Auxiliary unit for a motor vehicle

Abstract

The invention relates to an auxiliary unit (6) for a motor vehicle (2), in particular to an electromotive refrigerant compressor, which auxiliary unit has a first connection (12) for a low-voltage on-board electrical system (8). A supply input (36) of a control unit (24) is connected to the first connection (12) by means of a flyback converter (34) which has a primary coil (40) which is in electrical contact with the first connection (12), and a secondary coil (46) which is in electrical contact with the supply input (36). A voltage tester (54) is connected in parallel with the secondary coil (46) and is in contact with a monitoring input (38) of the control unit (24). The invention also relates to a motor vehicle (2).

Description

[0001] Description

[0002] Auxiliary unit for a motor vehicle

[0003] The invention relates to an auxiliary unit for a motor vehicle. The auxiliary unit has a first connection for a low-voltage electrical system and is, in particular, an electric motor-driven refrigerant compressor.

[0004] Motor vehicles typically have a variety of auxiliary units, designed, for example, as adjustment drives. These serve not primarily to propel the vehicle, but also, for example, to influence other functions of the vehicle. In particular, they serve to increase comfort. For this purpose, the auxiliary units typically have an electric motor, which drives other components. The electric motor is, for example, brushless. This reduces wear. The electric motor itself typically has a number of electromagnets, which create a rotating magnetic field during operation. At the very least, however, the magnetic field changes over time. For this purpose, or at least to adjust the speed of the electric motor, the auxiliary unit includes a control unit, which supplies the electromagnets with appropriate current.As a result, the control unit also influences the behavior of other components driven by the electric motor.

[0005] The control unit typically includes a microcontroller, which is programmable, for example. This allows for flexible adaptation to different motor vehicle types and / or intended uses. Alternatively, the control unit is formed by an application-specific integrated circuit (ASIC). If the electric motor is present and configured as a brushless DC motor, the control unit operates, in particular, a converter. The control unit generates control commands for semiconductor switches of the converter, depending on which commands the semiconductor switches are electrically conductive or electrically non-conductive.

[0006] To power the auxiliary unit, a vehicle's electrical system, such as a low-voltage electrical system, is typically used. This usually carries a direct current of 12 V, 24 V, or 48 V. This also represents the maximum electrical voltage that can then be applied to the electric motor by the control unit, particularly due to appropriate operation of any converter. If a comparatively high level of power is to be provided by the auxiliary unit, particularly since comparatively large forces are required to drive the other components, it is necessary to carry a comparatively high electrical current via the electrical system. This requires comparatively robust electrical cables, which increases manufacturing costs and weight.

[0007] To remedy this, motor vehicles are increasingly equipped with a high-voltage electrical system, which supplies a direct current of over 60 V, such as 400 V or 800 V. For example, the high-voltage electrical system is used to power the motor vehicle's main drive, particularly if the motor vehicle is designed as an electric vehicle. If the electric motor of the auxiliary unit is powered by the high-voltage electrical system, the required electrical current is reduced for the same power output. As a result, the demands on the electrical cables are reduced, and so are weight and manufacturing costs.

[0008] The control unit, however, contains microelectronics that cannot be operated with such high electrical voltages. Therefore, the low-voltage electrical system is usually used for this, so that the auxiliary unit has two connections for the different electrical systems. Typically, a converter is also assigned to the connection for the low-voltage electrical system, which reduces the electrical voltage supplied by the low-voltage electrical system, and the control unit is usually operated with an electrical voltage below 6 V. This makes it possible to design it comparatively cost-effectively. However, since the control unit operates the components of the low-voltage electrical system that are powered by the high-voltage electrical system, it is necessary to create galvanic isolation between the control unit and the low-voltage electrical system, so the converter is usually designed as a so-called flyback converter.

[0009] During operation of the vehicle, it is also possible that fluctuations may occur in the electrical voltage supplied by the low-voltage electrical system. If the electrical voltage is too high or too low, the voltage supplied by the converter is not suitable for fault-free operation of the control unit. Therefore, the electrical voltage present in the low-voltage electrical system is usually detected by a corresponding sensor and transmitted to the control unit via a galvanically isolated interface. This control unit is then shut down if the electrical voltage supplied by the low-voltage electrical system is too high or too low, preventing unforeseen behavior of the auxiliary unit.For cost reasons, the interface and / or the sensor are designed in binary form, and this is used to simply transmit to the control unit whether the electrical voltage supplied by the low-voltage vehicle electrical system is suitable for operation or not.

[0010] The invention is based on the object of specifying a particularly suitable auxiliary unit for a motor vehicle and a particularly suitable motor vehicle, wherein in particular manufacturing costs are reduced and / or functionality is increased.

[0011] With regard to the auxiliary unit, this object is achieved according to the invention by the features of claim 1 and with regard to the motor vehicle by the features of claim 9. Advantageous further developments and refinements are the subject of the respective subclaims. The auxiliary unit, in the assembled state, is expediently of a motor vehicle. Thus, the auxiliary unit is suitable, in particular intended and configured, to be mounted on other components of the motor vehicle. The auxiliary unit is also preferably intended for such operation. In this case, the auxiliary unit does not directly serve to propel the motor vehicle, but for example to operate a main drive and / or to provide comfort functions.

[0012] The motor vehicle is particularly land-based and preferably comprises a number of wheels by means of which contact with a roadway or the like is established. It is advantageously possible to position the motor vehicle anywhere on the roadway, making the motor vehicle independent of rails or the like. The motor vehicle is, for example, a commercial vehicle, such as a lorry or a bus. The motor vehicle is particularly preferably a passenger car.

[0013] For example, the auxiliary unit is a pump, in particular a water or oil pump, such as a lubricant pump. Alternatively, the auxiliary unit is an adjustment drive, such as a power steering system, a window regulator, or an electric seat adjustment. In another alternative, the auxiliary unit is, for example, an electric motor-driven refrigerant compressor. The electric motor-driven refrigerant compressor serves to compress refrigerant in a refrigerant circuit, i.e., to increase pressure. For example, the electric motor-driven refrigerant compressor is used to control the temperature of the interior of the motor vehicle and / or to cool an energy storage device of the motor vehicle, such as a high-voltage battery.

[0014] The auxiliary unit has a first connection for a low-voltage electrical system. In other words, the first connection is suitable, in particular provided and configured, for electrical contact with the low-voltage electrical system, so that during operation, the auxiliary unit is preferably at least partially supplied with power via the first connection. During operation, a direct voltage of less than 100 V or 60 V is supplied by the low-voltage electrical system. Alternatively, the electrical voltage supplied by the low-voltage electrical system is a direct voltage of 12 V, 24 V, or 48 V.

[0015] The auxiliary unit further comprises a control unit, by means of which, during operation, in particular the control and / or regulation of further functions of the auxiliary unit is carried out. Preferably, the control unit is used to generate control commands and / or evaluate data, for example measurement data provided by sensors assigned to the auxiliary unit. The control unit has, for example, a microprocessor, which is preferably designed to be programmable. For example, the control unit is formed by the microprocessor. Alternatively, the control unit has, for example, an application-specific integrated circuit (ASIC) and is formed by means of the latter. In a further alternative, the control unit is constructed from several discrete components. In a further embodiment, the control unit comprises parts thereof, so that it is constructed from different components.

[0016] The control unit has a supply input and a monitoring input. Power is supplied to the control unit via the supply input. In other words, operation of the control unit is only possible when an electrical voltage or at least an electrical potential is applied to the supply input. In particular, the control unit has a reference input which, in the assembled state, is suitably electrically connected to ground. Thus, it is only necessary to provide a single connector, pin, or the like at the supply input, and the electrical voltage is then applied between the reference input and the supply input. Alternatively, the supply input suitably comprises two different connectors / pins between which the electrical voltage is applied during operation.

[0017] The monitoring input is used, in particular, to monitor parameters. The control unit is preferably only operated or operable when an electrical voltage or a specific electrical potential is applied to the monitoring input. The monitoring input thus ensures that the control unit is not operated at parameters that could cause unwanted or unforeseen behavior.

[0018] The auxiliary unit further comprises a flyback converter. The flyback converter enables the conversion of an electrical direct voltage. For this purpose, the flyback converter has a primary coil and a secondary coil. The primary coil is electrically connected in series with a switch, in particular a semiconductor switch, which is actuated at a frequency of over 20 kHz during operation, for example. The primary coil is assigned to the first terminal, and the series circuit comprising the switch and the primary coil is preferably electrically contacted with the first terminal and preferably connected between them. Thus, during operation, provided the switch is closed, the electrical voltage applied to the first terminal is present at the primary coil.

[0019] The secondary coil is magnetically, but not electrically, coupled to the primary coil. Preferably, a series circuit comprising a blocking diode and a smoothing capacitor is connected in parallel with the secondary coil. The secondary coil, on the other hand, is electrically connected to the supply input, preferably via the blocking diode. Preferably, the supply input is directly electrically connected to the smoothing capacitor. For example, the smoothing capacitor is connected between the two plugs of the supply input. If a reference input is present, the smoothing capacitor is connected between ground and the supply input.

[0020] When the switch is actuated in rapid succession, a time-varying magnetic field is generated by the primary coil, which induces an electrical voltage in the secondary coil. This leads to an electrical current flow, particularly via any blocking diode, so that the smoothing capacitor is charged, resulting in an electrical voltage being applied to it. The ratio of the electrical voltage applied to the smoothing capacitor to the maximum voltage that can be applied to the primary coil, in particular the electrical voltage applied to the first terminal, is determined by the winding ratio of the primary coil and the secondary coil.

[0021] In summary, during operation, the electrical voltage applied, in particular, to the smoothing capacitor is present at the supply input. For example, two lines are routed from the flyback converter to the supply input. Preferably, however, one of the terminals of the secondary coil is electrically connected to ground, and the reference input of the control unit is also electrically connected to ground. The other terminal of the secondary coil, however, is routed to the supply input, preferably via the blocking diode. Thus, only a single electrical line is required to connect the flyback converter to the control unit, while the electrical voltage provided by the flyback converter is still applied to the control unit.

[0022] In particular, the electrical voltage provided by the secondary coil is lower than the electrical voltage applied to the primary coil / at the first terminal, allowing comparatively inexpensive components to be used for the control unit. In particular, the electrical voltage provided by the flyback converter is between 2 V and 6 V and is, for example, substantially equal to 3.3 V or 4 V.

[0023] The auxiliary unit further comprises a voltage tester. The voltage tester enables checking an electrical voltage. For example, the voltage tester comprises a sensor for detecting an electrical voltage, and the voltage tester is thus suitable, in particular provided and configured, to detect an electrical voltage, for example quantitatively or merely qualitatively. The voltage tester is connected in parallel to the secondary coil. Thus, during operation, the electrical voltage applied to the secondary coil is expediently detected by means of the voltage tester. The electrical voltage applied to the secondary coil is also applied to the voltage tester. This simplifies the detection of the electrical voltage applied to the secondary coil.

[0024] The voltage tester, in turn, is connected to the monitoring input of the control unit. The voltage tester, in particular, has a supply connection to which a signal corresponding to the electrical voltage detected by the voltage tester is applied or output. The monitoring input is connected at least signal-wise, preferably electrically, to the voltage tester, suitably the supply connection. For example, during operation, only digital data is provided by the voltage tester, or preferably analog data.

[0025] In summary, the electrical voltage applied to the secondary coil serves, on the one hand, to power the control unit so that it can operate. On the other hand, the electrical voltage applied to the secondary coil is monitored by the control unit, for which purpose the voltage tester is used.

[0026] Thanks to the voltage tester, the control unit has knowledge of the electrical voltage applied to the secondary coil. However, this electrical voltage depends on the voltage applied to the primary coil, i.e. the electrical voltage supplied by the low-voltage vehicle electrical system. In other words, there is a functional relationship between these electrical voltages. This makes it possible to use the control unit's monitoring input to check whether, for example, there are relatively large fluctuations in the low-voltage vehicle electrical system, which is why the electrical voltage supplied by the flyback converter is outside the range required for safe operation of the control unit. In this case, the operation of the control unit is preferably stopped or at least reduced to prevent unforeseen behavior. This increases the safety of the auxiliary unit during operation.The control unit is galvanically isolated from the low-voltage electrical system thanks to the flyback converter. This prevents interference between the two, further increasing safety. Nevertheless, the side of the auxiliary unit that is galvanically isolated from the low-voltage electrical system still has information about the electrical voltage supplied by the low-voltage electrical system, and no additional galvanically isolating interface is required to transmit the data. This reduces manufacturing costs. This also makes it possible to check whether, for example, the flyback converter is malfunctioning. This means that the electrical voltage supplied by the low-voltage electrical system is constant.However, if there is an insulation fault in the secondary coil, it is possible that fluctuations in the voltage applied to the supply input may occur due to an arc, and / or that this voltage may be reduced compared to the desired voltage. This can be determined using the voltage tester, thus increasing functionality. Preferably, such a fault leads to a shutdown or at least reduced operation of the control unit, thus also increasing safety.

[0027] In the case of the auxiliary unit, the control unit is preferably galvanically isolated from the first connection and / or the low-voltage vehicle electrical system. In the case of the auxiliary unit, with the exception of a primary side of the flyback converter, which has the primary coil, all other components are preferably galvanically isolated from the first connection / the low-voltage vehicle electrical system. This further increases safety. For example, the switch of the flyback converter is actuated by means of the control unit, or this is preferably operated by means of an oscillating circuit of the flyback converter itself, so that robustness is increased. This also enables operation of the flyback converter independently of the control unit. For example, the voltage tester and the flyback converter are two separate units. However, they are particularly preferably combined into a common unit. The flyback converter preferably comprises a voltage tester.

[0028] For example, the voltage tester comprises an electrical voltage sensor, in particular a circuit and / or a shunt. This allows comparatively accurate detection of the electrical voltage. However, the voltage tester preferably comprises a series circuit comprising a diode and a capacitor, which expediently comprises a capacitor and is formed by means of the capacitor, for example. The series circuit comprising the diode and the capacitor is connected in particular in parallel to the secondary coil. In particular, one side of the capacitor is connected directly to a terminal of the secondary coil, in particular via ground. The other side of the capacitor is electrically contacted with any supply terminal or forms this. This side of the capacitor is thus connected to the supply terminal. The electrical voltage arising across the capacitor is therefore present at the supply terminal.Due to the series connection, the capacitor is charged to a maximum value, which corresponds specifically to the maximum voltage applied to the secondary coil. In other words, the voltage tester determines the maximum voltage of the secondary coil during operation, i.e., the maximum voltage provided by the flyback converter.

[0029] A blocking diode and / or a smoothing capacitor are suitably present. The blocking diode and the smoothing capacitor are preferably connected electrically in parallel with the diode and the capacitor. The blocking direction of the two diodes is expediently different. When electrical energy is dissipated from the secondary coil, the electrical current flows via the blocking diode to the smoothing capacitor, so that it is charged. The diode, on the other hand, prevents current from flowing to the capacitor. When an opposite electrical current flows through the secondary coil, on the other hand, the electrical current flows from the capacitor via the diode to the secondary coil, which charges the capacitor. The electrical voltage to which the capacitor is charged is related to the electrical current flowing through the secondary coil, which results from the induction by the primary coil.Due to such a design, the manufacturing costs of the voltage tester are comparatively low, and robustness is increased. For example, the voltage tester is formed solely by a series of diodes and capacitors. However, it is particularly preferred that a first resistor be connected between the secondary coil and the series circuit. In other words, the first resistor is located between the series circuit and one of the two terminals of the secondary coil. Thus, the series circuit comprising the first resistor, the diode, and the capacitor is connected in parallel with the secondary coil, or additional components are present. The first resistor eliminates artifacts, particularly short-term oscillations.Alternatively or in combination with this, damping takes place in the resonant circuit formed by the secondary coil and the capacitance, so that there is no excessive influence on the electrical voltage required for the operation of the control unit.

[0030] Alternatively, or particularly preferably in combination with this, a second resistor is connected in parallel with the capacitor. This also serves to dampen oscillations. It also discharges the capacitor in a controlled manner, so that the secondary coil can always be recharged without destroying the capacitor. Alternatively, or in combination with this, the second resistor sets the maximum electrical voltage across the capacitor, thus facilitating further processing. This also ensures that the values ​​provided by the voltage tester are within a range that can be processed by the control unit.

[0031] Preferably, the supply input is electrically connected to the monitoring input. This transmits an analog signal to the monitoring input, enabling a comparatively precise check of the status of the flyback converter and, consequently, the low-voltage vehicle electrical system.

[0032] For example, the voltage tester is electrically connected directly to the monitoring input. For example, the supply input of the voltage tester is directly connected to the monitoring input. However, these are particularly preferably electrically connected to one another via a voltage divider. The voltage divider adjusts the electrical voltage provided by the voltage tester, which facilitates processing by the control unit. It is not necessary to adapt the voltage tester to the control unit, and this can be implemented using comparatively inexpensive components. For example, the voltage divider is a separate component or, preferably, is integrated into the voltage tester and / or the flyback converter, forming a common unit.

[0033] The voltage tester is connected to the supply input via the voltage divider. The voltage divider is thus connected to a fixed reference potential, namely the potential present at the supply input, which is provided by the flyback converter itself, thus reducing complexity and simplifying wiring. In summary, the voltage divider is connected in particular between the supply connection and the supply input. If the capacitance and / or the second resistor are present, the voltage divider is electrically connected in series with them, with this series connection preferably being connected in parallel to the secondary coil or, more preferably, to any smoothing capacitor. The voltage divider suitably has a third and a fourth resistor, which are electrically connected in series. A tap is formed between these, which is connected to the monitoring input.Due to such a design, the number of components required for the voltage divider is reduced, which means that manufacturing costs are reduced.

[0034] For example, no additional components are present for damping the electrical voltage applied to the secondary coil. However, it is particularly preferred that a "snubber" be connected in parallel to the secondary coil. This serves in particular to dampen high-frequency interference components, thus improving electromagnetic compatibility (EMC). The snubber expediently comprises a series circuit consisting of a capacitor and a resistor (RC element) or a snubber capacitor. In a further embodiment, the snubber comprises, for example, a protective diode or other electronic measures for interference suppression. Due to the snubber, the data provided by the voltage tester is reduced, thus simplifying evaluation by the control unit.

[0035] For example, the auxiliary unit has only the first connection and / or, in the assembled state, is only electrically connected to the low-voltage vehicle electrical system. However, the auxiliary unit particularly preferably comprises a second connection for a high-voltage vehicle electrical system. In the assembled state, a high-voltage vehicle electrical system of the motor vehicle is connected to the second connection, by means of which, in particular, a direct current voltage above 100 V or 200 V is provided. In particular, the electrical voltage provided by the high-voltage vehicle electrical system is substantially equal to 400 V or 800 V.

[0036] The second terminal is in particular connected to a converter of the auxiliary unit, which suitably comprises a number of adjustable components, in particular semiconductor switches. The converter preferably comprises a bridge circuit with a number of bridge branches, for example, three bridge branches. Preferably, each bridge branch is assigned a series circuit of two semiconductor switches, which are connected in parallel to each other and to the second terminal.

[0037] The converter is operated by means of the control unit. Preferably, the control unit comprises a driver circuit for the semiconductor switches, or at least one driver circuit is operated by means of the control unit. During operation, switching times for the semiconductor switches of the converter are specified by means of the control unit. Due to the second connection and the converter, it is possible to provide a comparatively high power by means of the auxiliary unit, wherein the required electrical currents are comparatively low due to the comparatively high electrical voltage applied to the second connection. Due to the flyback converter, a galvanic isolation of the control unit, which is connected to the second connection at least via the driver circuit or other component, from the first connection is achieved.Thus, the vehicle's two electrical systems—the on-board power system and the low-voltage power system—are galvanically isolated, even though both are used to operate the auxiliary unit. This increases safety and electromagnetic compatibility.

[0038] For example, an alternating voltage and / or an alternating current is provided by means of the converter. In particular, this is output from the auxiliary unit. However, the auxiliary unit particularly preferably comprises an electric motor which is operated by means of the converter. The converter preferably comprises a B6 circuit, and the electric motor has a three-phase design. In this case, the electric motor is expediently a brushless direct current motor (BLDC) and has three phases. In particular, each of the phases is assigned the same number of electromagnets. The phases of the electric motor are preferably connected to one another in a delta or star connection. In one alternative, the electric motor is, for example, brush-type and in particular a brush-type commutator motor.

[0039] Preferably, another component of the auxiliary unit is driven by the electric motor, for example, a pump impeller or, more preferably, a compressor. In this case, the auxiliary unit is expediently designed as an electric motor-driven refrigerant compressor. Due to the second connection, it is possible to generate a comparatively high power output using the electric motor, while the electrical cables used to power the auxiliary unit require only a low current-carrying capacity.

[0040] The motor vehicle is, for example, a commercial vehicle, such as a truck or bus. However, the motor vehicle is particularly preferably a passenger car (car). The motor vehicle in particular has a main drive by means of which locomotion of the motor vehicle can be realized. In other words, it is moved when the main drive of the motor vehicle is in operation. Furthermore, the motor vehicle comprises an auxiliary unit which therefore does not directly serve for propulsion. For example, the auxiliary unit is a pump. Particularly preferably, the auxiliary unit is an electric motor-driven refrigerant compressor. The electric motor-driven refrigerant compressor is in particular a component of a refrigerant circuit of the motor vehicle, which preferably also comprises an evaporator and at least one heat exchanger / heat transfer device. The electric motor-driven refrigerant compressor has a compressor head which is suitably driven by an electric motor of the auxiliary unit.

[0041] The auxiliary unit has a first connection for a low-voltage vehicle electrical system, and a supply input of a control unit of the auxiliary unit is connected to the first connection via a flyback converter, which comprises a primary coil electrically connected to the first connection and a secondary coil electrically connected to the supply input. A voltage tester is connected in parallel to the secondary coil and is connected to a monitoring input of the control unit.

[0042] The motor vehicle preferably includes the low-voltage electrical system, which provides a direct current between 12 V and 48 V. In particular, the first terminal is electrically connected to the low-voltage electrical system. Thus, when the motor vehicle is in operation, the flyback converter is powered by the low-voltage electrical system.

[0043] The further developments and advantages described in connection with the auxiliary unit are to be transferred analogously to the motor vehicle and vice versa.

[0044] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0045] Fig. 1 schematically shows a motor vehicle with an auxiliary unit,

[0046] Fig. 2 schematically simplifies the structure of the auxiliary unit, and

[0047] Fig. 3 shows a simplified schematic diagram of a section of the auxiliary unit. Corresponding parts are labeled the same in all figures.

[0048] Figure 1 shows a simplified schematic of a motor vehicle 2 in the form of a passenger car (car). The motor vehicle 2 has a number of wheels 4, by means of which contact is made with a road surface (not shown in detail). At least two of the wheels 4 are driven by a main drive (not shown in detail). Likewise, at least two of the wheels 4, which are driven or not driven, for example, by the main drive, are part of a steering system and can be rotated about a vertical axis relative to a body of the motor vehicle 2, thereby setting a direction of travel of the motor vehicle 2.

[0049] The motor vehicle 2 further comprises an auxiliary unit 6, which serves to provide comfort functions for a user of the motor vehicle and thus not for the direct propulsion of the motor vehicle 2. In this exemplary embodiment, the auxiliary unit 6 is an electric motor-driven refrigerant compressor. The auxiliary unit 6 is electrically connected to a low-voltage electrical system 8 of the motor vehicle 2, wherein the low-voltage electrical system 8 is fed by a low-voltage battery 10. A direct current of 12 V is provided by the low-voltage battery 10, which is thus carried by the low-voltage electrical system 8. The low-voltage electrical system 8 is connected to a first connection 12 of the auxiliary unit. Furthermore, the auxiliary unit 6 is electrically connected to a high-voltage electrical system 14, which is connected to a second connection 16 of the auxiliary unit 6.The high-voltage electrical system 14 is fed by a high-voltage battery 18, by means of which an electrical direct voltage of 400 V is provided.

[0050] The auxiliary unit 6 has an electric motor 20, which drives a compressor head (not shown in detail) of the electric motor-driven refrigerant compressor. The electric motor 20 is designed as a brushless direct current (BLDC) motor and has three phases. To power the electric motor 20, the auxiliary unit 6 includes an inverter 22, which has a bridge circuit, namely a B6 circuit. By actuating a

[0051] A suitable, time-varying electrical voltage is applied to the phases of the electric motor 20 via the bridge circuit switch, causing it to rotate. The electric motor 20 is thus driven by the converter 22.

[0052] The converter 20 is powered from the high-voltage vehicle electrical system 14 via the second terminal 16, so that the electrical voltage present at the second terminal 16 is applied to the bridge circuit. Thus, the second terminal 16 is electrically connected to the converter 22. A comparatively high power can be provided by the converter 22 and thus also by the electric motor 20.

[0053] The converter 22 is operated by a control unit 24. The switching time of the semiconductor switches of the converter 22 is specified by the control unit 24, so that the electric motor 20 operates at a predetermined rotational speed. The control unit 24, in turn, is powered by the low-voltage vehicle electrical system 8 via the first connection 12. Thus, it is not necessary to adapt the components of the control unit 24 to the comparatively high electrical voltage provided by the high-voltage vehicle electrical system 14, thus reducing manufacturing costs.

[0054] Figure 2 shows a simplified schematic block diagram of the structure of the auxiliary unit 6. The second connection 16 has two connectors or pins, each with a different electrical potential, so that a DC voltage of 400 V is applied between them. Each connector of the second connection 16 is electrically connected to the converter 22, which is connected to the electric motor 20 by means of three phase lines. Furthermore, one of the electrical potentials is connected to ground 26, which is defined in particular by the body of the motor vehicle 2.

[0055] Ground 26 is also connected to a reference input 28 of the control unit 24, which is signal-connected to the converter 20 via several control lines 30 (not shown in detail). There is no galvanic isolation between the control unit 24 and the converter 22, nor from the second connection 16, and therefore also not from the high-voltage vehicle electrical system 14. Rather, the second connection 16, the control unit 24, the converter 22, and the electric motor 20 are located within a common zone 32.

[0056] Zone 32 is galvanically isolated from the low-voltage vehicle electrical system 8 by means of a flyback converter 34, so that one boundary of zone 32 runs along the flyback converter 34. Outside zone 32, the flyback converter 34 is connected to the first terminal 12. Within zone 32, the flyback converter 34 is connected to a supply input 36 of the control unit 24 and to ground 26. When the flyback converter 34 is in operation, an electrical direct voltage of 3.3 V is provided between the supply input 36 and ground 26. Consequently, the first terminal 12 is connected to the control unit 24 by means of the flyback converter 34. In addition, the flyback converter 34 is connected, namely indirectly, to a monitoring input 38 of the control unit 24.

[0057] When the auxiliary unit 6 is operating, the flyback converter 34 provides an electrical voltage suitable for operating the control unit 24, namely 3.3 V, which is applied between the supply input 36 and ground 26, wherein the electrical voltage present at the first terminal 12 is queried via the monitoring input 38. If fluctuations occur in the electrical voltage of the low-voltage vehicle electrical system 8, these fluctuations also occur in the electrical voltage provided by the flyback converter 34 within the zone 32. The electrical DC voltage currently prevailing in the low-voltage vehicle electrical system 8 can be derived from the electrical potential applied to the monitoring input 38.If the electrical voltage is not suitable for safe operation of the flyback converter 34 and thus of the control unit 24, functions of the control unit 24 are restricted and, in particular, no more control commands are generated for the converter 22.

[0058] Figure 3 shows a simplified schematic section of a circuit diagram of the auxiliary unit 6, namely the first terminal 12, which is electrically connected to the flyback converter 34. The flyback converter 34 connects to a coil 40, which is electrically connected in series with a switch 42 between the terminal 12. If the switch 42 is closed, the electrical voltage provided by the low-voltage vehicle electrical system 8 is applied to the primary coil. Connected in parallel to the series circuit of the primary coil 40 and the switch 42 is an additional capacitor 44, by means of which the electrical voltage used to operate the primary coil 40 is at least partially stabilized.

[0059] The primary coil 40 is magnetically coupled to a secondary coil 46 of the flyback converter 34. The flyback converter 34 has a diode 48 connected in series with the secondary coil 46. This series connection is connected between ground 26 and the supply input 36, as well as to one of the flyback converter 34. Thus, the smoothing capacitor 50 is connected between ground 26 and the supply input 36, and by means of this capacitor, the electrical voltage provided by the flyback converter 34 is at least partially stabilized.

[0060] When the flyback converter 34 is operating, the switch 42 is periodically actuated, with the frequency being above 20 kHz, so that the operation of the flyback converter 34 is inaudible to humans. Actuating the switch 42 energizes the primary coil 40 at a variable rate over time, creating a variable magnetic field. This induces an electrical voltage in the secondary coil 46, which leads to an electrical current flow. Due to the diode 48, this current is conducted out of the secondary coil 46 in only one direction, namely to the supply input 36, charging the smoothing capacitor 50, which stabilizes the applied electrical voltage.

[0061] A snubber 52 comprising an RC element is connected in parallel with the secondary coil 46. The snubber 52 filters out high-frequency components of the electrical voltage provided by the secondary coil 46, so that, in conjunction with the smoothing capacitor 50, a substantially constant electrical voltage is applied to the supply input 46, at least as long as the electrical voltage provided by the vehicle electrical system 8 remains within a predetermined range.

[0062] The auxiliary unit 6 further comprises a voltage tester 54 connected in parallel to the secondary coil 46. The voltage tester 54 comprises a first resistor 56, a diode 58, and a capacitor 60, which are electrically connected in series with one another. This series circuit is thus connected between the supply input 36 and ground 26. The capacitor 60 is provided by a capacitor and bridged by a second resistor 62. The second resistor 62 is thus connected between ground 26 and the diode 58. In summary, the voltage tester 54 comprises the series circuit of the diode 58 and the capacitor 60, with the first resistor 56 connected between this series circuit and the secondary coil. The second resistor 62, in turn, is connected in parallel with the capacitor 60.

[0063] A supply output 64 of the voltage tester 54 is formed between the capacitor 60 and the diode 58, to which the second resistor 60 is also connected. A voltage divider 66 is connected between the supply output 64 and the supply input 36. The voltage divider 66 comprises a third resistor 68 and a fourth resistor 70 which are electrically connected in series. This series connection is connected between the supply output 64 and the supply input 36. A tap 20 is formed between the third and fourth resistors 68, 70 and is connected to the monitoring input 38. In summary, the voltage tester 54 is electrically contacted with the supply input 36 via the voltage divider 66, which comprises the third and fourth resistors 68, 70 which are electrically connected in series, with the tap 72 being formed between them and is connected to the monitoring input 38.

[0064] If, during operation, the secondary coil 46 is charged due to the magnetic field created by the primary coil 40, this can only occur via the voltage detector 54 due to the blocking diode 48. In other words, a current flows via the capacitor 60 and the diode 58 to the secondary coil 46. In this case, the capacitor 60 is charged to a value that corresponds to the maximum in c

[0065] 46. ​​Thus, during operation, the maximum electrical voltage induced in the secondary coil 46 due to the operation of the switch 42 is detected. This voltage depends on the electrical voltage applied to the first terminal 12, with the relationship being determined by the ratio of the number of windings of the primary coil 40 and the secondary coil 46.

[0066] The first and second resistors 56, 62 also adjust the voltage appropriately, allowing the capacitor 60 to be designed to be comparatively small. These resistors 56, 62 also provide attenuation, so that a substantially constant electrical voltage is applied to the capacitor 60. Consequently, the electrical potential of the supply output 64 is substantially constant. The electrical potential is set to a suitable value by the voltage divider 66, allowing a query to be performed by the control unit 24.

[0067] In summary, the supply input 36 of the control unit 24 is connected to the first terminal 12 via the flyback converter 34. The flyback converter 34 has the primary coil 40, which is electrically connected to the first terminal 12, and the secondary coil 46, which is electrically connected to the supply input 36. Connected in parallel to the secondary coil 36 is the voltage tester 54, which is connected to the monitoring input 38 of the control unit 24, namely via the voltage divider 66.

[0068] Thanks to the voltage tester 54, the electrical voltage in the low-voltage electrical system 8 can be measured by the control unit 24. If this voltage lies outside a specified range, this is detected by the control unit 24, and in this case, the operation of the converter 42 is stopped. The analog output via the tap 72 also makes it possible to perform more in-depth analyses. No additional galvanic isolation is required to determine the electrical voltage present in the low-voltage electrical system 8, which increases robustness.

[0069] Positioning costs reduced.

[0070] The invention is not limited to the exemplary embodiment described above. Rather, other variants of the invention can also be derived therefrom by those skilled in the art without departing from the subject matter of the invention. In particular, all individual features described in connection with the exemplary embodiment can also be combined with one another in other ways without departing from the subject matter of the invention.

[0071] List of reference symbols

[0072] 2 motor vehicles

[0073] 4 wheel

[0074] 6 Auxiliary unit

[0075] 8 Low-voltage electrical system

[0076] 10 low-voltage battery

[0077] 12 first connection

[0078] 14 High-voltage electrical system

[0079] 16 second connection

[0080] 18 high-voltage battery

[0081] 20 electric motor

[0082] 22 inverters

[0083] 24 Control unit

[0084] 26 Mass

[0085] 28 Reference input

[0086] 30 control line

[0087] 32 zones

[0088] 34 flyback converters

[0089] 36 Supply input

[0090] 38 Monitoring input

[0091] 40 Primary coil

[0092] 42 switches

[0093] 44 additional capacitor

[0094] 46 Secondary coil

[0095] 48 blocking diode

[0096] 50 smoothing capacitor

[0097] 52 snubbers

[0098] 54 voltage testers

[0099] 56 first resistance

[0100] 58 Diode

[0101] 60 capacity

[0102] 62 second resistor 64 provision output

[0103] 66 voltage dividers

[0104] 68 third resistance

[0105] 70 fourth resistor 72 tap

Claims

Claims 1 . Auxiliary unit (6) for a motor vehicle (2), in particular an electromotive refrigerant compressor, which has a first connection (12) for a low-voltage on-board network (8), wherein a supply input (36) of a control unit (24) is connected to the first connection (12) by means of a flyback converter (34) which has a primary coil (40) electrically contacted with the first connection (12) and a secondary coil (46) electrically contacted with the supply input (36), wherein a voltage tester (54) is connected in parallel to the secondary coil (46) and is contacted with a monitoring input (38) of the control unit (24).

2. Auxiliary unit (6) according to claim 1, characterized in that the voltage tester (54) comprises a series circuit of a diode (58) and a capacitor (60).

3. Auxiliary unit (6) according to claim 2, characterized in that a first resistor (56) is connected between the secondary coil (46) and the series circuit.

4. Auxiliary unit (6) according to claim 2 or 3, characterized in that a second resistor (62) is connected in parallel to the capacitor (60).

5. Auxiliary unit (6) according to one of claims 1 to 4, characterized in that the voltage tester (54) is electrically contacted with the supply input (36) via a voltage divider (66) which comprises a third and a fourth resistor (68, 70) which are electrically connected in series are, wherein a tap (72) is formed between them, c monitoring input (38) is guided.

6. Auxiliary unit (6) according to one of claims 1 to 5, characterized in that a snubber (52) is connected in parallel to the secondary coil (46).

7. Auxiliary unit (6) according to one of claims 1 to 6, characterized by a second connection (16) for a high-voltage vehicle electrical system (14), which is electrically contacted with a converter (22) which is operated by means of the control unit (24).

8. Auxiliary unit (6) according to claim 8, characterized in that an electric motor (20) is operated by means of the converter (22).

9. Motor vehicle (2) with an auxiliary unit (6) according to one of claims 1 to 8.

Images