System and method for compressing heated air

Abstract

The present disclosure provides "systems and methods for compression heating of air." The present disclosure provides methods and systems for compression heating of air. In one example, a method can include, during engine startup and prior to a first combustion event, deactivating cylinder exhaust valves while electrically and un-fueled rotating the engine until a threshold intake temperature is reached; and after the first combustion event, alternately activating and deactivating the exhaust valves of one or more cylinders to maintain an intake temperature above the threshold temperature. In this way, the temperature of the charge of air can be increased, resulting in improved fuel economy and reduced vehicle emissions.

Description

Technical Field

[0001] This specification generally relates to methods and systems for heating gases via a vehicle engine. Background Technology

[0002] Vehicle engine efficiency can decrease during cold starts and / or before the engine reaches steady-state operating temperature. For example, combustion may be less complete during engine start-up compared to when the engine is warmed up, thus reducing fuel economy and increasing vehicle emissions. In particular, when the vehicle is hybrid, equipped with a stop / start system, etc., the engine may operate intermittently, which can result in multiple engine starts within a single driving cycle. Therefore, systems and methods for improving combustion efficiency during initial operation are becoming increasingly important. Factors affecting complete combustion include combustion chamber wall temperature, combustion air temperature, fuel temperature, and engine speed. In particular, heating the combustion air (e.g., the air used for combustion reactions within the engine cylinders) can enhance complete combustion due to the effect of combustion air temperature on mixture preparation and reduced air intake.

[0003] Other attempts to address air heating include operating in an air-heated mode during the engine's starting sequence. Clarke et al. illustrate an exemplary method in US 5,117,790. In this method, the one or more cylinders in a multi-cylinder engine are operated in an air-heated mode by disabling their exhaust valves before combustion is initiated in one or more cylinders. Once each of the one or more cylinders is sufficiently heated, the corresponding exhaust valve is activated and fuel is injected to initiate combustion. The other one or more cylinders can then be operated in an air-heated mode before combustion is initiated in another one or more cylinders.

[0004] However, the inventors of this paper have recognized the potential problems of such systems. As an example, sequentially heating and initiating combustion in the cylinders of a multi-cylinder engine can prolong engine start-up time, leading to reduced driver satisfaction. Furthermore, the engine can benefit from continuous air heating, even after the first combustion event, especially when the engine remains below its steady-state operating temperature. Additionally, the hotter combustion air temperature can aid certain ignition strategies, such as compression ignition, even when the engine is preheated. Summary of the Invention

[0005] In one example, the problem discussed above can be addressed by a method for a hybrid electric vehicle, the method comprising: during engine start-up, deactivating the engine cylinder exhaust valves while activating the engine cylinder intake valves, and electrically rotating the engine without fuel until a threshold intake air temperature is reached; and after reaching the threshold intake air temperature, activating one or more cylinders and fueling the one or more cylinders to initiate combustion, and then alternating between deactivating the one or more cylinders and initiating combustion in the one or more cylinders until a threshold engine temperature is reached. In this manner, the engine can be started efficiently and has improved combustion completeness.

[0006] As an example, alternating between deactivating the one or more cylinders and conducting combustion in the one or more cylinders includes: during an engine cycle, maintaining the exhaust valves of the one or more cylinders closed while keeping the corresponding intake valves active, and prohibiting fuel injection into the one or more cylinders; and during a subsequent engine cycle, raising the intake and exhaust valves at the corresponding valve timings, supplying fuel via fuel injectors coupled to each of the one or more cylinders, and providing a spark via spark plugs coupled to each of the one or more cylinders. By alternating between deactivating the one or more cylinders and conducting combustion in the one or more cylinders, continuous air heating can be provided, even after the engine has been started and combustion has been initiated. For example, the threshold engine temperature could be the steady-state operating temperature of the engine. Therefore, continuous air heating can be provided when the engine is cold. In contrast, air heating prior to the first combustion event can be performed independently of the engine temperature. In this way, the air heating prior to the first combustion event can be provided even when the engine has not yet cooled significantly, such as when the engine is turned off and restarted while the vehicle is on. In other examples, continuous air heating can be provided to facilitate operation in compression ignition mode, in which the increased air charge temperature assists compression ignition. In summary, this improves fuel economy and reduces vehicle emissions.

[0007] It should be understood that the above description of the invention is provided to introduce a series of concepts in a simplified form, which are further described in the detailed embodiments. This does not imply identification of the key or essential features of the claimed subject matter, and the scope of the claimed subject matter is uniquely defined by the claims following the detailed embodiments. Furthermore, the claimed subject matter is not limited to implementations that address any of the shortcomings pointed out above or in any part of this disclosure. Attached Figure Description

[0008] Figure 1A schematic diagram of the vehicle's engine system is shown.

[0009] Figure 2 Exemplary graphs of air circulation in an idealized engine with and without exhaust valve deactivation are shown.

[0010] Figure 3 This is a high-level flowchart of an exemplary method for compressing and heating air in response to an engine start request.

[0011] Figure 4 This is a flowchart of an exemplary method for compressing and heating air after the initial ignition of an engine.

[0012] Figure 5 An indicative exemplary timeline is shown, illustrating the compression and heating of air via the exhaust valve during and after engine start-up. Detailed Implementation

[0013] The following description relates to the use of via engine cylinders (such as...) Figure 1 A system and method for increasing the temperature of a gas by compression heating within an engine cylinder (illustrated schematically). The gas may include a mixture of fresh air and residual exhaust gas, also referred to herein as "air". The thermodynamic mechanism leading to the temperature increase during compression heating is referenced in [reference needed]. Figure 2 The air circulation of the engine cylinders is described as shown. Compression heating can be used before the first combustion event of the engine (also referred to herein as "ignition") and after the first combustion event (such as according to...). Figure 3 and Figure 4 The exemplary method shown increases the temperature of the air intake. An example reference for operating an engine by compression heating is also provided. Figure 5 As shown.

[0014] Figure 1 An example of a cylinder 14 of an internal combustion engine 10 that may be included in an engine system 100 in vehicle 5 is depicted. The engine 10 may be controlled at least in part by a control system including a controller 12 and inputs 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. The crankshaft 140 may be coupled to at least one wheel 55 via a transmission 54, as further described below. Additionally, a starter motor (not shown) may be coupled to the crankshaft 140 via a flywheel to enable starting operation of the engine 10.

[0015] In some examples, vehicle 5 may be a hybrid vehicle with multiple torque sources available for use on one or more wheels 55. In other examples, vehicle 5 is a conventional vehicle with only an engine, or an electric vehicle with only one or more electric motors. Figure 1 In the example shown, vehicle 5 includes engine 10 and electric motor 52. Electric motor 52 can be a motor or a motor / generator. 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 56 is disposed between crankshaft 140 and electric motor 52, and a second clutch 56 is disposed between electric motor 52 and transmission 54. Controller 12 can send signals to the actuators 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 can be a gearbox, planetary gear system, or other type of transmission.

[0016] The powertrain can be configured in various ways, including as a parallel, series, or series-parallel hybrid vehicle. In an electric vehicle embodiment, the system battery 58 may be a traction battery that supplies electrical 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 starting, lighting, ignition (SLI) battery coupled to the alternator 46.

[0017] Alternator 46 can be configured to charge system battery 58 via crankshaft 140 using engine torque during engine operation. Furthermore, alternator 46 can supply power to one or more electrical systems of the engine, 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 cabin cooling requirements, battery charging requirements, other auxiliary vehicle system requirements, 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 requirements.

[0018] 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 examples, 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. Exhaust manifold 148 receives exhaust air from cylinder 14 and other cylinders of engine 10.

[0019] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown as including at least one intake lift valve 150 and at least one exhaust lift valve 156 located in the upper region of cylinder 14. In some examples, 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 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).

[0020] In some cases, controller 12 may 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 may be electrically actuated, cam-actuated, or a combination thereof. Intake and exhaust valve timing may be controlled simultaneously, or any of the following possibilities may be used: variable intake cam timing, variable exhaust cam timing, dual 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 switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) system operable by controller 12 to change valve operation. For example, cylinder 14 may alternatively include an intake valve controlled by electrically actuated valves and an exhaust valve controlled by cam actuation (including CPS and / or VCT). In other examples, 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). As an example, both exhaust valve 156 and intake valve 150 may be active when operating in combustion mode. As used herein, when referring to intake and exhaust valves, "active" or "enabled" means a valve operating state in which the valves open according to desired valve timing (e.g., lift), such as opening once per engine cycle.

[0021] In some examples, one or more of the intake valve 150 and exhaust valve 156 may be deactivated during a selected operating mode. As an example, during compression heating mode, the intake valve 150 may remain active while the exhaust valve 156 is deactivated, as will be discussed in reference to... Figures 2 to 4 As described herein. In one example, intake valve 150 and / or exhaust valve 156 may be deactivated via a hydraulically actuated lifter coupled to a valve pushrod or via a CPS mechanism in which a no-lift cam lobe is used for the deactivated valve. Other valve deactivation mechanisms may also be used, such as those for electrically actuated valves. In still other examples, one actuator may control the deactivation of all intake valves, while another different actuator controls the deactivation of all exhaust valves of engine 10. It should be understood that if a cylinder is a non-deactivatable cylinder, then the cylinder may not have any valve deactivation actuator. As used herein, when referring to intake and exhaust valves, "deactivation" means a valve operating state in which the valve remains closed (e.g., not lifted) for a desired number of engine cycles.

[0022] Cylinder 14 may have a compression ratio (CR), which is the ratio of the volume of piston 138 at bottom dead center (BDC) to the volume at top dead center (TDC). In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may occur, for example, when using fuels with higher octane ratings or higher latent enthalpy of vaporization. If direct injection is used, the compression ratio may also be increased due to the effect of direct injection on engine knock.

[0023] In some examples, engine 10 may be a variable compression ratio (VCR) engine, equipped with a mechanism that changes (e.g., mechanically) the volume ratio between the piston TDC and BDC as engine operating conditions change, thereby allowing for variations in the compression ratio. As a non-limiting example, the VCR engine may be configured with a mechanical piston displacement alteration mechanism (e.g., an eccentric wheel) that moves the piston closer to or further away from the cylinder head, thereby changing the size of the combustion chamber. In another example, the cylinder head volume may be mechanically altered.

[0024] like Figure 1 As shown, in some examples, the engine's compression ratio (CR) can be varied via VCR actuator 193 actuating VCR mechanism 194. In some examples, the CR can vary between a first lower CR (where the ratio of cylinder volume when the piston is in BDC to that when the piston is in TDC is smaller) and a second higher CR (where the ratio is higher). In other examples, a predetermined number of compression ratio stages can exist between the first lower CR and the second higher CR. In still other examples, the CR can vary continuously between the first lower CR and the second higher CR (to any CR in between).

[0025] In the depicted example, VCR mechanism 194 is coupled to piston 138, allowing the VCR mechanism to change the piston's TDC position. For example, piston 138 may be coupled to crankshaft 140 via VCR mechanism 194, which may be a piston position changing mechanism that moves the piston closer to or further away from the cylinder head, thereby changing the piston's position and thus the size of combustion chamber 14. Position sensor 196 may be coupled to VCR mechanism 194 and may be configured to provide feedback to controller 12 regarding the position of VCR mechanism 194 (and therefore the CR of the cylinder).

[0026] In one example, changing the piston's position within the combustion chamber also changes the piston's relative displacement within the cylinder. The piston position changing VCR mechanism can be coupled to a conventional or unconventional cranktrain. Non-limiting examples of unconventional cranktrains to which the VCR mechanism can be coupled include variable distance head crankshafts and variable motion length crankshafts. In one example, crankshaft 140 can be configured as an eccentric shaft. In another example, an eccentric wheel can be coupled to or located in the region of the piston pin, causing the eccentric wheel to change the piston's position within the combustion chamber. The movement of the eccentric wheel can be controlled by oil passages in the piston rod.

[0027] It should be understood that other VCR mechanisms can be used to mechanically change the compression ratio. For example, the CR of an engine can be changed via a VCR mechanism that alters the cylinder head volume (that is, the clearance volume within the cylinder head). In another example, the VCR mechanism may include a hydraulically reacting, air-pressure reacting, or mechanically reacting piston. Additionally, the VCR mechanism may include a multi-system, a lever mechanism, or other VCR mechanical structures.

[0028] It should be understood that, as used herein, a VCR engine can be configured to adjust the engine's CR via mechanical adjustments that change the piston position or cylinder head volume. Thus, the VCR mechanism does not include CR adjustment achieved through adjustments to valve or camshaft timing.

[0029] 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 combustion chamber 14 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 maximum brake 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 examples, the spark may be delayed after the MBT, such as to accelerate catalyst preheating during engine start-up or to reduce engine knock.

[0030] In some examples, engine 10 can operate in both spark ignition (SI) mode and spark-controlled compression ignition (SPCCI) mode, wherein the ignition mode is selected based on operating conditions. For example, SPCCI mode can be selected at lower engine speeds and loads and when the engine is warm, while SI mode can be selected at higher engine speeds and loads and when the engine is cold. In other examples, engine 10 can operate only in SI mode. In SI mode, the ignition spark from spark plug 192 initiates flame propagation combustion, and the air-fuel mixture in cylinder 14 remains at or near the stoichiometric air-fuel ratio (AFR). In SPCCI mode, the ignition spark from spark plug 192 ignites a rich air-fuel mixture confined to the area surrounding spark plug 192. This localized spark ignition combustion compresses the remaining lean air-fuel mixture in cylinder 14 by further increasing the temperature and pressure within cylinder 14. This compression effect simultaneously ignites the remaining (lean) air-fuel mixture in cylinder 14. Therefore, compared to the ignition spark used in SI mode, the ignition spark during SPCCI mode is used to control the timing of the compression ignition event, which involves higher pressure, higher temperature, and a leaner AFR mixture. Operating in SPCCI mode reduces cooling losses, reduces throttling losses, and improves fuel economy. Methods to increase the air charge temperature (such as referring to...) Figure 3 and Figure 4 The exemplary method described can help operate in SPCCI mode.

[0031] In some examples, each cylinder of engine 10 may be configured with one or more fuel injectors for supplying fuel thereto. As a non-limiting example, cylinder 14 is shown as 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 to inject fuel directly into it in proportion to the pulse width of the signal FPW received from controller 12 via electronic actuator 168. In this manner, fuel injector 166 provides so-called direct fuel injection into cylinder 14 (hereinafter also referred to as "DI"). Although Figure 1A fuel injector 166 is shown positioned on one side of cylinder 14, but alternatively, the fuel injector 166 may be located on top of the piston, such as near spark plug 192. This location enhances 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 or near the intake valve to enhance mixing. Fuel may 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.

[0032] In an alternative example, fuel injector 166 may be configured to be located in the intake passage rather than directly coupled to cylinder 14, providing so-called port injection (hereinafter also referred to as "PFI") of fuel into the intake passage upstream of cylinder 14. In yet another example, 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 way of example.

[0033] 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 this 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 the previous exhaust stroke, during the intake stroke, and / or during the 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 in a manner known as split fuel injection. In particular, split injection can be performed during SPCCI mode. For example, the first fuel injection during the intake stroke can produce a homogeneous lean air-fuel mixture, and the second injection during the compression stroke can produce a locally rich mixture around spark plug 192 for ignition.

[0034] The fuel tank in fuel system 8 can hold fuels of different types, such as fuels with different fuel masses and different fuel compositions. Differences may include different alcohol contents, different water contents, different octane numbers, different heats of vaporization, different fuel mixtures, and / or combinations thereof. An example of fuels with different heats of vaporization includes gasoline with a lower heat of vaporization as the first fuel type and ethanol with a higher heat of vaporization as the second fuel type. In another example, the engine can use gasoline as the first fuel type and an alcohol-containing fuel mixture (such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline)) as the second fuel type. Other possible substances include: water; methanol; mixtures of alcohol and water; mixtures of water and methanol; mixtures of alcohols, etc. In yet another example, the two fuels can be alcohol mixtures with different alcohol compositions, where the first fuel type can be a gasoline-alcohol mixture with a lower alcohol concentration, such as E10 (which is approximately 10% ethanol), while the second fuel type can be a gasoline-alcohol mixture with a higher alcohol concentration, such as E85 (which is approximately 85% ethanol). In addition, the first and second fuels may differ in other aspects of fuel quality, such as temperature, viscosity, and octane number. Furthermore, the fuel characteristics of one or both fuel tanks may frequently change, for example, due to daily variations in tank refilling.

[0035] Exhaust sensor 126 is shown coupled upstream of emission control device 178 to exhaust manifold 148, connected within exhaust passage 158. Exhaust sensor 126 can be selected from various sensors suitable for providing exhaust AFR indication, such as, for example, linear oxygen sensors or UEGO (universal or wide-range exhaust oxygen sensor), dual-state exhaust oxygen sensors or EGO, HEGO (heated EGO), nitrogen oxides (NOx), hydrocarbons (HC), or carbon monoxide (CO) sensors. Figure 1 In the 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. Emission control device 178 may be a three-way catalytic converter, a NOx trap, various other emission control devices, or a combination thereof. Figure 1 In the example, emission control device 178 is a three-way catalytic converter configured to reduce NOx and oxidize CO and unburned hydrocarbons.

[0036] Controller 12 in Figure 1The computer, shown as a microcomputer, 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 specific example 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 those previously discussed, and additionally including: the measurement of the introduced mass air flow (MAF) from the mass air flow sensor 122; the engine coolant temperature (ECT) from the engine coolant temperature sensor 116 connected to the cooling sleeve 118; the ambient temperature from the temperature sensor 123 connected to the intake manifold 142; the exhaust temperature from the temperature sensor 128 connected to the exhaust manifold 158; the profile ignition pickup signal (PIP) from the Hall effect sensor 120 (or other type of sensor) connected to the crankshaft 140; the 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 air-fuel ratio (AFR); and the absolute manifold pressure signal (MAP) from the MAP sensor 124. The engine speed signal RPM can be generated by controller 12 based on the signal PIP. The manifold pressure signal MAP from MAP sensor 124 can be used to provide an indication of vacuum or pressure in the intake manifold. Controller 12 can infer the engine temperature based on the engine coolant temperature. Additional sensors (such as various temperature, pressure, and humidity sensors) can be connected throughout the vehicle 5.

[0037] Controller 12 from Figure 1 Various sensors receive signals, and based on the received signals and instructions stored in the controller's memory, employ... Figure 1 Various actuators are used to adjust engine operation. For example, such as according to Figure 3 and Figure 4 An exemplary method, based on the signal ECT from the engine coolant temperature sensor 116, allows the controller to deactivate the exhaust valve 156 (e.g., via the exhaust valve actuator 154) and disable the fuel injector 166 so that the cylinder 14 operates in compression heating mode.

[0038] As mentioned above, Figure 1Only one cylinder of a multi-cylinder engine is shown. Thus, each cylinder may similarly include its own set of intake / exhaust valves, one or more 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... Figure 1 Some or all of the various components described and depicted with reference to cylinder 14.

[0039] As described above, one or more cylinders can operate in compression heating mode. Compression heating mode uses the compression and rapid expansion of air to increase the thermal energy of the air. Now turning to... Figure 2 This diagram 200 illustrates an exemplary curve of air circulation in the unfueled cylinders of an idealized four-stroke engine. Curve 201 shows the piston position, curve 202 shows the intake valve open, curve 204 shows the exhaust valve open, curve 206 shows the cylinder pressure, and curve 208 shows the cylinder air temperature. For all the above curves, the horizontal axis represents the crank angle, which increases from left to right along the horizontal axis. The vertical axis represents each labeled parameter. For curve 201, the piston position increases from bottom to top along the vertical axis. For curves 202 and 204, the vertical axis indicates whether the corresponding intake and exhaust valves are "open" or "closed." In this example, "open" means partially or fully open (e.g., not closed), and "closed" means fully closed (e.g., not lifted). For curve 206, the cylinder pressure increases from bottom to top along the vertical axis and is shown relative to atmospheric pressure ("atm"). For curve 208, the cylinder air temperature (e.g., the temperature of the air inside the cylinder, which may be a mixture of fresh air and residual exhaust gas) increases from bottom to top along the vertical axis. Engine strokes are labeled "I" for intake stroke, "C" for compression stroke, "P" for power stroke, and "E" for exhaust stroke. Differences in operation under compression heating mode will be described with reference to dashed segments 204a, 206a, and 208a.

[0040] During each intake stroke, the intake valve is open (curve 202) and the exhaust valve is closed (curve 204). With the cylinder connected to the atmosphere through the open intake valve, the cylinder pressure equals atmospheric pressure (curve 206) and the cylinder air temperature is low (curve 208). During the compression stroke, both the intake valve (curve 202) and the exhaust valve (curve 204) are closed, sealing the cylinder. During the compression stroke, as the piston rises within the cylinder (curve 201), the cylinder volume decreases. As the sealed cylinder volume decreases and the air (e.g., gas) within the cylinder is compressed (e.g., pressurized), the cylinder pressure (curve 206) increases. Furthermore, as the cylinder compression ratio increases, the maximum cylinder pressure reached during the compression stroke increases. The increased compression energy raises the temperature of the air within the cylinder (curve 208). As the cylinder compression ratio increases, the maximum cylinder air temperature reached during the compression stroke also increases.

[0041] During the power stroke, as the piston moves downward (curve 201), the cylinder volume expands, causing the cylinder pressure (curve 206) to drop back to atmospheric pressure. During the power stroke, the intake valve (curve 202) and exhaust valve (curve 204) remain closed. For example, in the absence of combustion and with the intake and exhaust valves closed, compressed air acts as an air spring, helping to push the piston back to its starting position. As the cylinder volume expands, the heat energy from the cylinder air is extracted by the piston to do work, resulting in a decrease in cylinder air temperature (curve 208). To some extent, Figure 2 The example shown is an adiabatic (no heat loss) process, where the cylinder pressure (curve 206) and cylinder air temperature (curve 208) at the end of the power stroke match those at the beginning of the compression stroke (e.g., the pressure and temperature during the compression and power strokes are roughly symmetrical).

[0042] During the exhaust stroke, the piston rises (curve 201), again reducing the cylinder volume. However, the exhaust valve is open (curve 204), forcing air out of the cylinder (e.g., into the exhaust manifold) rather than compressing it. Therefore, the cylinder pressure remains at atmospheric pressure (curve 206). In the idealized example of curve 200, the cylinder air is essentially unheated (curve 208), and due to energy conservation (e.g., compression is isentropic), the energy imparted to the air between intake strokes is equal. For example, the compression energy can be equal to and opposite to the expansion energy.

[0043] However, if the exhaust valve is instead kept closed (e.g., deactivated) during the exhaust stroke, as shown by dashed segment 204a, then the cylinder pressure (curve 206a) increases as the air in the cylinder is compressed by the rising piston, just as it does during the compression stroke. Similarly, as during the compression stroke, the cylinder air temperature increases (curve 208a) as the cylinder air is compressed. During the intake stroke, when the cylinder pressure is at its maximum, the intake valve opens (curve 202). Therefore, the compressed cylinder air expands rapidly from being pressurized to atmospheric pressure. For example, at least a portion of the compressed air can be expelled back into the engine's intake manifold through the open intake valve and via the intake passage. The air temperature does not change as rapidly as the cylinder pressure (curve 206a) (curve 208a). Instead of the compression energy being extracted by the piston to do work as during the power stroke, the compression energy remains as the heat energy of the air already compressed in the cylinder before the intake valve opens. Therefore, in addition to any heated air retained in the cylinder, the intake passage is filled with high-temperature intake air (e.g., air expelled back into the intake manifold). The completion of the four-stroke air cycle when operating in compression-heated mode may be referred to herein as the "compression-heated cycle". Then, during the intake stroke, as the piston moves downward (curve 201), the heated intake air can be drawn back into the cylinder, resulting in an increased cylinder air temperature (curve 208a) compared to when the exhaust valve is not deactivated (curve 208). As heat is transferred to the walls of the intake manifold and the combustion chamber, the temperature of the hot air can decrease (curve 208a). In this way, before the first ignition of the cylinder, or when fueling is prohibited after the first ignition, by deactivating the exhaust valve and maintaining the intake valve activity, the energy from compression can be used to increase the temperature of the charging air, as further described below.

[0044] then, Figure 3 This shows the use of engines (e.g., Figure 1 An exemplary method 300 for performing compression heating of air during the initial operation of the engine 10 shown. For example, prior to the first ignition event when requesting engine start, the engine cylinders may operate one or more compression heating cycles (such as those referenced above) in compression heating mode. Figure 2 As described herein, to increase the cylinder air temperature and intake air temperature, and thus increase the air charging temperature. Instructions for carrying out method 300 and the remaining methods included herein may be provided 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 of the engine system, such as those referenced above. Figure 1 The described sensor (e.g., Figure 1The ambient temperature sensor 123, the MAP sensor 124, and the engine coolant temperature sensor 116). The controller may employ the engine actuator of the engine system (e.g., according to the method described below). Figure 1 The motor 52 and exhaust valve actuator 154 are used to adjust engine operation.

[0045] Method 300 begins at 302 and includes: estimating and / or measuring operating conditions. Operating conditions may include, for example, ambient temperature, manifold pressure, throttle position (e.g., based on a signal TP output from a throttle position sensor), accelerator pedal position (e.g., based on a signal PP output from a pedal position sensor), engine coolant temperature, cylinder compression ratio (e.g., from...). Figure 1 The system includes a position sensor 196), engine status, and vehicle ignition status. Engine status can refer to whether the engine is on (e.g., operating at a non-zero speed and combustion is occurring in the engine cylinders) or off (e.g., stationary and no combustion is occurring in the engine cylinders). Vehicle ignition status can refer to the position of the ignition switch. As an example, the ignition switch can be in the "off" position, indicating that the vehicle is off (e.g., power is off and the vehicle speed is zero); or in the "on" position, indicating that the vehicle is on (e.g., power is supplied to the vehicle system). Engine status and vehicle status can differ. For example, the vehicle can be on and operating in pure electric mode, where the electric motor supplies torque to propel the vehicle and the engine is off and does not supply torque to propel the vehicle. As another example, during an idling stop where the engine is off and the vehicle remains on, the vehicle can be on and the engine can be off. In one example, when performing an idling stop, the vehicle can be stationary. In another example, when performing an idling stop, the vehicle can be in motion (e.g., coasting). Alternatively, when the engine includes an electric supercharger (e.g., an electromechanical supercharger), the electric supercharger can be engaged to increase cylinder mass, thereby increasing cylinder heat.

[0046] At point 304, it is determined whether an engine start request has been made. For example, engine start can be requested by the vehicle driver switching the ignition switch to the "on" position, such as by turning the ignition key, pressing the ignition button, or requesting engine start from a remote device (such as a key fob, smartphone, tablet, etc.). In another example, engine start can be requested via a controller to switch the vehicle from pure electric mode to engine mode, in which combustion occurs in the engine and the vehicle is at least partially propelled by torque from the engine. For example, when the system battery (e.g., Figure 1When the state of charge (SOC) of the system battery (58) drops below a threshold SOC, the vehicle may switch to engine mode. The threshold SOC can be a positive, non-zero battery SOC level below which the system battery may not be able to support or perform additional vehicle functions (e.g., 30%) while propelling the vehicle via torque from the electric motor. As another example, if torque demand rises above a threshold torque, the vehicle may switch to engine mode. For example, the threshold torque can be a positive, non-zero torque amount that, for example, the electric motor alone cannot achieve or maintain. In yet another example, engine start may be requested by the vehicle controller to exit idle stop.

[0047] If no engine start request is requested, then method 300 proceeds to 306 and includes maintaining the current engine state. For example, if the engine is on, then the engine will remain on. If the engine is off, then the engine will remain off. The method may optionally proceed to 320, wherein routines for uninterrupted gas heating may be executed, as will be described below.

[0048] If an engine start is requested, then method 300 proceeds to 308 and includes: deactivating the cylinder exhaust valves. For example, this can be achieved via a cam profile change mechanism using a lift-less cam or by actuating a valve deactivator to maintain the exhaust valve closure for each cylinder of the engine. As another example, when the exhaust valve is of the electric valve actuation type, the controller does not provide a signal to the exhaust valve actuator to open the exhaust valve. While the exhaust valves are deactivated, the cylinder intake valves remain active, such that the intake valves can be open during each intake stroke. Therefore, at 308, the engine cylinders can be switched to operate in compression-heated mode. In some examples, such as when engine hardware constraints allow for the deactivation of only a subset of engine cylinders, the exhaust valves of that subset of engine cylinders can be deactivated while the remaining (potentially undeactivated) exhaust valves remain active.

[0049] At 310, method 300 includes: determining the number of cycles to maintain exhaust valve deactivation based on an initial intake air temperature and a desired intake air (or air-charging) temperature. For example, an isentropic compression model that takes into account the initial intake air temperature and the engine's compression ratio can be used to determine the number of cycles (e.g., compression heating cycles) that will cause the intake air temperature to reach or exceed the desired intake air temperature (or air-charging temperature to reach or exceed the desired air-charging temperature). The initial intake air temperature may be equal to the ambient temperature, for example, when a compression heating cycle has not been previously performed. The desired intake air temperature may be a fixed, calibrable temperature value, such as a temperature value in the range of 200°C to 500°C. Each time a compression heating cycle is performed (e.g., once per cylinder per engine cycle), the intake air temperature increases as the compressed heated gas is expelled back from the cylinder into the intake manifold, as referenced. Figure 2 As described. Therefore, two compression heating cycles will increase the intake air temperature more than one compression heating cycle, three compression heating cycles will increase the temperature more than two compression heating cycles, and so on. Furthermore, the higher the engine's compression ratio, the greater the temperature increase within a single compression heating cycle. For example, for the same starting (e.g., ambient) temperature, a compression ratio of 10:1 will result in a greater intake air temperature than a compression ratio of 9:1. Therefore, in some examples, when the engine is a variable compression ratio engine, the compression ratio can be increased to cause the intake air temperature to rise more quickly (e.g., within fewer engine cycles) and / or to rise the intake air temperature to a higher temperature. For example, the controller can do this via a VCR actuator (e.g., Figure 1 The VCR actuator 193) actuates the VCR mechanism (e.g., Figure 1 The VCR mechanism (194) is used to increase the compression ratio of the engine.

[0050] As an example, the controller can use the following isentropic compression model to estimate the intake temperature (T2) after one compression heating cycle based on the initial intake temperature (T1), initial cylinder pressure (P1), final cylinder pressure (P2), and specific heat ratio (γ): In some examples, (P2 / P1) can be used to infer the pressure ratio from the compression ratio. Then, the temperature value T2 can be used as the initial intake temperature value T1 for the next compression heating cycle.

[0051] At 312, method 300 includes: turning the starter engine without fuel for a determined number of cycles. The engine can be an electric motor (such as a starter motor or an electric motor (e.g., Figure 1The electric motor 52) starts at high speeds (such as in the range of 600-2000 RPM). Because heat loss over time due to heat transfer to engine components (e.g., intake manifold walls, cylinder walls, etc.), starting at high speeds reduces heat loss. For example, increasing the starting speed from 200 RPM to 1000 RPM can reduce heat loss by a factor of 5. By reducing heat loss during starting, compression heating has a greater impact on air temperature. The energy supplied to the electric motor can be higher during each compression heating cycle compared to a non-compression heating start-up cycle at the same starting speed. For example, with the exhaust valve deactivated and the intake valve active, the additional compression during the exhaust stroke (due to the deactivated exhaust valve) and the lack of shaft work during the intake stroke (due to the active intake valve) increase the amount of electric motor torque required to maintain the starting speed during the compression heating cycle. Furthermore, when combustion is not performed and sparking adds a non-significant amount of energy to the air, the spark plugs connected to each cylinder (e.g., Figure 1 Spark plug 192 may not provide a spark.

[0052] At 314, method 300 includes: engaging the cylinder exhaust valve and initiating fuel injection to initiate combustion. That is, after a predetermined number of cycles of starting the engine without fuel injection while the exhaust valve is deactivated, the exhaust valve can be engaged and fuel injected via a fuel injector (e.g., Figure 1 The engine continues to rotate while the fuel injector 166 injects fuel. For example, the exhaust valve can be activated via a cam profile change mechanism using a lift cam or by actuating (e.g., deactivating) a valve deactivator. Therefore, at 314, method 300 includes switching the cylinder from operation in compression heating mode to operation in combustion mode.

[0053] To determine the amount of fuel to be injected when switching to combustion mode operation, method 300 further includes: inferring the intake air temperature based on the determined number of cycles, as indicated at 316, and calculating the initial air charge (e.g., the mass of air in the cylinder) based on the MAP and the inferred intake air temperature, as indicated at 318. The intake air temperature can be determined using the isentropic compression model described above at 310. The controller can then input the MAP and the inferred intake air temperature at intake valve closure into a lookup table, map, or function, and output the initial air charge. In some examples, the initial air charge can be further determined based on the cylinder volume at intake valve closure, which can also be input into a lookup table, function, or map. The cylinder volume can be a known volume stored in the controller's non-transitory memory. As an example, the controller determines the initial air charge by solving PV = mRT for the mass (m) of the air charge, where P is the pressure in the cylinder when the intake valve is closed (e.g., MAP when the intake valve is closed), V is the volume captured by the cylinder when the intake valve is closed, R is the ideal gas constant, and T is the inferred intake temperature (e.g., near the intake valve). The initial air charge can then be used to determine the amount of fuel to be injected for the initial ignition event. For example, the controller can determine the control signal to be sent to the fuel injector actuator, such as the pulse width of the signal, based on the initial air charge and the desired air-fuel ratio (AFR). The controller can determine the pulse width by directly considering the determination of the air charge and the desired AFR (e.g., by increasing the pulse width with increasing air charge). Alternatively, the controller can determine the pulse width via a lookup table, by inputting the initial air charge and AFR and outputting the pulse width. Furthermore, a spark can be provided to ignite combustion based on the timing determined by the operating conditions, such as a reference... Figure 1 As described. For example, a spark can be provided at or near the MBT timing to maximize the amount of combustion torque generated with each ignition event. As another example, the spark can be delayed from the MBT timing to help with the exhaust catalytic converter (e.g., Figure 1 The emission control device 178) heats the air. Due to heating, the density of the intake air decreases compared to when the intake air is not heated. Therefore, during the intake stroke following the compression heating cycle, a smaller mass of air is introduced into the cylinder. For example, the initial air charge can be lower compared to when the intake air temperature is lower (e.g., for the same throttle position). Therefore, the amount of fuel injected can be lower than when the intake air temperature is lower, resulting in a smaller amount of combustion torque during engine initial ignition. As the combustion torque increases, the electric motor torque can decrease until the electric motor torque decreases to zero and the engine rotates only via the combustion torque. In some examples, when the engine switches to operate via combustion torque and without electric motor torque, the engine speed can decrease from a high starting speed to a low engine idle speed.

[0054] In some examples, after a determined number of cycles, each engine cylinder switches to operation in combustion mode. In other examples, one or more cylinders (e.g., a subset of engine cylinders) may continue to operate in compression heating mode, without fuel and with the corresponding exhaust valve deactivated, while the remaining cylinders operate in combustion mode. Specifically, compression heating may continue when the engine temperature is low (e.g., below a threshold temperature, as further described herein) or when a higher desired intake air temperature is desired (e.g., for SPCCI). Therefore, at 320, method 300 may optionally include: performing compression heating in a subset of cylinders for gas heating, as referenced... Figure 4 As described. As an example, with the corresponding exhaust valve deactivated and no fuel added to the cylinder during the unignition cycle, each cylinder in the cylinder subgroup can be alternately ignited and deigned (e.g., each engine cycle alternates between operation in combustion mode and operation in compression heating mode) until the engine reaches the desired temperature. Method 300 ends after 320.

[0055] By disabling the exhaust valves and running the engine without fuel during engine start-up, the temperature of the intake and cylinder air is increased (and therefore the initial air charge temperature). During fuel injection, fuel evaporation is enhanced, and the homogeneity of the air-fuel mixture is increased. Therefore, fuel economy is improved and vehicle emissions are reduced compared to not preheating the initial air charge before the first combustion event. Furthermore, the reduced intake air density during initial ignition (due to the increased temperature) and the resulting reduced air charge allow for a gradual increase in engine combustion torque, providing a smoother feel and thus improved driver satisfaction.

[0056] then, Figure 4 This shows the use of engines (e.g., Figure 1 An exemplary method 400 for compressing and heating gases after the initial ignition of the engine 10 shown. For example, one or more engine cylinders may operate in a compression heating mode to increase the temperature of the gases (which include a mixture of fresh air and residual exhaust gas discharged to the intake system, and a mixture of fresh air and residual exhaust gas retained in one or more cylinders), while the remaining engine cylinders operate in combustion mode to generate combustion torque. By increasing the gas temperature, fuel evaporation is enhanced, resulting in improved fuel economy and reduced emissions, which is particularly beneficial when the engine has not yet been preheated. Furthermore, compression heating can be used to assist operation in SPCCI mode, where the higher in-cylinder temperature (compared to operation in SI mode) assists compression ignition. Method 400 can be used as... Figure 3A portion of method 300 (such as at 320) is performed. Alternatively, method 400 may be performed in response to any request for compression heating when the engine is started.

[0057] Method 400 begins at 402 and includes: estimating and / or measuring operating conditions. Operating conditions may include, for example, engine speed, engine load, throttle position (e.g., based on a signal TP output from a throttle position sensor), accelerator pedal position (e.g., based on a signal PP output from a pedal position sensor), engine temperature, catalyst temperature (e.g., as per...). Figure 1 The exhaust temperature is estimated by the exhaust temperature sensor 128, and the ambient temperature (e.g., as estimated by an ambient temperature sensor such as...). Figure 1 The temperature sensor 123 measures the temperature ratio and the compression ratio (e.g., from the temperature sensor 123) and the compression ratio. Figure 1 Position sensor 196). For example, engine speed can be based on a Hall effect sensor (e.g., Figure 1 The signal PIP output from the Hall effect sensor 120 can be used to determine the engine load, which can be based on the signal from the MAF sensor (e.g., Figure 1 The MAF of the engine can be determined by the measurement results of the MAF sensor 122, and the engine temperature can be determined by the engine coolant temperature sensor (e.g., Figure 1 The engine coolant temperature sensor 116 infers the engine coolant temperature based on its measurement results.

[0058] At 404, it is determined whether the conditions for compression heating are met. As an example, the conditions for compression heating are met when the engine temperature is below a threshold temperature. The threshold temperature may correspond to a non-zero positive temperature value above which the engine is considered warm and at a steady-state operating temperature (e.g., a temperature value in the range of 195-220℉). As another example, the conditions for compression heating may additionally or alternatively include indications such as desired operation in SPCCI mode, such as when the engine speed is in a low to medium range. As another example, the conditions for compression heating are met when using a fuel with low volatility (e.g., a fuel with a high percentage of ethanol). Any or all of the conditions for compression heating may be confirmed to initiate compression heating.

[0059] If the conditions for compression heating are not met, then method 400 proceeds to 406 and includes: maintaining the current engine state. For example, if the engine operates with all cylinders active (e.g., fuel is supplied to each cylinder, and each cylinder operates in combustion mode), then the engine will continue to operate with all cylinders active. If the engine operates in a variable displacement engine mode (where a subset of cylinders generates torque), then the engine will continue to operate in the variable displacement engine mode. Fueling of cylinders for air heating purposes (e.g., for operation in compression heating mode) will not be prohibited, and sparks will continue to be provided to initiate combustion in both SI and SPCCI modes. After 406, method 400 ends.

[0060] If the conditions for compression heating are met at 404, then method 400 proceeds to 408 and includes performing compression heating on a subset of the engine cylinders. Performing compression heating on a subset of the engine cylinders includes determining the number of cylinders to be operated without fuel (e.g., in compression heating mode) with the exhaust valve deactivated, as indicated at 410. The number of cylinders may be determined based on operating conditions such as those measured at 402. For example, a larger number of cylinders may be operated without fuel with the exhaust valve deactivated when torque demand decreases and / or when the difference between engine temperature and threshold temperature increases. Conversely, a smaller number of cylinders may be operated without fuel with the exhaust valve deactivated when torque demand increases and / or when the difference between engine temperature and threshold temperature decreases. Furthermore, the cylinder data may be constrained according to the engine configuration (e.g., cylinder layout and total number) to mitigate engine noise, vibration, and harshness (NVH). The controller can determine the number of cylinders to operate without fuel and with the exhaust valve deactivated by inputting operating conditions (such as one or more of torque demand and engine temperature) into one or more lookup tables, maps, or algorithms and outputting the number of cylinders to operate without fuel with the exhaust valve deactivated for a given condition. In some other examples, the controller can determine the desired induction ratio (the actual total number of cylinder ignition events divided by the actual total number of cylinder compression strokes) based at least in part on the torque demand. The controller can also select a cylinder mode for the determined number of cylinders or induction ratio. As an example, a mode corresponding to an induction ratio of 0.5 could include igniting every other cylinder (where combustion takes place in the cylinder and the intake and exhaust valves open and close during the cylinder cycle) or not igniting (where fuel is prohibited and the corresponding exhaust valve is deactivated while the intake valve remains active). Furthermore, the same mode can be used for each consecutive engine cycle, such that the same cylinders are not ignited in consecutive engine cycles, while the remaining cylinders are ignited in each engine cycle. In other examples, different cylinders may not be ignited in each engine cycle, so that ignition and non-ignition are cyclical or evenly distributed among engine cylinders. For example, cylinder modes may be selected based on hardware constraints or to mitigate engine NVH.

[0061] Performing compression heating in a subset of cylinders also includes disabling fuel injection to a determined number of cylinders, as indicated at 412. For example, a selected cylinder mode can be used to disable fuel injection to the determined number of cylinders and deactivate the corresponding exhaust valves. Each corresponding exhaust valve can be accessed via an actuator (e.g., Figure 1The exhaust valve actuator 154 can be disabled and re-enabled. Using a four-cylinder engine as an example, when the determined number of cylinders is two or the induction ratio is 0.5, fuel injection to the first two cylinders can be disabled and the exhaust valves of the first two cylinders can be shut off during the first engine cycle, while combustion continues in the second two cylinders. Then, during the second engine cycle, fuel injection to the second two cylinders can be disabled and the exhaust valves of the second two cylinders can be shut off, while fuel is added to the first two cylinders and their exhaust valves are enabled. Then, during the third engine cycle, fuel injection to the first two cylinders can be disabled and their exhaust valves can be shut off again, and so on. When fuel addition is disabled, spark generation in the corresponding cylinders is also prohibited, because combustion does not occur in the cylinders without fuel. Furthermore, although the determined number of cylinders operates in compression heating mode, engine operating parameters can be adjusted to maintain engine torque requirements while the remaining cylinders operate in combustion mode. For example, one or more of the airflow, spark timing, and cylinder valve timing can be adjusted to maintain engine torque requirements and minimize torque disturbances. In other examples, electric assistance can be provided to compensate for reduced combustion torque. In this example, the required engine torque can be generated by a combination of combustion torque and electric motor torque (e.g., from an electric motor, such as...). Figure 1 The combination of the motor 52) is provided. In this way, each cylinder can be alternately ignited and unignited to distribute compression heating evenly throughout the engine.

[0062] At 414, it is determined whether the conditions for interrupting compression heating are met. As an example, the conditions for interrupting compression heating, as defined above at 404, may be met when the engine temperature is above a threshold temperature. As another example, the conditions for interrupting compression heating may additionally or alternatively include an indication that operation in SI mode is desired, such as when the engine is operating in a high-speed range. As yet another example, the conditions for interrupting compression heating may include a torque demand exceeding a threshold torque demand, which corresponds to a torque demand that cannot be met in the event of reduced engine air intake due to compression heating. Any or all of the conditions for interrupting compression heating may be confirmed to cause the controller to interrupt compression heating.

[0063] If the conditions for interrupting compression heating are not met, for example, if the engine temperature is not greater than a threshold temperature, then method 400 returns to 408 to continue compression heating in a subset of cylinders. If the conditions for interrupting compression heating are met, then method 400 proceeds to 416 to activate the deactivated exhaust valves and begin fueling in all cylinders. With fuel supplied and the exhaust valves of each cylinder active and operating, a spark may also be supplied to each cylinder, causing combustion in all cylinders. For example, cylinders operating in compression heating mode can be switched to combustion mode. Furthermore, when combustion restarts in all cylinders, engine operating parameters can be adjusted. For example, one or more of the airflow, spark timing, and cylinder valve timing can be adjusted to maintain engine torque demand and minimize torque disturbances when combustion restarts in all engine cylinders. In some examples, the engine can be switched from operating in SPCCI mode to operating in SI mode. Thus, one or more of the desired AFR, fuel injection quantity or split ratio, and cylinder compression ratio can also be adjusted. For example, the desired AFR can be adjusted from a lean AFR used for operation in SPCCI mode to a stoichiometric AFR used for operation in SI mode. As another example, the compression ratio can be reduced from a higher compression ratio when operating in SPCCI mode to a lower compression ratio when operating in SI mode to avoid engine knock. The compression ratio can be adjusted via a VCR actuator (e.g., Figure 1 The VCR actuator 193) actuates the VCR mechanism (e.g., Figure 1 Adjust the VCR mechanism (194). After 416, method 400 ends.

[0064] In this way, by continuing to compress and heat the intake and cylinder air even after the first ignition event, the engine continues to benefit from enhanced mixture preparation, resulting in more complete combustion. This can improve fuel economy, for example, while reducing vehicle emissions. Furthermore, operation in SPCCI mode can be aided by increasing the intake air temperature (and therefore the air charging temperature), which further improves fuel economy and reduces vehicle emissions, while also increasing engine efficiency.

[0065] Therefore, in one example, Figure 4The method may include: determining air heating conditions, and in response, switching one or more cylinders to a compression heating mode; and determining non-heating conditions, and in response, operating all cylinders in a combustion mode. In some examples, operating one or more cylinders in a compression heating mode may occur during or when air heating conditions are present, and operating all cylinders in a combustion mode may occur when air heating conditions are absent and / or during or when non-heating conditions are present. Furthermore, the instructions stored in the memory may include instructions for: determining air heating conditions based on one or more of an engine coolant temperature sensor reading and an indication of operation in spark-controlled compression ignition mode, and in response, operating one or more cylinders to compression heating mode by sending a set of signals to actuators of the exhaust valves of each of the one or more cylinders and fuel injectors coupled to each of the one or more cylinders; and determining non-air heating conditions based on one or more of an engine coolant temperature sensor reading and an indication of operation in spark ignition mode, and in response, operating all cylinders in combustion mode by sending a different set of signals to actuators of the exhaust valves and fuel injectors coupled to each cylinder. In some examples, the method may include: determining whether to perform one or more of the following actions based on whether air heating conditions are present or absent: operating each of the one or more cylinders in compression heating mode and operating all cylinders in combustion mode. Furthermore, when one or more cylinders are operating in compression heating mode, the remaining number of cylinders may operate in combustion mode. In some examples, when air heating conditions are present, each engine cycle can cause a given cylinder to switch from combustion mode to compression heating mode and back to compression mode, so that the given cylinder alternates between operating in combustion mode and operating in compression heating mode.

[0066] then, Figure 5 Show the engine in the operating vehicle (e.g., Figure 1 The vehicle 5 shown has an engine 10) with an exemplary curve 500 showing the heating of air before and after the initial combustion event. For example, it can be based on... Figure 3 and Figure 4An exemplary method allows engine cylinders to switch between a compression heating mode and a combustion mode. Curve 502 shows engine speed, curve 504 shows engine temperature, curve 506 shows cylinder exhaust valve deactivation, curve 508 shows cylinder refueling, curve 510 shows the inferred intake air temperature, curve 512 shows electric motor torque, and curve 514 shows combustion torque. For all the above graphs, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each labeled parameter. For curves 502, 504, 510, 512, and 514, the values ​​increase from bottom to top along the vertical axis. For curves 506 and 508, the vertical axis represents the number of cylinders that experience exhaust valve deactivation and refueling, as labeled (e.g., 0, 1, 2, 3, or 4). Therefore, in the example of graph 500, the engine is a four-cylinder engine. Furthermore, in the example of graph 500, each exhaust valve (e.g., Figure 1 The exhaust valve 156 can be selected to be deactivated.

[0067] Before time t1, the engine is off and stationary, as indicated by zero engine speed (curve 502) and zero combustion torque (curve 514). Additionally, the electric motor (e.g., Figure 1 The electric motor 52 does not supply torque to the electric motor to rotate the engine (curve 512). With the engine off, the engine temperature (curve 504) is low, and the inferred intake air temperature (curve 510) is equal to the ambient temperature (indicated by the dashed line 520). Furthermore, when the engine is off, no engine cylinders are fueled (curve 508). When the engine is off, the exhaust valves can be in the default active state, and therefore no exhaust valves are deactivated (curve 506).

[0068] At time t1, the vehicle driver requests engine start. Therefore, the engine switches to operation in compression heating mode. Specifically, the exhaust valves of each cylinder (e.g., all four cylinders) are deactivated (curve 506), and the engine remains unfueled (curve 508). The controller (e.g., Figure 1 The controller 12) determines the number of engine cycles to be operated in compression heating mode for each cylinder before the first combustion event based on the intake air temperature at time t1 (curve 510) and the desired intake air temperature (indicated by dash 518), the intake air temperature being equal to the ambient temperature (dash 520).

[0069] Between time t1 and time t2, the engine is started from rest by the torque of the electric motor (curve 512) to bring the engine speed (curve 502) to a high starting speed. The electric motor torque is initially high to accelerate the engine from rest and then decreases to maintain the engine speed at the high starting speed. When the engine is started and the exhaust valve is deactivated between time t1 and time t2 for the determined number of engine cycles, the intake air temperature (curve 510) exceeds the desired intake air temperature (dash 518). Because no combustion occurs in the engine cylinders between time t1 and time t2, the combustion torque remains at zero (curve 514), and the engine temperature increases slightly due to friction and heat transfer from the intake air (curve 504).

[0070] When the last engine cycle of the determined number of engine cycles is completed at time t2, and in response to the engine temperature (curve 504) being less than the threshold engine temperature (indicated by dashed line 516) representing the steady-state operating temperature, two (e.g., a subset) of the engine cylinders continue to operate in compression heating mode without fuel and with their exhaust valves deactivated (curve 506). The remaining two cylinders switch to combustion mode, operating with fuel supplied (curve 508) and their exhaust valves activated. Furthermore, a spark (not shown) is provided in the cylinders operating in combustion mode to initiate combustion. As two cylinders operate in combustion mode, the combustion torque increases (curve 514). The combustion torque (curve 514) gradually increases due to the lower density air charge (e.g., due to the increased intake air temperature and cylinder temperature), while the electric motor torque (curve 512) decreases by a corresponding amount until the electric motor torque decreases to zero. In addition, the engine speed (curve 502) decreases to an idle speed below the high-speed starting speed (between time t1 and time t2).

[0071] When both (half) cylinders operate in compression heating mode between time t1 and time t2, the intake air temperature (curve 510) remains higher than the desired intake air temperature (dash 518) and the engine temperature (curve 504) increases rapidly. Figure 5In the example of graph 500, each engine cylinder alternates between operating in compression mode and combustion mode between time t2 and time t3. That is, during the first engine cycle, the first group of two cylinders operates in combustion mode, while the second group of two cylinders operates in compression heating mode; during the second engine cycle, the first group of two cylinders operates in combustion heating mode, while the second group of two cylinders operates in combustion mode; during the third engine cycle, the first group of two cylinders operates in combustion mode, while the second group of two cylinders operates in compression heating mode, and so on. In this way, each of the four engine cylinders alternates between operating in combustion heating mode (e.g., ignited) and operating in compression heating mode (e.g., not ignited) to achieve uniform engine and gas heating.

[0072] At time t3, the engine temperature (curve 504) reaches the threshold engine temperature (dash 516). Therefore, the operation of the two cylinders in compression heating mode switches to combustion mode. The cylinderless exhaust valve is deactivated (curve 506), and fuel is supplied to all four cylinders (curve 508). A spark is provided to ignite the air-fuel mixture in each cylinder (not shown). (See also...) Figure 4 As described, operating parameters (such as engine load, spark timing, etc.) are adjusted to minimize torque disturbances. However, combustion torque and engine speed can vary based on driver demand, as shown by curves 514 and 512, respectively. Without compressing and heating the gas, the intake air temperature decreases (curve 510). However, when the engine is warm and operating above a threshold engine temperature, the lower intake air temperature does not significantly affect complete combustion.

[0073] In this way, by heating the engine air (e.g., intake and air-charging) before the first combustion event by disabling the cylinder exhaust valves and simultaneously rotating the engine without adding fuel, engine efficiency can be improved while vehicle emissions are reduced. Specifically, the heated air enhances fuel evaporation and improves the homogeneity of the air-fuel mixture, resulting in a more complete initial combustion response. Furthermore, the reduced air-charging (due to the lower density of the heated air) allows the amount of combustion torque generated by the engine to gradually increase. Moreover, by operating a subset of engine cylinders in compression heating mode after the first combustion event (e.g., with the corresponding exhaust valves disabled and fuel not added to the subset), uninterrupted air heating can be provided to continuously improve engine efficiency and reduce vehicle emissions. In particular, uninterrupted air heating can improve combustion completeness when the engine is cold (e.g., not preheated to steady-state operating temperature) or promote operation in a more efficient spark-controlled combustion ignition mode. Therefore, fuel economy can be further improved.

[0074] The technical effect of operating one or more engine cylinders without fuel and with the exhaust valves closed is that the temperature of the engine intake air and the air inside the cylinders is increased by compression heating, thereby resulting in enhanced fuel evaporation, improved air-fuel mixture homogeneity, improved fuel economy, and reduced emissions during the subsequent combustion event.

[0075] As an example, a method for a hybrid electric vehicle includes: during engine start-up, deactivating the exhaust valves of engine cylinders while activating the intake valves of engine cylinders, and electrically rotating the engine without fuel until a threshold intake temperature is reached; and after reaching the threshold intake temperature, activating one or more cylinders and fueling the one or more cylinders to initiate combustion, then alternating between deactivating the one or more cylinders and initiating combustion in the one or more cylinders until a threshold engine temperature is reached. In the foregoing example, additionally or optionally, deactivating the one or more cylinders includes: during an engine cycle, maintaining the exhaust valves of the one or more cylinders closed and maintaining the intake valves of the one or more cylinders activated, while prohibiting fueling the one or more cylinders. In any or all of the foregoing examples, additionally or optionally, initiating combustion in the one or more cylinders includes: during an engine cycle, raising the intake valves and the exhaust valves at corresponding valve timings, supplying fuel via fuel injectors coupled to each of the one or more cylinders, and supplying a spark via spark plugs coupled to each of the one or more cylinders. In any or all of the foregoing examples, additionally or optionally, the intake air temperature is estimated based on an initial intake air temperature, the compression ratio of the engine cylinders, and the number of engine cycles in which the exhaust valves have been deactivated. In any or all of the foregoing examples, additionally or optionally, the initial intake air temperature is equal to the ambient temperature. In any or all of the foregoing examples, additionally or optionally, air charging is estimated based on the estimated intake air temperature, the intake air pressure, and the intake valve closing timing. In any or all of the foregoing examples, additionally or optionally, alternately deactivating the one or more cylinders and conducting combustion in the one or more cylinders includes determining the number and mode of the one or more cylinders based on at least one of engine torque demand, current engine temperature, and engine configuration. In any or all of the foregoing examples, additionally or optionally, the mode is the same or different from one engine cycle to the next. In any or all of the foregoing examples, additionally or optionally, the threshold engine temperature is the steady-state operating temperature of the engine.

[0076] As another example, one method includes performing compression heating on gas in one or more cylinders of a multi-cylinder engine before switching to a spark-controlled compression ignition mode. In the foregoing example, additionally or optionally, performing the compression heating includes: preventing fuel from being added to the one or more cylinders and deactivating the exhaust valves of the one or more cylinders while keeping the exhaust valves of the one or more cylinders active. In any or all of the foregoing examples, additionally or optionally, the gas comprises a mixture of fresh air and residual exhaust gas, and performing the compression heating includes: expelling at least a portion of the gas from the one or more cylinders into the intake passage via the intake valve. In any or all of the foregoing examples, additionally or optionally, during engine start-up from rest, the one or more cylinders are equal to each cylinder of the multi-cylinder engine, and the method further includes: determining the number of engine cycles to be performed for compression heating based on a desired intake air temperature and an initial intake air temperature via an isentropic compression model; rotating the engine to the determined number of engine cycles via electric motor torque and without combustion torque; after the determined number of engine cycles, initiating spark-controlled compression ignition combustion in the at least one cylinder by activating the exhaust valve of at least one cylinder and enabling fuel to be added to the at least one cylinder; and reducing the electric motor torque as the combustion torque increases. In any or all of the foregoing examples, additionally or optionally, the method further includes: determining the number and pattern of cylinders to be selected as the one or more cylinders based on one or more of the engine's torque requirements, engine temperature, and hardware constraints. In any or all of the foregoing examples, additionally or optionally, the determined pattern includes selecting the same one or more cylinders for each consecutive engine cycle or selecting different one or more cylinders for each consecutive engine cycle.

[0077] As another example, a system includes: an engine including a plurality of cylinders coupled to a crankshaft, each cylinder including a piston, an intake valve, an exhaust valve, a spark plug, and a fuel injector directly coupled to the cylinder; an electric motor coupled to the crankshaft and receiving power from a system battery; an intake manifold for supplying intake air to each cylinder via the intake valves; a first temperature sensor for estimating engine temperature; a second temperature sensor for estimating ambient temperature; and a pressure sensor coupled to the intake manifold. The manifold is used to measure intake pressure; and a controller stores executable instructions in a non-transitory memory, which, when executed, cause the controller to: operate each of the plurality of cylinders in compression heating mode for a certain number of engine cycles before initial ignition, while simultaneously rotating the engine via the electric motor, the number of engine cycles being determined based on the ambient temperature and the desired intake temperature; and after the initial ignition, in response to satisfying the conditions for compression heating, operate a subset of the plurality of cylinders in the compression heating mode and operate the remaining cylinders in combustion mode. In the foregoing example, additionally or alternatively, the compression heating mode includes: disabling the exhaust valve while maintaining the intake valve activity, not injecting fuel via the fuel injector, and not providing a spark via the spark plug; and the combustion mode includes: maintaining the intake valve and the exhaust valve activity, providing fuel via the fuel injector, and providing the spark via the spark plug. In any or all of the foregoing examples, additionally or alternatively, the conditions for compression heating include: the engine temperature being below a threshold temperature, the threshold temperature corresponding to steady-state engine operation. In any or all of the foregoing examples, additionally or optionally, the amount of fuel used for the initial ignition is determined based on the number of engine cycles, the ambient temperature, and the intake pressure. In any or all of the foregoing examples, additionally or optionally, the number of cylinders in the subset of the plurality of cylinders is determined based on at least one of torque requirement and engine temperature.

[0078] In another representation, a method includes: in response to at least one of an engine start request, an engine temperature below a threshold temperature, and operation in spark-controlled compression ignition mode, deactivating one or more cylinders of a multi-cylinder engine by preventing fuel supply to one or more cylinders and disabling the exhaust valves of said one or more cylinders. In the foregoing examples, additionally or alternatively, the intake valves of said one or more cylinders remain active during the deactivation. In any or all of the foregoing examples, in response to the engine start request, said one or more cylinders include each cylinder of the multi-cylinder engine. In any or all of the foregoing examples, the method further includes: determining the number of engine cycles to maintain the deactivation of said one or more cylinders. In any or all of the foregoing examples, additionally or alternatively, the number of engine cycles is determined based on at least one of intake air temperature and said engine temperature. In any or all of the foregoing examples, the method further includes: determining the number and identification of said one or more cylinders. In any or all of the foregoing examples, the number and identification of said one or more cylinders are determined based on at least one of engine torque requirements and the configuration of said multi-cylinder engine.

[0079] It should be noted that the exemplary control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-transitory memory and can be implemented by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of regulation strategies (such as event-driven, intermittent-driven, multitasking, multithreading, etc.). Thus, the various actions, operations, and / or functions shown can be performed in the order shown, can be performed in parallel, or, in some cases, can be omitted. Similarly, the order of regulation is not necessarily required 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 actions, operations, and / or functions shown can be repeatedly performed 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 implemented by executing the instructions in conjunction with an electronic controller in a system including various engine hardware components.

[0080] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, as many variations are possible. For example, the above techniques can be applied to V6, inline 4, inline 6, V12, opposed 4, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations disclosed herein, as well as other features, functions, and / or characteristics.

[0081] The following claims specifically point to certain combinations and sub-combinations that are considered novel and not obvious. These claims may refer to an “a” element or a “first” element or its equivalent. Such claims should be understood to include a combination 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 characteristics may be claimed by amending these claims or by presenting new claims in this application or related applications. Such claims are also considered to be included within the subject matter of this disclosure, whether they are broader, narrower, identical, or different in scope compared to the original claims.

[0082] According to the present invention, a method for a hybrid electric vehicle includes: during engine start-up, deactivating engine cylinder exhaust valves while activating engine cylinder intake valves, and electrically rotating the engine without fuel until a threshold intake temperature is reached; and after reaching the threshold intake temperature, activating one or more cylinders and fueling the one or more cylinders to initiate combustion, and then alternating between deactivating the one or more cylinders and initiating combustion in the one or more cylinders until a threshold engine temperature is reached.

[0083] According to an embodiment, deactivating the one or more cylinders includes: maintaining the exhaust valve of the one or more cylinders closed and maintaining the intake valve of the one or more cylinders open during an engine cycle, while prohibiting the addition of fuel to the one or more cylinders.

[0084] According to an embodiment, combustion in the one or more cylinders includes: during an engine cycle, raising the intake valve and the exhaust valve at corresponding valve timings, supplying fuel via a fuel injector connected to each of the one or more cylinders, and supplying a spark via a spark plug connected to each of the one or more cylinders.

[0085] According to an embodiment, the intake air temperature is estimated based on the initial intake air temperature, the compression ratio of the engine cylinder, and the number of engine cycles in which the exhaust valve has been deactivated.

[0086] According to an embodiment, the initial intake temperature is equal to the ambient temperature.

[0087] According to an embodiment, air inflation is estimated based on the estimated intake air temperature, the intake air pressure, and the closing timing of the intake valve.

[0088] According to an embodiment, alternately deactivating one or more cylinders and performing combustion in one or more cylinders includes determining the number and mode of the one or more cylinders based on at least one of engine torque demand, current engine temperature, and engine configuration.

[0089] According to an embodiment, the pattern may be the same or different from one engine cycle to the next.

[0090] According to an embodiment, the threshold engine temperature is the steady-state operating temperature of the engine.

[0091] According to the present invention, a method includes performing compression heating on gas in one or more cylinders of a multi-cylinder engine before switching to a spark-controlled compression ignition mode.

[0092] According to an embodiment, performing the compression heating includes: prohibiting the addition of fuel to the one or more cylinders and deactivating the exhaust valves of the one or more cylinders while keeping the exhaust valves of the one or more cylinders active.

[0093] According to an embodiment, the gas comprises a mixture of fresh air and residual exhaust gas, and performing the compression heating comprises: discharging at least a portion of the gas from the one or more cylinders into an intake passage via the intake valve.

[0094] According to an embodiment, during engine start-up from a standstill, the one or more cylinders are equivalent to each cylinder of the multi-cylinder engine, and the method further includes: determining the number of engine cycles to be performed for compression heating based on a desired intake air temperature and an initial intake air temperature via an isentropic compression model; rotating the engine to the determined number of engine cycles via electric motor torque and without combustion torque; after the determined number of engine cycles, initiating spark-controlled compression ignition combustion in the at least one cylinder by activating the exhaust valve of at least one cylinder and enabling fuel to be added to the at least one cylinder; and reducing the electric motor torque as the combustion torque increases.

[0095] According to an embodiment, a further feature of the invention is that the number and pattern of cylinders to be selected as the one or more cylinders are determined based on one or more of the engine's torque requirements, engine temperature, and hardware constraints.

[0096] According to an embodiment, the determined pattern includes selecting the same one or more cylinders for each continuous engine cycle or selecting different one or more cylinders for each continuous engine cycle.

[0097] 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 piston, an intake valve, an exhaust valve, a spark plug, and a fuel injector directly coupled to the cylinder; an electric motor coupled to the crankshaft and receiving power from a system battery; an intake manifold for supplying intake air to each cylinder via the intake valves; a first temperature sensor for estimating engine temperature; a second temperature sensor for estimating ambient temperature; and a pressure sensor coupled to the intake manifold. The manifold is used to measure intake pressure; and a controller stores executable instructions in a non-transitory memory, which, when executed, cause the controller to: operate each of the plurality of cylinders in compression heating mode for a certain number of engine cycles before initial ignition, while rotating the engine via the electric motor, the number of engine cycles being determined based on the ambient temperature and the desired intake temperature; and after the initial ignition, in response to satisfying the conditions for compression heating, operate a subset of the plurality of cylinders in the compression heating mode and operate the remaining cylinders in combustion mode.

[0098] According to an embodiment, the compression heating mode includes: deactivating the exhaust valve while maintaining the intake valve activity, not injecting fuel via the fuel injector, and not providing a spark via the spark plug; and the combustion mode includes: maintaining the intake valve and the exhaust valve activity, providing fuel via the fuel injector, and providing the spark via the spark plug.

[0099] According to an embodiment, the conditions for compression heating include: the engine temperature is below a threshold temperature, the threshold temperature corresponding to steady-state engine operation.

[0100] According to an embodiment, the amount of fuel used for the initial ignition is determined based on the number of engine cycles, the ambient temperature, and the intake pressure.

[0101] According to an embodiment, the number of cylinders in the subset of the plurality of cylinders is determined based on at least one of torque requirement and engine temperature.

Claims

1. A method for a hybrid electric vehicle, comprising: During engine start-up, the engine cylinder exhaust valve is deactivated while the engine cylinder intake valve is activated, and the engine is started electrically without fuel until the intake air temperature reaches a threshold. as well as After the threshold is reached, one or more cylinders are activated and fueled to initiate combustion, and then the process alternates between deactivating the one or more cylinders and initiating combustion in the one or more cylinders until the threshold engine temperature is reached.

2. The method of claim 1, wherein disabling the one or more cylinders comprises: During the engine cycle, the exhaust valve of the one or more cylinders is kept closed and the intake valve of the one or more cylinders is kept open, while fueling of the one or more cylinders is prohibited.

3. The method of claim 1, wherein combustion in the one or more cylinders comprises: During an engine cycle, the intake and exhaust valves are lifted at corresponding valve timings to supply fuel via fuel injectors connected to each of the one or more cylinders, and to supply sparks via spark plugs connected to each of the one or more cylinders.

4. The method of claim 1, wherein the intake air temperature is estimated based on an initial intake air temperature, the compression ratio of the one or more cylinders, and the number of engine cycles in which the exhaust valve has been deactivated.

5. The method of claim 4, wherein the initial intake temperature is equal to the ambient temperature.

6. The method of claim 4, wherein the air inflation is estimated based on the estimated intake air temperature, intake air pressure, and the closing timing of the intake valve.

7. The method of claim 1, wherein alternately deactivating the one or more cylinders and performing combustion in the one or more cylinders comprises: The number and configuration of the one or more cylinders are determined based on at least one of the following: engine torque requirement, current engine temperature, and engine configuration.

8. The method of claim 7, wherein the mode from one engine cycle to the next engine cycle is the same or different.

9. The method of claim 7, further comprising: In response to the engine torque demand exceeding the amount of combustion torque generated when the one or more cylinders are alternately deactivated and combustion occurs in the one or more cylinders, electric assistance is provided via electric motor torque.

10. The method of claim 1, wherein the threshold engine temperature is the steady-state operating temperature of the engine.

11. A system for a hybrid electric vehicle, comprising: An engine comprising a plurality of cylinders connected to a crankshaft, each cylinder comprising a piston, an intake valve, an exhaust valve, a spark plug, and a fuel injector directly connected to the cylinder; An electric motor, which is connected to the crankshaft and receives power from the system battery; An intake manifold for supplying intake air to each cylinder via the intake valve; A first temperature sensor is used to estimate the engine temperature. A second temperature sensor is used to estimate the ambient temperature. A pressure sensor, coupled to the intake manifold, is used to measure intake pressure; and The controller stores executable instructions in non-transitory memory, which, when executed, cause the controller to: Before initial ignition, each of the plurality of cylinders is operated in compression heating mode for a certain number of engine cycles, while the engine is rotated via the electric motor. The number of engine cycles is determined based on the ambient temperature and the desired intake air temperature. Following the initial ignition, in response to the conditions for compression heating being met, a subset of the plurality of cylinders is operated in the compression heating mode and the remaining cylinders are operated in the combustion mode.

12. The system of claim 11, wherein the compression heating mode includes: The exhaust valve is deactivated while the intake valve remains active, fuel is not injected through the fuel injector, and no spark is provided through the spark plug; The combustion mode includes: maintaining the activity of the intake valve and the exhaust valve, supplying fuel via the fuel injector, and supplying the spark via the spark plug.

13. The system of claim 11, wherein the conditions for compression heating include: The engine temperature is below a threshold temperature, which corresponds to steady-state engine operation.

14. The system of claim 11, wherein the amount of fuel used for the initial ignition is determined based on the number of engine cycles, the ambient temperature, and the intake pressure.

15. The system of claim 11, wherein the number of cylinders in the subset of the plurality of cylinders is determined based on at least one of torque requirement and engine temperature.

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