CONTROL DEVICE FOR A HYBRID VEHICLE AND CONTROL METHOD FOR A HYBRID VEHICLE

Abstract

A control device for a hybrid vehicle with an internal combustion engine and an electric motor, enabling both series hybrid operation and direct engine drive using the internal combustion engine and the electric motor, and having a NOx cleaning system with an SCR and an LNT catalyst in the exhaust stream of the internal combustion engine, wherein the control device comprises: a fault detection unit that detects an abnormality in the NOx cleaning system with respect to the LNT catalyst;and a driving condition control unit which, if an abnormality is detected, prevents the direct engine drive of the vehicle, restricts the driving mode to series hybrid operation, and operates the internal combustion engine at an approximately constant power output, where this engine power is equal to or greater than a predetermined value and lies within a power range in which the NOx emission of the engine does not exceed the possible NOx purification quantity of the NOx purification system with the SCR catalyst.

Description

Technical field

[0001] The present disclosure relates to a control device for a hybrid vehicle and a control method for a hybrid vehicle. State of the art

[0002] In recent years, the configurations of hybrid vehicles have become increasingly diversified due to the requirements for improved energy efficiency and reduced exhaust emissions (NOx).

[0003] For example, among current hybrid vehicles there are so-called series / parallel hybrid vehicles that can switch between a series driving mode and a parallel driving mode.

[0004] In general, series hybrid vehicles are powered by an electric motor, with the combustion engine serving solely to generate electricity. The generated electrical energy is used either to charge the battery or directly to power the electric motor.

[0005] The series hybrid vehicle has two driving modes: "EV driving mode" and "series driving mode." In EV driving mode, the hybrid vehicle moves using the drive power of the electric motor, which is powered by the battery. The combustion engine is not running in this mode. In series driving mode, the hybrid vehicle also moves using the drive power of the electric motor, but this motor is supplied with power from both the battery and the generator—or exclusively from the generator. The combustion engine is then operated to generate electrical energy in the generator. Series driving mode is advantageous because it allows the combustion engine to operate in a range close to its optimal fuel consumption.

[0006] The parallel hybrid vehicle can be powered either by the electric motor, the combustion engine, or both simultaneously. A mode in which the parallel hybrid vehicle is powered exclusively by the combustion engine is called "engine-only mode." A mode in which both the combustion engine and the electric motor provide power is called "parallel-only mode." Both engine-only and parallel-only modes are advantageous because they can reduce battery charging / discharging losses as well as various resistance losses associated with the operation of the electric motor and / or generator.

[0007] The series / parallel hybrid vehicle combines the two types mentioned above. This means that, in this design, the drive power transmission system switches between series and parallel operating modes depending on the driving condition of the hybrid vehicle by engaging or disengaging a clutch. The series / parallel hybrid vehicle combines the advantages of both the series and parallel hybrid vehicles.

[0008] To improve exhaust emissions (NOx) in such hybrid vehicles, it is necessary to optimize the operation of the entire vehicle, in particular through coordinated control of both the combustion engine and the electric motor (see e.g. PTL 1 and PTL 2). Patent literature PTL 1 Japanese Disclosure Document No. 2020-050009 PTL 2 Japanese Disclosure Document No. 2019-166943 Summary of the invention: Technical problem

[0009] Traditionally, vehicles of this type are often equipped with a NOx purification system (hereinafter also referred to as the "LNT system") which uses an LNT catalyst (also referred to as a NOx adsorption catalyst) as an exhaust gas purification device for the internal combustion engine.

[0010] In such vehicles, an ECU (electronic control unit) with a fault diagnosis function is typically installed to prevent NOx emissions. This function continuously checks, for example, whether the LNT system is functioning correctly, e.g., by monitoring temperature deviations of the LNT catalyst or by detecting a fault in the NOx sensor located upstream of the LNT catalyst.

[0011] Conventionally, such an ECU is configured to limit engine power (i.e., the amount of fuel injected) in the event of a detected abnormality in the LNT system, in order to reduce the NOx emissions of the internal combustion engine.

[0012] Fig. Figure 1 shows a diagram of an aspect of a state-of-the-art engine control system when an abnormality occurs in the LNT system.

[0013] As in Fig. As shown in Figure 1, limiting the engine power can suppress the amount of NOx emitted by the engine into the environment, even if NOx removal by the LNT catalyst is not functioning properly. However, with such a limitation of engine power, even if the vehicle maintains a minimum power output sufficient to reach a workshop, the vehicle's movement in traffic may be impaired in situations such as when loaded or being towed, where higher engine power is required than when unloaded.

[0014] The present invention was developed taking into account the problems mentioned above. The aim of the invention is to provide a control device and a control method for a hybrid vehicle that ensures good drivability even in the event of an abnormality in the LNT system, while simultaneously suppressing NOx emissions into the environment. Solution to the problem

[0015] A key feature of the present disclosure for solving the above-mentioned problems is a control device for a hybrid vehicle with an internal combustion engine and an electric motor as drive sources, which enables both series hybrid operation and direct engine drive using the internal combustion engine and the electric motor, and includes a NOx cleaning system with an SCR catalyst and an LNT catalyst in an exhaust stream of the internal combustion engine, wherein the control device comprises the following: a fault detection unit that detects an abnormality in the NOx purification system with respect to the LNT catalyst; and a driving condition control unit which, when the abnormality is detected, prohibits direct engine drive as the vehicle's driving mode and restricts the driving mode to series hybrid operation, and operates the internal combustion engine with an approximately constant engine power, where the engine power is equal to or greater than a predetermined value and is within a power range in which the NOx emission of the internal combustion engine does not exceed the possible NOx cleaning quantity of the NOx cleaning system using the SCR catalyst.

[0016] Another feature concerns a control method for a hybrid vehicle with an internal combustion engine and an electric motor as drive sources, which enables both series hybrid operation and direct engine drive using the internal combustion engine and the electric motor, and includes a NOx cleaning system with an SCR catalyst and an LNT catalyst in an exhaust stream of the internal combustion engine, wherein the control method comprises the following: a first step towards detecting an abnormality in the NOx purification system with respect to the LNT catalyst; and a second step to prohibit direct engine drive as the vehicle's driving mode, to restrict the driving mode to series hybrid operation and to operate the internal combustion engine with an approximately constant engine power, wherein the engine power is equal to or greater than a predetermined value and is within a power range in which the NOx emission of the internal combustion engine does not exceed the possible NOx cleaning quantity of the NOx cleaning system using the SCR catalyst, wherein the second step is carried out when the abnormality is detected in the first step. Advantageous effects of the invention

[0017] According to the control device for a hybrid vehicle according to the present invention, good drivability can be ensured even if an abnormality occurs in the LNT system, while at the same time suppressing the emission of NOx into the environment of the vehicle. Brief description of the drawings Fig. Figure 1 is a schematic representation of a motor control system according to the state of the art when an abnormality occurs in the LNT system. Fig. Figure 2 is a schematic representation of the overall configuration of a vehicle according to an embodiment of the present invention. Fig. Figure 3 is a representation of an example of the configuration of an exhaust gas purification device according to an embodiment of the present invention. Fig. Figure 4 is a representation of an example of the functional configuration of an ECU according to an embodiment of the present invention. Fig. Figure 5 is a representation of the engine control by the ECU according to an embodiment of the present invention when an abnormality occurs in the LNT system. Fig. 6A and Fig. Figure 6B shows representations of control maps for regulating the valve opening degree of an EGR device. Fig. 6A shows a control map for the fuel consumption priority mode, while Fig. 6B shows a control map for the NOx reduction mode. Fig. Figure 7 is a flowchart showing an example of a process related to the function for detecting abnormalities in the LNT system of the ECU according to an embodiment of the present invention. Description of the embodiments

[0018] A preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings. It should be noted that in this description and the drawings, components with essentially the same function are designated with the same reference numerals, and duplicate descriptions are omitted. <Gesamtkonfiguration des Fahrzeugs>

[0019] The following describes an example of the configuration of a hybrid vehicle (hereinafter referred to as "Vehicle 1") according to an embodiment of the present invention. In this embodiment, Vehicle 1 is a series / parallel hybrid vehicle that combines the series and the parallel systems.

[0020] Fig. Figure 2 schematically shows the overall configuration of vehicle 1.

[0021] Vehicle 1 includes a battery 10, an electric motor 20, a motor 30, a generator 40, a clutch 50, a transmission mechanism 60, an exhaust gas purification device 70, various sensors 80 (80a-80f) and an ECU 100.

[0022] Battery 10 is a lithium-ion battery that provides electrical energy at a high voltage, e.g., 200 to 350 V. Battery 10 is connected to electric motor 20 via cables and can supply the electrical energy stored in battery 10 to electric motor 20. Battery 10 is also connected in parallel to electric motor 20 via cables to generator 40 and can be charged with the electrical energy generated by generator 40.

[0023] The electric motor 20 generates motive power for the vehicle 1 using the electrical energy stored in the battery 10 and / or the electrical energy generated by the generator 40 (i.e., the electrical energy generated by the motor 30). The output torque generated by the electric motor 20 is transmitted to the drive wheels 1R of the vehicle 1 via the transmission mechanism 60. The rotor of the electric motor 20 is directly connected to the transmission mechanism 60. Furthermore, during regenerative braking, the electric motor 20 acts as a generator, with the electrical energy generated by the electric motor 20 being stored in the battery 10.

[0024] The electric motor 20 has an inverter (not shown) which converts the direct current supplied by the battery 10 or the generator 40 into alternating current. (In this embodiment, the generator 40 converts the alternating current it generates into direct current via its own inverter and feeds this to the electric motor 20 or the battery 10.)

[0025] Motor 30 is directly coupled to the rotor of generator 40. When clutch 50 is open and vehicle 1 is in series drive mode, motor 30 operates solely for power generation in generator 40. However, when clutch 50 is closed, the output power of motor 30 is transmitted directly as mechanical energy to the drive wheels 1R of vehicle 1 via generator 40, clutch 50, and transmission mechanism 60.

[0026] From the perspective of NOx emission reduction, the engine 30 is equipped with an exhaust gas recirculation device 30E (EGR device) (see Fig. 3) Furthermore, the exhaust gas purification device 70 is arranged in the exhaust stream 30T of the engine 30.

[0027] Generator 40 generates electrical energy using the power of motor 30. The electrical energy generated by generator 40 is either stored in battery 10 or supplied directly to electric motor 20. Generator 40 has an inverter (not shown) that converts the generated alternating current into direct current and supplies it to battery 10 or electric motor 20.

[0028] The clutch 50 disconnects the drive power transmission path from the motor 30 to the drive wheels 1R of the vehicle 1 depending on a control signal from the ECU 100.

[0029] The transmission mechanism 60 converts the drive force from the motor 30 via the generator 40 or the drive force from the electric motor 20 into a rotational speed and an output torque with a predetermined gear ratio and transmits this to the drive wheels 1R of the vehicle 1.

[0030] The various sensors 80 are sensors that detect the state of the individual components of the vehicle 1, the driver inputs, etc. The sensors 80 include, for example, a vehicle speed sensor for detecting the vehicle speed 1, an accelerator pedal opening sensor for detecting the driver's actuation of the accelerator pedal 1, a speed sensor for detecting the engine speed 30, a speed sensor for detecting the rotor speed of the generator 40, another speed sensor for detecting the rotor speed of the electric motor 20, a voltage sensor for detecting the state of charge of the battery 10, and sensors 80a-80f that detect the state of the individual components of the exhaust gas purification device 70 (which are described later with reference to Fig. 3 (described). The signals detected by the sensors 80 are transmitted to the ECU 100.

[0031] The ECU 100 controls the overall operation of the individual components of the vehicle 1 by communicating with the corresponding units. For example, the ECU 100 performs the switching of the drive power transmission system to the drive wheels 1R, controls the engagement and disengagement of the clutch 50, regulates the operation of the engine 30, the generator 40 and the electric motor 20, controls the charging and discharging of the battery 10, as well as the operation of the exhaust gas purification device 70, and similar functions.

[0032] In addition, the ECU 100 records sensor data from the various sensors 80 in the vehicle 1 and determines the operating status of the respective components.

[0033] The ECU 100, for example, comprises a central processing unit (CPU), a read-only memory (ROM), a read / write memory (RAM), an input port, and an output port. Each function of the ECU 100 is implemented, for instance, by the CPU accessing a control program and various data stored in the ROM or RAM. However, some or all functions can alternatively or additionally be implemented by a digital signal processor (DSP) or by special hardware circuits (e.g., ASIC or FPGA).

[0034] For example, vehicle 1 has the following driving modes: (a) EV driving mode, (b) serial driving mode, (c) engine driving mode and (d) parallel driving mode.

[0035] In EV driving mode, the clutch 50 is open and the engine 30 is switched off. Vehicle 1 is driven by the motive power of the electric motor 20, which is supplied by electrical energy from the battery 10.

[0036] In series drive mode, the clutch 50 is also open, and the engine 30 is operated to provide electrical energy, which the electric motor 20 uses to generate a driving force corresponding to the accelerator pedal angle, vehicle speed, etc. In this mode, vehicle 1 is driven by the electric motor 20, which is supplied with electrical energy from the generator 40. Additionally, auxiliary power from the battery 10 can also be supplied to the electric motor 20 in this mode.

[0037] In engine-driven mode, the clutch 50 is engaged, and vehicle 1 is driven exclusively by the drive force of the engine 30. When driving in engine-driven mode, the rotor of the electric motor 20 and the rotor of the generator 40 rotate together with the crankshaft of the engine 30.

[0038] In parallel driving mode, the clutch 50 is also engaged, and vehicle 1 is driven by the combined drive power of engine 30 and electric motor 20. When driving in parallel mode, the rotor of generator 40 also rotates together with the crankshaft of engine 30.

[0039] The ECU 100 switches between these driving modes to optimize energy efficiency (e.g., fuel consumption). This control strategy is well-known and therefore will not be explained in detail here.

[0040] In the following, driving in engine driving mode and in parallel driving mode will be referred to collectively as "direct engine drive", while driving in serial driving mode will be referred to as "serial hybrid operation". <Konfiguration der Abgasreinigungsvorrichtung 70>

[0041] Fig. Figure 3 shows an example of the configuration of the exhaust gas purification device 70.

[0042] The exhaust gas purification device 70 comprises an LNT catalyst 71, a PM filter 72, an SCR catalyst 73, an ASC catalyst 74 and a urea supply device 75. These catalysts or devices are arranged in the exhaust stream 30T of the engine 30 in the direction of exhaust gas flow - i.e. from upstream to downstream - in the following order: LNT catalyst 71, PM filter 72, SCR catalyst 73 and ASC catalyst 74.

[0043] The LNT catalyst 71 adsorbs NOx from the exhaust gas when there is excess oxygen and reduces the stored NOx in a reducing atmosphere by reacting with hydrocarbons or similar substances to harmless gases such as nitrogen, releasing the NOx in the process. The LNT catalyst 71 can, for example, consist of a catalyst support such as aluminum oxide coated with a NOx reduction catalyst such as platinum or rhodium and a NOx adsorption material such as calcium or barium.

[0044] However, the NOx storage capacity of the LNT catalyst 71 decreases when the LNT catalyst 71 is in a saturated state. For this reason, the ECU 100 monitors the NOx storage state in the LNT catalyst 71. That is, when the NOx storage level in the LNT catalyst 71 increases and approaches the saturation point, the ECU 100 operates the engine 30 with a rich air-fuel mixture (so-called "rich spike") in order to deliberately generate exhaust gas with a reducing atmosphere and regenerate the LNT catalyst 71 of NOx.

[0045] The PM filter 72 (particle filter) captures particles (PM) from the exhaust gas and consists of porous ceramic such as cordierite or silicon carbide.

[0046] The SCR catalyst 73 (also known as a NOx selective reduction catalyst) adsorbs ammonia, which is produced by hydrolysis of the supplied urea solution from the urea supply device 75, and selectively reduces NOx in the exhaust gas using the adsorbed ammonia. For example, a catalyst can be used as the SCR catalyst 73 in which a NOx reduction catalyst such as iron zeolite, copper zeolite, or vanadium is applied to the surface of a ceramic support.

[0047] The ASC catalyst 74 (also known as the ammonia slip catalyst) prevents ammonia that passes through the SCR catalyst 73 from being released into the environment. The ASC catalyst 74 oxidizes the remaining ammonia from the SCR catalyst 73 and decomposes it into water and nitrogen, thereby effectively suppressing ammonia slip from the SCR catalyst 73.

[0048] The urea supply device 75 injects urea solution upstream of the SCR catalyst 73 into the exhaust stream 30T. The urea supply device 75 comprises, for example, a urea metering valve, a urea tank, and a feed pump. In this urea supply device 75, the urea solution is forced from the urea tank by the feed pump and injected into the exhaust stream 30T via the urea metering valve.

[0049] The amount of urea solution injected into the exhaust stream 30T by the urea supply device 75 is controlled by regulating the opening of the urea metering valve. The opening of the urea metering valve is controlled by a control signal output by the ECU 100.

[0050] The control of the urea injection by the ECU 100 corresponds to the known state of the art and is therefore not described in detail here. The ECU 100 sets a target value for the amount of ammonia stored in the SCR catalyst 73, for example, based on the catalyst temperature of the SCR catalyst 73 measured by the first temperature sensor 80e. The ECU 100 then continuously calculates the ammonia consumption in the SCR catalyst 73 based on sensor values ​​such as those from the second NOx sensor 80c and the flow sensor 80a (i.e., the amount of NOx entering the SCR catalyst 73). The ECU 100 then regulates the urea injection from the urea supply device 75 so that the amount of ammonia stored in the SCR catalyst 73 is maintained at the target value.

[0051] In this way, in the exhaust gas purification device 70 according to this embodiment, both the SCR catalyst 73 and the LNT catalyst 71 are used to effectively minimize NOx emissions.

[0052] In general, the SCR catalyst 73 has a high NOx conversion rate, but is inactive at low exhaust gas temperatures (e.g., below 200 °C). By combining the SCR catalyst 73 and the LNT catalyst 71 in the exhaust stream 30T, the NOx emitted by the engine 30 can be cleaned by the LNT catalyst 71 at low exhaust gas temperatures – for example, during a cold start – when the SCR catalyst 73 is still inactive.

[0053] Furthermore, this configuration enables NOx purification by the SCR catalyst 73 even if an abnormality occurs in the NOx purification system that uses the LNT catalyst 71.

[0054] The exhaust gas purification device 70 is equipped with various sensors 80, including a flow sensor 80a that detects the amount of air entering the engine 30, a first NOx sensor 80b that detects the amount of NOx emitted by the engine 30, a second NOx sensor 80c that detects the amount of NOx entering the SCR catalyst 73, a third NOx sensor 80d that measures the amount of NOx emitted from the vehicle 1 to the outside, a first temperature sensor 80e that detects the temperature of the SCR catalyst 73, and a second temperature sensor 80f that measures the temperature of the LNT catalyst 71. These sensors 80 continuously transmit the detected sensor data to the ECU 100. [Detailed configuration of the ECU 100]

[0055] Fig. Figure 4 shows an example of the functional configuration of the ECU 100.

[0056] The ECU 100 has the following functional units: a fault detection unit 101, a driving condition control unit 102 and a rich spike execution unit 103. <Fehlererkennungseinheit 101>

[0057] The fault detection unit 101 detects abnormalities related to the NOx cleaning system (hereinafter also referred to as the "LNT system") which uses the LNT catalyst 71, which is located in the exhaust stream 30T of the engine 30.

[0058] An abnormality of the LNT system exists when the LNT catalyst 71 is no longer able to adequately clean NOx in the exhaust gas (i.e., in a fault condition where the cleaning performance of the LNT catalyst 71 can no longer be guaranteed).

[0059] Such abnormal conditions include, for example, an abnormal temperature of the LNT catalyst 71 or a faulty sensor reading or a malfunctioning operation of the first NOx sensor 80b, which is located upstream of the LNT catalyst 71.

[0060] A temperature deviation of the LNT catalyst 71 occurs, for example, when condensation from the engine 30 or from the upstream piping causes a temperature drop in the LNT catalyst 71. In such a condition, the NOx removal performance of the LNT catalyst 71 is impaired. Similarly, if the first NOx sensor 80b, located upstream of the LNT catalyst 71, malfunctions, the amount of NOx stored in the LNT catalyst 71 cannot be accurately measured. In these cases, the rich-spike execution unit 103 described below interrupts the execution of the rich spike. In other words, the LNT catalyst 71 could be in a saturated state, and its removal performance would then be reduced.

[0061] The fault detection unit 101 can detect a temperature deviation of the LNT catalyst 71, for example, based on the sensor value measured by the second temperature sensor 80f. Furthermore, the fault detection unit 101 detects an abnormality in the first NOx sensor 80b if the sensor value of the first NOx sensor 80b is implausible or if the sensor signal of the first NOx sensor 80b is interrupted. If the fault detection unit 101 detects such an abnormality in the LNT system, it sets a fault flag in a memory unit (e.g., in RAM) to switch the operating state of the vehicle 1.

[0062] Additionally, an oxygen concentration sensor (not shown) can be located in the exhaust stream 30T upstream of the LNT catalyst 71. If this oxygen concentration sensor malfunctions, there is also a risk that the cleaning performance of the LNT catalyst 71 cannot be guaranteed. Therefore, if this oxygen concentration sensor malfunctions, the fault detection unit 101 can also set the fault flag.

[0063] Furthermore, the fault detection unit 101 can also set the fault flag if a malfunction is detected in the flow sensor 80a or similar sensors. This is because, in such cases, the amount of NOx stored in the LNT catalyst 71 cannot be reliably determined. <Fahrzustands-Steuereinheit 102>

[0064] The driving condition control unit 102 controls the driving mode of vehicle 1.

[0065] As described above, under normal conditions (i.e., when the LNT system is in its normal state; this also applies to the following explanations), the driving mode of the vehicle 1 switches between the driving modes EV driving mode, serial driving mode, motor driving mode and parallel driving mode in order to maximize energy efficiency.

[0066] However, if the fault detection unit 101 detects an abnormality in the LNT system, the driving state control unit 102 disables direct engine drive as the driving mode of vehicle 1 and restricts the driving mode to series hybrid operation. Within this series hybrid operation, the driving state control unit 102 operates the engine at an approximately constant engine power output, which is equal to or greater than a predefined value and lies within a power range in which the NOx emission of the engine 30 does not exceed the possible NOx removal quantity of the NOx removal system with SCR catalyst 73.

[0067] This point will be described in detail below.

[0068] Fig. Figure 5 shows how the ECU 100 controls the motor 30 when an abnormality occurs in the LNT system.

[0069] As previously explained, in the prior art, if an abnormality occurs in the LNT system, the power (i.e., the fuel injection quantity) of engine 30 is limited in order to reduce the amount of NOx emitted externally by engine 30. In such cases, however, it can be difficult to move the vehicle under its own power in traffic, especially when engine power is required for driving compared to an empty state, such as when the vehicle is loaded or being towed.

[0070] In this context, the driving condition control unit 102, according to this embodiment, restricts the driving mode of the vehicle 1 to series hybrid operation and operates the engine 30 with an approximately constant engine power (i.e., in quasi-steady-state operation), wherein this engine power is equal to or greater than a predetermined value and lies within a power range in which the NOx emission of the engine 30 does not exceed the possible NOx cleaning quantity of the NOx cleaning system with SCR catalyst 73.

[0071] The engine power in this operating state is preferably set close to the maximum value within the stated power range; however, a value below the maximum value that takes into account a predetermined safety buffer is even more preferred, e.g., with regard to age-related changes in the cleaning performance of the SCR catalyst 73. Furthermore, the engine power can vary slightly in this quasi-steady-state operation to compensate for fluctuating demands on the vehicle's drive power.

[0072] Thus, even if an abnormality occurs in the LNT system, the required driving force for vehicle 1 can be provided without limiting the engine power, thereby maintaining good drivability.

[0073] In this case, the electric motor 20 provides the motive power required to propel the vehicle 1, while the motor 30 operates in generator mode. The motive power required for the vehicle 1's operation is determined, for example, based on the vehicle 1's speed and the accelerator pedal input (i.e., the accelerator pedal angle), and the electric motor 20 is controlled to generate this motive power. The electrical energy required to drive the electric motor 20 is supplied directly by the motor 30 (or the generator 40). Any potential power shortfall from the motor 30 (or the generator 40) is compensated for by the battery 10. Excess electrical energy generated by the motor 30 (or the generator 40) is stored in the battery 10.

[0074] In general, in direct engine drive mode (i.e., engine driving mode or parallel driving mode), the operating state of engine 30 must be adjusted depending on the acceleration requirements of vehicle 1. This tends to cause short-term increases in NOx emissions and thus also increase the amount of NOx emitted externally from vehicle 1. In contrast, during the quasi-steady-state operation of engine 30 within series hybrid operation, there are fewer fluctuations in exhaust gas temperature, volume flow, and NOx emissions, which effectively suppresses sudden NOx emissions, e.g., as a result of abrupt acceleration.

[0075] Furthermore, in this embodiment of vehicle 1, all NOx emitted by engine 30 is generally cleaned by the SCR catalyst 73. Therefore, even if the LNT catalyst 71 is not fully functional, the amount of NOx emitted from vehicle 1 can be reduced to an extremely low level.

[0076] The “performance range of the engine 30 in quasi-steady-state operation” (i.e. the range in which the NOx emissions of the engine 30 do not exceed the possible NOx cleaning quantity of the NOx cleaning system with SCR catalyst 73) can, for example, be determined in advance on the basis of tests or simulations, taking into account the NOx cleaning performance of the SCR catalyst 73 that can be expected under normal conditions.

[0077] Since the NOx removal performance of the SCR catalyst 73 is highly dependent on the specific operating conditions, it is desirable to define the aforementioned "power range of the engine 30 in quasi-steady-state operation" as precisely as possible, taking the current state into account. In this way, the engine 30 can be operated at the highest possible power output in quasi-steady-state operation. Specifically, the currently achievable NOx removal rate of the SCR catalyst 73 can be calculated, for example, based on the current temperature of the SCR catalyst 73 and the amount of ammonia stored in the SCR catalyst 73.From this possible NOx cleaning quantity, the power range of the engine 30 in which the NOx emission from the engine 30 does not exceed the possible NOx cleaning quantity can be calculated using a predefined control map - for example, a map that describes the relationship between possible NOx cleaning quantity and maximum permissible engine power based on experiments or simulations.

[0078] Furthermore, if an abnormality is detected in the LNT system, it is preferred that the driving condition control unit 102 operates the engine 30 in NOx reduction mode and not in fuel consumption priority mode. In fuel consumption priority mode, the operating condition of the engine 30 (e.g., engine speed, output torque, injection timing, EGR rate, turbocharger boost pressure, etc.) is optimized with regard to fuel efficiency. However, this fuel consumption priority mode is not necessarily advantageous with regard to reducing NOx emissions.

[0079] For this reason, in NOx reduction mode, the driving condition control unit 102, for example, increases the opening of the EGR device 30E to a value greater than the opening degree set in fuel consumption priority mode. This reduces the amount of NOx emitted by the engine 30.

[0080] The Fig. 6A and Fig. Figure 6B shows examples of control maps for regulating the opening degree of the EGR device 30E. Fig. Figure 6A shows a control map used in fuel consumption priority mode, while Fig. 6B represents a control map for the NOx reduction mode.

[0081] The opening degree is defined in the control map of the EGR device 30E as a function of engine speed and fuel injection quantity. In the Fig. 6A and Fig. 6B The terms "large" and "small" refer to the respective opening degree of the EGR device 30E. The darker the area shown, the larger the set valve opening.

[0082] In general, the formation of NOx, a pollutant, increases significantly at high combustion temperatures. The EGR device 30E recirculates a portion of the exhaust gases back into the intake system, reducing the oxygen concentration of the intake air and slowing down combustion. This lowers the combustion temperature and thus reduces NOx formation. However, the valve opening of the EGR device 30E not only affects NOx production but also the engine's output torque, white smoke emissions, and fuel consumption. Therefore, the control map of the EGR device 30E, with its optimal EGR valve opening, is created based on tests to match the engine's operating conditions.

[0083] In the control map used in NOx reduction mode, the valve opening is larger in every engine operating condition of engine 30 than in the control map of the fuel consumption priority mode. That is, in NOx reduction mode, the valve opening of the EGR device 30E is increased compared to normal operation (i.e., fuel consumption priority mode), and the EGR rate is increased. This reduces the amount of NOx emitted by engine 30.

[0084] Additionally, in NOx reduction mode, the boost pressure of the turbocharger (not shown) connected to engine 30 can be reduced, or the fuel injection timing can be delayed. This further reduces NOx emissions from engine 30.

[0085] In other words, when vehicle 1 is in series hybrid mode, engine 30 operates in fuel consumption priority mode at an operating point as close as possible to the most efficient operating point. In NOx reduction mode, however, as described above, the control of engine 30 is adjusted so that engine 30 operates at a different operating point than the most efficient one. Consequently, fuel efficiency is lower in NOx reduction mode than in fuel consumption priority mode.

[0086] Furthermore, in NOx reduction mode, ECU 100 preferably uses an electric heater (not shown) to heat the SCR catalyst 73 and increase its temperature if it is low. This is because, in NOx reduction mode, the increased valve opening of the EGR device 30E lowers the combustion temperature in the engine 30, which can also lower the exhaust gas temperature and thus prevent the SCR catalyst 73 from reaching its effective cleaning temperature. However, there may also be cases where the exhaust gas temperature does not decrease despite the reduced combustion temperature. Therefore, the switching on and off of the electric heater should preferably be controlled based on the actual temperature of the SCR catalyst 73. <Rich-Spike-Ausführungseinheit 103>

[0087] The rich spike execution unit 103 executes a so-called rich spike in the engine 30 based on the amount of NOx stored in the LNT catalyst 71.

[0088] The timing of the rich spike execution by the rich spike execution unit 103 is controlled by a known method and is therefore not described in detail. The rich spike execution unit 103 calculates the amount of NOx absorbed per unit of time either based on the sensor data from the flow sensor 80a and the first NOx sensor 80b or based on the estimated NOx emissions of the engine 30 and a model within the ECU 100. The amount of NOx absorbed in the LNT catalyst 71 is then estimated by integrating the amount of NOx absorbed at each point in time during driving. As soon as the amount of NOx absorbed in the LNT catalyst 71 exceeds a predetermined threshold (e.g., 80%), the rich spike execution unit 103 initiates the execution of a rich spike by the engine 30.

[0089] The execution of the rich spike can be stopped by the rich spike execution unit 103 if an abnormality is detected in the LNT system. <Ablaufsteuerung der ECU 100>

[0090] Fig. Figure 7 shows a flowchart of an example of the process of the fault detection function of the ECU 100 in connection with the LNT system.

[0091] In step S1, the ECU 100 determines whether an abnormality exists in the LNT system. If an abnormality is detected (S1: YES), the ECU 100 proceeds to step S2. If no abnormality is detected (S1: NO), the ECU 100 terminates the process according to the flowchart in [reference to flowchart]. Fig. 7 without further measures.

[0092] In step S2, the ECU 100 disables direct engine drive and restricts the driving mode of vehicle 1 to series hybrid operation. This means that if vehicle 1 is currently in direct engine drive mode, the ECU 100 switches the driving mode to series hybrid operation.

[0093] In step S3, the ECU 100 sets the operating state of the engine 30 to quasi-steady-state operation in NOx reduction mode. In this state, the ECU 100 operates the engine 30 at an almost constant engine power, whereby the engine power is equal to or greater than a predefined value and lies within a power range in which the NOx emission of the engine 30 does not exceed the possible NOx cleaning quantity of the NOx cleaning system with SCR catalyst 73.

[0094] At this point, the ECU 100 calculates the potential NOx purification quantity of the SCR catalyst 73 (i.e., the amount of NOx that can be purified by the SCR catalyst 73), for example, based on the current temperature of the SCR catalyst 73 and the amount of ammonia stored in the SCR catalyst 73. The ECU 100 then calculates the power range of the engine 30 in quasi-steady-state operation (i.e., the range in which the NOx emission of the engine 30 does not exceed the potential NOx purification quantity of the SCR catalyst 73), based on the calculated potential NOx purification quantity of the SCR catalyst 73 and a predefined control map.

[0095] Furthermore, in this state, the ECU 100 sets the operating mode of engine 30 to NOx reduction mode. This means that the ECU 100 controls engine operation by, for example, increasing the valve opening of the EGR device 30E, reducing the boost pressure of the turbocharger connected to engine 30, and retarding the injection timing.

[0096] By executing the control described above, the ECU 100 enables vehicle 1 to drive with the required driving force for vehicle 1, even if an abnormality occurs in the LNT system, while simultaneously suppressing the NOx emissions to the outside of vehicle 1. [Effect of the invention]

[0097] As described above, the present embodiment relates to a control device for a hybrid vehicle that has an internal combustion engine and an electric motor as drive sources, allows both series hybrid operation and direct engine drive using an internal combustion engine and an electric motor, and has a NOx purification system with an SCR catalyst and an LNT catalyst in the engine's exhaust system. The control device comprises: a fault detection unit that detects an abnormality in the NOx purification system with respect to the LNT catalyst; and A driving condition control unit which, when an abnormality is detected, prevents direct engine drive as the vehicle's driving mode, restricts the driving mode to series hybrid operation, and operates the engine at an approximately constant engine power, where this power is equal to or greater than a predetermined value and is within a power range in which the engine's NOx emission does not exceed the possible NOx cleaning quantity of the NOx cleaning system with SCR catalyst.

[0098] According to the control device of this embodiment, even in the event of an abnormality in the LNT system, the driving force required for operation can be provided, while suppressing the emission of NOx into the environment, thus maintaining good drivability.

[0099] Although specific embodiments of the present invention have been described in detail, these serve only for illustrative purposes and do not limit the scope of protection of the patent claims. The technology described in the claims also includes various modifications and alterations of the specific examples described above.

[0100] For example, the layout of the hybrid vehicle 1, to which the control device of the present invention is applied, can be in forms other than in Fig. 2 shown. In particular, the layout of the hybrid vehicle 1 can be designed such that the generator 40 and the axle are not arranged coaxially (e.g. a design in which the generator 40 is driven by a belt) or the electric motor 20 is arranged between the motor 30 and the transmission mechanism 60.

[0101] Furthermore, various modifications are possible with regard to the sensors 80 used in the hybrid vehicle 1. For example, the first NOx sensor 80b does not necessarily have to be present. In this case, the ECU 100 can estimate the amount of NOx emitted by the engine 30 based on the engine operating state of the engine 30 and the valve opening of the EGR device 30E.

[0102] This application claims priority over Japanese patent application No. 2024-186624 dated October 23, 2024, the full disclosure of which, including description, drawings and abstract, is hereby incorporated by reference. Industrial applicability

[0103] According to the control device for a hybrid vehicle according to the present invention, good drivability can be ensured even in the event of an abnormality in the LNT system, while the emission of NOx into the environment is effectively suppressed. Reference symbol list 1 vehicle 1R drive wheel 10 batteries 20 electric motor 30 engine 30E EGR device 40 Generator 50 Clutch 60 Gear mechanism 70 Exhaust gas purification device 71 LNT catalyst 72 PM filter 73 SCR catalyst 74 ASC catalyst 75 Urea delivery device 80a flow sensor 80b First NOx sensor 80c Second NOx sensor 80d Third NOx sensor 80e First temperature sensor 80f Second temperature sensor 100 ECU 101 Fault detection unit 102 Driving Condition Control Unit 103 Rich Spike Execution Unit QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2020-050009

[0008] JP 2019-166943

[0008] JP 2024-186624

[0102]

Claims

[1] A control device for a hybrid vehicle with an internal combustion engine and an electric motor as drive sources, enabling both series hybrid operation and direct engine drive using the internal combustion engine and the electric motor, and with a NOx cleaning system comprising an SCR catalyst and an LNT catalyst in an exhaust stream of the internal combustion engine, wherein the control device comprises: a fault detection unit that detects an abnormality in the NOx purification system with respect to the LNT catalyst; and a driving condition control unit which, when the abnormality is detected, prohibits direct engine drive as the vehicle's driving mode and restricts the driving mode to series hybrid operation, and operates the internal combustion engine at an approximately constant engine power, where the engine power is equal to or greater than a predetermined value and is within a power range in which the NOx emission of the internal combustion engine does not exceed the possible NOx cleaning quantity of the NOx cleaning system using the SCR catalyst. [2] The control device of the hybrid vehicle according to claim 1, wherein the driving condition control unit, when the abnormality is detected, operates the internal combustion engine in a NOx reduction mode instead of a fuel consumption priority mode. [3] The control device of the hybrid vehicle according to claim 2, wherein in NOx reduction mode the opening of an EGR valve of the internal combustion engine is increased to a value that is greater than the opening set in fuel consumption priority mode. [4] The control device of the hybrid vehicle according to claim 1, wherein the possible NOx cleaning quantity of the SCR catalyst is calculated based on the temperature of the SCR catalyst and the ammonia storage quantity of the SCR catalyst at the time of fault detection. [5] The control device of the hybrid vehicle according to claim 1, wherein the driving condition control unit, when the abnormality is detected, operates the internal combustion engine with an approximately constant engine power, wherein the engine power either corresponds to the maximum power within the power range or is a power which is a reserve above the maximum power. [6] The control device of the hybrid vehicle according to claim 1, wherein - when the abnormality is detected - engine power of the internal combustion engine is used by the electric motor, and a drive force requested by the driver by actuating the accelerator pedal is fulfilled by the power of the electric motor. [7] The control device of the hybrid vehicle according to claim 1, wherein the abnormality is a fault condition in which it is determined that the cleaning performance of the LNT catalyst cannot be guaranteed. [8] The control device of the hybrid vehicle according to claim 7, wherein the abnormality comprises a temperature deviation of the LNT catalyst as well as an abnormal sensor value and a malfunction of a NOx sensor located upstream of the LNT catalyst. [9] A control method for a hybrid vehicle with an internal combustion engine and an electric motor as drive sources, enabling both series hybrid operation and direct engine drive using the internal combustion engine and the electric motor, and comprising a NOx cleaning system with an SCR catalyst and an LNT catalyst in an exhaust stream of the internal combustion engine, wherein the control method comprises: a first step towards detecting an abnormality in the NOx purification system with respect to the LNT catalyst; and a second step to prohibit direct engine drive as the vehicle's driving mode, to restrict the driving mode to series hybrid operation and to operate the internal combustion engine with an approximately constant engine power, wherein the engine power is equal to or greater than a predetermined value and is within a power range in which the NOx emission of the internal combustion engine does not exceed the possible NOx cleaning quantity of the NOx cleaning system using the SCR catalyst, wherein the second step is carried out when the abnormality is detected in the first step.

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