Method for linear interpolation of the setpoint values of combustion parameters of an engine
Patent Information
- Application Number
- FR2021001032
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-02-03
- Publication Date
- 2025-03-14
- Estimated Expiration
- 2041-02-03
Smart Images
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Abstract
Description
Title of the invention: Method for linear interpolation of the setpoint values of combustion parameters of an engine. Technical field
[0001] The invention relates, in general, to the control of an internal combustion engine of a motor vehicle during a change in the combustion mode setting.
[0002] The invention relates in particular to changing the setting of a combustion mode independently of a change in the engine's operating point and without affecting the driver's sensations and driving. Previous techniques
[0003] In prior art motor vehicles, internal combustion engines operate according to different combustion modes in different situations. Each combustion mode is characterized by a specific purpose and by conditions specific to that combustion mode, for example, temperature or pressure. Furthermore, each combustion mode includes several settings capable of delivering the same performance or purpose.
[0004] At least one standard operating combustion mode is distinguished, which is that of a usual operation of the vehicle during a normal journey, in which the operating and combustion parameters of the engine are set to meet the need to produce a torque required by the driver, without taking into account other particular constraints.
[0005] A plurality of other combustion methods are implemented on a more ad hoc basis to take into account other constraints.
[0006] For example, there is a specific combustion mode for engine start-up in which, immediately after engine start-up, a degradation of combustion efficiency is anticipated. This is achieved by significantly altering the fuel injection timing to accelerate the heating of an engine exhaust gas aftertreatment system so that it quickly reaches a given minimum treatment efficiency. This is accomplished by increasing the injected fuel flow rate while delaying the injection timing, which allows both the maintenance of the target torque and an increase in exhaust heat losses.
[0007] Other combustion modes relate to aftertreatment systems. Indeed, these systems require certain conditions to be met in order to be effective. For example, a nitrogen oxide trap is purged more easily if it is subjected to an air-fuel ratio greater than 1 and high temperatures in a combustion mode. Similarly, there is a combustion mode for the regeneration of a possible particulate filter in which the richness and temperature of the filter are increased.
[0008] In practice, the on-board computer can switch from one combustion mode setting to another without direct command from the driver, depending on whether or not a particular combustion mode is required. More generally, the ability to obtain several combustion modes and several different combustion mode settings offers additional degrees of freedom that are useful for improving the efficiency of emissions control systems.
[0009] Similarly, the driver can change the engine's operating point (i.e., speed or load) while the on-board computer decides to stay on the same combustion mode setting.
[0010] In order to perform the functions of the different combustion modes, there are levers that can implement different variants or types for the same combustion mode, also called settings. In particular, partial exhaust gas recirculation circuits at the intake (Exhaust Gas Recycling in Anglo-Saxon terms) allow the combustion mode to be typed according to the availability or specificity of these recirculation circuits: for example, whether they operate preferentially at certain temperatures or pressures.
[0011] The drive system 1, according to the prior art and schematically illustrated in [Fig. 1], comprises a first circuit 2 for partial recirculation of exhaust gases at the high-pressure intake and a second circuit 3 for partial recirculation of exhaust gases at the low-pressure intake. The first circuit 2 draws exhaust gases from the outlet of the engine 4 upstream of the turbine 5 and reintroduces them downstream of the compressor 6 into the intake circuit 7. The second circuit 3 draws recirculated gases downstream of the turbine 5, at the outlet of pollution control devices 8, and reintroduces them upstream of the compressor 6 into the intake circuit 7.
[0012] Each of these circuits 2 and 3 is equipped with a recirculating gas flow control valve 9 in order to regulate their quantity in their mixture with the air in the intake circuit 7.
[0013] The flow rates of these recirculating gases are, like other parameters, used continuously to define a combustion mode setting.
[0014] In practice, the driver's depressment of a pedal is translated by an on-board computer 10 into a torque setpoint corresponding to the acceleration desired by the driver. This torque setpoint is translated into an air flow setpoint, as well as a fuel flow setpoint, fuel injection timing in the combustion cycle, and fuel rail pressure.
[0015] The combustion of air and fuel thus makes it possible to obtain the desired torque.
[0016] Furthermore, the supply of recirculated gas via recirculation circuits 2 and 3 into the combustion chamber of engine 4 reduces nitrogen oxide emissions. The on-board computer 10 also determines a flow rate setpoint for this recirculated gas.
[0017] The air flow rate is indirectly regulated by the position of the turbine blades 5, while the recirculated gas flow rate is regulated in a closed loop by the dedicated control valve 9 provided in each of the recirculation circuits 2 and 3. The total air and recirculated gas flow rate can then be regulated by the boost pressure in the intake manifold 11 or by the intake valve 12.
[0018] The rate of convergence towards the setpoint of each flow rate in recirculation circuits 2 and 3 is specific to each circuit and is not necessarily the same as that of the air flow rate. Indeed, the path to be followed is not necessarily the same, the cross-section of the ducts is not the same, or the valves 9 do not open at the same rate.
[0019] More generally, each combustion parameter, such as the air and recirculation gas flow rates, the quantity of fuel injected, or the number of injections, converges to its setpoint value at a different rate due, for example, to the different movement rates of each actuator of said combustion parameters. For example, the boost pressure of the intake manifold 11 converges to a new, higher setpoint value in about ten seconds, while the recirculation gas flow rate of a recirculation circuit 2 or 3 converges to its higher setpoint value in about one second.
[0020] The effect is that the rate of recirculating gas from recirculation circuit 2 or 3 becomes higher than desired and nitrogen oxide emissions are lower, but at the cost of more particulate emissions.
[0021] Conversely, the airflow is insufficient and the torque does not increase as rapidly as expected. Simultaneously, as the fuel flow increases almost instantaneously, an excessively rich mixture relative to the actual airflow may be observed, potentially resulting in exhaust fumes. Furthermore, immediately applying the fuel injection intended for the final airflow rate may disrupt the combustion process in the engine cylinders 4, as the quantity of air does not correspond to the quantity of fuel introduced.
[0022] It is understood from the foregoing that, in prior art combustion mode adjustment methods where an on-board computer 10 imposes all the setpoints for air flow, recirculation gas flow, rail pressure, and fuel flow, it simultaneously controls all the relevant actuators in order to adjust the various flow rates to their respective setpoints. However, since the actuators do not all converge at the same speed, the values of the various combustion parameters are no longer consistent with each other, a situation that is further exacerbated if the The combustion mode setting is again modified in a way that is not favorable to rectifying this consistency.
[0023] Engine 4 then encounters problems of excessive performance and emissions as well as potential jolts felt by passengers. Description of the invention
[0024] The present invention therefore aims to overcome the aforementioned disadvantages and to facilitate a smooth and trouble-free transition between two combustion mode settings.
[0025] It is based on the principle that such a transition is obtained, or at least favored, when the different output parameters between two successive combustion mode settings, such as the values of exhaust gas temperature, quantities of pollutant emissions, noise level, etc., evolve linearly over time, and on the proportionality of these output parameters with all the combustion parameters, such as the air flow, the fuel flow, etc.
[0026] The present invention relates to a method for linearly interpolating the value of the combustion parameter setpoints of an internal combustion engine during a change in combustion mode setting between a current combustion mode setting and a target combustion mode setting, comprising the following steps, carried out at each calculation step of a computer:
[0027] - Determination, for each combustion parameter, of the current value as a function of the setting of the current combustion mode; - Definition, for each combustion parameter, of a final target value as a function of the setting of the target combustion mode; - Calculation of the transition time required for each combustion parameter to go from its current value to its final target value; - Determination of the longest transition time of the parameters of combustion as the total transition time to go from the current value to the final target value of all combustion parameters; - Interpolation of a target value for each combustion parameter at a step of following calculation, pro rata to the number of calculation steps required taking into account the total transition time; - Transition of each combustion parameter to its target value at the next calculation step.
[0028] Thus, the method makes it possible to synchronize the interpolation of all the combustion parameters on the one with the lowest dynamics, so that all the values of the combustion parameters form at any instant of the transition a set Consistent values are used to achieve a combustion mode setting, or at least to transition to that setting. This helps prevent engine performance problems and excessive pollutant emissions.
[0029] Advantageously, the calculation of the transition time required for each combustion parameter to go from its current value to its final target value is carried out by extrapolation based on the maximum transition speed of each combustion parameter and considering that the current and target values of each parameter are stable during the transition.
[0030] In one implementation mode, the transition step of certain parameters only takes place when other parameters have reached a given transition percentage.
[0031] Advantageously, a combustion parameter taking discrete values transitions to a predefined value of this combustion parameter depending on the value of the interpolation.
[0032] Advantageously, the engine output parameters are proportional to the combustion parameters and the setpoints of the actuators controlling them.
[0033] In one embodiment, the method is implemented by an on-board computer of a motor vehicle. Brief description of the drawings
[0034] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:
[0035] [Fig. 1], which has already been mentioned, schematically illustrates various elements of a motor vehicle drive system involved in the implementation of a method according to the invention; and
[0036] [Fig.2] illustrates the different stages of the linear interpolation process of the value of the combustion parameter setpoints according to the invention. Detailed description of at least one embodiment
[0037] Figure 1 shows a simplified diagram representing various elements of a motorization device 1 of a motor vehicle according to the prior art and which can be used during the implementation of the method according to the invention. The method therefore does not require any additional equipment for its implementation.
[0038] Certain intrinsic parameters of certain elements of the motorization device 1 are combustion parameters or output parameters of the motor 4.
[0039] One objective of the method according to the invention is to ensure a linear, or as linear as possible, evolution of the various output parameters of the motor 4 such as torque, the noise or exhaust gas temperature, which undergo abrupt changes if the combustion parameters of engine 4 are not changed in a synchronized manner.
[0040] For example, when switching from a standard operating combustion mode setting to a combustion mode setting for particulate filter regeneration, the exhaust gas outlet temperature changes from 400°C to a required temperature of 600°C to allow the soot particles in the particulate filter to burn. It is therefore necessary to ensure a linear temperature increase to maintain the reliability of the engine 4 and to make the transition as seamless as possible.
[0041] In the method implemented by the vehicle's on-board computer 10, the output parameters of engine 4 are considered to be proportional to the combustion parameters and the resulting actuator commands. Furthermore, one objective of the method is to make each combustion parameter proportional to the other combustion parameters so that each combustion parameter of engine 4 evolves coherently with the others. The concept of proportionality here relates to the value of the engine 4 parameters before and after the change in the combustion mode setting. Similarly, "coherent" means that the values of the various engine 4 parameters evolve in a coordinated manner over time.
[0042] With this assumption, a barycenter is maintained identical for all combustion parameters at any instant of the change in combustion mode setting.
[0043] The on-board computer 10 also imposes a calculation step. At each calculation step, the process according to the invention is carried out so that each combustion parameter remains proportional and does not become inconsistent with respect to the other combustion parameters.
[0044] For the purposes of this text, the term "setting or current values" refers to the set of combustion parameters being applied at each instant of a combustion mode setting transition, and the term "target setting or values" refers to the set of combustion parameters to which the transition is made. The combustion parameters that are transitioned include, for example, the various air flow rates, recirculating gas flow rates, fuel flow rates, fuel rail pressures, and others, depending on the technical specifications of engine 4.
[0045] Figure 2 shows the different stages of the linear interpolation process of the value of combustion parameters according to the invention.
[0046] First, the on-board computer 10 performs a first step 21 of defining a final target value for each combustion parameter according to the setting of the target combustion mode. The setting of the target combustion mode is, for example, automatically determined by the on-board computer 10 to put in The regeneration of a particulate filter is carried out. The final target value of each combustion parameter is therefore the value of said combustion parameter that allows the drive unit 1 to set itself to the desired combustion mode. In addition, certain combustion parameter values are determined or imposed by the operating point of the engine 4, which depends on the driver's desired speed and acceleration.
[0047] In a second step 22, it is necessary to calculate the transition time required for each combustion parameter to go from its current value, which was determined in a previous step 20, for example by measurements or models, to its final target value. This step 22 is carried out by linear extrapolation of the gradient defined by the maximum transition speed of each combustion parameter and assuming that the current and target values of each parameter are stable during the transition. The transition time thus calculated is the minimum time it takes for a combustion parameter to complete its transition from its current value to its final target value. This minimum time is partly influenced by the speed of movement of the combustion parameter actuators.
[0048] In order for each combustion parameter to be proportional to the other combustion parameters, a step 23 for determining the longest transition time of the combustion parameters is implemented. This longest transition time is derived from the combustion parameter taking the longest to transition to its final target value and is defined as the total transition time from the current value to the final target value of all combustion parameters. In other words, each combustion parameter synchronizes with the slowest combustion parameter so that all combustion parameters are consistent and proportional to each other.
[0049] To achieve this, a step 24 is performed, interpolating a target value for each combustion parameter at the next calculation step, in proportion to the number of calculation steps required, taking into account the total transition time. In other words, at each calculation step, and for each combustion parameter, an intermediate setpoint to be reached at the next calculation step is redefined, taking into account the initial value of the combustion parameter at the current calculation step as well as the final target value.
[0050] Finally, a step 25 is performed to transition each combustion parameter to its target value at the next calculation step. The achievement of the target values by the actual values of the combustion parameters can be verified at the next step during the preliminary step 20 of determining the values of said parameters. The various steps of the process can then restart at the rate of the predetermined calculation step of the on-board computer 10. This allows, in the event of a rapid change in mode setting, combustion occurs even before the previous combustion mode setting has been reached, ensuring that all combustion parameters transition smoothly. At each calculation step, the process recalculates an intermediate trajectory for the convergence of combustion parameters towards their final target value.
[0051] In the case of a change of setting from a current operating combustion mode setting to a combustion mode for the regeneration of a particulate filter, the air flow and fuel injection setpoints must be modified to increase the exhaust gas temperature to allow the combustion of soot particles.
[0052] In this case, the air flow rate is the slowest combustion parameter to pass through. The other combustion parameters therefore adjust to its dynamics.
[0053] It is also possible in one implementation to have the slowest combustion parameter transition first and then, after an arbitrary time or as soon as the slowest parameter reaches a specific value, to trigger the transition of the other combustion parameters. The aim is also for all combustion parameters to complete the transition from one combustion mode setting to another simultaneously.
[0054] In an implementation requiring the transition of a combustion parameter whose values are discrete, for example the injection number, it is possible to define in advance the values taken by this combustion parameter as a function of a given interpolation. For example, it is possible to choose the first available value that is greater than the interpolation.
Claims
Claims
1. Method for linear interpolation of the value of the combustion parameter setpoints of an internal combustion engine (4) during a change of combustion mode setting between a current combustion mode setting and a target combustion mode setting, characterized in that it comprises the following steps, carried out at each calculation step of a computer (10): - Determination (step 20), for each combustion parameter, of a current value as a function of the current combustion mode setting; - Definition (step 21), for each combustion parameter of a final target value as a function of the target combustion mode setting;- Calculation (step 22) of the transition time required for each combustion parameter to go from its current value to its final target value by extrapolation based on the maximum transition speed of each combustion parameter and considering that the current and target values of each parameter are stable during the transition; - Determination (step 23) of the longest transition time of the combustion parameters as being the total transition time to go from the current value to the final target value of all the combustion parameters; - Interpolation (step 24) of a target value of each combustion parameter at the next calculation step, in proportion to the number of calculation steps required taking into account the total transition time; - Transition (step 25) of each combustion parameter to its target value at the next calculation step.;
2. Method according to claim 1, in which the step (25) of transitioning certain parameters is carried out only when other parameters have reached a given transition percentage.
3. Method according to one of claims 1 and 2, in which a combustion parameter taking discrete values transits (step 25) towards a predefined value of this combustion parameter as a function of the interpolation value.
4. Method according to any one of claims 1 to 3, in which the output parameters of the engine (4) are proportional to the combustion parameters and to the setpoints of the actuators controlling them.
5. Method according to any one of claims 1 to 4, characterized in that it is implemented by an on-board computer (10) of a motor vehicle.