Method and system for operating an exhaust system

Abstract

Method for operating an exhaust system (4) of a hybrid vehicle comprising an internal combustion engine (2) as a drive unit, to which the exhaust system (4) is connected, at least one electric machine (14) as a drive unit and a power network (8), wherein the at least one electric machine (14) and at least one electrical energy storage device (12) are integrated into the power network (8), wherein the power network (8) is operated in a given operating situation at an initial voltage of a standard level, wherein a heating element (6) is associated with the exhaust system (4), wherein the heating element (6) is connected to the power network (8) via a switching element (16), wherein the heating element (6) is electrically connected to the power network (8) in a first switching state of the switching element (16) when the switching element (16) is switched on, and in a second switching state of the switching element (16) when the switching element (16) is switched off.electrically disconnected from the power grid (8), wherein, when switching the switching element (16) between the two switching states, the voltage of the power grid (8) is adjusted by a control unit (18) from the initial position with the standard level to a switching position with a switching level and also again from the switching position with the switching level to the initial position with the standard level, wherein, in the case that the at least one electric machine (14) is operated as a motor during switching, the at least one electric machine (14) converts electrical energy from the at least one electrical energy storage device (12) into mechanical energy for driving the vehicle, and wherein, in the case that the at least one electric machine (14) is operated as a generator during switching, the at least one electric machine (14) converts mechanical energy of the vehicle into electrical energy,which is stored in the at least one electrical energy storage device (12).

Description

[0001] The invention relates to a method for operating an exhaust system of a vehicle and a system for operating an exhaust system.

[0002] To operate a vehicle's exhaust system, it is necessary to heat it to a suitable operating temperature.

[0003] The publication DE 100 42 524 A1 describes a power supply for a motor vehicle.

[0004] A power supply circuit for a motor vehicle electrical system with two voltage supply branches is known from publication DE 198 46 319 C1.

[0005] A vehicle and a method for electrifying a catalytic device are described in publication EP 2 546 487 A1.

[0006] German patent application DE 102 48 415 A1 describes a power supply circuit for a motor vehicle with two different consumer voltages. This power supply circuit is used to switch on high-power consumers, which may include a heated windshield or an air heater.

[0007] The publication DE 100 36 762 C1 describes a device and a method for regulating the output voltage of a generator in a motor vehicle.

[0008] Document US 2014 / 0060014 A1 describes an exhaust aftertreatment system for an internal combustion engine. This system comprises an exhaust line in fluid communication with the internal combustion engine for receiving exhaust gas from the engine, a generator operating at a generator speed to produce electrical power, and an electrically heated catalyst device in fluid communication with the exhaust line. The catalyst device comprises a monolithic structure divided into a plurality of segments defining discrete resistance paths, the resistance paths being selectively connected to the generator for receiving electrical power. A control module is in communication with the catalyst device, the generator, and the internal combustion engine, and includes at least one control logic for determining the generator speed and selectively connecting the resistance paths to the generator based on the generator speed.

[0009] From US patent 2012 / 0277973 A1, a power system for exciting an electrically heated catalyst located upstream of an oxidation catalyst is known. A battery is configured to output a first voltage. A generator is configured to output a second voltage, greater than the first, in response to receiving a first control signal. A controller is configured to generate further control signals to set switching devices to their respective operating states depending on the voltages of the battery and the generator.

[0010] The publication EP 0 763 650 A1 describes a device for controlling the supply of electrical energy from a power source to an electrically heated catalyst, which is arranged in the exhaust manifold of an internal combustion engine upstream of a conventional catalytic converter. The device also includes a power source circuit switching device, a start detector device, a timer device, a resistance detector device, and two electrical power supply control devices.

[0011] Against this background, the task was to easily control a heating element for a vehicle's exhaust system.

[0012] This problem is solved by a method and a system with the features of the independent claims. Embodiments of the method and the system are described in the dependent claims and the description.

[0013] The method according to the invention is designed for operating the exhaust system of a vehicle that has an internal combustion engine, to which the exhaust system is connected, and a power supply. The power supply is initially operated with a voltage at a given initial state in, for example, the current, original, and / or respective operating situation. A heating element is assigned to the exhaust system and is connected to the power supply via a switching element. In a first switching state of the switching element, when the switching element is closed, the heating element is electrically connected to the power supply. Furthermore, in a second switching state of the switching element, when the switching element is closed, the heating element is opened and electrically disconnected from the power supply.When the switching element switches between the two switching states, the voltage of the power grid is adjusted from the initial position to a switching position as a voltage level or switching level.

[0014] The method can be implemented for a vehicle that can be designed or described as a motor vehicle or car. The vehicle is powered, as needed, by the internal combustion engine as the drive unit and / or by at least one electric motor as the drive unit, with the vehicle being designed as a hybrid vehicle with multiple drive units. If the at least one electric motor is operated as a motor, for example, during switching, it converts electrical energy from at least one electrical energy storage device, such as a battery, in the vehicle, which is also integrated into the power grid, into mechanical energy to propel the vehicle. If the at least one electric motor is operated as a generator, it converts the vehicle's mechanical energy into electrical energy, which is stored in the at least one electrical energy storage device.

[0015] In this configuration, the voltage of the power grid is lowered or reduced in an operating situation from the initial state to the switching state, whereby it is possible that the at least one electric machine integrated into the power grid is operated as a motor during the switching process, here when the voltage is lowered from the initial state of, for example, approx. 43 V to the switching state of, for example, a maximum of approx. 40 V.

[0016] In an alternative configuration, the voltage of the power grid is increased or raised from the initial state to the switching state in an operating situation, whereby it is possible that the at least one electric machine integrated into the power grid is operated as a generator during the switching process, here during the raising of the voltage.

[0017] In this process, the voltage of at least one electric machine is adjusted from the currently set and / or prevailing initial state to a designated switching state, thus achieving an optimal voltage for switching. Furthermore, the voltage of at least one electric machine is adjusted from this switching state to an optimal voltage for the continued operation of the vehicle and / or power grid, e.g., to the designated standard state.

[0018] The power grid operates in standard mode with a standard voltage level of, for example, approximately 43 V. When the switching element switches between the two states, the voltage of the power grid is reduced from the standard voltage level to the switching voltage level of, for example, a maximum of approximately 40 V. This prevents the voltage of the power grid from being raised to an excessively high value by a switching pulse.

[0019] In a further refinement of the process, the power grid is operated with a starting voltage as the initial state during vehicle startup, for example, with a cold energy storage system or battery. When the switching element switches between the two switching states, the voltage of the power grid is adjusted from the starting state to the switching state, thereby increasing or raising it. This prevents the voltage of the power grid from being reduced to an excessively low value by the switching pulse.

[0020] Typically, the voltage is reduced to the switching state of, for example, a maximum of approximately 40 V, whenever the switching element is activated (e.g., when switching on) and / or when the switching element is deactivated (e.g., when switching off). Thus, in this configuration, the voltage is only reduced when switching from the standard state to the switching state. Therefore, after switching from the switching state, the voltage is raised back to the standard state. Consequently, when the switching element is in the first switching state and is activated (closed), the heating element for the exhaust system is supplied with voltage from the power grid at the standard state of, for example, approximately 43 V.

[0021] In a further embodiment, the voltage is reduced to a reduced switching position or switching level of, for example, a maximum of approximately 36 V when the switching element switches between the two switching states, which is even lower than the aforementioned higher switching level of, for example, approximately 40 V.

[0022] It is possible that the initial position, e.g., standard position, of the voltage has a value of approximately 43 V, approximately 48 V or approximately 52 V, and that the switching position of the voltage has a value of approximately 50 V, approximately 40 V or approximately 36 V.

[0023] Possible values ​​for the standard position as a possible starting position of the voltage and the corresponding reduced switching position usually depend on the specific design of the energy network or vehicle electrical system and the respective operating situation.

[0024] The value for the standard position is usually defined or specified, although even such a defined value for the standard position can fluctuate during operation by a tolerance of a few percent, e.g., 1% to 2%, within normal tolerances. It should be noted that the value of the switching position, regardless of its intended ratio to the value of the standard position, can also fluctuate during operation by a tolerance of a few percent, e.g., 1% to 2%.

[0025] The following relationship can apply to the ratio between the value of the standard position as the starting position and the value of the switching position: ((Value of standard position minus value of switching position voltage)) divided by (Value of standard position voltage).

[0026] If the standard position is, for example, 43 V, the switching position can be 40 V or 36 V, depending on the design.

[0027] The switching position value for the voltage is therefore at least 5% to 10%, e.g. (43 V - 40 V) / 43 V ∼ 7%, or 10% to 15% or 20%, e.g. (43 V - 36 V) / 43 V - 16% lower than the value of the standard position for the voltage.

[0028] If, on the other hand, the voltage is increased from the starting position as the initial position to the switching position, the ratio of the starting position as the initial position to the switching position may depend on the switching voltage required for switching and the initial position of the voltage, where the starting position is lower than the standard position and the switching position.

[0029] Once the heating element is connected to the power grid via the switching element, it is supplied with electrical energy from the grid and, depending on the definition, warms or heats the exhaust system. The switching element is activated when the current, measured, or determined temperature is lower than the operating temperature that the exhaust system must maintain to clean the combustion engine's exhaust gases. To warm or heat the exhaust system with the heating element, the element is connected to the power grid via the switching element for a specific period of time, during which the voltage remains at its initial state (e.g., standard state), and the heating element receives voltage from the power grid.Only for switching, i.e., to initiate and end the heating of the exhaust system, is the voltage reduced from the standard position to the switching position.

[0030] The system according to the invention is designed to operate the exhaust system of a vehicle that has an internal combustion engine, to which the exhaust system is connected, and a power supply. In each operating situation, the power supply initially has a voltage with a starting state, e.g., a standard state during continuous operation as the vehicle's operating state, or a starting state during starting as the vehicle's operating state. The system has a heating element and a switching element, wherein the heating element is associated with the exhaust system, e.g., is arranged within the exhaust system, and wherein the heating element is connected to the power supply via the switching element. In a first switching state of the switching element, when the switching element is activated, the heating element is electrically connected to the power supply. In a second switching state of the switching element, when the switching element is deactivated, the heating element is...The heating element is electrically disconnected from the power grid. When the switching element switches between the two switching states, the system is designed to adjust the voltage of the power grid from its initial state to the switching state.

[0031] In standard operation, the power grid maintains a voltage at a specific, designated standard level, for example, approximately 43 V. When the switching element switches between the two switching states, i.e., when switching from the first to the second state, but also when switching from the second to the first state, the voltage of the power grid is reduced to a specific, designated switching level, for example, a maximum of approximately 40 V.

[0032] The system is designed to adjust the voltage from its initial state to a predetermined voltage level, i.e., to the standard level during continuous operation of the power grid or to the switching position for switching the switching element. For this purpose, the system includes a control unit and at least one electric motor, which is / are designed to determine the predetermined switching position and adjust the voltage from the initial state to the switching position and back again. Thus, the voltage level in the power grid is reduced by the control unit and / or the at least one electric motor from the standard initial state to the switching position and increased from the switching position back to the standard initial state. Alternatively, the voltage level in the power grid is...The voltage of the power grid is raised from the starting position to the switching position and lowered from the switching position back to the starting position by the control unit and / or the at least one electric machine. However, it is conceivable that the voltage level, after being initially raised from the starting position to the switching position by the control unit and / or the at least one electric machine, is then set to the standard level for the respective operating situation. It is possible that the voltage level is raised from the switching position to the standard level if the standard level in the operating situation is higher than the switching position, or lowered from the switching position to the standard level if the standard level in the operating situation is lower than the switching position.

[0033] The heating element is designed as an ohmic resistor and / or load which, when the switching element is activated, is directly supplied with electrical energy from the power grid or vehicle electrical system and continues to be heated. The exhaust system, which is also heated by the heating element, may include a catalyst and / or be designed as a catalyst.

[0034] This method allows the heating element to be controlled, activated and / or operated as a heat source for the exhaust system via the switching element.

[0035] The method and system provide a concept for simplifying the control of an electric catalyst (eCat) as the exhaust system of a hybrid vehicle (mHEV plus 48V eCat), e.g., a mild hybrid vehicle. The standard voltage in the vehicle's power grid and / or on-board electrical system, i.e., the operating voltage, can be approximately 48 V during standard operation. In this case, the switching voltage can be approximately 40 V or approximately 36 V. Therefore, the ratio of the standard voltage to the switching voltage, calculated as (standard voltage - switching voltage) / (standard voltage) = at least 15%, e.g., 16.67%, and up to a maximum of 25%, can be as follows:

[0036] This involves a simple switch concept for switching the electric catalyst, i.e., for switching the electric catalyst on, operating the electric catalyst, and switching the electric catalyst off.

[0037] Here, the electrical resistor, acting as the heating element of the electric catalyst, is operated at a preferred voltage, i.e., the operating voltage, typically at a standard level of, for example, 43 V. This voltage of, for example, 43 V is generally not undershot during vehicle operation and can be kept constant by at least one electric motor operating as a generator. During recuperation, the voltage in the power grid rises to up to 52 V. This increases the power generated by the heating element at the electric catalyst, which acts as the exhaust system. However, this is not problematic, as no damage can occur because the mass flow of exhaust gas from the combustion engine is always sufficient. Therefore, a higher heating power output of the electrical resistor has a positive effect. Consequently, the voltage in the power grid can be temporarily higher than the defined standard level, depending on the operating conditions.In this case too, the heating element, if connected to the power grid via the connected switching element, can be supplied with electrical energy at the temporarily increased voltage above the standard level. If the initial voltage level, depending on the definition, is the standard level or starting level, during recuperation is approximately 52 V, it is possible that the voltage is reduced to, for example, 50 V as the switching level to prevent overvoltage.

[0038] The switching, i.e., the switching on and off, can be carried out at voltages starting from the standard level of, for example, 43 V, within a switching range of approximately 36 V to minimize the load peak. This voltage reduction can be achieved when at least one electric motor, or several electric motors, briefly provide high motor power. This leads to high discharge currents in an electrical energy storage device, such as a battery. Consequently, the voltage at the electric heating element associated with the exhaust system and catalytic converter drops significantly, allowing for switching on or off without large voltage and current peaks for the power grid.

[0039] The process can be implemented in various vehicle operating situations, with a specific function being performed in each situation. The process can be carried out when the vehicle is electrically powered, particularly in purely electric mode, when a boost function is performed (where mechanical energy for propelling the vehicle is generated jointly by the electric motor and the combustion engine), or when a torque is generated against a brake.

[0040] In this method, at least one resistive load and / or resistor is used as a heating element for the exhaust system. Switching on and off is accomplished via a simple switching element, eliminating the need for a DC-DC converter or pulse-width modulation (PWM). When switching the heating element on and off, the voltage is reduced or increased, for example, to approximately 36 V to 40 V, via at least one electric motor, thereby adjusting the voltage-dependent switching power to a level compatible with the power grid.

[0041] The switching element or concept used is very simple, very compact, inexpensive, and requires no cooling. In this process, the electric catalyst, acting as an exhaust system, is sufficiently heated by the heating element, which is supplied with electrical energy or voltage from the power grid, thus generating enough heat output for safe exhaust emission.

[0042] The voltage of the power grid is briefly adjusted when switching on and off, i.e., at least during each switching operation; it is either lowered or raised.

[0043] During boost operation, when the vehicle is powered by the combustion engine and at least one electric motor with a power output of, for example, approximately 20 kW, the voltage can be reduced to approximately 40 V to 36 V. The heating element can, for example, have an electrical resistance R of approximately 2.1 ohms. In this case, its power, e.g., nominal power, is given by P = U. 2 * R depending on a given voltage U: P (43 V) - 4 kW, P (52 V) - 5.7 kW and P (36 V) - 2.7 kW.

[0044] By lowering the voltage during hybrid operation, the switching power (i.e., the power required to switch on and / or switch off) can be reduced to a level that is safe for the power grid. Lowering the voltage during switching compensates for and / or addresses the high voltage dependency of the heating element, which is a purely resistive load. Therefore, lowering the voltage during hybrid operation allows for the use of a switching concept where, for example, a DC-DC converter is not strictly necessary. The heating element used in this process / system is more economical or less expensive compared to conventional heating devices and requires minimal installation space. Furthermore, otherwise necessary active components, such as cooling, can be omitted.

[0045] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0046] The invention is schematically illustrated with reference to embodiments in the drawing and is described schematically and in detail with reference to the drawing. Fig. Figure 1 shows a schematic representation of an embodiment of the system according to the invention when carrying out an embodiment of the method according to the invention for operating an exhaust system of a vehicle.

[0047] Fig. Figure 1 shows a schematic representation of an internal combustion engine 2 of a vehicle, here a motor vehicle or car, to which an exhaust system 4 is connected for cleaning the exhaust gas of the internal combustion engine 2. The exhaust system 4 has a heating element 6. Another component of the vehicle is shown in Fig. Figure 1 schematically represents an energy network 8 as the vehicle's on-board electrical system, in which at least one electrical consumer 10 and at least one electrical energy storage device 12, e.g., a battery, are integrated into or incorporated into this energy network 8. Furthermore, an electric motor 14 is also integrated into the energy network 8, which can drive the hybrid vehicle alternatively or additionally to the combustion engine 2 when operated as a motor and converting electrical energy into mechanical energy. The vehicle can also be braked by the electric motor 14 by converting kinetic energy into mechanical energy when the electric motor 14 is operated as a generator and thus also as an energy source, whereby recuperation can also be performed.

[0048] Fig.Figure 1 also shows a switching element 16, via which the heating element 6 is connected to the power supply 8, and a control unit 18. The control unit 18 is assigned to the power supply 8 and is also connected to the switching element 16 and the exhaust system 4. The control unit 18 is designed to adjust the voltage level, and thus the value of an electrical voltage, in the power supply 8 as required.

[0049] The heating element 6, the switching element 16 and the power network 8, at least the electric machine 14 arranged therein, and the control unit 18 are here designed as components of the embodiment of the system 20 according to the invention.

[0050] In a first switching state, the switching element 16 is switched on and electrically connects the heating element 6 to the power supply 8. In a second switching state, the switching element 16 is switched off and disconnects the heating element 6 from the power supply 8.

[0051] In standard operation, the power grid 8 has a voltage with a standard voltage level of approximately 43 V or is operated at a voltage of 43 V.

[0052] In this embodiment of the method for operating an exhaust system 4, the switching element 16 is initially switched off, thereby disconnecting the heating element 6 from the power supply 8. The control unit 18 then detects the respective temperature of the exhaust system.

[0053] Since the exhaust system 4 should have a minimum operating temperature for cleaning the exhaust gases from the combustion engine 2, it is intended to heat it with the heating element 6 if the control unit 18 detects that the temperature of the exhaust system 4 is lower than its intended operating temperature.

[0054] For this purpose, it is provided that, in standard operation, the standard voltage of the power grid 8, previously 43 V, is set by the control unit 18 to a switching voltage of a maximum of 40 V, thereby being lowered, and the switching element 16 is switched by the control unit 18 by energizing it. Electrical energy is then supplied to the heating element 6 from the power grid 8 via the now closed switching element 16, warming and / or heating the heating element 6, and also, depending on the definition, warming and / or heating the exhaust system 4. In this process, the electric machine 14 is operated as a motor to lower the voltage.

[0055] After switching on, in this embodiment of the method, the voltage in the power network 8 is raised back to the standard level of 43 V by the control unit 18, starting from the switching position. Once the exhaust system 4 has reached its operating temperature, the switching element 16 is switched off by the control unit 18. In this case as well, the voltage in the power network 8 is reduced back to the lower switching position of a maximum of 40 V for switching off, in this case for switching off, the heating element 6 is disconnected from the power network 8. After switching off, the voltage is raised back to the standard level of approximately 43 V by the control unit 18.

[0056] In an alternative embodiment of the method, the vehicle and / or the power grid 8 can be started. During startup, when the energy storage device 12 is still cold, the power grid 8 has a starting voltage that is lower than both the standard voltage and the switching voltage. In this case, the voltage in the power grid 8 is raised from the starting voltage to the switching voltage, and the electric machine 14 can be operated as a generator. Subsequently, depending on whether the switching voltage is higher or lower than the standard voltage, the voltage can be raised or lowered to the standard voltage. The electric machine 14 operates as a generator to raise the voltage and as a motor to lower it. REFERENCE NUMBERS: 2 Internal combustion engine 4 Exhaust system 6 heating element 8 Energy network 10 consumers 12 Energy storage devices 14 Electric machine 16 switching element 18 Control unit 20 System

Claims

[1] Method for operating an exhaust system (4) of a hybrid vehicle comprising an internal combustion engine (2) as a drive unit, to which the exhaust system (4) is connected, at least one electric machine (14) as a drive unit and a power network (8), wherein the at least one electric machine (14) and at least one electrical energy storage device (12) are integrated into the power network (8), wherein the power network (8) is operated in a given operating situation at an initial voltage of a standard level, wherein a heating element (6) is associated with the exhaust system (4), wherein the heating element (6) is connected to the power network (8) via a switching element (16), wherein the heating element (6) is electrically connected to the power network (8) in a first switching state of the switching element (16) when the switching element (16) is switched on, and in a second switching state of the switching element (16) when the switching element (16) is switched off,electrically disconnected from the power grid (8), wherein, when switching the switching element (16) between the two switching states, the voltage of the power grid (8) is adjusted by a control unit (18) from the initial position with the standard level to a switching position with a switching level and also again from the switching position with the switching level to the initial position with the standard level, wherein, in the case that the at least one electric machine (14) is operated as a motor during switching, the at least one electric machine (14) converts electrical energy from the at least one electrical energy storage device (12) into mechanical energy for driving the vehicle, and wherein, in the case that the at least one electric machine (14) is operated as a generator during switching, the at least one electric machine (14) converts mechanical energy of the vehicle into electrical energy,which is stored in the at least one electrical energy storage device (12). [2] Method according to claim 1, wherein the voltage of the power grid (8) is reduced from the standard level of the initial position to the switching level of the switching position or increased from the standard level of the initial position to the switching level of the switching position in the respective operating situation. [3] Method according to claim 1 or 2, wherein the power network (8) is operated in a standard operation with the standard voltage level at a standard position as the initial position, wherein when switching the switching element (16) between the two switching states the voltage of the power network (8) is adjusted from the standard position as the initial position to the switching position from the standard level to the switching level. [4] Method according to any of the preceding claims, wherein the standard voltage level is approximately 43 V, approximately 48 V or approximately 52 V, and wherein the switching voltage level is approximately 50 V, approximately 40 V or approximately 36 V. [5] System for operating an exhaust system (4) of a hybrid vehicle, comprising an internal combustion engine (2) as a drive unit to which the exhaust system (4) is connected, at least one electric machine (14) as a drive unit, a control unit (18), and a power network (8), wherein the at least one electric machine (14) and at least one electrical energy storage device (12) are integrated into the power network (8), wherein the power network (8) has a voltage with an output state in a given operating situation, wherein the system (20) comprises a heating element (6) and a switching element (16), wherein the heating element (6) is assigned to the exhaust system (4), wherein the heating element (6) is connected to the power network (8) via the switching element (16), wherein the heating element (6) is electrically connected to the power network (8) in a first switching state of the switching element (16) when the switching element (16) is switched on.and in a second switching state of the switching element (16), when the switching element (16) is switched off, is electrically disconnected from the power network (8), wherein the control unit (18) of the system (20) is configured, when switching the switching element (16) between the two switching states, to adjust the voltage of the power network (8) from the initial position with the standard level to a switching position with a switching level and also from the switching position with the switching level back to the initial position with the standard level, wherein, in the case that the at least one electric machine (14) is operated as a motor during the switching, the at least one electric machine (14) converts electrical energy from the at least one electrical energy storage device (12) into mechanical energy for driving the vehicle, and wherein, in the case that the at least one electric machine (14) is operated as a generator during the switching,the at least one electric machine (14) converts mechanical energy of the vehicle into electrical energy, which is stored in the at least one electrical energy storage device (12). [6] System according to claim 5, wherein the heating element (6) is configured as an ohmic resistor and / or load.

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