Method and system for controlling torque applied during gear shifting in a vehicle equipped with at least one exhaust gas recirculation system - Patents.com

Abstract

The invention relates to a method for controlling the torque applied during gear changes by a motor vehicle internal combustion engine equipped with at least one partial exhaust gas recirculation system at the engine intake, comprising the steps of determining (step 41) a target torque value (C_target) required for a gear ratio change, determining (step 42) from a current operating point of the engine a first torque value (C_withdrawal) that the engine can generate by implementing a retreat of the spark advance (step 45), and determining a second torque value (C_intermediate) lower than the current torque of the engine and from which the target torque value (C_target) can be generated using only the retreat of the spark advance of said engine (6).

Description

[Technical field]

[0001] The present invention relates to a motor vehicle internal combustion engine equipped with at least one partial exhaust gas recirculation circuit at the engine intake.

[0002] In particular, the invention, in one application of the invention, relates to the management of the torque applied by the motor in the case of speed changes. [Background technology]

[0003] In automobiles with internal combustion engines, and more particularly spark ignition engines, the vacuum in the engine's intake manifold is generally regulated by the engine's throttle housing to obtain a certain mass flow rate of air capable of generating engine torque, but causes pumping losses induced by the pressure difference between the intake manifold plenum and the engine's exhaust manifold.

[0004] Figure 1 shows a pressure-volume diagram, characterizing the operation of a conventional four-stroke engine. The pumping losses correspond to the shaded area 2, which represents the work consumed by the motor, as opposed to the shaded area 1, which represents the work provided by the motor. According to the conventional cycle of Figure 1, which represents the stages that the gases in the engine cylinder go through, the intake phase (intake stroke) corresponds to segment AB, compression corresponds to segment BC, combustion corresponds to segment CD, expansion corresponds to segment DE and exhaust corresponds to segment EA.

[0005] To reduce engine pumping losses, it is advantageous to raise the intake manifold pressure as close as possible to the engine exhaust manifold pressure, so that the pressure of the gases during the intake step approaches the pressure of the gases during the exhaust phase, reducing the amount of work consumed by the engine.

[0006] Traditionally, the vehicle driver determines the vehicle acceleration setpoint by actuating the accelerator pedal. From the acceleration setpoint and engine speed, a computer defines the engine torque setpoint that must be achieved to reach this acceleration setpoint. The torque setpoint is converted into an air mass flow setpoint, Qair, a spark advance value that generally optimizes efficiency, and a richness setpoint approximately equal to 1, which corresponds to the fuel flow rate that must be burned at stoichiometric ratios to obtain torque while operating the engine abatement catalyst in a catalyst operating range capable of handling unburned hydrocarbons, carbon monoxide, and nitrogen oxides.

[0007] Furthermore, if the vehicle is equipped with a partial exhaust gas recirculation circuit at the engine intake, a setpoint Qegr of the mass flow rate of the recirculated gases at the intake is also defined, which corresponds to the recirculation rate that must be applied to comply with the target fuel consumption. This exhaust gas recirculation (EGR) rate is defined as the ratio of the mass of reintroduced exhaust gases entering the intake system per unit time to the total mass of gases entering the engine combustion chamber per unit time.

[0008] The sum of the air flow Qair and the recirculated exhaust flow Qegr represents the total gas mass flow Qword entering the engine, which is generally adjusted by adjusting the position of a throttle housing in the engine intake circuit to obtain a pressure value Pcollar in the engine intake manifold that corresponds to the desired total flow.

[0009] The engine computer uses an air charge model to determine the minimum intake manifold pressure that meets the engine torque setpoint.

[0010] The filling pattern follows the formula:

[0011]

number

[0012] In the formula, η rdvl denotes the dimensionless volumetric efficiency or "packing"; Q wordrefers to the actual total incoming mass flow rate in kg / s, N is the rotation speed in revolutions per minute Displacement is m 3 means the displacement of the engine at P collar means the pressure in the intake manifold in Pa, T collar denotes the temperature in the intake manifold in K, R is the ideal gas mass constant for air, which is approximately equal to 287.058 J / kg×K.

[0013] The term "charge" is defined as equal to the ratio of the mass of air drawn in to the mass of air that could enter the cylinder if only the total volume of the cylinder was considered.

[0014] In either case, the efficiency η rdvl The value of is determined by the rotation speed N and the pressure P in the intake manifold. colar It depends on the.

[0015] At part load, i.e. when less airflow is required, the pressure in the intake manifold can be much lower than the atmospheric pressure corresponding to full load in the case of a naturally aspirated engine and when only air is admitted to the engine, resulting in significant pumping losses.

[0016] To reduce these pumping losses, the pressure in the intake manifold must be increased to approach as closely as possible the value of the pressure in the exhaust manifold.

[0017] One method of increasing pressure in the intake manifold is to use exhaust gas recirculation, or EGR.

[0018] This EGR method consists of sampling gases from the exhaust and sending them to the intake, for example downstream of the engine's airflow control valve. The supply of recirculated exhaust gases to the intake makes it possible to increase the pressure in the intake manifold of the engine at the same value as the airflow required to generate torque, thus reducing pumping losses and thus improving engine efficiency and fuel consumption.

[0019] Traditionally, engine spark advance values ​​are set to provide ignition just before top dead centre (TDC) to allow for the time it takes for combustion to develop.

[0020] Thus, to produce a given torque, the engine's spark advance value is typically set to a value equal to the optimum advance, or if that is not possible, closest to the optimum advance at which no knock occurs, to maximize combustion efficiency; i.e., the advance selected is the one that maximizes torque with the same air and fuel flows.

[0021] However, when shifting gears, the engine torque must momentarily be very low, near zero, to compensate for engine friction, and in this case, advance retardation is performed to reduce the torque value very quickly without changing the position of the air circuit actuators such as the butterfly housing or the EGR valve.

[0022] In fact, changing the spark advance is more effective at quickly reducing torque than changing the airflow control valve position because there is a much shorter response time for the torque to actually plummet when the advance is reversed.

[0023] However, when EGR is added to the combustion chamber, combustion is generally slower and more unstable than without EGR, so it is difficult to perform advance backoff without causing a sudden drop in torque and misfire when shifting, because combustion becomes so slow under the influence of such sub-advance that it stops completely.

[0024] Figure 2 shows the burn time as a function of EGR level in the combustion chamber. Note that higher EGR rates increase the burn time and can lead to combustion instability if the combustion cycle ends before all the trapped fuel is burned.

[0025] Figure 3 qualitatively shows the possible range of variation of the spark advance as a function of the EGR rate. The combustion efficiency corresponds to the engine torque obtained as a function of the spark advance with the same airflow and richness 1. The apex of each curve corresponds to the best combustion efficiency and the optimum advance for each EGR rate. All curves are limited on the right by the knocking phenomenon and on the left by combustion instability, i.e. increasing or decreasing the spark advance reaches a low threshold where the combustion becomes unstable and a high threshold where the combustion becomes uneven due to the autoignition of unburned gases typical of knocking.

[0026] The spark advance value can be reduced, in particular to reduce the combustion efficiency, as shown by curve 3 in figure 3, which corresponds to the case where there is no EGR in the combustion chamber. Thus, in the absence of EGR, the retreat of the advance with respect to the optimal advance makes it possible to reduce the torque generated by the engine almost instantly.

[0027] The problem is that as the EGR rate increases, the range of possible spark advance values ​​becomes smaller. In curves 3, 4, and 5 of FIG. 3, which correspond to 0%, 10%, and 20% EGR rates, respectively, the width of gap 3a-3b is larger than the width of gap 4a-4b, which is itself larger than the width of range 5a-5b. This means that as the EGR rate increases, there is less opportunity to reduce engine torque significantly by retarding the advance. Thus, as shown by curve 5 of FIG. 3, at high EGR levels, the combustion stability limit (5a) is reached long before torque can be significantly reduced.

[0028] In known methods of the state of the art, the EGR rate is not reduced, so the advance retardation performed to crash the torque down to the value required for the shift creates the risk of combustion instability that can lead to misfires that can reduce the activity of the catalyst and increase pollutant emissions. Summary of the Invention [Problem to be solved by the invention]

[0029] In view of the above, the present invention aims to reduce the risk of combustion instability during advance retardation performed to rapidly reduce the torque to the value required for shifting, while maintaining the EGR rate close to the optimum setting for consumption. [Means for solving the problem]

[0030] The present invention relates to a method for controlling the torque delivered during gear changes by a vehicle internal combustion engine having at least one partial exhaust gas recirculation system at its intake.

[0031] The method comprises: A step of determining a target torque value required for shifting; determining, from a current operating point of the engine, a first torque value that the engine can generate by implementing a retardation of the spark advance; determining a second torque value that is lower than the current torque of the engine and from which the target torque value can be generated using only retardation of the spark advance of the engine; Includes.

[0032] For example, the second torque value may be achieved by reducing the mass flow rate of air entering the engine.

[0033] Advantageously, the reduction in the mass air flow rate can be limited to a predetermined value such that torque can be restored within a predetermined maximum period of time.

[0034] For example, a reduction in the mass air flow rate is achieved by closing the throttle housing of the engine.

[0035] In another feature, the second torque value is calculated by a computer using a network of curves relating the torque value to the EGR rate.

[0036] For example, the torque set point of the motor is equal to the second torque value.

[0037] Advantageously, when the current torque provided by the engine reaches a second torque value, the computer can execute a spark advance retard to cause the engine to generate the target torque required for the gear ratio change.

[0038] Advantageously, if a second torque value is not found that allows the target torque to be reached by only retarding the advance, the computer sets a zero EGR setpoint and controls the reduction of the EGR rate by closing the EGR valve.

[0039] According to an advantageous feature, while the EGR rate is being reduced to the set value, the computer frequently evaluates the minimum torque achievable by retarding the advance only.

[0040] Advantageously, the computer performs the necessary retardation of the advance required to obtain the target torque required for the gear ratio change.

[0041] The present invention also relates to a system for controlling the torque delivered during gear changes by an automotive internal combustion engine having at least one partial exhaust gas recirculation system at its intake.

[0042] The torque control system comprises means for determining a target torque value required for a gear ratio change, means for determining, from a current operating point of the engine, a first torque value that the engine can generate by implementing a spark advance retardation, and means for determining a second torque value that is lower than the current torque of the engine and from which the target torque value can be generated by using only the spark advance retardation of the engine.

[0043] Other objects, features and advantages of the present invention will appear on reading the following description, given by way of non-limiting example only and made with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0044] [Figure 1] 1 shows a pressure-volume diagram for a cylinder of an automotive four-stroke internal combustion engine according to a conventional cycle. [Diagram 2]4 shows the combustion time as a function of the EGR rate in the combustion chamber. [Diagram 3] 4 shows the possible range of variation of spark advance as a function of EGR rate. [Figure 4] 1 shows a schematic diagram of the structure of an internal combustion engine of a motor vehicle equipped with a torque control system according to the invention; [Diagram 5] 4 shows a flow chart of a torque control method implemented by a control system according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] In the example shown in FIG. 4, the internal combustion engine 6 comprises, without limitation, three in-line cylinders 7 , an intake manifold 8 for fresh air, an exhaust manifold 9 and a turbocharging system or turbocharger 10 .

[0046] The cylinders 7 are supplied with air via an intake manifold 8 or intake distributor, itself supplied with air by a pipe 11 provided with an air filter 12 and by a turbocharger 10 of the engine 6 .

[0047] The turbocharger 10 essentially comprises a turbine 10a driven by the exhaust gases and a compressor 10b mounted on the same shaft as the turbine 10a and compressing the air distributed by an air filter 12, with the aim of increasing the amount of air (mass flow) introduced into the cylinders 7 of the engine 6 for the same volumetric flow rate.

[0048] The turbine 10a may be of the "variable geometry" type, i.e. the turbine impeller is provided with variable inclination vanes to modulate the amount of energy captured from the exhaust gases, and thus the boost pressure. Alternatively, the invention may use a turbine 10a with a fixed geometry. In the case of the use of a fixed geometry turbine 10a (not shown), the amount of energy captured by the turbine 10a is regulated by adjusting the proportion of the exhaust gas flow passing through the turbine, using an exhaust discharge valve mounted in a bypass circuit associated with the turbine 10a.

[0049] The internal combustion engine 6 therefore comprises an intake circuit Ca and an exhaust circuit Ce.

[0050] The intake circuit Ca is arranged as follows, from upstream to downstream in the air circulation direction: - air filter 12 or air box, a flow meter 13 arranged in the intake pipe 11 downstream of the air filter 12 and configured to measure the actual value of the air flow entering the engine 6; - Intake valve 14, a compressor 10b of the turbocharger 10 configured to compress the fresh intake gases and the recirculated exhaust gases at low pressure, as described below; - the throttle housing 15 or the intake valve of the engine, a heat exchanger 16 configured to cool the intake gas corresponding to the mixture of fresh air and recirculated gas after compression in the compressor 10b; and -Intake manifold 8 Includes.

[0051] The compressor is associated with a bypass circuit with an intake relief valve 17 which opens in the event of a sudden closure of the throttle housing 15, for example when the vehicle driver suddenly releases his foot from the accelerator pedal, to prevent compressed air located between the compressor 10b and the throttle housing 15 from passing through and degrading the compressor 10b.

[0052] The exhaust circuit Ce is arranged as follows, from upstream to downstream in the direction of the burnt gas flow: -Exhaust manifold 9, a turbine 10a of a turbocharger 10 configured to extract energy from the exhaust gases passing therethrough and to transmit said expansion energy via a common shaft to a compressor 10b for compression of the intake gases; and -Engine Combustion Gas Scavenging System18 Includes.

[0053] As regards the exhaust manifold 9, it collects the exhaust gases from the combustion and discharges them to the outside via an exhaust duct 19 leading to the turbine 10a of the turbocharger 10 and an exhaust line 20 attached downstream of the turbine 10a.

[0054] The engine 6 further comprises a partial exhaust gas recirculation (EGR) circuit 21 .

[0055] This circuit 21 is a low pressure exhaust gas recirculation circuit, referred to here without limitation as "LP EGR". It is connected to the exhaust line 20 downstream of said turbine 10a, in particular downstream of the gas abatement system 18, and returns the exhaust gases to the fresh air supply line 11 upstream of the compressor 10b of the turbocharger 10, in particular downstream of the flow meter 13. The flow meter 13 measures only the fresh air flow rate.

[0056] As shown, the recirculation circuit 21 includes a cooler 21a, a filter 21b, and a "V EGR BP" valve 21c configured to adjust the flow rate of low pressure exhaust gas recirculated to the engine intake in the direction of recirculation of the recirculated gas. The "V EGR LP" valve 21c is disposed downstream of the cooler 21a and the filter 21b and upstream of the compressor 10b.

[0057] It should be noted that the intake valve 14 can also be used to recirculate low pressure exhaust gas flow to the LP EGR circuit in the event that there is insufficient vacuum between the exhaust and intake circuits. In this case, closing the valve 14 creates a vacuum downstream, allowing gases from the LP EGR circuit to be drawn in.

[0058] The engine exhaust gas abatement system 18 includes a first aftertreatment device 22 including two electrically heatable three-way catalysts 22a, 22b in series, with at least one first oxygen probe 23 mounted upstream of the first aftertreatment device 22.

[0059] The first upstream oxygen probe 23 generally serves to regulate the richness value of the mixture in the engine in a closed loop around a set value, for example a value of 1, which corresponds to a stoichiometric mixture.

[0060] In addition, an optional second oxygen probe 24, for example of a binary or proportional type, can be installed downstream of the first aftertreatment device, particularly for the purpose of adjusting the amount of oxygen stored in the first abatement device 22 so that the setpoint of the richness control loop can be corrected.

[0061] The gas abatement system 18 further includes a second aftertreatment device 25, here a particulate filter, and a third aftertreatment device 26, e.g., a three-way catalyst. The gas abatement system 18 may also include a third oxygen probe 27, e.g., of the binary type, mounted downstream of the second device 25, e.g., for diagnostic purposes.

[0062] The engine 6 is associated with a fuel circuit which includes, for example, fuel injectors (not numbered) for injecting gasoline directly into each cylinder 7 from a fuel tank (not shown).

[0063] Additionally, engine 6 includes a computer 28 configured to control various elements of the internal combustion engine based on data collected by sensors at various locations on the engine.

[0064] The computer 28 comprises a calculation module 29 , a measurement module 30 and a control module 31 .

[0065] In a spark ignition engine, the engine speed-load operating point is adjusted by the engine computer 28 by adjusting, among other things, the amount of air, the amount of exhaust gas recirculated to the LP EGR intake, and the amount of fuel, where "amount" means mass flow.

[0066] A torque control method 40 implemented by a conventional cycle internal combustion engine as described above will now be described with reference to Figure 5. The method 40 makes it possible to control the value of the torque generated by the engine to reach the value required for shifting the gearbox.

[0067] Gearbox shifting may be initiated by the computer 28 or by the driver, for example by operating a gear shift lever.

[0068] For example, in the case of an automatic gearbox that makes gear shifting decisions independently of the driver's will, a strategy implemented by computer 28 could be to change the gear ratio at an operating point of the engine that has a torque different from the current torque in order to reduce the engine's consumption rate at an equal power output.

[0069] In a first step 41, the computer 28 detects that such a shift is taking place and requests the gearbox control system to determine a value for the torque C_target required by the gearbox during the shift, which should not be exceeded.

[0070] The value of C_target may be practically zero if it is only the motor that generates the torque transmitted to the gearbox input shaft. Alternatively, it may be slightly higher if the engine is installed in a hybrid vehicle in combination with an electric machine that applies a negative torque to the gearbox input shaft to compensate for the torque of the heat engine. Such a hybrid drive is disclosed, for example, in French patent application FR 3022495.

[0071] In the next step 42, the computer 28 determines the minimum torque C_withdrawal that the engine can develop without combustion instability by implementing a retreat of the advance from its current operating point. The operating point of the engine 6 is characterized by the current torque delivered by the engine with a specific airflow, a specific EGR rate and an optimal spark advance. At a given EGR rate, the torque C-withdrawal corresponds to the combustion stability limit as represented by the low threshold of the corresponding curve in FIG. 3, and its peak corresponds to the current torque obtained with the optimal spark advance.

[0072] In the next step 43, the computer 28 checks whether the torque value C_target determined in step 41 is less than the torque value C_withdrawal determined in step .

[0073] If not, there is no need to reduce the EGR rate or change the throttle housing position, and computer 28 simply performs the spark advance removal necessary to obtain the C_target torque without causing combustion instability (step 44).

[0074] If the torque value C_target determined in step 41 is less than the torque value C_withdrawal determined in step 42, the computer 28 determines in a next step 45 a torque value C_intermediate lower than the current torque, which is obtained by reducing the amount of air introduced (for example by closing the butterfly housing), whereas the torque C_target can be obtained only by retarding the advance. The amount of air is understood as a mass flow rate. The computer 28 limits the reduction in the air mass flow rate to a predetermined value that allows the torque to be restored after the gear ratio change within a predetermined maximum period. If there is a torque value C_intermediate, it is determined by the computer 28 on the basis of a network of curves, such as the one in FIG. 3, preprogrammed and stored in the memory of the computer 28, connecting different torque values ​​for a constant EGR rate of the current torque.

[0075] In the next step 46, the computer 28 checks whether such a torque value C_intermediate was found in step 45.

[0076] If found, then in a next step 47, computer 28 assigns the value C_intermediate to the torque setpoint, in particular reducing the airflow by closing the butterfly housing.

[0077] After obtaining the torque C_intermediate in step 47, the computer 28 executes a retardation of the spark advance that allows obtaining the torque C_target (step 48).

[0078] After making the gear ratio change, computer 28 restores the torque to the value C_intermediate by adjusting the previous spark advance value, and then increases the airflow, particularly by reopening the throttle housing, to obtain the torque value before the gear ratio change.

[0079] In the next step 49, if the torque value C_intermediate was not found in step 45, the computer 28 sets a zero EGR rate setpoint and commands the closing of the EGR valve 21c (step 49a). The actual reduction of the EGR rate to zero takes between 200ms and 1000ms depending on the engine flow rate and the amount of EGR at the intake. Most of this time corresponds to the gearbox preparation time, which may include, for example, engaging the next gear or slipping the clutch. During this time of reduction of the EGR rate, the computer 28 frequently re-evaluates the minimum torque achievable by only retarding the advance according to the new EGR rate (step 49b).

[0080] For example, computer 28 determines the value of the EGR rate that actually enters the cylinder after the EGR valve begins to close. The value of the flow rate through the EGR valve is calculated from the Saint-Venant equation, a delay time applied to account for the distance between EGR valve 21c and cylinder 7, and a model of the engine charge from this relationship.

[0081]

number

[0082] In the formula, η rdvl denotes the dimensionless volumetric efficiency or "packing"; Q word refers to the actual total incoming mass flow rate in kg / s, N is the rotation speed in revolutions per minute Displacement is m 3 means the displacement of the engine at P collar means the pressure in the intake manifold in Pa, T collardenotes the temperature in the intake manifold in K, R is the ideal gas mass constant for air, which is approximately equal to 287.058 J / kg×K.

[0083] In other words, computer 28 considers the EGR flow rate in the motor at the current time to be equal to the flow rate through the valve at a previous time the delay time value from the current time. As the EGR rate decreases to a zero value, computer 28 performs the spark advance removal necessary to obtain torque C_target without causing combustion instability (step 49c).

Claims

1. 1. A method for controlling torque delivered during gear shifting by an internal combustion engine (6) for a motor vehicle having at least one partial exhaust gas recirculation system (21) at the engine intake, comprising: determining a target torque value (C_target) required for changing the gear ratio; determining a first torque value (C_withdrawal) that the engine can generate by implementing a retreat of the spark advance from a current operating point of the engine; determining a second torque value (C_intermediate) that is lower than the current torque of the engine (6) and from which the target torque value (C_target) can be generated using only a retardation of the ignition advance of the engine (6); The method according to claim 1, further comprising:

2. 2. The method of claim 1, wherein said second torque value (C_intermediate) is obtained by reducing the mass flow rate of air entering said engine (6).

3. 3. The method of claim 2, wherein the reduction in mass air flow rate is limited to a predetermined value such that torque can be restored within a predetermined maximum period of time.

4. 4. The method of claim 3, wherein the reduction in mass air flow rate is accomplished by closing a butterfly housing.

5. 4. The method of claim 3, wherein the second torque value (C_intermediate) is calculated by a computer (28) using a curve network that relates torque values ​​to EGR rates.

6. The method according to any one of claims 3 to 5, wherein the torque setpoint of the motor (6) is equal to the second torque value (C_intermediate).

7. 7. The method of claim 6, wherein when the current torque provided by the engine reaches the second torque value (C_intermediate), the computer is capable of executing a spark advance retard to cause the engine (6) to generate the target torque (C_target) required for a gear ratio change.

8. In the method according to any one of claims 3 to 5, when a second torque value (C_intermediate) that enables the target torque (C_target) to be reached by only retarding the advance angle cannot be found, the computer sets a zero EGR setting value and controls to reduce the EGR rate by closing an EGR valve.

9. 9. The method of claim 8, wherein the computer frequently evaluates a minimum torque achievable by retarding only the advance while the EGR rate is decreasing to the set value.

10. 10. The method of claim 9, wherein the computer (28) performs the retardation of the advance required to obtain the target torque (C_target) required for a gear ratio change.

11. 1. A system for controlling torque delivered during gear shifting by an automotive internal combustion engine having at least one partial exhaust gas recirculation system at an intake, comprising: A means for calculating a target torque value (C_target) required for changing the gear ratio; means for determining, from a current operating point of the engine, a first torque value (C_withdrawal) that the engine can generate by implementing a retreat of the spark advance; means for determining a second torque value (C_intermediate) lower than the current torque of the engine (6) and from which the target torque value (C_target) can be generated using only retardation of the ignition advance of the engine (6); A system comprising:

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