, as the illustration in FIG. 1 shows, the thermistor is located as a temperature sensor 12 in one Voltage divider, together with a further resistor 24, which, however, only in the illustrated embodiment, a downstream Schmitt trigger 25 switches from a certain temperature. The Schmitt trigger enlarged then in turn via a further voltage divider from the resistors 26a, 26b to a current control input E1 of the electronic integrated module 14 the total resistance for the current control, so that in In this sense, a corresponding current limitation of the motor current can be achieved, which corresponds to the limitation, which is provided when the critical engine temperature is reached.

It goes without saying that the intervention of the temperature sensor 12 in the function of the integrated module 14 can basically be of any quality, for example following a continuous function, whereby initially, i.e. when the sensor is cold and consequently when it is cold Motor, the current limiting values are even raised above the specified setpoints for normal load cases can be and only then does the normal control effect of the current limitation set in, which is then applied with the appropriate Overloading the additional intervention via the temperature sensor 12 results.

The previously mentioned advantage of maximum load capacity for the first 1 to 2 seconds. of the machine operation can either be realized in that for this At the time the constantan wire forming the current sensor in the exemplary embodiment has not yet experienced any heating

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has, so that the associated temperature sensor 12 has a corresponding Prevention signal not yet generated, or you switch to input E1 of the current control module nor an integration capacitor 27, the size of which is then the corresponding time delay of 1 to 2 seconds or each as desired-intended for the use of the full load capacity.

All of the features presented in the description, the following claims and the drawing can both be essential to the invention individually as well as in any combination with one another *

Claims (11)

Dlpt.-lng. Peter Otte 72BO Leonbero Patent Attorney Tiroler Straße 15 1793 / ot / mü 29.05.1984 BSG-Schalttechnik GmbH & Co. KG Wilhelmstr. 8, 7460 Baiingen 1 claims 1.! Procedure for limiting the current of an electric motor, especially ^ - special for driving hand tools, chainsaws and the like., characterized in that, as seen per se, the current drawn by the motor from a Current series shunt detected as the first actual value sensor and influenced in the sense of a current control, simultaneously but the temperature response of the first actual value sensor as a simulation model for the temperature response of the electric motor from a second actual value sensor spatially assigned to the first actual value sensor (NTC resistor 12) is detected and also evaluated for the current control, the first actual value sensor for the current of the electric motor and the second actual value sensor for the indirect detection of the temperature of the Electric motor are arranged in the cooling air flow. 2. The method according to claim 1, characterized in that durcli the temperature control, which also intervenes in the current control of the electric motor, the current limitation when the engine is cold, it is limited to high values to enable heavy loads. / 2 May 29, 1984 '- 2 - 3. The method according to claim 1 or 2, characterized in that when a detected on the current actual value sensor is reached critical motor temperature the current consumption of the motor via the on the electronics of the motor current control Acting temperature actual value sensor (12) is noticeably withdrawn for the user, with the Possibility to keep the electric motor running and cool down quickly and without stress. 4. Device for limiting the current of an electric motor, in particular for driving hand tools, chain saws and the like., characterized in that a first actual value sensor designed as a series shunt (11) to the motor connections for the current of the electric motor and a second actual value sensor (NTC resistor 12) for indirect detection of the motor temperature are provided, which is thermally gekopj with the current actual value sensor (11) is, the two actual value sensors (11, 12) electrical A current control circuit for the electric motor is separate from the temperature-compensated current limitation apply in such a way that the temperature response developed by the current actual value sensor as a simulation model for the temperature behavior of the electric motor (10) is evaluated itself. 5. Apparatus according to claim 4, characterized in that the temperature actual value sensor which indirectly detects the engine temperature (NTC resistor 12) via a threshold value circuit to the control electronics for the Current control is switched. 6. Apparatus according to claim 5, characterized in that the threshold value circuit is a Schmitt trigger (25) is. / 3 1793 / ot / mü 3A22A85 May 29, 1984 - 3 - 7. Device according to one of claims 4 to 6, characterized in that the motor current limiting circuit an integrated module (14) is a triac (12) in the motor circuit after comparing it from Current actual value sensor (11) supplied actual current with specified Controls current setpoints and that the temperature actual value sensor the current setpoint generation is adjusted. 8. Device according to one of claims 4 to 7, characterized in that the target value for the current limitation from a voltage divider connected to the input (E1) of the current control circuit (integrated module 14) (26a, 26b) is generated, for specifying an initially higher current setpoint after switching on a time capacitor (27) is connected in parallel, optionally with further resistors and that the output of the controlled by the actual temperature sensor (12) Schmitt trigger connected to the connection point of the voltage divider setpoint circuit (26a, 26b) is. 9. Device according to one or more of claims 4 to 8, characterized in that the current actual value sensor is a constantan wire of predetermined length and cross section. 10. The device according to claim 9, characterized in that the temperature actual value sensor as an NTC resistor (12) is designed in the form of a resistor or pill and of at least one winding of the actual current value sensor forming constantan wire is tightly surrounded. / 4 1793 / ot / mü 34 2248 May 29, 1984 - 4 - 11. Apparatus according to claim 9 or 10, characterized in that to achieve a thermal coupling the winding of the constantan wire around the NTC resistor or thermistor with one of the two elements comprehensive predetermined amount of potting compound is provided and both arranged in the cooling air flow of the engine are.