WO2002025237A1

WO2002025237A1 - An arrangement and a method for the estimation of the point of time of the start of a combustion process of an internal combustion engine

Info

Publication number: WO2002025237A1
Application number: PCT/SE2001/002039
Authority: WO
Inventors: Mats JÄRGENSTEDT; Mikael Nordin; Magnus Pettersson
Original assignee: Scania Cv Ab
Priority date: 2000-09-22
Filing date: 2001-09-21
Publication date: 2002-03-28
Also published as: SE517008C2; DE10196662T1; AU2001288203A1; DE10196662B3; SE0003396D0; SE0003396L

Abstract

The present invention relates to an arrangement and a method for the estimation of a point of time of the start of a combustion process of an internal combustion engine (1). The arrangement comprises a first sensor (7), which senses at least a parameter related to the sound generated during the combustion process, signal treatment means (8-11), which transforms said signal to measurement values a, and a control unit (13), which is arranged to compare measurement values a with a reference value (aref). The point of time of the start of an actual combustion process is estimated to the point of time (t1) of a first measurement value (a1) which reaches the reference value (a¿ref) after that at least a previous measurement value a has been below the reference value (a¿ref?). Advantageously, the control unit (13) is also arranged to control the combustion processes of the internal combustion engine (1) with knowledge about the estimated point of time (t1) and to adjust the point of time of the injection (t0) of the injection member (5) of a fuel or a fuel mixture at need.

Description

An arrangement and a method for the estimation of the point of time of the start of a combustion process of an internal combustion engine

BACKGROUND OF THE INVENTION AND PRIOR ART

The invention relates to an arrangement and a method for the estimation of the point of time of the start of a combustion proc- ess of an internal combustion engine according to the preambles of claims 1 and 12.

The injection of the fuel in diesel engines is provided in newer engines by a so-called unit injector i.e. a high-pressure pump, which is built together with an injection nozzle. Such unit injectors are provided at each of the cylinders of the engine and comprise an individual electric control. Therefore, each individual unit injector has to be calibrated or controlled such that they inject fuel into the respective combustion space at a point of time such that a following combustion process in the combustion space is accomplished when the crankshaft of the engine is located in an optimal position for this. Alternatively, the fuel and air may be mixed in an induction pipe before the fuel mixture is injected into a combustion space.

In known control systems for the injection of fuel or a fuel mixture in a diesel engine, one adjusts, usually by a calibration method, the point of time when the injection is to occur. In certain control systems, one may then measure the point of time of the injection and adjust this point of time by a feed back coupling in the control system. In other control systems, one can for different reasons not measure the point of time of the injection, which makes it necessary to rely on expensive electronic injection equipment in order to accomplish injection at a substantially correct point of time. However, the combustion process itself starts with a certain delay in relation to the point of time of the injection. The magnitude of this delay depends i. a. on the quality of the fuel, the temperature of air and fuel, the humidity of the air and the quantity of returned exhausts. Even, if one thus measures the point of time of the fuel injection in the combus- tion space, the point of time of the start of the combustion process can not be exactly determined.

In the Swedish patent application 9804014-0, sound sensing sensors are used in order to sense a parameter, which is related to the combustion sound arising at the combustion processes during operation of an internal combustion engine. Hereby, the characteristic combustion sound for the engine may be identified and the point of time when the combustion process takes place may be determined. However, in this patent application, the ex- act point of time of the start of the combustion process is not defined.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement and a method, which in an uncomplicated manner provide a substantially exact estimation of the point of time at which a combustion process starts in a combustion space of an internal combustion engine. Another object is to control the combustion processes of the internal combustion engines with knowledge of this point of time.

The first mentioned object is achieved by the initially mentioned arrangement and method, which is characterised by that which is mentioned in the characterising parts of claims 1 and 12. When a combustion process takes place in a combustion space of an internal combustion engine, a combustion sound is provided. The sensor senses a parameter, which is related to the value of the combustion sound. However, the output signals of the sensor comprise disturbances, which depend on sound or vibrations, arising from other sources. For this reason, it is suitable that a measurement value first should reach a determined level in the form of a reference value such that one with certainty can establish that a combustion process really has started. Thereby, the risk for incorrect estimations of the start of a combustion process is minimised. Since the received measurement values obtain increasing values in connection with the start of a combustion process, the point of time of the start of a combustion process is estimated as the first measurement value, which reaches the reference value after that at least a previous measurement value has been below the reference value.

According to a preferred embodiment of the invention, the refer- ence value is arranged to constitute 20-40% of a maximum measurement value of a combustion process. In order to obtain a corresponding point of time of the start of a combustion process in different combustion spaces, it is suitable to relate the reference value to a maximum measurement value for the re- spective combustion space. Advantageously, therefore the largest received measurement value during the actual combustion process constitutes the maximum measurement value. Therefore, the point of time of the start of the actual combustion process can only be estimated when the combustion process is fin- ished. Alternatively, the reference value may be a maximum measurement value from a previous combustion process or an average of a plurality of maximum measurement values of previous combustion processes of the combustion space in question.

According to another preferred embodiment of the invention, said parameter comprises the vibrations arising in an engine block of the internal combustion engine. The sound generated during the combustion process creates vibrations in the engine block of the internal combustion engine. These vibrations may be measured with one or several accelerometers, which are applied at suitable locations directly on the engine block or on de- tails, which are in mechanical contact with the engine block. The location of the accelerometers is very important in order to obtain relevant measurement values. They ought to have a position such that vibrations originating from the combustion proc- esses are sensed as clearly as possible at the same as vibrations from disturbing sources as far as possible are avoided.

According to another preferred embodiment, said sensor is arranged to deliver an analogue signal and said signal treatment means comprises an analogue low-pass filter. Most sensors, such as accelerometers, provide an analogue output signal. The low-pass filter is used to filter out high frequency signal values which otherwise may give rise to problems when the signal is transformed into digital form. Advantageously, said signal treat- ment means therefore comprises an analogue-digital-converter, which transforms the analogue signal into digital signal values. The digital values ought to represent relatively short time intervals since a too coarse division in intervals restricts the accuracy of the estimation of the point of time of the start of the combustion process. Advantageously, said signal treatment means also comprises a digital band-pass filter. The sounds and vibrations generated during a combustion process arise substantially within a specified frequency range. Therefore, it is suitable to filter out frequencies outside this frequency range. Thereby, one obtains digital signal values with a reduced content of disturbances. Said signal treatment means may also comprise a unit, which is arranged to adjust the obtained digital signal values such they disclose the shape of a graph. Thereby, measurement values are obtained which follow a graph. Thus, the measurement values have no momentary fluctuations which otherwise may make the estimation of the start of the combustion process more difficult. The signal treatment means may entirely or partly consist of separate units. Alternatively, they may be comprised in the software of the control unit. According to another preferred embodiment of the invention, it is applicable to internal combustion engines having a crankshaft, which is arranged to be driven by said combustion processes and wherein the control unit is arranged to receive information from a second sensor concerning the position of the crankshaft. The control unit is arranged to check if the crankshaft is located in an optimal position for this, at the estimated point of time of the start of the combustion process, and to adjust the point of time when the injection member supplies the fuel or the fuel mixture at need. If the estimated point of time of the start of the combustion process discloses a time deviation from the point of time, when the crankshaft is located in an optimal position for this, the point of time for the supply of the fuel or the fuel mixture in the following combustion process may be put forward a time period corresponding to said deviation. Hereby, it is possible to accomplish an adjustment of the point of time of the supply of the fuel or the fuel mixture between two after each other following combustion processes in a combustion space. Alternatively, one can wait to adjust the point of time of the supply of the fuel or the fuel mixture until a plurality after each other following combustion processes disclose a combustion start with a time deviation from the point of time when the crankshaft is located in an optimal position. The point of time of the supply of the fuel or the fuel mixture may be adjusted with an average of these time deviations.

According to a preferred embodiment of the present invention, the injection member is arranged to inject the fuel or the fuel mixture into the combustion space and the internal combustion engine works with compression ignition. Advantageously, the injection member is here a so-called unit injector and the internal combustion engine a diesel engine. BRIEF DESCRIPTION OF THE DRAWINGS

In the following a preferred embodiment of the invention is described as an example with reference to the attached drawings, in which:

Fig 1 shows schematically an arrangement according to the present invention, Fig 2 shows an example of a signal obtained from an accel- erometer provided on an internal combustion engine with six cylinders, Fig 3 shows an example of measurement values obtained after a signal treatment and Fig 4 shows a flow diagram of a method according to the pre- sent invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig 1 shows schematically an arrangement for the estimation of the point of time t-i at which a combustion process of an internal combustion engine 1 starts and for controlling the combustion process with knowledge of this point of time t-j . The internal combustion engine 1 is here exemplified as a diesel engine with six cylinders of which three are marked in the figure with broken lines. Each of the cylinders 2 comprises, in a conventional manner, a combustion space 3 which downwards is restricted by a movable piston 4 provided in the cylinder 2. An injection mem- ber 5 is arranged to intermittently inject fuel or a fuel mixture, in the form of fuel and air, into each of the combustion spaces 3 such that momentary combustion processes are obtained. The hereby accomplished motions of the pistons 4 are arranged to drive a crankshaft 6 of the internal combustion engine 1. The internal combustion engine may, for example, consist of a direct injection diesel engine, which thus works with compression igni- tion of the fuel. The engine may be used as driving motor in heavier vehicles such as a lorry or a bus.

The arrangement comprises at least a sensor in the form of an accelerometer 7, which is located at a suitable place on a motor block of the internal combustion engine 1 . The accelerometer 7 may be provided directly on the motor block or on a detail, such as for example a suitable bolt, which is in direct contact with the engine block. The accelerometer 7 is arranged to sense the vi- brations, which arise in the motor block which are generated by the sound arising during the combustion processes in the combustion spaces 3. The accelerometer 7 is arranged to deliver an analogue signal related to the value of the vibrations. In the engine block, vibrations of other origin are also propagated. Such vibrations result in that the output signal contains disturbances. This signal is therefore usually not possible to use untreated in order to with a good accuracy estimate when a combustion process starts in a combustion space 3. Fig 2 shows an example of a signal obtained from an accelerometer 7, which is applied on the six cylindrical internal combustion engine 1. In the figure, the obtained signal ranges, for the respective cylinder, have been marked. The sequence depends on the ignition sequence of the cylinders. One may observe that the power of the signal increases significantly when a combustion process takes place in a cylinder. However, the power of the signal varies significantly between the different cylinders. The accelerometer 7 is here located between the cylinders 5 and 6, for which reason the most powerful signals are obtained from these cylinders.

In order to be able to estimate the start of the combustion processes with a good accuracy, the signal obtained from the accelerometer 7 has to be treated by signal treatment means. Said signal treatment means comprises initially an analogue low-pass filter 8. The low-pass filter 8 filter out the frequencies of the analogue signal, which are higher than a specific limit frequency of the low-pass filter 8. The low-pass filtered signal is then con- ducted to an analogue-digital-converter 9, which is arranged to transform the analogue signal into digital signal values. Hereby, the analogue signal is divided into a suitable number of digital signal values per time unit. Thereafter, the digital signal values are conducted through a digital band-pass filter 10. The digital band-pass filter 10 only lets through the frequencies of the digital signal values, which are within a certain frequency range. The vibrations, which arise in the engine block during the combustion processes, arise mainly within this frequency range. For example, the band-pass filter may let through signals within the frequency range 20-30 kHz and thus filter out frequencies lower than 20 kHz and higher than 30 kHz. The filtered out frequencies originate essentially from unwanted vibration sources. Finally, the signal values are treated in a unit 1 1 , which is ar- ranged to adjust the obtained digital signal values such that they disclose a continuous shape of a graph. For example, the peak values of these signals may be connected to each other such that a continuous graph 12 is obtained, which is shown in Fig 3. The digital signal values, which do not correspond to the graph, are adjusted such that measurement values a are obtained, which follow the graph 12. Such measurement values a are use- able in order to estimate the real point of time ti of the start of a combustion process with a high accuracy. The signal treatment means 8-1 1 may entirely or partly constitute separate units but they may also be comprised in the software of a control unit 13.

Such a control unit 13 is arranged to compare the obtained measurement values a with a reference value a_ref- The reference value a_rβf is arranged to constitute 20-40% of a maximum meas- urement value a_max of the actual combustion process. The point of time, at which a combustion process starts, is estimated to the point of time of a first measurement value a_{l 5} which reaches the reference value a_ref during a sequence of increasing measurement values. Hereby, at least a measurement value a, which precedes the measurement value a-i, ought to be below the reference value a_rθf. The magnitude of the obtained meas- urement values a from the different combustion processes in the combustion spaces 3 may vary, for example, depending on the distance of the accelerometer 7 to the different combustion spaces. Another reason may be that different accelerometers 7 provide signal values of different power. By relating such a reference value a_ref to a percentage part of a maximum measurement value a_max for the actual combustion process, a comparable point of time of the start of the combustion processes in the different combustion spaces may be obtained. The maximum measurement value a_max is the largest measurement value, which is received during an actual combustion process. The use of a reference value a_rβf also has the advantage that the risk for an incorrect indication of the start of a combustion process caused by vibrations from a disturbance source is substantially eliminated. After the end of the combustion process, when obtained measurement values again drop below the reference value a_rβf, the control unit 13 notes that the combustion process is finished. The control unit 13 registers the maximum measurement value a_max during the actual combustion process. With knowledge of the maximum measurement value a_max, the control unit 13 calculates the reference value a_rβf, which, for example, constitutes 30% of the maximum measurement value a_max. Thereafter, the control unit 13 determines the point of time t-i when a first measurement value a<_\ during the combustion proc- ess reached the reference value a_rβf. The point of time ti is estimated as the point of time at which the actual combustion process started.

A second sensor 14 is applied on the internal combustion engine 13 at a suitable place. The second sensor 14 is arranged to sense the position of the crankshaft 6 of the internal combustion engine 1. Thereby, the sensor 14 delivers a signal to the control unit 13 related to the position of the crankshaft 6. The control unit 13 checks in which position the crankshaft 6 was located at the estimated point of time t| . The point of time of the injection t₀ of the fuel or the fuel mixture in the combustion space 3 oc- curs with a time difference in relation to the point of time t_π of the start of the combustion process. The time difference between the point of time of injection t₀ and the estimated point of time ti may vary at different occasions for one and the same in- ternal combustion engine. The time difference may depend on the quality of the fuel, the temperature of air and fuel, humidity of air and the quantity of returned exhausts. The control unit 13 may here compare the estimated point of time ti for the combustion process with the point of time when the crankshaft 6 was located in the optimal position for the combustion process. If a time deviation here is the case, the control unit 13 adjusts the point of time of injection t₀ of the injection member 5 of the fuel in the following combustion process in said combustion space 3 with a value corresponding to this time deviation. Alternatively, such an adjustment of the point of time t₀ for the injection of the fuel or the fuel mixture may be based on an average of a plurality of such time deviations of previous combustion processes. The control unit 13 is also connected to an indication unit 15. The indication unit 15 is arranged to indicate, for example, to a driver of a vehicle about possible errors of the internal combustion engine 1 in connection with an incorrect start of the combustion. The indication member 15 may also indicate when it is not longer possible to compensate for an incorrect start of the combustion and inform about when the internal combustion en- gine 1 ought to go through a service.

Fig 4 shows a flow diagram for a method for the estimation of the point of time ti of the start of a combustion process for a cylinder 2 of an internal combustion engine 1. A corresponding method occurs at the same time in the other cylinders 2. Initially, the method comprises, at an initial step 16, to apply at least one accelerometer 7 in contact with the engine block of the internal combustion engine 1 . The location of the accelerometer 7 is important in order to obtain measurement values, which al- low an accurate estimation of the point of time ti when a combustion process starts. Consequently, the accelerometers 7 ought not to be placed in an area of the engine block, which is subject to disturbing vibrations from adjacent movable mechanical parts. The accelerometer 7 delivers an analogue signal, which is related to the value of the vibrations in the application area of the engine block.

At the step 17, the analogue signal is received and goes through a treatment process, which provides output digital measurement values. The treatment process comprises initially a low-pass fil- tering of the analogue signal. High frequencies above a limit value are filtered out. Thereafter, the analogue signal is transformed into digital signal values. The analogue signal is divided with suitable time intervals into digital signal values. The resulting digital signal values are then band-pass filtered within a fre- quency range, which comprises the most common vibration frequencies which originate from combustion processes of the actual kind of internal combustion engine 1. Higher and lower frequencies, which mainly comprise disturbances, are thus filtered out. Finally, the obtained digital signal values are adjusted into digital measurement values, which follow the shape of a graph. Thereby, occasional fluctuations of the measurement values are avoided.

At the step 18, the measurement values a, which are obtained during a combustion process, are received and registered. The maximum measurement value a_maXι which is the largest measurement value, which has been received during the actual combustion process, is noted. A reference value a_ref is calculated as 30% of a_max. The point of time t-i for a first measurement value a₁, which reaches the reference value a_ref after that at least a previous measurement value a has been below the reference value a_rΘf, is estimated as the point of time of the start of the combustion process.

At the step 19, information is received of the position of the crankshaft 9 of the internal combustion engine 1. Then, it is checked, if the crankshaft 9 was located in an optimum position at the estimated point of time ti of the start of the combustion process. If a deviation here is the case, the point of time t₀ of the injection of the injection member 5 is adjusted for the following combustion process in the combustion space 3.

Thereafter, the process is repeated, at the step 17, with reception of a new analogue signal concerning the following combustion process.

The invention is not in any way restricted to the described embodiment but may be varied freely within the scope of the claims. The arrangement and the method are applicable to internal combustion engines independently of the number of cylin- ders. The arrangement and the method are applicable on substantially all kinds of engines where a combustion process takes place and where a detectable combustion sound is obtained during the combustion process. Consequently, the invention is applicable, for example, to engines which works with compres- sion ignition of an homogenous fuel mixture so-called HCCI engines were the problem to determine the point of time of the start of the combustion process is present in the same way as in a conventional diesel engine.

Claims

1. An arrangement for the estimation of the point of time of the start of a combustion process of an internal combustion engine (1 ), wherein the internal combustion engine (1 ) comprises at least one injection member (5) arranged to supply a fuel or a fuel mixture to the combustion process and at least a combustion space (3) in which momentary combustion processes take place, wherein the arrangement comprises at least a first sensor (7) arranged to sense at least a parameter related to the sound generated during the combustion processes and deliver a signal related to the value of the parameter, signal treatment means (8-11 ) arranged to transform said signal into measurement values (a) and a control unit (13), characterised in that the control unit (13) is arranged to estimate the point of time, at which a combustion process starts, to the point of time (ti ) of a first measurement value (a , which reaches a reference value (a_rβf) after that at least one previous measurement value (a) has been below the reference value (a_ref).

2. An arrangement according to claim 1 , characterised in that the reference value (a_ref) is arranged to constitute 20-40% of a maximum measurement value (a_maχ)-

3. An arrangement according to claim 2, characterised in that the maximum measurement value (a_max) is the largest measurement value, which has been received during an actual combustion process.

4. An arrangement according to any one of the preceding claims, characterised in that said parameter is related to the vibrations, which arise in an engine block of the internal combustion engine (1 ).

5. An arrangement according to claim 4, characterised in that the first sensor comprises an accelerometer (7), which is provided in mechanical contact with the engine block.

6. An arrangement according to any one of the preceding claims, characterised in that the first sensor (7) is arranged to deliver an analogue signal and that said signal treatment means comprises an analogue low-pass filter (8).

7. An arrangement according to claim 6, characterised in that said signal treatment means comprises an analogue-digital- converter (9), which is arranged to transform the analogue signal into digital signal values.

8. An arrangement according to claim 7, characterised in that said signal treatment means comprises a digital band-pass filter (10).

9. An arrangement according to claim 8, characterised in that said signal treatment means comprises a unit (1 1 ), which is arranged to adjust the obtained digital signal values to measurement values (a) following a graph (12).

10. An arrangement according to any one of the preceding claims, wherein the internal combustion engine comprises a crankshaft (6), which is arranged to be driven by said combustion processes, and wherein the control unit (13) is arranged to receive information from an second sensor (14) related to the position of the crankshaft (6), characterised in that the control unit (13) is arranged to check if the crankshaft (6) is located in an optimal position for this at the estimated point of time (ti) of the start of the combustion process and to adjust the point of time of injection (t₀) of the injection member (5) at need.

1 1 . An arrangement according to any one of the preceding claims, characterised in that the injection member (5) is ar- ranged to inject the fuel or the fuel mixture into the combustion space (3) and that the internal combustion engine (1 ) works with compression ignition.

12. A method for the estimation of the point of time of the start of a combustion process of an internal combustion engine (1 ), wherein the internal combustion engine (1 ) comprises at least one injection member (5), which is arranged to supply a fuel or a fuel mixture to the combustion process, and a combustion space (3) in which momentary combustion processes take place, characterised in that at least a parameter is sensed, which is related to the sound generated during the combustion processes, and a signal is delivered related to the value of the parameter, that said signal is transformed to measurement values (a) and that the point of time, at which an actual combustion process starts, is estimated to the point of time (ti) of a first measurement value (ai) which exceeds a reference value (a_ref) after that at least a previous measurement value (a) has been below the reference value (a_ref).

13. A method according to claim 12, characterised in that the reference value (a_ref) is determined to be 20-40% of a maximum measurement value (a_maχ).

14. A method according to claim 13, characterised in that the maximum measurement value (a_max) is determined to be the largest measurement value, which has been received during an actual combustion process.

15. A method according to any one of the preceding claims 12-

14, characterised in that said parameter is related to the vibrations, which arise in an engine block of the internal combustion engine (1 ).

16. A method according to claim 15, characterised in that a first sensor (7) is applied in mechanical contact with the motor block.

17. A method according to any one of the preceding claims 12- 16, characterised in that the sensor (7) delivers an analogue signal and that said signal is low-pass filtered.

18. A method according to claim 17, characterised in that the analogue signal is transformed into digital signal values.

19. A method according to claim 18, characterised in that the digital signal values are band-pass filtered.

20. A method according to claim 19, characterised in that the obtained digital signal values are adjusted such that they follow a graph.

21. A method according to any one of the preceding claims 12- 20, wherein the internal combustion engine (1 ) comprises a crankshaft (6), which is arranged to be driven by said combustion processes, characterised in that information about the posi- tion of the crankshaft (6) is received and the position of the crankshaft (6), at the estimated point of time (ti ) of the start of the combustion process, is checked and if the crankshaft (6) is not located in an optimal position for this at the point of time (ti), the point of time of injection (t₀) of the injection member (5) is adjusted.

22 A method according to any one of the preceding claims 12- 20, characterised in that the fuel or the fuel mixture is injected into the combustion space (3), where it is arranged to be ignited by the compression in the combustion space (3).