Method for controlling the torque output by an internal combustion engine of a motor vehicle using an asymmetric cycle

Description

Technical field

[0001] The present invention relates to asymmetric cycle motor vehicle internal combustion engines, such as engines operating according to the Atkinson or Miller cycle, provided with a variable intake valve timing system.

[0002] In particular, in one application of the invention, it relates to the management of the torque supplied by the engine in the event of unavailability of the variable timing system. Previous techniques

[0003] Conventionally, the driver of the vehicle determines, by operating the accelerator pedal, an acceleration setpoint for the vehicle. From the acceleration setpoint and the engine speed, a computer defines an engine torque setpoint Csp to be obtained to reach this acceleration setpoint. The torque setpoint is translated into an air mass flow setpoint Qair,sp, into an ignition advance value optimizing efficiency, and into a richness setpoint generally equal to 1, which corresponds to the flow rate of the fuel that must be burned in stoichiometric proportions to obtain the torque while operating the catalyst in its catalytic operating range in which it is capable of treating unburned hydrocarbons, carbon monoxide and nitrogen oxides.

[0004] Furthermore, when the vehicle is equipped with a partial exhaust gas recirculation circuit at the engine intake, a recirculated gas flow rate setpoint Qegr,sp is also defined, which corresponds to the recirculation rate to be applied to meet the target fuel consumption.

[0005] An engine computer then adjusts various engine actuators to set the various parameters to their setpoint values.

[0006] The flow rate of the recirculated gases can be regulated by adjusting the position of a valve in the recirculation circuit. The total gas mass flow rate of air and recirculated gases can be regulated by adjusting the angular position of a throttle body of the engine and furthermore, in the case of a supercharged engine, by adjusting the boost pressure by varying, for example, the inclination of the turbine blades of a turbocharger of the engine, when it is a variable geometry turbine.

[0007] Ignition timing is adjusted by igniting a spark across the spark plugs located in the engine cylinders at a time corresponding to the best-performing timing. However, in modern processes, the engine computer constantly checks for knocking, for example using sensors located in the cylinders or on the engine block using accelerometers. If knocking occurs, timing is reduced, which reduces efficiency. The computer then recalculates an increased air flow corresponding to this lower ignition timing to maintain torque and readjusts the air chain actuators accordingly.

[0008] However, adjusting the air flow by adjusting the position of the throttle body and therefore creating a pressure in the engine's intake manifold that is lower downstream of the throttle valve as the throttle valve is closed, has the disadvantage of generating pumping losses, which are detrimental to engine efficiency, which is therefore rather detrimental at low load on a gasoline engine.

[0009] The use of asymmetric Atkinson or Miller cycles makes it possible to avoid these pumping losses, while controlling the mass of air admitted, that is to say while admitting the same mass flow of air necessary to produce the torque at richness 1 as if the throttle were partially closed. In both cases, the mass of air admitted into the combustion chamber is adjusted by controlling the intake valves, with intake valve closure delay (RFA) values ​​that are very offset from bottom dead center (BDC). More precisely, the closing of the intake valves occurs significantly later than BDC in the case of the Atkinson cycle, so that part of the air admitted into the cylinders up to BDC is forced out of each cylinder as the piston rises towards top dead center (TDC), until the intake valves close.In contrast, the intake valves close significantly ahead of BDC in the Miller cycle, so that air stops flowing into each cylinder before the piston reaches BDC. The main actuator for controlling the engine's air charge then becomes the variable intake valve timing system in both cases, instead of the throttle body in conventional engines that do not use one of these cycles.

[0010] The principle of the Atkinson / Miller cycles is twofold. It is not only a question of limiting pumping losses at partial load, but also of maximizing the expansion phase relative to the compression phase. Thus, the length of the stroke used for expansion between top dead center and bottom dead center becomes greater than the length of the stroke used for compression between the closing of the intake valves at the RFA and bottom dead center. However, this difference requires choosing a higher geometric compression ratio for the engine than in the case of a traditional engine.

[0011] A problem related to the high geometric compression ratios of Atkinson / Miller cycle engines can arise when variable valve timing, particularly the RFA, can no longer be controlled. Thus, in the event of a failure of the intake valve control system or its temporary functional unavailability, it is no longer possible to control the air charge by adjusting the RFA. The RFA and the engine compression ratio are then subject to the position in which the system malfunctions, whether it is the position defined as the rest or backup position of the system, or the position in which the system has failed.Thus, if this position introduces, for example, in the worst case, an intake valve closing angle close to or equal to the bottom dead center position, corresponding to the RFA position of full load, we then come to suffer the high geometric compression ratio of the Atkinson / Miller cycle engine and to have to adjust the mass of air admitted by the manifold pressure and the intake throttle.

[0012] The problem is that with such a compression ratio, the knocking reappears. This requires having to delay the ignition advance, which degrades the combustion efficiency, and therefore, for the same torque to be achieved, requires admitting even more air, thus increasing the effective compression ratio, defined as the ratio between the volume that the gases contained in the combustion chamber would occupy at atmospheric pressure at the end of intake and the residual volume of the combustion chamber at top dead center. This therefore causes a worsening of the knocking. This then results in a collapse in the engine's performance, leading to a very significant degradation of the available torque.

[0013] Document DE 10 2020 112111 A1 proposes an alternative solution for a Miller / Atkinson cycle motor vehicle internal combustion engine equipped with a variable intake valve timing system. In the event of a malfunction of the variable valve timing system, maximum torque control is performed based on the estimated fuel quantity using a determined intake valve closure delay value. Statement of the invention

[0014] In view of the above, the aim of the invention is to maintain the performance of an internal combustion engine of a motor vehicle with an asymmetric cycle of the Atkinson or Miller type in the event of a malfunction of the variable valve timing system of the engine.

[0015] The invention therefore relates to a method for controlling the torque delivered by an internal combustion engine of a motor vehicle with an asymmetric cycle of the Atkinson or Miller type, equipped with a variable valve timing system at the intake, in the event of a malfunction of the variable timing system.

[0016] This process includes the steps of: Detection of the unavailability of the variable distribution system, Determination of an intake closure delay (RFA) value corresponding to the blocking of the variable distribution system, Calculation of an effective compression ratio defined as the ratio between the volume of air in the combustion chamber at atmospheric pressure at the time of closing of the intake valves and the residual volume of the combustion chamber at top dead center, Calculation of a maximum admissible quantity of air for a pressure in the intake manifold equal to the atmospheric pressure and the temperature of the intake manifold, Calculation of the maximum pressure in the intake manifold as a function of the current temperature of the intake manifold and of a maximum achievable torque, from the maximum admissible quantity of air, Setting the pressure in the intake manifold to a value equal to the calculated maximum pressure and corresponding to the maximum achievable torque.

[0017] The torque control process is thus configured to maintain acceptable performance of the Atkinson or Miller type asymmetric cycle engine, in the event of a malfunction of the variable timing system.

[0018] In the case of a traditional naturally aspirated engine (not using the Atkinson or Miller cycle), for example, the effective compression ratio is limited to a predetermined value between 11:1 and 13:1, a range beyond which the knocking phenomenon becomes problematic.

[0019] In the case of a traditional supercharged engine, for example, the effective compression ratio is limited to a predetermined value between 9:1 and 11:1 for the same reasons.

[0020] For example, a preliminary step can be taken to detect the unavailability of the variable valve timing system. If the unavailability is proven, to determine an intake valve closure delay (IPD) value, the measured intake valve closure delay value can be used, for example, if this measurement is available. If measurement is not possible, the IPD value corresponding to full load can be used, corresponding to a position close to, or equal to, BDC; alternatively, a rest or backup value can also be used, if necessary, corresponding to a position that the variable valve timing system adopts mechanically when it is no longer controlled.

[0021] The invention also relates to a system for controlling the torque delivered by an internal combustion engine of an asymmetrical cycle motor vehicle equipped with a variable valve timing system at the intake, in the event of a malfunction of the variable valve timing system.

[0022] The torque control system comprises means for determining an intake closure delay value (RFA) corresponding to a blockage of the variable timing system, means for calculating a ratio between the volume occupied at atmospheric pressure by the air admitted into the combustion chamber, at the time of closing of the intake valves, and the residual volume of the combustion chamber at top dead center, means for limiting the calculated ratio, means for calculating a maximum admissible quantity of air for a pressure in the intake manifold equal to the atmospheric pressure and the temperature of the intake manifold, means for calculating the maximum pressure in the intake manifold as a function of the current temperature of the intake manifold and a maximum achievable torque, from the maximum admissible quantity of air,and means for adjusting the pressure in the intake manifold to a value equal to the calculated maximum pressure and corresponding to the maximum torque.,

[0023] In the case of a traditional naturally aspirated engine, for example, the control system is configured to limit the effective compression ratio to a predetermined value between 11:1 and 13:1.

[0024] In the case of a traditional supercharged engine, for example, the control system is configured to limit the effective compression ratio to a predetermined value between 9:1 and 11:1.

[0025] For example, the control system includes means for detecting the unavailability of the variable timing system. Brief description of the drawings

[0026] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely as a non-limiting example, and made with reference to the appended drawings in which: [ Fig 1 ] schematically illustrates the structure of an internal combustion engine of a motor vehicle equipped with a variable timing system and a torque control system according to the invention; [ Fig 2 ] illustrates a flowchart of the torque management method, implemented by the management system, according to an embodiment of the invention. Detailed description of at least one embodiment

[0027] In the example illustrated in the Figure 1, the internal combustion engine 10 comprises, in a non-limiting manner, three cylinders 12 in line, a fresh air intake manifold 14, an exhaust manifold 16, a turbo-compression system or turbocharger 18, a variable timing system 50 of the intake valves 51 of the engine and possibly also of the exhaust valves 52 of the engine.

[0028] The cylinders 12 are supplied with air via the intake manifold 14, or intake distributor, itself supplied by a pipe 20 provided with an air filter 22 and the turbocharger 18 of the engine 10.

[0029] The turbocharger 18 essentially comprises a turbine 18a driven by the exhaust gases and a compressor 18b mounted on the same shaft as the turbine 18a and providing compression of the air distributed by the air filter 22, with the aim of increasing the quantity (mass flow rate) of air admitted into the cylinders 12 of the engine 10 for an identical volume flow rate.

[0030] The turbine 18a may be of the "variable geometry" type, that is to say that the turbine wheel is equipped with blades with variable inclination in order to modulate the quantity of energy taken from the exhaust gases, and thus the boost pressure. Alternatively, the invention may use a turbine 18a with fixed geometry. In the case of the use (not shown) of a turbine 18a with fixed geometry, the quantity of energy taken by the turbine 18a is regulated by adjusting the proportion of the flow of exhaust gases passing through the turbine, using an exhaust wastegate, mounted on a bypass circuit associated with the turbine 18a.

[0031] The internal combustion engine 10 thus comprises an intake circuit Ca and an exhaust circuit Ce.

[0032] The intake circuit Ca includes, from upstream to downstream in the direction of air circulation: the air filter 22 or air box; a flow meter 26 arranged in the intake duct 20 downstream of the air filter 22; the flow meter 26 being configured to measure the actual value of the air flow entering the engine 10; an air intake valve 28; the compressor 18b of the turbocharger 18 configured to compress the recycled exhaust gases at low pressure, as will be described later; a throttle body 30 or a valve for admitting gases into the engine; a heat exchanger 32 configured to cool the intake gases corresponding to a mixture of fresh air and recirculated gases after their compression in the compressor 18b; and the intake manifold 14.

[0033] The compressor is associated with a bypass circuit equipped with an inlet relief valve 55 which opens in the event of sudden closure of the throttle body 30, to prevent the compressed air, located between the compressor 18b and the throttle body 30, from passing through the compressor 18b and damaging it, when, for example, the driver of the vehicle suddenly lifts his foot off the accelerator pedal.

[0034] The exhaust circuit This includes, from upstream to downstream in the direction of circulation of the burnt gases: the exhaust manifold 16; the turbine 18a of the turbocharger 18 configured to take energy from the exhaust gases which pass through the turbine, the expansion energy being transmitted to the compressor 18b via the common shaft, for the compression of the intake gases; and a system 40 for depolluting the combustion gases of the engine.

[0035] As regards the exhaust manifold 16, the latter recovers the exhaust gases from the combustion and evacuates them to the outside, via a gas exhaust duct 34 opening onto the turbine 18a of the turbocharger 18 and via an exhaust line 36 mounted downstream of the turbine 18a.

[0036] The engine 10 further comprises a partial recirculation circuit 38 of the exhaust gases to the intake, called the “EGR” circuit (“exhaust gas recirculation” in Anglo-Saxon terms).

[0037] This circuit 38 is, by way of non-limiting example, a low-pressure exhaust gas recirculation circuit, known as an "EGR BP" circuit. It is connected to the exhaust line 36, downstream of said turbine 18a, and in particular downstream of the exhaust gas purification system 40, and returns the exhaust gases to the fresh air supply pipe 20, upstream of the compressor 18b of the turbocharger 18, and in particular downstream of the flow meter 26. The flow meter 26 measures only the flow rate of fresh air alone.

[0038] As illustrated, this recirculation circuit 38 includes, in the direction of circulation of the recycled gases, a cooler 38a, a filter 38b, and a valve "V EGR BP" 38c configured to regulate the flow rate of the low-pressure exhaust gases. The valve "V EGR BP" 38c is arranged downstream of the cooler 38a and the filter 38b and upstream of the compressor 18b.

[0039] It will be noted that the air intake valve 28 can also be used to force the circulation of a flow of low-pressure exhaust gases into the BP EGR circuit in the event that the vacuum between the exhaust circuit and the intake circuit is insufficient. In this case, closing the valve 28 would create a vacuum downstream, capable of sucking gases from the BP EGR circuit.

[0040] The engine combustion gas depollution system 40 comprises a first post-treatment device 42 comprising two three-way catalysts 42a, 42b in series which can be electrically heated, with at least one first oxygen sensor 43a mounted upstream of the first post-treatment device 42.

[0041] The first upstream oxygen sensor 43a is generally used to regulate in a closed loop the value of the richness of the air-fuel mixture in the engine around a set value, for example the value 1 corresponding to an air-fuel mixture in stoichiometric proportions.

[0042] Furthermore, a second optional oxygen sensor 43b, for example of the binary or proportional type, can be mounted downstream of the first post-treatment device so as to be able to correct the set value of the richness regulation loop, in particular with the aim of adjusting the quantity of oxygen stored inside the first depollution device 42.

[0043] The gas pollution control system 40 further comprises a second post-treatment device 44 which is here a fine particle filter, and a third post-treatment device 46, for example a three-way catalyst. It may also comprise a third oxygen probe 43c, for example of the binary type, mounted downstream of the second device 44, for example for diagnostic purposes.

[0044] The engine is associated with a fuel circuit comprising, for example, fuel injectors (not referenced) injecting gasoline directly into each cylinder from a fuel tank (not shown).

[0045] Furthermore, the engine comprises an electronic control unit 70 configured to control the various elements of the internal combustion engine from data collected by sensors at different locations in the engine.

[0046] The electronic control unit 70 comprises a calculation module 72, a measurement module 73 and a control module 74.

[0047] In the spark-ignition engine, the engine speed-load operating point is set by the engine computer 70 by adjusting, in particular, a quantity of air, a quantity of BP EGR recirculation gases, and a quantity of fuel. By "quantity" here is meant a mass flow rate.

[0048] The air flow rate and the flow rate of the BP EGR recirculation gases can be adjusted to set values ​​by the engine computer 70 by adjusting: the position of the throttle body 30; the distribution law through the variable timing system 50, in particular predominantly the timing of the intake valves 51; the boost pressure of the turbocharger 18, which controls the total gas flow rate in the engine; and, the position of the “V EGR BP” valve 38c of the recirculation circuit 38, which controls only the flow rate of the BP EGR recirculation gases.

[0049] The fuel flow is adjusted by the engine computer 70 so as to adjust the richness of the air-fuel mixture admitted into the engine cylinders to a setpoint value λ_cons, for example a richness value equal to 1 corresponding to the stoichiometric proportions of the air-fuel mixture. In particular, a regulator (not shown of the PID type) and the actual richness value λ_mes deduced from the measurement of the first richness probe 43a are used to adjust said richness value in a closed loop to the setpoint value. In regulation modes, the setpoint value λ_cons is modified according to the indications of the second downstream richness probe 43b, in particular to allow the mass of oxygen stored OS in the first pollution control device 42 to be adjusted.

[0050] We will now describe with reference to the Figure 2a method 60 for managing torque provided by an Atkinson or Miller cycle internal combustion engine as described above. Such a method is notably implemented by the computer 70 from the measurements delivered by the various sensors of the engine and by controlling the various elements of the engine.

[0051] The method 60 comprises a prior step 61 of detecting the unavailability of the variable timing system 50.

[0052] The computer 70 is in fact configured to determine the presence of a case of unavailability of the variable timing system. For example, to detect the unavailability of the variable timing system 50, it is possible either to use fault detection means in the case of electromechanical variable timing systems 50, or, in the case of hydraulically controlled variable timing systems 50, to check the temperature and / or the oil pressure by comparing measured values ​​with predetermined values.

[0053] In the event of unavailability of the variable timing system 50, during a subsequent step 62, the measurement module 73 records the value of the intake closure delay (RFA) at which the variable timing system 50 is blocked. For example, the measurement module 73 can use a position feedback sensor 53, installed on the variable timing system 50. If the measurement module 73 cannot record the value of the RFA, for example because of a faulty sensor, it will retain the value of the RFA corresponding to full load, thus maximizing the value of the admitted flow rate; alternatively, it can retain a rest or backup value.

[0054] In the following step 63, the calculation module 72 calculates the effective compression ratio TCE, defined according to the following equation: TCE = Vpatm Vmort

[0055] With : TCE, the effective compression ratio, dimensionless; Vpatm, the volume that the air in the combustion chamber would occupy at atmospheric pressure at the moment the intake valves close, expressed in m 3 <; and Vmort the residual volume of the combustion chamber at top dead center, of a constant value and expressed in m 3 <.

[0056] To calculate Vpatm we use the following empirical equation: P × V = ν × R × T

[0057] With : P, the pressure expressed in Pa; V, the volume expressed in m 3<; v, the quantity of matter expressed in moles; R, the universal constant of ideal gases ≈8.314 JK -1< .mol ​​-1<; and T, the absolute temperature expressed in K;

[0058] In equation (2): the quantity of air v, is obtained from the total gas flow rate of fresh air and EGR BP (mass flow rate) as a function of the intake duration and including the filling effect which tends to take into account the inertia effects linked to the high gas speeds during distribution. the temperature T is the temperature measured in the intake manifold

[0059] In the case of a naturally aspirated engine, for example, the engine computer 70 is configured to limit the effective compression ratio to a predetermined TCElim value between 11:1 and 13:1.

[0060] In the case of a supercharged engine, for example, the engine computer 70 is configured to limit the effective compression ratio to a predetermined TCElim value between 9:1 and 11:1.

[0061] During the following step 64 of the method 60, the calculation module 72 calculates an air volume Vmax not to be exceeded, expressed in m3, from the dimensionless value TCElim and the volume Vmort expressed in m3, according to the following equation: Vmax = TCE lim × Vmort

[0062] From the maximum air volume Vmax, the calculation module 72 determines a maximum admissible quantity of air Mair, expressed in mol, according to the following equation: Mair = P 0 × Vmax R × Tcol

[0063] With : P0, the atmospheric pressure expressed in Pa; Vmax, the maximum admissible air volume expressed in m3; R, the universal constant of ideal gases ≈8.314 JK-1.mol-1; and Tcol, the collector temperature expressed in K.

[0064] The maximum air mass equivalent is determined from the maximum allowable air quantity Mair through the molar mass of air.

[0065] From the maximum admissible quantity of air Mair, the calculation module 72 determines the maximum pressure in the collector Pcolmax not to be exceeded (step 65), according to the following equation: Pcolmax = k × Mair × R × Tcol V

[0066] With : Pcolmax, maximum pressure in the manifold, not to be exceeded, expressed in Pa; k, a dimensionless coefficient of engine filling; Mair, maximum admissible quantity of air expressed in mol; R, the universal constant of ideal gases ≈8.314 JK-1.mol-1; Tcol, the manifold temperature expressed in K; and V, the cylinder volume for the crankshaft angle corresponding to the measured or retained value of the RFA, expressed in m3.

[0067] From the maximum permissible air quantity Mair and the engine speed, the engine computer 70 finally determines a maximum achievable torque Cmax.

[0068] Advantageously, the engine computer 70 controls the flow of fresh air passing through the throttle body 30, that is to say by adjusting the pressure in the intake manifold Ca by means of a partial closing of the throttle body 30, within the limit of the maximum torque Cmax.

[0069] The invention thus makes it possible, in the event of the driver pressing the accelerator pedal, corresponding to a higher torque request, to limit the torque setpoint to the maximum achievable value Cmax.

[0070] Thus, thanks to the invention, it is possible to avoid significantly degrading the engine's performance in the event of the variable valve timing system being unavailable on asymmetric cycle engines of the Atkinson or Miller type, by setting the maximum achievable torque.

Claims

1. Method for controlling the torque output by a motor vehicle internal combustion engine which has an asymmetric Atkinson or Miller cycle and is equipped with a variable intake valve timing system, in the event of malfunction of the variable timing system, characterized in that it comprises the steps of: a) determination of an intake closure delay (ICD) value corresponding to a blockage of the variable timing system, said determination being performed on the basis of a measured or stored position of the intake closure delay; b) calculation of a ratio between the volume occupied at atmospheric pressure by the air admitted into the combustion chamber, at the moment the intake valves close, and the residual volume of the combustion chamber at top dead center; c) calculation of a maximum permissible air quantity for a pressure in the intake manifold equal to atmospheric pressure and to the temperature of the intake manifold, based on a limitation of the calculated ratio; d) calculation of the maximum pressure in the intake manifold based on the instantaneous temperature of the intake manifold and a maximum achievable torque, from the maximum permissible air quantity; e) adjustment of the pressure in the intake manifold to a value equal to the calculated maximum pressure and corresponding to the maximum torque achievable.

2. Method according to claim 1, wherein the limitation of the calculated ratio has a predetermined value between 11:1 and 13:1 if the engine is naturally aspirated.

3. Method according to claim 1, wherein the limitation of the calculated ratio has a predetermined value between 9:1 and 11:1 if the engine is supercharged.

4. Method according to any of claims 1 to 3, wherein the value of the intake closure delay is equal to the measured value of the intake closure delay.

5. Method according to any of claims 1 to 3, wherein the value of the intake closure delay, when it is not measurable, is taken equal to the value of the intake closure delay corresponding to full load or equal to a backup position.

6. Method according to any of claims 1 to 5, comprising a prior step of detecting the unavailability of the variable timing system.

7. System for controlling the torque output by a motor vehicle internal combustion engine which has an asymmetric Atkinson or Miller cycle and is equipped with a variable intake valve timing system, in the event of malfunction of the variable timing system, characterized in that it comprises: a) means for determining an intake closure delay (ICD) value corresponding to a blockage of the variable timing system, said determination being performed on the basis of a measured or stored position of the intake closure delay; b) means for calculating a ratio between the volume occupied at atmospheric pressure by the air admitted to the combustion chamber, at the moment the intake valves close, and the residual volume of the combustion chamber at top dead center; c) means for limiting the calculated ratio; d) means for calculating a maximum permissible air quantity for a pressure in the intake manifold equal to atmospheric pressure and to the temperature of the intake manifold, based on a limitation of the calculated ratio; e) means for calculating the maximum pressure in the intake manifold based on the instantaneous pressure of the intake manifold and a maximum achievable torque, from the maximum permissible air quantity; f) means for adjusting the pressure in the intake manifold to a value equal to the maximum pressure calculated and corresponding to the maximum torque achievable.

8. System according to claim 7, provided with means for limiting the calculated ratio to a predetermined value between 11:1 and 13:1 if the engine is naturally aspirated.

9. System according to claim 7, provided with means for limiting the calculated ratio to a predetermined value between 9:1 and 11:1 if the engine is supercharged.

10. System according to any of claims 7 to 9, comprising means for detecting the unavailability of the variable timing system.