FR3134149A1 - Injection system configured for stabilizing the richness value of an air-fuel mixture as a function of the current oxygen storage capacity of a catalyst - Google Patents

Abstract

This air and fuel injection system (4) for an automobile vehicle (2) engine (6), for producing an air-fuel mixture, comprises a device (26) for timing the injection of fuel, the timing device (26) being configured to maintain the richness of the air-fuel mixture stable for a determined duration as a function of a ratio between a current oxygen storage capacity and a reference oxygen storage capacity in a catalyst (16) of a system (14) for treating polluting species from an exhaust line (8) of the automobile vehicle (2). Figure for abstract: Fig 1

Description

Injection system configured for stabilizing the richness value of an air-fuel mixture as a function of the current oxygen storage capacity of a catalyst

The present invention relates to an air and fuel injection system for a motor vehicle engine.

In particular, the present invention relates to maintaining a stable value of the richness of the air-fuel mixture injected during a gear change of a vehicle gearbox for a determined period.

Generally speaking, the present invention applies to driving situations in which a reduction in the richness of the injected air-fuel mixture causes an increase in the emission of polluting species, in particular nitrogen oxides (NOx).

Previous techniques

A motor vehicle equipped with a combustion engine is generally equipped with a system for post-treatment of polluting species in the vehicle's exhaust gases in order to reduce emissions of these polluting species.

The post-treatment system of a spark-ignition engine (the type running on gasoline in particular) generally includes a three-way catalyst. The treatment efficiency of different pollutant species depends on the quantity of oxygen stored in the catalyst.

When the quantity of oxygen stored is close to zero, the oxidation efficiency of certain polluting species decreases, such as for unburned hydrocarbons and carbon monoxide.

When the quantity of oxygen stored is close to the oxygen storage capacity of the catalyst, the oxidation efficiency of other polluting species decreases, such as for example nitrogen oxides.

The quantity of oxygen stored in the catalyst depends on the injection of an air-fuel mixture.

During certain driving situations, for example when changing gear, fuel injection is automatically cut off to reduce fuel consumption and air is sent into the after-effect system. treatment. The quantity of oxygen stored in the catalyst then increases, for example up to the maximum value of the storage capacity of the catalyst, and polluting species are no longer treated effectively, more particularly nitrogen oxides (NOx) essentially comprising nitric oxide and nitrogen dioxide.

When fuel injection resumes, when the amount of oxygen stored in the catalyst has reached the oxygen storage capacity and the catalyst is saturated with oxygen, a catalyst purge strategy is generally performed. The catalyst purge strategy includes an increase in the richness of the injected air-fuel mixture to a richness greater than 1, that is to say an increase in the proportion of fuel in the injected air-fuel mixture so that said proportion of fuel is greater than that present in the stoichiometric air-fuel mixture, so as to rapidly reduce the quantity of oxygen stored in the catalyst. However, the catalyst bleeding strategy significantly increases the vehicle's fuel consumption.

It is known that the richness of the injected air-fuel mixture influences the quantity of oxygen stored in the catalyst. Thus, a solution to limit the increase in the quantity of oxygen stored in the catalyst, for example when changing the gearbox ratio, is to maintain the richness of the injected air-fuel mixture in stoichiometric proportions by delaying the fuel injection cutoff previously mentioned so as not to saturate the catalyst with oxygen. The delay before fuel injection is cut off is generally set at a predetermined and constant duration. In particular, the constant duration does not depend on the state of wear of the vehicle and more particularly on the variation in the oxygen storage capacity of the catalyst during its aging, which leads to excess fuel consumption or saturation. of the catalyst into oxygen. The oxygen storage capacity of an aged catalyst compared to another new catalyst can, for example, vary by 35%.

The present invention therefore aims to overcome all or part of the aforementioned drawbacks and proposes an injection system for a motor vehicle engine making it possible to reduce the emission of polluting species and/or the fuel consumption of the vehicle.

The subject of the present invention is an air and fuel injection system for a motor vehicle engine, for producing an air-fuel mixture, comprising a fuel injection timing device, the timing device being configured to maintain the richness of the air-fuel mixture stable for a determined period as a function of a ratio between a current oxygen storage capacity and a reference oxygen storage capacity in a catalyst of a species treatment system pollutants from a motor vehicle exhaust line.

Thus, the present invention makes it possible to adapt the injection of fuel and air according to the current oxygen storage capacity of the catalyst, which varies depending on the state of wear of the catalyst.

Advantageously, the reference oxygen storage capacity is an average of the current oxygen storage capacities measured on several new and/or little-used catalysts.

Advantageously, the duration is zero when the ratio is greater than a predetermined ratio.

Optionally, the system comprises a driving situation detector configured to determine the driving situation of the motor vehicle, the timing device being configured to adapt the duration to the detected driving situation.

In one embodiment, the system includes means for determining the current oxygen storage capacity of the catalyst.

Advantageously, the timing device comprises a means of controlling the air and fuel injection parameters of the injection system intended to control the richness of the injected air-fuel mixture.

The present invention also relates to a motor vehicle comprising a system for treating polluting species comprising a catalyst, comprising an injection system as defined above.

The present invention also relates to a method for timing fuel injection in an injection system of a motor vehicle as defined above and comprising the following steps:

- Measurement of the current oxygen storage capacity of the catalyst;

- Calculation of a ratio between the current oxygen storage capacity and a reference oxygen storage capacity;

- Calculation of a duration based on the calculated ratio; And

- Maintaining the richness of the injected air-fuel mixture at a constant value during the calculated duration.

Advantageously, the duration is zero when the ratio is greater than a predetermined ratio and increases when the ratio decreases.

In one mode of implementation, the method is implemented during a gear change of a gearbox of the motor vehicle.

Other objectives, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

schematically illustrates a motor vehicle comprising an injection system according to the invention;

schematically illustrates the steps of a method for timing the injection of an engine of a motor vehicle according to the invention;

schematically illustrates variations in parameters of an injection system according to the invention around a driving situation; And

schematically illustrates a variation of a delay duration as a function of the ratio between a current oxygen storage capacity of a catalyst and a reference oxygen storage capacity.

Detailed presentation of at least one embodiment

We have shown schematically on the a motor vehicle 2 comprising an injection system 4 according to the invention. The vehicle 2 includes a spark-ignition engine 6 and an exhaust line 8.

The injection system 4 comprises an air injection housing 10 comprising for example an air intake throttle body and an intake manifold. The injection system 4 comprises a fuel injection unit 12 comprising for example a high pressure fuel injection pump and fuel injectors. The injection system 4 thus makes it possible to produce an air-fuel mixture.

The exhaust line 8 comprises a system 14 for treating polluting species provided with a catalyst 16, called a three-way catalyst, for the treatment of carbon monoxide, unburned hydrocarbons and nitrogen oxides contained in gases. combustion of engine 6.

Advantageously, the injection system 4 comprises means 17 for determining an oxygen storage capacity of the catalyst 16, in other words a current storage capacity OSC (illustrated below on the ). The determination means 17 comprise for example a proportional type oxygen probe 18 positioned in the exhaust line 8 downstream of the catalyst 16 for measuring a quantity of oxygen stored OS in the catalyst 16 and a mode module operating mode of the engine 6 (not shown) allowing a transition between two operating modes of the engine 6, in particular between a lean operating mode comprising a cut-off of the fuel injection and a rich operating mode comprising a richness of the RM air mixture -fuel injected greater than or equal to 1.

The determination means 17 may also include a temperature sensor 20 positioned in the exhaust line 8 downstream of the catalyst 16 for determining the temperature of the catalyst 16 and an exhaust gas flow probe 22 positioned in the line 8 exhaust upstream of the catalyst 16 for measuring the flow rate of the exhaust gases passing through the catalyst 16.

The current oxygen storage capacity OSC of the catalyst 16 can advantageously be determined regularly using the determination means 17, for example by analyzing the behavior of the catalyst 16 during a voluntary transition between two operating modes of the engine 6. In particular , we can use a known method described in publication FR3033364A1.

In one embodiment, the injection system 4 comprises a calculator device 24 making it possible to calculate a ratio R between the current oxygen storage capacity OSC of the catalyst 16 and a reference storage capacity OSCr. The reference storage capacity OSCr is for example calculated as the average of the current oxygen storage capacity OSC of several new catalysts 16 or as the average of the current oxygen storage capacity OSC of several rarely used catalysts 16, i.e. that is to say catalysts 16 whose state of wear corresponds to the state of wear of a catalyst 16 of a new automobile vehicle 2 having driven a maximum of 3000 km. The value of the ratio R makes it possible to determine the state of aging of the catalyst 16. When the ratio R is close to 1, for example greater than 0.95, the calculator device 24 determines that the catalyst 16 is new or recent. When the ratio R decreases, for example below 0.7, the calculator device 24 determines that the catalyst 16 is aged.

The injection system 4 further comprises a timing device 26 configured to maintain the richness of the mixture RM stable for a duration T determined as a function of the current oxygen storage capacity OSC of the catalyst 16. The duration T is more particularly determined as a function of the ratio R. The richness of the injected air-fuel mixture RM is for example kept stable during a particular SC driving situation such as a change of gear in a gearbox.

The timing device 26 comprises a means 28 for controlling the injection parameters of the air injection unit 10 and the fuel injection unit 12. The means 28 for controlling the injection parameters is therefore configured so as to control the richness of the RM air-fuel mixture injected.

Advantageously, the injection system 4 comprises a driving situation detector SC (not shown) so as to determine the driving situation SC of the automobile vehicle 2. The SC driving situation detector makes it possible, for example, to detect an SC driving situation such as a change of gear in a gearbox or a deceleration phase on a downhill road.

Furthermore, the driving situation detector SC associates a characteristic average duration with the driving situation SC. When the characteristic average duration is for example three times longer than the delay duration T, the quantity of oxygen stored OS in the catalyst 16 approaches the current oxygen storage capacity OSC of the catalyst 16 during the driving situation SC . In particular, the difference between the quantity of stored oxygen OS and the current oxygen storage capacity OSC is less than a difference in the quantity of oxygen M when the average duration characteristic of the driving situation SC has elapsed. To avoid this situation, the driving situation detector SC communicates before the end of the delay duration T a setpoint to the delay device 26 so that the delay device 26 maintains stable the richness of the RM air-fuel mixture injected for a period of time. longer duration. Thus, the difference between the quantity of oxygen stored OS and the current oxygen storage capacity OSC remains greater than the difference in quantity of oxygen M during the driving situation SC.

We have shown schematically on the a method 30 for timing the injection of an engine 6 of a motor vehicle 2 comprising an injection system 4 as described above.

Firstly, during a first step 32, the current oxygen capacity OSC of the catalyst 16 is measured using the determination means 17.

Then, we carry out a step 34 of calculating the ratio R between the current oxygen storage capacity OSC of the catalyst 16 and the reference oxygen storage capacity OSCr using the calculator device 24.

During the following step 36, the duration T is calculated as a function of the ratio R. The calculation step 36 can be carried out with the timing device 26 or with the calculator device 24.

Advantageously, a step 38 of detecting the driving situation SC is carried out with the driving situation detector SC.

Optionally, during the following step 40, the driving situation detector SC communicates a modification of the duration T to the timing device 26 so as to adapt the duration T to the driving situation SC.

Finally, a step 42 is carried out for stable maintenance of the richness of the RM air-fuel mixture during the calculated duration T, or the modified duration, thanks to the timing device 26 and the control means 28.

When implementing this method 30, the duration T is for example zero when the ratio R is greater than a predetermined ratio Rr and the duration T increases when the ratio R decreases.

Advantageously, the method 30 is implemented during a gear change of a gearbox of a thermal automobile vehicle 2.

We have shown schematically on the the variation of automobile operating parameters before, during and after a driving situation SC and in particular during the implementation of the steps of the method 30 according to the invention. The automobile operating parameters include in particular the richness of the injected air-fuel mixture RM, the quantity of oxygen stored OS in the catalyst 16, the pressure P in the intake manifold, the speed V of the vehicle 2 and the quantity of nitrogen oxides NOx emitted by the vehicle 2.

The driving situation SC includes for example a gear change of a manual or automatic gearbox of the vehicle 2 or a deceleration phase of the vehicle occurring after a stabilized operating phase at constant speed V, with a tolerance of 5%, and occurring before an acceleration phase.

The driving situation SC occurs for example after a first injection phase P1. The SC driving situation includes a second injection phase P2. A third injection phase P3 occurs after the driving situation SC.

The first injection phase P1 comprises for example a stabilized operating phase at constant speed V, with a tolerance of 5%, during which the quantity of oxygen stored OS in the catalyst 16 is close to a quantity of Optimal stored oxygen OSo to optimally treat polluting species. For example, when the quantity of oxygen stored OS in the catalyst 16 is the optimal quantity of oxygen stored OSo the automobile vehicle 2 emits little or no nitrogen oxide. In addition, during the first injection phase P1, the air intake throttle body is open, the pressure P in the intake manifold is constant, within 5%, the exhaust flow is constant, to within 5%, and the richness of the injected RM air-fuel mixture is for example close to 1.

The second injection phase P2 comprises for example a phase during which the speed V of the vehicle 2 decreases, for example following the driver's lifting of the foot relative to the accelerator pedal. When lifting the foot, the air intake throttle body is for example closed so that the air intake decreases and the pressure P in the collector reaches a constant pressure Pc.

In order to compensate for the excess of oxygen in the catalyst 16, the timing device 26 keeps the richness of the RM air-fuel mixture injected stable for the duration T, for example at a richness of the RM air-fuel mixture close to 1 for 0.3 seconds so that the quantity of oxygen stored OS in the catalyst 16 remains constant to within 5% during the duration T. Once the duration T has elapsed, the timing device 26 cuts off the fuel injection of so that the richness of the injected RM air-fuel mixture decreases to zero richness, a torque setting of the engine 6 is then zero and the quantity of oxygen stored OS in the catalyst 16 increases.

Optionally, the timing device 26 reduces the richness of the RM air-fuel mixture to a non-zero value then the timing device 26 maintains the richness of the injected RM air-fuel mixture stable for the duration T. In another mode of implemented, the timing device 26 adapts the richness of the RM air-fuel mixture injected during the duration T, for example by linearly decreasing the richness of the RM air-fuel mixture injected during the duration T.

Advantageously, the duration T during which the richness of the injected air-fuel mixture RM is kept stable allows the quantity of oxygen stored OS in the catalyst 16 to remain lower than the current oxygen storage capacity OSC of the catalyst 16. Optionally the second injection phase P2 includes a gear change phase of a manual gearbox.

The third injection phase P3 comprises for example an acceleration phase of the vehicle 2 and/or coupling following the gearbox gear change. The third injection phase P3 comprises for example the opening of the air intake throttle body, the increase in the exhaust flow and the increase in the richness of the injected air-fuel mixture RM, for example at a wealth close to 1.

Advantageously, at the start of the third injection phase P3, the quantity of oxygen stored OS in the catalyst 16 is less than the current oxygen storage capacity OSC of the catalyst 16. Thus, the catalyst 16 is not saturated with oxygen. An adjustment of the richness value close to 1 allows for example a progressive return of the quantity of oxygen stored OSo in the catalyst 16 to the optimal quantity of oxygen stored OSo. In addition, the emission of nitrogen oxide NOx increases little or is zero during the third injection phase P3, regardless of the state of wear of the catalyst 16

We have shown schematically on the a variation of the delay duration T as a function of the ratio R between a current oxygen storage capacity OSC of a catalyst 16 and a reference oxygen storage capacity OSCr. In this example, the duration T is zero when the catalyst 16 is new or recent, for example when the ratio R is less than a predetermined ratio Rr, here a predetermined ratio Rr of 0.7. Furthermore, the current oxygen storage capacity OSC of the catalyst 16 is close to the reference oxygen storage capacity OSCr and during the driving situation SC the catalyst 16 does not saturate with oxygen.

When the catalyst 16 is aged, the ratio R necessarily decreases and the delay time T increases while the ratio R decreases. When the ratio R is between 0.7 and 0.6, the duration T varies linearly as a function of the ratio R according to a first slope. When the ratio R is between 0.6 and 0.2, the duration T varies linearly as a function of the ratio R according to a second slope.

Advantageously the first and second slopes are chosen so that the difference between the quantity of stored oxygen OS and the current oxygen storage capacity OSC remains greater than the difference in quantity of oxygen M described previously. For example, the driving situation SC includes a gearbox gear change of known average duration and the difference in the quantity of oxygen M is 10 mmol of oxygen.

Claims (10)

Air and fuel injection system (4) for an engine (6) of a motor vehicle (2), for producing an air-fuel mixture, characterized in that it comprises a timing device (26). of fuel injection, the timing device (26) being configured to maintain the richness of the air-fuel mixture (RM) stable for a duration (T) determined as a function of a ratio (R) between a storage capacity in current oxygen (OSC) and a reference oxygen storage capacity (OSCr) in a catalyst (16) of a system (14) for treating polluting species of an exhaust line (8) of the vehicle (2 ) automobile. System (4) according to claim 1, in which the reference oxygen storage capacity (OSCr) is an average of the current oxygen storage capacities (OSC) measured on several new and/or little used catalysts (16). System (4) according to any one of claims 1 and 2, in which the duration (T) is zero when the ratio (R) is greater than a predetermined ratio (Rr). System (4) according to any one of claims 1 to 3, comprising a driving situation detector (SC) configured to determine the driving situation (SC) of the motor vehicle (2), the timing device (26) being configured to adapt the duration (T) to the driving situation (SC) detected. System (4) according to any one of claims 1 to 4, comprising means (17) for determining the current oxygen storage capacity (OSC) of the catalyst (16). System (4) according to any one of claims 1 to 5, in which the timing device (26) comprises means (28) for controlling the air and fuel injection parameters of the system (4) d injection intended to control the richness of the injected air-fuel mixture (RM). Motor vehicle (2) comprising a system (14) for treating polluting species comprising a catalyst (16), characterized in that it comprises an injection system (4) according to any one of claims 1 to 6. Method (30) for timing fuel injection in an injection system (4) of a motor vehicle (2) according to any one of claims 1 to 7, characterized in that it comprises the following steps :

• Measurement of the current oxygen storage capacity (OSC) of the catalyst (16);
• Calculation of a ratio (R) between the current oxygen storage capacity (OSC) and a reference oxygen storage capacity (OSCr);
• Calculation of a duration (T) based on the ratio (R) calculated; And
• Maintaining the richness of the injected air-fuel mixture (RM) at a constant value during the calculated duration (T).

Method (30) according to claim 8 in which the duration (T) is zero when the ratio (R) is greater than a predetermined ratio (Rr) and increases when the ratio (R) decreases. Method (30) according to any one of claims 8 and 9, implemented during a gear change of a gearbox of the automobile vehicle (2).