SYSTEM AND METHOD FOR A VARIABLE COMPENSATION RATIO ENGINE

Abstract

Method for an engine (10), comprising: calibrating a compression ratio scheme of the variable compression ratio engine (10) based on the fuel flow and peak torque of each cylinder (14) of the engine (10) at each individual compression ratio setting of the engine (10); and adjusting the exhaust gas recirculation (EGR) flow to the engine (10) according to an updated EGR calibration scheme based on the compression ratio scheme calibration.

Description

AREA

[0001] The present description relates generally to methods and systems for controlling the compression ratio of a variable compression ratio engine. BACKGROUND / SUMMARY

[0002] The compression ratio (CR) of an internal combustion engine is defined as the ratio of the cylinder volume at bottom dead center (BDC) to the cylinder volume at top dead center (TDC). Generally, the higher the compression ratio, the greater the thermal and fuel efficiency of the engine. Variable compression ratio (VCR) engines have been developed, allowing the compression ratio of each cylinder to be varied between higher and lower settings to improve engine performance. For example, the higher compression ratio setting can be used under non-knocking conditions to take advantage of high thermal efficiency, while the lower compression ratio setting can be used under knocking conditions.With VCR engines, a coupling or other mechanism (e.g., an eccentric) can be attached to the piston of each cylinder to mechanically vary the compression ratio between the higher and lower settings.

[0003] Caswell presents an example of a VCR engine in US 4,469,055. During engine operation, the common rail (CR) is adjusted based on the engine operating conditions. For example, the CR can be optimized for engine fuel efficiency, engine power, or both. The CR calibration, i.e., the CR that can be specified depending on engine speed and load, can be calibrated based on a prototype engine.

[0004] However, the inventors have identified potential problems with such systems. For example, adjusting the common rail (CR) during engine operation requires that the actual CR be precisely known. However, due to manufacturing tolerances, any engine can have a slightly different compression ratio (CR) in each cylinder. In a variable-compression (VCR) engine, each component of the VCR mechanism can have manufacturing tolerances that, in addition to the normal variation found in non-VCR engines, can lead to significant part-to-part variations. Therefore, calibrating a parameter that affects engine dilution, such as exhaust gas recirculation (EGR) calibration or variable cam timing (VCT) calibration, based on CR data from the prototype engine, may not be optimal for a production engine.The resulting greater variation in common rail (CR) from cylinder to cylinder can cause unstable combustion in cylinders with below-average CR, leading to increased noise, vibration, and harshness (NVH), a higher risk of misfires, and reduced efficiency in those cylinders. While the use of superior manufacturing processes and / or selected-fit parts can be employed to compensate for CR differences between cylinders, these approaches result in substantial cost increases.

[0005] In one example, the aforementioned problems can be addressed, at least partially, by a procedure comprising: calibrating a compression ratio scheme of a variable-compression engine based on the fuel flow and peak torque of each cylinder at each individual compression ratio setting of the engine; and adjusting the exhaust gas recirculation (EGR) flow to the engine according to an updated EGR calibration scheme based on the compression ratio scheme calibration. This improves the dilution optimization of a VCR engine.

[0006] As an example, the actual common rail (CR) of each cylinder in a variable compression ratio (VCR) engine can be quantified as a function of the individual VCR mechanism settings. For instance, the CR of each engine cylinder can be quantified at each of a variety of compression ratio settings. In one example, the CR of each cylinder can be quantified based on a determined fuel flow and internal mean effective pressure (IMEP) for each cylinder at the individual CR settings of the VCR engine. Then, a lowest of the quantified compression ratios can be identified. A nominal EGR or VCT scheme can then be updated based on the identified lowest CR of all cylinders. The nominal EGR / VCT scheme can be generated based on mapping data from a prototype engine.Under conditions where the engine load is higher than a threshold load, and engine dilution requirements are lower, engine dilution can be provided according to the nominal EGR / VCT scheme. Conversely, under conditions where the engine load is lower than the threshold load, and engine dilution requirements are higher, engine dilution can be provided according to the updated EGR / VCT scheme. In particular, if the lowest common denominator (CR) decreases, the provided engine dilution can be reduced, for example, by reducing the opening of an EGR valve or by advancing one or more intake valve closing and exhaust valve closing times (thereby reducing positive valve overlap).In one example, the actual common rail (CR) may be significantly lower than the specified CR due to deterioration of the variable-rate (VCR) mechanism or because initial conditions for optimal CR are not met (such as failure to meet temperature, oil pressure, and current limits). By adjusting the EGR / VCT scheme under these conditions, combustion stability and engine performance can be improved while compensating for the lack of optimal CR.

[0007] In this way, the efficiency of a VCR engine can be improved by better adjusting the engine dilution, taking into account the actual variations in the compression ratio from cylinder to cylinder. By determining the fuel flow and IMEP of all cylinders as a function of the individual CR settings of the VCR engine, CR variations of the actual engine can be determined, instead of relying on a prototype engine that may deviate significantly from the given engine. Furthermore, the EGR and VCT scheme of the VCR engine can be calibrated without resorting to expensive manufacturing processes and / or components.The technical effect of modifying a VCR engine's nominal EGR / VCT scheme based on the lowest allocated common rail (CR) of all engine cylinders is that the efficiency of a VCR engine can be increased by allowing the EGR / VCT baseline calibration to operate closer to the stability limit, while still providing protection for engines with relatively low CR on one or more cylinders (due to manufacturing variations). Modifying the engine's EGR and VCT scheme based on the actual CR allocation improves dilution control at low engine loads, resulting in improved combustion stability and reduced NVH (noise, vibration, and harshness). Overall, the engine power and fuel efficiency of a VCR engine can be improved.

[0008] It is understood that the above summary is intended to present, in a simplified manner, a selection of concepts that are further described in the detailed description. It is not intended to identify any decisive or essential features of the claimed subject matter, the scope of which is defined exclusively by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address the disadvantages listed above or elsewhere in this disclosure. List of characters Fig. Figure 1 shows an example engine system with variable compression ratio (VCR). Fig. Figure 2 shows an example flowchart for optimizing the CR calibration and dilution calibration of a VCR engine. Fig. Figure 3 shows another exemplary flowchart for optimizing the CR calibration and dilution calibration of a VCR engine. Fig. Figure 4 shows an example table indicating differences between the actual and expected CR of a VCR motor. Fig. Figure 5 shows exemplary differences between a nominal and a modified EGR and VCT scheme of a VCR engine. Fig. Figure 6 shows a prophetic example of VCR motor control. Fig. Figure 7 shows exemplary differences between a nominal and a modified CR scheme of a VCR motor. DETAILED DESCRIPTION

[0009] The following description concerns systems and procedures for an engine system configured with a variable compression ratio (VCR) mechanism, as described with reference to the engine system from Fig. 1 described. A controller can be configured to execute a control routine, such as the example routine from Fig. 2-3, to calibrate the specified CR at a given engine speed-load by determining actual cylinder-to-cylinder CR variations based on differences in fuel efficiency and output torque of each cylinder at each individual CR setting of the VCR engine. Under conditions where dilution control is required, the control unit can also modify a nominal EGR (exhaust gas recirculation) or VCT (variable cam timing) scheme based on the associated cylinder-to-cylinder CR variations. Exemplary modifications of a CR calibration and an EGR calibration are shown in the tables from Fig. 4-5 and Fig. Figure 7 shows an example of adjusting engine operation based on CR and EGR calibration. Fig. Figure 6 shows how the performance and fuel efficiency of a VCR engine can be improved in this way.

[0010] Fig. Figure 1 represents an embodiment of a combustion chamber or cylinder of an internal combustion engine. 10 The engine 10 can be integrated into a vehicle system 5 This could include, for example, a vehicle configured for on-road driving. The engine 10 control parameters from a control system that is a controller 12 includes, and input from a driver 130 via an input device 132 received. In this example, the input device includes 132 an accelerator pedal and a pedal position sensor 134 to generate a proportional pedal position signal PP. A cylinder (here also referred to as "combustion chamber") 14 of the engine 10 can combustion chamber walls 136 with pistons arranged therein 138include the piston 138 can be connected to a crankshaft 140 They are coupled so that a reciprocating motion of the piston is translated into a rotary motion of the crankshaft. A crankshaft 140 It can be coupled to at least one drive wheel of the motor vehicle via a transmission system. Furthermore, a starter motor can be connected to the crankshaft via a flywheel. 140 must be coupled to initiate an engine start-up process. 10 to enable.

[0011] The engine 10 It can be configured as a variable compression ratio (VCR) engine, where the compression ratio (CR) of each cylinder (i.e., the ratio of the cylinder volume when the piston is at bottom dead center (BDC) to the cylinder volume when the piston is at top dead center (TDC)) can be mechanically changed. The engine's CR can be adjusted via a VCR actuator. 192 can be varied, which has a VCR mechanism. 194actuated. In some embodiments, the CR can be varied between a first, low CR (where the ratio of the cylinder volume when the piston is at the BDC to the cylinder volume when the piston is at the TDC is smaller) and a second, higher CR (where the ratio is higher). In other embodiments, a predefined number of stepped compression ratios can be present. The CR can also be continuously variable between the first, lower CR and the second, higher CR (to any CR in between).

[0012] In the example shown, the VCR mechanism is... 194 to the piston 138 coupled in such a way that the VCR mechanism can change the TDC position of the piston. For example, the piston can 138 via a piston position change VCR mechanism 194, which moves the pistons closer to or further away from the cylinder head, thus changing the size of the combustion chamber 14 changes, to the crankshaft 140 be coupled. A position sensor 196 can be connected to the VCR mechanism 192 be coupled and can be configured to provide feedback regarding the position of the VCR mechanism applied to the cylinder 194 (and thus the compression ratio) to the control system 12 to provide.

[0013] In one example, changing the piston's position in the combustion chamber also changes the piston's relative displacement in the cylinder. The piston position change (VCR) mechanism can be coupled to a conventional or an unusual crankshaft. Non-restrictive examples of an unusual crankshaft to which the VCR mechanism can be coupled include variable-head-gap crankshafts and variable-kinetic-length crankshafts. In one example, the crankshaft 140 It can be configured as an eccentric shaft. In another example, an eccentric can be coupled to or located in the vicinity of a piston pin, with the eccentric changing the position of the piston in the combustion chamber. The movement of the eccentric can be controlled by oil channels in the piston rod.

[0014] It is understood that other VCR mechanisms can also be used that mechanically change the compression ratio. For example, the engine's common rail (CR) can be changed via a VCR mechanism that alters the cylinder head volume (i.e., the clearance volume in the cylinder head). In yet another example, the VCR mechanism may involve a hydraulically actuated, pneumatically actuated, or mechanically actuated spring-loaded piston. Furthermore, the VCR mechanism may include a multi-linkage mechanism or a bent-rod mechanism. Other VCR mechanizations are also possible. It is understood that, in the sense used here, the VCR engine is configured to adjust the engine's CR via mechanical adjustments that vary a piston position, a cylinder head position, or a cylinder head volume. In this way, the VCR mechanisms do not involve effective CR adjustments of valve timing or cam timing.

[0015] By adjusting the piston's position in the cylinder, the engine's actual (static) compression ratio (i.e., the difference in cylinder volume between a TDC and a BDC engine) can be varied. For example, reducing the compression ratio involves reducing the piston's displacement within the combustion chamber by increasing the distance between the top of the piston and the cylinder head.

[0016] For example, the engine can be operated at a first, lower compression ratio by the control unit sending a signal to actuate the VCR mechanism into a first position where the piston has less effective displacement in the combustion chamber. As another example, the engine can be operated at a second, higher compression ratio by the control unit sending a signal to actuate the VCR mechanism into a second position where the piston has greater effective displacement in the combustion chamber. Changes in the engine compression ratio can be used to improve fuel efficiency. For example, a higher compression ratio can be used to improve fuel efficiency at low to moderate engine loads until ignition retardation due to early knocking negates the fuel efficiency benefit.The engine can be switched to a lower compression ratio, thereby trading the efficiency benefits of a higher compression ratio for the efficiency benefits of optimized combustion control. Continuous VCR systems can continuously optimize the balance between combustion control and the efficiency benefits of a higher compression ratio to provide the best compression ratio between the limits for the higher and lower compression ratios under the given operating conditions. For example, an engine control unit can reference a lookup table to select an applicable compression ratio based on engine speed-load conditions.As discussed below, the selection can involve choosing a lower compression ratio at higher engine loads and choosing a higher compression ratio at lower engine loads.

[0017] The cylinder 14 can be achieved through a series of intake air tracts 142 , 144 and 146 Take in intake air. The intake air tract 146 can be used in addition to the cylinder 14 with other cylinders of the engine 10 are connected. In some embodiments, one or more of the intake tracts may include a pressure-relieving device such as a turbocharger or a pre-compressor. For example, shows Fig. 1 the engine 10 , which is configured with a turbocharger that has a compressor 174 between the intake manifolds 142 and 144 and an exhaust turbine 176 includes those attached to the exhaust pipe 148is arranged. The compressor 174 can be via a wave 180 at least partially through the exhaust turbine 176 will be driven if the overpressure device is configured as a turbocharger. In other examples, such as when the engine 10 equipped with a pre-compressor, the exhaust gas turbine 176 However, they can be optionally omitted, whereby the compressor 174 It can be driven by a mechanical input from an electric motor of the engine. A choke 20 with a throttle valve 164 It can be provided on the engine's intake tract to vary the flow rate and / or pressure of intake air supplied to the engine cylinders. For example, the throttle can 20 downstream of the compressor 174 be arranged as in Fig. 1 shown, or alternatively upstream of the compressor 174 be arranged.

[0018] The exhaust pipe148 exhaust gases from other cylinders of the engine 10 in addition to the cylinder 14 record an exhaust gas sensor. 128 is connected to an exhaust pipe 148 upstream of an emission control device 178 shown coupled. The sensor 128 The sensor used to provide an exhaust air-fuel ratio reading can be selected from various suitable sensors, such as a linear oxygen sensor or UEGO (universal exhaust gas oxygen), a dual-state oxygen sensor or EGO (as shown), a heated HEGO (heated EGO), a NOx, HC, or CO sensor. In the emission control device 178 It could be a three-way catalyst (TWC), a nitrogen oxide trap, various other emission control devices, or combinations thereof.

[0019] The exhaust gas temperature can be measured by one or more temperature sensors (not shown) in the exhaust pipe. 148 The exhaust gas temperature can be estimated. Alternatively, it can be derived based on engine operating conditions such as engine speed, load, air-fuel ratio (AFR), ignition delay, etc. Furthermore, the exhaust gas temperature can be measured by one or more exhaust gas sensors. 128 can be calculated. It is understood that the exhaust gas temperature can alternatively be estimated by any combination of the temperature estimation methods listed herein.

[0020] Each cylinder of the engine 10 It can include one or more intake valves and one or more exhaust valves. For example, the cylinder 14 with at least one intake plate valve 150 and at least one exhaust control valve 156 shown, located in an upper area of ​​the cylinder 14are arranged. In some embodiments, each cylinder of the engine can be 10 including the cylinder 14 comprising at least two intake poppet valves and at least two exhaust poppet valves, which are arranged in an upper area of ​​the cylinder

[0021] The intake valve 150 can be controlled 12 by cam actuation using a cam actuation system 151 can be controlled. The exhaust valve can also be controlled. 156 from the control 12 by means of a cam actuation system 153 They are controlled. The cam actuation systems 151 and 153They can each contain one or more cams and can use one or more from a cam profile switching (CPS), variable cam timing (VCT), variable valve timing (WT) and / or variable valve lift (WL) system controlled by the controller. 12 They can be operated to vary the valve operation. The position of the intake valve 150 and the exhaust valve 156 Each can be controlled by valve position sensors. 155 and 157 can be determined. In alternative embodiments, the intake and / or exhaust valve can be controlled by means of electric valve actuation. For example, the cylinder 14Alternatively, the system may include an intake valve controlled by electric valve actuation and an exhaust valve actuated by cam actuation, including CPS and / or VCT systems. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or by a valve actuator or actuation system with variable valve timing.

[0022] The cylinder 14 can have a compression ratio that is a ratio of the volume to the piston 138The compression ratio is the distance from bottom dead center to top dead center. Typically, the compression ratio is in the range of 9:1 to 10:1. However, in some cases where different fuels are used, the compression ratio may be higher. This can occur, for example, when using higher octane fuels or fuels with a higher latent heat of vaporization. The compression ratio may also be higher when using direct injection, as this affects engine knocking. The compression ratio can also be adjusted based on driver requests via settings on a VCR actuator. 192 , which has a VCR mechanism 194 actuated, which changes the effective position of the piston 138 in the combustion chamber 14 The compression ratio can be varied mechanically based on feedback from the sensor. 196 regarding the position of the VCR mechanism 194 can be derived.

[0023] In some embodiments, each cylinder of the engine can 10 a spark plug 192 to initiate combustion. An ignition system. 190 In selected operating modes, it can respond to an early ignition signal SA from the control unit. 12 via the spark plug 192 a spark to the combustion chamber 14 provide. In some embodiments, the spark plug 192 however, this would be eliminated, for example, if the engine 10 combustion can be initiated by self-ignition or by injecting fuel, as can be the case with some diesel engines.

[0024] In some embodiments, each cylinder of the engine can 10 It may be configured with one or more fuel injectors to supply fuel to it. As a non-restrictive example, the cylinder 14 with a fuel injector 166shown. The fuel injector. 166 is directly attached to the cylinder 14 shown coupled to be proportional to the pulse width of a signal FPW supplied by the controller 12 via an electronic driver 168 The fuel is received and injected directly. In this way, the fuel injector... 166 a so-called direct injection (hereinafter also referred to as "DI") of fuel into the combustion cylinder 14 ready. Although Fig. 1 the injector 166 As shown in the image of a side-mounted injector, it can also be located above the piston, such as near the spark plug position. 192The injector nozzle may be positioned above and near the intake valve. Due to the lower volatility of some alcohol-based fuels, such a position can improve mixing and combustion when the engine is running on an alcohol-based fuel. Alternatively, the injector nozzle may be positioned above and near the intake valve to improve mixing. 166 can be from a high-pressure fuel system 8 Fuel is supplied via fuel tanks, fuel pumps, and a fuel rail. Alternatively, fuel can be supplied by a single-stage fuel pump at a lower pressure, in which case there may be greater constraints regarding the timing of direct fuel injection during the compression stroke than when using a high-pressure fuel system. Although not shown, the fuel tanks may also include a pressure transducer that sends a signal to the control unit. 12provides. It goes without saying that the injector 166 In an alternative embodiment, it can be a channel injection nozzle that injects fuel into the intake manifold upstream of the cylinder. 14 provides.

[0025] It is also understood that while the illustrated embodiment shows that the engine is operated by injecting fuel via a single direct injection nozzle, in alternative embodiments the engine can be operated using two or more injection nozzles (for example, one direct injection nozzle and one channel injection nozzle per cylinder, or two direct injection nozzles / two channel injection nozzles per cylinder, etc.) and by varying a relative injection quantity into the cylinder from the individual injection nozzles.

[0026] The fuel injector can supply fuel to the cylinder during a single cylinder cycle. Furthermore, the distribution and / or relative quantity of fuel supplied by the injector can vary depending on operating conditions. In addition, multiple fuel injections can be performed per cycle for a single combustion event. These multiple injections can occur during the compression stroke, the intake stroke, or a suitable combination thereof. Fuel can also be injected during the cycle to adjust the air-to-fuel ratio (AFR) of the combustion. For example, fuel can be injected to provide a stoichiometric AFR. An AFR sensor can be provided to estimate the AFR in the cylinder. In one example, the AFR sensor could be an exhaust gas sensor, such as an EGO sensor.128 The sensor can determine the AFR by measuring the amount of residual oxygen (for lean mixtures) or unburned hydrocarbons (for rich mixtures) in the exhaust gas. The AFR can then be provided as a lambda (λ) value, which is the ratio of the actual AFR to the stoichiometry for a given mixture. A lambda value of 1.0 indicates a stoichiometric mixture; mixtures richer than the stoichiometry can have a lambda value below 1.0, and mixtures leaner than the stoichiometry can have a lambda value above 1.

[0027] As described above, shows Fig. 1 only one cylinder of a multi-cylinder engine. Therefore, each cylinder can contain its own set of intake / exhaust valves, fuel injector(s), spark plug, etc.

[0028] Fuel tanks in the fuel system 8Fuels can contain different fuel qualities, such as different fuel compositions. These differences can include different alcohol content, different octane ratings, different heats of vaporization, different fuel blends and / or combinations thereof, etc.

[0029] The engine 10 It can also have a knock sensor 90 include, which is attached to each cylinder 14 It is coupled to identify abnormal cylinder combustion events. In alternative embodiments, one or more knock sensors can be used. 90The knock sensor can be coupled to selected locations on the engine block. It can be an accelerometer on the cylinder block or an ionization sensor configured in the spark plug of each cylinder. The knock sensor output can be combined with the output of a crankshaft accelerometer to indicate an abnormal combustion event in the cylinder. For example, based on the knock sensor output... 90Within one or more defined windows (e.g., crankshaft timing windows), abnormal combustion due to one or more knocking and pre-ignition can be identified and differentiated. For example, knocking can be identified in response to the estimated knock sensor output being higher than a knock threshold within a knock window, while pre-ignition can be identified in response to the estimated knock sensor output being higher than an pre-ignition threshold within a pre-ignition window, where the pre-ignition threshold is higher than the knock threshold and the pre-ignition window occurs earlier than the knock window. Furthermore, the abnormal combustion can be corrected accordingly. For example, knocking can be corrected by reducing the compression ratio and / or retarding the ignition timing, while pre-ignition can be corrected by enriching the engine mixture and / or limiting the engine load.Furthermore, lowering the compression ratio also reduces the changes in further ignition timing.

[0030] The control 12 is shown as a microcomputer that contains a microprocessor unit 106 , Input / output connections 108 , an electronic storage medium for executable programs and calibration values, which in this particular example is a read-only memory chip 110 shown is a direct access memory 112 , a keep-alive memory 114 and includes a data bus. The control system 12 In addition to the signals discussed previously, it can receive various signals from sensors connected to the motor. 10 coupled, including a measurement of the induced mass air flow (MAF) from a mass air flow sensor 122 ; the engine coolant temperature (ECT) from a temperature sensor 116 , which is attached to a cooling sleeve118 coupled; an ignition pulse generator (profile ignition pickup - PIP) signal from a Hall sensor 120 (or other type) that connects to the crankshaft 140 coupled; a throttle position (TP) from a throttle position sensor; an absolute manifold pressure signal (MAP) from a sensor 124 , Cylinder AFR from an EGO sensor 128 , abnormal combustion from a knock sensor 90 and a crankshaft acceleration sensor and the VCR mechanism position from a position sensor 196 The motor speed signal, RPM, can be obtained from the controller. 12 The PIP signal is generated from the manifold pressure signal. The manifold pressure signal MAP from a manifold pressure sensor can be used to provide a reading of vacuum, or pressure, in the intake manifold. The control 12 receives signals from various sensors Fig. 1 and uses the various actuators from Fig. 1. To adjust engine operation based on received signals and instructions stored in the control unit's memory. For example, based on engine speed and load, the control unit can adjust the engine's compression ratio by sending a signal to the VCR actuator, which adjusts the VCR mechanism to mechanically move the piston closer to or further away from the cylinder head, thereby changing the combustion chamber volume.

[0031] The read-only memory 110 The non-transitory storage medium can be programmed with computer-readable data representing instructions to be executed by a processor. 106 are executable to carry out the procedures described below, as well as other variants that are provided for but not specifically listed.

[0032] In some examples, the vehicle 5a hybrid vehicle with multiple torque sources that supply one or more vehicle wheels 55 are available. In other examples, the vehicle 5 A conventional vehicle with only one engine or an electric vehicle with only one electric motor. In the example shown, the vehicle includes 5 the engine 10 and an electric machine 52 The electric machine 52 It could be an electric motor or an electric motor / generator. The crankshaft 140 of the engine 10 and the electric machine 52 are via a drivetrain 54 with vehicle wheels 55 connected when one or more couplings 56 are indented. In the example shown, a first coupling is 56 is between the crankshaft 140 and the electric machine 52 provided and a second coupling 56is between the electric machine 52 and the powertrain 54 planned. The control 12 Can a signal be sent to an actuator of any coupling? 56 send to engage or disengage the clutch to turn the crankshaft 140 with the electric machine 52 and to connect or disconnect the associated components and / or the electrical machine 52 with the drivetrain 54 and to connect or disconnect the associated components. The drivetrain 54 It can be a gearbox, a planetary gear system, or another type of drivetrain. The drivetrain can be configured in different ways, including as a parallel, a series, or a series-parallel hybrid vehicle.

[0033] The electric machine 52 receives electrical power from a traction battery 58 , to transfer torque to the vehicle wheels55 to provide. The electric machine 52 It can also be operated as a generator to provide electrical power for charging the battery. 58 to provide, for example during a braking process.

[0034] The actual common ratio (CR) of each cylinder influences that cylinder's knock limit, especially at high loads, as well as its dilution limits, particularly at low loads. Due to manufacturing tolerances of the individual cylinders... 30 of the engine 10With a coupled VCR mechanism, significant part-to-part variations can exist between the actual common rail (CR) of each cylinder and the expected CR for that cylinder. For a given expected CR, significant variations in the actual CR can occur from cylinder to cylinder. Due to these differences, the CR calibration may be suboptimal. Since an engine's CR also affects engine dilution tolerances, errors in CR estimation can also result in suboptimal EGR or VCT (or VVL, etc.) calibration. For example, a low CR setting may be specified in response to high-load conditions. However, because a cylinder's actual CR is higher than expected, the resulting suboptimal CR may be higher than desired, causing excessive knock limiting for that cylinder. Conversely, a higher CR setting may be specified in response to low-load conditions.However, since the actual CR of a cylinder is lower than expected, the resulting suboptimal CR may be lower than desired, causing a limitation in combustion stability and NVH of the cylinder.

[0035] As with reference to Fig. As discussed in sections 2-3, an engine control unit (ECU) can update a common rail (CR) calibration (i.e., calibrating the CR to a target value at a given engine speed and load) based on calculated differences in fuel consumption and torque output for each cylinder at every CR setting of the VCR engine. The ECU can also update an EGR and / or VCT calibration (i.e., calibrating the dilution to a target value at a given engine speed and load) based on calculated differences in fuel consumption and torque output for each cylinder at every CR setting of the VCR engine. In this way, VCR engine performance can be improved. Referring to Fig. 2 will be an exemplary routine 200This procedure is described for calibrating a VCR engine. The procedure reduces power loss due to variations in common rail (CR) from cylinder to cylinder caused by manufacturing tolerances. Instructions for performing the procedure are included. 200 and the other procedures contained herein can be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals from the sensors of the engine system, such as those referred to above. Fig. 1. Sensors described. The controller can use motor actuators of the motor system to adjust the motor operation according to the procedures described below.

[0036] At 202 The procedure includes 200Estimating and / or measuring engine operating conditions. Engine operating conditions may include, for example, driver-requested power (e.g., based on the output of a pedal position sensor coupled to a driver pedal); ambient temperature, pressure, and humidity; engine speed; engine temperature; manifold pressure (MAP); manifold airflow (MAF); catalytic converter temperature; intake air temperature; boost pressure level; fuel octane rating of the fuel available in the fuel tank; etc.

[0037] It goes without saying that the procedure 200 In an alternative example, it can be triggered during the first engine start after the engine has been manufactured, so that the engine can be calibrated. In other examples, the procedure can 200 triggered in response to engine repair or maintenance (as indicated by a disconnected battery, input from a diagnostic tool, or input via a GUI).

[0038] At 204 The procedure includes 200 Selecting a desired compression ratio for operating the engine based on estimated engine operating conditions. The engine can be equipped with a VCR mechanism (e.g., the VCR mechanism). 194 out of Fig. 1) It may be configured to mechanically change the engine's compression ratio between a first, lower, and a second, higher compression ratio setting. The VCR mechanism can achieve this by mechanically changing the position of a piston in a cylinder. Alternatively, several compression ratios between the first and second settings may be possible. The control unit can calculate the fuel efficiency at each possible compression ratio of the engine for the given power demand from the driver and select the compression ratio that provides the highest fuel efficiency.The control unit can compare fuel efficiency at each compression ratio by comparing the engine's brake-specific fuel consumption (BSFC) at each ratio, for example, using a lookup table stored in the control unit's memory. The lookup table is entered during engine calibration based on a prototype engine with substantially the same common rail (CR) on each cylinder. The engine's fuel efficiency at each compression ratio can be determined using a table, curve graph, algorithm, and / or equation, each stored as a function of operating conditions (e.g., engine speed, torque, temperature, humidity, derived fuel octane rating, etc.). These settings are entered during an initial engine calibration based on a prototype engine.In general, with increasing engine load or increasing BMEP, the selected compression ratio can be reduced due to a balance between the efficiency benefits of a higher common rail (predominant at lower loads) and the efficiency losses of knock-limited combustion control (predominant at higher loads). Thus, a lower compression ratio is selected at higher engine loads and a higher compression ratio at lower engine loads.

[0039] At 206 The procedure involves retrieving the actual compression ratio setting of each cylinder at the desired nominal compression ratio setting. For example, a lookup table such as the table from Fig. 4 can be referenced to determine whether the actual CR for the given cylinder is above or below a desired nominal CR setting.

[0040] At 208The procedure involves calculating fuel efficiency (or fuel consumption) for each cylinder at the retrieved actual compression ratio. For example, if the actual common rail (CR) of the selected cylinder is higher than the desired nominal CR setting, it can be determined that the fuel efficiency for that cylinder is worse at high loads due to additional ignition retardation (later knock-limited combustion control). 210 The procedure involves determining the overall fuel efficiency of the engine by summing the fuel efficiency of the individual cylinders.

[0041] At 212The procedure involves calculating fuel loss associated with each cylinder at the retrieved actual compression ratio. For example, if the actual common rail (CR) of the selected cylinder is higher than the desired nominal CR setting, and the engine is currently operating at high load with knock limiting, it can be determined that there is fuel loss for that cylinder, dependent on the actual CR of the selected cylinder and the desired nominal CR setting. 214 The procedure involves determining the total fuel loss of the engine by summing the fuel loss of each cylinder.

[0042] As an example, the actual CR data can be retrieved from a lookup table stored in the controller's memory, such as the table 400 out of Fig. 4. The data can be entered into the lookup table immediately after the engine is manufactured, replaced, or undergoes major maintenance. For example, the common rail (CR) of each cylinder can be quantified by measuring the dimensions of key engine components during manufacturing. Alternatively, the CR of each cylinder can be quantified during centrifugal tests at the end of the production line by measuring the cylinder pressure in each cylinder, using wireless transducers in each cylinder, or by measuring a crankshaft acceleration profile resolved for the crank angle. The known CR of each cylinder can be stored in the control unit's memory immediately after engine manufacturing and updated by a service technician after an engine replacement or major maintenance, if necessary. This allows it to be determined for each cylinder whether the actual CR for that cylinder is above or below the specified CR setting.Referring to the table. 400 out of Fig. 4 is, for example, the actual CR of cylinder 1 significantly higher than the expected setting, while the actual CR of cylinder 4 The CR is significantly lower than the expected setting, and the difference between expected and actual CR varies with the nominal CR. When the engine is operated at higher loads, the actual CR of cylinders can be significantly lower. 1 , which is higher than expected, cause a stronger knock limitation of the cylinder 1 This is more pronounced than in the other cylinders, requiring an additional ignition delay. This results in a loss of fuel efficiency for that cylinder. 1 under heavy loads.

[0043] At 216The total fuel loss due to the actual versus the nominal common rail (CR) can be compared to a threshold value. If the loss is lower than a threshold value, that is, if there is no significant fuel loss associated with the actual versus the nominal CR, the procedure includes... 218 continuing engine operation at the desired nominal CR setting, which is 204 was selected. For example, an engine with very little variation in the actual common rail from cylinder to cylinder operates where the 204 The selected desired nominal CR is most efficient because the desired nominal CR was determined from testing a prototype engine with very little variation in the actual CR from cylinder to cylinder (see, for example, curve). 702 from the curve diagram 700 out of Fig. 7).

[0044] However, if a significant loss of fuel efficiency is associated with the actual CR compared to the nominal CR, the procedure includes 220 Actuating the VCR mechanism to a lower CR setting. For example, the controller can send a signal to the VCR actuator to move the VCR mechanism and lower the CR by 0.2 ratios, and then continue the sequence of the procedure. 200 Repeat. For an engine with one or more cylinders exhibiting a CR higher than the nominal CR, operating at a higher load, and with engine knock limitation, the optimal CR is lower (as shown in curve). 704 of the diagram 700 out of Fig. 7 shown) as the desired nominal CR, which was determined by testing a prototype engine with only slight variation of the actual CR from cylinder to cylinder.

[0045] From 218 and 220The procedure continues at 222 to determine whether engine dilution control is required. In one example, engine dilution control is required when the engine load is below a threshold load where combustion stability is a constraint on the EGR and / or VCT (or VVL, etc.) scheme. In another example, engine dilution control is required below a threshold load that varies with engine speed, temperature, or other factors. If dilution control is not required, a VCT and / or EGR scheme can be retained at 224. Otherwise, if dilution control is required, the VCT and / or EGR scheme can be updated at 228. In particular, the control can modify the nominal EGR / VCT scheme based on the lowest CR of all cylinders, as determined at 206.Lower common ratio (CR) leads to poorer combustion stability at low loads, which reduces dilution tolerance and thus the optimal EGR rate. It also shifts the optimal VCT / VVL scheme towards lower "internal EGR" (lower exhaust valve overlap and / or earlier valve closing) and / or higher effective CR (earlier intake valve closing). Mapping data from a prototype engine with little variation in actual CR from cylinder to cylinder can be used to quantify the optimal (combustion stability-limited) EGR and / or VCT scheme as a function of CR. The combustion stability limit is determined by the "worst" cylinder, in this case, the cylinder with the lowest CR.Therefore, the EGR and / or VCT settings, which are limited by combustion stability at low loads, are simply determined using the common rail (CR) of the cylinder with the lowest CR, rather than using the nominal CR. For example, for an engine where one or more cylinders have a CR below the nominal CR and which operates below a load threshold where combustion stability is a constraint, a smaller EGR size and / or reduced valve overlap and / or an earlier EVC setting can be applied (as shown in the curves). 506 and 508 out of Fig. 5) shown.

[0046] As in Fig. As discussed in section 3, the EGR and / or VCT scheme can be modified at any time if the VCR mechanism deteriorates, as may occur due to component deterioration or because initial conditions are not met. In particular, it can be determined whether the actual VCR mechanism position differs from a desired VCR. The unmet VCR actuator initial conditions may include conditions related to temperature, oil pressure, electrical current limiting, etc. If VCR deterioration is detected, a smaller EGR size and / or a smaller valve overlap and / or an earlier EVC setting can be applied, as described in [reference to relevant section]. Fig. 5 shown.

[0047] Referring to Fig. 3 is another exemplary procedure 300 demonstrated for calibrating a VCR motor.

[0048] At 302 The procedure includes 300 as with 202Estimating and / or measuring engine operating conditions. Engine operating conditions may include, for example, driver-requested power (e.g., based on the output of a pedal position sensor coupled to a driver pedal); ambient temperature, pressure, and humidity; engine speed; engine temperature; manifold pressure (MAP); manifold airflow (MAF); catalytic converter temperature; intake air temperatures; boost pressure levels; fuel octane rating of the fuel available in the fuel tank; etc.

[0049] It goes without saying that the procedure 300 In some cases, this can be triggered during the first engine start after the engine has been manufactured, so that the engine can be calibrated. In other cases, the procedure can 300 triggered in response to engine repair or maintenance (such as by a disconnected battery, input from a diagnostic tool, or input via a GUI).

[0050] At 304 The procedure includes 300 Quantifying the actual common rail (CR) of each cylinder of the engine at every single CR setting of the engine. As an example, the actual CR data can be retrieved from a lookup table stored in the control unit's memory, such as the table 400 out of Fig. 4. The data can be entered into the lookup table immediately after the engine is manufactured, replaced, or undergoes major maintenance. For example, the common rail (CR) of each cylinder can be quantified during centrifugal tests at the end of the production line, based on measured cylinder pressure, using radio frequency transducers in each cylinder, based on a measured crankshaft acceleration profile resolved for the crank angle, or based on measured dimensions of key engine components. The known CR of each cylinder can be stored in the control unit's memory immediately after engine manufacturing and updated by a maintenance technician after an engine replacement or major maintenance, if necessary. This allows it to be determined for each cylinder whether the actual CR for that cylinder is above or below the specified CR setting. (See Table...) 400 out of Fig. 4 is, for example, the actual CR of cylinder 1 significantly higher than the expected setting, while the actual CR of cylinder 4 The CR is significantly lower than the expected setting, and the difference between expected and actual CR varies with the nominal CR. When the engine is operated at higher loads, the actual CR of cylinders can be significantly lower. 1 , which is higher than expected, cause a stronger knock limitation of the cylinder 1 This is more pronounced than in the other cylinders, requiring an additional ignition delay. This results in a loss of fuel efficiency.

[0051] At 306 The procedure includes 300Quantifying the fuel flow and maximum in-cylinder mean effective pressure (IMEP) of each cylinder as a function of the VCR mechanism setting (nominal CR) under current operating conditions. The control unit calculates the fuel flow and IMEP for each individual cylinder at its actual compression ratio for every possible nominal CR setting. The control unit can compare the fuel flow and IMEP at each compression ratio using a lookup table stored in the control unit's memory. The lookup table is entered during engine calibration based on a prototype engine with substantially the same CR at each cylinder. The fuel flow per cylinder on the prototype engine is simply the total fuel flow divided by the number of cylinders. The IMEP is based on cylinder pressure data from the prototype engine. 306The IMEP and fuel flow for each cylinder are calculated for each nominal CR (VCR mechanism setting), but using the actual CR of each cylinder. If an engine has little variation in CR from cylinder to cylinder, the calculated IMEP and fuel flow in each cylinder will be nearly identical, and the engine's minimum overall IMEP and fuel flow will be achieved at the same CR as the minimum fuel flow and IMEP for the prototype engine. For an engine with high variation in CR from cylinder to cylinder (such as the engine from Fig. 4) During operation at high loads, when the engine has knock limiting, the calculated fuel flow and IMEP will differ for each cylinder. For the cylinder 1 of the engine Fig. In Figure 4, the common ratio (CR) used in the fuel flow calculation is higher, and the internal mean effective pressure (IMEP) is lower at higher CR values ​​due to knock-limiting combustion control. The effects of knock-limiting combustion control are non-linear, so the optimal nominal CR cannot be determined simply by averaging the CR values ​​of all cylinders; the cylinder with the highest CR has a disproportionately large effect under knock-limiting conditions. At high loads, the optimal nominal CR for this engine is lower than for the prototype engine, as indicated by the dashed line in Figure 4. Fig. 7 shown.

[0052] Although the procedure suggests quantifying the fuel flow and IMEP of each cylinder, it is understood that this is not restrictive and that alternative examples may use other cylinder parameters that indicate fuel efficiency and power. For example, in alternative examples, the metric quantified by the control unit (at part-load conditions, such as below a threshold load) may include efficiency or brake-specific fuel consumption (BSFC), while the metric quantified at higher load conditions (such as near peak load or above the threshold load) may include torque, power, or brake-specific air consumption (BSAC).

[0053] At 310It can be determined whether the driver demand exceeds a threshold. This threshold can be based on the accelerator pedal position. In this way, it can be inferred that above the threshold, the driver prioritizes performance over efficiency, while below the threshold, maximum performance is not required and the VCR control can be optimized for efficiency.

[0054] If the driver demand is below the threshold, the procedure at 312 involves selecting the VCR setting that corresponds to the minimum total engine fuel flow. By selecting the VCR setting that corresponds to the minimum total engine fuel flow under part-load conditions, fuel consumption and CO2 emissions can be minimized. However, if... 314If the driver demand exceeds the threshold load, the procedure involves selecting the VCR setting that corresponds to the maximum total IMEP. By selecting the VCR setting corresponding to the maximum total IMEP under peak load conditions, vehicle acceleration performance can be maximized.

[0055] From 312 and 314 The procedure is carried out in each case with 316 to determine if engine dilution control is required. In one example, engine dilution control is required if the engine load is below the threshold load. If dilution control is required, then 320The VCT and / or EGR scheme can be updated. In particular, the control unit can modify the nominal EGR / VCT scheme based on the lowest common denominator (CR) of all cylinders. The lower CR results in poorer combustion stability at low loads, which reduces dilution tolerance and thus the optimal EGR rate. It also shifts the optimal VCT scheme towards a lower "internal EGR" (lower exhaust valve overlap and / or earlier valve closing) and / or a higher effective CR (earlier intake valve closing). Mapping data from a prototype engine with little variation in the actual CR from cylinder to cylinder can be used to quantify the optimal (combustion stability-limited) EGR and / or VCT scheme as a function of the CR. The combustion stability limit is determined by the "worst" cylinder, in this case, the cylinder with the lowest CR.Therefore, the EGR and / or VCT settings, which are limited with regard to combustion stability at low loads, are determined based on the cylinder with the lowest CR, rather than using the nominal CR. For example, for an engine where one or more cylinders have a CR below the nominal CR and which operates below a load threshold where combustion stability is a constraint, a smaller EGR size and / or reduced valve overlap and / or an earlier EVC setting can be applied, as shown in [reference]. Fig. 5 shown.

[0056] If no engine dilution control is required, then at 318It can be determined whether there is deterioration or malfunction of the VCR mechanism. In particular, it can be determined whether the actual VCR mechanism position differs from a desired VCR position. VCR deterioration can be determined in response to VCR component deterioration or due to failure to meet VCR actuator start-up conditions. These non-met VCR actuator start-up conditions can include conditions related to temperature, oil pressure, electrical current limiting, etc. If VCR deterioration is detected, a smaller EGR size and / or a smaller valve overlap and / or an earlier EVC setting can be applied, as described in Fig. 5 shown.

[0057] If no VCR degradation is detected, then... 322A nominal VCT and / or EGR scheme is maintained. The nominal EGR and / or VCT scheme may be based on engine operating conditions. However, if VCR deterioration is determined, the procedure reverts to 320 back to work with the modified EGR and / or VCT scheme.

[0058] Fig. Figure 5 represents the effective EGR scheme for a load (BMEP) deflection at various CRs based on data from the prototype engine with essentially the same CR on each cylinder. The curve 504 The EGR scheme shows the curve at a CR of 12:1. 506 The EGR scheme is shown at a CR of 10:1 and the curve 508The EGR scheme is shown at a common rail (CR) ratio of 8:1. It is understood that the EGR scheme can also depend on engine speed, engine temperature, air temperature and humidity, etc. The EGR scheme exhibits maximum EGR rates at a medium BMEP (BMetic Fuel Trim). At a higher BMEP, the EGR rate may decrease due to the negative effects of EGR on volumetric efficiency. At a lower BMEP, the EGR rate may decrease due to the negative effects of EGR on combustion stability. However, combustion stability also deteriorates at a lower CR. For example, a load threshold value 502The table shows below which combustion stability deteriorates. Therefore, lower EGR rates are used when the common rail (CR) of one or more cylinders is lower. To create the table, mapping data from the prototype engine with essentially the same CR at each cylinder is used, but to determine the current desired EGR rate, the cylinder with the lowest actual CR is used in conjunction with the table. Similar procedures would be used to limit the "internal EGR" by modifying the scheme used for VCT, VVL, etc., depending on the cylinder with the lowest CR. Fig. Figure 6 presents trends in fuel consumption versus load (BMEP) for various common rail systems (CRs). These trends are familiar to those skilled in the field, as they result from the fundamental balancing of the efficiency gains of a higher CR against the efficiency losses of knock-limited combustion control. The results of this balancing determine which CR is optimal for each BMEP (the optimal CR also varies with engine speed, fuel octane rating, intake air temperature, humidity, etc.). The efficiency gains of a higher CR prevail at a lower BMEP, while the efficiency losses of knock-limited combustion control predominate at a higher BMEP, as shown by the load-limited curve. 604 shown. With a low BMEP and no knock limiting on the engine, the optimal CR is therefore high, and Fig. Figure 6 shows that the lowest fuel consumption occurs at the highest CR of 13:1. The curves 602a-h The data shows that fuel consumption decreases with increasing common rail (CR). Therefore, with a high BMEP (BMe Energy Performance) and the engine's strongest knock limitation, the optimal CR is low, and Fig. Figure 6 shows that the lowest fuel consumption occurs at the lowest common denominator (CR) of 8:1. At a medium BMEP, the two factors balance each other in different ways, and the lowest fuel flow occurs at various CR ratios between low and high. The trends from Fig. 6 are quantified by testing a prototype engine and used to determine an optimal or desired nominal CR depending on BMEP, engine speed, fuel octane number, intake air temperature, humidity, etc., which is, for example, in step 204 from Fig. 2 and step 306 from Fig. 3 is used.

[0059] Using the methods described above, variations in the compression ratio from cylinder to cylinder can be better detected and accounted for. By determining the fuel flow and IMEP of all cylinders as a function of each desired nominal CR setting of a VCR engine, variations in the engine's actual CR can be identified and distinguished from CR data obtained on a prototype engine. Furthermore, the VCR engine can be calibrated reliably and cost-effectively using existing sensors and actuators. By adjusting the CR setting to provide the highest fuel efficiency at low load conditions and the highest engine output at high load conditions, engine performance can be improved despite the variations in CR from cylinder to cylinder.By also adjusting the EGR and VCT scheme of the VCR engine based on the assigned common rail of all engine cylinders, dilution control is improved, allowing the engine to operate closer to the combustion stability limit with fewer NVH issues. Overall, engine power and fuel efficiency are increased through improved VCR engine calibration.

[0060] An exemplary procedure for an engine comprises calibrating a compression ratio scheme of a variable-compression engine based on the fuel flow and peak torque of each cylinder at each compression ratio setting of the engine; and adjusting the exhaust gas recirculation (EGR) flow to the engine according to an updated EGR calibration scheme based on the compression ratio scheme calibration. In the foregoing example, the calibration for each cylinder additionally or optionally includes determining a difference between the actual compression ratio and a predetermined compression ratio at each of a plurality of compression ratio settings.In one or all of the above examples, the adjustment additionally or optionally includes: identifying an engine cylinder with the greatest difference between the actual compression ratio and the specified compression ratio, where the actual compression ratio is lower than the specified compression ratio; and adjusting an EGR flow to the engine based on the actual compression ratio of the identified engine cylinder. In one or all of the above examples, the adjustment additionally or optionally includes: identifying an engine cylinder with the lowest actual compression ratio; and adjusting an EGR flow to the engine based on the actual compression ratio of the identified engine cylinder.In one or all of the foregoing examples, adjusting according to an updated EGR calibration scheme additionally or optionally involves adjusting based on the lowest of a variety of compression ratio settings for an individual cylinder of the engine. In one or all of the foregoing examples, adjusting when the engine load is lower than a threshold load additionally or optionally involves reducing an EGR flow when the lowest of a variety of compression ratio settings decreases, with the reduction of the EGR flow involving one or more of the following: reducing the opening of an EGR valve, adjusting a cylinder valve timing to advance the closing of the exhaust valve, and adjusting the cylinder valve timing to reduce positive intake-exhaust valve overlap.In one or all of the above examples, the engine is additionally or optionally coupled in a vehicle, and the updated EGR calibration scheme is updated from a nominal EGR calibration scheme based on pre-vehicle-manufactured engine tests, the vehicle being a hybrid electric vehicle. In one or all of the above examples, adjusting when the engine load is higher than the threshold load additionally or optionally involves adjusting the EGR flow to the engine according to the standard EGR calibration scheme.In one or all of the foregoing examples, the compression ratio scheme calibration additionally or optionally includes: estimating each of a fuel flow and peak torque of each cylinder at each of a variety of engine compression ratio settings; determining a first parameter specifying the engine's fuel flow at each of the variety of compression ratio settings; determining a second, distinct parameter specifying the engine's torque at each of the variety of compression ratio settings; and actuating a variable compression ratio mechanism of each engine cylinder based on a selection of one of the first and second parameters, the selection being based on the torque requested by the driver.In one or all of the above examples, the selection additionally or optionally includes selecting the first parameter and not the second parameter if the torque requested by the driver is below a threshold, and selecting the second parameter and not the first parameter if the torque requested by the driver is above the threshold, wherein the first parameter includes one of total engine fuel flow and brake-specific total fuel consumption, and the second parameter includes one of total engine torque and mean effective total cylinder pressure.In one or all of the above examples, actuation based on selection additionally or optionally involves actuating the variable compression ratio mechanism based on an engine cylinder with a lowest value of the first parameter when the torque requested by the driver is below a threshold, and actuating the variable compression ratio mechanism based on the engine cylinder with a highest value of the second parameter when the torque requested by the driver is above the threshold.

[0061] Another exemplary procedure involves: comparing a predetermined compression ratio with an actual compression ratio for each cylinder of a variable-compression engine that has a multitude of compression ratio settings; and adjusting an exhaust gas recirculation (EGR) flow to the engine based on the actual compression ratio of an engine cylinder with the lowest actual compression ratio. In the above examples, additionally or optionally, the EGR flow to the engine is reduced from a nominal EGR flow as a value of the lowest actual compression ratio decreases.In one or all of the foregoing examples, adjusting the EGR flow additionally or optionally occurs in response to an engine load lower than a threshold load, the method further comprising maintaining the nominal EGR flow in response to an engine load higher than the threshold load. In one or all of the foregoing examples, reducing the EGR flow additionally or optionally includes one or more of the following: reducing the opening of an EGR valve, changing the valve timing to reduce positive valve overlap, and advancing an exhaust valve timing to an earlier exhaust valve closing time.In one or all of the above examples, the method further comprises, if the engine load is higher than a threshold load, in response to the fact that a difference between the specified compression ratio and the actual compression ratio of an engine cylinder is higher than a threshold difference, additionally or optionally switching to a lower compression ratio by mechanically actuating a variable compression ratio mechanism.

[0062] Another exemplary engine system comprises: an engine with a plurality of cylinders; a VCR mechanism coupled to a piston of each cylinder of the plurality of cylinders to apply one of a plurality of compression ratio settings in a given cylinder by mechanically changing a piston position within the given cylinder; an EGR channel with an EGR valve for recirculating exhaust gas from an engine exhaust to an engine intake; and a control unit with computer-readable instructions stored in non-transient memory to: update a nominal compression ratio calibration of the engine based on each of the fuel flow and peak torque of each cylinder at each of the plurality of compression ratio settings; adjust the EGR flow to the engine based on the nominal compression ratio calibration at an engine load above a threshold load;and adjusting the EGR flow to the engine based on a lowest compression ratio from the updated compression ratio calibration at an engine load below the threshold load. In the foregoing example, adjusting the EGR flow based on the lowest compression ratio additionally or optionally includes: identifying one of the multitude of cylinders that has a lowest actual compression ratio; estimating the engine dilution for the identified multitude of cylinders; and adjusting an EGR valve opening based on the estimated engine dilution.

[0063] In one or all of the above examples, adjusting the EGR flow based on the lowest compression ratio additionally or optionally involves reducing the opening of the EGR valve as the lowest compression ratio decreases. In one or all of the above examples, the engine is additionally or optionally coupled in a hybrid electric vehicle, and the nominal compression ratio calibration and the nominal EGR calibration are each based on engine test data collected prior to vehicle manufacturing.

[0064] Another exemplary procedure for an engine involves actuating a variable compression ratio mechanism of an engine to mechanically adjust a target compression ratio of the engine according to an updated calibration, the updated calibration being based on the fuel flow and peak torque of each cylinder at each individual compression ratio setting of the mechanism.In the above example, the updated calibration additionally or optionally includes: estimating the fuel flow and peak torque of each cylinder at a variety of compression ratio settings; quantifying a total engine fuel flow at each of the variety of compression ratio settings as a sum of the fuel flow of each cylinder at a corresponding compression ratio setting; and determining a total engine torque at each of the variety of compression ratio settings as a sum of the torque of each cylinder at the corresponding compression ratio setting.In one or all of the foregoing examples, actuation additionally or optionally involves: if the torque requested by the driver is lower than a threshold, actuating the mechanism to one of a variety of compression ratio settings that exhibits the lowest overall engine fuel flow; and if the torque requested by the driver is higher than the threshold, actuating the mechanism to another of the variety of compression ratio settings that exhibits the highest overall engine torque. In one or all of the foregoing examples, the threshold is additionally or optionally based on one or more of the accelerator pedal position, engine speed, fuel octane rating, ambient temperature, and ambient humidity.In one or all of the foregoing examples, the method additionally or optionally includes adjusting an engine dilution calibration based on the lowest of a plurality of compression ratios of individual cylinders. In one or all of the foregoing examples, adjusting the engine dilution additionally or optionally includes, when the engine load is lower than a threshold, using less dilution as the lowest of the plurality of compression ratios decreases. In one or all of the foregoing examples, the method additionally or optionally includes selecting the nominal compression ratio of the engine according to a nominal calibration.In one or all of the above examples, the engine is additionally or optionally coupled in a vehicle, the method further comprising updating the nominal calibration of the engine in response to engine operation following vehicle manufacture, wherein the nominal calibration is based on an engine test prior to vehicle manufacture, and wherein the vehicle comprises a hybrid electric vehicle.

[0065] Another exemplary procedure involves: comparing a target compression ratio for an engine with the actual compression ratio of each cylinder of the engine; calculating a fuel loss associated with the target compression ratio based on a cumulative difference between the actual compression ratio of each cylinder of the engine and the target compression ratio; and switching to a lower compression ratio if the fuel loss exceeds a threshold. In the foregoing example, the target compression ratio and the actual compression ratio additionally or optionally apply to a defined compression ratio setting of a variable compression ratio mechanism, the compression ratio setting being one of a plurality of compression ratio settings of the engine.In one or all of the foregoing examples, the override additionally or optionally involves actuating a variable compression ratio mechanism to mechanically change the actual compression ratio of each cylinder of the engine. In one or all of the foregoing examples, the method additionally or optionally involves adjusting engine dilution in response to the override, the adjustment involving, when the engine load is lower than a threshold, comparing the actual compression ratio of each cylinder of the engine and applying an engine dilution setting corresponding to the lowest of the actual compression ratio of each cylinder. In one or all of the foregoing examples, the adjustment of engine dilution additionally or optionally involves adjusting an exhaust gas recirculation (EGR) quantity and a variable cam timing scheme.In one or all of the above examples, a lower EGR quantity, lower valve overlap, and earlier exhaust valve closing time are additionally or optionally applied when the lowest of the actual compression ratio of each cylinder decreases.

[0066] Another exemplary engine system comprises: an engine with a plurality of cylinders; a VCR mechanism coupled to a piston of each cylinder of the plurality of cylinders to apply one of a plurality of compression ratio settings in a given cylinder by mechanically changing a piston position within the given cylinder; an EGR channel with an EGR valve to recirculate exhaust gas from an engine exhaust to an engine intake; and a controller with computer-readable instructions stored in non-transient memory to: update a compression ratio calibration of the engine based on each of the fuel flow and peak torque of each cylinder at each of the plurality of compression ratio settings;and actuating the variable compression ratio mechanism of an engine to mechanically set a target compression ratio of the engine according to an updated calibration, the calibration being based in each case on the fuel flow and peak torque of each cylinder at each compression ratio setting of the mechanism. In the foregoing, "updating" additionally or optionally includes estimating the fuel flow and peak torque of each of the plurality of cylinders at each of the plurality of compression ratio settings; for each cylinder, quantifying a total engine fuel flow as a sum of the fuel flows at each of the plurality of compression ratio settings;and determining a total engine torque at each of the plurality of compression ratio settings as the sum of the torques of each of the plurality of cylinders at a corresponding plurality of compression ratio settings. In one or all of the foregoing examples, the control further includes, additionally or optionally, instructions to: if the torque requested by the driver is lower than a threshold, actuate the mechanism to one of a plurality of compression ratio settings that exhibits the lowest total engine fuel flow;and if the torque requested by the driver is higher than the threshold, actuate the mechanism to another of the multitude of compression ratio settings that exhibits the highest overall engine torque. In one or all of the foregoing examples, an update from a nominal compression ratio calibration based on engine testing prior to vehicle production is additionally or optionally performed. In one or all of the foregoing examples, the vehicle is additionally or optionally a hybrid electric vehicle, and the update is performed in response to engine operation following vehicle production. In one or all of the foregoing examples, the control system additionally or optionally includes instructions to: update an EGR calibration of the engine based on the lowest compression ratio setting of one of the multitude of engine cylinders during the updated compression ratio calibration;and actuation of the EGR valve based on engine load and also based on the updated EGR calibration.;

[0067] It should be noted that the exemplary control and estimation routines contained herein can be used with various engine and / or vehicle system configurations. The control procedures and routines disclosed herein can be stored as executable instructions in non-transient memory and can be executed by the control system in combination with the 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, multitasking, multithreading, and the like. In this way, various actions, operations, and / or functions can be performed in the sequence shown, in parallel, or, in some cases, omitted.Likewise, the processing sequence is not strictly necessary to achieve the features and advantages of the exemplary embodiments described here, but is provided for ease of presentation and description. One or more of the actions, processes, and / or functions can be performed repeatedly, depending on the strategy used. Furthermore, the described actions, processes, and / or functions can graphically represent code that is programmed into non-transient memory of the computer-readable storage medium in the engine control system, with the described actions being executed by carrying out the instructions in a system that includes the various engine hardware components in combination with the electronic control unit.

[0068] It is understood that the configurations and routines disclosed herein are exemplary and that these specific embodiments are not to be considered limiting, as numerous modifications are possible. For example, the foregoing technology can be applied to V-6, I-4, I-6, V-12, 4-cylinder opposed-piston, and other types of engines. The subject matter of this 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.

[0069] The following claims specifically disclose certain combinations and subcombinations that are considered novel and not self-evident. These claims may refer to "one" element or "a first" element or its equivalent. Such claims are to be understood as including one or more of these elements and neither requiring nor excluding two or more of these elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by filing new claims in this or a related application. These claims, whether broader or narrower, of the same or different scope as the original claims, are also considered to be included in the subject matter of the present disclosure.

[0070] According to the present invention, a method for an engine comprises calibrating a compression ratio scheme of a variable compression ratio engine based on the fuel flow and peak torque of each cylinder at each individual compression ratio setting of the engine; and adjusting the exhaust gas recirculation (EGR) flow to the engine according to an updated EGR calibration scheme based on the compression ratio scheme calibration.

[0071] According to one embodiment, the calibration for each cylinder involves determining a difference between the actual compression ratio and a predetermined compression ratio at each of a plurality of compression ratio settings.

[0072] According to one embodiment, the adjustment involves identifying an engine cylinder with the highest difference between the actual compression ratio and the specified compression ratio, wherein the actual compression ratio is lower than the specified compression ratio; and adjusting an EGR flow to the engine based on the actual compression ratio of the identified engine cylinder.

[0073] According to one embodiment, the adjustment involves identifying an engine cylinder with the lowest actual compression ratio; and adjusting an EGR flow to the engine based on the actual compression ratio of the identified engine cylinder.

[0074] According to one embodiment, adjusting according to an updated EGR calibration scheme involves adjusting based on the lowest of a multitude of compression ratio settings of an individual cylinder of the engine.

[0075] According to one embodiment, adjusting when the engine load is lower than a threshold load involves reducing an EGR flow when the lowest of a plurality of compression ratio settings decreases, wherein reducing the EGR flow involves one or more of reducing the opening of an EGR valve, adjusting a cylinder valve timing to advance the closing of the exhaust valve, and adjusting the cylinder valve timing to reduce positive intake-exhaust valve overlap.

[0076] According to one embodiment, the engine is coupled in a vehicle, and the updated EGR calibration scheme is updated from a nominal EGR calibration scheme based on engine tests prior to vehicle manufacturing, wherein the vehicle is a hybrid electric vehicle.

[0077] According to one embodiment, adjusting when the engine load is higher than the threshold load involves adjusting the EGR flow to the engine according to the standard EGR calibration scheme.

[0078] According to one embodiment, the compression ratio scheme calibration involves estimating each of the fuel flow and peak torque of each cylinder at each of a plurality of compression ratio settings of the engine; determining a first parameter that specifies the fuel flow of the engine at each of the plurality of compression ratio settings; determining a second, distinct parameter that specifies the torque of the engine at each of the plurality of compression ratio settings; and actuating a variable compression ratio mechanism of each engine cylinder based on a selection of one of the first and second parameters, the selection being based on the torque requested by the driver.

[0079] According to one embodiment, the selection involves selecting the first parameter and not the second parameter if the torque requested by the driver is below a threshold, and selecting the second parameter and not the first parameter if the torque requested by the driver is above the threshold, wherein the first parameter includes one of total engine fuel flow and brake-specific total fuel consumption, and the second parameter includes one of total engine torque and mean effective total cylinder pressure.

[0080] According to one embodiment, actuation based on selection involves actuating the variable compression ratio mechanism based on an engine cylinder with a lowest value of the first parameter when the torque requested by the driver is below a threshold, and actuating the variable compression ratio mechanism based on the engine cylinder with a highest value of the second parameter when the torque requested by the driver is above the threshold.

[0081] According to the present invention, a method comprises comparing a predetermined compression ratio with an actual compression ratio for each cylinder of a variable compression ratio engine having a plurality of compression ratio settings; and adjusting an exhaust gas recirculation (EGR) flow to the engine based on the actual compression ratio of an engine cylinder with the lowest actual compression ratio.

[0082] According to one embodiment, the EGR flow to the engine is reduced from a nominal EGR flow when a value of the lowest actual compression ratio decreases.

[0083] According to one embodiment, the EGR flow is adjusted in response to an engine load that is lower than a threshold load, the method further comprising maintaining the nominal EGR flow in response to an engine load that is higher than the threshold load.

[0084] According to one embodiment, reducing the EGR flow includes one or more of reducing the opening of an EGR valve, changing the valve timing to lower the positive valve overlap, and advancing an exhaust valve timing to an earlier exhaust valve closing time.

[0085] According to one embodiment, the invention is further characterized by the following: when the engine load is higher than a threshold load, in response to the fact that a difference between the predetermined compression ratio and the actual compression ratio of an engine cylinder is higher than a threshold difference, switching to a lower compression ratio by means of mechanical actuation of a variable compression ratio mechanism.

[0086] According to one embodiment, an engine system comprises an engine with a plurality of cylinders; a VCR mechanism coupled to a piston of each cylinder of the plurality of cylinders to apply one of a plurality of compression ratio settings in a given cylinder by mechanically changing a piston position within the given cylinder; an EGR channel with an EGR valve for recirculating exhaust gas from an engine outlet to an engine intake; and a controller with computer-readable instructions stored in non-transient memory for: updating a nominal compression ratio calibration of the engine based on each of the fuel flow and peak torque of each cylinder at each of the plurality of compression ratio settings; adjusting the EGR flow to the engine based on the nominal compression ratio calibration at an engine load above a threshold load;and adjusting the EGR flow to the engine based on the lowest compression ratio of the updated compression ratio calibration at an engine load below the threshold load.

[0087] According to one embodiment, adjusting the EGR flow based on the lowest compression ratio involves: identifying one of the plurality of cylinders that has the lowest actual compression ratio; estimating the engine dilution for the identified plurality of cylinders; and adjusting an opening of the EGR valve based on the estimated engine dilution.

[0088] According to one embodiment, adjusting the EGR flow based on the lowest compression ratio involves reducing the opening of the EGR valve as the lowest compression ratio decreases.

[0089] According to one embodiment, the engine is coupled in a hybrid electric vehicle, and the nominal compression ratio calibration and the nominal EGR calibration are each based on engine test data collected prior to vehicle manufacturing. QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] US 4469055

[0003]

Claims

[1] Method for an engine, comprising: Calibrating a compression ratio scheme of a variable-compression engine based on the fuel flow and peak torque of each cylinder at each individual compression ratio setting of the engine; and Adjusting the exhaust gas recirculation (EGR) flow to the engine according to an updated EGR calibration scheme based on the compression ratio scheme calibration. [2] Method according to claim 1, wherein the calibration for each cylinder includes determining a difference between the actual compression ratio and a predetermined compression ratio at each of a plurality of compression ratio settings. [3] Method according to claim 1, wherein the setting includes: Identifying an engine cylinder with the highest difference between the actual compression ratio and the specified compression ratio, where the actual compression ratio is lower than the specified compression ratio; and Adjusting the EGR flow to the engine based on the actual compression ratio of the identified engine cylinder. [4] Method according to claim 1, wherein the setting includes: Identifying an engine cylinder with the lowest actual compression ratio; and Adjusting the EGR flow to the engine based on the actual compression ratio of the identified engine cylinder. [5] Method according to claim 1, wherein the adjustment according to an updated EGR calibration scheme includes adjustment based on a lowest of a plurality of compression ratio settings of an individual cylinder of the engine. [6] Method according to claim 5, wherein the adjustment further comprises, when the engine load is lower than a threshold load, reducing an EGR flow when the lowest of a plurality of compression ratio settings decreases, wherein the reduction of the EGR flow comprises one or more of reducing an opening of an EGR valve, adjusting a cylinder valve timing to advance the closing of the exhaust valve and adjusting the cylinder valve timing to reduce positive intake with exhaust valve overlap. [7] Method according to claim 6, wherein the engine is coupled in a vehicle, and wherein the updated EGR calibration scheme is updated from a nominal EGR calibration scheme based on engine tests prior to vehicle manufacturing, wherein the vehicle comprises a hybrid electric vehicle. [8] Method according to claim 7, wherein the adjustment, when the engine load is higher than the threshold load, further includes adjusting the EGR flow to the engine according to the standard EGR calibration scheme. [9] Method according to claim 1, wherein the compression ratio scheme calibration includes: Estimating each of the fuel flow and peak torque of each cylinder at each of a variety of engine compression ratio settings; Determining a first parameter that specifies the engine's fuel flow at each of the multitude of compression ratio settings; Determining a second, distinct parameter that specifies the engine's torque at each of the multitude of compression ratio settings; and Actuating a variable compression ratio mechanism for each engine cylinder based on a selection of one of the first and second parameters, the selection being based on the torque requested by the driver. [10] Method according to claim 9, wherein the selection includes selecting the first parameter and not the second parameter when the torque requested by the driver is below a threshold value, and selecting the second parameter and not the first parameter when the torque requested by the driver is above the threshold value, wherein the first parameter includes one of total engine fuel flow and brake-specific total fuel consumption, and the second parameter includes one of total engine torque and mean effective total cylinder pressure. [11] Method according to claim 9, wherein actuation based on selection includes actuating the variable compression ratio mechanism based on an engine cylinder with a lowest value of the first parameter when the torque requested by the driver is below a threshold, and actuating the variable compression ratio mechanism based on the engine cylinder with a highest value of the second parameter when the torque requested by the driver is above the threshold. [12] Engine system, comprising: an engine with a large number of cylinders; a VCR mechanism coupled to a piston of each cylinder of the plurality of cylinders to apply in a given cylinder one of a plurality of compression ratio settings by mechanically changing a piston position within a given cylinder; an EGR channel with an EGR valve for recirculating exhaust gas from an engine outlet to an engine intake; and a controller with computer-readable instructions stored in non-transient memory for: Updating a nominal compression ratio calibration of the engine based on each of the fuel flow and peak torque of each cylinder at each of the multitude of compression ratio settings; Adjusting the EGR flow to the engine based on the nominal compression ratio calibration at an engine load above a threshold load; and Adjusting the EGR flow to the engine based on the lowest compression ratio of the updated compression ratio calibration at an engine load below the threshold load. [13] System according to claim 12, wherein adjusting the EGR flow includes the following: Identifying one of the many cylinders that has the lowest actual compression ratio; Estimating engine dilution for the identified multitude of cylinders; and Adjusting the EGR valve opening based on the estimated engine dilution. [14] System according to claim 12, wherein adjusting the EGR flow based on the lowest compression ratio includes reducing the opening of the EGR valve as the lowest compression ratio decreases. [15] System according to claim 12, wherein the engine is coupled in a hybrid electric vehicle and wherein the nominal compression ratio calibration and the nominal EGR calibration are each based on engine test data collected prior to vehicle manufacturing.

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