BRAKE DEVICE

Description

[0001] The present invention relates to a braking device for a movable door leaf.

[0002] Door closers for movable door leaves with a mechanical energy storage device and a braking device are known from the prior art. When the door leaf is opened, the mechanical energy storage device is charged with potential energy, which closes the released door leaf again. The mechanical energy storage device is designed, for example, as a spring, which is tensioned when the door leaf is opened. The potential energy in the spring then closes the door leaf. The closing moment of the door leaf is determined by the current spring tension and the various transmission ratios in the system. The closing speed itself is dampened in the braking device, for example, by oil in a damper. The desired closing behavior of the door leaf can be adjusted using various hydraulic valves and their settings. This enables a cost-effective and self-sufficient implementation of the door closer, i.e.The door closer works without the need for external energy.

[0003] However, the closing speed of the door leaf can only be adjusted to a limited extent with valves. For example, a latching function always has the same activation point, as only the flow rate, not the position of the valve, can be adjusted. Furthermore, functions that depend on the current speed of the door leaf are difficult to implement. Controlling the closing speed, for example to a desired closing time for the door leaf, is also difficult. The valves must be adjusted accordingly through trial and error. If the temperature of the damper oil or the friction conditions in the door closer then change, the closing time also changes. In addition, escaping damper oil can pollute the environment if the door closer develops a leak, and the damper oil must then be disposed of.In addition, the damper oil is usually flammable, which can contribute to the spread of a fire if it leaks and ignites in the event of a fire.

[0004] To avoid such disadvantages, the braking device can comprise an electric motor operated as a generator, the motor shaft of which can be rotated by movement of the door leaf and which outputs a movement-dependent motor voltage, as well as a braking circuit to which the motor voltage is applied or can be applied and via which the electric motor can be short-circuited in order to dampen movement of the door leaf. Damping is therefore not achieved by forcing damper oil through valves, but rather by the electric motor operating as a generator generating electrical energy, which is consumed by the short-circuiting. Such a braking device can also be provided for a non-electrically operated door closer, since in principle no power source is required to operate the braking device. Thus, a braking device with a generator-operated, short-circuitable electric motor also enables a self-sufficient implementation of the door closer.Depending on the design, the braking device, in particular the aforementioned braking circuit, may also comprise switching elements that require a power supply for their control. Furthermore, the braking device may be incorporated into an electric door drive, in which case the electric motor, in addition to its function as a generator for the braking device, may also serve as the motor for the door drive, for which it then requires a power supply.

[0005] DE 10 2005 028 007 B4 discloses a door drive for operating a movable door leaf with such a braking device. The braking circuit of this braking device has a switching element embodied as a field-effect transistor, via which the motor terminals of the electric motor can be short-circuited. A drain-source path of the field-effect transistor is arranged in the braking circuit, and a voltage between the gate and source of the field-effect transistor is adjusted via a potentiometer, which is arranged in parallel with the drain-source path of the field-effect transistor. A voltage tap of the potentiometer is connected to the gate terminal of the field-effect transistor.Thus, the field-effect transistor is operated as a voltage-dependent load resistor for the electric motor, so that the braking force of the braking device depends on the output voltage of the electric motor operated as a generator and can also be adjusted via the potentiometer.

[0006] A similar braking device is known from DE 10 2015 200 284 B3. This braking device has an evaluation and control unit that performs pulse-width modulation of the motor current via a switching element in the braking circuit, thereby setting an effective braking force to dampen the movement of the door leaf. This allows the desired closing behavior to be adjusted particularly flexibly. The pulse-width modulation of the motor current caused by the evaluation and control unit can be specified in a variety of ways and, in particular, can also be dependent on conditions detected by sensors, e.g., the current closing speed or the angular position of the door leaf, thus also enabling the closing speed to be regulated to achieve a desired closing behavior.

[0007] The braking device is generally designed for proper use of the respective door leaf, e.g., with regard to the forces required for normal opening and closing of the door leaf, and / or, when used with a door closer, with regard to its spring force. However, it can happen that greater forces are exerted on the door leaf, for example, by wind, vandalism, or children playing with the door leaf. Such potential additional forces not only strain the mechanics of the respective door closer or door drive, but can also impair the respective braking device.

[0008] In hydraulically damped door closers, hydraulic valves can be built into the hydraulic circuit to protect against damage. These valves open in the event of overload, thereby allowing the door leaf to move. Braking devices that dampen the door leaf's movement by short-circuiting a generator-driven electric motor cannot be protected by simple valves and are therefore at risk of damage from overload. Excessive force acting on the door leaf, resulting in high door speeds, can generate high voltages in the generator-driven electric motor of the braking device, resulting in correspondingly high currents flowing when the electric motor is short-circuited. However, these high voltages and / or currents can destroy components of the braking device, rendering the braking device inoperable.In addition, excessive force combined with simultaneous damping puts a great deal of strain on the mechanism between the braking device and the door leaf, which can also lead to damage.

[0009] A braking device having the features of the preamble of claim 1 is known from US 2011 / 0185941 A1.

[0010] It is an object of the invention to provide a braking device of the type mentioned which has improved safety against overloading.

[0011] The object is achieved by a braking device having the features of claim 1. Advantageous embodiments of the invention emerge from the subclaims, the present description and the drawings.

[0012] The braking device according to the invention comprises a protective device with a current sensor designed to detect a current generated by the electric motor. The protective device is designed to modify the braking circuit depending on the detected current such that the current in the braking circuit is reduced when a predetermined or predeterminable overload current is reached or exceeded.

[0013] The protective device can thus protect the remaining braking device, in particular, from excessive currents in the braking circuit. This also allows the electric motor to be protected from excessive currents in the event of a short circuit in the braking circuit. The protective device intervenes in the braking circuit in such a way that the current in the braking circuit is reduced. This also reduces, in particular, the damping acting on the door leaf. This allows the door leaf to move when excessive force is applied, similar to an overload valve on a hydraulic door closer, or at least allows the damping of the door leaf to give way sufficiently so that the load on the braking device does not exceed a tolerable level.

[0014] Reducing the damping not only protects the braking device itself, but also the mechanism between the braking device and the door leaf, for example, the motor gear of a door closer or a door drive, as part of which the braking device is provided. Therefore, the intervention of the protective device does not necessarily have to be designed to prevent damage to the braking device. Rather, the intervention of the protective device can be triggered even when the braking device itself is not yet at risk of overload, but the mechanism is reaching its load-bearing capacity.

[0015] The current generated by the electric motor is used as a criterion for determining whether intervention in the braking circuit is necessary. This can be done directly by measuring the current itself or indirectly, e.g., by measuring a voltage from which the current can be derived. This current is detected using a current sensor in the protective device. The current sensor can, in principle, be located at any point on the braking device that allows for reliable detection of overload.

[0016] The current does not necessarily have to be measured at a location where the current is highest or where an excessive current would most likely cause damage. To determine an overload, it may be sufficient to measure a current at one location that may not be problematic at that location, but which allows the conclusion that a current is present at another location that could cause an overload of the braking device.

[0017] According to the invention, the braking circuit comprises a switching element that can be switched by means of an evaluation and control unit, via which the electric motor is short-circuited depending on the switching state of the switching element. Such a switching element enables simple yet flexible control of the short circuit. Switching a switching element not only makes it possible to simply switch the damping on when needed and off otherwise. It is also possible to set a medium intensity of the damping, in particular by switching the switching element with pulse width modulation. By adjusting the ratio between the pulse duration of the short circuit and the duration of the short circuit interruption, the desired damping behavior can be achieved flexibly.

[0018] In such an embodiment, in which a switching element of the braking circuit can be switched by means of the evaluation and control unit, the current sensor is advantageously designed to output a load signal dependent on the detected current intensity to the evaluation and control unit. The evaluation and control unit is then designed to switch the switching element depending on the load signal in such a way that the current intensity in the braking circuit is thereby reduced.

[0019] Preferably, the current sensor is designed to detect the current in the braking circuit. This has the advantage, for example, that no current sensor needs to be provided on the electric motor, and the electric motor therefore does not need to be specially designed.

[0020] The current reduction is triggered at least when the specified overload current is reached or exceeded. This overload current can be predefined in the braking device, as it can be predefined for a particular braking device by the components used in that braking device and their respective load capacities. Advantageously, however, the overload current can be specified at least once, so that it can be adapted to the respective door leaf or to a mechanism of the door closer or door drive that incorporates the braking device, for example, after the installation of a door closer or a door drive that incorporates the braking device.

[0021] To protect the braking device and / or a mechanism on the door leaf from overload, the damping can, for example, be reduced to such an extent that the highest possible damping is maintained, at which an overload just does not occur. However, in certain circumstances, it may be preferable, particularly for safety reasons, for the protective device to be designed to modify the braking circuit depending on the detected current strength in such a way that when a predetermined or predeterminable overload current strength is reached or exceeded, the current flow in the braking circuit is interrupted. Such an interruption of the current flow completely eliminates the short circuit via the braking circuit, so that the damping of the door leaf is also suspended, thereby enabling the movement of the leaf.

[0022] The current sensor of the safety device can, in principle, be very simple and comprise, for example, a shunt resistor or a coil. However, a current measurement performed via such an element can influence the circuit in which the current measurement is performed. However, the current sensor should preferably detect the current without altering the normal functionality of the braking circuit. Therefore, the current sensor is preferably designed to be non-reactive, in that the current in the braking circuit is not affected by the current sensor detecting the current.

[0023] According to a preferred embodiment, this can be achieved by the current sensor comprising a Hall sensor. In particular, the current sensor can be designed as a Hall sensor. Such a design has the advantage that the current flowing through the Hall sensor can be detected via the Hall voltage generated at the Hall sensor, which can be done essentially without affecting the current flow itself. This enables a comparatively simple, non-interference detection of the current.

[0024] The evaluation and control unit can, in particular, comprise a microcontroller that can receive the load signal from the current sensor and switch the respective switching element of the braking circuit. The use of a microcontroller enables a particularly variable definition of the relationship between the respective detected current and the influence of the damping in response to the detected current.

[0025] According to an advantageous development, the evaluation and control unit is designed to switch the switching element when the detected current intensity underlying the load signal reaches or exceeds the overload current intensity, interrupting the current flow in the braking circuit. Thus, the evaluation and control unit completely suspends the damping when an overload threatens. This provides particularly reliable protection for the braking device and / or a mechanism between the braking device and the door leaf.

[0026] According to an alternative development, the evaluation and control unit is designed to switch the switching element when the detected current underlying the load signal reaches or exceeds the overload current, such that the current in the braking circuit is limited to a maximum current, in particular to the overload current, preferably by means of pulse width modulation. In this way, the damping is therefore not completely suspended, but merely reduced, at least to such an extent that the current does not exceed a maximum current. This can be done in particular in the form of a control so that the current is at least essentially kept at the maximum current. This has the advantage that the damping can be kept at a comparatively high value, but at the same time the braking device or the mechanism between the braking device and the door leaf is protected.

[0027] The maximum current can, in particular, correspond to the overload current. However, it can also be provided that an overload current is defined, upon reaching or exceeding which the attenuation is reduced, but that the current is then limited to a different, particularly lower, maximum current, so that a kind of buffer remains between the maximum current and the overload current, which can further improve protection against overload.

[0028] In particular, if the reduction or regulation of the current intensity is achieved by means of pulse width modulation, the said current intensity can mean an effective current intensity, which can be defined as a moving time average over the pulsed current intensity.

[0029] According to a further advantageous embodiment, the current sensor is designed to output a value proportional to the detected current intensity to the evaluation and control unit as the load signal mentioned. The output value can, for example, be amplified compared to the detected current intensity. Or, for example, a voltage proportional to the current intensity is output. Such a load signal can, in principle, continuously assume different values ​​and is, in particular, analog. In such an embodiment, an evaluation as to whether a reduction in the current intensity in the braking circuit should be carried out in response to a respective load signal output by the current sensor can take place outside the current sensor, e.g. in the evaluation and control unit mentioned.

[0030] In contrast, according to an alternative example, the current sensor can be designed to compare the detected current with the overload current and to output a specific overload signal as the load signal when the detected current has reached or exceeded the overload current, and to output a specific normal signal otherwise. In this respect, the current sensor outputs a binary load signal that can only assume two different states or values: the overload signal or the normal signal. The overload current, upon reaching or exceeding which triggers the reduction of the current in the braking circuit, is then preferably present directly in the current sensor as a parameter, so that a type of evaluation can be carried out in the current sensor by comparing the detected current with the overload current.

[0031] Such an example makes it fundamentally possible to dispense with a separate evaluation and control unit, unless one is already provided for the braking circuit. This is because a switching element of the braking circuit can, for example, be switched directly via the load signal output by the current sensor between a closed state, in which the braking circuit is closed to short-circuit the electric motor, and an open state, in which the short circuit via the braking circuit is interrupted. In such a case, the evaluation and control unit can also be considered integrated into the current sensor.

[0032] According to such a further advantageous embodiment, it is therefore provided that the braking circuit comprises a switchable switching element, via which the electric motor is short-circuited depending on the switching state of the switching element, and that the current sensor is designed to compare the detected current intensity with the overload current intensity and to switch the switching element into an open state when the detected current intensity has reached or exceeded the overload current intensity, and to switch the switching element into a closed state otherwise.

[0033] Preferably, the specified overload current is adjustable. For example, the overload current can be specified for the current sensor and / or the specified evaluation and control unit as a parameter, but can be adjustable. This allows this parameter to be adapted, for example, to different versions of a particular door closer or door drive, as well as to different stop types. The overload current can be adjusted particularly conveniently if it can be changed wirelessly, e.g., via NFC.

[0034] According to a further advantageous embodiment, the electric motor is designed as a brushless electric motor with multiple stator coils, in each of which an alternating voltage is induced depending on the movement of the door leaf. Using the current sensor, the current in a single stator coil can then be directly measured, for example. This can be sufficient as a criterion for determining whether or not there is an overload of the braking device and / or a mechanism between the braking device and the door leaf. In particular, it is therefore not absolutely necessary to measure the current in all stator coils and / or in the braking circuit.

[0035] In such an embodiment, the electric motor can, in particular, have at least one contact pair to which it outputs one of the alternating voltages induced in the stator coils, while the braking circuit comprises a partial braking circuit to which the alternating voltage output at the contact pair is applied or can be applied and via which the contact pair can be short-circuited. The protective device is then advantageously designed to modify the partial braking circuit depending on the detected current intensity such that the current intensity in the partial braking circuit is reduced when the overload current intensity is reached or exceeded.If, for damping the door leaf, the electric motor as a whole is not short-circuited via a uniform braking circuit, but individual stator coils are short-circuited via a different partial braking circuit, it may be advisable to protect the partial braking circuits separately against overload.

[0036] If the electric motor has a plurality of contact pairs, in particular a contact pair for each stator coil, at each of which it outputs a different one of the alternating voltages induced in the stator coils, and the braking circuit comprises a plurality of partial braking circuits, to each of which a different one of the alternating voltages output at the contact pairs is applied or can be applied and via which the respective contact pair can be short-circuited, it is further preferred if the protective device is designed to modify the partial braking circuits depending on the detected current intensity in such a way that when the overload current intensity is reached or exceeded, the current intensity in all partial braking circuits is reduced.In principle, each of the partial brake circuits is at risk of being damaged by an overload, independently of the other partial brake circuits, so that it is advantageous to reduce the current in all partial brake circuits when an overload is detected.

[0037] In the above embodiments, in which individual stator coils can be short-circuited via respective partial brake circuits, it may in principle be sufficient to detect the current intensity directly in one of the stator coils. Alternatively or additionally, the current intensity can also be detected in at least one partial brake circuit. Particularly comprehensive monitoring for the presence of an overload can be achieved in particular by designing the current sensor to detect the current intensity in all partial brake circuits of the brake circuit. For this purpose, a separate individual current sensor can be provided on each partial brake circuit, so that the aforementioned current sensor is designed as an arrangement of several individual current sensors.

[0038] The invention will be further explained below by way of example only with reference to the figure.

[0039] The figure shows an embodiment of a braking device 11 according to the invention in a schematic representation as a simplified circuit diagram.

[0040] The braking device 11 comprises an electric motor 13, whose motor shaft is coupled to a door leaf in such a way that movement of the door leaf causes the motor shaft to rotate. This causes the electric motor to operate as a generator and output a motor voltage.

[0041] The motor voltage is applied to a braking circuit 15 of the braking device 11, via which the electric motor 13 can be short-circuited. Short-circuiting the electric motor 13 converts electrical energy into heat, thus removing energy from the movement of the door leaf, which leads to a damping of the movement. The degree of damping depends in particular on the short-circuit current in the braking circuit 15.

[0042] The short circuit is caused by closing a switching element 17. In contrast, the current flow through the braking circuit 15 is interrupted when the switching element 17 is open. In order to be able to set at least a medium current flow in the braking circuit and thus change the strength of the damping, an evaluation and control unit 19 is provided which switches the switching element 17 in a pulse-width modulated manner in order to achieve a predetermined desired damping behavior. As a result of the pulse width modulation, the switching element 17 is alternately closed for a specific pulse duration and open for a specific pulse-pause duration. The variable ratio between the pulse duration and the pulse-pause duration then achieves a medium current flow through the braking circuit 15, which effects a specific damping of the door leaf.

[0043] The switching of the switching element 17 by means of the evaluation and control unit 19 is symbolized in the figure by the arrow that connects the evaluation and control unit 19 to the switching element 17. In the embodiment shown, the evaluation and control unit 19 is designed as a microcontroller. In addition to the elements shown, the evaluation and control unit 19 can also be connected to other elements, for example, to detect a speed and / or a direction of movement of the door leaf, thus enabling direction-dependent damping and / or general control of the damping taking external parameters into account.

[0044] To protect against excessive loading of the braking device 11 and / or a mechanism connecting the braking device 11 to the door leaf, the braking device 11 has a protective device 21. This protective device 21 comprises a current sensor 23 arranged in the braking circuit 15. To detect a current in the braking circuit 15, the current sensor 23 has a Hall sensor, which makes it possible to detect the current in the braking circuit 15 without impairing the function of the braking circuit.

[0045] The current intensity detected by the current sensor 23 is output by the current sensor 23 to the evaluation and control unit 19 as a load signal in the form of a measured value corresponding to the detected current intensity, in particular a measured value proportional to the detected current intensity. The measured value is output to the evaluation and control unit 19 via an amplifier 25, which adapts the load signal to an input sensitivity of the evaluation and control unit 19.

[0046] In this way, the evaluation and control unit 19 can take the detected current into account when controlling the switching element 17. In particular, the evaluation and control unit 19 compares the detected current with an overload current that can be specified to the evaluation and control unit 19 and is stored in the evaluation and control unit 19. If the detected current reaches or exceeds the overload current, the evaluation and control unit 19 switches the switching element 17 in such a way that the current in the braking circuit 15 is reduced, thus reducing the damping of the door leaf. For this purpose, the evaluation and control unit 19 adjusts the pulse width modulation in such a way that the current in the braking circuit falls to a value below the overload current.This protects the braking device 11 and the mechanism between the braking device 11 and the door leaf from excessive stress.

[0047] In this embodiment, the evaluation and control unit 19, which is provided in the braking device 11 to implement a desired damping behavior by means of pulse width modulation, is at the same time a functional part of the protective device 21. The signal path through this protective device 21, which, in addition to the evaluation and control unit 19, also includes the current sensor 23 and the amplifier 25, is shown in the figure by broken lines.

[0048] However, the figure also shows an alternative embodiment, which is shown superimposed on the embodiment described above and whose signal curve is represented by a dotted line. The protective device 21' of this alternative embodiment comprises only the current sensor 23, which in this embodiment is designed to compare the detected current strength with the predetermined or predeterminable overload current strength. For this purpose, the overload current strength can be stored as a parameter in the current sensor 23 and, in particular, can be changed externally. To compare the detected current strength with the overload current strength, the current sensor 23 can, for example, comprise a comparator in addition to a Hall sensor.

[0049] In such a protective device 21', the current sensor 23 can directly control the switching element 17, as shown, which is symbolized in the figure by the arrow connecting the current sensor 23 to the switching element 17. In particular, the current sensor 23 can be designed in this case to open the switching element 17 when the detected current reaches or exceeds the overload current. Reaching or exceeding the overload current then leads to a complete interruption of the current flow in the braking circuit, so that the damping of the door leaf is suspended. In this embodiment, a distinction is therefore only made as to whether an overload is imminent or not, and the braking circuit is simply interrupted if necessary.

[0050] While a protective device 21, in which a continuously variable load signal is output to the evaluation and control unit 19 and then a pulse width modulation of the switching element 17 is adjusted depending on the load signal, can at least maintain a reduced level of damping in the event of an overload, such a flexible adjustment of the damping is not possible with the alternative protective device 21', whose current sensor 23 merely distinguishes between the presence and absence of an overload and directly opens or closes the switching element 17 accordingly. However, this alternative embodiment has the advantage of a simpler structure.What both embodiments have in common is that they each improve the safety of the braking device 11, since in each case an impending overload is reacted to in a manner by which damage to the braking device 11 and / or a mechanism acting between the braking device 11 and the door leaf as a result of an overload can be prevented by reducing the current intensity in the braking circuit. Reference symbol

[0051] 11Braking device 13Electric motor 15Braking circuit 17Switching element 19Evaluation and control unit 21, 21'Protection device 23Current sensor 25Amplifier

Claims

1. Braking device (11) for a movable door leaf, comprising an electric motor (13) which is operated as a generator, the motor shaft of which can be rotated by a movement of the door leaf and which outputs a movement-dependent motor voltage, and comprising a braking circuit (15), to which the motor voltage is applied or can be applied and via which the electric motor (13) can be short-circuited in order to dampen a movement of the door leaf, wherein the braking device (11) comprises a protective device (21) with a current sensor (23) which is designed to capture a current intensity generated by the electric motor (13), characterized in that the protective device (21) is designed to modify the braking circuit (15) on the basis of the captured current intensity in such a way that, when a predefined or predefinable overload current intensity is reached or exceeded, the current intensity in the braking circuit (15) is reduced; the braking device (11) comprises an evaluation and control unit (19), the braking circuit (15) comprises a switching element (17) which can be switched by means of the evaluation and control unit (19) and via which the electric motor (13) is short-circuited depending on the switching state of the switching element (17), the current sensor (23) is designed to output a load signal, which is dependent on the captured current intensity, to the evaluation and control unit (19), and the evaluation and control unit (19) is designed to switch the switching element (17) on the basis of the load signal in such a way that the current intensity in the braking circuit (15) is reduced thereby.

2. Braking device according to Claim 1, characterized in that the current sensor (23) is designed to capture the current intensity in the braking circuit (15).

3. Braking device according to Claim 1 or 2, characterized in that the protective device (21) is designed to modify the braking circuit (15) on the basis of the captured current intensity in such a way that, when the overload current intensity is reached or exceeded, the current flow in the braking circuit (15) is interrupted.

4. Braking device according to at least one of the preceding claims, characterized in that the current sensor (23) is designed to be free of reaction in so far as the current intensity in the braking circuit (15) is not affected by the capture of the current intensity by means of the current sensor (23).

5. Braking device according to at least one of the preceding claims, characterized in that the current sensor (23) comprises a Hall sensor.

6. Braking device according to Claim 1, characterized in that the evaluation and control unit (19) is designed to switch the switching element (17), when the captured current intensity underlying the load signal reaches or exceeds the overload current intensity, in such a way that the current flow in the braking circuit (15) is interrupted.

7. Braking device according to Claim 1, characterized in that the evaluation and control unit (19) is designed to switch the switching element (17), when the captured current intensity underlying the load signal reaches or exceeds the overload current intensity, in such a way that the current intensity in the braking circuit (15) is thereby limited to a maximum current intensity, in particular to the overload current intensity, preferably by means of pulse width modulation.

8. Braking device according to at least one of Claims 1 to 7, characterized in that the current sensor (23) is designed to output a value proportional to the captured current intensity to the evaluation and control unit (19) as said load signal.

9. Braking device according to at least one of Claims 1 to 7, characterized in that the current sensor (23) is designed to compare the captured current intensity with the overload current intensity and to output a specific overload signal as said load signal when the captured current intensity has reached or exceeded the overload current intensity, and otherwise to output a specific normal signal.

10. Braking device according to at least one of the preceding claims, characterized in that the overload current intensity is adjustable.

11. Braking device according to at least one of the preceding claims, characterized in that the electric motor (13) is designed as a brushless electric motor with a plurality of stator coils, in each of which an AC voltage is induced on the basis of the movement of the door leaf, in that the electric motor (13) has at least one contact pair at which it outputs one of the AC voltages induced in the stator coils, in that the braking circuit (15) comprises a partial braking circuit, to which the AC voltage output at the contact pair is applied or can be applied and via which the contact pair can be short-circuited, and in that the protective device (21) is designed to modify the partial braking circuit on the basis of the captured current intensity in such a way that, when the overload current intensity is reached or exceeded, the current intensity in the partial braking circuit is reduced.

12. Braking device according to Claim 11, characterized in that the electric motor (13) has a plurality of contact pairs, in particular in each case one contact pair for each stator coil, at which it outputs in each case another of the AC voltages induced in the stator coils, in that the braking circuit (15) comprises a plurality of partial braking circuits, to each of which another of the AC voltages output at the contact pairs is applied or can be applied and via which the respective contact pair can be short-circuited, and in that the protective device (21) is designed to modify the partial braking circuits on the basis of the captured current intensity in such a way that, when the overload current intensity is reached or exceeded, the current intensity in all partial braking circuits is reduced.

13. Braking device according to Claim 11 or 12, characterized in that the current sensor (23) is designed to capture the current intensity in the partial braking circuit or in at least one partial braking circuit, in particular in all partial braking circuits, of the braking circuit (15).