Method and system for fuel injection control

Abstract

The present invention relates to methods and systems for fuel injection control, and methods and systems for adjusting direct fuel injection split ratio and injection timing in a variable compression ratio engine are disclosed. In one example, as the compression ratio increases, the split ratio of fuel injected during the intake stroke relative to the compression stroke is increased, wherein the start of the intake stroke injection is delayed and the start of the compression stroke injection is advanced. In addition, the direct fuel injection split ratio and injection timing can be adjusted in response to an indication of pre-ignition or knock.

Description

Technical Field

[0001] The present invention generally relates to methods and systems for controlling fuel injection in a variable compression ratio engine. Background Art

[0002] The compression ratio of an internal combustion engine is defined as the ratio of the cylinder volume when the piston is at the bottom dead center (BDC) in the cylinder to the cylinder volume when the piston is at the top dead center (TDC). In general, the higher the compression ratio, the higher the thermal efficiency of the internal combustion engine. This in turn leads to improved fuel economy and a higher ratio of the output energy to the input energy of the engine. In conventional engines, the compression ratio is fixed, and therefore, the engine efficiency cannot be optimized during different operating conditions in order to improve fuel economy and engine power performance. However, in a variable compression ratio (VCR) engine, the engine can be equipped with various mechanisms to mechanically change the volume ratio between the piston TDC and BDC, thereby allowing the compression ratio to change as the engine operating conditions change. As a non-limiting example, a VCR engine can be configured with a mechanical piston displacement changing mechanism (e.g., an eccentric wheel) that moves the piston closer to or further away from the cylinder head to thereby change the size of the combustion chamber. Other engines can mechanically change the cylinder head volume.

[0003] A VCR engine can be at least partially fueled by direct injection (hereinafter also referred to as "DI"), in which fuel is injected directly into the engine cylinder. The timing of the direct injection can be selected according to the crankshaft position and can be arranged for duration. In addition, the direct injection can be arranged during the intake stroke, the compression stroke, or a combination thereof, which is called split injection. In a conventional engine, the crankshaft position corresponds to a specific position of the piston relative to the cylinder head. However, in a VCR engine, since the position of the piston relative to the cylinder head can be changed based on the compression ratio, the actual injection timing can be different from the expected injection timing if selected based on the crankshaft position. For example, during the intake stroke when the piston is moving downward, the piston will be higher in the cylinder bore at a higher compression ratio relative to a lower compression ratio, and therefore, for two compression ratios, direct injection at the same crankshaft position will result in different actual injection timings. If the piston is close to the fuel injector when fuel injection occurs, more fuel can adhere to the piston, resulting in increased particulate matter emissions.

[0004] Kurashima et al. in US9,291,108 show an example method for adjusting direct fuel injection based on the compression ratio in a VCR engine. Therein, the fuel is injected as an intake stroke direct injection or a compression stroke direct injection. When the intake stroke injection is applied, the intake stroke injection timing is delayed as the compression ratio increases. Otherwise, if the compression stroke injection is applied, the compression stroke injection timing is advanced as the compression ratio increases. In addition, as the compression ratio increases, the compression stroke injection is divided into a greater number of segmented injections. Therefore, the injection period of each injection is shortened, reducing the penetration of the fuel spray and thereby reducing emissions. Summary of the invention

[0005] However, the inventors herein have recognized that further improvements in combustion performance can be achieved by utilizing different vaporization properties of the injected fuel when the engine is operated at different compression ratios. For example, the fuel can be vaporized more easily in the compression stroke, requiring less fuel mass to be delivered. In addition, combustion stability is improved at higher compression ratios. The different fuel vaporization properties can be further exploited under the different charge cooling effects achieved by injecting the fuel in the intake stroke relative to the compression stroke to reduce the propensity for abnormal combustion events, such as can occur due to extended engine operation in higher compression ratios. In addition, at higher compression ratios, fewer compression stroke injections can be used because the smaller cylinder volume at TDC relative to the smaller compression ratio produces a sufficiently rich air-fuel ratio near the spark plug to promote combustion.

[0006] In one example, the performance of a VCR engine can be improved by a method for an engine, the method comprising: actuating a variable compression ratio mechanism of a cylinder to provide a compression ratio selected based on engine operating conditions; and adjusting the amount of fuel injected directly into the cylinder during an intake stroke relative to a compression stroke based on the selected compression ratio. In this way, fuel can be delivered in a split injection manner during the intake stroke and the compression stroke, wherein the split ratio is adjusted for a given compression ratio, thereby improving fuel vaporization and combustion stability.

[0007] As an example, the compression ratio of the engine operation and the total fuel mass to be delivered can be selected based on the engine operating conditions, including engine speed-load and operator torque demand. Based on the selected compression ratio, the variable compression ratio mechanism can be actuated to change the piston clearance volume. In addition, the total fuel mass can be delivered in a segmented direct injection manner, wherein the first portion of the total fuel mass is delivered in the intake stroke, and the second remaining portion of the total fuel mass is delivered in the compression stroke. As the compression ratio increases, the segment ratio of the first intake stroke portion to the second compression stroke portion can be changed so that a larger portion of the total fuel mass is delivered in the intake stroke. In this article, the fuel mass delivered in the compression stroke can be reduced to take advantage of the improved vaporization of the fuel injected at a higher compression ratio in the compression stroke. At the same time, by delivering a larger fuel mass in the intake stroke when operating at a higher compression ratio, the increased charge cooling effect of the intake stroke injection can be used to reduce the tendency of abnormal combustion events (such as knock and pre-ignition) when operating at a higher compression ratio. In addition, multiple short duration intake stroke injections can be used to reduce fuel penetration, especially when tumble is highest, thereby avoiding impact on the cylinder wall and the top of the piston, and thereby reducing soot formation. The split ratio can be further adjusted based on the alcohol content or octane number of the injected fuel, such as by further reducing the portion of fuel delivered in the compression stroke as the alcohol content of the fuel increases. In addition to adjusting the fuel split ratio, the timing of the injection can also be adjusted, such as by delaying the timing start of the intake stroke injection while advancing the timing start of the compression stroke injection as the compression ratio increases. In addition, each of the intake stroke injection and the compression stroke injection can be divided into multiple injections.

[0008] In this way, the fuel injection distribution map (including fuel split ratio, injection timing and number of injections) can be adjusted based on the selected compression ratio to improve engine performance. The technical effect of reducing the mass of fuel injected in the compression stroke as the compression ratio increases while correspondingly increasing the mass of fuel injected in the intake stroke is that the increased fuel vaporization at a higher compression ratio in the compression stroke can be used to improve combustion stability. At the same time, the higher charge cooling effect of the intake stroke fuel injection can be used to reduce the incidence of knock and pre-ignition. By reducing the tendency of abnormal combustion, fuel economy is improved due to the reduced need for spark retardation or cylinder enrichment, and engine component life is extended. In addition, the engine can run for a longer duration at a more fuel-efficient compression ratio. By adjusting the injection timing based on the compression ratio, while taking into account the properties of the VCR mechanism that provides the selected compression ratio, the fuel can be injected at the optimal piston height in the cylinder, thereby reducing fuel adhesion to the piston and thereby reducing particulate matter emissions.

[0009] It should be understood that the above summary is provided to introduce some concepts in a simplified form, which are further described in the detailed description. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the appended claims. Furthermore, the claimed subject matter is not limited to embodiments that address any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An example engine system configured with a variable compression ratio mechanism is illustrated.

[0011] Figure 2 An example method for adjusting direct fuel injection split ratio and timing based on a selected compression ratio in a variable compression ratio engine is shown.

[0012] Figure 3 An example method for further adjusting direct fuel injection split ratio and timing in response to an indication of abnormal combustion in a variable compression ratio engine is shown.

[0013] Figure 4 is an example graph illustrating the relationship between cylinder compression ratio and the proportion of fuel injected during the intake stroke and the compression stroke.

[0014] Figure 5 is an example graph illustrating how fuel injection timing is adjusted with respect to crank angle for high compression ratio and low compression ratio engines.

[0015] Figure 6 Depicted are examples of predictions of compression ratio and fuel split ratio adjustments during engine operation. DETAILED DESCRIPTION

[0016] The following description relates to a method for adjusting an engine system equipped with a variable compression ratio (VCR) mechanism, such as Figure 1 The system and method of fuel direct injection split ratio and injection timing in an example engine system of . By actuating the VCR mechanism, the position of the piston in the cylinder of the engine and thus the compression ratio of the engine can be changed, thereby allowing for improvements in thermal efficiency. The controller can be configured to execute a control program (such as Figure 2 ) to change the fuel split ratio and injection timing based on the compression ratio of the engine, such as at Figure 4 and Figure 5 In response to an indication of abnormal combustion (such as knock or pre-ignition), the controller may perform mitigation measures, for example, based on Figure 3 The method prevents further abnormal combustion. Figure 6An exemplary engine operation utilizing compression ratio, fuel split ratio, and fuel injection timing adjustments is shown in FIG. In this way, injection timing and amount can be optimized for a given compression ratio, thereby increasing combustion stability and maximizing engine efficiency over a range of engine operating conditions.

[0017] Figure 1 An example embodiment of a combustion chamber (also referred to herein as a "cylinder") 14 of an internal combustion engine 10 is described, which may be included in a passenger vehicle. Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder 14 of engine 10 may include combustion chamber walls 136 with piston 138 disposed therein. Piston 138 may be coupled to a crankshaft 140 such that reciprocating motion of the piston is converted into rotational motion of the crankshaft. Crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Additionally, a starter motor may be coupled to crankshaft 140 via a flywheel to enable a starting operation of engine 10.

[0018] The engine 10 may be configured as a VCR engine, in which the compression ratio (CR) of each cylinder - the ratio of the cylinder volume when the piston is at the bottom dead center (BDC) to the cylinder volume when the piston is at the top dead center (TDC) - can be mechanically changed. The CR of the engine may be changed by actuating a VCR mechanism 194 via a VCR actuator 192. In some example embodiments, the CR may be changed between a first lower CR (where the ratio of the cylinder volume when the piston is at BDC to the cylinder volume when the piston is at TDC is smaller) and a second higher CR (where the ratio is higher). In other example embodiments, there may be a predetermined number of step compression ratios between the first lower CR and the second higher CR. In addition, the CR may be continuously variable between a first lower CR and a second higher CR (to any CR between the two).

[0019] In the depicted example, VCR mechanism 194 is coupled to piston 138 so that the VCR mechanism can change the piston TDC position. For example, piston 138 can be coupled to crankshaft 140 via VCR mechanism 194, which can be a piston position changing mechanism that moves the piston closer to or further away from the cylinder head, thereby changing the position of the piston and thereby changing the size of combustion chamber 14. Position sensor 196 can be coupled to VCR mechanism 194 and can be configured to provide feedback to controller 12 regarding the position of the VCR mechanism 194 (and thus the CR) of the cylinder.

[0020] In one example, changing the position of the piston in the combustion chamber also changes the relative displacement of the piston in the cylinder. The piston position changing VCR mechanism can be coupled to a conventional crankshaft system (cranktrain) or an unconventional crankshaft system. Non-limiting examples of unconventional crankshaft systems that can be coupled with a VCR mechanism include variable distance overhead crankshafts (head crankshafts) and variable motion length crankshafts. In one example, the crankshaft 140 can be configured as an eccentric shaft. In another example, the eccentric shaft can be coupled to a piston pin or in the area of ​​the piston pin, wherein the eccentric shaft changes the position of the piston in the combustion chamber. The movement of the eccentric shaft can be controlled by the oil passage of the piston rod.

[0021] It should be appreciated that other VCR mechanisms that mechanically change the compression ratio may be used. For example, the CR of the engine may be changed via a VCR mechanism that changes the cylinder head volume (i.e., the clearance volume in the cylinder head). In another example, the VCR mechanism may include a hydraulic pressure reaction piston, an air pressure reaction piston, or a mechanical reaction piston. In addition, the VCR mechanism may include a multi-link mechanism, a bent rod mechanism, or other VCR mechanization structures.

[0022] It should be appreciated that as used herein, a VCR engine can be configured to adjust the CR of the engine via mechanical adjustments that change piston position or cylinder head volume. Thus, a VCR mechanism does not include CR adjustments that are achieved via adjustments to valve timing or cam timing.

[0023] By adjusting the position of the piston in the cylinder, the effective (static) compression ratio of the engine (e.g., the difference between the cylinder volume at TDC relative to BDC) can be changed. In one example, reducing the compression ratio includes reducing the displacement of the piston in the combustion chamber by increasing the distance between the top of the piston and the cylinder head. For example, the engine can be operated with a first lower compression ratio by sending a signal to the VCR actuator 192 by the controller to actuate the VCR mechanism 194 to a first position where the piston has a smaller effective displacement in the combustion chamber. As another example, the engine can be operated with a second higher compression ratio by sending a signal to the VCR actuator 192 by the controller to actuate the VCR mechanism 194 to a second position where the piston has a larger effective displacement in the combustion chamber. The change in the engine compression ratio can be advantageously used to improve fuel economy. For example, a higher compression ratio can be used to improve fuel economy at light engine loads to medium engine loads until the spark delay from early knocking damages the fuel economy. The engine can then be switched to a lower compression ratio, thereby trading off thermal efficiency for combustion phasing efficiency. The continuous VCR system can continuously optimize combustion phasing and thermal efficiency to provide the best compression ratio between the upper compression ratio limit and the lower compression ratio limit under given operating conditions.

[0024] Return to Figure 1 Cylinder 14 may receive intake air via a series of intake passages 142, 144, and 146. In addition to cylinder 14, intake passage 146 may also communicate with other cylinders of engine 10. In some embodiments, one or more intake passages may include a boost device, such as a turbocharger or a supercharger. For example, Figure 1 Engine 10 is shown configured with a turbocharger including a compressor 174 arranged between intake passages 142 and 144, and an exhaust turbine 176 arranged along exhaust passage 148. As shown, compressor 174 may be at least partially powered by exhaust turbine 176 via shaft 180. However, in other examples, such as where engine 10 is configured with a supercharger, exhaust turbine 176 may be selectively omitted and compressor 174 may instead be powered by mechanical input from a motor of the engine.

[0025] A throttle 20 including a throttle plate 164 may be provided between intake passages 144 and 146 to vary the intake flow rate and / or intake pressure provided to the engine cylinders. For example, throttle 20 may be provided downstream of compressor 174 (e.g., at Figure 1 ), or may alternatively be provided upstream of compressor 174.

[0026] Exhaust passage 148 may receive exhaust gas from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of emission control device 178. Exhaust gas sensor 128 may be any suitable sensor for providing an indication of exhaust air-fuel ratio (AFR), such as a linear oxygen sensor or a UEGO sensor (universal or wide range exhaust gas oxygen sensor), a two-state oxygen sensor or an EGO sensor (as described), a HEGO (heated EGO) sensor, a NOx sensor, an HC sensor, or a CO sensor. Emission control device 178 may be a three way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof.

[0027] Exhaust temperature may be estimated by one or more temperature sensors (not shown) located in exhaust passage 148. Alternatively, exhaust temperature may be inferred based on engine operating conditions, such as engine speed, engine load, AFR, spark timing, etc. Further, exhaust temperature may be determined based on one or more exhaust oxygen sensors 128. It will be appreciated that, alternatively, exhaust temperature may be estimated by any combination of the temperature estimation methods listed herein.

[0028] 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 one intake poppet valve 150 and one exhaust poppet valve 156 located at an upper region of cylinder 14. In some embodiments, each cylinder of engine 10 (including cylinder 14) may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder.

[0029] The intake valve 150 can be controlled by the controller 12 through the cam actuation of the cam actuation system 151. Similarly, the exhaust valve 156 can be controlled by the controller 12 through the cam actuation system 153. The cam actuation systems 151 and 153 can each include one or more cams, and can use one or more of the cam profile switching (CPS) system, the variable cam timing (VCT) system, the variable valve timing (VVT) system, and / or the variable valve lift (VVL) system that can be operated by the controller 12 to change the valve operation. The positions of the intake valve 150 and the exhaust valve 156 can be determined by valve position sensors 155 and 157, respectively. In an alternative embodiment, the intake valve and / or the exhaust valve can be controlled by electric valve actuation. For example, the cylinder 14 can alternatively include an intake valve controlled by electric valve actuation and an exhaust valve controlled by cam actuation including a CPS system and / or a VCT system. In other embodiments, 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.

[0030] Cylinder 14 can have an associated compression ratio, which, as described above, is the ratio of volume when piston 138 is at BDC to when it is at TDC. Typically, the compression ratio is in the range of 9:1 to 10:1. However, in some examples using different fuels, the compression ratio can be increased. For example, this can occur when using a higher octane fuel or a fuel with a higher potential enthalpy. If direct injection is used, the compression ratio can also be increased due to its effect on engine knock. The compression ratio can also be changed based on driver demand via adjustment of the VCR actuator 192 that actuates the VCR mechanism 194 to change the effective position of the piston 138 within the combustion chamber 14. The compression ratio can be inferred based on feedback from the sensor 196 regarding the position of the VCR mechanism 194.

[0031] In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Under select operating modes, ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 in response to spark advance signal SA from controller 12. However, in some embodiments, spark plug 192 may be omitted, such as where engine 10 may initiate combustion via auto-ignition or fuel injection, as is the case with some diesel engines.

[0032] In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors for providing fuel into the cylinder. As a non-limiting example, cylinder 14 is shown as including one fuel injector 166. Fuel injector 166 is shown coupled directly to cylinder 14 for injecting fuel directly into cylinder 14 in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection ("DI") of fuel into combustion chamber 14. Although Figure 1 Injector 166 is shown as a side injector, but injector 166 can also be located above the piston, such as near the position of spark plug 192. When the engine is operated with alcohol-based fuel, due to the lower volatility of some alcohol-based fuels, such a position can improve mixing and combustion. Alternatively, the injector can be arranged at the top and near the intake valve to improve mixing. Fuel can be delivered to fuel injector 166 from a high-pressure fuel system 8, which may include one or more fuel tanks, fuel pumps and fuel rails. Alternatively, the fuel can be delivered by a single-stage fuel pump at a lower pressure, and the timing of direct fuel injection in this case can be more restricted during the compression stroke than when using a high-pressure fuel system. In addition, although not shown, one or more fuel tanks may have a pressure transducer that provides a signal to controller 12. It should be appreciated that in an alternative embodiment, injector 166 may be an intake port injector that provides fuel to the intake port upstream of cylinder 14.

[0033] It should also be appreciated that although the described embodiments illustrate the engine operating by injecting fuel via a single direct injector; in alternative embodiments, the engine may be operated by using two or more injectors (e.g., a direct injector and an intake port injector for each cylinder, or two direct injectors / two intake port injectors for each cylinder, etc.) and varying the relative injection amounts from each injector into the cylinder.

[0034] During a single cycle of the cylinder, fuel may be delivered to the cylinder by the injector. In addition, the distribution and / or relative amount of fuel delivered from the injector may vary with operating conditions. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. Multiple injections may be performed during the compression stroke, the intake stroke, or any suitable combination thereof in so-called split injection. For example, as the compression ratio increases, the split ratio of the intake stroke injection to the compression stroke injection may increase, as described with respect to FIG. Figure 2 and Figure 4 Further described. Moreover, fuel may be injected during the cycle to adjust the air-fuel ratio (AFR) of the combustion. For example, fuel may be injected to provide a stoichiometric AFR. An AFR sensor may be included to provide an estimate of the in-cylinder AFR. In one example, the AFR sensor may be an exhaust gas sensor, such as an EGO sensor 128. By measuring the amount of oxygen in the exhaust gas (a lean mixture has a higher amount of oxygen and a rich mixture has a lower amount of oxygen), the sensor may determine the AFR. Thus, the AFR may be provided as a lambda (λ) value, which is the ratio of the determined AFR to the stoichiometric AFR of a given mixture. Thus, a λ value of 1.0 represents a stoichiometric mixture (e.g., an AFR at which a complete combustion reaction occurs), while a λ value of less than 1.0 represents a richer than stoichiometric mixture and a λ value of greater than 1.0 represents a leaner than stoichiometric mixture.

[0035] As described above, Figure 1 Only one cylinder of a multi-cylinder engine is shown. Therefore, each cylinder may similarly include its own set of intake / exhaust valves, (one or more) fuel injectors, (one or more) spark plugs, etc.

[0036] The fuel tanks in the fuel system 8 may contain fuels having different fuel properties, such as different fuel compositions. These differences may include different alcohol content, different octane ratings, different heats of vaporization, different fuel blends, and / or combinations thereof, etc.

[0037] The engine 10 may further include a knock sensor 90 coupled to each cylinder 14 for identifying abnormal cylinder combustion events. In an alternative embodiment, one or more knock sensors 90 may be coupled to a selected cylinder block location. The knock sensor may be an accelerometer on the cylinder block or an ion sensor configured in the spark plug of each cylinder. The output of the knock sensor may be combined with the output of the crankshaft acceleration sensor to indicate an abnormal combustion event in the cylinder. In one example, based on the output of the knock sensor 90 in one or more defined windows (e.g., a crank angle timing window), abnormal combustion caused by one or more of knock and pre-ignition may be identified and distinguished. For example, knock may be identified in response to a knock sensor output obtained in a knock window being higher than a knock threshold, and pre-ignition may be identified in response to a knock sensor output obtained in a pre-ignition window being higher than a pre-ignition threshold. For example, the pre-ignition threshold may be higher than the knock threshold, and the pre-ignition window may be earlier than the knock window. In addition, once identified and distinguished, the abnormal combustion event may be resolved accordingly. For example, knock can be addressed by adjusting fuel split ratio and injection timing and / or retarding spark timing, while pre-ignition can be addressed by increasing the AFR for rich combustion and / or reducing the compression ratio, as described in relation to Figure 3 Further described.

[0038] Return to Figure 1 , the controller 12 is Figure 1 10 is shown as a microcomputer, including a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values ​​shown in this specific example as a read-only memory chip 110, a random access memory 112, a keep alive memory 114, and a data bus. In addition to those signals previously discussed, the controller 12 may also receive various signals from sensors coupled to the engine 10, including a measurement of an intake mass air flow meter (MAF) from a mass air flow sensor 122, an engine coolant temperature (ECT) from a temperature sensor 116 coupled to a cooling sleeve 118, a surface ignition sensing signal (PIP) from a Hall effect sensor 120 (or other type) coupled to the crankshaft 140, a throttle position (TP) from a throttle position sensor, an absolute manifold pressure signal (MAP) from a MAP sensor 124, a cylinder AFR from an EGO sensor 128, abnormal combustion from a knock sensor 90 and a crankshaft acceleration sensor, and a VCR mechanism position from a position sensor 196. Engine speed signal RPM may be generated by controller 12 based on signal PIP. Signal MAP from MAP sensor 124 may be used to provide an indication of vacuum, or pressure, in the intake manifold. Controller 12 may generate signal MAP based on signal PIP. Figure 1The various sensors receive signals and take actions based on the received signals and the instructions stored in the memory of the controller. Figure 1 The controller may adjust the engine operation by using various actuators. For example, based on engine speed and load, the controller may adjust the compression ratio of the engine by sending a signal to a VCR actuator 192, which actuates a VCR mechanism 194 to mechanically move the piston closer to or further away from the cylinder head, thereby changing the volume of the combustion chamber.

[0039] Non-transitory storage medium read-only memory 110 can be programmed with computer readable data representing instructions executable by microprocessor unit 106 for performing the methods described below as well as other variants that are anticipated but not specifically listed.

[0040] In this way, Figure 1 A system is provided, comprising: an engine having a cylinder; a variable compression ratio mechanism for mechanically varying a piston position within the cylinder; a position sensor coupled to the variable compression ratio mechanism; a spark plug for providing a spark to the cylinder; a fuel injector for injecting fuel directly into the cylinder; a knock sensor; and a controller configured with computer-readable instructions stored on a non-transitory memory for the following operations: actuating the variable compression ratio mechanism to provide a compression ratio selected based on engine operating conditions; and operating in one of a first mode and a second mode based on the selected compression ratio, the first mode having a higher split ratio of fuel injected directly during an intake stroke to fuel injected directly during a compression stroke, and the second mode having a lower split ratio of fuel injected directly during an intake stroke to fuel injected directly during a compression stroke. As an example, the first mode may be selected when the compression ratio is high, and the second mode may be selected when the compression ratio is low. The higher intake stroke direct injected fuel to compression stroke direct injected fuel split ratio may include delivering a greater portion of fuel during the intake stroke and a smaller portion of fuel during the compression stroke relative to the lower intake stroke direct injected fuel to compression stroke split ratio. As another example, for the first operating mode, fuel may be directly injected later during the intake stroke and injected earlier during the compression stroke relative to the second operating mode. As a further example, the number of intake stroke direct injections performed in the first mode may be higher than the number of intake stroke direct injections performed in the second mode. As yet another example, the number of compression stroke direct injections performed in the first mode may be lower than the number of compression stroke direct injections performed in the second mode.

[0041] Now turn to Figure 2 , shows a method for adjusting a VCR engine (such as Figure 1 An example method 200 is provided for determining a compression ratio of an engine 10 and adjusting fuel injection timing and split ratio based on the compression ratio. For example, the ratio of the amount of fuel injected during the intake stroke to the amount of fuel injected during the compression stroke may be adjusted. Instructions for executing method 200 and the remaining methods included herein may be provided by a controller (e.g., Figure 1 The controller 12) is based on instructions stored in the memory of the controller and in conjunction with sensors from the engine system (such as those described above with reference to Figure 1 The controller may use an engine actuator of the engine system to adjust the engine operation according to the method described below.

[0042] At 202, method 200 includes estimating and / or measuring engine operating conditions. Engine operating conditions may include, for example (e.g., as based on the output of a pedal position sensor coupled to an operator pedal) driver power demand; ambient temperature, pressure, and humidity; engine temperature; manifold pressure (MAP); manifold air flow (MAF); catalyst temperature; intake air temperature; boost level; fuel octane rating of fuel available in a fuel tank; etc.

[0043] At 204, method 200 includes selecting a compression ratio for operating the engine based on the estimated engine operating conditions. The engine may be configured with a VCR mechanism (e.g., Figure 1 VCR mechanism 194). The VCR mechanism can achieve this operation by mechanically changing the position of the piston in the cylinder in response to a command received from the engine controller. Therefore, operating the engine at a first higher compression ratio may include operating the engine in a first mode, and operating the engine at a second lower compression ratio may include operating the engine in a second mode. Alternatively, multiple compression ratios between the first compression ratio and the second compression ratio may be feasible. The controller can compare the fuel efficiency of the engine at each compression ratio under a given driver power demand, and select the compression ratio that provides the highest fuel efficiency. For example, the controller can compare the fuel efficiency at each compression ratio by comparing the brake specific fuel consumption (BSFC) of the engine at each compression ratio. The fuel efficiency of the engine at each compression ratio can each be determined via a table, map, algorithm and / or equation stored according to operating conditions (e.g., engine speed, torque, temperature, humidity, inferred fuel octane number, etc.).

[0044] At 206, method 200 includes actuating the VCR mechanism to provide the selected compression ratio. For example, the controller may provide a VCR actuator (e.g., Figure 1 The controller may send a signal to a VCR actuator 192 to actuate the mechanism to a position that provides a selected compression ratio. In one example, the controller may send a signal to actuate the VCR mechanism to a higher compression ratio setting at low to medium engine speeds and loads. As another example, the controller may send a signal to actuate the VCR mechanism to a lower compression ratio setting at medium to high engine speeds and loads.

[0045] At 208, method 200 includes adjusting the fuel split ratio based on the selected compression ratio. For example, during the compression stroke, due to the smaller volume at TDC for high compression ratios, less fuel is consumed at high compression ratios than at low compression ratios to make the AFR rich enough for combustion near the spark plug. Therefore, the AFR near the spark plug can be controlled using less fuel at high compression ratios. In addition, the fuel can be better vaporized at high compression ratios. As another example, injecting less fuel at high compression ratios during the compression stroke can help avoid piston shock and the resulting smoke and soot formation. Therefore, at higher compression ratios, the amount of fuel injected during the compression stroke can be reduced relative to the amount of fuel injected during the intake stroke. For example, the controller can refer to a lookup table, a map, an algorithm and / or an equation to output the fuel split ratio for a given compression ratio input. Thus, when the engine is operated in the first mode, a higher split ratio of fuel injected directly during the intake stroke to fuel injected directly during the compression stroke may be used, and when the engine is operated in the second mode, a lower split ratio of fuel injected directly during the intake stroke to fuel injected directly during the compression stroke may be used. The controller may further consider the alcohol content of the fuel in adjusting the fuel split ratio. For example, as the alcohol content of the fuel increases, the amount of fuel injected during the compression stroke may be further reduced due to increased alcohol volatility.

[0046] In addition to updating the split ratio, the number of injections of the split injection may also be adjusted. For example, the total number of injections may increase as the compression ratio increases, especially at the highest tumble conditions. This includes delivering an increased intake stroke injection with an adjusted split ratio along with multiple shorter intake stroke injections. Additionally, a reduced compression stroke injection with an adjusted split ratio may also be delivered along with multiple shorter compression stroke injections. In one example, after adjusting the split ratio, the number of intake stroke injections may be higher than the number of compression stroke injections. Multiple shorter intake stroke injections and compression stroke injections are less likely to sufficiently penetrate the air-fuel mixture, thereby reducing impact on the cylinder wall or piston crown, reducing soot formation.

[0047] It will be appreciated that in a further example, the engine controller may maintain the fuel split ratio while adjusting the number of intake stroke injections and compression stroke injections based on the compression ratio selection. For example, as the compression ratio increases, the number of intake stroke injections and compression stroke injections may increase, each of which has a pulse width below a threshold pulse width, while the split ratio is maintained.

[0048] Turn briefly Figure 4 , shows an example graph 400 illustrating the relationship between the compression ratio of an engine and the split ratio of fuel delivered via direct injection. The X-axis represents the compression ratio, where the values ​​increase from left to right, and the Y-axis represents the percentage of fuel injected, where the values ​​increase from bottom to top. Intake stroke fuel injection is shown in curve 402, and compression stroke fuel injection is shown in curve 404.

[0049] As the compression ratio increases, the split ratio of the intake stroke injection to the compression stroke injection increases. For example, at the lowest compression ratio, 70% of the total fuel amount is injected during the intake stroke (curve 402), and 30% of the total fuel amount is injected during the compression stroke (curve 404). At the highest compression ratio, 90% of the total fuel amount is injected during the intake stroke (curve 402), and 10% of the total fuel amount is injected during the compression stroke (curve 404). Figure 4 In the example of , curves 402 and 404 are linear. However, in other examples, curves 402 and 404 can be non-linear curves, such as exponential curves, with a general trend that intake stroke fuel injection (curve 402) increases as compression ratio increases and compression stroke fuel injection (curve 404) decreases as compression ratio increases, where the total fuel mass injected at a given compression ratio within the engine cycle (e.g., the sum of the percentage of fuel injected during the intake stroke and the percentage of fuel injected during the compression stroke) is equal to 100%. Note that the split injection ratio does not limit the amount of fuel injected, which can be calculated based on engine operating conditions to achieve a desired AFR. In addition, the octane number and alcohol content of the fuel can affect the shape of curves 402 and 404.

[0050] Return to Figure 2, at 210, method 200 includes adjusting the fuel injection timing based on the selected compression ratio. For example, as the compression ratio increases, the intake stroke injection timing (e.g., the start of injection) can be delayed, and the compression stroke injection timing can be advanced. The number of crank angles by which the start of injection during each stroke is advanced or delayed can be related to the relative position of the piston in the cylinder, which can be defined by the position of the VCR mechanism. For example, the controller can refer to a lookup table in which the VCR mechanism position (or the selected compression ratio) is used as an input and the intake stroke injection timing and the compression stroke injection timing are used as outputs. In addition, the injection timing can be affected by the type of VCR mechanism used (e.g., a mechanism that changes the piston position versus a mechanism that moves the cylinder head). For example, if the VCR mechanism includes a pressure-reacting piston, the intake stroke injection timing and the compression stroke injection timing may not be adjusted based on the compression ratio because the piston deflection occurs after both fuel injection and combustion have ended. As another example, since the alignment of the fuel injector changes as the head is tilted, a VCR mechanism using a tilted head can utilize alternative injection timing adjustments. By varying the fuel injection timing based on the compression ratio, direct fuel injection can be initiated at a specific piston position rather than a set crank angle.

[0051] Turn briefly Figure 5 , an example graph 500 depicting how to change the direct fuel injection timing and split ratio based on the engine compression ratio is shown. A fuel injection command for operating the engine at a high compression ratio (HCR) in the first mode is shown at 502, and a fuel injection command for operating the engine at a low compression ratio (LCR) in the second mode is shown at 504. The Y-axis of each curve represents the marked parameter, where the value increases from the bottom to the top. All of the above X-axes represent the engine position in crank angle degrees, where each stroke in each combustion cycle is marked. For a given crank angle, as the engine compression ratio increases, the piston position becomes higher (e.g., compared to the HCR engine, the LCR engine has a reduced piston displacement). Three combustion cycles are shown to illustrate three example fueling strategies, where "X" marks the spark timing (e.g., before the TDC of the compression stroke). For example, in combustion cycle 1, for a total of two injections, one fuel injection is performed during the intake stroke, and one fuel injection is performed during the compression stroke. In combustion cycle 2, a total of four injections are split between the intake stroke and the compression stroke. In combustion cycle 3, the number of injections performed during each stroke is increased for the HCR engine compared to the LCR engine. Thus, for each combustion cycle, a first portion of the total fuel mass is delivered in the intake stroke and a second remaining portion of the total fuel mass is delivered in the compression stroke, wherein the number of injections delivering the first portion and the second portion is varied.

[0052] During the intake stroke of combustion cycle 1, a greater mass of fuel is injected (e.g., using a greater FPW) for the engine operating at HCR (curve 502) than for the engine operating at LCR (curve 504) due to the better fuel vaporization achieved at a higher compression ratio. Due to the reduced piston displacement of the LCR engine compared to the HCR engine, as the piston travels from TDC to BDC, the piston of the LCR engine can reach a specific cylinder height at a smaller number of crank angles than the HCR engine. Therefore, for the intake stroke, the start of injection for the LCR engine (curve 504) is earlier than the start of injection for the HCR engine (curve 502).

[0053] During the compression stroke of combustion cycle 1, more fuel is injected for the LCR engine (curve 504) than the HCR engine (curve 502) so that the same total fuel mass is injected in each engine before spark ignition. In addition, due to the reduced piston displacement of the LCR engine compared to the HCR engine, it takes more crank angle degrees for the piston in the LCR engine to reach the same position in the cylinder as the piston in the HCR engine as the piston travels from BDC to TDC. Therefore, for the compression stroke, the start of injection for the HCR engine (curve 502) is earlier than the start of injection for the LCR engine (curve 504).

[0054] During combustion cycle 2, the same total fuel amount as in combustion cycle 1 is injected, the segment ratio remains the same, and for both HCR engines and LCR engines, the start of injection occurs at the same engine position as in combustion cycle 1. However, fuel is delivered via multiple injections during each stroke. Performing a series of shorter duration injections can promote fuel vaporization because each injection delivers less fuel. In addition, fuel penetration can be reduced by delivering the same amount of fuel through multiple shorter duration bursts, which in turn can reduce fuel adhesion to the piston. In the example of combustion cycle 2, for HRC engines (curve 502), intake stroke injection is segmented into three shorter duration injections, while for LCR engines (curve 504), intake stroke injection is segmented into two shorter duration injections, and for LCR engines, compression stroke injection is segmented into two shorter duration injections. As shown, the amount of fuel delivered by each intake stroke injection or compression stroke injection can be consistent, wherein the predetermined duration elapses between each injection. However, in other examples, the amount of fuel injected per injection may be inconsistent and / or the duration between each injection may be distinct. It will be appreciated that in further examples, the engine calibration may be updated based on a particular engine design and VCR configuration.

[0055] During combustion cycle 3, the same total fuel amount is injected as in combustion cycles 1 and 2, the split ratio remains the same, and the start of injection occurs at the same engine location as in combustion cycles 1 and 2 for both the HCR engine and the LCR engine. As with combustion cycle 2, fuel is delivered via multiple injections during each stroke. However, during combustion cycle 3, the number of injections is adjusted based on the compression ratio, as described with respect to Figure 2 5. Instead of performing the same total number of injections for both the HCR engine and the LCR engine (e.g., as in combustion cycles 1 and 2), the same total number of injections is performed for both the HCR engine and the LCR engine as described above. While the fueling strategy for combustion cycle 3 remains the same for the LCR engine (curve 504) as for combustion cycle 2, the number of injections performed during both the intake stroke and the compression stroke is increased for the HCR engine (curve 502). In the example of combustion cycle 3, eight short intake stroke injections and two short compression stroke injections are performed for the HCR engine, further reducing fuel impingement on the cylinder wall or piston crown, and reducing soot formation.

[0056] Return to Figure 2 At 212, it is determined whether abnormal combustion is detected. For example, abnormal combustion may be based on a knock sensor (e.g. Figure 1 The knock sensor 90) and the output of the crankshaft acceleration sensor are detected. Figure 1 As described, abnormal combustion may be distinguished as knock in response to a knock sensor output obtained in a knock window being higher than a knock threshold, or may be distinguished as pre-ignition in response to a knock sensor output obtained in a pre-ignition window being higher than a pre-ignition threshold (which is higher than the knock threshold). The knock window for a cylinder may include a crank angle window after a spark event in the cylinder, and the pre-ignition window for a cylinder may include a crank angle window before a spark event in the cylinder. The knock window and the pre-ignition window may not overlap or may partially overlap.

[0057] If abnormal combustion is not detected, method 200 proceeds to 214 and includes maintaining engine settings. For example, the engine's compression ratio, fuel injection timing and amount, and spark timing can continue to be nominally adjusted based on engine operating conditions (including changing operator torque requirements and compression ratio selections). After 214, method 200 ends.

[0058] If abnormal combustion is detected, method 200 proceeds to 216 and includes executing mitigation measures based on the type of abnormal combustion, as will be described below with respect to Figure 3 For example, different mitigation measures may be performed in response to an indication of knock than in response to an indication of pre-ignition. After 216, method 200 ends.

[0059] In this way, Figure 2 A method is provided for adjusting the split ratio and direct injection timing of fuel based on the compression ratio of the engine. For example, due to increased fuel vaporization at higher compression ratios, the amount of fuel injected during the intake stroke relative to the compression stroke may increase as the compression ratio of the engine increases, as also described with respect to Figure 4 and Figure 5 Additionally, the start of injection during each stroke can be adjusted so that fuel is delivered at the same piston position within the cylinder, which can vary relative to the crankshaft position based on the compression ratio, as also described with respect to Figure 5 Descriptive.

[0060] Steering Figure 3 , an example method 300 for performing mitigation actions in response to an indication of abnormal combustion in a VCR engine is provided, which may reduce the propensity for subsequent abnormal combustion events. For example, the method 300 may be used as Figure 2 A portion of method 200 (eg, at 216) is performed.

[0061] Method 300 begins at 302 and includes determining whether pre-ignition is detected. Figure 1 As described, in response to a knock sensor (e.g., Figure 1 The output of the knock sensor 90) is higher than the pre-ignition threshold, and pre-ignition can be detected.

[0062] When method 300 is executed in response to an indication of abnormal combustion, if pre-ignition is not detected, it can be assumed that knock is detected. Therefore, if pre-ignition is not detected at 302, method 300 proceeds to 304 and includes adjusting the fuel split ratio to increase the fraction of fuel injected during the intake stroke. That is, in response to the indication of knock, the split ratio of the fuel injected during the intake stroke and the compression stroke can be adjusted so that the injection ratio during the intake stroke is nominal for a given compression ratio (e.g., as in Figure 2 The increased amount of intake stroke injection is used to increase cylinder charge cooling, thereby reducing the occurrence of further knock. In one example, if the nominal split ratio for a given compression ratio is 90% intake injection and 10% compression injection, the split ratio can be adjusted to 95% intake injection and 5% compression injection. The degree to which the fraction of intake injection is increased can be determined based on the intensity and / or number of knock events, wherein the fraction of intake injection is further increased as the intensity and / or number of knock events increases.

[0063] At 306 , method 300 includes advancing the timing of intake stroke fuel injection. Since more fuel than nominal for a given compression ratio is delivered during the intake stroke, the start of injection may be advanced so that the injection is completed, for example, by a predetermined timing.

[0064] At 308, method 300 includes retarding spark timing. For example, spark timing may be retarded from a nominal timing set based on compression ratio and engine operating conditions. The nominal timing may be set by a controller (e.g., Figure 1 The controller 12) is selected by referencing a map, algorithm or lookup table with compression ratio (or VCR mechanism position), engine speed, intake air temperature, MAP, MAF and air-fuel ratio as inputs and spark timing as output. The controller can then retard the timing, for example, in response to an indication of knock (e.g., as determined at 302). The degree to which the spark timing is retarded can be determined based on the intensity and / or number of knock events, where the amount of spark retard from the nominal setting increases with the intensity and / or number of knock events until the spark retard usage limit is reached. In addition, when operating in a higher compression ratio, a greater amount of spark retard usage (and therefore a larger spark retard limit) can be tolerated, while when operating in a lower compression ratio, a lesser amount of spark retard usage (and therefore a smaller spark retard limit) can be tolerated. The limit can define the amount of spark retard, beyond which engine power loss, overheating tendency and high emissions may occur at the commanded compression ratio, and therefore the spark will not be further retarded from the limit.

[0065] Additionally, the amount of spark retard used may be adjusted based on the determined fuel split ratio. For example, by increasing the amount of fuel delivered during the intake stroke, the amount of spark retard required for knock mitigation may be reduced. After 308, method 300 ends.

[0066] Returning to 302, if pre-ignition is detected, method 300 proceeds to 310 and includes enriching the pre-ignited cylinder. Increasing the amount of fuel delivered to the pre-ignited cylinder relative to the amount of air (e.g., causing the cylinder to operate at an AFR richer than the stoichiometric ratio) results in a charge cooling effect that reduces the temperature within the pre-ignited cylinder. By cooling the pre-ignition cylinder, further occurrences of pre-ignition are mitigated. Because fuel enrichment can degrade fuel economy, degrade exhaust emissions, and result in a possible reduction in torque, (one or more) pre-ignition cylinders can be selectively enriched rather than enriching every cylinder of the engine. In addition, fuel enrichment can be performed over multiple engine cycles, after which the fuel fill can be returned to a nominal amount, as further described below.

[0067] At 312 , method 300 includes adjusting the split ratio to increase the fraction of intake stroke fuel injection. That is, the proportion of fuel delivered during the intake stroke is increased and the proportion of fuel delivered during the compression stroke is decreased compared to a nominal setting for the compression ratio of the engine, as described at 304 .

[0068] At 314, it is determined whether the compression ratio is at a threshold ratio. For example, the threshold ratio may refer to a minimum compression ratio that may be applied, below which engine performance may degrade. Additionally, the threshold ratio may be a hard limit defined by the VCR mechanism (e.g., due to a specific configuration of the piston on an eccentric shaft).

[0069] If the compression ratio is at the threshold, the method 300 proceeds to 316 and includes advancing the spark timing based on enrichment. For example, the spark timing may be advanced from the maximum brake torque (MBT) based on enrichment and further based on a bounded (BDL) spark limit at the current operating conditions. Specifically, it may be determined that significant charge cooling benefits may be achieved by enrichment, and the spark may be advanced (e.g., operated closer to MBT) to recover some of the torque loss due to cylinder operation at a richer than best torque richness (RBT). After 316, the method 300 ends.

[0070] If the compression ratio is not at the threshold at 314, the method 300 proceeds to 318 and includes reducing the compression ratio based on the pre-ignition history. For example, the engine pre-ignition count can be retrieved. The engine pre-ignition count can include the total pre-ignition count of the engine. In addition, the pre-ignition count of each cylinder can also be retrieved. Therefore, the pre-ignition count of the engine (or cylinder) can reflect its tendency to pre-ignite. Therefore, as the pre-ignition count increases, the probability of pre-ignition in the engine (or given cylinder) can be higher. Using the pre-ignition count, the compression ratio can be reduced (or cut) to the feedback level. Specifically, the compression ratio can be reduced from the nominal level for a given engine speed and load to the feedback level (lower than the nominal level), wherein the degree of reduction is based on the pre-ignition history. Therefore, as the pre-ignition count of the engine increases (and the tendency of the engine to pre-ignite increases), the feedback compression ratio level can be further reduced from the nominal compression ratio level. The reduction can be gradual, or alternatively, as the pre-ignition count increases by a threshold amount, the compression ratio can be (step by step) reduced by a predetermined amount.

[0071] In addition to determining the feedback compression ratio level, the piston displacement corresponding to the feedback compression ratio level can also be determined. In one example, the piston displacement corresponding to the feedback compression ratio can include less than a maximum piston displacement, where the piston moves closer (but not all the way closer) to the cylinder head in the combustion chamber. In other words, as the feedback compression ratio level decreases, the amount of space between the cylinder head and the final position of the piston (e.g., TDC) can be increased.

[0072] At 320, method 300 includes reducing the fueling amount and the fraction of intake stroke fuel injection. As the compression ratio is reduced, the likelihood of pre-ignition is also reduced. Therefore, fuel enrichment is no longer required to mitigate pre-ignition, and a nominal fuel amount for engine operating conditions, such as to achieve stoichiometric AFR, can be provided. In addition, the split ratio of the fuel can be adjusted for the reduced compression ratio, wherein the fraction of intake injection is correspondingly reduced (and the fraction of compression injection is increased). For example, the split ratio can be determined based on feedback compression ratio, such as with respect to Figure 2 (e.g., as described at 208). In addition, the injection timing may be adjusted based on the feedback compression ratio (e.g., as described at Figure 2 210 places).

[0073] At 322, method 300 includes determining whether pre-ignition continues to be detected even after pre-ignition mitigation enrichment is performed. If pre-ignition is detected, such as occurs when there is persistent pre-ignition, method 300 proceeds to 324 and includes further reducing the compression ratio, adjusting the injection timing and correspondingly reducing the fraction of intake stroke fuel injection. For example, since the displacement of the piston decreases as the compression ratio decreases, the intake stroke injection timing can be advanced and the compression stroke injection can be delayed compared to the previous higher compression ratio setting. In addition, due to the reduced fuel vaporization at a lower compression ratio, the amount of fuel injected during the compression stroke relative to the intake stroke can be increased. In one example, the compression ratio can be gradually reduced, wherein the fuel injection timing and the split ratio are adjusted accordingly for each reduced compression ratio until pre-ignition is no longer detected. After 324, method 300 ends.

[0074] If pre-ignition is not detected at 322, method 300 proceeds to 326 and includes gradually increasing the compression ratio, adjusting the injection timing, and increasing the fraction of intake stroke fuel injection accordingly. For example, since piston displacement increases as compression ratio increases, the intake stroke injection timing may be retarded and the compression stroke injection may be advanced compared to a previous lower compression ratio setting. Additionally, due to increased fuel vaporization at higher compression ratios, the amount of fuel injected during the intake stroke relative to the compression stroke may be increased. After 326, method 300 ends.

[0075] In this way, Figure 3 A method for performing mitigation measures is provided, including further adjusting fuel direct injection timing and split ratio in response to indications of abnormal combustion (such as knock and pre-ignition) in a VCR engine to reduce additional occurrences of abnormal combustion. Reducing the occurrence of knock and pre-ignition can help extend the life of engine components.

[0076] Now turn to Figure 6 , shows an example graph 600 of compression ratio and fuel split ratio adjustments during engine operation. Engine load is depicted in curve 602, knock signal is shown in curve 604, compression ratio (CR) is shown in curve 610, and fuel injection amount is depicted in curve 612. In addition, the knock signal is shown relative to a knock threshold (shown by dashed line 606) and a pre-ignition threshold (shown by dashed line 608). In addition, the fuel injection amount is divided into an amount delivered via direct injection via stroke (diagonal shaded area) and an amount delivered via compression stroke injection (unshaded area). For all of the above, the X-axis represents time, where time increases from left to right. The Y-axis of each curve represents the labeled parameter, where the value increases from bottom to top.

[0077] Prior to t1, in response to a lower operator torque demand and correspondingly lower engine load (plot 602), the engine is operated at a high compression ratio, as shown in plot 610. For example, the engine may be operated in a first mode in which the VCR mechanism (e.g., Figure 1 The position of the VCR mechanism 194 is actuated to a first position corresponding to a high compression ratio. The total amount of fuel injected within the engine cycle (curve 612) corresponds to the engine load (curve 602), wherein the amount of fuel increases as the engine load increases. As shown in curve 612, at a high compression ratio, a small portion (e.g., 10%) of the fuel is injected during the compression stroke (unshaded area), wherein the remainder (e.g., 90%) is delivered during the intake stroke (diagonal shaded area). Since the engine is running at a relatively low engine load, knock does not occur, as indicated by a knock signal (e.g., a knock sensor (such as Figure 1 The output of the knock sensor 90) is shown as being maintained below the knock threshold (dashed line 606).

[0078] Between t1 and t2, the engine load (curve 602) increases in response to operator demand, and the amount of fuel injected (curve 612) increases accordingly. The engine remains at a high compression ratio (curve 610). At higher engine loads at high compression ratios, knock occurs, as shown by the knock signal (curve 604) exceeding the knock threshold (dashed line 606). In response to the occurrence of knock, the fuel split ratio is adjusted to increase the fraction of fuel injected during the intake stroke and decrease the fraction of fuel injected during the compression stroke, as shown by the smaller proportion of compression stroke injection (unshaded area) of curve 612 between t1 and t2 compared to before t1. In addition, the start of the intake stroke injection can be advanced (not shown), and the spark timing can be retarded (not shown).

[0079] Beginning at t2, the engine load (curve 602) continues to increase in response to further increases in the operator pedal position. If the engine is maintained at a high compression ratio, the knock tendency of the engine will increase, resulting in a further need for spark retard. The spark retard fuel penalty will offset the fuel efficiency of the higher compression ratio. The engine is therefore transitioned to the second operating mode.

[0080] Between t2 and t3, the engine is operated in a second mode in which the VCR mechanism is actuated to a position corresponding to a low compression ratio (curve 610). The amount of fuel injected (curve 612) increases in response to the engine load, and the step ratio is adjusted. At low compression ratios, a higher proportion (e.g., 30%) of the fuel is injected during the compression stroke (unshaded area) than when the engine is operating at a high compression ratio (e.g., such as before t1). In addition, at low compression ratios, the tendency to knock is reduced, and the knock signal (curve 604) remains below the knock threshold (dashed line 606). In addition, compared to operating at a high compression ratio, the start of intake stroke injection is advanced, and the start of compression stroke injection is delayed, as shown with respect to Figure 5 shown.

[0081] At t3, in response to a decrease in engine load (curve 602), for example, due to an operator pressing the accelerator pedal, the engine is transitioned back to the first operating mode in which the engine is operated at a high compression ratio (curve 610). Accordingly, the VCR mechanism is actuated to a position corresponding to the high compression ratio. The fuel split ratio is adjusted so that the proportion of fuel injected during the intake stroke is increased and the proportion of fuel injected during the compression stroke is reduced compared to operation at a low compression ratio, as shown by the proportional reduction in the unshaded area of ​​the bar of curve 612 between t3 and t4. In addition, the state of the intake stroke injection is again advanced compared to operation at a low compression ratio, and the start of the compression stroke injection is delayed so as to maintain the injection timing relative to the piston position, as shown with respect to Figure 2 and Figure 5 Further described.

[0082] At t4, pre-ignition occurs, as shown by the knock signal (curve 604) exceeding a pre-ignition threshold (dashed line 608). For example, pre-ignition may occur due to increased in-cylinder temperature and pressure, which may be exacerbated by a high compression ratio. In response to the indication of pre-ignition, the pre-igniting cylinder is enriched, where the split ratio is adjusted to further increase the fraction of fuel delivered during the intake stroke (curve 612). For example, the fraction of fuel delivered during the intake stroke may be increased from 90% to 95%. After the first enrichment event, the compression ratio (curve 610) is gradually reduced until pre-ignition no longer occurs or the compression ratio reaches a threshold ratio, as shown with respect to Figure 3 When pre-ignition no longer occurs (e.g., before t5), such as for a stoichiometric AFR, the fuel amount (curve 612) is reduced to a nominal amount. Additionally, the fraction of fuel injected during the intake stroke is reduced, and the injection timing may be optimized for an actual (e.g., measured) compression ratio.

[0083] In response to no further indication of pre-ignition (e.g., no pre-ignition is detected for a threshold duration), the compression ratio may be gradually increased to provide a nominal compression ratio for a given engine operating condition (such as speed and load). Thus, after t5, the compression ratio (curve 610) is gradually increased to an intermediate compression ratio by actuating the VCR mechanism. After no further indication of pre-ignition, the compression ratio is further increased until the nominal compression ratio (e.g., high compression ratio) is reached. As the compression ratio is increased, the fraction of compression stroke injection is reduced, as shown by reducing the proportion of the unshaded area of ​​the bar of curve 612. Thus, the fuel injection timing and split ratio may be returned to, for example, Figure 4 and Figure 5 The nominal values ​​for a given compression ratio are depicted in the examples.

[0084] In this way, the direct fuel injection timing and split ratio can be optimized based on the compression ratio of the VCR engine. Since the piston displacement is different based on the compression ratio, adjusting the start of the injection relative to the crankshaft position ensures that the fuel is injected when the piston is at the appropriate distance from the cylinder head, thereby reducing the amount of fuel adhering to the piston crown and, in turn, reducing emissions. In addition, the fuel has different vaporization properties at different compression ratios, with higher compression ratios increasing fuel vaporization. Thus, during the compression stroke, less fuel can be injected at a higher compression ratio than at a lower compression ratio. By optimizing the split ratio of the directly injected fuel based on the compression ratio, good combustion stability can be maintained. In addition, in the event of knock or pre-ignition, the fuel injection timing and split ratio can be further adjusted to extend the life of engine components by reducing further occurrences of abnormal combustion.

[0085] As an example, a method for an engine includes: actuating a variable compression ratio mechanism of a cylinder to provide a compression ratio selected based on engine operating conditions; and adjusting the amount of fuel injected directly into the cylinder in an intake stroke relative to a compression stroke based on the selected compression ratio. In the foregoing examples, additionally or alternatively, actuating the variable compression ratio mechanism mechanically changes piston displacement in the cylinder. In any one or all of the foregoing examples, additionally or alternatively, adjusting the split ratio of the fuel injected directly into the cylinder in the intake stroke relative to the compression stroke based on the selected compression ratio includes: increasing the amount of fuel injected during the intake stroke relative to the amount of fuel injected during the compression stroke as the selected compression ratio increases. In any one or all of the foregoing examples, additionally or alternatively, adjusting the split ratio of the fuel injected directly into the cylinder in the intake stroke relative to the compression stroke based on the selected compression ratio includes: adjusting the number of intake stroke fuel injections relative to compression stroke fuel injections. In any or all of the foregoing examples, additionally or alternatively, adjusting the number of intake stroke fuel injections relative to compression stroke fuel injections includes increasing the number of intake stroke injections while decreasing the number of compression stroke injections as the selected compression ratio increases. In any or all of the foregoing examples, the method additionally or alternatively includes adjusting the timing of direct fuel injection into the cylinder based on the selected compression ratio. In any or all of the foregoing examples, additionally or alternatively, adjusting the timing of direct fuel injection into the cylinder based on the selected compression ratio includes retarding the start of injection of the intake stroke direct injection and advancing the start of injection of the compression stroke direct injection as the selected compression ratio increases. In any or all of the foregoing examples, the method additionally or alternatively includes, in response to an indication of knock, increasing the split ratio of fuel injected directly into the cylinder in the intake stroke relative to the compression stroke from a split ratio determined based on the selected compression ratio, advancing the timing of the intake stroke direct injection from a timing determined based on the selected compression ratio, and retarding spark timing. In any or all of the foregoing examples, the method additionally or alternatively includes, in response to an indication of pre-ignition, reducing the compression ratio to a feedback level, adjusting the split ratio of fuel injected directly into the cylinder in the intake stroke relative to the compression stroke based on the feedback compression ratio, and adjusting the timing of direct injection of fuel into the cylinder based on the feedback compression ratio.

[0086] As another example, a method for an engine includes: as the compression ratio applied to the engine cylinder increases, increasing the split ratio of fuel delivered to the cylinder via intake stroke direct injection relative to compression stroke direct injection, while retarding the intake stroke direct injection and advancing the compression stroke direct injection. In the foregoing example, the method additionally or alternatively includes: in response to an indication of pre-ignition, enriching the engine over a plurality of engine cycles while maintaining the compression ratio, and thereafter, reducing the compression ratio until a threshold compression ratio is reached while operating the engine at a stoichiometric ratio; and in response to an indication of knock, further increasing the split ratio of fuel delivered via intake stroke direct injection relative to compression stroke direct injection, further advancing the intake stroke direct injection, and retarding spark timing. In any or all of the foregoing examples, additionally or alternatively, enriching the engine includes: in the plurality of engine cycles, increasing the split ratio of fuel delivered via intake stroke direct injection relative to compression stroke direct injection. In any or all of the foregoing examples, additionally or alternatively, reducing the compression ratio includes mechanically reducing piston displacement within the corresponding cylinder by actuating a variable compression ratio mechanism. In any or all of the foregoing examples, the method additionally or alternatively includes: in response to not receiving further indication of pre-ignition after the enriching and the reducing the compression ratio, increasing the compression ratio for a duration by increasing piston displacement within the combustion chamber for a duration.

[0087] As another example, a system includes: an engine having a cylinder; a variable compression ratio mechanism for mechanically changing a piston position within the cylinder; a position sensor coupled to the variable compression ratio mechanism; a spark plug for providing a spark to the cylinder; a fuel injector for injecting fuel directly into the cylinder; a knock sensor; and a controller configured with computer-readable instructions stored on a non-transitory memory for the following operations: actuating the variable compression ratio mechanism to provide a compression ratio selected based on engine operating conditions; and operating in one of a first mode and a second mode based on the selected compression ratio, the first mode having a higher split ratio of fuel injected directly during the intake stroke to fuel injected directly during the compression stroke, and the second mode having a lower split ratio of fuel injected directly during the intake stroke to fuel injected directly during the compression stroke. In the foregoing example, additionally or alternatively, the first mode is selected when the compression ratio is high, and the second mode is selected when the compression ratio is low. In any or all of the foregoing examples, additionally or alternatively, the higher intake stroke direct injected fuel to compression stroke direct injected fuel split ratio includes delivering a larger portion of fuel during the intake stroke and delivering a smaller portion of fuel during the compression stroke relative to the lower intake stroke direct injected fuel to compression stroke split ratio. In any or all of the foregoing examples, additionally or alternatively, for the first operating mode, fuel is directly injected late during the intake stroke and is directly injected earlier during the compression stroke relative to the second operating mode. In any or all of the foregoing examples, additionally or alternatively, the number of intake stroke direct injections performed in the first mode is higher than the number of intake stroke direct injections performed in the second mode. In any or all of the foregoing examples, additionally or alternatively, the number of compression stroke direct injections performed in the first mode is lower than the number of compression stroke direct injections performed in the second mode.

[0088] In further representation, a method for an engine includes: actuating a variable compression ratio mechanism of a cylinder to provide a compression ratio selected based on engine operating conditions, delivering a fuel amount into the cylinder in a split injection, the split injection having a split ratio of fuel delivered in an intake stroke relative to a compression stroke, the split ratio being based on the engine operating conditions, and adjusting a number of injections, within which fuel is delivered in each of the intake stroke and the compression stroke based on the selected compression ratio. In the foregoing examples, the adjusting includes delivering the fuel in a plurality of fuel injections in the intake stroke and delivering the fuel in a plurality of fuel injections in the compression stroke while maintaining the split ratio. In any or all of the foregoing examples, each of the plurality of fuel injections in the intake stroke and the compression stroke has a pulse width that is less than a threshold pulse width. In any or all of the foregoing examples, the number of the plurality of fuel injections in the intake stroke is higher than the number of the plurality of fuel injections in the compression stroke. In any or all of the foregoing examples, the method further comprises adjusting the split ratio based on a selected compression ratio, the amount of fuel delivered in the intake stroke increasing as the selected compression ratio increases, and the amount of fuel delivered in the compression stroke decreasing as the selected compression ratio increases to maintain a total fuel mass delivered to the cylinder.

[0089] Note that the example control and estimation programs 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 a non-temporary memory and can be executed by a control system including a controller combined with various sensors, actuators and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threaded, and the like. Therefore, the various actions, operations and / or functions described can be performed in the order shown, in parallel, or omitted in some cases. Similarly, the processing order is not required to achieve the features and advantages of the example embodiments of the present invention described herein, but is provided for ease of illustration and description. Depending on the specific strategy used, one or more of the actions, operations and / or functions shown can be repeatedly performed. In addition, the described actions, operations and / or functions can graphically represent the code in the non-temporary memory of a computer-readable storage medium programmed into the engine control system, wherein the described actions are implemented by executing instructions in a system including various engine hardware components in conjunction with an electronic controller.

[0090] It should be appreciated that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments are not to be considered limiting, as many variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein.

[0091] The following claims specifically point out certain combinations and subcombinations believed to be novel and non-obvious. The claims may refer to "an" element or a "first" element or the equivalent thereof. The claims should be understood to include the incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or characteristics may be claimed by amendment of the existing claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal or different in scope to the original claims, are deemed to be included within the subject matter of the present disclosure.

Claims

1. A method for an engine, comprising: actuating a variable compression ratio mechanism of the cylinder to provide a compression ratio selected based on engine operating conditions; adjusting a split ratio of fuel injected directly into the cylinder during an intake stroke relative to a compression stroke based on the selected compression ratio; and A timing of a start of injection of an intake stroke direct fuel injection during the intake stroke is adjusted based on the selected compression ratio. 2 . The method of claim 1 , wherein actuating the variable compression ratio mechanism mechanically changes piston displacement within the cylinder.

3. The method of claim 1 , wherein adjusting a split ratio of fuel injected directly into the cylinder during the intake stroke relative to the compression stroke based on the selected compression ratio comprises: As the selected compression ratio increases, the amount of fuel injected during the intake stroke is increased relative to the amount of fuel injected during the compression stroke.

4. The method of claim 1 , wherein adjusting the split ratio of fuel injected directly into the cylinder during the intake stroke relative to the compression stroke based on the selected compression ratio comprises: Adjusts the number of intake stroke fuel injections relative to compression stroke fuel injections.

5. The method of claim 4 wherein adjusting the number of intake stroke fuel injections relative to compression stroke fuel injections comprises increasing the number of intake stroke injections while decreasing the number of compression stroke injections as the selected compression ratio increases.

6. The method of claim 1 , wherein adjusting the timing of direct fuel injection into the cylinder based on the selected compression ratio comprises: As the selected compression ratio increases, the start of injection of the intake stroke direct injection is retarded and the start of injection of the compression stroke direct injection is advanced.

7. The method according to claim 1, further comprising: In response to an indication of knock, the split ratio of fuel directly injected into the cylinder in the intake stroke relative to the compression stroke is increased from a split ratio determined based on the selected compression ratio, the timing of the intake stroke direct injection is advanced from a timing determined based on the selected compression ratio, and spark timing is retarded.

8. The method according to claim 1, further comprising: In response to an indication of pre-ignition, the compression ratio is reduced to a feedback level, the split ratio of fuel injected directly into the cylinder during the intake stroke relative to the compression stroke is adjusted based on the feedback compression ratio, and the timing of direct fuel injection into the cylinder is adjusted based on the feedback compression ratio.

9. A system for an engine, comprising: an engine having a cylinder; a variable compression ratio mechanism for mechanically changing a piston position in the cylinder; a position sensor coupled to the variable compression ratio mechanism; a spark plug, the spark plug being used to provide sparks to the cylinder; a fuel injector for injecting fuel directly into the cylinder; Knock sensor; as well as A controller configured with computer readable instructions stored on a non-transitory memory for: actuating the variable compression ratio mechanism to provide a compression ratio selected based on engine operating conditions; operating in one of a first mode and a second mode based on the selected compression ratio, the first mode having a higher split ratio of fuel directly injected during the intake stroke to fuel directly injected during the compression stroke, and the second mode having a lower split ratio of fuel directly injected during the intake stroke to fuel directly injected during the compression stroke; Wherein for the first operating mode, fuel is directly injected late during the intake stroke and is directly injected early during the compression stroke relative to the second operating mode.

10. The system of claim 9, wherein the first mode is selected when the compression ratio is high, and the second mode is selected when the compression ratio is low.

11. The system of claim 9, wherein the split ratio of the higher intake stroke injected fuel to compression stroke direct injected fuel comprises: A larger portion of the fuel is delivered during the intake stroke and a smaller portion of the fuel is delivered during the compression stroke relative to the lower intake stroke direct injected fuel to compression stroke direct injected fuel split ratio. 12 . The system of claim 9 , wherein the number of intake stroke direct injections performed in the first mode is higher than the number of intake stroke direct injections performed in the second mode.

13. The system of claim 9, wherein the number of compression stroke direct injections performed in the first mode is lower than the number of compression stroke direct injections performed in the second mode.

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