Method for optimizing an exhaust aftertreatment system for a hybrid vehicle

Abstract

Method for optimizing an exhaust aftertreatment system (1) for a hybrid vehicle (100), - wherein the exhaust aftertreatment system (1) includes at least one particulate filter (11), - wherein, when it is detected that a regeneration of the particulate filter (11) is necessary or will soon be necessary, the state of charge of the energy storage device (321) is detected, and - if the state of charge of the energy storage device (321) is sufficient for the duration of at least partial regeneration of the particulate filter (11) during purely electric driving to fulfill the driving request (40) and maintain the torque of the combustion engine (31) during overrun operation, in a first step (S1) at least the particulate filter (11) is heated, and in a subsequent second step (S2) the regeneration is carried out, and - if, upon detection, it is determined that the charge level of the energy storage device (321) is insufficient for the duration of at least partial regeneration of the particulate filter (11) during purely electric driving to fulfill the driving request (40) and maintain the torque of the combustion engine (31) during overrun operation, - in the first step (S1) an intervention in the energy operating strategy of the vehicle (100) takes place, such that in the first step (S1) the energy storage for the operation of the electric motor (32) is charged by an amount up to a minimum predetermined state of charge, which enables regeneration of the particulate filter (11) of a predetermined percentage within a regeneration process, such that the state of charge of the energy storage (321) is sufficient for the duration of at least partial regeneration of the particulate filter (11) during purely electric driving to fulfill the driving request (40) and to maintain the torque of the combustion engine (31) during overrun operation, and at least the particulate filter (11) is heated, whereby - in the subsequent second step (S2) the regeneration is carried out.

Description

[0001] The invention relates to a method for optimizing an exhaust aftertreatment system for a hybrid vehicle.

[0002] Many vehicles, currently especially diesel-powered vehicles, are equipped with particulate filters to reduce emissions. These particulate filters must be regenerated regularly, meaning the particles accumulated in the particulate filter must be removed from the filter. Exhaust backpressure increases when the particulate filter is loaded with soot, thus causing more emissions to be released.

[0003] Once the filter has reached a certain level of loading, it must be regenerated, which is often referred to as burn-off. For this to happen, the filter must be as hot as possible and oxygen must be supplied to trigger a reaction in which the particles are burned at very high temperatures. The oxygen present in the ambient air is usually sufficient for this. This means that before regeneration, the exhaust system must first be warmed up. After this, oxygen, which is needed to convert the soot, is sucked in from the ambient air by the piston engine or supplied separately via a secondary air pump. The engine management system usually intervenes to heat the exhaust system, e.g. by means of multiple injection, ignition retardation and / or exhaust spread.

[0004] To pump the oxygen or ambient air required for combustion into the exhaust system without a secondary air pump, the particulate filter relies on random overrun phases initiated by the driver, during which the injection is shut off and fresh air is pumped through the piston engine. These phases cannot be planned and, due to the high oxygen storage capacity of the catalytic converter, are often too short to ensure effective conversion in the particulate filter.

[0005] Particulate filters will soon also be mandatory for hybrid vehicles. Hybrid vehicles, such as plug-in hybrids, will then be equipped with a particulate filter and a traction electric motor powerful enough to at least partially satisfy the driver's commands. The hybrid vehicle will then, just like existing vehicles, detect the particulate filter's loading level and the need for discharge, i.e., regeneration.

[0006] From DE 10 2008 035 451 A1 a method for optimising a hybrid operation of a hybrid vehicle is known, in which a power output or power consumption of an electric motor is controlled or regulated in such a way that a power output of an internal combustion engine is controlled or regulated to a load point which is optimal for an operating state of the internal combustion engine, wherein a total power of the hybrid vehicle, which is composed of the power of the electric motor and the power of the internal combustion engine, remains constant or continues to correspond to the specification of the driver.

[0007] Further prior art relating to the regeneration of particle filters can be found in DE 10 2017 005 238 A1, DE 11 2014 006 318 T5, GB 2 451 562 A, WO 2015 / 159 218 A2, DE 10 2014 220 860 A1, US 2011 / 0 072 791 A1, DE 10 2015 211 570 A1, DE 10 2013 202 142 A1, and DE 10 2015 015 794 A1.

[0008] All previously known strategies for regenerating particulate filters have advantages, but still have room for improvement. Therefore, it is an object of this invention to provide a method that optimizes the exhaust aftertreatment system in hybrid vehicles. This object is achieved according to the invention by the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims.

[0009] A method is proposed for optimising an exhaust gas aftertreatment system for a hybrid vehicle, wherein the exhaust gas aftertreatment system has at least one particulate filter, wherein upon detection that regeneration of the particulate filter is necessary or will be necessary soon, the charge state of the energy storage device is detected, and if the charge state of the energy storage device is sufficient for the duration of at least partial regeneration of the particulate filter during purely electric driving to fulfil the driving request and to maintain the torque of the internal combustion engine in overrun mode, at least the particulate filter is heated up in a first step, and in a second step the regeneration is carried out.

[0010] If it is detected that the energy storage system's charge level is sufficient for the combustion engine to operate in coasting mode during purely electric driving, i.e., act as a primary air pump, and the driver's command can be met, no intervention in the energy-related operating strategy is necessary. Instead, the warm-up phase can begin immediately, allowing the system to proceed to the step in which regeneration is initiated.

[0011] Furthermore, if it is detected that the charge level of the energy storage device is insufficient for the duration of at least partial regeneration of the particulate filter during purely electric driving to fulfill the driving request and maintain the torque of the combustion engine during overrun, the vehicle's energy operating strategy is intervened in a first step. In the first step, the energy storage device for operating the electric motor is charged by an amount such that the charge level of the energy storage device is sufficient for the duration of at least partial regeneration of the particulate filter during purely electric driving to fulfill the driving request and maintain the torque of the combustion engine during overrun. At least the particulate filter is heated up, with regeneration being carried out in the subsequent second step.

[0012] If it is detected that the energy storage system's charge level is insufficient for the combustion engine to operate in coasting mode during purely electric driving, i.e., act as a primary air pump, and the driver's command can be met, the energy-related operating strategy must be adjusted to achieve an appropriate charge level. The warm-up phase can then advantageously take place in parallel with charging.

[0013] Furthermore, it is provided that the energy storage device is charged to at least a predetermined charge level that enables regeneration of the particulate filter by at least a predetermined percentage within a burn-off process. For example, it can be specified that 30% or more regeneration should be possible within a burn-off process. This can prevent burn-off from occurring at a charge level that hinders rapid and efficient burn-off of the particulate filter.

[0014] The proposed method not only saves material but also enables faster and more efficient regeneration of the particulate filter. Furthermore, the filter can be regenerated even when the driver has a very unfavorable driving profile—i.e., no or hardly any overrun phases. This prevents a driver with an unfavorable driving profile from having to visit a workshop to clean or replace the particulate filter. Furthermore, other measures to induce overrun phases are activated less frequently, e.g., generally preventing the combustion engine from shutting down until the vehicle comes to a standstill, so that the fuel consumption advantage of the hybrid vehicle becomes apparent more frequently. This also increases customer satisfaction.

[0015] Furthermore, it is planned that, in the first step, the energy storage device is charged by raising the load point of the combustion engine to the specified charge level. Raising the load point of the combustion engine will charge the energy storage device and heat up the exhaust system more quickly.

[0016] Furthermore, in the first step, the load point of the combustion engine is raised until a specified particulate filter temperature is reached, which is required to start partial or full regeneration. Depending on whether full or partial regeneration is desired and how quickly regeneration should occur, the load point can be raised to a specified value that meets the conditions.

[0017] Furthermore, the combustion engine, which is shut down in the second step, serves as the primary air pump to supply ambient air for at least partial regeneration of the particulate filter. Thus, no additional pump is required to supply ambient air.

[0018] Furthermore, the energy storage device is designed to be charged to a level that allows complete regeneration of the particulate filter within a single burn-off process. This allows for rapid and efficient burn-off of the particulate filter in a single process.

[0019] Furthermore, a control unit is provided which is configured to receive data which enable the loading state of a particulate filter in a hybrid vehicle to be determined, to process this data and, in the event that regeneration of the particulate filter present in the hybrid vehicle is necessary, to output signals by means of which regeneration of the particulate filter is carried out according to the described method.

[0020] Furthermore, an exhaust gas aftertreatment system of a hybrid vehicle is provided, comprising a particulate filter, wherein the regeneration of the particulate filter is controlled by means of a described control unit.

[0021] Furthermore, a hybrid vehicle with a described exhaust aftertreatment system is provided.

[0022] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details of the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0023] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 shows a flowchart of the method according to an embodiment of the present invention. Fig. 2 shows a schematic representation of important components for carrying out the method in a hybrid vehicle according to an embodiment of the present invention.

[0024] As in Fig. As shown schematically in Figure 1, the method according to the invention comprises two steps. In the first step S1, the regeneration of the particulate filter is prepared, which is finally carried out in the second step S2. Before the first step S1 is carried out, a detection must be made, e.g., by a control unit, that the particulate filter 11 needs to be regenerated or that this will soon be necessary. A time interval in which regeneration must take place can also be specified.

[0025] To implement the method according to the invention for optimizing an exhaust gas aftertreatment system for a hybrid vehicle 100 with a particulate filter 11, upon detection, e.g., by a control unit 2, that regeneration of the particulate filter 11 is necessary or will be necessary soon, an intervention in the energy operating strategy of the vehicle takes place if it has been detected that the state of charge SOC of the energy storage device 321 is insufficient to fulfill the driver's request and simultaneously maintain the combustion engine in overrun mode, so that it acts as a primary air pump. Therefore, in such a case, in a first step S1, the energy storage device 321 is charged by a predetermined amount to operate the electric motor 32.This charging process continues until the state of charge SOC of the energy storage device 321 has reached a level necessary for the duration of at least partial regeneration of the particulate filter 11 during purely electric driving, i.e., with the combustion engine 31 switched off and connected. It should be noted that the charging quantity or the to-be-achieved state of charge SOC of the energy storage device 321 is selected such that it is sufficient to fulfill the driving request 40 and maintain the torque of the combustion engine 31 in overrun mode, i.e., in a switched-off but not disconnected mode. The driving request 40 can be determined, for example, via the position of the accelerator pedal or via a setting of driver assistance systems, e.g., by a control unit 2.

[0026] To charge the energy storage device 321, the energy operating strategy of the vehicle 100 is intervened, e.g., by the control unit 2, so that the load point of the combustion engine 31 is advantageously raised. This is also advantageous for heating the exhaust system, which in turn enables faster regeneration.

[0027] However, if it has been detected that the state of charge SOC of the energy storage device 321 is sufficient to fulfill the driver's request and at the same time to keep the combustion engine in overrun mode so that it acts as a primary air pump, then no intervention in the energetic operating strategy is necessary since the regeneration can be started immediately.

[0028] After charging, or when it has been determined that regeneration can begin immediately, the combustion engine 31 is brought into the coupled overrun cutoff state in a second step S2. The traction electric motor, i.e., the electric motor 32, fulfills the driving request 40 to the best of its ability and maintains the torque required to rotate the combustion engine 31. This allows for efficient regeneration of the particulate filter 11.

[0029] The charging strategy or the specification of the state of charge (SOC) aims to ensure that both conditions, i.e., fulfilling the driving request 40 and maintaining the torque, can be met. This is generally achieved by calculating or predicting a required state of charge (SOC) based on available data such as traffic information, route, driver characteristics, etc. However, should an unforeseen driving request 40 occur during the regeneration phase, this can be shortened or divided into several phases depending on the performance of the electrical system, i.e., electric motor and energy storage device, which depends, for example, on the state of charge (SOC) or existing degradation.

[0030] Switching from normal driving to this state of preparation and execution of regeneration requires certain entry conditions, including a minimum charge level of the high-voltage battery and a powerful electrical system—i.e., the electric motor and energy storage system—with little or no degradation. Multiple warm-up or regeneration cycles are also possible if the entry conditions are not met or, as mentioned above, an unforeseen driving request or other unforeseen event prevents the planned duration of regeneration.

[0031] Important during the charging phase in the first step S1 is the requirement that the exhaust system is hot enough to initiate regeneration. A further condition is that the driving request 40 is met and the required torque of the deactivated but connected combustion engine 31 is maintained. This means that the electrical system must have sufficient performance to meet the driver's request so that the electric motor 32 can overcome the basic friction of the connected combustion engine 31 during overrun fuel cutoff. The energy storage device 321 itself must have a charge level that allows the entire intended duration of the regeneration cycle to be completed.

[0032] In the second step S2, it should be noted that by shutting down the combustion engine 31, it operates as a primary air pump, i.e., it pumps the oxygen or ambient air required for regeneration into the exhaust system. Thus, no additional pump, often referred to as a secondary air pump, is required.

[0033] This effect is achieved by deliberately reducing the efficiency of the combustion engine 31 during towing operation, i.e., when the combustion engine 31 is switched off but connected. This results in faster regeneration of the particulate filter 11 and an emissions advantage due to the rapid reusability of the particulate filter 11.

[0034] In principle, several components in the hybrid vehicle 100 are required to carry out the method, as shown schematically in Fig.2. The hybrid vehicle 100 should have a drive system 3, which includes an internal combustion engine 31 and an electric motor 32. Furthermore, an exhaust aftertreatment system 1 is present, which includes a particulate filter 11. The particulate filter is preferably a gasoline particulate filter, but can also be a different particulate filter if the hybrid vehicle uses a different fuel that requires a particulate filter, e.g., diesel. Other components may be present, but are not required to carry out the method and are therefore not mentioned.

[0035] Furthermore, the hybrid vehicle 100 has at least one control unit 2, which can receive, process, and forward data. The control unit 2 serves to influence at least the energy management and engine management of the hybrid vehicle 100 based on the detection that regeneration of the particulate filter 11 is necessary or will soon be necessary, so that the method according to the invention can be carried out. The detection that the particulate filter 11 needs to be regenerated can be detected by the control unit 2 either based on measurement data from existing sensors, or, for example, tables are stored that prescribe regeneration at predetermined times. This means that the control unit 2 is not limited to merely receiving and forwarding data; rather, it can also perform its own processing, based on the result of which regeneration can be initiated.Furthermore, the control unit 2 receives information about the driving request 40, e.g. by detecting an accelerator pedal position or a request made via a driver assistance system.

Claims

[1] Method for optimising an exhaust aftertreatment system (1) for a hybrid vehicle (100), - wherein the exhaust gas aftertreatment system (1) has at least one particle filter (11), - wherein upon detection that regeneration of the particle filter (11) is necessary or will be necessary soon, the charge state of the energy storage device (321) is detected, and - if the charge state of the energy storage device (321) is sufficient for the duration of an at least partial regeneration of the particulate filter (11) during purely electric driving to fulfil the driving request (40) and to maintain the torque of the internal combustion engine (31) in overrun mode, at least the particulate filter (11) is heated up in a first step (S1), and in a subsequent second step (S2) the regeneration is carried out, and - if it is detected that the charge state of the energy storage device (321) is insufficient for the duration of at least partial regeneration of the particle filter (11) during purely electric driving to fulfil the driving request (40) and to maintain the torque of the internal combustion engine (31) in overrun mode, - in the first step (S1), an intervention in the energetic operating strategy of the vehicle (100) takes place, so that in the first step (S1), the energy storage device for operating the electric motor (32) is charged by an amount up to an at least predetermined charge level that enables regeneration of the particulate filter (11) by a predetermined percentage within a burn-off process, such that the charge level of the energy storage device (321) is sufficient for the duration of at least partial regeneration of the particulate filter (11) during purely electric driving to fulfill the driving request (40) and to maintain the torque of the internal combustion engine (31) in overrun mode, and at least the particulate filter (11) is heated up, wherein - in the subsequent second step (S2) the regeneration is carried out. [2] Method according to claim 1, wherein in the first step (S1) the charging of the energy storage device (321) is carried out by raising the load point of the internal combustion engine (31) up to the predetermined charge state. [3] Method according to claim 1 or 2, wherein in the first step (S1) the load point of the internal combustion engine (31) is raised until a predetermined particulate filter temperature, which is required for starting a partial or complete regeneration, is reached. [4] Method according to one of the preceding claims, wherein the combustion engine (31) switched off in the second step (S2) serves as a primary air pump for supplying ambient air for at least partial regeneration of the particulate filter (11). [5] Method according to one of claims 1 to 4, wherein the energy storage device (321) is charged to a charge state which enables complete regeneration of the particulate filter (11) within a burn-off process. [6] Control device (2) which is designed to - to receive data which enable the loading state of a particle filter (11) in a hybrid vehicle (100) to be determined, - to process this data and, in the event that regeneration of the particulate filter (11) present in the hybrid vehicle (100) is necessary, - to output signals by means of which a regeneration of the particle filter (11) is carried out according to the method according to one of claims 1 to 5. [7] Exhaust gas aftertreatment system (1) of a hybrid vehicle (100), comprising a particle filter (11), wherein the regeneration of the particle filter (11) is controlled by means of a control unit (2) according to claim 6. [8] Hybrid vehicle (100) with an exhaust aftertreatment system (1) according to claim 7.

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