System and method for controlling internal combustion engine during foot lift phase

Abstract

A method for controlling a spark-ignited internal combustion engine (10) of a motor vehicle, provided with a variable valve timing system (50, 52) and a system (40) for purifying contaminants, the system (40) comprising at least one three-way catalyst (42a), the method comprising the following consecutive steps: cutting off the fuel injection when a foot lift phase is detected, and a subsequent step of maintaining the cutting until the injection is resumed; overlapping the intake valve (51) and the exhaust valve (53); -performing a de-overlap of the intake valve (51) and the exhaust valve (53) when a non-zero torque request, or a predetermined re-injection speed, or an engine disengagement is detected; and resuming the injection.

Description

Technical Field

[0001] The technical field of this invention is the control of spark-ignition internal combustion engines, and more specifically, the control of such engines in order to reduce the emission of pollutants. Background Technology

[0002] Motor vehicles equipped with spark-ignition internal combustion engines (especially gasoline-powered types) are equipped with after-treatment systems to treat pollutants in their exhaust to meet pollution control standards. These after-treatment systems typically include a three-way catalytic converter capable of oxidizing unburned hydrocarbons (HC) and carbon monoxide (CO) and reducing nitrogen oxides (NOx).

[0003] Spark-ignition engines operate essentially with a richness of 1 (i.e., the air-fuel mixture is stoichiometric), and the amount of fuel injected into the engine is typically regulated to maintain a richness of around 1 in a closed-loop manner.

[0004] However, to optimize the treatment efficiency for different pollutants, it is also known to adjust the amount of fuel injected into the engine to regulate the amount of oxygen stored in the catalyst according to a set value, also known as OS (short for Oxygen Storage). This set value is a predetermined value that lies strictly between zero and the maximum oxygen storage capacity of the catalyst, also known as OSC (short for Oxygen Storage Capacity).

[0005] This predetermined value is both far enough from zero to allow for sufficient oxidation of HC and CO, and far enough from the OSC value to allow for sufficient reduction of NOx. This value can be selected experimentally and depends on several parameters, including at least the flow rate of the combustion gases through the catalyst and the temperature of the catalyst.

[0006] For specific details, refer to the published document FR-A1-310110, which discloses a method for adjusting the amount of stored oxygen OS to a set value determined based on the flow rate of combustion gases through the catalytic converter and the temperature of the catalytic converter.

[0007] Generally speaking, the closer the amount of OS oxygen in the catalyst is to zero, the greater the reduction in oxidation efficiency of HC and CO. Conversely, the closer the amount of OS oxygen is to OSC, the lower the reduction efficiency of NOx.

[0008] During certain driving conditions, such as during gear shifts or the so-called "foot lift" phase (where the driver fully releases the accelerator pedal), fuel injection is automatically cut off to reduce fuel consumption, and air is sent to the aftertreatment system. The amount of oxygen stored in the catalytic converter then increases, for example, up to OSC, and once fuel is injected again, pollutants (especially NOx) are no longer effectively treated.

[0009] When fuel injection resumes, and the amount of oxygen stored in the catalyst has reached OSC (meaning the catalyst is oxygen-saturated), a strategy to purge or reduce the oxygen load on the catalyst is typically implemented. This catalyst scavenging strategy involves increasing the saturation of the injected air-fuel mixture to a saturation greater than 1 (i.e., increasing the proportion of fuel in the injected air-fuel mixture), making the proportion of fuel greater than the stoichiometric proportion of fuel present in the air-fuel mixture, thereby rapidly reducing the amount of oxygen stored in the catalyst. However, catalyst scavenging strategies significantly increase vehicle fuel consumption and CO2 emissions.

[0010] There are several ways to limit the flow of exhaust air during the fuel injection cut-off phase, thereby limiting the oxygen saturation of the catalytic converter.

[0011] For example, the throttle body at the intake can be closed to mechanically limit the flow of air drawn in at the intake, and thus limit the flow of air carried into the exhaust. However, in addition to the limited overall gain, this results in a drop in intake manifold pressure, which can lead to increased fuel consumption.

[0012] For example, in situations requiring zero torque (where you lift your foot off the accelerator), the engine can be disconnected from the transmission and left to idle, or even completely shut off. However, such a solution is incompatible with mechanical transmissions because it requires an automatic transmission system or at least one controlled clutch.

[0013] Document FR-A1-3120253 describes a method for controlling a spark-ignition engine to prevent the exhaust-mounted catalytic converter from being saturated with oxygen when there is no torque demand (typically during the lift-off phase). According to this document, the mass of air entering the engine is reduced by recirculating it to the exhaust intake via an exhaust gas recirculation (EGR) loop or by using a variable valve timing system, and fuel is injected after combustion to increase redundancy without burning fuel in the cylinder, i.e., without generating torque. However, such fuel injection increases vehicle fuel consumption and CO2 emissions. Furthermore, delayed fuel injection causes exothermic reactions in the catalytic converter, potentially damaging it. Summary of the Invention

[0014] The purpose of this invention is to eliminate NOx emission peaks during the acceleration phase following the accelerator pedal lift-off phase using an optimized engine control method, thereby avoiding oxygen saturation of the depollution system and eliminating the aforementioned fuel consumption and catalyst degradation problems.

[0015] The subject of this invention is a method for controlling a spark-ignition internal combustion engine in a motor vehicle, the internal combustion engine being equipped with a variable valve timing system and a pollution control system including at least one three-way catalytic converter.

[0016] The method comprises the following sequential steps:

[0017] - When the lift-off phase is detected, cut off fuel injection and maintain this cut-off until the subsequent step of resuming injection;

[0018] - Make the intake valve and exhaust valve overlap (cross);

[0019] - When a non-zero torque demand is detected, or a predetermined re-injection speed is reached, or the engine disengages, the intake and exhaust valves are uncrossed.

[0020] - Resume spraying.

[0021] Advantageously, when the flow rate of fresh air entering the engine exceeds a predetermined value, a step to resume injection is performed to prevent misfire.

[0022] Preferably, in the unoverlapping step, a zero value is assigned to the torque setpoint and held until injection resumes.

[0023] According to an advantageous feature, from the start of injection recovery, the value of the torque setpoint converges to the value requested by the driver.

[0024] For example, the convergence can be achieved using filters or time ramps.

[0025] According to another feature, the overlap of the intake and exhaust valves in each engine cycle has a duration ranging from 40°Vil to 120°Vil.

[0026] According to another aspect, the present invention relates to a control system for a spark-ignition internal combustion engine for a motor vehicle, the internal combustion engine being provided with a valve timing system and a system for purifying pollutants including at least one three-way catalytic converter, the control system including an electronic control unit and configured to implement the control method described above.

[0027] According to another aspect, the present invention relates to a spark-ignition internal combustion engine comprising a valve timing system and a system for purifying pollutants including at least one three-way catalytic converter, the engine being provided with a control system configured to implement the control method described above.

[0028] According to another aspect, the present invention relates to a motor vehicle equipped with an engine as described above. Attached Figure Description

[0029] Other objects, features, and advantages of the present invention will become apparent from the following description, which is given only by way of non-limiting embodiments and with reference to the accompanying drawings, wherein:

[0030] Figure 1 The structure of a motor vehicle internal combustion engine equipped with an engine control system according to the present invention is schematically shown;

[0031] Figure 2 The invention illustrates a method for controlling Figure 1 A flowchart of the method for using a motor; and

[0032] Figure 3 The diagram illustrates the changes over time in different parameters of a motor controlled by the control method according to the present invention. Detailed Implementation

[0033] exist Figure 1 In the example shown, the internal combustion engine 10 is of the spark-ignition type and includes, by way of example, three cylinders 12 arranged in a straight line, a fresh air intake manifold 14, an exhaust manifold 16, and a turbo compression system or turbocharger 18.

[0034] Cylinder 12 is supplied with air through intake manifold 14 or distributor, which is itself supplied by pipe 20 equipped with air filter 22 and compressor 18a of turbocharger 18 of engine 10.

[0035] The turbocharger 18 mainly includes an exhaust-driven turbine 18b and a compressor 18a mounted coaxially with the turbine 18b. The compressor 18a compresses the air distributed through the air filter 22 or airbox to increase the amount (mass flow rate) of air entering the cylinder 12 of the engine 10 for the same volumetric flow rate.

[0036] Therefore, the internal combustion engine 10 includes an intake circuit Ca and an exhaust circuit Ce.

[0037] The intake circuit Ca, from upstream to downstream in the air circulation direction, includes:

[0038] - Air filter 22;

[0039] - A flow meter 26 located inside the intake duct 20 and downstream of the air filter 22 is used to measure the actual mass flow rate of the air entering the engine 10.

[0040] - Intake valve 9;

[0041] - Compressor 18a of turbocharger 18;

[0042] - Throttle body 30 or air intake valve in the engine;

[0043] - Heat exchanger 32 is configured to cool the intake air corresponding to the mixture of fresh air and recirculated gas compressed in compressor 18a;

[0044] - Pressure and temperature sensor 33, used to measure pressure and temperature within intake manifold 14; and

[0045] - Intake manifold 14.

[0046] The compressor is associated with a bypass circuit equipped with an intake pressure relief valve 39, which opens when the throttle body 30 is suddenly closed (e.g., when the vehicle driver suddenly lifts his foot off the accelerator pedal) to prevent compressed air located between the compressor 18a and the throttle body 30 from flowing through the compressor 18a and causing damage to it.

[0047] The exhaust circuit Ce, from upstream to downstream in the direction of combustion gas flow, includes:

[0048] - Exhaust manifold 16;

[0049] - Turbocharger 18's turbine 18b; and

[0050] - A system 40 for purifying contaminants from engine combustion gases, which specifically includes a three-way catalytic converter.

[0051] The exhaust manifold 16 collects the exhaust gas produced by combustion and discharges it to the outside through the exhaust pipe 34, which is open at the inlet of the turbine 18b of the turbocharger 18, and the exhaust pipe 36 installed downstream of the turbine 18b.

[0052] Engine 10 also includes a partial exhaust gas recirculation circuit 38 called the EGR circuit.

[0053] The motor 10 may not have an EGR circuit, which does not depart from the scope of the present invention.

[0054] The circuit 38 is, in a non-limiting manner, a low-pressure exhaust gas recirculation circuit. It is connected to exhaust duct 36 at a point downstream of turbine 18b, and particularly downstream of the gas pollution control system, and returns exhaust gas to the fresh air supply duct 20 upstream of compressor 18a of turbocharger 18, particularly downstream of flow meter 26. Flow meter 26 measures only the flow rate of fresh air.

[0055] As shown in the figure, the recirculation loop 38 includes a cooler 38a, a filter 38b, and a valve 38c configured to regulate the flow rate of low-pressure exhaust gas in the direction of recirculated gas flow. The valve 38c is located downstream of the cooler 38a and the filter 38b, and upstream of the compressor 18a.

[0056] The engine exhaust pollution control system 40 includes a first aftertreatment device 42 and at least one first oxygen probe 43a installed upstream of the first aftertreatment device 42. The first aftertreatment device 42 includes at least one electrically heated three-way catalytic converter 42a.

[0057] The first upstream oxygen probe 43a is typically used to adjust the margin of the air-fuel mixture in the engine to a set value (e.g., a value of 1 corresponding to the stoichiometric ratio of the air-fuel mixture) in a closed-loop manner.

[0058] In addition, an optional second oxygen probe 43b (e.g., binary or proportional type) can be installed downstream of the first aftertreatment device 42 to enable calibration of the setpoint value of the surplus adjustment loop, specifically for adjusting the amount of oxygen stored in the catalyst 42a.

[0059] The gas purification system 40 also includes a second post-treatment device 44, which is a fine particulate filter. The system 40 may also include a third oxygen sensor 43c (e.g., binary type) connected downstream of the second device 44, for example for diagnostic purposes.

[0060] Engine 10 also includes a variable valve timing system 50 for the intake valves 51 of the engine, and optionally a variable valve timing system 52 for the exhaust valves 53 of the engine. The variable valve timing system 50 for the intake valves is equipped with a sensor 54 that can determine its angular position at any given time, corresponding to the defined times of opening and closing of the intake valves 51 during the engine's combustion cycle (these times are typically measured in crankshaft degrees relative to top dead center, denoted as °Vil). The variable valve timing system 52 for the exhaust valves, if present, is also equipped with a sensor 55 that can determine its angular position at any given time, also corresponding to the defined times of opening and closing of the exhaust valves 53 during the engine's combustion cycle.

[0061] The engine is associated with a fuel circuit that includes, for example, fuel injectors (not labeled) that inject gasoline directly from the fuel tank (not shown) into each cylinder.

[0062] In addition, the engine is equipped with a control system 60 of an electronic control unit 61, which is configured to control the various components of the internal combustion engine based on data collected by sensors at different locations on the engine.

[0063] The electronic control unit 61 includes a calculation module 62, a measurement module 63, and a control module 64.

[0064] Figure 2 A flowchart of the control method according to the present invention is shown.

[0065] The method begins with a previous step 65, which detects the foot-release phase, corresponding to the period when the driver is not pressing the accelerator pedal. During the foot-release phase, the engine's torque demand is zero.

[0066] The method continues to step 66, which involves cutting off fuel injection. Injection remains cut off until the subsequent step 69, where injection is resumed.

[0067] In the subsequent overlap step 67, the electronic control unit 61 controls the variable valve timing systems 50 and 52 to perform the overlap phase of the intake valve 51 and exhaust valve 53 (i.e., the phase during which the intake valve 51 and exhaust valve 53 are simultaneously open during the intake phase). By combining this with the setpoint of the camshaft phaser position, the flow rate of fresh air entering the engine and being exhausted to the exhaust can be limited. Therefore, the oxygen supply to the catalytic converter 42a is limited during the lift-off phase, and the oxygen saturation and NOx handling capacity are better controlled during the subsequent recovery injection phase.

[0068] It is important to note that if engine 10 is equipped only with a variable intake valve timing system 50, the overlap phase is achieved solely through a single offset of the intake valve 51, while the exhaust valve timing 53 remains unchanged. For example, the amount of air entering the combustion chamber can be reduced using a Miller cycle or an Atkinson cycle. The Miller cycle or Atkinson cycle specifies either an earlier or later closing of the intake valves relative to bottom dead center. In both cases, engine pumping losses are limited, and engine fuel consumption is improved.

[0069] Preferably, the overlap of the intake valve 51 and exhaust valve 53 in each engine cycle has a duration ranging from 40°Vil to 120°Vil.

[0070] Step 68, which maintains the overlap phase until the overlap is released, is executed when the control system detects a non-zero torque request, a re-injection rate, or engine disengagement.

[0071] The detection of a re-injection or "re-engagement" scheme involves detecting a predetermined scheme from which re-injection is desired. The value of the predetermined speed depends in particular on the engaged gearbox ratio, engine temperature, and altitude. Valve de-overlap can also be anticipated by monitoring the approach of the re-injection scheme. Therefore, by considering the instantaneous value of the engine's current speed and its rate of decrease, valve de-overlap can be controlled so that the valves reach a position that allows sufficient air to enter the combustion chamber when the engine reaches the predetermined re-injection speed, thus preventing misfire.

[0072] Engine disengagement is detected when the engine is decoupled from the transmission to engage another gear or when the vehicle is marked to stop. In the case of engine disengagement, the valves are de-overlapped to allow sufficient air into the combustion chamber to prevent misfires when injection is resumed.

[0073] Detecting non-zero torque demand involves detecting the torque request made by the driver by pressing the accelerator pedal or resetting cruise control. Once a non-zero torque demand is detected, valve de-overlap is controlled to position the valves to allow sufficient air into the combustion chamber to prevent misfire when injection resumes. To ensure the engine can generate torque without misfire, the torque request is delayed. Therefore, a zero value is assigned to the torque setpoint and maintained as long as injection has not resumed.

[0074] The method continues with step 69, which is performed when the flow rate of fresh air entering the engine exceeds a predetermined value to prevent misfire. This step ensures that the injected fuel burns properly in the combustion chamber.

[0075] From the moment injection resumes, the torque setpoint converges to the value requested by the driver. Preferably, convergence is achieved using a filter or a time ramp function. Therefore, the driver-requested torque is filtered based on the maximum torque gradient (i.e., the maximum time derivative of the torque). This filtering prevents the torque setpoint from causing a vibration felt by the driver upon torque engagement.

[0076] Figure 3 The changes of different parameters of the motor 10 controlled by the control method according to the present invention over time are shown.

[0077] Curve 70 shows the driver's torque demand. The area marked 71 corresponds to the stage where the driver's torque demand is zero when lifting the accelerator.

[0078] When the lift-off phase 71 begins, the injection 72 is cut off, followed by valve overlap 73, which causes a significant decrease in the intake airflow 74 into the engine, especially below the minimum intake airflow value 75 required to prevent misfire.

[0079] When the lift-off phase 71 ends, the valve overlap is de-compensated (valve overlap ends 73), and zero value is assigned to the torque setpoint 76, which is held until injection resumes.

[0080] When the intake air flow 74 exceeds the minimum value 75, injection is resumed (injection 72 is cut off) to prevent misfire. From the same moment, the value of setpoint 76 converges to the driver's torque demand value 70.

Claims

1. A method for controlling a motor vehicle spark-ignition internal combustion engine (10) provided with a variable valve timing system (50, 52) and a system (40) for purifying polluting substances, said system (40) comprising at least one three-way catalyst (42a), the method being characterized in that it comprises the following successive steps: - cutting off fuel injection when a foot-off phase is detected, and maintaining said cut-off until a subsequent step of resuming injection; - overlapping an intake valve (51) and an exhaust valve (53); - performing a de-overlapping of said intake valve (51) and said exhaust valve (53) when a non-zero torque demand is detected, or a predetermined re-injection speed, or an engine decoupling; and - resuming injection.

2. The method of claim 1, wherein, The step of resuming injection is performed when the flow rate of fresh air entering said engine (10) exceeds a predetermined value, to avoid misfires.

3. The method of claim 1 or 2, wherein, In the de-overlapping step, a zero value is assigned to a torque setpoint, and said setpoint is maintained until said injection resumes.

4. The method of claim 3, wherein, From the injection resumption, the value of said torque setpoint converges to the value of the torque demand of the driver.

5. The method of claim 4, wherein, The convergence is performed using a filter or a time ramp.

6. The method of any one of claims 1 to 5, wherein, The overlap of said intake valve (51) and said exhaust valve (53) has a duration in the range 40°Vil to 120°Vil per engine cycle.

7. A control system (60) of a motor vehicle spark-ignition internal combustion engine (10) equipped with a variable valve timing system (50, 52) and a system (40) for purifying polluting substances, said system (40) comprising at least one three-way catalyst (42a), said control system (60) comprising an electronic control unit (61) and being configured to implement the control method according to any one of claims 1 to 6.

8. A spark-ignition internal combustion engine (10) comprising a variable valve timing system (50, 52) and a system (40) for purifying polluting substances, said system (40) comprising at least one three-way catalyst (42a), said engine (10) being provided with a control system (60) configured to implement the control method according to any one of claims 1 to 6.

9. A motor vehicle provided with an engine according to claim 8.

Images