CN111602330A - Electronic short-circuit braking device for electric motor - Google Patents

Abstract

The invention relates to a brake device for an electric motor (12), comprising at least one first switching unit (14) having at least two switching elements (16, 18, 20) and at least one second switching unit (22) having at least two switching elements (24, 26, 28), wherein the first switching unit (14) and the second switching unit (22) are electrically conductively connected to the electric motor (12) at least for supplying power. It is proposed that the braking device (10) comprises at least one control and/or regulating unit (30) which is provided to alternately switch all switching elements (16, 18, 20) of the first switching unit (14) and all switching elements (24, 26, 28) of the second switching unit (22) for short-circuit braking of the electric motor (12).

Description

Electronic short-circuit braking device for electric motors

Background technique

DE 10 2014 016 822 A1 has already proposed a braking device for an electric motor, which has at least one first switching unit and at least one second switching unit, the first switching unit having at least two A switching element, the second switching unit has at least two switching elements, wherein the first switching unit and the second switching unit are electrically conductively connected to the electric motor at least for supplying power. In DE 10 2014 016 822 A1, only a part of the switching elements of the first switching unit and a part of the switching elements of the second switching unit are switched alternately for short-circuit braking of the electric motor. In DE 10 2014 016 822 A1, if all switching elements of one of the switching units are switched to short-circuit braking, no alternation between the two switching units occurs.

SUMMARY OF THE INVENTION

The invention proceeds from a braking device for an electric motor, which has at least one first switching unit and at least one second switching unit, the first switching unit having at least two switching elements, the second switching unit The switching unit has at least two switching elements, wherein the first switching unit and the second switching unit are electrically conductively connected to the electric motor at least for power supply.

It is proposed that the braking device comprises at least one control and/or regulating unit, which is provided to alternately switch all switching elements of the first switching unit and the second switching unit for short-circuit braking of the electric motor. All switching elements.

The first switching unit and the second switching unit preferably together form a bridge circuit. In particular, the bridge circuit can be designed as a B-4 bridge, a B-6 bridge, an H bridge, in particular a B2 bridge with freewheeling diodes, or any other bridge circuit that is deemed expedient by a person skilled in the art. The electric motor can preferably be designed as a two-phase electric motor or as a three-phase electric motor. In particular, the first switching unit of the braking device according to the invention for a two-phase electric motor comprises exactly two switching elements. In particular, the second switching unit of the braking device according to the invention for a two-phase electric motor comprises exactly two switching elements. The first switching unit and the second switching unit of the braking device for the two-phase electric motor preferably form a B-4 bridge or an H bridge. The first switching unit of the braking device according to the invention for a three-phase electric motor comprises, in particular, exactly three switching elements. In particular, the second switching unit of the braking device according to the invention for a three-phase electric motor comprises exactly three switching elements. The first switching unit and the second switching unit of the braking device for the three-phase electric motor preferably form a B-6 bridge or an H bridge.

Preferably, the first switching unit and the second switching unit are provided for supplying the electric motor with electrical energy, in particular from an energy source, such as a mains voltage source, a battery or the like, in particular via the switching elements of the two switching units. Preferably, the switching elements of the first switching unit and the second switching unit, in particular the switching elements of both switching units, are provided to electrically connect the electric motor to the energy source, in particular for the current supply. The switching element preferably has at least two states, particularly preferably exactly two states. The switching element in particular inhibits the flow of current through the switching element in the first state when it is not switched on. The switching element in particular allows current to flow through the switching element in the switched second state. Preferably, the control and/or regulation of the electric motor can take place by specifically switching the switching element between two states of the switching element. Preferably, the switching element is switched by the control and/or regulating unit. A “control and/or regulating unit” is to be understood in particular as a unit having at least one control electronics. “Control electronics” is to be understood in particular as a unit having a processor unit and a memory unit and an operating program stored in this memory unit. The control and/or regulation unit can in particular be designed as a microcomputer. Alternatively, it is conceivable that the control and/or regulation unit is designed as an ASIC (application specific integrated circuit), in particular as a gate driver. "Provided" is to be understood in particular as specially programmed, designed and/or equipped. The provision of an object for a specific function should in particular be understood to mean that the object fulfills and/or implements this specific function in at least one application and/or operating state.

For short-circuit braking of the electric motor, the electric motor, in particular the windings of the electric motor, is preferably electrically short-circuited. Preferably, a back electromotive force acts when the motor is short-circuited, which in particular causes a short-circuit current. The short-circuit braking preferably brakes the electric motor for a shorter period of time than by interrupting the current supply to the electric motor or compared to the use of residual energy by reducing the PWM control signal (pulse-width-modulated control signal), in particular until the motor stops. Preferably, short-circuit braking is performed alternately by, in particular at least substantially simultaneously switching on all switching elements of the first switching unit and by switching on, in particular at least substantially simultaneously, all switching elements of the second switching unit. In this case, “switching on the switching element” should be understood in particular to mean switching the switching element from the non-switching state of the switching element to the switching-on state. The short-circuit current preferably flows through the switched switching element, in particular until the standstill state of the electric motor has been reached. For short-circuit braking of the electric motor, the control and/or regulating unit is preferably provided for switching all switching elements of the first switching unit at least substantially simultaneously, in particular. Preferably, the control and/or regulating unit is provided for switching all switching elements of the switching unit simultaneously, or switching the switching units sequentially in time, in particular if the control and/or regulating unit is designed as a two-phase or three-phase gate driver of all switching elements, especially at such short time intervals that the motor behaves as if the switching elements were switched at the same time. For short-circuit braking of the electric motor, the control and/or regulating unit is preferably provided for switching all switching elements of the first switching unit back to the non-switched state, in particular at least substantially simultaneously, and the second switching unit, in particular after a certain time period. In particular, all switching elements of the cell are switched on at least substantially simultaneously. Preferably, the control and/or regulation unit is provided for switching all switching elements of the second switching unit, in particular at least substantially simultaneously, back to the non-switched state, in particular after a certain time period. Preferably, the control and/or regulation unit is provided for cyclically repeating alternately switching on all switching elements of the first switching unit and all switching elements of the second switching unit, in particular until a standstill of the electric motor.

The configuration of the braking device according to the invention advantageously enables efficient and in particular faster braking of the electric motor than by interrupting the current supply to the electric motor or compared to the use of excess energy by reducing the PWM control signal. In particular compared to short-circuit braking by only a single switching unit, the load on the switching elements can advantageously be reduced. Advantageously, switching elements with lower resistance and thus in particular more cost-effective can be installed. Advantageously, a durable, safe and cost-effective braking device can be provided.

Furthermore, it is proposed that each of the switching elements of the first switching unit and each of the switching elements of the second switching unit are each connected in an electrically conductive manner to a phase of the electric motor. The first switching unit preferably has as many switching elements as the number of phases of the electric motor. The second switching unit preferably has as many switching elements as the number of phases of the electric motor. Preferably, a switching element of the first switching unit and a switching element of the second switching unit are each electrically conductively connected to a phase of the electric motor via a common electrical line. The phase of the electric motor is electrically conductively connected between the output of the switching element of the second switching unit and the input of the switching element of the first switching unit, in particular via electrical lines. The switching element of the first switching unit and the switching element of the second switching unit are preferably electrically connected in series with each other. Preferably, the two switching elements of the first switching unit and the second switching unit are electrically connected in parallel with other pairs of switching elements of the first switching unit and the second switching unit. In particular, each pair of switching elements of the first switching unit and the second switching unit is electrically conductively connected to a phase of the other pair of switching elements of the electric motor that is different from the first switching unit and the second switching unit. Advantageously, a circuit can be provided which not only enables the current supply of the electric motor, but also the short-circuit braking of the electric motor. A separate circuit for braking the motor can advantageously be omitted. A cost-effective braking device can advantageously be provided.

Furthermore, it is proposed that the switching elements of the first switching unit and the switching elements of the second switching unit are designed as semiconductor switches. In particular, the switching elements of the first switching unit and the switching elements of the second switching unit can be designed as bipolar transistors, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), IGBTs (Insulated Gate Bipolar Transistors) or those skilled in the art think Other semiconductor switches that make sense. All switching elements of the first switching unit and all switching elements of the second switching unit are preferably constructed as semiconductor switches of the same structure. The switching element can preferably be switched on by applying a voltage and/or a current to the gate electrode of the switching element. The control and/or regulation unit is provided in particular for applying a voltage and/or a current to the gate electrode of the switching element in order to switch the switching element on. The control and/or regulation unit is preferably provided for switching the switching element from the ON state back to the non-ON state by interrupting the voltage and/or current on the gate electrode of the switching element. Advantageously, efficient switching of the switching elements of the first switching unit and the switching elements of the second switching unit can be achieved.

Furthermore, it is proposed that the control and/or regulating unit is provided for switching the first switching unit and the second switching unit into the non-switching state of the switching unit between two successive electrical short-circuits of the electric motor. The control and/or regulation unit is in particular provided for switching all switching elements of the first switching unit and all switching elements of the second switching unit to the non-switched state of the switching elements between two successive electrical short-circuits of the electric motor . Preferably, in the non-switched state of the switching unit, the commutation of the electric motor takes place by means of diodes, for example by means of intrinsic diodes or the like of switching elements designed as MOSFETs. Especially after commutation, current flow is prohibited between two electrical shorts. The duration of the non-switching state of the switching unit between two electrical short-circuits of the electric motor is shorter than the duration of the electric short-circuits of the electric motor, preferably at least 50% shorter, particularly preferably at least 75% shorter. The switching on of all switching elements of the first switching unit and the switching on of all switching elements of the second switching unit can advantageously be separated in time. A supply of current to the electric motor during the braking process can advantageously be prevented and an efficient braking process can be achieved.

Furthermore, it is proposed that the control and/or regulation unit is provided for adjusting the alternating frequency of the electrical short-circuit. In particular, the alternating frequency of the electrical short-circuit is switched by the control and/or regulating unit between the switching elements of the first switching unit, in particular all switching elements, and the switching elements, in particular all switching elements, of the second switching unit. frequency. Preferably, the user and/or the manufacturer of the braking device can predetermine the frequency of the electrical short-circuit alternation of the control and/or regulating unit, which is adjusted by the control and/or regulating unit, in particular programmed into the control and/or regulating unit. The alternating frequency especially has a value of at least 0.1 kHz, preferably a value of 1 kHz, particularly preferably a value of at least 10 kHz. Preferably, the transient thermal resistance of the switching element, in particular the thermal resistance between the semiconductor chip of the switching element and the housing, depends on the alternating frequency. The transient thermal resistance of the switching element especially decreases as the alternating frequency increases. The amount of energy available for residual utilization during the braking process preferably depends on the frequency of the alternation. The amount of energy available for residual energy utilization increases especially as the alternation frequency increases. Advantageously, the alternating frequency of the electrical shorts can be adjusted. Component loads can advantageously be controlled by alternating frequencies. Advantageously, an efficient and durable braking arrangement can be provided.

Furthermore, it is proposed that the control and/or regulation unit is provided for adjusting the duration of a braking cycle during which the first switching unit and the second switching unit each short-circuit the electric motor once. The braking cycle includes in particular the switching on of the switching elements (preferably all switching elements) of the first switching unit, the interruption of the current supply of the electric motor, the switching on of the switching elements (preferably all switching elements) of the second switching unit and the current supply of the electric motor another interruption. The control and/or regulation unit is preferably provided for the same adjustment of the duration of all braking cycles of the braking process. Alternatively, it is conceivable that the control and/or regulation unit is provided for varying the duration of the different braking cycles during the braking process. The control and/or regulation unit is preferably provided for adjusting the duration of the different phases of the braking cycle. A complete control and/or regulation of the braking process can advantageously be achieved. The braking process can advantageously be flexibly adapted to the purpose of use. Advantageously, an efficient braking arrangement can be provided.

Furthermore, it is proposed that the control and/or regulation unit is provided for controlling and/or regulating the first switching unit and the second switching unit in such a way that the first switching unit and the second switching unit short-circuit the electric motor for the same length of time during the braking cycle. duration. The control and/or regulation unit preferably switches the switching elements of the first switching unit, preferably all switching elements and the switching elements, preferably all switching elements of the second switching unit, such that the switching elements of the first switching unit, preferably all switching elements and the second switching unit The switching elements of the two switching units, preferably all switching elements, are in the switched-on state of the switching elements for the same length of time over the duration of the braking cycle. Preferably, the current flowing through the switching element of the first switching unit during the braking period corresponds to the current flowing through the switching element of the second switching unit during the braking period. A uniform loading of the switching elements of the first switching unit and the switching elements of the second switching unit can advantageously be achieved. Advantageously, a durable braking device can be provided.

Furthermore, it is proposed that the control and/or regulation unit is provided for controlling and/or regulating the first switching unit and the second switching unit in such a way that the first switching unit and the second switching unit short-circuit the electric motor for different lengths of time during the braking cycle. duration. The control and/or regulation unit preferably switches the switching elements of the first switching unit, preferably all switching elements and the switching elements, preferably all switching elements of the second switching unit, such that the switching elements of the first switching unit, preferably all switching elements and the second switching unit The switching elements of the two switching units, preferably all switching elements, are in the switched-on state of the switching elements for different lengths of time over the duration of the braking cycle. Preferably, the current flowing through the switching element of the first switching unit during the braking period is different from the current flowing through the switching element of the second switching unit during the braking period. The braking cycle can advantageously be adapted to the application purpose of the braking device. Advantageously, a flexibly usable braking device can be provided.

Furthermore, the invention proceeds from a method for operating a brake device, in particular the brake device according to the invention.

It is proposed that, in particular, in at least one method step, all switching elements of the first switching unit and all switching elements of the second switching unit are switched alternately for short-circuit braking of the electric motor. All switching elements of the first switching unit and all switching elements of the second switching unit are preferably switched alternately by means of the control and/or regulating unit. Advantageously, a method of braking that is safe and protects the component can be provided.

Furthermore, the invention is based on a power tool having at least one electric motor and at least one braking device according to the invention. In particular, the electric motor can be designed as a two-phase electric motor or as a three-phase electric motor. The power tool can in particular be designed as a circular saw, jigsaw, drill, angle grinder, lawn mower, brush cutter, cross-cut saw, table-top circular saw, band saw or other tools deemed useful by those skilled in the art machine. The power tool preferably includes further components, in particular necessary for operating the power tool. In particular, the power tool can comprise at least one power supply unit (eg battery, power cable, etc.), a tool chuck, a housing and/or other components deemed useful by those skilled in the art. Advantageously, a durable, user-safe and cost-effective power tool can be provided.

In this case, the braking device according to the invention, the method according to the invention and/or the power tool according to the invention should not be limited to the above-described applications and exemplary embodiments. The braking device according to the invention, the method according to the invention and/or the power tool according to the invention can in particular have individual elements, components and units and method steps that differ from the number mentioned above in order to implement the functional manner described here. . Furthermore, within the range of values stated in this disclosure, the values within the limits mentioned should also be considered disclosed and can be used arbitrarily.

Description of drawings

Additional advantages emerge from the description of the figures that follow. Embodiments of the invention are shown in the drawings. The drawings, description and claims contain features in many combinations. Those skilled in the art will also expediently consider these features individually and combine said features into meaningful other combinations.

In the attached picture:

FIG. 1 shows a machine tool according to the invention in a schematic diagram;

FIG. 2 shows a schematic representation of the braking device according to the invention with a switch element that is not switched on;

3 shows a schematic representation of a braking device with a switching element of a first switching unit;

4 shows a schematic representation of a braking device with a switching element of a second switching unit;

Fig. 5 shows the braking cycle in a schematic diagram;

Fig. 6 shows another braking cycle in a schematic diagram;

Figure 7 shows a schematic diagram of the effect of alternating frequency on transient thermal resistance.

Detailed ways

FIG. 1 shows the power tool 38 in a schematic diagram. The power tool 38 is designed as a hand-held power tool. The power tool 38 is designed as a drilling machine. Alternatively, it is conceivable that the power tool 38 is designed as a circular saw, jigsaw, angle grinder, lawn mower, brush cutter, cross-cut saw, table-top circular saw, band saw, or the like. The power tool 38 has a housing unit 40 . The power tool 38 has the electric motor 12 . The electric motor 12 is constructed as a three-phase electric motor. Alternatively, it is conceivable that the electric motor 12 is constructed as a two-phase electric motor. The electric motor 12 is arranged within the housing unit 40 . The electric motor 12 is provided for driving a plug-in tool 42 of the power tool 38 . The insert tool 42 is designed as a drill. The plug-in tool 42 is partially arranged in a tool chuck 44 of the power tool 38 . The power tool 38 has a braking device 10 for the electric motor 12 . The braking device 10 is arranged in a housing unit 40 of the power tool 38 .

FIG. 2 shows a schematic representation of the braking device 10 with the switching elements 16 , 18 , 20 , 24 , 26 , 28 that are not switched on. The braking device 10 includes a first switching unit 14 . The first switching unit 14 has a first switching element 16 of the first switching unit 14 , a second switching element 18 of the first switching unit 14 and a third switching element 20 of the first switching unit 14 . The braking device 10 includes a second switching unit 22 . The second switching unit 22 has a first switching element 24 of the second switching unit 22 , a second switching element 26 of the second switching unit 22 and a third switching element 28 of the second switching unit 22 . The first switch unit 14 and the second switch unit 22 constitute a bridge circuit. The bridge circuit composed of the first switching unit 14 and the second switching unit 22 is configured as a B-6 bridge. Alternatively, it is conceivable that the bridge circuit formed by the first switching unit 14 and the second switching unit 22 is designed as an H-bridge. The first switching unit 14 and the second switching unit 22 are electrically conductively connected to the electric motor 12 for current supply. Each of the switching elements 16 , 18 , 20 of the first switching unit 14 and each of the switching elements 24 , 26 , 28 of the second switching unit 22 are electrically conductively connected to one phase 32 , 34 , 36 of the electric motor 12 , respectively. . The first switching element 16 of the first switching unit 14 and the first switching element 24 of the second switching unit 22 are electrically conductively connected to the first phase 32 of the electric motor 12 via a first electrical line 46 . The first switching element 16 of the first switching unit 14 and the first switching element 24 of the second switching unit 22 are electrically connected in series and constitute a first switching element pair. The second switching element 18 of the first switching unit 14 and the second switching element 26 of the second switching unit 22 are electrically conductively connected to the second phase 34 of the electric motor 12 via a second electrical line 48 . The second switching element 18 of the first switching unit 14 and the second switching element 26 of the second switching unit 22 are electrically connected in series and constitute a second switching element pair. The third switching element 20 of the first switching unit 14 and the third switching element 28 of the second switching unit 22 are electrically conductively connected to the third phase 36 of the electric motor 12 via a third electrical line 50 . The third switching element 20 of the first switching unit 14 and the third switching element 28 of the second switching unit 22 are electrically connected in series and constitute a third switching element pair. The first switching element pair, the second switching element pair, and the third switching element pair are electrically connected in parallel with each other.

The switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 are designed as semiconductor switches. The switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 are designed as semiconductor switches of the same structure. The switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 are designed as bipolar transistors. Alternatively, it is conceivable that the switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 are designed as MOSFETs or IGBTs. The switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 are switchable to supply electrical energy to the electric motor 12 via the energy source 52 . By switching on the switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 , the electric motor 12 can be connected to the energy source 52 in an electrically conductive manner. The energy source 52 is designed as a battery. Alternatively, it is conceivable that the energy source 52 is designed as a mains voltage source.

The braking device 10 has a control and/or regulation unit 30 . The control and/or regulation unit 30 is designed as a microcomputer. Alternatively, it is conceivable that the control and/or regulation unit 30 is designed as an ASIC. The control and/or regulation unit 30 is provided for alternately switching all switching elements 16 , 18 , 20 of the first switching unit 14 and all switching elements 24 , 26 , 28 of the second switching unit 22 for the electric motor 12 . Short-circuit braking. The switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 are shown in the non-switched state. In the off state, the current flowing through the switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 is inhibited. In the ON state of the switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 , a current can flow through the switching elements 16 , 18 of the first switching unit 14 , 20 and the switching elements 24 , 26 , 28 of the second switching unit 22 . The control and/or regulation unit 30 is electrically conductively connected to the first gate electrode 56 of the first electrical switching element 16 of the first switching unit 14 via a fourth electrical line 54 . The control and/or regulation unit 30 is electrically conductively connected to the second gate electrode 60 of the second electrical switching element 18 of the first switching unit 14 via a fifth electrical line 58 . The control and/or regulation unit 30 is electrically conductively connected to the third gate electrode 64 of the third electrical switching element 20 of the first switching unit 14 via a sixth electrical line 62 . The control and/or regulation unit 30 is electrically conductively connected to the fourth gate electrode 68 of the first electrical switching element 24 of the second switching unit 22 via a seventh electrical line 66 . The control and/or regulation unit 30 is electrically conductively connected to the fifth gate electrode 72 of the second electrical switching element 26 of the second switching unit 22 via an eighth electrical line 70 . The control and/or regulation unit 30 is electrically conductively connected to the sixth gate electrode 76 of the third electrical switching element 28 of the second switching unit 22 via a ninth electrical line 74 . In order to switch on the switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements 24 , 26 , 28 of the second switching unit 22 , the control and/or regulating unit 30 is provided for applying a current to the first switching unit On the gate electrodes 56 , 60 , 64 of the switching elements 16 , 18 , 20 of 14 and the gate electrodes 68 , 72 , 76 of the switching elements 24 , 26 , 28 of the second switching unit 22 .

FIG. 3 shows a schematic representation of the braking device 10 with the switching elements 16 , 18 , 20 of the first switching unit 14 . All switching elements 16 , 18 , 20 of the first switching unit 14 are switched by a control and/or regulation unit 30 . The electric motor 12 is short-circuited by the switched switching elements 16 , 18 , 20 of the first switching unit 14 . A counter electromotive force acts, which causes a first short-circuit current 78 through the switching elements 16 , 18 , 20 of the first switching unit 14 . The electric motor 12 is braked by short-circuit braking by means of the first switching unit 14 . The state of the braking device 10 shown in FIG. 3 corresponds to the first phase 80 of the braking cycle. The second phase 82 of the braking cycle occurs between two successive electrical shorts of the electric motor 12 . The control and/or regulating unit 30 is provided for switching the first switching unit 14 and the second switching unit 22 to the non-switching state of the switching units 14 , 22 between two successive electrical short-circuits of the electric motor 12 . The control and/or regulation unit 30 is provided for switching all switching elements 16 , 18 , 20 of the first switching unit 14 and all switching elements 24 of the second switching unit 22 between two successive electrical short-circuits of the electric motor 12 . , 26 , 28 switch to the non-switched state of the switching elements 16 , 18 , 20 , 24 , 26 , 28 (see FIG. 2 ). The commutation of the electric motor 12 takes place in the non-switched state of the switching units 14 , 22 by means of diodes (not shown further). After commutation, current flow is inhibited between the two electrical shorts. The duration of the switching unit 14 , 22 being in the non-connected state between two electrical short circuits of the electric motor 12 is shorter than the duration of the electrical short circuit of the electric motor 12 .

FIG. 4 shows a schematic representation of the braking device 10 with the switched switching elements 24 , 26 , 28 of the second switching unit 22 . All switching elements 24 , 26 , 28 of the second switching unit 22 are switched on by the control and/or regulating unit 30 . The electric motor 12 is short-circuited by the switched switching elements 24 , 26 , 28 of the second switching unit 22 . A counter electromotive force acts, which causes a second short-circuit current 84 through the switching elements 24 , 26 , 28 of the second switching unit 22 . The electric motor 12 is braked by short-circuit braking by means of the second switching unit 22 . The state of the braking device 10 shown in FIG. 4 corresponds to the third phase 86 of the braking cycle. The fourth phase 88 of the braking cycle, which follows the third phase 86 of the braking cycle, corresponds to the second phase 82 of the braking cycle.

FIG. 5 shows a braking cycle in a schematic diagram. A first graph 90 with a first abscissa axis 92 and a first ordinate axis 94 is shown. Duration is plotted on the first abscissa axis 92 . The switching states of the switching elements 16 , 18 , 20 , 24 , 26 , 28 are plotted on the first ordinate axis 94 . The switching states of the switching elements 16 , 18 , 20 of the first switching unit 14 are plotted on the positive part 96 of the first ordinate axis 94 . The switching states of the switching elements 24 , 26 , 28 of the second switching unit 22 are plotted on the negative part 98 of the first ordinate axis 94 . The control and/or regulation unit 30 is provided for adjusting the duration of the braking cycle during which the first switching unit 14 and the second switching unit 22 each short-circuit the electric motor 12 once. The control and/or regulation unit 30 is provided for controlling and/or regulating the first switching unit 14 and the second switching unit 22 in such a way that the first switching unit 14 and the second switching unit 22 short-circuit the electric motor 12 during a braking cycle the same long duration. The duration of the first phase 80 of the braking cycle corresponds to the duration of the third phase 86 of the braking cycle, in which all switching elements 16 , 18 , 20 of the first switching unit 14 are switched on, in which In this third phase all switching elements 24 , 26 , 28 of the second switching unit 22 are switched on. The duration of the second phase 82 of the braking cycle corresponds to the duration of the fourth phase 88 of the braking cycle. During the second phase 82 of the braking cycle and the fourth phase 88 of the braking cycle, the first switching unit 14 and the second switching unit 22 are in an off state. In the second phase 82 of the braking cycle and in the fourth phase 88 of the braking cycle, the control and/or regulation unit 30 switches all the switching elements 16 , 18 , 20 of the first switching unit 14 and the switching elements of the second switching unit 22 . All switching elements 24, 26, 28 are switched to the non-switched state.

FIG. 6 shows another braking cycle in a schematic diagram. The control and/or regulation unit 30 is provided for controlling and/or regulating the first switching unit 14 and the second switching unit 22 in such a way that the first switching unit 14 and the second switching unit 22 are during said further braking cycle The motor 12 is short-circuited for varying durations. The duration of the first phase 80 of the further braking cycle in which all the switching elements 16 , 18, 20 are switched on, in this third phase all switching elements 24, 26, 28 of the second switching unit 22 are switched on. The duration of the first phase 80 of the further braking cycle in which all the switches of the first switching unit 14 are twice as long as the duration of the third phase 86 of the further braking cycle The elements 16 , 18 , 20 are switched on, in this third phase all switching elements 24 , 26 , 28 of the second switching unit 22 are switched on. The duration of the second phase 82 of the further braking cycle corresponds to the duration of the fourth phase 88 of the further braking cycle. In the second phase 82 of the further braking cycle and in the fourth phase 88 of the further braking cycle, the first switching unit 14 and the second switching unit 22 are in an off state. During the second phase 82 of the further braking cycle and the fourth phase 88 of the further braking cycle, the control and/or regulation unit 30 switches all switching elements 16 , 18 , 20 of the first switching unit 14 and all switching elements 24 , 26 , 28 of the second switching unit 22 are switched to the non-switched state.

FIG. 7 shows the effect of the alternating frequency of electrical short circuits on the transient thermal resistance of the switching elements 16 , 18 , 20 , 24 , 26 , 28 . A second graph 100 with a second axis of abscissa 102 and a second axis of ordinate 104 is shown. The second graph 100 is constructed logarithmically. On the second abscissa axis 102 are plotted the switch-on durations of the switching elements 16 , 18 , 20 of the first switching unit 14 or of the switching elements 24 , 26 , 28 of the second switching unit 22 . The switching-on duration of the switching elements 16 , 18 , 20 of the first switching unit 14 or the switching elements 24 , 26 , 28 of the second switching unit 22 corresponds substantially to the reverse alternating frequency of the electrical short-circuit. The switching elements 16 , 18 , 20 , 24 , 26 , 28 are plotted on the second ordinate axis 104 as thermal resistance between the chip and the housing of the switching elements 16 , 18 , 20 , 24 , 26 , 28 transient thermal resistance. The control and/or regulation unit 30 is arranged to adjust the alternating frequency of the electrical short circuit. The transient thermal resistance of the switching elements 16, 18, 20, 24, 26, 28 depends on the alternating frequency of the electrical shorts. The higher the alternating frequency of the electrical shorts, the lower the transient thermal resistance of the switching elements 16, 18, 20, 24, 26, 28. The transient thermal resistance of the switching elements 16 , 18 , 20 , 24 , 26 , 28 is higher at the first point 106 corresponding to the alternating frequency of 1 kHz than at the second point 108 corresponding to the alternating frequency of 10 kHz. The transient thermal resistance of the switching elements 16, 18, 20, 24, 26, 28 at the first point 106 corresponding to the alternating frequency of 1 kHz is twice as high as at the second point 108 corresponding to the alternating frequency of 10 kHz.

Next, a method for operating the brake device 10 is described. In at least one method step, all switching elements 16 , 18 , 20 of the first switching unit 14 and all switching elements 24 , 26 , 28 of the second switching unit 22 are switched alternately for short-circuit braking of the electric motor 12 . With regard to further method steps of the method for operating the brake device 10 , reference may be made to the previous description of the brake device 10 , since this also applies analogously to the method, so that all features concerning the brake device 10 are also considered to be is disclosed for a method for operating the braking device 10 .

Claims (10)

1. A braking device for an electric motor (12), having at least one first switching unit (14) having at least two switching elements (16, 18, 20) and at least one second switching unit (22) having at least two switching elements (24, 26, 28), wherein the first switching unit (14) and the second switching unit (22) are connected in an electrically conductive manner to the electric motor (12) at least for the purpose of current supply, characterized by at least one control and/or regulating unit (30) which is provided to alternately switch all switching elements (16, 18, 20) of the first switching unit (14) and all switching elements (24) of the second switching unit (22) for short-circuit braking of the electric motor (12), 26, 28).

2. A braking device according to claim 1, characterized in that each of the switching elements (16, 18, 20) of the first switching unit (14) and each of the switching elements (24, 26, 28) of the second switching unit (22) is electrically conductively connected with one phase (32, 34, 36) of the electric motor (12), respectively.

3. A braking device according to claim 2, characterized in that the switching elements (16, 18, 20) of the first switching unit (14) and the switching elements (24, 26, 28) of the second switching unit (22) are configured as semiconductor switches.

4. A braking device according to any one of the foregoing claims, characterised in that the control and/or regulating unit (30) is provided for switching the first switching unit (14) and the second switching unit (22) to the non-switched-on state of the switching units (14, 22) between two mutually successive electrical short circuits of the electric motor (12).

5. Braking apparatus according to any one of the preceding claims, characterized in that the control and/or regulating unit (30) is provided for adjusting the frequency of alternation of the electrical short-circuits.

6. A braking device according to any one of the foregoing claims, characterised in that the control and/or regulating unit (30) is provided for adjusting the duration of a braking cycle during which the first switching unit (14) and the second switching unit (22) short-circuit the electric motor (12) once, respectively.

7. A braking device according to claim 6, characterized in that the control and/or regulating unit (30) is provided for controlling and/or regulating the first switching unit (14) and the second switching unit (22) in such a way that the first switching unit (14) and the second switching unit (22) short-circuit the electric motor (12) for the same duration during a braking cycle.

8. A braking device according to claim 6, characterized in that the control and/or regulating unit (30) is provided for controlling and/or regulating the first switching unit (14) and the second switching unit (22) in such a way that the first switching unit (14) and the second switching unit (22) short-circuit the electric motor (12) for different durations during a braking cycle.

9. A method for operating a brake device, in particular a brake device (10) according to one of the preceding claims, characterized in that for short-circuit braking of the electric motor (12), all switching elements (16, 18, 20) of the first switching unit (14) and all switching elements (24, 26, 28) of the second switching unit (22) are switched alternately.

10. Machine tool having at least one electric motor (12) and at least one braking device (10) according to one of claims 1 to 8.

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