Power converter for an electric motor of a reversible belt retractor, and reversible belt retractor

Abstract

The present invention relates to a power converter (12) for an electric motor (14) of a reversible belt retractor (10), and to a reversible belt retractor (10). The power converter (12) comprises at least two half-bridges (18) which are arranged in parallel and which each have at least two switching devices (20, 22). Each half-bridge (18) has a center tap (24) between the at least two switching devices (20, 22) for the purposes of providing an associated output signal for the electric motor (14). The power converter (12) is coupled, at input terminals, to a DC voltage source (26). The power converter (12) has, between the DC voltage source (26) and the at least two half-bridges (18), at least one step-up converter (27) which is configured to provide a supply voltage for at least the half-bridges (18), said supply voltage having an increased voltage amplitude in relation to an input voltage provided at the input terminals. The power converter (12) comprises a control device (46) which is coupled at least to the step-up converter (27) and which is configured to activate the step-up converter (27) before or during a tautening phase of the reversible belt retractor (10).

Description

[0001] Power converter for an electric motor of a reversible belt retractor and reversible belt retractor

[0002] The present invention relates to a power converter for an electric motor of a reversible belt retractor and a reversible belt retractor.

[0003] By using sensors, e.g. in a distance radar, which records brake pressure, optical detection of the surroundings, recording yaw rate, etc., a critical driving situation that could lead to a dangerous situation can be detected in advance, i.e. before the critical driving situation actually occurs. Since the critical driving situation can be detected before impact thanks to the environmental sensors, the time span from detection of the potentially critical driving situation to the start of occupant forward displacement, which is intended to protect the occupants, is extended. This extended time span means that reversible belt pretensioners can be used. In contrast to belt pretensioners with pyrotechnic-based drives, reversible belt pretensioners can continue to be used after they have been activated, since belt pretensioners with pyrotechnic-based drives must be replaced after activation or triggering.With reversible belt tensioners, the required belt retraction to secure the occupant is achieved with the help of an electric motor and an optional gearbox.

[0004] To avoid overloading the vehicle's electrical system, the supply currents are limited to a maximum value. However, in a rotating electric motor, the movement of the armature also induces a countervoltage proportional to the speed, which counteracts the applied voltage, for example the voltage output to the electric motor by a power converter. As a result, the electric motor, for a constant supply voltage, consumes less current as the speed increases, thereby reducing the (consumed) electrical power. In other words, the induced countervoltage reduces the voltage effectively acting in the motor windings. This generally lengthens the time it takes to achieve the desired belt retraction.

[0005] The invention is based on the object of eliminating or at least mitigating the disadvantages of the prior art. In particular, it is intended to create a way to ensure a desired target torque over a wide speed range. In other words, the goal is to design the electrical supply to the electric motor in such a way that the electric motor draws the permissible maximum supply power over the widest possible range of the tensioning process. This then accordingly results in the maximum output power being able to be delivered over the wide range, which has a positive effect on the tensioning performance.

[0006] The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are specified in the dependent patent claims and the following description, each of which, individually or in (sub)combination, may represent aspects of the invention. Individual aspects are presented with reference to different devices, but are to be applied accordingly.

[0007] According to one aspect, a power converter for an electric motor of a reversible belt retractor is provided. The power converter comprises at least two half-bridges arranged in parallel, each having at least two switching devices. Each half-bridge has a center tap between the at least two switching devices for providing a respective output signal for the electric motor. The power converter is coupled to a DC voltage source at input terminals. The power converter has at least one boost converter between the DC voltage source and the at least two half-bridges. The boost converter is configured to provide a supply voltage for at least the half-bridges that has an increased voltage amplitude compared to an input voltage provided at the input terminals.The power converter comprises a control device which is coupled at least to the boost converter and is configured to activate the boost converter before or during a tensioning phase of the reversible belt retractor.

[0008] The rotation of the electric motor causes or induces a countervoltage, which reduces the effective voltage acting on the motor windings. As a result, the voltage provided by the half-bridges to the electric motor is no longer sufficient for the electric motor to absorb the maximum permissible supply power. The power converter described here can compensate for this power reduction by ensuring a temporary increase in the amplitude of the supply voltage for the half-bridges via the boost converter. This ensures a voltage amplitude that is higher than that provided by the DC voltage source, thus compensating for the effect of the induced countervoltage. This prevents a drop in the torque output by the electric motor despite the induced countervoltage.

[0009] In particular, the power converter can be designed such that the electrical power provided by the supply voltage ensures that a desired belt retraction speed is achieved within a specified time interval. The belt retractor thus retracts the belt, thereby pulling the occupant back. These improvements are made possible despite the avoidance of pyrotechnic drives, so that the functionality of the underlying belt retractor is increased compared to previous approaches, as comfort and safety functions can be ensured simultaneously. Furthermore, the adaptability of the power converter and thus also of the belt retractor is increased. The aforementioned advantages also apply when used in conjunction with a pyrotechnic belt tensioner.

[0010] Preferably, the control device is configured to activate the boost converter if a target motor power specified for the electric motor is greater than a limit power determined as a function of the motor speed. Optionally, the limit power also depends on the supply voltage. The limit power corresponds to the maximum possible input power of the electric motor at a given time.

[0011] Alternatively, a difference threshold can be provided regarding a difference between a target motor power specified for the electric motor and the limit power determined depending on the engine speed. The control device is then configured to activate the boost converter when the difference threshold is exceeded or undershot (depending on the definition of the difference). The target motor power and the absorbed motor power refer here to electrical power. If the target motor power exceeds the maximum possible absorbed power of the electric motor (limit power), this can be considered an indication that the electrical power actually absorbed by the electric motor will fall below the permissible absorbed power from the vehicle electrical system. This, in turn, leads to a drop in the mechanical power output by the electric motor.In other words, the differential threshold provides a tool for assessing whether the engine speed is such that a power consumption limit of the electric motor is reached, neglecting the boost converter. If the differential threshold is exceeded or undershot, it is clear that the boost converter must be activated to ensure the desired power consumption for the electric motor.

[0012] In some embodiments, the difference threshold, or alternatively the limiting power, is temporally variable. The difference threshold, or alternatively the limiting power, can then depend, for example, in particular on certain operating parameters of the power converter and / or the electric motor. This means that the difference threshold or the limiting power can be raised or lowered as needed for certain operating states, for example, to enable adaptability with respect to certain operating states. This increases the variability with respect to different operating states. Since the motor speed of the electric motor directly influences the induced counter voltage, it is thus possible to determine more accurately whether activation of the boost converter is necessary.

[0013] Alternatively, the difference threshold can also be predetermined. This enables particularly simple control of the boost converter's activation.

[0014] Optionally, the boost converter comprises at least one boost inductor, one boost switching device, one boost diode, and one boost capacitor. These components can be used to increase the voltage amplitude of the supply voltage provided to the half-bridges.

[0015] The boost diode can be bridged. If the boost diode is bridged, the power loss can be reduced.

[0016] In some embodiments, the boost switching device is arranged in parallel with the at least two half-bridges. The boost inductor is arranged between the DC voltage source and the boost switching device. The bridgeable boost diode is arranged in the forward direction between the boost switching device and the parallel half-bridges. The boost capacitor is arranged in parallel with the half-bridges. Thus, the boost inductor and the boost capacitor can be used to collect electrical charge so that the amplitude of the supply voltage provided to the half-bridges can be varied. The state of the boost converter can be controlled as needed using the boost switching device and the bridgeable boost diode.

[0017] Preferably, the boost converter is configured to ensure a voltage amplitude at the boost capacitor that is higher than that of the input voltage provided at the input terminals.

[0018] In some embodiments, the control device is configured to output a digital control signal to the boost switching device to activate the boost converter. The boost switching device may, for example, comprise a transistor. The boost converter is deactivated when the boost switching device (transistor) is permanently blocked. To activate, high-frequency switched on-state and off-state phases (on states vs. off states) of the boost switching device must alternate. While the boost switching device is in the on-state, the current through the boost inductor increases, and energy is stored in the boost inductor. If the boost switching device is then switched to the off-state, the voltage on the anode side of the boost diode increases. This causes the boost diode to conduct (or is actively bypassed), and the voltage across the boost capacitor increases.“Activating” the boost converter therefore corresponds to a high-frequency change between the on-state and off-state of the boost switching device.

[0019] Optionally, the voltage amplitude of an output voltage of the boost converter can be adjusted based on a varying duty cycle of at least one digital control signal output by the control device. Typically, the digital control signal has an upper and a lower signal level, with the relative distribution of the signal levels being described by the duty cycle. By varying the duty cycle, the activity state of the boost converter can then be adjusted such that a desired output voltage is ensured by the boost converter, at least within a limited range.

[0020] Preferably, the output voltage provided by the boost converter is provided as the supply voltage for the half-bridges of the power converter.

[0021] In some embodiments, the power converter further comprises at least one filter device. The filter device is configured to attenuate the conducted interference emitted into a higher-level vehicle electrical system. The filter device is arranged between the DC voltage source and the boost converter. This prevents interference with the higher-level vehicle electrical system.

[0022] Optionally, the filter device comprises an LC element. A capacitor of the LC element is arranged in parallel with the half-bridges. This allows the conducted interference to be dampened particularly efficiently. In some embodiments, the filter device further comprises at least one reverse polarity protection device arranged in series between the DC voltage source and the boost converter. This prevents damage caused by an incorrectly polarized connection of a DC voltage source that provides the input voltage for the power converter.

[0023] Optionally, the boost converter further comprises at least one safety switching device arranged in series with the boost switching device. The safety switching device is configured to compensate for a failure of the power converter caused by a defect in the boost switching device. Without the safety switching device, a failure of the boost switching device could lead to a short circuit in the boost converter. The short circuit could affect other components of the power converter, the on-board electrical system, or the supply network, for example, the electric motor itself. The safety switching device is configured to prevent such a short circuit. This reduces the risk of damage to the power converter or other components.In other words, the safety switching device can ensure that the power converter can still operate if the boost switching device is defective, albeit possibly without an activatable boost converter. If the boost switching device is defective and a short circuit is prevented by opening the safety switching device, the boost converter is deactivated. The power converter can then still provide the power, but the motor cannot absorb it at the given output voltage (depending on the speed). In other words, a supply voltage for the half-bridges of the power converter can still be guaranteed, so the electric motor can still be used.

[0024] The boost converter preferably has at least one safety diode arranged in the forward direction parallel to a series circuit comprising at least the boost inductor and the bridgeable boost diode. The safety diode is configured to compensate for a failure of the power converter caused by a defect in the boost inductor and / or the bridgeable boost diode. In other words, the safety diode ensures an alternative current path that can be used if the boost inductor and / or the bridgeable boost diode are defective. Thus, the basic functionality of the power converter is ensured, but the functionality of the boost converter cannot be utilized.

[0025] In some embodiments, the boost inductor comprises several separate inductors arranged in parallel, i.e., individual inductive components. The inverse of the total inductance Lges ) of the boost inductance is the sum of the inverses of the individual inductances to L„):

[0026] Redundancy can be created by connecting several individual inductors in parallel. If one or more of the individual inductors fail, the power converter remains usable, even with the boost converter still activated. Only the total inductance resulting from the parallel connection of the individual inductors changes. This means that the boost converter has different characteristics but is still usable, even to increase the voltage amplitude of the supply voltage.

[0027] Preferably, the boost capacitor can also comprise several separate capacitors arranged in parallel. The total capacitance (C ges ) of the boost capacitor is then:

[0028] Ctotal = Ci + C2+ C3+ •••

[0029] This also creates redundancy with regard to the boost capacitor. If a single capacitor or multiple capacitors fail, the boost converter can still be used. Only the characteristics of the boost converter are affected. In general, the boost converter can still be used (depending on the fault scenario of the defective capacitor) to increase the voltage amplitude of the supply voltage.

[0030] From a theoretical perspective, the operating situation of the electric motor can be described using the electrical differential equation of a DC motor: Here, u describes the motor terminal voltage, i.e. the motor terminal voltage provided by the half-bridges, R A the armature resistance, L A the armature inductance, the induced counter voltage, k eis the magnetic feedback constant, n is the speed of the electric motor, and i is the electric current. Time-invariant variables are denoted by capital letters (e.g., II, I). For stationary operating points, the following applies: dl

[0031] — = 0. dt

[0032] Then the following applies:

[0033] U = R ■ I + k e n.

[0034] With the electrical power P e = U ■ I then: r, (Uk e n) U 2 UK e n

[0035] P p e = u - - — = - RRR which describes a linear function of first degree

[0036] Since the supply voltage is included in both summands, it can be seen that a change in the supply voltage leads to a change in both the slope and the y-axis intercept. As a result, for each supply voltage U, a speed n max(U') exists, above which a given electrical power can no longer be absorbed by the electric motor. Above this speed, the boost converter is activated to increase the amplitude of the output voltage provided by the boost converter as the supply voltage for the half-bridges.

[0037] According to a further aspect, a reversible belt retractor for a vehicle is also provided. The belt retractor comprises at least one electric motor and a power converter associated with the electric motor, as described above. This creates a belt retractor that non-destructively ensures the desired belt webbing force and / or the desired belt webbing retraction speed within a predetermined time interval, so that the belt retractor retracts the belt webbing, whereby the occupant is retracted in a shorter time interval (compared to previously known reversible belt retractors) or the belt slack is reduced more quickly. The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the example illustrated in the drawing.The features shown in the description and the drawings can be used according to the invention individually or in any combination. They show:

[0038] Fig. 1 is a schematic representation of a reversible belt retractor according to the invention with a power converter according to the invention and an electric motor associated with the power converter, and

[0039] Fig. 2a and 2b are schematic representations of the functional principle of the power converter according to the invention and the corresponding signal curves over time.

[0040] All features disclosed below with respect to the embodiments and / or the accompanying figures may be combined alone or in any sub-combination with features of the aspects of the present disclosure, including features of preferred embodiments, provided that the resulting combination of features is meaningful to a person skilled in the art.

[0041] Fig. 1 shows a schematic representation of a reversible belt retractor 10 according to the invention with a power converter 12 according to the invention and an electric motor 14 assigned to the power converter 12. Components of the belt retractor 10 that are not essential to the invention are not shown in the figures.

[0042] The power converter 12 comprises a power stage 15 with an H-bridge 16, which in this case comprises two half-bridges 18. The following functionality is only illustrated with reference to one half-bridge 18, but is applicable to all half-bridges 18.

[0043] Each half-bridge 18 comprises a first switching device 20, for example, a field-effect transistor, which acts as a high-side switch, and a second switching device 22, for example, another field-effect transistor, which acts as a low-side switch. Between the first switching device 20 and the second switching device 22, each half-bridge 18 comprises a center tap 24 for providing a respective output signal for the electric motor 14.

[0044] The electric motor 14 can, for example, be a brushed DC motor.

[0045] The two half-bridges 18 supply the electric motor 14 with supply signals, the modulation of which is realized via pulse-width modulation of the half-bridges 18. Other topologies, such as a three-phase or six-phase electric motor, are also possible, which then require corresponding modifications of the power converter 12, for example, alternating current signals.

[0046] The respective half-bridges 18 are coupled to lines of the power converter 12. The half-bridges 18 are arranged parallel to one another in a known manner. The power converter 12 is coupled to a DC voltage source 26. The DC voltage source 26 comprises connection terminals between which an input voltage UJn for the power converter 12 is provided.

[0047] In this case, the power converter 12 also includes a boost converter 27. The boost converter 27 has a boost switching device 28 and another switching device embodied as a bridgeable boost diode 30. By implementing the bridgeable boost diode 30 in the form of a transistor, the power loss caused during the bridge operation can be reduced. The boost switching device 28 is arranged in parallel with the half-bridges 18. The bridgeable boost diode 30 is arranged between the boost switching device 28 and the half-bridges 18.

[0048] Furthermore, the boost converter 27 comprises a boost capacitor 32, which is arranged on the output side of the boost diode 30 in parallel with the half bridges 18.

[0049] In addition, a boost inductor 34 of the boost converter 27 is arranged on the input side between the DC voltage source 26 and the boost switching device 28. The boost inductor 34 comprises several individual inductors arranged in parallel, thereby creating a safety mechanism in the event of a failure of one of the individual inductors. The boost capacitor 32 can also comprise several separate individual capacitors arranged in parallel.

[0050] Furthermore, the power converter 12 has a filter device 36 comprising an LC element. The filter device 36 has an inductor 38 and a capacitor 40. The capacitor 40 is arranged on the input side of the boost inductor 34 in parallel with the boost switching device 28. The inductor 38 of the filter device 36 is arranged in a series circuit with a reverse polarity protection device 42 (another switching device) on the input side of the power converter 12 between the DC voltage source 26 and the capacitor 40 arranged in parallel with the boost switching device 28.

[0051] By means of the filter device 36, the conducted interference emitted into a higher-level vehicle electrical system can be attenuated.

[0052] The boost capacitor 32 provides an additional filter function on the output side of the boost switching device 28. This improves the signal quality for the half-bridges 18 and thus the downstream electric motor 14.

[0053] In series with the boost switching device 28, a further switching device, designed as a safety switching device 44, is also arranged. Should the boost switching device 28 be defective and permanently conductive, the safety switching device 44 can be used to prevent a short circuit in the boost converter 27. The safety switching device 44 is then permanently switched to the off state. This prevents an increase in the amplitude of the output voltage of the boost converter 27.

[0054] This means that the power converter 12, starting from the DC voltage source 26, has the inductance 38 of the filter device 36 and then the reverse polarity protection device 42 on a first arm of the lines of the power converter 12. This is followed by a node that is coupled via the capacitor 40 of the filter device 36 to a node of the opposite second arm of the lines of the power converter 12. Starting from the node, the first arm then has the boost inductance 34. This is followed by another node of the first arm, which in turn is coupled to another node of the second arm of the lines and comprises a series circuit of the boost switching device 28 and the safety switching device 44. Starting from the second node, the first arm of the lines then has the boost diode 30. This is followed by a third node of the first arm, which in turn is coupled to an opposite node of the second arm and comprises the boost capacitor 32.For this purpose, the half bridges 18 are arranged in parallel.

[0055] Using the boost converter 27, an output voltage can be provided as a supply voltage for the power stage 15, which has an amplitude which is increased compared to the amplitude of the input voltage of the DC voltage source 26.

[0056] In addition, the power converter 12 has a safety diode 45 arranged in parallel with the series connection of the boost inductor 34 with the bridgeable boost diode 30. Should the boost inductor 34 or the bridgeable boost diode 30 fail, the safety diode 45 can be used to ensure basic functionality of the power converter 12, but without an increase in the voltage amplitude caused by the boost converter 27.

[0057] Furthermore, the power converter 12 has a control device 46 which, based on a data processing device, provides control signals for the switching devices 20, 22 of the half-bridges 18 and at least the boost switching device 28, for example, at the respective gate electrodes 48. In this case, the control signals are based on pulse width modulation (PWM). Varying the duty cycle of the PWM signal can influence the functioning of the power converter 12. In particular, adjusting the duty cycle can influence an increase in the amplitude of the output voltage of the boost converter 27. Thus, sufficient electrical power can be ensured for the power stage 15 and thus for the electric motor 14 despite the induced countervoltage, so that the effect caused by the induced countervoltage can be compensated.

[0058] Optionally, the control device 46 can also provide control signals for the bridgeable boost diode 30, the polarity reversal protection device 42, and the safety switching device 44. In general, the control device 46 is configured to control the switching devices 20, 22 of the half-bridges 18 such that demand-based output signals are provided for the electric motor 14, for example, depending on the relative positions of the rotor and stator of the electric motor 14 and / or the rotational speed of the electric motor 14. For this purpose, the control device can be coupled to further components, for example, corresponding sensors. Furthermore, the control device 46 can also be coupled to the DC voltage source 26 or a control unit therefor. In addition, the control device 46 is generally coupled to an external higher-level control device, for example, an airbag control device.From this, the control device 46 receives information about an engine power request. For example, the airbag control device can request a specific tensioning profile to be operated by the belt retractor 10. The tensioning profiles can be stored, for example, in a memory device coupled to the control device 46. Based on the tensioning profile, the control device 46 can adapt the control of the power converter 12 and in particular of the down converter 27 accordingly. The sensors can, for example, detect the output signals of the power stage 15. From this, the maximum electrical power that the electric motor 14 can actually absorb can be determined depending on the speed of the electric motor 14, whereby a difference between the target engine power specified for the electric motor and a limit power determined depending on an engine speed can be determined.If a corresponding difference threshold is exceeded or undershot (depending on the difference value formation), the boost converter 27 can be activated by the control device 46. In particular, the control device 46 can be configured to activate the boost converter 27 before or during a tensioning phase of the reversible belt retractor 10.

[0059] Fig. 2a and 2b show schematic representations of the functional principle of the power converter 12 according to the invention and the corresponding signal curves over time.

[0060] P_on corresponds to the closed (conductive) boost switching device 28 (on state). P_off corresponds to the open (non-conductive) boost switching device 28 (off state). After the voltage received by the power converter 12 from the DC voltage source 26 is filtered by the LC element using the inductor 38 and the capacitor 40, the input voltage UJn is applied to the open boost switching device 28. The capacitor 40 assumes the function of an input capacitance with respect to the boost converter 27 of the power converter 12.

[0061] The boost inductance 34 performs the task of storing charge depending on the switching position of the boost switching device 28.

[0062] The bridgeable boost diode 30 acts as an optional output-side blocking element of the boost converter 27 of the power converter 12. Whether it switches through depends largely on the voltage amplitude of the voltage across the boost switching device 28 and on the voltage across the boost capacitor 32.

[0063] The boost capacitor 32 acts as the output capacitance of the step-up converter 27 and thus as an additional attenuation element of the subordinate half-bridges 18 or the electric motor 14.

[0064] In Fig. 2b, it can be seen that as long as the boost switching device 28 is closed (conducting; P_on), the voltage U_switch across the boost switching device 28 is low because a short circuit is created. Consequently, the current l_switch across the boost switching device 28 increases during P_on. Since U_switch is lower than U_mot, the boost diode 30 is off. Therefore, l_diode is low (or negligible). The boost inductor 34 acts as a charge collector, which is why IJnd increases across the boost inductor 34 during P_on. When the boost diode 30 is off, the electric motor 14 is supplied from the boost capacitor 32.

[0065] If the boost switching device 28 is opened (non-conductive; P_off), the voltage U_switch across the boost switching device 28 increases suddenly. In particular, it increases so sharply that it is greater than the voltage across the boost capacitor (32). This causes the boost diode 30 to conduct, and the electrical charge stored by the boost inductor 34 during P_on can be released. As a result, IJnd decreases from an initial maximum value during P_off. Consequently, the current l_diode across the boost diode 30 also initially shows a maximum value and decreases during P_off. Because the boost switching device 28 is in the open position, no further current can flow across it, which is why l_switch is zero during P_off.

[0066] It can also be seen that the current I_mot output to the electric motor 14 remains constant during P_on and P_off. The countervoltage induced by the rotation of the electric motor 14 is not shown. However, varying the supply voltage U_mot output to the electric motor 14 can compensate for the effect of the induced countervoltage. This allows the electric motor 14 to maintain a constant electrical input power despite the countervoltage induced by the rotation of the electric motor 14.

[0067] Certain embodiments disclosed herein, in particular the respective module(s), use circuitry (e.g., one or more circuits) to implement standards, protocols, methods, or technologies disclosed herein, operatively couple two or more components, generate information, process information, analyze information, generate signals, encode / decode signals, convert signals, transmit and / or receive signals, control other devices, etc. Circuitry of any type may be used.

[0068] In one embodiment, a circuit (circuit) includes, among other things, one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a system on a chip (SoC), or the like, or any combination thereof, and may include discrete digital or analog circuit elements or electronics, or combinations thereof. In one embodiment, the circuit includes hardware circuit implementations (e.g., implementations in analog circuits, implementations in digital circuits, and the like, and combinations thereof).

[0069] In one embodiment, circuitry includes combinations of circuitry and computer program products with software or firmware instructions stored on one or more computer-readable memories that cooperate to cause a device to execute one or more of the protocols, methods, or technologies described herein. In one embodiment, the circuitry includes circuitry, such as microprocessors or portions of microprocessors, that require software, firmware, and the like to operate. In one embodiment, the circuitry includes one or more processors or portions thereof and the associated software, firmware, hardware, and the like.

[0070] In the present application, reference may be made to quantities and numbers. Unless expressly stated, such quantities and numbers are not to be considered limiting, but rather as examples of the possible quantities or numbers in the context of the present application. In this context, the term "plurality" may also be used in the present application to refer to a quantity or number. In this context, the term "plurality" means any number greater than one, e.g., two, three, four, five, etc. The terms "about," "approximately," "near," etc., mean plus or minus 5% of the stated value.

[0071] Although the disclosure has been illustrated and described with respect to one or more implementations, those skilled in the art will recognize equivalent changes and modifications upon reading and understanding this description and the accompanying drawings. Although a particular feature of the disclosure has been disclosed with respect to only one of several embodiments, that feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for a given or particular application.

Claims

Patent claims 1. A power converter (12) for an electric motor (14) of a reversible belt retractor (10), comprising at least two parallel-arranged half-bridges (18), each having at least two switching devices (20, 22), each half-bridge (18) having a center tap (24) between the at least two switching devices (20, 22) for providing a respective output signal for the electric motor (14), the power converter (12) being coupled to a DC voltage source (26) at input terminals, the power converter (12) having at least one boost converter (27) between the DC voltage source (26) and the at least two half-bridges (18), which boost converter is configured to provide a supply voltage for at least the half-bridges (18) that has an increased voltage amplitude compared to an input voltage provided at the input terminals, and the power converter (12) comprising a control device (46),which is coupled at least to the boost converter (27) and is arranged to activate the boost converter (27) before or during a tensioning phase of the reversible belt retractor (10).

2. Power converter (12) according to claim 1, characterized in that the control device (46) is designed to activate the boost converter (27) if a difference between a target motor power specified for the electric motor (14) and a maximum input power of the electric motor (14) that can be absorbed by the electric motor (14) exceeds or falls below a difference threshold value.

3. Power converter (12) according to claim 2, characterized in that the difference threshold value depends at least on the supply voltage and a motor speed of the electric motor (14).

4. Power converter (12) according to one of the preceding claims, characterized in that the boost converter (27) has at least one boost inductor (34), a boost switching device (28), a boost diode (30) and a boost capacitor (32).

5. Power converter (12) according to claim 4, characterized in that the boost switching device (28) is arranged parallel to the half-bridges (18), wherein the boost inductance (34) is arranged between the DC voltage source (26) and the boost switching device (28), wherein the boost diode (30) is arranged in the forward direction between the boost switching device (28) and the half-bridges (18) arranged in parallel, and wherein the boost capacitor (32) is arranged in parallel to the half-bridges (18).

6. Power converter (12) according to claim 4 or 5, characterized in that the boost converter (27) is arranged to ensure a voltage amplitude at the boost capacitor (32) which is higher than that of the input voltage provided at the input terminals.

7. Power converter (12) according to one of the preceding claims, characterized in that the voltage amplitude of the output voltage of the boost converter (27) can be adjusted based on a varying duty cycle of at least one digital control signal output by the control device (46).

8. Power converter (12) according to one of claims 4 to 7, characterized in that the boost converter (27) further comprises at least one safety switching device (44) which is designed to compensate for a failure of the power converter (12) due to a defect in the boost switching device (28).

9. Power converter (12) according to one of claims 4 to 8, characterized in that the boost converter (27) has at least one safety diode (45) which is arranged in the forward direction parallel to a series circuit comprising at least the boost inductance (34) and the boost diode (30), and which is designed to compensate for a failure of the power converter (12) due to a defect in the boost inductance (34) and / or the boost diode (30).

10. Power converter (12) according to one of claims 4 to 9, characterized in that the boost inductance (34) has a plurality of separate individual inductances arranged parallel to one another.

11. Power converter (12) according to one of claims 4 to 10, characterized in that the boost capacitor (32) has a plurality of separate individual capacitors arranged in parallel to one another.

12. Reversible belt retractor (10) for a vehicle, comprising at least one electric motor (14) and a power converter (12) associated with the electric motor (14) according to one of the preceding claims.

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