Method and system for diagnosing operation of engine compression ratio changing mechanism

Abstract

The present disclosure provides "Methods and systems for diagnosing operation of an engine compression ratio changing mechanism." Methods and systems for diagnosing operation of a compression ratio adjustment mechanism are described. In one example, an output of a pressure sensor is sampled and an evaluation of a current compression ratio of an engine is made after adjusting the sampling of the output. Engine operation can be adjusted in response to whether degradation of the compression ratio adjustment mechanism is indicated.

Description

TECHNICAL FIELD

[0001] The present specification relates to a method and system for diagnosing operation of a cylinder compression ratio changing mechanism. The method and system can be implemented without forcing a disturbance in engine torque production. BACKGROUND

[0002] Engines can include a compression ratio changing mechanism to improve engine efficiency at low engine loads and reduce the likelihood of engine knock at higher engine loads. The compression ratio changing mechanism can change the height of a piston, change the length of a connecting rod, or change the orientation of a connecting rod to change the cylinder clearance volume of a top dead center compression stroke. The compression ratio of a cylinder can be dynamically changed as engine speed and engine load change. However, the compression ratio changing mechanism can degrade such that it does not change the compression ratio of a cylinder in a desired manner. Furthermore, it can be desirable to determine whether the compression ratio changing mechanism is operating as expected, but changing the compression ratio of an engine can be annoying to a vehicle occupant when changing the compression ratio of the engine can cause engine knock or a noticeable driveline torque change. Accordingly, it can be desirable to diagnose operation of the compression ratio changing mechanism in a manner that does not disturb operation of the vehicle. SUMMARY

[0003] The inventors have recognized the above-referenced drawbacks and have developed a method for operating an engine, the method comprising adjusting a sampling of a poppet valve timing and pressure via a controller in response to a request to diagnose a variable compression ratio changing mechanism.

[0004] By adjusting the sampling of the poppet valve timing and pressure, operation of the compression ratio changing mechanism can be diagnosed in a manner that does not disturb a vehicle occupant. In one example, the poppet valve timing can be advanced from a reference timing to improve a signal-to-noise ratio of an intake manifold pressure or an exhaust manifold pressure such that the compression ratio changing mechanism of the engine can be diagnosed as degraded or functioning as expected. Furthermore, the diagnosis can be performed during a deceleration fuel cut (DFSO) when the engine is not producing torque, such that driveline torque disturbance can be reduced and the signal-to-noise ratio can be improved.

[0005] The present specification can provide several advantages. In particular, the method can diagnose operation of a cylinder compression changing mechanism without a vehicle occupant being aware that the compression changing mechanism is being diagnosed. Additionally, the method can be performed with existing sensors such that system cost can not be increased. Furthermore, the method can diagnose more than two operational states of the compression changing mechanism.

[0006] The above and other advantages and features of the present specification will be apparent from the following detailed description, when taken in conjunction with the accompanying drawings, alone or as

[0007] It is to be understood that the above overview is provided as an overview of some aspects of the subject matter described in this disclosure and is not intended to describe each described aspect or every implementation of the subject matter described in this disclosure. The foregoing has outlined rather broadly the features of the subject matter described in this disclosure so that the detailed description that follows can be better understood. The features described, however, can be implemented in various ways and should not limit the scope of the subject matter described in this disclosure. Furthermore, the subject matter described in this disclosure is not limited to implementing any of the features set forth. BRIEF DESCRIPTION OF DRAWINGS

[0008] The advantages described herein will be more fully understood from the following detailed description, taken in conjunction with the drawings, in which:

[0009] Figure 1 is a schematic illustration of an engine;

[0010] Figure 2 and Figure 3 is an exemplary diagnostic sequence; and

[0011] Figure 4A and Figure 4B shows a flowchart of an exemplary method for diagnosing a compression ratio changing mechanism and operating an engine. DETAILED DESCRIPTION

[0012] This specification relates to diagnosing a cylinder compression ratio changing mechanism and operating an engine in response to the diagnosis. Figure 1 An exemplary engine is shown that can be operated at different compression ratios over an engine operating range. Figure 2 and Figure 3 diagnostic sequence for a compression ratio changing mechanism according to the method of Figure 4A and Figure 4B Figure 4A and Figure 4B The method of Figure 1 may be incorporated into the system of

[0013] Referring to Figure 1 , an internal combustion engine 10 includes a plurality of cylinders, one of which is shown in Figure 1 ​As shown, the engine 10 is controlled by an electronic engine controller 12. The engine 10 includes combustion chambers 30 and cylinder walls 32 with pistons 36 located therein and connected to a crankshaft 40. The engine can include one or more compression ratio changing mechanisms 37a-37c to change the compression ratio of the cylinder to two or more compression ratios. For example, the compression ratio changing mechanisms can change the compression ratio of the cylinder from 9: 1 to 12: 1 and compression ratios in between. In one example, the compression ratio changing mechanism 37b can adjust the piston height as described in U.S. Patent 6,568,357, which is incorporated by reference herein in its entirety for all purposes and intents. Alternatively, the compression ratio changing mechanism 37a can change the length of the connecting rod as described in U.S. Patent 6,622,669, which is incorporated by reference herein in its entirety for all purposes and intents. In another alternative, the compression ratio changing mechanism can include a connecting rod system as described in U.S. Patent 6,684,828, which is incorporated by reference herein in its entirety for all purposes and intents.

[0014] A flywheel 97 and ring gear 99 are coupled to the crankshaft 40. A starter 96 includes a pinion shaft 98 and pinion gear 95. The pinion shaft 98 can selectively advance the pinion gear 95 to engage the ring gear 99. The starter 96 can be mounted directly to the front of the engine or to the rear of the engine. In some examples, the starter 96 can selectively supply torque to the crankshaft 40 via a belt or chain. In one example, the starter 96 is in a base state when not engaged to the engine crankshaft. The combustion chambers 30 are shown in communication with an intake manifold 44 and exhaust manifold 48 via respective intake poppet valves 52 and exhaust poppet valves 54. Each intake and exhaust valve can be operated by an intake cam 51 and exhaust cam 53. The position of the intake cam 51 can be determined by an intake cam sensor 55. The position of the exhaust cam 53 can be determined by an exhaust cam sensor 57. The intake cam 51 and exhaust cam 53 can be moved relative to the crankshaft 40 via door adjustment mechanisms 71 and 73. The door adjustment mechanisms 71 and 73 can also deactivate the intake and / or exhaust valves in a closed position such that the intake valves 52 and exhaust valves 54 remain closed during a cylinder cycle (e.g., two engine revolutions for a four-stroke engine).

[0015] The fuel injectors 66 are shown positioned to inject fuel directly into the cylinders 30, which is known to those skilled in the art as direct injection. Alternatively, the fuel can be injected into the intake port, which is known to those skilled in the art as port injection. The fuel injectors 66 deliver liquid fuel in proportion to the pulse width of a signal from the controller 12. The fuel is delivered to the fuel injectors 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail (not shown). In one example, a high pressure two-stage fuel system can be used to generate higher fuel pressures. Additionally, the intake manifold 44 is shown in communication with an optional electronic throttle 62 that adjusts the position of a throttle plate 64 to control airflow from the intake ports 42 to the intake manifold 44. In some examples, the throttle 62 and throttle plate 64 can be positioned between the intake valves 52 and the intake manifold 44 such that the throttle 62 is a port throttle.

[0016] A distributorless ignition system 88 provides an ignition spark to the combustion chambers 30 via spark plugs 92 in response to the controller 12. A universal exhaust gas oxygen (UEGO) sensor 132 is shown coupled to the exhaust manifold 48 upstream of the catalytic converter 70. Alternatively, a bi-state exhaust gas oxygen sensor can be used in place of the UEGO sensor 126.

[0017] In one example, the converter 70 can include a plurality of catalyst bricks. In another example, a plurality of emission control mechanisms can be used, each having a plurality of bricks. In one example, the converter 70 can be a three-way catalyst.

[0018] The controller 12 receives sensor inputs from a variety of sources, including the engine speed sensor 120, the throttle position sensor 122, the manifold absolute pressure sensor 124, the engine coolant temperature sensor 128, the intake air temperature sensor 130, the mass air flow sensor 134, and the throttle position sensor 136. Figure 1The microcomputer is shown as a conventional microcomputer including a microprocessor unit 102, input / output ports 104, read only memory 106 (e.g., non-transitory memory), random access memory 108, wear correction factor memory 110, and a conventional data bus. In addition to those signals discussed previously, the controller 12 is shown as receiving various signals from sensors coupled to the engine 10 including: engine coolant temperature (ECT) from a temperature sensor 112 coupled to the cooling jacket 114; position from a position sensor 134 coupled to the accelerator pedal 130 to sense the force applied by the human driver 132; a measure of engine manifold pressure (MAP) from a pressure sensor 115 coupled to the intake manifold 44; pressure from an exhaust pressure sensor 133 coupled to the exhaust manifold 48; engine position sensor from a Hall effect sensor 118 that senses the position of the crankshaft 40; a measure of mass of air entering the engine from sensor 117; brake pedal position from a brake pedal position sensor 154 when the brake pedal 150 is applied by the human driver 132; and a measure of throttle position from sensor 58. Atmospheric pressure can also be sensed (sensor not shown) for processing by the controller 12. In one preferred aspect of the present description, the engine position sensor 118 produces a predetermined number of equally spaced pulses per rotation of the crankshaft from which engine revolutions per minute (RPM) can be determined.

[0019] The controller 12 can also interface with the vehicle occupants via a human / machine interface 133. The human / machine interface 133 can include a visual display that provides visual feedback to the vehicle occupants and receives input from the vehicle passengers.

[0020] During operation, each cylinder within engine 10 typically undergoes a four stroke cycle: the cycle includes an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. During the intake stroke, typically exhaust valve 54 is closed and intake valve 52 is open. Air is introduced to combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder to increase the volume within combustion chamber 30. The position of piston 36 near the bottom of the cylinder and at the end of its stroke (e.g., when combustion chamber 30 is at its maximum volume) is commonly referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head to compress the air within combustion chamber 30. The point at which piston 36 is at the end of its stroke and closest to the cylinder head (e.g., when combustion chamber 30 is at its minimum volume) is commonly referred to by those skilled in the art as top dead center (TDC). During a process hereinafter referred to as injection, fuel is introduced to the combustion chamber. During a process hereinafter referred to as ignition, the injected fuel is ignited by a known ignition device such as spark plug 92, causing combustion. During the expansion stroke, the expanding gases push piston 36 back to BDC. Crankshaft 40 converts the piston motion to rotational torque of the rotational shaft. Finally, during the exhaust stroke, exhaust valve 54 opens to release the combusted air-fuel mixture to exhaust manifold 48, and the piston returns to TDC. It should be noted that the above is shown by way of example only, and the intake and exhaust valve opening and / or closing timing can be varied, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0021] Thus, Figure 1 The system of claim 1, wherein the engine operating system comprises an engine comprising a pressure sensor and a compression ratio adjustment mechanism that changes a cylinder volume at a top dead center compression stroke, and a controller comprising executable instructions for operating the adjustment mechanism to change an engine compression ratio in response to a request to diagnose the compression ratio adjustment mechanism and estimating the engine compression ratio from an output of the pressure sensor. The engine operating system comprises a case where the compression ratio is estimated in response to a pressure ratio where a derivative of the output of the pressure sensor is zero. The engine operating system comprises a case where the compression ratio is estimated in response to an integral of the output from the pressure sensor. The engine operating system comprises a case where the output is integrated from a time when an exhaust valve opens during a cylinder cycle to reach a predetermined crank angle after a top dead center exhaust stroke of the cylinder cycle. The engine operating system further comprises additional instructions to change the engine compression ratio during a deceleration fuel cut. The engine operating system further comprises sampling the output of the pressure sensor in response to diagnosing the compression ratio adjustment mechanism.

[0022] Reference is now made to Figure 2diagnostic sequence for cylinder compression ratio change is shown. Figure 2 The sequence of FIG. 1 can be provided via Figure 1 The system of FIG. 1 in combination with Figure 4A and Figure 4B The graphs shown are time aligned and occur simultaneously. The vertical lines at times t0-t3 represent times of interest during the sequence. Figure 2 The sequence of FIG. 1 is for a four-stroke, four-cylinder engine operating at constant engine speed. In this example, the intake and exhaust valve timings move together and by the same amount, but in other examples, the intake and exhaust valve timings can be adjusted by different amounts.

[0023] Figure 2 The first graph at the top is a graph of cylinder stroke and intake and exhaust valve timing versus time for a cylinder (e.g., cylinder one) of the engine. The cylinder strokes are separated via vertical lines, and each cylinder stroke is identified by a letter. Specifically, the letter I represents an intake stroke, the letter P represents a power stroke, the letter C represents a compression stroke, and the letter E represents an exhaust stroke. The vertical lines represent the top dead center and bottom dead center positions of the cylinder for a particular stroke. Intake valve timing is indicated by the thin line 202, while exhaust valve timing is indicated by the thick line 204.

[0024] Figure 2 The second graph at the top is a graph of engine intake manifold pressure versus time. Trace 206 represents engine intake manifold pressure. The vertical axis represents engine intake manifold pressure, and engine intake manifold pressure increases along the vertical axis arrow direction. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Time interval 206a shows the time interval during which engine intake manifold pressure increases due to the piston in the cylinder pushing exhaust back into the engine intake manifold pressure. Peak cylinder pressure 206b can indicate the compression ratio of the cylinder. Further, engine intake manifold pressure can be numerically integrated during time interval 206a, and the integrated value can indicate the compression ratio of the cylinder. It should be noted that for each intake manifold pressure increase caused by the intake valve opening of each engine cylinder, there is a pressure peak as shown at 206b. Thus, there are four intake manifold pressure peaks for every two engine revolutions, and intake manifold pressure interval 206a corresponds to the engine intake manifold pressure change due to the intake valve opening of cylinder one shown at 202 between time t1 and time t2.

[0025] Figure 2 The third graph at the top is a graph of compression ratio versus time for a cylinder of the engine. Trace 208 represents the compression ratio of the cylinder. The vertical axis represents cylinder compression ratio, and cylinder compression ratio increases along the vertical axis arrow direction. The horizontal axis represents time, and time increases from the right side of the graph to the left side of the graph.

[0026] Figure 2 The fourth plot at the top is a plot of engine intake manifold pressure sampling time (e.g., time at which the controller takes a sample of the intake manifold pressure) versus time for cylinder one. Trace 210 represents the time at which a sample of the engine intake manifold pressure is taken. The horizontal axis represents time, and time increases from the left side of the plot to the right side of the plot. Figure 2 Figure 2

[0027] Figure 2 The fifth plot at the top is a plot of intake and exhaust valve timing versus time. Trace 212 represents the intake and exhaust valve timing. The vertical axis represents the intake and exhaust valve timing, and the intake and exhaust valve timing progresses along the vertical axis arrow direction. The horizontal axis represents time, and time increases from the left side of the plot to the right side of the plot.

[0028] Figure 2 The sixth plot at the top is a plot of variable compression ratio (VCR) diagnostic requests, which can be referred to as requests to diagnose the variable compression ratio changing mechanism versus time. Trace 214 represents the VCR diagnostic requests, and a diagnosis is requested when trace 214 is near the horizontal of the vertical axis arrow. When trace 214 is near the horizontal axis, no VCR diagnosis is requested. The horizontal axis represents time, and time increases from the left side of the plot to the right side of the plot.

[0029] At time tO, the engine is combusting air and fuel at a constant rate, and the engine is rotating in an engine cycle. The engine intake manifold pressure is at an intermediate level, and the cylinder is operating at a higher compression ratio that is activated. For each cycle of cylinder one, the intake manifold pressure is sampled twice. In this example, the sampling is performed near the top dead center intake stroke and the bottom dead center intake stroke, but sampling can be performed at different crank angles in different examples. The samples are taken at predetermined crank positions (e.g., 10 crank angles before the top dead center intake stroke and 10 crank angles before the bottom dead center intake stroke). The intake and exhaust valve timing is at a lower intermediate level, and there is no VCR diagnostic request.

[0030] Between time tO and time ti, the engine intake manifold pressure is sampled in response to the engine crank angle being at a predetermined crank angle. The exhaust valve is closed after the top dead center intake stroke of cylinder one, and the intake valve is opened near the top dead center intake stroke of cylinder one. The intake manifold pressure varies in response to the intake valve timing. No VCR diagnosis is requested.

[0031] ​​At time tl, a VCR diagnosis is requested as indicated by the transition of trace 214 to a higher level. The VCR diagnosis can be requested after the vehicle has traveled a predetermined distance or in response to other vehicle conditions. The intake manifold pressure is regulated to begin sampling at a predetermined crank angle and to stop sampling for cylinder one at a predetermined crank angle. The intake manifold pressure is sampled in response to the time between the crank angle at which sampling of the intake manifold pressure for cylinder one begins and the crank angle at which sampling of the intake manifold pressure for cylinder one stops. For example, the intake manifold pressure can be sampled at a rate of 1 kHz between the two predetermined crank angles. This high rate sampling is indicated by the blacked out area 210 between times tl and t3. The intake valve and exhaust valve timing is advanced to improve the signal to noise ratio of the intake manifold pressure. By advancing the intake valve and exhaust valve timing, more exhaust gas in the cylinder is pushed back into the engine intake manifold so that a higher peak intake manifold pressure can be observed and used to determine a better estimate of the cylinder compression ratio.

[0032] Between times tl and t2, the engine intake manifold pressure for diagnosing the variable compression ratio changing mechanism of cylinder one is sampled at a high rate as indicated by the samples close together and forming a black box at 210 between times tl and t2. A large number of samples can be taken and stored into controller memory for subsequent processing. The processing can include integrating the intake manifold pressure and determining the highest intake manifold pressure observed during the period in which the samples were taken. The compression ratio is held at a higher level and the valve timing is held advanced. Thus, in one engine cycle, the intake manifold pressure can be the basis for determining whether a higher compression ratio is occupied or not.

[0033] At time t2, the compression ratio of the cylinder is switched to a lower compression ratio. The intake valve and exhaust valve timing is held advanced and the VCR diagnosis request remains active.

[0034] Between times t2 and t3, the engine intake manifold pressure for diagnosing the variable compression ratio changing mechanism of cylinder one continues to be sampled at a high rate as indicated by the samples close together and forming a black box at 210 between times t2 and t3. The compression ratio of the cylinder has been reduced and the reduction in cylinder compression ratio is represented by the lower peak cylinder pressure as shown by 206c. The intake valve and exhaust valve timing is held advanced to improve the intake manifold pressure signal to noise ratio.

[0035] At time t3, the variable compression ratio change mechanism diagnostic request is canceled, and the compression ratio of the cylinders is switched back to the higher compression ratio. The intake manifold pressure sampling rate is reduced, and the total number of actual samples taken per cylinder cycle is reduced. The intake and exhaust valve timings are also returned to the previously more retarded state. As described in further detail in method 400, the VCR diagnostic request can be canceled when all desired engine compression ratios have been commanded and compared to expected values.

[0036] In this way, the intake manifold pressure can be the basis for determining whether the cylinder compression ratio change mechanism is degraded. In some examples, a similar sequence to that of Figure 3 is performed when the engine enters a deceleration fuel cut mode (e.g., the engine is rotating but not being supplied fuel and no combustion is occurring), which can improve the signal to noise ratio of the intake pressure signal.

[0037] Reference is now made to Figure 3 , which shows a cylinder compression ratio change diagnostic sequence. Figure 1 The sequence of Figure 4A can be provided via the system of Figure 4B and the method of Figure 3 . The illustrated graphs are time aligned and occur simultaneously. The vertical lines at times t10-t13 represent times of interest during the sequence. Figure 3 The sequence of

[0038] Figure 3 The first graph at the top is a plot of cylinder stroke and intake and exhaust valve timing versus time for a cylinder (e.g., cylinder one) of the engine. The cylinder strokes are separated via vertical lines, and each cylinder stroke is identified by a letter. Specifically, the letter I represents an intake stroke, the letter P represents a power stroke, the letter C represents a compression stroke, and the letter E represents an exhaust stroke. The vertical lines represent the top dead center and bottom dead center positions of the cylinder for a particular stroke. The intake valve timing is indicated by the thin line 302, while the exhaust valve timing is indicated by the thick line 304.

[0039] Figure 3The second plot on the top is a plot of engine exhaust manifold pressure versus time. Trace 306 represents engine exhaust manifold pressure. The vertical axis represents engine exhaust manifold pressure, and engine exhaust manifold pressure increases along the vertical axis arrow direction. The horizontal axis represents time, and time increases from the left side of the plot to the right side of the plot. Time interval 306a shows the time interval during which the engine exhaust manifold pressure increases due to the pistons in the cylinders pushing exhaust back into the engine exhaust manifold pressure. Peak cylinder pressure 306b can indicate the compression ratio of the cylinders. In addition, the engine exhaust manifold pressure can be numerically integrated during time interval 306a, and the integrated value can indicate the compression ratio of the cylinders. It should be noted that for each exhaust manifold pressure increase caused by the exhaust valve of each engine cylinder opening, there is a pressure peak as shown at 306b. Thus, there are four exhaust manifold pressure peaks for every two engine revolutions, and exhaust manifold pressure interval 306a corresponds to the engine exhaust manifold pressure change due to the number one cylinder exhaust valve opening shown at 304 between time ti 1 and time t12.

[0040] Figure 3 The third plot on the top is a plot of the compression ratio of the engine cylinders versus time. Trace 308 represents the compression ratio of the cylinders. The vertical axis represents cylinder compression ratio, and cylinder compression ratio increases along the vertical axis arrow direction. The horizontal axis represents time, and time increases from the right side of the plot to the left side of the plot.

[0041] Figure 3 The fourth plot on the top is a plot of the engine exhaust manifold pressure sampling time (e.g., the time at which the controller takes a sample of the exhaust manifold pressure) of the number one cylinder versus time. Trace 310 represents the time at which a sample of the engine exhaust manifold pressure is taken. The horizontal axis represents time, and time increases from the right side of the plot to the left side of the plot. Figure 3 Figure 3

[0042] Figure 3 The fifth plot on the top is a plot of intake and exhaust valve timing versus time. Trace 312 represents intake and exhaust valve timing. The vertical axis represents intake and exhaust valve timing, and intake and exhaust valve timing advances along the vertical axis arrow direction. The horizontal axis represents time, and time increases from the left side of the plot to the right side of the plot.

[0043] Figure 4A The sixth plot on the top is a plot of variable compression ratio (VCR) diagnostic requests, which can be referred to as requests to diagnose the variable compression ratio changing mechanism versus time. Trace 314 represents VCR diagnostic requests, and a diagnosis is requested when trace 314 is near the horizontal of the vertical axis arrow. When trace 314 is near the horizontal axis, no VCR diagnosis is requested. The horizontal axis represents time, and time increases from the left side of the plot to the right side of the plot. ​​

[0044] At time tlO, the engine is burning air and fuel at a constant rate, and the engine is rotating in an engine cycle. The engine exhaust manifold pressure is at an intermediate level, and the cylinder is operating at the higher compression ratio that is enabled. For each cycle of cylinder one, a sample of the exhaust manifold pressure is taken. In this example, the sample is taken near the bottom dead center exhaust stroke, but in different examples, the sample can be taken at different crank angles. The sample is taken at a predetermined crank position, for example, 10 crank angles before the bottom dead center exhaust stroke. The intake and exhaust valve timings are at the lower intermediate levels, and there is no VCR diagnostic request.

[0045] Between time tlO and time tl 1, the engine exhaust manifold pressure is sampled in response to the engine crank angle being at a predetermined crank angle. The exhaust valve is closed after the top dead center intake stroke of cylinder one, and the intake valve is open near the top dead center intake stroke of cylinder one. The exhaust manifold pressure varies in response to the exhaust valve timing. The VCR diagnostic is not requested.

[0046] At time tl 1, the VCR diagnostic is requested as indicated by the trace 314 transitioning to a higher level. The VCR diagnostic can be requested after the vehicle has traveled a predetermined distance or in response to other vehicle conditions. The exhaust manifold pressure is regulated to begin sampling at a predetermined crank angle and to stop sampling for cylinder one at a predetermined crank angle. The exhaust manifold pressure is sampled in response to the time between the crank angle at which sampling for cylinder one begins and the crank angle at which sampling for cylinder one stops. For example, the exhaust manifold pressure can be sampled at a rate of 1 kHz between the two predetermined crank angles. This high rate of sampling is indicated by the blacked out area 310 between times tl 1 and tl 3. The intake and exhaust valve timings are advanced to improve the signal to noise ratio of the exhaust manifold pressure. By advancing the intake and exhaust valve timings, more exhaust gas in the cylinder can exit the cylinder when the exhaust valve is open so that a higher peak exhaust manifold pressure can be observed and used to determine a better estimate of the cylinder compression ratio.

[0047] Between times tl 1 and tl 2, the engine exhaust manifold pressure is sampled at a high rate for diagnosing the variable compression ratio changing mechanism of cylinder one, as indicated by the samples 310 near together and forming a black box between times tl 1 and tl 2. A large number of samples can be taken and stored into controller memory for subsequent processing. The processing can include integrating the exhaust manifold pressure and determining the highest exhaust manifold pressure observed during the period in which the samples were taken. The compression ratio remains at the higher level, and the valve timings remain advanced. Thus, in one engine cycle, the exhaust manifold pressure can be the basis for determining whether the higher compression ratio is occupied or unoccupied.

[0048] At time t12, the compression ratio of the cylinder is switched to a lower compression ratio. The intake and exhaust valve timing remains advanced, and the VCR diagnostic request remains active.

[0049] Between time t12 and time t13, the engine exhaust manifold pressure for the variable compression ratio changing mechanism diagnostic of cylinder one continues to be sampled at a high rate, as indicated by the samples coming close together and forming a black box at 310 between time t12 and time t13. The compression ratio of the cylinder has been reduced, and the reduction in the cylinder compression ratio is represented by the lower peak cylinder pressure as shown at 306c. The intake and exhaust valve timing remains advanced to improve the exhaust manifold pressure signal to noise ratio.

[0050] At time t13, the variable compression ratio changing mechanism diagnostic request is withdrawn, and the compression ratio of the cylinder is switched back to a higher compression ratio. The exhaust manifold pressure sampling rate is reduced, and the total number of actual samples taken per cylinder cycle is reduced. The intake and exhaust valve timing is also returned to the previously more retarded state. The VCR diagnostic request can be cancelled when all expected engine compression ratios have been commanded and compared to expected values, as described in further detail in method 400.

[0051] In this way, the exhaust manifold pressure can be the basis for determining whether the cylinder compression ratio changing mechanism is degraded. In some examples, a similar sequence to that of Figure 4B is performed when the engine enters a deceleration fuel cut mode, so that the signal to noise ratio of the exhaust pressure signal can be improved.

[0052] Referring now to Figure 1 and Figure 4A , methods for operating a cylinder compression changing mechanism and operating an engine are shown. The methods can be included in the system of Figure 4B as executable instructions stored in a non-transitory memory. Additionally, Figure 1 and Figure 4A the methods can be coordinated with the system of Figure 4B to adjust actuators and operate the engine in the physical world.

[0053] At 402, the method 400 determines whether a variable compression ratio (VCR) diagnosis (e.g., a diagnosis of a cylinder compression ratio changing mechanism) is requested. In one example, a cylinder compression ratio changing mechanism diagnosis can be requested in response to a vehicle traveling a predetermined distance, engine performance being poor, engine performance being excellent, or other vehicle operating conditions. If the method 400 determines that a cylinder compression ratio changing mechanism diagnosis is requested, the answer is yes and the method 400 proceeds to 404. Otherwise, the answer is no and the method 400 proceeds to 440. Further, if the answer is yes, the method 400 can command the cylinder compression ratio changing mechanism to a predetermined position corresponding to a predetermined compression ratio of the cylinder (e.g., a highest compression ratio).

[0054] At 440, the method 400 operates the engine with basic intake and exhaust valve timing (e.g., intake and exhaust valve timing that is responsive to engine speed and load and does not initiate when a compression ratio changing diagnosis is requested). The basic intake and exhaust valve timing can be empirically determined in response to engine power output and engine emissions output. Further, intake manifold pressure and exhaust manifold pressure sampling is synchronized with engine position and is not time-based sampling. In one example, for each cylinder combustion event, the intake manifold pressure and exhaust manifold pressure is sampled once or twice. The method 400 proceeds to exit.

[0055] At 404, the method 400 determines whether a cylinder compression ratio changing diagnosis is to be performed during DFSO, and if so, the answer is yes and the method 400 proceeds to 406. Otherwise, the answer is no and the method 400 proceeds to 450. In one example, the method 400 determines whether a cylinder compression ratio changing diagnosis should be performed during DFSO in response to engine configuration (e.g., based on the number of engine cylinders and intake manifold and exhaust manifold pressure signal characteristics).

[0056] At 406, the method 400 determines whether the engine and vehicle are operating in desired conditions for performing a cylinder compression ratio changing mechanism diagnosis. In one example, the desired conditions can be that the engine is in DFSO mode and the engine speed is decreasing at less than a threshold rate. Further, the method 400 can require that the engine speed be within a desired speed range (e.g., between 1000 RPM and 2000 RPM). If the method 400 determines that the engine and vehicle are operating in desired operating conditions for performing a cylinder compression ratio changing diagnosis, the answer is yes and the method 400 proceeds to 408. Otherwise, the answer is no and the method 400 remains at 406. It is noted that the method 400 can also exit if there are selected conditions. For example, the method 400 can exit if a vehicle operator applies an accelerator pedal.

[0057] At 408, the method 400 determines whether engine exhaust pressure should be sensed and the basis for diagnosing the cylinder compression ratio changing mechanism. In one example, the method 400 can determine to sense exhaust pressure when an exhaust pressure sensor is available. Further, the method 400 can determine to sense exhaust pressure if the exhaust pressure sensor output signal has a higher signal-to-noise ratio than the intake manifold pressure sensor output at the current engine operating conditions. If the method 400 determines to sample exhaust pressure, the answer is yes and the method 400 proceeds to 410. Otherwise, the answer is no and the method 400 proceeds to 430.

[0058] At 410, the method 400 adjusts intake and exhaust valve timing. In one example, the intake and exhaust valve timing is advanced from a reference valve timing to improve the signal-to-noise ratio of the exhaust pressure sensor output. By advancing the exhaust valve timing, a higher exhaust pressure can be observed via the exhaust pressure sensor. The method 400 proceeds to 412.

[0059] At 412, the method 400 adjusts exhaust pressure sensor sampling. In one example, the exhaust pressure of a particular cylinder is sampled at a predetermined rate (e.g., 1 kHz) that begins at the exhaust valve opening time of the cylinder and ends at a predetermined crankshaft angle (e.g., 10 degrees after the bottom dead center exhaust stroke of the cylinder). The exhaust pressure sensor output is sampled at a high rate so that the exhaust peak (highest pressure during the cylinder cycle) pressure can be determined so that an accurate exhaust pressure integral value can be determined. The method 400 proceeds to 414.

[0060] At 414, the method 400 locates the peak exhaust pressure of the cylinder during the cylinder cycle. In one example, the peak cylinder pressure of the cylinder during the cylinder cycle can be determined by finding a sampled exhaust pressure that is greater than other exhaust pressures sampled during a crankshaft interval (e.g., from the exhaust valve opening of the cylinder to a predetermined crankshaft angle). In other examples, the method 400 can determine the exhaust pressure where the derivative of the exhaust pressure is zero to determine the peak exhaust pressure. Alternatively, the method 400 can determine an integral value of the sampled cylinder exhaust pressure. The integrated exhaust pressure can be determined via numerically integrating the cylinder exhaust pressure sampled during a crankshaft interval (e.g., from the exhaust valve opening of the cylinder to a predetermined crankshaft angle).

[0061] Further, the method 400 can estimate the compression ratio of the cylinder via comparing the peak exhaust pressure to a predetermined pressure in the memory. Specifically, the compression ratio of the cylinder is estimated by selecting the compression ratio associated with the pressure (also stored in the memory) in the memory that is within a predetermined value of the peak pressure determined at 414. Further, the method 400 can estimate the compression ratio of the cylinder via comparing the integrated exhaust pressure to a predetermined value in the memory. The compression ratio of the cylinder can be estimated by selecting the compression ratio stored in the memory that is associated with a value (also stored in the memory) that is within a predetermined value of the integrated pressure determined at 414.

[0062] In yet another example, the cylinder compression ratio can be estimated from the rate of pressure rise of the exhaust pressure. In one example, the rate of pressure rise of the exhaust pressure is compared to empirically determined rates of pressure rise of the exhaust pressure stored in the controller memory. The compression ratio stored in the controller memory and associated with the rate of pressure rise of the exhaust pressure that is closest to the measured rate of pressure rise of the exhaust pressure can be estimated as the compression ratio of the cylinder. The method 400 proceeds to 416.

[0063] At 416, the method 400 determines whether the peak pressure determined at 414 is within an expected pressure range. In one example, the method 400 determines whether the peak pressure determined at 414 is less than X kPa and greater than Y kPa. The values of the variables X and Y can be predetermined and stored in the controller memory, and they can be retrieved in response to the cylinder compression ratio changing mechanism being commanded to provide a compression ratio, an engine speed, and an engine temperature. If the method 400 determines that the peak pressure determined at 414 is not within the expected pressure range, the cylinder compression ratio changing mechanism can be indicated to be degraded. The cylinder compression ratio changing mechanism can be indicated to be degraded via changing the values of variables in the memory and via providing a visual or audible indication to the vehicle occupant via a human / machine interface. If the peak pressure determined at 414 is greater than Y kPa, the method 400 can determine that the cylinder compression ratio changing mechanism is providing a higher cylinder compression ratio. If the peak pressure determined at 414 is less than X kPa, the method 400 can determine that the cylinder compression ratio changing mechanism is providing a higher cylinder compression ratio.

[0064] In another example, the method 400 determines whether the integrated value of the exhaust pressure determined at 414 is within a desired range. In one example, the method 400 determines whether the integrated exhaust pressure determined at 414 is less than A and greater than B, where A and B are variables representing numerical values. The values of A and B can be predetermined and stored in the controller memory, and can be retrieved in response to the cylinder compression ratio changing mechanism being commanded to provide a compression ratio, an engine speed, and an engine temperature. If the method 400 determines that the integrated exhaust pressure determined at 414 is not within the desired range, the cylinder compression ratio changing mechanism can be indicated to be degraded. The cylinder compression ratio changing mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupants via the human / machine interface. If the integrated pressure determined at 414 is greater than B, the method 400 can determine that the cylinder compression ratio changing mechanism is providing a higher cylinder compression ratio than desired. If the integrated pressure determined at 434 is less than A, the method 400 can determine that the cylinder compression ratio changing mechanism is providing a higher cylinder compression ratio. The method 400 proceeds to 418.

[0065] Alternatively, if the method 400 determines that the cylinder compression ratio determined at 414 is not within a threshold compression ratio of the commanded cylinder compression ratio, the method 400 can determine that the cylinder compression ratio changing mechanism can be indicated to be degraded.

[0066] At 418, the method 400 determines whether all of the desired compression ratios (CR) have been evaluated. The cylinder compression ratio changing mechanism can be commanded to provide a plurality of cylinder compression ratios (e.g., 8: 1, 9: 1, 10: 1, 11: 1). If the method 400 determines that all of the desired compression ratios have been evaluated, the answer is yes and the method 400 proceeds to 420. Otherwise, the answer is no and the method 400 proceeds to 428.

[0067] At 428, the method 400 adjusts the cylinder compression ratio changing mechanism to provide a different compression ratio that has not yet been evaluated. After the cylinder compression ratio changing mechanism is commanded, the method 400 returns to 408.

[0068] At 430, the method 400 adjusts the intake and exhaust valve timing. In one example, the intake and exhaust valve timing is advanced from the baseline valve timing to improve the signal-to-noise ratio of the intake pressure sensor output. By advancing the intake valve timing, a higher intake manifold pressure can be observed via the engine intake pressure sensor. The method 400 proceeds to 432.

[0069] At 432, the method 400 adjusts intake manifold pressure sensor sampling. In one example, the engine intake manifold pressure of a particular cylinder is sampled at a predetermined rate (e.g., 1 kHz) that begins at the intake valve opening time of the cylinder and ends at a predetermined crank angle (e.g., 10 degrees after top dead center intake stroke of the cylinder). The intake manifold pressure sensor output is sampled at a high rate so that the intake manifold peak (highest pressure during the cylinder cycle) pressure can be determined so that an accurate intake manifold pressure integral value can be determined. The method 400 proceeds to 434.

[0070] At 434, the method 400 locates the peak intake manifold pressure of the cylinder during the cylinder cycle. In one example, the peak cylinder pressure during the cylinder cycle can be determined by finding a sampled intake manifold pressure that is greater than other sampled intake manifold pressures during a crank interval (e.g., from intake valve opening of the cylinder to a predetermined crank angle). In other examples, the method 400 can determine an exhaust pressure where the derivative of the exhaust pressure is zero to determine the peak exhaust pressure. Alternatively, the method 400 can determine an integrated value of the sampled cylinder intake manifold pressure. The integrated intake manifold pressure can be determined via numerically integrating the sampled cylinder intake manifold pressure during a crank interval (e.g., from intake valve opening of the cylinder to a predetermined crank angle).

[0071] Further, the method 400 can estimate the compression ratio of the cylinder via comparing the peak intake manifold pressure to predetermined pressures in memory. Specifically, the compression ratio of the cylinder is estimated by selecting the compression ratio associated with a pressure (also stored in memory) in memory that is within a predetermined pressure of the peak pressure determined at 434. Further, the method 400 can estimate the compression ratio of the cylinder via comparing the integrated intake manifold pressure to predetermined values in memory. The compression ratio of the cylinder can be estimated by selecting the compression ratio associated with a value (also stored in memory) in memory that is within a predetermined value of the integrated pressure determined at 434.

[0072] In yet another example, the cylinder compression ratio can be estimated from the rate of pressure rise of the intake manifold pressure. In one example, the rate of pressure rise of the intake manifold pressure is compared to empirically determined rates of pressure rise of the intake manifold pressure stored in controller memory. The compression ratio associated with the rate of pressure rise of the intake manifold pressure stored in controller memory that is closest to the measured rate of pressure rise of the intake manifold pressure can be estimated as the compression ratio of the cylinder. The method 400 proceeds to 436.

[0073] At 436, the method 400 determines whether the peak pressure determined at 434 is within a desired pressure range. In one example, the method 400 determines whether the peak pressure determined at 434 is less than P kPa and greater than Q kPa. The values of the variables P and Q can be predetermined and stored in the controller memory and can be retrieved in response to the cylinder compression ratio varying mechanism being commanded to provide a compression ratio, an engine speed, and an engine temperature. If the method 400 determines that the peak pressure determined at 434 is not within the desired pressure range, the cylinder compression ratio varying mechanism can be indicated to be degraded. The cylinder compression ratio varying mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupants via the human / machine interface. If the peak pressure determined at 434 is greater than Q kPa, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. If the peak pressure determined at 434 is less than P kPa, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio.

[0074] In another example, the method 400 determines whether the integral value of the intake manifold pressure determined at 434 is within a desired range. In one example, the method 400 determines whether the integral intake manifold pressure determined at 434 is less than C and greater than D, where C and D are variables representing numerical values. The values of C and D can be predetermined and stored in the controller memory and can be retrieved in response to the cylinder compression ratio varying mechanism being commanded to provide a compression ratio, an engine speed, and an engine temperature. If the method 400 determines that the integral intake manifold pressure determined at 434 is not within the desired range, the cylinder compression ratio varying mechanism can be indicated to be degraded. The cylinder compression ratio varying mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupants via the human / machine interface. If the integral pressure determined at 434 is greater than D, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. If the integral pressure determined at 434 is less than C, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. The method 400 proceeds to 418.

[0075] Alternatively, if the method 400 determines that the cylinder compression ratio determined at 434 is not within the threshold compression ratio of the commanded cylinder compression ratio, the method 400 can determine that the cylinder compression ratio varying mechanism can be indicated to be degraded.

[0076] At 420, the method 400 returns the intake and exhaust valve timing to the baseline timing. In addition, the sampling of the intake manifold pressure and the exhaust pressure is returned to being synchronized with the engine position. Thus, the time-based intake manifold and exhaust manifold pressure stops. The method 400 proceeds to 422.

[0077] At 422, if the cylinder compression altering mechanism is indicated to be degraded, the method 400 adjusts engine operation in response to the cylinder compression altering mechanism being degraded. In one example, engine spark timing and valve timing are adjusted in response to the cylinder compression altering mechanism being degraded. Specifically, if the method 400 determines that the cylinder compression ratio is greater than a desired value, the method 400 can retard the spark timing to reduce the likelihood of engine knock. In addition, the method 400 can retard the intake valve timing in response to the cylinder compression ratio being greater than the desired value to reduce cylinder pressure. Alternatively, if the method 400 determines that the cylinder compression ratio is less than the desired value, the method 400 can advance the spark timing and the intake valve timing. Thus, if the cylinder compression ratio is lower than the desired value, the method 400 can improve engine efficiency. The method 400 proceeds to exit.

[0078] At 450, the method 400 determines whether the engine and vehicle are operating under desired conditions for performing the cylinder compression ratio altering mechanism diagnosis. In one example, the desired conditions can be that the engine is operating at substantially constant speed and torque (e.g., changes less than ±5 percent) within a predetermined engine speed and torque range. If the method 400 determines that the engine and vehicle are under the desired operating conditions for performing the cylinder compression ratio altering diagnosis, the answer is yes and the method 400 proceeds to 452. Otherwise, the answer is no, and the method 400 remains at 450. It should be noted that the method 400 can also exit if there are selected conditions. For example, the method 400 can exit if the vehicle operator applies the accelerator pedal.

[0079] At 452, the method 400 determines whether engine exhaust pressure should be sensed and the basis for diagnosing the cylinder compression ratio altering mechanism. In one example, the method 400 can determine to sense exhaust pressure when an exhaust pressure sensor is available. In addition, the method 400 can determine to sense exhaust pressure if the exhaust pressure sensor output signal has a higher signal-to-noise ratio than the signal-to-noise ratio output by the intake manifold pressure sensor under the current engine operating conditions. If the method 400 determines that exhaust pressure is to be sampled, the answer is yes and the method 400 proceeds to 454. Otherwise, the answer is no, and the method 400 proceeds to 480.

[0080] At 454, the method 400 adjusts the intake and exhaust valve timing. In one example, the intake and exhaust valve timing is advanced from a reference valve timing to improve the signal-to-noise ratio of the exhaust pressure sensor output. By advancing the exhaust valve timing, a higher exhaust pressure can be observed via the exhaust pressure sensor. The method 400 proceeds to 456.

[0081] At 456, the method 400 adjusts the exhaust pressure sensor sampling. In one example, the exhaust pressure of a particular cylinder is sampled at a predetermined rate (e.g., 1 kHz) that begins at the exhaust valve opening time of the cylinder and ends at a predetermined crank angle (e.g., 10 degrees after the bottom dead center exhaust stroke of the cylinder). The exhaust pressure sensor output is sampled at a high rate so that the exhaust peak (the highest pressure during the cylinder cycle) pressure can be determined so that an accurate exhaust pressure integral value can be determined. The method 400 proceeds to 458.

[0082] At 458, the method 400 locates the peak exhaust pressure of the cylinder during the cylinder cycle. In one example, the peak cylinder pressure of the cylinder during the cylinder cycle can be determined by finding a sampled exhaust pressure that is greater than other exhaust pressures sampled during a crank interval (e.g., from the exhaust valve opening of the cylinder to a predetermined crank angle). In other examples, the method 400 can determine the exhaust pressure where the derivative of the exhaust pressure is zero to determine the peak exhaust pressure. Alternatively, the method 400 can determine the integral of the sampled cylinder exhaust pressure. The integrated exhaust pressure can be determined via numerically integrating the cylinder exhaust pressure sampled during a crank interval (e.g., from the exhaust valve opening of the cylinder to a predetermined crank angle).

[0083] Further, the method 400 can estimate the compression ratio of the cylinder via comparing the peak exhaust pressure to predetermined pressures in memory. Specifically, the compression ratio of the cylinder is estimated by selecting the compression ratio in memory associated with a pressure (also stored in memory) that is within a predetermined pressure of the peak pressure determined at 458. Further, the method 400 can estimate the cylinder compression ratio via comparing the integrated exhaust pressure to predetermined values in memory. The compression ratio of the cylinder can be estimated by selecting the compression ratio stored in memory associated with a value (also stored in memory) that is within a predetermined value of the integrated pressure determined at 458. The method 400 proceeds to 460.

[0084] At 460, the method 400 determines whether the peak pressure determined at 458 is within a desired pressure range. In one example, the method 400 determines whether the peak pressure determined at 458 is less than E kPa and greater than F kPa. The values of the variables E and F can be predetermined and stored in the controller memory and can be retrieved in response to the cylinder compression ratio varying mechanism being commanded to provide a compression ratio, an engine speed, and an engine temperature. If the method 400 determines that the peak pressure determined at 458 is not within the desired pressure range, the cylinder compression ratio varying mechanism can be indicated to be degraded. The cylinder compression ratio varying mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupant via the human / machine interface. If the peak pressure determined at 458 is greater than F kPa, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. If the peak pressure determined at 458 is less than E kPa, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio.

[0085] In another example, the method 400 determines whether the integrated value of the exhaust pressure determined at 458 is within a desired range. In one example, the method 400 determines whether the integrated exhaust pressure determined at 458 is less than N and greater than M, where N and M are variables representing numerical values. The values of N and M can be predetermined and stored in the controller memory and can be retrieved in response to the cylinder compression ratio varying mechanism being commanded to provide a compression ratio, an engine speed, and an engine temperature. If the method 400 determines that the integrated exhaust pressure determined at 458 is not within the desired range, the cylinder compression ratio varying mechanism can be indicated to be degraded. The cylinder compression ratio varying mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupant via the human / machine interface. If the integrated pressure determined at 458 is greater than M, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio than desired. If the integrated pressure determined at 458 is less than N, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. The method 400 proceeds to 462.

[0086] At 462, the method 400 determines whether all of the desired compression ratios (CRs) have been evaluated. The cylinder compression ratio varying mechanism can be commanded to provide a plurality of cylinder compression ratios (e.g., 8: 1, 9: 1, 10: 1, 11: 1). If the method 400 determines that all of the desired compression ratios have been evaluated, the answer is yes and the method 400 proceeds to 464. Otherwise, the answer is no and the method 400 proceeds to 469.

[0087] At 469, the method 400 adjusts the cylinder compression ratio changing mechanism to provide a different compression ratio that has not yet been evaluated. After commanding the cylinder compression ratio changing mechanism, the method 400 returns to 452.

[0088] At 480, the method 400 adjusts intake and exhaust valve timing. In one example, the intake and exhaust valve timing is advanced from the baseline valve timing to improve the signal-to-noise ratio of the intake pressure sensor output. By advancing the intake valve timing, a higher intake manifold pressure can be observed via the engine intake pressure sensor. The method 400 proceeds to 482.

[0089] At 482, the method 400 adjusts intake manifold pressure sensor sampling. In one example, the engine intake manifold pressure of a particular cylinder is sampled at a predetermined rate (e.g., 1 kHz) that begins at the intake valve opening time of the cylinder and ends at a predetermined crankshaft angle (e.g., 10 degrees after top dead center intake stroke of the cylinder). The intake manifold pressure sensor output is sampled at a high rate so that the intake manifold peak (highest pressure during the cylinder cycle) pressure can be determined so that an accurate intake manifold pressure integral value can be determined. The method 400 proceeds to 484.

[0090] At 484, the method 400 locates the peak intake manifold pressure of the cylinder during the cylinder cycle. In one example, the peak cylinder pressure of the cylinder during the cylinder cycle can be determined by finding that the sampled intake manifold pressure is greater than other intake manifold pressures sampled during a crankshaft interval (e.g., from intake valve opening of the cylinder to a predetermined crankshaft angle). In other examples, the method 400 can determine the exhaust pressure where the derivative of the exhaust pressure is zero to determine the peak exhaust pressure. Alternatively, the method 400 can determine the integral of the sampled cylinder intake manifold pressure. The integrated intake manifold pressure can be determined via numerically integrating the cylinder intake manifold pressure sampled during a crankshaft interval (e.g., from intake valve opening of the cylinder to a predetermined crankshaft angle).

[0091] Further, the method 400 can estimate the compression ratio of the cylinder via comparing the peak exhaust pressure to predetermined pressures in memory. Specifically, the compression ratio of the cylinder is estimated by selecting the compression ratio in memory associated with a pressure (also stored in memory) that is within a predetermined pressure of the peak pressure determined at 484. Further, the method 400 can estimate the compression ratio of the cylinder via comparing the integrated exhaust pressure to predetermined values in memory. The compression ratio of the cylinder can be estimated by selecting the compression ratio stored in memory associated with a value (also stored in memory) that is within a predetermined value of the integrated pressure determined at 484. The method 400 proceeds to 486.

[0092] At 486, the method 400 determines whether the peak pressure determined at 484 is within a desired pressure range. In one example, the method 400 determines whether the peak pressure determined at 484 is less than I kPa and greater than J kPa. The values of the variables I and J can be predetermined and stored in the controller memory and can be retrieved in response to the compression ratio provided by the cylinder compression ratio varying mechanism, the engine speed, and the engine temperature for which the cylinder compression ratio varying mechanism is commanded to provide. If the method 400 determines that the peak pressure determined at 484 is not within the desired pressure range, the cylinder compression ratio varying mechanism can be indicated to be degraded. The cylinder compression ratio varying mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupants via the human / machine interface. If the peak pressure determined at 484 is greater than J kPa, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. If the peak pressure determined at 484 is less than I kPa, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio.

[0093] In another example, the method 400 determines whether the integrated value of the intake manifold pressure determined at 484 is within a desired range. In one example, the method 400 determines whether the integrated intake manifold pressure determined at 484 is less than I and greater than J, where I and J are variables representing numerical values. The values of I and J can be predetermined and stored in the controller memory and can be retrieved in response to the compression ratio provided by the cylinder compression ratio varying mechanism, the engine speed, and the engine temperature for which the cylinder compression ratio varying mechanism is commanded to provide. If the method 400 determines that the integrated intake manifold pressure determined at 484 is not within the desired range, the cylinder compression ratio varying mechanism can be indicated to be degraded. The cylinder compression ratio varying mechanism can be indicated to be degraded via changing the values of the variables in the memory and via providing a visual or audible indication to the vehicle occupants via the human / machine interface. If the integrated pressure determined at 484 is greater than J, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. If the integrated pressure determined at 484 is less than I, the method 400 can determine that the cylinder compression ratio varying mechanism is providing a higher cylinder compression ratio. The method 400 proceeds to 462.

[0094] At 464, the method 400 returns the intake and exhaust valve timing to the baseline timing. In addition, the sampling of the intake manifold pressure and the exhaust pressure is returned to being synchronized with the engine position. Thus, the time-based intake and exhaust manifold pressure stops. The method 400 proceeds to 466.

[0095] At 466, if the cylinder compression varying mechanism is indicated to be degraded, the method 400 adjusts engine operation in response to the cylinder compression varying mechanism being degraded. In one example, engine spark timing and valve timing are adjusted in response to the cylinder compression varying mechanism being degraded. Specifically, if the method 400 determines that the cylinder compression ratio is greater than a desired value, the method 400 can retard spark timing to reduce the likelihood of engine knock. Further, the method 400 can retard intake valve timing in response to the cylinder compression ratio being greater than a desired value to reduce cylinder pressure. Alternatively, if the method 400 determines that the cylinder compression ratio is less than a desired value, the method 400 can advance spark timing and intake valve timing. Thus, if the cylinder compression ratio is lower than a desired value, the method 400 can improve engine efficiency. The method 400 proceeds to exit.

[0096] In these ways, the method 400 can diagnose whether the cylinder compression ratio varying mechanism is operating as expected. If the method 400 determines that the cylinder compression ratio varying mechanism is not operating as expected, engine operation can be adjusted to improve engine operation.

[0097] Thus, Figure 4A and Figure 4B The method of claim 1, further comprising adjusting the sampling of the pressure includes adjusting a timing and a sampling rate at which the pressure is sampled. The method of claim 1, further comprising increasing the sampling rate. The method of claim 1, further comprising adjusting a compression ratio of the cylinder in response to diagnosing the variable compression ratio varying mechanism.

[0098] ​ and ​ The method of claim 1, further comprising adjusting the sampling of the pressure includes adjusting a timing and a sampling rate at which the pressure is sampled. The method of claim 1, further comprising increasing the sampling rate. The method of claim 1, further comprising adjusting a compression ratio of the cylinder in response to diagnosing the variable compression ratio varying mechanism.

[0099] As those skilled in the art will appreciate, the methods described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated can be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily restricted to that which is shown, and the various steps or functions can be re-ordered or combined in some cases. Although not explicitly shown, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions can be repeated, depending on the particular strategy being used.

[0100] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. Those of ordinary skill in the art will appreciate that many changes and modifications can be made to the description without departing from the spirit and scope thereof. For example, vehicles including electric motor propulsion systems, hybrid motor propulsion systems, or internal combustion engine propulsion systems can benefit from the present description.

[0101] According to the present invention, a method for operating an engine includes adjusting, via a controller, a poppet valve timing and a pressure sampling in response to a request to diagnose a variable compression ratio changing mechanism.

[0102] According to one embodiment, the pressure is an exhaust gas pressure.

[0103] According to one embodiment, the pressure is an intake manifold pressure.

[0104] According to one embodiment, adjusting the poppet valve timing includes advancing the poppet valve timing.

[0105] According to one embodiment, adjusting the sampling of the pressure includes adjusting a timing and a sampling rate at which the pressure is sampled, and further includes estimating a compression ratio of the cylinder in response to a rate of rise of the pressure.

[0106] According to one embodiment, the sampling rate is increased.

[0107] According to one embodiment, the present invention features further adjusting a compression ratio of the cylinder in response to diagnosing the variable compression ratio changing mechanism.

[0108] According to the present invention, a method for operating an engine includes adjusting, via a controller, a poppet valve timing and a pressure sampling in response to a request to diagnose a variable compression ratio changing mechanism; and sampling the pressure during a deceleration fuel cut.

[0109] According to one embodiment, the present invention features further integrating at least some samples of the pressure taken during the deceleration fuel cut to determine an integrated value.

[0110] According to one embodiment, the application features further indicating the variable compression ratio changing mechanism to be degraded in response to the integral value being less than a threshold value.

[0111] According to one embodiment, the application features further determining the value of the peak pressure by sampling the pressure during a cylinder cycle.

[0112] According to one embodiment, the application features further indicating the variable compression ratio changing mechanism to be degraded in response to the peak pressure value being less than a threshold value.

[0113] According to one embodiment, adjusting the sampling of the pressure includes changing from sampling the pressure at predetermined crank angle intervals to sampling the pressure at predetermined time intervals.

[0114] According to one embodiment, adjusting the sampling of the pressure includes changing from sampling the pressure at predetermined crank angle intervals to sampling the pressure at predetermined time intervals.

[0115] According to the application, there is provided an engine operating system having an engine including a pressure sensor and a compression ratio adjusting mechanism that changes cylinder volume at top dead center compression stroke, and a controller including executable instructions for operating the adjusting mechanism to change engine compression ratio in response to a request to diagnose the compression ratio adjusting mechanism and to estimate engine compression ratio from output of the pressure sensor.

[0116] According to one embodiment, the compression ratio is estimated in response to a pressure ratio for which a derivative of the output of the pressure sensor is zero.

[0117] According to one embodiment, the compression ratio is estimated in response to an integral from the output of the pressure sensor.

[0118] According to one embodiment, the output is integrated from a time at which an exhaust valve opens during a cylinder cycle to reach a predetermined crank angle after a top dead center exhaust stroke of the cylinder cycle.

[0119] According to one embodiment, the application features further additional instructions to change engine compression ratio during deceleration fuel cut.

[0120] According to one embodiment, the application features further adjusting the sampling of the output of the pressure sensor in response to diagnosing the compression ratio adjusting mechanism.

Claims

1. A method for operating an engine, the method comprising: In response to a request to diagnose the variable compression ratio mechanism, the timing of the intake lift valve and the exhaust lift valve are adjusted via the controller, and pressure is sampled, wherein the pressure is either intake manifold pressure or exhaust manifold pressure; and The pressure is used to indicate a malfunction of the variable compression ratio mechanism.

2. The method of claim 1, wherein adjusting the timing of the intake lift valve and the exhaust lift valve includes advancing the timing of the intake lift valve and the exhaust lift valve.

3. The method of claim 1, wherein adjusting the sampling of the pressure includes adjusting the timing and sampling rate of sampling the pressure, and further includes: The compression ratio of the cylinder is estimated in response to the rate of increase of the pressure.

4. The method of claim 3, wherein the sampling rate is increased.

5. The method of claim 3, further comprising adjusting the compression ratio of the cylinder in response to diagnosing the variable compression ratio mechanism.

6. The method of claim 1, further comprising: The pressure is sampled during the deceleration fuel cut-off period.

7. The method of claim 6, further comprising integrating at least some samples of the pressure acquired during deceleration fuel cut-off to determine an integral value.

8. An engine operating system, the engine operating system comprising: An engine, the engine including a pressure sensor and a compression ratio adjustment mechanism, the compression ratio adjustment mechanism changing the volume of the cylinder during the top dead center compression stroke, wherein the pressure sensor is an intake manifold pressure sensor or an exhaust manifold pressure sensor. as well as A controller includes executable instructions to operate the compression ratio adjustment mechanism to change the engine compression ratio in response to a request to diagnose the compression ratio adjustment mechanism and to estimate the engine compression ratio based on the output of the pressure sensor, wherein the controller, in response to a request to diagnose the compression ratio adjustment mechanism, adjusts the timing of the intake lift valve and the exhaust lift valve and samples the output of the pressure sensor, wherein the output is used to indicate a fault in the compression ratio adjustment mechanism.

9. The engine operating system of claim 8, wherein the engine compression ratio is estimated in response to the pressure ratio in which the derivative of the output of the pressure sensor is zero.

10. The engine operating system of claim 8, wherein the engine compression ratio is estimated in response to the integral of the output from the pressure sensor.

11. The engine operating system of claim 10, wherein the output is an integral of the time from when the exhaust valve opens during the cylinder cycle to reach a predetermined crankshaft angle after the top dead center exhaust stroke of the cylinder cycle.

12. The engine operating system of claim 8, further comprising additional instructions to change the engine compression ratio during deceleration fuel cut-off.

Images