WO2022043271A1

WO2022043271A1 - Method for operating a unit of a motor vehicle

Info

Publication number: WO2022043271A1
Application number: PCT/EP2021/073292
Authority: WO
Inventors: Christian Bienick; Marco Stock; Stefan Schiegel
Original assignee: Brose Fahrzeugteile SE & Co. Kommanditgesellschaft, Würzburg
Priority date: 2020-08-31
Filing date: 2021-08-23
Publication date: 2022-03-03
Also published as: DE102020210982A1; CN115804004A

Abstract

The invention relates to a method (100) for operating a unit (12) of a motor vehicle (2), in particular an electric motor-powered coolant compressor, which comprises an intermediate circuit capacitor (58), a brushless direct current motor (28), and a converter (62) connected therebetween, a discharge circuit (70) being connected in parallel with the intermediate circuit capacitor (58). As a first condition (118), it is checked whether a request (120) for discharge of the intermediate circuit capacitor (58) is present. Depending on a second condition (108), the intermediate circuit capacitor (58) is discharged via the discharge circuit (70) or the direct current motor (28). The invention further relates to a unit (12) of a motor vehicle (2) and to a computer program product (98).

Description

description

Method for operating an assembly of a motor vehicle

The invention relates to a method for operating an assembly of a motor vehicle and an assembly of a motor vehicle and a computer program product. The unit includes an intermediate circuit capacitor, a brushless DC motor and a converter connected in between. The unit is preferably an electric motor refrigerant compressor.

Motor vehicles usually have an air conditioning system, by means of which the temperature of an interior of the motor vehicle is controlled. The required energy stores, such as a high-voltage battery, are also cooled in motor vehicles driven by an electric motor. The air conditioning system has a refrigerant circuit which includes a refrigerant compressor, a condenser downstream of this and an evaporator downstream of this in terms of fluid technology. In terms of fluid technology, this is followed by another heat exchanger, which is in thermal contact with a blower line that leads into the interior of the motor vehicle, or with any energy cells of the high-voltage energy storage device. The refrigerant circuit is filled with a refrigerant such as R134a, R1234yf or CO2.

During operation, a pressure of the refrigerant is increased by means of the refrigerant compressor, which leads to an increase in the temperature of the refrigerant. This is conducted to the capacitor, which is in thermal contact with an environment of the motor vehicle. This results in a temperature reduction of the refrigerant, which in turn is expanded to the original pressure in the downstream evaporator, which is why the temperature of the refrigerant is further reduced. In the downstream heat exchanger, thermal energy is transferred to the refrigerant from the component that is in thermal contact with the heat exchanger transferred, which leads to a cooling of the component and a heating of the refrigerant. The heated refrigerant is returned to the refrigerant compressor to close the refrigerant circuit.

So that the air conditioning system can be operated independently of the current operation of an internal combustion engine of the motor vehicle or also in an electric vehicle, the refrigerant compressor is increasingly being designed as an electric motor and thus includes an electric motor, by means of which a compressor head is driven. In order to reduce wear and increase efficiency, the electric motor is usually designed to be brushless and is energized by means of a converter, which in turn is fed by means of an on-board network of the motor vehicle. If several electrical consumers are operated with the same vehicle electrical system, fluctuations occur in the electrical DC voltage provided when these consumers are switched on or off. So that essentially undisturbed operation is made possible, an intermediate circuit capacitor is usually connected in parallel with the converter as an energy store.

So that the maximum output of the electromotive refrigerant compressor is comparatively high, it is necessary to provide a comparatively large amount of electrical energy via the vehicle electrical system. If the maximum electrical current made available is increased for this purpose, it is necessary to increase a cross section of the electrical lines used, which in turn leads to increased weight. Therefore, the electrical voltage that is applied to the electromotive refrigerant compressor, namely the converter, is increasing to an increasing extent, so that the electromotive refrigerant compressor is connected, for example, to a 48 V vehicle electrical system or to a high-voltage vehicle electrical system, which is also used for propulsion, for example of the motor vehicle is used if it is designed as an electric vehicle. In this case, the applied electrical voltage is usually more than 200 V. However, if there is a malfunction in the motor vehicle or at least in the electric motor refrigerant compressor, it is necessary to discharge the intermediate circuit capacitor, to which the respective electrical voltage is also applied, so that a uncontrolled discharging via, for example, an into the housing of the electromotive refrigerant compressor, such as an arm during maintenance or another part of the motor vehicle in the event of an accident, is avoided, which could endanger a person.

The invention is based on the object of specifying a particularly suitable method for operating a unit of a motor vehicle and a particularly suitable unit of a motor vehicle as well as a particularly suitable computer program product, safety being advantageously increased and production costs expediently not being increased.

With regard to the method, this object is achieved by the features of claim 1, with regard to the unit by the features of claim 11 and with regard to the computer program product by the features of claim 12. Advantageous developments and refinements are the subject of the respective dependent claims.

The method is used to operate a unit of a motor vehicle. The motor vehicle is in particular land-based and preferably designed with multiple lanes. It is suitably possible here to position the motor vehicle essentially freely, in particular on a corresponding roadway. For this purpose, the motor vehicle has, in particular, appropriate wheels. In summary, it is preferably possible to position the motor vehicle essentially independently of other conditions on land. In other words, the motor vehicle is suitably not rail-guided. The motor vehicle is preferably a passenger car (car) or a commercial vehicle, such as a truck (truck) or bus.

The aggregate has a brushless direct current motor (BLDC) which is operated by means of a converter. The brushless direct current motor thus includes, in particular, a number of electrical coils that are connected to one another to form a plurality of phases. The phases are interconnected to form a delta or star connection. Preferably, a stator of the brushless DC motor includes the electrical coils and the brushless DC motor has a rotor which preferably comprises a number of permanent magnets. The brushless DC motor is preferably a synchronous motor.

In particular, the converter includes a bridge circuit, for example a B6 circuit or a B12 circuit. The number of bridge arms of the converter corresponds to the number of phases of the brushless direct current motor, also simply referred to below as direct current motor. The assembly also includes an intermediate circuit capacitor, by means of which the converter is fed. The converter is thus connected between the intermediate circuit capacitor and the brushless DC motor. In the intended state, the intermediate circuit capacitor itself is in particular in contact with an on-board network of the motor vehicle, so that the electrical voltage carried by the on-board network in particular is present at the intermediate circuit capacitor. In particular, at least one of the electrical potentials of the intermediate circuit capacitor is connected to ground. The electrical voltage is in particular an electrical direct voltage and is, for example, 12 V, 24 V, 48 V. However, the electrical voltage is particularly preferably greater than 100 V and, for example, greater than 200 V. The electrical (direct) voltage is preferably equal to 288 V, 560V or 830V

Furthermore, the assembly has a discharge circuit which is connected in parallel with the intermediate circuit capacitor. The discharge circuit is used for discharge charging of the intermediate circuit capacitor and is suitable for this purpose, in particular provided and set up. The discharging circuit preferably comprises a strand which has a resistor, preferably an ohmic resistor, and a semiconductor switch which are electrically connected in series. In other words, the intermediate circuit capacitor is bridged by means of the series connection made up of the resistor and the semiconductor switch. Thus, when the semiconductor switch is actuated, the intermediate circuit capacitor is discharged via the semiconductor switch and the resistor, with the electrical energy being converted into thermal energy due to the heating of the resistor. Alternatively or in combination, the electrical energy is converted by means of the semiconductor switch. For this purpose, it is expediently controlled in linear mode. the A semiconductor switch is, for example, a field effect transistor, in particular a MOSFET or IGBT.

In addition, the intermediate circuit capacitor is preferably bridged by means of a Zener diode and an additional resistor, with a center tap being formed between these, which is routed to the control input of the semiconductor switch. In this case, the Zener diode is arranged in such a way that one of its inputs is connected at low resistance to one of the terminals of the resistor, which forms the series circuit with the semiconductor switch. Because of the resistor and the zener diode, a voltage divider is provided, with the zener diode ensuring that the maximum electrical voltage present at the control input of the semiconductor switch is limited.

The zener diode in turn is preferably bridged by means of an adjustable zener diode and by means of a further strand which comprises a further resistor and a temperature-dependent resistor which is designed in particular as an NTC resistor and which is in thermal contact with the semiconductor switch . The center tap present between the temperature-dependent resistor and the further resistor is routed in particular to the control input of the adjustable zener diode. The Zener diode is additionally bridged by means of a further semiconductor switch, which is actuated by means of a control module.

For discharging, the further semiconductor is actuated by means of the control module in such a way that the semiconductor switch is actuated in turn and an electric current flows through it. Due to the temperature-dependent resistance, it is ensured that the semiconductor switch cannot be destroyed when the intermediate circuit capacitor discharges and the semiconductor switch is heated as a result due to the increased electric current flow, namely by the latter then being actuated accordingly. In particular, the electric current flowing (discharge current) is reduced in this case, namely preferably by the electric voltage present at the control input of the semiconductor switch being reduced. The method provides that, as a first condition, it is checked whether there is a request to discharge the intermediate circuit capacitor. In other words, the first condition is met when there is a request to discharge the intermediate circuit capacitor. The request to discharge the intermediate circuit capacitor specifies that it should be electrically voltage-free, so that its two connections, ie its two electrodes, have the same electrical potential or a potential difference that is less than a specific value. 60V is preferably used as such a value, so that the request to discharge the intermediate circuit capacitor specifies that both connections have a maximum potential difference of less than 60V. With such a potential difference, there is protection against accidental contact, so that safety is increased.

If the first condition is met, the intermediate circuit capacitor is discharged so that its two electrodes subsequently have essentially the same electrical potential. In this case, the discharging takes place as a function of a second condition, namely via the discharging circuit or the DC motor. In particular, if the second condition is met, the discharge is carried out via the DC motors, and otherwise via the discharge circuit. Two different types of discharge are thus available, which is why there is redundancy, and the type of discharge used is selected from the two possibilities, namely as a function of the second condition. As a result, security is increased. In this case, no further components are required in addition to the discharge circuit, which is why production costs are not increased. For example, the second condition specifies that discharging takes place either via the discharging circuit or the DC motor. In a further development, the second condition can also be used to specify that the discharging takes place via the discharging circuit and the DC motor.

For example, the unit is coupled to a bus system in terms of signals, in particular a LIN or CAN bus. Via the bus system, during operation of the motor vehicle in particular transmit control commands, so that the unit is operated according to the control commands.

In particular, the intermediate circuit capacitor is in direct contact with the on-board electrical system of the motor vehicle, which is preferably fed by means of a corresponding energy store, such as a battery, expediently a high-voltage battery. In a further development, further components, such as inductors or semiconductor switches, are arranged between the intermediate circuit capacitor and the capacitor. If there is a request for discharging the intermediate circuit capacitor, a request for discharging the vehicle electrical system is also included, or it is checked as an additional part of the first condition whether a corresponding request is present. In particular in the event of an accident or a visit to a workshop, it is necessary for all other units/consumers that are in electrical contact with the on-board network to be voltage-free or at least only to have a specific maximum voltage applied to them. In particular, only a maximum electrical voltage should be applied to these, such as 60 V or 10 V, in particular after a certain period of time after the request to discharge the vehicle electrical system has been given. For example, 1 second and 2 seconds, 3 seconds or 5 seconds is used as such a period of time. In this case, the other units/consumers are also connected electrically in parallel with the intermediate circuit capacitor, but are not part of the unit. In order to achieve the voltage-free state, the energy store, ie in particular the battery, is usually electrically isolated from the vehicle electrical system. In this case, however, it is possible that due to the existing capacities or other components of the other units/consumers, an electrical voltage is still present. If the first condition is met, this is reduced in particular by means of the unit, namely either by means of the discharge circuit or via the DC motor, so that no additional discharge circuit is required for the other units/consumers. Consequently, manufacturing costs are reduced.

The unit is, for example, a main drive of the motor vehicle and is therefore used directly to propel the motor vehicle. Alternatively, the aggregate an auxiliary unit and is therefore not used directly to propel the motor vehicle. For example, the accessory is an electric motor oil pump, such as an electric motor lubricant pump. An oil, such as engine oil or gear oil, is used as a lubricant, for example. As an alternative to this, the unit is, for example, an electric motor water pump or an electric motor coolant pump. In a further alternative, the assembly is a power steering system, or a component thereof. As a further alternative, for example, an electromotive adjustment drive, such as an electromotive window winder, an electromotive seat adjustment or an electromotive actuated sunroof, is used as a unit.

However, the unit is particularly preferably an electromotive refrigerant compressor, also referred to simply as a refrigerant compressor below. During operation, a refrigerant is compressed by means of the (electric motor) refrigerant compressor. The refrigerant is, for example, a chemical refrigerant such as R134a or R1234yf. Alternatively, the refrigerant is CO2. The refrigerant compressor is preferably designed in such a way that it can be used to compress the respective refrigerant, with a pressure increase of between 5 bar and 20 bar occurring, for example.

The refrigerant compressor is in particular a component of a refrigerant circuit (refrigeration circuit), which is used, for example, to air condition an interior or to cool down an energy store of the motor vehicle, such as a high-voltage battery. The refrigerant circuit also includes in particular an (air conditioning) condenser and an evaporator. The condenser is fluidly connected between the electric motor refrigerant compressor and the evaporator. The refrigerant circuit preferably includes a further heat exchanger which is connected between the evaporator and the electromotive refrigerant compressor and which is preferably in thermal contact with another component of the motor vehicle, such as a blower line of an air conditioning system or an energy storage device, such as a high-voltage energy storage device. The refrigerant circuit is in particular filled with a refrigerant, for example a chemical refrigerant such as R134a, R1234yf, or with CO2. By means of the electromotive refrigerant compressor, a pressure of the refrigerant is increased during operation, which is then conducted to the condenser, which is preferably in thermal contact with an environment of the motor vehicle. The temperature of the refrigerant is suitably adjusted to the ambient temperature or at least the temperature of the refrigerant is reduced by means of the condenser. With the downstream evaporator, the refrigerant is expanded, which is why the temperature of the refrigerant is further reduced. In the further heat exchanger connected downstream, thermal energy is transferred from the component that is in thermal contact with the further heat exchanger to the refrigerant, which leads to a cooling of the component and a heating of the refrigerant. The heated refrigerant is preferably fed back to the refrigerant compressor to close the refrigerant circuit.

The electromotive refrigerant compressor has a compressor head that is driven by the DC motor. The compressor head itself is used to move and compress the refrigerant. The compressor head is suitably set up and provided for this purpose. For example, the compression head has a number of components that can be moved relative to one another in order to achieve compression. The compressor head has a compressor outlet through which, in use, the compressed refrigerant is expelled. In particular, the compressor head has a compressor inlet through which the uncompressed refrigerant is introduced, for example sucked in, during operation. In this case, the density of the refrigerant on the side of the compressor inlet is lower than on the side of the compressor outlet when the electromotive refrigerant compressor is in operation. For example, the refrigerant is sucked in continuously during operation.

For example, the second condition is periodically met, so that both the discharge circuit and the DC motor are evenly loaded. However, the second condition is particularly preferably generated by a self-test. For this purpose, in particular, a self-test of the discharge circuit and/or the DC motor takes place. In the self-test, in particular, a temperature is used to determine the second condition. For example, if the temperature of the DC motor is above a certain limit temperature, the second condition in particular is not met, so that a discharge, if this is to take place, takes place via the discharge circuit. If, on the other hand, the temperature of the discharge circuit is above a further limit temperature, the second condition is met and the discharge takes place, in particular, via the DC motor. If the discharge circuit includes the semiconductor switch, which is actuated as a function of its heating, its switching state is preferably used as the second condition. The second condition is met, so that the discharge takes place via the direct current motor if the first condition is present, in particular when no discharge or no sufficiently rapid discharge can take place via the discharge circuit due to the heating of the semiconductor switch. In other words, the switching state of the semiconductor switch is determined as a self-test.

For example, the self-test is essentially carried out continuously and thus the functional capability of the two discharge paths, ie via the discharge circuit and via the DC motor, is continuously determined. In order to determine the functionality of the two discharge paths, that is to say for the self-test, the respective electric current carried is expediently determined while a discharge is being carried out. The functionality is derived from this. The electrical current conducted via the discharge circuit and the DC motor is thus preferably detected and the second condition is generated from this.

The self-test is carried out, for example, before a discharge is carried out, so that when the first condition is present, the discharge can take place comparatively promptly. As an alternative to this, the self-test is carried out, for example, during the discharge. This ensures that the discharge is carried out correctly. It is possible in particular for the second condition to change during the discharge, so that when the intermediate circuit capacitor is not yet completely discharged, for example a discharge via the discharge circuit is interrupted and continued via the DC motor. Thus, security is increased. In particular, after the second condition has been determined independently by the assembly, this is communicated to other components of the motor vehicle, in particular via a bus system. A corresponding flag is suitably set for this. If the unit is also to be used to discharge the other units/consumers, they know whether the discharge circuit or the DC motor is used for this purpose, especially if the time periods until the respective discharge is completed differ. It is also possible on the basis of the message to output a message so that, for example, the user of the motor vehicle is prompted to go to a workshop, so that any error that caused the second condition to be created accordingly can be corrected. It is also possible, for example, to encourage the user to behave appropriately, so that the unit is switched off, for example, and consequently the load on the unit is reduced. As an alternative to this, the bus system is used to indicate whether discharge can currently be carried out or whether there is damage. How the discharge is carried out when the corresponding request is present is not transmitted.

For example, the electrical current conducted via the discharge circuit is recorded for the self-test and the second condition is generated from this. In particular, if a discharge is to take place, it is checked whether the electrical energy stored in the intermediate circuit capacitor is actually being dissipated via the discharge circuit. If this is not the case, the second condition is adjusted accordingly and is in particular met, so that the discharge then takes place via the DC motor. Due to the generation of the second condition based on the electrical current that is conducted, the susceptibility to errors is reduced in the self-test. This is also comparatively easy to implement. In particular, the electrical current carried is detected while the intermediate circuit capacitor is discharging. However, this is particularly preferably carried out alternatively or in combination when no discharge is to take place. If an electric current is nevertheless passed through the discharge circuit during this, there is a short circuit, for example, so that a Functional safety of the discharge circuit is not given. The second condition is then adapted so that the discharge takes place via the DC motor when the first condition is met.

For example, the self-test is carried out cyclically. Thus, security is increased. However, the self-test is particularly preferably not carried out cyclically, but only when a specific condition is met. This avoids excessive execution of self-tests, which is why an excessive number of resources are not required for this.

The specific condition used is, for example, that an electrical voltage present at the intermediate circuit capacitor exceeds a first limit value. In this case, in particular when the electrical voltage reaches the first limit value, the self-test is carried out directly or at a time interval therefrom. In particular, the time interval is less than 1 second and for example between 10 ms and 100 ms. The first limit value is preferably below an operating voltage of the intermediate circuit capacitor and is, for example, a quarter, a third or half of the operating voltage. The self-test is thus carried out essentially after the assembly has been connected to the vehicle electrical system or when the vehicle electrical system begins to feed the unit. In particular, the self-test is thus carried out when the motor vehicle is switched to the operating state. The second condition is thus determined comparatively early, and thus whether the discharge circuit and/or the DC motor can be operated safely. Consequently increased security. Expediently, a subpoena is not affected due to the self-test.

In particular, the first limit value is greater than 100 V and, for example, greater than 150 V. The self-test is preferably carried out when the electrical voltage applied has exceeded 172 V, namely 0.5 seconds later. The first limit value corresponds in particular to the minimum electrical voltage to be expected, which is provided by means of the vehicle electrical system, in particular any battery, minus a tolerance value. Using the tolerance value In particular, any measurement errors when detecting the electrical voltage are also taken into account.

Alternatively or in combination with this, the condition under which the self-test is carried out is that there is a request to operate the DC motor. In other words, the request to operate the DC motor is first detected. The second condition is thus determined before actual operation is started, so that in the event of a fault the assembly or at least the intermediate circuit capacitor can be transferred to a safe state, namely in particular the de-energized state, in a comparatively prompt manner. For example, whenever there is a request to operate the DC motor, the self-test is carried out. Particularly preferably, however, this only takes place if the second condition has not yet been generated. This reduces the number of self-tests. The second condition is preferably first deleted each time the motor vehicle is restarted, so that it is not present.

If the discharge is to take place via the DC motor, the converter is preferably controlled in such a way that at least one of the electrical phases of the DC motor, preferably all of them, are live. Thus, existing components of the direct current motor are used to reduce the electrical voltage, which is why no adjustment of the direct current motor is required. For example, the DC motor is rotated here. However, the control is particularly preferably carried out in such a way that there is no rotational movement of the DC motor. Thus, in particular, there is also no rotation of a component driven by means of the DC motor, such as the impeller, the compressor, or the adjustment of an adjustment part. The discharge therefore has no effect on the other components of the unit and therefore also not on the motor vehicle, which could endanger a person or damage other components of the motor vehicle. Consequently, security is increased. Controlling the direct current motor for discharging the intermediate circuit capacitor, with the direct current motor not rotating, is independent of checking for the first condition and discharging as a function of the second condition and is rather regarded as an independent invention.

For example, all electrical phases are activated at the same time. The resulting magnetic field is therefore static, so that the rotor of the DC motor does not rotate. Due to such a control, a comparatively time-saving discharging of the intermediate circuit capacitor is possible. In a particularly preferred manner, however, due to the control of the converter, the DC motor is subjected to an electrical current that corresponds to a speed above a second limit value. In other words, a rotating magnetic field is created in the DC motor due to the control by means of the converter, with the speed of the magnetic field being above the second limit value in particular. In this case, the second limit value is adapted to an inertia of the DC motor, in particular of the rotor. All speeds above the second limit value are such that the rotor can no longer follow the magnetic field due to its inertia, so that it stands still. In this case, in particular, a corresponding (electrical) current without a ramp function or the like is created by means of the converter. Because of such a control, phases of the direct current motor are not always continuously live, which is why excessive heating and associated damage are avoided.

For example, the request to discharge the intermediate circuit capacitor is received and consequently generated externally. In particular, the request is received via the possible bus system of the motor vehicle. Alternatively or particularly preferably in combination with this, the request to discharge the intermediate circuit capacitor is derived by means of the unit itself. For this purpose, the electrical voltage applied to the intermediate circuit capacitor is detected at two different points in time and the request is derived from this. When the intermediate circuit capacitor is fully charged, and subsequently at the two different points in time the applied electrical voltage is detected, this is essentially the same if there is no fault and if in particular there is no excessive power demand on the DC motor. If, on the other hand, there is a discrepancy between the two detected electrical voltages, i.e. in particular the difference between them is greater than a certain value, a fault can be assumed, such as a disconnection from the vehicle electrical system and/or at least a partial tear of an electrical line in the vehicle electrical system . Due to the derivation of the request to discharge the intermediate circuit capacitor by the unit itself, even if there is no communication with a higher-level control unit or another malfunction of the bus system, an on-board computer, which is used, for example, to monitor the motor vehicle, and/or other components of the motor vehicle, by means of which this is sent to the unit, ensures that in the event of a fault, the intermediate circuit capacitor is safely discharged, so that security is increased.

The electrical voltages are preferably detected redundantly, so that the voltage measurement is carried out twice. The two values determined are preferably compared with one another in order to detect a faulty voltage measurement. If this is the case, the intermediate circuit capacitor is expediently discharged essentially immediately and/or the second condition, ie in particular the discharge strategy, is adapted. Preferably, if communication with the possible bus system is no longer possible, the intermediate circuit capacitor is permanently discharged.

When detecting the electrical voltages, particular attention is paid to whether there is an excessive power demand on the direct current motor, in which case the intermediate circuit capacitor is at least partially discharged. If this is the case, the times in particular will be shifted accordingly. This avoids incorrect creation of the request to discharge the intermediate circuit capacitor. However, the electrical voltage is preferably only detected when communication with other components of the motor vehicle is no longer possible, in particular via the possible bus system. In this If the DC motor is not operated, so that there is no longer any power requirement for it.

The detected electrical voltages present are particularly preferably set in relation to one another and compared with a third limit value. In this case, the request to discharge the intermediate circuit capacitor is generated as a function of the comparison. If a line of the vehicle electrical system is torn off from the assembly, the intermediate circuit capacitor is discharged, which in particular is passive. The time profile of the electrical voltage present at the intermediate circuit capacitor is exponential. Due to the ratio of the two detected electrical voltages present to one another, it is irrelevant how great the electrical voltage present at the intermediate circuit capacitor was originally. If the exponential drop is present, the ratio is always equal to a specific value that depends on the intermediate circuit capacitor used and the time interval between the two points in time. The third limit value is preferably adapted in such a way that in the event of an (unwanted) exponential discharge of the intermediate circuit capacitor, the request to discharge the intermediate circuit capacitor is generated. In other words, the third limit value is suitably adjusted in such a way that the request for discharge is generated for a discharge that corresponds to the self-discharge curve of the component, caused by the equivalent parallel resistance of the component to the intermediate circuit. In this case, the component is in particular the intermediate circuit capacitor. Because of the ratio, it is thus possible to use the method in a large number of different units and/or different intermediate circuit capacitors, with only the third limit value having to be adjusted accordingly. In this case, due to the constant ratio, it is also irrelevant how large the time interval is between the first determination of the electrical voltage present and the time when the electrical line is torn off from the unit. Thus, security is increased. Particularly preferably, the applied electrical voltage is recorded several times at two different points in time in each case and these are compared to one another in each case. The time interval between the points in time is constant in each case. Suitably, between the two points in time, by means of which a ratio is formed, the applied electrical voltage is recorded several times, with these recorded electrical voltages being related to a corresponding recorded electrical voltage that was recorded following the respective time interval. In particular, 1024 ms is used as the time interval, and the electrical voltage is recorded every 16 ms, for example. Thus, after 2048 ms, there are a total of 64 ratios.

The request to discharge the intermediate circuit capacitor is generated when the ratios, that is, for example, the 64 ratios, differ from the third limit value by less than a fourth limit value. In other words, it is checked whether all ratios are within a certain range. If an exponential discharge of the intermediate circuit capacitor takes place, all of the ratios are theoretically the same, and the fourth limit value can be selected to be comparatively small. A comparatively reliable detection of a torn line of the vehicle electrical system and the subsequent uncontrolled discharge of the intermediate circuit capacitor resulting therefrom can be determined, so that the request to discharge the intermediate circuit capacitor is generated comparatively promptly. Thus, security is increased. Comparatively few calculation steps are also required for the determination, so that the determination can be carried out comparatively promptly. It is also possible, by forming the respective ratio or ratios, to monitor whether the (intended) discharging of the intermediate circuit capacitor is functioning correctly.

The method in which the applied electrical voltages are recorded several times at different points in time and these are set in relation to each other, with the time interval between the points in time being constant, and it is checked whether they deviate from the third limit value differ by more than the fourth limit value is independent of the design of the method for operating the unit, in which it is checked whether the first condition is present and then the discharge is carried out as a function of the second condition. Such a method is used, in particular, to determine that a line has broken off from the assembly or some other fault situation, or, for example, to determine that the intermediate circuit capacitor is being discharged. In summary, such a method is thus regarded as an independent invention.

The assembly is a component of a motor vehicle, which is in particular land-based and is, for example, a truck (lorry), bus or preferably a passenger car (car). The assembly is, for example, a main drive of the motor vehicle or particularly preferably an auxiliary assembly. The unit has an intermediate circuit capacitor, a DC motor and a converter connected in between. In particular, the converter comprises a bridge circuit, such as a B6 circuit.

A discharge circuit is connected in parallel with the intermediate circuit capacitor and has, in particular, a semiconductor switch and a resistor electrically connected in series therewith, the intermediate circuit capacitor being bridged by means of this series connection. In particular, an additional resistor and a Zener diode are also connected in parallel with the intermediate circuit capacitor, with a center tap being formed between these, which is routed to the control input of the semiconductor switch. It is thus ensured that a maximum of a specific electrical potential is always present at the control input of the semiconductor switch. The zener diode in turn is bridged with an adjustable zener diode, a further semiconductor switch and a further series connection of a further resistor and a temperature-dependent resistor, the temperature-dependent resistor being in thermal contact with the semiconductor switch. The electrical voltage present at the input of the semiconductor switch is adjusted by means of the adjustable Zener diode. The other semiconductor switch is actuated by means of a control module, and a control input of the adjustable zener diode is against the center tap out between the further resistor and the temperature-dependent resistor, the temperature resistor being an NTC resistor.

The assembly is operated according to a method in which a first condition is checked as to whether there is a request to discharge the intermediate circuit capacitor. Depending on a second condition, the intermediate circuit capacitor is discharged either via the discharge circuit or the DC motor, or both.

The unit has in particular a control unit which is suitable, in particular provided and set up, to carry out the method. The control unit includes, for example, an application-specific integrated circuit (ASIC) or, particularly preferably, a computer that is suitably designed to be programmable. In particular, the control unit comprises a storage medium on which a computer program product, also referred to as a computer program, is stored, with the computer being prompted to carry out the method when this computer program product, ie the program, is executed.

In particular, the unit is a pump, such as an oil pump or water pump. However, the unit is particularly preferably an electric motor-driven refrigerant compressor.

The computer program product comprises a number of instructions which, when the program (computer program product) is executed by a computer, cause the computer to use a method for operating a unit of a motor vehicle which has an intermediate circuit capacitor, a brushless direct current motor and a converter connected in between, with parallel to the Intermediate circuit capacitor is connected to a discharge circuit to perform. The unit is in particular an electric motor refrigerant compressor. According to the method, a check is made as a first condition as to whether there is a request to discharge the intermediate circuit capacitor. Depending on a second condition, the intermediate circuit capacitor is discharged via the discharge circuit or the DC motor. The computer is expediently a component part of a control unit or electronics and is formed by means of these, for example. The computer preferably includes or is formed by a microprocessor. The computer program product is, for example, a file or a data carrier that contains an executable program that automatically runs the method when installed on a computer.

The invention also relates to a storage medium on which the computer program product is stored. Such a storage medium is, for example, a CD-ROM, a DVD or a Blu-Ray Disc. Alternatively, the storage medium is a USB stick or some other memory which can be rewritten or only written once, for example. Such a memory is, for example, a flash memory, a RAM or a ROM. The invention also relates to a motor vehicle that has such a unit and a control unit for carrying out the method, which is therefore suitable, in particular provided and set up, for this purpose.

The developments and advantages explained in connection with the method can also be transferred to the computer program product/the unit/the storage medium/the motor vehicle/the control unit and to each other and vice versa.

If an object is referred to as the first, second, third, ... object, this is to be understood in particular as merely referring to a specific object. In particular, this does not mean that there is a certain number of such objects. In particular, this does not imply that, for example, the first or second limit value is present if the third limit value is present.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. Show in it: 1 shows a motor vehicle with a unit in the form of an electric motor-driven refrigerant compressor,

2 shows a schematic of the electromotive refrigerant compressor, FIG. 3 shows a wiring of the electromotive refrigerant compressor, FIG. 4 shows a method for operating a unit, namely the electromotive refrigerant compressor, and

Fig. 5 schematically simplified a time course of an applied electrical voltage.

Corresponding parts are provided with the same reference symbols in all figures.

In Fig. 1, a motor vehicle 2 in the form of a passenger car (passenger car) is shown in a schematically simplified manner, with two front wheels 4 and two rear wheels 6 . At least two of the wheels 4, 6 are driven by a main drive, not shown in detail, for example an internal combustion engine/combustion engine, an electric motor or a combination thereof. The motor vehicle 2 includes a refrigerant circuit 8, which is part of an air conditioning system. The refrigerant circuit 8 is filled with a refrigerant 10, for example CO2, R1234yf or R134a.

The motor vehicle 2 has a unit 12, namely an auxiliary unit in the form of an electric motor refrigerant compressor (eKMV), which is not used directly to propel the motor vehicle 2. The refrigerant 10 is compressed by means of the unit 12 and fed to a condenser 14 which is connected downstream in terms of fluid technology and which is subjected to ambient air, which leads to a reduction in the temperature of the refrigerant 10 . The pressure and thus the temperature of the refrigerant 10 is lowered by means of a downstream evaporator 16, which includes a further heat exchanger, not shown in detail, which is thermally coupled to a blower line of the air conditioning system. Depending on a user setting, the blower line conveys cooled air into an interior of motor vehicle 2. The electric motor-driven refrigerant compressor 12 is coupled in terms of signals to a motor vehicle controller 20, such as an on-board computer, by means of a bus system 18, which is a CAN bus system or a Lin bus system. The electric motor refrigerant compressor 12 is energized by means of an on-board network 22, which is fed by a battery 24. The battery 24 is designed as a high-voltage battery, and an electrical DC voltage of more than 250 V is provided by means of this.

Fig. 2 shows a schematically simplified unit 12, namely the (electric motor) refrigerant compressor 12, in a sectional view along an axis of rotation (axis of rotation) 26 of a brushless direct current motor (BLDC) 28 of the refrigerant compressor 12. The direct current motor 28 has a cylindrical rotor 30, which is surrounded on the circumference by a hollow cylindrical stator 32 . The rotor 30 is fixed in a rotationally fixed manner to a shaft 34 which is arranged concentrically to the axis of rotation 26 and which is rotatably mounted about the axis of rotation 26 by means of two bearings in the form of ball bearings which are not shown in detail.

The DC motor 28 is arranged in a motor housing 36 which extends along the axis of rotation 28 and is designed as a hollow cylinder. A hollow-cylindrical electronics compartment 38 is formed flush at one end of the motor housing 36 and is separated from the latter by means of a partition wall 40 which is arranged essentially perpendicularly to the axis of rotation 28 . Electronics 42 are arranged inside electronics compartment 38 and are connected to bus system 18 and vehicle electrical system 22 . The electronics 42 are in electrical contact with the stator 32 via a through-connection 44 which is pressure-tight, so that the stator 32 is energized by the electronics 42 during operation.

The electronics compartment 38, the motor housing 33 and the partition 40 are created in one piece with each other and made of aluminum in a die-casting process. In other words, the electronics compartment 38, the motor housing 33 and the partition 40 are an aluminum die casting. The electronics compartment 38 is closed with a housing cover 46 on the side opposite the partition wall 40, which is made of a metal and is detachably fastened to the electronics compartment 38 by means of screws.

On the opposite side of the motor housing 36 from the electronics compartment 38, a compressor housing 48 is detachably connected to the motor housing in alignment, which is also made of aluminum using a die-casting process. The compressor housing 48 is designed in one piece and essentially in the shape of a pot, with the pot opening being closed by means of the motor housing 36 . The compressor housing 48 has a compressor compartment 50 within which a compressor head 52 in the form of a scroll compressor head is arranged. The scroll compressor head has two scrolls, namely a fixed scroll and a rotatable scrolls. The fixed scroll member is non-rotatably attached to the compressor housing 48 . The rotatable scroll is operatively connected to the shaft 34 such that rotational movement of the shaft 34 moves the rotatable scroll with respect to the fixed scroll. A number of chambers are formed between the two scroll parts, the volume of which is changed when the shaft 36 rotates. In the process, the coolant 10 located in the chambers is successively compressed.

During operation, the refrigerant 10 is conducted into the motor housing 36 in the area of the partition wall 40 via an inlet 54 of the motor housing 36 . The separating wall 40 prevents the coolant 10 from passing into the electronics housing 38 . The refrigerant 10 is sucked along the DC motor 28 to the compressor head 52 and is compressed there, so that the pressure is increased and the refrigerant 10 is therefore also compressed. The compressed refrigerant 10 is routed to the condenser 14 via a compressor outlet 56, which has an oil separator that is not shown in detail.

FIG. 3 shows an interconnection of the unit 12 in a schematically simplified manner. The assembly 12 has an intermediate circuit capacitor 58 which is electrically connected to the vehicle electrical system 22 . For this purpose, the two electrodes of the intermediate circuit capacitor 58 are each contacted with a wire of a line (not shown) of the vehicle electrical system 22 . So it's up to that Intermediate circuit capacitor 58 also applies the electrical direct voltage of more than 250 V provided by battery 24 during operation. A converter 62 is fed by means of the intermediate circuit capacitor 58 .

The converter 62 is designed as an inverter and has a bridge circuit, namely a B6 circuit with a total of six power semiconductor switches 64. Two of the power semiconductor switches 64 are used to form a series circuit connected in parallel with the intermediate circuit capacitor 58, with each series circuit containing one of the total three phases 66 of the brushless DC motor 28 is assigned. The power semiconductor switches 64 are actuated by means of a driver circuit 68 as a function of current requirements, namely a desired cooling capacity.

The unit 12 also has a discharge circuit 70 which is connected in parallel with the intermediate circuit capacitor 58 . The discharge circuit 70 includes a semiconductor switch 72 and a resistor 74, by means of which a series circuit is formed which is connected in parallel to the intermediate circuit capacitor 58. This series circuit is bridged by means of a series circuit made up of an additional resistor 76 and a Zener diode 78, between which a first center tap 78 is formed. This is routed to a control input 80 of the semiconductor switch 72 .

The zener diode 78 is bridged by means of an adjustable zener diode 82 whose control input is routed to a second center tap 82 which is located between a further resistor 84 and a temperature-dependent resistor 86 . The temperature dependent resistor 86 is an NTC resistor which is in thermal contact with the semiconductor switch 72 . A series circuit is formed by means of the further resistor 84 and the temperature-dependent resistor 86, by means of which the Zener diode 78 is bridged. The Zener diode 78 is also bridged by means of a further semiconductor switch 88 which is actuated by means of a control module 90. When the discharge circuit 70 is in operation, the further semiconductor switch 88 is actuated accordingly by means of the control module 90, which is why the semiconductor switch 72 is placed in the electrically conductive state. The intermediate circuit capacitor 58 is thus short-circuited and the electrical current flows away via the resistor 74, with the electrical energy being converted into thermal energy both in the semiconductor switch 72, which is driven in linear operation, and in the resistor 74. In this case, the semiconductor switch 72 is additionally heated, which leads to a change in the resistance value of the temperature-dependent resistor 86 . If the heating of the semiconductor switch 72 is excessive, the electrical potential present at the control input 80 of the semiconductor switch 72 is changed due to the changing resistance value of the temperature-dependent resistor 86, so that the electrical current conducted via the semiconductor switch 72 is reduced until thermal equilibrium is reached adjusts Overloading of the semiconductor switch 72 is thus avoided.

The unit 12 also has a control unit 92 with a computer 94 which is designed as a programmable microprocessor. The control unit 92 is a component of the electronics 42, as is the discharge circuit 70 and the converter 62. The control units 92 also control the control module 90 and the driver circuit 68. The control unit 92 has a storage medium 96 in the form of a memory, such as a RAMs or ROMs. A computer program product 98 is stored on the storage medium 96, which has a number of instructions, with execution by the computer 94 prompting the latter to carry out a method 100, shown in FIG. 4, for operating the unit 12. The unit 12 is thus operated according to the method 100 .

In a first work step 102, operation of the unit 12 is started. For this purpose, the intermediate circuit capacitor 58 is electrically connected to the vehicle electrical system 22 so that it is charged. In a subsequent second work step 104, it is checked whether a specific condition is present. As the specific condition is used whether a at the Electrical voltage 105 applied to the intermediate circuit capacitor 54 exceeds a first limit value 106 . In this case, 172 volts is used as the first limit value 106 . If the electrical voltage 105 that is present exceeds the first limit value 106 and if 0.5 s have elapsed after it was exceeded, the specific condition is met.

Alternatively, the specific condition is met when there is a request to operate the DC motor 28 . The request to operate the DC motor 28 is transmitted to the unit 12 via the bus system 18 and is therefore present if the unit 12 is to be used to compress the coolant 10 . In this case, the specific condition is only met if a second condition 108 has not yet been generated.

If the specific condition is present, a third work step 110 is carried out. In the third work step 110, a self-test 112 of the unit 12 is carried out. For this purpose, an electrical current conducted via the discharge circuit 70 is detected. If no electric current flows through the discharge circuits 70 when the semiconductor switch 72 is open, the semiconductor switch 72 is then closed for a short period of time and it is then checked whether the resulting electric current corresponds to a theoretical specification that is dependent on the resistor 74. If this is the case in each case, the second condition 108 is not met. Otherwise, ie if an electric current is conducted via the discharge circuit 70 despite the open semiconductor switch 72, or if no electric current is conducted via the discharge circuit 70 when the semiconductor switch 72 is actuated, the second condition 108 is present. The second condition 108 is thus generated on the basis of the electrical current conducted via the discharge circuit 70, and if the second condition 108 is present, a temporary/brief defect or at least a temporary/brief functional restriction of the discharge circuit 70 can be assumed.

Subsequently, in a fourth step 114, which is carried out when the intermediate circuit capacitor 58 has been fully charged, the DC motor 28 is energized by means of the converter 20, so that the rotor 30 around the Axis of rotation 26 is rotated. As a result, the refrigerant 10 is compressed.

In this case, the electric motor 28 is energized as a function of an existing power requirement.

In a fifth work step 116, a first condition 118 is checked to determine whether a request 120 to discharge the intermediate circuit capacitor 58 is present. The request 120 to discharge the intermediate circuit capacitor 58 can be transmitted to the unit 12 via the bus network 18 . This occurs, for example, when motor vehicle 2 is in maintenance mode or an accident involving motor vehicle 2 has been registered. The request 120 to discharge the intermediate circuit capacitor 58 is also transmitted via the bus network 18 when the battery 24 is disconnected from the vehicle electrical system.

The request 120 for discharging the intermediate circuit capacitor 58 is also derived by the unit 12 itself using the electrical voltage 105 which is present at the intermediate circuit capacitor 58 . If the assembly 12 is working correctly and is still in electrical contact with the vehicle electrical system 22, the applied electrical voltage 105 is constant. If, on the other hand, the line of the vehicle electrical system 22 breaks away from the unit 12, the electrical voltage 105 has a time profile shown in FIG. In this case, the applied electrical voltage 105 drops exponentially, the exponent being dependent on the construction of the intermediate circuit capacitor 58 . The request 120 for discharging the intermediate circuit capacitor 58 by the unit 12 itself preferably only occurs if undisturbed communication via the bus system 18 is not possible (e.g. due to subnetwork operation/LIN fault or tear). Otherwise, only the request 120 transmitted via the bus system 18 to discharge the intermediate circuit capacitor 58 is used.

For deriving request 120 for discharging intermediate circuit capacitor 58 by unit 12 itself, electrical voltage 105 present at intermediate circuit capacitor 58 is detected every 16 ms for a time window of 2048 ms. Thus, at a total of 128 consecutive points in time 122, the value of the electrical voltage 105 is known, and the values of the electrical Voltage 105 at different points in time 122 are set in a ratio 124 to one another. The points in time 122 that are at a fixed time interval 126 from one another are used for this purpose, with the time interval 126 being equal to 1024 ms.

The total of 64 ratios 124 are then each compared with a third limit value 128 which is adapted to the intermediate circuit capacitor 58 . If the ratios 124 do not differ from the third limit value 128 by more than a fourth limit value 130, the request 120 to discharge the intermediate circuit capacitor 58 is generated. In summary, the electrical voltage 105 present at the intermediate circuit capacitor 58 is thus detected several times at two different points in time 122 and these are each set to one another in the ratio 124, the time interval 126 between the points in time 122 that are assigned to the same ratio 124 being constant. Request 120 for discharging intermediate circuit capacitor 58 is generated when all ratios 124 each differ from third limit value 128 by less than fourth limit value 130 .

If request 120 for discharging intermediate circuit capacitor 58 is present, first condition 118 is met, and a seventh work step 132 is carried out. In the seventh work step 132, the intermediate circuit capacitor 58 is discharged. If the intermediate circuit capacitor 58 is still in electrical contact with the vehicle electrical system 22, all other consumers/further units that are electrically contacted with the vehicle electrical system 22 are also discharged. Discharging takes place as a function of second condition 108. If second condition 108 is not met, intermediate circuit capacitor 58 is discharged via discharge circuit 70. For this purpose, the control module 90 is actuated accordingly, so that the semiconductor switch 72 and the resistor 74 are live. During the discharging, the electric current conducted by means of the discharging circuit 70 is recorded at least periodically. If the semiconductor switch 72 is actuated due to excessive heating and is therefore no longer conducting, the second condition 108 is met, so that the discharge by means of the DC motor 28 is continued. If the second condition 108 is met, the intermediate circuit capacitor 58 is discharged via the direct current motor 28 . For this purpose, the direct current motor 28 is controlled by means of the converter 62 in such a way that the phases 66 of the direct current motor 28 are live at least temporarily, with the direct current motor 28, i.e. the rotor 30, not rotating about the axis of rotation 26. For this purpose, the DC motor 28 is supplied with an electric current by means of the converter 62 , which current corresponds to a speed above a second limit value 134 . A magnetic field rotating about the axis of rotation 26 is thus created by means of the stator 32 , the speed of which is greater than the second limit value 134 . For this purpose, the phases 66 are always successively live. The second limit value 134 corresponds to 12,000 revolutions/min. Because of the inertia of the rotor 30, it does not follow the magnetic field but stands still, and the electrical energy stored in the intermediate circuit capacitor 58 is dissipated.

In an alternative, for example, the discharge is always carried out simultaneously via the discharge circuit 70 and the DC motor 28, or at least when the second condition 108 is not met. If, on the other hand, this is fulfilled, the discharge takes place, for example only via the direct current motor 28.

The invention is not limited to the embodiment described above. On the contrary, other variants of the invention can also be derived from this by a person skilled in the art without departing from the subject matter of the invention. In particular, all of the 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. Reference List

2 motor vehicle

4 front wheel

6 rear wheel

8 refrigerant circuit

10 refrigerants

12 aggregate

14 condenser

16 evaporators

18 bus system

20 motor vehicle control

22 on-board network

24 battery

26 axis of rotation

28 DC motor

30 rotors

32 stator

34 wave

36 motor housing

38 electronics compartment

40 partition

42 electronics

44 via

46 housing cover

48 compressor housing

50 compressor compartment

52 compressor head

54 inflow

56 compressor outlet

58 intermediate circuit capacitor

62 converters

64 power semiconductor switches Phase Driver circuit Discharge circuit Semiconductor switch Resistance Additional resistance First center tap Control input Second center tap Additional resistance Temperature-dependent resistance Additional semiconductor switch Control module Control unit Computer Storage medium Computer program product Method First step Second step Electrical voltage First limit value Second condition Third step Self-test Fourth step Fifth step First condition Prompt to discharge the intermediate circuit capacitor Point in time Ratio Time interval third limit fourth limit seventh step second limit

Claims

33

Claims Method (100) for operating an assembly (12) of a motor vehicle (2), in particular an electric motor refrigerant compressor, which has an intermediate circuit capacitor (58), a brushless direct current motor (28) and a converter (62) connected in between, with parallel to the intermediate circuit capacitor (58) a discharge circuit (70) is connected, in which

- It is checked as a first condition (118) whether there is a request (120) to discharge the intermediate circuit capacitor (58), and

- Depending on a second condition (108), the intermediate circuit capacitor (58) is discharged via the discharge circuit (70) or the DC motor (28). Method (100) according to Claim 1, characterized in that the second condition (108) is generated using a self-test (112). Method (100) according to Claim 2, characterized in that an electric current conducted via the discharge circuit (70) is detected and the second condition (108) is generated therefrom. Method (100) according to Claim 2 or 3, characterized in that the self-test (112) is carried out when an electrical voltage present at the intermediate circuit capacitor (54) exceeds a first limit value (106). Method (100) according to one of Claims 2 to 4, characterized in that 34 that the self-test (112) is carried out when there is a request to operate the DC motor (28) and the second condition (108) has not yet been generated. Method (100) according to one of Claims 1 to 5, characterized in that when there is a discharge via the DC motor (28), the converter (62) is controlled in such a way that the electrical phases (66) of the DC motor (28) are live, with a rotational movement of the DC motor (28) is omitted. Method (100) according to Claim 6, characterized in that the DC motor (28) is supplied with an electric current which corresponds to a speed above a second limit value (134). Method (100) according to one of Claims 1 to 7, characterized in that the electrical voltage (105) present at the intermediate circuit capacitor (58) is detected at two different points in time (122) and the request (120) to discharge the intermediate circuit capacitor (58 ) is derived. Method (100) according to Claim 8, characterized in that the detected electrical voltages (105) present are set in a ratio (124) to one another and compared with a third limit value (128), the request (120) for discharging the intermediate circuit capacitor ( 58) is generated depending on the comparison. Method (100) according to Claim 9, characterized in that that the applied electrical voltage (105) is detected several times at two different points in time (122) and these are set in the ratio (124) to one another, the time interval (126) between the points in time (122) being constant, and the request (120) for discharging the intermediate circuit capacitor (58) is generated when the ratios (125) differ by less than a fourth limit value (130) from the third limit value (128). Unit (12) of a motor vehicle (2), in particular an electric motor refrigerant compressor, which has an intermediate circuit capacitor (58), a brushless direct current motor (28) and a converter (62) connected in between, a discharge circuit (70) being connected in parallel with the intermediate circuit capacitor (58). switched, and which is operated according to a method (100) according to any one of claims 1 to 10. A computer program product (98) comprising instructions which, when the program is executed by a computer (94), cause it to carry out the method (100) according to any one of claims 1 to 10.