METHOD FOR OPERATING A DRIVE DEVICE FOR A MOTOR VEHICLE AND CORRESPONDING DRIVE DEVICE

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which comprises an exhaust gas-generating drive unit, an exhaust gas aftertreatment device, and a heating device for heating the exhaust gas aftertreatment device, wherein the electrical connections of the heating device are electrically connected to a control unit via electrical supply connections. The invention further relates to a drive unit for a motor vehicle.

[0002] For example, German patent application DE 43 36 091 B4 is known from the prior art. This document describes a device for monitoring a heating element in a catalytic converter of a motor vehicle. The heating element has a first and a second electrical connection, and when an electrical voltage is applied to both connections of the heating element, an electric current flows through the heating element, heating it. A central tap is provided between the first and second connections of the heating element, and the voltage applied to the central tap is used to determine whether the heating element is functioning correctly. Further drive devices are described in the following publications: US 5,758,492 A, EP 0 839 994 A2, US 5 555 725 A, DE 10 2013 226687 A1, and DE 43 36 091 B4.

[0003] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling a more precise diagnosis of the heating unit and its electrical connection to the control unit.

[0004] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that a voltage applied to the heating device is measured by the control unit by means of measuring lines separate from the supply connections, which are electrically connected on one side to the control unit and on the other side to the terminals, whereby a deviation of the measured voltage from a predefined value indicates a fault in the supply connections.

[0005] Advantageous embodiments with appropriate further developments of the invention are specified in the dependent claims.

[0006] The method serves to operate the drive unit. The drive unit, in turn, is designed and configured to propel the motor vehicle, thus providing a drive torque directed towards propelling the motor vehicle. For this purpose, the drive unit has the drive engine, which generates exhaust gas during its operation or at least intermittently. Preferably, the drive engine is in the form of an internal combustion engine.

[0007] The exhaust gas generated by the engine is discharged towards the outside environment. Since the exhaust gas contains pollutants that should not be released into the environment, or at least not completely, it is routed to the exhaust aftertreatment system before being discharged. This preferably applies to all of the exhaust gas generated by the engine. The exhaust aftertreatment system is designed to convert the pollutants, at least temporarily and at least partially, into less harmful products, particularly through catalytic means. After passing through the exhaust aftertreatment system, the exhaust gas is discharged into the outside environment. The exhaust aftertreatment system is preferably a vehicle catalyst, such as a three-way catalyst, an oxidation catalyst, a storage catalyst (including NOₓ storage catalysts), or an SCR catalyst.

[0008] The exhaust aftertreatment system has a temperature-dependent conversion rate for pollutants. Therefore, an operating temperature is defined for the exhaust aftertreatment system at which it exhibits particularly high effectiveness. This means that, for one or more pollutants, it achieves a particularly high conversion rate for the respective pollutant at this operating temperature. The operating temperature is higher than the ambient temperature found under typical vehicle operating conditions. At the start of operation, the temperature of the exhaust aftertreatment system is therefore lower than its operating temperature.

[0009] It is therefore necessary to raise the temperature of the exhaust aftertreatment system towards or to its operating temperature in order to effectively treat the exhaust gas. Part of the heat required to raise the temperature is provided by the exhaust gas itself or transferred into the aftertreatment system by the exhaust gas. However, this requires that the exhaust gas flows through the aftertreatment system. Consequently, pollutants can pass through the aftertreatment system even when it is operating below its operating temperature.

[0010] To reduce the amount of pollutants passing through the exhaust aftertreatment system, it is therefore planned to heat the system using the heating unit. The heating unit thus supplies heat to the exhaust aftertreatment system, raising its temperature towards or to its operating temperature.

[0011] The heating device, for example, supplies heat directly to the exhaust gas aftertreatment system and is connected to it via a thermal conductor or heat transfer mechanism. For instance, the heating device may be located within or surrounding the exhaust gas aftertreatment system. However, it is also possible for the heating device to supply heat to the exhaust gas aftertreatment system only indirectly, namely via the exhaust gas. In this case, the heating device heats the exhaust gas, at least temporarily, upstream of the exhaust gas aftertreatment system. The heated exhaust gas then flows through the exhaust gas aftertreatment system, thus heating it up more quickly than it would without the heating device.

[0012] The heating device is an electric heating device. It has electrical connections through which it is electrically connected to the control unit. The electrical connection of the heating device's terminals to the control unit is made via the supply connections. The supply connections preferably include at least electrical supply lines and – optionally – additional connections for the lines through which these are electrically connected to the control unit on the one hand and to the heating device on the other. The supply lines and their connections to the control unit and the heating device each have an electrical resistance, which can be described by an equivalent resistance.

[0013] For diagnosing the heating system and its supply connections, the control unit may, for example, measure the voltage and / or current flowing through the supply connections during operation (i.e., while electrical current is being supplied from the control unit to the heating system). If the voltage and / or current deviates from a specified value, a fault in the heating system or its supply connections can be detected.

[0014] However, since both the heating power of the heating element and manufacturing tolerances are quite high, monitoring tolerances must be set relatively large. Therefore, a fault can only be detected when there is a significant deviation in voltage or current from the selected target value. If the fault lies in the power supply connections and not in the heating element itself, the inaccuracy of the monitoring can lead to thermal overload of the supply connections, which in turn can damage the drive unit.

[0015] For this reason, according to the invention, it is provided that the voltage applied to the heating element is measured not, or at least not solely, by the control unit, but rather the voltage applied to the heating element itself. For this purpose, the control unit is electrically connected to the heating element via measuring lines separate from the supply connections. The measuring lines are thus electrically connected separately from the supply connections, on the one hand to the control unit and on the other hand to the heating element. This results in a four-wire connection between the heating element and the control unit, and the voltage applied to the heating element is measured using a four-wire measurement.

[0016] This procedure prevents the resistance of the supply lines and / or the connection resistance of the supply lines to the control unit and / or the heating element from influencing the measurement of the voltage applied to the heating element. Instead, the voltage is determined with extreme precision and can therefore be compared to the target value with minimal tolerances. If the measured voltage deviates from a target value, a fault in the supply connections is detected. Otherwise, if the measured voltage corresponds to the target value, the proper functioning of the supply connections is confirmed. A tolerance, which can be arbitrarily chosen, can be applied when comparing the measured voltage with the target value.

[0017] The described procedure enables dedicated diagnosis of the supply connections and thus extremely precise fault detection. It is particularly preferred to diagnose the heating system in the manner described above and additionally to diagnose the supply connections using the outlined procedure. This ensures a high level of operational reliability for the drive unit.

[0018] A further development of the invention provides that the voltage is measured using measuring leads that are connected to the electrical terminals at a distance from the supply connections. This means that the measuring leads and the supply connections on the heating element side are only electrically connected to each other via the heating element's electrical terminals. It is expressly not intended to connect the measuring leads and the supply connections to the electrical terminals together, as in this case only the voltage between the supply connections, and not between the electrical terminals, would be measured. However, it is explicitly intended to measure the voltage applied to the heating element, and thus the voltage present between the heating element's electrical terminals, using the separate measuring leads.This achieves the described measurement accuracy without the influence of the electrical power transmitted via the supply connections.

[0019] According to the invention, the voltage used is a differential voltage between a supply voltage applied by the control unit to the supply connections and a test voltage measured by the control unit at the measuring leads. The supply connections are electrically connected to the control unit's electrical terminals on one side and to the heating device's electrical terminals on the other. The voltage present at the control unit's terminals is referred to as the supply voltage. It is applied to the supply connections via the control unit's terminals.

[0020] The test voltage is understood to be the voltage measured at the measuring leads.

[0021] Both the supply voltage and the test voltage are provided by the control unit. Instead of measuring the supply voltage and the test voltage separately, the system is designed to measure only the differential voltage between the supply connections and the test leads on the control unit and use this as the measured voltage, i.e., to compare it with the target value. This simplifies the electronic circuitry in the control unit used for voltage measurement. Furthermore, the target value does not need to be specified absolutely; it describes the test voltage relative to the supply voltage.

[0022] A further development of the invention provides that the voltage is measured during the switching-on of the heating device, and in particular only during the switching-on process. When the heating device is switched off, the electrical power supplied to the heating device by the control unit is lower than when the heating device is switched on, and in particular, it is zero. When the heating device is switched on, however, the control unit supplies the heating device with electrical power via the supply connections, which is sufficient to heat the exhaust aftertreatment system. The change from the switched-off state of the heating device to its switched-on state is referred to as switching on. Immediately before the heating device is switched on, the lower electrical power is present, and immediately after switching on, the higher electrical power is present.

[0023] To perform a particularly reliable diagnosis of the heating device and / or the supply connections, the voltage is measured during switch-on, i.e., during the increase in power from the lower power level towards the higher power level, or after reaching the higher power level, especially immediately after reaching the higher power level. This allows for a particularly reliable determination of whether the heating device is operating reliably. Preferably, the voltage is measured only during switch-on, thus verifying that the heating device is functioning correctly at the start of its operation. However, it is also possible to measure the voltage periodically after switch-on, particularly at specific, for example, regular, intervals. This ensures particularly reliable operation of the drive unit.

[0024] A further development of the invention provides that, when the heating device is switched on, at least one electrical parameter of the supply connections is measured by the control unit, and a deviation of this parameter from a further predefined value indicates a fault in the heating device. Thus, not only is the voltage applied to the heating device measured using the measuring leads, but the control unit also determines at least one electrical parameter of the supply connections. If this parameter, or its measured value, deviates from the further predefined value, a fault in the heating device is detected. Therefore, it is possible to diagnose the condition of the supply connections by measuring the voltage using the measuring leads and, furthermore, to infer the condition of the heating device by measuring the electrical parameter.This enables a comprehensive diagnosis of the heating system and its electrical connection to the control unit.

[0025] A further development of the invention provides that the electrical quantity used is the supply voltage applied to the supply connections by the control unit and / or the current flowing through the supply connections. More generally, the quantity referred to above can be a voltage, a current, or both. The voltage used is the supply voltage applied to the supply connections by the control unit. The current is the current flowing through the supply connections. The described procedure enables simple diagnostics of the heating device itself.

[0026] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method as described herein, comprising an exhaust gas-generating drive unit, an exhaust gas aftertreatment device, and a heating device for heating the exhaust gas aftertreatment device, wherein the electrical connections of the heating device are electrically connected to a control unit via electrical supply connections. The drive unit is designed and configured to measure the voltage applied to the heating device by means of measuring lines separate from the supply connections, which are electrically connected on one side to the control unit and on the other side to the connections, whereby a deviation of the measured voltage from a predefined value indicates a fault in the supply connections.

[0027] The advantages of such a drive system design and such a procedure have already been mentioned. Both the drive system and the method for operating it can be further developed as described in this document, and reference is made to these details.

[0028] A further development of the invention provides that the supply connections comprise two supply lines and first connections for electrically connecting the supply lines to the control unit and second connections for electrically connecting the supply lines to the connections of the heating device. The control unit and the heating device are thus electrically connected to each other via the two supply lines. One of the first connections and one of the second connections are electrically connected to each of the supply lines, so that the first connection and the second connection are electrically connected to each other via the respective supply line.

[0029] The first terminals of the two supply lines are connected to the terminals of the control unit, and the second terminals of the supply lines are connected to the terminals of the heating unit. The supply connections explicitly include the connection of the supply lines to the terminals of the control unit and / or the connection of the supply lines to the terminals of the heating unit. It is important that the supply connections include both the supply lines themselves and the first terminals, so that voltage measurement allows for the verification of not only the supply lines but also their connection to the control unit and the heating unit. This enables a comprehensive diagnosis.

[0030] A further development of the invention provides that each of the measuring leads is electrically connected to the supply connections on the heating device only via the respective connection of the heating device. The measuring leads are thus not directly connected to the supply connections or supply lines on the heating device side, but only indirectly, namely via the connections of the heating device. The measuring leads and the supply connections are connected to the connections of the heating device independently of each other, in such a way that they are only electrically connected to each other via the respective connection. This ensures that the measuring leads can actually be used to diagnose the connection of the supply lines to the connections of the heating device, and not merely the supply lines themselves.

[0031] A further development of the invention provides that insulating elements are arranged between the measuring terminals of the measuring leads and the second terminals of the supply lines. The indirect connection of the measuring leads to the supply lines via the connections of the heating device is achieved by means of the insulating elements. One of the insulating elements is positioned between one of the second terminals of the supply lines and a terminal of the respective measuring lead, thus electrically isolating them from each other.

[0032] For example, the connections of the heating unit are designed as pins, specifically threaded pins. One of the second supply line connections is first attached to each of these threaded pins, followed by one of the insulating elements, and then one of the measuring leads or its connection. This arrangement is secured, for example, with a nut or similar fastener. This design allows for a connection of the supply lines to the heating unit that enables particularly comprehensive diagnostics.

[0033] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0034] The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawing, without limiting the invention. The drawing shows: Figure 1 is a schematic representation of an area of ​​a drive unit for a motor vehicle, namely a control unit and a heating device electrically connected to the control unit, and Figure 2 is a schematic representation of an area of ​​a heating device and supply connections via which the heating device is electrically connected to the control unit.

[0035] The Figure 1Figure 1 shows a schematic representation of a section of a drive unit 1 for a motor vehicle. The drive unit 1 has a drive assembly (not shown) by means of which a drive torque directed towards propelling the motor vehicle can be provided. During operation of the drive assembly, exhaust gas is produced, which is fed to an exhaust aftertreatment system 2. A heating unit 3 is also provided for heating the exhaust aftertreatment system 2. Electrical connections 4 and 5 of the heating unit 3 are connected via supply connections 6 and 7 to a control unit 8 of the drive unit 1, specifically to connections 9 and 10 of the control unit 8.

[0036] To connect supply lines 6 and 7 to the heating unit 3 and the control unit 8, supply lines 6 and 7 each have first connections 11 and 12 and second connections 13 and 14. Connections 11 and 13, and 12 and 14, respectively, are electrically connected to each other via supply lines 15 and 16 of supply lines 6 and 7. Equivalent resistors 17, 18, 19, 20, 21, and 22 are shown for supply lines 6 and 7. The equivalent resistances 17 and 20 describe the electrical resistance between the control unit 8 or its terminals 9 and 10 and the supply lines 15 and 16, the equivalent resistances 18 and 21 the electrical resistance of the supply lines 15 and 16 and the equivalent resistances 19 and 22 the electrical resistance of the connection of the supply lines 15 and 16 to the heating device 3 or its terminals 4 and 5.

[0037] Furthermore, the drive unit 1 has measuring lines 23 and 24, which are electrically connected to the control unit 8 on one side and to terminals 4 and 5 of the heating unit 3 on the other. Measuring lines 3 and 4 are used to measure the voltage present at terminals 4 and 5. This enables a four-wire voltage measurement. During operation of the drive unit 1, the voltage present at the heating unit 3, specifically at its terminals 4 and 5, is measured using measuring lines 23 and 24. If the measured voltage deviates from a predefined value, a fault in the supply connections 6 and 7 is detected. Conversely, if the voltage corresponds to the predefined value, the proper functioning of the supply connections 6 and 7 is detected.

[0038] The Figure 2Figure 1 shows a schematic representation of a section of the heating device 3, namely connection 4, with connection 5 being identically designed. Connection 4 is in the form of a pin or bolt, in particular a threaded bolt, to which connection 13 of the supply connection 6 is initially connected. The measuring line 23, or a contact thereof, is also connected to connection 4, in particular by being plugged onto it. Connection 13 and the measuring line 23 are held to connection 4 by means of a nut 25, which is screwed to connection 4.

[0039] To connect the measuring lead 23 separately from the supply connection 6 to terminal 4, an insulating element 26 is arranged between terminal 13 and the measuring lead 23. This provides electrical insulation between terminal 13 and the measuring lead 23, so that terminal 13 and the measuring lead 23 are only indirectly connected to each other via terminal 4, but not directly. This enables the aforementioned four-wire measurement, allowing for a particularly precise diagnosis of the heating device 3 and the supply connections 6 and 7. For the sake of completeness, it should be mentioned that the supply line 15 has insulation 27, from which it protrudes only at its end, as shown. LIST OF REFERENCE SYMBOLS:

[0040] 1 Drive unit 2 Exhaust aftertreatment unit 3 Heating unit 4 Connection 5 Connection 6 Supply connection 7 Supply connection 8 Control unit 9 Connection 10 Connection 11 1st Connection 12 1st Connection 13 2nd Connection 14 2nd Connection 15 Supply line 16 Supply line 17 Replacement resistor 18 Replacement resistor 19 Replacement resistor 20 Replacement resistor 21 Replacement resistor 22 Replacement resistor 23 Measuring lead 24 Measuring lead 25 Screw nut 26 Insulating element 27 Insulation

Claims

1. Method for operating a drive device (1) for a motor vehicle, which has an exhaust gas-generating drive unit, an exhaust gas aftertreatment device (2) and a heating device (3) for heating the exhaust gas aftertreatment device (2), wherein electrical terminals (4, 5) of the heating device (3) are electrically connected to a control device (8) via electrical supply connections (6, 7), wherein a voltage applied to the heating device (3) is measured by the control device (8) by means of measuring lines (23, 24) which are electrically connected on the one hand to the control device (8) and on the other hand to the terminals (4, 5), wherein a fault in the supply connections (6, 7) is detected if the measured voltage deviates from a preset value, characterised in that a differential voltage between a supply voltage applied by the control device (8) to the supply connections (6, 7) and a test voltage measured by the control device (8) on the measuring lines (23, 24) is used as the voltage.

2. Method according to claim 1, characterised in that the voltage is measured by means of the measuring lines (23, 24) which are connected to the electrical terminals (4, 5) at a distance from the supply connections (6, 7).

3. Method according to one of the preceding claims, characterised in that the measurement of the voltage is carried out during power-up of the heating device (3).

4. Method according to one of the preceding claims, characterised in that, when the heating device (3) is powered-up, at least one electrical property of the supply connections (6, 7) is measured by the control device (8) and, if the variable deviates from a further preset value, a fault in the heating device (3) is detected.

5. Method according to claim 4, characterised in that the supply voltage applied to the supply connections (6, 7) by the control device (8) and / or a current intensity of the electric current flowing via the supply connections (6, 7) is used as the electrical property.

6. Drive device (1) for a motor vehicle for carrying out the method according to one or more of the preceding claims, which has an exhaust-gas-generating drive unit, an exhaust-gas aftertreatment device (2) and a heating device (3) for heating the exhaust-gas aftertreatment device (2), wherein electrical terminals (4, 5) of the heating device (3) are electrically connected to a control device (8) via electrical supply connections (6, 7), wherein the drive device (1) is provided and designed to measure a voltage applied to the heating device (3) by means of measuring lines (23, 7) separate from the supply connections (6, 7), which are electrically connected on the one hand to the control device (8) and on the other hand to the terminals (4, 5), wherein a fault in the supply connections (6, 7) is detected if the measured voltage deviates from a preset value, characterised in that a differential voltage between a supply voltage applied by the control device (8) to the supply connections (6, 7) and a test voltage measured by the control device (8) on the measuring lines (23, 24) is used as the voltage.

7. Drive device according to claim 6, characterised in that the supply connections (6, 7) comprise two supply lines (15, 16) and first terminals (11, 12) for the electrical connection of the supply lines (15, 16) to the control device (8) and second terminals (13, 14) for the electrical connection of the supply lines (15, 16) to the terminals (4, 5) of the heating device (3).

8. Drive device according to claim 6 or 7, characterised in that, on the side of the heating device (3), each of the measuring lines (23, 24) is electrically connected to the supply connections (6, 7) only via the respective terminal (4, 5) of the heating device (3).

9. Drive device according to claims 7 and 8, characterised in that insulating elements (26) are arranged between the measuring terminals of the measuring lines (23, 24) and the second terminals (13, 14) of the supply lines (15, 16).