METHOD AND SYSTEM FOR ENGINE CONTROL

Abstract

Procedure, comprehensive: Mechanically varying the compression ratio of an engine by means of a variable compression ratio mechanism; and In response to the deteriorating mechanism, limiting the engine load.

Description

Area

[0001] The present description generally concerns methods and systems for controlling an engine in response to a deterioration of a variable compression ratio mechanism. General state of the art / Summary

[0002] The compression ratio of an internal combustion engine is defined as 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). Generally, the higher the compression ratio, the higher the thermal efficiency of the internal combustion engine. This, in turn, leads to improved fuel efficiency and a higher ratio of output energy to input energy. In conventional engines, the compression ratio is fixed, meaning that engine efficiency cannot be optimized during operation to improve fuel efficiency and engine performance.

[0003] In variable compression ratio (VCR) engines, the engine can be equipped with various mechanisms for changing the volumetric ratio between the piston's top dead center (TDC) and bottom dead center (BDC) positions, thus allowing the compression ratio to change as engine operating conditions change. As a non-limiting example, the VCR engine can be designed with a displacement-changing mechanism (e.g., an eccentric) that moves the pistons closer to or further away from the cylinder head, thereby changing the size of the combustion chambers. Other engines can vary the cylinder head volume.

[0004] An exemplary approach to exploiting the advantages of a VCR mechanism is presented by Kolmanovsky et al. in US 6,553,949 B1. A high compression ratio can be used in low engine speed / load ranges to increase thermal efficiency. A low compression ratio can be used in higher engine speed / load ranges. Furthermore, knocking in the low speed / load range can be mitigated using retarded ignition timing, while knocking in the higher speed / load range is mitigated by adjusting the compression ratio. If the engine is restricted with respect to ignition timing while operating at the higher compression ratio, the retarded combustion phase control can diminish the thermal efficiency benefit of the higher compression ratio.At this point, the compression ratio can be reduced while the ignition timing is advanced to provide a more effective balance between combustion phase control and thermal efficiency. Furthermore, the sawing effect between different compression levels is reduced, and each compression ratio can be used more effectively. Further prior art is known from DE 10 2012 113 004 A1 and DE 11 2013 001 353 T5.

[0005] However, the inventors of the present invention have recognized potential problems associated with such a system. For example, the VCR mechanism may deteriorate, resulting in the engine operating at a compression ratio other than the desired one. For instance, the VCR mechanism may become stuck. If the mechanism becomes stuck at a higher compression ratio than desired—for example, if it becomes stuck while in a higher compression ratio setting or during a transition to a lower compression ratio setting (but before the lower compression ratio setting is reached)—the risk of engine knocking and pre-ignition may increase.In particular, higher pressures at the ignition point can lead to higher temperatures and a greater likelihood of pre-ignition of the unburned exhaust gases. The occurrence of knocking and pre-ignition can reduce the service life of engine components.

[0006] The object of the present invention is therefore to address at least part of the above problem.

[0007] This problem is solved by the features of the independent patent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0008] In one example, the aforementioned problem can be addressed, at least partially, by a procedure for an engine that includes: mechanically varying the compression ratio of an engine by means of a variable compression ratio (VCR) mechanism; and, in response to the mechanism's deterioration, limiting the engine load. This reduces knocking or pre-ignition caused by deterioration of the VCR mechanism.

[0009] For example, an engine may be designed with a VCR mechanism that, when actuated, mechanically varies the position of a piston in the combustion chamber, thereby varying the compression ratio. In response to engine operating conditions, the compression ratio can be varied, for example, by applying a comparatively higher compression ratio at low engine loads to benefit from increased thermal efficiency, while at higher engine loads, a comparatively lower compression ratio is used to take advantage of combustion phase control. The VCR mechanism may become stuck during the transition between the higher and lower compression ratio settings.Deterioration of the VCR mechanism can be inferred from feedback regarding its position, for example, via a position sensor coupled to the mechanism. For instance, if the detected position differs from the commanded position, it can be inferred that the mechanism has become stuck at the wrong compression ratio. Alternatively, deterioration of the VCR mechanism can be inferred from the occurrence of knocking that is higher than expected and / or adaptive knocking that is delayed earlier than expected to reach a threshold. The stuck compression ratio can be determined based on feedback from a position sensor or based on the occurrence of knocking.The engine load can then be limited to a threshold corresponding to the highest possible load for the respective stuck compression ratio. Intake air charge can be reduced to limit the load, for example by decreasing the opening of an intake throttle or by increasing the opening of an exhaust wastegate valve. Furthermore, ignition timing can be adjusted based on the stuck compression ratio. The ignition timing can then be advanced.

[0010] In this way, a variable compression ratio mechanism can be better protected against recurring knocking and pre-ignition. The technical benefit of restricting the intake air charge to limit engine load in response to deterioration of the variable compression ratio mechanism is that recurring knocking can be prevented. In particular, thermal stress that can be triggered in a cylinder due to operation at a higher-than-intended compression ratio can be reduced (which can occur, for example, because the mechanism may become stuck in a setting with a higher-than-expected compression ratio). Furthermore, the engine can be operated with ignition timing advanced beyond its retarded ignition limit. Overall, the service life of the engine components can be extended.

[0011] It is understood that the foregoing summary is provided to present, in simplified form, a selection of concepts that are described in more detail in the full description. It is not intended to highlight important or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the full description. Furthermore, the claimed subject matter is not limited to implementations that address the disadvantages mentioned above or in any part of this disclosure. Brief description of the drawings Fig. Figure 1 illustrates an exemplary engine system designed with a variable compression ratio mechanism. Fig. Figure 2 shows a higher-level flowchart for limiting engine load in response to an indication of deterioration of the VCR mechanism. Fig. Figure 3 shows a higher-level flowchart for detecting deterioration of the VCR mechanism. Fig. Figure 4 shows a predictive example of VCR and engine load adjustments during engine operation. Fig. Figure 5 shows an example lookup table that can be used to represent a compression ratio versus engine speed / load conditions. Detailed description

[0012] The following description concerns systems and methods for reducing the risk of knocking and pre-ignition in an engine system designed with a VCR (Variable Compression Ratio) mechanism, as described in relation to the engine system from Fig. 1 described. By actuating the VCR mechanism, the position of a piston in a combustion chamber can be varied, which allows for improvements in thermal efficiency. A control system can be designed to execute a control sequence such as the example sequence from Fig. 2. To perform a change in the engine's compression ratio based on engine operating conditions, for example by referring to the table from Fig. 5. In response to deterioration of the VCR mechanism, the control unit can block engine load based on the compression ratio at which the mechanism became stuck. The control unit can detect deterioration of the VCR mechanism based on feedback regarding the position of the mechanism or based on knock frequency and the use of adaptive retardation, as described in Fig. 3 described. An example of engine operation with VCR and engine load settings is shown in Fig. Figure 4 illustrates this. In this way, VCR deterioration can be detected and addressed early.

[0013] Fig. Figure 1 depicts an exemplary embodiment of a combustion chamber or cylinder of an internal combustion engine 10. The engine 10 can receive control parameters from a control system, which includes the controller 12, and input from an operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (here also referred to as the "combustion chamber") 14 of the engine 10 can have combustion chamber walls 136, inside which a piston 138 is arranged. The piston 138 can be coupled to the crankshaft 140, so that an alternating motion of the piston is translated into a rotational motion of the crankshaft. The crankshaft 140 can be coupled to at least one drive wheel of the passenger car via a transmission system.Furthermore, a starter can be coupled to the crankshaft 140 via a flywheel to enable a starting process of the internal combustion engine 10.

[0014] The internal combustion engine 10 can be configured as a variable compression ratio (VCR) engine, wherein 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 CR of the internal combustion engine can be varied via a VCR actuating element 192, which actuates a VCR mechanism 194. In some embodiments, the CR can be varied 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 lower) and a second, higher CR (where the ratio is higher). In other embodiments, a predetermined number of stepped compression ratios can be provided.Furthermore, the CR can be continuously variable between the first, lower CR and the second, higher CR (or any CR in between).

[0015] In the illustrated example, the VCR mechanism 194 is coupled to the piston 138, allowing the VCR mechanism to change the piston's TDC position. For example, the piston 138 can be coupled to the crankshaft 140 via a VCR mechanism 194 for changing the piston position, which moves the piston closer to or further away from the cylinder head, thereby changing the size of the combustion chamber 14. A position sensor 196 can be coupled to the VCR mechanism 192 and can be configured to provide feedback to the control unit 12 regarding the position of the VCR mechanism 194 (and thus the compression ratio) applied to the cylinder.

[0016] In one example, changing the piston's position in the combustion chamber also changes the piston's relative stroke in the cylinder. The VCR (Variable Control Reduction) mechanism for changing the piston position can be coupled to a conventional crankshaft or a non-conventional crankshaft. Non-restrictive examples of a non-conventional crankshaft to which the VCR mechanism can be coupled include variable-distance crankshafts and variable-kinematic-length crankshafts. In one example, the crankshaft 140 can be configured as an eccentric shaft. In another example, an eccentric can be coupled to or in the region of a piston pin, with the eccentric changing the piston's position in the combustion chamber. The eccentric's movement can be controlled by oil channels in the piston rod.

[0017] It is understood that other VCR mechanisms that mechanically change the compression ratio can be used. For example, the common rail (CR) of the internal combustion engine can be varied via a VCR mechanism that changes the cylinder head volume (i.e., the dead space in the cylinder head). In another example, the VCR mechanism may involve a piston that responds to hydraulic pressure, air pressure, or mechanical action. Furthermore, the VCR mechanism may include a multi-linkage mechanism or a bent-rod mechanism. Other combinations are possible. It is understood that, in the sense used here, the VCR engine may be designed to adjust the engine's CR via mechanical adjustments that vary piston position or cylinder head volume. Therefore, VCR mechanisms do not include CR adjustments achieved through valve or cam adjustment settings.

[0018] By adjusting the piston's position within the cylinder, the effective (static) compression ratio of the internal combustion engine (i.e., the difference between the cylinder volumes at top dead center (TDC) relative to bottom dead center (BDC)) can be varied. In one example, reducing the compression ratio involves decreasing the piston's stroke within the combustion chamber by increasing the distance between the top of the piston and the cylinder head. For instance, the internal combustion engine can be operated at a lower compression ratio by having the control unit send a signal to actuate the variable compression ratio (VCR) mechanism to a position where the piston has a smaller effective stroke within the combustion chamber.In another example, the internal combustion engine can be operated at a second, higher compression ratio by having the control unit send a signal to move the VCR mechanism to a second position, in which the piston has a greater effective stroke within the combustion chamber. Changes to the engine's compression ratio can be advantageously used to improve fuel efficiency. For example, a higher compression ratio can be used to improve fuel efficiency at light to moderate engine loads until the retarded ignition from the early onset of knocking diminishes the fuel efficiency benefit. The engine can then be switched to a lower compression ratio, trading thermal efficiency for combustion phase control efficiency.Continuous VCR systems can continuously optimize combustion phase control and thermal efficiency to provide the best compression ratio between the limits for higher and lower compression ratios under given operating conditions. For example, an engine control unit can consult a lookup table, such as Table 500 from [reference missing]. Fig. 5. To select an applicable compression ratio based on engine speed / load conditions. As discussed below, the selection may involve choosing a lower compression ratio at higher engine loads and choosing a higher compression ratio at lower engine loads.

[0019] There may be conditions under which the VCR mechanism deteriorates, for example, if the mechanism becomes stuck in an unintended compression ratio. For instance, the mechanism may become stuck in a higher compression ratio setting when a transition to a lower compression ratio setting is commanded. Prolonged unintended operation at the higher compression ratio can result in an increased tendency to knock and pre-ignition. As described in reference to Fig. As explained in section 2, in response to an indication of deterioration of a VCR mechanism, the control unit can restrict engine load to reduce the occurrence of knocking and pre-ignition. Furthermore, the indication of VCR mechanism deterioration can be derived based on feedback from a position sensor coupled to the VCR mechanism (such as position sensor 196) and / or based on the knock frequency and the use of adaptive ignition in response to the occurrence of knocking.

[0020] Cylinder 14 can draw in intake air via a series of intake air channels 142, 144, and 146. Intake air channel 146 can communicate with other cylinders of the internal combustion engine 10 in addition to cylinder 14. In some embodiments, one or more of the intake channels can include a charging device such as a turbocharger or a mechanical supercharger. For example, Figure 1 shows... Fig. 1. An internal combustion engine 10, which is equipped with a turbocharger including a compressor 174 arranged between the intake ports 142 and 144 and an exhaust turbine 176 arranged along an exhaust port 148. The compressor 174 can be supplied with energy, at least partially, via a shaft 180 from the exhaust turbine 176, the charging device being configured as a turbocharger. In other examples, such as when the internal combustion engine 10 is equipped with a mechanical supercharger, the exhaust turbine 176 can optionally be omitted, with the compressor 174 being supplied with energy by mechanical input from an electric motor or the internal combustion engine. A throttle 20, comprising a throttle plate 164, can be provided along an intake port of the internal combustion engine for varying the flow rate and / or pressure of the intake air supplied to the cylinders of the internal combustion engine.For example, the throttle 20 can be arranged downstream of the compressor 174, as in . Fig. 1 shown, or alternatively it can be provided upstream of the compressor 174.

[0021] The exhaust port 148 can receive exhaust gases from other cylinders of the internal combustion engine 10 in addition to cylinder 14. The exhaust gas sensor 128 is shown coupled to an exhaust port 148 located upstream of the emission control device 178. The sensor 128 can be selected from various suitable sensors to provide an indication of an exhaust air / fuel ratio, such as a linear lambda sensor or UEGO (Universal Exhaust Gas Oxygen), a dual-state lambda sensor or EGO (as shown), a HEGO (heated EGO), a NOx, HC, or CO sensor. The emission control device 178 can be a three-way catalytic converter (TWC), a NOx trap, various other emission control devices, or combinations thereof.

[0022] The exhaust gas temperature can be estimated by one or more temperature sensors (not shown) arranged in the exhaust port 148. Alternatively, the exhaust gas temperature can be derived from engine operating conditions such as engine speed, load, air-fuel ratio (AFR), ignition timing, etc. Furthermore, the exhaust gas temperature can be calculated from one or more exhaust gas sensors 128. It is understood that the exhaust gas temperature can alternatively be estimated by any combination of the temperature estimation methods listed herein.

[0023] Each cylinder of the internal combustion engine 10 can comprise one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown comprising at least one intake control valve 150 and at least one exhaust control valve 156, which is arranged in an upper region of cylinder 14. In some embodiments, each cylinder of the internal combustion engine 10, including cylinder 14, can comprise at least two intake control valves and at least two exhaust control valves, which are arranged in an upper region of the cylinder.

[0024] The inlet valve 150 can be controlled by a controller 12 via a cam actuation system 151. Similarly, the exhaust valve 156 can be controlled by the controller 12 via a cam actuation system 153. The cam actuation systems 151 and 153 can include one or more cams and utilize one or more of the following systems: cam profile adjustment (CPS), variable cam actuation (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems, which can be operated by the controller 12 to vary the valve operation. The position of the inlet valve 150 and the exhaust valve 156 can be determined by the valve position sensors 155 and 157, respectively. In alternative embodiments, the inlet and / or exhaust valve can be controlled by an electric valve actuator.For example, cylinder 14 may alternatively comprise an inlet valve controlled by an electric valve actuator and an exhaust valve controlled by cam actuation systems, including CPS and / or VCT systems. In other embodiments, the inlet and exhaust valves may be controlled by a common valve actuator or actuation system, or by a variable valve actuation element or system.

[0025] Cylinder 14 can have a compression ratio, which is the ratio of the volumes when the piston 138 is at bottom dead center (BDC) up to top dead center (TDC). Traditionally, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio can be increased. This can occur, for example, when fuels with a higher octane rating or fuels with a higher latent heat of vaporization are used. The compression ratio can also be increased when using direct injection due to its effect on internal combustion engine knock. The compression ratio can also be varied based on the control requirements via settings of a VCR actuator 192, which actuates a VCR mechanism 194, thereby varying the effective position of the piston 138 in the combustion chamber 14.The compression ratio can be derived based on feedback from sensor 196 regarding the position of VCR mechanism 194.

[0026] In some embodiments, each cylinder of the engine 10 may have a spark plug 192 to initiate combustion. Under selected operating modes, the ignition system 190 can provide a spark to the combustion chamber 14 via the spark plug 192 in response to a pre-ignition signal SA from the control unit 12. However, in some embodiments, the spark plug 192 may be omitted, for example, if the engine 10 can initiate combustion by auto-ignition or by fuel injection, as may be the case with some diesel engines.

[0027] In some embodiments, each cylinder of the engine 10 can be equipped with one or more injection devices for supplying fuel to it. As a non-limiting example, cylinder 14 is shown to include an injection device 166. In the illustration, the injection device 166 is directly coupled to cylinder 14 to inject fuel directly into it in proportion to the pulse width of a signal FPW received by the controller 12 via the electronic driver 168. In this way, the injection device 166 provides so-called direct injection (hereinafter also referred to as "DI") of fuel into the combustion cylinder 14. Fig. Figure 1 shows the injection device 166 as a side-mounted injection device; it can also be located above the piston, for example, near the position of the spark plug 192. Such a position can improve mixing and combustion when the engine is operated with an alcohol-based fuel, since some alcohol-based fuels have lower volatility. Alternatively, the injection device can be located above and near the intake valve to improve mixing. The fuel can be supplied to the fuel injection device 166 from a high-pressure fuel system 8, which includes fuel tanks, fuel pumps, and a fuel distributor. Alternatively, the fuel can be supplied at a lower pressure by a single-stage fuel pump, in which case the timing of the direct fuel injection during the compression stroke may be more restricted than when using a high-pressure fuel system.Furthermore, the fuel tanks, although not shown, may have a pressure converter that provides a signal to the control unit 12. It is understood that, in an alternative embodiment, the injection device 166 may be a port fuel injection device that supplies fuel to the intake manifold upstream of the cylinder 14.

[0028] It is further understood that, while in the illustrated embodiment the engine is operated by injecting fuel via a single direct injection valve, in alternative embodiments the engine can be operated by using two or more injection devices (for example, one direct injection device and one port injection device per cylinder, or two direct injection devices / two port injection devices per cylinder, etc.) and by varying a relative injection quantity into the cylinder from each injection device.

[0029] Fuel can be supplied to the cylinder via the injection system during a single cylinder stroke. Furthermore, the amount and / or relative quantity of fuel supplied by the injection system can vary depending on operating conditions. Multiple fuel injections can also be performed per stroke for a single combustion event. These multiple injections can occur during the compression stroke, intake stroke, or suitable combinations thereof. Additionally, fuel can be injected during the stroke to adjust the air-to-fuel ratio (AFR) for combustion. For example, fuel can be injected to provide a stoichiometric AFR. An AFR sensor can be included to provide an estimate of the AFR in the cylinder.In one example, the AFR sensor could be an exhaust gas sensor such as a lambda probe 128. By measuring the amount of residual oxygen (for lean mixtures) or unburned hydrocarbons (for rich mixtures) in the exhaust gas, the sensor can determine the AFR. The AFR can then be provided as a lambda (λ) value, that is, as the ratio of the actual AFR to the stoichiometry for a specific mixture. Thus, a lambda value of 1.0 indicates a stoichiometric mixture, mixtures that are richer than stoichiometric mixtures have a lambda value less than 1.0, and mixtures that are leaner than stoichiometric mixtures have a lambda value greater than 1.

[0030] As described above, Fig. 1. Only one cylinder of a multi-cylinder internal combustion engine. Basically, each cylinder can equally include its own set of intake / exhaust valves, fuel injection device(s), spark plug, etc.

[0031] Fuel tanks in fuel system 8 can contain fuel with different properties, for example, different fuel compositions. These differences can include different alcohol contents, different octane ratings, different heats of vaporization, different fuel mixtures and / or combinations thereof, etc.

[0032] The internal combustion engine 10 can further include a knock sensor 90 coupled to each cylinder 14 for detecting abnormal cylinder combustion events. In alternative embodiments, one or more knock sensors 90 can be coupled to selected locations on the engine block. The knock sensor can be an accelerometer on the cylinder block or an ionization sensor integrated into the spark plug of each cylinder. The output of the knock sensor can be combined with the output of a crankshaft accelerometer to indicate an abnormal combustion event in the cylinder. In one example, abnormal combustion due to one or more knocking events and pre-ignition can be detected and distinguished from one another based on the output of the knock sensor 90 within one or more defined windows (e.g., windows for crankshaft angle adjustment).For example, knocking can be detected as a reaction to a knock sensor output estimated within a knock window exceeding a knock threshold, while pre-ignition can be detected as a reaction to a knock sensor output estimated within an ignition advance window exceeding an ignition advance threshold, the ignition advance threshold exceeding the knock threshold, and the ignition advance window being ahead of 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 is corrected by enriching the mixture and / or limiting the engine load. Moreover, reducing the compression ratio also reduces changes in further ignition advance. As discussed here with reference to... Fig. 3. A knock frequency can also be used to indicate a deterioration of a VCR mechanism, which may occur, for example, if the VCR mechanism has become stuck in an unintended compression ratio setting (which is higher or lower than the intended compression ratio setting).

[0033] With renewed reference to Fig. Figure 1 shows the control unit 12 as a microcomputer, which includes a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, represented in this specific example as read-only memory 110, direct access memory 112, keep-alive memory 114 and a data bus.In addition to the signals discussed previously, the control unit 12 receives various signals from sensors coupled to the internal combustion engine 10, including the measurement of the mass airflow (MAF) from the mass airflow sensor 122; the engine coolant temperature (ECT) from the temperature sensor 116, which is coupled to a cooling sleeve 118; a profile ignition pulse (PIP) signal from the Hall effect sensor 120 (or other) which is coupled to the crankshaft 140; a throttle position (TP) from a throttle position sensor; the manifold absolute pressure (MAP) signal from sensor 124; the cylinder AFR from the oxygen sensor 128; abnormal combustion from the knock sensor 90; and a crankshaft acceleration sensor and VCR mechanism position from a position sensor 196. An internal combustion engine speed signal, RPM, can be generated by the control unit 12 from the PIP signal.The manifold pressure signal (MAP) from a manifold pressure sensor can be used to provide an indication of vacuum or pressure in the intake manifold. The control unit 12 receives signals from the various sensors. Fig. 1 and suspends the various actuating elements Fig. 1. The control unit adjusts the internal combustion engine operation based on received signals and instructions stored in a memory of the control unit. 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 actuates the VCR mechanism to mechanically move the piston closer to or further away from the cylinder head, thereby changing the combustion chamber volume. In another example, the control unit can compare an output from the position sensor coupled to the VCR mechanism with a commanded signal to the VCR mechanism to determine whether the VCR mechanism has become stuck in an unintended compression ratio setting.In response to the VCR mechanism sticking, for example with a compression ratio setting above the intended one, the control unit can send a signal to an intake throttle to restrict the air supply to the engine, thereby limiting the engine load to reduce the tendency for knocking and pre-ignition caused by continued operation at the increased compression ratio setting.

[0034] A non-volatile read-only storage medium 110 may contain computer-readable data that represents instructions executable by a processor 106 to perform the procedures described below, as well as other variants that are assumed and not explicitly listed.

[0035] In this way, the systems display Fig. 1. An engine system comprising: an engine having one cylinder; a variable compression ratio mechanism to mechanically change a piston's position in the cylinder; a position sensor coupled to the variable compression ratio mechanism; a spark plug to provide a spark to the cylinder; an intake throttle; a turbocharger having an intake compressor driven by an exhaust turbine; a wastegate having a wastegate actuator coupled to the exhaust turbine; a knock sensor; and a control system designed with computer-readable instructions stored on non-volatile memory to: actuate the variable compression ratio mechanism to move the engine from a higher compression ratio setting to a lower compression ratio setting; display,that the mechanism has stuck in the higher compression ratio setting, based on an output from one or more of the position sensor and the knock sensor; and in response to the indication of a reduction in air charge supplied to the engine during ignition timing retardation. The indication may include an indication that the mechanism has stuck in the higher compression ratio setting, in response to one or more of the following: that a knock frequency, as indicated based on the output from the knock sensor, is above a frequency threshold; and that an actual position of the mechanism, as indicated based on the output from the position sensor, differs from a commanded position.where each is based on the commanded position and frequency threshold of the lower compression ratio setting. Reducing the air charge may involve one or more of the following: decreasing an intake throttle opening and increasing a wastegate actuator opening to limit the maximum engine load permissible at the higher compression ratio setting. The control unit may include further instructions to limit the maximum engine load permissible at the higher compression ratio setting in response to an indication of pre-ignition other than knocking, as indicated based on the knock sensor output following the reduction in intake air charge.

[0036] In relation to Fig. Section 2 describes an exemplary procedure 200 for limiting engine load in response to an indication of deterioration of the VCR mechanism. This procedure reduces the occurrence of knocking and pre-ignition caused by sustained operation at a higher than intended compression ratio. Instructions for executing procedure 200 and the other procedures contained herein can be issued by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the internal combustion engine system, such as those described above with respect to 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.

[0037] In procedure 200, section 202 involves estimating and / or measuring engine operating conditions. Engine operating conditions may include, for example, driver power demand (e.g., based on output from a pedal position sensor coupled to a vehicle driver's pedal); ambient temperature, pressure, and humidity; engine temperature; manifold pressure (MAP); manifold air flow (MAF); catalytic converter temperature; intake air temperature; charge level; fuel octane rating of the fuel available in a fuel tank, etc.

[0038] In the case of 204, procedure 200 involves selecting a compression ratio for operating the engine based on the estimated engine operating conditions. The engine can be equipped with a VCR mechanism (e.g., the VCR mechanism 194 from Fig. 1) The system may be designed 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, multiple compression ratios between the first and second settings may be possible. The control unit can compare the fuel efficiency of each engine compression ratio under the driver's power demand and select the compression ratio that provides the highest fuel efficiency. The control unit can compare fuel efficiency at the two compression ratios, for example, by comparing the engine's base fuel consumption (BSFC) at each compression ratio.The fuel efficiency of the engine can be stored for each compression ratio using a table, a diagram, an algorithm and / or an equation as a function of the operating conditions (e.g. engine speed, torque, temperature, humidity, derived octane rating of the fuel, etc.).

[0039] In one example, the controller can refer to a lookup table or a chart, for example, Table 500 from Fig. 5, to select a compression ratio for operating the engine based on engine speed / load conditions. As shown in Diagram 500, if the engine load or BMEP increases, the selected compression ratio may be reduced. Accordingly, a lower compression ratio is selected at higher engine loads and a higher compression ratio is selected at lower engine loads.

[0040] In 206, procedure 200 involves actuating the VCR mechanism to provide the selected compression ratio. For example, the controller can send a signal to a VCR actuator (e.g., VCR actuator 192 from Fig. 1) which is coupled to the VCR mechanism, to move the mechanism to a position that provides the selected compression ratio. In one example, the controller can send a signal to move the VCR mechanism to a higher compression ratio setting at low to moderate engine speeds and loads. In another example, the controller can send a signal to move the VCR mechanism to a lower compression ratio setting at moderate to high engine speeds and loads.

[0041] In the case of 208, procedure 200 involves determining whether the VCR mechanism has deteriorated. Specifically, it can be determined whether the VCR mechanism has become stuck at a compression ratio setting that differs from the intended compression ratio setting for the given engine speed / load conditions. As detailed below with reference to Fig. As explained in section 3, deterioration of the VCR mechanism can be inferred from an output of a VCR position sensor indicating that the VCR mechanism's position differs from an expected position based on the intended compression ratio setting. In another example, deterioration of the VCR mechanism can be inferred from an output of a knock sensor indicating that the knock frequency exceeds a knock threshold. Furthermore, deterioration of the VCR mechanism can be observed as a result of adaptive ignition retardation exceeding expectations.

[0042] If it is determined that the VCR mechanism has not deteriorated, procedure 200 proceeds to 210, with the control unit continuing to adjust the engine's compression ratio based on engine operating conditions via VCR mechanism settings. For example, the control unit may continue to compare fuel efficiency at each engine compression ratio for the driver's power requirements and select the compression ratio that provides the highest fuel efficiency, as described in 204, and continue to actuate the VCR actuator to operate the VCR mechanism that provides the selected compression ratio, as described in 206. Procedure 200 may then proceed to 220, as described below.

[0043] If the control unit (CCU) detects deterioration of the VCR mechanism at step 208, it proceeds to step 211 to determine the stuck compression ratio. For example, the VCR mechanism may deteriorate during a transition between compression ratio settings (for example, if the engine is in a higher compression ratio setting and is commanded to switch to a lower compression ratio setting, or if the engine is in a lower compression ratio setting and is commanded to switch to a higher compression ratio setting). The control unit can determine the stuck compression ratio based on a detected position of the VCR mechanism. For example, it can determine the stuck compression ratio based on an output from a position sensor coupled to the VCR mechanism (e.g., sensor 196). Fig. 1) The control unit determines the actual position of the VCR mechanism. If the actual position detected does not match the expected position commanded, the control unit can learn the actual position as a stuck position and determine the corresponding stuck compression ratio. The VCR mechanism may stick at the lower compression ratio when commanded at the higher ratio, may stick at the higher compression ratio when commanded at the lower ratio, or may stick in a position between the original and commanded ratios. In other examples, the stuck compression ratios may be derived based on the occurrence of knocking, adaptive ignition, etc.

[0044] The procedure then proceeds to 212, where the procedure involves limiting the engine load by restricting the air charge to the engine in response to the indication of deterioration of the VCR mechanism. Specifically, the control unit can limit the maximum permissible engine load based on the stuck compression ratio, regardless of the intended compression ratio. In one example, if it is commanded to move to a lower compression ratio setting, the VCR mechanism can remain stuck in a higher compression ratio setting (or between the higher and lower compression ratio settings). For instance, the control unit can operate the engine at the higher compression ratio due to the increased thermal efficiency at the higher compression ratio setting, given lower torque demands from the driver (and lower engine loads).However, knocking can occur at the higher compression ratio, necessitating the use of retarded ignition. Once adaptive ignition has been successfully retarded, the engine's ignition timing can be restricted until the point at which the retardation of the combustion phase control diminishes the thermal efficiency benefit of operating at the higher compression ratio. In response to adaptive ignition being retarded to a certain limit while operating at the higher compression ratio, the control unit may command a transition to the lower compression ratio. However, the VCR mechanism may become stuck at the higher compression ratio setting (or between the higher and lower compression ratio settings) during the transition.Here, in response to the indication of VCR mechanism deterioration, the control unit can reduce the maximum air charge that can be drawn into the engine while it is stuck in the higher compression ratio setting, thereby reducing the maximum engine load and boost pressure achievable at the stuck compression ratio. Consequently, the cylinder can operate at the higher compression ratio with a less restricted engine load (and less restricted air charge flow) if the VCR mechanism has not deteriorated, but can operate at the higher compression ratio with a more restricted engine load (and more restricted air charge flow) if the VCR mechanism has deteriorated.

[0045] By restricting the intake air fill, the engine load can be actively kept below a limit for the cylinder in the stuck compression ratio.

[0046] Consequently, high-pressure oscillations in the cylinder, caused by knocking and / or pre-ignition, which can occur due to prolonged operation at a stuck compression ratio, can be reduced. By decreasing the tendency to knock and pre-ignition when operating at an unintended compression ratio due to deterioration of the VCR mechanism, the service life of engine components can be improved and the VCR's lifespan can be stabilized.

[0047] Restricting the engine load by restricting the air supply to the engine can involve adjusting an intake throttle opening, as shown in 214, and / or adjusting a wastegate valve opening, as shown in 216. For example, a throttle valve (e.g., throttle valve 20) can be adjusted. Fig. 1) that is located in an air intake duct of the engine can be moved to a more closed position, thereby reducing the intake throttle opening at the stuck compression ratio. This reduces the amount of air flowing through the throttle valve and into the engine's cylinders. In another example, if the engine is a turbocharged engine, a wastegate valve or actuator of a wastegate coupled across an exhaust turbine can be moved to a more open position. Enlarging the orifice of the wastegate actuator can increase the amount of exhaust gas flowing through the wastegate as it bypasses the exhaust turbine, thereby reducing the turbine speed and, in turn, the mass flow through an intake compressor driven by the exhaust turbine. The reduced mass flow through the compressor decreases the boost pressure and air-charge flow to the engine.

[0048] The required degree of load limitation and the corresponding position of the throttle valve or wastegate actuator being commanded can be determined as a function of the stuck compression ratio and other engine operating conditions, such as MAF and MAP. For example, a higher degree of load limitation may be applied if the VCR mechanism has stuck at a higher compression ratio than intended, since prolonged operation at a higher compression ratio than intended can increase the tendency for abnormal combustion events such as knocking and pre-ignition. Conversely, a lower degree of load limitation may be applied if the VCR mechanism has stuck at a lower compression ratio than intended. The control can be based on a graph, an algorithm, a lookup table, etc.These examples refer to parameters that take the stuck compression ratio and a desired compression ratio as inputs and the desired degree of load limitation (including a corresponding throttle position and / or wastegate valve position) as outputs. In some examples, the wastegate valve position may also be based on the intake throttle position.

[0049] In procedure 200, part 218 involves setting an ignition timing based on the measured position of the VCR mechanism (as determined, for example, based on the output of the position sensor). This means that the ignition is scheduled based on the stuck compression ratio and independently of the intended compression ratio (and the intended VCR position). For example, the ignition timing for the stuck compression ratio at the measured VCR position can be selected (e.g., accelerated or retarded) based on the actual or detected position of the VCR mechanism, rather than setting an ignition timing for the intended compression ratio based on the commanded position of the VCR mechanism.In the absence of VCR mechanism deterioration, ignition timing adjustments can be made nominally when a piston is at a specific position in a cylinder (e.g., before top dead center) to maximize the amount of force on the piston generated by the expansion of combustion gases. Since the piston's position in the cylinder changes at a given crankshaft angle based on the VCR mechanism's position, the optimal ignition timing also changes based on the VCR mechanism's position. Accordingly, if the VCR mechanism deteriorates and the actual compression ratio at which the engine has become stuck differs from the intended compression ratio, the ignition timing is adjusted to compensate for the difference.The control unit can, for example, select an ignition timing for the stuck compression ratio by referring to a diagram, an algorithm, or a lookup table with the detected position of the VCR mechanism, engine speed, intake air temperature, MAP, MAP, and air-fuel ratio as inputs and the ignition timing as output.

[0050] Scheduling the ignition timing at the measured VCR position can involve scheduling it based on the measured VCR position itself, as well as on the engine speed and load at that position. For example, at an engine speed of 2500 rpm and a BMEP pressure of 10 bar, a measured VCR position corresponding to a compression ratio of 13:1 might require scheduling the ignition at 2 degrees BTDC. In another example, for the same engine speed and load, a measured VCR position corresponding to a compression ratio of 8:1 might require scheduling the ignition at 22 degrees BTDC.

[0051] In the case of 220, procedure 200 involves determining whether a knock is detected. As in relation to Fig. As described in section 1, knocking can be based on an output from a knock sensor (e.g., knock sensor 90 from Fig. 1) in combination with the output of a crankshaft acceleration sensor obtained during a defined knock window. In particular, the tendency to knock increases at high cylinder pressures, which can occur if the engine is operated for an extended period at a compression ratio higher than intended. When knock is detected, procedure 200 proceeds to 222 to perform a knock mitigation operation involving retardation of the ignition timing. For example, at 210, the ignition timing may be retarded from a nominal point determined based on the actual compression ratio if the VCR mechanism has not deteriorated, or at 218, from a point based on the stuck compression ratio if the compression ratio has deteriorated.In one example, the nominal ignition timing applied when the VCR mechanism is not deteriorating is advanced more than the ignition timing used when the VCR mechanism has deteriorated. In another example, at higher loads, if the engine has become stuck at a higher compression ratio, the ignition may need to be retarded more to prevent knocking. Following 222, procedure 200 ends.

[0052] If no knock is detected, procedure 200 proceeds to 224 and involves determining whether pre-ignition is detected. Pre-ignition can be detected based on output from the knock sensor and the crankshaft accelerometer obtained during a pre-ignition window. For example, the pre-ignition window may occur at an earlier crankshaft angle than the knock window. In one example, pre-ignition in a cylinder may be indicated if abnormal combustion occurs before an ignition event in that cylinder. Conversely, knock in a cylinder may be indicated if abnormal combustion occurs after an ignition event in that cylinder.Furthermore, knocking can be detected based on the knock sensor output within the knock window relative to a knock threshold, while pre-ignition can be detected based on the knock sensor output within the pre-ignition window relative to a pre-ignition threshold, where the pre-ignition threshold is higher than the knock threshold. In this way, pre-ignition can be differentiated based on the knock sensor output in different windows and relative to different thresholds.

[0053] If no pre-ignition is detected, procedure 200 proceeds to 226 and involves maintaining the engine settings. For example, ignition timing, fuel supply, and engine load can continue to be set to their nominal values, based on engine operating conditions, including any changes in the driver's torque requirements. Procedure 200 ends after 226.

[0054] If pre-ignition is detected, procedure 200 proceeds to perform one or more actions to mitigate the pre-ignition, which includes enriching the pre-ignition cylinder at 228. By increasing the amount of fuel supplied to the pre-ignition cylinder relative to the amount of air, in order to run the cylinder richer than stoichiometric, a charge-cooling effect is achieved, which reduces the temperature in the pre-ignition cylinder. Cooling the cylinder reduces the likelihood of further pre-ignition occurring in that cylinder. Because fuel enrichment can result in a deterioration of fuel efficiency, worsened exhaust emissions, and a possible reduction in torque, only the pre-ignition cylinder(s) can be selectively enriched.

[0055] At 230, procedure 200 involves a (further) restriction of the engine load to decrease the probability of further pre-ignition. For example, in response to an indication of pre-ignition received while the engine is in the stuck compression ratio (where the engine load has already been restricted, at 212), the engine load may be further restricted. This may involve further decreasing the opening of the intake throttle valve and / or further increasing the opening of the wastegate actuator to further reduce the intake air charge and the maximum boost pressure permissible in the stuck compression ratio. The further restricted engine load may be determined using a graph, a lookup table, or an algorithm. Following 230, procedure 200 ends.

[0056] Thus, it Fig. 2. A method for adjusting engine operation in response to an indication of deterioration of the VCR mechanism is provided, which can reduce the tendency for abnormal combustion events such as knocking and pre-ignition. Reducing the occurrence of knocking and pre-ignition can help extend the service life of engine components.

[0057] In relation to Fig. 3 is an exemplary procedure 300 for determining whether a VCR mechanism (e.g. the VCR mechanism 194 from Fig. 1) has deteriorated an engine, as shown. As in relation to Fig. As described in section 1, the VCR mechanism can deteriorate if it becomes stuck in a cylinder compression ratio other than the intended one. If the mechanism becomes stuck in a lower than intended compression ratio, the engine's thermal efficiency may decrease, resulting in reduced fuel efficiency. If the mechanism becomes stuck in a higher than intended compression ratio, the tendency to knock and pre-ignition may increase. For example, procedure 300 can be used as part of procedure 200 from Fig. 2 (e.g. at 208) will be executed.

[0058] Procedure 300 begins with 302 and involves determining whether feedback regarding the position of the VCR mechanism is available. For example, feedback regarding the position of the VCR mechanism may be available if a position sensor is coupled to the VCR mechanism (e.g., position sensor 196 from Fig. 1).

[0059] If feedback regarding the position of the VCR mechanism is available, procedure 300 transitions to 304 and involves receiving feedback regarding the position of the VCR mechanism. For example, the position of the VCR mechanism can be determined based on an output from the position sensor coupled to the VCR mechanism. In one example, determining the position of the VCR mechanism might involve determining the actual compression ratio of the cylinder.

[0060] In 306, after determining the actual position of the VCR mechanism (also referred to here as the actual VCR position), it can be determined whether the actual (detected) position of the VCR mechanism differs from an expected position. The expected or intended position may correspond to a position of the VCR mechanism based on an instruction sent by the controller to the VCR actuator. The expected position may be a commanded position that provides a compression ratio selected by the controller based on engine speed / load conditions (e.g., as in 204). Fig. 2 selected). If the VCR mechanism deteriorates, the actual position may correspond to a different compression ratio than the commanded one.

[0061] If the actual position of the VCR mechanism does not differ from the expected position (e.g., the actual position is the same as the expected position or within a threshold of the expected position), the procedure at 320 includes an indication that the VCR mechanism has not deteriorated. With a functioning VCR mechanism, the control unit can continue to adjust the compression ratio based on engine operating conditions via VCR mechanism settings (e.g., as previously at 210). Fig. 2 executed). Following 320, the procedure ends in 300.

[0062] If the actual position of the VCR mechanism differs from the expected position (e.g., the actual position is outside a threshold of the expected position), the procedure at 308 includes indicating that the VCR mechanism has deteriorated. Indicating that the VCR mechanism has deteriorated may involve setting a diagnostic trouble code (DTC) and may further involve illuminating a malfunction indicator lamp (MIL) to alert a driver to the deteriorating condition. In one example, indicating that the VCR mechanism has deteriorated includes indicating that the VCR mechanism has become stuck in a position different from the intended one, resulting in the engine operating at a compression ratio different from the intended compression ratio (e.g.,higher or lower).

[0063] In the case of 310, the procedure involves learning the measured (stuck) position and the corresponding stuck compression ratio. For example, the stuck compression ratio corresponding to the actual position of the VCR mechanism can be determined based on the feedback received from the VCR mechanism position sensor. Here, the actual VCR position is a measured position. Subsequently, a maximum engine load and a maximum boost pressure permissible at the stuck compression ratio can be restricted (i.e., reduced or decreased) to limit the tendency for abnormal combustion events at the stuck compression ratio, for example, according to the procedure from Fig. 2 to reduce. Following 310, the procedure ends in 300.

[0064] Again referring to 302, if feedback regarding the position of the VCR mechanism is not available, procedure 300 transitions to 312 and involves determining whether knocking is detected. For example, knocking can be detected based on an output from a knock sensor coupled along an engine block (e.g., knock sensor 90 from Fig. 1) which is combined with an output from a crankshaft acceleration sensor. In an example, knocking in a cylinder can be determined if the output of a knock sensor coupled to the cylinder, where the output is captured within a crankshaft angle window occurring after an ignition event in the corresponding cylinder, is higher than a knocking threshold.

[0065] The inventors of the present invention have found that operating at a high compression ratio, for example when torque demand is increased, can enable improved thermal efficiency. However, when torque demand is increased and the engine is operated at high engine speeds and loads and at a high compression ratio, there is a tendency to knock. This tendency increases in turbocharged engine applications if a VCR mechanism becomes stuck at a relatively high compression ratio. Accordingly, by monitoring for the occurrence of knocking in an engine operating at a specified compression ratio, it can be determined whether the compression ratio has become stuck.In particular, if the VCR mechanism becomes stuck in a state with a higher than intended compression ratio, knocking may begin to increase, and the use of retarded ignition may result in a lock-up. In another example, if the VCR mechanism becomes stuck in a state with a lower than intended compression ratio, the control unit may attempt to move to a higher compression ratio and increase ignition advance.If the ignition timing can be advanced before the MBT (maximum brake torque) at the highest commanded compression ratio without causing knocking at moderate to high engine loads, the control system may determine that the VCR mechanism is stuck in a low compression ratio position and operate the ignition timing so that it is not advanced before the MBT or the limit as determined by the head control system.

[0066] If no knocking is detected, the procedure at 320 includes an indication that the VCR mechanism has not deteriorated. For example, even without feedback regarding the position of the VCR mechanism, it can be inferred that the engine is operating at the commanded compression ratio without deterioration of the VCR mechanism if no knocking occurs (or if the occurrence of knocking is less than a threshold).

[0067] When knocking is detected, the procedure at 312 involves retarding the ignition timing. Retarding the ignition timing in response to a knock indication reduces cylinder pressures, thereby decreasing the likelihood of further knocking. The applied degree of retardation can be determined based on the initial ignition timing and the knock indication. For example, as the knock indication increases (e.g., because the knock sensor output exceeds the knock threshold), the applied degree of retardation can be increased. Similarly, if the baseline retard is closer to the maximum knock threshold (MBT), the applied degree of retardation can be increased. In one example, the ignition timing can be retarded by 1-2 degrees of crankshaft angle in response to a knock indication.

[0068] In 316, procedure 300 involves determining whether the use of retarded ignition is at a limit. That is, it can be determined whether the use of retarded ignition reaches a limit. The limit can be determined as a function of the commanded compression ratio. For example, a greater degree of retarded ignition use (and thus a higher retarded ignition limit) may be tolerated when operating at a higher compression ratio, whereas a small degree of retarded ignition use (and thus a lower retarded ignition limit) may be tolerated when operating at a lower compression ratio. The limit can define a degree of retarded ignition beyond which engine power losses, overheating tendencies, and high emissions may occur at the commanded compression ratio. The ignition cannot be retarded further beyond the limit.

[0069] If the use of a retarded ignition is borderline, procedure 300 transitions to 308 and includes indicating that the VCR mechanism has deteriorated, as described above. For example, if the use of a retarded ignition is borderline, it may be determined that the VCR mechanism has become stuck at a compression ratio higher than intended.

[0070] If the use of delayed ignition is not at the limit, the procedure transitions from 300 to 318 and involves determining whether the knock frequency is greater than a threshold. If the knock frequency is greater than the threshold, that is, if recurrent knocking occurs even when using delayed ignition, the procedure transitions from 300 to 308 and involves indicating that the VCR mechanism has deteriorated. Furthermore, if the knock frequency is not greater than the threshold, the procedure transitions from 300 to 320 and involves indicating that the VCR mechanism has not deteriorated. In alternative examples, instead of monitoring the knock frequency, the knock intensity for each knocking situation can be integrated, and if the integrated knock intensity over several knocking situations exceeds a threshold for intensity, it can be determined that the VCR mechanism has deteriorated.

[0071] In other examples, knock intensity and the use of delayed firing can each be combined to determine whether the VCR mechanism has deteriorated. For instance, if an integrated value determined by a combination of delayed firing and knock intensity exceeds a threshold over several knocking situations, it can be determined that the VCR mechanism has deteriorated. In another example, if each delayed firing reaches a lock or limit, and the knock frequency or the integrated knock intensity reaches a threshold, it can be determined that the VCR mechanism has deteriorated.

[0072] In this way, an engine control unit can indicate deterioration of a variable compression ratio mechanism that mechanically changes a piston's position in a cylinder based on one or more of the following: output from a position sensor coupled to the mechanism, knock sensor output, and adaptive ignition; and in response to the indication, the control unit can limit engine load and advance ignition timing, thereby reducing the likelihood of further knocking or pre-ignition. For example, indicating deterioration might include indicating that the engine is operating at a stuck compression ratio that differs from an intended compression ratio.The indication may include a warning of deterioration if one or more of the mechanism's actual position, based on the position sensor output, differs from the mechanism's expected position, based on the engine's expected compression ratio; the knock frequency, based on the knock sensor output, is higher than a frequency threshold expected for the intended compression ratio, and the adaptive ignition is retarded to a threshold based on the intended compression ratio. Engine load restriction may include reducing the maximum engine load and the maximum boost pressure permissible at the stuck compression ratio.In one example, limiting the engine load can be achieved by reducing an intake throttle opening at the stuck compression ratio and increasing a wastegate actuator opening at the stuck compression ratio. Furthermore, in response to the indicator, the control unit can advance the ignition timing based on the stuck compression ratio, regardless of the intended compression ratio.

[0073] In relation to Fig. Figure 4 shows an example of engine load adjustment in response to a VCR mechanism diagnosis. Fig. Curve 402 represents a pedal position (PP) that indicates a torque requirement from the driver. Fig.Furthermore, curve 404 represents the intake throttle position, curve 406 the ignition timing, curve 408 the cylinder compression ratio (cylinder CR), and curve 410 the knock sensor output. The knock sensor output is shown relative to each of the following: a knock threshold (Schw_Klo) and a pre-ignition threshold (Schw_FZ). The ignition timing is shown in relation to the maximum operating temperature (MBT) (dashed line) and the borderline spark (BDL). All curves are plotted against time along the x-axis.

[0074] Before t1, the engine operates at a higher compression ratio (curve 408) in response to a lower torque demand from the driver (curve 402). For example, the engine is brought into a first position corresponding to the higher compression ratio (high CR) by actuating the VCR mechanism. Furthermore, the throttle opening is set to a smaller degree to meet the lower torque demand. The ignition timing is held at or around the MBT at this point (for example, slightly retarded from the MBT). Because the engine is operating at a low engine speed and load, and at the higher compression ratio, the engine's tendency to knock remains low, and actual knocking does not occur, as the knock sensor output remains below the knock threshold Schw_Klo.

[0075] At t1, the driver applies the accelerator pedal. For example, this occurs during a transition from low to medium engine load. The throttle opening is enlarged in response to the increased torque demand. Furthermore, since the engine is not yet restricted against knocking, the higher compression ratio is maintained. For example, the VCR mechanism is held in the first position corresponding to the higher compression ratio. In addition, the limit ignition (BDL, dashed line) and ignition timing are retarded by the MBT due to the engine's increased tendency to knock at the higher engine load and with the higher compression ratio (that is, the engine is more restricted against knocking).The knock sensor output is approaching the knock threshold while remaining below it, indicating that the engine is more restricted with respect to knocking than it was before t1. However, actual knocking only occurs because the knock sensor output remains below the knock threshold Schw_Klo.

[0076] At t2, the pedal position increases further. If the engine were kept at the higher compression ratio, its tendency to knock would increase due to the need for retarded ignition timing. The increased fuel consumption resulting from the retarded ignition would offset the fuel efficiency gains at the higher compression ratio. Therefore, in response to the changing torque demand, the engine transitions from the higher compression ratio to a lower one. For example, the VCR mechanism is instructed to move from the first position, corresponding to the high compression ratio, to a second position, corresponding to a lower compression ratio. Additionally, the throttle opening is enlarged to meet the increased torque demand.If the compression ratio is reduced and the throttle opening is increased, the engine is less restricted with regard to knocking, and the BDL (boost pressure regulator) can be advanced relative to its position before t2. Furthermore, the ignition timing can revert to a nominal point around the MBT (main boost pressure). The knock sensor output can remain close to, but below, the knock threshold.

[0077] At t3, the driver applies the accelerator pedal again. In response to the increased torque demand from the driver, the throttle opening is enlarged while the engine is maintained at the lower compression ratio. For example, the VCR mechanism is held in the second position. Because the engine is more restricted from knocking under these conditions, the MBT retards the BDL and ignition timing, while keeping the knock sensor output below the knock threshold.

[0078] In the t4 configuration, the ignition timing was retarded to a point where the increased fuel consumption associated with late ignition offsets the fuel efficiency gains of operation at the selected compression ratio. Accordingly, at this point, the compression ratio is ordered to be further reduced.

[0079] For example, the VCR mechanism is commanded to transition from the second position to a third position, which corresponds to a compression ratio lower than the compression ratio in the second position. As a result of the reduced compression ratio, the BDL (boost pressure drop) is advanced, and the ignition timing is also advanced to a nominal point around the MBT (main boost pressure).

[0080] Following the commanded transition, particularly from t5 onwards, the tendency to knock begins to increase. Specifically, intermittent knocking occurs when the knock sensor output intermittently exceeds the knock threshold Schw_Klo. In response to each indication of knocking, the ignition timing is gradually retarded by the MBT.

[0081] Shortly before t6, the ignition timing is retarded to a limit (or a stop) in response to intermittent knocking. As a result of the increased knock frequency even with the retarded ignition timing (relative to the stop), it can be deduced that the VCR mechanism deteriorated during the transition commanded at t4. Specifically, it can be deduced that the engine's actual compression ratio (represented by solid line 408) is higher than the engine's intended compression ratio (represented by dashed line 409) because the VCR mechanism was stuck between the second and third positions. As an example, the stuck compression ratio can be deduced from a measured position of the VCR mechanism (between the second and third positions), as indicated by a position sensor.

[0082] In response to the deterioration of the VCR mechanism, the engine load is restricted at t6. Specifically, the maximum permissible engine load during operation at the measured VCR position (the stuck, higher-than-intended compression ratio) is reduced. In the illustrated example, the engine load is reduced by decreasing the intake throttle opening from a maximum permissible opening to a smaller opening (curve 404, solid line). As a result, the air supply flowing through the engine is reduced. In alternative examples, the engine load can be further or optionally reduced by increasing the opening of an exhaust wastegate actuator coupled across an exhaust turbine driving an intake compressor. As a result, the maximum permissible boost pressure in the respective common rail is reduced.In addition to limiting the engine load, the MBT delays the BDL and ignition timing.

[0083] Therefore, if the engine load had not been limited, continued operation at the higher than intended common rail (CR) would have resulted in increased pressures and temperatures in the cylinder. This would have led to an increased occurrence of knocking. Furthermore, pre-ignition could occur, with the knock sensor output exceeding a pre-ignition threshold (Schw_FZ) that is higher than a knock threshold (Schw_Klo). It is understood that if pre-ignition occurs even after reducing the engine load, as illustrated, for example, by the dashed segment 412, the engine load can be reduced further. For example, in response to a pre-ignition indication after t6, the throttle opening can be further reduced (below the level shown at 404), as illustrated, for example, by the dashed segment 405.

[0084] In t7, after limiting the engine load, if the tendency to knock has been sufficiently reduced, the BDL is advanced and the ignition timing is retarded by the MBT, while the engine load remains limited and the throttle opening reduced.

[0085] In this way, a variable compression ratio (VCR) mechanism can be diagnosed and addressed promptly. By relying on adaptive ignition being delayed to a lockout when a lower compression ratio is commanded, it can be reliably determined that a VCR mechanism has become stuck in a position with a higher than intended compression ratio. Applying engine load restriction in response to a stuck VCR mechanism can mitigate knocking and pre-ignition resulting from continued engine operation at the higher than intended compression ratio.By restricting air intake to reduce permissible engine load and advancing ignition timing from the retard limit when the variable compression ratio (VCR) mechanism has become stuck at a higher compression ratio than intended, cylinder pressures and temperatures can be reduced, thereby decreasing the tendency for recurrent knocking or pre-ignition. Reducing the thermal stress placed on an engine when a VCR mechanism deteriorates can improve the service life of engine components.

[0086] An exemplary procedure comprises the following: mechanically varying an engine's compression ratio by means of a variable-compression-ratio mechanism; and, in response to the mechanism's deterioration, limiting an engine load. In the foregoing example, the deteriorating mechanism additionally or optionally includes the engine becoming stuck at a compression ratio different from an intended compression ratio for a given engine speed / load condition. In any or all of the foregoing examples, limiting the engine load additionally or optionally includes limiting a maximum allowable engine load based on the stuck compression ratio and independent of the intended compression ratio.In any or all of the foregoing examples, limiting the engine load additionally or optionally involves reducing the opening of an intake throttle to restrict the air intake of the engine at the stuck compression ratio. In any or all of the foregoing examples, limiting the engine load additionally or optionally involves limiting the boost pressure by increasing the opening of an exhaust wastegate actuator coupled to an exhaust turbine.In any or all of the foregoing examples, the method additionally or optionally further includes indicating that the mechanism has deteriorated in response to an actual position of the mechanism, based on a sensor output from a position sensor coupled to the mechanism, differing from a commanded position of the mechanism, the commanded position being based on the intended compression ratio for the respective engine speed / load condition.In any or all of the foregoing examples, the method additionally or optionally further includes indicating that the mechanism has deteriorated in response to one or more of the following: that the adaptive ignition is retarded beyond a threshold based on the intended compression ratio, and that the knock frequency is higher than a frequency threshold while the adaptive ignition is retarded. In any or all of the foregoing examples, the method additionally or optionally further includes advancing the ignition timing in response to a reduction in engine load, the advancing of the ignition timing being based on the stuck compression ratio.In one or all of the foregoing examples, the method further comprises, additionally or optionally, retarding the ignition timing in response to a knock indication received during the stuck compression ratio. In one or all of the foregoing examples, the method further comprises, additionally or optionally, further limiting the engine load based on the ignition advance indication in response to an ignition advance indication received during the stuck compression ratio.

[0087] Another exemplary procedure comprises the following: indicating deterioration of a variable compression ratio mechanism that mechanically changes a piston position in a cylinder based on one or more inputs from a position sensor coupled to the mechanism, a knock sensor output, and the use of adaptive retardation; and, in response to the indication, restricting engine load while advancing the ignition timing towards MBT. In the foregoing example, indicating deterioration additionally or optionally includes indicating that the engine is operating at a stuck compression ratio other than an intended compression ratio.In any or all of the foregoing examples, the method additionally or optionally includes indicating deterioration if one or more of the mechanism's actual position, based on the position sensor output, differs from the mechanism's expected position, based on an expected engine compression ratio; the knock frequency, based on the knock sensor output, is higher than a frequency threshold expected for the intended compression ratio; and the adaptive ignition timing, based on the intended compression ratio, is retarded to a threshold. In any or all of the foregoing examples, limiting the engine load additionally or optionally includes reducing a maximum engine load and a maximum boost pressure permissible at the stuck compression ratio.In any or all of the foregoing examples, restricting the engine load additionally or optionally includes one or more of the following: reducing an intake throttle opening at the stuck compression ratio and increasing a wastegate actuator opening at the stuck compression ratio. In any or all of the foregoing examples, the method further additionally or optionally includes, in response to the indication, advancing a limit ignition timing based on the stuck compression ratio and the restriction of the engine load, and irrespective of the intended compression ratio.

[0088] Another exemplary engine system comprises the following: an engine having one cylinder; a variable compression ratio mechanism to mechanically change a piston's position in the cylinder; a position sensor coupled to the variable compression ratio mechanism; a spark plug to provide a spark to the cylinder; an intake throttle; a turbocharger having an intake compressor driven by an exhaust turbine; a wastegate, including a wastegate actuator coupled to the exhaust turbine; a knock sensor; and a control system designed with computer-readable instructions stored on non-volatile memory to: actuate the variable compression ratio mechanism to transition the engine from a higher compression ratio setting to a lower compression ratio setting; display,that the mechanism has stuck in the higher compression ratio setting, based on an output from one or more of the position sensor and the knock sensor; and in response to the indication of a decrease in air charge supplied to the engine during ignition timing retardation. In the foregoing example, the indication additionally or optionally includes an indication that the mechanism has stuck in the higher compression ratio setting, in response to one or more of the following: that a knock frequency, as indicated based on the output from the knock sensor, is above a threshold frequency while the ignition timing is retarded; and that an actual position of the mechanism, as indicated based on the output from the position sensor, differs from a commanded position.where each is based on the commanded position and frequency threshold at the lower compression ratio setting. In any or all of the foregoing examples, reducing the air charge additionally or optionally includes one or more of the following: reducing an intake throttle opening and increasing a wastegate actuator opening to limit a maximum engine load permissible at the higher compression ratio setting. In any or all of the foregoing examples, the control additionally or optionally further includes instructions to: limit the maximum engine load permissible at the higher compression ratio setting in response to an indication of pre-ignition other than knock, as indicated based on the knock sensor output following the reduction of the intake air charge.

[0089] In another interpretation, a method for a supercharged engine comprises commanding a transition of the variable compression ratio mechanism from a higher compression ratio setting to a lower compression ratio setting in response to adaptive ignition being delayed to a limit; and in response to the mechanism becoming stuck in the higher compression ratio setting following the command, reducing a maximum engine load permissible at the higher compression ratio setting.

[0090] It should be noted that the exemplary control and estimation routines contained herein can be used in conjunction with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-volatile memory and executed by the control system, which includes the control unit 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. Thus, various actions, processes, and / or functions shown can be performed in the sequence shown, in parallel, or, in some cases, omitted.Furthermore, the processing sequence is not strictly necessary to achieve the features and advantages of the exemplary embodiments described herein, but is provided for the sake of simplicity and clarity. One or more of the illustrated actions, processes, and / or functions can be executed repeatedly, depending on the specific strategy employed. Moreover, the described actions, processes, and / or functions can graphically represent code to be programmed in the non-volatile memory of the computer-readable storage medium within the engine control system. The described actions are executed by carrying out the instructions in a system that incorporates the various engine hardware components in combination with the electronic control unit.

[0091] It is understood that the configurations and routines disclosed herein are exemplary and that these specific embodiments are not to be interpreted in a limiting sense, as numerous variations are possible. For example, the foregoing technology can be applied to V6, I4, I6, V12, 4-cylinder boxer, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the different systems and configurations, and other features, functions, and / or properties disclosed herein.

[0092] The following claims, in particular, describe certain combinations and subcombinations that are considered novel and not obvious. These claims may refer to "one" element, "a first" element, or the equivalent thereof. Such claims are to be understood as including one or more such elements and neither requiring nor excluding two or more such 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. Such claims, whether broader, narrower, the same, or different in scope compared with the original claims, are also considered to be included in the subject matter of the present disclosure.

Claims

[1] Procedure, encompassing: Mechanically varying the compression ratio of an engine by means of a variable compression ratio mechanism; and In response to the deteriorating mechanism, limiting the engine load. [2] Method according to claim 1, wherein the deteriorated mechanism includes the engine being stuck in a compression ratio that differs from an intended compression ratio for a given engine speed / load condition. [3] Method according to claim 2, wherein limiting the engine load includes limiting the maximum engine load that is permissible based on the stuck compression ratio and regardless of the intended compression ratio. [4] Method according to claim 3, wherein limiting the engine load includes limiting the opening of an intake throttle to limit the air filling of the engine at the stuck compression ratio. [5] Method according to claim 3, wherein limiting the engine load includes limiting the boost pressure by enlarging an opening of an exhaust wastegate actuating element coupled to an exhaust turbine. [6] Method according to claim 2, further comprising indicating that the mechanism has deteriorated in response to the fact that an actual position of the mechanism based on a sensor output from a position sensor coupled to the mechanism differs from a commanded position of the mechanism, wherein the commanded position is based on the intended compression ratio for the respective engine speed / load condition. [7] Method according to claim 2, further comprising an indication that the mechanism has deteriorated in response to one or more of the following: that the adaptive ignition is delayed beyond a threshold based on the intended compression ratio, and that the knock frequency is higher than a threshold for frequency while the adaptive ignition is delayed. [8] Method according to claim 2, further comprising advancing the ignition timing in response to a reduction in engine load, wherein the advancing of the ignition timing is based on the stuck compression ratio. [9] Method according to claim 8, further comprising, in response to a knock indication received during the stuck compression ratio, a delay of the ignition timing. [10] Method according to claim 8, further comprising, in response to an indication of pre-ignition received during the stuck compression ratio, a further restriction of the engine load based on the indication of pre-ignition. [11] Engine system, comprising: an engine that has one cylinder; a mechanism for a variable compression ratio to mechanically change a piston position within the cylinder; a position sensor coupled to the mechanism for a variable compression ratio; a spark plug to provide a spark to the cylinder; an intake throttle; a turbocharger which has an intake compressor driven by an exhaust turbine; a wastegate that includes a wastegate actuating element coupled to the exhaust turbine; a knock sensor; and a controller designed with computer-readable instructions stored in non-volatile memory for the following: Actuating the variable compression ratio mechanism to move the engine from a higher compression ratio setting to a lower compression ratio setting; Indicates that the mechanism is stuck in the higher compression ratio setting, based on an output from one or more of the position sensor and the knock sensor; and in response to the indication, the amount of air supplied to the engine is reduced while the ignition timing is advanced. [12] System according to claim 11, wherein the display includes an indication that the mechanism has stuck at the higher compression ratio setting, in response to one or more of the following: that a knock frequency, as indicated based on the output from the knock sensor, is above a frequency threshold while the ignition timing is retarded; and that an actual position of the mechanism, as indicated based on the output from the position sensor, differs from a commanded position, each being based on the lower compression ratio setting and the frequency threshold. [13] System according to claim 11, wherein reducing the air filling of one or more by reducing an opening of the intake throttle and increasing an opening of the wastegate actuating element to limit a maximum engine load that is permissible when set with a higher compression ratio. [14] System according to claim 13, wherein the control includes further instructions to: in response to an indication of pre-ignition that differs from knocking, as indicated on the basis of the knock sensor output after reducing the intake air charge, to limit the maximum engine load that is permissible when set with the higher compression ratio.

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