WO2017091130A1 - Method and device for determining in-cylinder pressure of a combustion engine - Google Patents

Method and device for determining in-cylinder pressure of a combustion engine Download PDF

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Publication number
WO2017091130A1
WO2017091130A1 PCT/SE2016/051132 SE2016051132W WO2017091130A1 WO 2017091130 A1 WO2017091130 A1 WO 2017091130A1 SE 2016051132 W SE2016051132 W SE 2016051132W WO 2017091130 A1 WO2017091130 A1 WO 2017091130A1
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WO
WIPO (PCT)
Prior art keywords
cylinder
model
sensor
curve
pressure curve
Prior art date
Application number
PCT/SE2016/051132
Other languages
French (fr)
Inventor
Ola Stenlåås
Mikael Nordin
Christian RUGLAND
Original Assignee
Scania Cv Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from SE1551525A external-priority patent/SE539584C2/en
Application filed by Scania Cv Ab filed Critical Scania Cv Ab
Priority to DE112016004758.4T priority Critical patent/DE112016004758T5/en
Publication of WO2017091130A1 publication Critical patent/WO2017091130A1/en

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D35/00Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for
    • F02D35/02Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions
    • F02D35/023Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions by determining the cylinder pressure
    • F02D35/024Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions by determining the cylinder pressure using an estimation
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1497With detection of the mechanical response of the engine
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L23/00Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid
    • G01L23/26Details or accessories
    • G01L23/32Apparatus specially adapted for recording pressure changes measured by indicators
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1401Introducing closed-loop corrections characterised by the control or regulation method
    • F02D2041/1413Controller structures or design
    • F02D2041/1432Controller structures or design the system including a filter, e.g. a low pass or high pass filter
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/24Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
    • F02D41/26Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using computer, e.g. microprocessor
    • F02D41/28Interface circuits
    • F02D2041/281Interface circuits between sensors and control unit
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D35/00Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for
    • F02D35/02Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions
    • F02D35/027Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions using knock sensors

Definitions

  • the present invention relates to a method and a device for determination of in-cyli nder pressure of a combustion engine.
  • US 8396649 describes a method whereby some in- cylinder pressure data can be reconstructed usi ng a vibration signal from a vibration sensor located outside the cylinder.
  • a method of processing a signal generated by a sensor adapted to sense pressure variations generated in a cylinder of a combustion engine is provided.
  • the sensor is mounted on the engine outside the cylinder.
  • the method comprise low-pass filtering the signal from the sensor forming at least a part of an in-cylinder pressure curve.
  • the in- cylinder pressure curve is then scaled using a model of the compression in the cylinder forming a scaled pressure curve of the at least a part of the in-cylinder pressure curve.
  • the in-cylinder pressure curve thus formed can represent the entire in-cylinder pressure curve of a complete working cycle of a cylinder or in some applications only a part thereof.
  • the working cycle can be for a four stroke engine or a two-stroke engine.
  • the formed in-cylinder pressure curve is phase aligned.
  • a part or parts of the formed-in-cylinder pressure curve is replaced by pressure values determined from a model.
  • the part or parts being replaced can correspond to parts of the in-cylinder curve that are determined to comprise noise above a predetermined threshold level.
  • the formed in-cyl inder curve is smoothened to generate a curve that can be differentiated in each point of the in-cylinder curve.
  • the sensor senses sig nals on the long side of the engine.
  • the sensor can sense signals on the long side of the engine with the lower temperature compared to the other long side of the engine. I n accordance with another embodiment the sensor is located on the warm side of the en- gine.
  • the signals can typically be a vibration signal or a displacement signal .
  • the compression model is an adiabatic compression model .
  • the senor senses a vibration or a displacement in the engi ne.
  • the invention also relates to a device for performing the method as set out above, and to a motor vehicle comprising such a device.
  • the invention also relates to a computer program , a computer program product, an electronic control device, and a motor vehi- cle.
  • the i nvention is not li mited to any specific type of combustion engine, but encompasses spark ig nited engines as well as compression ignited engines, nor to any specific fuel .
  • Non-exhaustive examples comprise fuel in the form of petrol, ethanol, diesel and gas.
  • the invention encompasses combustion engines in- tended for all types of use, such as in industrial applications, in crushing machines and various types of motor vehicles, wheeled motor vehicles as well as trucks and buses, and boats and crawlers or similar vehicles.
  • combustion engines in- tended for all types of use, such as in industrial applications, in crushing machines and various types of motor vehicles, wheeled motor vehicles as well as trucks and buses, and boats and crawlers or similar vehicles.
  • Fig. 1 is a schematic view illustrating a part of a combustion engine
  • Fig.2 is a flow chart illustrating some steps performed when processing a sensor signal
  • Fig.3 is a diagram of an electronic control device Fig.4 shows a possible placement of a sensor element
  • Fig.5 illustrates a sensor signal, cylinder pressure and heat release for a compression cycle
  • Fig.6 is similar to Fig. 5 with averaged and filtered signal data
  • Fig.7 illustrates a magnitude spectrum of measured pressure and sensed signal
  • Figs.8 and 9 illustrate a typical adiabatic compression curve
  • Fig. 10 depicts a filtered and scaled sensor signal
  • Fig. 11 depicts a signal modelled using pre-compression model
  • Fig. 12 illustrates a smoothed curve
  • Fig. 13 illustrates adding of a phase compensation to the signal
  • Fig. 14 illustrates the use of a post-power model in the signal processing
  • Fig. 15 illustrates the final result using an advanced model.
  • Fig. 1 illustrates schematically a combustion engine 1, which engine is here arranged in an implied motor vehicle 2, for example a truck.
  • the engine is equipped with a device 3, indicated with a dashed line, adapted to detect operating conditions in the engine, and such device has a schematically drawn device 4, which is adapted to detect pressure changes in the cylinder chambers 5 of the combustion engi ne's cyli nders 61 -66, of wh ich there are six in this case, but of which there may be any number.
  • the device 4 has in this example one sensor element 7 per cyl- inder 61 -66, and this is provided outside the associated cyl inder chamber 5.
  • the sensor elements are adapted to sense vibrations or displacements and in particu lar adapted to sense displacements or vibrations in the engine resulti ng from pressure variations i n the cyl inders thereof.
  • the terms vibrations/ displacement are used herein to refer to any movement in the engi ne that can be sensed by the sensor element 7.
  • the sensors can be piezo resistive or piezo electrical sensors, or other types of vibration or displacement sensing elements such as strai n measurement device for example a strain gauge.
  • the device 3 also comprises a u nit 9, which may consist of the veh icle's 2 electronic control device adapted to receive information about the detected movements from the sensor elements) 7, and to compare such information , or information calcu- lated based on such sensor information , with stored values, and to del iver measuri ng val ues for the state of the engine 1 and/or processes i n the engine.
  • a u nit 9 may consist of the veh icle's 2 electronic control device adapted to receive information about the detected movements from the sensor elements) 7, and to compare such information , or information calcu- lated based on such sensor information , with stored values, and to del iver measuri ng val ues for the state of the engine 1 and/or processes i n the engine.
  • information about the engine's operati ng conditions or divergences from these which suitably provide the bases for control of various components i n the com- bus
  • Fig . 2 shows a flow chart illustrati ng an embodiment of a method for processing a signal generated by a sensor adapted to sense vibrations or displacements generated in a cylinder of a combustion engine.
  • the sensor is mou nted on the engine outside the cyli nder.
  • the signal from the sensor is low pass filtered to form at least a part of an i n-cylinder pressu re curve.
  • the in-cylinder pressure curve is scaled using a model of the compression i n the cyli nder to forming a scaled pressure curve of the at least a part of the in- cyli nder pressure curve.
  • the compression model used in step 203 is an adiabatic compression model . Additional processing and modelling steps can also be performed as is indicated by step 205. The order in which the steps 201 - 205 are performed can be different in different processing implementations for processing the vibration sig nal to form an in-cylinder pressu re curve or a part thereof.
  • a computer program code for the i mplementation of a method according to the i nvention is suitably included in a computer pro- gram , loadable i nto the i nternal memory of a computer, such as the internal memory of an electronic control device of a combustion engine.
  • a computer program is suitably provided via a computer program product, comprisi ng a non-transitory data storage medi um readable by an electronic control device, wh ich data storage medi um has the computer prog ram stored thereon .
  • Said data storage medium is e.g.
  • an optical data storage medium in the form of a CD-ROM, a DVD, etc., a magnetic data storage medium in the form of a hard disk drive, a diskette, a cassette, etc., or a Flash memory or a ROM, PROM, EPROM or EEPROM type memory.
  • Fig. 3 schematically illustrates an electronic control device 9 comprising execution means 17, such as a central processor unit (CPU), for the execution of computer software.
  • the execution means 17 communicates with a memory 18, e.g. a RAM memory, via a data bus 19.
  • the control device 9 also comprises a data storage medium 20, e.g. in the form of a Flash memory or a ROM, PROM, EPROM or EEPROM type memory.
  • the execution means 17 communicates with the data storage means 20 via the data bus 19.
  • a computer program comprising computer program code for the implementation of a method according to the invention is stored on the data storage medium 20.
  • Fig.4 shows a possible sensor placement.
  • the sensor element 7 is here placed on the engine.
  • the sensor element can be placed on a section on the cylinder head.
  • the sensor elements/sensors 7 may be of a suitable type, e.g. piezo resistive or piezo electrical elements or optical sensors.
  • the sensor element may be placed on the engine in an area adjacent to the out- let of the exhaust channel from a cylinder. For example, it may be placed on a surface on the engine next to the outlet, on the engine, of the exhaust channel from a cylinder.
  • the surface where the sensor 7 is placed may be substantially vertical.
  • the sensor may be arranged to detect vibrations or displacements, which are perpendicular to the movements of the piston.
  • the sensor may also be arranged to detect vibrations or displacements, which are perpendicular both i n relation to the piston's direction of movement and in relation to the engine's longitudinal direction .
  • the sensor is located on the en- gine's long side.
  • the sensor may be arranged to detect vibrations or displacements i n a direction , which is perpendicular in relation to the surface on which it is placed.
  • the sensor element 7 may be placed in a corresponding man ner as when placed on the engine at the outlet of the exhaust chan nel from a cylinder, but instead placed in a corresponding location on the engine, at the suction channel's i nlet to a cylinder.
  • the signal detected by the sensor element 7 may be treated i n various ways as will be exemplified below.
  • the signal from the sensor senses vibrations are low-pass filtered to generate an in- cylinder pressure curve or at least a part thereof.
  • the in-cyl inder pressure curve can typically be a continuous curve.
  • the th us formed pressure curve can be used to calculate different values at engine control .
  • the in-cylinder pressure curve can be processed further in one or more modell ing steps and refi tation steps.
  • modelling steps and refinement steps are described by way of detailed implementation examples.
  • the invention is not limited in any way to the embodiments described, but n umerous possible modifications thereof can be envisaged.
  • steps can be omitted or steps from different embod- iments can be combi ned or performed in other sequences than the ones described.
  • Fig . 5 An exemplary recurring appearance can be seen in Fig . 5 where the sensor signal (knock signal) is plotted together with the cylinder pressure.
  • Data is in this example based on a run of 1 200RPM at 1 00% load. Other setting are of course possible.
  • the sensor data can i n accordance with some embodi ments be averaged. For example the data can be averaged over 1 0 cycles and Savitzky-Golay smoothed (optimized at Polynom ial order 2 and frame size 1 1 1 ) , the resu lt of the operation is depicted in Fig . 6.
  • the sensor signal can be compared for different operati ng points to verify if the same appearance could be seen in all modes.
  • an estimated pressure model can com- prise at least one of the steps of : filteri ng out h igh frequency noise, adjusting phase sh ifts, scaling and replaci ng noisy parts of the signal with known physical models or assumptions.
  • the model can be based on a high resolution Crank Ang le Degree (CAD) signal of for example 0.1 degrees. Also other resolution can be used such as 6 degrees resol ution . Values in between the acqui red data samples can be modelled. The modelled values can for example be generated by a virtual sensor.
  • the models can be combined.
  • a first model with l ight signal processing to minim ize the model dependencies and focus on achieving a low average offset of the maxi mum pressure amplitude relatively to the measu rement data.
  • a second more advanced model will have heavier signal processing incl ud- ing phase alignment, post power stroke modelling , h igh engine load dependencies and more focus on achievi ng full pressure signal correlation .
  • the two models can also be combined.
  • a compression model can be used for scali ng purposes.
  • the compression model is based on the ideal adiabatic equations for compression of a gas to compensate for engine/load variance as well as possible non-l inear Heat transfer losses.
  • a Heat trans- fer model based on Woschn i/Hohenberger model can be used .
  • the heat transfer model can for example be mu ltiplied by a coefficient of in the range of 1 - 1 0 such as in the range of 1 - 5 i n order to compensate for all modelled losses and the wall temperatu re coefficient can be adjusted depending on engi ne speed and load to obtain a proper exponential increase du ring the compression stroke.
  • each step of the process is iteratively calcu lated based on the thermodynamic first law, where first the number of moles are calculated using the in let manifold pressure and inlet manifold temperature as in itial values for the model as well as the cylinder vol ume calcu lation at CAD - 1 80 degrees, i .e. Bottom Dead Centre BDC prior to Top Dead Centre for combustion .
  • a first estimate of the index, in particular an adiabatic index is then calculated using an index function . In case the model is adiabatic the index will be an adiabatic index.
  • the mai n dependency of this function can be the current temper- atu re and lambda.
  • Heat loss from the heat transfer is calculated , which then provides the information needed to calculate the pressure derivate, the heat transfer is primari ly used to compensate for the heati ng loss/gai n due to the temperature in the cylinder wall .
  • Temperature, (adiabatic) index and the cyli nder pres- sure can be iteratively calculated up to CAD 1 60 in order to obtain the full cycle.
  • the pressure related signal content of the signal from the vibra- tion sensor is of relatively low frequency content compared to the whole frequency spectrum , the high frequency noise is reduced by applying a low-pass digital filter to the signal .
  • the magnitude spectrum of the relevant frequency range can be seen in Fig . 7 which depicts the sensed signal (knock signal) with a measured cylinder pressu re (pressure reference) .
  • Different real-ti me filters such as Butterworth , El liptic, Chebyl and Cheby2 can be used.
  • minimizing roll-off effects by the real-time filters can be performed with a Fourier Transform filter.
  • a 1 0th order Butterworth filter with a normalized cut-off frequency of about 0.04 can be used.
  • Phase-shift can in some embodiments be avoided by applyi ng zero-phase filteri ng (forward and reverse filtering) , hence the signal is then filtered e.g . with two consecutive 1 0th order Butterworth filters. scaling
  • the obtained sensor signal can be received in any amplitude.
  • I n accordance with some embodiments data can be received in order of 1 - 1 0 V but it could be in other amplitude ranges depending on the amplifier and settings used as well as the engine speed and load.
  • a pressure model in particular an adiabatic pressure model , can be used to adjust the scaling to the correct level independent of ampl ifier, setti ngs and the cu rrent operati ng point.
  • a proper scaling can in accordance with some embodiments be achieved by mini mizing the average difference between the filtered sensor signal and the pressu re model .
  • the minim ization can for example be performed between two CADs with negative val ues such as -28 CAD and -3 CAD, i .e. during the compression phase.
  • all operating poi nts approximately have the same appearance (but not necessarily the same ampl itude, hence individual scaling factors are used for each operating poi nt) .
  • the earlier stage of the compression stroke is cluttered and dis- torted by various noises, to reduce the amount of filtering needed and since the beginning of the compression stroke can be idealized as a compression the model can be replaced between some negative values such as starting in the range of -150 to -110 CAD and ending in the range of - 30 to - 5 CAD.
  • some negative values such as starting in the range of -150 to -110 CAD and ending in the range of - 30 to - 5 CAD.
  • - 130 CAD to -15 CAD can be used with the scaling model above. This is done on the assumption that the state of the signal in this region coincides with the model used. inlet-exhaust model
  • the opening of the inlet valve will level the cylinder pressure at approximately manifold pressure, hence the inlet stroke of the signal can be replaced with an averaged value of the manifold pressure for the specific operating point to minimize signal filtering and smoothing, to reduce the number of needed parameters the exhaust stroke has been set to the same level.
  • the average inlet manifold pressure and exhaust manifold pressure are approximately the same, but with available sensors this assumption can be replaced by the actual exhaust manifold pressure if required.
  • the replaced inlet region is between some negative CAD values, for example -360 CAD to -130 CAD can be used and the replaced exhaust region is between some positive CAD values, for example 190 CAD to 360 CAD can be used. smoothing
  • the sensor is typically consistently registering somewhat higher peaks than the measured pressure curve.
  • the signal can be smoothed. This can in accordance with some embodiments be performed using a filter for example using a first order Savitzky-Golay smoothi ng filter (for all operating points) .
  • a filter for example using a first order Savitzky-Golay smoothi ng filter (for all operating points) .
  • Preservation of the content surroundi ng the Start of Combustion (SOC) is sign ificant, hence a second sig nal can be smoothed with a smaller frame size.
  • a smooth transition can i n some embodiments be obtained by iteratively comparing the two smoothed sig nals and choosing the lower value of them for the region around 0 CAD for example between -5 CAD to +5 CAD or some other range around 0 CAD.
  • the low pass filtered signal can be phase shifted before scaling in order to raise the power stroke of the sig nal to the correct level .
  • the phase shift model used can be a lag compensator, e.g . a second order lag compensator.
  • the val ue can be optim ized by comparing measured pressure curve and phase shifted model .
  • phase lag compensator wi ll typically only m inimize a certain amount of phase indifferences between the signal and the reference pressure sig nal . I n some examples minim izing further phase differences can be done usi ng higher orders of models. However a si mple second order model typically works with reasonable re- suits for all operating points without adj usting its parameters too much . scaling
  • the filtered sensor sig nal can be scaled with the same adiabatic compression model as used for the light model above. post-power model
  • the phase adjustment typically does not correct for al l irregu lari- ties i n the power stroke, hence a region du ring valve opening can be replaced with a similar model that was used to scale the signal .
  • the reg ion can be arou nd 80 CAD such as between CAD 20 to CAD 1 35.
  • the requi red initial temperature can be obtained through the thermodynamic first law with total amou nt of moles obtained from the estimated value in the scali ng model , initial pressure and volu me taken at arou nd CAD 20 or some CAD value in that region such as in the range of CAD 1 0 - 30.
  • the offset can be based on a sensor measuring the amount of fuel injected and optim ized by comparing the amount injected to the current relative load (from measurements) .
  • the offset for 75% relative load and above is in accordance with some examples 0.1 0, 0.07 for 50%, 0.03 for 25% and 0 for 0% relative load and motored cycles.
  • a linear in- terpolation can be done between the last value, for example at CAD 1 35, to the replaced manifold pressure value, for example at CAD 200.
  • smoothing The signal can be smoothed to adjust scaling issues. This will remove irreg ularities in the crossovers between models and assumptions. For example a 1 th Savitzky-Golay smoothing filter with a frame size of 1 1 can be used.
  • a combined model can be developed to obtain better correlation in the power stroke and around the pressure peak.
  • the light pressure model developed can be used as base with the advanced pressu re model replaci ng the light model between some positive CAD values.
  • the range can start at about 0 - 5 CAD and end at about 1 80 - 200 CAD. For example from CAD 2.5 to CAD 1 95.
  • smoothing is obtained by choosing the higher val ue between the two models i n the above stated reg ion . smoothing
  • the signal can be smoothed a final time to remove irregularities in the crossovers between models.
  • a first order Savitzky-Golay smooth ing filter with a frame size of 35 can be used based on measurements for non-motored cycles and frame size of 51 for motored cycles.
  • the motored cycles can be indicated by the available sensor measuring injected fuel .
  • the adiabatic scaling model can advantageously be individually calculated for each operating point prior to scaling to get correct pressure levels from the current sensor readings. filtering
  • Fig. 10 depicts the filtered and scaled sensor signal (Filtered and Scaled).
  • the signal in Fig. 10 is also scaled using scaling model (here an adiabatic scaling model). pre-compression model
  • the curve in Fig. 11 is the replaced inlet and exhaust content which is very accurately following the measured pressure, the curve (inlet exhaust model) shows the noise replaced. smoothing
  • Fig. 12 shows the model (Pressure - model light) compared with the cylinder pressure (Pressure Refer- ence) . From the start of the combustion cycle up to near pressure peak the model accurately follows the measured pressu re.
  • Fig . 1 3 shows the model (Pressure - model phase compensated and scaled) compared with the cyli nder pressure (Pressure Reference) .
  • the sig nal has now better correlation with the measured cylinder pressure during the power and exhaust stroke. scaling
  • the replaced curve is less noisy and much smoother.
  • the pressure peak can in accordance with some embodi ments be l ifted for most operating points. Smoothing the curve with a larger frame results i n that the increase in peak amplitude is slightly lowered and yields better correlation with the measured pressure trace, the resu lts is seen i n Fig . 1 4, which shows a smoothened curve for the model curve (Pressure - model postpower and smoothed) compared with the cylinder pressure (Pressure Reference) .
  • a last smoothing can be performed to remove any discontinuities in the advanced model.
  • motored cycles can be smoothed.
  • a first order Savitzky- Golay smoothing filter with a frame size of 51 and non-motored cycles are using a frame size of 25 are used.
  • the final result can be seen in Fig 15, which shows a resulting model curve (Pressure - model Advanced) compared with the cylinder pressure (Pressure Reference).
  • the processing of a vibration signal from a sensor outside a cylinder of a combustion engine to generate an in-cylinder pressure curve is performed using a model.
  • the overall model can involve several steps but is nonetheless simple.
  • the filtering can be per- formed with simple real-time Butter-worth filters and performed using only a single cut-off frequency for all studied operating points, fuels and cylinders.
  • the intake-exhaust model shows minimal difference between the measured pressure at the inlet manifold pressure for the measurements compared herein. In accord- ance with some embodiments individual exhaust sensor readings can be added.
  • the smoothing steps are mainly to minimize discontinues between the different models applied and performed with relatively few frames.
  • the smoothing performed with the larger frame is performed mainly to minimize the peak of certain pressure peaks. This can be performed to counter that the sensor signal registers higher peaks than measured with the pressure sensor.
  • the phase alignment is giving an increase in pressure correlation for all operating points in various degrees.

Abstract

Methods and devices for processing a signal generated by a sensor (7) adapted to sense pressure variations generated in a cylinder (61- 66) of a combustion engine (1) are described. The sensor is mounted on the combustion engine outside the cylinder. The sensor signal is low-pass filtered (201) forming at least a part of an in-cylinder pressure curve, and the in-cylinder pressure curve is scaled using a model of the compression in the cylinder forming a scaled pressure curve of the at least a part of the in-cylinder pressure curve.

Description

METHOD AND DEVICE FOR DETERMINING IN-CYLINDER
PRESSU RE OF A COMBUSTION ENGINE
FI ELD OF TH E INVENTION
The present invention relates to a method and a device for determination of in-cyli nder pressure of a combustion engine.
BACKG ROUN D
There is a constant aspiration to achieve control of a combustion engine i n such a manner that fuel used therein is burned in the engine's cylinders, while generati ng a maximu m amou nt of work output from the engine and a mini mum amount of emissions of environmentally hazardous poll utants. It is of importance in such aspiration to have constant knowledge of the combustion en- gine's operati ng conditions. One important source of information is the pressure in the cylinder(s) of the combustion engi ne.
Further, US 8396649 describes a method whereby some in- cylinder pressure data can be reconstructed usi ng a vibration signal from a vibration sensor located outside the cylinder.
SUMMARY OF TH E I NVENTION
It is an object of the present invention to provide methods and devices, which at least partly solve the above problems, and which are i mproved in at least some respect in relation to prior art methods and devices.
This object is ach ieved with the method and the devices as set out i n the accompanying claims. In accordance with one embodiment a method of processing a signal generated by a sensor adapted to sense pressure variations generated in a cylinder of a combustion engine is provided. The sensor is mounted on the engine outside the cylinder. The method comprise low-pass filtering the signal from the sensor forming at least a part of an in-cylinder pressure curve. The in- cylinder pressure curve is then scaled using a model of the compression in the cylinder forming a scaled pressure curve of the at least a part of the in-cylinder pressure curve. By first generating an in-cylinder pressure curve and then scale the thus acquired curve it is possible to generate an in-cylinder pressure curve that with a low amount of processing represents the in-cylinder pressure curve both in terms of its shape and also in terms of the absolute pressure values.
The in-cylinder pressure curve thus formed can represent the entire in-cylinder pressure curve of a complete working cycle of a cylinder or in some applications only a part thereof. The working cycle can be for a four stroke engine or a two-stroke engine.
In accordance with some embodiments the formed in-cylinder pressure curve is phase aligned.
In accordance with some embodiments a part or parts of the formed-in-cylinder pressure curve is replaced by pressure values determined from a model. The part or parts being replaced can correspond to parts of the in-cylinder curve that are determined to comprise noise above a predetermined threshold level. In accordance with some embodi ments the formed in-cyl inder curve is smoothened to generate a curve that can be differentiated in each point of the in-cylinder curve. In accordance with some embodi ments the sensor senses sig nals on the long side of the engine. The sensor can sense signals on the long side of the engine with the lower temperature compared to the other long side of the engine. I n accordance with another embodiment the sensor is located on the warm side of the en- gine. The signals can typically be a vibration signal or a displacement signal .
In accordance with some embodiments the compression model is an adiabatic compression model .
In accordance with some embodiments the sensor senses a vibration or a displacement in the engi ne.
The invention also relates to a device for performing the method as set out above, and to a motor vehicle comprising such a device.
The invention also relates to a computer program , a computer program product, an electronic control device, and a motor vehi- cle.
The i nvention is not li mited to any specific type of combustion engine, but encompasses spark ig nited engines as well as compression ignited engines, nor to any specific fuel . Non-exhaustive examples comprise fuel in the form of petrol, ethanol, diesel and gas.
Likewise, the invention encompasses combustion engines in- tended for all types of use, such as in industrial applications, in crushing machines and various types of motor vehicles, wheeled motor vehicles as well as trucks and buses, and boats and crawlers or similar vehicles. Other advantageous features and advantages with the invention are set out in the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
Below are descriptions of example embodiments of the invention, with reference to the enclosed drawings, in which:
Fig. 1 is a schematic view illustrating a part of a combustion engine Fig.2 is a flow chart illustrating some steps performed when processing a sensor signal,
Fig.3 is a diagram of an electronic control device Fig.4 shows a possible placement of a sensor element
Fig.5 illustrates a sensor signal, cylinder pressure and heat release for a compression cycle, Fig.6 is similar to Fig. 5 with averaged and filtered signal data
Fig.7 illustrates a magnitude spectrum of measured pressure and sensed signal
Figs.8 and 9 illustrate a typical adiabatic compression curve
Fig. 10 depicts a filtered and scaled sensor signal
Fig. 11 depicts a signal modelled using pre-compression model,
Fig. 12 illustrates a smoothed curve,
Fig. 13 illustrates adding of a phase compensation to the signal,
Fig. 14 illustrates the use of a post-power model in the signal processing, and
Fig. 15 illustrates the final result using an advanced model.
DETAILED DESCRIPTION OF EMBODIMENTS
Fig. 1 illustrates schematically a combustion engine 1, which engine is here arranged in an implied motor vehicle 2, for example a truck. The engine is equipped with a device 3, indicated with a dashed line, adapted to detect operating conditions in the engine, and such device has a schematically drawn device 4, which is adapted to detect pressure changes in the cylinder chambers 5 of the combustion engi ne's cyli nders 61 -66, of wh ich there are six in this case, but of which there may be any number.
The device 4 has in this example one sensor element 7 per cyl- inder 61 -66, and this is provided outside the associated cyl inder chamber 5. The sensor elements are adapted to sense vibrations or displacements and in particu lar adapted to sense displacements or vibrations in the engine resulti ng from pressure variations i n the cyl inders thereof. The terms vibrations/ displacement are used herein to refer to any movement in the engi ne that can be sensed by the sensor element 7. The sensors can be piezo resistive or piezo electrical sensors, or other types of vibration or displacement sensing elements such as strai n measurement device for example a strain gauge.
The device 3 also comprises a u nit 9, which may consist of the veh icle's 2 electronic control device adapted to receive information about the detected movements from the sensor elements) 7, and to compare such information , or information calcu- lated based on such sensor information , with stored values, and to del iver measuri ng val ues for the state of the engine 1 and/or processes i n the engine. Th us, information about the engine's operati ng conditions or divergences from these, which suitably provide the bases for control of various components i n the com- bustion engine, such as for example fuel injection , may be obtai ned based on the sensor elements' 7 detection .
As has been real ized pressure changes in the cylinder chamber 5, can be sensed by a sensor outside the cyli nder chamber to produce high quality signals, which require a simple filtering or processi ng , to be used when forming an in-cyli nder pressure curve or a part thereof.
Fig . 2 shows a flow chart illustrati ng an embodiment of a method for processing a signal generated by a sensor adapted to sense vibrations or displacements generated in a cylinder of a combustion engine. The sensor is mou nted on the engine outside the cyli nder. First, in a step 201 , the signal from the sensor is low pass filtered to form at least a part of an i n-cylinder pressu re curve. Then , in a step 203, the in-cylinder pressure curve is scaled using a model of the compression i n the cyli nder to forming a scaled pressure curve of the at least a part of the in- cyli nder pressure curve. I n accordance with one exemplary embodiment the compression model used in step 203 is an adiabatic compression model . Additional processing and modelling steps can also be performed as is indicated by step 205. The order in which the steps 201 - 205 are performed can be different in different processing implementations for processing the vibration sig nal to form an in-cylinder pressu re curve or a part thereof.
Processi ng and modelli ng steps that can be performed will be exemplified in more detail below.
A computer program code for the i mplementation of a method according to the i nvention is suitably included in a computer pro- gram , loadable i nto the i nternal memory of a computer, such as the internal memory of an electronic control device of a combustion engine. Such a computer program is suitably provided via a computer program product, comprisi ng a non-transitory data storage medi um readable by an electronic control device, wh ich data storage medi um has the computer prog ram stored thereon . Said data storage medium is e.g. an optical data storage medium in the form of a CD-ROM, a DVD, etc., a magnetic data storage medium in the form of a hard disk drive, a diskette, a cassette, etc., or a Flash memory or a ROM, PROM, EPROM or EEPROM type memory.
Fig. 3 schematically illustrates an electronic control device 9 comprising execution means 17, such as a central processor unit (CPU), for the execution of computer software. The execution means 17 communicates with a memory 18, e.g. a RAM memory, via a data bus 19. The control device 9 also comprises a data storage medium 20, e.g. in the form of a Flash memory or a ROM, PROM, EPROM or EEPROM type memory. The execution means 17 communicates with the data storage means 20 via the data bus 19. A computer program comprising computer program code for the implementation of a method according to the invention is stored on the data storage medium 20.
Fig.4 shows a possible sensor placement. The sensor element 7 is here placed on the engine. In particular the sensor element can be placed on a section on the cylinder head. The sensor elements/sensors 7 may be of a suitable type, e.g. piezo resistive or piezo electrical elements or optical sensors. The sensor element may be placed on the engine in an area adjacent to the out- let of the exhaust channel from a cylinder. For example, it may be placed on a surface on the engine next to the outlet, on the engine, of the exhaust channel from a cylinder. The surface where the sensor 7 is placed may be substantially vertical. The sensor may be arranged to detect vibrations or displacements, which are perpendicular to the movements of the piston. The sensor may also be arranged to detect vibrations or displacements, which are perpendicular both i n relation to the piston's direction of movement and in relation to the engine's longitudinal direction . In one embodiment, the sensor is located on the en- gine's long side. The sensor may be arranged to detect vibrations or displacements i n a direction , which is perpendicular in relation to the surface on which it is placed.
In another embodi ment (not shown) , the sensor element 7 may be placed in a corresponding man ner as when placed on the engine at the outlet of the exhaust chan nel from a cylinder, but instead placed in a corresponding location on the engine, at the suction channel's i nlet to a cylinder. The signal detected by the sensor element 7 may be treated i n various ways as will be exemplified below. The signal from the sensor senses vibrations are low-pass filtered to generate an in- cylinder pressure curve or at least a part thereof. The in-cyl inder pressure curve can typically be a continuous curve. The th us formed pressure curve can be used to calculate different values at engine control . To enhance the accuracy of the in-cyl inder pressure curve, the in-cylinder pressure curve can be processed further in one or more modell ing steps and refi nement steps. Below some of such modelling steps and refinement steps are described by way of detailed implementation examples. The invention is not limited in any way to the embodiments described, but n umerous possible modifications thereof can be envisaged. In particular steps can be omitted or steps from different embod- iments can be combi ned or performed in other sequences than the ones described.
Sig nal Content Identification
An exemplary recurring appearance can be seen in Fig . 5 where the sensor signal (knock signal) is plotted together with the cylinder pressure. Data is in this example based on a run of 1 200RPM at 1 00% load. Other setting are of course possible. The sensor data can i n accordance with some embodi ments be averaged. For example the data can be averaged over 1 0 cycles and Savitzky-Golay smoothed (optimized at Polynom ial order 2 and frame size 1 1 1 ) , the resu lt of the operation is depicted in Fig . 6. The sensor signal can be compared for different operati ng points to verify if the same appearance could be seen in all modes.
Model development
The process in obtaini ng an estimated pressure model can com- prise at least one of the steps of : filteri ng out h igh frequency noise, adjusting phase sh ifts, scaling and replaci ng noisy parts of the signal with known physical models or assumptions. The model can be based on a high resolution Crank Ang le Degree (CAD) signal of for example 0.1 degrees. Also other resolution can be used such as 6 degrees resol ution . Values in between the acqui red data samples can be modelled. The modelled values can for example be generated by a virtual sensor.
To address robustness different models can be used. The models can be combined. Here two models are described. A first model with l ight signal processing to minim ize the model dependencies and focus on achieving a low average offset of the maxi mum pressure amplitude relatively to the measu rement data. A second more advanced model will have heavier signal processing incl ud- ing phase alignment, post power stroke modelling , h igh engine load dependencies and more focus on achievi ng full pressure signal correlation . The two models can also be combined.
Compression Model
A compression model can be used for scali ng purposes. In accordance with some exemplary embodiments the compression model is based on the ideal adiabatic equations for compression of a gas to compensate for engine/load variance as well as possible non-l inear Heat transfer losses. For example a Heat trans- fer model based on Woschn i/Hohenberger model can be used . The heat transfer model can for example be mu ltiplied by a coefficient of in the range of 1 - 1 0 such as in the range of 1 - 5 i n order to compensate for all modelled losses and the wall temperatu re coefficient can be adjusted depending on engi ne speed and load to obtain a proper exponential increase du ring the compression stroke. These variables can be tested du ring the tolerance analysis in order to investigate the affect these decisions has on the model . In accordance with one embodiment each step of the process is iteratively calcu lated based on the thermodynamic first law, where first the number of moles are calculated using the in let manifold pressure and inlet manifold temperature as in itial values for the model as well as the cylinder vol ume calcu lation at CAD - 1 80 degrees, i .e. Bottom Dead Centre BDC prior to Top Dead Centre for combustion . A first estimate of the index, in particular an adiabatic index, is then calculated using an index function . In case the model is adiabatic the index will be an adiabatic index. The mai n dependency of this function can be the current temper- atu re and lambda. Heat loss from the heat transfer is calculated , which then provides the information needed to calculate the pressure derivate, the heat transfer is primari ly used to compensate for the heati ng loss/gai n due to the temperature in the cylinder wall . Temperature, (adiabatic) index and the cyli nder pres- sure can be iteratively calculated up to CAD 1 60 in order to obtain the full cycle.
Below two models (Lig ht and Advanced) are further exemplified for a typical test i mplementation .
Pressure model Light filteri ng
The pressure related signal content of the signal from the vibra- tion sensor is of relatively low frequency content compared to the whole frequency spectrum , the high frequency noise is reduced by applying a low-pass digital filter to the signal . The magnitude spectrum of the relevant frequency range can be seen in Fig . 7 which depicts the sensed signal (knock signal) with a measured cylinder pressu re (pressure reference) .
Different real-ti me filters such as Butterworth , El liptic, Chebyl and Cheby2 can be used. Typically there will be a trade-off between filtering too much information near the start of combustion and obtaining a relatively (dependi ng on the operating poi nt) clear signal peak. In accordance with some embodiments minimizing roll-off effects by the real-time filters can be performed with a Fourier Transform filter. In accordance with some embodiments a 1 0th order Butterworth filter with a normalized cut-off frequency of about 0.04 can be used. Phase-shift can in some embodiments be avoided by applyi ng zero-phase filteri ng (forward and reverse filtering) , hence the signal is then filtered e.g . with two consecutive 1 0th order Butterworth filters. scaling
The obtained sensor signal can be received in any amplitude. I n accordance with some embodiments data can be received in order of 1 - 1 0 V but it could be in other amplitude ranges depending on the amplifier and settings used as well as the engine speed and load. A pressure model , in particular an adiabatic pressure model , can be used to adjust the scaling to the correct level independent of ampl ifier, setti ngs and the cu rrent operati ng point.
A proper scaling can in accordance with some embodiments be achieved by mini mizing the average difference between the filtered sensor signal and the pressu re model . The minim ization can for example be performed between two CADs with negative val ues such as -28 CAD and -3 CAD, i .e. during the compression phase. Here all operating poi nts approximately have the same appearance (but not necessarily the same ampl itude, hence individual scaling factors are used for each operating poi nt) . pre-compression model
The earlier stage of the compression stroke is cluttered and dis- torted by various noises, to reduce the amount of filtering needed and since the beginning of the compression stroke can be idealized as a compression the model can be replaced between some negative values such as starting in the range of -150 to -110 CAD and ending in the range of - 30 to - 5 CAD. For example - 130 CAD to -15 CAD can be used with the scaling model above. This is done on the assumption that the state of the signal in this region coincides with the model used. inlet-exhaust model
The opening of the inlet valve will level the cylinder pressure at approximately manifold pressure, hence the inlet stroke of the signal can be replaced with an averaged value of the manifold pressure for the specific operating point to minimize signal filtering and smoothing, to reduce the number of needed parameters the exhaust stroke has been set to the same level. For example based on measurements from an experimental campaign, it is true that the average inlet manifold pressure and exhaust manifold pressure are approximately the same, but with available sensors this assumption can be replaced by the actual exhaust manifold pressure if required. The replaced inlet region is between some negative CAD values, for example -360 CAD to -130 CAD can be used and the replaced exhaust region is between some positive CAD values, for example 190 CAD to 360 CAD can be used. smoothing
The sensor is typically consistently registering somewhat higher peaks than the measured pressure curve. In order to get a smoother peak and minimise the discontinuities between the re- placed pre-compression model and inlet/outlet model the signal can be smoothed. This can in accordance with some embodiments be performed using a filter for example using a first order Savitzky-Golay smoothi ng filter (for all operating points) . Preservation of the content surroundi ng the Start of Combustion (SOC) is sign ificant, hence a second sig nal can be smoothed with a smaller frame size. A smooth transition can i n some embodiments be obtained by iteratively comparing the two smoothed sig nals and choosing the lower value of them for the region around 0 CAD for example between -5 CAD to +5 CAD or some other range around 0 CAD.
Pressure model Advanced phase alig nment
The low pass filtered signal can be phase shifted before scaling in order to raise the power stroke of the sig nal to the correct level . In accordance with some embodiments the phase shift model used can be a lag compensator, e.g . a second order lag compensator. In an exemplary embodiment the position of the pole is p = 1 e- 1 2 for all operating points and the position of the zero is varied ranging from z = 4.25e-04 to z = 3e-04 or some other suitable values with i ncreasing speed and cyli nder used. The val ue can be optim ized by comparing measured pressure curve and phase shifted model .
The phase lag compensator wi ll typically only m inimize a certain amount of phase indifferences between the signal and the reference pressure sig nal . I n some examples minim izing further phase differences can be done usi ng higher orders of models. However a si mple second order model typically works with reasonable re- suits for all operating points without adj usting its parameters too much . scaling
The filtered sensor sig nal can be scaled with the same adiabatic compression model as used for the light model above. post-power model
The phase adjustment typically does not correct for al l irregu lari- ties i n the power stroke, hence a region du ring valve opening can be replaced with a similar model that was used to scale the signal . The reg ion can be arou nd 80 CAD such as between CAD 20 to CAD 1 35. The requi red initial temperature can be obtained through the thermodynamic first law with total amou nt of moles obtained from the estimated value in the scali ng model , initial pressure and volu me taken at arou nd CAD 20 or some CAD value in that region such as in the range of CAD 1 0 - 30. Instead of compensating for heat transfer losses with a model a simple offset based on measurement can be used, the offset can be based on a sensor measuring the amount of fuel injected and optim ized by comparing the amount injected to the current relative load (from measurements) . The offset for 75% relative load and above is in accordance with some examples 0.1 0, 0.07 for 50%, 0.03 for 25% and 0 for 0% relative load and motored cycles. A linear in- terpolation can be done between the last value, for example at CAD 1 35, to the replaced manifold pressure value, for example at CAD 200. smoothing The signal can be smoothed to adjust scaling issues. This will remove irreg ularities in the crossovers between models and assumptions. For example a 1 th Savitzky-Golay smoothing filter with a frame size of 1 1 1 can be used.
Combined model
A combined model can be developed to obtain better correlation in the power stroke and around the pressure peak. For example the light pressure model developed can be used as base with the advanced pressu re model replaci ng the light model between some positive CAD values. The range can start at about 0 - 5 CAD and end at about 1 80 - 200 CAD. For example from CAD 2.5 to CAD 1 95. Hereby a smooth transition is obtained by choosing the higher val ue between the two models i n the above stated reg ion . smoothing
The signal can be smoothed a final time to remove irregularities in the crossovers between models. In accordance with one ex- emplary embodiment a first order Savitzky-Golay smooth ing filter with a frame size of 35 can be used based on measurements for non-motored cycles and frame size of 51 for motored cycles. The motored cycles can be indicated by the available sensor measuring injected fuel .
Test Results
Adiabatic pressure model
The fi nal resu lt of a typical adiabatic compression cu rve can be seen in Fig . 8 and Fig . 9, where Fig . 9 shows a detail of Fig . 8. In Figs. 8 and 9 the model curve (Adiabatic model) is compared to the measured pressure (reference pressure).
The adiabatic scaling model can advantageously be individually calculated for each operating point prior to scaling to get correct pressure levels from the current sensor readings. filtering
The filtered signal can be seen in Fig. 10. The high frequency noise is removed from the sensor signal and the remaining oscillations are related to lower frequency readings. Fig. 10 depicts the filtered and scaled sensor signal (Filtered and Scaled). The signal in Fig. 10 is also scaled using scaling model (here an adiabatic scaling model). pre-compression model
The result of the replaced pre-compression content is clearly seen to smooth the curve during the start of compression as seen in Fig. 11 for the pressure model (Pre-compression model). inlet-exhaust model
The curve in Fig. 11 is the replaced inlet and exhaust content which is very accurately following the measured pressure, the curve (inlet exhaust model) shows the noise replaced. smoothing
The smoothed curve and the final results of the Pressure model light is seen in Fig. 12, which shows the model (Pressure - model light) compared with the cylinder pressure (Pressure Refer- ence) . From the start of the combustion cycle up to near pressure peak the model accurately follows the measured pressu re.
Pressure model Advanced phase alig nment
The resu lts of adding phase compensation to the sig nal is seen in Fig . 1 3 , which shows the model (Pressure - model phase compensated and scaled) compared with the cyli nder pressure (Pressure Reference) . The sig nal has now better correlation with the measured cylinder pressure during the power and exhaust stroke. scaling
The model is scaled in the same way as the light model usi ng the same adiabatic scaling model . The results can be seen in Fig . 1 3. post-power model
The replaced curve is less noisy and much smoother. The pressure peak can in accordance with some embodi ments be l ifted for most operating points. Smoothing the curve with a larger frame results i n that the increase in peak amplitude is slightly lowered and yields better correlation with the measured pressure trace, the resu lts is seen i n Fig . 1 4, which shows a smoothened curve for the model curve (Pressure - model postpower and smoothed) compared with the cylinder pressure (Pressure Reference) .
Advanced model smoothing
A last smoothing can be performed to remove any discontinuities in the advanced model. Hence motored cycles can be smoothed. In accordance with some embodiments a first order Savitzky- Golay smoothing filter with a frame size of 51 and non-motored cycles are using a frame size of 25 are used. The final result can be seen in Fig 15, which shows a resulting model curve (Pressure - model Advanced) compared with the cylinder pressure (Pressure Reference).
The processing of a vibration signal from a sensor outside a cylinder of a combustion engine to generate an in-cylinder pressure curve is performed using a model. The overall model can involve several steps but is nonetheless simple. The filtering can be per- formed with simple real-time Butter-worth filters and performed using only a single cut-off frequency for all studied operating points, fuels and cylinders. The intake-exhaust model shows minimal difference between the measured pressure at the inlet manifold pressure for the measurements compared herein. In accord- ance with some embodiments individual exhaust sensor readings can be added. The smoothing steps are mainly to minimize discontinues between the different models applied and performed with relatively few frames. The smoothing performed with the larger frame is performed mainly to minimize the peak of certain pressure peaks. This can be performed to counter that the sensor signal registers higher peaks than measured with the pressure sensor. The phase alignment is giving an increase in pressure correlation for all operating points in various degrees.

Claims

Claims
1. A method of processing a signal generated by a sensor (7) adapted to sense pressure variations generated in a cylinder (61- 66) of a combustion engine (1) and where the sensor is mounted on the combustion engine outside the cylinder, characterized by:
- low-pass filtering (201) the signal from the sensor forming at least a part of an in-cylinder pressure curve, and
- scaling (203) the in-cylinder pressure curve using a model of the compression in the cylinder forming a scaled pressure curve of the at least a part of the in-cylinder pressure curve.
2. The method according to claim 1, wherein the entire in- cylinder pressure curve of a complete working cycle of a cylinder is formed.
3. The method according to any of claims 1 or 2, wherein the formed in-cylinder pressure curve is phase aligned.
4. The method according to any of claims 1 - 3, wherein a part or parts of the formed in-cylinder pressure curve is replaced by pressure values determined from a model.
5. The method according to claim 4, wherein the part or parts be- ing replaced correspond to parts of the in-cylinder curve that are determined to comprise noise above a predetermined threshold level.
6. The method according to any of claims 4 - 5 wherei n the formed i n-cyl inder curve is smoothened to generate a curve that can be differentiated in each point of the in-cylinder curve.
7. The method according to any of claims 1 - 6, wherein the sensor senses signals on the long side of the engine.
8. The method accordi ng to any of clai ms 1 - 7, wherei n the compression model is an adiabatic compression model .
9. The method according to any of claims 1 - 8, wherei n the sensor senses a vibration or a displacement in the engine.
1 0. A device (3) for processing a signal generated by a sensor adapted to sense pressure changes generated in a cylinder of a combustion engine and where the sensor is mounted on the engine outside the cylinder, characterized by:
- a low pass filter adapted to low-pass filter the signal from the sensor and adapted to output at least a part of an in-cylinder pressure curve, and
- a scal ing module adapted to scale the in-cylinder pressure curve using a model of the compression in the cyli nder and adapted to form a scaled pressure curve of the at least a part of the in-cylinder pressu re cu rve.
1 1 . A combustion engine ( 1 ) , characterised i n that it comprises a device according to claim 1 0.
12. A computer program downloadable into an internal memory of a computer, which computer program comprises a computer program code adapted to make the computer control the steps according to any of claims 1 - 9 when said computer program is executed in the computer.
13. A computer program product comprising a non-transitory data storage medium, which is readable by a computer, and having the computer program code according to claim 12 stored thereon.
14. Motor vehicle (2), characterised in that it comprises a combustion engine (1) according to claim 11.
PCT/SE2016/051132 2015-11-23 2016-11-17 Method and device for determining in-cylinder pressure of a combustion engine WO2017091130A1 (en)

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