WO2017039614A1

WO2017039614A1 - Individual cylinder pressure estimation

Info

Publication number: WO2017039614A1
Application number: PCT/US2015/047733
Authority: WO
Inventors: Phanindra V. GARIMELLA; Ming-Feng Hsieh
Original assignee: Cummins Inc.
Priority date: 2015-08-31
Filing date: 2015-08-31
Publication date: 2017-03-09

Abstract

A system and method for determining an estimated absolute in-cylinder pressure for one or more engine cylinders that do not have an in-cylinder pressure sensor. According to certain embodiments, an absolute in-cylinder pressure in a first cylinder may be measured using an in-cylinder pressure sensor. Further, one or more engine dynamics may be measured or determined and used with a model to determine a relative in-cylinder pressure between the first cylinder and the one or more cylinders that do not have an in-cylinder pressure sensor. The measured absolute in-cylinder pressure of the first cylinder may be adjusted using the determined relative in-cylinder pressure(s) to estimate an in-cylinder pressure(s) for the one or more engine cylinders that do not have an in-cylinder pressure sensor.

Description

INDIVIDUAL CYLINDER PRESSURE ESTIMATION

BACKGROUND

[0001] Embodiments of the present invention generally relate to feedback for closed- looped engine controls. More particularly, but not exclusively, embodiments of the present invention relate to estimation of in-cylinder pressures for plurality of engine cylinders.

[0002] In-cylinder pressure sensors can provide valuable feedback for closed-loop engine control, including, for example, feedback relating to CA50 crank angle data, peak cylinder pressure (PCP), indicated mean effective pressure (IMEP), coefficient of variation (COV) of IMEP, engine knock, engine cylinder misfire, and cylinder-to-cylinder variation, among other feedback. Further, engine performance and robustness can be improved by controlling an engine with in-cylinder pressure feedbacks. However, generally, capturing the above-identified feedback information and information regarding cylinder-to-cylinder variation, among other similar information, typically is limited to situations in which each cylinder of the engine has an in-cylinder pressure sensor. Yet, the inclusion of an in-cylinder pressure sensor for each cylinder may relatively significantly increase the total cost of the engine system.

[0003] Conversely, while reducing the number of in-cylinder pressure sensors may offer a relatively significant cost-saving, the corresponding information provided by those sensors, and/or the use of such information, may be limited. For example, a reduced number of in- cylinder pressure sensors may limit and/or preclude the ability to attain information regarding cylinder-to-cylinder variations, which may thereby adversely impact engine performance and robustness.

[0004] Alternatively, certain studies have been conducted that have attempted to use crank angle information to estimate in-cylinder pressure. However, such estimation typically requires a relatively significant amount of calibration. Further, the accuracy of such estimations can be significantly affected by different operating conditions. Moreover, different applications, such as, for example, different drivelines and/or vehicle loads, can alter crank shaft dynamics, which may make accurate in-cylinder pressure estimation based on crank speed challenging in practice. BRIEF SUMMARY

[0005] An aspect of an embodiment of the present invention is a method that includes measuring, by an in-cylinder pressure sensor, an absolute in-cylinder pressure in a first cylinder of an engine. Further, a relative in-cylinder pressure between the first cylinder and a second cylinder of the engine is determined. The measured absolute in-cylinder pressure in the first cylinder and the determined relative in-cylinder pressure between the first and second cylinders are used to determine an estimated absolute in-cylinder pressure for the second cylinder.

[0006] Another aspect of an embodiment of the present invention is a method that includes detecting, by an in-cylinder pressure sensor, an absolute in-cylinder pressure in a first cylinder of an engine. An on-engine measurement of the engine is determined and used in the determination of a relative in-cylinder pressure between the first cylinder and at least one other cylinder. Additionally, the determined relative in-cylinder pressure is used in adjusting the detected absolute in-cylinder pressure of the first cylinder to estimate an absolute in-cylinder pressure for the at least one other cylinder.

[0007] Additionally, an aspect of an embodiment of the present invention is a system that includes an in-cylinder pressure sensor that is positioned in a first cylinder of an engine. The in- cylinder pressure sensor may be structured to measure an absolute in-cylinder pressure of the first cylinder. The system also includes at least one sensor that is structured to provide at least one on-engine measurement and model that is adapted to use the at least one on-engine measurement to output a relative in-cylinder pressure between the first cylinder and at least one other cylinder of the engine. The system further includes a module that is adapted to output an estimated absolute in-cylinder pressure for the at least one other cylinder using the absolute in- cylinder pressure of the first cylinder and the relative in-cylinder pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The description herein makes reference to the accompanying figures wherein like reference numerals refer to like parts throughout the several views.

[0009] Figure 1 illustrates a schematic block diagram of an exemplary internal combustion engine system.

[00010] Figure 2 illustrate a schematic block diagram of an exemplary cylinder that includes an in-cylinder pressure sensor. [00011] Figure 3 illustrates a schematic diagram depicting an exemplary control system in which a single in-cylinder pressure sensor, crank angle, and crank shaft model are utilized to provide estimations of relative and absolute in-cylinder pressures for engine cylinders.

[00012] Figure 4 illustrates a graphical representation of a relationship between a crank speed measurement (crank shaft acceleration) and an in-cylinder pressure (torque), as presented in Liu, F., Amaratunga, G., Collings, N., and Soliman, A., "An Experimental Study on Engine Dynamics Model Based In-Cylinder Pressure Estimation," SAE Technical Paper 2012-01-0896, 2012, doi: 10.4271/2012-01-0896.

[00013] Figure 5 illustrates a schematic diagram depicting an exemplary control system in which a single in-cylinder pressure sensor, sensed or measured engine knock, and an engine knock model are utilized to provide estimations of relative and absolute in-cylinder pressures for engine cylinders.

[00014] Figure 6 illustrates an exemplary relation between in-cylinder pressure and engine knock sensor measurement (engine knock index).

[00015] The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentalities shown in the attached drawings.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[00016] Certain terminology is used in the foregoing description for convenience and is not intended to be limiting. Words such as "upper," "lower," "top," "bottom," "first," and "second" designate directions in the drawings to which reference is made. This terminology includes the words specifically noted above, derivatives thereof, and words of similar import. Additionally, the words "a" and "one" are defined as including one or more of the referenced item unless specifically noted. The phrase "at least one of followed by a list of two or more items, such as "A, B or C," means any individual one of A, B or C, as well as any combination thereof.

[00017] Figure 1 illustrates a schematic block diagram of an exemplary internal combustion engine system 100 that includes an internal combustion engine 102 that is connected to an intake system 104 and an exhaust system 106. It shall be appreciated that the illustrated configuration and components of the engine system 100 are but one example, and that the disclosure contemplates that a variety of different engine systems 100 and the associated components may be utilized. Further, the engine system 100 may be used in a variety of different applications or platforms, and moreover with a variety of different types of machines, vehicles, and/or devices, including, but not limited to, stationary devices as well as on-road vehicles, including automotive applications. The engine 102 may receive fuel from one or more fuel sources 108, including, for example, fuel such as diesel fuel, gaseous fuel, natural gas, bio- gas, methane, propane, ethanol, producer gas, field gas, liquefied natural gas, compressed natural gas, and/or landfill gas, among other fuels.

[00018] The engine 102 includes an engine block 110 that may define at least a portion of one or more cylinders 1 12. For example, in the depicted embodiment, the engine 102 includes six cylinders 112 in an in-line arrangement. However, the engine 102 may have any different number of cylinders 112, as well as cylinders 112 in a variety of different arrangements. Additionally, each cylinder 112 is sized to accommodate the slideable displacement of a piston 114 along at least a portion of the cylinder 112 such that the pistons 114 may reciprocate between a top-dead-center position and a bottom-dead-center position. Each of the cylinders 112, its respective piston 114 and cylinder head 116, form a combustion chamber 118. Further, at least a portion of the forces generated by the slideable displacement of the piston 114 along at least a portion of the cylinder 112 during combustion events in the combustion chamber 118 are transmitted to a mechanical drive system 122. For example, the pistons 114 are typically operably coupled to a crank shaft 120 of a mechanical drive system 122 of the engine system 100 that converts the reciprocal movement of the pistons 114 of the engine 102 into rotational movement.

[00019] The cylinders 112 are in selective fluid communication with the intake system

104 such that a charged air flow maybe delivered to the combustion chamber 118. The cylinders 112 are also in selective fluid communication with the exhaust system 106 such that exhaust gases produced by combustion of fuel(s) in the combustion chambers 118 may be delivered through an exhaust manifold 124 to the exhaust system 106. The exhaust system 106 may include a variety of different components, such as, for example, one or more turbochargers 126, as well as an after-treatment system 128. According to certain embodiments, the after-treatment system may include an exhaust gas recirculation (EGR) system 130 that is in fluid communication with the intake system 104. The EGR system 130 may include a variety of different components, including, for example, a cooler 132, a bypass 134, and a control valve 136. The EGR system 130 may, during at least certain operating conditions, recirculate at least a portion the exhaust outputted from one or more of the cylinders 112 to the intake system 104.

[00020] A variety of different turbochargers 126 may be utilized, if any, including, for example, variable-geometry turbine turbochargers and waste-gated turbochargers. The turbocharger 126 may include a turbine 138 that receives a flow of exhaust gas and which is connected via a shaft 140 to a compressor 142 that is in fluid communication with an intake air supply 144 through which a fresh air supply is provided to the compressor 142. Operation of the compressor 142 may provide a charged air flow, which may pass through a charge air cooler 146 before being distributed by one or more inlet supply conduits 148 to an engine intake manifold 150 that distributes the charged air flow to the cylinders 112 of the engine 102. Moreover, the compressor 142, which may be a fixed or variable geometry compressor, is configured to compress the air or a combined flow of air and exhaust gas from the EGR system 130 to a predetermined pressure level to provide a charged air flow to the engine 102. Further, the fresh air flow or combined flows in the intake system 104 can be filtered, unfiltered, and/or conditioned in any known manner, either before or after mixing with the EGR flow from the EGR system 130, when provided. The intake system 104 may include components configured to facilitate or control introduction of the charged air flow to engine 102, such as, for example, an intake throttle (not shown) that is configured to regulate a flow of atmospheric air and/or combined air/EGR flow to engine 102.

[00021] In certain embodiments, the cylinders 112 each include at least one of a port injector or a direct injector 160 for injecting fuel that is delivered from the fuel source 108 into the combustion chamber 118. Additionally, and/or alternatively, an injector at the compressor 142 can be provided for delivery or induction of fuel from the fuel source 108 and/or a supplemental fuel source, to the charge air flow that is delivered to cylinders 112. Further, the engine system 100 may include one or more crank sensors 152 that may be used to detect a position and/or speed of the crank shaft 120, such as, for example, an angular position and/or rotational speed of the crank shaft 120. A variety of different types of crank sensors 152 may be employed, including, for example, a magnetic pickup coil, a Hall-effect sensor, a magneto- resistive element, and/or an optical sensor. Additionally, or alternatively, the engine system 100 may include one or more engine knock sensors 158 to estimate engine knock of one or more, including all, of the cylinders 112.

[00022] As indicated at least by Figure 2, operation of fuel injection events in which charge flow is delivered, and fuel is injected, into the combustion chambers 118 may be electrically controlled by a control system 154 of the engine system 100. The control system 154 may include a controller 156 which may be configured to control various operational aspects of engine system 100, including fuel injection events, among other operations. The controller 156 may be implemented in a number of ways. Further, the controller 156 may execute operating logic that defines various control, management, and/or regulation functions. The operating logic may be in the form of one or more microcontroller or microprocessor routines stored in a non- transitory memory, dedicated hardware, such as a hardwired state machine, analog calculating machine, various types of programming instructions, and/or other forms as would occur to those skilled in the art.

[00023] Additionally, the controller 156 may be provided as a single component, or a collection of operatively coupled components, and may comprise digital circuitry, analog circuitry, or a hybrid combination of both of these types. When of a multi-component form, the controller 156 may have one or more components remotely located relative to the others in a distributed arrangement. The controller 156 can include multiple processing units arranged to operate independently, in a pipeline processing arrangement, in a parallel processing arrangement, or the like. In one embodiment, the controller 156 includes several programmable microprocessing units of a solid-state, integrated circuit type that are distributed throughout the engine system 100 that each includes one or more processing units and non-transitory memory. For the depicted embodiment, the controller 156 includes a computer network interface to facilitate communications using standard Controller Area Network (CAN) communications or the like among various system control units. It should be appreciated that the depicted modules or other organizational units of the controller 156 refer to certain operating logic performing indicated operations that may each be implemented in a physically separate controller of the controller 156 and/or may be virtually implemented in the same controller.

[00024] The description herein including modules and/or organizational units emphasizes the structural independence of the aspects of the controller 156, and illustrates one grouping of operations and responsibilities of the controller 156. Other groupings that execute similar overall operations are understood within the scope of the present application. Modules and/or organizational units may be implemented in hardware and/or as computer instructions on a non- transient computer readable storage medium, and may be distributed across various hardware or computer based components.

[00025] Example and non-limiting implementation elements of modules and/or organizational units of the controller 156 include sensors providing any value determined herein, sensors providing any value that is a precursor to a value determined herein, datalink and/or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers, and/or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a particular non-transient state configured according to the module specification, any actuator including at least an electrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp, analog control elements (springs, filters, integrators, adders, dividers, gain elements), and/or digital control elements.

[00026] The controller 156 and/or any of its constituent processors/controllers may include one or more signal conditioners, modulators, demodulators, Arithmetic Logic Units (ALUs), Central Processing Units (CPUs), limiters, oscillators, control clocks, amplifiers, signal conditioners, filters, format converters, communication ports, clamps, delay devices, memory devices, Analog to Digital (A/D) converters, Digital to Analog (D/A) converters, and/or different circuitry or functional components as would occur to those skilled in the art to perform the desired communications.

[00027] The controller 156 may provide fueling commands in accordance with operating conditions of the engine 102 and/or operator demand that may activate and/or deactivate at least the operation of one or more fuel pumps and/or fuel injectors 160 as well as provide control commands that regulate the amount, timing and duration of fuel injection events. Further, in connection with such combustion events, the controller 156 may control the operation of one or more intake valves 162 and exhaust valves 164 so as to control the flow of charged air into, and the discharge of exhaust gases from, the cylinder 112. Moreover, the controller 156 may utilize a valve control system, or a variable valve timing system, to control the flow of intake air or air/fuel mixture into, and exhaust gases out of, the cylinders 112. [00028] Fueling commands from the controller 156 may be based on a variety of different considerations and information, including information provided by fueling maps, control algorithms, or other fueling rate/amount determination sources stored or accessible to the controller 156. Additionally, the controller 156 can be connected to a variety of components of the engine system 100, including, but not limited to, sensors, actuators, switches, shutoff valves, intake throttles, bypass valves for the compressor 142 and/or turbine 138, and may control the charge flow delivered to the cylinders 112 as well as the flow of exhaust gases that are released from the cylinders 112.

[00029] The control system 154 of the present invention may also be communicatively coupled to an in-cylinder pressure sensor 166 that is positioned in at least one of the cylinders 112 such that one or more signals from the in-cylinder pressure sensor 166 is communicated to control system 154, and more specifically to the controller 156. Moreover, according to certain embodiments, only one of the plurality of cylinders 112 may include an in-cylinder pressure sensor 166. The in-cylinder pressure sensor 166 may provide a measured or detected indication of an engine operating condition(s) relating to at least combustion events in the combustion chamber 118 of that cylinder 112 that may be used to at least assist in management of combustion events during the compression and/or expansion strokes of the piston 114. For example, according to certain embodiments, the in-cylinder pressure sensor 166 may be used to provide an indicated mean effective pressure (IMEP), knock intensity, start of combustion, combustion rate, combustion duration, crank angle at which peak cylinder pressure occurs, combustion event or heat release placement, effective expansion ratio, a parameter indicative of a centroid of heat release placement, and/or location and end of combustion data, among other information. The signal(s) provided from the in-cylinder pressure sensor 166 to the controller 156 may thus be used by the controller 156 to determine an actual or absolute operating condition(s) associated with the combustion in combustion chamber 118.

[00030] According to certain embodiments, information from the in-cylinder pressure sensor 166 of one, if not more, of the cylinders 112, such as actual or absolute in-cylinder pressure in that cylinder 112, may be used with determined relative pressures for one or more other cylinders 112 that do not contain an in-cylinder pressure sensor 166 to estimate an absolute in-cylinder pressure for that/those other cylinder(s) 112. The relative pressures for those other cylinders 112 that do not contain an in-cylinder pressure sensor 166 may be obtained in a variety of manners, such as, for example, from models that may utilize tables, charts, and/or algorithms, among other information and on-engine measurements and/or predictions, including, but not limited to, information from one or more crank sensors 152 and/or engine knock sensors 158. The absolute pressure, as measured by the in-cylinder pressure sensor 166, may then be used with the determined relative pressure(s) for one or more other cylinders 1 12 that do not contain an in-cylinder pressure sensor 166 to estimate an absolute in-cylinder pressure for that/those other cylinder(s) 112.

[00031] For example, Figure 3 illustrates a schematic diagram depicting an exemplary control system 154 in which a single in-cylinder pressure sensor 166 in a first cylinder (Cyli) is used to measure or determine an absolute in-cylinder pressure measurement (Cylinder Pressure Measurement of Cyl. 1) in that first cylinder (Cyli). The term "first" cylinder, as well as similar terms, including "second" and "third" cylinders, is provided for purposes of explanation, and may correspond to a cylinder(s) 112 at a variety of locations in the engine block 110. Additionally, according to the illustrated embodiment, a crank shaft model 168 is provided with information or data indicating an on-engine measured or predicted value, such as, for example, measured or determined information from a crank sensor 152 that indicates crank shaft 120 dynamics (Crank Angle), such as, but not limited to, crank shaft speed and/or angular position. The crank shaft model 168 may use the provided information (Crank Angle) to predict or determine a corresponding relative in-cylinder pressure for the other cylinders (Cyl₂, Cyl₃ ... Cyl_N) relative to the first cylinder (Cyli). Again, as previously discussed, the crank shaft model 168 may be based on, or utilize, a variety of different types of information, including, but not limited to, algorithms, look-up tables, and/or reference tables, among other information. For example, Figure 4 illustrates a graphical representation of an exemplary relationship between a crank speed measurement (crank shaft acceleration) and an in-cylinder pressure (torque). Accordingly, in such an embodiment, for the other cylinders (Cyl₂, Cyl₃ ... Cy^), which do not have an in-cylinder pressure sensor 166, information provided from the crank sensor 152 relating to crank shaft speed may be utilized by the crank shaft model 168 to determine a relative in- cylinder pressure between the first cylinder (Cyli) and the other cylinders (Cyli, Cyl₂, Cyl₃ ... CylN). For example, according to the illustrated embodiment in which the in-cylinder pressure sensor 166 is located in the first cylinder (Cyli), the crank shaft model 168 may determine a relative in-cylinder pressure between the first cylinder (Cyli) to the second cylinder (Cyl₂), between the first cylinder (Cyli) to the third cylinder (Cyl₃), and as well as the relative in- cylinder pressures between the first cylinder (Cyli) to the remaining, or "N", cylinders (Cy ).

[00032] As shown in Figure 3, the relative pressure determination from the crank shaft model 168, as determined for the second cylinder (Cyl₂), may be provided to a corresponding module 170a that also receives information relating to the absolute in-cylinder pressure of the first cylinder (Cylinder Pressure Measurement of Cyl. 1), as determined or measured using the in-cylinder pressure sensor 166 of the first cylinder (Cyli). The module 170a may then perform a summation function using the determined relative in-cylinder pressure between the first cylinder (Cyli,) to the second cylinder (Cyl₂) and the absolute in-cylinder pressure of the first cylinder (Cyli) to estimate an absolute in-cylinder pressure for the second cylinder (Cyl₂).

[00033] Similarly, the relative first cylinder (Cyli) to the third cylinder (Cyl₃) in-cylinder pressure determination from the crank shaft model 168 may be provided to a corresponding module 170b that also receives information relating to the absolute in-cylinder pressure of the first cylinder (Cylinder Pressure Measurement of Cyl. 1), as determined or measured using the in-cylinder pressure sensor 166 of the first cylinder (Cyli). The module 170b, which may the same or different than the module 170a used to estimate an absolute in-cylinder pressure for the second cylinder (Cyl₂), may then perform a summation function using the determined relative in- cylinder pressure between the first cylinder (Cyli,) to the third cylinder (Cyl₃) and the absolute pressure of the first in-cylinder cylinder (Cyli) to estimate an absolute in-cylinder pressure for the third cylinder (Cyl₃). Similar processes may also be employed to estimate an absolute in- cylinder pressure for other cylinders (Cyl ) in the engine 102 that do not include an in-cylinder pressure sensor 166.

[00034] Accordingly, with the availability of at least one in-cylinder pressure sensor 166, a relatively accurate crank shaft dynamics/model can be estimated online using the detected in- cylinder pressure from the in-cylinder pressure sensor 166 and sensed crank shaft 120 to relatively accurately predicted an in-cylinder pressure for cylinders 112 that do not have an in- cylinder pressure sensor 166. Such a configuration may therefore not only assist with enhancing engine performance and robustness, but also reduce the total cost of the engine system 100 by not relying on individual in-cylinder pressure sensors 166 in multiple cylinders 112, and more specifically, for at least certain embodiments, utilizing an in-cylinder pressure sensor 166 in only one cylinder 112. [00035] While the embodiment illustrated in Figure 3 is discussed above in terms of utilizing crank shaft 120 dynamics (Crank Angle) and a crank shaft model, other on-engine measurements or determinations may be utilized in addition to, or in lieu of, measured or determined crank shaft 120 information. For example, as shown in Figure 5, in at least certain applications, such as applications in which the engine 102 receives fuel from a natural gas fuel source 108, among other applications, information from one or more engine knock sensors 158 may be used to estimate relative in-cylinder pressures between the cylinder(s) (Cyli) that has an in-cylinder pressure sensor 166 and the other cylinders (Cyl₂, Cyl₃ . .. CVIN). According to such embodiment, an engine knock model 172 may use a correlation(s) between engine knock indexes, as estimated from the one or more engine knock sensor(s) 158 (Engine Knock), and in- cylinder pressure, as shown, for example, by at least Figure 6. For example, as illustrated by Figure 1 , according to certain embodiments, a plurality of engine knock sensors 158 may be utilized to estimate engine knock of each cylinder (Cyli, Cyl₂, Cyl₃ . .. CVIN) accurately, and more specifically, engine knock for at least those cylinders (Cyl₂, Cyl₃ . .. Cyl_N) that do not include an in-cylinder pressure sensor 166. Measured or determined engine knock information (Engine Knock) may thus be used to by the engine knock model 172 to estimate relative in- cylinder pressures between the first cylinder (Cyli) and the cylinders (Cyl₂, Cyl₃ . . . CVIN) that do not have an in-cylinder pressure sensor 166. Similar to the embodiment discussed above with respect to Figure 3, the relative in-cylinder pressures provided by the engine knock model 172 may then be provided to one or more modules 174a, 174b that also receive information relating to the absolute pressure of the first cylinder (Cylinder Pressure Measurement of Cyl. 1), as determined or measured using the in-cylinder pressure sensor 166 of the first cylinder (Cyli). The module 174a, 174b may then perform a summation function using the determined relative in-cylinder pressure between the first cylinder (Cyli) and the other cylinder (Cyl₂, Cyl₃, CVIN) and the absolute in-cylinder pressure of the first cylinder (Cyli) to estimate an absolute in- cylinder pressure for the other cylinder (Cyl₂, Cyl₃, Cyl_N). Such a procedure may be performed to at least estimate an absolute in-cylinder pressure for each of the cylinders (Cyl₂, Cyl₃, Cyl_N) that do not include an in-cylinder pressure sensor 166, as previously discussed.

[00036] According to other embodiments, the above-discussed in-cylinder pressure estimations may be used in connection with diagnostics of in-cylinder pressure sensors 166 that are positioned in a plurality of the cylinders 1 12. For example, according to certain embodiments, a plurality of cylinders (CylN, CylN+i, Cy +2), if not all of the cylinders (CylN, CylN+i, CylN+2, · · · CylN+i), may have an in-cylinder pressure sensor 166. In such situations, the accuracy and/or operability of the in-cylinder pressure sensors 166 may be evaluated based on, at least in part, a comparison of the measurements provided by the in-cylinder pressure sensors 166 with the predicted absolute in-cylinder pressures for those cylinders, as determined, for example, by the methods discussed above with respect to at least Figures 3 and 5. For example, the pressure measurement(s) provided by an in-cylinder pressure sensor 166 in a cylinder (Cy ) may be compared to the predicted absolute pressure for that same cylinder (Cy ) that is determined using a measured pressure from an in-cylinder pressure sensor 166 in another cylinder (Cyl_N+i) and the predicted relative pressure, as determined, for example, using the above discussed crank shaft and/or engine knock models 168, 172. Similarly, the pressure in the other cylinder (CylN+i), as measured by the pressure sensor 166 in that cylinder (CylN+i), may also be compared to a predicted absolute pressure, as determined using the absolute pressure measurement from the in-cylinder pressure sensor 166 of another cylinder (Cy^) in a manner similar to that which is described above with respect to at least Figures 3 and 5. Such comparisons can provide an indication of at least the accuracy and/or operability of the in- cylinder pressure sensors 166 in each of the cylinders (Cy , CylN+i). Further, the results of such comparison for a particular cylinder (Cy^) may be compared with the results of a similar comparison for another (Cy +i) in connection with indicating, and/or diagnosing the source of, potential problems or issues in the engine system 100.

[00037] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as "a," "an," "at least one" and "at least a portion" are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language "at least a portion" and/or "a portion" is used the item may include a portion and/or the entire item unless specifically stated to the contrary.

Claims

1. A method comprising:

measuring, by an in-cylinder pressure sensor, an absolute in-cylinder pressure in a first cylinder of an engine;

determining a relative in-cylinder pressure between the first cylinder and a second cylinder of the engine; and

determining, using the measured absolute in-cylinder pressure in the first cylinder and the determined relative in-cylinder pressure between the first and second cylinders, an estimated absolute in-cylinder pressure for the second cylinder.

2. The method of claim 1, further including the step of measuring an on-engine measurement, and wherein the step of determining the relative in-cylinder pressure includes using the measured on-engine measurement and a model to determine the relative in-cylinder pressure, and wherein the second cylinder does not include an in-cylinder pressure sensor.

3. The method of claim 2, wherein the on-engine measurement is one or more dynamics of a crank shaft of the engine, and wherein the model is a crank shaft model that uses the one or more dynamics of the crank shaft to determine the relative in-cylinder pressure between the first and second cylinders.

4. The method of claim 3, wherein the one or more dynamics of the crank shaft is at least one of a rotational speed and an angular position of the crank shaft.

5. The method of claim 2, wherein the on-engine measurement is a measured engine knock of the second cylinder, and wherein the model is an engine knock model that uses the measured engine knock to determine the relative in-cylinder pressure between the first and second cylinders.

6. The method of claim 1, further including the steps of:

determining a relative in-cylinder pressure between the first cylinder and a third cylinder of the engine; and determining, using the measured absolute in-cylinder pressure in the first cylinder and the determined relative in-cylinder pressure between the first cylinder and the third cylinder, an estimated absolute in-cylinder pressure for the third cylinder.

7. The method of claim 6, further including the steps of sensing by a first sensor a first on- engine dynamic for the second cylinder, and sensing by a second sensor a second on-engine dynamic for the third cylinder.

8. The method of claim 7, wherein the step of determining the relative in-cylinder pressure between the first and second cylinders includes using the sensed first on-engine measurement and a model to determine the relative in-cylinder pressure between the first and second cylinders, and wherein the step of determining the relative in-cylinder pressure between the first and third cylinders includes using the sensed second on-engine measurement and the model to determine the relative in-cylinder pressure between the first and third cylinders.

9. The method of claim 7, wherein the first and second sensors are the same crank sensor, and wherein the sensed first and second on-engine dynamics is a crank shaft dynamic.

10. The method of claim 9, wherein the crank shaft dynamic is at least one of a rotational speed and angular position of the crank shaft.

11. The method of claim 8, wherein the first sensor is a first engine knock sensor and the first on-engine measurement is an engine knock of the second cylinder, and further wherein the second sensor is a second engine knock sensor and the second on-engine measurement is an engine knock of the third cylinder.

12. A method comprising:

detecting, by an in-cylinder pressure sensor, an absolute in-cylinder pressure in a first cylinder of an engine;

determining an on-engine measurement of the engine;

determining, using the determined on-engine measurement, a relative in-cylinder pressure between the first cylinder and at least one other cylinder; and adjusting, using the determined relative in-cylinder pressure, the detected absolute in- cylinder pressure of the first cylinder to estimate an absolute in-cylinder pressure for the at least one other cylinder.

13. The method of claim 14, wherein the step of determining the on-engine measurement of the engine comprises measuring a dynamic of a crank shaft of the engine, and wherein the step of determining a relative in-cylinder pressure comprises determining, by a crank shaft model using the measured dynamic of the crank shaft, the relative in-cylinder pressure.

14. The method of claim 13, wherein the measured dynamic of the crank shaft is at least one of a rotational speed and angular position of the crank shaft.

15. The method of claim 12, wherein the step of determining the on-engine measurement of the engine comprises measuring an engine knock for each of the at least one other cylinder, and wherein the step of determining a relative in-cylinder pressure comprises determining, by an engine knock model using of the measured engine knock, the relative in-cylinder pressure.

16. The method of claim method 12 further comprising:

detecting, by a second in-cylinder pressure sensor, a second absolute in-cylinder pressure in a second cylinder of the engine;

determining, using the determined on-engine measurement, a second relative in- cylinder pressure between the second cylinder and the first cylinder;

adjusting, using the determined second relative in-cylinder pressure, the second detected absolute in-cylinder pressure of the second cylinder to estimate an absolute in-cylinder pressure for the first cylinder; and

comparing the estimated absolute in-cylinder pressure for the first cylinder with the detected absolute in-cylinder pressure in the first cylinder.

17. A system comprising :

an in-cylinder pressure sensor positioned in a first cylinder of an engine, the in-cylinder pressure sensor structured to measure an absolute in-cylinder pressure of the first cylinder;

at least one sensor structured to provide at least one on-engine measurement; a model adapted to use the at least one on-engine measurement to output a relative in- cylinder pressure between the first cylinder and at least one other cylinder of the engine;

a module adapted to output an estimated absolute in-cylinder pressure for the at least one other cylinder using the absolute in-cylinder pressure of the first cylinder and the relative in- cylinder pressure.

18. The system of claim 17, wherein the at least one other cylinder does not include an in- cylinder pressure sensor.

19. The system of claim 18, wherein the at least one sensor is a crank shaft sensor, and wherein the at least one on-engine measurement is at least one of an angular position and a rotational speed of a crank shaft of the engine.

20. The system of claim 19, wherein the at least one sensor comprises one or more engine knock sensors, and wherein the at least one on-engine measurement is an engine knock sensed by the one or more engine knock sensors.