WO2019239025A1

WO2019239025A1 - Method for detecting an oxidation catalyst in the exhaust line of a diesel engine and a law for controlling the implementation thereof

Info

Publication number: WO2019239025A1
Application number: PCT/FR2019/051203
Authority: WO
Inventors: Jean Francois LEGROS; Jean BARATTE
Original assignee: Psa Automobiles Sa
Priority date: 2018-06-11
Filing date: 2019-05-24
Publication date: 2019-12-19
Also published as: FR3082236B1; EP3803073A1; FR3082236A1

Abstract

The invention relates to a method for detecting a catalyst in an exhaust line, characterised in that it comprises the following operations: - shutting down the engine and thermally stabilising the exhaust line to achieve a balance between the temperature upstream (T4) and the temperature (T5) downstream of the catalytic region, - starting up the engine and recording the charging time (t1) at the end of which the upstream temperature reaches a predetermined threshold (T4s) corresponding to a minimum thermal input in the catalytic region, and recording the transfer time (t2) at the end of which the downstream temperature reaches a predetermined temperature threshold (T5s) corresponding to the passage of said input through said region, - calculating the interval (t3) between the charging time and the transfer time and - comparing said interval with a reference period (t3s) to determine if said interval is greater than or equal to said period.

Description

Method of detecting an oxidation catalyst in the exhaust line of a diesel engine and use of said method for motor vehicles equipped with diesel engines

The invention relates to a method for the detection of an oxidation catalyst in the exhaust line of a diesel engine.

More particularly, the invention relates to a method for diagnosing the possible presence of an active oxidation catalyst in the exhaust line of a diesel-powered vehicle as well as a control law for the implementation of said process.

The invention also relates to the use of this detection method for integration into the control laws of diesel engines conforming to the Euro 6.3 standard.

PRIOR STATE OF THE ART

In general, the modes of detection of the presence of an active oxidation catalyst in an exhaust line of a combustion engine use the energy absorption properties of the catalyst.

The presence of a catalyst causes a temperature difference between the upstream and downstream of the catalytic zone which is higher than in the absence of the catalyst under identical diagnostic conditions.

The absorption capacity of the catalyst can therefore be evaluated by measuring the temperatures upstream and downstream of the catalytic zone of the exhaust line, after a first start of the engine following a preliminary rest period at the end of which the temperatures, upstream and downstream of this zone, are uniform and substantially equal to the outside temperature.

The known methods thus consist in measuring the difference between the temperature T4 upstream of the catalyst and the temperature T5 downstream, respectively, in the initial rest phase (T4i, T5i) and in steady engine operating conditions ( T4, T5). When predefined diagnostic conditions are met (mentioned below), the calculation of a parameter called “enthalpy” is then launched using the following formula: absolute value of (((T4-T4i) - (T5 -T5i))) / (273.15 + T4- 0.5x (T4i-T5i)) which is integrated as a function of time.

When the value of this integral exceeds a calibrated and fixed threshold value, it is concluded that a catalyst is present in the catalytic zone. On the other hand, if this threshold is not exceeded after a certain time, under the conditions of activation of the diagnosis (these conditions being modifiable), it is concluded that the catalyst is not present.

Temperature conditions, the duration of the rest phase with engine shutdown and the minimum and maximum quantity of diesel injected, make it possible to decide when the calculation of the enthalpy integral must be carried out. These conditions generally constitute the prerequisites for activating the diagnostic phase.

Traditional methods, such as that described in US 2011/0143449, thus consist of setting the time after the engine starts at which the temperature measurements are made. These temperatures are then compared with reference values to determine the possible presence of a catalyst.

The methods described in US 2016/0363032 and in DE 10 2014 203327 provide temperature threshold values for ruling on the presence of a catalyst but without imposing a waiting period before performing the measurements .

However, it has been demonstrated that the value of the enthalpy (and therefore that of its integral) depends on several parameters and mainly on the quantity of fuel injected which conditions the rise in temperature upstream.

In addition, depending on the operating conditions of the engine after starting: idling with or without air conditioning, vehicle movement, etc., the enthalpy is also strongly impacted, which results in significant dispersion of the diagnostic results . Indeed, the influence of the engine load results in a certain amount of heat entering the catalytic zone. As a result, a test with a high engine load but without catalyst leads to the same result, as regards the calculation of the diagnostic criterion, as a test with a low engine load and a catalyst.

Consequently, it is very difficult, if not impossible, with current detection methods, to reliably diagnose the presence or absence of the catalyst.

In this context, it appeared necessary to improve the known methods by simplifying their implementation while seeking to obtain a higher level of confidence in the results of the diagnosis.

STATEMENT OF THE INVENTION

To solve the technical problems posed by the prior art, the invention consisted in not only taking into account the temperature differences between the upstream and downstream of the catalytic zone but to consider the time elapsed between a instant corresponding to reaching an upstream temperature threshold after starting the engine and an instant corresponding to reaching a downstream temperature threshold.

This object is achieved, according to the invention, by means of a method of detecting the oxidation catalyst in the exhaust line of a diesel engine by measuring the temperatures upstream and downstream of the catalytic zone. , characterized in that it comprises the following operations:

- engine shutdown and thermal stabilization of the exhaust line to achieve a balance between the upstream temperature and the downstream temperature of the catalytic zone,

- engine start-up and joint recording, on the one hand, of the charging time at the end of which the upstream temperature reaches a predetermined threshold corresponding to a minimum heat input into the catalytic zone and, on the other hand, of the transfer time at the end from which the downstream temperature reaches a predetermined temperature threshold corresponding to the passage of said heat input through the catalytic zone,

- calculation of the interval between the charging time and the transfer time and,

- Comparing said interval with a reference duration to determine whether said interval is greater than or equal to said duration.

According to an advantageous characteristic, the threshold of the downstream temperature is lower than the threshold of the upstream temperature.

According to a first variant implementation of the method of the invention, if the interval between the charging time and the transfer time is greater than or equal to the reference duration, it is concluded that the catalyst is present the catalytic zone or otherwise its absence.

According to a second variant implementation of the method of the invention, if the interval between the charging time and the transfer time is greater than or equal to the reference duration, the integral is calculated of the enthalpy defined by the formula: absolute value of (((T4-T4i) - (T5-T5i))) / (273.15 + T4-0.5x (T4i-T5i)) where T4i and T5i are the values initials, respectively, of the upstream temperature (T4) and the downstream temperature (T5) at the end of the stabilization operation.

According to a characteristic of this second variant, if the value of the enthalpy is greater than or equal to a predetermined threshold, it is concluded that the catalyst is present in the catalytic zone or otherwise is absent.

This variant increases the numerical difference between the tests with and without catalyst because the calculation of the enthalpy integral is dependent on the presence of the catalyst and that its value increases faster when a catalyst is present.

Yet another variant implementation of the method as defined above is characterized in that when at time (t2) the downstream temperature has reached the threshold value, then the end Boolean indicator diagnostic (END) goes to 1 signifying that the diagnostic result is then reliable, and that simultaneously the time counter (t3), initiated when the upstream temperature has reached the threshold value, has not exceeded a threshold value corresponding to the reference duration (t3s), then the Boolean diagnostic result (RES) is 1 indicating the absence of a catalyst.

Yet another object of the invention is a use of the detection method having the characteristics defined above for diesel vehicles and, in particular, for integration into the control laws of diesel engines conforming to the Euro standard. 6.3.

The method of the invention takes into account the energy supplied to the catalyst to reliably distinguish the presence or absence of the catalyst

While simplifying the calibration operations, the method of the invention allows a single adjustment for all diesel engines and the different shapes of motor vehicles, unlike previous methods. This setting can thus be pre-calibrated with a high level of confidence.

In addition, the method of the invention is robust to variations in the engine load conditions which makes it possible to avoid doubtful results and detection errors as to the presence or absence of the catalyst which are sources of recourse warranty.

The method of the invention thus offers, at the same time, an economic gain from the fact that the frequency of testing and control operations and the risks of replacing parts are significantly reduced and an improvement in the quality and Branding.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will emerge on reading the description which follows, with reference to the appended and detailed figures below.

Figures IA and IB are graphs illustrating an embodiment of the method of the invention, respectively, in the presence of a catalyst in the exhaust line and in the absence of such a catalyst. FIG. 2 is a block diagram illustrating an embodiment of the control law of the method of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Naturally, the embodiments described below are given only by way of nonlimiting examples. It is explicitly provided that one can combine these different modes to propose others.

The detection method of the present invention is based on the phenomenon of energy absorption by the catalyst.

The absorption capacity of the catalyst can be evaluated by observing the temperatures, respectively, upstream T4 and downstream T5 of the catalytic zone of the exhaust line, that is to say, the zone in which the catalyst provided is normally arranged.

These temperatures are observed during the first start of the engine after a thermal stabilization period, called "maceration", of the exhaust line, corresponding to the establishment of a balance between the upstream temperature T4 and the temperature downstream T5 from the catalytic zone. This stabilization phase guarantees the convergence of the temperatures of all the engine components and its exhaust line. At the end of this phase, the temperatures upstream T4, downstream T5 and that of the outside air are identical and stable.

The next step is to start the engine and then observe the temperature changes upstream and downstream of the catalytic zone.

11 is, in a first phase, to observe the gradual increases in the upstream temperature T4 and the downstream temperature T5, following start-up and after maceration. These increases correspond to the thermal energy input resulting from the combustion and exhaust of gases, at the entry then at the exit of the catalytic zone.

However, the observation of the increase in the downstream temperature T5 will be relevant, to determine the possible presence of the catalyst, only if there has been a sufficient supply of thermal energy upstream of the catalytic zone. It is considered that this energy supply is sufficient when the upstream temperature T4 reaches or exceeds, at the end of a charging time t1, a threshold T4s corresponding to a minimum and predetermined thermal contribution, as illustrated by FIGS. IA and IB.

The increase in temperature T5 downstream of the catalytic zone is also gradual but delayed compared to the increase in temperature upstream T4. This delay is explained by the transfer of the heat input from upstream to downstream through the catalytic zone. The transfer time t2 depends on the length of this zone and on the presence or absence of a catalyst capable of absorbing, at an intermediate level, at least part of the initial heat input.

For these same reasons, the downstream temperature T5 will generally be lower (or occasionally equal) than the upstream temperature T4, whatever the observation time.

At the same time, the method of the invention provides for fixing a threshold of the downstream temperature T5s corresponding to the passage of the heat input through the catalytic zone and to its arrival at the point of observation of the temperature T5 in a transfer time t2.

The method of the invention consists in correlatively recording the charging time tl and the transfer time t2 under which the upstream temperature T4 and the downstream temperature T5 reach their predetermined thresholds T4s and T5s.

According to a first variant of the method, it is the results of these time measurements which make it possible to conclude on the presence or absence of a catalyst in the catalytic zone of the exhaust line.

Indeed, the interval (t2-tl), referenced t3, between the charging time tl and the transfer time t2 represents the delay in the rise in temperature T5 to the threshold T5s, at the output of the catalytic zone.

The invention provides for fixing a threshold time value or reference duration t3s corresponding to the positive value interval t2-tl and calculated in considering the presence of a catalyst having a capacity for absorbing the given thermal energy which is the cause of the delay.

Under these conditions, if the interval between the charging time tl and the transfer time t2 is greater than or equal to this reference duration t3s, it can be concluded that the catalyst is present in the catalytic zone, as illustrated by Figure IA.

On the other hand, if this interval is less than the reference duration see negative (t2 then being less than tl), it can be concluded that there is a rapid or even anticipated rise in the downstream temperature T5 to T5s which reflects the absence of a catalyst in the catalytic zone, as illustrated in FIG. 1B. According to another variant of the method of the invention, if the interval between the charging time tl and the transfer time t2 is greater than or equal to the reference duration t3s, the calculation of the integral is then carried out the enthalpy defined by the following formula in absolute value;

((T4-T4i) - (T5-T5i)) / (273.15 + T4-0.5x (T4i-T5i)) where T4i and T5i are the initial temperatures, respectively, upstream and downstream at the end of the phase stabilization or maceration.

If the value of the enthalpy is greater than or equal to a predetermined threshold, the diagnosis concludes with the presence of the catalyst in the catalytic zone or otherwise with its absence. The detection method of the invention is associated with the control law described below and illustrated in Figure 2.

When at time t2 the downstream temperature T5a reaches the threshold value T5s, then the boolean end of diagnosis indicator (END) changes to 1 signifying that the result of the diagnosis is then reliable, and that simultaneously the counter time t3, initiated when the upstream temperature T4a reaches the threshold value T4s, has not exceeded the threshold value corresponding to the reference duration t3s, then the boolean diagnostic result (RES) is 1 indicating the absence of a catalyst. The method of the invention applies to the detection of the oxidation catalyst in the exhaust lines for integration into the control laws of diesel engines in accordance with the Euro 6.3 standard.

Claims

claims

1. Method for detecting an oxidation catalyst in the exhaust line of a diesel engine by measuring the temperatures upstream (T4) and downstream (T5) of the catalytic zone, characterized in that it comprises the operations following:

- engine shutdown and thermal stabilization of the exhaust line to achieve a balance between the upstream temperature (T4) and the downstream temperature (T5) of the catalytic zone,

- starting the engine and joint recording, on the one hand, of the charging time (tl) at the end of which the upstream temperature (T4) reaches a predetermined threshold (T4s) corresponding to a minimum thermal contribution in the catalytic zone and, on the other hand, the transfer time (t2) at the end of which the downstream temperature (T5) reaches a predetermined threshold (T5s) of temperature corresponding to the passage of said heat input through the catalytic zone,

- calculation of the interval (t3) between the charging time (tl) and the transfer time (t2) and,

comparing said interval with a reference duration (t3s) to determine whether said interval is greater than or equal to said duration.

2. Detection method according to claim 1, characterized in that the threshold of the downstream temperature (T5s) is lower than the threshold of the upstream temperature (T4s).

3. Detection method according to one of the preceding claims, characterized in that if the interval (t3) between the charging time (tl) and the transfer time (t2) is greater than or equal to the reference duration ( t3s), it is concluded that the catalyst is present in the catalytic zone or otherwise is absent.

4. Detection method according to one of claims 1 or 2, characterized in that if the interval between the charging time (tl) and the transfer time (t2) is greater than or equal to the reference duration (t3s ), the integral of the enthalpy defined by the formula is calculated:

absolute value of (((T4-T4i) - (T5-T5i))) / (273.15 + T4-0.5x (T4i-T5i)), where T4i and T5i are the initial values, respectively, of the upstream temperature (T4) and the downstream temperature (T5) at the end of the stabilization operation.

5. Detection method according to the preceding claim, characterized in that if the value of the enthalpy is greater than or equal to a predetermined threshold, it is concluded that the catalyst is present in the catalytic zone or otherwise is absent.

6. Detection method according to one of the preceding claims, characterized in that, when at time (t2) the downstream temperature (T5) has reached the threshold value (T5s), then the boolean indicator of end diagnostic (END) goes to 1 meaning that the diagnostic result is then reliable, and that simultaneously the time counter (t3), initiated when the upstream temperature (T4) has reached the threshold value (T4s), has not exceeded the threshold value corresponding to the reference duration (t3s), then the boolean diagnostic result (RES) is 1 indicating the absence of a catalyst

7. Use of the detection method according to one of claims 1 to 6, for motor vehicles equipped with diesel engines.