System and method for catalyst heating

Abstract

The present disclosure provides "Systems and methods for catalyst heating." Methods and systems for exhaust catalyst heating strategies are provided that use spark retard to increase heat output by an engine without combustion stability limitations. In one example, a method can include, during a cold start of an engine, applying a firing spark at a timing that produces substantially zero combustion torque while maintaining an engine speed greater than a threshold speed via an electric motor torque. Further, heat output by the engine can be controlled, such as by adjusting airflow through the engine, such as by adjusting one or more of a throttle position and the engine speed.

Description

Technical Field

[0001] This specification generally relates to systems and methods for accelerating the heating of exhaust catalysts while controlling engine idling speed. Background Technology

[0002] Vehicles include emission control devices, such as exhaust catalysts, to reduce emissions generated through combustion. However, the effectiveness of such emission control devices varies with operating temperature. Typically, the "ignition" temperature is used to indicate a temperature above which high catalyst efficiency is achieved, allowing the catalyst to effectively reduce vehicle emissions. Therefore, various control strategies can be employed to accelerate catalyst heating during engine cold starts. As an example, spark timing can be delayed to increase exhaust heat, thereby increasing catalyst temperature at a faster rate. However, as spark timing is further delayed (to obtain more heat), combustion stability (e.g., the consistency of the amount of combustion torque generated from the combustion event) decreases. This inconsistency in combustion torque leads to inconsistent engine speeds, which can result in engine vibration that may reduce customer satisfaction. Furthermore, this vibration can also reduce engine idle control and cause engine stall. Therefore, the exhaust heat generated by delaying spark timing is limited by combustion stability.

[0003] Other attempts to address combustion stability issues caused by delayed spark timing during catalyst heating include using torque from an electric motor to compensate for reduced ignition efficiency (e.g., the ability to generate torque through combustion). Kim et al. illustrate an exemplary method in US 2008 / 0066457 A1. In this method, the spark timing is delayed to within the range of 50% to 70% of maximum ignition efficiency, and the electric motor torque is used to compensate for the reduced ignition efficiency and maintain stable no-load operation of the engine.

[0004] However, the inventors have recognized the potential problems of such a system herein. As an example, providing spark timing within a 50% to 70% ignition efficiency range can produce highly variable combustion torque. Highly variable combustion torque can lead to variable engine speeds, which may result in noise, vibration, and harshness (NVH) problems that reduce customer satisfaction. Summary of the Invention

[0005] In one example, the aforementioned problem can be addressed by a method comprising: during a cold start of the engine, applying an ignition spark at an ignition timing set to produce substantially zero combustion torque to combust fuel and a portion of the air entering the engine, while simultaneously rotating the engine with an electric motor and maintaining the engine speed above a threshold speed via the electric motor torque; and adjusting the amount of air entering the engine based on desired engine exhaust heat. In this way, the engine speed can be kept substantially constant during catalyst heating, thereby reducing engine vibration and improving customer satisfaction.

[0006] As an example, the timing that produces substantially zero combustion torque corresponds to a timing region that minimizes the indicated mean effective pressure (IMEP) within the engine cylinders and has minimal variability. Utilizing minimal IMEP variability reduces inter-cycle variations in combustion torque, and consequently, reduces inter-cycle variations in engine speed. Instead of combustion torque that rotates the engine, the engine rotates at a substantially constant speed via an electric motor. Furthermore, when a desired increase in engine exhaust heat is desired, the engine airflow rate can be regulated by increasing the intake throttle opening. If additional exhaust heat (e.g., engine heat output) is required at full throttle opening, the engine speed can be increased, for example, by increasing the electric motor torque, to further increase the engine airflow rate. By first regulating the intake throttle opening to provide the desired engine exhaust heat, engine speed variations can be further reduced. In this way, the heat output by the engine can be controlled independently of combustion stability and without engine speed variations that could be negatively perceived by the customer.

[0007] In another example, a method includes: in response to a cold start condition of an engine included in a vehicle, providing a spark at an ignition timing delayed from a timing delay for maximum starting torque to ignite fuel and a portion of the air entering the engine, the delayed ignition timing being determined based on vehicle occupancy and providing simultaneously electric motor torque to the engine via an electric motor to maintain the engine speed above a threshold speed; and adjusting one or more of the position of a throttle valve connected to the engine's intake manifold and the engine speed maintained by the electric motor based on the temperature of a catalyst coupled to the exhaust manifold of the engine and the vehicle's occupancy. For example, when the vehicle is occupied, the spark may be further delayed (e.g., delayed to a region producing substantially zero combustion torque), and when the vehicle is not occupied (e.g., such as when the vehicle is autonomous), the spark may be delayed less (e.g., delayed to a region with low combustion stability), thereby reducing the amount of electric motor torque provided by the electric motor. In this way, engine speed variations can be minimized when occupants are present, thereby increasing occupant satisfaction, and energy consumption can be reduced when the vehicle is not occupied.

[0008] It should be understood that the above overview is provided to present, in a simplified form, some concepts further described in the detailed description. This is not intended to identify key or essential features of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that address any of the shortcomings mentioned above or in any part of this disclosure. Attached Figure Description

[0009] Figure 1 A schematic diagram of an exemplary vehicle system is shown.

[0010] Figure 2 An exemplary method is shown for operating in catalyst heating mode during engine cold start.

[0011] Figure 3 A graph showing the relationship between spark timing and mean indicated effective pressure is plotted.

[0012] Figure 4 The graphs show the throttle position and / or engine speed adjustments that can be performed to increase the heat output from the engine.

[0013] Figure 5 This presents a predictive exemplary timeline of engine parameter adjustments as the engine switches between entering and exiting catalyst heating modes in response to a cold start. Detailed Implementation

[0014] The following description relates to systems and methods for operating an engine in catalytic-heated mode without combustion stability limitations. As used herein, the term "combustion stability" refers to the similarity of combustion torque from one combustion event to the next. Engines may be found in vehicles, such as... Figure 1 The vehicle illustrated herein may be an autonomous vehicle in some instances. For example, the engine may be rotated via deeply delayed spark timing and torque from an electric motor to achieve, for example, according to Figure 2 An exemplary method is used to maintain a consistent engine speed for operation in catalytic-heated mode. In some instances, the spark may be delayed to a timing corresponding to a zero indicated mean effective pressure, thus preventing the generation of combustion torque. The relationship between spark timing and indicated mean effective pressure is as follows: Figure 3 As shown. Furthermore, as... Figure 4 As shown, when operating in catalytic converter heating mode, the heat output by the engine can be controlled by adjusting the airflow rate through the engine, such as by adjusting the intake throttle position and / or by adjusting the engine speed. (Reference) Figure 5 An example of the engine operating in catalyst heating mode is shown, which can differ depending on whether the vehicle is occupied or an unoccupied autonomous vehicle.

[0015] Figure 1 An example of a cylinder 14 of an internal combustion engine 10, which may be included in an engine system 100 in a vehicle 5, is depicted. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle driver 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder 14 of the engine 10 (also referred to herein as a “combustion chamber”) may include a combustion chamber wall 136, in which a piston 138 is positioned. The piston 138 may be coupled to a crankshaft 140 such that the reciprocating motion of the piston is converted into rotational motion of the crankshaft. As further described below, the crankshaft 140 may be coupled to at least one wheel 55 via a transmission 54. Furthermore, a starter motor (not shown) may be coupled to the crankshaft 140 via a flywheel to enable starting operation of the engine 10.

[0016] In some instances, vehicle 5 may be a hybrid vehicle with multiple torque sources available for one or more wheels 55. In other instances, vehicle 5 may be a conventional vehicle with only an engine or an electric vehicle with only an electric motor. Figure 1 In the illustrated example, vehicle 5 includes engine 10 and electric motor 52. Electric motor 52 may be a motor or a motor / generator. For example, electric motor 52 may be a 48 V (or higher) system with an operating power of at least 10 kW. When one or more clutches 56 are engaged, the crankshaft 140 of engine 10 and electric motor 52 are connected to wheels 55 via transmission 54. In the depicted example, a first clutch is disposed between crankshaft 140 and electric motor 52, and a second clutch is disposed between electric motor 52 and transmission 54. Controller 12 may send signals to the actuator of each clutch 56 to engage or disengage the clutch, thereby connecting or disconnecting crankshaft 140 from electric motor 52 and its connected components, and / or connecting or disconnecting electric motor 52 from transmission 54 and its connected components. Transmission 54 may be a gearbox, a planetary gear system, or another type of transmission.

[0017] The powertrain can be configured in various ways, including in parallel, series, or series-parallel hybrid vehicles. In an electric vehicle embodiment, the system battery 58 may be a traction battery that delivers power to the motor 52 to provide torque to the wheels 55. In some embodiments, the motor 52 may also operate as a generator to provide power, for example, during braking operations, to charge the system battery 58. It should be understood that in other embodiments, including non-electric vehicle embodiments, the system battery 58 may be a typical starter, lighting, ignition (SLI) battery coupled to the alternator 46.

[0018] Alternator 46 can be configured to charge system battery 58 using engine torque via crankshaft 140 during engine operation. Furthermore, alternator 46 can power one or more electrical systems corresponding to the engine's electrical needs, such as one or more auxiliary systems, including heating, ventilation, and air conditioning (HVAC) systems, lighting, in-vehicle entertainment systems, and other auxiliary systems. In one example, the current drawn from the alternator can vary continuously based on each of the following: cabin cooling needs, battery charging requirements, other auxiliary vehicle system needs, and motor torque. A voltage regulator can be coupled to alternator 46 to regulate the alternator's power output based on system usage requirements, including auxiliary system needs.

[0019] In the case of an autonomous vehicle (AV), driver 130 may be replaced before or during a designated journey by an autonomous vehicle controller, namely AV controller 191, included in the control system and communicating with controller 12. AV controller 191 may provide controller 12 with outputs indicating and / or requesting instructions from vehicle 5. Controller 12 may then actuate various vehicle actuators to propel the vehicle in response to requests from AV controller 191. In the case of an AV, vehicle 5 may include various devices for detecting the vehicle's surroundings, such as radar, laser, GPS, rangefinders, and computer vision sensors. An advanced control system, as part of AV controller 191, may interpret the sensor information to identify appropriate navigation paths and obstacles and relevant signs (e.g., speed limits, traffic signals, etc.). AV controller 191 may also include executable instructions capable of analyzing sensor data to distinguish different vehicles on the road, which can help plan a path to a desired destination; and executable instructions for combining with sensor feedback to park the vehicle in a designated or detected available parking space. For example, the AV controller 191 may include executable instructions for detecting road type (e.g., one-way street, highway, lane-separated highway, etc.) or available parking spaces (e.g., vacant space with sufficient clearance for vehicles not prohibited based on time of day or loading area). Thus, in some instances, vehicle 5 can be controlled using input from vehicle driver 130, and in other instances, such as when vehicle driver 130 is not present, vehicle 5 can be controlled using executable instructions included in the AV controller 191 without input from vehicle driver 130. Furthermore, the AV may include an occupancy sensor 193 to determine the presence of passengers. The occupancy sensor 193 may include one or more of the following sensors: a camera, an infrared sensor, a microphone, a door half-open sensor, a seat pressure sensor, a seatbelt sensor, or any other sensor that can be used to determine whether the vehicle is occupied by one or more occupants (e.g., passengers) and can communicate with controller 12 and / or AV controller 191. For example, based on the output received by controller 12 via occupancy sensor 193, controller 12 may determine whether at least one passenger is present in vehicle 5. Based on the determination that there is at least one passenger in vehicle 5, AV controller 191 and / or controller 12 can change the operation of engine 10. For example, as per [the relevant regulations / regulations]... Figure 2 As further described, the spark timing adjustment performed during engine cold start may differ for the occupied AV and the unoccupied AV.

[0020] Furthermore, in some instances, the controller 12 can communicate with a remote engine start receiver 195 (or transceiver) that receives a wireless signal 107 from a key fob 104 having a remote start button 105. In other instances (not shown), remote engine start can be initiated via a cellular phone or a smartphone-based system, where the user's phone sends data to a server and the server communicates with the vehicle to start the engine. Therefore, even when the vehicle 5 is not an AV, it can be started when no occupants, including the driver 130, are present in the vehicle.

[0021] Cylinder 14 of engine 10 receives intake air via intake passage 142 and intake manifold 146. In addition to cylinder 14, intake manifold 146 may also communicate with other cylinders of engine 10. In some instances, when the engine system is a turbocharged engine system, intake passage 142 may include one or more supercharging devices, such as turbochargers or superchargers, coupled therein. Throttle valve 162, including throttle plate 164, may be disposed in the intake passage to change the flow rate and / or pressure of the intake air supplied to the engine cylinders. The position of throttle valve 162 may be determined using a throttle position sensor, which outputs a signal TP to controller 12 proportional to the position of throttle valve 162. As further described herein, during catalyst heating operating mode, the heat output by engine 10 may be controlled, for example, by adjusting the throttle position, by regulating the airflow rate through the engine. Exhaust manifold 148 receives exhaust from cylinder 14 and other cylinders of engine 10.

[0022] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one intake lift valve and at least one exhaust lift valve located in the upper region of cylinder 14. In some instances, each cylinder of engine 10 (including cylinder 14) may include at least two intake lift valves and at least two exhaust lift valves located in the upper region of the cylinder. Intake valve 150 may be controlled by controller 12 via actuator 152. Similarly, exhaust valve 156 may be controlled by controller 12 via actuator 154. The positions of intake valve 150 and exhaust valve 156 may be determined by corresponding valve position sensors (not shown).

[0023] During certain conditions, controller 12 can modify the signals provided to actuators 152 and 154 to control the opening and closing of the corresponding intake and exhaust valves. The valve actuators can be electrically actuated, cam-actuated, or a combination thereof. Intake and exhaust valve timing can be controlled simultaneously, or any of the following possibilities can be used: variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, or fixed cam timing. Each cam-actuated system may include one or more cams and may utilize one or more of a cam profile transformation (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or a variable valve lift (VVL) system operable by controller 12 to change valve operation. For example, cylinder 14 may optionally include an intake valve controlled by electrically actuated valves and an exhaust valve controlled by cam actuation including CPS and / or VCT. In other instances, the intake and exhaust valves may be controlled by a common valve actuator (or actuation system) or a variable valve timing actuator (or actuation system).

[0024] Cylinder 14 may have a compression ratio, which is the ratio of the volume when piston 138 is at bottom dead center (BDC) to that at top dead center (TDC). In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some instances using different fuels, the compression ratio may be increased. This may occur, for example, when using higher octane fuels or fuels with higher latent enthalpy of vaporization. If direct injection is used due to its effect on engine knock, the compression ratio may also be increased.

[0025] Each cylinder of engine 10 may include a spark plug 192 for initiating combustion. In a selected operating mode, ignition system 190 may provide an ignition spark to the combustion chamber via spark plug 192 in response to a spark advance signal SA from controller 12. The timing of signal SA may be adjusted based on engine operating conditions and driver torque demand. For example, a spark may be provided at the maximum braking torque (MBT) timing to maximize engine power and efficiency. Controller 12 may input engine operating conditions (including engine speed, engine load, and exhaust AFR) into a lookup table and output the corresponding MBT timing for the input engine operating conditions. In other instances, the spark may be delayed from the MBT, such as to accelerate catalyst preheating during engine start-up or reduce engine knocking. As further described herein, during catalyst heating operating mode, the spark may be delayed until the resulting combustion torque is at or near zero while the engine is rotated via motor 52.

[0026] In some instances, each cylinder of engine 10 may be configured with one or more fuel injectors to supply fuel thereto. As a non-limiting example, cylinder 14 is shown including a fuel injector 166. Fuel injector 166 may be configured to deliver fuel received from fuel system 8. Fuel system 8 may include one or more fuel tanks, fuel pumps, and fuel rails. Fuel injector 166 is shown directly coupled to cylinder 14 for injecting fuel directly therein in proportion to the pulse width of the signal FPW received from controller 12 via electronic actuator 168. In this way, fuel injector 166 provides so-called direct fuel injection (hereinafter also referred to as "DI") into cylinder 14. Although Figure 1 A fuel injector 166 is shown positioned on one side of cylinder 14, but the fuel injector 166 may optionally be located on top of the piston, such as near spark plug 192. This location can increase mixing and combustion when the engine is operated with alcohol-based fuels due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located on top of and near the intake valve to further enhance mixing. Fuel can be delivered from the fuel tank of fuel system 8 to the fuel injector 166 via a high-pressure fuel pump and fuel rail. Furthermore, the fuel tank may have a pressure sensor that provides a signal to controller 12.

[0027] In an alternative embodiment, the fuel injector 166 may be arranged in the intake manifold rather than directly coupled to the cylinder 14, a configuration that provides so-called port fuel injection (hereinafter also referred to as "PFI") into the intake manifold upstream of the cylinder 14. In other embodiments, the cylinder 14 may include multiple injectors, which may be configured as direct fuel injectors, port fuel injectors, or combinations thereof. Therefore, it should be understood that the fuel system described herein should not be limited to the specific fuel injector configurations described herein by example.

[0028] Fuel injector 166 can be configured to receive different fuels as fuel mixtures from fuel system 8 in different relative amounts, and is further configured to inject said fuel mixture directly into the cylinder. Furthermore, fuel can be delivered to cylinder 14 during different strokes of a single cycle of the cylinder. For example, directly injected fuel can be delivered at least partially during a previous exhaust stroke, during an intake stroke, and / or during a compression stroke. Thus, for a single combustion event, one or more fuel injections can be performed per cycle. Multiple injections can be performed during the compression stroke, intake stroke, or any suitable combination thereof, a process known as staged fuel injection.

[0029] The fuel tank in fuel system 8 can store fuels of different types, such as fuels with different fuel qualities and different fuel compositions. These differences may include different alcohol contents, different water contents, different octane numbers, different heats of vaporization, different fuel blends, and / or combinations thereof. An example of fuels with different heats of vaporization includes gasoline as a primary fuel type with a lower heat of vaporization and ethanol as a secondary fuel type with a higher heat of vaporization. In another example, the engine can use gasoline as the primary fuel type and an alcohol-containing fuel blend such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline) as the secondary fuel type. Other feasible substances include water, methanol, mixtures of alcohol and water, mixtures of water and methanol, mixtures of alcohols, etc. In another example, the two fuels can be blends of alcohols with different alcohol compositions. The first fuel type can be a gasoline-ethanol blend with a lower alcohol concentration, such as E10 (which contains approximately 10% ethanol), while the second fuel type can be a gasoline-ethanol blend with a higher alcohol concentration, such as E85 (which contains approximately 85% ethanol). Furthermore, the first and second fuels can also differ in other fuel qualities, such as temperature, viscosity, octane number, etc. In addition, the fuel characteristics of one or both fuel tanks may change frequently, for example, due to daily variations in fuel tank refills.

[0030] Exhaust sensor 126 is shown connected to exhaust manifold 148 upstream of emission control device 178, within exhaust duct 158. For example, exhaust sensor 126 can be selected from a variety of suitable sensors to provide an indication of exhaust air-fuel ratio (AFR), such as linear oxygen sensors or UEGO (universal or wide-range exhaust oxygen sensor), dual-state oxygen sensors or EGO, HEGO (heated EGO), NOx, HC, or CO sensors. Figure 1 In this example, exhaust sensor 126 is a UEGO sensor configured to provide an output, such as a voltage signal, proportional to the amount of oxygen present in the exhaust. The output current of UEGO sensor 126 can be used to regulate engine operation. For example, the amount of fuel delivered to cylinder 14 can be changed using feedforward (e.g., based on desired engine torque, engine airflow, etc.) and / or feedback (e.g., using oxygen sensor output) methods to achieve a desired air-fuel ratio (AFR), such as stoichiometry. Emission control device 178 can be a three-way catalytic converter, a NOx trap, various other emission control devices, or combinations thereof. Figure 1 In this example, emission control device 178 is a three-way catalyst (also referred to herein as a “catalyst”), which is configured to reduce NOx and oxidize CO and unburned hydrocarbons in the exhaust from engine 10.

[0031] Controller 12 in Figure 1 The microcomputer shown in the image includes a microprocessor unit 106, an input / output port 108, an electronic storage medium for executable programs (e.g., executable instructions) and calibration values, shown in this particular instance as a non-transitory read-only memory chip 110, a random access memory 112, a keep-alive memory 114, and a data bus. The controller 12 can receive various signals from sensors connected to the engine 10, including the signals previously discussed and additionally including measurements of the following: intake mass airflow (MAF) from the mass airflow (MAF) sensor 122; engine coolant temperature (ECT) from the engine coolant temperature sensor 116 connected to the cooling sleeve 118; ambient temperature from the temperature sensor 123 connected to the intake manifold 142; exhaust temperature from the temperature sensor 128 connected to the exhaust manifold 158; surface ignition sensing signal (PIP) from the Hall effect sensor 120 (or other type) connected to the crankshaft 140; throttle position (TP) from the throttle position sensor; the UEGO signal from the exhaust sensor 126, which can be used by the controller 12 to determine the exhaust airflow rate (AFR); and the manifold absolute pressure signal (MAP) from the MAP sensor 124. The engine speed signal RPM can be generated by the controller 12 based on the PIP signal. The manifold pressure signal MAP from the MAP sensor 124 can be used to provide an indication of vacuum or pressure in the intake manifold. The controller 12 can infer the engine temperature based on the engine coolant temperature. Additional sensors, such as various temperature sensors, pressure sensors, and humidity sensors, can be connected throughout the vehicle 5.

[0032] Controller 12 receives from Figure 1 Signals from various sensors and employing Figure 1 Various actuators adjust engine operation based on received signals and instructions stored in the controller's memory. For example, as per [reference to...] Figure 2 As described, controller 12 can determine a cold start condition based on the signal ECT from engine coolant temperature sensor 116, and in response to said condition, operate in catalytic converter heating mode. When operating in catalytic converter heating mode, controller 12 can adjust the timing of signal SA sent to ignition system 190, thereby adjusting the timing of the spark provided by spark plug 192. Furthermore, controller 12 can actuate motor 52 and a first clutch to connect motor 52 to crankshaft 140 to electrically rotate engine 10.

[0033] As mentioned above, Figure 1The diagram shows only one cylinder of a multi-cylinder engine. Therefore, each cylinder may similarly include its own set of intake / exhaust valves, fuel injectors, spark plugs, etc. It should be understood that engine 10 may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Furthermore, each of these cylinders may include a reference cylinder 14 via... Figure 1 Some or all of the various components described and depicted.

[0034] Next, Figure 2 The diagram illustrates an engine system for operating a vehicle in catalytic converter heating mode (e.g., including...). Figure 1 A flowchart of an exemplary method 200 for an engine system 100 in vehicle 5. For example, a catalyst heating mode can be used in a starter motor or electric motor with an operating power of at least 8 kW (e.g., Figure 1 In vehicles with motor 52, so as to carry catalyst (e.g., Figure 1 The emission control device 178) rapidly raises the catalyst temperature above its ignition temperature. A starter motor or electric motor of at least 8 kW is capable of rotating the engine at a high speed (e.g., at least 1000 RPM) for an extended duration (e.g., at least 10 seconds) without combustion torque. Therefore, as described below, energy from combustion can be used to generate heat to raise the catalyst temperature, rather than generating engine torque to rotate the engine. By rapidly raising the catalyst temperature above its ignition temperature, cold-start emissions are reduced. Furthermore, by electrically rotating the engine, the heat generated by ignition delay is not limited by combustion stability. Additionally, different adjustments can be performed during catalyst heating mode depending on whether the vehicle is occupied, such as when the vehicle is an autonomous vehicle (AV) or a non-AV that has been remotely started. The instructions for performing method 200 and the remainder of the method included herein can be controlled by a controller (e.g., Figure 1 The controller 12) executes based on instructions stored in the controller's memory and in conjunction with signals received from sensors in the engine system, as described above. Figure 1 The described sensor (e.g., Figure 1 The engine coolant temperature sensor 116, exhaust temperature sensor 128, and occupancy sensor 193 are included. The controller may employ an engine actuator from the engine system (e.g., Figure 1 The motor 52, spark plug 192 and throttle body 162) are used to adjust engine operation according to the following method.

[0035] Method 200 begins at 202 and includes estimating and / or measuring operating conditions. For example, operating conditions may include engine speed, engine load, throttle position (e.g., from a signal TP output from a throttle position sensor), accelerator pedal position (e.g., from a signal PP output from a pedal position sensor), engine temperature, catalyst temperature (e.g., as shown in the image from...). Figure 1 The exhaust temperature sensor 128 estimates the temperature of the exhaust gas and the ambient temperature (e.g., as measured by an ambient temperature sensor, such as...). Figure 1 Temperature sensor 123). For example, engine speed can be based on a Hall effect sensor (e.g., Figure 1 The signal PIP output by the Hall effect sensor 120 can be used to determine this. It can also be based on the signal from the MAF sensor (e.g., Figure 1 The MAF (MAF) of the MAF sensor 122 is used to determine the engine load. The operating condition may also include the engine state and the vehicle's ignition state. The engine state may refer to whether the engine is on (e.g., operating at a non-zero speed, where combustion occurs in the engine cylinders) or off (e.g., stationary, where no combustion occurs in the engine cylinders). The vehicle's ignition state may refer to the position of the ignition switch. As an example, the ignition switch may be in the "off" position, indicating that the vehicle is off (e.g., power is off, where the vehicle speed is zero). As another example, the ignition switch may be in the off position but in which (e.g., by the vehicle driver) the ignition key is inserted, indicating that the vehicle can be started soon. As yet another example, the vehicle may be on and operating in a purely electric mode, where the electric motor (e.g., ... Figure 1 The motor 52 provides torque to propel the vehicle, and the engine is off and no torque is supplied to propel the vehicle. Operating conditions may also include indications of whether the vehicle is operated by an AV or a driver, such as based on whether controller 12 receives information from the vehicle driver (e.g., Figure 1 The driver (130) or receives from the AV controller (e.g., Figure 1 The input to the AV controller 191. Such as when the vehicle is remotely started (e.g., via a remote starter, such as...). Figure 1 As shown in the key fob 104, or when the vehicle is an AV, the operating condition may also include an indication of whether the vehicle is occupied or not. For example, the controller may use one or more vehicle occupancy sensors (e.g., Figure 1 The vehicle occupancy sensor 193 is used to determine vehicle occupancy. When vehicle occupancy is greater than zero (e.g., there is at least one driver or passenger), the vehicle is considered occupied, and when vehicle occupancy is equal to zero (e.g., there is no driver or passenger present), the vehicle is considered unoccupied.

[0036] At point 204, it is determined whether an engine cold start condition exists. A cold start condition can be confirmed when the engine has been inactive for an extended period and / or when the engine temperature is below a first threshold temperature (e.g., by the vehicle driver or by the AV controller) and a request to start the engine is made. For example, a cold start condition can be confirmed when the engine has been inactive for more than a first threshold duration, which may correspond to a non-zero time quantity (e.g., day, week, or month). The first threshold temperature may correspond to a temperature below the nominal engine operating temperature. As another example, a cold start condition can be confirmed when the engine temperature is substantially equal to the ambient temperature (e.g., within a threshold of the ambient temperature, such as within 10 degrees Celsius) when an engine start request is made. As yet another example, the first threshold temperature may correspond to the ignition temperature of the catalyst, and a cold start condition can be confirmed when the catalyst is below its ignition temperature. As an example, the catalyst temperature may be an inferred catalyst temperature modeled based on exhaust heat calculations that take into account fuel flow and spark delay.

[0037] If there is no cold start condition, then method 200 proceeds to 206 and includes maintaining the engine operating state. For example, if the engine is off (e.g., stationary, with no combustion occurring in the engine cylinders), then the engine will remain off. If the engine is on and operating (e.g., operating at a non-zero speed, where combustion occurs in the engine cylinders), then the engine will remain on to provide torque in response to the needs of the driver or AV controller. After 206, method 200 ends.

[0038] If a cold start condition exists, then method 200 proceeds to 208 and includes operating in catalytic-heated mode by rotating the engine via electric motor torque while simultaneously reducing combustion torque via spark delay. For example, the engine can be (e.g., using a starter motor or electric motor) rotated from a stationary crankshaft to a speed exceeding a threshold speed, while simultaneously providing fuel and spark to initiate combustion. The threshold speed may correspond to a non-zero speed, such as 1000 RPM. (See reference...) Figure 3Further described, operation in catalytic-heated mode includes determining spark timing based on vehicle occupancy. For example, when the vehicle has at least one occupant (e.g., the vehicle driver and / or passenger), spark timing may be further delayed, such as to a region producing zero indicated mean effective pressure (IMEP), said region having minimal variability from engine cycle to engine cycle. As another example, when the vehicle does not have at least one occupant (e.g., when the vehicle is an AV or remotely started without passengers), spark timing may be delayed less, such as to a region producing a non-zero IMEP with high variability from engine cycle to engine cycle. A spark may then be provided at the determined spark timing to reduce combustion torque. The amount of fuel provided may be determined based on engine load and desired air-fuel ratio (AFR) to minimize vehicle emissions, for example, by inputting engine load and desired AFR into a lookup table or function via a controller and outputting the fuel amount.

[0039] As an alternative example, when an engine cold start occurs during extreme environmental conditions, such as when the ambient temperature is below a lower threshold temperature (e.g., -40 °C), starting the engine may take priority over NVH or emissions; therefore, combustion torque can be used to start a cold (high-friction) engine regardless of vehicle occupancy. In this example, a spark can be provided near the MBT timing to operate the spark timing without reducing combustion torque.

[0040] Temporary turn Figure 3 Figure 300 shows the relationship between IMEP and spark timing. The horizontal axis represents spark timing in crank angles after top dead center (ATDC) of the power stroke. Therefore, zero crank angles at ATDC refer to spark timing at TDC of the power stroke, and negative values ​​refer to spark timing occurring before top dead center (BTDC) of the power stroke. The vertical axis represents IMEP, which can also represent the indicated torque. Note that at zero IMEP, the mean effective pressure at startup (BMEP) may be negative due to the mean effective friction pressure (FMEP). In figure 300, curve 302 represents the average IMEP, curve 304 represents two standard deviations (σ) above the average IMEP (e.g., +2σ), and curve 306 represents two standard deviations below the average IMEP (e.g., -2σ).

[0041] The spark timing at which the average IMEP (curve 302) is highest can be called the MBT timing. At and around the MBT timing, IMEP variability is minimal; +2σ IMEP (curve 304) and -2σ IMEP (curve 306) are close to the average IMEP (curve 302). As the spark timing is further delayed from the MBT timing, IMEP variability (e.g., the distance between +2σ IMEP and -2σ IMEP) increases until it reaches peak IMEP variability. If a spark is provided at the peak IMEP variability, the amount of torque produced from the combustion event to the combustion event can vary widely. For example, if a spark is provided at 15 degrees of the power stroke ATDC, the piston has already begun to travel downwards, resulting in an increase in the combustion chamber volume (e.g., from the minimum at TDC). Therefore, the pressure within the cylinder decreases during combustion. Furthermore, the piston travels a shorter distance before reaching BDC, resulting in a lower leverage ratio. Additionally, the air-fuel mixture can diffuse throughout the larger combustion chamber volume. Therefore, the workload generated in the power stroke is reduced and varies greatly, and instead of generating torque in the power stroke, a larger amount of energy from the combustion event can be released as heat in the exhaust stroke.

[0042] As spark timing is further delayed from the peak IMEP variability, +2σ IMEP (curve 304) and -2σ IMEP (curve 306) approach the average IMEP (curve 302), both of which are close to zero (e.g., approximately 60-90 degrees of crank angle in the power stroke ATDC). For example, with the spark depth delayed to 90 degrees of ATDC, most of the piston travel has already occurred in the BDC by the time combustion occurs, so even if combustion pressure changes occur, their contribution to the work in the power stroke is very small, and the average IMEP (and indicated torque) is repeatably zero. Therefore, when the vehicle is occupied, a spark can be provided at the timing within the diagonally shaded area 308 to minimize inter-cycle variation, thereby reducing engine vibration and increasing vehicle customer satisfaction.

[0043] However, unless electric assistance is provided, the engine does not rotate when operating at zero IMEP (e.g., negative BMEP). For example, when operating at or near zero IMEP, sufficient torque is provided from the electric motor to overcome the engine's mechanical friction torque (e.g., FMEP) and maintain the engine at a non-zero, consistent speed. As an example, the amount of electrical power supplied to the motor can be kept substantially constant (e.g., 3 kW) to provide substantially constant electric motor torque to maintain a constant engine speed after initially supplying a higher amount of electric motor torque to accelerate the engine from a standstill. Thus, energy from combustion is used to increase exhaust temperature rather than generate the torque needed to rotate the engine, which instead utilizes the electric motor torque to rotate.

[0044] Furthermore, in an unoccupied vehicle, where engine speed variability will not disturb passengers, energy can be saved by using less electric assistance. For example, a larger proportion of the total engine torque (e.g., the sum of combustion torque and electric motor torque) can be provided by combustion torque compared to when the vehicle is occupied and the combustion torque produced in catalytic converter mode is essentially zero (e.g., a percentage of the amount of torque required to operate the engine without electric motor torque, such as a percentage in the range of 5-10%). Therefore, when the vehicle is an unoccupied AV, a spark can be provided at the timing within the vertical shaded area 310, which has a higher IMEP variability than the diagonal shaded area 308.

[0045] return Figure 2 As shown at 212, operation in catalytic-heated mode also includes adjusting the electric motor torque based on combustion torque to maintain a consistent engine speed. For example, the controller can monitor combustion torque and counteract it by reducing the electric motor torque. Combustion torque can be inferred from crankshaft acceleration during the power stroke, for example. As another example, combustion torque can be calculated by multiplying the measured combustion pressure by the crankshaft leverage ratio, which is a function of the crankshaft angle. Integrating the combustion torque at one angle produces a workload. This workload can be subtracted from the average electrical power supplied to the motor to reduce the electric motor torque. As an example, although... Figure 3 The zero IMEP region, as shown, provides sparking with minimal inter-cycle variations for occupied vehicles (e.g., -2σ IMEP and +2σ IMEP close to the average IMEP). However, by adjusting the electric motor torque, any unintentional inter-cycle variations in fuel torque will not be perceived by vehicle occupants (e.g., the driver and / or any passengers), further enhancing customer satisfaction. As another example, in an unoccupied vehicle where engine speed variations will not be perceived, the engine speed can be maintained within a threshold engine speed range (e.g., within a threshold of the desired engine speed, such as within 50 RPM) to prevent engine stall. As yet another example, when the vehicle is occupied, the threshold engine speed range can be even smaller (e.g., within 5 RPM).

[0046] As shown at 214, operation in catalytic-heated mode also includes determining the desired engine thermal output. The desired engine thermal output (e.g., heat flux) can be determined based on the catalyst temperature at engine start and the desired catalyst temperature (e.g., the catalyst ignition temperature). The desired engine thermal output can be proportional to the difference between the catalyst temperature at engine start and the desired catalyst temperature. For example, at a lower catalyst temperature, the desired engine thermal output can be higher, and at a higher catalyst temperature, the desired engine thermal output can be lower. As an example, if the catalyst ignition temperature is 400°C and the current catalyst temperature is 20°C, then catalytic heating can be maximized, where the desired exhaust heat is 20 kW to 50 kW.

[0047] As shown at 216, operation in catalyst heating mode also includes adjusting the throttle valve based on desired engine thermal output and vehicle occupancy (e.g., Figure 1 The position of the throttle body (162) and / or engine speed (via an electric motor) are adjusted. By regulating the throttle position and / or engine speed, the airflow rate through the engine is regulated, which in turn affects the exhaust mass flow rate (and exhaust heat). A higher exhaust mass flow rate (and a higher fuel flow rate to maintain the desired AFR) provides more heat to the catalyst, while a lower exhaust mass flow rate provides less heat to the catalyst. The controller determines the combination of throttle position and engine speed regulation, which will use one or more lookup tables, algorithms, or mappings to produce the desired engine heat output, which may differ for occupied and unoccupied AVs.

[0048] Temporary turn Figure 4 A graph 400 illustrates an exemplary relationship between throttle position and engine speed regulation for occupied vehicles (solid curve 402) and unoccupied vehicles (dashed curve 404). The horizontal axis represents engine speed, which increases from left to right along the horizontal axis. The vertical axis represents throttle position, where the throttle opening increases from fully closed to fully open (e.g., fully open throttle) along the vertical axis. The desired increase in engine heat output is indicated by the direction of the arrows on curves 402 and 404.

[0049] As curve 402 illustrates, as the desired engine heat output in the occupied vehicle increases, the throttle can be further opened while maintaining a constant engine speed, until the throttle is nearly fully open. If the desired engine heat output is not achieved, the engine speed can be increased, for example, by increasing the amount of electrical power supplied to the electric motor to provide additional electric motor torque. In this example, by first adjusting the throttle position and then adjusting the engine speed as needed based on the desired engine heat output, the engine can maintain a substantially constant speed even when engine heat output changes, which increases vehicle customer satisfaction.

[0050] As shown in curve 404, when the desired heat output increases in an unoccupied vehicle, at lower engine speeds, the engine speed can increase more significantly and the throttle opening less, while at higher engine speeds, the throttle opening can increase more significantly and the engine speed increases less. If the vehicle occupants do not perceive a change in engine speed, an initial increase in engine speed can be implemented to increase engine heat output rather than an increase in throttle opening, because more combustion events occur at higher engine speeds compared to lower engine speeds over a fixed duration, which may increase the heat generated.

[0051] It should be noted that in other instances, the shapes of curves 402 and 404 may differ. For example, each of curves 402 and 404 may be any linear or non-linear curve, where the throttle position and / or engine speed typically increase with an increase in desired engine thermal output. Therefore, Figure 4 Curves 402 and 404 shown are illustrative rather than restrictive.

[0052] return Figure 2 In some instances, operating at 208 in catalytic-heated mode may further include deactivating a subset of engine cylinders, such as by keeping the corresponding intake and exhaust valves of the subset of engine cylinders closed and disabling fueling and sparking to said subset. By deactivating a subset of engine cylinders, cylinder heating can be concentrated on the remaining active cylinders.

[0053] At 218, it is determined whether the conditions for exiting the catalytic converter heating mode are met. As an example, the conditions for exiting the catalytic converter heating mode may be met in response to the catalyst temperature exceeding a second threshold temperature. For example, the second threshold temperature may be the ignition temperature of the catalyst (e.g., 400°C), above which the catalyst efficiently purifies exhaust components. The second threshold temperature may be the same as or different from the first threshold temperature used to confirm a cold start condition (e.g., as described at 204). As another example, the conditions for exiting the catalytic converter heating mode may include the passage of a second threshold duration (which is less than the first threshold duration used to confirm the cold start condition described at 204). The second threshold duration may be a predetermined fixed duration, such as a duration in the range of 10-15 seconds, during which the engine operates in catalytic converter heating mode during engine cold starts. Optionally, the second threshold duration may be adjusted based on operating conditions, such as one or more of the ambient temperature, engine temperature, and catalyst temperature when an engine cold start is requested. For example, the controller can input operating conditions (e.g., ambient temperature, engine temperature, and / or catalyst temperature) into one or more lookup tables, algorithms, and mappings, and output the corresponding duration for operation in catalyst heating mode.

[0054] If the conditions for exiting the catalytic converter heating mode are not met, then method 200 returns to 208 and includes continuing to operate in catalytic converter heating mode, where the engine is electrically rotated while the combustion torque is reduced via spark delay. If the conditions for exiting the catalytic converter heating mode are met, then method 200 proceeds to 220 and includes switching to a nominal engine operating mode. Switching to a nominal engine operating mode includes adjusting the spark timing to increase the combustion torque of one cylinder at a time, as shown at 222; adjusting the electric motor torque based on the combustion torque to maintain a consistent engine speed until the electric motor torque is reduced to zero, as shown at 224; and adjusting the throttle position and / or engine speed based on torque demand, as shown at 226. For example, the controller may adjust (e.g., advance) the spark timing of the first cylinder from a determined spark timing for the reduced combustion torque (e.g., as determined at 210) to a timing corresponding to the desired engine torque for a given engine speed and load, such as adjusting to a timing at or near the MBT. For example, the controller can determine the spark timing for the increased combustion torque by inputting engine speed and load into a lookup table. Providing a spark at the determined spark timing for the increased combustion torque in the first cylinder increases the amount of combustion torque generated in the first cylinder, while maintaining the reduced (or substantially zero) combustion torque generated in the remaining cylinders, thereby increasing the total amount of combustion torque generated in the engine. As described at 212, as a result of the increased combustion torque, the electric motor torque decreases by a corresponding amount. The controller can then adjust the spark timing of the next (e.g., the second) cylinder to the determined spark timing to increase the combustion torque and correspondingly reduce the electric motor torque. Furthermore, the controller can know the combustion torque generated by the first cylinder and use said value to more precisely reduce the electric motor torque during spark timing adjustments in each subsequent cylinder to avoid engine speed disturbances. The controller can continue to adjust the spark timing of each subsequent cylinder one at a time (e.g., one cylinder per engine cycle or one cylinder per multiple engine cycles) until all cylinders utilize spark operation provided at a defined spark timing for increasing combustion torque and reduce the electric motor torque to zero. Furthermore, the throttle position and / or engine speed can be adjusted based on torque demands such as those required by the vehicle driver or AV controller. For example, as combustion torque increases, the throttle can be adjusted to a further closed position to prevent fluctuations in torque output. By gradually transitioning the engine from producing essentially no combustion torque (or a small amount of combustion torque compared to the desired torque amount when the engine is operated at the desired speed) to providing all engine torque through combustion, engine speed variations can be reduced, thereby improving customer satisfaction and / or reducing the incidence of engine stall. Method 200 then ends.

[0055] Therefore, as illustrated by the examples herein, a method of operating and performing actions in response to determining an engine cold start condition may include operating under a cold start condition (e.g., operating with the engine burning and rotating at a non-zero speed), determining the presence of said condition (such as based on the output of an engine coolant temperature sensor), and performing actions in response to said determination, as well as operating in the absence of said condition, determining the absence of said condition, and performing different actions in response to said determination. For example, in response to the determination of an engine cold start condition, the controller may switch the engine to operation in a catalytic converter heating mode by delaying the timing of the ignition spark provided by the spark plugs, providing electric motor torque to maintain the engine speed above a threshold speed, and regulating the heat output of the engine by adjusting one or more of the intake throttle position and engine speed. In response to the determination that an engine cold start condition is absent, the engine may operate in a nominal operating mode. When operating in the nominal operating mode, the controller may adjust the ignition spark timing, engine speed, and intake throttle position in response to torque demand. Furthermore, when operating in catalytic-heated mode, in response to determining that a cold start condition no longer exists (e.g., based on the temperature of the exhaust catalyst or the duration of operation in catalytic-heated mode in the past), the controller can switch the engine from catalytic-heated mode to nominal operating mode. Switching from catalytic-heated mode to nominal operating mode may involve advancing the ignition timing cylinder by cylinder until no engine cylinder operates at the delayed timing and no electric motor torque is provided to maintain the engine speed above a threshold speed.

[0056] Next, Figure 5 The following diagram illustrates a method for heating a vehicle catalyst during engine cold start (e.g., without combustion stability limitations). Figure 1 An exemplary timeline 500 of the emission control device 178). For example, such as according to Figure 2Method 200 allows the engine to operate in catalytic converter heating mode. Furthermore, operation in catalytic converter heating mode may differ when the vehicle is not occupied, compared to when the vehicle is occupied. As will be further described below, dashed segments are provided for comparison between operation in catalytic converter heating mode when the vehicle is occupied (solid lines) and when it is not occupied (dashed segments). Curve 502 shows engine speed, curve 504 shows combustion torque, curve 506 shows electric motor torque, curve 508 shows catalyst temperature, curve 510 shows throttle position, curve 512 shows spark delay, and curve 513 shows fuel flow. For all the above graphs, the horizontal axis represents time, which increases from left to right along the horizontal axis. The vertical axis represents the parameter for each marker, where the value increases from bottom to top along the vertical axis. Dashed line 514 indicates the ignition temperature of the catalyst, above which the catalyst is able to efficiently purify exhaust components. Additionally, MBT spark timing is indicated by dashed line 516. Although in Figure 5 The dashed line 516 is shown as a straight line, but it should be understood that the MBT spark timing varies based on operating conditions such as engine speed and load. Furthermore, curve 512 represents the average spark delay across all cylinders of the engine, including... Figure 5 The example has four cylinders. Unless otherwise stated below (e.g., during the transition out of the catalytic heating mode), all cylinders operate at the same spark timing, in which case the average spark timing is also equal to the spark timing of each cylinder.

[0057] Before time t1, the engine is off (e.g., the speed is zero, as shown in curve 502). No combustion occurs in the engine cylinders, and therefore the combustion torque is zero (curve 504). Furthermore, as shown in curve 506, the engine is not electrically rotating, meaning there is no electric motor torque passing through the motor (e.g., Figure 1 The electric motor 52) is applied to the engine. The throttle is closed (curve 510), and no spark (curve 512) or fuel is supplied (curve 513).

[0058] At time t1, an engine start is requested. The requested engine start is a cold start, where the catalyst temperature (curve 508) is below the ignition temperature (dashed line 514). Therefore, the engine operates in catalyst heating mode. Between time t1 and time t2, the engine speed (curve 502) increases as the engine cranks (curve 506) using torque from the electric motor (curve 506). A higher amount of electric motor torque is initially provided between time t1 and time t2 to accelerate the engine from a standstill. A spark is provided at a highly delayed timing from the MBT timing (curve 512) to ignite the air-fuel mixture in each cylinder at a highly delayed timing, resulting in essentially zero combustion torque (curve 504). When the vehicle is not occupied, a spark can be provided at a less delayed timing than from the MBT timing (dashed segment 512b) compared to when the vehicle is occupied (curve 512), resulting in non-zero, highly variable combustion torque (dashed segment 504b). The throttle is opened to a high degree (curve 510) to increase airflow through the engine and increase engine heat output. For example, the throttle can be adjusted to correspond to a desired engine heat output, where the desired heat output is determined based on the difference between the catalyst temperature (curve 508) and the ignition temperature (dashed line 514) at time t1. When the vehicle is not occupied, the throttle can be opened to a lesser extent compared to when the vehicle is occupied (curve 510) (dashed line segment 510b). Furthermore, the fuel flow rate (curve 513) increases to a relatively high amount between time t1 and time t2, corresponding to a high airflow through the engine to operate at the desired AFR and provide high exhaust heat output.

[0059] In response to the engine reaching the desired high idle operating speed (e.g., 1200 RPM), at time t2, the electric motor torque decreases (curve 506) and subsequently remains substantially constant to overcome engine friction and maintain the high idle speed. The catalyst temperature (curve 508) increases between time t2 and time t3 due to increased airflow through the engine (e.g., due to further throttle opening and high idle speed), high fuel flow (curve 513), and combustion energy that generates exhaust heat rather than combustion torque.

[0060] In contrast, as shown by dashed segment 502b, the desired high idle speed can be higher when the vehicle is not occupied compared to when the vehicle is occupied (e.g., greater than 1200 RPM). Electric motor torque (dashed segment 506b) is provided to compensate for the reduced combustion torque, thereby maintaining the engine speed (dashed segment 502b) within the threshold range defined by the lower limit (dashed line 518) and the upper limit (dashed line 520). Furthermore, as regarding... Figure 3As described, between time t2 and time t3, the combustion torque exhibits high inter-cycle variability for unoccupied vehicles due to the high variability of combustion pressure (dashed segment 504b). Therefore, the provided electric motor torque (dashed segment 506b) is also highly variable.

[0061] At time t3, the catalyst temperature (curve 508) reaches the ignition temperature (dashed line 514). (Note that although at...) Figure 5 In the example, the catalyst temperature is shown as a single curve, and time t3 is shown at the same timing for both the occupied vehicle and the unoccupied AV. However, in other examples, the catalyst temperature may increase at different rates in the occupied and unoccupied vehicles using different adjustments. Therefore, the engine switches out of the catalyst heating mode and into the nominal engine operating mode. The spark timing of the first of the four cylinders is advanced to the MBT timing, while the remaining three cylinders remain at a highly delayed timing, resulting in a less delayed average spark timing (curve 512 and dashed segment 512b). Therefore, the combustion torque produced by all four cylinders in the engine (curve 504 and dashed segment 504b) increases. In the first example, when the vehicle is occupied, non-zero combustion torque is produced in the first cylinder, while the remaining three cylinders continue to produce zero combustion torque. In the second example, when the vehicle is unoccupied, the remaining three cylinders, not operating at the MBT spark timing, continue to produce lower variable combustion torque. In response to the increased combustion torque generated by the engine, the torque provided by the electric motor to rotate the engine (curves 506 and dashed segment 506b) is reduced by a corresponding amount to maintain the engine at a consistent speed (when the vehicle is in an occupied state, as shown by curve 502) or within a speed threshold (when the vehicle is in an unoccupied state, as shown by dashed segment 502b). Furthermore, the throttle position (curves 510 and dashed segment 510b) is adjusted to a further closed (e.g., slightly open) position to reduce the airflow through the engine and, correspondingly, the fuel flow (curve 513). By reducing the airflow and fuel flow through the engine, the heat output of the engine is reduced.

[0062] At time t4, the spark timing of the second of the four cylinders is advanced to the MBT timing, while the remaining two cylinders remain at a highly delayed timing, resulting in a less delayed average spark timing (curve 512 and dashed segment 512b). In the first instance, when the vehicle is occupied, non-zero combustion torque is generated in the first and second cylinders, while the remaining two cylinders continue to generate zero combustion torque. In the second instance, when the vehicle is not occupied, the remaining two cylinders, which are not operating at the MBT spark timing, continue to generate lower variable combustion torque. Therefore, the average combustion torque generated by all four cylinders in the engine (curve 504 and dashed segment 504b) is further increased, and the electric motor torque provided to rotate the engine (curve 506 and dashed segment 506b) is further reduced to maintain the engine at a consistent speed (when the vehicle is occupied, as shown in curve 502) or within the speed threshold (when the vehicle is not occupied, as shown in dashed segment 502b). Furthermore, the throttle position (curve 510 and dashed segment 510b) is further closed, and the fuel flow (curve 513) is further reduced.

[0063] At time t5, the spark timing of the third cylinder of the four cylinders is advanced to the MBT timing, while the fourth cylinder continues to operate at a high-delay timing, resulting in a further reduction in the average spark delay (curve 512 and dashed segment 512b). In the first example, when the vehicle is occupied, non-zero combustion torque is generated in the first, second, and third cylinders, while the fourth cylinder continues to generate zero combustion torque. In the second example, when the vehicle is not occupied, the fourth cylinder continues to generate a lower variable combustion torque. Therefore, the average combustion torque generated in the engine by all four cylinders (curve 504 and dashed segment 504b) still increases further, and the electric motor torque provided to rotate the engine (curve 506 and dashed segment 506b) decreases accordingly to maintain the engine at a consistent speed (when the vehicle is occupied, as shown by curve 502) or within the speed threshold (when the vehicle is not occupied, as shown by dashed segment 502b). Furthermore, the throttle position (curve 510 and dashed segment 510b) is further closed, and the fuel flow (curve 513) is further reduced.

[0064] At time t6, the spark timing of the fourth cylinder is advanced to the MBT timing, resulting in an average spark timing (curve 512 and dashed segment 512b) equal to the MBT timing (dashed line 516) by time t7. With all four cylinders operating using sparks provided at or near the MBT timing (e.g., to maximize combustion torque), the combustion torque (curve 504 and dashed segment 504b) is sufficient to maintain engine speed (curve 502 and dashed segment 502b), and therefore the electric motor torque decreases to zero by time t7 (curve 506 and dashed segment 506b). The throttle is adjusted to a further closed position corresponding to idling engine operation outside of the catalytic converter heating mode (curve 510 and dashed segment 510b). Furthermore, after time t7, the engine speed decreases to a low idle speed (e.g., the engine's nominal idle speed). When all engine cylinders are operated with spark timing at or near MBT timing (dashed line 516) after time t7 (curve 512), the resulting combustion torque has low inter-cycle variability (curve 504) and engine speed has low variability for both occupied and unoccupied vehicles (curve 502). After time t7, such as the vehicle driver or AV controller (e.g., Figure 1 As required by the AV controller 191, it can adjust the throttle position (curve 510) and engine speed (curve 502) in response to torque demand.

[0065] In this way, energy from combustion is used to heat the catalyst in response to a cold start, rather than to provide torque to rotate the engine and increase the heat output of the engine. Because the engine is electrically rotated and generates little or no combustion torque, the catalyst reaches its ignition temperature much faster than when energy from combustion is used to generate torque to rotate the engine, thus reducing vehicle emissions during cold starts. Furthermore, the heat output of the engine can be controlled independently of combustion stability by adjusting the airflow rate through the engine, such as by adjusting the position of the intake throttle or regulating the engine speed. Moreover, by reducing the amount of combustion torque generated to zero via a highly delayed spark timing, the variability of combustion torque between cycles is minimized. Therefore, engine speed variations are minimized, thereby reducing noise, vibration, and harshness (NVH) issues during cold starts and improving customer satisfaction. Additionally, by further delaying the spark timing and generating more (and more variable) combustion torque when the vehicle is not occupied, less electric motor torque can be used, thus reducing power consumption.

[0066] The effect of deep-delayed spark timing, which allows the engine to be electrically rotated, is that the energy from combustion can be used to accelerate catalyst heating rather than provide combustion torque, where the heat output of the engine is changed by adjusting one or more of the throttle position and engine speed.

[0067] As an example, one method includes: during a cold start of the engine, applying an ignition spark at an ignition timing set to produce substantially zero combustion torque to burn fuel and a portion of the air entering the engine, while simultaneously rotating the engine with an electric motor and maintaining the engine speed above a threshold speed via electric motor torque; and adjusting the amount of air entering the engine based on desired engine exhaust heat. In the foregoing examples, additionally or optionally, the ignition timing set to produce substantially zero combustion torque corresponds to a substantially zero mean effective pressure indicated by the cylinder in the spark timing region. In any or all of the foregoing examples, additionally or optionally, rotating the engine with an electric motor includes rotating the engine at a substantially constant speed. In any or all of the foregoing examples, additionally or optionally, supplying a substantially constant amount of electrical power to the electric motor generates sufficient electric motor torque to overcome the mechanical friction of the engine and rotate the engine at a speed above a threshold speed. In any or all of the foregoing examples, the method additionally or optionally includes determining the amount of combustion torque produced; and reducing the amount of electrical power supplied to the electric motor to offset the determined amount of combustion torque. In any or all of the foregoing examples, additionally or optionally, adjusting the amount of air entering the engine based on the desired engine exhaust heat includes increasing the opening of the throttle valve coupled to the engine intake port and / or increasing the engine speed via an electric motor as the desired engine exhaust heat output increases. In any or all of the foregoing examples, additionally or optionally, the desired engine exhaust heat is determined based on the difference between the temperature of the catalyst coupled to the engine exhaust port and the ignition temperature of the catalyst. In any or all of the foregoing examples, the method further or optionally includes, after the catalyst temperature reaches the ignition temperature, gradually increasing the amount of combustion torque generated while decreasing the amount of electric motor torque used to rotate the engine by a corresponding amount until no electric motor torque is used to rotate the engine. In any or all of the foregoing examples, additionally or optionally, the engine includes multiple cylinders, and gradually increasing the amount of combustion torque generated includes advancing the ignition spark timing one cylinder at a time until each cylinder operates at the advanced timing. In any or all of the foregoing instances, additionally or optionally, the timing advance of the ignition spark includes providing the ignition spark at the timing that produces the maximum combustion torque.

[0068] As a second example, a method includes: in response to a cold start condition of an engine included in a vehicle, providing a spark at an ignition timing delayed from a timing for maximum opening torque to ignite fuel and a portion of air entering the engine, the delayed ignition timing being determined based on vehicle occupancy and providing simultaneously electric motor torque to the engine via an electric motor to maintain the engine speed above a threshold speed; and adjusting one or more of the position of a throttle valve connected to the engine's intake manifold and the engine speed maintained by the electric motor based on the temperature of a catalyst connected to the engine's exhaust manifold and the vehicle's occupancy. In the foregoing examples, additionally or optionally, providing a spark at an ignition timing determined based on vehicle occupancy includes delaying the spark from the timing for maximum opening torque to a greater extent when the vehicle is occupied, and delaying the spark from the timing for maximum opening torque to a smaller extent when the vehicle is unoccupied. In any or all of the foregoing examples, additionally or optionally, the occupied vehicle is one of a driver-operated vehicle and an autonomous vehicle with one or more passengers, and the unoccupied vehicle is an autonomous vehicle without passengers. In any or all of the foregoing examples, additionally or optionally, delaying the spark from the timing for maximum opening torque to a greater extent includes providing a spark at a timing that produces substantially zero combustion torque, and delaying the spark from the timing for maximum opening torque to a lesser extent includes providing a spark at a timing that produces variable combustion torque. In any or all of the foregoing examples, additionally or optionally, adjusting one or more of the throttle position and engine speed based on catalyst temperature and vehicle occupancy includes, for the same catalyst temperature, adjusting the throttle position to a greater extent and the engine speed to a lesser extent when the vehicle is occupied, and adjusting the throttle position to a lesser extent and the engine speed to a greater extent when the vehicle is not occupied.

[0069] As another example, a system includes: an engine including a plurality of cylinders coupled to a crankshaft, each cylinder including a spark plug for initiating combustion; an electric motor coupled to the crankshaft and receiving electrical power from a system battery; a throttle valve coupled to the engine's intake manifold; an engine coolant temperature sensor for estimating engine temperature; a temperature sensor for inferring the temperature of a catalyst coupled to the engine's exhaust manifold; and a controller storing executable instructions in a non-transitory memory, the instructions causing the controller to... The device operates the engine in a catalytic converter heating mode during cold starts, the catalytic converter heating mode comprising delaying the timing of the spark produced by the spark plug to reduce the amount of torque generated by combustion, while rotating the engine via torque from the electric motor to maintain the engine above a threshold speed; adjusting the airflow through the engine based on a desired heat flux through the engine while operating in the catalytic converter heating mode; and switching from the catalytic converter heating mode to a nominal engine mode based on at least one of the catalyst temperature exceeding a threshold temperature and the threshold duration of operation in the catalytic converter heating mode. In the foregoing examples, operation in the catalytic converter heating mode may further, or optionally, include adjusting the amount of torque from the electric motor based on the amount of torque generated by combustion. In any or all of the foregoing examples, may further, or optionally, determine the desired heat flux through the engine based on the catalyst temperature, and adjusting the airflow through the engine may include increasing at least one of engine speed and throttle opening as the desired heat flux through the engine increases. In any or all of the foregoing examples, the system may additionally or optionally include: an autonomous vehicle controller and a vehicle occupancy sensor, each of the autonomous vehicle controller and the vehicle occupancy sensor being communicatively coupled to the controller, wherein the controller stores additional executable instructions in a non-transitory memory, and when executing the instructions during operation in the catalytic converter heating mode, causes the controller to: determine the vehicle occupancy based on the output from the vehicle occupancy sensor; when the occupancy is at least one, delay the timing of the spark generated by the spark plug to a greater extent, and when the occupancy is less than one, delay the timing of the spark generated by the spark plug to a lesser extent; and for the same desired heat flux through the engine, increase the engine speed to a lesser extent when the occupancy is at least one, and increase the engine speed to a greater extent when the occupancy is less than one.In any or all of the foregoing instances, additionally or optionally, switching from catalytic-heated mode to nominal engine mode includes: advancing the timing of the spark produced by the spark plugs of each of the multiple cylinders sequentially over multiple engine cycles until no cylinder operates at a delayed timing and the torque from the electric motor is reduced to zero.

[0070] In another representation, a method includes: determining vehicle occupancy in response to a cold start condition of a spark-ignition engine included in an autonomous vehicle; providing a spark at a timing determined based on the vehicle occupancy; providing electric motor torque via an electric motor to maintain the engine speed within a threshold range while providing the spark at the determined timing; and adjusting one or more of the position of a throttle valve connected to the engine intake manifold and the engine speed via the electric motor based on the temperature of a catalyst coupled to the exhaust manifold of the engine and the vehicle occupancy. In the foregoing example, additionally or optionally, providing a spark at a timing determined based on vehicle occupancy includes: providing a spark with a further delay from the timing corresponding to the maximum opening torque when the occupancy is at least one, and providing a spark with a less delay from the timing corresponding to the maximum opening torque when the occupancy is less than one. In any or all of the foregoing examples, additionally or optionally, adjusting one or more of the throttle position connected to the engine's intake manifold and the engine speed via the electric motor based on the temperature of the catalyst connected to the engine's exhaust manifold and the vehicle's occupancy includes, for the same catalyst temperature, adjusting the throttle position more significantly and the engine speed less significantly when the occupancy is at least one, and adjusting the throttle position less significantly and the engine speed more significantly when the occupancy is less than one. In any or all of the foregoing examples, additionally or optionally, the threshold range is smaller when the occupancy is at least one compared to when the occupancy is less than one.

[0071] It should be noted that the exemplary control and estimation programs included herein can be used with various engine and / or vehicle system configurations. The control methods and programs disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific programs described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, etc. Therefore, the various actions, operations, and / or functions shown may be executed in the shown sequence, in parallel, or in some cases omitted. Similarly, the processing order is not necessarily necessary to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the shown actions, operations, and / or functions can be repeatedly executed according to the specific strategy used. Furthermore, the described actions, operations, and / or functions can be graphically represented as code to be programmed into a non-transitory memory of a computer-readable storage medium in an engine control system, wherein the described actions are performed by executing instructions in a system including various engine hardware components in combination with an electronic controller.

[0072] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, as many variations are possible. For example, the above-described techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of various systems and configurations, as well as other features, functions, and / or properties disclosed herein.

[0073] The following claims specifically point to certain combinations and sub-combinations considered novel and non-obvious. These claims may refer to an “a” element or a “first” element or its equivalent. These claims should be understood to include the incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by modifying these claims or by presenting new claims in the said or related applications. These claims, whether broader, narrower, identical, or different in scope from the original claims, are considered to be included within the subject matter of this disclosure.

[0074] According to the present invention, a method includes: during a cold start of an engine, applying an ignition spark at an ignition timing set to produce substantially zero combustion torque to burn fuel and a portion of the air entering the engine, while rotating the engine with an electric motor and maintaining the engine speed above a threshold speed via the electric motor torque; and adjusting the amount of air entering the engine based on desired engine exhaust heat.

[0075] According to an embodiment, the ignition timing, which is set to produce essentially zero combustion torque, corresponds to an essentially zero mean effective pressure indicated by the cylinder in the spark timing region.

[0076] According to an embodiment, rotating the engine using the electric motor includes rotating the engine at a substantially constant speed.

[0077] According to an embodiment, the invention is further characterized in that: a substantially constant amount of electrical power is supplied to the electric motor, the substantially constant amount of electrical power generating sufficient electric motor torque to overcome the mechanical friction of the engine and to cause the engine to rotate at a speed greater than the threshold speed.

[0078] According to an embodiment, the invention is further characterized by: determining the amount of combustion torque generated; and reducing the amount of electrical power supplied to the electric motor to offset the determined amount of combustion torque.

[0079] According to an embodiment, adjusting the amount of air entering the engine based on the desired engine exhaust heat includes increasing the opening of the throttle valve connected to the engine intake and / or increasing the engine speed via the electric motor when the desired engine exhaust heat output increases.

[0080] According to an embodiment, the desired engine exhaust heat is determined based on the difference between the temperature of the catalyst connected to the engine exhaust port and the ignition temperature of the catalyst.

[0081] According to an embodiment, the present invention is further characterized in that: after the temperature of the catalyst reaches the ignition temperature, the amount of combustion torque generated is gradually increased, while the amount of electric motor torque used to rotate the engine is reduced by a corresponding amount, until no electric motor torque is used to rotate the engine.

[0082] According to an embodiment, the engine includes a plurality of cylinders, and gradually increasing the amount of combustion torque generated includes advancing the timing of the ignition spark one cylinder at a time until each cylinder operates at the advanced timing.

[0083] According to an embodiment, the timing advance of the ignition spark includes providing the ignition spark at the timing that generates the maximum combustion torque.

[0084] According to the present invention, a method includes: in response to a cold start condition of an engine included in a vehicle, providing a spark at an ignition timing delayed from a timing delay for maximum starting torque to ignite fuel and a portion of air entering the engine, the delayed ignition timing being determined based on vehicle occupancy and providing simultaneously electric motor torque to the engine via an electric motor to maintain the engine speed above a threshold speed; and adjusting one or more of the position of a throttle valve connected to the engine intake manifold and the engine speed maintained by the electric motor based on the temperature of a catalyst connected to the exhaust manifold of the engine and the vehicle occupancy.

[0085] According to an embodiment, the invention is further characterized in that: providing a spark at the ignition timing determined based on the vehicle's occupancy includes delaying the spark from the timing for maximum opening torque to a greater extent when the vehicle is occupied, and delaying the spark from the timing for maximum opening torque to a lesser extent when the vehicle is unoccupied.

[0086] According to an embodiment, the occupied vehicle is one of a driver-operated vehicle and an autonomous vehicle with one or more passengers, and the unoccupied vehicle is an autonomous vehicle without passengers.

[0087] According to an embodiment, the invention is further characterized in that: delaying the spark from the timing for maximum starting torque to a greater extent includes providing the spark at a timing that produces substantially zero combustion torque, and delaying the spark from the timing for maximum starting torque to a lesser extent includes providing the spark at a timing that produces variable combustion torque.

[0088] According to an embodiment, the invention is further characterized in that: adjusting one or more of the throttle position and the engine speed based on the temperature of the catalyst and the occupancy of the vehicle includes, for the same catalyst temperature, adjusting the throttle position to a greater extent and adjusting the engine speed to a lesser extent when the vehicle is occupied, and adjusting the throttle position to a lesser extent and adjusting the engine speed to a greater extent when the vehicle is not occupied.

[0089] According to the present invention, a system is provided comprising: an engine including a plurality of cylinders coupled to a crankshaft, each cylinder including a spark plug for initiating combustion; an electric motor coupled to the crankshaft and receiving electrical power from a system battery; a throttle valve coupled to an intake manifold of the engine; an engine coolant temperature sensor for estimating engine temperature; a temperature sensor for inferring the temperature of a catalyst coupled to an exhaust manifold of the engine; and a controller storing executable instructions in a non-transitory memory, the instructions causing the engine to... The controller: operates the engine in a catalytic converter heating mode during cold start conditions, the catalytic converter heating mode including delaying the timing of the spark generated by the spark plug to reduce the amount of torque generated by combustion, while rotating the engine via torque from the electric motor to maintain the engine above a threshold speed; while operating in the catalytic converter heating mode, adjusting the airflow through the engine based on a desired heat flux through the engine; and switching from the catalytic converter heating mode to a nominal engine mode based on at least one of the catalytic converter temperature exceeding a threshold temperature and the threshold duration of operation in the catalytic converter heating mode.

[0090] According to an embodiment, operation in the catalyst heating mode further includes adjusting the amount of torque from the electric motor based on the amount of torque generated by combustion.

[0091] According to an embodiment, the desired heat flux through the engine is determined based on the temperature of the catalyst, and adjusting the airflow through the engine includes increasing at least one of the engine speed and the throttle opening when the desired heat flux through the engine increases.

[0092] According to an embodiment, the invention is further characterized by: an autonomous vehicle controller and a vehicle occupancy sensor, each of the autonomous vehicle controller and the vehicle occupancy sensor being communicatively coupled to the controller, wherein the controller stores additional executable instructions in a non-transitory memory, and when executing the instructions during operation in the catalyst heating mode, causes the controller to: determine the vehicle occupancy based on the output from the vehicle occupancy sensor; when the occupancy is at least one, delay the timing of the spark generated by the spark plug to a greater extent, and when the occupancy is less than one, delay the timing of the spark generated by the spark plug to a lesser extent; and for the same desired heat flux through the engine, increase the engine speed to a lesser extent when the occupancy is at least one, and increase the engine speed to a greater extent when the occupancy is less than one.

[0093] According to an embodiment, switching from the catalyst heating mode to the nominal engine mode includes: advancing the timing of the spark generated by the spark plug of each of the plurality of cylinders sequentially within a plurality of engine cycles until no cylinder operates at the delayed timing and the torque from the electric motor is reduced to zero.

Claims

1. A method for an engine, comprising: During the cold start of the engine, the timing of the ignition spark is delayed to reduce the amount of torque generated by combustion, while the engine is rotated by an electric motor and the engine speed is maintained above a threshold speed by the torque of the electric motor. The airflow through the engine is regulated based on the desired heat flux through the engine and the vehicle occupancy. When the vehicle is occupied, the timing of the ignition spark is delayed to a greater extent, and when the vehicle is not occupied, the timing of the ignition spark is delayed to a lesser extent. as well as For the same desired heat flux through the engine, the engine speed is increased to a smaller extent when the vehicle is occupied, and to a greater extent when the vehicle is not occupied.

2. The method of claim 1, wherein the timing of the ignition spark is delayed to a greater extent including delaying the mean effective pressure of the cylinder indication to essentially zero.

3. The method of claim 1, wherein rotating the engine with the electric motor comprises rotating the engine at a substantially constant rotational speed.

4. The method of claim 3, wherein a substantially constant amount of electrical power is supplied to the electric motor, the substantially constant amount of electrical power generating sufficient electric motor torque to overcome the mechanical friction of the engine and to cause the engine to rotate at a speed greater than the threshold speed.

5. The method of claim 3, further comprising: Determine the amount of combustion torque generated; as well as The amount of electrical power supplied to the electric motor is reduced to offset the determined amount of combustion torque.

6. The method of claim 1, wherein adjusting the airflow through the engine based on a desired heat flux through the engine includes increasing the opening of a throttle valve coupled to the intake port of the engine and / or increasing the engine speed via the electric motor when the desired heat flux through the engine increases.

7. The method of claim 1, wherein the desired heat flux through the engine is determined based on the difference between the temperature of the catalyst coupled to the engine exhaust port and the ignition temperature of the catalyst.

8. The method of claim 7, further comprising, after the temperature of the catalyst reaches the ignition temperature, gradually increasing the amount of combustion torque generated while decreasing the amount of electric motor torque used to rotate the engine by a corresponding amount, until no electric motor torque is used to rotate the engine.

9. The method of claim 8, wherein the engine comprises a plurality of cylinders, and gradually increasing the amount of the generated combustion torque comprises advancing the timing of the ignition spark one cylinder at a time until each cylinder operates at the advanced timing.

10. The method of claim 9, wherein advancing the timing of the ignition spark includes providing the ignition spark at a timing that generates maximum combustion torque.

11. A system for an engine, comprising: An engine, the engine including a plurality of cylinders coupled to a crankshaft, each cylinder including a spark plug for initiating combustion; An electric motor, connected to the crankshaft, receives electrical power from the system battery; Throttle valve, which is connected to the intake manifold of the engine; An engine coolant temperature sensor, the engine coolant temperature sensor being used to estimate engine temperature; A temperature sensor for inferring the temperature of a catalyst connected in the exhaust manifold of the engine; Autonomous vehicle controller; Vehicle occupancy sensor; as well as The controller stores executable instructions in non-transitory memory, which, when executed, cause the controller to: During cold start conditions, the engine is operated in a catalyst heating mode, which includes delaying the timing of the spark generated by the spark plug to reduce the amount of torque generated by combustion, while rotating the engine via torque from the electric motor to maintain the engine above a threshold speed. When operating in the catalyst heating mode, the airflow through the engine is adjusted based on the desired heat flux through the engine; as well as The system switches from the catalyst heating mode to the nominal engine mode based on at least one of the following: the catalyst temperature exceeds a threshold temperature and the duration of operation in the catalyst heating mode exceeds a threshold. Each of the autonomous vehicle controller and the vehicle occupancy sensor is communicatively coupled to the controller, and the controller stores additional executable instructions in a non-transitory memory, which, when executed during operation in the catalyst heating mode, cause the controller to: The occupancy of the vehicle is determined based on the output from the vehicle occupancy sensor; When the vehicle is occupied, the timing of the spark generated by the spark plug is delayed to a greater extent, and when the vehicle is not occupied, the timing of the spark generated by the spark plug is delayed to a lesser extent. as well as For the same desired heat flux through the engine, the engine speed is increased to a smaller extent when the vehicle is occupied, and to a greater extent when the vehicle is not occupied.

12. The system of claim 11, wherein operation in the catalyst heating mode further includes adjusting the amount of torque from the electric motor based on the amount of torque generated by combustion.

13. The system of claim 12, wherein the desired heat flux through the engine is determined based on the temperature of the catalyst, and adjusting the airflow through the engine includes increasing at least one of the engine speed and the throttle opening as the desired heat flux through the engine increases.

14. The system of claim 12, wherein switching from the catalyst heating mode to the nominal engine mode comprises: In multiple engine cycles, the timing of the spark generated by the spark plug of each of the plurality of cylinders is advanced sequentially until no cylinder operates at the delayed timing and the torque from the electric motor is reduced to zero.

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