Inverter for electric motor of reversible seat belt retractor and reversible seat belt retractor

Abstract

The invention relates to an inverter (12) for an electric motor (14) of a reversible seat belt retractor (10) and to a reversible seat belt retractor (10). The inverter (12) comprises at least two half-bridges (18) arranged in parallel, each having at least two switching means (20, 22). Each half-bridge (18) has a center tap (24) between the at least two switching means (20, 22) for providing a corresponding output signal for the electric motor (14). The inverter (12) is coupled at input terminals to a DC voltage source (26). The inverter (12) has at least one boost converter (27) between the DC voltage source (26) and the at least two half-bridges (18), which is provided for supplying the at least half-bridges (18) with a supply voltage having an increased voltage amplitude compared to an input voltage provided at the input terminals. The inverter (12) comprises a control device (46) coupled at least to the boost converter (27) and provided for activating the boost converter (27) before or during a tightening phase of the reversible seat belt retractor (10).

Description

Technical Field

[0001] This invention relates to a converter for an electric motor used in a reversible seatbelt retractor, and to a reversible seatbelt retractor. Background Technology

[0002] By using sensors (such as ranging radar, brake pressure detection, environmental optical recognition, yaw rate detection, etc.), critical driving situations that could lead to dangerous situations can be detected in advance (i.e., before they actually occur). Because critical driving situations can be detected before a collision based on environmental sensors, the time period from detecting a potential critical driving situation to initiating occupant pre-displacement is extended, thereby protecting the occupants. This extended time period allows for the use of reversible seatbelt pretensioners. Unlike seatbelt pretensioners with pyrotechnic actuators, reversible seatbelt pretensioners remain usable after activation, as pyrotechnic actuator pretensioners must be replaced after activation or triggering.

[0003] In reversible seatbelt pretensioners, the required seatbelt webbing retraction is achieved by using an electric motor and an optional transmission to restrain the occupant.

[0004] To prevent overloading the vehicle's electrical system, the feed current is limited to its maximum value. However, in a rotating electric motor, the armature's motion also induces a back electromotive force (EMF) proportional to the rotational speed, which cancels out the applied voltage (e.g., the voltage output to the motor from the converter). As a result, the motor draws less current with increasing rotational speed at the same supply voltage, and thus the (absorbed) electrical power decreases. In other words, the induced back EMF reduces the effective voltage acting on the motor windings. Typically, this prolongs the time until the desired seatbelt webbing retraction is achieved. Summary of the Invention

[0005] The object of this invention is to eliminate or at least reduce the disadvantages of the prior art. Specifically, it is intended to provide a possibility to ensure that the desired target torque is achieved over a wide range of speeds. In other words, the objective is to design the electrical supply of the motor in such a way that the motor absorbs the maximum permissible supply power over the widest possible range of the tightening process. The resulting consequence is that maximum output power can be delivered over a wide range, which is beneficial for tightening performance.

[0006] This objective is achieved through the technical solutions provided in the independent claims. Advantageous designs are given in the dependent claims and the following description, each of which may constitute aspects of the invention individually or in combination. The aspects are described in relation to different devices, but should be applied accordingly.

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

[0008] The rotation of the electric motor induces or generates a back electromotive force (EMF), thereby reducing the effective voltage across the motor windings. As a result, the voltage supplied to the motor via the half-bridge is no longer sufficient for the motor to absorb its maximum permissible power. The converter described herein compensates for this power reduction by ensuring that the boost converter temporarily increases the amplitude of the supply voltage to the half-bridge. This ensures that the amplitude of the supply voltage is higher than that supplied by the DC voltage source, thus compensating for the effect of the induced back EMF. In this way, despite the presence of the induced back EMF, a decrease in the power output torque of the motor is prevented.

[0009] Specifically, the converter can be configured such that the electrical power supplied based on the supply voltage ensures the desired seatbelt webbing retraction speed is achieved within a given time interval. This causes the seatbelt retractor to retract the seatbelt webbing, thereby pulling the occupant back. These improvements are achievable even without using pyrotechnic actuators, thus enhancing the functionality of the seatbelt retractor compared to existing solutions, as both comfort and safety functions can be ensured simultaneously. Furthermore, the adaptability of the converter is improved, and therefore the adaptability of the seatbelt retractor is also improved.

[0010] Of course, the above advantages also apply when used with a pyrotechnics safety belt tensioner.

[0011] Preferably, the control device is configured to activate the boost converter if a pre-given target motor power exceeds a limiting power determined based on the motor speed. Optionally, the limiting power also depends on the supply voltage. The limiting power corresponds to the maximum possible power absorbed by the motor at a given moment.

[0012] Alternatively, a difference threshold can be provided regarding the difference between a pre-given target motor power and a limit power determined based on the motor speed. The control device is then configured to activate the boost converter if the difference threshold is exceeded or fallen below (depending on the definition of the difference). Here, the target motor power and the absorbed motor power refer to electrical power. If the target motor power exceeds the motor's maximum possible absorbable power (limit power), it can be considered that this indicates the actual electrical power absorbed by the motor will be lower than the permissible absorbable power from the vehicle's electrical system. This, in turn, leads to a decrease in the mechanical power output by the motor. In other words, the difference threshold represents an auxiliary means by which to determine whether the motor speed has reached such a level that the motor's power absorption limit has been reached without considering the boost converter. If the difference threshold is exceeded or fallen below, it is clear that the boost converter must be activated to ensure the required power absorption by the motor.

[0013] In some embodiments, the differential threshold or alternative limiting power is variable over time. The differential threshold or alternative limiting power can thus depend, for example, specifically on the specific operating parameters of the converter and / or the motor. This means that the differential threshold or limiting power can be raised or lowered as needed for specific operating conditions, for example, enabling adaptability to specific operating conditions. This improves variability with respect to different operating conditions. Since the motor speed directly affects the induced back electromotive force, the need for activation of the boost converter can be determined as needed.

[0014] Alternatively, the difference threshold can also be predetermined. This allows for a particularly simple control method regarding the activation of the boost converter.

[0015] Optionally, the boost converter includes at least a boost inductor, a boost switching device, a boost diode, and a boost capacitor. These components enable an increase in the voltage amplitude of the supply voltage provided to the half-bridge.

[0016] Boost diodes can be bridged. When boost diodes are bridged, power loss can be reduced.

[0017] In some implementations, the boost switching device is arranged in parallel with at least two half-bridges. A boost inductor is positioned between the DC voltage source and the boost switching device. A bridgeable boost diode is positioned in the conduction direction between the boost switching device and the parallel-connected half-bridges. A boost capacitor is arranged in parallel with the half-bridges. Therefore, the boost inductor and boost capacitor can be used to collect charge, allowing the amplitude of the supply voltage to the half-bridges to be varied. The state of the boost converter can be controlled as needed using the boost switching device and the bridgeable boost diode.

[0018] Preferably, the boost converter is configured to ensure that the voltage amplitude across the boost capacitor is higher than the voltage amplitude of the input voltage supplied at the input terminal.

[0019] 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 include, for example, a transistor. If the boost switching device (transistor) is continuously blocked, the boost converter is disabled. To activate, the high-frequency switching of the boost switching device's on and off phases (on state and off state) must alternate. When the boost switching device is in the on state, the current flowing through the boost inductor increases, and energy is stored in the boost inductor. When the boost switching device is then switched to the off state, the voltage on the anode side of the boost diode increases. The boost diode thus becomes on (or actively bridged), and the voltage across the boost capacitor increases. "Activating" the boost converter therefore corresponds to the high-frequency alternation between the on and off states of the boost switching device.

[0020] Optionally, the voltage amplitude of the boost converter's output voltage can be adapted based on the varying duty cycle of at least one digital control signal output from the control device. Typically, the digital control signal has an upper signal level and a lower signal level, where the relative distribution of the signal levels is described by the duty cycle. By varying the duty cycle, the operating state of the boost converter can be adapted to ensure the desired output voltage, at least within a finite range.

[0021] Preferably, the output voltage provided by the boost converter is used as the supply voltage for the half-bridge of the converter.

[0022] In some embodiments, the converter further includes at least one filter. The filter is configured to attenuate conducted interference output to the upstream vehicle electrical system. The filter is positioned between the DC voltage source and the boost converter. This prevents interference with the upstream vehicle electrical system.

[0023] Alternatively, the filtering device includes LC elements. The capacitors of the LC elements are arranged in parallel with the half-bridge. This allows for particularly efficient attenuation of conducted interference.

[0024] In some embodiments, the filtering device further includes at least one reverse connection protection device arranged in series between the DC voltage source and the boost converter. This prevents damage caused by incorrect polarity connection of the DC voltage source, which provides the input voltage to the converter.

[0025] Optionally, the boost converter also includes at least one safety switch device arranged in series with the boost switch device. The safety switch device is configured to compensate for converter failure caused by a defect in the boost switch device. Without the safety switch device, a failure of the boost switch device could lead to a short circuit in the boost converter. A short circuit can affect other components of the converter, the vehicle's electrical system, or the power supply network, such as even the motor itself. The safety switch device is configured to prevent such a short circuit. This reduces the risk of damage to the converter or other components. In other words, the safety switch device ensures that the converter can still operate even with a defective boost switch device, although in some cases there may be no activatable boost converter. If the boost switch device is defective, and a short circuit is prevented by opening the safety switch device, then the boost converter is disabled. The converter can then still provide power, but the motor cannot absorb that power at a given output voltage (depending on the speed). In other words, the supply voltage to the half-bridge of the converter can still be ensured, so that the motor remains usable.

[0026] Preferably, the boost converter has at least one safety diode arranged in parallel in the conduction direction with a series circuit comprising at least a boost inductor and a bridgeable boost diode. The safety diode is configured to compensate for converter failure caused by defects 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 is defective. This ensures the basic function of the converter, but the functionality of the boost converter cannot be utilized.

[0027] In some implementations, the boost inductor has multiple individual inductors, i.e., individual inductor elements, arranged in parallel with each other. The total inductance of the boost inductor (L) ges The reciprocal of ) is given by a single inductor (L1 to L) n The sum of the reciprocals of ) yields: .

[0028] Redundancy can be created by connecting multiple individual inductors in parallel. Even if one or more of these individual inductors fail, the converter remains usable, and even the boost converter can still be activated. Only the total inductance resulting from the parallel connection of individual inductors changes. This means that the boost converter will have different characteristics but will still be usable, and even used to increase the amplitude of the supply voltage.

[0029] Preferably, the boost capacitor may also have multiple individual capacitors arranged in parallel with each other. Then the total capacitance of the boost capacitor (C) ges )for: .

[0030] This also creates redundancy for the boost capacitors. When a single capacitor or multiple capacitors fail, the boost converter can still be used. However, the characteristics of the boost converter will be affected. Typically, the boost converter can still be used to increase the voltage amplitude of the supply voltage, depending on the failure condition of the defective capacitor.

[0031] In one theoretical approach, the operating condition of a DC motor can be described using its electrical differential equations: .

[0032] in, This describes the motor terminal voltage, specifically the motor terminal voltage provided by the half-bridge, R. A L represents armature resistance. A Indicates armature inductance, u i k represents the induced back electromotive force. e Let represent the magnetic feedback constant, n represent the motor speed, and i represent the current. In the following text, time-invariant variables are represented by their corresponding uppercase letters (e.g., U, I). For the steady-state operating point, the applicable formula is: .

[0033] Therefore, the applicable ones are: .

[0034] For electrical power Applicable to: , This is a first-order linear function.

[0035] Since the supply voltage appears in both summation terms, it can be seen that changes in the supply voltage lead to changes in both the slope and the y-intercept. As a result, for each supply voltage U, there exists a rotational speed n. max (U) Above this speed, the motor can no longer absorb the predetermined electrical power. Above this speed, the boost converter is activated to increase the amplitude of the output voltage supplied to the half-bridge by the boost converter as the supply voltage.

[0036] According to another aspect, a reversible seatbelt retractor for a vehicle is also provided. The seatbelt retractor includes at least one electric motor and a converter as described above associated with the electric motor. This results in a seatbelt retractor that non-destructively ensures a desired seatbelt webbing force and / or a desired seatbelt webbing retraction speed within a predetermined time interval, such that the seatbelt retractor causes the seatbelt webbing to retract, thereby allowing the occupant to be pulled back or the seatbelt slack to be reduced more quickly in a shorter time interval (compared to reversible seatbelt retractors known to date). Attached Figure Description

[0037] The invention, its further advantageous embodiments, and improvements thereof are described and illustrated in more detail below with reference to the examples shown. Features that can be derived from the specification and drawings can be applied according to the invention, individually or in any combination of multiple features. Wherein: Figure 1 A schematic diagram of a reversible seatbelt retractor according to the invention, comprising a converter according to the invention and a motor associated with the converter; and Figure 2a and 2b A schematic diagram showing the functional principle of the converter according to the present invention and the corresponding signal change curves relative to time is provided. Detailed Implementation

[0038] All features disclosed below with respect to the embodiments and / or drawings may be combined individually or in any sub-combination of features with features of various aspects of this application (including features of preferred embodiments), provided that the resulting combination of features is reasonable to those skilled in the art.

[0039] Figure 1 A schematic diagram of a reversible seatbelt retractor 10 according to the present invention is shown, which includes a converter 12 according to the present invention and a motor 14 associated with the converter 12. Components of the seatbelt retractor 10 that are not essential to the present invention are not shown in the drawings.

[0040] The converter 12 includes a power stage 15 with an H-bridge 16, which here comprises two half-bridges 18. The following functions are shown for only one half-bridge 18, but are to be applied accordingly to all half-bridges 18.

[0041] Currently, each half-bridge 18 includes: a first switching device 20 (e.g., a field-effect transistor) which acts as a high-side switch; and a second switching device 22 (e.g., 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 includes a center tap 24 for providing a corresponding output signal to the motor 14.

[0042] The motor 14 may be, for example, a brushed DC motor.

[0043] Through these two half-bridges 18, the motor 14 is supplied with power signals, which are modulated by pulse width modulation of the half-bridges 18. However, other topologies are also possible, such as three-phase or six-phase motors, which require corresponding modifications to the converter 12, such as the need for AC signals.

[0044] The corresponding half-bridge 18 is line-coupled to the converter 12. The half-bridges 18 are arranged in parallel with each other in a known manner. The converter 12 is coupled to a DC voltage source 26. The DC voltage source 26 includes terminals between which an input voltage U_in for the converter 12 is provided.

[0045] Currently, converter 12 additionally includes boost converter 27. Boost converter 27 has a boost switching device 28 and another switching device, which is formed as a bridgeable boost diode 30. By configuring the bridgeable boost diode 30 as a transistor, the resulting power loss can be reduced in the bridging case. Boost switching device 28 is arranged in parallel with half-bridge 18. The bridgeable boost diode 30 is arranged between boost switching device 28 and half-bridge 18.

[0046] In addition, the boost converter 27 includes a boost capacitor 32, which is arranged in parallel with the half-bridge 18 on the output side of the boost diode 30.

[0047] Furthermore, the 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 here has multiple individual inductors arranged in parallel with each other, thereby providing a safety mechanism in case one of the individual inductors fails.

[0048] The boost capacitor 32 may also have multiple individual capacitors arranged in parallel.

[0049] Furthermore, the converter 12 has a filter 36 including LC elements. The filter 36 has an inductor 38 and a capacitor 40. The capacitor 40 is arranged in parallel with the boost switching device 28 on the input side of the boost inductor 34. The inductor 38 of the filter 36 is connected in series with the reverse connection protection device 42 (another switching device) and is arranged on the input side of the converter 12 between the DC voltage source 26 and the capacitor 40 arranged in parallel with the boost switching device 28.

[0050] The filter device 36 can attenuate conducted interference to the higher-level vehicle electrical system.

[0051] Additional filtering is provided on the output side of the boost switching device 28 via the boost capacitor 32. This improves the signal quality for the half-bridge 18 and, consequently, for the downstream motor 14.

[0052] Furthermore, another switching device, forming a safety switch 44, is arranged in series with the boost switching device 28. If the boost switching device 28 malfunctions and remains on, the safety switch 44 can be used to prevent a short circuit in the boost converter 27. Then, the safety switch 44 is permanently set to the blocking state. This prevents an increase in the amplitude of the output voltage of the boost converter 27.

[0053] This means that the converter 12, starting from the DC voltage source 26, has an inductor 38 of a filter 36 on the first branch of its line, followed by a reverse connection protection device 42. Next is a node that is coupled via a capacitor 40 of the filter 36 to a node on the opposite second branch of the converter 12's line. From this node, the first branch then has a boost inductor 34. Next is another node on the first branch, which is coupled to another node on the second branch of the line and includes a series circuit consisting of a boost switch 28 and a safety switch 44. From this second node, the first branch then has a boost diode 30. Next is a third node on the first branch, which is coupled to the opposite node on the second branch and includes a boost capacitor 32. Furthermore, the half-bridges 18 are arranged in parallel.

[0054] The boost converter 27 can provide an output voltage as the supply voltage for the power stage 15, which has an increased magnitude relative to the input voltage of the DC voltage source 26.

[0055] Additionally, converter 12 has a safety diode 45, which is arranged in parallel with a series circuit consisting of boost inductor 34 and a bridgeable boost diode 30. If boost inductor 34 or bridgeable boost diode 30 fails, safety diode 45 can be used to ensure the basic function of converter 12, but the voltage amplitude increase caused by boost converter 27 cannot be achieved in this case.

[0056] Furthermore, converter 12 has a control device 46 that provides control signals, for example, to the switching devices 20, 22 of half-bridge 18 and at least the boost switching device 28, based on a data processing device, for example, to the corresponding gate electrodes 48. The control signals are currently based on pulse width modulation (PWM). The function of converter 12 can be affected by variations in the duty cycle of the PWM signal. In particular, by adjusting the duty cycle, the amplitude of the output voltage of boost converter 27 can be increased. Therefore, despite the presence of induced back EMF, sufficient electrical power can be ensured for power stage 15 and thus for motor 14 to compensate for the effects caused by the induced back EMF.

[0057] Optionally, the control device 46 may also provide control signals for the bridgeable boost diode 30, reverse connection protection device 42, and safety switch device 44.

[0058] Typically, control device 46 is configured to control the switching devices 20, 22 of half-bridge 18 in such a way that it provides the motor 14 with an output signal adapted to the demand, the control depending, for example, on the relative position of the rotor and stator of the motor 14 and / or the rotational speed of the motor 14. For this purpose, control device 46 may be coupled to other components, such as corresponding sensors. Furthermore, control device 46 may also be coupled to DC voltage source 26 or control equipment for DC voltage source. Additionally, control device 46 is typically coupled to an external higher-level control device, such as an airbag control device. Control device 46 receives information about the motor power demand from this external higher-level control device. For example, the airbag control device may request a specific tightening curve, which is to be executed by the reversible seatbelt retractor 10. The tightening curve may, for example, be stored in a storage device coupled to control device 46. Based on the tightening curve, control device 46 may accordingly adjust the control of converter 12 and, in particular, the control of boost converter 27. The output signal of power stage 15 may be detected, for example, by sensors. Therefore, the maximum electrical power that the motor 14 can actually absorb can be determined based on the rotational speed of the motor 14, thereby determining the difference between the target motor power and the limit power depending on the motor speed. If the difference exceeds or falls below the corresponding difference threshold (depending on the formation of the difference), 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 the tightening phase of the reversible seat belt retractor 10.

[0059] Figure 2a and Figure 2b A schematic diagram showing the functional principle of the converter 12 of the present invention and the corresponding signal change curve relative to time is shown.

[0060] P_on corresponds to the closed (conducting) boost switch 28 (conducting state). P_off corresponds to the open (non-conducting) boost switch 28 (blocking state). After the voltage received by the converter 12 through the DC voltage source 26 is filtered by the inductor 38 and capacitor 40 based on LC elements, an input voltage U_in is applied at the open boost switch 28. At this time, capacitor 40 assumes the input capacitor function associated with the boost converter 27 of the converter 12.

[0061] The boost inductor 34 is responsible for storing charge according to the switching state of the boost switching device 28.

[0062] The bridged boost diode 30 acts as an optional output-side blocking element for the boost converter 27 of the inverter 12. Whether it conducts depends primarily on the voltage magnitude at the boost switching device 28 and the voltage at the boost capacitor 32.

[0063] The boost capacitor 32 serves as the output capacitor of the boost converter 27 and thus as an additional damping element for the downstream half-bridge 18 or the motor 14.

[0064] from Figure 2b As can be seen, as long as the boost switch 28 is closed (conducting; P_on), the voltage U_switch on the boost switch 28 is low because a short circuit occurs. Therefore, during P_on, the current I_switch on the boost switch 28 rises. Since U_switch is lower than U_mot, the boost diode 30 is blocked. Therefore, I_diode is low (or negligible). The boost inductor 34 acts as a charge collector, so I_ind on the boost inductor 34 rises during P_on. When the boost diode 30 is blocked, the motor 14 is powered by the boost capacitor 32.

[0065] When the boost switch 28 is turned on (non-conducting; P_off), the voltage U_switch on the boost switch 28 rises sharply. In particular, it rises so high that it exceeds the voltage on the boost capacitor (32). As a result, the boost diode 30 turns on, and the charge stored in the boost inductor 34 during P_on can be released. Therefore, during P_off, I_ind decreases from its initial maximum value. Consequently, the current I_diode on the boost diode 30 also first reaches its maximum value and decreases during P_off. Since the boost switch 28 is in the on switching state, no current flows, making I_switch zero during P_off.

[0066] Furthermore, it can be seen that the current intensity I_mot output to motor 14 is constant during P_on and P_off. The back electromotive force induced by the rotation of motor 14 is not shown. However, the variation in the supply voltage U_mot output to motor 14 can compensate for the effect of the back electromotive force. Therefore, despite the existence of the back electromotive force induced by the rotation of motor 14, constant power absorption by motor 14 can be achieved.

[0067] Some embodiments disclosed herein, particularly the various modules, use circuitry (e.g., one or more circuits) to implement the standards, protocols, methods, or techniques disclosed herein, to functionally 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. Any type of circuitry can be used.

[0068] In one embodiment, the circuit (Schaltkreis) includes, but is not limited to, one or more computing devices, such as a processor (e.g., a microprocessor), a central 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 electronic components, or combinations thereof. In one embodiment, the circuit includes a hardware circuit implementation (e.g., an implementation in analog circuitry, an implementation in digital circuitry, etc., or combinations thereof).

[0069] In one embodiment, the circuit includes a combination of circuitry and a computer program product having software or firmware instructions stored on one or more computer-readable storage media, and the instructions cooperating to cause the device to perform one or more protocols, methods, or techniques described herein. In one embodiment, the circuitry technology includes circuitry that requires software, firmware, etc., to function, such as a microprocessor or microprocessor component. In one embodiment, the circuitry includes one or more processors or components thereof, and corresponding software, firmware, hardware, etc.

[0070] In this application, quantities and numerical values ​​may be mentioned. Unless otherwise expressly stated, these quantities and numerical values ​​should not be construed as limiting, but rather as examples of possible quantities or numerical values ​​relating to this application. In this context, the term "multiple" may also be used to refer to quantities or numerical values. In this context, the term "multiple" means any numerical value greater than one, such as two, three, four, five, etc. The terms "approximately," "about," "close to," etc., indicate a deviation of ±5% from a given numerical value.

[0071] Although this application has been illustrated and described with respect to one or more embodiments, those skilled in the art will recognize equivalent changes and modifications upon reading and understanding this specification and the accompanying drawings. Furthermore, while specific features of this application are disclosed with respect to only one of several embodiments, such features may be combined with one or more other features of other embodiments, as may be desirable and advantageous for a given or particular application.

Claims

1. A converter (12) for a motor (14) of a reversible seatbelt retractor (10), the converter comprising at least two half-bridges (18) arranged in parallel, each half-bridge having at least two switching devices (20, 22), wherein each half-bridge (18) has a center tap (24) between the at least two switching devices (20, 22) for providing a corresponding output signal to the motor (14), wherein the converter (12) is coupled to a DC voltage source (26) at its input terminals, wherein the converter (12) is coupled to a DC voltage source (26) at its input terminals. The current voltage source (26) has at least one boost converter (27) between it and the at least two half-bridges (18), the boost converter being configured to provide a supply voltage to at least the half-bridges (18) having a voltage amplitude that is increased compared to the input voltage provided at the input terminals, and the converter (12) includes a control device (46) that is at least coupled to the boost converter (27) and configured to activate the boost converter (27) before or during the tightening phase of the reversible seat belt retractor (10).

2. The converter (12) according to claim 1, characterized in that, The control device (46) is configured to activate the boost converter (27) if the difference between the target motor power given in advance for the motor (14) and the maximum absorbable power that the motor (14) can absorb exceeds or falls below a difference threshold.

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

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

5. The converter (12) according to claim 4, characterized in that, The boost switch (28) is arranged in parallel with the half-bridge (18), the boost inductor (34) is arranged between the DC voltage source (26) and the boost switch (28), the boost diode (30) is arranged in the conduction direction between the boost switch (28) and the parallel half-bridge (18), and the boost capacitor (32) is arranged in parallel with the half-bridge (18).

6. The converter (12) according to claim 4 or 5, characterized in that, The boost converter (27) is configured to ensure that the voltage amplitude on the boost capacitor (32) is higher than the voltage amplitude of the input voltage provided at the input terminal.

7. The converter (12) according to any one of the preceding claims, characterized in that, The voltage amplitude of the output voltage of the boost converter (27) can be adapted to the changing duty cycle of at least one digital control signal output by the control device (46).

8. The converter (12) according to any one of claims 4 to 7, characterized in that, The boost converter (27) also has at least one safety switch (44) configured to compensate for failure of the converter (12) due to a defect in the boost switch (28).

9. The converter (12) according to any one of claims 4 to 8, characterized in that, The boost converter (27) has at least one safety diode (45) arranged in parallel in the conduction direction with a series circuit including at least the boost inductor (34) and the boost diode (30), and the safety diode is configured to compensate for failure of the converter (12) due to defects in the boost inductor (34) and / or the boost diode (30).

10. The converter (12) according to any one of claims 4 to 9, characterized in that, The boost inductor (34) has multiple individual inductors arranged in parallel with each other.

11. The converter (12) according to any one of claims 4 to 10, characterized in that, The boost capacitor (32) has multiple individual capacitors arranged in parallel with each other.

12. A reversible seatbelt retractor (10) for a vehicle, comprising at least one electric motor (14) and a converter (12) associated with said electric motor (14) according to any of the preceding claims.

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