FR2936567A1 - Combustion quality evaluation parameter e.g. combustion noise, estimating method for e.g. four stroke diesel engine, involves controlling sensors such that reference of cylinders responds to series defined by specific parameters - Google Patents

Abstract

The method involves measuring an estimation parameter by a pressure sensor (16) and a crankshaft angle sensor (17) for estimating a combustion quality evaluation parameter in four cylinders (1-4). The sensors are controlled by a logic controller (15) such that a reference of the cylinders responds to a series defined by a specific parameters, in which time interval between beginning of two measurements of the estimation parameter in two of the cylinders is equal to kP, where k is a whole number larger than 1 and P is a period. An independent claim is also included for a device for estimating a combustion quality evaluation parameter of four cylinders in a four stroke internal combustion engine.

Description

The invention relates to a method for estimating a parameter for evaluating the quality of combustion in an internal combustion engine, a method for estimating a combustion quality parameter in an internal combustion engine, and more particularly a method of estimating the combustion noise. It also relates to a device for implementing the method. The performance of an internal combustion engine, and in particular a conventional four-stroke diesel engine, is the sum of the performances of each of the engine cylinders. The performance may relate to the torque provided by the engine, the combustion noise, the level of pollution, or any other measure that may be performed on each of the engine cylinders. If a cylinder only is less efficient than expected, the whole engine will be less efficient. The reasons for the differences in performance from one cylinder to the other are multiple. It can for example be a poor state of a cylinder relative to others, the configuration of the air inlet which does not allow to fill all the cylinders as well, a fouled injector or any other physical reason. There are thus parameters revealing the quality of combustion, and therefore the performance of the engine. These evaluation parameters of the combustion quality can generally be estimated from estimation parameters in the cylinders. An evaluation parameter of the combustion quality may be for example the indicated average torque or the combustion noise. If the noise measured or estimated in a cylinder is not that expected, we can then assume that the injection settings are bad, and optimize them to improve combustion, and for example limit pollutant emissions.

One way to equalize the performance of different cylinders is to measure or estimate these evaluation parameters of the quality of combustion, then to equalize them. In particular, the combustion noise of each cylinder can be measured to compare the performance of the different cylinders. However, the measurement or estimation of the evaluation parameters requires large resources in computing capacity.

The present invention aims to overcome these disadvantages. The invention proposes a method for calculating a parameter for evaluating the quality of combustion in an internal combustion engine, the method requiring little computing resources. The subject of the invention is thus a method for estimating a parameter for evaluating the quality of combustion, in a four-stroke internal combustion engine and n cylinders referenced 1 to n, the combustion cycles of two cylinders of consecutive references being offset by a period P; from the measurement in the cylinders of one or more estimation parameters of said evaluation parameter of the combustion quality. The measurement can be performed during one or more motor cycles. According to the method according to the invention, the reference of the consecutive cylinders measured obeys the series up (k, n) defined by: uo = i, i being an integer between 1 and n, up = uP_1 + k if (up_1 + k) <_ n, where k is an integer greater than 1 where k and n are prime to each other, and up = up-1 + kn if (up-1 + k)> n, and the time interval between the beginning of the measurement of an estimation parameter in a reference cylinder up and the beginning of the measurement of the estimation parameter in the reference cylinder up + 1 is equal to kP. Thus, the measurements on two consecutive reference cylinders are spaced by kP, which makes it possible to reduce the measurement acquisition time and the estimation time, while estimating the evaluation parameter of the combustion quality on the all n cylinders, because the numbers k and n are prime between them. Each cylinder can form a combustion chamber whose volume is delimited by a piston sliding in the cylinder in a reciprocating rectilinear motion transformed into a rotational movement via a connecting rod connecting the piston to a crankshaft, and the parameters estimation of the evaluation parameter of the combustion quality may be the pressure in the combustion chamber and the crankshaft angle.

The evaluation parameter of the combustion quality may be the combustion noise, the average torque indicated or the average power indicated. The combustion noise is preferably used. The combustion noise within the meaning of the invention is the noise audible by the human ear of a combustion engine. The period P advantageously corresponds to the duration of 2 / n engine revolutions. Indeed, the four times of the combustion cycle being distributed over two engine revolutions, a period of 2 / n turns allows a better cooperation of the cylinders. The engine is typically a four-cylinder engine. However, it is also possible to use a three-cylinder engine, or five-cylinder or more. In the case of a four-cylinder engine, to obtain a good compromise between the accuracy of the estimate and the economy in terms of calculation, k is preferably equal to 3. The method may furthermore comprise a comparison step. between them estimated values of said evaluation parameter of the combustion quality, and a step of adjusting the injection parameters if one or more deviations between the compared values are greater than one or more predetermined values. Injection parameters include fuel flow and injection timing. The invention also aims at a device for estimating a parameter for evaluating the quality of combustion in a four-stroke internal combustion engine and n cylinders referenced 1 to n, the combustion cycles of two reference cylinders. consecutive devices being shifted by a period P, the device comprising in the cylinders means for measuring one or more parameters for estimating said parameter for evaluating the quality of combustion, the measuring means being connected to a suitable calculator estimating the evaluation parameter of the combustion quality from the measurements obtained. In the device according to the invention, the computer is able to control the measuring means so that the reference of the consecutive cylinders measured obey the series up (k, n) defined by: uo = i, i being a an integer from 1 to n, up = uP_1 + k if (up_1 + k) <_ n, where k is an integer greater than 1 such that k and n are prime to each other, and 10 up = up.1 + kn if (up-1 + k)> n, and in such a way that the time interval between the beginning of the measurement of an estimation parameter in a reference cylinder up and the beginning of the measurement of the parameter of estimate in the reference cylinder up + 1 is equal to kP. The evaluation parameter of the combustion quality may be the combustion noise. In this case, each cylinder forming a combustion chamber whose volume is delimited by a piston sliding in the cylinder in a reciprocating rectilinear motion transformed into a rotational movement via a connecting rod connecting the piston to a crankshaft, the combustion noise estimation parameters may be the pressure in the combustion chamber and the crankshaft angle. Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example, and with reference to the accompanying drawings, in which: FIG. 1 schematically illustrates a device implementation of a method according to the invention - Figure 2 is a comparative diagram of implementation of a method according to the state of the art and a method according to the invention in a combustion engine FIG. 3 is a schematic diagram of a device for implementing the method according to the invention. FIG. 4 is a schematic diagram of a device for implementing the method according to the invention. FIG. . The engine, as illustrated in FIG. 1, comprises four cylinders 1, 2, 3, 4, each forming a combustion chamber 5. In each cylinder 1, 2, 3, 4, a piston 6 slides in an alternating rectilinear motion . This movement is then transformed into a continuous rotational movement via a connecting rod 7 connecting the piston 6 to a crankshaft 8. Each cylinder 1,2,3,4 is further closed by a cylinder head 9 equipped with two valves 10,12: an intake valve 10 connecting the combustion chamber 5 to an intake zone 11, and allowing the combustion chamber 5 to be fed with an air / fuel mixture (in the case of a conventional gasoline engine) , or in air (in the case of a conventional diesel engine), and an exhaust valve 12, connecting the combustion chamber 5 to an exhaust zone 13, so as to allow the evacuation of the burnt gases that are expanded towards the exhaust. The positioning of the valves 10, 12 is controlled by a camshaft, not shown, connected to the crankshaft 8. The device also comprises an element 14, which is a spark plug in the case of a gasoline engine, or a fuel injector in the case of a diesel engine.

The device further comprises a computer 15 connected to a pressure sensor 16 in the combustion chamber 5 and to a crank angle sensor 17. The estimation of the combustion noise can be carried out in the computer 15 by calculations according to the pressure in the combustion chamber 5 and the crankshaft angle 8, for example from the measurement of the pressure gradient in the cylinder 1,2,3,4. A method of determining the combustion noise is described for example in the document FR 2 909 762. In a method according to the state of the art, as illustrated on the upper part of the diagram of FIG. 2, the measurement of the pressure in the combustion chamber and the crankshaft angle are carried out continuously and in all the cylinders referenced 1 to 4 in their order of ignition, which requires significant computing capacity and storage of the computer. To know the combustion noise of an engine, it is necessary to estimate the combustion noise of each of its cylinders 1,2,3,4. In four-stroke four-cylinder engines 1,2,3,4, a complete combustion cycle is performed on two turns and the cycles are generally offset by a half-turn of crankshaft. To calculate the combustion noise, the pressure is measured throughout the cycle and then the calculation is started. However, the combustion characteristics of a cylinder 1,2,3,4 do not change enormously from one crankshaft revolution to another, especially when the regime is substantially stable. The invention proposes not to calculate the combustion noise at each combustion, in order to save computing time. If we calculate the combustion noise only one cylinder out of two, for example the cylinder 1, then the cylinder 3, then the cylinder 1, etc., then we will calculate the combustion noise of only two cylinders, the cylinders 2 and 4 never taken into account. This is why the noise is measured every k cylinders, where k is an integer such that k and 4 are prime between them. k is for example equal to 3, so that the noise is measured every 3 cylinders, as shown in the lower part of the diagram of Figure 2. Thus, by measuring the noise every 3 cylinders, and in starting from the cylinder 1, we will successively measure the noise on the cylinder 1, then the cylinder 4, then the cylinder 3, then the cylinder 2, then the cylinder 1, and so on. We could also consider that k is greater than 3, for example k = 5. In this case, the noise of one cylinder out of five is calculated, namely on the cylinder 1, then the cylinder 2, then the cylinder 3, then the cylinder 4, then the cylinder 1, and so on, the measurements on two cylinders consecutive being spaced two turns and a half motor. This embodiment, in which the values of the estimation parameters are recovered from one cylinder at a time, is adapted to the case where the resources of the computer are very small.

The calculations of the combustion noise being performed less often, only one time out of three only, it also saves the necessary memory space. In addition, since the computer only acquires the measurement of one or two cylinders at the same time, instead of the four cylinders permanently in the method of the state of the art, it also saves acquisition time. This economy facilitates the acquisition of the many other measures arriving at the engine calculator. Figure 3 illustrates the different steps of the process. The engine calculating device is first synchronized, i.e. it recognizes the crankshaft angle and the cylinder in which it is to be injected. In four-stroke diesel engines, the combustion cycle occurs schematically as follows: a) admission of fresh air into the cylinder, b) compression of the air contained in the cylinder, 15 c) fuel injection and combustion of this one, and d) exhaust out of the cylinder of the products of the combustion. The injection of the fuel is, for a given cylinder, every two turns of crankshaft. Each phase lasts about half a turn. On four-stroke four-stroke engines, there is therefore an injection every half revolution in one of the four cylinders. The computer then prepares to record the pressure and angle values of the crankshaft that will happen to the next cylinder that will start its combustion cycle. Let i be the reference of this next cylinder. As soon as the combustion cycle of the cylinder i begins, the computer 25 records the pressure and angle values of the crankshaft of the cylinder i. A lap and a half after the start of the recordings, the computer records the crankshaft pressure and angle values of cylinder i + 3. If i + 3 is strictly greater than 4, which is the number of cylinders, we subtract 4 to i + 3 and we find the cylinder reference to be recorded, between 1 and 4. 30 Thus, if i is 2, then i + 3 = 5, which is strictly greater than 4. Then we subtract 4 to 5. The cylinder to be recorded is therefore cylinder 1.

A half-turn later, we thus have the pressure values of the cylinder i over the whole cycle, ie on two turns. The calculator stops the pressure and crankshaft angle recordings on the cylinder i, while continuing the pressure and crank angle records on the cylinder i + 3, and calculates the combustion noise of the cylinder i.

The index i + 3 is then replaced by i. The process continues by recording the crankshaft pressure and crank angle values of the cylinder i + 3, which is subtracted, if necessary, to obtain a cylinder reference of between 1 and 4, as indicated above.

The four-cylinder engine 18, 1,2,3,4, as illustrated in FIG. 4, is connected to the computer 15, which performs the following operations:

storage of the pressure and crankshaft angle values from the cylinders 1 to 4,

- Calculation of the combustion noise, - if necessary calculation of the regulation of the combustion noise and regulation by sending a command to the actuators of the engine.

A method of estimating the combustion noise has been described above. The invention is however not limited to this embodiment and other evaluation parameters of the combustion quality can be estimated, such as, for example, the indicated average torque (MIC) or the indicated average pressure (PMI).

The pressure sensor and the crankshaft angle sensor can indeed provide an estimation of the engine torque according to the following relation: 1 Name PMI Vcyl CMI = L f Pi (a Vi 4n i-1 47t with:

crank angle;

Vi: volume of the cylinder's combustion chamber i throughout the cycle;

Vcyl: unit capacity, 25 ft. Pressure in the combustion chamber of cylinder i; Ncyl: number of cylinders of the engine.

CMI is the Indicated Medium Torque and PMI is the Indicated Mean Pressure, which is proportional to the CMI.

Claims (9)

REVENDICATIONS1. Method for estimating a parameter for evaluating the quality of combustion, in a four-stroke internal combustion engine (18) and n cylinders (1, 2, 3, 4), referenced 1 to n, the combustion cycles two cylinders (1,2,3,4) of consecutive references being offset by a period P; from the measurement in the cylinders (1, 2, 3, 4) of one or more estimation parameters of said evaluation parameter of the combustion quality, characterized in that the reference of the cylinders (1, 2, 3,4) measured in accordance with the series up (k, n) defined by: uo = i, i being an integer between 1 and n, up = uP_1 + k if (up_1 + k) <_ n, where k is an integer greater than 1 such that k and n are prime to each other, and up = up-1 + kn if (up-1 + k) 'n, and in that the time interval between the beginning of the measurement of an estimation parameter in a cylinder (1,2,3,4) of reference up and the beginning of the measurement of the estimation parameter in the cylinder (1,2,3,4) of reference up + 1 is equal to kP. 2. Method according to claim 1, characterized in that each cylinder (1,2,3,4) forms a combustion chamber (5) whose volume is delimited by a piston (6) sliding in the cylinder (1,2 , 3,4) in an alternating rectilinear motion transformed into a rotational movement by means of a connecting rod (7) connecting the piston (6) to a crankshaft (8), and in that the estimation parameters are the pressure in the combustion chamber (5) and the angle of the crankshaft (8). 3. Method according to claim 1 or 2, characterized in that the evaluation parameter of the combustion quality is the combustion noise, the average torque indicated or the average power indicated. 4. Method according to one of claims 1 to 3, characterized in that the period P corresponds to the duration of 2 / n engine revolutions (18). 5. Method according to one of claims 1 to 4, characterized in that the engine (18) is a motor (18) four cylinders (1,2,3,4). 6. Method according to claim 5, characterized in that k = 3. 7. Method according to one of claims 1 to 6, characterized in that it further comprises a step of comparing them n estimated values of the evaluation parameter of the combustion quality, and a step of adjusting the injection parameters if one or more deviations between the compared values are greater than one or more predetermined values. 8. A device for estimating a parameter for evaluating the quality of combustion in a four-stroke internal combustion engine (18) and n cylinders (1, 2, 3, 4) referenced 1 to n, the cycles of combustion of two cylinders (1,2,3,4) consecutive references being offset by a period P, the device comprising in the cylinders (1,2,3,4) measuring means (16,17) of one or more parameters for estimating said evaluation parameter of the combustion quality, the measurement means (16, 17) being connected to a computer (15) capable of estimating the evaluation parameter of the combustion quality from obtained measurements, characterized in that the computer (15) is able to control the measuring means (16,17) so that the reference of the cylinders (1,2,3,4) consecutive measured obey the series up (k, n) defined by: uo = i, where i is an integer between 1 and n, up = uP_1 + k if (uP_1 + k) <_ n, where k is an integer greater than 1 where k and n are prime between them, and up = 1 + kn if (up-1 + k)> n, and so that the time interval between the beginning of the measurement of an estimation parameter in the reference cylinder (1,2,3,4) up and the beginning of the measurement of the estimation parameter in the reference cylinder (1,2,3,4) up + 1 is equal at kP. 9. Device according to claim 8, characterized in that the evaluation parameter of the combustion quality is the combustion noise, and in that each cylinder (1,2,3,4) forming a combustion chamber ( 5) whose volume is delimited by a piston (6) sliding in the cylinder (1, 2, 3, 4) in a reciprocating rectilinear motion transformed into a rotational movement by means of a connecting rod (7) connecting the piston (6) to a crankshaft (8), the combustion noise estimation parameters are the pressure in the combustion chamber (5) and the angle of the crankshaft (8). 1215