WO2001004465A1

WO2001004465A1 - Method for controlling an internal combustion engine to correct cylinder dispersion in terms of gas torque

Info

Publication number: WO2001004465A1
Application number: PCT/FR2000/002019
Authority: WO
Inventors: Alain Fernandez
Original assignee: Renault
Priority date: 1999-07-12
Filing date: 2000-07-12
Publication date: 2001-01-18
Also published as: FR2796417A1; FR2796417B1

Abstract

The invention concerns a method for controlling a four-stroke internal combustion engine, characterised in that it consists in determining the gas torque value for each cylinder (10A, 10B) and then, to bring the gas torque of all the cylinders (10A, 10B) to a common value, modifying the opening and/or closing time of the intake valve, and/or modifying the opening and/or closing time of the exhaust valve.

Description

"Method of controlling a combustion engine in order to correct the dispersion of the cylinders in terms of gas torque"

The present invention relates to a combustion engine, in particular a heat engine of a motor vehicle.

The invention relates more particularly to a method of controlling a four-stroke combustion engine in order to correct the dispersion of the cylinders in terms of gas torque.

The invention relates more particularly to a combustion engine whose intake and exhaust valves of each cylinder are each individually controlled by means of a linear actuator, in particular of an electromagnetic actuator, each actuator of a valve being connected to an electronic engine control unit. Such a combustion engine without camshafts, also called "camless" engine, offers great possibilities for the individualized control of the intake and exhaust valves independently of the general distribution diagram (s) of the engine. The cylinders of a combustion engine are naturally dispersed in terms of gas torque. The gas torque of a cylinder is the product of combustion recovered from the drive shaft at the level of this cylinder and it can be expressed according to the formula C = J ^* dω / dt where J is a moment of inertia, dω / dt is the derivative with respect to the speed of rotation of the motor shaft.

The dispersion of the cylinders in terms of gas torque creates an imbalance in the operation of the engine. This is reflected in particular by annoying vibrations which are transmitted to the entire vehicle.

In conventional engines with camshafts, the main sources of dispersion are the variations in injector flow and the camshaft laws. In "camless" engines whose valves are individually controlled, the sources of dispersion in terms of gas torque are increased. Indeed, instead of the dispersion of the camshaft laws, there is a dispersion of the valve opening times. The higher the number of valves, the more sources of dispersion there will be.

The invention aims to propose a method for controlling such an engine without camshafts in order to correct the dispersion of the cylinders in terms of gas torque. To this end, the invention provides a method for controlling a four-stroke combustion engine, of the type comprising at least two cylinders each provided with an air intake circuit or air / fuel mixture and a burnt gas exhaust circuit, circuits which communicate with a combustion chamber, of the type in which the communications of the intake and exhaust circuits with the chamber are each capable of being closed off by at least one valve, respectively intake and exhaust, with opening controlled by a linear actuator, in particular by an electromagnetic actuator, connected to an electronic control unit, with a view to correcting the dispersion of the cylinders in terms of gas torque, characterized in that it consists in determining the value of the gas torque for each cylinder re then, to bring the gas torque of all the cylinders to the same value, to modify the instant of opening and / or fe the intake valve, and / or to modify the instant of opening and / or closing of the exhaust valve.

Thanks to such a method, the cyclical regularity of the engine is improved. This control over the operation of the engine makes it possible in particular to minimize the vibrations induced by the engine both in the vehicle body and in the transmission members.

According to other characteristics of the invention: - before correcting the dispersion of the cylinders in terms of gas torque, the dispersion of the cylinders in terms of richness is corrected;

- to reduce the gas torque of all the cylinders to the same value, the instant of closing of the intake valve is modified and / or the instant of opening of the exhaust valve is modified;

- if the instant of closing of the intake valve is before the bottom dead center of the piston stroke, the value of the gas torque of a cylinder is reduced or increased, respectively by advancing or delaying the instant of closing the intake valve and, if the instant of closing of the intake valve is after the bottom dead center of the piston stroke, the value of the gas torque of a cylinder is reduced or increased , respectively by delaying or advancing the time of closing of the intake valve;

- the value of the gas torque of a cylinder is reduced or increased, respectively by advancing or delaying the opening of the exhaust valve with respect to an initial opening instant situated before the bottom dead center;

- for each cylinder, the gas torque is made to converge towards a maximum gas torque of the cylinder, by an optimal setting of the instant of opening of the exhaust valve, and then the gas torque of all the cylinders is brought back to the same value by the only modification of the instant of closing of the intake valve of each cylinder;

- the value to which the gas torque of all the cylinders is brought back is either the value of the overall average torque, or the highest torque value of all the cylinders, or the lowest torque value of all the cylinders, or a predetermined overall average torque value;

- to determine the value of the gas torque of a cylinder, a signal emitted by a torque meter is used; - the corrections made to the opening and / or closing times of the valves call for calculations of the Proportional-Integral-Derivative type or of the constant step type; - weighting coefficients are applied to the correction calculations to take into account the filling acoustics and / or the engine operating conditions;

- in the case of an engine in which each cylinder has several intake valves and / or several exhaust valves, one acts either on a single intake or exhaust valve, or on several intake valves or 'exhaust;

- as a function of the values of the gas torque deviations and / or as a function of the total values of the corrections carried out on the cylinders, operating anomalies are detected and an alert signal is triggered.

Other characteristics and advantages of the invention will appear on reading the following detailed description for the understanding of which reference will be made to the appended drawings in which:

- Figure 1 is a partial schematic sectional view of a portion of an internal combustion engine with valves without camshafts and controlled according to a method according to the teachings of the invention; - Figure 2 is a distribution diagram of a four-stroke engine in normal operation;

- Figure 3 is a diagram for illustrating the implementation of the method according to the invention applied to two cylinders; - Figure 4 is a flowchart for the illustration of the implementation of the method according to the invention in order to reduce the torque of a cylinder to the value of the overall average torque by modifying the instant of closing of the valve admission; - Figure 5 is an inogram for the illustration of the implementation of the method according to the invention to determine the optimal setting of the closure of the exhaust valve to obtain maximum efficiency of the cylinder. FIG. 1 shows a cylinder 10 of a four-stroke internal combustion engine, the upper part of which forms a combustion chamber 12 delimited by a movable piston 14 and by a cylinder head 15.

The cylinder re 1 0 is supplied with air / fuel mixture by an intake circuit 16 which opens into the combustion chamber 12 through an intake valve 18 whose movements are controlled by a linear electromagnetic actuator 1 1 in order to shut off or not the communication between the intake circuit 16 and the combustion chamber 12.

An exhaust circuit 17 is provided for evacuating the burnt gases from the combustion chamber 12 through an exhaust valve 1 9 also controlled by an electromagnetic linear actuator 13. The control of the intake valves 18 and exhaust 19 is provided by an electronic control unit (not shown) which controls the actuators 1 1, 13, and which also controls the injection of fuel, here indirect, by means of an injector 20, as well as ignition by means of a spark plug (not shown).

The electronic control unit comprises in particular means for storing one or more engine operating maps.

The electronic control unit receives signals representative of operating parameters such as engine speed, atmospheric pressure, pressure in each cylinder, flow of intake and / or exhaust gases, instantaneous torque supplied, etc. According to the principle of the four-stroke cycle of a combustion engine, this is carried out in two rotations of the crankshaft and in four strokes of the piston 14, the four times of the cycle being the intake, the compression, the combustion and the exhaust.

The diagram in Figure 2 shows an example of a valve distribution law.

A few degrees of angle of rotation before the top dead center PM H of the stroke of the piston ^" 14, the intake valve 18 opens at an instant OA. This is the start of the intake phase.

A few degrees of rotation angle after the bottom dead center PMB of the stroke of the piston 14, the intake valve 18 closes at a time FA. It is the end of the intake phase and the start of the compression phase until TDC top dead center.

When the TDC top dead center is reached, the ignition is triggered or occurs. It is the beginning of the combustion and expansion phase. Some deg ang ang rotation before the bottom dead center PMB, the exhaust valve 1 9 opens at an instant OE. It is the end of the expansion phase and the beginning of the exhaust phase.

A few degrees of angle of rotation before the top dead center TDC, the inlet valve 18 opens again then, a few degrees of angle of rotation after the top dead center

TDC, the exhaust valve 1 9 closes at an instant FE.

It's the end of the exhaust phase.

Note that in the vicinity of the top dead center PM H there is a crossing of the valves since the intake valve 18 opens before the closing FE of the exhaust valve 19. This crossing has the main advantage of causing a recirculation of burnt gases in cylinder 10. These recirculated burnt gases make it possible in particular to reduce polluting emissions by slowing combustion.

The control method according to the invention is illustrated diagrammatically in FIG. 3 in the case of a two-cylinder engine 10A, 10B. The diagram is symmetrical and the identical elements bear indices A and B according to whether they are associated and function with the cylinder 10A or the cylinder 10B respectively.

Each cylinder 10A, 10B corresponds to a torque meter 23A, 23B, a fuel injection control unit 22A, 22B, as well as a valve control unit 25A, 25B. The torque meters 23A, 23B are connected to an electronic gas torque analysis unit 24 common to the two cylinders 10A, 10B. Finally, a richness probe 21 determines the richness RA, RB of the gases for each cylinder 1 0A, 1 0B.

The richness is the ratio between the volume of air and the volume of fuel introduced simultaneously into the combustion chamber of a cylinder.

The richness probe 21 is, for example, an oxygen probe. It is located in a part of the exhaust circuit common to all the cylinders 1 0A, 1 0B.

The richness probe 21 measures the richness of the exhaust gases at an instant T1. These exhaust gases come from a cylinder which emitted them at an instant T0. Knowing the value of the interval T1 -T0 as a function of the operating conditions of the engine, the richness probe 21 is capable of determining to which cylinder 1 0A, 1 0B belongs the richness measurement which it has carried out.

Preferably, before correcting the dispersion of the cylinders 10A, 10B in terms of gas torque, action is taken on all the parameters or at least on the main parameters which contribute to the existence of this dispersion.

The differences in richness between the cylinders 10A, 10B are an important source of gas torque differences between the cylinders 10A, 10B. Consequently, before correcting the dispersion of the cylinders 10A, 10B in terms of gas torque, a correction is made to the differences in richness between the cylinders 10A, 10B in order to bring the richness value RA, RB of each cylinder re 10A, 10B at a setpoint of the richness CR.

The wealth differences are corrected by modifying the quantities of fuel injected as a function of the wealth measurements provided by the wealth sensor 21. This process being known from the state of the art, it will not be developed here.

The correction of the differences in richness makes it possible to reduce the differences in gas torque between the cylinders 1 0A, 1 0B. It is now a question of balancing the gas couples of the cylinders 10A, 10B. Each cylinder 10A, 10B produces an instantaneous torque which fluctuates around a given average torque value CA, CB. A global average value CG of the gas couples is expressed by the quotient of the sum of the average couples CA, CB by the number of cylinders. Balancing of the gas pairs CA, C B of cylinders 1 0A,

10B can be carried out according to different strategies. Either we reduce each average couple CA, CB to the value of the global average couple CG. Either we reduce each average torque CA, CB to the highest torque value. Either we reduce each average torque CA, CB to the lowest torque value. Or again, each average couple CA, CB is reduced to a value of the global average couple CG predetermined by mapping.

Each torque meter 23A, 23B measures the average value of the gas torque CA, CB of the associated cylinder 10A, 10B.

The gas torque analysis unit 24 compares these gas torque values with each other or with the global average value CG.

Then the unit 24 transmits this information to the fuel injection control 22A, 22B and electronic valve control units 25A, 25B.

To correct differences in gas torque, the electronic valve control units 25A, 25B modify the valve opening laws. The modification of the valve opening laws makes it possible to act on the gas torque according to two methods, which can be implemented separately or jointly.

According to a first method, to correct the gas torque differences, the air filling of the cylinders 10A, 10B is modified during the intake phase. In fact, the gas torque is directly linked to the quantity of fuel mixture present in the cylinder.

This modification of the filling can be done in two ways. Either one acts on the quantity of air admitted, or one acts on the quantity of burnt residual gases present in the cylinder during the admission. These two actions can be carried out separately or jointly.

In addition to correcting the filling differences, the fuel injection control units 22A, 22B modify the injection times to maintain a constant richness RA, RB.

According to a preferred embodiment of the invention, the filling is modified by acting on the quantity of air admitted by modifying the closing instant FA of the intake valve 1 8. Depending on whether one advance or delay this closing time FA, and depending on whether it is before or after the bottom dead center PMB, more or less air is admitted into the cylinder. The action on the quantity of air admitted supposes that the residual burnt gases remaining in the combustion chamber 12 at the end of the exhaust phase are constant so as not to complicate the corrections. Modifying only the closing instant FA and not the opening instant OA of the intake valve 1 8 allows this assumption to be relatively accurate. Small inaccuracies are compensated for by the various loops in the correction strategy. We illustrated schematically in fig ure 4 the mode of action on the amount of air ad put in a cylinder to decrease the value of the torque CA of the cylinder 1 0A. It is assumed in this example that one wishes to reduce the torque CA of the cylinder 10A to the value of the overall average torque CG which is less than CA.

The initials “FA” correspond to the value of the angle of rotation of the instant of closing FA of the intake valve 18 represented in the diagram of FIG. 2. The term “Cor” represents a correction value in degrees vilebreq uin, for example from a Proportional-Integral-Derivative (PID) calculation with respect to the gas torque difference to be made up, and the term "Cor _ot " represents a total correction value which is the sum of the values of Cor correction already performed on cylinder 10A. The initial “S” represents a predetermined threshold value for the total correction value Cor _tot - When a term has an ind ice “t” or “t-1” it means that its value is measured at a present time t or at a previous time t-1.

To decrease the quantity of air admitted into the cylinder 10A, we begin by determining whether the closing instant FA of the intake valve 1 8 is before or after the bottom dead center PMB.

If the closing instant FA is before the bottom dead center PMB, the closing FA of the inlet valve 18 is advanced at an instant FA _t by subtracting the correction value Cor from the initial value FA _t- ι of l 'angle of rotation.

It is then determined whether the gas torque CA of the cylinder 10A is equal to the value of the overall average torque CG. If the answer is positive, the action is finished, otherwise we carry out a correction in a loop by continuing to subtract the correction value Cor from the value of the angle of rotation FA until the gas torque CA of the cylinder re 10A is equal to the value of the overall average torque CG. If the closing instant FA is after the bottom dead center PMB, the same operations are carried out as in the previous case, but seeking to delay the closing FA of the intake valve 18. For this, the correction value is added. Cor at the initial value FA _t- ι of the angle of rotation. In both cases, at each loop, it is checked that the total correction value Cor _tot is less than the threshold value S. Beyond this threshold value S, it is considered that the dispersions of the cylinders 10A, 10B are not more acceptable. There is then a technical problem which requires the intervention of a specialist. The problem is signaled to the user by an alert light and the corrections are stopped.

We have explained above a mode of action to reduce the gas CA torque. If it is desired to increase the gas torque CA of the cylinder 10A, still by acting on the quantity of air admitted into the cylinder 10A, it suffices to reverse the direction of the corrections Cor with respect to the direction described in FIG. 4. By For example, instead of subtracting the correction value Cor from the value of the angle of rotation FA _t- ι, the correction value Cor is added to it. The Cor correction value can be fixed or a regulator can determine different Cor correction values with each new correction.

In a variant of the embodiment which has just been described, it is possible to act on the quantity of air admitted into the cylinder 10A by modifying the instant of opening OA of the intake valve 18. However, the modification of the instant of opening OA of the inlet valve 1 8 has consequences on the quantity of recirculated burnt gases. This mode of action then requires a readjustment of the adjustment parameters which manage the recirculated burnt gases.

To modify the air filling of the cylinders 10A,

10B, it is possible to act directly on the quantity of burnt gases recirculated by modifying the crossing of the valves. We will proceed according to a strategy similar to that described above.

For example, if the duration of valve crossing is increased, the amount of recirculated burnt gas is increased, which decreases the amount of air supplied. By decreasing the quantity of air admitted, the value of the gas couple of the cylinder considered is reduced.

One can act on the quantity of burnt gases recirculated even if there is no crossing of the valves. To decrease the value of the gas torque, the quantity of recirculated burnt gases will then be increased according to known methods.

According to a second method, to correct the differences in gas torque, the combustion efficiency is acted upon through the expansion rate. The expansion rate is the quotient of the final volume in which the burnt gases relax by the initial volume in which the mixture was ignited. When the expansion rate of a cylinder is increased, the combustion efficiency is improved, which increases the value of the gas torque of the cylinder considered.

The combustion efficiency is directly linked to the use of the energy supplied to the piston 14 by the combustion during the expansion phase. This phase ends with the opening OE of the exhaust valve 1 9 before the bottom dead center PMB. A premature OE opening of the exhaust valve 19 cuts off the expansion phase. This has the effect of reducing the expansion rate and therefore of decreasing the value of the gas torque for the cylinder considered. It is noted that this method does not require the correction of the fuel injection times because the modification of the opening time OE of the exhaust valve 1 9 does not vary the richness measured at the exhaust.

Failure to optimize the expansion rate of a cylinder has a major influence on fuel consumption. A shift of the opening time OE of the exhaust valve 1 9 by several crank degrees relative to an optimal setting can cause overconsumption by several p rents.

Consequently, for the sake of lower consumption, the action on the combustion efficiency will preferably be limited to an increase in the torque CA, CB for the cases in which the cylinders 10A, 10B considered are not at their efficiency. maximum.

For the cylinders 1 0A, 10B whose average torque CA, CB is greater than the overall average torque CG, we can consider that their performance is good and that an action on filling to reduce their average torque CA, CB enough.

Advantageously, it will be sought to achieve for each cylinder 10A, 10B a maximum efficiency by optimizing the instant of opening OE of the exhaust valve 19 according to the strategy represented in FIG. 5. In FIG. 5 we have adopted the same type of notation as in FIG. 4. The initials “OE” correspond to the value of the angle of rotation of the opening instant OE of the exhaust valve 19 shown in the diagram in FIG. 2. For to simplify the writing, we have used the notation “Cor” to identify the correction value in FIG. 5. However, the correction value Cor in FIG. 5 is independent of that in FIG. 4.

To find the maximum efficiency of cylinder 10A, we delay the opening time OE of the valve. exhaust 19 by adding the correction value Cor to the value of the angle of rotation OE. As long as the new couple CA _t at the instant t resulting from the correction is greater than the old couple CA _t- ι at the previous instant t-1, a loop correction is carried out by continuing to add the value of correction Cor to the value of the angle of rotation OE.

When the new torque CA _t becomes less than or equal to the old torque CA _t- ι, we return to the previous value of the angle of rotation OE to find the old torque CA _t -ι. The opening time OE of the exhaust valve 19 is then advanced by subtracting the correction value Cor from the angle of rotation OE. As long as the new torque CA _t at the instant t resulting from the correction is greater than the old torque CA _t -ι, a loop is produced by continuing to subtract the correction value Cor from the value of the angle of rotation oE.

When the new torque CA _t becomes less than or equal to the old torque CA _t- ι, we return to the previous value of the angle of rotation OE. The value of the angle of rotation OE for which the efficiency of the cylinder 10A is optimal has been determined here, since the gas torque value CA is obtained as high as possible.

At each loop, it is checked that the total correction value Cor _ot is less than the threshold value S. Beyond this threshold value S, it is considered that the dispersions of the cylinders 10A, 10B are no longer acceptable. There is then a technical problem which requires the intervention of a specialist. The problem is signaled to the user by an alert light and the corrections are stopped.

Preferably, to correct the differences in gas torque, we choose to act on the combustion efficiency rather than on the air filling of the cylinders 10A, 10B when we want to favor the reduction of polluting emissions from the engine, for example in the phases of priming a catalyst and / or of raising the temperature of the engine. The corrections made, on the one hand, to the instants of opening or closing of the valves by the electronic control units of valves 25A, 25 B and, on the other hand, on the times of injection by the electronic units fuel injection control 22A, 22B call, for example, calculations of the Proportional-lntég rale- Derivative type (PI D) or of the constant step type.

Weights can be applied to the correction calculations. These weighting coefficients are, for example, a function of the load and of the engine speed, to take into account the filling acoustics and / or the operating conditions of the engine.

Corrections, depending on the type of engine, are applied to all or part of the engine's operating range.

Alternatively, the method according to the invention may provide for acting on one or both intake valves or on one or both exhaust valves, if it is an engine of which each cylinder has several intake valves and / or several exhaust valves (engine-multi-valves).

The method according to the invention can also provide for acting no longer only on the instants of closing of the intake valves or on the instants of opening of the exhaust valves, but only on the instants of opening of the intake valves. intake or when closing the exhaust valves. The process then combines the action on the filling and on the recirculated burnt gases (GBR). The method can also provide for acting on both the opening and closing of the intake or exhaust valves.

The method according to the invention also makes it possible to provide a diagnostic function since, when the correction value total exceeds the predetermined threshold value S, the user can be advised to carry out a mechanical examination by lighting an warning light on the dashboard.

Mechanical examination can also be advised as soon as there is an excessively large gas torque deviation from the average or from a given cartog value. This observation is made for example by the electronic unit for analyzing the gas couples 24.

Claims

REVENDICATIO NS

1. Method for controlling a four-stroke combustion engine, of the type comprising at least two cylinders (10A, 10B) each provided with an air intake circuit (16) or with an air / fuel mixture and with a exhaust gas exhaust circuit (17), circuits which communicate with a combustion chamber (12), of the type in which the communications of the intake (16) and exhaust (17) circuits with the chamber (12) are likely to be closed each by at least one valve, respectively intake (18) and exhaust (1 9), with opening controlled by a linear actuator (1 1), in particular by an electromagnetic actuator, connected to an electronic control unit (25A, 25B), in order to correct the dispersion of the cylinders (10A, 10B) in terms of gas torque, characterized in that it consists in determining the value of the gas torque for each cylinder (10A, 10B) then, to bring back the gas torque of all the cylinders (10A, 10B) at the same value, to modify the closing instant (FA) of the intake valve (18), and / or to modify the opening instant (OE) of the exhaust valve (19).

2. Method according to the preceding claim, characterized in that, before correcting the dispersion of the cylinders (10A, 10B) in terms of gas torque, the dispersion of the cylinders (10A, 10B) is corrected in terms of richness.

3. Method according to any one of the preceding claims, characterized in that, if the closing instant (FA) of the intake valve (18) is located before the bottom dead center (PMB) of the piston stroke (14), the value of the gas torque of a cylinder is reduced or increased, respectively by advancing or delaying the closing instant (FA) of the intake valve and in that, if the closing instant (FA) of the intake valve is located after the bottom dead center (PMB) of the stroke of the piston (14), the value of the gas torque of a cylinder is reduced or increased, respectively by delaying or advancing the closing instant (FA) of the intake valve.

4. Method according to any one of the preceding claims, characterized in that the value of the gas torque of a cylinder is reduced or increased, respectively by advancing or delaying the opening (OE) of the valve exhaust relative to an initial opening instant located before bottom dead center (PM B).

5. Method according to claims 3 and 4 taken in combination, characterized in that, for each cylinder (10A, 10B), the gas couple (CA, CB) is converged towards a maximum gas torque of the cylinder, by optimal timing from the instant of opening (OE) of the exhaust valve (1 9), and in that the gas torque (CA, CB) of all the cylinders (10A, 10B) is then reduced to the same value by only modifying the closing instant (FA) of the intake valve (1 8) of each cylinder (10A, 10B).

6. Method according to any one of the preceding resells, characterized in that the value to which the gas torque (CA, CB) of all the res cylinders (10A, 10B) is brought back is either the value of the overall average torque ( CG), either the highest torque value of all cylinders (10A, 10B), or the lowest torque value of all cylinders (10A, 10B), or a predetermined overall average torque value.

7. Method according to any one of the preceding claims, characterized in that, to determine the value of the gas torque (CA, CB) of a cylinder (10A, 10B), a signal emitted by a torque meter (23A, 23B).

8. Method according to any one of the preceding res ications, characterized in that the corrections made to the instants of opening and / or closing of the valves make call to calculations of the Proportional-I ntég rale-Derivative (PI D) type or of the constant step type.

9. Method according to the preceding claim, characterized in that the weighting coefficients are applied to the correction calculations to take into account the filling acoustics and / or the operating conditions of the engine.

10. Method according to any one of the preceding claims, characterized in that, in the case of an engine in which each cylinder re (10A, 10B) comprises several intake valves (18) and / or several exhaust valves (1 9), one acts either on a single inlet (1 8) or exhaust (19) valve, or on several inlet (1 8) or exhaust (19) valves.

1 1. Method according to any one of the preceding claims, characterized in that, as a function of the values of the gas torque deviations and / or as a function of the total values of the corrections ^" made (Cor _tot ) on the cylinders (1 0A, 1 0B) , operational anomalies are detected and an alert signal is triggered.