WO2007074271A1

WO2007074271A1 - Engine control method for improving an engine combustion diagnosis

Info

Publication number: WO2007074271A1
Application number: PCT/FR2006/051353
Authority: WO
Inventors: Pascal Emery; Laurent Jacquot
Original assignee: Renault S.A.S.
Priority date: 2005-12-20
Filing date: 2006-12-14
Publication date: 2007-07-05
Also published as: EP1963648A1; FR2895024B1; FR2895024A1

Abstract

The invention concerns engine control. More particularly, it concerns a method for controlling an engine characterized in that it comprises a step which consists in determining the possible occurrence of combustion loss or misfiring in a combustion chamber of the engine by comparing (102) the value of a moving average of a predetermined quantity (101) of the engine to a predetermined threshold value.

Description

A method of controlling an engine for improving an engine combustion diagnosis

The present invention relates to a control method of a vehicle engine, especially automobile.

In particular, the invention relates to a method of controlling an engine comprising a step of determining whether a misfire occurs during a combustion cycle in a combustion chamber of the engine.

Such a step is already known.

It can be implemented to control the pollutant emissions of the vehicle and thus ensure compliance with anti-pollution standards. It is known that such misfires can have a significant influence on this emission.

By way of non-limiting example, in an engine comprising a catalytic converter, it is known that a misfiring can cause degradation of this pot. One reason is that unburned fuel, when circulating indoors, can ignite and damage materials, especially those intended to be in contact with engine exhaust.

In order to limit such failures, a known technique consists in detecting them by analyzing a pressure in a manifold of the engine. In this regard, reference may be made to US 2002/0134356 in which this pressure is used in combination with a neuron network whose training is implemented at the time of calibration of the engine on a test bench.

Another known technique consists in detecting misfires by means of a pressure of a recirculated exhaust gas, which is commonly designated by gas EGR (EGR is the acronym for "Exhaust Gas Recirculation" in English language).

This technique is described in particular in US 5 193513.

Although having rendered many services, these techniques now offer limited performance.

One reason is that as pollution standards become ever more stringent, the specifications concerning the control of combustion, and even misfires, become more and more demanding. By way of non-limiting example, the detection of misfires is not precise enough and effective.

In particular, a signal-to-noise ratio related to a measurement that is necessary for the detection and control of combustion is still too low. Moreover, these techniques do not always make it possible to provide an appropriate response when a failure has been detected.

For example, simple detection of a misfire should not necessarily lead to intervention in the control of combustion. A more detailed analysis of this type of disturbance must be implemented to allow a better diagnosis and a more relevant intervention.

Similarly, despite efforts in this direction, the time required to detect a failure is much too long according to these techniques. An object of the invention is therefore to overcome at least these disadvantages. In particular, the object of the invention is a method in which the presence of a misfire or a loss of combustion is detected reliably and quickly.

For this purpose, according to the invention, a method for controlling an engine is proposed, characterized in that it comprises a step in which the eventual occurrence of a loss or misfire in a combustion chamber of the combustion chamber is determined. motor by comparing the value of a sliding average of a predetermined magnitude of the motor with a predetermined threshold value. The use of such a comparison offers the particular advantage of reducing the measurement noise of the size.

It also reduces the influence of a misfire on the determination of a loss of combustion, which allows to intervene quickly on the engine combustion process in cases where it is really worth it.

Preferred but non-limiting aspects of the process according to the invention are the following:

the method further comprises a step in which at least one value of the quantity, which is taken into account in the sliding average, is modified when one of the misfires is detected;

the value of the quantity which is taken into account for the first time in the determination of the sliding average is modified;

- the modification of the value consists in replacing it by that of an average carried out on a number m of the values of the quantity smaller than a number n of values taken into account in the sliding average or by the last determined value of the sliding average ; the step of modifying the value of the quantity is carried out if the presence of a loss of combustion has been determined;

the method further comprises a step where the values taken into account in the sliding average are initialized if the presence of a loss of combustion has been determined;

the possible presence of each of the combustion misfires is determined by comparing the value of the quantity with a predetermined threshold value;

the quantity is selected from the following group: a pressure of a gas in a cylinder of the engine, a mean pressure indicated in the cylinder, a specified specific consumption of a fuel injected into the cylinder, a torque of the engine;

the magnitude depends on an energy release of a gas present in the combustion chamber;

the magnitude is estimated iteratively according to a crankshaft angle and in that this iterative estimate is in the form of:

where C is the estimated quantity, θ is the crank angle, γ is the ratio of specific heats (Lp and Cv), V is the volume of a cylinder in the combustion chamber, and p and T is a pressure and a temperature in the cylinder . Other aspects, objects and advantages of the invention will appear better on reading the following description of the invention, with reference to the appended drawings in which: FIG. 1 is a motor adapted to implement the method of the invention; 'invention, FIG. 2 is a general flowchart of one embodiment of the method of the invention; FIG. 3 corresponds to a flowchart showing steps implemented according to a particular aspect of this embodiment.

Referring now to FIG. 1, the motor in the invention typically comprises an injector or spark plug 1, one end of which is in contact with an internal zone of a combustion chamber 4. In the combustion chamber 4, a piston 6 can in known manner slide along an axis of the chamber to rotate a crankshaft 10 via a connecting rod 7.

Furthermore, inlet ports 3 and gas outlet 2 in the chamber are also provided. The fitter further includes sensors for measuring engine magnitudes.

At least one of these quantities will be used in the control method of the engine according to the invention.

In this respect, a pressure in the cylinder of the chamber, an indicated average pressure (PMI), a specified specific consumption (CSI) or a motor torque can be used as a quantity.

It will be noted moreover that the method uses a crank angle in particular to know a state of a combustion cycle.

The sensors concerned are represented by the reference 9 for the crankshaft angle, and 5 for the aforementioned quantities. The engine further comprises an electronic box 8 adapted to implement the method of the invention.

More specifically, this box has inputs 11, 12 to which are routed signals from the aforementioned sensors. It furthermore has at least one output 13 from which it is able to deliver a signal to an actuator of the engine which plays a role in the control method.

In the nonlimiting example illustrated in FIG. 1, the actuator corresponds to the above-mentioned spark plug or injector 1. We will now describe an embodiment of the method implemented in particular by the housing 8.

It will be assumed in this description that the magnitude involved in this process is the pressure in the cylinder.

Of course, those skilled in the art will understand that this description can be obviously adapted to other quantities such as those mentioned above.

Figure 2 shows a flowchart of this embodiment.

It is considered that one has just performed a k-th combustion cycle and a k-th measurement of the pressure in the cylinder. In a step 100, consider the last n-1 values of the measurements of this pressure (n is an integer).

In this regard, the value of a pressure measured at the current cycle k has been designated by the variable yc (k).

Therefore, the aforementioned n-1 values are contained in an interval [yc (k-n + 1), yc (kl)]. According to the invention, a sliding average, denoted y, based on the n-1 values of said interval and on the value yc (k) is determined in a step 101.

In other words, this sliding average is determined at step k by a relation of the type:

In a step 102, the value of the sliding average thus obtained is compared with a predetermined threshold value Sl.

If it is greater than Sl, the process proceeds to a step 103 where the step k is incremented for a next combustion cycle, then to a step 104 where the last values of the measured pressure are updated in the cylinder.

It follows for example that the value yc (k) becomes yc (kl), yc (k-n + 2) becomes yc (k-n + l) and the old value yc (k-n + l) n ' is more taken into account in the sliding average. In the opposite case where y (k) is less than or equal to Sl in step

102, it is considered according to the invention that there is a loss of combustion.

And the process then proceeds to a step 105 where this loss of combustion is recorded by means of a variable Loss (k) provided for this purpose.

More precisely, this variable initially contains zeros indicating by default an absence of combustion loss.

And, at the step k in question, a value of 1 is assigned to this variable when step 105 is implemented so as to indicate that a loss of combustion has been detected.

It should be noted here that such a recording makes it possible in particular to subsequently provide a history of combustion losses and then to establish a diagnosis that will enable any appropriate actions to be taken (for example a replacement of the candle, etc.).

Nevertheless, as soon as the loss of combustion at step k is detected, the method used may carry out other operations. In this respect a test 106 is performed to determine whether a particular action is to be implemented.

If so, the method sets up these actions (step 107).

If not, it waits for the next burn cycle and returns to step 100. Different tests may be used.

In particular, according to one aspect of the invention, a test 106 may consist of analyzing whether at the step k where the loss of combustion is detected, a misfire has also been detected.

To do this, the test 106 in FIG. 2 may comprise a step 200 shown in FIG. 3, where the value yc (k) is directly compared with a predetermined threshold value S2.

If this value yc (k) is less than or equal to S2, it is considered that there is a misfire.

We then go to a step 201 where this misfire is recorded using a missed variable (k) provided for this purpose.

More precisely, this variable initially contains zeros indicating by default an absence of misfire.

And, at the step k in question, a value of 1 is assigned to this variable when step 201 is implemented so as to indicate that a misfire has been detected. In the opposite case where yc (k) is greater than S2, in step 202 the value 0 is assigned to the failed variable (k).

It should be noted here that such a recording makes it possible in particular to subsequently provide a history of misfires and then establish a diagnosis that will enable any appropriate action to be taken.

(new engine setting, etc.).

When in cycle k the presence of both a misfire and a loss of combustion has been detected, then action step 107 is passed.

According to one aspect of the invention, in this step 107 the value of the sliding average is modified.

For this purpose, various possibilities are provided by the invention.

For example, this value can be modified by modifying at least one value yc contained in said interval taken into account in the calculation.

According to a preferred aspect, the sliding average is initialized so that it becomes equal to the current value yc (k).

For this purpose, we can replace each of the n-1 values taken into account in this average by said current value.

We can also choose that the moving average be determined on yc (k) alone. In other words, from the step k this average is no longer based on n values but only one, and more precisely the current value yc (k).

We then reconstruct the set of n values on which the average must ultimately be determined as and when the combustion cycles.

For example, at the next step k, that is to say corresponding to k equal to k plus 1, the average will be based on two values. The one we just talked about and the new value yc (k) measured at this step k.

As will be understood, it will therefore n iterations to reconstruct a sliding average on n values yc. An advantage of such a reset is that the detection of a loss of combustion by the process is carried out more quickly.

According to another aspect of the invention, the test 106 which is capable of initiating this reset of the sliding average does not include the above condition of absence of misfire. Thus, the reset takes place when the combustion loss has been detected (this amounts to saying that there is a direct link between step 105 and step 107 of reset).

According to yet another aspect of the invention, it is the presence of a misfire which will condition the implementation of an appropriate action.

This is illustrated in FIG. 3, which shows step 200 of the test on a misfiring followed by step 102 in which the presence of a loss of combustion is tested.

If in this last step, it is concluded that there is no loss of combustion, go to a step 203, where appropriate action may possibly be implemented.

As indicated above, such an action may consist in further modifying the value of the moving average.

For this purpose, one can use the same techniques as before. But according to a preferred aspect of the invention, two cases will be distinguished. In a first case we choose not to take into account the misfire yc (k) in the calculation of the sliding average.

Note that this amounts to saying that there is an additional test between the steps 200 and 201 of looking at whether one is in said first case or the second case that we will see later.

Moreover, in said first case, the value of the sliding average is chosen so that it is equal to the value yc (kl) at the preceding step, so that it is equal to an average of m of n values. For example in the latter case, we can consider the last m measured values yc, current value y (k) being excluded, consider an interval [yc (k-m-l); yc (k-l)].

Then, calculate the average of these m values and then replace the n values yc useful for calculating the sliding average at step 104 by this calculated average.

In the second case, it is chosen to reconstitute the sliding average only for the value y (k) as previously described when this average is reset in the case of detection of a loss of combustion. Thus, the moving average is based solely on a single value, which corresponds to the value yc during the misfiring, or yc (k).

Then, the current value yc (k) is replaced either by the previous value yc (kl) or by the average on m of the n preceding values, in step 104. An advantage of such modifications is to be able to mitigate the effect of a misfire on the detection of a loss of combustion.

Moreover, the second case makes it possible to better restore the processed signal.

Indeed, when a misfire is detected, its influence does not affect the calculation of the sliding average after this failure.

The sliding average is then more faithful to the signal it filters.

According to another aspect of the invention is used in the method described above a quantity which depends on an apparent energy release in the combustion chamber. In particular, this quantity denoted C can be expressed in the following form:

c = 1 V ^ dθ (D

where V represents a volume in the combustion chamber, Q an energy present in the gases of the combustion chamber and θ the crankshaft angle.

In practice, calculating the derivative in the expression above makes the quantity C quite noisy.

Multiplication by 1 / V has the particular advantage of reducing this noise. In particular, the noise is advantageously reduced just before and after the bottom dead center.

In addition, the expression (1) makes it possible to obtain a signal whose amplitude is particularly high at the moment of the top dead center, which offers an advantage for SOC start-up detection (SOC for "Start of Combustion"). in the Anglo-Saxon language). In order to facilitate the calculation of the expression (1) by the control unit, and in particular to reduce the computing power required, it is transformed into a discretized expression of recursive-type which is in the form: _c

where γ, p and T correspond to a ratio of the specific heats cp and cv, a pressure and a temperature in the cylinder.

Such expression was obtained by starting from the expression above C and an expression for the derivative dQ / dθ of the type: dQ _l _ fj) £ _ dm dT __P_ dVΛ _J_ dV dθ γ ^~ -l Ua dθ ⁺ T dθ V dθ J ⁺ γ -l ^P dθ where m is a mass of gases in the cylinder.

Note that in this last expression, one could replace the variable θ by a time t.

But the Applicant has determined that the use of the Q variable is advantageous because the method is independent of a rotational speed of the engine.

It will furthermore be noted that by using the angular derivative dθ and the derivative of the temperature dT, it is advantageous to avoid using the derivative of the pressure p, which generally introduces a large noise into the determination of the quantity C. According to a preferred aspect , V, p, T, γ and m are function variables of the angle θ and the only variables measured are p and θ.

In addition, it is assumed that the mass m is constant. It is further assumed that the ratio γ is constant, preferably equal to 1.4, before combustion and up to the first instants thereof. According to this preferred aspect, the estimation of the volume V and its derivative is obtained by reading in a table of the volume function of the angle θ.

And for the estimation of the temperature T and of its derivative dT / dθ one supposes the perfect gases so as to be able to write:

J_ dT _ J_ dp _ ^ dV T dθ ^~ p dθ ⁺ V dθ

In order not to reintroduce the derivative dp of the pressure into the expression of C, it is preferred to discretize this expression and make it iterative. In particular, the following expression is used: 1 T _e - T _e _ _Ae _ 1 p _e - p _e _ _{Ae |} 1 Fri - Aug- _A

T _θ Δθ p _θ Δθ V _θ Δθ with Δθ an angular constant.

It can be deduced that the temperature is iteratively estimated at the angle θ as a function of the temperature at the angle Θ-ΔΘ by an expression of the type:

1

T ₀ = T, Θ-ΔΘ

Pe- Δθ V,

+ - Θ-ΔΘ -1

Pe ^V Θ And, advantageously, the temperature is estimated at each angle θ as a function of an initial temperature corresponding to the temperature in the cylinder at a time when an intake valve closes.

It will be noted that, alternatively, it is possible to use an initial temperature which depends on a measurement of an air temperature admitted into the engine. In all cases, from this recursive expression of the temperature, the expression (1) above is easily deduced.

As will be understood, in the method of the invention the quantity C is therefore estimated during a cycle. If during this cycle it has remained above a predetermined threshold value S2, it is considered that there has been no misfire.

And we assign a low value 0 to yc (k), for example the value 0.

In the opposite case where the quantity C has remained below the threshold S2 until the end of the combustion cycle, a strong value is assigned to yc (k), for example the value 1.

In all the cases described above, it will be noted here that the threshold values can be determined once and for all at the time of engine tuning, for example on a test bench. For example, in the case of the threshold value S 2 to be compared with the quantity C, the value 0.5 will preferably be used in the example mentioned above.

The threshold values can also be variable in time.

For example, it is advantageous to vary certain threshold values according to an operating point of the engine, preferably an amount of fuel injected per cycle in the combustion chamber or a motor speed.

Of course, the present invention is not limited to the embodiment described above and shown in the drawings.

In particular, those skilled in the art can easily determine other actions to implement once they have detected a failure and / or loss of combustion according to the method of the invention.

Moreover, other quantities than those mentioned above can be used in the context of this process, as long as they lead to a diagnosis of misfires and combustion losses. In this respect, the method also applies in the case of diesel combustion or homogeneous gasoline (HCCI type) than in the case of conventional combustion in gasoline or diesel.

Similarly, those skilled in the art will clearly identify other sliding average criteria that can be used to conclude that a misfire and / or loss of combustion has occurred.

Claims

1. A method of controlling an engine characterized in that it comprises a step where it is determined the possible occurrence of a loss or misfires in a combustion chamber of the engine by comparing

(102) the value of a sliding average of a predetermined magnitude (101) of the motor at a predetermined threshold value.

2. Method according to claim 1, characterized in that it further comprises a step (107) where one modifies at least one value of the magnitude which is taken into account in the sliding average, when one of the failures of combustion is detected.

3. Method according to claim 2, characterized in that the value of the quantity which is taken into account for the first time in the determination of the sliding average is modified.

4. Method according to claim 2, characterized in that the modification of the value consists in replacing it by that of an average carried out on a number m of values of the magnitude less than a number n of values taken into account in the average. slippery or by the last determined value of the sliding average.

5. Method according to one of claims 2 to 4, characterized in that it implements the step of changing the value of the size if it has been determined the presence of a loss of combustion.

6. Method according to one of the preceding claims, characterized in that it further comprises a step (107) where the values taken into account in the sliding average are initialized if it has been determined the presence of a loss of combustion.

7. Method according to one of the preceding claims, characterized in that one determines the possible presence of each of the misfires by comparing (200) the value of the quantity to a predetermined threshold value.

8. Method according to one of the preceding claims, characterized in that the quantity is selected from the following group: a pressure of a gas in a cylinder of the engine, a mean pressure indicated in the cylinder, a specified specific consumption of a fuel injected into the cylinder, a torque of the engine.

9. Method according to one of the preceding claims, characterized in that the size depends on an energy release of a gas present in the combustion chamber.

10. Method according to claim 9, characterized in that the magnitude is estimated iteratively at a crankshaft angle and in that this iterative estimate is in a form of the type: _c

where C is the estimated quantity, θ the crankshaft angle, γ the ratio of specific heats (Cp and Cv), V the volume of a cylinder of the combustion chamber, and p and T a pressure and a temperature in the cylinder .